NASA/SP-2007-6105

Rev1

NASA

Systems Engineering

Handbook
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NASA/SP-2007-6105 Rev1

Systems Engineering Handbook

National Aeronautics and Space Administration

NASA Headquarters

Washington, D.C. 20546

December 2007
To request print or electronic copies or provide comments,

contact the Office of the Chief Engineer via

SP6105rev1SEHandbook@nasa.gov 

Electronic copies are also available from

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7115 Standard Drive

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at

http://ntrs.nasa.gov/
NASA Systems Engineering Handbook  iii

Table of Contents

Preface..............................................................................................................................................................xiii

Acknowledgments............................................................................................................................................xv

1.0 Introduction ...............................................................................................................................................1

1.1 Purpose ....................................................................................................................................................................... 1

1.2 Scope and Depth........................................................................................................................................................ 1

2.0 Fundamentals of Systems Engineering.....................................................................................................3

2.1 The Common Technical Processes and the SE Engine ......................................................................................... 4

2.2 An Overview of the SE Engine by Project Phase................................................................................................... 6

2.3 Example of Using the SE Engine.............................................................................................................................. 7

2.3.1 Detailed Example........................................................................................................................................... 8

2.3.2 Example Premise............................................................................................................................................ 8

2.3.2.1 Example Phase A System Design Passes....................................................................................... 8

2.3.2.2 Example Product Realization Passes........................................................................................... 12

2.3.2.3 Example Use of the SE Engine in Phases B Through D............................................................ 14

2.3.2.4 Example Use of the SE Engine in Phases E and F ..................................................................... 14

2.4 Distinctions Between Product Verification and Product Validation................................................................ 15

2.5 Cost Aspect of Systems Engineering..................................................................................................................... 16

3.0 NASA Program/Project Life Cycle............................................................................................................ 19

3.1 Program Formulation.............................................................................................................................................. 19

3.2 Program Implementation ....................................................................................................................................... 21

3.3 Project Pre-Phase A: Concept Studies .................................................................................................................. 22

3.4 Project Phase A: Concept and Technology Development.................................................................................. 22

3.5 Project Phase B: Preliminary Design and Technology Completion ................................................................. 24

3.6 Project Phase C: Final Design and Fabrication.................................................................................................... 25

3.7 Project Phase D: System Assembly, Integration and Test, Launch.................................................................... 25

3.8 Project Phase E: Operations and Sustainment..................................................................................................... 28

3.9 Project Phase F: Closeout ....................................................................................................................................... 28

3.10 Funding: The Budget Cycle..................................................................................................................................... 29

4.0 System Design......................................................................................................................................... 31

4.1 Stakeholder Expectations Definition..................................................................................................................... 33

4.1.1 Process Description..................................................................................................................................... 33

4.1.1.1 Inputs .............................................................................................................................................. 33

4.1.1.2 Process Activities........................................................................................................................... 33

4.1.1.3 Outputs........................................................................................................................................... 35

4.1.2 Stakeholder Expectations Definition Guidance....................................................................................... 35

4.1.2.1 Concept of Operations.................................................................................................................. 35

4.2 Technical Requirements Definition....................................................................................................................... 40

4.2.1 Process Description..................................................................................................................................... 40

4.2.1.1 Inputs .............................................................................................................................................. 41

4.2.1.2 Process Activities........................................................................................................................... 41

4.2.1.3 Outputs........................................................................................................................................... 41

4.2.2 Technical Requirements Definition Guidance......................................................................................... 41

4.2.2.1 Types of Requirements.................................................................................................................. 41
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Table of Contents

4.2.2.2 Human Factors Engineering Requirements............................................................................... 45

4.2.2.3 Requirements Decomposition, Allocation, and Validation..................................................... 45

4.2.2.4 Capturing Requirements and the Requirements Database...................................................... 47

4.2.2.5 Technical Standards ...................................................................................................................... 47

4.3 Logical Decomposition........................................................................................................................................... 49

4.3.1 Process Description .................................................................................................................................... 49

4.3.1.1 Inputs .............................................................................................................................................. 49

4.3.1.2 Process Activities........................................................................................................................... 49

4.3.1.3 Outputs........................................................................................................................................... 51

4.3.2 Logical Decomposition Guidance ............................................................................................................. 52

4.3.2.1 Product Breakdown Structure ..................................................................................................... 52

4.3.2.2 Functional Analysis Techniques.................................................................................................. 52

4.4 Design Solution Definition....................................................................................................................................... 55

4.4.1 Process Description........................................................................................................................................ 55

4.4.1.1 Inputs ................................................................................................................................................ 55

4.4.1.2 Process Activities............................................................................................................................. 56

4.4.1.3 Outputs............................................................................................................................................. 61

4.4.2 Design Solution Definition Guidance.......................................................................................................... 62

4.4.2.1 Technology Assessment................................................................................................................ 62

4.4.2.2 Integrating Engineering Specialties into the Systems Engineering Process.......................... 62

5.0 Product Realization................................................................................................................................. 71

5.1 Product Implementation......................................................................................................................................... 73

5.1.1 Process Description..................................................................................................................................... 73

5.1.1.1 Inputs .............................................................................................................................................. 73

5.1.1.2 Process Activities .......................................................................................................................... 74

5.1.1.3 Outputs........................................................................................................................................... 75

5.1.2 Product Implementation Guidance........................................................................................................... 76

5.1.2.1 Buying Off-the-Shelf Products .................................................................................................... 76

5.1.2.2 Heritage........................................................................................................................................... 76

5.2 Product Integration ................................................................................................................................................. 78

5.2.1 Process Description..................................................................................................................................... 78

5.2.1.1 Inputs ............................................................................................................................................. 79

5.2.1.2 Process Activities........................................................................................................................... 79

5.2.1.3 Outputs........................................................................................................................................... 79

5.2.2 Product Integration Guidance ................................................................................................................... 80

5.2.2.1 Integration Strategy....................................................................................................................... 80

5.2.2.2 Relationship to Product Implementation .................................................................................. 80

5.2.2.3 Product/Interface Integration Support....................................................................................... 80

5.2.2.4 Product Integration of the Design Solution............................................................................... 81

5.2.2.5 Interface Management.................................................................................................................. 81

5.2.2.6 Compatibility Analysis.................................................................................................................. 81

5.2.2.7 Interface Management Tasks........................................................................................................ 81

5.3 Product Verification ............................................................................................................................................... 83

5.3.1 Process Description..................................................................................................................................... 83

5.3.1.1 Inputs .............................................................................................................................................. 83

5.3.1.2 Process Activities........................................................................................................................... 84

5.3.1.3 Outputs........................................................................................................................................... 89

5.3.2 Product Verification Guidance................................................................................................................... 89

5.3.2.1 Verification Program..................................................................................................................... 89

5.3.2.2 Verification in the Life Cycle........................................................................................................ 89

5.3.2.3 Verification Procedures ................................................................................................................ 92
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NASA Systems Engineering Handbook  v

5.3.2.4 Verification Reports ...................................................................................................................... 93

5.3.2.5 End-to-End System Testing ......................................................................................................... 93

5.3.2.6 Modeling and Simulation............................................................................................................. 96

5.3.2.7 Hardware-in-the-Loop ................................................................................................................. 96

5.4 Product Validation................................................................................................................................................... 98

5.4.1 Process Description..................................................................................................................................... 98

5.4.1.1 Inputs .............................................................................................................................................. 98

5.4.1.2 Process Activities........................................................................................................................... 99

5.4.1.3 Outputs......................................................................................................................................... 104

5.4.2 Product Validation Guidance................................................................................................................... 104

5.4.2.1 Modeling and Simulation........................................................................................................... 104

5.4.2.2 Software ........................................................................................................................................ 104

5.5 Product Transition ................................................................................................................................................ 106

5.5.1 Process Description................................................................................................................................... 106

5.5.1.1 Inputs ............................................................................................................................................ 106

5.5.1.2 Process Activities......................................................................................................................... 107

5.5.1.3 Outputs......................................................................................................................................... 109

5.5.2 Product Transition Guidance................................................................................................................... 110

5.5.2.1 Additional Product Transition Input Considerations ............................................................ 110

5.5.2.2 After Product Transition to the End User—What Next?....................................................... 110

6.0 Crosscutting Technical Management .................................................................................................. 111

6.1 Technical Planning ................................................................................................................................................ 112

6.1.1 Process Description................................................................................................................................... 112

6.1.1.1 Inputs ............................................................................................................................................ 112

6.1.1.2 Process Activities......................................................................................................................... 113

6.1.1.3 Outputs......................................................................................................................................... 122

6.1.2 Technical Planning Guidance .................................................................................................................. 122

6.1.2.1 Work Breakdown Structure........................................................................................................ 122

6.1.2.2 Cost Definition and Modeling................................................................................................... 125

6.1.2.3 Lessons Learned .......................................................................................................................... 129

6.2 Requirements Management.................................................................................................................................. 131

6.2.1 Process Description................................................................................................................................... 131

6.2.1.1 Inputs ............................................................................................................................................ 131

6.2.1.2 Process Activities......................................................................................................................... 132

6.2.1.3 Outputs......................................................................................................................................... 134

6.2.2 Requirements Management Guidance.................................................................................................... 134

6.2.2.1 Requirements Management Plan .............................................................................................. 134

6.2.2.2 Requirements Management Tools............................................................................................. 135

6.3 Interface Management .......................................................................................................................................... 136

6.3.1 Process Description................................................................................................................................... 136

6.3.1.1 Inputs ............................................................................................................................................ 136

6.3.1.2 Process Activities......................................................................................................................... 136

6.3.1.3 Outputs......................................................................................................................................... 137

6.3.2 Interface Management Guidance............................................................................................................. 137

6.3.2.1 Interface Requirements Document........................................................................................... 137

6.3.2.2 Interface Control Document or Interface Control Drawing ................................................. 137

6.3.2.3 Interface Definition Document ................................................................................................ 138

6.3.2.4 Interface Control Plan................................................................................................................. 138

6.4 Technical Risk Management................................................................................................................................. 139

6.4.1 Process Description................................................................................................................................... 140

6.4.1.1 Inputs ............................................................................................................................................ 140
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6.4.1.2 Process Activities......................................................................................................................... 140

6.4.1.3 Outputs......................................................................................................................................... 141

6.4.2 Technical Risk Management Guidance................................................................................................... 141

6.4.2.1 Role of Continuous Risk Management in Technical Risk Management ............................. 142

6.4.2.2 The Interface Between CRM and Risk-Informed Decision Analysis................................... 142

6.4.2.3 Selection and Application of Appropriate Risk Methods....................................................... 143

6.5 Configuration Management ................................................................................................................................ 151

6.5.1 Process Description................................................................................................................................... 151

6.5.1.1 Inputs ............................................................................................................................................ 151

6.5.1.2 Process Activities......................................................................................................................... 151

6.5.1.3 Outputs......................................................................................................................................... 156

6.5.2 CM Guidance ............................................................................................................................................. 156

6.5.2.1 What Is the Impact of Not Doing CM?.................................................................................... 156

6.5.2.2 When Is It Acceptable to Use Redline Drawings?................................................................... 157

6.6 Technical Data Management................................................................................................................................ 158

6.6.1 Process Description................................................................................................................................... 158

6.6.1.1 Inputs ............................................................................................................................................ 158

6.6.1.2 Process Activities........................................................................................................................ 158

6.6.1.3 Outputs......................................................................................................................................... 162

6.6.2 Technical Data Management Guidance.................................................................................................. 162

6.6.2.1 Data Security and ITAR.............................................................................................................. 162

6.7 Technical Assessment............................................................................................................................................ 166

6.7.1 Process Description................................................................................................................................... 166

6.7.1.1 Inputs ............................................................................................................................................ 166

6.7.1.2 Process Activities......................................................................................................................... 166

6.7.1.3 Outputs......................................................................................................................................... 167

6.7.2 Technical Assessment Guidance.............................................................................................................. 168

6.7.2.1 Reviews, Audits, and Key Decision Points .............................................................................. 168

6.7.2.2 Status Reporting and Assessment.............................................................................................. 190

6.8 Decision Analysis................................................................................................................................................... 197

6.8.1 Process Description................................................................................................................................... 197

6.8.1.1 Inputs ............................................................................................................................................ 198

6.8.1.2 Process Activities......................................................................................................................... 199

6.8.1.3 Outputs......................................................................................................................................... 202

6.8.2 Decision Analysis Guidance..................................................................................................................... 203

6.8.2.1 Systems Analysis, Simulation, and Performance..................................................................... 203

6.8.2.2 Trade Studies................................................................................................................................ 205

6.8.2.3 Cost-Benefit Analysis.................................................................................................................. 209

6.8.2.4 Influence Diagrams..................................................................................................................... 210

6.8.2.5 Decision Trees.............................................................................................................................. 210

6.8.2.6 Multi-Criteria Decision Analysis .............................................................................................. 211

6.8.2.7 Utility Analysis............................................................................................................................. 212

6.8.2.8 Risk-Informed Decision Analysis Process Example............................................................... 213

7.0 Special Topics ........................................................................................................................................ 217

7.1 Engineering with Contracts ................................................................................................................................. 217

7.1.1 Introduction, Purpose, and Scope........................................................................................................... 217

7.1.2 Acquisition Strategy................................................................................................................................... 217

7.1.2.1 Develop an Acquisition Strategy ............................................................................................... 218

7.1.2.2 Acquisition Life Cycle ................................................................................................................. 218

7.1.2.3 NASA Responsibility for Systems Engineering ....................................................................... 218

7.1.3 Prior to Contract Award ........................................................................................................................... 219
Table of Contents

NASA Systems Engineering Handbook  vii

7.1.3.1 Acquisition Planning................................................................................................................... 219

7.1.3.2 Develop the Statement of Work................................................................................................. 223

7.1.3.3 Task Order Contracts.................................................................................................................. 225

7.1.3.4 Surveillance Plan ......................................................................................................................... 225

7.1.3.5 Writing Proposal Instructions and Evaluation Criteria ......................................................... 226

7.1.3.6 Selection of COTS Products ...................................................................................................... 226

7.1.3.7 Acquisition-Unique Risks .......................................................................................................... 227

7.1.4 During Contract Performance ................................................................................................................. 227

7.1.4.1 Performing Technical Surveillance .......................................................................................... 227

7.1.4.2 Evaluating Work Products.......................................................................................................... 229

7.1.4.3 Issues with Contract-Subcontract Arrangements................................................................... 229

7.1.5 Contract Completion ............................................................................................................................... 230

7.1.5.1 Acceptance of Final Deliverables............................................................................................... 230

7.1.5.2 Transition Management.............................................................................................................. 231

7.1.5.3 Transition to Operations and Support...................................................................................... 232

7.1.5.4 Decommissioning and Disposal................................................................................................ 233

7.1.5.5 Final Evaluation of Contractor Performance........................................................................... 233

7.2 Integrated Design Facilities.................................................................................................................................. 234

7.2.1 Introduction .............................................................................................................................................. 234

7.2.2 CACE Overview and Importance............................................................................................................ 234

7.2.3 CACE Purpose and Benefits..................................................................................................................... 235

7.2.4 CACE Staffing............................................................................................................................................. 235

7.2.5 CACE Process............................................................................................................................................. 236

7.2.5.1 Planning and Preparation........................................................................................................... 236

7.2.5.2 Activity Execution Phase............................................................................................................ 236

7.2.5.3 Activity Wrap-Up ....................................................................................................................... 237

7.2.6 CACE Engineering Tools and Techniques ............................................................................................ 237

7.2.7 CACE Facility, Information Infrastructure, and Staffing ..................................................................... 238

7.2.7.1 Facility........................................................................................................................................... 238

7.2.7.2 Information Infrastructure......................................................................................................... 238

7.2.7.3 Facility Support Staff Responsibilities....................................................................................... 239

7.2.8 CACE Products ......................................................................................................................................... 239

7.2.9 CACE Best Practices.................................................................................................................................. 239

7.2.9.1 People ............................................................................................................................................ 240

7.2.9.2 Process and Tools ........................................................................................................................ 240

7.2.9.3 Facility........................................................................................................................................... 240

7.3 Selecting Engineering Design Tools..................................................................................................................... 242

7.3.1 Program and Project Considerations...................................................................................................... 242

7.3.2 Policy and Processes.................................................................................................................................. 242

7.3.3 Collaboration.............................................................................................................................................. 242

7.3.4 Design Standards....................................................................................................................................... 243

7.3.5 Existing IT Architecture............................................................................................................................ 243

7.3.6 Tool Interfaces............................................................................................................................................ 243

7.3.7 Interoperability and Data Formats.......................................................................................................... 243

7.3.8 Backward Compatibility ........................................................................................................................... 244

7.3.9 Platform....................................................................................................................................................... 244

7.3.10 Tool Configuration Control...................................................................................................................... 244

7.3.11 Security/Access Control............................................................................................................................ 244

7.3.12 Training....................................................................................................................................................... 244

7.3.13 Licenses....................................................................................................................................................... 244

7.3.14 Stability of Vendor and Customer Support ............................................................................................ 244

7.4 Human Factors Engineering ................................................................................................................................ 246
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7.4.1 Basic HF Model.......................................................................................................................................... 247

7.4.2 HF Analysis and Evaluation Techniques................................................................................................ 247

7.5 Environmental, Nuclear Safety, Planetary Protection, and Asset Protection Policy Compliance .............. 256

7.5.1 NEPA and EO 12114 ................................................................................................................................. 256

7.5.1.1 National Environmental Policy Act .......................................................................................... 256

7.5.1.2 EO 12114 Environmental Effects Abroad of Major Federal Actions ................................... 257

7.5.2 PD/NSC-25................................................................................................................................................. 257

7.5.3 Planetary Protection.................................................................................................................................. 258

7.5.4 Space Asset Protection .............................................................................................................................. 260

7.5.4.1 Protection Policy.......................................................................................................................... 260

7.5.4.2 Goal ............................................................................................................................................... 260

7.5.4.3 Scoping.......................................................................................................................................... 260

7.5.4.4 Protection Planning .................................................................................................................... 260

7.6 Use of Metric System ............................................................................................................................................ 261

Appendix A: Acronyms................................................................................................................................. 263

Appendix B: Glossary................................................................................................................................... 266

Appendix C: How to Write a Good Requirement........................................................................................ 279

Appendix D: Requirements Verification Matrix......................................................................................... 282

Appendix E: Creating the Validation Plan (Including Validation Requirements Matrix)........................ 284

Appendix F: Functional, Timing, and State Analysis ................................................................................. 285

Appendix G: Technology Assessment/Insertion........................................................................................ 293

Appendix H: Integration Plan Outline ........................................................................................................ 299

Appendix I: Verification and Validation Plan Sample Outline .................................................................. 301

Appendix J: SEMP Content Outline............................................................................................................. 303

Appendix K: Plans ........................................................................................................................................ 308

Appendix L: Interface Requirements Document Outline.......................................................................... 309

Appendix M: CM Plan Outline ..................................................................................................................... 311

Appendix N: Guidance on Technical Peer Reviews/Inspections .............................................................. 312

Appendix O: Tradeoff Examples.................................................................................................................. 316

Appendix P: SOW Review Checklist............................................................................................................ 317

Appendix Q: Project Protection Plan Outline ............................................................................................ 321

References...................................................................................................................................................... 323

Bibliography .................................................................................................................................................. 327

Index............................................................................................................................................................... 332
Table of Contents

NASA Systems Engineering Handbook  ix

Figures

2.0-1 SE in context of overall project management...................................................................................................... 4

2.1-1 The systems engineering engine............................................................................................................................ 5

2.2-1 A miniaturized conceptualization of the poster-size NASA project life-cycle process flow for 

flight and ground systems accompanying this handbook................................................................................. 6

2.3-1 SE engine tracking icon.......................................................................................................................................... 8

2.3-2 Product hierarchy, tier 1: first pass through the SE engine................................................................................ 9

2.3-3 Product hierarchy, tier 2: external tank.............................................................................................................. 10

2.3-4 Product hierarchy, tier 2: orbiter......................................................................................................................... 10

2.3-5 Product hierarchy, tier 3: avionics system.......................................................................................................... 11

2.3-6 Product hierarchy: complete pass through system design processes side of the SE engine........................ 11

2.3-7 Model of typical activities during operational phase (Phase E) of a product ............................................... 14

2.3-8 New products or upgrades reentering the SE engine ....................................................................................... 15

2.5-1 The enveloping surface of nondominated designs............................................................................................ 16

2.5-2 Estimates of outcomes to be obtained from several design concepts including uncertainty...................... 17

3.0-1 NASA program life cycle...................................................................................................................................... 20

3.0-2 NASA project life cycle......................................................................................................................................... 20

3.10-1 Typical NASA budget cycle .............................................................................................................................. 29

4.0-1 Interrelationships among the system design processes.................................................................................... 31

4.1-1 Stakeholder Expectations Definition Process.................................................................................................... 33

4.1-2 Product flow for stakeholder expectations ........................................................................................................ 34

4.1-3 Typical ConOps development for a science mission........................................................................................ 36

4.1-4 Example of an associated end-to-end operational architecture ..................................................................... 36

4.1-5a Example of a lunar sortie timeline developed early in the life cycle............................................................. 37

4.1-5b Example of a lunar sortie DRM early in the life cycle.................................................................................... 37

4.1-6 Example of a more detailed, integrated timeline later in the life cycle for a science mission..................... 38

4.2-1 Technical Requirements Definition Process...................................................................................................... 40

4.2-2 Characteristics of functional, operational, reliability, safety, and specialty requirements........................... 43

4.2-3 The flowdown of requirements............................................................................................................................ 46

4.2-4 Allocation and flowdown of science pointing requirements........................................................................... 47

4.3-1 Logical Decomposition Process.......................................................................................................................... 49

4.3-2 Example of a PBS................................................................................................................................................... 52

4.3-3 Example of a functional flow block diagram..................................................................................................... 53

4.3-4 Example of an N2 diagram .................................................................................................................................. 54

4.4-1 Design Solution Definition Process .................................................................................................................... 55

4.4-2 The doctrine of successive refinement................................................................................................................. 56

4.4-3 A quantitative objective function, dependent on life-cycle cost and all aspects of effectiveness ................ 58

5.0-1 Product realization................................................................................................................................................ 71

5.1-1 Product Implementation Process........................................................................................................................ 73

5.2-1 Product Integration Process ................................................................................................................................ 78

5.3-1 Product Verification Process ............................................................................................................................... 84

5.3-2 Bottom-up realization process ............................................................................................................................ 90

5.3-3 Example of end-to-end data flow for a scientific satellite mission ................................................................. 94

5.4-1 Product Validation Process.................................................................................................................................. 99

5.5-1 Product Transition Process................................................................................................................................ 106

6.1-1 Technical Planning Process ............................................................................................................................... 112

6.1-2 Activity-on-arrow and precedence diagrams for network schedules........................................................... 116

6.1-3 Gantt chart ........................................................................................................................................................... 118

6.1-4 Relationship between a system, a PBS, and a WBS ........................................................................................ 123

6.1-5 Examples of WBS development errors............................................................................................................. 125

6.2-1 Requirements Management Process................................................................................................................. 131

6.3-1 Interface Management Process.......................................................................................................................... 136
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6.4-1 Technical Risk Management Process................................................................................................................ 140

6.4-2 Scenario-based modeling of hazards................................................................................................................ 141

6.4-3 Risk as a set of triplets ........................................................................................................................................ 141

6.4-4 Continuous risk management ........................................................................................................................... 142

6.4-5 The interface between CRM and risk-informed decision analysis............................................................... 143

6.4-6 Risk analysis of decision alternatives................................................................................................................ 144

6.4-7 Risk matrix........................................................................................................................................................... 145

6.4-8 Example of a fault tree ........................................................................................................................................ 146

6.4-9 Deliberation ......................................................................................................................................................... 147

6.4-10 Performance monitoring and control of deviations..................................................................................... 149

6.4-11 Margin management method.......................................................................................................................... 150

6.5-1 CM Process.......................................................................................................................................................... 151

6.5-2 Five elements of configuration management .................................................................................................. 152

6.5-3 Evolution of technical baseline.......................................................................................................................... 153

6.5-4 Typical change control process.......................................................................................................................... 155

6.6-1 Technical Data Management Process............................................................................................................... 158

6.7-1 Technical Assessment Process........................................................................................................................... 166

6.7-2 Planning and status reportingfeedback loop................................................................................................... 167

6.7-3 Cost and schedule variances.............................................................................................................................. 190

6.7-4 Relationships of MOEs, MOPs,and TPMs....................................................................................................... 192

6.7-5 Use of the planned profile method for the weight TPM with rebaseline in Chandra Project .................. 194

6.7-6 Use of the margin management method for the mass TPM in Sojourner.................................................. 194

6.8-1 Decision Analysis Process.................................................................................................................................. 198

6.8-2 Example of a decision matrix ........................................................................................................................... 201

6.8-3 Systems analysis across the life cycle ................................................................................................................ 203

6.8-4 Simulation model analysis techniques ............................................................................................................. 204

6.8-5 Trade study process............................................................................................................................................. 205

6.8-6 Influence diagrams.............................................................................................................................................. 210

6.8-7 Decision tree ........................................................................................................................................................ 211

6.8-8 Utility function for a “volume” performance measure................................................................................... 213

6.8-9 Risk-informed Decision Analysis Process....................................................................................................... 214

6.8-10 Example of an objectives hierarchy ................................................................................................................ 215

7.1-1 Acquisition life cycle .......................................................................................................................................... 218

7.1-2 Contract requirements development process.................................................................................................. 223

7.2-1 CACE people/process/tools/facility paradigm................................................................................................ 234

7.4-1 Human factors interaction model..................................................................................................................... 247

7.4-2 HF engineering process and its links to the NASA program/project life cycle .......................................... 248

F-1 FFBD flowdown ..................................................................................................................................................... 286

F-2 FFBD: example 1 .................................................................................................................................................... 287

F-3 FFBD showing additional control constructs: example 2................................................................................. 287

F-4 Enhanced FFBD: example 3.................................................................................................................................. 288

F-5 Requirements allocation sheet.............................................................................................................................. 289

F-6 N2 diagram for orbital equipment ...................................................................................................................... 289

F-7 Timing diagram example ...................................................................................................................................... 290

F-8 Slew command status state diagram.................................................................................................................... 291

G-1 PBS example........................................................................................................................................................... 294

G-2 Technology assessment process........................................................................................................................... 295

G-3 Architectural studies and technology development......................................................................................... 296

G-4 Technology readiness levels................................................................................................................................. 296

G-5 The TMA thought process................................................................................................................................... 297

G-6 TRL assessment matrix......................................................................................................................................... 298

N-1 The peer review/inspection process.................................................................................................................... 312
Table of Contents

NASA Systems Engineering Handbook  xi

N-2 Peer reviews/inspections quick reference guide ............................................................................................... 315

Tables

2.3-1 Project Life-Cycle Phases....................................................................................................................................... 7

4.1-1 Typical Operational Phases for a NASA Mission ............................................................................................. 39

4.2-1 Benefits of Well-Written Requirements............................................................................................................. 42

4.2-2 Requirements Metadata ....................................................................................................................................... 48

4.4-1 ILS Technical Disciplines...................................................................................................................................... 66

6.6-1 Technical Data Tasks .......................................................................................................................................... 163

6.7-1 Program Technical Reviews............................................................................................................................... 170

6.7-2 P/SRR Entrance and Success Criteria............................................................................................................... 171

6.7-3 P/SDR Entrance and Success Criteria .............................................................................................................. 172

6.7-4 MCR Entrance and Success Criteria................................................................................................................. 173

6.7-5 SRR Entrance and Success Criteria................................................................................................................... 174

6.7-6 MDR Entrance and Success Criteria ................................................................................................................ 175

6.7-7 SDR Entrance and Success Criteria .................................................................................................................. 176

6.7-8 PDR Entrance and Success Criteria.................................................................................................................. 177

6.7-9 CDR Entrance and Success Criteria ................................................................................................................. 178

6.7-10 PRR Entrance and Success Criteria ................................................................................................................ 179

6.7-11 SIR Entrance and Success Criteria.................................................................................................................. 180

6.7-12 TRR Entrance and Success Criteria................................................................................................................ 181

6.7-13 SAR Entrance and Success Criteria ................................................................................................................ 182

6.7-14 ORR Entrance and Success Criteria .............................................................................................................. 183

6.7-15 FRR Entrance and Success Criteria ............................................................................................................... 184

6.7-16 PLAR Entrance and Success Criteria ............................................................................................................ 185

6.7-17 CERR Entrance and Success Criteria ............................................................................................................. 186

6.7-18 PFAR Entrance and Success Criteria.............................................................................................................. 186

6.7-19 DR Entrance and Success Criteria .................................................................................................................. 187

6.7-20 Functional and Physical Configuration Audits ............................................................................................ 189

6.7-21 Systems Engineering Process Metrics............................................................................................................ 196

6.8-1 Consequence Table ............................................................................................................................................. 199

6.8-2 Typical Information to Capture in a Decision Report .................................................................................. 202

7.1-1 Applying the Technical Processes on Contract............................................................................................... 220

7.1-2 Steps in the Requirements Development Process .......................................................................................... 224

7.1-3 Proposal Evaluation Criteria ............................................................................................................................. 227

7.1-4 Risks in Acquisition............................................................................................................................................ 228

7.1-5 Typical Work Product Documents................................................................................................................... 230

7.1-6 Contract-Subcontract Issues.............................................................................................................................. 231

7.4-1 Human and Organizational Analysis Techniques ......................................................................................... 249

7.5-1 Planetary Protection Mission Categories......................................................................................................... 259

7.5-2 Summarized Planetary Protection Requirements .......................................................................................... 259

D-1 Requirements Verification Matrix ...................................................................................................................... 283

E-1 Validation Requirements Matrix ......................................................................................................................... 284

G-1 Products Provided by the TA as a Function of Program/Project Phase ........................................................ 294

H-1 Integration Plan Contents.................................................................................................................................... 300

M-1 CM Plan Outline .................................................................................................................................................. 311

O-1 Typical Tradeoffs for Space Systems................................................................................................................... 316

O-2 Typical Tradeoffs in the Acquisition Process..................................................................................................... 316

O-3 Typical Tradeoffs Throughout the Project Life Cycle....................................................................................... 316
xii  NASA Systems Engineering Handbook

Table of Contents

Boxes

System Cost, Effectiveness, and Cost-Effectiveness..................................................................................................... 16

The Systems Engineer’s Dilemma .................................................................................................................................. 17

Program Formulation...................................................................................................................................................... 21

Program Implementation................................................................................................................................................ 21

Pre-Phase A: Concept Studies........................................................................................................................................ 22

Phase A: Concept and Technology Development........................................................................................................ 23

Phase B: Preliminary Design and Technology Completion ....................................................................................... 24

Phase C: Final Design and Fabrication ......................................................................................................................... 26

Phase D: System Assembly, Integration and Test, Launch.......................................................................................... 27

Phase E: Operations and Sustainment........................................................................................................................... 28

Phase F: Closeout ............................................................................................................................................................. 28

System Design Keys......................................................................................................................................................... 32

Example of Functional and Performance Requirements............................................................................................ 43

Rationale............................................................................................................................................................................ 48

DOD Architecture Framework ...................................................................................................................................... 51

Prototypes ......................................................................................................................................................................... 67

Product Realization Keys................................................................................................................................................ 72

Differences Between Verification and Validation Testing........................................................................................... 83

Types of Testing................................................................................................................................................................ 85

Types of Verification ........................................................................................................................................................ 86

Differences Between Verification and Validation Testing........................................................................................... 98

Types of Validation......................................................................................................................................................... 100

Examples of Enabling Products and Support Resources for Preparing to Conduct Validation.......................... 102

Model Verification and Validation............................................................................................................................... 104

Crosscutting Technical Management Keys................................................................................................................. 111

Gantt Chart Features...................................................................................................................................................... 117

WBS Hierarchies for Systems....................................................................................................................................... 126

Definitions....................................................................................................................................................................... 132

Typical Interface Management Checklist.................................................................................................................... 138

Key Concepts in Technical Risk Management .......................................................................................................... 139

Example Sources of Risk ............................................................................................................................................... 145

Limitations of Risk Matrices......................................................................................................................................... 145

Types of Configuration Change Management Changes ........................................................................................... 154

Warning Signs/Red Flags (How Do You Know When You’re in Trouble?)............................................................ 156

Redlines Were identified as One of the Major Causes of the NOAA N-Prime Mishap ....................................... 157

Inappropriate Uses of Technical Data.......................................................................................................................... 160

Data Collection Checklist ............................................................................................................................................. 162

Termination Review....................................................................................................................................................... 169

Analyzing the Estimate at Completion........................................................................................................................ 191

Examples of Technical Performance Measures ......................................................................................................... 193

An Example of a Trade Tree for a Mars Rover........................................................................................................... 207

Trade Study Reports....................................................................................................................................................... 208

Solicitations..................................................................................................................................................................... 219

Source Evaluation Board............................................................................................................................................... 226

Context Diagrams.......................................................................................................................................................... 292
NASA Systems Engineering Handbook  xiii

Preface

Since the writing of NASA/SP-6105 in 1995, systems 

engineering at the National Aeronautics and Space Administration (NASA), within national and international 

standard bodies, and as a discipline has undergone rapid 

evolution. Changes include implementing standards 

in the International Organization for Standardization 

(ISO) 9000, the use of Carnegie Mellon Software Engineering Institute’s Capability Maturity Model® Integration (CMMI®) to improve development and delivery of 

products, and the impacts of mission failures. Lessons 

learned on systems engineering were documented in reports such as those by the NASA Integrated Action Team 

(NIAT), the Columbia Accident Investigation Board 

(CAIB), and the follow-on Diaz Report. Out of these 

efforts came the NASA Office of the Chief Engineer 

(OCE) initiative to improve the overall Agency systems 

engineering infrastructure and capability for the efficient 

and effective engineering of NASA systems, to produce 

quality products, and to achieve mission success. In addition, Agency policy and requirements for systems engineering have been established. This handbook update 

is a part of the OCE-sponsored Agencywide systems engineering initiative.

In 1995, SP-6105 was initially published to bring the 

fundamental concepts and techniques of systems engineering to NASA personnel in a way that recognizes the 

nature of NASA systems and the NASA environment. 

This revision of SP-6105 maintains that original philosophy while updating the Agency’s systems engineering 

body of knowledge, providing guidance for insight into 

current best Agency practices, and aligning the handbook with the new Agency systems engineering policy.

The update of this handbook was twofold: a top-down 

compatibility with higher level Agency policy and a 

bottom-up infusion of guidance from the NASA practitioners in the field. The approach provided the opportunity to obtain best practices from across NASA and 

bridge the information to the established NASA systems engineering process. The attempt is to communicate principles of good practice as well as alternative 

approaches rather than specify a particular way to accomplish a task. The result embodied in this handbook is 

a top-level implementation approach on the practice of 

systems engineering unique to NASA. The material for 

updating this handbook was drawn from many different 

sources, including NASA procedural requirements, field 

center systems engineering handbooks and processes, as 

well as non-NASA systems engineering textbooks and 

guides.

This handbook consists of six core chapters: (1) systems 

engineering fundamentals discussion, (2) the NASA 

program/project life cycles, (3) systems engineering processes to get from a concept to a design, (4) systems engineering processes to get from a design to a final product, 

(5) crosscutting management processes in systems engineering, and (6) special topics relative to systems engineering. These core chapters are supplemented by appendices that provide outlines, examples, and further 

information to illustrate topics in the core chapters. The 

handbook makes extensive use of boxes and figures to 

define, refine, illustrate, and extend concepts in the core 

chapters without diverting the reader from the main information.

The handbook provides top-level guidelines for good 

systems engineering practices; it is not intended in any 

way to be a directive.

NASA/SP-2007-6105 Rev1 supersedes SP-6105, dated 

June 1995.

NASA Systems Engineering Handbook  xv

Acknowledgments

Primary points of contact: Stephen J. Kapurch, Office 

of the Chief Engineer, NASA Headquarters, and Neil E. 

Rainwater, Marshall Space Flight Center.

The following individuals are recognized as contributing 

practitioners to the content of this handbook revision:

■ Core Team Member (or Representative) from Center, 

Directorate, or Office

◆ Integration Team Member

• Subject Matter Expert Team Champion

 Subject Matter Expert

Arden Acord, NASA/Jet Propulsion Laboratory 

Danette Allen, NASA/Langley Research Center 

Deborah Amato, NASA/Goddard Space Flight Center •

Jim Andary, NASA/Goddard Space Flight Center ◆

Tim Beard, NASA/Ames Research Center 

Jim Bilbro, NASA/Marshall Space Flight Center 

Mike Blythe, NASA/Headquarters ■

Linda Bromley, NASA/Johnson Space Center ◆•■

Dave Brown, Defense Acquisition University 

John Brunson, NASA/Marshall Space Flight Center •

Joe Burt, NASA/Goddard Space Flight Center 

Glenn Campbell, NASA/Headquarters 

Joyce Carpenter, NASA/Johnson Space Center •

Keith Chamberlin, NASA/Goddard Space Flight Center 

Peggy Chun, NASA/NASA Engineering and Safety 

Center ◆•■

Cindy Coker, NASA/Marshall Space Flight Center 

Nita Congress, Graphic Designer ◆

Catharine Conley, NASA/Headquarters 

Shelley Delay, NASA/Marshall Space Flight Center 

Rebecca Deschamp, NASA/Stennis Space Center 

Homayoon Dezfuli, NASA/Headquarters •

Olga Dominguez, NASA/Headquarters 

Rajiv Doreswamy, NASA/Headquarters ■

Larry Dyer, NASA/Johnson Space Center 

Nelson Eng, NASA/Johnson Space Center 

Patricia Eng, NASA/Headquarters 

Amy Epps, NASA/Marshall Space Flight Center 

Chester Everline, NASA/Jet Propulsion Laboratory 

Karen Fashimpaur, Arctic Slope Regional Corporation ◆

Orlando Figueroa, NASA/Goddard Space Flight Center ■

Stanley Fishkind, NASA/Headquarters ■

Brad Flick, NASA/Dryden Flight Research Center ■

Marton Forkosh, NASA/Glenn Research Center ■

Dan Freund, NASA/Johnson Space Center 

Greg Galbreath, NASA/Johnson Space Center 

Louie Galland, NASA/Langley Research Center 

Yuri Gawdiak, NASA/Headquarters ■•

Theresa Gibson, NASA/Glenn Research Center 

Ronnie Gillian, NASA/Langley Research Center 

Julius Giriunas, NASA/Glenn Research Center 

Ed Gollop, NASA/Marshall Space Flight Center 

Lee Graham, NASA/Johnson Space Center 

Larry Green, NASA/Langley Research Center 

Owen Greulich, NASA/Headquarters ■

Ben Hanel, NASA/Ames Research Center 

Gena Henderson, NASA/Kennedy Space Center •

Amy Hemken, NASA/Marshall Space Flight Center 

Bob Hennessy, NASA/NASA Engineering and Safety 

Center 

Ellen Herring, NASA/Goddard Space Flight Center •

Renee Hugger, NASA/Johnson Space Center 

Brian Hughitt, NASA/Headquarters 

Eric Isaac, NASA/Goddard Space Flight Center ■

Tom Jacks, NASA/Stennis Space Center 

Ken Johnson, NASA/NASA Engineering and Safety 

Center 

Ross Jones, NASA/Jet Propulsion Laboratory ■

John Juhasz, NASA/Johnson Space Center 

Stephen Kapurch, NASA/Headquarters ■◆•

Jason Kastner, NASA/Jet Propulsion Laboratory 

Kristen Kehrer, NASA/Kennedy Space Center 

John Kelly, NASA/Headquarters 

Kriss Kennedy, NASA/Johnson Space Center 
xvi  NASA Systems Engineering Handbook

Acknowledgments

Steven Kennedy, NASA/Kennedy Space Center 

Tracey Kickbusch, NASA/Kennedy Space Center ■

Casey Kirchner, NASA/Stennis Space Center 

Kenneth Kumor, NASA/Headquarters 

Janne Lady, SAITECH/CSC 

Jerry Lake, Systems Management international 

Kenneth W. Ledbetter, NASA/Headquarters ■

Steve Leete, NASA/Goddard Space Flight Center 

William Lincoln, NASA/Jet Propulsion Laboratory 

Dave Littman, NASA/Goddard Space Flight Center 

John Lucero, NASA/Glenn Research Center 

Paul Luz, NASA/Marshall Space Flight Center 

Todd MacLeod, NASA/Marshall Space Flight Center 

Roger Mathews, NASA/Kennedy Space Center •

Bryon Maynard, NASA/Stennis Space Center 

Patrick McDuffee, NASA/Marshall Space Flight Center 

Mark McElyea, NASA/Marshall Space Flight Center 

William McGovern, Defense Acquisition University ◆

Colleen McGraw, NASA/Goddard Space Flight 

Center ◆•

Melissa McGuire, NASA/Glenn Research Center 

Don Mendoza, NASA/Ames Research Center 

Leila Meshkat, NASA/Jet Propulsion Laboratory 

Elizabeth Messer, NASA/Stennis Space Center •

Chuck Miller, NASA/Headquarters 

Scott Mimbs, NASA/Kennedy Space Center 

Steve Newton, NASA/Marshall Space Flight Center 

Tri Nguyen, NASA/Johnson Space Center 

Chuck Niles, NASA/Langley Research Center •

Cynthia Null, NASA/NASA Engineering and Safety 

Center 

John Olson, NASA/Headquarters 

Tim Olson, QIC, Inc. 

Sam Padgett, NASA/Johnson Space Center 

Christine Powell, NASA/Stennis Space Center ◆•■

Steve Prahst, NASA/Glenn Research Center 

Pete Prassinos, NASA/Headquarters ■

Mark Prill, NASA/Marshall Space Flight Center 

Neil Rainwater, NASA/Marshall Space Flight Center ■◆

Ron Ray, NASA/Dryden Flight Research Center 

Gary Rawitscher, NASA/Headquarters 

Joshua Reinert, ISL Inc. 

Norman Rioux, NASA/Goddard Space Flight Center 

Steve Robbins, NASA/Marshall Space Flight Center •

Dennis Rohn, NASA/Glenn Research Center ◆

Jim Rose, NASA/Jet Propulsion Laboratory 

Arnie Ruskin,* NASA/Jet Propulsion Laboratory •

Harry Ryan, NASA/Stennis Space Center 

George Salazar, NASA/Johnson Space Center 

Nina Scheller, NASA/Ames Research Center ■

Pat Schuler, NASA/Langley Research Center •

Randy Seftas, NASA/Goddard Space Flight Center 

Joey Shelton, NASA/Marshall Space Flight Center •

Robert Shishko, NASA/Jet Propulsion Laboratory ◆

Burton Sigal, NASA/Jet Propulsion Laboratory 

Sandra Smalley, NASA/Headquarters 

Richard Smith, NASA/Kennedy Space Center 

John Snoderly, Defense Acquisition University 

Richard Sorge, NASA/Glenn Research Center 

Michael Stamatelatos, NASA/Headquarters ■

Tom Sutliff, NASA/Glenn Research Center •

Todd Tofil, NASA/Glenn Research Center 

John Tinsley, NASA/Headquarters 

Rob Traister, Graphic Designer ◆

Clayton Turner, NASA/Langley Research Center ■

Paul VanDamme, NASA/Jet Propulsion Laboratory 

Karen Vaner, NASA/Stennis Space Center 

Lynn Vernon, NASA/Johnson Space Center 

Linda Voss, Technical Writer ◆

Britt Walters, NASA/Johnson Space Center ■

Tommy Watts, NASA/Marshall Space Flight Center 

Richard Weinstein, NASA/Headquarters 

Katie Weiss, NASA/Jet Propulsion Laboratory •

Martha Wetherholt, NASA/Headquarters 

Becky Wheeler, NASA/Jet Propulsion Laboratory 

Cathy White, NASA/Marshall Space Flight Center 

Reed Wilcox, NASA/Jet Propulsion Laboratory 

Barbara Woolford, NASA/Johnson Space Center •

Felicia Wright, NASA/Langley Research Center 

Robert Youngblood, ISL Inc. 

Tom Zang, NASA/Langley Research Center 

*In memory of.
NASA Systems Engineering Handbook  1

1.1 Purpose

This handbook is intended to provide general guidance 

and information on systems engineering that will be 

useful to the NASA community. It provides a generic description of Systems Engineering (SE) as it should be applied throughout NASA. A goal of the handbook is to increase awareness and consistency across the Agency and 

advance the practice of SE. This handbook provides perspectives relevant to NASA and data particular to NASA.

This handbook should be used as a companion for implementing NPR 7123.1, Systems Engineering Processes 

and Requirements, as well as the Center-specific handbooks and directives developed for implementing systems engineering at NASA. It provides a companion reference book for the various systems engineering related 

courses being offered under NASA’s auspices.

1.2 Scope and Depth

The coverage in this handbook is limited to general 

concepts and generic descriptions of processes, tools, 

and techniques. It provides information on systems engineering best practices and pitfalls to avoid. There are 

many Center-specific handbooks and directives as well as 

textbooks that can be consulted for in-depth tutorials.

This handbook describes systems engineering as it should 

be applied to the development and implementation of 

large and small NASA programs and projects. NASA 

has defined different life cycles that specifically address 

the major project categories, or product lines, which 

are: Flight Systems and Ground Support (FS&GS), Research and Technology (R&T), Construction of Facilities (CoF), and Environmental Compliance and Restoration (ECR). The technical content of the handbook 

provides systems engineering best practices that should 

be incorporated into all NASA product lines. (Check 

the NASA On-Line Directives Information System 

(NODIS) electronic document library for applicable 

NASA directives on topics such as product lines.) For 

simplicity this handbook uses the FS&GS product line 

as an example. The specifics of FS&GS can be seen in 

the description of the life cycle and the details of the 

milestone reviews. Each product line will vary in these 

two areas; therefore, the reader should refer to the applicable NASA procedural requirements for the specific 

requirements for their life cycle and reviews. The engineering of NASA systems requires a systematic and 

disciplined set of processes that are applied recursively 

and iteratively for the design, development, operation, 

maintenance, and closeout of systems throughout the 

life cycle of the programs and projects.

The handbook’s scope properly includes systems engineering functions regardless of whether they are performed by a manager or an engineer, in-house, or by a 

contractor.

1.0 Introduction

NASA Systems Engineering Handbook  3

Systems engineering is a methodical, disciplined approach for the design, realization, technical management, operations, and retirement of a system. A “system” 

is a construct or collection of different elements that together produce results not obtainable by the elements 

alone. The elements, or parts, can include people, hardware, software, facilities, policies, and documents; that is, 

all things required to produce system-level results. The 

results include system-level qualities, properties, characteristics, functions, behavior, and performance. The 

value added by the system as a whole, beyond that contributed independently by the parts, is primarily created 

by the relationship among the parts; that is, how they are 

interconnected.1 It is a way of looking at the “big picture” 

when making technical decisions. It is a way of achieving 

stakeholder functional, physical, and operational performance requirements in the intended use environment 

over the planned life of the systems. In other words, systems engineering is a logical way of thinking.

Systems engineering is the art and science of developing an operable system capable of meeting requirements within often opposed constraints. Systems engineering is a holistic, integrative discipline, wherein the 

contributions of structural engineers, electrical engineers, mechanism designers, power engineers, human 

factors engineers, and many more disciplines are evaluated and balanced, one against another, to produce a coherent whole that is not dominated by the perspective of 

a single discipline.2

Systems engineering seeks a safe and balanced design in 

the face of opposing interests and multiple, sometimes 

conflicting constraints. The systems engineer must develop the skill and instinct for identifying and focusing 

efforts on assessments to optimize the overall design 

1

Rechtin, Systems Architecting of Organizations: Why Eagles 

Can’t Swim.

2

Comments on systems engineering throughout Chapter 2.0 

are extracted from the speech “System Engineering and the 

Two Cultures of Engineering” by Michael D. Griffin, NASA 

Administrator. 

and not favor one system/subsystem at the expense 

of another. The art is in knowing when and where to 

probe. Personnel with these skills are usually tagged as 

“systems engineers.” They may have other titles—lead 

systems engineer, technical manager, chief engineer—

but for this document, we will use the term systems engineer.

The exact role and responsibility of the systems engineer may change from project to project depending on 

the size and complexity of the project and from phase 

to phase of the life cycle. For large projects, there may 

be one or more systems engineers. For small projects, 

sometimes the project manager may perform these 

practices. But, whoever assumes those responsibilities, 

the systems engineering functions must be performed. 

The actual assignment of the roles and responsibilities 

of the named systems engineer may also therefore vary. 

The lead systems engineer ensures that the system technically fulfills the defined needs and requirements and 

that a proper systems engineering approach is being followed. The systems engineer oversees the project’s systems engineering activities as performed by the technical team and directs, communicates, monitors, and 

coordinates tasks. The systems engineer reviews and 

evaluates the technical aspects of the project to ensure 

that the systems/subsystems engineering processes are 

functioning properly and evolves the system from concept to product. The entire technical team is involved in 

the systems engineering process.

The systems engineer will usually play the key role in 

leading the development of the system architecture, defining and allocating requirements, evaluating design 

tradeoffs, balancing technical risk between systems, defining and assessing interfaces, providing oversight of 

verification and validation activities, as well as many 

other tasks. The systems engineer will usually have the 

prime responsibility in developing many of the project 

documents, including the Systems Engineering Management Plan (SEMP), requirements/specification documents, verification and validation documents, certification packages, and other technical documentation. 

2.0 Fundamentals of Systems Engineering
4  NASA Systems Engineering Handbook

2.0 Fundamentals of Systems Engineering

In summary, the systems engineer is skilled in the art 

and science of balancing organizational and technical interactions in complex systems. However, since the entire 

team is involved in the systems engineering approach, 

in some ways everyone is a systems engineer. Systems 

engineering is about tradeoffs and compromises, about 

generalists rather than specialists. Systems engineering is 

about looking at the “big picture” and not only ensuring 

that they get the design right (meet requirements) but 

that they get the right design.

To explore this further, put SE in the context of project 

management. As discussed in NPR 7120.5, NASA Space 

Flight Program and Project Management Requirements, 

project management is the function of planning, overseeing, and directing the numerous activities required 

to achieve the requirements, goals, and objectives of the 

customer and other stakeholders within specified cost, 

quality, and schedule constraints. Project management 

can be thought of as having two major areas of emphasis, 

both of equal weight and importance. These areas are 

systems engineering and project control. Figure 2.0-1 is 

a notional graphic depicting this concept. Note that there 

are areas where the two cornerstones of project management overlap. In these areas, SE provides the technical 

aspects or inputs; whereas project control provides the 

programmatic, cost, and schedule inputs.

This document will focus on the SE side of the diagram. 

These practices/processes are taken from NPR 7123.1, 

NASA Systems Engineering Processes and Requirements. 

Each will be described in much greater detail in subsequent chapters of this document, but an overview is 

given below.

2.1 The Common Technical Processes 

and the SE Engine

There are three sets of common technical processes in 

NPR 7123.1, NASA Systems Engineering Processes and 

Requirements: system design, product realization, and 

technical management. The processes in each set and 

their interactions and flows are illustrated by the NPR 

systems engineering “engine” shown in Figure 2.1-1. The 

processes of the SE engine are used to develop and realize 

the end products. This chapter provides the application 

context of the 17 common technical processes required 

in NPR 7123.1. The system design processes, the product realization processes, and the technical management 

processes are discussed in more details in Chapters 4.0, 

5.0, and 6.0, respectively. Steps 1 through 9 indicated in 

Figure 2.1-1 represent the tasks in execution of a project. 

Steps 10 through 17 are crosscutting tools for carrying 

out the processes.

z System Design Processes: The four system design 

processes shown in Figure 2.1-1 are used to define 

and baseline stakeholder expectations, generate 

and baseline technical requirements, and convert 

the technical requirements into a design solution 

that will satisfy the baselined stakeholder expectations. These processes are 

applied to each product of 

the system structure from 

the top of the structure to 

the bottom until the lowest 

products in any system 

structure branch are defined to the point where 

they can be built, bought, 

or reused. All other products in the system structure 

are realized by integration. 

Designers not only develop 

the design solutions to the 

products intended to perform the operational functions of the system, but also 

SYSTEMS ENGINEERING PROJECT CONTROL

� System Design

– Requirements Denition

– Technical Solution Denition

� Product Realization

– Design Realization

– Evaluation

– Product Transition

� Technical Management

– Technical Planning

– Technical Control

 – Technical Assessment

 – Technical Decision Analysis

� Management Planning

� Integrated Assessment

� Schedule Management

� Conguration Management

� Resource Management

� Documentation and Data

Management

� Acquisition Management

� Planning

� Risk Management

� Conguration 

Management

� Data Management 

� Assessment

� Decision Analysis 

Figure 2.0‐1 SE in context of overall project management
2.1 The Common Technical Processes and the SE Engine

NASA Systems Engineering Handbook  5

establish requirements for the products and services 

that enable each operational/mission product in the 

system structure.

z Product Realization Processes: The product realization processes are applied to each operational/mission product in the system structure starting from 

the lowest level product and working up to higher 

level integrated products. These processes are used to 

create the design solution for each product (e.g., by 

the Product Implementation or Product Integration 

Process) and to verify, validate, and transition up to 

the next hierarchical level products that satisfy their 

design solutions and meet stakeholder expectations as 

a function of the applicable life-cycle phase.

z Technical Management Processes: The technical 

management processes are used to establish and 

evolve technical plans for the project, to manage 

communication across interfaces, to assess progress 

against the plans and requirements for the system 

products or services, to control technical execution of 

the project through to completion, and to aid in the 

decisionmaking process.

The processes within the SE engine are used both iteratively and recursively. As defined in NPR 7123.1, “iterative” is the “application of a process to the same product 

or set of products to correct a discovered discrepancy 

or other variation from requirements,” whereas “recursive” is defined as adding value to the system “by the 

repeated application of processes to design next lower 

layer system products or to realize next upper layer end 

products within the system structure. This also applies to 

repeating application of the same processes to the system 

structure in the next life-cycle phase to mature the 

system definition and satisfy phase success criteria.” The 

example used in Section 2.3 will further explain these 

concepts. The technical processes are applied recursively 

and iteratively to break down the initializing concepts of 

the system to a level of detail concrete enough that the 

technical team can implement a product from the information. Then the processes are applied recursively and 

Figure 2.1‐1 The systems engineering engine

Requirements flow down

from level above

Requirements flow down

to level below

Realized products

from level below 

PRODUCT

REALIZATION

PROCESSES

TECHNICAL MANAGEMENT

PROCESSES

Technical Decision Analysis

Process

17. Decision Analysis

Technical Planning

Process

10. Technical Planning

Technical Control

Processes

11. Requirements Management

12. Interface Management

15. Technical Data Management

14. Configuration Management

13. Technical Risk Management

Technical Assessment

Process

16. Technical Assessment

Realized products

to level above 

System design processes

applied to each work breakdown 

structure model down and 

across system structure 

Product realization processes

applied to each product

up and across

system structure

SYSTEM

DESIGN

PROCESSES

Requirements Definition

Processes

1. Stakeholder Expectations 

Definition

2. Technical Requirements

Definition

Technical Solution

Definition Processes 

3. Logical Decomposition

4. Design Solution Definition

Product Transition Process

9. Product Transition

Evaluation Processes

7. Product Verification

8. Product Validation

Design Realization

Processes

5. Product Implementation

6. Product Integration
6  NASA Systems Engineering Handbook

2.0 Fundamentals of Systems Engineering

iteratively to integrate the smallest product into greater 

and larger systems until the whole of the system has been 

assembled, verified, validated, and transitioned.

2.2 An Overview of the SE Engine by 

Project Phase

Figure 2.2-1 conceptually illustrates how the SE engine 

is used during each of the seven phases of a project. 

Figure 2.2-1 is a conceptual diagram. For all of the details, refer to the poster version of this figure, which accompanies this handbook.

The uppermost horizontal portion of this chart is used as 

a reference to project system maturity, as the project progresses from a feasible concept to an as-deployed system; 

phase activities; Key Decision Points (KDPs); and major 

project reviews.

The next major horizontal band shows the technical development processes (steps 1 through 9) in each project 

phase. The systems engineering engine cycles five times 

from Pre-Phase A through Phase D. Please note that 

NASA’s management has structured Phases C and D 

to “split” the technical development processes in half in 

Phases C and D to ensure closer management control. The 

engine is bound by a dashed line in Phases C and D.

Once a project enters into its operational state (Phase E) 

and closes with a closeout phase (Phase F), the technical 

work shifts to activities commensurate with these last 

two project phases.

The next major horizontal band shows the eight technical management processes (steps 10 through 17) in 

each project phase. The SE engine cycles the technical 

management processes seven times from Pre-Phase A 

through Phase F. 

Each of the engine entries is given a 6105 paragraph label 

that is keyed to Chapters 4.0, 5.0, and 6.0 in this handbook. For example, in the technical development processes, “Get Stakeholder Expectations” discussions and 

details are in Section 4.1. 

Pre-Phase A:

Concept Studies 

Approval Implementation

Technical Development Technical Management

5.2

Key Decision Points:

Major Reviews:

Feasible Concept Top-Level Architecture Functional Baseline Allocated

Baseline As-Deployed Baseline

6.1

6.8

6.1 

6.8 

6.1 

6.8 

6.1 

6.8 

6.1 

6.8 

6.1 

6.8 

6.1 

6.8 

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5.5

5.1

4.2

4.1

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4.4

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4.2

4.1

4.3

4.4

5.1

5.3

5.4

5.5

5.2

Product

Baseline

Phase F:

Closeout

Phase E:

Operations &

Sustainment

Phase D:

System Assembly,

Integration & Test, Launch

Phase B:

Preliminary Design &

Technology Completion

Phase A:

Concept & Technology

Development 

Phase C:

Final Design &

Fabrication

6.2

6.7

6.6

6.5

6.4

6.3

Formulation

Figure 2.2-1 A miniaturized conceptualization of the poster-size NASA project life-cycle process flow for 

flight and ground systems accompanying this handbook
2.3 Example of Using the SE Engine

NASA Systems Engineering Handbook  7

2.3 Example of Using the SE Engine

To help in understanding how the SE engine is applied, 

an example will be posed and walked through the processes. Pertinent to this discussion are the phases of the 

program and project life cycles, which will be discussed 

in greater depth in Chapter 3.0 of this document. As described in Chapter 3.0, NPR 7120.5 defines the life cycle 

used for NASA programs and projects. The life-cycle 

phases are described in Table 2.3-1.

Use of the different phases of a life cycle allows the various products of a project to be gradually developed and 

matured from initial concepts through the fielding of the 

product and to its final retirement. The SE engine shown 

in Figure 2.1-1 is used throughout all phases. 

In Pre-Phase A, the SE engine is used to develop the 

initial concepts; develop a preliminary/draft set of key 

high-level requirements; realize these concepts through 

modeling, mockups, simulation, or other means; and 

verify and validate that these concepts and products 

would be able to meet the key high-level requirements. 

Note that this is not the formal verification and validation program that will be performed on the final product 

but is a methodical runthrough ensuring that the concepts that are being developed in this Pre-Phase A would 

be able to meet the likely requirements and expectations 

of the stakeholders. Concepts would be developed to the 

lowest level necessary to ensure that the concepts are feasible and to a level that will reduce the risk low enough to 

satisfy the project. Academically, this process could proceed down to the circuit board level for every system. 

Table 2.3‐1 Project Life-Cycle Phases

Phase Purpose Typical Output

Formulation

Pre-Phase A

Concept 

Studies

To produce a broad spectrum of ideas and alternatives for missions 

from which new programs/projects can be selected. Determine feasibility of desired system, develop mission concepts, draft system-level 

requirements, identify potential technology needs.

Feasible system concepts 

in the form of simulations, 

analysis, study reports, 

models, and mockups

Phase A

Concept and 

Technology 

Development

To determine the feasibility and desirability of a suggested new major 

system and establish an initial baseline compatibility with NASA’s strategic plans. Develop final mission concept, system-level requirements, 

and needed system structure technology developments.

System concept definition 

in the form of simulations, 

analysis, engineering 

models, and mockups and 

trade study definition

Phase B

Preliminary 

Design and 

Technology 

Completion

To define the project in enough detail to establish an initial baseline 

capable of meeting mission needs. Develop system structure end 

product (and enabling product) requirements and generate a preliminary design for each system structure end product.

End products in the form 

of mockups, trade study 

results, specification and 

interface documents, and 

prototypes

Implementation

Phase C

Final Design 

and Fabrication

To complete the detailed design of the system (and its associated 

subsystems, including its operations systems), fabricate hardware, and 

code software. Generate final designs for each system structure end 

product.

End product detailed 

designs, end product 

component fabrication, 

and software development

Phase D

System 

Assembly, 

Integration and 

Test, Launch

To assemble and integrate the products to create the system, meanwhile developing confidence that it will be able to meet the system 

requirements. Launch and prepare for operations. Perform system 

end product implementation, assembly, integration and test, and 

transition to use.

Operations-ready system 

end product with supporting related enabling 

products

Phase E

Operations and 

Sustainment

To conduct the mission and meet the initially identified need and 

maintain support for that need. Implement the mission operations 

plan.

Desired system

Phase F

Closeout

To implement the systems decommissioning/disposal plan developed 

in Phase E and perform analyses of the returned data and any 

returned samples.

Product closeout 
8  NASA Systems Engineering Handbook

2.0 Fundamentals of Systems Engineering

However, that would involve a great deal of time and 

money. There may be a higher level or tier of product 

than circuit board level that would enable designers to 

accurately determine the feasibility of accomplishing the 

project (purpose of Pre-Phase A).

During Phase A, the recursive use of the SE engine is 

continued, this time taking the concepts and draft key 

requirements that were developed and validated during 

Pre-Phase A and fleshing them out to become the set of 

baseline system requirements and Concept of Operations (ConOps). During this phase, key areas of high risk 

might be simulated or prototyped to ensure that the concepts and requirements being developed are good ones 

and to identify verification and validation tools and techniques that will be needed in later phases.

During Phase B, the SE engine is applied recursively to 

further mature requirements for all products in the developing product tree, develop ConOps preliminary designs, and perform feasibility analysis of the verification 

and validation concepts to ensure the designs will likely 

be able to meet their requirements.

Phase C again uses the left side of the SE engine to finalize all requirement updates, finalize ConOps, develop 

the final designs to the lowest level of the product tree, 

and begin fabrication. Phase D uses the right side of the 

SE engine to recursively perform the final implementation, integration, verification, and validation of the end 

product, and at the final pass, transition the end product 

to the user. The technical management processes of the 

SE engine are used in Phases E and F to monitor performance; control configuration; and make decisions associated with the operations, sustaining engineering, and 

closeout of the system. Any new capabilities or upgrades 

of the existing system would reenter the SE engine as 

new developments.

2.3.1 Detailed Example

Since it is already well known, the NASA Space Transportation System (STS) will be used as an example to 

look at how the SE engine would be used in Phase A. 

This example will be simplified to illustrate the application of the SE processes in the engine, but will in no way 

be as detailed as necessary to actually build the highly 

complex vehicle. The SE engine is used recursively to 

drive out more and more detail with each pass. The icon 

shown in Figure 2.3-1 will be used to keep track of the applicable place in the SE engine. The numbers in the icon 

correspond to the numbered processes within 

the SE engine as shown 

in Figure 2.1-1. The various layers of the product 

hierarchy will be called 

“tiers.” Tiers are also 

called “layers,” or “levels.” 

But basically, the higher 

the number of the tier or level, the lower in the product 

hierarchy the product is going and the more detailed the 

product is becoming (e.g., going from boxes, to circuit 

boards, to components).

2.3.2 Example Premise

NASA decides that there is a need for a transportation 

system that will act like a “truck” to carry large pieces 

of equipment and crew into Low Earth Orbit (LEO). 

Referring back to the project life cycle, the project first 

enters the Pre-Phase A. During this phase, several concept studies are performed, and it is determined that it 

is feasible to develop such a “space truck.” This is determined through combinations of simulations, mockups, 

analyses, or other like means. For simplicity, assume feasibility will be proven through concept models. The processes and framework of the SE engine will be used to 

design and implement these models. The project would 

then enter the Phase A activities to take the Pre-Phase A 

concepts and refine them and define the system requirements for the end product. The detailed example will 

begin in Phase A and show how the SE engine is used. 

As described in the overview, a similar process is used 

for the other project phases.

2.3.2.1 Example Phase A System Design Passes

First Pass

Taking the preliminary concepts and drafting key system 

requirements developed during the Pre-Phase A activities, the SE engine is entered at the first process 

and used to determine 

who the product (i.e., 

the STS) stakeholders 

are and what they want. 

During Pre-Phase A these needs and expectations were 

pretty general ideas, probably just saying the Agency 

needs a “space truck” that will carry X tons of payload 

into LEO, accommodate a payload of so-and-so size, 

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Figure 2.3‐1 SE engine 

tracking icon

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2.3 Example of Using the SE Engine

NASA Systems Engineering Handbook  9

carry a crew of seven, etc. During this Phase A pass, 

these general concepts are detailed out and agreed to. 

The ConOps (sometimes referred to as operational concept) generated in Pre-Phase A is also detailed out and 

agreed to to ensure all stakeholders are in agreement as 

to what is really expected of the product—in this case 

the transportation system. The detailed expectations are 

then converted into good requirement statements. (For 

more information on what constitutes a good requirement, see Appendix C.) Subsequent passes and subsequent phases will refine these requirements into specifications that can actually be built. Also note that all of the 

technical management processes (SE engine processes 

numbered 10 through 17) are also used during this and 

all subsequent passes and activities. These ensure that all 

the proper planning, control, assessment, and decisions 

are used and maintained. Although for simplification 

they will not be mentioned in the rest of this example, 

they will always be in effect.

Next, using the requirements and the ConOps 

previously developed, 

logical decomposition 

models/diagrams are 

built up to help bring the 

requirements into perspective and to show their relationship. Finally, these diagrams, requirements, and ConOps 

documents are used to develop one or more feasible design solutions. Note that at this point, since this is only the 

first pass through the SE engine, these design solutions 

are not detailed enough to actually build anything. Consequently, the design solutions might be summarized as, 

“To accomplish this transportation system, the best option in our trade studies is a three-part system: a reusable orbiter for the crew and cargo, a large external tank 

to hold the propellants, and two solid rocket boosters to 

give extra power for liftoff that can be recovered, refurbished, and reused.” (Of course, the actual design solution would be much more descriptive and detailed). So, 

for this first pass, the first tier of the product hierarchy 

might look like Figure 2.3-2. There would also be other 

enabling products that might appear in the product tree, 

but for simplicity only, the main products are shown in 

this example.

Now, obviously design solution is not yet at a detailed 

enough level to actually build the prototypes or models 

of any of these products. The requirements, ConOps, 

functional diagrams, and design solutions are still at a 

pretty high, general level. Note that the SE processes on 

the right side (i.e., the product realization processes) of 

the SE engine have yet to be addressed. The design must 

first be at a level that something can actually be built, 

coded, or reused before that side of the SE engine can be 

used. So, a second pass of the left side of the SE engine 

will be started.

Second Pass

The SE engine is completely recursive. That is, each of 

the three elements shown in the tier 1 diagram can now 

be considered a product 

of its own and the SE engine is therefore applied 

to each of the three elements separately. For example, the external tank 

is considered an end product and the SE engine resets 

back to the first processes. So now, just focusing on the 

external tank, who are the stakeholders and what they 

expect of the external tank is determined. Of course, one 

of the main stakeholders will be the owners of the tier 1 

requirements and the STS as an end product, but there 

will also be other new stakeholders. A new ConOps for 

how the external tank would operate is generated. The 

tier 1 requirements that are applicable (allocated) to the 

external tank would be “flowed down” and validated. 

Usually, some of these will be too general to implement 

into a design, so the requirements will have to be detailed out. To these derived requirements, there will also 

be added new requirements that are generated from the 

stakeholder expectations, and other applicable standards 

for workmanship, safety, quality, etc.

Next, the external tank requirements and the external 

tank ConOps are established, and functional diagrams 

are developed as was done in the first pass with the STS 

product. Finally, these diagrams, requirements, and 

ConOps documents are used to develop some feasible 

design solutions for the external tank. At this pass, there 

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External

Tank

Orbiter Tier 1

Tier 0

Solid

Rocket Booster

Space

Transportation System 

Figure 2.3‐2 Product hierarchy, tier 1: first pass 

through the SE engine

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10  NASA Systems Engineering Handbook

2.0 Fundamentals of Systems Engineering

will also not be enough 

detail to actually build 

or prototype the external 

tank. The design solution 

might be summarized as, 

“To build this external 

tank, since our trade studies showed the best option was 

to use cryogenic propellants, a tank for the liquid hydrogen will be needed as will another tank for the liquid 

oxygen, instrumentation, and an outer structure of aluminum coated with foam.” Thus, the tier 2 product tree 

for the external tank might look like Figure 2.3-3.

In a similar manner, the 

orbiter would also take 

another pass through the 

SE engine starting with 

identifying the stakeholders and their expectations, and generating a ConOps for the orbiter element. 

The tier 1 requirements that are applicable (allocated) to 

the orbiter would be “flowed down” and validated; new 

requirements derived from them and any additional 

requirements (including interfaces with the other elements) would be added.

Next, the orbiter requirements and the ConOps 

are taken, functional diagrams are developed, 

and one or more feasible 

design solutions for the 

orbiter are generated. As with the external tank, at this 

pass, there will not be enough detail to actually build or 

do a complex model of the orbiter. The orbiter design 

solution might be summarized as, “To build this orbiter 

will require a winged vehicle with a thermal protection 

system; an avionics system; a guidance, navigation, and 

control system; a propulsion system; an environmental 

control system; etc.” So the tier 2 product tree for the 

orbiter element might look like Figure 2.3-4.

Likewise, the solid rocket booster would also be considered an end product, and a pass through the SE engine 

would generate a tier 2 design concept, just as was done 

with the external tank and the orbiter.

Third Pass

Each of the tier 2 elements is also considered an end 

product, and each undergoes another pass through 

the SE engine, defining 

stakeholders, generating 

ConOps, flowing down 

allocated requirements, 

generating new and derived requirements, and 

developing functional diagrams and design solution 

concepts. As an example of just the avionics system element, the tier 3 product hierarchy tree might look like 

Figure 2.3-5.

Passes 4 Through n

For this Phase A set of passes, this recursive process is 

continued for each product (model) on each tier down 

to the lowest level in the product tree. Note that in some 

projects it may not be feasible, given an estimated project 

cost and schedule, to perform this recursive process completely down to the smallest component during Phase A. 

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Figure 2.3‐3 Product hierarchy, tier 2: 

external tank

External

Tank

Orbiter Solid

Rocket

Booster

Space

Transportation

System 

Tier 1

Tier 0

Tier 2 Hydrogen

Tank

InstrumentationExternal

Structure

Oxygen

Tank

External

Tank

Orbiter Solid

Rocket

Booster

Space

Transportation

System 

Tier 1

Tier 0

Tier 2

External

Structure

Environmental

Control

System

Avionics

System

Thermal

Protection

System

Etc.

Figure 2.3‐4 Product hierarchy, tier 2: orbiter

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2.3 Example of Using the SE Engine

NASA Systems Engineering Handbook  11

In these cases, engineering judgment must 

be used to determine 

what level of the product 

tier is feasible. Note that 

the lowest feasible level 

may occur at different tiers depending on the productline complexity. For example, for one product line it may 

occur at tier 2; whereas, for a more complex product, it 

could occur at tier 8. This also means that it will take different amounts of time to reach the bottom. Thus, for 

any given program or project, products will be at various stages of development. For this Phase A example, 

Figure 2.3-6 depicts the STS product hierarchy after completely passing through the system design processes side 

of the SE engine. At the end of this set of passes, system 

requirements, ConOps, and high-level conceptual functional and physical architectures for each product in the 

tree would exist. Note that these would not yet be the 

detailed or even preliminary designs for the end prod1

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Figure 2.3‐5 Product hierarchy, tier 3: avionics system

External

Tank

Orbiter Solid

Rocket Booster

Space

Transportation System 

Tier 1

Tier 0

Tier 2

External

Structure

Environmental

Control System

Avionics

System

Thermal

Protection

System

Etc.

Tier 3

Communication

System

Displays &

Controls

Command & Data

Handling System

Instrumentation

System

Etc.

Figure 2.3‐6 Product hierarchy: complete pass through system design processes side of the SE engine

Note: The unshaded boxes represent bottom-level phase products.

External

Tank

Orbiter Solid

Rocket Booster

Space

Transportation System 

Tier 1

Tier 0

Tier 2

Tier 3

Tier 4

Tier 5

Tier 6

A B C n A B C n A B

Aa Ab Ba Bb Ca Cn Aa Ab Ba Bb

Aaa Aab Baa Bab Caa Cab

Baaa Baab Caba Cabb

Baaba Baabb

Aa Ab Ba Bb Ca Cn

Aba Abb Caa Cab

Caba Cabb

Aaa Aab Bba Bbb

Bbaa Bbbb
12  NASA Systems Engineering Handbook

2.0 Fundamentals of Systems Engineering

ucts. These will come later in the life cycle. At this point, 

enough conceptual design work has been done to ensure 

that at least the high-risk requirements are achievable as 

will be shown in the following passes.

2.3.2.2 Example Product Realization Passes

So now that the requirements and conceptual designs for 

the principal Phase A products have been developed, they 

need to be checked to ensure they are achievable. Note that 

there are two types of products. The first product is the 

“end product”—the one that will actually be delivered to 

the final user. The second type of product will be called 

a “phase product.” A phase product is generated within a 

particular life-cycle phase that helps move the project toward delivering a final product. For example, while in PrePhase A, a foam-core mockup might be built to help visualize some of the concepts. Those mockups would not be 

the final “end product,” but would be the “phase product.” 

For this Phase A example, assume some computer models 

will be created and simulations performed of these key 

concepts to show that they are achievable. These will be 

the phase product for our example. 

Now the focus shifts to the right side (i.e., product realization processes) of the SE engine, which will be applied 

recursively, starting at the bottom of the product hierarchy and moving upwards.

First Pass 

Each of the phase products (i.e., our computer models) 

for the bottom-level product tier (ones that are unshaded 

in Figure 2.3-6) is taken 

individually and realized—that is, it is either 

bought, built, coded, or 

reused. For our example, 

assume the external tank 

product model Aa is a standard Commercial-Off-theShelf (COTS) product that is bought. Aba is a model that 

can be reused from another project, and product Abb is 

a model that will have to be developed with an in-house 

design that is to be built. Note that these models are 

parts of a larger model product that will be assembled 

or integrated on a subsequent runthrough of the SE engine. That is, to realize the model for product Ab of the 

external tank, models for products Aba and Abb must 

be first implemented and then later integrated together. 

This pass of the SE engine will be the realizing part. Likewise, each of the unshaded bottom-level model products 

is realized in this first pass. The models will help us understand and plan the method to implement the final 

end product and will ensure the feasibility of the implemented method.

Next, each of the realized 

models (phase products) 

are used to verify that the 

end product would likely 

meet the requirements as 

defined in the Technical 

Requirements Definition Process during the system design pass for this product. This shows the product would 

likely meet the “shall” statements that were allocated, 

derived, or generated for it by method of test, analysis, 

inspection, or demonstration—that it was “built right.” 

Verification is performed for each of the unshaded 

bottom-level model products. Note that during this 

Phase A pass, this process is not the formal verification 

of the final end product. However, using analysis, simulation, models, or other means shows that the requirements are good (verifiable) and that the concepts will 

most likely satisfy them. This also allows draft verification procedures of key areas to be developed. What can 

be formally verified, however, is that the phase product 

(the model) meets the requirements for the model.

After the phase product 

(models) has been verified and used for planning 

the end product verification, the models are then 

used for validation. That 

is, additional test, analysis, inspection, or demonstrations 

are conducted to ensure that the proposed conceptual designs will likely meet the expectations of the stakeholders 

for this phase product and for the end product. This will 

track back to the ConOps that was mutually developed 

with the stakeholders during the Stakeholder Expectations Definition Process of the system design pass for 

this product. This will help ensure that the project has 

“built the right” product at this level.

After verification and 

validation of the phase 

product (models) and 

using it for planning the 

verification and validation of the end product, 

it is time to prepare the model for transition to the next 

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2.3 Example of Using the SE Engine

NASA Systems Engineering Handbook  13

level up. Depending on complexity, where the model will 

be transitioned, security requirements, etc., transition 

may involve crating and shipment, transmitting over a 

network, or hand carrying over to the next lab. Whatever 

is appropriate, each model for the bottom-level product 

is prepared and handed to the next level up for further 

integration.

Second Pass

Now that all the models (phase products) for the bottomlevel end products are realized, verified, validated, and 

transitioned, it is time 

to start integrating them 

into the next higher level 

product. For example, for 

the external tank, realized 

tier 4 models for product 

Aba and Abb are integrated to form the model for the 

tier 3 product Ab. Note that the Product Implementation 

Process only occurs at the bottommost product. All subsequent passes of the SE engine will employ the Product 

Integration Process since already realized products will 

be integrated to form the new higher level products. Integrating the lower tier phase products will result in the 

next-higher-tier phase product. This integration process 

can also be used for planning the integration of the final 

end products.

After the new integrated 

phase product (model) 

has been formed (tier 3 

product Ab for example), 

it must now be proven 

that it meets its requirements. These will be the allocated, derived, or generated 

requirements developed during the Technical Requirements Definition Process during the system design pass 

for the model for this integrated product. This ensures that 

the integrated product was built (assembled) right. Note 

that just verifying the component parts (i.e., the individual 

models) that were used in the integration is not sufficient 

to assume that the integrated product will work right. 

There are many sources of problems that could occur—

incomplete requirements at the interfaces, wrong assumptions during design, etc. The only sure way of knowing if 

an integrated product is good is to perform verification 

and validation at each stage. The knowledge gained from 

verifying this integrated phase product can also be used 

for planning the verification of the final end products.

Likewise, after the integrated phase product is 

verified, it needs to be 

validated to show that it 

meets the expectations 

as documented in the 

ConOps for the model of the product at this level. Even 

though the component parts making up the integrated 

product will have been validated at this point, the only 

way to know that the project has built the “right” integrated product is to perform validation on the integrated 

product itself. Again, this information will help in the 

planning for the validation of the end products.

The model for the integrated phase product at 

this level (tier 3 product 

Ab for example) is now 

ready to be transitioned 

to the next higher level 

(tier 2 for the example). As with the products in the first 

pass, the integrated phase product is prepared according 

to its needs/requirements and shipped or handed over. 

In the example, the model for the external tank tier 3 integrated product Ab is transitioned to the owners of the 

model for the tier 2 product A. This effort with the phase 

products will be useful in planning for the transition of 

the end products.

Passes 3 Through n

In a similar manner as the second pass, the tier 3 models 

for the products are integrated together, realized, verified, validated, and transitioned to the next higher 

tier. For the example, 

the realized model for 

external tank tier 3 integrated phase product 

Ab is integrated with the model for tier 3 realized phase 

product Aa to form the tier 2 phase product A. Note that 

tier 3 product Aa is a bottom-tier product that has yet 

to go through the integration process. It may also have 

been realized some time ago and has been waiting for the 

Ab product line to become realized. Part of its transition 

might have been to place it in secure storage until the 

Ab product line became available. Or it could be that Aa 

was the long-lead item and product Ab had been completed some time ago and was waiting for the Aa purchase to arrive before they could be integrated together. 

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The length of the branch of the product tree does not necessarily translate to a corresponding length of time. This 

is why good planning in the first part of a project is so 

critical.

Final Pass

At some point, all the models for the tier 1 phase products will each have been used to ensure the system requirements and concepts developed during 

this Phase A cycle can be 

implemented, integrated, 

verified, validated, and 

transitioned. The elements are now defined as the external tank, the orbiter, 

and the solid rocket boosters. One final pass through 

the SE engine will show that they will likely be successfully implemented, integrated, verified, and validated. 

The final of these products—in the form of the baselined system requirements, ConOps, conceptual functional and physical designs—are made to provide inputs 

into the next life-cycle phase (B) where they will be further matured. In later phases, the products will actually 

be built into physical form. At this stage of the project, 

the key characteristics of each product are passed downstream in key SE documentation, as noted.

2.3.2.3 Example Use of the SE Engine in 

Phases B Through D

Phase B begins the preliminary design of the final end 

product. The recursive passes through the SE engine are 

repeated in a similar manner to that discussed in the detailed Phase A example. At this phase, the phase product 

might be a prototype of the product(s). Prototypes could 

be developed and then put through the planned verification and validation processes to ensure the design will 

likely meet all the requirements and expectations prior 

to the build of the final flight units. Any mistakes found 

on prototypes are much easier and less costly to correct 

than if not found until the flight units are built and undergoing the certification process.

Whereas the previous phases dealt with the final product 

in the form of analysis, concepts, or prototypes, Phases 

C and D work with the final end product itself. During 

Phase C, we recursively use the left side of the SE engine 

to develop the final design. In Phase D, we recursively use 

the right side of the SE engine to realize the final product 

and conduct the formal verification and validation of the 

final product. As we come out of the last pass of the SE 

engine in Phase D, we have the final fully realized end 

product, the STS, ready to be delivered for launch.

2.3.2.4 Example Use of the SE Engine in 

Phases E and F

Even in Phase E (Operations and Sustainment) and 

Phase F (Closeout) of the life cycle, the technical management processes in the 

SE engine are still being 

used. During the operations phase of a project, 

a number of activities are 

still going on. In addition to the day-to-day use of the product, there is a need 

to monitor or manage various aspects of the system. 

This is where the key Technical Performance Measures 

(TPMs) that were defined in the early stages of development continue to play a part. (TPMs are described in 

Subsection 6.7.2.) These are great measures to monitor 

to ensure the product continues to perform as designed 

and expected. Configurations are still under control, still 

executing the Configuration Management Process. Decisions are still being made using the Decision Analysis 

Process. Indeed, all of the technical management processes still apply. For this discussion, the term “systems 

management” will be used for this aspect of operations. 

In addition to systems management and systems operation, there may also be a need for periodic refurbishment, repairing broken parts, cleaning, sparing, logistics, or other activities. Although other terms are used, 

for the purposes of this discussion the term “sustaining 

engineering” will be used for these activities. Again, all of 

the technical management processes still apply to these 

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Figure 2.3‐7 Model of typical activities during 

operational phase (Phase E) of a product

Sustaining

Engineering

SystemsManagement

Phase E

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2.3 Example of Using the SE Engine

NASA Systems Engineering Handbook  15

activities. Figure 2.3-7 represents these three activities 

occurring simultaneously and continuously throughout 

the operational lifetime of the final product. Some portions of the SE processes need to continue even after the 

system becomes nonoperational to handle retirement, 

decommissioning, and disposal. This is consistent with 

the basic SE principle of handling the full system life 

cycle from “cradle to grave.”

However, if at any point in this phase a new product, a 

change that affects the design or certification of a product, 

or an upgrade to an existing product is needed, the development processes of the SE engine are reentered at the 

top. That is, the first thing that is done for an upgrade is 

to determine who the stakeholders are and what they expect. The entire SE engine is used just as for a newly developed product. This might be pictorially portrayed as in 

Figure 2.3-8. Note that in the figure although the SE engine 

is shown only once, it is used recursively down through 

the product hierarchy for upgraded products, just as described in our detailed example for the initial product.

2.4 Distinctions Between Product 

Verification and Product 

Validation

From a process perspective, the Product Verification and 

Product Validation Processes may be similar in nature, 

but the objectives are fundamentally different. Verification of a product shows proof of compliance with requirements—that the product can meet each “shall” statement 

as proven though performance of a test, analysis, inspection, or demonstration. Validation of a product shows that 

the product accomplishes the intended purpose in the intended environment—that it meets the expectations of the 

customer and other stakeholders as shown through performance of a test, analysis, inspection, or demonstration.

Verification testing relates back to the approved requirements set and can be performed at different stages in the 

product life cycle. The approved specifications, drawings, parts lists, and other configuration documentation establish the configuration baseline of that product, 

which may have to be modified at a later time. Without a 

verified baseline and appropriate configuration controls, 

later modifications could be costly or cause major performance problems. 

Validation relates back to the ConOps document. Validation testing is conducted under realistic conditions (or 

simulated conditions) on end products for the purpose 

of determining the effectiveness and suitability of the 

product for use in mission operations by typical users. 

The selection of the verification or validation method is 

based on engineering judgment as to which is the most 

effective way to reliably show the product’s conformance 

to requirements or that it will operate as intended and 

described in the ConOps. 

Figure 2.3‐8 New products or upgrades reentering the SE engine

Susta ni ing

Engineering

SystemsManagement

Phase B

Phase C

P

hase

D

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Initial Idea

Phase F 

Closeout

Upgrades/Changes Reenter SE Engine

at Stakeholder Expectations Denition

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16  NASA Systems Engineering Handbook

2.0 Fundamentals of Systems Engineering

2.5 Cost Aspect of Systems 

Engineering

The objective of systems engineering is to see that the 

system is designed, built, and operated so that it accomplishes its purpose safely in the most cost-effective way 

possible considering performance, cost, schedule, and 

risk.

A cost-effective and safe system must provide a particular kind of balance between effectiveness and cost: the 

system must provide the most effectiveness for the resources expended, or equivalently, it must be the least 

expensive for the effectiveness it provides. This condition 

is a weak one because there are usually many designs 

that meet the condition. Think of each possible design 

as a point in the tradeoff space between effectiveness and 

cost. A graph plotting the maximum achievable effectiveness of designs available with current technology as 

a function of cost would, in general, yield a curved line 

such as the one shown in Figure 2.5-1. (In the figure, all 

the dimensions of effectiveness are represented by the 

ordinate (y axis) and all the dimensions of cost by the 

abscissa (x axis).) In other words, the curved line represents the envelope of the currently available technology 

in terms of cost-effectiveness. 

Points above the line cannot be achieved with currently 

available technology; that is, they do not represent feasible designs. (Some of those points may be feasible in 

the future when further technological advances have 

been made.) Points inside the envelope are feasible, but 

are said to be dominated by designs whose combined 

cost and effectiveness lie on the envelope line. Designs 

represented by points on the envelope line are called 

cost-effective (or efficient or nondominated) solutions. 

Design trade studies, an important part of the systems 

engineering process, often attempt to find designs that 

provide a better combination of the various dimensions 

of cost and effectiveness. When the starting point for a 

design trade study is inside the envelope, there are alternatives that either reduce costs with change to the overall 

effectiveness or alternatives that improve effectiveness 

without a cost increase (i.e., moving closer to the envelope curve). Then, the systems engineer’s decision is easy. 

Other than in the sizing of subsystems, such “win-win” 

design trades are uncommon, but by no means rare. 

When the alternatives in a design trade study require 

trading cost for effectiveness, or even one dimension of 

effectiveness for another at the same cost (i.e., moving 

parallel to the envelope curve), the decisions become 

harder.

System Cost, Effectiveness, and 

Cost-Effectiveness

z Cost: The cost of a system is the value of the resources needed to design, build, operate, and 

dispose of it. Because resources come in many 

forms—work performed by NASA personnel and 

contractors; materials; energy; and the use of facilities and equipment such as wind tunnels, factories, 

offices, and computers—it is convenient to express 

these values in common terms by using monetary 

units (such as dollars of a specified year).

z Effectiveness: The effectiveness of a system is a 

quantitative measure of the degree to which the 

system’s purpose is achieved. Effectiveness measures are usually very dependent upon system performance. For example, launch vehicle effectiveness depends on the probability of successfully 

injecting a payload onto a usable trajectory. The 

associated system performance attributes include 

the mass that can be put into a specified nominal 

orbit, the trade between injected mass and launch 

velocity, and launch availability.

z Cost-Effectiveness: The cost-effectiveness of a system combines both the cost and the effectiveness 

of the system in the context of its objectives. While 

it may be necessary to measure either or both of 

those in terms of several numbers, it is sometimes 

possible to combine the components into a meaningful, single-valued objective function for use in design optimization. Even without knowing how to 

trade effectiveness for cost, designs that have lower 

cost and higher effectiveness are always preferred.

Figure 2.5‐1 The enveloping surface of 

nondominated designs

Cost

Eectiveness

There are no designs

that produce results in

this portion of the

trade space 

All possible designs with

currently known technology

produce results somewhere 

in this portion of the trade

space 
2.5 Cost Aspect of Systems Engineering

NASA Systems Engineering Handbook  17

The process of finding the most cost-effective design is 

further complicated by uncertainty, which is shown in 

Figure 2.5-2. Exactly what outcomes will be realized by 

a particular system design cannot be known in advance 

with certainty, so the projected cost and effectiveness of a 

design are better described by a probability distribution 

than by a point. This distribution can be thought of as a 

cloud that is thickest at the most likely value and thinnest 

farthest away from the most likely point, as is shown for 

design concept A in the figure. Distributions resulting 

from designs that have little uncertainty are dense and 

highly compact, as is shown for concept B. Distributions 

associated with risky designs may have significant probabilities of producing highly undesirable outcomes, as is 

suggested by the presence of an additional low-effectiveness/high-cost cloud for concept C. (Of course, the envelope of such clouds cannot be a sharp line such as is 

shown in the figure, but must itself be rather fuzzy. The 

line can now be thought of as representing the envelope 

at some fixed confidence level, that is, a specific, numerical probability of achieving that effectiveness.) 

Both effectiveness and cost may require several descriptors. Even the Echo balloons (circa 1960), in addition 

to their primary mission as communications satellites, 

obtained scientific data on the electromagnetic environment and atmospheric drag. Furthermore, Echo was 

the first satellite visible to the naked eye, an unquantifiable—but not unrecognized at the beginning of the 

space race—aspect of its effectiveness. Sputnik (circa 

1957), for example, drew much of its effectiveness from 

the fact that it was a “first.” Costs, the expenditure of limited resources, may be measured in the several dimensions of funding, personnel, use of facilities, and so on. 

Schedule may appear as an attribute of effectiveness or 

cost, or as a constraint. A mission to Mars that misses its 

launch window has to wait about two years for another 

opportunity—a clear schedule constraint.

In some contexts, it is appropriate to seek the most effectiveness possible within a fixed budget and with a fixed 

risk; in other contexts, it is more appropriate to seek the 

least cost possible with specified effectiveness and risk. 

In these cases, there is the question of what level of effectiveness to specify or what level of costs to fix. In practice, these may be mandated in the form of performance 

or cost requirements. It then becomes appropriate to ask 

whether a slight relaxation of requirements could produce a significantly cheaper system or whether a few 

more resources could produce a significantly more effective system. 

The technical team must choose among designs that 

differ in terms of numerous attributes. A variety of 

methods have been developed that can be used to help 

uncover preferences between attributes and to quantify 

subjective assessments of relative value. When this can 

be done, trades between attributes can be assessed quantitatively. Often, however, the attributes seem to be truly 

incommensurate: decisions need to be made in spite of 

this multiplicity.

Figure 2.5‐2 Estimates of outcomes to be 

obtained from several design concepts including 

uncertainty

Note: A, B, and C are design concepts with different risk patterns.

B

C

A

Cost

Eectiveness

The Systems Engineer’s Dilemma

At each cost-effective solution:

z To reduce cost at constant risk, performance must 

be reduced.

z To reduce risk at constant cost, performance must 

be reduced.

z To reduce cost at constant performance, higher 

risks must be accepted.

z To reduce risk at constant performance, higher 

costs must be accepted.

In this context, time in the schedule is often a critical 

resource, so that schedule behaves like a kind of cost.

NASA Systems Engineering Handbook  19

3.0 NASA Program/Project Life Cycle

One of the fundamental concepts used within NASA for 

the management of major systems is the program/project 

life cycle, which consists of a categorization of everything 

that should be done to accomplish a program or project 

into distinct phases, separated by Key Decision Points 

(KDPs). KDPs are the events at which the decision authority determines the readiness of a program/project to 

progress to the next phase of the life cycle (or to the next 

KDP). Phase boundaries are defined so that they provide 

more or less natural points for Go or No-Go decisions. 

Decisions to proceed may be qualified by liens that must 

be removed within an agreed to time period. A program 

or project that fails to pass a KDP may be allowed to “go 

back to the drawing board” to try again later—or it may 

be terminated.

All systems start with the recognition of a need or the 

discovery of an opportunity and proceed through various stages of development to a final disposition. While 

the most dramatic impacts of the analysis and optimization activities associated with systems engineering are 

obtained in the early stages, decisions that affect millions 

of dollars of value or cost continue to be amenable to the 

systems approach even as the end of the system lifetime 

approaches.

Decomposing the program/project life cycle into phases 

organizes the entire process into more manageable pieces. 

The program/project life cycle should provide managers 

with incremental visibility into the progress being made 

at points in time that fit with the management and budgetary environments.

NPR 7120.5, NASA Space Flight Program and Project 

Management Requirements defines the major NASA 

life-cycle phases as Formulation and Implementation. 

For Flight Systems and Ground Support (FS&GS) 

projects, the NASA life-cycle phases of Formulation 

and Implementation divide into the following seven 

incremental pieces. The phases of the project life cycle 

are:

z Pre-Phase A: Concept Studies (i.e., identify feasible 

alternatives)

z Phase A: Concept and Technology Development (i.e., 

define the project and identify and initiate necessary 

technology)

z Phase B: Preliminary Design and Technology Completion (i.e., establish a preliminary design and develop necessary technology)

z Phase C: Final Design and Fabrication (i.e., complete 

the system design and build/code the components)

z Phase D: System Assembly, Integration and Test, 

Launch (i.e., integrate components, and verify the 

system, prepare for operations, and launch)

z Phase E: Operations and Sustainment (i.e., operate 

and maintain the system)

z Phase F: Closeout (i.e., disposal of systems and analysis of data)

Figure 3.0-1 (NASA program life cycle) and Figure 3.0-2 

(NASA project life cycle) identify the KDPs and reviews that characterize the phases. Sections 3.1 and 3.2 

contain narrative descriptions of the purposes, major 

activities, products, and KDPs of the NASA program 

life-cycle phases. Sections 3.3 to 3.9 contain narrative 

descriptions of the purposes, major activities, products, and KDPs of the NASA project life-cycle phases. 

Section 3.10 describes the NASA budget cycle within 

which program/project managers and systems engineers must operate.

3.1 Program Formulation

The program Formulation phase establishes a cost-effective program that is demonstrably capable of meeting 

Agency and mission directorate goals and objectives. 

The program Formulation Authorization Document 

(FAD) authorizes a Program Manager (PM) to initiate 

the planning of a new program and to perform the analyses required to formulate a sound program plan. Major 

reviews leading to approval at KDP I are the P/SRR, 

P/SDR, PAR, and governing Program Management 

Council (PMC) review. (See full list of reviews in the 

program and project life cycle figures on the next page.) 

A summary of the required gate products for the pro-
20  NASA Systems Engineering Handbook

3.0 NASA Program/Project Life Cycle

Formulation Implementation

KDP 0 KDP I KDP II KDP III KDP IV

NASA LifeCycle Phases

Approval

Major Program

Reviews

Key Decision

Points KDP n

P/SRR P/SDR

PSR

PDR CDR ORR

Uncoupled & Loosely Coupled Programs

Or

Single-Project & Tightly Coupled Programs

SIR C TRR ERR

PSRs, PIRs, and KDPs are conducted ~ every 2 years

Or

FRR PLAR PSR

Figure 3.0‐1 NASA program life cycle

Formulation Implementation

MCR PDR SAR FRR PLAR CERR DR

MCR

SRR SDR

SRR MDR PDR

CDR/PRR

CDR/PRR FRR

ORR

ORR DR

SIR

SIR PLAR CERR

PFAR

KDP A KDP B KDP C KDP D KDP E

Launch

NASA LifeCycle Phases

Approval

Project LifeCycle Phases

Supporting

Reviews

Robotic Mission

Reviews

Human Space

Flight Reviews

Key Decision

Points

Phase F:

Closeout 

Phase E:

Operations &

Sustainment 

Phase D:

System Assembly,

Integration & Test,

Launch

Pre-Phase A:

Concept

Studies

Phase B:

Preliminary

Design &

Technology

Completion

Phase A:

Concept & Technology

Development 

Phase C:

Final Design &

Fabrication

KDP F

Peer Reviews, Subsystem Reviews, and System Reviews

TRR

TRR

Figure 3.0‐2 NASA project life cycle

CDR Critical Design Review

CERR Critical Events Readiness Review

DR Decommissioning Review

FRR Flight Readiness Review

KDP Key Decision Point

MCR Mission Concept Review

MDR Mission Definition Review

ORR Operational Readiness Review

PDR Preliminary Design Review

PFAR Post-Flight Assessment Review

PIR Program Implementation Review

PLAR Post-Launch Assessment Review

PRR Production Readiness Review

P/SDR Program/System Definition Review

P/SRR Program/System Requirements Review

PSR Program Status Review

SAR System Acceptance Review

SDR System Definition Review

SIR System Integration Review

SRR System Requirements Review

TRR Test Readiness Review
3.1 Program Formulation

NASA Systems Engineering Handbook  21

gram Formulation phase can be found in NPR 7120.5. 

Formulation for all program types is the same, involving 

one or more program reviews followed by KDP I where 

a decision is made approving a program to begin implementation. Typically, there is no incentive to move a program into implementation until its first project is ready 

for implementation.

3.2 Program Implementation

During the program Implementation phase, the PM 

works with the Mission Directorate Associate Administrator (MDAA) and the constituent project managers to execute the program plan cost effectively. 

Program reviews ensure that the program continues 

to contribute to Agency and mission directorate goals 

and objectives within funding constraints. A summary of the required gate products for the program 

Implementation phase can be found in NPR 7120.5. 

The program life cycle has two different implementation paths, depending on program type. Each implementation path has different types of major reviews. 

For uncoupled and loosely coupled programs, the 

Implementation phase only requires PSRs and PIRs 

to assess the program’s performance and make a recommendation on its authorization at KDPs approximately every two years. Single-project and tightly 

coupled programs are more complex. For singleproject programs, the Implementation phase program 

reviews shown in Figure 3.0-1 are synonymous (not 

duplicative) with the project reviews in the project life 

cycle (see Figure 3.0-2) through Phase D. Once in operations, these programs usually have biennial KDPs 

preceded by attendant PSRs/PIRs. Tightly coupled 

programs during implementation have program reviews tied to the project reviews to ensure the proper 

integration of projects into the larger system. Once in 

operations, tightly coupled programs also have biennial PSRs/PIRs/KDPs to assess the program’s performance and authorize its continuation.

Program Formulation

Purpose

To establish a cost-effective program that is demonstrably capable of meeting Agency and mission directorate goals and objectives

Typical Activities and Their Products

z Develop program requirements and allocate them 

to initial projects 

z Define and approve program acquisition strategies

z Develop interfaces to other programs

z Start development of technologies that cut across 

multiple projects within the program

z Derive initial cost estimates and approve a program 

budget

z Perform required program Formulation technical 

activities defined in NPR 7120.5

z Satisfy program Formulation reviews’ entrance/success criteria detailed in NPR 7123.1

Reviews

z P/SRR 

z P/SDR Program Implementation

Purpose

To execute the program and constituent projects 

and ensure the program continues to contribute to 

Agency goals and objectives within funding constraints

Typical Activities and Their Products

z Initiate projects through direct assignment or competitive process (e.g., Request for Proposal (RFP), 

Announcement of Opportunity (AO)

z Monitor project’s formulation, approval, implementation, integration, operation, and ultimate decommissioning

z Adjust program as resources and requirements 

change

z Perform required program Implementation technical activities from NPR 7120.5

z Satisfy program Implementation reviews’ entrance/

success criteria from NPR 7123.1

Reviews

z PSR/PIR (uncoupled and loosely coupled programs 

only)

z Reviews synonymous (not duplicative) with the 

project reviews in the project life cycle (see Figure 3.0-2) through Phase D (single-project and 

tightly coupled programs only)
22  NASA Systems Engineering Handbook

3.0 NASA Program/Project Life Cycle

3.3 Project Pre-Phase A: Concept 

Studies

The purpose of this phase, which is usually performed 

more or less continually by concept study groups, is to 

devise various feasible concepts from which new projects (programs) can be selected. Typically, this activity 

consists of loosely structured examinations of new ideas, 

usually without central control and mostly oriented toward small studies. Its major product is a list of suggested projects, based on the identification of needs and 

the discovery of opportunities that are potentially consistent with NASA’s mission, capabilities, priorities, and 

resources.

Advanced studies may extend for several years and may 

be a sequence of papers that are only loosely connected. 

These studies typically focus on establishing mission 

goals and formulating top-level system requirements 

and ConOps. Conceptual designs are often offered to 

demonstrate feasibility and support programmatic estimates. The emphasis is on establishing feasibility and 

desirability rather than optimality. Analyses and designs 

are accordingly limited in both depth and number of options.

3.4 Project Phase A: Concept and 

Technology Development

During Phase A, activities are performed to fully develop 

a baseline mission concept and begin or assume responsibility for the development of needed technologies. This 

work, along with interactions with stakeholders, helps 

establish a mission concept and the program requirements on the project. 

In Phase A, a team—often associated with a program or 

informal project office—readdresses the mission concept to ensure that the project justification and practicality are sufficient to warrant a place in NASA’s budget. 

The team’s effort focuses on analyzing mission requirements and establishing a mission architecture. Activities become formal, and the emphasis shifts toward establishing optimality rather than feasibility. The effort 

addresses more depth and considers many alternatives. 

Goals and objectives are solidified, and the project develops more definition in the system requirements, toplevel system architecture, and ConOps. Conceptual designs are developed and exhibit more engineering detail 

than in advanced studies. Technical risks are identified 

in more detail, and technology development needs become focused.

In Phase A, the effort focuses on allocating functions to 

particular items of hardware, software, personnel, etc. 

System functional and performance requirements, along 

with architectures and designs, become firm as system 

tradeoffs and subsystem tradeoffs iterate back and forth 

Pre-Phase A: Concept Studies

Purpose

To produce a broad spectrum of ideas and alternatives for missions from which new programs/projects 

can be selected

Typical Activities and Products

(Note: AO projects will have defined the deliverable 

products.)

z Identify missions and architecture consistent with 

charter

z Identify and involve users and other stakeholders

z Identify and perform tradeoffs and analyses 

z Identify requirements, which include:

▶ Mission,

▶ Science, and

▶ Top-level system.

z Define measures of effectiveness and measures of 

performance

z Identify top-level technical performance measures 

z Perform preliminary evaluations of possible missions

z Prepare program/project proposals, which may include:

▶ Mission justification and objectives;

▶ Possible ConOps;

▶ High-level WBSs;

▶ Cost, schedule, and risk estimates; and

▶ Technology assessment and maturation strategies.

z Prepare preliminary mission concept report

z Perform required Pre-Phase A technical activities 

from NPR 7120.5

z Satisfy MCR entrance/success criteria from NPR7123.1

Reviews

z MCR

z Informal proposal review
3.4 Project Phase A: Concept and Technology Development

NASA Systems Engineering Handbook  23

Phase A: Concept and Technology Development

Purpose

To determine the feasibility and desirability of a suggested new major system and establish an initial baseline compatibility with NASA’s strategic plans

Typical Activities and Their Products

z Prepare and initiate a project plan

z Develop top-level requirements and constraints

z Define and document system requirements (hardware and software)

z Allocate preliminary system requirements to next lower level

z Define system software functionality description and requirements

z Define and document internal and external interface requirements

z Identify integrated logistics support requirements

z Develop corresponding evaluation criteria and metrics

z Document the ConOps

z Baseline the mission concept report

z Demonstrate that credible, feasible design(s) exist

z Perform and archive trade studies

z Develop mission architecture

z Initiate environmental evaluation/National Environmental Policy Act process

z Develop initial orbital debris assessment (NASA Safety Standard 1740.14)

z Establish technical resource estimates

z Define life-cycle cost estimates and develop system-level cost-effectiveness model

z Define the WBS

z Develop SOWs

z Acquire systems engineering tools and models

z Baseline the SEMP

z Develop system risk analyses

z Prepare and initiate a risk management plan

z Prepare and Initiate a configuration management plan

z Prepare and initiate a data management plan

z Prepare engineering specialty plans (e.g., contamination control plan, electromagnetic interference/electromagnetic 

compatibility control plan, reliability plan, quality control plan, parts management plan)

z Prepare a safety and mission assurance plan

z Prepare a software development or management plan (see NPR 7150.2)

z Prepare a technology development plan and initiate advanced technology development

z Establish human rating plan

z Define verification and validation approach and document it in verification and validation plans

z Perform required Phase A technical activities from NPR 7120.5

z Satisfy Phase A reviews’ entrance/success criteria from NPR 7123.1

Reviews

z SRR

z MDR (robotic mission only)

z SDR (human space flight only)
24  NASA Systems Engineering Handbook

3.0 NASA Program/Project Life Cycle

in the effort to seek out more cost-effective designs. 

(Trade studies should precede—rather than follow—

system design decisions.) Major products to this point 

include an accepted functional baseline for the system 

and its major end items. The effort also produces various engineering and management plans to prepare for 

managing the project’s downstream processes, such as 

verification and operations, and for implementing engineering specialty programs.

3.5 Project Phase B: Preliminary 

Design and Technology 

Completion

During Phase B, activities are performed to establish 

an initial project baseline, which (according to NPR 

7120.5 and NPR 7123.1) includes “a formal flow down 

of the project-level performance requirements to a 

complete set of system and subsystem design specifications for both flight and ground elements” and 

“corresponding preliminary designs.” The technical 

requirements should be sufficiently detailed to establish firm schedule and cost estimates for the project. 

It also should be noted, especially for AO-driven projects, that Phase B is where the top-level requirements 

and the requirements flowed down to the next level 

are finalized and placed under configuration control. While the requirements should be baselined in 

Phase A, there are just enough changes resulting from 

the trade studies and analyses in late Phase A and 

early Phase B that changes are inevitable. However, by 

mid-Phase B, the top-level requirements should be finalized.

Actually, the Phase B baseline consists of a collection 

of evolving baselines covering technical and business 

aspects of the project: system (and subsystem) requirements and specifications, designs, verification 

and operations plans, and so on in the technical portion of the baseline, and schedules, cost projections, 

and management plans in the business portion. Establishment of baselines implies the implementation 

of configuration management procedures. (See Section 6.5.)

In Phase B, the effort shifts to establishing a functionally complete preliminary design solution (i.e., a functional baseline) that meets mission goals and objectives. Trade studies continue. Interfaces among the 

Phase B: Preliminary Design and 

Technology Completion

Purpose

To define the project in enough detail to establish an 

initial baseline capable of meeting mission needs

Typical Activities and Their Products

z Baseline the project plan

z Review and update documents developed and 

baselined in Phase A

z Develop science/exploration operations plan based 

on matured ConOps

z Update engineering specialty plans (e.g., contamination control plan, electromagnetic interference/

electromagnetic compatibility control plan, reliability plan, quality control plan, parts management 

plan)

z Update technology maturation planning

z Report technology development results

z Update risk management plan

z Update cost and schedule data

z Finalize and approve top-level requirements and 

flowdown to the next level of requirements

z Establish and baseline design-to specifications 

(hardware and software) and drawings, verification 

and validation plans, and interface documents at 

lower levels

z Perform and archive trade studies’ results

z Perform design analyses and report results

z Conduct engineering development tests and report results

z Select a baseline design solution 

z Baseline a preliminary design report

z Define internal and external interface design solutions (e.g., interface control documents)

z Define system operations as well as PI/contract proposal management, review, and access and contingency planning

z Develop appropriate level safety data package

z Develop preliminary orbital debris assessment

z Perform required Phase B technical activities from 

NPR 7120.5

z Satisfy Phase B reviews’ entrance/success criteria 

from NPR 7123.1

Reviews

z PDR

z Safety review
3.5 Project Phase B: Preliminary Design and Technology Completion

NASA Systems Engineering Handbook  25

major end items are defined. Engineering test items 

may be developed and used to derive data for further 

design work, and project risks are reduced by successful technology developments and demonstrations. 

Phase B culminates in a series of PDRs, containing the 

system-level PDR and PDRs for lower level end items 

as appropriate. The PDRs reflect the successive refinement of requirements into designs. (See the doctrine 

of successive refinement in Subsection 4.4.1.2 and 

Figure 4.4-2.) Design issues uncovered in the PDRs 

should be resolved so that final design can begin with 

unambiguous design-to specifications. From this point 

on, almost all changes to the baseline are expected to 

represent successive refinements, not fundamental 

changes. Prior to baselining, the system architecture, 

preliminary design, and ConOps must have been validated by enough technical analysis and design work 

to establish a credible, feasible design in greater detail 

than was sufficient for Phase A.

3.6 Project Phase C: Final Design and 

Fabrication

During Phase C, activities are performed to establish a 

complete design (allocated baseline), fabricate or produce hardware, and code software in preparation for 

integration. Trade studies continue. Engineering test 

units more closely resembling actual hardware are built 

and tested to establish confidence that the design will 

function in the expected environments. Engineering 

specialty analysis results are integrated into the design, and the manufacturing process and controls are 

defined and validated. All the planning initiated back 

in Phase A for the testing and operational equipment, 

processes and analysis, integration of the engineering 

specialty analysis, and manufacturing processes and 

controls is implemented. Configuration management 

continues to track and control design changes as detailed interfaces are defined. At each step in the successive refinement of the final design, corresponding integration and verification activities are planned in greater 

detail. During this phase, technical parameters, schedules, and budgets are closely tracked to ensure that 

undesirable trends (such as an unexpected growth in 

spacecraft mass or increase in its cost) are recognized 

early enough to take corrective action. These activities 

focus on preparing for the CDR, PRR (if required), and 

the SIR.

Phase C contains a series of CDRs containing the 

system-level CDR and CDRs corresponding to the different levels of the system hierarchy. A CDR for each 

end item should be held prior to the start of fabrication/production for hardware and prior to the start 

of coding of deliverable software products. Typically, 

the sequence of CDRs reflects the integration process 

that will occur in the next phase—that is, from lower 

level CDRs to the system-level CDR. Projects, however, should tailor the sequencing of the reviews to 

meet the needs of the project. If there is a production 

run of products, a PRR will be performed to ensure the 

production plans, facilities, and personnel are ready to 

begin production. Phase C culminates with an SIR. The 

final product of this phase is a product ready for integration.

3.7 Project Phase D: System 

Assembly, Integration and Test, 

Launch

During Phase D, activities are performed to assemble, 

integrate, test, and launch the system. These activities 

focus on preparing for the FRR. Activities include assembly, integration, verification, and validation of the 

system, including testing the flight system to expected 

environments within margin. Other activities include 

the initial training of operating personnel and implementation of the logistics and spares planning. For flight 

projects, the focus of activities then shifts to prelaunch 

integration and launch. Although all these activities are 

conducted in this phase of a project, the planning for 

these activities was initiated in Phase A. The planning 

for the activities cannot be delayed until Phase D begins because the design of the project is too advanced 

to incorporate requirements for testing and operations. 

Phase D concludes with a system that has been shown 

to be capable of accomplishing the purpose for which 

it was created.
26  NASA Systems Engineering Handbook

3.0 NASA Program/Project Life Cycle

Phase C: Final Design and Fabrication

Purpose

To complete the detailed design of the system (and its associated subsystems, including its operations systems), fabricate hardware, and code software

Typical Activities and Their Products

z Update documents developed and baselined in Phase B

z Update interface documents

z Update mission operations plan based on matured ConOps

z Update engineering specialty plans (e.g., contamination control plan, electromagnetic interference/electromagnetic 

compatibility control plan, reliability plan, quality control plan, parts management plan)

z Augment baselined documents to reflect the growing maturity of the system, including the system architecture, WBS, 

and project plans

z Update and baseline production plans

z Refine integration procedures

z Baseline logistics support plan

z Add remaining lower level design specifications to the system architecture

z Complete manufacturing and assembly plans and procedures

z Establish and baseline build-to specifications (hardware and software) and drawings, verification and validation plans, 

and interface documents at all levels

z Baseline detailed design report

z Maintain requirements documents

z Maintain verification and validation plans

z Monitor project progress against project plans

z Develop verification and validation procedures

z Develop hardware and software detailed designs

z Develop the system integration plan and the system operation plan

z Develop the end-to-end information system design

z Develop spares planning

z Develop command and telemetry list

z Prepare launch site checkout and operations plans

z Prepare operations and activation plan

z Prepare system decommissioning/disposal plan, including human capital transition, for use in Phase F

z Finalize appropriate level safety data package

z Develop preliminary operations handbook

z Perform and archive trade studies

z Fabricate (or code) the product

z Perform testing at the component or subsystem level

z Identify opportunities for preplanned product improvement

z Baseline orbital debris assessment

z Perform required Phase C technical activities from NPR 7120.5

z Satisfy Phase C reviews’ entrance/success criteria from NPR 7123.1

Reviews

z CDR

z PRR

z SIR

z Safety review
3.7 Project Phase D: System Assembly, Integration and Test, Launch

NASA Systems Engineering Handbook  27

Phase D: System Assembly, Integration and Test, Launch

Purpose

To assemble and integrate the products and create the system, meanwhile developing confidence that it will be able to 

meet the system requirements; conduct launch and prepare for operations

Typical Activities and Their Products

z Integrate and verify items according to the integration and verification plans, yielding verified components and (subsystems)

z Monitor project progress against project plans

z Refine verification and validation procedures at all levels

z Perform system qualification verifications

z Perform system acceptance verifications and validation(s) (e.g., end-to-end tests encompassing all elements (i.e., 

space element, ground system, data processing system)

z Perform system environmental testing

z Assess and approve verification and validation results

z Resolve verification and validation discrepancies

z Archive documentation for verifications and validations performed

z Baseline verification and validation report

z Baseline “as-built” hardware and software documentation

z Update logistics support plan

z Document lessons learned

z Prepare and baseline operator’s manuals

z Prepare and baseline maintenance manuals

z Approve and baseline operations handbook

z Train initial system operators and maintainers

z Train on contingency planning

z Finalize and implement spares planning

z Confirm telemetry validation and ground data processing

z Confirm system and support elements are ready for flight

z Integrate with launch vehicle(s) and launch, perform orbit insertion, etc., to achieve a deployed system

z Perform initial operational verification(s) and validation(s)

z Perform required Phase D technical activities from NPR 7120.5

z Satisfy Phase D reviews’ entrance/success criteria from NPR 7123.1

Reviews

z TRR (at all levels)

z SAR (human space flight only)

z ORR

z FRR

z System functional and physical configuration audits

z Safety review
28  NASA Systems Engineering Handbook

3.0 NASA Program/Project Life Cycle

3.8 Project Phase E: Operations and 

Sustainment

During Phase E, activities are performed to conduct the 

prime mission and meet the initially identified need and 

maintain support for that need. The products of the phase 

are the results of the mission. This phase encompasses 

the evolution of the system only insofar as that evolution 

does not involve major changes to the system architecture. Changes of that scope constitute new “needs,” and 

the project life cycle starts over. For large flight projects, 

there may be an extended period of cruise, orbit insertion, on-orbit assembly, and initial shakedown operations. Near the end of the prime mission, the project may 

apply for a mission extension to continue mission activities or attempt to perform additional mission objectives.

3.9 Project Phase F: Closeout

During Phase F, activities are performed to implement 

the systems decommissioning disposal planning and analyze any returned data and samples. The products of the 

phase are the results of the mission.

Phase F deals with the final closeout of the system when 

it has completed its mission; the time at which this occurs depends on many factors. For a flight system that 

returns to Earth with a short mission duration, closeout

may require little more than deintegration of the hardware and its return to its owner. On flight projects of long 

duration, closeout may proceed according to established 

plans or may begin as a result of unplanned events, such 

as failures. Refer to NPD 8010.3, Notification of Intent to 

Decommission or Terminate Operating Space Systems and 

Terminate Missions for terminating an operating mission. Alternatively, technological advances may make it 

uneconomical to continue operating the system either in 

its current configuration or an improved one.

Phase E: Operations and Sustainment

Purpose

To conduct the mission and meet the initially identified need and maintain support for that need

Typical Activities and Their Products

z Conduct launch vehicle performance assessment

z Conduct in-orbit spacecraft checkout

z Commission and activate science instruments

z Conduct the intended prime mission(s)

z Collect engineering and science data

z Train replacement operators and maintainers

z Train the flight team for future mission phases (e.g., 

planetary landed operations)

z Maintain and approve operations and maintenance logs

z Maintain and upgrade the system

z Address problem/failure reports

z Process and analyze mission data

z Apply for mission extensions, if warranted, and conduct mission activities if awarded

z Prepare for deactivation, disassembly, decommissioning as planned (subject to mission extension)

z Complete post-flight evaluation reports

z Complete final mission report

z Perform required Phase E technical activities from 

NPR 7120.5

z Satisfy Phase E reviews’ entrance/success criteria 

from NPR 7123.1

Reviews

z PLAR

z CERR

z PFAR (human space flight only)

z System upgrade review

z Safety review

Phase F: Closeout

Purpose

To implement the systems decommissioning/disposal plan developed in Phase C and analyze any returned data and samples 

Typical Activities and Their Products

z Dispose of the system and supporting processes

z Document lessons learned

z Baseline mission final report

z Archive data

z Begin transition of human capital (if applicable)

z Perform required Phase F technical activities from 

NPR 7120.5

z Satisfy Phase F reviews’ entrance/success criteria 

from NPR 7123.1

Reviews

z DR
3.9 Project Phase F: Closeout

NASA Systems Engineering Handbook  29

To limit space debris, NPR 8715.6, NASA Procedural Requirements for Limiting Orbital Debris provides guidelines for removing Earth-orbiting robotic 

satellites from their operational orbits at the end of 

their useful life. For Low Earth Orbiting (LEO) missions, the satellite is usually deorbited. For small satellites, this is accomplished by allowing the orbit to 

slowly decay until the satellite eventually burns up 

in the Earth’s atmosphere. Larger, more massive satellites and observatories must be designed to demise 

or deorbited in a controlled manner so that they can 

be safely targeted for impact in a remote area of the 

ocean. The Geostationary (GEO) satellites at 35,790 

km above the Earth cannot be practically deorbited, 

so they are boosted to a higher orbit well beyond the 

crowded operational GEO orbit.

In addition to uncertainty as to when this part of the 

phase begins, the activities associated with safe closeout 

of a system may be long and complex and may affect 

the system design. Consequently, different options and 

strategies should be considered during the project’s earlier phases along with the costs and risks associated with 

the different options. 

3.10 Funding: The Budget Cycle

NASA operates with annual funding from Congress. 

This funding results, however, from a continuous rolling 

process of budget formulation, budget enactment, and 

finally, budget execution. NASA’s Financial Management Requirements (FMR) Volume 4 provides the concepts, the goals, and an overview of NASA’s budget 

system of resource alignment referred to as Planning, 

Programming, Budgeting, and Execution (PPBE) and 

establishes guidance on the programming and budgeting phases of the PPBE process, which are critical to 

budget formulation for NASA. Volume 4 includes strategic budget planning and resources guidance, program 

review, budget development, budget presentation, and 

justification of estimates to the Office of Management 

and Budget (OMB) and to Congress. It also provides 

detailed descriptions of the roles and responsibilities 

for key players in each step of the process. It consolidates current legal, regulatory, and administrative policies and procedures applicable to NASA. A highly simplified representation of the typical NASA budget cycle 

is shown in Figure 3.10-1.

EXECUTION

Internal/External

Studies and

Analysis

PLANNING

NASA

Strategic

Plan

Annual

Performance

Goals

Implementation

Planning

Strategic

Planning

Guidance

Performance and

Accountability

Report

Closeout

Analysis of

Performance/

Expenditures

Monthly

Phasing

Plans

Operating Plan

and

Reprogramming

Pd()m

PROGRAMMING

Program

Decision

Memorandum

Program

Review/Issues

Book

Institutional

Infrastructure

Analysis

Program

Analysis and

Alignment

Program and

Resource

Guidance

BUDGETING

Appropriation

President’s

Budget

OMB Budget

Programmatic

and Institutional

Guidance

Figure 3.10‐1 Typical NASA budget cycle 
30  NASA Systems Engineering Handbook

3.0 NASA Program/Project Life Cycle

NASA typically starts developing its budget each February with economic forecasts and general guidelines as 

identified in the most recent President’s budget. By late 

August, NASA has completed the planning, programming, and budgeting phases of the PPBE process and 

prepares for submittal of a preliminary NASA budget 

to the OMB. A final NASA budget is submitted to the 

OMB in September for incorporation into the President’s budget transmittal to Congress, which generally occurs in January. This proposed budget is then 

subjected to congressional review and approval, culminating in the passage of bills authorizing NASA to 

obligate funds in accordance with congressional stipulations and appropriating those funds. The congressional process generally lasts through the summer. In 

recent years, however, final bills have often been delayed past the start of the fiscal year on October 1. In 

those years, NASA has operated on continuing resolution by Congress.

With annual funding, there is an implicit funding control gate at the beginning of every fiscal year. While these 

gates place planning requirements on the project and 

can make significant replanning necessary, they are not 

part of an orderly systems engineering process. Rather, 

they constitute one of the sources of uncertainty that affect project risks, and they are essential to consider in 

project planning.
NASA Systems Engineering Handbook  31

4.0 System Design

This chapter describes the activities in the system design processes listed in Figure 2.1-1. The chapter is separated into sections corresponding to steps 1 to 4 listed 

in Figure 2.1-1. The processes within each step are discussed in terms of inputs, activities, and outputs. Additional guidance is provided using examples that are relevant to NASA projects. The system design processes are 

four interdependent, highly iterative and recursive processes, resulting in a validated set of requirements and a 

validated design solution that satisfies a set of stakeholder 

expectations. The four system design processes are to develop stakeholder expectations, technical requirements, 

logical decompositions, and design solutions. 

Figure 4.0-1 illustrates the recursive relationship among 

the four system design processes. These processes start 

with a study team collecting and clarifying the stakeholder expectations, including the mission objectives, 

constraints, design drivers, operational objectives, and 

criteria for defining mission success. This set of stakeholder expectations and high-level requirements is used 

to drive an iterative design loop where a strawman architecture/design, the concept of operations, and derived requirements are developed. These three products 

must be consistent with each other and will require iterations and design decisions to achieve this consistency. 

Once consistency is achieved, analyses allow the project 

team to validate the design against the stakeholder expectations. A simplified validation asks the questions: 

Does the system work? Is the system safe and reliable? Is 

the system achievable within budget and schedule constraints? If the answer to any of these questions is no, 

Figure 4.0‐1 Interrelationships among the system design processes

Rebaseline No Yes

requirements?

No

Mission

Authority

Yes

Functional &

Performance

Analysis Yes

High-Level

Requirements

Select

Baseline

Start

Stakeholder

Expectations 

Mission

Objectives &

Constraints

Operational

Objectives

Mission

Success

Criteria

Trade Studies and Iterative Design Loop

ConOps 

Design and

Product

Breakdown

Structure 

Derived and

Allocated

Requirements

� Functional

� Performance

� Interface

� Operational

� “Ilities”

Work?

Safe & reliable?

Aordable?

Sucient

depth?

No − Next Level

Stakeholder Expectations Denition

Technical Requirements Denition

Logical Decomposition

Design Solution Denition

Decision Analysis

Legend:

Functional

and Logical

Decomposition
32  NASA Systems Engineering Handbook

4.0 System Design

then changes to the design or stakeholder expectations 

will be required, and the process started again. This process continues until the system—architecture, ConOps, 

and requirements—meets the stakeholder expectations.

The depth of the design effort must be sufficient to allow 

analytical verification of the design to the requirements. 

The design must be feasible and credible when judged 

by a knowledgeable independent review team and must 

have sufficient depth to support cost modeling. 

Once the system meets the stakeholder expectations, the 

study team baselines the products and prepares for the 

next phase. Often, intermediate levels of decomposition 

are validated as part of the process. In the next level of 

decomposition, the baselined derived (and allocated) requirements become the set of high-level requirements 

for the decomposed elements and the process begins 

again. These system design processes are primarily applied in Pre-Phase A and continue through Phase C.

The system design processes during Pre-Phase A focus 

on producing a feasible design that will lead to Formulation approval. During Phase A, alternative designs and 

additional analytical maturity are pursued to optimize 

the design architecture. Phase B results in a preliminary design that satisfies the approval criteria. During 

Phase C, detailed, build-to designs are completed. 

This has been a simplified description intended to demonstrate the recursive relationship among the system design processes. These processes should be used as guidance and tailored for each study team depending on the 

size of the project and the hierarchical level of the study 

team. The next sections describe each of the four system 

design processes and their associated products for a 

given NASA mission.

System Design Keys

z Successfully understanding and defining the mission objectives and operational concepts are keys 

to capturing the stakeholder expectations, which 

will translate into quality requirements over the life 

cycle of the project.

z Complete and thorough requirements traceability 

is a critical factor in successful validation of requirements.

z Clear and unambiguous requirements will help 

avoid misunderstanding when developing the 

overall system and when making major or minor 

changes.

z Document all decisions made during the development of the original design concept in the technical data package. This will make the original design 

philosophy and negotiation results available to 

assess future proposed changes and modifications 

against.

z The design solution verification occurs when an 

acceptable design solution has been selected and 

documented in a technical data package. The design solution is verified against the system requirements and constraints. However, the validation of 

a design solution is a continuing recursive and iterative process during which the design solution is 

evaluated against stakeholder expectations.
NASA Systems Engineering Handbook  33

The Stakeholder Expectations Definition Process is the initial process within the SE engine that establishes the foundation from which the system is designed and the product 

is realized. The main purpose of this process is to identify 

who the stakeholders are and how they intend to use the 

product. This is usually accomplished through use-case scenarios, Design Reference Missions (DRMs), and ConOps.

4.1.1 Process Description

Figure 4.1-1 provides a typical flow diagram for the 

Stakeholder Expectations Definition Process and identifies typical inputs, outputs, and activities to consider in 

addressing stakeholder expectations definition.

4.1.1.1 Inputs

Typical inputs needed for the Stakeholder Expectations 

Definition Process would include the following:

z Upper Level Requirements and Expectations: These 

would be the requirements and expectations (e.g., 

needs, wants, desires, capabilities, constraints, external interfaces) that are being flowed down to a particular system of interest from a higher level (e.g., program, project, etc.).

z Identified Customers and Stakeholders: The organization or individual who has requested the product(s) 

and those who are affected by or are in some way accountable for the product’s outcome.

4.1.1.2 Process Activities

Identifying Stakeholders

Advocacy for new programs and projects may originate in 

many organizations. These include Presidential directives, 

Congress, NASA Headquarters (HQ), the NASA Centers, 

NASA advisory committees, the National Academy of Sci4.1 Stakeholder Expectations Definition

Customer Flowdown 

Requirements

Initial Customer

Expectations 

Enabling Product

Support Strategies

Concept of Operations

Measures of Effectiveness 

Validated Stakeholder

Expectations

Other Stakeholder

Expectations 

From project

From Design Solution

Denition (recursive loop) and

Requirements Management and 

Interface Management Processes 

To Technical

Requirements Denition and

Requirements Management and 

Interface Management Processes

To Technical Requirements

Denition and Technical Data

Management Processes

To Technical

Requirements Denition

and Conguration

Management Processes

Establish list of stakeholders

Define stakeholder expectations in acceptable

statements 

Validate that defined expectation statements 

reflect bidirectional traceability

Elicit stakeholder expectations

Establish operations concept and support

strategies

Analyze expectation statements for measures 

of effectiveness

Baseline stakeholder expectations

Obtain stakeholder commitments to the 

validated set of expectations

Figure 4.1-1 Stakeholder Expectations Definition Process
34  NASA Systems Engineering Handbook

4.0 System Design

ences, the National Space Council, and many other groups 

in the science and space communities. These organizations 

are commonly referred to as stakeholders. A stakeholder is 

a group or individual who is affected by or is in some way 

accountable for the outcome of an undertaking.

Stakeholders can be classified as customers and other 

interested parties. Customers are those who will receive 

the goods or services and are the direct beneficiaries of 

the work. Examples of customers are scientists, project 

managers, and subsystems engineers.

Other interested parties are those who affect the project 

by providing broad, overarching constraints within 

which the customers’ needs must be achieved. These parties may be affected by the resulting product, the manner 

in which the product is used, or have a responsibility for 

providing life-cycle support services. Examples include 

Congress, advisory planning teams, program managers, 

users, operators, maintainers, mission partners, and 

NASA contractors. It is important that the list of stakeholders be identified early in the process, as well as the 

primary stakeholders who will have the most significant 

influence over the project.

Identifying Stakeholder Expectations

Stakeholder expectations, the vision of a particular stakeholder individual or group, result when they specify what is 

desired as an end state or as an item to be produced and put 

bounds upon the achievement of the goals. These bounds 

may encompass expenditures (resources), time to deliver, 

performance objectives, or other less obvious quantities 

such as organizational needs or geopolitical goals.

Figure 4.1-2 shows the type of information needed when 

defining stakeholder expectations and depicts how the 

information evolves into a set of high-level requirements. The yellow paths depict validation paths. Examples of the types of information that would be defined 

during each step are also provided.

Defining stakeholder expectations begins with the mission authority and strategic objectives that the mission is 

meant to achieve. Mission authority changes depending 

on the category of the mission. For example, science missions are usually driven by NASA Science Mission Directorate strategic plans; whereas the exploration missions may be driven by a Presidential directive. 

An early task in defining stakeholder expectations is 

understanding the objectives of the mission. Clearly describing and documenting them helps ensure that the 

project team is working toward a common goal. These 

objectives form the basis for developing the mission, so 

they need to be clearly defined and articulated. 

Defining the objectives is done by eliciting the needs, 

wants, desires, capabilities, external interfaces, assumptions, and constraints from the stakeholders. Arriving 

at an agreed-to set of objectives can be a long and arduous task. The proactive iteration with the stakeholders 

throughout the systems engineering process is the way 

Mission

Authority

Mission

Objectives 

Success

Criteria

Design

Drivers 

� Agency Strategic

Plans

� Announcements of

Opportunity

� Road Maps

� Directed Missions

� Science Objectives

� Exploration 

Objectives 

� Technology

Demonstration

Objectives

� Technology

Development

Objectives

� Programmatic

Objectives 

Operational

Objectives

Operational Drivers

� What measurements?

� How well?

Measurements

Explorations

Mission Drivers

� Integration and Test

� Launch

� On-Orbit

� Transfer

� Surface

� Science Data

Distribution

� . . . � What explorations?

� What goals?

� Launch Date

� Mission Duration

� Orbit

� . . .

Figure 4.1-2 Product flow for stakeholder expectations
4.1 Stakeholder Expectations Definition

NASA Systems Engineering Handbook  35

that all parties can come to a true understanding of what 

should be done and what it takes to do the job. It is important to know who the primary stakeholders are and 

who has the decision authority to help resolve conflicts.

The project team should also identify the constraints

that may apply. A constraint is a condition that must be 

met. Sometimes a constraint is dictated by external factors such as orbital mechanics or the state of technology; 

sometimes constraints are the result of the overall budget 

environment. It is important to document the constraints 

and assumptions along with the mission objectives. 

Operational objectives also need to be included in defining the stakeholder expectations. The operational objectives identify how the mission must be operated to 

achieve the mission objectives.

The mission and operational success criteria define what 

the mission must accomplish to be successful. This will 

be in the form of a measurement concept for science 

missions and exploration concept for human exploration missions. The success criteria also define how well 

the concept measurements or exploration activities must 

be accomplished. The success criteria capture the stakeholder expectations and, along with programmatic requirements and constraints, are used within the highlevel requirements. 

The design drivers will be strongly dependent upon the 

ConOps, including the operational environment, orbit, 

and mission duration requirements. For science missions, the design drivers may include, at a minimum, the 

mission launch date, duration, and orbit. If alternative 

orbits are to be considered, a separate concept is needed 

for each orbit. Exploration missions must consider the 

destination, the duration, the operational sequence (and 

system configuration changes), and the in situ exploration activities that allow the exploration to succeed.

The end result of this step is the discovery and delineation 

of the system’s goals, which generally express the agreements, desires, and requirements of the eventual users of 

the system. The high-level requirements and success criteria are examples of the products representing the consensus of the stakeholders. 

4.1.1.3 Outputs

Typical outputs for capturing stakeholder expectations 

would include the following:

z Top-Level Requirements and Expectations: These 

would be the top-level requirements and expectations 

(e.g., needs, wants, desires, capabilities, constraints, 

and external interfaces) for the product(s) to be developed.

z ConOps: This describes how the system will be operated during the life-cycle phases to meet stakeholder 

expectations. It describes the system characteristics from an operational perspective and helps facilitate an understanding of the system goals. Examples 

would be the ConOps document or a DRM.

4.1.2 Stakeholder Expectations Definition 

Guidance

4.1.2.1 Concept of Operations

The ConOps is an important component in capturing 

stakeholder expectations, requirements, and the architecture of a project. It stimulates the development of 

the requirements and architecture related to the user 

elements of the system. It serves as the basis for subsequent definition documents such as the operations plan, 

launch and early orbit plan, and operations handbook 

and provides the foundation for the long-range operational planning activities such as operational facilities, 

staffing, and network scheduling. 

The ConOps is an important driver in the system requirements and therefore must be considered early 

in the system design processes. Thinking through the 

ConOps and use cases often reveals requirements and 

design functions that might otherwise be overlooked. A 

simple example to illustrate this point is adding system 

requirements to allow for communication during a particular phase of a mission. This may require an additional 

antenna in a specific location that may not be required 

during the nominal mission.

The ConOps is important for all projects. For science 

projects, the ConOps describes how the systems will be 

operated to achieve the measurement set required for a 

Note: It is extremely important to involve stakeholders in all phases of a project. Such involvement should 

be built in as a self-correcting feedback loop that will 

significantly enhance the chances of mission success. 

Involving stakeholders in a project builds confidence 

in the end product and serves as a validation and acceptance with the target audience.
36  NASA Systems Engineering Handbook

4.0 System Design

successful mission. They are usually driven by the data 

volume of the measurement set. The ConOps for exploration projects is likely to be more complex. There are 

typically more operational phases, more configuration 

changes, and additional communication links required 

for human interaction. For human spaceflight, functions 

and objectives must be clearly allocated between human 

operators and systems early in the project. 

The ConOps should consider all aspects of operations 

including integration, test, and launch through disposal. 

Typical information contained in the ConOps includes 

a description of the major phases; operation timelines; 

operational scenarios and/or DRM; end-to-end communications strategy; command and data architecture; operational facilities; integrated logistic support (resupply, 

maintenance, and assembly); and critical events. The operational scenarios describe the dynamic view of the systems’ operations and include how the system is perceived 

to function throughout the various modes and mode 

transitions, including interactions with external interfaces. For exploration missions, multiple DRMs make up 

a ConOps. The design and performance analysis leading 

to the requirements must satisfy all of them. Figure 4.1-3 

Mission Operations Center

Instrument

SOC

Acquisition Data 

Observatory Commands

Tracking Data 

Station Status 

Instrument Commands/Leads

Data Distribution

System

Station Control 

Same Interfaces

as Prime Ground Site

External

Tracking Station Acquisition

Data

Cmd

Trending

Ground Station Control System

Instrument

SOC

S-Band:

TRK, Cmd, and HK Tlm

DDS

Control System Alert Notication

System

Flight Software

Maintenance Lab

Flight Software

Memory Dumps Simulated

Commands

Instrument

SOC

Instrument

#1

Science Data

55 Mbps

Science Planning

and FDS Products

R/T Housekeeping Telemetry

R/T Housekeeping Telemetry

R/T Housekeeping Telemetry

Mission Planning ahd Scheduling

Plan daily/periodic events

Create engineering plan

Generate daily loads 

Flight Dynamics System

Orbit Determination

Manuever Planning

Product Generation

R/T Attitude Determination

Sensor/Actuator Calibration

Telemetry and

Command System

ASIST/FEDS

Telemetry Monitoring

Command Management

HK Data Archival

HK Level-0 Processing

Automated Operations

DDS Control Anomaly Detection 

DDS Status (Including ShortTerm Science Data Storage)

 Ground Site #1

S-Band

Ground System

(Including Short-Term

S-Band Data Storage)

Ka-Band

Ground System

Ka

Science Data

Observatory Housekeeping Telemetry 

 Ground Site #2

S-Band

Ground System

(Including Short-Term

S-Band Data Storage)

Ka-Band

Ground System

S-Band:

TRK, Cmd, and HK Tlm

Ka-Band:

150 Mbps

Science Data

Ka-Band:

150 Mbps

Science Data

S-Band:

HK Tlm, TRK Data

Instrument

#2

Science Data

2 Mbps

Instrument

#3

Science Data

58 Mbps

S-Band:

TRK, Cmd,

and HK Tlm

Figure 4.1-4 Example of an associated end-to-end operational architecture 

Figure 4.1-3 Typical ConOps development for a 

science mission

Develop

 operational

requirements

Define

end-to-end

communication

links

Identify

operational

facilities

Develop

organizational

responsibilities

Develop

project

operations

timeline

Develop

critical

events

Develop

operational

configurations

Define

operational

launch

segment

drivers

Define

operational

ground

segment

drivers

Define

operational

flight

segment

drivers
4.1 Stakeholder Expectations Definition

NASA Systems Engineering Handbook  37

illustrates typical information included in the ConOps 

for a science mission, and Figure 4.1-4 is an example of 

an end-to-end operational architecture. For more information about developing the ConOps, see ANSI/AIAA 

G-043-1992, Guide for the Preparation of Operational 

Concept Documents.

The operation timelines provide the basis for defining 

system configurations, operational activities, and other 

sequenced related elements necessary to achieve the 

mission objectives for each operational phase. It describes the activities, tasks, and other sequenced related 

elements necessary to achieve the mission objectives in 

each of the phases. Depending on the type of project 

(science, exploration, operational), the timeline could 

become quite complex.

The timeline matures along with the design. It starts as 

a simple time-sequenced order of the major events and 

matures into a detailed description of subsystem operations during all major mission modes or transitions. 

An example of a lunar sortie timeline and DRM early in 

the life cycle are shown in Figures 4.1-5a and b, respectively. An example of a more detailed, integrated timeFigure 4.1-5a Example of a lunar sortie timeline 

developed early in the life cycle

Launch Operations

LEO Operations

Lunar Orbit Operations

Reentry and Landing Operations

Lunar Surface Operations

Lunar Transfer Operations

Earth Transfer Operations

Integration and Test

0 1 2 3 4

Elapsed Time (Weeks)

Figure 4.1-5b Example of a lunar sortie DRM early in the life cycle

100 km

Low Lunar Orbit

Low Earth

Orbit

Ascent Stage

 Expended

Lunar

Surface

Access

Module

(LSAM) Crew Exploration Vehicle

Earth Departure

Stage Expended

Direct or Skip

Land Entry

Earth

Moon

LSAM Performs Lunar Orbit Injection

Earth Departure Stage

line later in the life cycle for a science mission is shown 

in Figure 4.1-6.

An important part of the ConOps is defining the operational phases, which will span project Phases D, E, 

and F. The operational phases provide a time-sequenced 
38  NASA Systems Engineering Handbook

4.0 System Design

Coverage

Atlas EELV

GN&C

Propulsion

C&DH/RF

Power/

Electricity

Deployables

Thermal

Instruments

Ground

USN Sites

TDRs

Control Mode

Recorder

S-Downlink

IRUs On

ACE-A On

RWAs O

STs O

DSS O

ACS thr ISo Valves Open

S/C Load

S-XMTR

MOC

L-0.5 Launch Sep L+1 L+1.5

Update on-board EPV

Decontamination Heaters On

GCE Powered On

FDF Receives MECO State

Vector From EELV

1 Hour Launch Window

HMI EB & OP O

AIA EB & Op O

EVE EB & Op O

Survival Heaters Enabled

SADS & HGADS Damper Heaters On Solar Array Deployment

Detect Separation Then:

- Initiate SA Deployment

- Power on RWAs

XMTR on Coherent

Sun Acquisition

Complete

616 W 656 W

804 W

846 W

551 W

1095 W

293 W 258 W

Record 16 kbps

64 kbps

Hardline

2 kbps

Hardline

100% SOC

Acquire Sun

Sun Acquisition Mode

(If High Tipo Rates, Delta-H If Needed

by Ground Command Only)

RWAs Powered On

Null Rates

(Wheels)

Start XMTR On

Sequencer (RTS)

Fairing

JettisonMECO SECO-1

Coast

& 1RPM Roll

SECO-2

12:00Z 12:30Z Separation: 11:30:58Z 10:59:13Z 4/18/08

9:59:13Z

(Hrs)

Launch

Overburg, S. Africa - 25 mins (11:30:46Z - 11:56:04Z)

Dongara, Australia - 9.4 hrs (11:45:38Z - 21:00:23z)

Dump Recorder

240 kbps on Carrier

Prep Lines & HGA Survival Heaters Come On

>95% SOC

L-5 mins

SAS O

Go to Internal Power

>95% Battery SOC Launch Criteria - Once on internal Power, >95% Allows >15 minutes Before Launch or Scrub

XMTR on Noncoherent

via Stored Command

2 kbps on Carrier

2 kbps Command Uplink

LV to Sep Attitude

Separation

L-31 mins 45 secs

Altitude = 300 km

TDRS: Prime at Sep Then Backup/Contingency Only

Note: Nominally Acquire TDRS Pre-Sep and Stay on Until Acquisition at Dongara

ACE-B Powered On

64 kbps on Subcarrier/Ranging on Carrier

Power Positive Charge Battery @ 10 Amps

Figure 4.1-6 Example of a more detailed, integrated timeline later in the life cycle for a science mission

structure for defining the configuration changes and operational activities needed to be carried out to meet the 

goals of the mission. For each of the operational phases, 

facilities, equipment, and critical events should also be 

included. Table 4.1-1 identifies some common examples 

of operational phases for a NASA mission.
4.1 Stakeholder Expectations Definition

NASA Systems Engineering Handbook  39

Table 4.1‐1 Typical Operational Phases for a NASA Mission

Operational Phase Description

Integration and test 

operations

Project Integration and Test: During the latter period of project integration and test, the system 

is tested by performing operational simulations during functional and environmental testing. The 

simulations typically exercise the end-to-end command and data system to provide a complete verification of system functionality and performance against simulated project operational scenarios.

Launch Integration: The launch integration phase may repeat integration and test operational and 

functional verification in the launch-integrated configuration.

Launch operations Launch: Launch operation occurs during the launch countdown, launch ascent, and orbit injection. 

Critical event telemetry is an important driver during this phase.

Deployment: Following orbit injection, spacecraft deployment operations reconfigure the spacecraft to its orbital configuration. Typically, critical events covering solar array, antenna, and other 

deployments and orbit trim maneuvers occur during this phase.

In-Orbit Checkout: In-orbit checkout is used to perform a verification that all systems are healthy. 

This is followed by on-orbit alignment, calibration, and parameterization of the flight systems to 

prepare for science operations.

Science operations The majority of the operational lifetime is used to perform science operations.

Safe-hold 

operations

As a result of on-board fault detection or by ground command, the spacecraft may transition to a 

safe-hold mode. This mode is designed to maintain the spacecraft in a power positive, thermally 

stable state until the fault is resolved and science operations can resume.

Anomaly resolution 

and maintenance 

operations

Anomaly resolution and maintenance operations occur throughout the mission. They may require 

resources beyond established operational resources. 

Disposal operations Disposal operations occur at the end of project life. These operations are used to either provide a 

controlled reentry of the spacecraft or a repositioning of the spacecraft to a disposal orbit. In the 

latter case, the dissipation of stored fuel and electrical energy is required.
40  NASA Systems Engineering Handbook

4.0 System Design

The Technical Requirements Definition Process transforms the stakeholder expectations into a definition of 

the problem and then into a complete set of validated 

technical requirements expressed as “shall” statements 

that can be used for defining a design solution for the 

Product Breakdown Structure (PBS) model and related 

enabling products. The process of requirements definition 

is a recursive and iterative one that develops the stakeholders’ requirements, product requirements, and lower 

level product/component requirements (e.g., PBS model 

products such as systems or subsystems and related enabling products such as external systems that provide or 

consume data). The requirements should enable the description of all inputs, outputs, and required relationships 

between inputs and outputs. The requirements documents 

organize and communicate requirements to the customer 

and other stakeholders and the technical community.

Technical requirements definition activities apply to the 

definition of all technical requirements from the program, project, and system levels down to the lowest level 

product/component requirements document. 

4.2.1 Process Description

Figure 4.2-1 provides a typical flow diagram for the 

Technical Requirements Definition Process and identifies typical inputs, outputs, and activities to consider in 

addressing technical requirements definition.

4.2 Technical Requirements Definition

It is important to note that the team must not rely 

solely on the requirements received to design and 

build the system. Communication and iteration with 

the relevant stakeholders are essential to ensure a 

mutual understanding of each requirement. Otherwise, the designers run the risk of misunderstanding 

and implementing an unwanted solution to a different interpretation of the requirements. 

Technical Performance

Measures

Baselined Stakeholder 

Expectations Validated Technical

Requirements 

Baselined Concept of

Operations 

Measures of

Effectiveness 

Baselined Enabling

Support Strategies 

From Stakeholder

Expectations Denition

and Conguration 

Management Processes

Measures of

Performance 

To Logical Decomposition

and Technical Data

Management Processes

To Technical

Assessment Process

To Logical Decomposition

and Requirements

Management and Interface

Management Processes 

From Stakeholder

Expectations Denition

and Technical Data

Management Processes

Define performance

requirements for each

defined functional and

behavioral expectation 

Define technical

performance measures 

Define design and

product constraints 

Validate technical

requirements 

Establish technical

requirements baseline 

Define functional and 

behavioral expectation in

technical terms 

Analyze scope of problem

Define technical requirements in acceptable 

“shall” statements 

Define measures of

performance for each

measure of effectiveness

Figure 4.2-1 Technical Requirements Definition Process
4.2 Technical Requirements Definition

NASA Systems Engineering Handbook  41

4.2.1.1 Inputs

Typical inputs needed for the requirements process 

would include the following:

z Top-Level Requirements and Expectations: These 

would be the agreed-to top-level requirements and 

expectations (e.g., needs, wants, desires, capabilities, 

constraints, external interfaces) for the product(s) to 

be developed coming from the customer and other 

stakeholders.

z Concept of Operations: This describes how the 

system will be operated during the life-cycle phases to 

meet stakeholder expectations. It describes the system 

characteristics from an operational perspective and 

helps facilitate an understanding of the system goals. 

Examples would be a ConOps document or a DRM.

4.2.1.2 Process Activities

The top-level requirements and expectations are initially assessed to understand the technical problem to be 

solved and establish the design boundary. This boundary is typically established by performing the following 

activities:

z Defining constraints that the design must adhere to or 

how the system will be used. The constraints are typically 

not able to be changed based on tradeoff analyses.

z Identifying those elements that are already under design control and cannot be changed. This helps establish those areas where further trades will be performed to narrow potential design solutions.

z Establishing physical and functional interfaces (e.g., 

mechanical, electrical, thermal, human, etc.) with 

which the system must interact. 

z Defining functional and behavioral expectations for 

the range of anticipated uses of the system as identified 

in the ConOps. The ConOps describes how the system 

will be operated and the possible use-case scenarios.

With an overall understanding of the constraints, physical/functional interfaces, and functional/behavioral expectations, the requirements can be further defined by 

establishing performance criteria. The performance is 

expressed as the quantitative part of the requirement to 

indicate how well each product function is expected to 

be accomplished.

Finally, the requirements should be defined in acceptable “shall” statements, which are complete sentences 

with a single “shall” per statement. See Appendix C for 

guidance on how to write good requirements and Appendix E for validating requirements. A well-written 

requirements document provides several specific benefits to both the stakeholders and the technical team, as 

shown in Table 4.2-1.

4.2.1.3 Outputs

Typical outputs for the Technical Requirements Definition Process would include the following:

z Technical Requirements: This would be the approved 

set of requirements that represents a complete description of the problem to be solved and requirements that 

have been validated and approved by the customer and 

stakeholders. Examples of documentation that capture 

the requirements are a System Requirements Document (SRD), Project Requirements Document (PRD), 

Interface Requirements Document (IRD), etc.

z Technical Measures: An established set of measures 

based on the expectations and requirements that will 

be tracked and assessed to determine overall system 

or product effectiveness and customer satisfaction. 

Common terms for these measures are Measures 

of Effectiveness (MOEs), Measures of Performance 

(MOPs), and Technical Performance Measures 

(TPMs). See Section 6.7 for further details.

4.2.2 Technical Requirements Definition 

Guidance

4.2.2.1 Types of Requirements

A complete set of project requirements includes the 

functional needs requirements (what functions need to 

be performed), performance requirements (how well 

these functions must be performed), and interface requirements (design element interface requirements). For 

space projects, these requirements are decomposed and 

allocated down to design elements through the PBS.

Functional, performance, and interface requirements 

are very important but do not constitute the entire set 

of requirements necessary for project success. The space 

segment design elements must also survive and continue to perform in the project environment. These environmental drivers include radiation, thermal, acoustic, 

mechanical loads, contamination, radio frequency, and 

others. In addition, reliability requirements drive design 

choices in design robustness, failure tolerance, and redundancy. Safety requirements drive design choices in 

providing diverse functional redundancy. Other spe-
42  NASA Systems Engineering Handbook

4.0 System Design

cialty requirements also may affect design choices. These 

may include producibility, maintainability, availability, 

upgradeability, human factors, and others. Unlike functional needs requirements, which are decomposed and 

allocated to design elements, these requirements are 

levied across major project elements. Designing to meet 

these requirements requires careful analysis of design 

alternatives. Figure 4.2-2 shows the characteristics of 

functional, operational, reliability, safety, and specialty 

requirements. Top-level mission requirements are generated from mission objectives, programmatic constraints, 

and assumptions. These are normally grouped into function and performance requirements and include the categories of requirements in Figure 4.2-2.

Functional Requirements

The functional requirements need to be specified for 

all intended uses of the product over its entire lifetime. 

Functional analysis is used to draw out both functional 

and performance requirements. Requirements are partitioned into groups, based on established criteria (e.g., 

similar functionality, performance, or coupling, etc.), 

to facilitate and focus the requirements analysis. Functional and performance requirements are allocated to 

functional partitions and subfunctions, objects, people, 

or processes. Sequencing of time-critical functions is 

considered. Each function is identified and described 

in terms of inputs, outputs, and interface requirements 

from the top down so that the decomposed functions are 

recognized as part of larger functional groupings. Functions are arranged in a logical sequence so that any specified operational usage of the system can be traced in an 

end-to-end path to indicate the sequential relationship of 

all functions that must be accomplished by the system.

It is helpful to walk through the ConOps and scenarios 

asking the following types of questions: what functions 

need to be performed, where do they need to be performed, how often, under what operational and environTable 4.2-1 Benefits of Well-Written Requirements

Benefit Rationale

Establish the basis for agreement between the stakeholders and the developers on 

what the product is to do

The complete description of the functions to be performed by the product specified in the 

requirements will assist the potential users in determining if the product specified meets 

their needs or how the product must be modified to meet their needs. During system 

design, requirements are allocated to subsystems (e.g., hardware, software, and other 

major components of the system), people, or processes.

Reduce the development 

effort because less rework is 

required to address poorly 

written, missing, and misunderstood requirements

The Technical Requirements Definition Process activities force the relevant stakeholders 

to consider rigorously all of the requirements before design begins. Careful review of the 

requirements can reveal omissions, misunderstandings, and inconsistencies early in the 

development cycle when these problems are easier to correct thereby reducing costly 

redesign, remanufacture, recoding, and retesting in later life-cycle phases.

Provide a basis for estimating 

costs and schedules 

The description of the product to be developed as given in the requirements is a realistic 

basis for estimating project costs and can be used to evaluate bids or price estimates.

Provide a baseline for validation and verificationOrganizations can develop their validation and verification plans much more productively 

from a good requirements document. Both system and subsystem test plans and procedures are generated from the requirements. As part of the development, the requirements 

document provides a baseline against which compliance can be measured. The requirements are also used to provide the stakeholders with a basis for acceptance of the system.

Facilitate transfer The requirements make it easier to transfer the product to new users or new machines. 

Stakeholders thus find it easier to transfer the product to other parts of their organization, 

and developers find it easier to transfer it to new stakeholders or reuse it.

Serve as a basis for enhancement The requirements serve as a basis for later enhancement or alteration of the finished 

product.

Functional requirements define what functions need 

to be done to accomplish the objectives.

Performance requirements define how well the system needs to perform the functions.
4.2 Technical Requirements Definition

NASA Systems Engineering Handbook  43

mental conditions, etc. Thinking through this process 

often reveals additional functional requirements.

Performance Requirements

Performance requirements quantitatively define how 

well the system needs to perform the functions. Again, 

walking through the ConOps and the scenarios often 

draws out the performance requirements by asking the 

following types of questions: how often and how well, 

to what accuracy (e.g., how good does the measurement need to be), what is the quality and quantity of the 

output, under what stress (maximum simultaneous data 

requests) or environmental conditions, for what duration, at what range of values, at what tolerance, and at 

what maximum throughput or bandwidth capacity.

Operational Requirements – 

Drive Functional Requirements 

Reliability Requirements – Project Standards – 

Levied Across Systems 

Mission Timeline Sequence

Mission Configurations

Command and Telemetry Strategy

Specialty Requirements – Project Standards – 

Drive Product Designs 

Producibility

Maintainability

Asset Protection

...

Safety Requirements – Project Standards – 

Levied Across Systems

Orbital Debris and Reentry

Planetary Protection

Toxic Substances

Pressurized Vessels

Radio Frequency Energy

System Safety

...

Mission Environments

Robustness, Fault Tolerance, Diverse Redundancy

Verification

Process and Workmanship

Functional Requirements

Performance Requirements

Interface Requirements

Technical Requirements – 

Allocation Hierarchically to PBS

Figure 4.2-2 Characteristics of functional, 

operational, reliability, safety, and specialty 

requirements

Example of Functional and Performance 

Requirements

Initial Function Statement

The Thrust Vector Controller (TVC) shall provide vehicle control about the pitch and yaw axes.

This statement describes a high-level function that 

the TVC must perform. The technical team needs to 

transform this statement into a set of design-to functional and performance requirements. 

Functional Requirements with Associated 

Performance Requirements

z The TVC shall gimbal the engine a maximum of 

9 degrees, ± 0.1 degree.

z The TVC shall gimbal the engine at a maximum rate 

of 5 degrees/second ± 0.3 degrees/second.

z The TVC shall provide a force of 40,000 pounds, 

± 500 pounds.

z The TVC shall have a frequency response of 20 Hz, 

± 0.1 Hz.

Be careful not to make performance requirements too 

restrictive. For example, for a system that must be able 

to run on rechargeable batteries, if the performance requirements specify that the time to recharge should be 

less than 3 hours when a 12-hour recharge time would 

be sufficient, potential design solutions are eliminated. 

In the same sense, if the performance requirements 

specify that a weight must be within ±0.5 kg, when 

±2.5 kg is sufficient, metrology cost will increase without adding value to the product. 

Wherever possible, define the performance requirements 

in terms of (1) a threshold value (the minimum acceptable value needed for the system to carry out its mission) 

and (2) the baseline level of performance desired. Specifying performance in terms of thresholds and baseline 

requirements provides the system designers with trade 

space in which to investigate alternative designs.

All qualitative performance expectations must be analyzed and translated into quantified performance requirements. Trade studies often help quantify performance 

requirements. For example, tradeoffs can show whether 
44  NASA Systems Engineering Handbook

4.0 System Design

a slight relaxation of the performance requirement could 

produce a significantly cheaper system or whether a few 

more resources could produce a significantly more effective system. The rationale for thresholds and goals should 

be documented with the requirements to understand the 

reason and origin for the performance requirement in 

case it must be changed. The performance requirements 

that can be quantified by or changed by tradeoff analysis 

should be identified. See Section 6.8, Decision Analysis, 

for more information on tradeoff analysis.

Interface Requirements

It is important to define all interface requirements for the 

system, including those to enabling systems. The external 

interfaces form the boundaries between the product and 

the rest of the world. Types of interfaces include: operational 

command and control, computer to computer, mechanical, 

electrical, thermal, and data. One useful tool in defining interfaces is the context diagram (see Appendix F), which depicts the product and all of its external interfaces. Once the 

product components are defined, a block diagram showing 

the major components, interconnections, and external interfaces of the system should be developed to define both 

the components and their interactions. 

Interfaces associated with all product life-cycle phases 

should also be considered. Examples include interfaces 

with test equipment; transportation systems; Integrated 

Logistics Support (ILS) systems; and manufacturing facilities, operators, users, and maintainers. 

As the technical requirements are defined, the interface 

diagram should be revisited and the documented interface requirements refined to include newly identified interfaces information for requirements both internal and 

external. More information regarding interfaces can be 

found in Section 6.3.

Environmental Requirements

Each space mission has a unique set of environmental 

requirements that apply to the flight segment elements. 

It is a critical function of systems engineering to identify 

the external and internal environments for the particular mission, analyze and quantify the expected environments, develop design guidance, and establish a margin 

philosophy against the expected environments. 

The environments envelope should consider what can be 

encountered during ground test, storage, transportation, 

launch, deployment, and normal operations from beginning of life to end of life. Requirements derived from the 

mission environments should be included in the system 

requirements.

External and internal environment concerns that must 

be addressed include acceleration, vibration, shock, static 

loads, acoustic, thermal, contamination, crew-induced 

loads, total dose radiation/radiation effects, Single-Event 

Effects (SEEs), surface and internal charging, orbital debris, atmospheric (atomic oxygen) control and quality, 

attitude control system disturbance (atmospheric drag, 

gravity gradient, and solar pressure), magnetic, pressure 

gradient during launch, microbial growth, and radio frequency exposure on the ground and on orbit.

The requirements structure must address the specialty 

engineering disciplines that apply to the mission environments across project elements. These discipline areas 

levy requirements on system elements regarding Electromagnetic Interference, Electromagnetic Compatibility 

(EMI/EMC), grounding, radiation and other shielding, 

contamination protection, and reliability. 

Reliability Requirements

Reliability can be defined as the probability that a device, 

product, or system will not fail for a given period of time 

under specified operating conditions. Reliability is an inherent system design characteristic. As a principal contributing factor in operations and support costs and in 

system effectiveness, reliability plays a key role in determining the system’s cost-effectiveness.

Reliability engineering is a major specialty discipline that 

contributes to the goal of a cost-effective system. This is 

primarily accomplished in the systems engineering process through an active role in implementing specific design features to ensure that the system can perform in the 

predicted physical environments throughout the mission, and by making independent predictions of system 

reliability for design trades and for test program, operations, and integrated logistics support planning.

Reliability requirements ensure that the system (and 

subsystems, e.g., software and hardware) can perform in 

the predicted environments and conditions as expected 

throughout the mission and that the system has the 

ability to withstand certain numbers and types of faults, 

errors, or failures (e.g., withstand vibration, predicted 

data rates, command and/or data errors, single-event 
4.2 Technical Requirements Definition

NASA Systems Engineering Handbook  45

upsets, and temperature variances to specified limits). 

Environments can include ground (transportation and 

handling), launch, on-orbit (Earth or other), planetary, reentry, and landing, or they might be for software 

within certain modes or states of operation. Reliability 

addresses design and verification requirements to meet 

the requested level of operation as well as fault and/or 

failure tolerance for all expected environments and conditions. Reliability requirements cover fault/failure prevention, detection, isolation, and recovery.

Safety Requirements

NASA uses the term “safety” broadly to include human 

(public and workforce), environmental, and asset safety. 

There are two types of safety requirements—deterministic and risk-informed. A deterministic safety requirement is the qualitative or quantitative definition of a 

threshold of action or performance that must be met by 

a mission-related design item, system, or activity for that 

item, system, or activity to be acceptably safe. Examples 

of deterministic safety requirements are incorporation of 

safety devices (e.g., build physical hardware stops into the 

system to prevent the hydraulic lift/arm from extending 

past allowed safety height and length limits); limits on the 

range of values a system input variable is allowed to take 

on; and limit checks on input commands to ensure they 

are within specified safety limits or constraints for that 

mode or state of the system (e.g., the command to retract the landing gear is only allowed if the airplane is in 

the airborne state). For those components identified as 

“safety critical,” requirements include functional redundancy or failure tolerance to allow the system to meet its 

requirements in the presence of one or more failures or 

to take the system to a safe state with reduced functionality (e.g., dual redundant computer processors, safe-state 

backup processor); detection and automatic system shutdown if specified values (e.g., temperature) exceed prescribed safety limits; use of only a subset that is approved 

for safety-critical software of a particular computer language; caution or warning devices; and safety procedures. 

A risk-informed safety requirement is a requirement that 

has been established, at least in part, on the basis of the 

consideration of safety-related TPMs and their associated uncertainty. An example of a risk-informed safety 

requirement is the Probability of Loss of Crew (P(LOC)) 

not exceeding a certain value “p” with a certain confidence level. Meeting safety requirements involves identification and elimination of hazards, reducing the likelihood of the accidents associated with hazards, or reducing 

the impact from the hazard associated with these accidents 

to within acceptable levels. (For additional information 

concerning safety, see, for example, NPR 8705.2, HumanRating Requirements for Space Systems, NPR 8715.3, NASA 

General Safety Program Requirements, and NASA-STD8719.13, Software Safety Standard.)

4.2.2.2 Human Factors Engineering 

Requirements

In human spaceflight, the human—as operator and as 

maintainer—is a critical component of the mission and 

system design. Human capabilities and limitations must 

enter into designs in the same way that the properties of 

materials and characteristics of electronic components 

do. Human factors engineering is the discipline that 

studies human-system interfaces and interactions and 

provides requirements, standards, and guidelines to ensure the entire system can function as designed with effective accommodation of the human component. 

Humans are initially integrated into systems through 

analysis of the overall mission. Mission functions are 

allocated to humans as appropriate to the system architecture, technical capabilities, cost factors, and crew 

capabilities. Once functions are allocated, human factors analysts work with system designers to ensure that 

human operators and maintainers are provided the 

equipment, tools, and interfaces to perform their assigned tasks safely and effectively. 

NASA-STD-3001, NASA Space Flight Human System 

Standards Volume 1: Crew Health ensures that systems 

are safe and effective for humans. The standards focus 

on the human integrated with the system, the measures 

needed (rest, nutrition, medical care, exercise, etc.) to 

ensure that the human stays healthy and effective, the 

workplace environment, and crew-system physical and 

cognitive interfaces.

4.2.2.3 Requirements Decomposition, 

Allocation, and Validation

Requirements are decomposed in a hierarchical structure starting with the highest level requirements imposed by Presidential directives, mission directorates, 

program, Agency, and customer and other stakeholders. 

These high-level requirements are decomposed into 

functional and performance requirements and allocated 

across the system. These are then further decomposed 

and allocated among the elements and subsystems. This 
46  NASA Systems Engineering Handbook

4.0 System Design

decomposition and allocation process continues until a 

complete set of design-to requirements is achieved. At 

each level of decomposition (system, subsystem, component, etc.), the total set of derived requirements must be 

validated against the stakeholder expectations or higher 

level parent requirements before proceeding to the next 

level of decomposition.

The traceability of requirements to the lowest level ensures that each requirement is necessary to meet the 

stakeholder expectations. Requirements that are not allocated to lower levels or are not implemented at a lower 

level result in a design that does not meet objectives and 

is, therefore, not valid. Conversely, lower level requirements that are not traceable to higher level requirements 

result in an overdesign that is not justified. This hierarchical flowdown is illustrated in Figure 4.2-3. 

Figure 4.2-4 is an example of how science pointing requirements are successively decomposed and allocated 

from the top down for a typical science mission. It is important to understand and document the relationship between requirements. This will reduce the possibility of 

misinterpretation and the possibility of an unsatisfactory 

design and associated cost increases. 

Throughout Phases A and B, changes in requirements and 

constraints will occur. It is imperative that all changes be 

thoroughly evaluated to determine the impacts on both 

higher and lower hierarchical levels. All changes must be 

System

Performance

Requirements

Environmental

and Other Design

Requirements

and Guidelines 

Institutional

Constraints

Assumptions

Implementing

Organizations

Customer

Programmatics:

� Cost

� Schedule

� Constraints

� Mission Classification

Mission

Objectives 

System

Functional

Requirements 

Subsystem A

Functional and

Performance

Requirements

Subsystem

C

Mission

Requirements 

Allocated

Requirements

Derived

Requirements

Subsystem X

Functional and

Performance

Requirements

Allocated

Requirements

Derived

Requirements

Subsystem

B

...

Mission

Authority 

Figure 4.2-3 The flowdown of requirements
4.2 Technical Requirements Definition

NASA Systems Engineering Handbook  47

subjected to a review and approval cycle as part of a formal 

change control process to maintain traceability and to ensure the impacts of any changes are fully assessed for all 

parts of the system. A more formal change control process is required if the mission is very large and involves 

more than one Center or crosses other jurisdictional or 

organizational boundaries.

4.2.2.4 Capturing Requirements and the 

Requirements Database

At the time the requirements are written, it is important 

to capture the requirements statements along with the 

metadata associated with each requirement. The metadata is the supporting information necessary to help 

clarify and link the requirements. 

The method of verification must also be thought through 

and captured for each requirement at the time it is developed. The verification method includes test, inspection, analysis, and demonstration. Be sure to document 

any new or derived requirements that are uncovered 

during determination of the verification method. An 

example is requiring an additional test port to give 

visibility to an internal signal during integration and 

test. If a requirement cannot be verified, then either it 

should not be a requirement or the requirement statement needs to be rewritten. For example, the requirement 

to “minimize noise” is vague and cannot be verified. If the 

requirement is restated as “the noise level of the component X shall remain under Y decibels” then it is clearly verifiable. Examples of the types of metadata are provided in 

Table 4.2-2. 

The requirements database is an extremely useful tool for 

capturing the requirements and the associated metadata and 

for showing the bidirectional traceability between requirements. The database evolves over time and could be used 

for tracking status information related to requirements such 

as To Be Determined (TBD)/To Be Resolved (TBR) status, 

resolution date, and verification status. Each project should 

decide what metadata will be captured. The database is usually in a central location that is made available to the entire 

project team. (See Appendix D for a sample requirements 

verification matrix.)

4.2.2.5 Technical Standards

Importance of Standards Application

Standards provide a proven basis for establishing 

common technical requirements across a program or 

Figure 4.2-4 Allocation and flowdown of science pointing requirements

Science Pointing

Requirements

Spacecraft

Requirements 

Ground

Requirements 

Attitude

Determination

Requirements 

Science Axis

Knowledge

Requirements 

Total Gyro to

Star Tracker

Error 

Science Axis to

Attitude Control

System Reference

Instrument

Boresight to

Science Axis 

Attitude

Estimation

Error 

Main

Structure

Thermal

Deformation

Gyro to Star

Tracker

Calibration

Uncertainty

Optical

Bench

Thermal

Deformation

Filter

Estimation

Error 

Gyro

Bias Rate

Drift 

Instrument

Calibration

Error 

Instrument

Thermal

Deformation

Star

Catalog

Location

Error

Velocity

Aberration 
48  NASA Systems Engineering Handbook

4.0 System Design

project to avoid incompatibilities and ensure that at least 

minimum requirements are met. Common standards 

can also lower implementation cost as well as costs for 

inspection, common supplies, etc. Typically, standards 

(and specifications) are used throughout the product life 

cycle to establish design requirements and margins, materials and process specifications, test methods, and interface specifications. Standards are used as requirements 

(and guidelines) for design, fabrication, verification, validation, acceptance, operations, and maintenance.

Selection of Standards

NASA policy for technical standards is provided in NPD 

8070.6, Technical Standards, which addresses selection, 

tailoring, application, and control of standards. In general, the order of authority among standards for NASA 

programs and projects is as follows:

z Standards mandated by law (e.g., environmental standards),

z National or international voluntary consensus standards recognized by industry,

z Other Government standards,

z NASA policy directives, and 

z NASA technical standards.

NASA may also designate mandatory or “core” standards that must be applied to all programs where technically applicable. Waivers to designated core standards 

must be justified and approved at the Agency level unless 

otherwise delegated.

Table 4.2‐2 Requirements Metadata

Item Function

Requirement ID Provides a unique numbering system for sorting and tracking.

Rationale Provides additional information to help clarify the intent of the requirements at the time they were 

written. (See “Rationale” box below on what should be captured.)

Traced from Captures the bidirectional traceability between parent requirements and lower level (derived) 

requirements and the relationships between requirements.

Owner Person or group responsible for writing, managing, and/or approving changes to this requirement.

Verification method Captures the method of verification (test, inspection, analysis, demonstration) and should be 

determined as the requirements are developed.

Verification lead Person or group assigned responsibility for verifying the requirement. 

Verification level Specifies the level in the hierarchy at which the requirements will be verified (e.g., system, subsystem, element).

Rationale

The rationale should be kept up to date and include the following information:

z Reason for the Requirement: Often the reason for the requirement is not obvious, and it may be lost if not recorded 

as the requirement is being documented. The reason may point to a constraint or concept of operations. If there is a 

clear parent requirement or trade study that explains the reason, then reference it. 

z Document Assumptions: If a requirement was written assuming the completion of a technology development program or a successful technology mission, document the assumption. 

z Document Relationships: The relationships with the product’s expected operations (e.g., expectations about how 

stakeholders will use a product). This may be done with a link to the ConOps.

z Document Design Constraints: Imposed by the results from decisions made as the design evolves. If the requirement states a method of implementation, the rationale should state why the decision was made to limit the solution 

to this one method of implementation.
NASA Systems Engineering Handbook  49

Logical Decomposition is the process for creating the 

detailed functional requirements that enable NASA programs and projects to meet the stakeholder expectations. 

This process identifies the “what” that must be achieved 

by the system at each level to enable a successful project. 

Logical decomposition utilizes functional analysis to 

create a system architecture and to decompose top-level 

(or parent) requirements and allocate them down to the 

lowest desired levels of the project.

The Logical Decomposition Process is used to:

z Improve understanding of the defined technical requirements and the relationships among the requirements (e.g., functional, behavioral, and temporal), 

and

z Decompose the parent requirements into a set of logical decomposition models and their associated sets 

of derived technical requirements for input to the Design Solution Definition Process.

4.3.1 Process Description 

Figure 4.3-1 provides a typical flow diagram for the Logical Decomposition Process and identifies typical inputs, 

outputs, and activities to consider in addressing logical 

decomposition.

4.3.1.1 Inputs

Typical inputs needed for the Logical Decomposition 

Process would include the following:

z Technical Requirements: A validated set of requirements that represent a description of the problem to 

be solved, have been established by functional and 

performance analysis, and have been approved by the 

customer and other stakeholders. Examples of documentation that capture the requirements are an SRD, 

PRD, and IRD.

z Technical Measures: An established set of measures 

based on the expectations and requirements that will 

be tracked and assessed to determine overall system 

or product effectiveness and customer satisfaction. 

These measures are MOEs, MOPs, and a special 

subset of these called TPMs. See Subsection 6.7.2.2 

for further details.

4.3.1.2 Process Activities

The key first step in the Logical Decomposition Process is establishing the system architecture model. The 

system architecture activity defines the underlying structure and relationships of hardware, software, communications, operations, etc., that provide for the implementation of Agency, mission directorate, program, project, 

and subsequent levels of the 

requirements. System architecture activities drive the 

partitioning of system elements and requirements to 

lower level functions and 

requirements to the point 

that design work can be accomplished. Interfaces and 

relationships between partitioned subsystems and elements are defined as well.

Once the top-level (or 

parent) functional requirements and constraints have 

been established, the system 

designer uses functional 

analysis to begin to formulate a conceptual system architecture. The system ar4.3 Logical Decomposition

From Technical

Requirements Denition

and Conguration

Management Processes

To Technical Data

Management Process

Derived Technical

Requirements

Logical Decomposition

Work Products

Baselined Technical 

Requirements

Measures of

Performance

To Design Solution

Denition and Requirements

Management and Interface

Management Processes

Logical Decomposition

Models

From Technical

Requirements Denition

and Technical Data

Management Processes

To Design Solution

Denition and Conguration

Management Processes

Dene one or more logical

decomposition models

Allocate technical requirements to

logical decomposition models to form

a set of derived technical requirements

Resolve derived technical 

requirement conicts

Validate the resulting set of derived

technical requirements 

Establish the derived technical

requirements baseline

Figure 4.3-1 Logical Decomposition Process
50  NASA Systems Engineering Handbook

4.0 System Design

chitecture can be seen as the strategic organization of 

the functional elements of the system, laid out to enable 

the roles, relationships, dependencies, and interfaces between elements to be clearly defined and understood. It 

is strategic in its focus on the overarching structure of the 

system and how its elements fit together to contribute to 

the whole, instead of on the particular workings of the 

elements themselves. It enables the elements to be developed separately from each other while ensuring that 

they work together effectively to achieve the top-level (or 

parent) requirements.

Much like the other elements of functional decomposition, the development of a good system-level architecture is a creative, recursive, and iterative process that 

combines an excellent understanding of the project’s end 

objectives and constraints with an equally good knowledge of various potential technical means of delivering 

the end products. 

Focusing on the project’s ends, top-level (or parent) requirements, and constraints, the system architect must 

develop at least one, but preferably multiple, concept architectures capable of achieving program objectives. Each 

architecture concept involves specification of the functional elements (what the pieces do), their relationships 

to each other (interface definition), and the ConOps, i.e., 

how the various segments, subsystems, elements, units, 

etc., will operate as a system when distributed by location and environment from the start of operations to the 

end of the mission. 

The development process for the architectural concepts 

must be recursive and iterative, with feedback from 

stakeholders and external reviewers, as well as from subsystem designers and operators, provided as often as 

possible to increase the likelihood of achieving the program’s ends, while reducing the likelihood of cost and 

schedule overruns.

In the early stages of the mission, multiple concepts are 

developed. Cost and schedule constraints will ultimately 

limit how long a program or project can maintain multiple architectural concepts. For all NASA programs, architecture design is completed during the Formulation 

phase. For most NASA projects (and tightly coupled programs), the selection of a single architecture will happen 

during Phase A, and the architecture and ConOps will 

be baselined during Phase B. Architectural changes at 

higher levels occasionally occur as decomposition to 

lower levels produces complications in design, cost, or 

schedule that necessitate such changes.

Aside from the creative minds of the architects, there are 

multiple tools that can be utilized to develop a system’s 

architecture. These are primarily modeling and simulation tools, functional analysis tools, architecture frameworks, and trade studies. (For example, one way of doing 

architecture is the Department of Defense (DOD) Architecture Framework (DODAF). See box.) As each 

concept is developed, analytical models of the architecture, its elements, and their operations will be developed 

with increased fidelity as the project evolves. Functional 

decomposition, requirements development, and trade 

studies are subsequently undertaken. Multiple iterations 

of these activities feed back to the evolving architectural 

concept as the requirements flow down and the design 

matures.

Functional analysis is the primary method used in 

system architecture development and functional requirement decomposition. It is the systematic process 

of identifying, describing, and relating the functions a 

system must perform to fulfill its goals and objectives. 

Functional analysis identifies and links system functions, 

trade studies, interface characteristics, and rationales to 

requirements. It is usually based on the ConOps for the 

system of interest.

Three key steps in performing functional analysis are:

z Translate top-level requirements into functions that 

must be performed to accomplish the requirements. 

z Decompose and allocate the functions to lower levels 

of the product breakdown structure.

z Identify and describe functional and subsystem interfaces.

The process involves analyzing each system requirement 

to identify all of the functions that must be performed 

to meet the requirement. Each function identified is described in terms of inputs, outputs, and interface requirements. The process is repeated from the top down so that 

subfunctions are recognized as part of larger functional 

areas. Functions are arranged in a logical sequence so 

that any specified operational usage of the system can be 

traced in an end-to-end path.

The process is recursive and iterative and continues until 

all desired levels of the architecture/system have been 

analyzed, defined, and baselined. There will almost cer-
4.3 Logical Decomposition

NASA Systems Engineering Handbook  51

tainly be alternative ways to decompose functions; therefore, the outcome is highly dependent on the creativity, 

skills, and experience of the engineers doing the analysis. 

As the analysis proceeds to lower levels of the architecture and system and the system is better understood, the 

systems engineer must keep an open mind and a willingness to go back and change previously established architecture and system requirements. These changes will 

then have to be decomposed down through the architecture and systems again, with the recursive process continuing until the system is fully defined, with all of the 

requirements understood and known to be viable, verifiable, and internally consistent. Only at that point should 

the system architecture and requirements be baselined.

4.3.1.3 Outputs

Typical outputs of the Logical Decomposition Process 

would include the following:

z System Architecture Model: Defines the underlying structure and relationship of the elements of the 

DOD Architecture Framework

New ways, called architecture frameworks, have been developed in the last decade to describe and characterize evolving, complex system-of-systems. In such circumstances, architecture descriptions are very useful in ensuring that stakeholder needs are clearly understood and prioritized, that critical details such as interoperability are addressed upfront, 

and that major investment decisions are made strategically. In recognition of this, the U.S. Department of Defense has 

established policies that mandate the use of the DODAF in capital planning, acquisition, and joint capabilities integration.

An architecture can be understood as “the structure of components, their relationships, and the principles and guidelines governing their design and evolution over time.”* To describe an architecture, the DODAF defines several views: 

operational, systems, and technical standards. In addition, a dictionary and summary information are also required. (See 

figure below.)

Within each of these views, DODAF contains specific products. For example, within the Operational View is a description 

of the operational nodes, their connectivity, and information exchange requirements. Within the Systems View is a description of all the systems contained in the operational nodes and their interconnectivity. Not all DODAF products are 

relevant to NASA systems engineering, but its underlying concepts and formalisms may be useful in structuring complex problems for the Technical Requirements Definition and Decision Analysis Processes.

*Definition based on Institute of Electrical and Electronics Engineers (IEEE) STD 610.12.

Source: DOD, DOD Architecture Framework.

Operational View

Identifies what needs to be

accomplished and by whom

Technical Standards View

Prescribes standards

and conventions

Systems View

Relates systems and characteristics

to operational needs

Specic System Capabilities

Required to Satisfy

Information Exchanges

Technical Standards Criteria

Governing Interoperable

Implementation/Procurement

of the Selected System Capabilities

Systems That

Support the

Activities and

Information

Exchanges

� What Needs to Be Done

� Who Does It

� Information Exchanges

Required to Get It Done

� Basic Technology

Supportability

� New Technical

Capabilities

Operational Requirements

and Capabilities
52  NASA Systems Engineering Handbook

4.0 System Design

system (e.g., hardware, software, communications, 

operations, etc.) and the basis for the partitioning of 

requirements into lower levels to the point that design 

work can be accomplished.

z End Product Requirements: A defined set of maketo, buy-to, code-to, and other requirements from 

which design solutions can be accomplished.

4.3.2 Logical Decomposition Guidance

4.3.2.1 Product Breakdown Structure

The decompositions represented by the PBS and the 

Work Breakdown Structure (WBS) form important perspectives on the desired product system. The WBS is a 

hierarchical breakdown of the work necessary to complete the project. See Subsection 6.1.2.1 for further information on WBS development. The WBS contains the 

PBS, which is the hierarchical breakdown of the products such as hardware items, software items, and information items (documents, databases, etc.). The PBS is 

used during the Logical Decomposition and functional 

analysis processes. The PBS should be carried down to 

the lowest level for which there is a cognizant engineer 

or manager. Figure 4.3-2 is an example of a PBS.

4.3.2.2 Functional Analysis Techniques

Although there are many techniques available to perform functional analysis, some of the more popular are 

(1) Functional Flow Block Diagrams (FFBDs) to depict 

task sequences and relationships, (2) N2 diagrams (or 

N x N interaction matrix) to identify interactions or interfaces between major factors from a systems perspective, and (3) Timeline Analyses (TLAs) to depict the time 

sequence of time-critical functions.

Functional Flow Block Diagrams

The primary functional analysis technique is the functional flow block diagram. The purpose of the FFBD is to 

indicate the sequential relationship of all functions that 

must be accomplished by a system. When completed, 

these diagrams show the entire network of actions that 

lead to the fulfillment of a function. 

FFBDs specifically depict each functional event (represented by a block) occurring following the preceding 

function. Some functions may be performed in parallel, 

or alternative paths may be taken. The FFBD network 

shows the logical sequence of “what” must happen; it 

does not ascribe a time duration to functions or between 

functions. The duration of 

the function and the time 

between functions may vary 

from a fraction of a second 

to many weeks. To understand time-critical requirements, a TLA is used. (See 

the TLA discussion later in 

this subsection.)

The FFBDs are function 

oriented, not equipment 

oriented. In other words, 

they identify “what” must 

happen and must not assume a particular answer 

to “how” a function will be 

performed. The “how” is 

then defined for each block 

at a given level by defining 

the “what” functions at the 

next lower level necessary 

to accomplish that block. 

In this way, FFBDs are developed from the top down, 

Flight Segment

Launch

Accommodations 

Spacecraft

Bus 

Payload

Element 

Electrical

Payload

Attached

Fitting

Supply

Command

& Data

Guidance,

Navigation &

Control

Mechanisms

Electronics Propulsion

Detectors

Telescope

Thermal

Electrical

Power

Structure

Payload

Interface

CommunicationsSpacecraft

Interface

Figure 4.3-2 Example of a PBS
4.3 Logical Decomposition

NASA Systems Engineering Handbook  53

in a series of levels, with tasks at each level identified 

through functional decomposition of a single task at a 

higher level. The FFBD displays all of the tasks at each 

level in their logical, sequential relationship, with their 

required inputs and anticipated outputs (including metrics, if applicable), plus a clear link back to the single, 

higher level task. 

An example of an FFBD is shown in Figure 4.3-3. The 

FFBD depicts the entire flight mission of a spacecraft. 

Each block in the first level of the diagram is expanded 

to a series of functions, as shown in the second-level diagram for “Perform Mission Operations.” Note that the 

diagram shows both input (“Transfer to OPS Orbit”) and 

output (“Transfer to STS Orbit”), thus initiating the interface identification and control process. Each block in 

the second-level diagram can be progressively developed 

into a series of functions, as shown in the third-level diagram.

TOP LEVEL

1.0

Ascent Into

Orbit Injection

(6.0) Ref.

Transfer to

STS Orbit

(3.0) Ref.

Transfer to

OPS Orbit 

AND

 (4.10) Ref.

Transmit Payload & Subsystem Data 

(4.7) Ref.

Store/Process

Command

OR

THIRD LEVEL

SECOND LEVEL

2.0

Check Out

and Deploy

3.0

Transfer to

OPS Orbit

5.0

Contingency

Operations

6.0

Transfer to

STS Orbit

7.0

Retrieve

Spacecraft

8.0

Reenter and

Land

4.1

Provide

Electric Power

4.2

Provide

Attitude

Stabilization

4.3

Provide

Thermal

Control

4.4

Provide Orbit

Main

4.5

Receive

Command

4.6

Receive Command (Omni)

4.7

Store/Process

Command

4.8

Acquire

Payload Data

4.0

Perform

Mission

Operations

4.10

Transmit Payload & Subsystem Data

OR

4.9

Acquire

Subsystem

Status Data

4.11

Transmit

Subsystem

Data

4.8.1

Compute TDRS

Pointing

Vector

4.8.2

Slew to

and Track

TDRS

4.8.3

Radar to

Standby

4.8.4

Compute LOS

Pointing

Vector

4.8.5

Slew S/C

to LOS

Vector

4.8.6

Command 

ERP PW

Radar On

4.8.7

Process Receiving Signal

and Format

4.8.8

Radar to

Standby

4.8.9

Radar O

OR OR

OR

Figure 4.3-3 Example of a functional flow block diagram
54  NASA Systems Engineering Handbook

4.0 System Design

FFBDs are used to develop, analyze, and flow down requirements, as well as to identify profitable trade studies, 

by identifying alternative approaches to performing each 

function. In certain cases, alternative FFBDs may be 

used to represent various means of satisfying a particular 

function until trade study data are acquired to permit selection among the alternatives. 

The flow diagram also provides an understanding of 

the total operation of the system, serves as a basis for 

development of operational and contingency procedures, and pinpoints areas where changes in operational procedures could simplify the overall system 

operation. 

N2 Diagrams

The N-squared (N2 or N2) diagram is used to develop 

system interfaces. An example of an N2 diagram is 

shown in Figure 4.3-4. The system components or 

functions are placed on the diagonal; the remainder of 

the squares in the N x N matrix represent the interface 

inputs and outputs. Where a blank appears, there is 

no interface between the respective components or 

functions. The N2 diagram can be taken down into 

successively lower levels to the component functional 

levels. In addition to defining the interfaces, the N2 

diagram also pinpoints areas where conflicts could 

arise in interfaces, and highlights input and output 

dependency assumptions and requirements. 

Timeline Analysis

TLA adds consideration of functional durations and is 

performed on those areas where time is critical to mission 

success, safety, utilization of resources, minimization of 

downtime, and/or increasing availability. TLA can be applied to such diverse operational functions as spacecraft 

command sequencing and launch; but for those functional 

sequences where time is not a critical factor, FFBDs or N2 

diagrams are sufficient. The following areas are often categorized as time-critical: (1) functions affecting system 

reaction time, (2) mission 

turnaround time, (3) time 

countdown activities, and 

(4) functions for which optimum equipment and/or 

personnel utilization are dependent on the timing of 

particular activities. 

Timeline Sheets (TLSs) are 

used to perform and record 

the analysis of time-critical 

functions and functional 

sequences. For time-critical 

functional sequences, the 

time requirements are specified with associated tolerances. Additional tools such 

as mathematical models and 

computer simulations may 

be necessary to establish the 

duration of each timeline. 

For additional information 

on FFBD, N2 diagrams, 

timeline analysis, and other 

functional analysis methods, 

see Appendix F.

A

B

C

D

E

F

G

H

SS

M

M

M

M

E E

E E

Output

Beta

Input

Alpha

E M SS

E M SS

E M SS E M SS

Legend:

E Electrical

M Mechanical

SS Supplied Services

Interface

A–H: System or Subsystem 

Figure 4.3-4 Example of an N2 diagram
NASA Systems Engineering Handbook  55

4.4 Design Solution Definition

The Design Solution Definition Process is used to translate the high-level requirements derived from the stakeholder expectations and the outputs of the Logical Decomposition Process into a design solution. This involves 

transforming the defined logical decomposition models 

and their associated sets of derived technical requirements into alternative solutions. These alternative solutions are then analyzed through detailed trade studies 

that result in the selection of a preferred alternative. This 

preferred alternative is then fully defined into a final design solution that will satisfy the technical requirements. 

This design solution definition will be used to generate 

the end product specifications that will be used produce 

the product and to conduct product verification. This 

process may be further refined depending on whether 

there are additional subsystems of the end product that 

need to be defined.

4.4.1 Process Description

Figure 4.4-1 provides a typical flow diagram for the Design Solution Definition Process and identifies typical 

inputs, outputs, and activities to consider in addressing 

design solution definition.

4.4.1.1 Inputs

There are several fundamental inputs needed to initiate 

the Design Solution Definition Process:

z Technical Requirements: The customer and stakeholder needs that have been translated into a reason

Figure 4.4-1 Design Solution Definition Process 

* To Product Implementation Process

Baselined Logical

Decomposition

Models 

System-Specied

Requirements

To Requirements Management

and Interface Management Processes

Initial Subsystem

Specications

To Stakeholder Expectations Denition

and Requirements Management and Interface

Management Processes

Product Validation

Plan 

To Product Validation Process

Logistics and OperateTo Procedures

To Technical Data Management Process

Enabling Product

Requirements

To Stakeholder Expectations Denition

or Product Implementation and

Requirements Management and

Interface Management Processes 

From Logical 

Decomposition and

Conguration Management

Processes

Initiate development

of enabling products 

No Yes

Initiate development

of next lower level

products 

Dene alternative design solutions

Analyze each alternative design solution

Select best design solution alternative

Generate full design description of the

selected solution

Verify the fully dened design solution

Baseline design solution specied requirements

and design descriptions 

No

*

Need

lower level

product?

Yes

*

Enabling

product

exists?

End Product–Specied

Requirements

Product Verication

Plan 

To Product Verication Process

Baselined Derived

Technical

Requirements
56  NASA Systems Engineering Handbook

4.0 System Design

ably complete set of validated requirements for the 

system, including all interface requirements.

z Logical Decomposition Models: Requirements decomposed by one or more different methods (e.g., 

function, time, behavior, data flow, states, modes, 

system architecture, etc.).

4.4.1.2 Process Activities

Define Alternative Design Solutions

The realization of a system over its life cycle involves 

a succession of decisions among alternative courses of 

action. If the alternatives are precisely defined and thoroughly understood to be well differentiated in the costeffectiveness space, then the systems engineer can make 

choices among them with confidence.

To obtain assessments that are crisp enough to facilitate good decisions, it is often necessary to delve more 

deeply into the space of possible designs than has yet 

been done, as is illustrated in Figure 4.4-2. It should be 

realized, however, that this illustration represents neither 

the project life cycle, which encompasses the system development process from inception through disposal, nor 

the product development process by which the system 

design is developed and implemented.

Each create concepts step in Figure 4.4-2 involves a recursive and iterative design loop driven by the set of stakeholder expectations where a strawman architecture/

design, the associated ConOps, and the derived requirements are developed. These three products must be consistent with each other and will require iterations and design decisions to achieve this consistency. This recursive 

and iterative design loop is illustrated in Figure 4.0-1.

Each create concepts step also involves an assessment of 

potential capabilities offered by the continually changing 

state of technology and potential pitfalls captured through 

experience-based review of prior program/project lessons learned data. It is imperative that there be a continual interaction between the technology development 

process and the design process to ensure that the design 

reflects the realities of the available technology and that 

overreliance on immature technology is avoided. Additionally, the state of any technology that is considered 

enabling must be properly monitored, and care must be 

taken when assessing the impact of this technology on 

the concept performance. This interaction is facilitated 

through a periodic assessment of the design with respect 

to the maturity of the technology required to implement 

the design. (See Subsection 4.4.2.1 for a more detailed 

discussion of technology assessment.) These technology 

elements usually exist at a lower level in the PBS. Although the process of design concept development by 

the integration of lower level elements is a part of the systems engineering process, there is always a danger that 

the top-down process cannot keep up with the bottomup process. Therefore, system architecture issues need to 

be resolved early so that the system can be modeled with 

sufficient realism to do reliable trade studies.

As the system is realized, its particulars become clearer—

but also harder to change. The purpose of systems engineering is to make sure that the Design Solution Definition Process happens in a way that leads to the most 

cost-effective final system. The basic idea is that before 

those decisions that are hard to undo are made, the alternatives should be carefully assessed, particularly with 

respect to the maturity of the required technology.

Create Alternative Design Concepts

Once it is understood what the system is to accomplish, 

it is possible to devise a variety of ways that those goals 

can be met. Sometimes, that comes about as a consequence of considering alternative functional allocations 

and integrating available subsystem design options, all of 

Figure 4.4-2 The doctrine of successive refinement which can have technologies at varying degrees of matuRecognize 

need/

opportunity

Identify and

quantify goals

co

Create

ncepts

Identify and

quantify goals

Identify and

quantify goals

concept

Create 

s

concept

Create 

s

conce

Create

pts

Identify and 

quantify goals

Do trade 

studies

Do trade 

studies

Do trade 

studies

Select

design

Select

design

Select

design

Select

design

Do trade 

studies

Increase

resolution

Perform

mission

Implement decisions

Increase

resolution

Increase

resolution
4.4 Design Solution Definition

NASA Systems Engineering Handbook  57

rity. Ideally, as wide a range of plausible alternatives as is 

consistent with the design organization’s charter should 

be defined, keeping in mind the current stage in the process of successive refinement. When the bottom-up process is operating, a problem for the systems engineer is 

that the designers tend to become fond of the designs 

they create, so they lose their objectivity; the systems engineer often must stay an “outsider” so that there is more 

objectivity. This is particularly true in the assessment of 

the technological maturity of the subsystems and components required for implementation. There is a tendency on the part of technology developers and project 

management to overestimate the maturity and applicability of a technology that is required to implement a design. This is especially true of “heritage” equipment. The 

result is that critical aspects of systems engineering are 

often overlooked.

On the first turn of the successive refinement in 

Figure 4.4-2, the subject is often general approaches or 

strategies, sometimes architectural concepts. On the next, 

it is likely to be functional design, then detailed design, 

and so on. The reason for avoiding a premature focus on 

a single design is to permit discovery of the truly best design. Part of the systems engineer’s job is to ensure that 

the design concepts to be compared take into account all 

interface requirements. “Did you include the cabling?” 

is a characteristic question. When possible, each design 

concept should be described in terms of controllable design parameters so that each represents as wide a class 

of designs as is reasonable. In doing so, the systems engineer should keep in mind that the potentials for change 

may include organizational structure, schedules, procedures, and any of the other things that make up a system. 

When possible, constraints should also be described by 

parameters.

Analyze Each Alternative Design Solution

The technical team analyzes how well each of the design 

alternatives meets the system goals (technology gaps, effectiveness, cost, schedule, and risk, both quantified and 

otherwise). This assessment is accomplished through 

the use of trade studies. The purpose of the trade study 

process is to ensure that the system architecture and design decisions move toward the best solution that can be 

achieved with the available resources. The basic steps in 

that process are:

z Devise some alternative means to meet the functional 

requirements. In the early phases of the project lifecycle, this means focusing on system architectures; in 

later phases, emphasis is given to system designs.

z Evaluate these alternatives in terms of the MOEs 

and system cost. Mathematical models are useful in 

this step not only for forcing recognition of the relationships among the outcome variables, but also for 

helping to determine what the measures of performance must be quantitatively.

z Rank the alternatives according to appropriate selection criteria.

z Drop less promising alternatives and proceed to the 

next level of resolution, if needed. 

The trade study process must be done openly and inclusively. While quantitative techniques and rules are 

used, subjectivity also plays a significant role. To make 

the process work effectively, participants must have open 

minds, and individuals with different skills—systems engineers, design engineers, specialty engineers, program 

analysts, decision scientists, and project managers—

must cooperate. The right quantitative methods and selection criteria must be used. Trade study assumptions, 

models, and results must be documented as part of the 

project archives. The participants must remain focused 

on the functional requirements, including those for enabling products. For an in-depth discussion of the trade 

study process, see Section 6.8. The ability to perform 

these studies is enhanced by the development of system 

models that relate the design parameters to those assessments—but it does not depend upon them. 

The technical team must consider a broad range of concepts when developing the system model. The model 

must define the roles of crew, hardware, and software in 

the system. It must identify the critical technologies required to implement the mission and must consider the 

entire life cycle, from fabrication to disposal. Evaluation 

criteria for selecting concepts must be established. Cost 

is always a limiting factor. However, other criteria, such 

as time to develop and certify a unit, risk, and reliability, 

also are critical. This stage cannot be accomplished 

without addressing the roles of operators and maintainers. These contribute significantly to life-cycle costs 

and to the system reliability. Reliability analysis should 

be performed based upon estimates of component 

failure rates for hardware. If probabilistic risk assessment 

models are applied, it may be necessary to include occurrence rates or probabilities for software faults or human 

error events. Assessments of the maturity of the required 
58  NASA Systems Engineering Handbook

4.0 System Design

technology must be done and a technology development 

plan developed.

Controlled modification and development of design concepts, together with such system models, often permits 

the use of formal optimization techniques to find regions 

of the design space that warrant further investigation.

Whether system models are used or not, the design 

concepts are developed, modified, reassessed, and compared against competing alternatives in a closed-loop 

process that seeks the best choices for further development. System and subsystem sizes are often determined 

during the trade studies. The end result is the determination of bounds on the relative cost-effectiveness of the 

design alternatives, measured in terms of the quantified 

system goals. (Only bounds, rather than final values, are 

possible because determination of the final details of the 

design is intentionally deferred.) Increasing detail associated with the continually improving resolution reduces 

the spread between upper and lower bounds as the process proceeds.

Select the Best Design Solution Alternative

The technical team selects the best design solution from 

among the alternative design concepts, taking into account subjective factors that the team was unable to 

quantify as well as estimates of how well the alternatives meet the quantitative requirements; the maturity 

of the available technology; and any effectiveness, cost, 

schedule, risk, or other constraints.

The Decision Analysis Process, as described in Section 6.8, should be used to make an evaluation of the alternative design concepts and to recommend the “best” 

design solution.

When it is possible, it is usually well worth the trouble 

to develop a mathematical expression, called an “objective function,” that expresses the values of combinations 

of possible outcomes as a single measure of cost-effectiveness, as illustrated in Figure 4.4-3, even if both cost 

and effectiveness must be described by more than one 

measure. 

The objective function (or “cost function”) assigns a real 

number to candidate solutions or “feasible solutions” in 

the alternative space or “search space.” A feasible solution that minimizes (or maximizes, if that is the goal) the 

objective function is called an “optimal solution.” When 

achievement of the goals can be quantitatively expressed 

by such an objective function, designs can be compared 

in terms of their value. Risks associated with design concepts can cause these evaluations to be somewhat nebulous (because they are uncertain and are best described 

by probability distributions). 

In Figure 4.4-3, the risks are relatively high for design 

concept A. There is little risk in either effectiveness or 

cost for concept B, while the risk of an expensive failure 

is high for concept C, as is shown by the cloud of probability near the x axis with a high cost and essentially no 

effectiveness. Schedule factors may affect the effectiveness and cost values and the risk distributions.

The mission success criteria for systems differ significantly. In some cases, effectiveness goals may be much 

more important than all others. Other projects may demand low costs, have an immutable schedule, or require 

minimization of some kinds of risks. Rarely (if ever) is 

it possible to produce a combined quantitative measure 

that relates all of the important factors, even if it is expressed as a vector with several components. Even when 

that can be done, it is essential that the underlying factors and relationships be thoroughly revealed to and understood by the systems engineer. The systems engineer 

Figure 4.4-3 A quantitative objective function, 

dependent on life-cycle cost and all aspects of 

effectiveness

Note: The different shaded areas indicate different levels of 

uncertainty. Dashed lines represent constant values of objective 

function (cost-effectiveness). Higher values of cost-effectiveness 

are achieved by moving toward upper left. A, B, and C are design 

concepts with different risk patterns.

B

C

A

Life-Cycle Cost, Expressed in Constant Dollars

Some Aspect of Eectiveness,

Expressed in Quantitative Units
4.4 Design Solution Definition

NASA Systems Engineering Handbook  59

must weigh the importance of the unquantifiable factors 

along with the quantitative data.

Technical reviews of the data and analyses, including 

technology maturity assessments, are an important 

part of the decision support packages prepared for the 

technical team. The decisions that are made are generally entered into the configuration management system 

as changes to (or elaborations of) the system baseline. 

The supporting trade studies are archived for future use. 

An essential feature of the systems engineering process 

is that trade studies are performed before decisions are 

made. They can then be baselined with much more confidence.

Increase the Resolution of the Design

The successive refinement process of Figure 4.4-2 illustrates a continuing refinement of the system design. At 

each level of decomposition, the baselined derived (and 

allocated) requirements become the set of high-level requirements for the decomposed elements, and the process begins again. One might ask, “When do we stop refining the design?” The answer is that the design ef­fort 

precedes to a depth that is sufficient to meet several 

needs: the design must penetrate sufficiently to allow analytical validation of the design to the requirements; it 

must also have sufficient depth to support cost modeling 

and to convince a review team of a feasible design with 

performance, cost, and risk margins.

The systems engineering engine is applied again and 

again as the system is developed. As the system is realized, the issues addressed evolve and the particulars of 

the activity change. Most of the major system decisions 

(goals, architecture, acceptable life-cycle cost, etc.) are 

made during the early phases of the project, so the successive refinements do not correspond precisely to the 

phases of the system life cycle. Much of the system architecture can be seen even at the outset, so the successive 

refinements do not correspond exactly to development 

of the architectural hierarchy, either. Rather, they correspond to the successively greater resolution by which the 

system is defined.

It is reasonable to expect the system to be defined with 

better resolution as time passes. This tendency is formalized at some point (in Phase B) by defining a baseline 

system definition. Usually, the goals, objectives, and constraints are baselined as the requirements portion of the 

baseline. The entire baseline is then subjected to configuration control in an attempt to ensure that any subsequent changes are indeed justified and affordable.

At this point in the systems engineering process, there is 

a logical branch point. For those issues for which the process of successive refinement has proceeded far enough, 

the next step is to implement the decisions at that level 

of resolution. For those issues that are still insufficiently 

resolved, the next step is to refine the development further.

Fully Describe the Design Solution

Once the preferred design alternative has been selected 

and the proper level of refinement has been completed, 

then the design is fully defined into a final design solution that will satisfy the technical requirements. The design solution definition will be used to generate the end 

product specifications that will be used to produce the 

product and to conduct product verification. This process may be further refined depending on whether there 

are additional subsystems of the end product that need 

to be defined. 

The scope and content of the full design description 

must be appropriate for the product life-cycle phase, the 

phase success criteria, and the product position in the 

PBS (system structure). Depending on these factors, the 

form of the design solution definition could be simply a 

simulation model or a paper study report. The technical 

data package evolves from phase to phase, starting with 

conceptual sketches or models and ending with complete 

drawings, parts list, and other details needed for product 

implementation or product integration. Typical output 

definitions from the Design Solution Definition Process 

are shown in Figure 4.4-1 and are described in Subsection 4.4.1.3. 

Verify the Design Solution

Once an acceptable design solution has been selected 

from among the various alternative designs and documented in a technical data package, the design solution 

must next be verified against the system requirements 

and constraints. A method to achieve this verification 

is by means of a peer review to evaluate the resulting 

design solution definition. Guidelines for conducting a 

peer review are discussed in Section 6.7.

In addition, peer reviews play a significant role as a detailed technical component of higher level technical and 
60  NASA Systems Engineering Handbook

4.0 System Design

programmatic reviews. For example, the peer review of 

a component battery design can go into much more technical detail on the battery than the integrated power subsystem review. Peer reviews can cover the components of 

a subsystem down to the level appropriate for verifying 

the design against the requirements. Concerns raised at 

the peer review might have implications on the power 

subsystem design and verification and therefore must 

be reported at the next higher level review of the power 

subsystem.

The verification must show that the design solution definition:

z Is realizable within the constraints imposed on the 

technical effort;

z Has specified requirements that are stated in acceptable statements and have bidirectional traceability 

with the derived technical requirements, technical requirements, and stakeholder expectations; and

z Has decisions and assumptions made in forming the 

solution consistent with its set of derived technical 

requirements, separately allocated technical requirements, and identified system product and service 

constraints.

This design solution verification is in contrast to the 

verification of the end product described in the end 

product verification plan which is part of the technical 

data package. That verification occurs in a later life-cycle 

phase and is a result of the Product Verification Process 

(see Section 5.3) applied to the realization of the design 

solution as an end product.

Validate the Design Solution

The validation of the design solution is a recursive and 

iterative process as shown in Figure 4.0-1. Each alternative design concept is validated against the set of stakeholder expectations. The stakeholder expectations drive 

the iterative design loop in which a strawman architecture/design, the ConOps, and the derived requirements 

are developed. These three products must be consistent 

with each other and will require iterations and design 

decisions to achieve this consistency. Once consistency 

is achieved, functional analyses allow the study team 

to validate the design against the stakeholder expectations. A simplified validation asks the questions: Does 

the system work? Is the system safe and reliable? Is the 

system affordable? If the answer to any of these questions 

is no, then changes to the design or stakeholder expectations will be required, and the process is started over 

again. This process continues until the system—architecture, ConOps, and requirements—meets the stakeholder 

expectations.

This design solution validation is in contrast to the validation of the end product described in the end product 

validation plan, which is part of the technical data 

package. That validation occurs in a later life-cycle phase 

and is a result of the Product Validation Process (see Section 5.4) applied to the realization of the design solution 

as an end product.

Identify Enabling Products

Enabling products are the life-cycle support products 

and services (e.g., production, test, deployment, training, 

maintenance, and disposal) that facilitate the progression 

and use of the operational end product through its life 

cycle. Since the end product and its enabling products 

are interdependent, they are viewed as a system. Project 

responsibility thus extends to responsibility for acquiring 

services from the relevant enabling products in each lifecycle phase. When a suitable enabling product does not 

already exist, the project that is responsible for the end 

product also can be responsible for creating and using 

the enabling product. 

Therefore, an important activity in the Design Solution 

Definition Process is the identification of the enabling 

products that will be required during the life cycle of the 

selected design solution and then initiating the acquisition or development of those enabling products. Need 

dates for the enabling products must be realistically 

identified on the project schedules, incorporating appropriate schedule slack. Then firm commitments in the 

form of contracts, agreements, and/or operational plans 

must be put in place to ensure that the enabling products 

will be available when needed to support the productline life-cycle phase activities. The enabling product requirements are documented as part of the technical data 

package for the Design Solution Definition Process.

An environmental test chamber would be an example of 

an enabling product whose use would be acquired at an 

appropriate time during the test phase of a space flight 

system.

Special test fixtures or special mechanical handling devices would be examples of enabling products that 

would have to be created by the project. Because of long 
4.4 Design Solution Definition

NASA Systems Engineering Handbook  61

development times as well as oversubscribed facilities, it 

is important to identify enabling products and secure the 

commitments for them as early in the design phase as 

possible. 

Baseline the Design Solution

As shown earlier in Figure 4.0-1, once the selected system 

design solution meets the stakeholder expectations, the 

study team baselines the products and prepares for the 

next life-cycle phase. Because of the recursive nature of 

successive refinement, intermediate levels of decomposition are often validated and baselined as part of the process. In the next level of decomposition, the baselined 

requirements become the set of high-level requirements 

for the decomposed elements, and the process begins 

again. 

Baselining a particular design solution enables the technical team to focus on one design out of all the alternative design concepts. This is a critical point in the design 

process. It puts a stake in the ground and gets everyone 

on the design team focused on the same concept. When 

dealing with complex systems, it is difficult for team 

members to design their portion of the system if the 

system design is a moving target. The baselined design 

is documented and placed under configuration control. 

This includes the system requirements, specifications, 

and configuration descriptions. 

While baselining a design is beneficial to the design process, there is a danger if it is exercised too early in the Design Solution Definition Process. The early exploration 

of alternative designs should be free and open to a wide 

range of ideas, concepts, and implementations. Baselining too early takes the inventive nature out of the concept exploration. Therefore baselining should be one of 

the last steps in the Design Solution Definition Process. 

4.4.1.3 Outputs

Outputs of the Design Solution Definition Process are 

the specifications and plans that are passed on to the 

product realization processes. They contain the designto, build-to, and code-to documentation that complies 

with the approved baseline for the system.

As mentioned earlier, the scope and content of the full 

design description must be appropriate for the productline life-cycle phase, the phase success criteria, and the 

product position in the PBS.

Outputs of the Design Solution Definition Process include the following:

z The System Specification: The system specification 

contains the functional baseline for the system that is 

the result of the Design Solution Definition Process. 

The system design specification provides sufficient 

guidance, constraints, and system requirements for 

the design engineers to execute the design.

z The System External Interface Specifications: The 

system external interface specifications describe the 

functional baseline for the behavior and characteristics of all physical interfaces that the system has 

with the external world. These include all structural, 

thermal, electrical, and signal interfaces, as well as the 

human-system interfaces.

z The End-Product Specifications: The end-product 

specifications contain the detailed build-to and codeto requirements for the end product. They are detailed, exact statements of design particulars, such 

as statements prescribing materials, dimensions, and 

quality of work to build, install, or manufacture the 

end product.

z The End-Product Interface Specifications: The 

end-product interface specifications contain the 

detailed build-to and code-to requirements for 

the behavior and characteristics of all logical and 

physical interfaces that the end product has with 

external elements, including the human-system interfaces.

z Initial Subsystem Specifications: The end-product 

subsystem initial specifications provide detailed information on subsystems if they are required.

z Enabling Product Requirements: The requirements 

for associated supporting enabling products provide 

details of all enabling products. Enabling products are 

the life-cycle support products and services that facilitate the progression and use of the operational end 

product through its life cycle. They are viewed as part 

of the system since the end product and its enabling 

products are interdependent.

z Product Verification Plan: The end-product verification plan provides the content and depth of detail necessary to provide full visibility of all verification activities for the end product. Depending on the scope of 

the end product, the plan encompasses qualification, 

acceptance, prelaunch, operational, and disposal verification activities for flight hardware and software.
62  NASA Systems Engineering Handbook

4.0 System Design

z Product Validation Plan: The end-product validation plan provides the content and depth of detail 

necessary to provide full visibility of all activities to 

validate the realized product against the baselined 

stakeholder expectations. The plan identifies the type 

of validation, the validation procedures, and the validation environment that are appropriate to confirm 

that the realized end product conforms to stakeholder 

expectations. 

z Logistics and Operate-to Procedures: The applicable 

logistics and operate-to procedures for the system describe such things as handling, transportation, maintenance, long-term storage, and operational considerations for the particular design solution.

4.4.2 Design Solution Definition Guidance

4.4.2.1 Technology Assessment

As mentioned in the process description (Subsection 4.4.1), the creation of alternative design solutions involves assessment of potential capabilities offered by the 

continually changing state of technology. A continual interaction between the technology development process 

and the design process ensures that the design reflects 

the realities of the available technology. This interaction 

is facilitated through periodic assessment of the design 

with respect to the maturity of the technology required 

to implement the design.

After identifying the technology gaps existing in a given 

design concept, it will frequently be necessary to undertake technology development in order to ascertain viability. Given that resources will always be limited, it will 

be necessary to pursue only the most promising technologies that are required to enable a given concept. 

If requirements are defined without fully understanding 

the resources required to accomplish needed technology 

developments then the program/project is at risk. Technology assessment must be done iteratively until requirements and available resources are aligned within an acceptable risk posture. Technology development plays a 

far greater role in the life cycle of a program/project than 

has been traditionally considered, and it is the role of the 

systems engineer to develop an understanding of the extent of program/project impacts—maximizing benefits 

and minimizing adverse effects. Traditionally, from a 

program/project perspective, technology development 

has been associated with the development and incorporation of any “new” technology necessary to meet requirements. However, a frequently overlooked area is 

that associated with the modification of “heritage” systems incorporated into different architectures and operating in different environments from the ones for which 

they were designed. If the required modifications and/

or operating environments fall outside the realm of experience, then these too should be considered technology 

development. 

To understand whether or not technology development 

is required—and to subsequently quantify the associated 

cost, schedule, and risk—it is necessary to systematically 

assess the maturity of each system, subsystem, or component in terms of the architecture and operational environment. It is then necessary to assess what is required in 

the way of development to advance the maturity to a point 

where it can successfully be incorporated within cost, 

schedule, and performance constraints. A process for accomplishing this assessment is described in Appendix G. 

Because technology development has the potential for 

such significant impacts on a program/project, technology 

assessment needs to play a role throughout the design and 

development process from concept development through 

Preliminary Design Review (PDR). Lessons learned from 

a technology development point of view should then be 

captured in the final phase of the program.

4.4.2.2 Integrating Engineering Specialties 

into the Systems Engineering Process

As part of the technical effort, specialty engineers in 

cooperation with systems engineering and subsystem 

designers often perform tasks that are common across 

disciplines. Foremost, they apply specialized analytical 

techniques to create information needed by the project 

manager and systems engineer. They also help define 

and write system requirements in their areas of expertise, 

and they review data packages, Engineering Change Requests (ECRs), test results, and documentation for major 

project reviews. The project manager and/or systems engineer needs to ensure that the information and products so generated add value to the project commensurate 

with their cost. The specialty engineering technical effort 

should be well integrated into the project. The roles and 

responsibilities of the specialty engineering disciplines 

should be summarized in the SEMP.

The specialty engineering disciplines included in this 

handbook are safety and reliability, Quality Assurance 
4.4 Design Solution Definition

NASA Systems Engineering Handbook  63

(QA), ILS, maintainability, producibility, and human 

factors. An overview of these specialty engineering disciplines is provided to give systems engineers a brief introduction. It is not intended to be a handbook for any of 

these discipline specialties.

Safety and Reliability

Overview and Purpose

A reliable system ensures mission success by functioning 

properly over its intended life. It has a low and acceptable 

probability of failure, achieved through simplicity, proper 

design, and proper application of reliable parts and materials. In addition to long life, a reliable system is robust and 

fault tolerant, meaning it can tolerate failures and variations in its operating parameters and environments.

Safety and Reliability in the System Design 

Process

A focus on safety and reliability throughout the mission 

life cycle is essential for ensuring mission success. The 

fidelity to which safety and reliability are designed and 

built into the system depends on the information needed 

and the type of mission. For human-rated systems, safety 

and reliability is the primary objective throughout the 

design process. For science missions, safety and reliability should be commensurate with the funding and 

level of risk a program or project is willing to accept. Regardless of the type of mission, safety and reliability considerations must be an intricate part of the system design 

processes.

To realize the maximum benefit from reliability analysis, 

it is essential to integrate the risk and reliability analysts 

within the design teams. The importance of this cannot 

be overstated. In many cases, the reliability and risk analysts perform the analysis on the design after it has been 

formulated. In this case, safety and reliability features are 

added on or outsourced rather than designed in. This 

results in unrealistic analysis that is not focused on risk 

drivers and does not provide value to the design. 

Risk and reliability analyses evolve to answer key questions about design trades as the design matures. Reliability analyses utilize information about the system, 

identify sources of risk and risk drivers, and provide 

an important input for decisionmaking. NASA-STD8729.1, Planning, Developing, and Maintaining an Effective Reliability and Maintainability (R&M) Program 

outlines engineering activities that should be tailored 

for each specific project. The concept is to choose an effective set of reliability and maintainability engineering 

activities to ensure that the systems designed, built, and 

deployed will operate successfully for the required mission life cycle.

In the early phases of a project, risk and reliability analyses help designers understand the interrelationships of 

requirements, constraints, and resources, and uncover 

key relationships and drivers so they can be properly considered. The analyst must help designers go beyond the 

requirements to understand implicit dependencies that 

emerge as the design concept matures. It is unrealistic to 

assume that design requirements will correctly capture 

all risk and reliability issues and “force” a reliable design. 

The systems engineer should develop a system strategy 

mapped to the PBS on how to allocate and coordinate 

reliability, fault tolerance, and recovery between systems 

both horizontally and vertically within the architecture 

to meet the total mission requirements. System impacts 

of designs must play a key role in the design. Making 

designers aware of impacts of their decisions on overall 

mission reliability is key. 

As the design matures, preliminary reliability analysis 

occurs using established techniques. The design and 

concept of operations should be thoroughly examined 

for accident initiators and hazards that could lead to 

mishaps. Conservative estimates of likelihood and consequences of the hazards can be used as a basis for applying design resources to reduce the risk of failures. The 

team should also ensure that the goals can be met and 

failure modes are considered and take into account the 

entire system.

During the latter phases of a project, the team uses risk 

assessments and reliability techniques to verify that the 

design is meeting its risk and reliability goals and to help 

develop mitigation strategies when the goals are not met 

or discrepancies/failures occur. 

Analysis Techniques and Methods

This subsection provides a brief summary of the types of 

analysis techniques and methods.

z Event sequence diagrams/event trees are models that 

describe the sequence of events and responses to offnominal conditions that can occur during a mission.

z Failure Modes and Effects Analyses (FMEAs) are 

bottom-up analyses that identify the types of failures 
64  NASA Systems Engineering Handbook

4.0 System Design

that can occur within a system and identify the causes, 

effects, and mitigating strategies that can be employed 

to control the effects of the failures. 

z Qualitative top-down logic models identify how failures within a system can combine to cause an undesired event.

z Quantitative logic models (probabilistic risk assessment) extend the qualitative models to include the 

likelihood of failure. These models involve developing 

failure criteria based on system physics and system 

success criteria, and employing statistical techniques 

to estimate the likelihood of failure along with uncertainty. 

z Reliability block diagrams are diagrams of the elements to evaluate the reliability of a system to provide 

a function. 

z Preliminary Hazard Analysis (PHA) is performed 

early based on the functions performed during the 

mission. Preliminary hazard analysis is a “what if” 

process that considers the potential hazard, initiating 

event scenarios, effects, and potential corrective measures and controls. The objective is to determine if the 

hazard can be eliminated, and if not, how it can be 

controlled.

z Hazard analysis evaluates the completed design. 

Hazard analysis is a “what if” process that considers 

the potential hazard, initiating event, effects, and potential corrective measures and controls. The objective is to determine if the hazard can be eliminated, 

and if not, how it can be controlled.

z Human reliability analysis is a method to understand 

how human failures can lead to system failure and estimate the likelihood of those failures.

z Probabilistic structural analysis provides a way to 

combine uncertainties in materials and loads to evaluate the failure of a structural element.

z Sparing/logistics models provide a means to estimate 

the interactions of systems in time. These models include ground-processing simulations and mission 

campaign simulations.

Limitations on Reliability Analysis

The engineering design team must understand that reliability is expressed as the probability of mission success. 

Probability is a mathematical measure expressing the 

likelihood of occurrence of a specific event. Therefore, 

probability estimates should be based on engineering 

and historical data, and any stated probabilities should 

include some measure of the uncertainty surrounding 

that estimate. 

Uncertainty expresses the degree of belief analysts have 

in their estimates. Uncertainty decreases as the quality of 

data and understanding of the system improve. The initial estimates of failure rates or failure probability might 

be based on comparison to similar equipment, historical 

data (heritage), failure rate data from handbooks, or expert elicitation.

In summary, 

z Reliability estimates express probability of success. 

z Uncertainty should be included with reliability estimates.

z Reliability estimates combined with FMEAs provide 

additional and valuable information to aid in the decisionmaking process.

Quality Assurance

Even with the best designs, hardware fabrication and 

testing are subject to human error. The systems engineer 

needs to have some confidence that the system actually 

produced and delivered is in accordance with its functional, performance, and design requirements. QA provides an independent assessment to the project manager/

systems engineer of the items produced and processes 

used during the project life cycle. The project manager/

systems engineer must work with the quality assurance 

engineer to develop a quality assurance program (the extent, responsibility, and timing of QA activities) tailored 

to the project it supports.

QA is the mainstay of quality as practiced at NASA. 

NPD 8730.5, NASA Quality Assurance Program Policy 

states that NASA’s policy is “to comply with prescribed 

requirements for performance of work and to provide 

for independent assurance of compliance through implementation of a quality assurance program.” The quality 

function of Safety and Mission Assurance (SMA) ensures that both contractors and other NASA functions 

do what they say they will do and say what they intend to 

do. This ensures that end product and program quality, 

reliability, and overall risk are at the level planned.

The Systems Engineer’s Relationship to QA 

As with reliability, producibility, and other characteristics, quality must be designed as an integral part of any 
4.4 Design Solution Definition

NASA Systems Engineering Handbook  65

system. It is important that the systems engineer understands SMA’s safeguarding role in the broad context of 

total risk and supports the quality role explicitly and vigorously. All of this is easier if the SMA quality function is 

actively included and if quality is designed in with buyin by all roles, starting at concept development. This will 

help mitigate conflicts between design and quality requirements, which can take on the effect of “tolerance 

stacking.”

Quality is a vital part of risk management. Errors, variability, omissions, and other problems cost time, program resources, taxpayer dollars, and even lives. It is incumbent on the systems engineer to know how quality 

affects their projects and to encourage best practices to 

achieve the quality level.

Rigid adherence to procedural requirements is necessary 

in high-risk, low-volume manufacturing. In the absence 

of large samples and long production runs, compliance 

to these written procedures is a strong step toward ensuring process, and, thereby, product consistency. To address this, NASA requires QA programs to be designed 

to mitigate risks associated with noncompliance to those 

requirements.

There will be a large number of requirements and procedures thus created. These must be flowed down to the 

supply chain, even to lowest tier suppliers. For circumstances where noncompliance can result in loss of life 

or loss of mission, there is a requirement to insert into 

procedures Government Mandatory Inspection Points 

(GMIPs) to ensure 100 percent compliance with safety/

mission-critical attributes. Safety/mission-critical attributes include hardware characteristics, manufacturing 

process requirements, operating conditions, and functional performance criteria that, if not met, can result 

in loss of life or loss of mission. There will be in place 

a Program/Project Quality Assurance Surveillance Plan 

(PQASP) as mandated by Federal Acquisition Regulation (FAR) Subpart 46.4. Preparation and content for 

PQASPs are outlined in NPR 8735.2, Management of 

Government Quality Assurance Functions for NASA Contracts. This document covers quality assurance requirements for both low-risk and high-risk acquisitions and 

includes functions such as document review, product 

examination, process witnessing, quality system evaluation, nonconformance reporting and corrective action, 

planning for quality assurance and surveillance, and 

GMIPs. In addition, most NASA projects are required to 

adhere to either ISO 9001 (noncritical work) or AS9100 

(critical work) requirements for management of quality 

systems. Training in these systems is mandatory for most 

NASA functions, so knowledge of their applicability by 

the systems engineer is assumed. Their texts and intent 

are strongly reflected in NASA’s quality procedural documents.

Integrated Logistics Support

The objective of ILS activities within the systems engineering process is to ensure that the product system is 

supported during development (Phase D) and operations (Phase E) in a cost-effective manner. ILS is particularly important to projects that are reusable or serviceable. Projects whose primary product does not evolve 

over its operations phase typically only apply ILS to 

parts of the project (for example, the ground system) or 

to some of the elements (for example, transportation). 

ILS is primarily accomplished by early, concurrent consideration of supportability characteristics; performing 

trade studies on alternative system and ILS concepts; 

quantifying resource requirements for each ILS element 

using best practices; and acquiring the support items associated with each ILS element. During operations, ILS 

activities support the system while seeking improvements in cost-effectiveness by conducting analyses in response to actual operational conditions. These analyses 

continually reshape the ILS system and its resource requirements. Neglecting ILS or poor ILS decisions invariably have adverse effects on the life-cycle cost of the 

resultant system. Table 4.4-1 summarizes the ILS disciplines. 

ILS planning should begin early in the project life cycle 

and should be documented. This plan should address the 

elements above including how they will be considered, 

conducted, and integrated into the systems engineering 

process needs.

Maintainability

Maintainability is defined as the measure of the ability 

of an item to be retained in or restored to specified conditions when maintenance is performed by personnel 

having specified skill levels, using prescribed procedures 

and resources, at each prescribed level of maintenance. It 

is the inherent characteristics of a design or installation 

that contribute to the ease, economy, safety, and accuracy 

with which maintenance actions can be performed.
66  NASA Systems Engineering Handbook

4.0 System Design

Role of the Maintainability Engineer

Maintainability engineering is another major specialty 

discipline that contributes to the goal of a supportable 

system. This is primarily accomplished in the systems 

engineering process through an active role in implementing specific design features to facilitate safe and 

effective maintenance actions in the predicted physical 

environments, and through a central role in developing 

the ILS system. Example tasks of the maintainability engineer include: developing and maintaining a system 

maintenance concept, establishing and allocating maintainability requirements, performing analysis to quantify 

the system’s maintenance resource requirements, and 

verifying the system’s maintainability requirements.

Producibility

Producibility is a system characteristic associated with 

the ease and economy with which a completed design 

can be transformed (i.e., fabricated, manufactured, or 

coded) into a hardware and/or software realization. 

While major NASA systems tend to be produced in small 

quantities, a particular producibility feature can be critical to a system’s cost-effectiveness, as experience with 

the shuttle’s thermal tiles has shown. Factors that influence the producibility of a design include the choice of 

materials, simplicity of design, flexibility in production 

alternatives, tight tolerance requirements, and clarity 

and simplicity of the technical data package.

Role of the Production Engineer

The production engineer supports the systems engineering process (as a part of the multidisciplinary product 

development team) by taking an active role in implementing specific design features to enhance producibility 

and by performing the production engineering analyses 

needed by the project. These tasks and analyses include: 

z Performing the manufacturing/fabrication portion 

of the system risk management program. This is accomplished by conducting a rigorous production risk 

assessment and by planning effective risk mitigation 

actions.

z Identifying system design features that enhance producibility. Efforts usually focus on design simplificaTable 4.4-1 ILS Technical Disciplines

Technical Discipline Definition

Maintenance support 

planning

Ongoing and iterative planning, organization, and management activities necessary to ensure 

that the logistics requirements for any given program are properly coordinated and implemented

Design interface The interaction and relationship of logistics with the systems engineering process to ensure that 

supportability influences the definition and design of the system so as to reduce life-cycle cost

Technical data and 

technical publications

The recorded scientific, engineering, technical, and cost information used to define, produce, test, 

evaluate, modify, deliver, support, and operate the system

Training and training 

support

Encompasses all personnel, equipment, facilities, data/documentation, and associated resources 

necessary for the training of operational and maintenance personnel

Supply support Actions required to provide all the necessary material to ensure the system’s supportability and 

usability objectives are met

Test and support 

equipment

All tools, condition-monitoring equipment, diagnostic and checkout equipment, special test 

equipment, metrology and calibration equipment, maintenance fixtures and stands, and special 

handling equipment required to support operational maintenance functions

Packaging, handling, 

storage, and transportation

All materials, equipment, special provisions, containers (reusable and disposable), and supplies 

necessary to support the packaging, safety and preservation, storage, handling, and transportation of the prime mission-related elements of the system, including personnel, spare and repair 

parts, test and support equipment, technical data computer resources, and mobile facilities

Personnel Involves identification and acquisition of personnel with skills and grades required to operate and 

maintain a system over its lifetime

Logistics facilities All special facilities that are unique and are required to support logistics activities, including storage buildings and warehouses and maintenance facilities at all levels

Computer resources 

support

All computers, associated software, connecting components, networks, and interfaces necessary 

to support the day-to-day flow of information for all logistics functions

Source: Blanchard, System Engineering Management.
4.4 Design Solution Definition

NASA Systems Engineering Handbook  67

tion, fabrication tolerances, and avoidance of hazardous materials.

z Conducting producibility trade studies to determine 

the most cost-effective fabrication/manufacturing 

process.

z Assessing production feasibility within project constraints. This may include assessing contractor and 

principal subcontractor production experience and 

capability, new fabrication technology, special tooling, 

and production personnel training requirements.

z Identifying long-lead items and critical materials.

z Estimating production costs as a part of life-cycle cost 

management.

z Supporting technology readiness assessments.

z Developing production schedules.

z Developing approaches and plans to validate fabrication/manufacturing processes. 

The results of these tasks and production engineering 

analyses are documented in the manufacturing plan 

with a level of detail appropriate to the phase of the 

project. The production engineer also participates in and 

contributes to major project reviews (primarily PDR and 

Critical Design Review (CDR)) on the above items, and 

to special interim reviews such as the PRR.

Human Factors Engineering

Overview and Purpose

Consideration of human operators and maintainers of 

systems is a critical part of the design process. Human 

factors engineering is the discipline that studies the 

human-system interfaces and provides requirements, 

standards, and guidelines to ensure the human component of the integrated system is able to function as intended. Human roles include operators (flight crews 

and ground crews), designers, manufacturers, ground 

support, maintainers, and passengers. Flight crew 

functions include system operation, troubleshooting, 

and in-flight maintenance. Ground crew functions include spacecraft and ground system manufacturing, assembly, test, checkout, logistics, ground maintenance, 

repair, refurbishment, launch control, and mission control.

Human factors are generally considered in four categories. The first is anthropometry and biomechanics—

the physical size, shape, and strength of the humans. 

The second is sensation and perception—primarily 

vision and hearing, but senses such as touch are also 

important. The environment is a third factor—ambient noise and lighting, vibration, temperature and 

humidity, atmospheric composition, and contaminants. Psychological factors comprise memory; information processing components such as pattern 

recognition, decisionmaking, and signal detection; 

and affective factors—e.g., emotions, cultural patterns, and habits.

Human Factors Engineering in the System 

Design Process

z Stakeholder Expectations: The operators, maintainers, and passengers are all stakeholders in the 

system. The human factors specialist identifies roles 

and responsibilities that can be performed by humans and scenarios that exceed human capabilities. 

The human factors specialist ensures that system operational concept development includes task analysis and human/system function allocation. As these 

are refined, function allocation distributes operator 

roles and responsibilities for subtasks to the crew, external support teams, and automation. (For example, 

in aviation, tasks may be allocated to crew, air traffic 

controllers, or autopilots. In spacecraft, tasks may be 

performed by crew, mission control, or onboard systems.) 

Prototypes

Experience has shown that prototype systems can be 

effective in enabling efficient producibility even when 

building only a single flight system. Prototypes are 

built early in the life cycle and they are made as close 

to the flight item in form, fit, and function as is feasible at that stage of the development. The prototype 

is used to “wring out” the design solution so that experience gained from the prototype can be fed back 

into design changes that will improve the manufacture, integration, and maintainability of a single flight 

item or the production run of several flight items. Unfortunately, prototypes are often deleted from projects to save cost. Along with that decision, the project accepts an increased risk in the development 

phase of the life cycle. Fortunately, advancements in 

computer-aided design and manufacturing have mitigated that risk somewhat by enabling the designer 

to visualize the design and “walk through” the integration sequence to uncover problems before they become a costly reality.
68  NASA Systems Engineering Handbook

4.0 System Design

z Requirements Definition: Human factors requirements for spacecraft and space habitats are program/

project dependent, derived from NASA-STD-3001, 

NASA Space Flight Human System Standard Volume 1: 

Crew Health. Other human factors requirements of 

other missions and Earth-based activities for human 

space flight missions are derived from human factors standards such as MIL-STD-1472, Human Engineering; NUREG-0700, Human-System Interface 

Design Review Guidelines; and the Federal Aviation 

Administration’s Human Factors Design Standard.

z Technical Solution: Consider the human as a central 

component when doing logical decomposition and 

developing design concepts. The users—operators or 

maintainers—will not see the entire system as the designer does, only as the system interfaces with them. 

In engineering design reviews, human factors specialists promote the usability of the design solution. 

With early involvement, human factors assessments 

may catch usability problems at very early stages. 

For example, in one International Space Station payload design project, a human factors assessment of a 

very early block diagram of the layout of stowage and 

hardware identified problems that would have made 

operations very difficult. Changes were made to the 

conceptual design at negligible cost—i.e., rearranging 

conceptual block diagrams based on the sequence in 

which users would access items.

z Usability Evaluations of Design Concepts: Evaluations can be performed easily using rapid prototyping 

tools for hardware and software interfaces, standard 

human factors engineering data-gathering and analysis tools, and metrics such as task completion time 

and number of errors. Systematically collected subjective reports from operators also provide useful 

data. New technologies provide detailed objective information—e.g., eye tracking for display and control 

layout assessment. Human factors specialists provide 

assessment capabilities throughout the iterative design process.

z Verification: As mentioned, verification of requirements for usability, error rates, task completion times, 

and workload is challenging. Methods range from tests 

with trained personnel in mockups and simulators, to 

models of human performance, to inspection by experts. As members of the systems engineering team, 

human factors specialists provide verification guidance 

from the time requirements are first developed.

Human Factors Engineering Analyses 

Techniques and Methods

Example methods used to provide human performance 

data, predict human-system performance, and evaluate 

human-system designs include:

z Task Analysis: Produces a detailed description of the 

things a person must do in a system to accomplish a 

task, with emphasis on requirements for information 

presentation, decisions to be made, task times, operator actions, and environmental conditions. 

z Timeline Analysis: Follows from task analysis. Durations of tasks are identified in task analyses, and the 

times at which these tasks occur are plotted in graphs, 

which also show the task sequences. The purpose is to 

identify requirements for simultaneous incompatible 

activities and activities that take longer than is available. Timelines for a given task can describe the activities of multiple operators or crewmembers.

z Modeling and Simulation: Models or mockups to 

make predictions about system performance, compare configurations, evaluate procedures, and evaluate alternatives. Simulations can be as simple as 

positioning a graphical human model with realistic 

anthropometric dimensions with a graphical model 

of an operator station, or they can be complex stochastic models capturing decision points, error opportunities, etc.

z Usability Testing: Based on a task analysis and preliminary design, realistic tasks are carried out in a controlled environment with monitoring and recording 

equipment. Objective measures such as performance 

time and number of errors are evaluated; subjective 

ratings are collected. The outputs systematically report on strengths and weaknesses of candidate design 

solutions.

z Workload Assessment: Measurement on a standardized scale such as the NASA-TLX or the CooperHarper rating scales of the amount and type of work. 

It assesses operator and crew task loading, which determines the ability of a human to perform the required 

tasks in the desired time with the desired accuracy.

z Human Error and Human Reliability Assessment: 

Top-down (fault tree analyses) and bottom-up (human 

factors process failure modes and effects analysis) 

analyses. The goal is to promote human reliability by 

creating a system that can tolerate and recover from 

human errors. Such a system must also support the 

human role in adding reliability to the system.
4.4 Design Solution Definition

NASA Systems Engineering Handbook  69

Roles of the Human Factors Specialist

The human factors specialist supports the systems engineering process by representing the users’ and maintainers’ requirements and capabilities throughout the design, 

production, and operations stages. Human factors specialists’ roles include:

z Identify applicable requirements based on Agency 

standards for human-system integration during the 

requirements definition phase.

z Support development of mission concepts by providing information on human performance capabilities and limitations.

z Support task analysis and function allocation with information on human capabilities and limitations.

z Identify system design features that enhance usability. 

This integrates knowledge of human performance capabilities and design features.

z Support trade studies by providing data on effects of 

alternative designs on time to complete tasks, workload, and error rates.

z Support trade studies by providing data on effects of 

alternative designs on skills and training required to 

operate the system.

z Support design reviews to ensure compliance with 

human-systems integration requirements.

z Conduct evaluations using mockups and prototypes to provide detailed data on user performance.

z Support development of training and maintenance 

procedures in conjunction with hardware designers 

and mission planners.

z Collect data on human-system integration issues 

during operations to inform future designs.

NASA Systems Engineering Handbook  71

This chapter describes the activities in the product realization processes listed in Figure 2.1-1. The chapter is 

separated into sections corresponding to steps 5 through 

9 listed in Figure 2.1-1. The processes within each step 

are discussed in terms of the inputs, the activities, and 

the outputs. Additional guidance is provided using examples that are relevant to NASA projects. 

The product realization side of the SE engine is where 

the rubber meets the road. In this portion of the engine, five interdependent processes result in systems that 

meet the design specifications and stakeholder expectations. These products are produced, acquired, reused, or 

coded; integrated into higher level assemblies; verified 

against design specifications; validated against stakeholder expectations; and transitioned to the next level of 

the system. As has been mentioned in previous sections, 

products can be models and simulations, paper studies 

or proposals, or hardware and software. The type and 

level of product depends on the phase of the life cycle 

and the product’s specific objectives. But whatever the 

product, all must effectively use the processes to ensure 

the system meets the intended operational concept.

This effort starts with the technical team taking the output 

from the system design processes and using the appropriate crosscutting functions, such as data and configuration management, and technical assessments to make, 

buy, or reuse subsystems. Once these subsystems are realized, they must be integrated to the appropriate level 

as designated by the appropriate interface requirements. 

These products are then verified through the Technical 

Assessment Process to ensure they are consistent with 

the technical data package and that “the product was 

built right.” Once consistency is achieved, the technical 

team will validate the products against the stakeholder 

expectations that “the right product was built.” Upon 

successful completion of validation, the products are 

transitioned to the next level of the system. Figure 5.0-1 

illustrates these processes.

This is an iterative and recursive process. Early in the life 

cycle, paper products, models, and simulations are run 

through the five realization processes. As the system matures and progresses through the life cycle, hardware and 

software products are run through these processes. It is 

important to catch errors and failures at the lowest level 

of integration and early in the life cycle so that changes 

can be made through the design processes with minimum impact to the project.

The next sections describe each of the five product realization processes and their associated products for a 

given NASA mission. 

5.0 Product Realization

DESIGN REALIZATION

PRODUCT

TRANSITION

PROCESS

EVALUATION PROCESSES

� Acquire

� Make/Code

� Reuse

Product

Implementation

Product

Integration

Product

Verification

Product

Validation

Product

Transition

� Assembly

� Functional

Evaluation

� Functional

� Environmental

� Operational Testing in Integration

& Test Environment

� Operational 

Testing in Mission

Environment

� Delivery to Next

Higher Level in PBS

� Delivery to 

Operational

System

Figure 5.0-1 Product realization
72  NASA Systems Engineering Handbook

5.0 Product Realization

Product Realization Keys

z Generate and manage requirements for off-the-shelf hardware/software products as for all other products. 

z Understand the differences between verification testing and validation testing.

▶ Verification Testing: Verification testing relates back to the approved requirements set (such as a System Requirements Document (SRD)) and can be performed at different stages in the product life cycle. Verification testing includes: (1) any testing used to assist in the development and maturation of products, product elements, or manufacturing or support processes; and/or (2) any engineering-type test used to verify status of technical progress, to 

verify that design risks are minimized, to substantiate achievement of contract technical performance, and to certify readiness for initial validation testing. Verification tests use instrumentation and measurements, and are generally accomplished by engineers, technicians, or operator-maintainer test personnel in a controlled environment to 

facilitate failure analysis.

▶ Validation Testing: Validation relates back to the ConOps document. Validation testing is conducted under realistic conditions (or simulated conditions) on any end product for the purpose of determining the effectiveness and 

suitability of the product for use in mission operations by typical users; and the evaluation of the results of such 

tests. Testing is the detailed quantifying method of both verification and validation. However, testing is required to 

validate final end products to be produced and deployed.

z Consider all customer, stakeholder, technical, programmatic, and safety requirements when evaluating the input necessary to achieve a successful product transition. 

z Analyze for any potential incompatibilities with interfaces as early as possible.

z Completely understand and analyze all test data for trends and anomalies.

z Understand the limitations of the testing and any assumptions that are made.

z Ensure that a reused product meets the verification and validation required for the relevant system in which it is to be 

used, as opposed to relying on the original verification and validation it met for the system of its original use. It would 

then be required to meet the same verification and validation as a purchased product or a built product. The “pedigree” of a reused product in its original application should not be relied upon in a different system, subsystem, or application.
NASA Systems Engineering Handbook  73

Product implementation is the first process encountered 

in the SE engine that begins the movement from the 

bottom of the product hierarchy up towards the Product 

Transition Process. This is where the plans, designs, analysis, requirements development, and drawings are realized into actual products.

Product implementation is used to generate a specified product of a project or activity through buying, 

making/coding, or reusing previously developed hardware, software, models, or studies to generate a product 

appropriate for the phase of the life cycle. The product 

must satisfy the design solution and its specified requirements.

The Product Implementation Process is the key activity 

that moves the project from plans and designs into realized products. Depending on the project and life-cycle 

phase within the project, the product may be hardware, 

software, a model, simulations, mockups, study reports, 

or other tangible results. These products may be realized 

through their purchase from commercial or other vendors, generated from scratch, or through partial or complete reuse of products from other projects or activities. 

The decision as to which of these realization strategies, 

or which combination of strategies, will be used for the 

products of this project will have been made early in the 

life cycle using the Decision Analysis Process.

5.1.1 Process Description

Figure 5.1-1 provides a typical flow diagram for the 

Product Implementation Process and identifies typical 

inputs, outputs, and activities to consider in addressing 

product implementation.

5.1.1.1 Inputs

Inputs to the Product Implementation activity depend 

primarily on the decision as to whether the end product will be purchased, developed from scratch, or if the 

product will be formed by reusing part or all of products 

from other projects. Typical inputs are shown in Figure 5.1-1.

z Inputs if Purchasing the End Product: If the decision was made to purchase part or all of the products 

for this project, the end product design specifications 

are obtained from the configuration management 

system as well as other applicable documents such as 

the SEMP.

z Inputs if Making/Coding the End Product: For end 

products that will be made/coded by the technical 

5.1 Product Implementation

End Product

Documents and

Manuals 

From Configuration

Management Process

Desired End

Product 

To Product

Verification Process

End Product Design

Specications and

Conguration

Documentation 

Product

Implementation–

Enabling Products

To Technical Data

Management Process

Product

Implementation

Work Products

From existing

resources or Product

Transition Process

Required Raw

Materials 

From existing

resources or

external sources 

Make the specied end product

Capture product implementation

work products 

Prepare to conduct implementation

If implemented by 

buying:

Participate in purchase

of specied end product

Prepare appropriate

product support documentation

If implemented by

reuse:

Participate in acquiring

the reuse end product 

If implemented by making:

Evaluate readiness of

product implementation–

enabling products 

Figure 5.1-1 Product Implementation Process
74  NASA Systems Engineering Handbook

5.0 Product Realization

team, the inputs will be the configuration controlled 

design specifications and raw materials as provided to 

or purchased by the project.

z Inputs Needed if Reusing an End Product: For end 

products that will reuse part or all of products generated by other projects, the inputs may be the documentation associated with the product, as well as the 

product itself. Care must be taken to ensure that these 

products will indeed meet the specifications and environments for this project. These would have been 

factors involved in the Decision Analysis Process to 

determine the make/buy/reuse decision.

5.1.1.2 Process Activities 

Implementing the product can take one of three forms:

z Purchase/buy,

z Make/code, or

z Reuse.

These three forms will be discussed in the following subsections. Figure 5.1-1 shows what kind of inputs, outputs, 

and activities are performed during product implementation regardless of where in the product hierarchy or 

life cycle it is. These activities include preparing to conduct the implementation, purchasing/making/reusing 

the product, and capturing the product implementation 

work product. In some cases, implementing a product 

may have aspects of more than one of these forms (such 

as a build-to-print). In those cases, the appropriate aspects of the applicable forms are used.

Prepare to Conduct Implementation

Preparing to conduct the product implementation is a 

key first step regardless of what form of implementation 

has been selected. For complex projects, implementation 

strategy and detailed planning or procedures need to be 

developed and documented. For less complex projects, 

the implementation strategy and planning will need to 

be discussed, approved, and documented as appropriate 

for the complexity of the project.

The documentation, specifications, and other inputs will 

also need to be reviewed to ensure they are ready and at 

an appropriate level of detail to adequately complete the 

type of implementation form being employed and for 

the product life-cycle phase. For example, if the “make” 

implementation form is being employed, the design 

specifications will need to be reviewed to ensure they are 

at a design-to level that will allow the product to be developed. If the product is to be bought as a pure Commercial-Off-the-Shelf (COTS) item, the specifications 

will need to be checked to make sure they adequately 

describe the vendor characteristics to narrow to a single 

make/model of their product line.

Finally, the availability and skills of personnel needed to 

conduct the implementation as well as the availability of 

any necessary raw materials, enabling products, or special services should also be reviewed. Any special training 

necessary for the personnel to perform their tasks needs 

to be performed by this time.

Purchase, Make, or Reuse the Product

Purchase the Product

In the first case, the end product is to be purchased from 

a commercial or other vendor. Design/purchase specifications will have been generated during requirements 

development and provided as inputs. The technical team 

will need to review these specifications and ensure they 

are in a form adequate for the contract or purchase order. 

This may include the generation of contracts, Statements 

of Work (SOWs), requests for proposals, purchase orders, or other purchasing mechanisms. The responsibilities of the Government and contractor team should 

have been documented in the SEMP. This will define, 

for example, whether NASA expects the vendor to provide a fully verified and validated product or whether the 

NASA technical team will be performing those duties. 

The team will need to work with the acquisition team 

to ensure the accuracy of the contract SOW or purchase 

order and to ensure that adequate documentation, certificates of compliance, or other specific needs are requested of the vendor. 

For contracted purchases, as proposals come back from 

the vendors, the technical team should work with the 

contracting officer and participate in the review of the 

technical information and in the selection of the vendor 

that best meets the design requirements for acceptable 

cost and schedule.

As the purchased products arrive, the technical team 

should assist in the inspection of the delivered product 

and its accompanying documentation. The team should 

ensure that the requested product was indeed the one 

delivered, and that all necessary documentation, such 

as source code, operator manuals, certificates of compliance, safety information, or drawings have been received. 
5.1 Product Implementation

NASA Systems Engineering Handbook  75

The technical team should also ensure that any enabling 

products necessary to provide test, operations, maintenance, and disposal support for the product also are 

ready or provided as defined in the contract. 

Depending on the strategy and roles/responsibilities of 

the vendor, as documented in the SEMP, a determination/analysis of the vendor’s verification and validation 

compliance may need to be reviewed. This may be done 

informally or formally as appropriate for the complexity 

of the product. For products that were verified and validated by the vendor, after ensuring that all work products from this phase have been captured, the product 

may be ready to enter the Product Transition Process to 

be delivered to the next higher level or to its final end 

user. For products that will be verified and validated by 

the technical team, the product will be ready to be verified after ensuring that all work products for this phase 

have been captured.

Make/Code the Product

If the strategy is to make or code the product, the technical team should first ensure that the enabling products are ready. This may include ensuring all piece parts 

are available, drawings are complete and adequate, software design is complete and reviewed, machines to cut 

the material are available, interface specifications are approved, operators are trained and available, procedures/

processes are ready, software personnel are trained and 

available to generate code, test fixtures are developed and 

ready to hold products while being generated, and software test cases are available and ready to begin model 

generation.

The product is then made or coded in accordance with 

the specified requirements, configuration documentation, and applicable standards. Throughout this process, 

the technical team should work with the quality organization to review, inspect, and discuss progress and status 

within the team and with higher levels of management as 

appropriate. Progress should be documented within the 

technical schedules. Peer reviews, audits, unit testing, 

code inspections, simulation checkout, and other techniques may be used to ensure the made or coded product 

is ready for the verification process.

Reuse 

If the strategy is to reuse a product that already exists, 

care must be taken to ensure that the product is truly applicable to this project and for the intended uses and the 

environment in which it will be used. This should have 

been a factor used in the decision strategy to make/buy/

reuse.

The documentation available from the reuse product 

should be reviewed by the technical team to become 

completely familiar with the product and to ensure it 

will meet the requirements in the intended environment. 

Any supporting manuals, drawings, or other documentation available should also be gathered.

The availability of any supporting or enabling products 

or infrastructure needed to complete the fabrication, 

coding, testing, analysis, verification, validation, or shipping of the product needs to be determined. If any of 

these products or services are lacking, they will need to 

be developed or arranged for before progressing to the 

next phase.

Special arrangements may need to be made or forms 

such as nondisclosure agreements may need to be acquired before the reuse product can be received.

A reused product will frequently have to undergo the 

same verification and validation as a purchased product 

or a built product. Relying on prior verification and validation should only be considered if the product’s verification and validation documentation meets the verification, validation, and documentation requirements of the 

current project and the documentation demonstrates 

that the product was verified and validated against equivalent requirements and expectations. The savings gained 

from reuse is not necessarily from reduced testing, but 

in a lower likelihood that the item will fail tests and generate rework.

Capture Work Products

Regardless of what implementation form was selected, 

all work products from the make/buy/reuse process 

should be captured, including design drawings, design 

documentation, code listings, model descriptions, procedures used, operator manuals, maintenance manuals, 

or other documentation as appropriate.

5.1.1.3 Outputs

z End Product for Verification: Unless the vendor 

performs verification, the made/coded, purchased, 

or reused end product, in a form appropriate for the 

life-cycle phase, is provided for the verification process. The form of the end product is a function of the 
76  NASA Systems Engineering Handbook

5.0 Product Realization

life-cycle phase and the placement within the system 

structure (the form of the end product could be hardware, software, model, prototype, first article for test, 

or single operational article or multiple production 

article).

z End Product Documents and Manuals: Appropriate 

documentation is also delivered with the end product 

to the verification process and to the technical data 

management process. Documentation may include 

applicable design drawings; operation, user, maintenance, or training manuals; applicable baseline documents (configuration baseline, specifications, stakeholder expectations); certificates of compliance; or 

other vendor documentation. 

The process is complete when the following activities 

have been accomplished:

z End product is fabricated, purchased, or reuse modules acquired.

z End products are reviewed, checked, and ready for 

verification.

z Procedures, decisions, assumptions, anomalies, corrective actions, lessons learned, etc., resulting from 

the make/buy/reuse are recorded.

5.1.2 Product Implementation Guidance

5.1.2.1 Buying Off-the-Shelf Products

Off-the-Shelf (OTS) products are hardware/software 

that has an existing heritage and usually originates from 

one of several sources, which include commercial, military, and NASA programs. Special care needs to be taken 

when purchasing OTS products for use in the space environment. Most OTS products were developed for use 

in the more benign environments of Earth and may not 

be suitable to endure the harsh space environments, including vacuum, radiation, extreme temperature ranges, 

extreme lighting conditions, zero gravity, atomic oxygen, 

lack of convection cooling, launch vibration or acceleration, and shock loads.

When purchasing OTS products, requirements should 

still be generated and managed. A survey of available 

OTS is made and evaluated as to the extent they satisfy 

the requirements. Products that meet all the requirements are a good candidate for selection. If no product 

can be found to meet all the requirements, a trade study 

needs to be performed to determine whether the requirements can be relaxed or waived, the OTS can be modified to bring it into compliance, or whether another option to build or reuse should be selected.

Several additional factors should be considered when selecting the OTS option:

z Heritage of the product;

z Critical or noncritical application;

z Amount of modification required and who performs 

it;

z Whether sufficient documentation is available;

z Proprietary, usage, ownership, warranty, and licensing 

rights;

z Future support for the product from the vendor/provider;

z Any additional validation of the product needed by 

the project; and

z Agreement on disclosure of defects discovered by the 

community of users of the product.

5.1.2.2 Heritage

“Heritage” refers to the original manufacturer’s level of 

quality and reliability that is built into parts and which 

has been proven by (1) time in service, (2) number of 

units in service, (3) mean time between failure performance, and (4) number of use cycles. High-heritage 

products are from the original supplier, who has maintained the great majority of the original service, design, 

performance, and manufacturing characteristics. Lowheritage products are those that (1) were not built by 

the original manufacturer; (2) do not have a significant 

history of test and usage; or (3) have had significant aspects of the original service, design, performance, or 

manufacturing characteristics altered. An important 

factor in assessing the heritage of a COTS product is 

to ensure that the use/application of the product is relevant to the application for which it is now intended. A 

product that has high heritage in a ground-based application could have a low heritage when placed in a space 

environment.

The focus of a “heritage review” is to confirm the applicability of the component for the current application. 

Assessments must be made regarding not only technical 

interfaces (hardware and software) and performance, 

but also the environments to which the unit has been 

previously qualified, including electromagnetic compatibility, radiation, and contamination. The compatibility 

of the design with parts quality requirements must also 
5.1 Product Implementation

NASA Systems Engineering Handbook  77

be assessed. All noncompliances must be identified, documented, and addressed either by modification to bring 

the component into compliance or formal waivers/deviations for accepted deficiencies. This heritage review is 

commonly held closely after contract award.

When reviewing a product’s applicability, it is important to consider the nature of the application. A “catastrophic” application is one where a failure could cause 

loss of life or vehicle. A “critical” application is one where 

failure could cause loss of mission. For use in these applications, several additional precautions should be taken, 

including ensuring the product will not be used near the 

boundaries of its performance or environmental envelopes. Extra scrutiny by experts should be applied during 

Preliminary Design Reviews (PDRs) and Critical Design 

Reviews (CDRs) to ensure the appropriateness of its 

use.

Modification of an OTS product may be required for it 

to be suitable for a NASA application. This affects the 

product’s heritage, and therefore, the modified product 

should be treated as a new design. If the product is modified by NASA and not the manufacturer, it would be 

beneficial for the supplier to have some involvement in 

reviewing the modification. NASA modification may 

also require the purchase of additional documentation 

from the supplier such as drawings, code, or other design and test descriptions.

For additional information and suggested test and analysis requirements for OTS products, see JSC EA-WI-016 

or MSFC MWI 8060.1 both titled Off the Shelf Hardware 

Utilization in Flight Hardware Development and G-118-

2006e AIAA Guide for Managing the Use of Commercial 

Off the Shelf (COTS) Software Components for MissionCritical Systems.
78  NASA Systems Engineering Handbook

5.0 Product Realization

Product Integration is one of the SE engine product realization processes that make up the system structure. 

In this process, lower level products are assembled into 

higher level products and checked to make sure that the 

integrated product functions properly. It is an element 

of the processes that lead realized products from a level 

below to realized end products at a level above, between 

the Product Implementation, Verification, and Validation Processes.

The purpose of the Product Integration Process is to 

systematically assemble the higher level product from 

the lower level products or subsystems (e.g., product 

elements, units, components, subsystems, or operator 

tasks); ensure that the product, as integrated, functions 

properly; and deliver the product. Product integration 

is required at each level of the system hierarchy. The 

activities associated with product integrations occur 

throughout the entire product life cycle. This includes 

all of the incremental steps, including level-appropriate 

testing, necessary to complete assembly of a product 

and to enable the top-level 

product tests to be conducted. The Product Integration Process may include 

and often begins with analysis and simulations (e.g., 

various types of prototypes) 

and progresses through increasingly more realistic 

incremental functionality 

until the final product is 

achieved. In each successive build, prototypes are 

constructed, evaluated, improved, and reconstructed 

based upon knowledge 

gained in the evaluation 

process. The degree of virtual versus physical prototyping required depends 

on the functionality of the 

design tools and the complexity of the product and 

its associated risk. There is 

a high probability that the 

product, integrated in this 

manner, will pass product verification and validation. 

For some products, the last integration phase will occur 

when the product is deployed at its intended operational 

site. If any problems of incompatibility are discovered 

during the product verification and validation testing 

phase, they are resolved one at a time.

The Product Integration Process applies not only to hardware and software systems but also to service-oriented solutions, requirements, specifications, plans, and concepts. 

The ultimate purpose of product integration is to ensure 

that the system elements will function as a whole. 

5.2.1 Process Description

Figure 5.2-1 provides a typical flow diagram for the 

Product Integration Process and identifies typical inputs, outputs, and activities to consider in addressing 

product integration. The activities of the Product Integration Process are truncated to indicate the action and 

object of the action.

5.2 Product Integration

Product Documents

and Manuals 

To Product

Verication Process

Lower Level

Products to Be

Integrated 

End Product Design

Specications and

Conguration

Documentation 

Product Integration–

Enabling Products

To Technical Data

Management Process

From Product

Transition Process

From Conguration

Management Process

From existing

resources or Product

Transition Process

Desired Product

Product Integration

Work Products 

Conrm that received products

have been validated 

Prepare the integration environment

for assembly and integration

Assemble and integrate the

received products into the desired

end product

Obtain lower level products for

assembly and integration 

Capture product integration work

products 

Prepare to conduct product

integration

Prepare appropriate product

support documentation 

Figure 5.2-1 Product Integration Process
5.2 Product Integration

NASA Systems Engineering Handbook  79

5.2.1.1 Inputs 

Product Integration encompasses more than a one-time 

assembly of the lower level products and operator tasks 

at the end of the design and fabrication phase of the life 

cycle. An integration plan must be developed and documented. An example outline for an integration plan is 

provided in Appendix H. Product Integration is conducted incrementally, using a recursive process of assembling lower level products and operator tasks; evaluating 

them through test, inspection, analysis, or demonstration; and then assembling more lower level products and 

operator tasks. Planning for Product Integration should 

be initiated during the concept formulation phase of the 

life cycle. The basic tasks that need to be established involve the management of internal and external interfaces 

of the various levels of products and operator tasks to 

support product integration and are as follows:

z Define interfaces;

z Identify the characteristics of the interfaces (physical, 

electrical, mechanical, etc.);

z Ensure interface compatibility at all defined interfaces 

by using a process documented and approved by the 

project;

z Ensure interface compatibility at all defined interfaces;

z Strictly control all of the interface processes during 

design, construction, operation, etc.;

z Identify lower level products to be assembled and integrated (from the Product Transition Process);

z Identify assembly drawings or other documentation 

that show the complete configuration of the product 

being integrated, a parts list, and any assembly instructions (e.g., torque requirements for fasteners);

z Identify end-product, design-definition-specified requirements (specifications), and configuration documentation for the applicable work breakdown structure model, including interface specifications, in the 

form appropriate to satisfy the product-line life-cycle 

phase success criteria (from the Configuration Management Process); and

z Identify Product Integration–enabling products (from 

existing resources or the Product Transition Process 

for enabling product realization).

5.2.1.2 Process Activities

This subsection addresses the approach to the top-level 

implementation of the Product Integration Process, including the activities required to support the process, 

The project would follow this approach throughout its 

life cycle.

The following are typical activities that support the Product Integration Process:

z Prepare to conduct Product Integration by (1) preparing 

a product integration strategy, detailed planning for the 

integration, and integration sequences and procedures 

and (2) determining whether the product configuration documentation is adequate to conduct the type of 

product integration applicable for the product-line lifecycle phase, location of the product in the system structure, and management phase success criteria.

z Obtain lower level products required to assemble and 

integrate into the desired product.

z Confirm that the received products that are to be assembled and integrated have been validated to demonstrate that the individual products satisfy the 

agreed-to set of stakeholder expectations, including 

interface requirements.

z Prepare the integration environment in which assembly and integration will take place, including evaluating the readiness of the product integration–enabling products and the assigned workforce. 

z Assemble and integrate the received products into the 

desired end product in accordance with the specified 

requirements, configuration documentation, interface requirements, applicable standards, and integration sequencing and procedures. 

z Conduct functional testing to ensure that assembly is 

ready to enter verification testing and ready to be integrated into the next level.

z Prepare appropriate product support documentation 

such as special procedures for performing product 

verification and product validation.

z Capture work products and related information generated while performing the product integration process activities.

5.2.1.3 Outputs

The following are typical outputs from this process and 

destinations for the products from this process:

z Integrated product(s) in the form appropriate to the 

product-line life-cycle phase and to satisfy phase success criteria (to the Product Verification Process).

z Documentation and manuals in a form appropriate 

for satisfying the life-cycle phase success criteria, in-
80  NASA Systems Engineering Handbook

5.0 Product Realization

cluding as-integrated product descriptions and operate-to and maintenance manuals (to the Technical 

Data Management Process).

z Work products, including reports, records, and nondeliverable outcomes of product integration activities (to support the Technical Data Management Process); integration strategy document; assembly/check 

area drawings; system/component documentation sequences and rationale for selected assemblies; interface 

management documentation; personnel requirements; 

special handling requirements; system documentation; shipping schedules; test equipment and drivers’ 

requirements; emulator requirements; and identification of limitations for both hardware and software.

5.2.2 Product Integration Guidance

5.2.2.1 Integration Strategy

An integration strategy is developed, as well as supporting 

documentation, to identify optimal sequence of receipt, 

assembly, and activation of the various components that 

make up the system. This strategy should use business as 

well as technical factors to ensure an assembly, activation, 

and loading sequence that minimizes cost and assembly 

difficulties. The larger or more complex the system or the 

more delicate the element, the more critical the proper 

sequence becomes, as small changes can cause large impacts on project results.

The optimal sequence of assembly is built from the 

bottom up as components become subelements, elements, and subsystems, each of which must be checked 

prior to fitting into the next higher assembly. The sequence will encompass any effort needed to establish 

and equip the assembly facilities (e.g., raised floor, hoists, 

jigs, test equipment, input/output, and power connections). Once established, the sequence must be periodically reviewed to ensure that variations in production 

and delivery schedules have not had an adverse impact 

on the sequence or compromised the factors on which 

earlier decisions were made.

5.2.2.2 Relationship to Product 

Implementation 

As previously described, Product Implementation is 

where the plans, designs, analysis, requirements development, and drawings are realized into actual products. 

Product Integration concentrates on the control of the 

interfaces and the verification and validation to achieve 

the correct product to meet the requirements. Product 

Integration can be thought of as released or phased deliveries. Product Integration is the process that pulls together new and existing products and ensures that they 

all combine properly into a complete product without 

interference or complications. If there are issues, the 

Product Integration Process documents the exceptions, 

which can then be evaluated to determine if the product 

is ready for implementation/operations.

Integration occurs at every stage of a project’s life cycle. 

In the Formulation phase, the decomposed requirements 

need to be integrated into a complete system to verify that 

nothing is missing or duplicated. In the Implementation 

phase, the design and hardware need to be integrated into 

an overall system to verify that they meet the requirements and that there are no duplications or omissions. 

The emphasis on the recursive, iterative, and integrated 

nature of systems engineering highlights how the product 

integration activities are not only integrated across all of 

the phases of the entire life cycle in the initial planning 

stages of the project, but also used recursively across all 

of the life-cycle phases as the project product proceeds 

through the flow down and flow up conveyed by the SE 

engine. This ensures that when changes occur to requirements, design concepts, etc.—usually in response to updates from stakeholders and results from analysis, modeling, or testing—that adequate course corrections are 

made to the project. This is accomplished through reevaluation by driving through the SE engine, enabling all 

aspects of the product integration activities to be appropriately updated. The result is a product that meets all of 

the new modifications approved by the project and eliminates the opportunities for costly and time-consuming 

modifications in the later stages of the project.

5.2.2.3 Product/Interface Integration Support

There are several processes that support the integration of 

products and interfaces. Each process allows either the integration of products and interfaces or the validation that 

the integrated products meet the needs of the project.

The following is a list of typical example processes and 

products that support the integration of products and 

interfaces and that should be addressed by the project 

in the overall approach to Product Integration: requirements documents; requirements reviews; design reviews; design drawings and specifications; integration 

and test plans; hardware configuration control docu-
5.2 Product Integration

NASA Systems Engineering Handbook  81

mentation; quality assurance records; interface control 

requirements/documents; ConOps documents; verification requirement documents; verification reports/analysis; NASA, military, and industry standards; best practices; and lessons learned.

5.2.2.4 Product Integration of the Design 

Solution

This subsection addresses the more specific implementation of Product Integration related to the selected design 

solution.

Generally, system/product designs are an aggregation of 

subsystems and components. This is relatively obvious 

for complex hardware and/or software systems. The same 

holds true for many service-oriented solutions. For example, a solution to provide a single person access to the 

Internet involves hardware, software, and a communications interface. The purpose of Product Integration is to 

ensure that combination of these elements achieves the 

required result (i.e., works as expected). Consequently, 

internal and external interfaces must be considered in 

the design and evaluated prior to production. 

There are a variety of different testing requirements to 

verify product integration at all levels. Qualification 

testing and acceptance testing are examples of two of 

these test types that are performed as the product is integrated. Another type of testing that is important to the 

design and ultimate product integration is a planned test 

process in which development items are tested under actual or simulated mission profile environments to disclose design deficiencies and to provide engineering 

information on failure modes and mechanisms. If accomplished with development items, this provides early 

insight into any issues that may otherwise only be observed at the late stages of product integration where 

it becomes costly to incorporate corrective actions. For 

large, complex system/products, integration/verification 

efforts are accomplished using a prototype.

5.2.2.5 Interface Management

The objective of the interface management is to achieve 

functional and physical compatibility among all interrelated system elements. Interface management is defined in more detail in Section 6.3. An interface is any 

boundary between one area and another. It may be cognitive, external, internal, functional, or physical. Interfaces occur within the system (internal) as well as between the system and another system (external) and may 

be functional or physical (e.g., mechanical, electrical) in 

nature. Interface requirements are documented in an Interface Requirements Document (IRD). Care should be 

taken to define interface requirements and to avoid specifying design solutions when creating the IRD. In its final 

form, the Interface Control Document (ICD) describes 

the detailed implementation of the requirements contained in the IRD. An interface control plan describes 

the management process for IRDs and ICDs. This plan 

provides the means to identify and resolve interface incompatibilities and to determine the impact of interface 

design changes.

5.2.2.6 Compatibility Analysis

During the program’s life, compatibility and accessibility must be maintained for the many diverse elements. 

Compatibility analysis of the interface definition demonstrates completeness of the interface and traceability 

records. As changes are made, an authoritative means 

of controlling the design of interfaces must be managed 

with appropriate documentation, thereby avoiding the 

situation in which hardware or software, when integrated 

into the system, fails to function as part of the system as 

intended. Ensuring that all system pieces work together 

is a complex task that involves teams, stakeholders, contractors, and program management from the end of the 

initial concept definition stage through the operations 

and support stage. Physical integration is accomplished 

during Phase D. At the finer levels of resolution, pieces 

must be tested, assembled and/or integrated, and tested 

again. The systems engineer role includes performance 

of the delegated management duties such as configuration control and overseeing the integration, verification, 

and validation processes.

5.2.2.7 Interface Management Tasks

The interface management tasks begin early in the development effort, when interface requirements can be influenced by all engineering disciplines and applicable interface standards can be invoked. They continue through 

design and checkout. During design, emphasis is on ensuring that interface specifications are documented and 

communicated. During system element checkout, both 

prior to assembly and in the assembled configuration, 

emphasis is on verifying the implemented interfaces. 

Throughout the product integration process activities, 

interface baselines are controlled to ensure that changes 
82  NASA Systems Engineering Handbook

5.0 Product Realization

in the design of system elements have minimal impact 

on other elements with which they interface. During 

testing or other validation and verification activities, 

multiple system elements are checked out as integrated 

subsystems or systems. The following provides more details on these tasks.

Define Interfaces

The bulk of integration problems arise from unknown or 

uncontrolled aspects of interfaces. Therefore, system and 

subsystem interfaces are specified as early as possible in 

the development effort. Interface specifications address 

logical, physical, electrical, mechanical, human, and environmental parameters as appropriate. Intra-system interfaces are the first design consideration for developers 

of the system’s subsystems. Interfaces are used from previous development efforts or are developed in accordance with interface standards for the given discipline 

or technology. Novel interfaces are constructed only for 

compelling reasons. Interface specifications are verified 

against interface requirements. Typical products include 

interface descriptions, ICDs, interface requirements, and 

specifications.

Verify Interfaces

In verifying the interfaces, the systems engineer must ensure that the interfaces of each element of the system or 

subsystem are controlled and known to the developers. 

Additionally, when changes to the interfaces are needed, 

the changes must at least be evaluated for possible impact on other interfacing elements and then communicated to the affected developers. Although all affected 

developers are part of the group that makes changes, 

such changes need to be captured in a readily accessible 

place so that the current state of the interfaces can be 

known to all. Typical products include ICDs and exception reports.

The use of emulators for verifying hardware and software interfaces is acceptable where the limitations of the 

emulator are well characterized and meet the operating 

environment characteristics and behavior requirements 

for interface verification. The integration plan should 

specifically document the scope of use for emulators. 

Inspect and Acknowledge System and Subsystem 

Element Receipt

Acknowledging receipt and inspecting the condition of 

each system or subsystem element is required prior to 

assembling the system in accordance with the intended 

design. The elements are checked for quantity, obvious 

damage, and consistency between the element description and a list of element requirements. Typical products 

include acceptance documents, delivery receipts, and 

checked packing list.

Verify System and Subsystem Elements

System and subsystem element verification confirms 

that the implemented design features of developed or 

purchased system elements meet their requirements. 

This is intended to ensure that each element of the 

system or subsystem functions in its intended environment, including those elements that are OTS for other 

environments. Such verifications may be by test (e.g., 

regression testing as a tool or subsystem/elements are 

combined), inspection, analysis (deficiency or compliance reports), or demonstration and may be executed 

either by the organization that will assemble the system 

or subsystem or by the producing organization. A 

method of discerning the elements that “passed” verification from those elements that “failed” needs to be in 

place. Typical products include verified system features 

and exception reports.

Verify Element Interfaces

Verification of the system element interfaces ensures 

that the elements comply with the interface specification 

prior to assembly in the system. The intent is to ensure 

that the interface of each element of the system or subsystem is verified against its corresponding interface 

specification. Such verification may be by test, inspection, analysis, or demonstration and may be executed 

by the organization that will assemble the system or 

subsystem or by another organization. Typical products include verified system element interfaces, test reports, and exception reports.

Integrate and Verify

Assembly of the elements of the system should be performed in accordance with the established integration 

strategy. This ensures that the assembly of the system elements into larger or more complex assemblies is conducted in accordance with the planned strategy. To 

ensure that the integration has been completed, a verification of the integrated system interfaces should be performed. Typical products include integration reports, 

exception reports, and an integrated system.
NASA Systems Engineering Handbook  83

The Product Verification Process is the first of the verification and validation processes conducted on a realized 

end product. As used in the context of the systems engineering common technical processes, a realized product 

is one provided by either the Product Implementation 

Process or the Product Integration Process in a form 

suitable for meeting applicable life-cycle phase success 

criteria. Realization is the act of verifying, validating, and 

transitioning the realized product for use at the next level 

up of the system structure or to the customer. Simply 

put, the Product Verification Process answers the critical question, Was the end product realized right? The 

Product Validation Process addresses the equally critical 

question, Was the right end product realized?

Verification proves that a realized product for any system 

model within the system structure conforms to the buildto requirements (for software elements) or realize-to specifications and design descriptive documents (for hardware 

elements, manual procedures, or composite products of 

hardware, software, and manual procedures). 

Distinctions Between Product Verification and 

Product Validation

From a process perspective, product verification and validation may be similar in nature, but the objectives are 

fundamentally different.

It is essential to confirm that the realized product is in 

conformance with its specifications and design description documentation (i.e., verification). Such specifications and documents will establish the configuration 

baseline of that product, which may have to be modified 

at a later time. Without a verified baseline and appropriate configuration controls, such later modifications 

could be costly or cause major performance problems. 

However, from a customer point of view, the interest is in 

whether the end product provided will do what the customer intended within the environment of use (i.e., validation). When cost effective and warranted by analysis, 

the expense of validation testing alone can be mitigated 

by combining tests to perform verification and validation simultaneously.

The outcome of the Product Verification Process is 

confirmation that the “as-realized product,” whether 

achieved by implementation or integration, conforms 

to its specified requirements, i.e., verification of the end 

product. This subsection discusses the process activities, 

inputs, outcomes, and potential deficiencies.

5.3.1 Process Description

Figure 5.3-1 provides a typical flow diagram for the 

Product Verification Process and identifies typical inputs, outputs, and activities to consider in addressing 

product verification.

5.3.1.1 Inputs

Key inputs to the process are the product to be verified, 

verification plan, specified requirements baseline, and 

any enabling products needed to perform the Product 

Verification Process (including the ConOps, mission 

needs and goals, requirements and specifications, in5.3 Product Verification 

Differences Between Verification and 

Validation Testing

Verification Testing

Verification testing relates back to the approved requirements set (such as an SRD) and can be performed at different stages in the product life cycle. 

Verification testing includes: (1) any testing used to 

assist in the development and maturation of products, product elements, or manufacturing or support 

processes; and/or (2) any engineering-type test used 

to verify the status of technical progress, verify that 

design risks are minimized, substantiate achievement 

of contract technical performance, and certify readiness for initial validation testing. Verification tests use 

instrumentation and measurements and are generally accomplished by engineers, technicians, or operator-maintainer test personnel in a controlled environment to facilitate failure analysis. 

Validation Testing

Validation relates back to the ConOps document. Validation testing is conducted under realistic conditions 

(or simulated conditions) on any end product to determine the effectiveness and suitability of the product for use in mission operations by typical users and 

to evaluate the results of such tests. Testing is the detailed quantifying method of both verification and 

validation. However, testing is required to validate final end products to be produced and deployed. 
84  NASA Systems Engineering Handbook

5.0 Product Realization

terface control drawings, testing standards and policies, 

and Agency standards and policies).

5.3.1.2 Process Activities

There are five major steps in the Product Verification 

Process: (1) verification planning (prepare to implement 

the verification plan); (2) verification preparation (prepare for conducting verification); (3) conduct verification (perform verification); (4) analyze verification results; and (5) capture the verification work products. 

The objective of the Product Verification Process is to 

generate evidence necessary to confirm that end products, from the lowest level of the system structure to the 

highest, conform to the specified requirements (specifications and descriptive documents) to which they were 

realized whether by the Product Implementation Process or by the Product Integration Process.

Product Verification is usually performed by the developer that produced (or “realized”) the end product, with 

participation of the end user and customer. Product 

Verification confirms that the as-realized product, 

whether it was achieved by Product Implementation or 

Product Integration, conforms to its specified requirements (specifications and descriptive documentation) 

used for making or assembling and integrating the end 

product. Developers of the system, as well as the users, 

are typically involved in verification testing. The customer and Quality Assurance (QA) personnel are also 

critical in the verification planning and execution activities.

Product Verification Planning 

Planning to conduct the product verification is a key first 

step. From relevant specifications and product form, the 

type of verification (e.g., analysis, demonstration, inspection, or test) should be established based on the life-cycle 

phase, cost, schedule, resources, and the position of the 

end product within the system structure. The verification plan should be reviewed (an output of the Technical 

Planning Process, based on design solution outputs) for 

any specific procedures, constraints, success criteria, or 

other verification requirements. (See Appendix I for a 

sample verification plan outline.)

Verification Plan and Methods 

The task of preparing the verification plan includes establishing the type of verification to be performed, deFigure 5.3-1 Product Verification Process

Product Verification

Results 

Product Verification

Report 

From Product

Implementation or

Product Integration Process

End Product

to Be Verified 

Product Verification

Plan

Specified Requirements

Baseline 

Product Verification–

Enabling Products

To Technical

Assessment Process

From Design Solution 

Denition and Technical

Planning Processes

Verified End Product

To Product

Validation Process

To Technical Data

Management Process

From Conguration

Management Process

From existing

resources or Product

Transition Process Product Verification

Work Products 

Perform the product

verification

Analyze the outcomes of

the product verification

Capture the work products

from product verification 

Prepare a product

verification report 

Prepare to conduct product

verification
5.3 Product Verification

NASA Systems Engineering Handbook  85

pendent on the life-cycle phase; position of the product 

in the system structure; the form of the product used; 

and related costs of verification of individual specified 

requirements. The types of verification include analyses, 

inspection, demonstration, and test or some combination of these four. The verification plan, typically written 

at a detailed technical level, plays a pivotal role in bottomup product realization. 

z Flight units (end product that is flown, including protoflight units).

Any of these types of product forms may be in any of 

these states:

z Produced (built, fabricated, manufactured, or coded);

z Reused (modified internal nondevelopmental products or OTS product); and 

z Assembled and integrated (a composite of lower level 

products).

The conditions and environment under which the 

product is to be verified should be established and the 

verification planned based on the associated entrance/

success criteria identified. The Decision Analysis Process 

should be used to help finalize the planning details. 

Procedures should be prepared to conduct verification 

based on the type (e.g., analysis, inspection, demonstration, or test) planned. These procedures are typically developed during the design phase of the project life cycle 

and matured as the design is matured. Operational use 

Types of Testing

There are many different types of testing that can be used in verification of an end product. These examples are provided for consideration:

z Aerodynamic z Acceptance z Acoustic 

z Burn-in z Characterization z Component 

z Drop z Electromagnetic Compatibility z Electromagnetic Interference

z Environmental z G-loading z Go or No-Go 

z High-/Low-Voltage Limits z Human Factors Engineering/

Human-in-the-Loop Testing

z Integration 

z Leak Rates z Lifetime/Cycling z Manufacturing/Random Defects

z Nominal z Off-Nominal z Operational

z Parametric z Performance z Pressure Cycling 

z Pressure Limits z Qualification Flow z Structural Functional

z Security Checks z System z Thermal Cycling

z Thermal Limits z Thermal Vacuum z Vibration

Note: The final, official verification of the end product should be for a controlled unit. Typically, attempting to “buy off” a “shall” on a prototype is not acceptable; it is usually completed on a qualification, flight, 

or other more final, controlled unit. 

Note: Close alignment of the verification plan with 

the project’s SEMP is absolutely essential.

Verification can be performed recursively throughout 

the project life cycle and on a wide variety of product 

forms. For example:

z Simulated (algorithmic models, virtual reality simulator);

z Mockup (plywood, brass board, breadboard);

z Concept description (paper report); 

z Prototype (product with partial functionality);

z Engineering unit (fully functional but may not be 

same form/fit);

z Design verification test units (form, fit, and function 

is the same, but they may not have flight parts);

z Qualification units (identical to flight units but may 

be subjected to extreme environments); and
86  NASA Systems Engineering Handbook

5.0 Product Realization

scenarios are thought through so as to explore all possible verification activities to be performed. 

Outcomes of verification planning include the following:

z The verification type that is appropriate for showing 

or proving the realized product conforms to its specified requirements is selected.

z The product verification procedures are clearly defined based on: (1) the procedures for each type of 

verification selected, (2) the purpose and objective of 

each procedure, (3) any pre-verification and post-verification actions, and (4) the criteria for determining 

the success or failure of the procedure.

z The verification environment (e.g., facilities, equipment, tools, simulations, measuring devices, personnel, and climatic conditions) in which the verification procedures will be implemented is defined. 

z As appropriate, project risk items are updated based 

on approved verification strategies that cannot duplicate fully integrated test systems, configurations, 

and/or target operating environments. Rationales, 

trade space, optimization results, and implications of 

the approaches are documented in the new or revised 

risk statements as well as references to accommodate 

future design, test, and operational changes to the 

project baseline.

Product Verification Preparation

In preparation for verification, the specified requirements (outputs of the Design Solution Process) are collected and confirmed. The product to be verified is obtained (output from implementation or integration), as 

are any enabling products and support resources that 

are necessary for verification (requirements identified 

and acquisition initiated by design solution definition 

Types of Verification

z Analysis: The use of mathematical modeling and analytical techniques to predict the suitability of a design to stakeholder expectations based on calculated data or data derived from lower system structure end product verifications. 

Analysis is generally used when a prototype; engineering model; or fabricated, assembled, and integrated product is 

not available. Analysis includes the use of modeling and simulation as analytical tools. A model is a mathematical representation of reality. A simulation is the manipulation of a model.

z Demonstration: Showing that the use of an end product achieves the individual specified requirement. It is generally a basic confirmation of performance capability, differentiated from testing by the lack of detailed data gathering. 

Demonstrations can involve the use of physical models or mockups; for example, a requirement that all controls shall 

be reachable by the pilot could be verified by having a pilot perform flight-related tasks in a cockpit mockup or simulator. A demonstration could also be the actual operation of the end product by highly qualified personnel, such as 

test pilots, who perform a one-time event that demonstrates a capability to operate at extreme limits of system performance, an operation not normally expected from a representative operational pilot. 

z Inspection: The visual examination of a realized end product. Inspection is generally used to verify physical design 

features or specific manufacturer identification. For example, if there is a requirement that the safety arming pin has a 

red flag with the words “Remove Before Flight” stenciled on the flag in black letters, a visual inspection of the arming 

pin flag can be used to determine if this requirement was met. 

z Test: The use of an end product to obtain detailed data needed to verify performance, or provide sufficient information to verify performance through further analysis. Testing can be conducted on final end products, breadboards, 

brass boards or prototypes. Testing produces data at discrete points for each specified requirement under controlled 

conditions and is the most resource-intensive verification technique. As the saying goes, “Test as you fly, and fly as you 

test.” (See Subsection 5.3.2.5.)

Note: Verification planning is begun early in the project life cycle during the requirements development 

phase. (See Section 4.2.) Which verification approach 

to use should be included as part of the requirements 

development to plan for the future activities, establish special requirements derived from verificationenabling products identified, and to ensure that the 

technical statement is a verifiable requirement. Updates to verification planning continue throughout 

logical decomposition and design development, especially as design reviews and simulations shed light 

on items under consideration. (See Section 6.1.)
5.3 Product Verification

NASA Systems Engineering Handbook  87

activities). The final element of verification preparation 

includes the preparation of the verification environment 

(e.g., facilities, equipment, tools, simulations, measuring 

devices, personnel, and climatic conditions). Identification of the environmental requirements is necessary and 

the implications of those requirements must be carefully 

considered.

Outcomes of verification preparation include the following:

z The preparations for performing the verification as 

planned are completed;

z An appropriate set of specified requirements and supporting configuration documentation is available and 

on hand;

z Articles/models to be used for verification are on 

hand, assembled, and integrated with the verification environment according to verification plans and 

schedules;

z The resources needed to conduct the verification 

are available according to the verification plans and 

schedules; and

z The verification environment is evaluated for adequacy, completeness, readiness, and integration.

Conduct Planned Product Verification 

The actual act of verifying the end product is conducted 

as spelled out in the plans and procedures and conformance established to each specified verification requirement. The responsible engineer should ensure that the 

procedures were followed and performed as planned, 

the verification-enabling products were calibrated correctly, and the data were collected and recorded for required verification measures.

The Decision Analysis Process should be used to help 

make decisions with respect to making needed changes 

in the verification plans, environment, and/or conduct.

Outcomes of conducting verification include the following:

z A verified product is established with supporting confirmation that the appropriate results were collected 

and evaluated to show completion of verification objectives,

z A determination as to whether the realized end 

product (in the appropriate form for the life-cycle 

phase) complies with its specified requirements,

z A determination that the verification product was appropriately integrated with the verification environment and each specified requirement was properly 

verified, and

z A determination that product functions were verified both together and with interfacing products 

throughout their performance envelope.

Analyze Product Verification Results

Once the verification activities have been completed, 

the results are collected and analyzed. The data are analyzed for quality, integrity, correctness, consistency, 

and validity, and any verification anomalies, variations, 

and out-of-compliance conditions are identified and reviewed.

Variations, anomalies, and out-of-compliance conditions must be recorded and reported for followup action 

and closure. Verification results should be recorded in 

the requirements compliance matrix developed during 

the Technical Requirements Definition Process or other 

mechanism to trace compliance for each verification requirement. 

System design and product realization process activities 

may be required to resolve anomalies not resulting from 

poor verification conduct, design, or conditions. If there 

are anomalies not resulting from the verification conduct, design, or conditions, and the mitigation of these 

Note: Depending on the nature of the verification effort and the life-cycle phase the program is in, some 

type of review to assess readiness for verification (as 

well as validation later) is typically held. In earlier 

phases of the life cycle, these reviews may be held informally; in later phases of the life cycle, this review 

becomes a formal event called a Test Readiness Review. TRRs and other technical reviews are an activity 

of the Technical Assessment Process. 

On most projects, a number of TRRs with tailored entrance/success criteria are held to assess the readiness 

and availability of test ranges; test facilities; trained 

testers; instrumentation; integration labs; support 

equipment; and other enabling products; etc. 

Peer reviews are additional reviews that may be conducted formally or informally to ensure readiness for 

verification (as well as the results of the verification 

process).
88  NASA Systems Engineering Handbook

5.0 Product Realization

anomalies results in a change to the product, the verification may need to be planned and conducted again. 

Outcomes of analyzing the verification results include 

the following:

z End-product variations, anomalies, and out-of-compliance conditions have been identified;

z Appropriate replanning, redefinition of requirements, 

design and reverification have been accomplished for 

resolution for anomalies, variations, or out-of-compliance conditions (for problems not caused by poor 

verification conduct);

z Variances, discrepancies, or waiver conditions have 

been accepted or dispositioned;

z Discrepancy and corrective action reports have been 

generated as needed; and

z The verification report is completed.

Reengineering

Based on analysis of verification results, it could be necessary to re-realize the end product used for verification 

or to reengineer the end products assembled and integrated into the product being verified, based on where 

and what type of defect was found.

Reengineering could require the reapplication of the 

system design processes (Stakeholder Expectations Definition, Technical Requirements Definition, Logical Decomposition, and Design Solution Definition). 

Verification Deficiencies

Verification test outcomes can be unsatisfactory for several reasons. One reason is poor conduct of the verification (e.g., procedures not followed, equipment not calibrated, improper verification environmental conditions, 

or failure to control other variables not involved in verifying a specified requirement). A second reason could 

be that the realized end product used was not realized 

correctly. Reapplying the system design processes could 

create the need for the following:

z Reengineering products lower in the system structure 

that make up the product that were found to be defective (i.e., they failed to satisfy verification requirements) and/or

z Reperforming the Product Verification Process.

Pass Verification But Fail Validation? 

Many systems successfully complete verification but then 

are unsuccessful in some critical phase of the validation 

process, delaying development and causing extensive rework and possible compromises with the stakeholder. 

Developing a solid ConOps in early phases of the project 

(and refining it through the requirements development 

and design phases) is critical to preventing unsuccessful 

validation. Communications with stakeholders helps to 

identify operational scenarios and key needs that must 

be understood when designing and implementing the 

end product. Should the product fail validation, redesign may be a necessary reality. Review of the understood requirements set, the existing design, operational 

scenarios, and support material may be necessary, as 

well as negotiations and compromises with the customer, other stakeholders, and/or end users to determine what, if anything, can be done to correct or resolve the situation. This can add time and cost to the 

overall project or, in some cases, cause the project to 

fail or be cancelled.

Capture Product Verification Work Products

Verification work products (inputs to the Technical Data 

Management Process) take many forms and involve 

many sources of information. The capture and recording 

of verification results and related data is a very important, but often underemphasized, step in the Product 

Verification Process.

Verification results, anomalies, and any corrective 

action(s) taken should be captured, as should all relevant 

results from the application of the Product Verification 

Process (related decisions, rationale for the decisions 

made, assumptions, and lessons learned). 

Outcomes of capturing verification work products include the following:

z Verification of work products are recorded, e.g., type 

of verification, procedures, environments, outcomes, 

decisions, assumptions, corrective actions, lessons 

learned.

Note: Nonconformances and discrepancy reports 

may be directly linked with the Technical Risk Management Process. Depending on the nature of the 

nonconformance, approval through such bodies as a 

material review board or configuration control board 

(which typically includes risk management participation) may be required.
5.3 Product Verification

NASA Systems Engineering Handbook  89

z Variations, anomalies, and out-of-compliance conditions have been identified and documented, including 

the actions taken to resolve them.

z Proof that the realized end product did or did not satisfy the specified requirements is documented. 

z The verification report is developed, including:

▶ Recorded test/verification results/data;

▶ Version of the set of specified requirements used;

▶ Version of the product verified;

▶ Version or standard for tools, data, and equipment 

used;

▶ Results of each verification including pass or fail 

declarations; and

▶ Expected versus actual discrepancies.

5.3.1.3 Outputs

Key outputs from the process are: 

z Discrepancy reports and identified corrective actions;

z Verified product to validation or integration; and

z Verification report(s) and updates to requirements 

compliance documentation (including verification 

plans, verification procedures, verification matrices, 

verification results and analysis, and test/demonstration/inspection/analysis records).

Success criteria include: (1) documented objective evidence of compliance (or waiver, as appropriate) with 

each system-of-interest requirement and (2) closure of 

all discrepancy reports. The Product Verification Process is not considered or designated complete until all 

discrepancy reports are closed (i.e., all errors tracked to 

closure).

5.3.2 Product Verification Guidance

5.3.2.1 Verification Program

A verification program should be tailored to the project 

it supports. The project manager/systems engineer must 

work with the verification engineer to develop a verification program concept. Many factors need to be considered in developing this concept and the subsequent 

verification program. These factors include:

z Project type, especially for flight projects. Verification 

methods and timing depend on:

▶ The type of flight article involved (e.g., an experiment, payload, or launch vehicle). 

▶ NASA payload classification (NPR 8705.4, Risk 

Classification for NASA Payloads). Guidelines are 

intended to serve as a starting point for establishment of the formality of test programs which can be 

tailored to the needs of a specific project based on 

the “A-D” payload classification.

▶ Project cost and schedule implications. Verification activities can be significant drivers of a 

project’s cost and schedule; these implications 

should be considered early in the development 

of the verification program. Trade studies should 

be performed to support decisions about verification methods and requirements and the selection of facility types and locations. For example, a 

trade study might be made to decide between performing a test at a centralized facility or at several 

decentralized locations.

▶ Risk implications. Risk management must be considered in the development of the verification program. Qualitative risk assessments and quantitative 

risk analyses (e.g., a Failure Mode and Effects Analysis (FMECA)) often identify new concerns that can 

be mitigated by additional testing, thus increasing 

the extent of verification activities. Other risk assessments contribute to trade studies that determine 

the preferred methods of verification to be used and 

when those methods should be performed. For example, a trade might be made between performing 

a model test versus determining model characteristics by a less costly, but less revealing, analysis. The 

project manager/systems engineer must determine 

what risks are acceptable in terms of the project’s 

cost and schedule. 

z Availability of verification facilities/sites and transportation assets to move an article from one location 

to another (when needed). This requires coordination 

with the Integrated Logistics Support (ILS) engineer.

z Acquisition strategy (i.e., in-house development or 

system contract). Often, a NASA field center can 

shape a contractor’s verification process through the 

project’s SOW.

z Degree of design inheritance and hardware/software 

reuse.

5.3.2.2 Verification in the Life Cycle

The type of verification completed will be a function of 

the life-cycle phase and the position of the end product 
90  NASA Systems Engineering Handbook

5.0 Product Realization

within the system structure. The end product must be 

verified and validated before it is transitioned to the next 

level up as part of the bottom-up realization process. 

(See Figure 5.3-2.)

While illustrated here as separate processes, there can be 

considerable overlap between some verification and validation events when implemented. 

Quality Assurance in Verification

Even with the best of available designs, hardware fabrication, software coding, and testing, projects are subject 

to the vagaries of nature and human beings. The systems 

engineer needs to have some confidence that the system 

actually produced and delivered is in accordance with its 

functional, performance, and design requirements. QA 

provides an independent assessment to the project manager/systems engineer of the items produced and processes used during the project life cycle. The QA engineer typically acts as the systems engineer’s eyes and ears 

in this context. 

The QA engineer typically monitors the resolution and 

closeout of nonconformances and problem/failure reports; verifies that the physical configuration of the 

system conforms to the build-to (or code-to) documentation approved at CDR; and collects and maintains QA 

data for subsequent failure analyses. The QA engineer also 

participates in major reviews (primarily SRR, PDR, CDR, 

and FRR) on issues of design, materials, workmanship, 

fabrication and verification processes, and other characteristics that could degrade product system quality.

The project manager/systems engineer must work with 

the QA engineer to develop a QA program (the extent, 

responsibility, and timing of QA activities) tailored to 

the project it supports. In part, the QA program ensures 

verification requirements are properly specified, especially with respect to test environments, test configurations, and pass/fail criteria, and monitors qualification 

and acceptance tests to ensure compliance with verification requirements and test procedures to ensure that test 

data are correct and complete. 

Tier 1

End Product

Deliver veried

end product

Validate against stakeholder

expectations and ConOps

To end user/

use environment

Deliver veried

end product

Deliver veried

end product

Deliver veried

end product

Deliver veried

end product

Validate against stakeholder

expectations and ConOps 

Validate against stakeholder

expectations and ConOps

Validate against stakeholder

expectations and ConOps 

Verify against

end product

specied

requirements

Verify against

end product

specied

requirements

Verify against

end product

specied

requirements

Verify against

end product

specied

requirements

Verify against

end product

specied

requirements

Tier 2

End Product

Tier 3

End Product

Tier 4

End Product

Tier 5

End Product

Figure 5.3-2 Bottom-up realization process
5.3 Product Verification

NASA Systems Engineering Handbook  91

Configuration Verification

Configuration verification is the process of verifying that 

resulting products (e.g., hardware and software items) 

conform to the baselined design and that the baseline 

documentation is current and accurate. Configuration 

verification is accomplished by two types of control gate 

activity: audits and technical reviews. 

Qualification Verification 

Qualification-stage verification activities begin after 

completion of development of the flight/operations hardware designs and include analyses and testing to ensure 

that the flight/operations or flight-type hardware (and 

software) will meet functional and performance requirements in anticipated environmental conditions. During 

this stage, many performance requirements are verified, 

while analyses and models are updated as test data are acquired. Qualification tests generally are designed to subject the hardware to worst-case loads and environmental 

stresses plus a defined level of margin. Some of the verifications performed to ensure hardware compliance are 

vibration/acoustic, pressure limits, leak rates, thermal 

vacuum, thermal cycling, Electromagnetic Interference 

and Electromagnetic Compatibility (EMI/EMC), highand low-voltage limits, and lifetime/cycling. Safety requirements, defined by hazard analysis reports, may also 

be satisfied by qualification testing.

Qualification usually occurs at the component or subsystem level, but could occur at the system level as well. A 

project deciding against building dedicated qualification 

hardware—and using the flight/operations hardware itself for qualification purposes—is termed “protoflight.”

Here, the requirements being verified are typically less 

than that of qualification levels but higher than that of 

acceptance levels.

Qualification verification verifies the soundness of the 

design. Test levels are typically set with some margin 

above expected flight/operations levels, including the 

maximum number of cycles that can be accumulated 

during acceptance testing. These margins are set to address design safety margins in general, and care should 

be exercised not to set test levels so that unrealistic failure 

modes are created.

Acceptance Verification 

Acceptance-stage verification activities provide the assurance that the flight/operations hardware and software are in compliance with all functional, performance, 

and design requirements and are ready for shipment to 

the launch site. The acceptance stage begins with the acceptance of each individual component or piece part for 

assembly into the flight/operations article, continuing 

through the System Acceptance Review (SAR). (See 

Subsection 6.7.2.1.) 

Some verifications cannot be performed after a flight/

operations article, especially a large one, has been assembled and integrated (e.g., due to inaccessibility). When 

this occurs, these verifications are to be performed during 

fabrication and integration, and are known as “in-process” tests. In this case, acceptance testing begins with inprocess testing and continues through functional testing, 

environmental testing, and end-to-end compatibility 

testing. Functional testing normally begins at the component level and continues at the systems level, ending 

with all systems operating simultaneously. 

When flight/operations hardware is unavailable, or its 

use is inappropriate for a specific test, simulators may be 

used to verify interfaces. Anomalies occurring during 

a test are documented on the appropriate reporting 

system, and a proposed resolution should be defined before testing continues. Major anomalies, or those that are 

not easily dispositioned, may require resolution by a collaborative effort of the systems engineer and the design, 

test, and other organizations. Where appropriate, analyses and models are validated and updated as test data 

are acquired.

Acceptance verification verifies workmanship, not design. Test levels are set to stress items so that failures arise 

from defects in parts, materials, and workmanship. As 

such, test levels are those anticipated during flight/operations with no additional margin.

Deployment Verification 

The pre-launch verification stage begins with the arrival 

of the flight/operations article at the launch site and concludes at liftoff. During this stage, the flight/operations 

article is processed and integrated with the launch vehicle. The launch vehicle could be the shuttle or some 

other launch vehicle, or the flight/operations article 

could be part of the launch vehicle. Verifications performed during this stage ensure that no visible damage 

to the system has occurred during shipment and that the 

system continues to function properly. 
92  NASA Systems Engineering Handbook

5.0 Product Realization

If system elements are shipped separately and integrated 

at the launch site, testing of the system and system interfaces is generally required. If the system is integrated 

into a carrier, the interface to the carrier must also be 

verified. Other verifications include those that occur following integration into the launch vehicle and those that 

occur at the launch pad; these are intended to ensure that 

the system is functioning and in its proper launch configuration. Contingency verifications and procedures are 

developed for any contingencies that can be foreseen to 

occur during pre-launch and countdown. These contingency verifications and procedures are critical in that 

some contingencies may require a return of the launch 

vehicle or flight/operations article from the launch pad 

to a processing facility.

Operational and Disposal Verification 

Operational verification begins in Phase E and provides 

the assurance that the system functions properly in a relevant environment. These verifications are performed 

through system activation and operation, rather than 

through a verification activity. Systems that are assembled on-orbit must have each interface verified and must 

function properly during end-to-end testing. Mechanical interfaces that provide fluid and gas flow must be 

verified to ensure no leakage occurs and that pressures 

and flow rates are within specification. Environmental 

systems must be verified. 

Disposal verification provides the assurance that the 

safe deactivation and disposal of all system products 

and processes has occurred. The disposal stage begins in 

Phase F at the appropriate time (i.e., either as scheduled, 

or earlier in the event of premature failure or accident) 

and concludes when all mission data have been acquired 

and verifications necessary to establish compliance with 

disposal requirements are finished. 

Both operational and disposal verification activities may 

also include validation assessments, that is, assessments 

of the degree to which the system accomplished the desired mission goals/objectives.

5.3.2.3 Verification Procedures 

Verification procedures provide step-by-step instructions 

for performing a given verification activity. This procedure could be a test, demonstration, or any other verification-related activity. The procedure to be used is written 

and submitted for review and approval at the Test Readiness Review (TRR) for the verification activity. (See Test 

Readiness Review discussion in Subsection 6.7.2.1.) 

Procedures are also used to verify the acceptance of facilities, electrical and mechanical ground support equipment, and special test equipment. The information generally contained in a procedure is as follows, but it may 

vary according to the activity and test article:

z Nomenclature and identification of the test article or 

material;

z Identification of test configuration and any differences 

from flight/operations configuration;

z Identification of objectives and criteria established for 

the test by the applicable verification specification;

z Characteristics and design criteria to be inspected or 

tested, including values, with tolerances, for acceptance or rejection;

z Description, in sequence, of steps and operations to 

be taken;

z Identification of computer software required;

z Identification of measuring, test, and recording equipment to be used, specifying range, accuracy, and type;

z Credentials showing that required computer test programs/support equipment and software have been 

verified prior to use with flight/operations hardware;

z Any special instructions for operating data recording 

equipment or other automated test equipment as applicable;

z Layouts, schematics, or diagrams showing identification, location, and interconnection of test equipment, 

test articles, and measuring points;

z Identification of hazardous situations or operations;

z Precautions and safety instructions to ensure safety of 

personnel and prevent degradation of test articles and 

measuring equipment;

z Environmental and/or other conditions to be maintained with tolerances;

z Constraints on inspection or testing;

z Special instructions for nonconformances and anomalous occurrences or results; and

z Specifications for facility, equipment maintenance, 

housekeeping, quality inspection, and safety and handling requirements before, during, and after the total 

verification activity.

The written procedure may provide blank spaces in the 

format for the recording of results and narrative com-
5.3 Product Verification

NASA Systems Engineering Handbook  93

ments so that the completed procedure can serve as part 

of the verification report. The as-run and certified copy 

of the procedure is maintained as part of the project’s archives.

5.3.2.4 Verification Reports

A verification report should be provided for each analysis and, at a minimum, for each major test activity—

such as functional testing, environmental testing, and 

end-to-end compatibility testing—occurring over long 

periods of time or separated by other activities. Verification reports may be needed for each individual test 

activity, such as functional testing, acoustic testing, vibration testing, and thermal vacuum/thermal balance 

testing. Verification reports should be completed within 

a few weeks following a test and should provide evidence 

of compliance with the verification requirements for 

which it was conducted. 

The verification report should include as appropriate:

z Verification objectives and the degree to which they 

were met;

z Description of verification activity;

z Test configuration and differences from flight/operations configuration;

z Specific result of each test and each procedure, including annotated tests;

z Specific result of each analysis;

z Test performance data tables, graphs, illustrations, 

and pictures;

z Descriptions of deviations from nominal results, 

problems/failures, approved anomaly corrective actions, and retest activity;

z Summary of nonconformance/discrepancy reports, 

including dispositions;

z Conclusions and recommendations relative to success 

of verification activity;

z Status of support equipment as affected by test;

z Copy of as-run procedure; and

z Authentication of test results and authorization of acceptability.

5.3.2.5 End-to-End System Testing 

The objective of end-to-end testing is to demonstrate 

interface compatibility and desired total functionality 

among different elements of a system, between systems, 

and within a system as a whole. End-to-end tests performed on the integrated ground and flight system include all elements of the payload, its control, stimulation, 

communications, and data processing to demonstrate 

that the entire system is operating in a manner to fulfill 

all mission requirements and objectives. 

End-to-end testing includes executing complete threads 

or operational scenarios across multiple configuration 

items, ensuring that all mission and performance requirements are verified. Operational scenarios are used 

extensively to ensure that the system (or collections of 

systems) will successfully execute mission requirements. 

Operational scenarios are a step-by-step description of 

how the system should operate and interact with its users 

and its external interfaces (e.g., other systems). Scenarios 

should be described in a manner that will allow engineers to walk through them and gain an understanding 

of how all the various parts of the system should function 

and interact as well as verify that the system will satisfy 

the user’s needs and expectations. Operational scenarios 

should be described for all operational modes, mission phases (e.g., installation, startup, typical examples 

of normal and contingency operations, shutdown, and 

maintenance), and critical sequences of activities for all 

classes of users identified. Each scenario should include 

events, actions, stimuli, information, and interactions as 

appropriate to provide a comprehensive understanding 

of the operational aspects of the system.

Note: It is important to understand that, over the lifetime of a system, requirements may change or component obsolescence may make a design solution 

too difficult to produce from either a cost or technical 

standpoint. In these instances, it is critical to employ 

the systems engineering design processes at a lower 

level to ensure the modified design provides a proper 

design solution. An evaluation should be made to determine the magnitude of the change required, and 

the process should be tailored to address the issues 

appropriately. A modified qualification, verification, 

and validation process may be required to baseline a 

new design solution, consistent with the intent previously described for those processes. The acceptance 

testing will also need to be updated as necessary to 

verify that the new product has been manufactured 

and coded in compliance with the revised baselined 

design.
94  NASA Systems Engineering Handbook

5.0 Product Realization

Figure 5.3-3 presents an example of an end-to-end data 

flow for a scientific satellite mission. Each arrow in the 

diagram represents one or more data or control flows 

between two hardware, software, subsystem, or system 

configuration items. End-to-end testing verifies that the 

data flows throughout the multisystem environment are 

correct, that the system provides the required functionality, and that the outputs at the eventual end points correspond to expected results. Since the test environment is 

as close an approximation as possible to the operational 

environment, performance requirements testing is also 

included. This figure is not intended to show the full extent of end-to-end testing. Each system shown would 

need to be broken down into a further level of granularity for completeness.

End-to-end testing is an integral part of the verification 

and validation of the total system and is an activity that 

is employed during selected hardware, software, and 

system phases throughout the life cycle. In comparison 

with configuration item testing, end-to-end testing addresses each configuration item only down to the level 

where it interfaces externally to other configuration 

items, which can be either hardware, software, or human 

based. Internal interfaces (e.g., software subroutine calls, 

analog-to-digital conversion) of a configuration item are 

not within the scope of end-to-end testing.

How to Perform End-to-End Testing 

End-to-end testing is probably the most significant element of any project verification program and the test 

should be designed to satisfy the edict to “test the way 

we fly.” This means assembling the system in its realistic configuration, subjecting it to a realistic environment and then “flying” it through all of its expected operational modes. For a scientific robotic mission, targets 

and stimuli should be designed to provide realistic inputs to the scientific instruments. The output signals 

from the instruments would flow through the satellite 

data-handling system and then be transmitted to the 

actual ground station through the satellite communications system. If data are transferred to the ground station 

through one or more satellite or ground relays (e.g., the 

Tracking and Data Relay Satellite System (TDRSS)) then 

those elements must be included as part of the test. 

The end-to-end compatibility test encompasses the entire chain of operations that will occur during all mission 

modes in such a manner as to ensure that the system will 

fulfill mission requirements. The mission environment 

should be simulated as realistically as possible, and the 

instruments should receive stimuli of the kind they will 

receive during the mission. The Radio Frequency (RF) 

links, ground station operations, and software functions 

should be fully exercised. When acceptable simulation 

Figure 5.3-3 Example of end-to-end data flow for a scientific satellite mission

EXTERNAL

STIMULI

Instrument

Set B 

X-rays

Infrared

Visible

Ultraviolet

Microwave

Instrument

Set A

Spacecraft

Execution

Scientic

Community

Mission

Planning

Data

Capture

Software

Loads

Command

Generation Planning

Archival

Transmission

Analysis

Uplink Process

Downlink Process

EXTERNAL

SYSTEMS

GROUND SYSTEM FLIGHT SYSTEM
5.3 Product Verification

NASA Systems Engineering Handbook  95

facilities are available for portions of the operational systems, they may be used for the test instead of the actual 

system elements. The specific environments under which 

the end-to-end test is conducted and the stimuli, payload configuration, RF links, and other system elements 

to be used must be determined in accordance with the 

characteristics of the mission.

Although end-to-end testing is probably the most complex test in any system verification program, the same 

careful preparation is necessary as for any other systemlevel test. For example, a test lead must be appointed and 

the test team selected and trained. Adequate time must 

be allocated for test planning and coordination with the 

design team. Test procedures and test software must be 

documented, approved, and placed under configuration 

control.

Plans, agreements, and facilities must be put in place well 

in advance of the test to enable end-to-end testing between all components of the system. 

Once the tests are run, the test results are documented 

and any discrepancies carefully recorded and reported. 

All test data must be maintained under configuration 

control.

Before completing end-to-end testing, the following activities are completed for each configuration item:

z All requirements, interfaces, states, and state transitions of each configuration item should be tested 

through the exercise of comprehensive test procedures and test cases to ensure the configuration items 

are complete and correct. 

z A full set of operational range checking tests should 

be conducted on software variables to ensure that the 

software performs as expected within its complete 

range and fails, or warns, appropriately for out-ofrange values or conditions. 

End-to-end testing activities include the following:

1. Operational scenarios are created that span all of the 

following items (during nominal, off-nominal, and 

stressful conditions) that could occur during the 

mission:

z Mission phase, mode, and state transitions;

z First-time events;

z Operational performance limits;

z Fault protection routines;

z Failure Detection, Isolation, and Recovery (FDIR) 

logic;

z Safety properties;

z Operational responses to transient or off-nominal sensor signals; and

z Communication uplink and downlink. 

2. The operational scenarios are used to test the configuration items, interfaces, and end-to-end performance as early as possible in the configuration items’ 

development life cycle. This typically means simulators or software stubs have to be created to implement a full scenario. It is extremely important to 

produce a skeleton of the actual system to run full 

scenarios as soon as possible with both simulated/

stubbed-out and actual configuration items.

3. A complete diagram and inventory of all interfaces 

are documented.

4. Test cases are executed to cover human-human, 

human-hardware, human-software, hardware-software, software-software, and subsystem-subsystem 

interfaces and associated inputs, outputs, and modes 

of operation (including safing modes).

5. It is strongly recommended that during end-to-end 

testing, an operations staff member who has not previously been involved in the testing activities be designated to exercise the system as it is intended to be 

used to determine if it will fail.

6. The test environment should approximate/simulate 

the actual operational conditions when possible. The 

fidelity of the test environment should be authenticated. Differences between the test and operational 

environment should be documented in the test or 

verification plan.

7. When testing of a requirement is not possible, verification is demonstrated by other means (e.g., model 

checking, analysis, or simulation). If true end-to-end 

testing cannot be achieved, then the testing must 

be done piecemeal and patched together by analysis and simulation. An example of this would be a 

system that is assembled on orbit where the various 

elements come together for the first time on orbit.

8. When an error in the developed system is identified 

and fixed, regression testing of the system or compoNote: This is particularly important when missions are 

developed with international or external partners.
96  NASA Systems Engineering Handbook

5.0 Product Realization

nent is performed to ensure that modifications have 

not caused unintended effects and that the system 

or component still complies with previously tested 

specified requirements.

9. When tests are aborted or a test is known to be flawed 

(e.g., due to configuration, test environment), the test 

should be rerun after the identified problem is fixed.

10. The operational scenarios should be used to formulate the final operations plan.

11. Prior to system delivery, as part of the system qualification testing, test cases should be executed to cover 

all of the plans documented in the operations plan in 

the order in which they are expected to occur during 

the mission.

End-to-end test documentation includes the following:

z Inclusion of end-to-end testing plans as a part of the 

test or verification plan.

z A document, matrix, or database under configuration control that traces the end-to-end system test 

suite to the results. Data that are typically recorded 

include the test-case identifier, subsystems/hardware/

program sets exercised, list of the requirements being 

verified, interfaces exercised, date, and outcome of 

test (i.e., whether the test actual output met the expected output).

z End-to-end test cases and procedures (including inputs and expected outputs).

z A record of end-to-end problems/failures/anomalies.

End-to-end testing can be integrated with other project 

testing activities; however, the documentation mentioned in this subsection should be readily extractable 

for review, status, and assessment.

5.3.2.6 Modeling and Simulation

For the Product Verification Process, a model is a physical, mathematical, or logical representation of an end 

product to be verified. Modeling and Simulation (M&S) 

can be used to augment and support the Product Verification Process and is an effective tool for performing the 

verification whether in early life-cycle phases or later. Both 

the facilities and the model itself are developed using the 

system design and product realization processes. 

The model used, as well as the M&S facility, are enabling 

products and must use the 17 technical processes (see NPR 

7123.1, NASA Systems Engineering Processes and Requirements) for their development and realization (including 

acceptance by the operational community) to ensure that 

the model and simulation adequately represent the operational environment and performance of the modeled end 

product. Additionally, in some cases certification is required before models and simulations can be used. 

M&S assets can come from a variety of sources; for example, contractors, other Government agencies, or laboratories can provide models that address specific system 

attributes.

5.3.2.7 Hardware-in-the-Loop

Fully functional end products, such as an actual piece of 

hardware, may be combined with models and simulations that simulate the inputs and outputs of other end 

products of the system. This is referred to as “Hardwarein-the-Loop” (HWIL) testing. HWIL testing links all elements (subsystems and test facilities) together within 

a synthetic environment to provide a high-fidelity, realtime operational evaluation for the real system or subsystems. The operator can be intimately involved in the 

testing, and HWIL resources can be connected to other 

facilities for distributed test and analysis applications. 

One of the uses of HWIL testing is to get as close to the 

actual concept of operation as possible to support verification and validation when the operational environment 

is difficult or expensive to recreate. 

During development, this HWIL verification normally 

takes place in an integration laboratory or test facility. For 

example, HWIL could be a complete spacecraft in a special test chamber, with the inputs/outputs being provided 

as output from models that simulate the system in an operational environment. Real-time computers are used to 

control the spacecraft and subsystems in projected operational scenarios. Flight dynamics, responding to the 

Note: The development of the physical, mathematical, or logical model includes evaluating whether the 

model to be used as representative of the system end 

product was realized according to its design–solution-specified requirements for a model and whether 

it will be valid for use as a model. In some cases, the 

model must also be accredited to certify the range of 

specific uses for which the model can be used. Like 

any other enabling product, budget and time must 

be planned for creating and evaluating the model to 

be used to verify the applicable system end product.
5.3 Product Verification

NASA Systems Engineering Handbook  97

commands issued by the guidance and control system 

hardware/software, are simulated in real-time to determine the trajectory and to calculate system flight conditions. HWIL testing verifies that the end product being 

evaluated meets the interface requirements, properly 

transforming inputs to required outputs. HWIL modeling can provide a valuable means of testing physical 

end products lower in the system structure by providing 

simulated inputs to the end product or receiving outputs 

from the end product to evaluate the quality of those outputs. This tool can be used throughout the life cycle of a 

program or project. The shuttle program uses an HWIL 

to verify software and hardware updates for the control 

of the shuttle main engines. 

Modeling, simulation, and hardware/human-in-theloop technology, when appropriately integrated and sequenced with testing, provide a verification method at 

a reasonable cost. This integrated testing process specifically (1) reduces the cost of life-cycle testing, (2) provides significantly more engineering/performance insights into each system evaluated, and (3) reduces test 

time and lowers project risk. This process also significantly reduces the number of destructive tests required 

over the life of the product. The integration of M&S 

into verification testing provides insights into trends 

and tendencies of system and subsystem performance 

that might not otherwise be possible due to hardware 

limitations. 
98  NASA Systems Engineering Handbook

5.0 Product Realization

The Product Validation Process is the second of the verification and validation processes conducted on a realized end product. While verification proves whether 

“the system was done right,” validation proves whether 

“the right system was done.” In other words, verification provides objective evidence that every “shall” statement was met, whereas validation is performed for the 

benefit of the customers and users to ensure that the 

system functions in the expected manner when placed 

in the intended environment. This is achieved by examining the products of the system at every level of the 

structure.

Validation confirms that realized end products at any 

position within the system structure conform to their 

set of stakeholder expectations captured in the ConOps, 

and ensures that any anomalies discovered during validation are appropriately resolved prior to product delivery. This section discusses the process activities, 

types of validation, inputs and outputs, and potential 

deficiencies.

Distinctions Between Product Verification and 

Product Validation

From a process perspective, Product Verification and 

Product Validation may be similar in nature, but the objectives are fundamentally different.

From a customer point of view, the interest is in whether 

the end product provided will do what they intend within 

the environment of use. It is essential to confirm that the 

realized product is in conformance with its specifications 

and design description documentation because these 

specifications and documents will establish the configuration baseline of the product, which may have to be modified at a later time. Without a verified baseline and appropriate configuration controls, such later modifications 

could be costly or cause major performance problems.

When cost-effective and warranted by analysis, various combined tests are used. The expense of validation 

testing alone can be mitigated by ensuring that each end 

product in the system structure was correctly realized in 

accordance with its specified requirements before conducting validation.

5.4.1 Process Description

Figure 5.4-1 provides a typical flow diagram for the 

Product Validation Process and identifies typical inputs, 

outputs, and activities to consider in addressing product 

validation.

5.4.1.1 Inputs

Key inputs to the process are: 

z Verified product,

z Validation plan,

z Baselined stakeholder expectations (including ConOps 

and mission needs and goals), and

z Any enabling products needed to perform the Product 

Validation Process.

5.4 Product Validation

Differences Between Verification and Validation Testing

z Verification Testing: Verification testing relates back to the approved requirements set (such as an SRD) and can be 

performed at different stages in the product life cycle. Verification testing includes: (1) any testing used to assist in the 

development and maturation of products, product elements, or manufacturing or support processes; and/or (2) any 

engineering-type test used to verify status of technical progress, to verify that design risks are minimized, to substantiate achievement of contract technical performance, and to certify readiness for initial validation testing. Verification 

tests use instrumentation and measurements, and are generally accomplished by engineers, technicians, or operatormaintainer test personnel in a controlled environment to facilitate failure analysis. 

z Validation Testing: Validation relates back to the ConOps document. Validation testing is conducted under realistic 

conditions (or simulated conditions) on any end product for the purpose of determining the effectiveness and suitability of the product for use in mission operations by typical users; and the evaluation of the results of such tests. Testing is the detailed quantifying method of both verification and validation. However, testing is required to validate final end products to be produced and deployed. 
5.4 Product Validation

NASA Systems Engineering Handbook  99

5.4.1.2 Process Activities

The Product Validation Process demonstrates that the 

realized end product satisfies its stakeholder (customer 

and other interested party) expectations within the intended operational environments, with validation performed by anticipated operators and/or users. The type 

of validation is a function of the life-cycle phase and the 

position of the end product within the system structure. 

There are five major steps in the validation process: 

(1) validation planning (prepare to implement the validation plan), (2) validation preparation (prepare for 

conducting validation), (3) conduct planned validation 

(perform validation), (4) analyze validation results, and 

(5) capture the validation work products.

The objectives of the Product Validation Process are: 

z To confirm that

▶ The right product was realized—the one wanted by 

the customer,

▶ The realized product can be used by intended operators/users, and

▶ The Measures of Effectiveness (MOEs) are satisfied.

z To confirm that the realized product fulfills its intended 

use when operated in its intended environment:

▶ Validation is performed for each realized (implemented or integrated) product from the lowest end 

product in a system structure branch up to the top 

WBS model end product. 

▶ Evidence is generated as necessary to confirm that 

products at each layer of the system structure meet 

the capability and other operational expectations 

of the customer/user/operator and other interested 

parties.

z To ensure that any problems discovered are appropriately resolved prior to delivery of the realized product 

(if validation is done by the supplier of the product) or 

prior to integration with other products into a higher 

level assembled product (if validation is done by the 

receiver of the product).

Verification and validation events are illustrated as separate processes, but when used, can considerably overlap. 

When cost effective and warranted by analysis, various 

combined tests are used. However, while from a process 

perspective verification and validation are similar in nature, their objectives are fundamentally different. 

From a customer’s point of view, the interest is in whether 

the end product provided will supply the needed capabilities within the intended environments of use. The 

Figure 5.4-1 Product Validation Process

From Product

Verication Process To Product

Transition Process

Product Validation

Results 

Product Validation

Report

End Product

to Be Validated 

Product Validation

Plan

Stakeholder Expectation

Baseline 

Product Validation–

Enabling Products

To Technical

Assessment Process

From Design Solution 

Denition and Technical

Planning Processes

Validated End Product

To Technical Data

Management Process

From Conguration

Management Process

From existing

resources or Product

Transition Process Product Validation

Work Products 

Perform the product

validation

Analyze the outcomes of

the product validation

Capture the work products

from product validation 

Prepare a product

validation report 

Prepare to conduct product

validation
100  NASA Systems Engineering Handbook

5.0 Product Realization

expense of validation testing alone can be mitigated by 

ensuring that each end product in the system structure 

was correctly realized in accordance with its specified requirements prior to validation, during verification. It is 

possible that the system design was not done properly 

and, even though the verification tests were successful 

(satisfying the specified requirements), the validation 

tests would still fail (stakeholder expectations not satisfied). Thus, it is essential that validation of lower products in the system structure be conducted as well as verification so as to catch design failures or deficiencies as 

early as possible.

Product Validation Planning 

Planning to conduct the product validation is a key first 

step. The type of validation to be used (e.g., analysis, 

demonstration, inspection, or test) should be established 

based on the form of the realized end product, the applicable life-cycle phase, cost, schedule, resources available, 

and location of the system product within the system 

structure. (See Appendix I for a sample verification and 

validation plan outline.)

An established set or subset of requirements to be validated should be identified and the validation plan reviewed (an output of the Technical Planning Process, 

based on design solution outputs) for any specific procedures, constraints, success criteria, or other validation 

requirements. The conditions and environment under 

which the product is to be validated should be established and the validation planned based on the relevant 

life-cycle phase and associated success criteria identified. 

The Decision Analysis Process should be used to help finalize the planning details. 

It is important to review the validation plans with relevant stakeholders and understand the relationship between the context of the validation and the context of use 

(human involvement). As part of the planning process, 

validation-enabling products should be identified, and 

scheduling and/or acquisition initiated. 

Procedures should be prepared to conduct validation 

based on the type (e.g., analysis, inspection, demonstration, or test) planned. These procedures are typically developed during the design phase of the project 

life cycle and matured as the design is matured. Operational and use-case scenarios are thought through 

so as to explore all possible validation activities to be 

performed. 

Validation Plan and Methods 

The validation plan is one of the work products of the 

Technical Planning Process and is generated during the 

Design Solution Process to validate the realized product 

against the baselined stakeholder expectations. This plan 

can take many forms. The plan describes the total Test 

and Evaluation (T&E) planning from development of 

lower end through higher end products in the system 

structure and through operational T&E into production 

and acceptance. It may include the verification and validation plan. (See Appendix I for a sample verification 

and validation plan outline.)

The types of validation include test, demonstration, inspection, and analysis. While the name of each method 

Types of Validation

z Analysis: The use of mathematical modeling and 

analytical techniques to predict the suitability of a 

design to stakeholder expectations based on calculated data or data derived from lower system 

structure end product validations. It is generally 

used when a prototype; engineering model; or fabricated, assembled, and integrated product is not 

available. Analysis includes the use of both modeling and simulation.

z Demonstration: The use of a realized end product 

to show that a set of stakeholder expectations can 

be achieved. It is generally used for a basic confirmation of performance capability and is differentiated from testing by the lack of detailed data gathering. Validation is done under realistic conditions 

for any end product within the system structure for 

the purpose of determining the effectiveness and 

suitability of the product for use in NASA missions 

or mission support by typical users and evaluating 

the results of such tests.

z Inspection: The visual examination of a realized 

end product. It is generally used to validate physical design features or specific manufacturer identification.

z Test: The use of a realized end product to obtain 

detailed data to validate performance or to provide sufficient information to validate performance 

through further analysis. Testing is the detailed 

quantifying method of both verification and validation but it is required in order to validate final end 

products to be produced and deployed.
5.4 Product Validation

NASA Systems Engineering Handbook  101

is the same as the name of the methods for verification, 

the purpose and intent are quite different.

Validation is conducted by the user/operator or by the 

developer, as determined by NASA Center directives or 

the contract with the developers. Systems-level validation (e.g., customer T&E and some other types of validation) may be performed by an acquirer testing organization. For those portions of validation performed by the 

developer, appropriate agreements must be negotiated to 

ensure that validation proof-of-documentation is delivered with the realized product. 

All realized end products, regardless of the source (buy, 

make, reuse, assemble and integrate) and the position 

in the system structure, should be validated to demonstrate/confirm satisfaction of stakeholder expectations. 

Variations, anomalies, and out-of-compliance conditions, where such have been detected, are documented 

along with the actions taken to resolve the discrepancies. 

Validation is typically carried out in the intended operational environment under simulated or actual operational conditions, not under the controlled conditions 

usually employed for the Product Verification Process. 

Validation can be performed recursively throughout the 

project life cycle and on a wide variety of product forms. 

For example:

z Simulated (algorithmic models, virtual reality simulator);

z Mockup (plywood, brassboard, breadboard);

z Concept description (paper report);

z Prototype (product with partial functionality);

z Engineering unit (fully functional but may not be 

same form/fit);

z Design validation test units (form, fit and function 

may be the same, but they may not have flight parts);

z Qualification unit (identical to flight unit but may be 

subjected to extreme environments); or

z Flight unit (end product that is flown).

Any of these types of product forms may be in any of 

these states:

z Produced (built, fabricated, manufactured, or coded);

z Reused (modified internal nondevelopmental products or off-the-shelf product); or 

z Assembled and integrated (a composite of lower level 

products).

Outcomes of validation planning include the following:

z The validation type that is appropriate to confirm that 

the realized product or products conform to stakeholder expectations (based on the form of the realized end product) has been identified.

z Validation procedures are defined based on: (1) the 

needed procedures for each type of validation selected, (2) the purpose and objective of each procedure step, (3) any pre-test and post-test actions, and 

(4) the criteria for determining the success or failure 

of the procedure.

z A validation environment (e.g., facilities, equipment, 

tools, simulations, measuring devices, personnel, and 

operational conditions) in which the validation procedures will be implemented has been defined.

Product Validation Preparation

To prepare for performing product validation, the appropriate set of expectations against which the validation is to be made should be obtained. Also, the product 

to be validated (output from implementation, or integration and verification), as well as the validation-enabling 

products and support resources (requirements identified and acquisition initiated by design solution activities) with which validation will be conducted, should be 

collected. 

Note: The final, official validation of the end product 

should be for a controlled unit. Typically, attempting final validation against operational concepts on 

a prototype is not acceptable: it is usually completed 

on a qualification, flight, or other more final, controlled unit. 

Note: In planning for validation, consideration should 

be given to the extent to which validation testing will 

be done. In many instances, off-nominal operational 

scenarios and nominal operational scenarios should 

be utilized. Off-nominal testing offers insight into a 

system’s total performance characteristics and often 

assists in identification of design issues and humanmachine interface, training, and procedural changes 

required to meet the mission goals and objectives. 

Off-nominal testing, as well as nominal testing, should 

be included when planning for validation.
102  NASA Systems Engineering Handbook

5.0 Product Realization

The validation environment is then prepared (set up the 

equipments, sensors, recording devices, etc., that will be 

involved in the validation conduct) and the validation 

procedures reviewed to identify and resolve any issues 

impacting validation.

Outcomes of validation preparation include the following:

z Preparation for doing the planned validation is completed;

z Appropriate set of stakeholder expectations are available and on hand;

z Articles or models to be used for validation with the 

validation product and enabling products are integrated within the validation environment according 

to plans and schedules;

z Resources are available according to validation plans 

and schedules; and

z The validation environment is evaluated for adequacy, 

completeness, readiness, and integration.

Conduct Planned Product Validation 

The act of validating the end product is conducted as 

spelled out in the validation plans and procedures and 

conformance established to each specified validation requirement. The responsible engineer should ensure that 

the procedures were followed and performed as planned, 

the validation-enabling products were calibrated correctly, and the data were collected and recorded for required validation measures. 

When poor validation conduct, design, or conditions 

cause anomalies, the validation should be replanned as 

necessary, the environment preparation anomalies corrected, and the validation conducted again with improved or correct procedures and resources. The Decision Analysis Process should be used to make decisions 

for issues identified that may require alternative choices 

to be evaluated and a selection made or when needed 

changes to the validation plans, environment, and/or 

conduct are required.

Outcomes of conducting validation include the following:

z A validated product is established with supporting 

confirmation that the appropriate results were collected and evaluated to show completion of validation 

objectives. 

z A determination is made as to whether the fabricated/

manufactured or assembled and integrated products 

(including software or firmware builds, as applicable) 

comply with their respective stakeholder expectations.

z A determination is made that the validated product 

was appropriately integrated with the validation environment and the selected stakeholder expectations 

set was properly validated. 

z A determination is made that the product being validated functions together with interfacing products 

throughout their performance envelopes.

Analyze Product Validation Results

Once the validation activities have been completed, the 

results are collected and the data are analyzed to confirm 

that the end product provided will supply the customer’s 

needed capabilities within the intended environments of 

use, validation procedures were followed, and enabling 

products and supporting resources functioned correctly. 

The data are also analyzed for quality, integrity, correctness, consistency, and validity and any unsuitable products or product attributes are identified and reported. 

It is important to compare the actual validation results to 

the expected results and to conduct any required system 

design and product realization process activities to resolve deficiencies. The deficiencies, along with recomExamples of Enabling Products and Support 

Resources for Preparing to Conduct 

Validation

One of the key tasks in the Product Validation Process 

“prepare for conducting validation” is to obtain necessary enabling products and support resources needed 

to conduct validation. Examples of these include:

z Measurement tools (scopes, electronic devices, 

probes);

z Embedded test software;

z Test wiring, measurement devices, and telemetry 

equipment;

z Recording equipment (to capture test results);

z End products in the loop (software, electronics, or 

mechanics) for hardware-in-the-loop simulations;

z External interfacing products of other systems;

z Actual external interfacing products of other systems (aircraft, vehicles, humans); and

z Facilities and skilled operators.
5.4 Product Validation

NASA Systems Engineering Handbook  103

mended corrective actions and resolution results, should 

be recorded and validation repeated, as required.

Outcomes of analyzing validation results include the following:

z Product deficiencies and/or issues are identified. 

z Assurances that appropriate replanning, redefinition 

of requirements, design, and revalidation have been 

accomplished for resolution of anomalies, variations, 

or out-of-compliance conditions (for problems not 

caused by poor validation conduct). 

z Discrepancy and corrective action reports are generated as needed. 

z The validation report is completed. 

Validation Notes 

The types of validation used are dependent on the lifecycle phase; the product’s location in the system structure; and cost, schedule, and resources available. Validation of products within a single system model may be 

conducted together (e.g., an end product with its relevant 

enabling products, such as operational (control center or a 

radar with its display), maintenance (required tools work 

with product), or logistical (launcher or transporter).

Each realized product of system structure should be validated against stakeholder expectations before being integrated into a higher level product. 

Reengineering

Based on the results of the Product Validation Process, 

it could become necessary to reengineer a deficient end 

product. Care should be taken that correcting a deficiency, 

or set of deficiencies, does not generate a new issue with 

a part or performance that had previously operated satisfactorily. Regression testing, a formal process of rerunning previously used acceptance tests primarily used for 

software, is one method to ensure a change did not affect 

function or performance that was previously accepted. 

Validation Deficiencies

Validation outcomes can be unsatisfactory for several 

reasons. One reason is poor conduct of the validation 

(e.g., enabling products and supporting resources missing or not functioning correctly, untrained operators, 

procedures not followed, equipment not calibrated, or 

improper validation environmental conditions) and failure to control other variables not involved in validating 

a set of stakeholder expectations. A second reason could 

be a shortfall in the verification process of the end product. This could create the need for: 

z Reengineering end products lower in the system structure that make up the end product that was found to 

be deficient (which failed to satisfy validation requirements) and/or

z Reperforming any needed verification and validation 

processes.

Other reasons for validation deficiencies (particularly 

when M&S are involved) may be incorrect and/or inappropriate initial or boundary conditions; poor formulation of the modeled equations or behaviors; the impact of 

approximations within the modeled equations or behaviors; failure to provide the required geometric and physics 

fidelities needed for credible simulations for the intended 

purpose; referent for comparison of poor or unknown uncertainty quantification quality; and/or poor spatial, temporal, and perhaps, statistical resolution of physical phenomena used in M&S.

Note: Care should be exercised to ensure that the corrective actions identified to remove validation deficiencies do not conflict with the baselined stakeholder expectations without first coordinating such 

changes with the appropriate stakeholders.

Capture Product Validation Work Products

Validation work products (inputs to the Technical Data 

Management Process) take many forms and involve 

many sources of information. The capture and recording 

of validation-related data is a very important, but often underemphasized, step in the Product Validation Process.

Validation results, deficiencies identified, and corrective 

actions taken should be captured, as should all relevant 

results from the application of the Product Validation 

Process (related decisions, rationale for decisions made, 

assumptions, and lessons learned).

Outcomes of capturing validation work products include 

the following:

z Work products and related information generated 

while doing Product Validation Process activities and 

tasks are recorded; i.e., type of validation conducted, 

the form of the end product used for validation, val-
104  NASA Systems Engineering Handbook

5.0 Product Realization

idation procedures used, validation environments, 

outcomes, decisions, assumptions, corrective actions, 

lessons learned, etc. (often captured in a matrix or 

other tool—see Appendix E).

z Deficiencies (e.g., variations and anomalies and 

out-of-compliance conditions) are identified and 

documented, including the actions taken to resolve.

z Proof is provided that the realized product is in conformance with the stakeholder expectation set used in 

the validation. 

z Validation report including:

▶ Recorded validation results/data;

▶ Version of the set of stakeholder expectations used;

▶ Version and form of the end product validated;

▶ Version or standard for tools and equipment used, 

together with applicable calibration data;

▶ Outcome of each validation including pass or fail 

declarations; and

▶ Discrepancy between expected and actual results.

5.4.1.3 Outputs

Key outputs of validation are:

z Validated product,

z Discrepancy reports and identified corrective actions, 

and

z Validation reports.

Success criteria for this process include: (1) objective evidence of performance and the results of each systemof-interest validation activity are documented, and (2) 

the validation process should not be considered or designated as complete until all issues and actions are resolved.

5.4.2 Product Validation Guidance

The following is some generic guidance for the Product 

Validation Process.

5.4.2.1 Modeling and Simulation

As stressed in the verification process material, M&S is 

also an important validation tool. M&S usage considerations involve the verification, validation, and certification of the models and simulations.

5.4.2.2 Software

Software verification is a software engineering activity 

that demonstrates the software products meet specified 

requirements. Methods of software verification include 

peer reviews/inspections of software engineering products for discovery of defects, software verification of requirements by use of simulations, black box and white 

box testing techniques, analyses of requirement implementation, and software product demonstrations.

Software validation is a software engineering activity 

that demonstrates the as-built software product or software product component satisfies its intended use in its 

intended environment. Methods of software validation 

include: peer reviews/inspections of software product 

component behavior in a simulated environment, acceptance testing against mathematical models, analyses, 

and operational environment demonstrations. The project’s approach for software verification and validation is 

documented in the software development plan. Specific 

Agency-level requirements for software verification and 

validation, peer reviews (see Appendix N), testing and 

reporting are contained in NPR 7150.2, NASA Software 

Requirements.

Note: For systems where only a single deliverable item 

is developed, the Product Validation Process normally 

completes acceptance testing of the system. However, for systems with several production units, it is 

important to understand that continuing verification 

and validation is not an appropriate approach to use 

for the items following the first deliverable. Instead, 

acceptance testing is the preferred means to ensure 

that subsequent deliverables comply with the baselined design.

Model Verification and Validation

z Model Verification: Degree to which a model accurately meets its specifications. Answers “Is it what 

I intended?” 

z Model Validation: The process of determining the 

degree to which a model is an accurate representation of the real world from the perspective of the intended uses of the model.

z Model Certification: Certification for use for a specific 

purpose. Answers, “Should I endorse this model?”
5.4 Product Validation

NASA Systems Engineering Handbook  105

The rigor and techniques used to verify and validate 

software depend upon software classifications (which 

are different from project and payload classifications). A 

complex project will typically contain multiple systems 

and subsystems having different software classifications. 

It is important for the project to classify its software and 

plan verification and validation approaches that appropriately address the risks associated with each class.

In some instances, NASA management may select 

a project for additional independent software verification and validation by the NASA Software Independent Verification and Validation (IV&V) Facility in Fairmount, West Virginia. In this case a 

Memorandum of Understanding (MOU) and separate software IV&V plan will be created and implemented.
106  NASA Systems Engineering Handbook

5.0 Product Realization

The Product Transition Process is used to transition a 

verified and validated end product that has been generated by product implementation or product integration 

to the customer at the next level in the system structure 

for integration into an end product or, for the top-level 

end product, transitioned to the intended end user. The 

form of the product transitioned will be a function of the 

product-line life-cycle phase success criteria and the location within the system structure of the WBS model in 

which the end product exits. 

Product transition occurs during all phases of the life 

cycle. During the early phases, the technical team’s products are documents, models, studies, and reports. As the 

project moves through the life cycle, these paper or soft 

products are transformed through implementation and 

integration processes into hardware and software solutions to meet the stakeholder expectations. They are repeated with different degrees of rigor throughout the life 

cycle. The Product Transition Process includes product 

transitions from one level of the system architecture upward. The Product Transition Process is the last of the 

product realization processes, and it is a bridge 

from one level of the system 

to the next higher level.

The Product Transition Process is the key to bridge from 

one activity, subsystem, or 

element to the overall engineered system. As the system 

development nears completion, the Product Transition 

Process is again applied for 

the end product, but with 

much more rigor since now 

the transition objective is 

delivery of the system-level 

end product to the actual 

end user. Depending on the 

kind or category of system 

developed, this may involve 

a Center or the Agency and 

impact thousands of individuals storing, handling, 

and transporting multiple 

5.5 Product Transition 

end products; preparing user sites; training operators 

and maintenance personnel; and installing and sustaining, as applicable. Examples are transitioning the 

external tank, solid rocket boosters, and orbiter to Kennedy Space Center (KSC) for integration and flight.

5.5.1 Process Description

Figure 5.5-1 provides a typical flow diagram for the 

Product Transition Process and identifies typical inputs, 

outputs, and activities to consider in addressing product 

transition.

5.5.1.1 Inputs

Inputs to the Product Transition Process depend primarily on the transition requirements, the product that is being 

transitioned, the form of the product transition that is taking place, and where the product is transitioning to. Typical inputs are shown in Figure 5.5-1 and described below.

z The End Product or Products To Be Transitioned 

(from Product Validation Process): The product to 

be transitioned can take several forms. It can be a subFigure 5.5-1 Product Transition Process

To Product

Implementation,

Integration, Verication,

Validation, and

Transition Processes 

Product Transition

Work Products

End Product to Be

Transitioned 

Documentation to

Accompany the

Delivered End Product

Product Transition–

Enabling Products

To Technical Data

Management Process

From Product

Validation Process

From Technical Data

Management Process

From existing

resources or Product

Transition Process

Delivered End Product

With Applicable

Documentation

Realized Enabling

Products 

Prepare the end product for transition 

Prepare sites, as required, where the

end product will be stored, assembled,

integrated, installed, used, and/or

maintained

Evaluate the end product, personnel,

and enabling product readiness for

product transition 

Capture product implementation

work products

Prepare to conduct product

transition

Transition the end product to the 

customer with required documentation

based on the type of transition required

To end user or Product

Integration Process

(recursive loop)
5.5 Product Transition

NASA Systems Engineering Handbook  107

system component, system assembly, or top-level end 

product. It can be hardware or software. It can be newly 

built, purchased, or reused. A product can transition 

from a lower system product to a higher one by being 

integrated with other transitioned products. This process may be repeated until the final end product is 

achieved. Each succeeding transition requires unique 

input considerations when preparing for the validated 

product for transition to the next level. 

Early phase products can take the form of information or data generated from basic or applied research 

using analytical or physical models and often are in 

paper or electronic form. In fact, the end product for 

many NASA research projects or science activities is a 

report, paper, or even an oral presentation. In a sense, 

the dissemination of information gathered through 

NASA research and development is an important 

form of product transition.

z Documentation Including Manuals, Procedures, 

and Processes That Are To Accompany the End 

Product (from Technical Data Management Process): The documentation required for the Product 

Transition Process depends on the specific end 

product; its current location within the system structure; and the requirements identified in various agreements, plans, or requirements documents. Typically, 

a product has a unique identification (i.e., serial 

number) and may have a pedigree (documentation) 

that specifies its heritage and current state. Pertinent 

information may be documented through a configuration management system or work order system as 

well as design drawings and test reports. Documentation often includes proof of verification and validation conformance. A COTS product would typically 

contain a manufacturer’s specification or fact sheet. 

Documentation may include operations manuals, installation instructions, and other information.

The documentation level of detail is dependent upon 

where the product is within the product hierarchy 

and the life cycle. Early in the life cycle, this documentation may be preliminary in nature. Later in the 

life cycle, the documentation may be detailed design 

documents, user manuals, drawings, or other work 

products. Documentation that is gathered during 

the input process for the transition phase may require editing, assembling, or repackaging to ensure 

it is in the required condition for acceptance by the 

customer.

Special consideration must be given to safety, including clearly identifiable tags and markings that 

identify the use of hazardous materials, special handling instructions, and storage requirements. 

z Product-Transition-Enabling Products, Including 

Packaging Materials; Containers; Handling Equipment; and Storage, Receiving, and Shipping Facilities (from Existing Resources or Product Transition 

Process for Enabling Product Realization): Producttransition-enabling products may be required to facilitate the implementation, integration, evaluation, 

transition, training, operations, support, and/or retirement of the transition product at its next higher level 

or for the transition of the final end product. Some or 

all of the enabling products may be defined in transition-related agreements, system requirements documents, or project plans. In some cases, product-transition-enabling products are developed during the 

realization of the product itself or may be required to 

be developed during the transition stage. 

As a product is developed, special containers, holders, 

or other devices may also be developed to aid in the 

storing and transporting of the product through development and realization. These may be temporary 

accommodations that do not satisfy all the transition 

requirements, but allow the product to be initiated 

into the transition process. In such cases, the temporary accommodations will have to be modified or new 

accommodations will need to be designed and built 

or procured to meet specific transportation, handling, 

storage, and shipping requirements. 

Sensitive or hazardous products may require special 

enabling products such as monitoring equipment, 

inspection devices, safety devices, and personnel 

training to ensure adequate safety and environmental 

requirements are achieved and maintained.

5.5.1.2 Process Activities

Transitioning the product can take one of two forms:

z The delivery of lower system end products to higher 

ones for integration into another end product or

z The delivery of the final end product to the customer 

or user that will use it in its operational environment.

In the first case, the end product is one of perhaps several 

other pieces that will ultimately be integrated together to 

form the item in the second case for final delivery to the 

customer. For example, the end product might be one of 
108  NASA Systems Engineering Handbook

5.0 Product Realization

several circuit cards that will be integrated together to 

form the final unit that is delivered. Or that unit might 

also be one of several units that have to be integrated together to form the final product. 

The form of the product transitioned is not only a function of the location of that product within the system 

product hierarchy (i.e., WBS model), but also a function of the life-cycle phase. Early life-cycle phase products may be in the form of paper, electronic files, physical models, or technology demonstration prototypes. 

Later phase products may be preproduction prototypes 

(engineering models), the final study report, or the flight 

units.

Figure 5.5-1 shows what kind of inputs, outputs, and activities are performed during product transition regardless of where in the product hierarchy or life cycle the 

product is. These activities include preparing to conduct 

the transition; making sure the end product, all personnel, and any enabling products are ready for transitioning; preparing the site; and performing the transition including capturing and documenting all work 

products.

How these activities are performed and what form the 

documentation takes will depend on where the end 

items are in the product hierarchy (WBS model) and its 

life-cycle phase.

Prepare to Implement Transition

The first task is to identify which of the two forms of 

transition is needed: (1) the delivery of lower system end 

products to higher ones for integration into another end 

product or (2) the delivery of the final end product to 

the customer or user that will use the end product in its 

operational environment. The form of the product being 

transitioned will affect transition planning and the kind 

of packaging, handling, storage, and transportation that 

will be required. The customer and other stakeholder expectations, as well as the specific design solution, may indicate special transition procedures or enabling product 

needs for packaging, storage, handling, shipping/transporting, site preparation, installation, and/or sustainability. These requirements need to be reviewed during 

the preparation stage.

Other tasks in preparing to transition a product involve 

making sure the end product, personnel, and any enabling products are ready for that transition. This includes the availability of the documentation that will be 

sent with the end product, including proof of verification and validation conformance. The appropriateness 

of detail for that documentation depends upon where 

the product is within the product hierarchy and the life 

cycle. Early in the life cycle, this documentation may be 

preliminary in nature. Later in the life cycle, the documentation may be detailed design documents, user manuals, drawings, or other work products. Procedures necessary for conducting the transition should be reviewed 

and approved by this time. This includes all necessary 

approvals by management, legal, safety, quality, property, 

or other organizations as identified in the SEMP.

Finally, the availability and skills of personnel needed to 

conduct the transition as well as the availability of any 

necessary packaging materials/containers, handling 

equipment, storage facilities, and shipping/transporter 

services should also be reviewed. Any special training 

necessary for the personnel to perform their tasks needs 

to be performed by this time.

Prepare the Product for Transition

Whether transitioning a product to the next room for 

integration into the next higher assembly, or for final 

transportation across the country to the customer, care 

must be taken to ensure the safe transportation of the 

product. The requirements for packaging, handling, 

storage, and transportation should have been identified 

during system design. Preparing for the packaging for 

protection, security, and prevention of deterioration is 

critical for products placed in storage or when it is necessary to transport or ship between and within organizational facilities or between organizations by land, air, 

and/or water vehicles. Particular emphasis needs to be 

on protecting surfaces from physical damage, preventing 

corrosion, eliminating damage to electronic wiring or 

cabling, shock or stress damage, heat warping or cold 

fractures, moisture, and other particulate intrusion that 

could damage moving parts.

The design requirements should have already addressed 

the ease of handling or transporting the product such as 

component staking, addition of transportation hooks, 

crating, etc. The ease and safety of packing and unpacking the product should also have been addressed. 

Additional measures may also need to be implemented 

to show accountability and to securely track the product 

during transportation. In cases where hazardous mate-
5.5 Product Transition

NASA Systems Engineering Handbook  109

rials are involved, special labeling or handling needs including transportation routes need to be in place.

Prepare the Site to Receive the Product

For either of the forms of product transition, the receiving site needs to be prepared to receive the product. 

Here the end product will be stored, assembled, integrated, installed, used, and/or maintained, as appropriate 

for the life-cycle phase, position of the end product in 

the system structure, and customer agreement. 

A vast number of key complex activities, many of them 

outside direct control of the technical team, have to be 

synchronized to ensure smooth transition to the end 

user. If transition activities are not carefully controlled, 

there can be impacts on schedule, cost, and safety of the 

end product.

A site survey may need to be performed to determine 

the issues and needs. This should address the adequacy 

of existing facilities to accept, store, and operate the new 

end product and identify any logistical-support-enabling products and services required but not planned 

for. Additionally, any modifications to existing facilities 

must be planned well in advance of fielding; therefore, 

the site survey should be made during an early phase in 

the product life cycle. These may include logistical enabling products and services to provide support for endproduct use, operations, maintenance, and disposal. 

Training for users, operators, maintainers, and other 

support personnel may need to be conducted. National 

Environmental Policy Act documentation or approvals 

may need to be obtained prior to the receipt of the end 

product.

Prior to shipment or after receipt, the end product may 

need to be stored in suitable storage conditions to protect and secure the product and prevent damage or the 

deterioration of it. These conditions should have been 

identified early in the design life cycle. 

Transition the Product

The end product is then transitioned (i.e., moved, transported, or shipped) with required documentation to the 

customer based on the type of transition required, e.g., 

to the next higher level item in the Product Breakdown 

Structure (PBS) for product integration or to the end 

user. Documentation may include operations manuals, 

installation instructions, and other information.

The end product is finally installed into the next higher 

assembly or into the customer/user site using the preapproved installation procedures.

Confirm Ready to Support

After installation, whether into the next higher assembly 

or into the final customer site, functional and acceptance 

testing of the end product should be conducted. This ensures no damage from the shipping/handling process 

has occurred and that the product is ready for support. 

Any final transitional work products should be captured 

as well as documentation of product acceptance.

5.5.1.3 Outputs

z Delivered End Product for Integration to Next Level 

up in System Structure: This includes the appropriate 

documentation. The form of the end product and applicable documentation are a function of the life-cycle 

phase and the placement within the system structure. 

(The form of the end product could be hardware, software, model, prototype, first article for test, or single 

operational article or multiple production article.) 

Documentation includes applicable draft installation, 

operation, user, maintenance, or training manuals; 

applicable baseline documents (configuration baseline, specifications, and stakeholder expectations); 

and test results that reflect completion of verification 

and validation of the end product.

z Delivered Operational End Product for End Users:

The appropriate documentation is to be delivered with 

the delivered end product as well as the operational 

end product appropriately packaged. Documentation 

includes applicable final installation, operation, user, 

maintenance, or training manuals; applicable baseline documents (configuration baseline, specifications, 

stakeholder expectations); and test results that reflect 

completion of verification and validation of the end 

product. If the end user will perform end product validation, sufficient documentation to support end user 

validation activities is delivered with the end product.

z Work Products from Transition Activities to Technical Data Management: Work products could include the transition plan, site surveys, measures, 

training modules, procedures, decisions, lessons 

learned, corrective actions, etc.

z Realized Enabling End Products to Appropriate 

Life-Cycle Support Organization: Some of the enabling products that were developed during the var-
110  NASA Systems Engineering Handbook

5.0 Product Realization

ious phases could include fabrication or integration 

specialized machines; tools; jigs; fabrication processes 

and manuals; integration processes and manuals; 

specialized inspection, analysis, demonstration, or 

test equipment; tools; test stands; specialized packaging materials and containers; handling equipment; 

storage-site environments; shipping or transportation vehicles or equipment; specialized courseware; 

instructional site environments; and delivery of the 

training instruction. For the later life-cycle phases, 

enabling products that are to be delivered may include 

specialized mission control equipment; data collection equipment; data analysis equipment; operations 

manuals; specialized maintenance equipment, tools, 

manuals, and spare parts; specialized recovery equipment; disposal equipment; and readying recovery or 

disposal site environments.

The process is complete when the following activities 

have been accomplished:

z The end product is validated against stakeholder expectations unless the validation is to be done by the 

integrator before integration is accomplished.

z For deliveries to the integration path, the end product is 

delivered to intended usage sites in a condition suitable 

for integration with other end products or composites 

of end products. Procedures, decisions, assumptions, 

anomalies, corrective actions, lessons learned, etc., resulting from transition for integration are recorded.

z For delivery to the end user path, the end products 

are installed at the appropriate sites; appropriate acceptance and certification activities are completed; 

training of users, operators, maintainers, and other necessary personnel is completed; and delivery is closed 

out with appropriate acceptance documentation.

z Any realized enabling end products are also delivered as 

appropriate including procedures, decisions, assumptions, anomalies, corrective actions, lessons learned, 

etc., resulting from transition-enabling products.

5.5.2 Product Transition Guidance

5.5.2.1 Additional Product Transition Input 

Considerations

It is important to consider all customer, stakeholder, technical, programmatic, and safety requirements 

when evaluating the input necessary to achieve a successful Product Transition Process. This includes the 

following:

z Transportability Requirements: If applicable, requirements in this section define the required configuration of the system of interest for transport. Further, this section details the external systems (and the 

interfaces to those systems) required for transport of 

the system of interest.

z Environmental Requirements: Requirements in this 

section define the environmental conditions in which 

the system of interest is required to be during transition (including storage and transportation).

z Maintainability Requirements: Requirements in this 

section detail how frequently, by whom, and by what 

means the system of interest will require maintenance 

(also any “care and feeding,” if required).

z Safety Requirements: Requirements in this section define the life-cycle safety requirements for the 

system of interest and associated equipment, facilities, 

and personnel.

z Security Requirements: This section defines the Information Technology (IT) requirements, Federal and 

international export and security requirements, and 

physical security requirements for the system of interest.

z Programmatic Requirements: Requirements in this 

section define cost and schedule requirements. 

5.5.2.2 After Product Transition to the End 

User—What Next?

As mentioned in Chapter 2.0, there is a relationship between the SE engine and the activities performed after 

the product is transitioned to the end user. As shown in 

Figure 2.3-8, after the final deployment to the end user, 

the end product is operated, managed, and maintained 

through sustaining engineering functions. The technical management processes described in Section 6.0 are 

used during these activities. If at any time a new capability, upgrade, or enabling product is needed, the developmental processes of the engine are reengaged. When 

the end product’s use is completed, the plans developed 

early in the life cycle to dispose, retire, or phase out the 

product are enacted.
NASA Systems Engineering Handbook  111

6.0 Crosscutting Technical Management

This chapter describes the activities in the technical management processes listed in Figure 2.1-1. The chapter 

is separated into sections corresponding to steps 10 

through 17 listed in Figure 2.1-1. The processes within 

each step are discussed in terms of the inputs, the activities, and the outputs. Additional guidance is provided 

using examples that are relevant to NASA projects.

The technical management processes are the bridges between project management and the technical team. In 

this portion of the engine, eight crosscutting processes 

provide the integration of the crosscutting functions that 

allow the design solution to be realized. Even though 

every technical team member might not be directly involved with these eight processes, they are indirectly affected by these key functions. Every member of the technical team relies on technical planning; management 

of requirements, interfaces, technical risk, configuration, and technical data; technical assessment; and decision analysis to meet the project’s objectives. Without 

these crosscutting processes, individual members and 

tasks cannot be integrated into a functioning system that 

meets the ConOps within cost and schedule. The project 

management team also uses these crosscutting functions 

to execute project control on the apportioned tasks.

This effort starts with the technical team conducting extensive planning early in Pre-Phase A. With this early, 

detailed baseline plan, technical team members will 

understand the roles and responsibilities of each team 

member, and the project can establish its program cost 

and schedule goals and objectives. From this effort, the 

Systems Engineering Management Plan (SEMP) is developed and baselined. Once a SEMP has been established, 

it must be synchronized with the project master plans 

and schedule. In addition, the plans for establishing and 

executing all technical contracting efforts are identified.

This is a recursive and iterative process. Early in the life 

cycle, the plans are established and synchronized to run 

the design and realization processes. As the system matures and progresses through the life cycle, these plans 

must be updated as necessary to reflect the current environment and resources and to control the project’s 

performance, cost, and schedule. At a minimum, these 

updates will occur at every Key Decision Point (KDP). 

However, if there is a significant change in the project, 

such as new stakeholder expectations, resource adjustments, or other constraints, all plans must be analyzed 

for the impact of these changes to the baselined project.

The next sections describe each of the eight technical 

management processes and their associated products for 

a given NASA mission. 

Crosscutting Technical Management Keys

z Thoroughly understand and plan the scope of the 

technical effort by investing time upfront to develop the technical product breakdown structure, 

the technical schedule and workflow diagrams, 

and the technical resource requirements and constraints (funding, budget, facilities, and long-lead 

items) that will be the technical planning infrastructure.

z Define all interfaces and assign interface authorities and responsibilities to each, both intra- and 

interorganizational. This includes understanding 

potential incompatibilities and defining the transition processes.

z Control of the configuration is critical to understanding how changes will impact the system. 

For example, changes in design and environment 

could invalidate previous analysis results.

z Conduct milestone reviews to enable a critical and 

valuable assessment to be performed. These reviews are not to be used to meet contractual or 

scheduling incentives. These reviews have specific 

entrance criteria and should be conducted when 

these are met. 

z Understand any biases, assumptions, and constraints that impact the analysis results.

z Place all analysis under configuration control to be 

able to track the impact of changes and understand 

when the analysis needs to be reevaluated. 
112  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

6.1 Technical Planning

The Technical Planning Process, the first of the eight 

technical management processes contained in the systems engineering engine, establishes a plan for applying 

and managing each of the common technical processes 

that will be used to drive the development of system 

products and associated work products. This process also 

establishes a plan for identifying and defining the technical effort required to satisfy the project objectives and 

life-cycle phase success criteria within the cost, schedule, 

and risk constraints of the project. 

6.1.1 Process Description

Figure 6.1-1 provides a typical flow diagram for the Technical Planning Process and identifies typical inputs, outputs, and activities to consider in addressing technical 

planning.

6.1.1.1 Inputs

Input to the Technical Planning Process comes from 

both the project management and technical teams as 

outputs from the other common technical processes. Initial planning utilizing external inputs from the project to 

determine the general scope and framework of the technical effort will be based on known technical and programmatic requirements, constraints, policies, and processes. Throughout the project’s life cycle, the technical 

team continually incorporates results into the technical 

planning strategy and documentation and any internal 

changes based on decisions and assessments generated 

by the other processes of the SE engine or from requirements and constraints mandated by the project. 

As the project progresses through the life-cycle phases, 

technical planning for each subsequent phase must be 

assessed and continually updated. When a project transitions from one life-cycle phase to the next, the technical planning for the upcoming phase must be assessed 

and updated to reflect the most recent project data.

z External Inputs from the Project: The project plan 

provides the project’s top-level technical requirements, the available budget allocated to the project 

Project Technical Effort

Requirements and Project

Resource Constraints

To Technical Data

Management Process

From project 

From Technical Data

Management Process

To Technical

Assessment Process

To project 

To applicable technical

processes

To applicable technical teams

From Technical Assessment

and Technical Risk

Management Processes

Prepare to conduct technical

planning

Define the technical work

Schedule, organize, and cost

the technical work

Prepare SEMP and other

technical plans

Obtain stakeholder commitments

to technical plans

Issue authorized technical

work directives

Capture technical planning

work products

Agreements, Capability

Needs, Applicable ProductLine Life-Cycle Phase

Applicable Policies,

Procedures, Standards,

and Organizational 

Processes

Prior Phase or

Baseline Plans

Replanning Needs

Cost Estimates,

Schedules, and Resource

Requests

Product and Process

Measures

SEMP and Other

Technical Plans

Technical Planning

Work Products

Technical Work Directives

Figure 6.1-1 Technical Planning Process
6.1 Technical Planning

NASA Systems Engineering Handbook  113

from the program, and the desired schedule for the 

project to support overall program needs. Although 

the budget and schedule allocated to the project will 

serve as constraints on the project, the technical team 

will generate a technical cost estimate and schedule 

based on the actual work required to satisfy the project’s technical requirements. Discrepancies between 

the project’s allocated budget and schedule and the 

technical team’s actual cost estimate and schedule 

must be reconciled continuously throughout the project’s life cycle.

The project plan also defines the applicable project 

life-cycle phases and milestones, as well as any internal and external agreements or capability needs 

required for successful project execution. The project’s life-cycle phases and programmatic milestones 

will provide the general framework for establishing 

the technical planning effort and for generating the 

detailed technical activities and products required to 

meet the overall project milestones in each of the lifecycle phases.

Finally, the project plan will include all programmatic 

policies, procedures, standards, and organizational 

processes that must be adhered to during execution 

of the technical effort. The technical team must develop a technical approach that ensures the project 

requirements will be satisfied and that any technical 

procedures, processes, and standards to be used in developing the intermediate and final products comply 

with the policies and processes mandated in the 

project plan.

z Internal Inputs from Other Common Technical 

Processes: The latest technical plans (either baselined 

or from the previous life-cycle phase) from the Data 

Management or Configuration Management Processes should be used in updating the technical planning for the upcoming life-cycle phase.

Technical planning updates may be required based on 

results from technical reviews conducted in the Technical Assessment Process, issues identified during the 

Technical Risk Management Process, or from decisions made during the Decision Analysis Process.

6.1.1.2 Process Activities

Technical planning as it relates to systems engineering at 

NASA is intended to identify, define, and plan how the 

17 common technical processes in NPR 7123.1, NASA 

Systems Engineering Processes and Requirements will be 

applied in each life-cycle phase for all levels of the WBS 

model (see Subsection 6.1.2.1) within the system structure to meet product-line life-cycle phase success criteria. 

A key document generated by this process is the SEMP.

The SEMP is a subordinate document to the project 

plan. While the SEMP defines to all project participants 

how the project will be technically managed within the 

constraints established by the project, the project plan 

defines how the project will be managed to achieve its 

goals and objectives within defined programmatic constraints. The SEMP also communicates how the systems 

engineering management techniques will be applied 

throughout all phases of the project life cycle.

Technical planning should be tightly integrated with the 

Technical Risk Management Process (see Section 6.4) 

and the Technical Assessment Process (see Section 6.7) 

to ensure corrective action for future activities will be incorporated based on current issues identified within the 

project.

Technical planning, as opposed to program or project 

planning, addresses the scope of the technical effort required to develop the system products. While the project 

manager concentrates on managing the overall project 

life cycle, the technical team, led by the systems engineer, 

concentrates on managing the technical aspects of the 

project. The technical team identifies, defines, and develops plans for performing decomposition, definition, 

integration, verification, and validation of the system 

while orchestrating and incorporating the appropriate 

concurrent engineering. Additional planning will include defining and planning for the appropriate technical reviews, audits, assessments, and status reports and 

determining any specialty engineering and/or design 

verification requirements.

This section describes how to perform the activities 

contained in the Technical Planning Process shown in 

Figure 6.1-1. The initial technical planning at the beginning of the project will establish the technical team 

members; their roles and responsibilities; and the tools, 

processes, and resources that will be utilized in executing 

the technical effort. In addition, the expected activities 

the technical team will perform and the products it will 

produce will be identified, defined, and scheduled. Technical planning will continue to evolve as actual data from 

completed tasks are received and details of near-term 

and future activities are known. 
114  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Technical Planning Preparation

For technical planning to be conducted properly, the 

processes and procedures to conduct technical planning should be identified, defined, and communicated. 

As participants are identified, their roles and responsibilities and any training and/or certification activities 

should be clearly defined and communicated.

Once the processes, people, and roles and responsibilities are in place, a planning strategy may be formulated 

for the technical effort. A basic technical planning strategy should address the following:

z The level of planning documentation required for the 

SEMP and all other technical planning documents;

z Identifying and collecting input documentation;

z The sequence of technical work to be conducted, including inputs and outputs;

z The deliverable products from the technical work;

z How to capture the work products of technical activities;

z How technical risks will be identified and managed;

z The tools, methods, and training needed to conduct 

the technical effort;

z The involvement of stakeholders in each facet of the 

technical effort;

z How the NASA technical team will be involved with 

the technical efforts of external contractors;

z The entry and success criteria for milestones, such as 

technical reviews and life-cycle phases;

z The identification, definition, and control of internal 

and external interfaces; 

z The identification and incorporation of relevant lessons learned into the technical planning;

z The approach for technology development and how 

the resulting technology will be incorporated into the 

project;

z The identification and definition of the technical metrics for measuring and tracking progress to the realized product;

z The criteria for make, buy, or reuse decisions and incorporation criteria for Commercial Off-the-Shelf 

(COTS) software and hardware;

z The plan to identify and mitigate off-nominal performance;

z The “how-tos” for contingency planning and replanning;

z The plan for status assessment and reporting; and

z The approach to decision analysis, including materials 

needed, required skills, and expectations in terms of 

accuracy. 

By addressing these items and others unique to the 

project, the technical team will have a basis for understanding and defining the scope of the technical effort, 

including the deliverable products that the overall technical effort will produce, the schedule and key milestones 

for the project that the technical team must support, and 

the resources required by the technical team to perform 

the work.

A key element in defining the technical planning effort is 

understanding the amount of work associated with performing the identified activities. Once the scope of the 

technical effort begins to coalesce, the technical team 

may begin to define specific planning activities and to 

estimate the amount of effort and resources required to 

perform each task. Historically, many projects have underestimated the resources required to perform proper 

planning activities and have been forced into a position 

of continuous crisis management in order to keep up 

with changes in the project.

Define the Technical Work

The technical effort must be thoroughly defined. When 

performing the technical planning, realistic values for 

cost, schedule, and labor resources should be used. 

Whether extrapolated from historical databases or from 

interactive planning sessions with the project and stakeholders, realistic values must be calculated and provided 

to the project team. Contingency should be included in 

any estimate and based on complexity and criticality of 

the effort. Contingency planning must be conducted. 

The following are examples of contingency planning:

z Additional, unplanned-for software engineering resources are typically needed during hardware and 

systems development and testing to aid in troubleshooting errors/anomalies. Frequently, software engineers are called upon to help troubleshoot problems 

and pinpoint the source of errors in hardware and systems development and testing (e.g., for writing addition test drivers to debug hardware problems). Additional software staff should be planned into the project 

contingencies to accommodate inevitable component 

and system debugging and avoid cost and schedule 

overruns.
6.1 Technical Planning

NASA Systems Engineering Handbook  115

z Hardware-in-the-Loop (HWIL) must be accounted 

for in the technical planning contingencies. HWIL 

testing is typically accomplished as a debugging exercise where the hardware and software are brought 

together for the first time in the costly environment of 

an HWIL. If upfront work is not done to understand 

the messages and errors arising during this test, additional time in the HWIL facility may result in significant cost and schedule impacts. Impacts may be 

mitigated through upfront planning, such as making 

appropriate debugging software available to the technical team prior to the test, etc.

Schedule, Organize, and Cost the Technical Effort

Once the technical team has defined the technical work 

to be done, efforts can focus on producing a schedule 

and cost estimate for the technical portion of the project. 

The technical team must organize the technical tasks 

according to the project WBS in a logical sequence of 

events, taking into consideration the major project milestones, phasing of available funding, and timing of availability of supporting resources.

Scheduling

Products described in the WBS are the result of activities that take time to complete. These activities have time 

precedence relationships among them that may used 

to create a network schedule explicitly defining the dependencies of each activity on other activities, the availability of resources, and the receipt of receivables from

outside sources. 

Scheduling is an essential component of planning and 

managing the activities of a project. The process of creating a network schedule provides a standard method 

for defining and communicating what needs to be done, 

how long it will take, and how each element of the project 

WBS might affect other elements. A complete network 

schedule may be used to calculate how long it will take to 

complete a project; which activities determine that duration (i.e., critical path activities); and how much spare 

time (i.e., float) exists for all the other activities of the 

project. 

“Critical path” is the sequence of dependent tasks that 

determines the longest duration of time needed to complete the project. These tasks drive the schedule and continually change, so they must be updated. The critical 

path may encompass only one task or a series of interrelated tasks. It is important to identify the critical path 

and the resources needed to complete the critical tasks 

along the path if the project is to be completed on time 

and within its resources. As the project progresses, the 

critical path will change as the critical tasks are completed or as other tasks are delayed. This evolving critical 

path with its identified tasks needs to be carefully monitored during the progression of the project.

Network scheduling systems help managers accurately 

assess the impact of both technical and resource changes 

on the cost and schedule of a project. Cost and technical 

problems often show up first as schedule problems. Understanding the project’s schedule is a prerequisite for 

determining an accurate project budget and for tracking 

performance and progress. Because network schedules 

show how each activity affects other activities, they assist 

in assessing and predicting the consequences of schedule 

slips or accelerations of an activity on the entire project.

Network Schedule Data and Graphical 

Formats

Network schedule data consist of:

z Activities and associated tasks;

z Dependencies among activities (e.g., where an activity 

depends upon another activity for a receivable);

z Products or milestones that occur as a result of one or 

more activities; and

z Duration of each activity.

A network schedule contains all four of the above data 

items. When creating a network schedule, creating 

graphical formats of these data elements may be a useful 

first step in planning and organizing schedule data.

Workflow Diagrams

A workflow diagram is a graphical display of the first 

three data items. Two general types of graphical formats 

are used as shown in Figure 6.1-2. One places activities 

on arrows, with products and dependencies at the beginning and end of the arrow. This is the typical format of 

the Program Evaluation and Review Technique (PERT) 

chart. 

The second format, called precedence diagrams, uses 

boxes to represent activities; dependencies are then 

shown by arrows. The precedence diagram format allows for simple depiction of the following logical relationships:
116  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

z Activity B begins when Activity A begins (start-start).

z Activity B begins only after Activity A ends (finishstart).

z Activity B ends when Activity A ends (finish-finish).

Each of these three activity relationships may be modified 

by attaching a lag (+ or –) to the relationship, as shown 

in Figure 6.1-2. It is possible to summarize a number of 

low-level activities in a precedence diagram with a single 

activity. One takes the initial low-level activity and attaches a summary activity to it using the start-start relationship described above. The summary activity is then 

attached to the final low-level activity using the finishstart relationship. The most common relationship used 

in precedence diagrams is the finish-start one. The activity-on-arrow format can represent the identical timeprecedence logic as a precedence diagram by creating artificial events and activities as needed.

Establishing a Network Schedule

Scheduling begins with project-level schedule objectives for delivering the products described in the upper 

levels of the WBS. To develop network schedules that are 

consistent with the project’s objectives, the following six 

steps are applied to each element at the lowest available 

level of the WBS.

Step 1: Identify activities and dependencies needed to 

complete each WBS element. Enough activities should 

be identified to show exact schedule dependencies between activities and other WBS elements. This first step 

is most easily accomplished by:

z Ensuring that the WBS model is extended downward 

to describe all significant products including documents, reports, and hardware and software items.

z For each product, listing the steps required for its generation and drawing the process as a workflow diagram.

z Indicating the dependencies among the products, and 

any integration and verification steps within the work 

package.

Step 2: Identify and negotiate external dependencies. External dependencies are any receivables from outside of, 

and any deliverables that go outside of, the WBS element. 

Negotiations should occur to ensure that there is agreement with respect to the content, format, and labeling of 

products that move across WBS elements so that lower 

level schedules can be integrated.

Step 3: Estimate durations of all activities. Assumptions 

behind these estimates (workforce, availability of facilities, etc.) should be written down for future reference.

Step 4: Enter the data for each WBS element into a scheduling program to obtain a network schedule and an estimate of the critical path for that element. It is not unusual at this point for some iteration of steps 1 to 4 to 

obtain a satisfactory schedule. Reserve is often added to 

critical-path activities to ensure that schedule commitments can be met within targeted risk levels.

Step 5: Integrate schedules of lower level WBS elements 

so that all dependencies among elements are correctly 

included in a project network. It is important to include 

the impacts of holidays, weekends, etc., by this point. 

The critical path for the project is discovered at this step 

in the process.

Step 6: Review the workforce level and funding profile 

over time and make a final set of adjustments to logic 

and durations so that workforce levels and funding levels 

are within project constraints. Adjustments to the logic 

and the durations of activities may be needed to conActivity-on-Arrow Diagram

Precedence Diagram

5 5

5

5

SS5

10

A

10

B

Activity description, including an action

and the subject of that action

Activity duration (e.g., days)

Means that 

Activity B can

start 5 days after

Activity A starts

A1 A2

B1

B2

Activity A articially divided 

into two separate activities

Activity duration

(e.g., days)

Activity description, including an action

and the subject of that action

Figure 6.1-2 Activity-on-arrow and precedence 

diagrams for network schedules
6.1 Technical Planning

NASA Systems Engineering Handbook  117

verge to the schedule targets established at the project 

level. Adjustments may include adding more activities to 

some WBS elements, deleting redundant activities, increasing the workforce for some activities that are on the 

critical path, or finding ways to do more activities in parallel, rather than in series. 

Again, it is good practice to have some schedule reserve, 

or float, as part of a risk mitigation strategy. The product 

of these last steps is a feasible baseline schedule for each 

WBS element that is consistent with the activities of all 

other WBS elements. The sum of all of these schedules 

should be consistent with both the technical scope and 

the schedule goals of the project. There should be enough 

float in this integrated master schedule so that schedule 

and associated cost risk are acceptable to the project and 

to the project’s customer. Even when this is done, time 

estimates for many WBS elements will have been underestimated or work on some WBS elements will not start 

as early as had been originally assumed due to late arrival of receivables. Consequently, replanning is almost 

always needed to meet the project’s goals.

Reporting Techniques

Summary data about a schedule is usually described in 

charts. A Gantt chart is a bar chart that depicts a project 

schedule using start and finish dates of the appropriate 

product elements tied to the project WBS of a project. 

Some Gantt charts also show the dependency (i.e., precedence and critical path) relationships among activities 

and also current status. A good example of a Gantt chart is 

shown in Figure 6.1-3. (See box on Gantt chart features.) 

Another type of output format is a table that shows the 

float and recent changes in float of key activities. For example, a project manager may wish to know precisely 

how much schedule reserve has been consumed by critical path activities, and whether reserves are being consumed or are being preserved in the latest reporting 

period. This table provides information on the rate of 

change of schedule reserve.

Resource Leveling

Good scheduling systems provide capabilities to show resource requirements over time and to make adjustments 

so that the schedule is feasible with respect to resource 

constraints over time. Resources may include workforce 

level, funding profiles, important facilities, etc. The objective is to move the start dates of tasks that have float to 

points where the resource profile is feasible. If that is not 

sufficient, then the assumed task durations for resourceintensive activities should be reexamined and, accordingly, the resource levels changed.

Budgeting

Budgeting and resource planning involve the establishment of a reasonable project baseline budget and the 

capability to analyze changes to that baseline resulting 

from technical and/or schedule changes. The project’s 

WBS, baseline schedule, and budget should be viewed 

as mutually dependent, reflecting the technical content, 

time, and cost of meeting the project’s goals and objectives. The budgeting process needs to take into account 

Gantt Chart Features

The Gantt chart shown in Figure 6.1-3 illustrates the 

following desirable features:

z A heading that describes the WBS element, identifies the responsible manager, and provides the 

date of the baseline used and the date that status 

was reported.

z A milestone section in the main body (lines 1 and 2).

z An activity section in the main body. Activity data 

shown includes:

▶ WBS elements (lines 3, 5, 8, 12, 16, and 21);

▶ Activities (indented from WBS elements);

▶ Current plan (shown as thick bars);

▶ Baseline plan (same as current plan, or if different, 

represented by thin bars under the thick bars);

▶ Slack for each activity (dotted horizontal line before the milestone on line 12);

▶ Schedule slips from the baseline (dotted horizontal lines after the current plan bars);

▶ The critical path is shown encompassing lines 18 

through 21 and impacting line 24; and

▶ Status line (dotted vertical line from top to bottom of the main body of the chart) at the date 

the status was reported.

z A legend explaining the symbols in the chart.

This Gantt chart shows only 24 lines, which is a summary of the activities currently being worked for this 

WBS element. It is appropriate to tailor the amount of 

detail reported to those items most pertinent at the 

time of status reporting.
118  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

ACTIVITY

1 Milestones – Subsystem

2 – Assembly

3 Management

4 Quarterly Assessments

5 System Engineering

6 Assembly Design

7 Subassembly Requirements

8 Subassembly #1

9 Design

10 Fabricate

11 Test

12 Subassembly #2

13 Design

14 Fabricate

15 Test

16 Subassembly #3

17 Design

18 Fabricate Phase 1

19 Fabricate Phase 2

20 Test

21 Integration and Test

22 Plans

23 Procedures

24 Integrate and Test

2006 2007

FY 2007

SYSTEM (TIER 2)

SUBSYSTEM (TIER 3)

ASSEMBLY (TIER 4)

EXAMPLE PROJECT Page 1/2

Status as of: Jan 20, 2007

Revision Date: Dec 23, 2006

CDR

CDR

SDR

PDR

PDR

Approval

Approval

Rec’d Requirements

Deliver

To Integration & Test

To Integration & Test

To Integration & Test

Final

Fixtures

Receive All

Subassemblies

Today’s Date

Approval

Responsible Manager:

Legend:

Float, positive or negative, is shown above the activity bars and event symbols.

The baselined schedule is shown below revised schedule, if they dier.

Critical Path

Not Completed

Completed

End of Task Schedule

Major Milestone

Scheduled Period of Performance for Activity

Figure 6.1-3 Gantt chart

whether a fixed cost cap or cost profile exists. When no 

such cap or profile exists, a baseline budget is developed 

from the WBS and network schedule. This specifically 

involves combining the project’s workforce and other resource needs with the appropriate workforce rates and 

other financial and programmatic factors to obtain cost 

element estimates. These elements of cost include:

z Direct labor costs,

z Overhead costs,

z Other direct costs (travel, data processing, etc.),

z Subcontract costs,

z Material costs,

z General and administrative costs,

z Cost of money (i.e., interest payments, if applicable),

z Fee (if applicable), and

z Contingency.

When there is a cost cap or a fixed cost profile, there are 

additional logic gates that must be satisfied before completing the budgeting and planning process. A determination needs to be made whether the WBS and network 

schedule are feasible with respect to mandated cost caps 

and/or cost profiles. If not, it will be necessary to consider stretching out a project (usually at an increase in 

the total cost) or descoping the project’s goals and objectives, requirements, design, and/or implementation approach. 
6.1 Technical Planning

NASA Systems Engineering Handbook  119

If a cost cap or fixed cost profile exists, it is important to 

control costs after they have been baselined. An important 

aspect of cost control is project cost and schedule status reporting and assessment, methods for which are discussed 

in Section 6.7. Another is cost and schedule risk planning, 

such as developing risk avoidance and workaround strategies. At the project level, budgeting and resource planning 

must ensure that an adequate level of contingency funds is 

included to deal with unforeseen events.

The maturity of the Life-Cycle Cost Estimate (LCCE) 

should progress as follows:

z Pre-Phase A: Initial LCCE (70 percent confidence 

level; however, much uncertainty is expected) 

z Phase A: Preliminary commitment to LCCE

z Phase B: Approve LCCE (70 percent confidence level 

at PDR commitment)

z Phase C, D, and E report variances to LCCE baseline 

using Earned Value Management (EVM) and LCCE 

updates

Credibility of the cost estimate is suspect if:

z WBS cost estimates are expressed only in dollars with 

no other identifiable units, indicating that requirements are not sufficiently defined for processes and 

resources to be identified.

z The basis of estimates does not contain sufficient detail for independent verification that work scope and 

estimated cost (and schedule) are reasonable.

z Actual costs vary significantly from the LCCE.

z Work is performed that was not originally planned, 

causing cost or schedule variance.

z Schedule and cost earned value performance trends 

readily indicate unfavorable performance.

Prepare the SEMP and Other Technical Plans

The SEMP is the primary, top-level technical management document for the project and is developed early 

in the Formulation phase and updated throughout the 

project life cycle. The SEMP is driven by the type of 

project, the phase in the project life cycle, and the technical development risks and is written specifically for 

each project or project element. While the specific content of the SEMP is tailored to the project, the recommended content is discussed in Appendix J.

The technical team, working under the overall project 

plan, develops and updates the SEMP as necessary. The 

technical team works with the project manager to review 

the content and obtain concurrence. This allows for thorough discussion and coordination of how the proposed 

technical activities would impact the programmatic, cost, 

and schedule aspects of the project. The SEMP provides 

the specifics of the technical effort and describes what 

technical processes will be used, how the processes will be 

applied using appropriate activities, how the project will 

be organized to accomplish the activities, and the cost and 

schedule associated with accomplishing the activities.

The physical length of a SEMP is not what is important. 

This will vary from project to project. The plan needs to 

be adequate to address the specific technical needs of the 

project. It is a living document that is updated as often as 

necessary to incorporate new information as it becomes 

available and as the project develops through Implementation. The SEMP should not duplicate other project 

documents; however, the SEMP should reference and 

summarize the content of other technical plans. 

The systems engineer and project manager must identify additional required technical plans based on the 

project scope and type. If plans are not included in the 

SEMP, they should be referenced and coordinated in the 

development of the SEMP. Other plans, such as system 

safety and the probabilistic risk assessment, also need 

to be planned for and coordinated with the SEMP. If a 

technical plan is a stand-alone, it should be referenced 

in the SEMP. Depending on the size and complexity of 

the project, these may be separate plans or may be included within the SEMP. Once identified, the plans can 

be developed, training on these plans established, and 

the plans implemented. Examples of technical plans in 

addition to the SEMP are listed in Appendix K.

The SEMP must be developed concurrently with the 

project plan. In developing the SEMP, the technical approach to the project and, hence, the technical aspect of 

the project life cycle is developed. This determines the 

project’s length and cost. The development of the programmatic and technical management approaches 

requires that the key project personnel develop an 

understanding of the work to be performed and the relationships among the various parts of that work. Refer 

to Subsections 6.1.2.1 and 6.1.1.2 on WBSs and network 

scheduling, respectively.

The SEMP’s development requires contributions from 

knowledgeable programmatic and technical experts from 

all areas of the project that can significantly influence the 
120  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

project’s outcome. The involvement of recognized experts is needed to establish a SEMP that is credible to the 

project manager and to secure the full commitment of 

the project team.

Role of the SEMP

The SEMP is the rule book that describes to all participants how the project will be technically managed. The 

NASA field center responsible for the project should 

have a SEMP to describe how it will conduct its technical 

management, and each contractor should have a SEMP 

to describe how it will manage in accordance with both 

its contract and NASA’s technical management practices. 

Each Center that is involved with the project should also 

have a SEMP for its part of the project, which would interface with the project SEMP of the responsible NASA 

Center, but this lower tier SEMP specifically will address 

that Center’s technical effort and how it interfaces with 

the overall project. Since the SEMP is project- and contract-unique, it must be updated for each significant programmatic change, or it will become outmoded and unused, and the project could slide into an uncontrolled state. 

The lead NASA field center should have its SEMP developed before attempting to prepare an initial cost estimate, 

since activities that incur cost, such as technical risk reduction, need to be identified and described beforehand. 

The contractor should have its SEMP developed during 

the proposal process (prior to costing and pricing) because the SEMP describes the technical content of the 

project, the potentially costly risk management activities, and the verification and validation techniques to be 

used, all of which must be included in the preparation of 

project cost estimates. The SEMPs from the supporting 

Centers should be developed along with the primary 

project SEMP. The project SEMP is the senior technical 

management document for the project: all other technical plans must comply with it. The SEMP should be 

comprehensive and describe how a fully integrated engineering effort will be managed and conducted.

Obtain Stakeholder Commitments to Technical 

Plans

To obtain commitments to the technical plans by the 

stakeholders, the technical team should ensure that the 

appropriate stakeholders have a method to provide inputs and to review the project planning for implementation of stakeholder interests. During Formulation, 

the roles of the stakeholders should be defined in the 

project plan and the SEMP. Review of these plans and 

the agreement from the stakeholders of the content of 

these plans will constitute buy-in from the stakeholders 

in the technical approach. Later in the project life cycle, 

stakeholders may be responsible for delivery of products 

to the project. Initial agreements regarding the responsibilities of the stakeholders are key to ensuring that the 

project technical team obtains the appropriate deliveries 

from stakeholders.

The identification of stakeholders is one of the early steps in 

the systems engineering process. As the project progresses, 

stakeholder expectations are flowed down through the 

Logical Decomposition Process, and specific stakeholders 

are identified for all of the primary and derived requirements. A critical part of the stakeholders’ involvement is 

in the definition of the technical requirements. As requirements and ConOps are developed, the stakeholders will 

be required to agree to these products. Inadequate stakeholder involvement will lead to inadequate requirements 

and a resultant product that does not meet the stakeholder 

expectations. Status on relevant stakeholder involvement 

should be tracked and corrective action taken if stakeholders are not participating as planned.

Throughout the project life cycle, communication with 

the stakeholders and commitment from the stakeholders 

may be accomplished through the use of agreements. Organizations may use an Internal Task Agreement (ITA), 

a Memorandum of Understanding (MOU), or other 

similar documentation to establish the relationship between the project and the stakeholder. These agreements 

also are used to document the customer and provider responsibilities for definition of products to be delivered. 

These agreements should establish the Measures of Effectiveness (MOEs) or Measures of Performance (MOPs) 

that will be used to monitor the progress of activities. Reporting requirements and schedule requirements should 

be established in these agreements. Preparation of these 

agreements will ensure that the stakeholders’ roles and 

responsibilities support the project goals and that the 

project has a method to address risks and issues as they 

are identified.

During development of the project plan and the SEMP, 

forums are established to facilitate communication and 

document decisions during the life cycle of the project. 

These forums include meetings, working groups, decision panels, and control boards. Each of these forums 

should establish a charter to define the scope and authority of the forum and identify necessary voting or 
6.1 Technical Planning

NASA Systems Engineering Handbook  121

nonvoting participants. Ad hoc members may be identified when the expertise or input of specific stakeholders 

is needed when specific topics are addressed. Ensure that 

stakeholders have been identified to support the forum.

Issue Technical Work Directives

The technical team provides technical work directives 

to Cost Account Managers (CAMs). This enables the 

CAMs to prepare detailed plans that are mutually consistent and collectively address all of the work to be performed. These plans include the detailed schedules and 

budgets for cost accounts that are needed for cost management and EVM. 

Issuing technical work directives is an essential activity 

during Phase B of a project, when a detailed planning 

baseline is required. If this activity is not implemented, 

then the CAMs are often left with insufficient guidance 

for detailed planning. The schedules and budgets that are 

needed for EVM will then be based on assumptions and 

local interpretations of project-level information. If this 

is the case, it is highly likely that substantial variances 

will occur between the baseline plan and the work performed. Providing technical work directives to CAMs 

produces a more organized technical team. This activity 

may be repeated when replanning occurs.

This activity is not limited to systems engineering. This 

is a normal part of project planning wherever there is a 

need for an accurate planning baseline. 

The technical team will provide technical directives to 

CAMs for every cost account within the SE element of 

the WBS. These directives may be in any format, but 

should clearly communicate the following information 

for each account:

z Technical products expected;

z Documents and technical reporting requirements for 

each cost account;

z Critical events, and specific products expected from a 

particular CAM in support of this event (e.g., this cost 

account is expected to deliver a presentation on specific topics at the PDR);

z References to applicable requirements, policies, and 

standards;

z Identification of particular tools that should be used; 

z Instructions on how the technical team wants to coordinate and review cost account plans before they go 

to project management; and

z Decisions that have been made on how work is to be 

performed and who is to perform it. 

CAMs receive these technical directives, along with the 

project planning guidelines, and prepare cost account 

plans. These plans may be in any format and may have 

various names at different Centers, but minimally they 

will include:

z Scope of the cost account, which includes:

▶ Technical products delivered;

▶ Other products developed that will be needed to 

complete deliverables (e.g., a Configuration Management (CM) system may need development in 

order to deliver the product of a “managed configuration”);

▶ A brief description of the procedures that will be 

followed to complete work on these products, such 

as:

• Product X will be prepared in-house, using the 

local procedure A, which is commonly used in 

Organization ABC,

• Product X will be verified/validated in the following manner...,

• Product X will be delivered to the project in the 

following manner...,

• Product X delivery will include the following reports (e.g., delivery of a CM system to the project 

would include regular reports on the status of the 

configuration, etc.),

• Product Y will be procured in accordance with 

procurement procedure B.

z A schedule attached to this plan in a format compatible with project guidelines for schedules. This 

schedule would contain each of the procedures and 

deliverables mentioned above and provide additional 

information on the activity steps of each procedure.

z A budget attached to this plan in a system compatible with project guidelines for budgets. This budget 

would be consistent with the resources needed to accomplish the scheduled activities.

z Any necessary agreements and approvals. 

If the project is going to use EVM, then the scope of a 

cost account needs to further identify a number of “work 

packages,” which are units of work that can be scheduled and given cost estimates. Work packages should be 

based on completed products to the greatest extent pos-
122  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

sible, but may also be based on completed procedures 

(e.g., completion of validation). Each work package 

will have its own schedule and a budget. The budget for 

this work package becomes part of the Budgeted Cost 

of Work Scheduled (BCWS) in the EVM system. When 

this unit of work is completed, the project’s earned value 

will increase by this amount. There may be future work 

in this cost account that is not well enough defined to 

be described as a set of work packages. For example, 

launch operations will be supported by the technical 

team, but the details of what will be done often have not 

been worked out during Phase B. In this case, this future 

work is called a “planning package,” which has a highlevel schedule and an overall budget. When this work is 

understood better, the planning package will be broken 

up into work packages, so that the EVM system can continue to operate during launch operations.

Cost account plans should be reviewed and approved by 

the technical team and by the line manager of the cost 

account manager’s home organization. Planning guidelines may identify additional review and approval requirements.

The planning process described above is not limited to 

systems engineering. This is the expected process for all 

elements of a flight project. One role that the systems engineer may have in planning is to verify that the scope of 

work described in cost account plans across the project 

is consistent with the project WBS dictionary, and that 

the WBS dictionary is consistent with the architecture 

of the project.

Capture Technical Planning Work Products

The work products from the Technical Planning process should be managed using either the Technical 

Data Management Process or the Configuration Management Process as required. Some of the more important products of technical planning (i.e., the WBS, the 

SEMP, and the schedule, etc.) are kept under configuration control and captured using the CM process. The 

Technical Data Management Process is used to capture 

trade studies, cost estimates, technical analyses, reports, 

and other important documents not under formal configuration control. Work products, such as meeting 

minutes and correspondence (including e-mail) containing decisions or agreements with stakeholders also 

should be retained and stored in project files for later 

reference.

6.1.1.3 Outputs

Typical outputs from technical planning activities are:

z Technical work cost estimates, schedules, and resource needs, e.g., funds, workforce, facilities, and 

equipment (to project), within the project resources;

z Product and process measures needed to assess progress of the technical effort and the effectiveness of 

processes (to Technical Assessment Process);

z Technical planning strategy, WBS, SEMP, and other 

technical plans that support implementation of the 

technical effort (to all processes; applicable plans to 

technical processes);

z Technical work directives, e.g., work packages or task 

orders with work authorization (to applicable technical teams); and

z Technical Planning Process work products needed 

to provide reports, records, and nondeliverable outcomes of process activities (to Technical Data Management Process).

The resulting technical planning strategy would constitute an outline, or rough draft, of the SEMP. This would 

serve as a starting part for the overall Technical Planning 

Process after initial preparation is complete. When preparations for technical planning are complete, the technical team should have a cost estimate and schedule for 

the technical planning effort. The budget and schedule to 

support the defined technical planning effort can then be 

negotiated with the project manager to resolve any discrepancies between what is needed and what is available. 

The SEMP baseline needs to be completed. Planning for 

the update of the SEMP based on programmatic changes 

needs to be developed and implemented. The SEMP needs 

to be approved by the appropriate level of authority.

This “technical work directives” step produces: (1) planning directives to cost account managers that result in 

(2) a consistent set of cost account plans. Where EVM 

is called for, it produces (3) an EVM planning baseline, 

including a BCWS. 

6.1.2 Technical Planning Guidance

6.1.2.1 Work Breakdown Structure

A work breakdown structure is a hierarchical breakdown of the work necessary to complete a project. The 

WBS should be a product-based, hierarchical division 

of deliverable items and associated services. As such, it 
6.1 Technical Planning

NASA Systems Engineering Handbook  123

should contain the project’s Product Breakdown Structure (PBS) with the specified prime product(s) at the top 

and the systems, segments, subsystems, etc., at successive lower levels. At the lowest level are products such as 

hardware items, software items, and information items 

(documents, databases, etc.) for which there is a cognizant engineer or manager. Branch points in the hierarchy 

should show how the PBS elements are to be integrated. 

The WBS is built, in part, from the PBS by adding, at each 

branch point of the PBS, any necessary service elements, 

such as management, systems engineering, Integration 

and Verification (I&V), and integrated logistics support. 

If several WBS elements require similar equipment or 

software, then a higher level WBS element might be defined from the system level to perform a block buy or a 

development activity (e.g., system support equipment). 

Figure 6.1-4 shows the relationship between a system, a 

PBS, and a WBS. In summary, the WBS is a combination 

of the PBS and input from the system level. The system 

level is incorporated to capture and integrate similarities 

across WBS elements.

A project WBS should be carried down to the cost account level appropriate to the risks to be managed. The 

appropriate level of detail for a cost account is determined by management’s desire to have visibility into 

costs, balanced against the cost of planning and reporting. Contractors may have a Contract WBS (CWBS) that 

is appropriate to their need to control costs. A summary 

CWBS, consisting of the upper levels of the full CWBS, 

is usually included in the project WBS to report costs to 

the contracting organization. WBS elements should be 

identified by title and by a numbering system that performs the following functions:

z Identifies the level of the WBS element,

z Identifies the higher level element into which the 

WBS element will be integrated, and

z Shows the cost account number of the element.

A WBS should also have a companion WBS dictionary 

that contains each element’s title, identification number, 

objective, description, and any dependencies (e.g., receivables) on other WBS elements. This dictionary provides a structured project description that is valuable for 

orienting project members and other interested parties. 

It fully describes the products and/or services expected 

from each WBS element. This subsection provides some 

techniques for developing a WBS and points out some 

mistakes to avoid.

Role of the WBS

The technical team should receive planning guidelines 

from the project office. The technical team should provide the project office with any appropriate tailoring or 

expansion of the systems engineering WBS element, and 

have project-level concurrence on the WBS and WBS 

dictionary before issuing technical work directives.

A product-based WBS is the organizing structure for:

z Project and technical planning and scheduling.

z Cost estimation and budget formulation. (In particular, costs collected in a product-based WBS can be 

compared to historical data. This is identified as a primary objective by DOD standards for WBSs.)

Figure 6.1-4 Relationship between a system, a 

PBS, and a WBS

The whole does more

than the sum of the parts.

The whole takes more work

than the sum of the parts.

Subsystem A

SYSTEM

Components

(subsystems)

held together

by “glue”

(integration)

PBS

Shows the components

that form the system

System

A B C D

The individual

system components

WBS

All work components

necessary to produce

a complete system

System

A B C D

Work to produce

the individual

system components

Work to integrate the

components into a system

Mgmt SE I&V ILS

Subsystem B

Subsystem C

Subsystem D
124  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

z Defining the scope of statements of work and specifications for contract efforts.

z Project status reporting, including schedule, cost, 

workforce, technical performance, and integrated 

cost/schedule data (such as earned value and estimated cost at completion).

z Plans, such as the SEMP, and other documentation 

products, such as specifications and drawings.

It provides a logical outline and vocabulary that describes the entire project, and integrates information in 

a consistent way. If there is a schedule slip in one element of a WBS, an observer can determine which other 

WBS elements are most likely to be affected. Cost impacts are more accurately estimated. If there is a design 

change in one element of the WBS, an observer can determine which other WBS elements will most likely be 

affected, and these elements can be consulted for potential adverse impacts.

Techniques for Developing the WBS

Developing a successful project WBS is likely to require 

several iterations through the project life cycle since it 

is not always obvious at the outset what the full extent 

of the work may be. Prior to developing a preliminary 

WBS, there should be some development of the system 

architecture to the point where a preliminary PBS can be 

created. The PBS and associated WBS can then be developed level by level from the top down. In this approach, 

a project-level systems engineer finalizes the PBS at the 

project level and provides a draft PBS for the next lower 

level. The WBS is then derived by adding appropriate 

services such as management and systems engineering to 

that lower level. This process is repeated recursively until 

a WBS exists down to the desired cost account level. An 

alternative approach is to define all levels of a complete 

PBS in one design activity and then develop the complete WBS. When this approach is taken, it is necessary 

to take great care to develop the PBS so that all products 

are included and all assembly/I&V branches are correct. 

The involvement of people who will be responsible for 

the lower level WBS elements is recommended.

Common Errors in Developing a WBS 

There are three common errors found in WBSs.

z Error 1: The WBS describes functions, not products. 

This makes the project manager the only one formally 

responsible for products.

z Error 2: The WBS has branch points that are not 

consistent with how the WBS elements will be integrated. For instance, in a flight operations system 

with a distributed architecture, there is typically 

software associated with hardware items that will be 

integrated and verified at lower levels of a WBS. It 

would then be inappropriate to separate hardware 

and software as if they were separate systems to be 

integrated at the system level. This would make it 

difficult to assign accountability for integration and 

to identify the costs of integrating and testing components of a system.

z Error 3: The WBS is inconsistent with the PBS. This 

makes it possible that the PBS will not be fully implemented and generally complicates the management 

process. 

Some examples of these errors are shown in Figure 6.1-5. 

Each one prevents the WBS from successfully performing 

its roles in project planning and organizing. These errors 

are avoided by using the WBS development techniques 

described above.

Common to both the project management and systems 

engineering disciplines is the requirement for organizing 

and managing a system throughout its life cycle within 

a systematic and structured framework, reflective of the 

work to be performed and the associated cost, schedule, 

technical, and risk data to be accumulated, summarized, 

and reported. (See NPR 7120.5.)

A key element of this framework is a hierarchical, 

product-oriented WBS. Derived from both the physical 

and system architectures, the WBS provides a systematic, logical approach for defining and translating initial mission goals and technical concepts into tangible 

project goals, system products, and life-cycle support (or 

enabling) functions.

When appropriately structured and used in conjunction 

with sound engineering principles, the WBS supplies a 

common framework for subdividing the total project 

into clearly defined, product-oriented work components, logically related and sequenced according to hierarchy, schedule, and responsibility assignment. 

The composition and level of detail required in the WBS 

hierarchy is determined by the project management and 

technical teams based on careful consideration of the 

project’s size and the complexity, constraints, and risk 

associated with the technical effort. The initial WBS will 
6.1 Technical Planning

NASA Systems Engineering Handbook  125

provide a structured framework for conceptualizing and 

defining the program/project objectives and for translating the initial concepts into the major systems, component products, and services to be developed, produced, and/or obtained. As successive levels of detail 

are defined, the WBS hierarchy will evolve to reflect a 

comprehensive, complete view of both the total project 

effort and each system or end product to be realized 

throughout the project’s life cycle. 

Decomposition of the major deliverables into unique, 

tangible product or service elements should continue to 

a level representative of how each WBS element will be 

planned and managed. Whether assigned to in-house or 

contractor organizations, these lower WBS elements will 

be subdivided into subordinate tasks and activities and 

aggregated into the work packages and control accounts 

utilized to populate the project’s cost plans, schedules, 

and performance metrics. 

At a minimum, the WBS should reflect the major system 

products and services to be developed and/or procured, 

the enabling (support) products and services, and any 

high-cost and/or high-risk product elements residing at 

lower levels in the hierarchy.1 The baseline WBS configuration will be documented as part of the program plan 

and utilized to structure the SEMP. The cost estimates 

and the WBS dictionary are maintained throughout the 

project’s life cycle to reflect the project’s current scope. 

The preparation and approval of three key program/

project documents, the Formulation Authorization Document (FAD), the program commitment agreement, and 

the program/project plans are significant contributors to 

early WBS development.

The initial contents of these documents will establish the 

purpose, scope, objectives, and applicable agreements 

for the program of interest and will include a list of approved projects, control plans, management approaches, 

and any commitments and constraints identified.

The technical team selects the appropriate system design 

processes to be employed in the top-down definition of 

each product in the system structure. Subdivision of the 

project and system architecture into smaller, more manageable components will provide logical summary points 

for assessing the overall project’s accomplishments and 

for measuring cost and schedule performance. 

Once the initial mission goals and objectives have evolved 

into the build-to or final design, the WBS will be refined 

and updated to reflect the evolving scope and architecture of the project and the bottom-up realization of each 

product in the system structure.

Throughout the applicable life-cycle phases, the WBS 

and WBS dictionary will be updated to reflect the project’s current scope and to ensure control of high-risk and 

cost/schedule performance issues.

6.1.2.2 Cost Definition and Modeling

This subsection deals with the role of cost in the systems 

analysis and engineering process, how to measure it, 

how to control it, and how to obtain estimates of it. The 

reason costs and their estimates are of great importance 

1

IEEE Standard 1220, Section C.3, “The system products 

and life cycle enabling products should be jointly engineered 

and once the enabling products and services are identified, 

should be treated as systems in the overall system hierarchy.”

Figure 6.1-5 Examples of WBS development 

errors

Error 1: Functions Without Products

Error 3: Inconsistency With PBS

Error 2: Inappropriate Branches

Project

Management Engineering Fabrication Verication

Distributed

Information System

Software Hardware

Transmitter TWT Amplier

Subsystem Subsystem

Transmitter

TWT Amplier

WBS PBS
126  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

in systems engineering goes back to a principal objective of systems engineering: fulfilling the system’s goals 

in the most cost-effective manner. The cost of each alternative should be one of the most important outcome 

variables in trade studies performed during the systems 

engineering process. 

One role, then, for cost estimates is in helping to choose 

rationally among alternatives. Another is as a control 

mechanism during the project life cycle. Cost measures 

produced for project life-cycle reviews are important in 

determining whether the system goals and objectives 

are still deemed valid and achievable, and whether constraints and boundaries are worth maintaining. These 

measures are also useful in determining whether system 

goals and objectives have properly flowed down through 

to the various subsystems. 

As system designs and ConOps mature, cost estimates 

should mature as well. At each review, cost estimates 

need to be presented and compared to the funds likely 

to be available to complete the project. The cost estimates 

presented at early reviews must be given special attention 

since they usually form the basis for the initial cost commitment for the project. The systems engineer must be 

able to provide realistic cost estimates to the project manager. In the absence of such estimates, overruns are likely 

to occur, and the credibility of the entire system development process, both internal and external, is threatened.

Life-Cycle Cost and Other Cost Measures

A number of questions need to be addressed so that costs 

are properly treated in systems analysis and engineering. 

These questions include:

WBS Hierarchies for Systems

It is important to note that while product-oriented in nature, the standard WBS mandated for NASA space flight projects in NPR 7120.5 approaches WBS development from a project and not a system perspective. The WBS mandated reflects the scope of a major Agency project and, therefore, is structured to include the development, operation, and disposal of more than one major system of interest during the project’s normal life cycle.

WBS hierarchies for NASA’s space flight projects will include high-level system products, such as payload, spacecraft, 

and ground systems, and enabling products and services, such as project management, systems engineering, and education. These standard product elements have been established to facilitate alignment with the Agency’s accounting, 

acquisition, and reporting systems.

Unlike the project-view WBS approach described in NPR 7120.5, creation of a technical WBS focuses on the development and realization of both the overall end product and each subproduct included as a lower level element in the 

overall system structure. 

NPR 7123.1, NASA Systems Engineering Processes and Requirements mandates a standard, systematic technical approach 

to system or end-product development and realization. Utilizing a building-block or product-hierarchy approach, the 

system architecture is successively defined and decomposed into subsystems (elements performing the operational 

functions of the system) and associated and interrelated subelements (assemblies, components, parts, and enabling 

life-cycle products).

The resulting hierarchy or family-product tree depicts the entire system architecture in a PBS. Recognized by Government and industry as a “best practice,” utilization of the PBS and its building-block configuration facilitates both the application of NPR 7123.1’s 17 common technical processes at all levels of the PBS structure and the definition and realization of successively lower level elements of the system’s hierarchy. 

Definition and application of the work effort to the PBS structure yields a series of functional subproducts or “children” 

WBS models. The overall parent or system WBS model is realized through the rollup of successive levels of these product-based, subelement WBS models. 

Each WBS model represents one unique unit or functional end product in the overall system configuration and, when 

related by the PBS into a hierarchy of individual models, represents one functional system end product or “parent” WBS 

model. 

(See NPR 7120.5, NASA Space Flight Program and Project Management Requirements.)
6.1 Technical Planning

NASA Systems Engineering Handbook  127

z What costs should be counted?

z How should costs occurring at different times be 

treated?

z What about costs that cannot easily be measured in 

dollars?

What Costs Should Be Counted 

The most comprehensive measure of the cost of an alternative is its life-cycle cost. According to NPR 7120.5, 

a system’s life-cycle cost is, “the total of the direct, indirect, recurring, nonrecurring, and other related expenses 

incurred, or estimated to be incurred, in the design, development, verification, production, operation, maintenance, support, and disposal of a project. The life-cycle 

cost of a project or system can also be defined as the total 

cost of ownership over the project or system’s life cycle 

from Formulation through Implementation. It includes 

all design, development, deployment, operation and 

maintenance, and disposal costs.”

Costs Occurring Over Time 

The life-cycle cost combines costs that typically occur over 

a period of several years. To facilitate engineering trades 

and comparison of system costs, these real year costs are 

deescalated to constant year values. This removes the 

impact of inflation from all estimates and allows ready 

comparison of alternative approaches. In those instances 

where major portfolio architectural trades are being conducted, it may be necessary to perform formal cost benefit analyses or evaluate leasing versus purchase alternatives. In those trades, engineers and cost analysts should 

follow the guidance provided in Office of Management 

and Budget (OMB) Circular A-94 on rate of return and 

net present value calculation in comparing alternatives. 

Difficult-to-Measure Costs 

In practice, estimating some costs poses special problems. These special problems, which are not unique to 

NASA systems, usually occur in two areas: (1) when alternatives have differences in the irreducible chances of 

loss of life, and (2) when externalities are present. Two 

examples of externalities that impose costs are pollution 

caused by some launch systems and the creation of orbital debris. Because it is difficult to place a dollar figure 

on these resource uses, they are generally called “incommensurable costs.” The general treatment of these types 

of costs in trade studies is not to ignore them, but instead 

to keep track of them along with other costs. If these elements are part of the trade space, it is generally advisable 

to apply Circular A-94 approaches to those trades.

Controlling Life-Cycle Costs

The project manager/systems engineer must ensure that 

the probabilistic life-cycle cost estimate is compatible 

with NASA’s budget and strategic priorities. The current 

policy is that projects are to submit budgets sufficient to 

ensure a 70 percent probability of achieving the objectives within the proposed resources. Project managers 

and systems engineers must establish processes to estimate, assess, monitor, and control the project’s life-cycle 

cost through every phase of the project. 

Early decisions in the systems engineering process tend to

have the greatest effect on the resultant system life-cycle 

cost. Typically, by the time the preferred system architecture is selected, between 50 and 70 percent of the system’s life-cycle cost has been locked in. By the time a preliminary system design is selected, this figure may be as 

high as 90 percent. This presents a major dilemma to the 

systems engineer, who must lead this selection process. 

Just at the time when decisions are most critical, the state 

of information about the alternatives is least certain. Uncertainty about costs is a fact of systems engineering, 

and that uncertainty must be accommodated by complete and careful analysis of the project risks and provision of sufficient margins (cost, technical, and schedule) 

to ensure success. There are a number of estimating techniques to assist the systems engineer and project manager in providing for uncertainty and unknown requirements. Additional information on these techniques can 

be found in the NASA Cost Estimating Handbook.

This suggests that efforts to acquire better information 

about the life-cycle cost of each alternative early in the 

project life cycle (Phases A and B) potentially have very 

high payoffs. The systems engineer needs to identify the 

principal life-cycle cost drivers and the risks associated 

with the system design, manufacturing, and operations. 

Consequently, it is particularly important with such a 

system to bring in the specialty engineering disciplines 

such as reliability, maintainability, supportability, and 

operations engineering early in the systems engineering 

process, as they are essential to proper life-cycle cost estimation. 

One mechanism for controlling life-cycle cost is to establish a life-cycle cost management program as part of the 

project’s management approach. (Life-cycle cost man-
128  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

agement has sometimes been called “design-to-life-cycle 

cost.”) Such a program establishes life-cycle cost as a design goal, perhaps with subgoals for acquisition costs or 

operations and support costs. More specifically, the objectives of a life-cycle cost management program are to:

z Identify a common set of ground rules and assumptions for life-cycle cost estimation;

z Manage to a cost baseline and maintain traceability to 

the technical baseline with documentation for subsequent cost changes;

z Ensure that best-practice methods, tools, and models 

are used for life-cycle cost analysis;

z Track the estimated life-cycle cost throughout the 

project life cycle; and, most important

z Integrate life-cycle cost considerations into the design 

and development process via trade studies and formal 

change request assessments.

Trade studies and formal change request assessments 

provide the means to balance the effectiveness and lifecycle cost of the system. The complexity of integrating 

life-cycle cost considerations into the design and development process should not be underestimated, but neither should the benefits, which can be measured in terms 

of greater cost-effectiveness. The existence of a rich set 

of potential life-cycle cost trades makes this complexity 

even greater. 

Cost-Estimating Methods

Various cost-estimating methodologies are utilized 

throughout a program’s life cycle. These include parametric, analogous, and engineering (grassroots). 

z Parametric: Parametric cost models are used in the 

early stages of project development when there is limited program and technical definition. Such models 

involve collecting relevant historical data at an aggregated level of detail and relating it to the area to be estimated through the use of mathematical techniques 

to create cost-estimating relationships. Normally, less 

detail is required for this approach than for other 

methods. 

z Analogous: This is based on most new programs 

originated or evolved from existing programs or 

simply representing a new combination of existing 

components. It uses actual costs of similar existing or 

past programs and adjusts for complexity, technical, 

or physical differences to derive the new system estimate. This method would be used when there is insufficient actual cost data to use as a basis for a detailed 

approach but there is a sufficient amount of program 

and technical definition.

z Engineering (Grassroots): These bottom-up estimates are the result of rolling up the costs estimated 

by each organization performing work described in 

the WBS. Properly done, grassroots estimates can be 

quite accurate, but each time a “what if” question is 

raised, a new estimate needs to be made. Each change 

of assumptions voids at least part of the old estimate. 

Because the process of obtaining grassroots estimates 

is typically time consuming and labor intensive, the 

number of such estimates that can be prepared during 

trade studies is in reality severely limited. 

The type of cost estimating method used will depend on 

the adequacy of program definition, level of detail required, availability of data, and time constraints. For example, during the early stages of a program, a conceptual 

study considering several options would dictate an estimating method requiring no actual cost data and limited program definition on the systems being estimated. 

A parametric model would be a sound approach at this 

point. Once a design is baselined and the program is 

more adequately defined, an analogy approach becomes 

appropriate. As detailed actual cost data are accumulated, a grassroots methodology is used.

More information on cost-estimating methods and the 

development of cost estimates can be found in the NASA 

Cost Estimating Handbook.

Integrating Cost Model Results for a Complete 

Life-Cycle Cost Estimate 

A number of parametric cost models are available for 

costing NASA systems. A list of the models currently in 

use may be found in an appendix in the NASA Cost Estimating Handbook. Unfortunately, none alone is sufficient 

to estimate life-cycle cost. Assembling an estimate of lifecycle cost often requires that several different models 

(along with the other two techniques) be used together. 

Whether generated by parametric models, analogous, 

or grassroots methods, the estimated cost of the hardware element must frequently be “wrapped” or have factors applied to estimate the costs associated with management, systems engineering, test, etc., of the systems 

being estimated. The NASA full-cost factors also must 

be applied separately. 
6.1 Technical Planning

NASA Systems Engineering Handbook  129

To integrate the costs being estimated by these different models, the systems engineer should ensure 

that the inputs to and assumptions of the models are 

consistent, that all relevant life-cycle cost components 

are covered, and that the phasing of costs is correct. 

Estimates from different sources are often expressed 

in different year constant dollars which must be combined. Appropriate inflation factors must be applied 

to enable construction of a total life-cycle cost estimate in real year dollars. Guidance on the use of inflation rates for new projects and for budget submissions for ongoing projects can be found in the annual 

NASA strategic guidance. 

Cost models frequently produce a cost estimate for the 

first unit of a hardware item, but where the project requires multiple units a learning curve can be applied to 

the first unit cost to obtain the required multiple-unit 

estimate. Learning curves are based on the concept that 

resources required to produce each additional unit decline as the total number of units produced increases. 

The learning curve concept is used primarily for uninterrupted manufacturing and assembly tasks, which are 

highly repetitive and labor intensive. The major premise 

of learning curves is that each time the product quantity 

doubles, the resources (labor hours) required to produce 

the product will reduce by a determined percentage of 

the prior quantity resource requirements. The two types 

of learning curve approaches are unit curve and cumulative average curve. The systems engineer can learn more 

about the calculation and use of learning curves in the 

NASA Cost Estimating Handbook.

Models frequently provide a cost estimate of the total 

acquisition effort without providing a recommended 

phasing of costs over the life cycle. The systems engineer 

can use a set of phasing algorithms based on the typical 

ramping-up and subsequent ramping-down of acquisition costs for that type of project if a detailed project 

schedule is not available to form a basis for the phasing 

of the effort. A normal distribution curve, or beta curve, 

is one type of function used for spreading parametrically 

derived cost estimates and for R&D contracts where costs 

build up slowly during the initial phases and then escalate as the midpoint of the contract approaches. A beta 

curve is a combination of percent spent against percent 

time elapsed between two points in time. More about 

beta curves can be found in an appendix of the NASA 

Cost Estimating Handbook.

Although parametric cost models for space systems are 

already available, their proper use usually requires a considerable investment in learning how to appropriately 

utilize the models. For projects outside of the domains 

of these existing cost models, new cost models may be 

needed to support trade studies. Efforts to develop these 

models need to begin early in the project life cycle to ensure their timely application during the systems engineering process. Whether existing models or newly created ones are used, the SEMP and its associated life-cycle 

cost management plan should identify which (and how) 

models are to be used during each phase of the project 

life cycle.

6.1.2.3 Lessons Learned 

No section on technical planning guidance would be 

complete without the effective integration and incorporation of the lessons learned relevant to the project. 

Systems Engineering Role in Lessons Learned 

Systems engineers are the main users and contributors 

to lessons learned systems. A lesson learned is knowledge or understanding gained by experience—either 

a successful test or mission or a mishap or failure. Systems engineers compile lessons learned to serve as historical documents, requirements’ rationales, and other 

supporting data analysis. Systems engineering practitioners collect lessons learned during program and project 

plans, key decision points, life-cycle phases, systems engineering processes and technical reviews. Systems engineers’ responsibilities include knowing how to utilize, 

manage, create, and store lessons learned and knowledge 

management best practices.

Utilization of Lessons Learned Best Practice

Lessons learned are important to future programs, projects, and processes because they show hypotheses and 

conclusive insights from previous projects or processes. 

Practitioners determine how previous lessons from processes or tasks impact risks to current projects and implement those lessons learned that improve design and/

or performance. 

To pull in lessons learned at the start of a project or task:

z Search the NASA Lessons Learned Information 

System (LLIS) database using keywords of interest 

to the new program or project. The process for recording lessons learned is explained in NPR 7120.6, 
130  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Lessons Learned Process. In addition, other organizations doing similar work may have publicly available databases with lessons learned. For example, the 

Chemical Safety Board has a good series of case study 

reports on mishaps.

z Supporting lessons from each engineering discipline 

should be reflected in the program and project plans. 

Even if little information was found, the search for lessons learned can be documented. 

z Compile lessons by topic and/or discipline.

z Review and select knowledge gained from particular 

lessons learned.

z Determine how these lessons learned may represent 

potential risk to the current program or project.

z Incorporate knowledge gained into the project database for risk management, cost estimate, and any 

other supporting data analysis. 

As an example, a systems engineer working on the concept for an instrument for a spacecraft might search the 

lessons learned database using the keywords “environment,” “mishap,” or “configuration management.” One of 

the lessons learned that search would bring up is #1514. 

The lesson was from Chandra. A rebaseline of the program in 1992 removed two instruments, changed Chandra’s orbit from low Earth to high elliptical, and simplified the thermal control concept from the active control 

required by one of the descoped instruments to passive “cold-biased” surface plus heaters. This change in 

thermal control concept mandated silver Teflon thermal 

control surfaces. The event driving the lesson was a severe spacecraft charging and an electrostatic discharge 

environment. The event necessitated an aggressive electrostatic discharge test and circuit protection effort that 

cost over $1 million, according to the database. The 

Teflon thermal control surfaces plus the high elliptical 

orbit created the electrostatic problem. Design solutions 

for one environment were inappropriate in another environment. The lesson learned was that any orbit modifications should trigger a complete new iteration of the systems engineering processes starting from requirements 

definition. Rebaselining a program should take into account change in the natural environment before new design decisions are made. This lesson would be valuable 

to keep in mind when changes occur to baselines on the 

program currently being worked on.

Management of Lessons Learned Best Practice

Capturing lessons learned is a function of good management practice and discipline. Too often lessons learned 

are missed because they should have been developed and 

managed within, across, or between life-cycle phases. 

There is a tendency to wait until resolution of a situation to document a lesson learned, but the unfolding of 

a problem at the beginning is valuable information and 

hard to recreate later. It is important to document a lesson 

learned as it unfolds, particularly as resolution may not 

be reached until a later phase. Since detailed lessons are 

often hard for the human mind to recover, waiting until a 

technical review or the end of a project to collect the lessons learned hinders the use of lessons and the evolution 

of practice. A mechanism for managing and leveraging 

lessons as they occur, such as monthly lessons learned 

briefings or some periodic sharing forums, facilitates incorporating lessons into practice and carrying lessons 

into the next phase.

At the end of each life-cycle phase, practitioners should 

use systems engineering processes and procedural tasks 

as control gate cues. All information passed across control gates must be managed in order to successfully enter 

the next phase, process, or task. 

The systems engineering practitioner should make sure 

all lessons learned in the present phase are concise and 

conclusive. Conclusive lessons learned contain series of 

events that formulate abstracts and driving events. Irresolute lessons learned may be rolled into the next phase 

to await proper supporting evidence. Project managers 

and the project technical team are to make sure lessons 

learned are recorded in the Agency database at the end 

of all life-cycle phases, major systems engineering processes, key decision points, and technical reviews.
NASA Systems Engineering Handbook  131

6.2 Requirements Management

Requirements management activities apply to the management of all stakeholder expectations, customer requirements, and technical product requirements down 

to the lowest level product component requirements 

(hereafter referred to as expectations and requirements). 

The Requirements Management Process is used to: 

z Manage the product requirements identified, baselined, and used in the definition of the WBS model 

products during system design; 

z Provide bidirectional traceability back to the top WBS 

model requirements; and 

z Manage the changes to established requirement baselines over the life cycle of the system products.

6.2.1 Process Description

Figure 6.2-1 provides a typical flow diagram for the Requirements Management Process and identifies typical 

inputs, outputs, and activities to consider in addressing 

requirements management. 

6.2.1.1 Inputs

There are several fundamental inputs to the Requirements Management Process.

z Requirements and stakeholder expectations are identified during the system design processes, primarily 

from the Stakeholder Expectation Definition Process 

and the Technical Requirements Definition Process. 

z The Requirements Management Process must be prepared to deal with requirement change requests that 

can be generated at any time during the project life 

cycle or as a result of reviews and assessments as part 

of the Technical Assessment Process. 

z TPM estimation/evaluation results from the Technical Assessment Process provide an early warning of 

Figure 6.2-1 Requirements Management Process

Expectations and 

Requirements to Be

Managed

From system design processes 

From Product Verification

and Product Validation

Processes

To Technical Data

Management Process

To Configuration

Management Process

Prepare to conduct

requirements management

Conduct requirements

management

Conduct expectations and 

requirements traceability

Manage expectations

and requirements changes

Capture work products from

requirements management

activities

Requirements Change

Requests

TPM Estimation/

Evaluation Results

Requirements

Documents

Approved Changes to

Requirements Baselines

Requirements

Management Work

Products

From project and Technical

Assessment Process

From Technical

Assessment Process

Product Verication and

Product Validation Results

Note: Requirements can be generated from nonobvious stakeholders and may not directly support the 

current mission and its objectives, but instead provide an opportunity to gain additional benefits or 

information that can support the Agency or the Nation. Early in the process, the systems engineer can 

help identify potential areas where the system can be 

used to collect unique information that is not directly 

related to the primary mission. Often outside groups 

are not aware of the system goals and capabilities until it is almost too late in the process.
132  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

the adequacy of a design in satisfying selected critical 

technical parameter requirements. Variances from 

expected values of product performance may trigger 

changes to requirements.

z Product verification and product validation results from 

the Product Verification and Product Validation Processes are mapped into the requirements database with 

the goal of verifying and validating all requirements.

6.2.1.2 Process Activities

The Requirements Management Process involves managing all changes to expectations and requirements baselines over the life of the product and maintaining bidirectional traceability between stakeholder expectations, 

customer requirements, technical product requirements, 

product component requirements, design documents, 

and test plans and procedures. The successful management of requirements involves several key activities:

z Establish a plan for executing requirements management. 

z Receive requirements from the system design processes 

and organize them in a hierarchical tree structure.

z Establish bidirectional traceability between requirements. 

z Validate requirements against the stakeholder expectations, the mission objectives and constraints, the operational objectives, and the mission success criteria. 

z Define a verification method for each requirement.

z Baseline requirements.

z Evaluate all change requests to the requirements baseline over the life of the project and make changes if 

approved by change board.

z Maintain consistency between the requirements, the 

ConOps, and the architecture/design and initiate corrective actions to eliminate inconsistencies.

Requirements Traceability

As each requirement is documented, its bidirectional 

traceability should be recorded. Each requirement should 

be traced back to a parent/source requirement or expectation in a baselined document or identify the requirement as self-derived and seek concurrence on it from the 

next higher level requirements sources. Examples of selfderived requirements are requirements that are locally 

adopted as good practices or are the result of design decisions made while performing the activities of the Logical Decomposition and Design Solution Processes. 

The requirements should be evaluated, independently 

if possible, to ensure that the requirements trace is correct and that it fully addresses its parent requirements. 

If it does not, some other requirement(s) must complete 

fulfillment of the parent requirement and be included in 

the traceability matrix. In addition, ensure that all toplevel parent document requirements have been allocated 

to the lower level requirements. If there is no parent for 

a particular requirement and it is not an acceptable selfderived requirement, it should be assumed either that 

the traceability process is flawed and should be redone 

or that the requirement is “gold plating” and should be 

eliminated. Duplication between levels must be resolved. 

If a requirement is simply repeated at a lower level and it 

is not an externally imposed constraint, perhaps the requirement does not belong at the higher level. Requirements traceability is usually recorded in a requirements 

matrix. (See Appendix D.)

Definitions

Traceability: A discernible association between two 

or more logical entities such as requirements, system 

elements, verifications, or tasks. 

Bidirectional traceability: An association between 

two or more logical entities that is discernible in either direction (i.e., to and from an entity).

Requirements Validation

An important part of requirements management is the 

validation of the requirements against the stakeholder 

expectations, the mission objectives and constraints, the 

operational objectives, and the mission success criteria. 

Validating requirements can be broken into three steps:

1. Are Requirements Written Correctly: Identify and 

correct requirements “shall” statement format errors 

and editorial errors.

2. Are Requirements Technically Correct: A few 

trained reviewers from the technical team identify 

and remove as many technical errors as possible 

before having all the relevant stakeholders review 

the requirements. The reviewers should check that 

the requirement statements (1) have bidirectional 

traceability to the baselined stakeholder expectations; (2) were formed using valid assumptions; and 

(3) are essential to, and consistent with, designing 

and realizing the appropriate product solution form 
6.2 Requirements Management

NASA Systems Engineering Handbook  133

that will satisfy the applicable product-line life-cycle 

phase success criteria. 

3. Do Requirements Satisfy Stakeholders: All relevant 

stakeholder groups identify and remove defects. 

Requirements validation results are often a deciding 

factor in whether to proceed with the next process of Logical Decomposition or Design Solution Definition. The 

project team should be prepared to: (1) demonstrate that 

the project requirements are complete and understandable; (2) demonstrate that prioritized evaluation criteria 

are consistent with requirements and the operations and 

logistics concepts; (3) confirm that requirements and 

evaluation criteria are consistent with stakeholder needs; 

(4) demonstrate that operations and architecture concepts support mission needs, goals, objectives, assumptions, guidelines, and constraints; and (5) demonstrate 

that the process for managing change in requirements is 

established, documented in the project information repository, and communicated to stakeholders.

Managing Requirement Changes

Throughout Phases A and B, changes in requirements 

and constraints will occur. It is imperative that all changes 

be thoroughly evaluated to determine the impacts on the 

architecture, design, interfaces, ConOps, and higher and 

lower level requirements. Performing functional and 

sensitivity analyses will ensure that the requirements are 

realistic and evenly allocated. Rigorous requirements 

verification and validation ensure that the requirements 

can be satisfied and conform to mission objectives. All 

changes must be subjected to a review and approval cycle 

to maintain traceability and to ensure that the impacts 

are fully assessed for all parts of the system.

Once the requirements have been validated and reviewed in the System Requirements Review they are 

placed under formal configuration control. Thereafter, 

any changes to the requirements must be approved by 

the Configuration Control Board (CCB). The systems 

engineer, project manager, and other key engineers usually participate in the CCB approval processes to assess 

the impact of the change including cost, performance, 

programmatic, and safety. 

The technical team should also ensure that the approved 

requirements are communicated in a timely manner to 

all relevant people. Each project should have already established the mechanism to track and disseminate the 

latest project information. Further information on Configuration Management (CM) can be found in Section 6.5. 

Key Issues for Requirements Management

Requirements Changes

Effective management of requirements changes requires 

a process that assesses the impact of the proposed 

changes prior to approval and implementation of the 

change. This is normally accomplished through the use 

of the Configuration Management Process. In order for 

CM to perform this function, a baseline configuration 

must be documented and tools used to assess impacts 

to the baseline. Typical tools used to analyze the change 

impacts are as follows:

z Performance Margins: This tool is a list of key performance margins for the system and the current status 

of the margin. For example, the propellant performance margin will provide the necessary propellant 

available versus the propellant necessary to complete 

the mission. Changes should be assessed for their impact to performance margins.

z CM Topic Evaluators List: This list is developed by 

the project office to ensure that the appropriate persons are evaluating the changes and providing impacts to the change. All changes need to be routed to 

the appropriate individuals to ensure that the change 

has had all impacts identified. This list will need to be 

updated periodically.

z Risk System and Threats List: The risk system can 

be used to identify risks to the project and the cost, 

schedule, and technical aspects of the risk. Changes 

to the baseline can affect the consequences and likelihood of identified risk or can introduce new risk to 

the project. A threats list is normally used to identify 

the costs associated with all the risks for the project. 

Project reserves are used to mitigate the appropriate 

risk. Analyses of the reserves available versus the 

needs identified by the threats list assist in the prioritization for reserve use.

The process for managing requirements changes needs 

to take into account the distribution of information related to the decisions made during the change process. 

The Configuration Management Process needs to communicate the requirements change decisions to the affected organizations. During a board meeting to approve 

a change, actions to update documentation need to be 

included as part of the change package. These actions 
134  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

should be tracked to ensure that affected documentation 

is updated in a timely manner.

Feedback to the Requirements Baseline

During development of the system components, it will 

be necessary to provide feedback to the requirements. 

This feedback is usually generated during the product 

design, validation, and verification processes. The feedback to the project will include design implementation 

issues that impact the interfaces or operations of the 

system. In many cases, the design may introduce constraints on how the component can be operated, maintained, or stored. This information needs to be communicated to the project team to evaluate the impact to the 

affected system operation or architecture. Each system 

component will optimize the component design and operation. It is the systems engineering function to evaluate 

the impact of this optimization at the component level to 

the optimization of the entire system. 

Requirements Creep

“Requirements creep” is the term used to describe the 

subtle way that requirements grow imperceptibly during 

the course of a project. The tendency for the set of requirements is to relentlessly increase in size during the 

course of development, resulting in a system that is more 

expensive and complex than originally intended. Often 

the changes are quite innocent and what appear to be 

changes to a system are really enhancements in disguise. 

However, some of the requirements creep involves truly 

new requirements that did not exist, and could not have 

been anticipated, during the Technical Requirements 

Definition Process. These new requirements are the result of evolution, and if we are to build a relevant system, 

we cannot ignore them. 

There are several techniques for avoiding or at least minimizing requirements creep:

z In the early requirements definition phase, flush out 

the conscious, unconscious, and undreamt-of requirements that might otherwise not be stated.

z Establish a strict process for assessing requirement 

changes as part of the Configuration Management 

Process. 

z Establish official channels for submitting change requests. This will determine who has the authority to 

generate requirement changes and submit them formally to the CCB (e.g., the contractor-designated representative, project technical leads, customer/science 

team lead, or user). 

z Measure the functionality of each requirement change 

request and assess its impact on the rest of the system. 

Compare this impact with the consequences of not 

approving the change. What is the risk if the change 

is not approved?

z Determine if the proposed change can be accommodated within the fiscal and technical resource budgets. 

If it cannot be accommodated within the established 

resource margins, then the change most likely should 

be denied. 

6.2.1.3 Outputs

Typical outputs from the requirements management activities are:

z Requirements Documents: Requirements documents 

are submitted to the Configuration Management Process when the requirements are baselined. The official 

controlled versions of these documents are generally 

maintained in electronic format within the requirements management tool that has been selected by the 

project. In this way they are linked to the requirements 

matrix with all of its traceable relationships.

z Approved Changes to the Requirements Baselines:

Approved changes to the requirements baselines are 

issued as an output of the Requirements Management 

Process after careful assessment of all the impacts of 

the requirements change across the entire product 

or system. A single change can have a far-reaching 

ripple effect which may result in several requirement 

changes in a number of documents.

z Various Requirements Management Work Products: Requirements management work products are 

any reports, records, and undeliverable outcomes of 

the Requirements Management Process. For example, 

the bidirectional traceability status would be one of 

the work products that would be used in the verification and validation reports.

6.2.2 Requirements Management 

Guidance

6.2.2.1 Requirements Management Plan

The technical team should prepare a plan for performing the requirements management activities. This plan is 

normally part of the SEMP but also can stand alone. The 

plan should:
6.2 Requirements Management

NASA Systems Engineering Handbook  135

z Identify the relevant stakeholders who will be involved 

in the Requirements Management Process (e.g., those 

who may be affected by, or may affect, the product as 

well as the processes).

z Provide a schedule for performing the requirements 

management procedures and activities.

z Assign responsibility, authority, and adequate resources for performing the requirements management activities, developing the requirements management work products, and providing the requirements 

management services defined in the activities (e.g., 

staff, requirements management database tool, etc.).

z Define the level of configuration management/data 

management control for all requirements management work products. 

z Identify the training for those who will be performing 

the requirements management activities.

6.2.2.2 Requirements Management Tools

For small projects and products, the requirements can 

usually be managed using a spreadsheet program. However, the larger programs and projects require the use 

of one of the available requirements management tools. 

In selecting a tool, it is important to define the project’s 

procedure for specifying how the requirements will be 

organized in the requirements management database 

tool and how the tool will be used. It is possible, given 

modern requirements management tools, to create a 

requirements management database that can store and 

sort requirements data in multiple ways according to the 

particular needs of the technical team. The organization 

of the database is not a trivial exercise and has consequences on how the requirements data can be viewed for 

the life of the project. Organize the database so that it 

has all the views into the requirements information that 

the technical team is likely to need. Careful consideration should be given to how flowdown of requirements 

and bidirectional traceability will be represented in the 

database. Sophisticated requirements management database tools also have the ability to capture numerous requirement attributes in the tools’ requirements matrix, 

including the requirements traceability and allocation 

links. For each requirement in the requirements matrix, 

the verification method(s), level, and phase are documented in the verification requirements matrix housed 

in the requirements management database tool (e.g., the 

tool associates the attributes of method, level, and phase 

with each requirement). It is important to make sure that 

the requirements management database tool is compatible with the verification and validation tools chosen for 

the project.
136  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

The management and control of interfaces is crucial to 

successful programs or projects. Interface management 

is a process to assist in controlling product development when efforts are divided among parties (e.g., Government, contractors, geographically diverse technical 

teams, etc.) and/or to define and maintain compliance 

among the products that must interoperate.

6.3.1 Process Description

Figure 6.3-1 provides a typical flow diagram for the Interface Management Process and identifies typical inputs, outputs, and activities to consider in addressing 

interface management.

6.3.1.1 Inputs

Typical inputs needed to understand and address interface management would include the following:

z System Description: This allows the design of the 

system to be explored and examined to determine 

where system interfaces exist. Contractor arrangements will also dictate where interfaces are needed.

z System Boundaries: Document physical boundaries, 

components, and/or subsystems, which are all drivers 

for determining where interfaces exist.

z Organizational Structure: Decide which organization will dictate interfaces, particularly when there is 

the need to jointly agree on shared interface param6.3 Interface Management

eters of a system. The program and project WBS will 

also provide interface boundaries.

z Boards Structure: The SEMP should provide insight 

into organizational interface responsibilities and drive 

out interface locations.

z Interface Requirements: The internal and external 

functional and physical interface requirements developed as part of the Technical Requirements Definition Process for the product(s).

z Interface Change Requests: These include changes 

resulting from program or project agreements or 

changes on the part of the technical team as part of 

the Technical Assessment Process.

6.3.1.2 Process Activities

During project Formulation, the ConOps of the product 

is analyzed to identify both external and internal interfaces. This analysis will establish the origin, destination, 

stimuli, and special characteristics of the interfaces that 

need to be documented and maintained. As the system 

structure and architecture emerges, interfaces will be 

added and existing interfaces will be changed and must 

be maintained. Thus, the Interface Management Process 

has a close relationship to other areas, such as requirements definition and configuration management during 

this period. Typically, an Interface Working Group 

(IWG) establishes communication links between those 

From project and

Technical Assessment

Process

From user or program and

system design processes 

To Technical Data

Management Process

To Conguration

Management Process

Interface

Requirements 

Interface Control

Documents 

Approved Interface

Requirement

Changes

Interface Management

Work Products

Prepare or update interface

management procedures 

Conduct interface management during

system design activities for each WBSlike model in the system structure

Conduct interface control 

Conduct interface management during

product integration activities 

Capture work products from interface

management activities 

Interface

Changes 

Figure 6.3-1 Interface Management Process
6.3 Interface Management

NASA Systems Engineering Handbook  137

responsible for interfacing systems, end products, enabling products, and subsystems. The IWG has the responsibility to ensure accomplishment of the planning, 

scheduling, and execution of all interface activities. An 

IWG is typically a technical team with appropriate technical membership from the interfacing parties (e.g., the 

project, the contractor, etc.). 

During product integration, interface management activities would support the review of integration and assembly procedures to ensure interfaces are properly 

marked and compatible with specifications and interface 

control documents. The interface management process 

has a close relationship to verification and validation. Interface control documentation and approved interface 

requirement changes are used as inputs to the Product 

Verification Process and the Product Validation Process, 

particularly where verification test constraints and interface parameters are needed to set the test objectives and 

test plans. Interface requirements verification is a critical 

aspect of the overall system verification.

6.3.1.3 Outputs

Typical outputs needed to capture interface management 

would include interface control documentation. This is 

the documentation that identifies and captures the interface information and the approved interface change requests. Types of interface documentation include the Interface Requirements Document (IRD), Interface Control 

Document/Drawing (ICD), Interface Definition Document (IDD), and Interface Control Plan (ICP). These outputs will then be maintained and approved using the Configuration Management Process and become a part of the 

overall technical data package for the project.

6.3.2 Interface Management Guidance

6.3.2.1 Interface Requirements Document

An interface requirement defines the functional, performance, electrical, environmental, human, and physical 

requirements and constraints that exist at a common 

boundary between two or more functions, system elements, configuration items, or systems. Interface requirements include both logical and physical interfaces. They 

include, as necessary, physical measurements, definitions of sequences of energy or information transfer, and 

all other significant interactions between items. For example, communication interfaces involve the movement 

and transfer of data and information within the system, 

and between the system and its environment. Proper 

evaluation of communications requirements involves 

definition of both the structural components of communications (e.g., bandwidth, data rate, distribution, etc.) 

and content requirements (what data/information is being communicated, what is being moved among the system components, and the criticality of this information 

to system functionality). Interface requirements can be 

derived from the functional allocation if function inputs 

and outputs have been defined. For example: 

z If function F1 outputs item A to function F2, and 

z Function F1 is allocated to component C1, and 

z Function F2 is allocated to component C2, 

z Then there is an implicit requirement that the interface between components C1 and C2 pass item A, 

whether item A is a liquid, a solid, or a message containing data.

The IRD is a document that defines all physical, functional, and procedural interface requirements between 

two or more end items, elements, or components of a 

system and ensures project hardware and software compatibility. An IRD is composed of physical and functional requirements and constraints imposed on hardware configuration items and/or software configuration 

items. The purpose of the IRD is to control the interfaces 

between interrelated components of the system under 

development, as well as between the system under development and any external systems (either existing or 

under development) that comprise a total architecture. 

Interface requirements may be contained in the SRD 

until the point in the development process where the individual interfaces are determined. IRDs are useful when 

separate organizations are developing components of the 

system or when the system must levy requirements on 

other systems outside program/project control. During 

both Phase A and Phase B, multiple IRDs are drafted for 

different levels of interfaces. By SRR, draft IRDs would be 

complete for system-to-external-system interfaces (e.g., 

the shuttle to the International Space Station), and segment-to-segment interfaces (e.g., the shuttle to the launch 

pad). An IRD generic outline is described in Appendix L.

6.3.2.2 Interface Control Document or 

Interface Control Drawing

An interface control document or drawing details the 

physical interface between two system elements, including the number and types of connectors, electrical 

parameters, mechanical properties, and environmental 

constraints. The ICD identifies the design solution to the 
138  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

interface requirement. ICDs are useful when separate 

organizations are developing design solutions to be adhered to at a particular interface. 

6.3.2.3 Interface Definition Document 

An IDD is a unilateral document controlled by the enditem provider, and it basically provides the details of the 

interface for a design solution that is already established. 

This document is sometimes referred to as a “one-sided 

ICD.” The user of the IDD is provided connectors, electrical parameters, mechanical properties, environmental 

constraints, etc., of the existing design. The user must 

then design the interface of the system to be compatible 

with the already existing design interface. 

6.3.2.4 Interface Control Plan

An ICP should be developed to address the process for 

controlling identified interfaces and the related interface 

documentation. Key content for the ICP is the list of interfaces by category and who owns the interface. The 

ICP should also address the configuration control forum 

and mechanisms to implement the change process (e.g., 

Preliminary Interface Revision Notice (PIRN)/Interface 

Revision Notice (IRN)) for the documents.

Typical Interface Management Checklist

z Use the generic outline provided when developing 

the IRD. Define a “reserved” placeholder if a paragraph or section is not applicable.

z Ensure that there are two or more specifications 

that are being used to serve as the parent for the 

IRD specific requirements. 

z Ensure that “shall” statements are used to define 

specific requirements. 

z Each organization must approve and sign the IRD. 

z A control process must be established to manage 

changes to the IRD. 

z Corresponding ICDs are developed based upon the 

requirements in the IRD. 

z Confirm connectivity between the interface requirements and the Product Verification and Product Validation Processes.

z Define the SEMP content to address interface management.

z Each major program or project should include an 

ICP to describe the how and what of interface management products.
NASA Systems Engineering Handbook  139

The Technical Risk Management Process is one of the 

crosscutting technical management processes. Risk is defined as the combination of (1) the probability that a program or project will experience an undesired event and 

(2) the consequences, impact, or severity of the undesired event, were it to occur. The undesired event might 

come from technical or programmatic sources (e.g., a 

cost overrun, schedule slippage, safety mishap, health 

problem, malicious activities, environmental impact, 

6.4 Technical Risk Management

or failure to achieve a needed scientific or technological objective or success criterion). Both the probability 

and consequences may have associated uncertainties. 

Technical risk management is an organized, systematic 

risk-informed decisionmaking discipline that proactively identifies, analyzes, plans, tracks, controls, communicates, documents, and manages risk to increase 

the likelihood of achieving project goals. The Technical 

Risk Management Process focuses on project objectives, 

Key Concepts in Technical Risk Management 

z Risk: Risk is a measure of the inability to achieve overall program objectives within defined cost, schedule, and technical constraints and has two components: (1) the probability of failing to achieve a particular outcome and (2) the 

consequences/impacts of failing to achieve that outcome. 

z Cost Risk: This is the risk associated with the ability of the program/project to achieve its life-cycle cost objectives and 

secure appropriate funding. Two risk areas bearing on cost are (1) the risk that the cost estimates and objectives are 

not accurate and reasonable and (2) the risk that program execution will not meet the cost objectives as a result of a 

failure to handle cost, schedule, and performance risks.

z Schedule Risk: Schedule risks are those associated with the adequacy of the time estimated and allocated for the development, production, implementation, and operation of the system. Two risk areas bearing on schedule risk are (1) 

the risk that the schedule estimates and objectives are not realistic and reasonable and (2) the risk that program execution will fall short of the schedule objectives as a result of failure to handle cost, schedule, or performance risks.

z Technical Risk: This is the risk associated with the evolution of the design and the production of the system of interest affecting the level of performance necessary to meet the stakeholder expectations and technical requirements. 

The design, test, and production processes (process risk) influence the technical risk and the nature of the product as 

depicted in the various levels of the PBS (product risk).

z Programmatic Risk: This is the risk associated with action or inaction from outside the project, over which the project manager has no control, but which may have significant impact on the project. These impacts may manifest 

themselves in terms of technical, cost, and/or schedule. This includes such activities as: International Traffic in Arms 

Requirements (ITAR), import/export control, partner agreements with other domestic or foreign organizations, congressional direction or earmarks, Office of Management and Budget direction, industrial contractor restructuring, external organizational changes, etc.

z Hazard Versus Risk: Hazard is distinguished from risk. A hazard represents a potential for harm, while risk includes consideration of not only the potential for harm, but also the scenarios leading to adverse outcomes and the likelihood of 

these outcomes. In the context of safety, “risk” considers the likelihood of undesired consequences occurring.

z Probabilistic Risk Assessment (PRA): PRA is a scenario-based risk assessment technique that quantifies the likelihoods of various possible undesired scenarios and their consequences, as well as the uncertainties in the likelihoods 

and consequences. Traditionally, design organizations have relied on surrogate criteria such as system redundancy 

or system-level reliability measures, partly because the difficulties of directly quantifying actual safety impacts, as opposed to simpler surrogates, seemed insurmountable. Depending on the detailed formulation of the objectives hierarchy, PRA can be applied to quantify Technical Performance Measures (TPMs) that are very closely related to fundamental objectives (e.g., Probability of Loss of Crew (P(LOC))). PRA focuses on the development of a comprehensive 

scenario set, which has immediate application to identify key and candidate contributors to risk. In all but the simplest 

systems, this requires the use of models to capture the important scenarios, to assess consequences, and to systematically quantify scenario likelihoods. These models include reliability models, system safety models, simulation models, performance models, and logic models.
140  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

bringing to bear an analytical basis for risk management 

decisions and the ensuing management activities, and a 

framework for dealing with uncertainty.

Strategies for risk management include transferring performance risk, eliminating the risk, reducing the likelihood of undesired events, reducing the negative effects 

of the risk (i.e., reducing consequence severity), reducing 

uncertainties if warranted, and accepting some or all of 

the consequences of a particular risk. Once a strategy 

is selected, technical risk management ensures its successful implementation through planning and implementation of the risk tracking and controlling activities. 

Technical risk management focuses on risk that relates 

to technical performance. However, management of 

technical risk has an impact on the nontechnical risk by 

affecting budget, schedule, and other stakeholder expectations. This discussion of technical risk management is 

applicable to technical and nontechnical risk issues, but 

the focus of this section is on technical risk issues.

6.4.1 Process Description

Figure 6.4-1 provides a typical flow diagram for the Technical Risk Management Process and identifies typical inputs, activities, and outputs to consider in addressing 

technical risk management. 

6.4.1.1 Inputs

The following are typical inputs to technical risk management:

z Plans and Policies: Risk management plan, risk reporting requirements, systems engineering management plan, form of technical data products, and policy 

input to metrics and thresholds.

z Technical Inputs: Technical performance measures, 

program alternatives to be assessed, technical issues, 

and current program baseline.

z Inputs Needed for Risk Analysis of Alternatives:

Design information and relevant experience data.

6.4.1.2 Process Activities

Technical risk management is an iterative process that considers activity requirements, constraints, and priorities to:

z Identify and assess the risks associated with the implementation of technical alternatives;

z Analyze, prioritize, plan, track and control risk and 

the implementation of the selected alternative; 

z Plan, track, and control the risk and the implementation of the selected alternative; 

z Implement contingency action plans as triggered;

Figure 6.4-1 Technical Risk Management Process

From Technical

Assessment and

Decision Analysis

Processes 

From project and all

technical processes

To project and Technical

Data Management

Process 

To Technical Data

Management Process

To Technical

Planning Process

Technical Risk Status

Measurements 

Technical Risk

Reporting

Requirements 

Technical Risk

Issues

Technical Risk

Mitigation and/or

Contingency Actions

Technical Risk

Reports 

Work Products of

Technical Risk

Management

From project and

Technical Assessment

Process 

From project

Project Risk

Management Plan 

Prepare a strategy to conduct technical

risk management

Identify technical risks

Prepare for technical risk mitigation

Conduct technical risk assessment

Monitor the status of each technical

risk periodically 

Implement technical risk mitigation and

contingency action plans as triggered 

Capture work products from technical

risk management activities
6.4 Technical Risk Management

NASA Systems Engineering Handbook  141

z Communicate, deliberate, and document work products and the risk; and

z Iterate with previous steps in light of new information 

throughout the life cycle.

6.4.1.3 Outputs

Following are key technical risk outputs from activities:

z Plans and Policies: Baseline-specific plan for tracking 

and controlling risk

z Technical Outputs: Technical risk mitigation or contingency actions and tracking results, status findings, 

and emergent issues

z Outputs from Risk Analysis of Alternatives: Identified, analyzed, prioritized, and assigned risk; and risk 

analysis updates

6.4.2 Technical Risk Management Guidance

A widely used conceptualization of risk is the scenarios, likelihoods, and consequences concept as shown 

in Figures 6.4-2 and 6.4-3. 

The scenarios, along with 

consequences, likelihoods, 

and associated uncertainties, make up the complete 

risk triplet (risk as a set of 

triplets—scenarios, likelihoods, consequences). The 

triplet concept applies in principle to all risk types, and 

includes the information needed for quantifying simpler 

measures, such as expected consequences. Estimates of 

expected consequences (probability or frequency multiplied by consequences) alone do not adequately inform 

technical decisions. Scenario-based analyses provide 

more of the information that risk-informed decisions 

need. For example, a rare but severe risk contributor 

may warrant a response different from that warranted 

by a frequent, less severe contributor, even though both 

have the same expected consequences. In all but the simplest systems, this requires the use of detailed models to 

capture the important scenarios, to assess consequences, 

and to systematically quantify scenario likelihoods. For 

additional information on probabilistic risk assessments, 

refer to NPR 8705.3, Probabilistic Risk Assessment Procedures Guide for NASA Managers and Practitioners.

Figure 6.4-2 Scenario-based modeling of hazards

Accident Mitigation Layers

Safety Adverse

Consequence 

Hazards

System does not

limit the severity

of consequence

Accident Prevention Layers 

Initiating

Event

Accident

(Mishap) 

System does not

compensate

(failure of controls)

Hazards

RISK �

Structure of Scenario

Likelihood and

Its Uncertainty

Consequence Severity

and Its Uncertainty

Structure of Scenario

Likelihood and

Its Uncertainty

Consequence Severity

and Its Uncertainty

Structure of Scenario

Likelihood and

Its Uncertainty

Consequence Severity

and Its Uncertainty

Figure 6.4-3 Risk as a set of triplets 
142  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

6.4.2.1 Role of Continuous Risk Management 

in Technical Risk Management 

Continuous Risk Management (CRM) is a widely used 

technique within NASA, initiated at the beginning and 

continuing throughout the program life cycle to monitor and control risk. It is an iterative and adaptive process, which promotes the successful handling of risk. 

Each step of the paradigm builds on the previous step, 

leading to improved designs and processes through the 

feedback of information generated. Figure 6.4-4 suggests 

this adaptive feature of CRM. 

A brief overview of CRM is provided below for reference:

z Identify: Identify program risk by identifying scenarios having adverse consequences (deviations from 

program intent). CRM addresses risk related to safety, 

technical performance, cost, schedule, and other risk 

that is specific to the program. 

z Analyze: Estimate the likelihood and consequence 

components of the risk through analysis, including 

uncertainty in the likelihoods and consequences, and 

the timeframes in which risk mitigation actions must 

be taken.

z Plan: Plan the track and control actions. Decide what 

will be tracked, decision thresholds for corrective action, and proposed risk control actions. 

z Track: Track program observables relating to TPMs 

(performance data, schedule variances, etc.), measuring how close the program performance is compared to its plan.

z Control: Given an emergent risk issue, execute the 

appropriate control action and verify its effectiveness.

z Communicate, Deliberate, and Document: This is 

an element of each of the previous steps. Focus on understanding and communicating all risk information 

throughout each program phase. Document the risk, 

risk control plans, and closure/acceptance rationale. 

Deliberate on decisions throughout the CRM process.

6.4.2.2 The Interface Between CRM and RiskInformed Decision Analysis

Figure 6.4-5 shows the interface between CRM and riskinformed decision analysis. (See Subsection 6.8.2 for 

more on the Decision Analysis Process.) The following 

steps are a risk-informed Decision Analysis Process:

1. Formulate the objectives hierarchy and TPMs.

2. Propose and identify decision alternatives. Alternatives from this process are combined with the alternatives identified in the other systems engineering 

processes, including design solution, verification, 

and validation as well as production.

3. Perform risk analysis and rank decision alternatives.

4. Evaluate and recommend decision alternative.

5. Track the implementation of the decision.

These steps support good decisions by focusing first on 

objectives, next on developing decision alternatives with 

those objectives clearly in mind, and using decision alternatives that have been developed under other systems 

engineering processes. The later steps of the decision 

analysis interrelate heavily with the Technical Risk Management Process, as indicated in Figure 6.4-5.

The risk analysis of decision alternatives (third box) not 

only guides selection of a preferred alternative, it also carries out the “identify” and “analyze” steps of CRM. Selection of a preferred alternative is based in part on an understanding of the risks associated with that alternative. 

Alternative selection is followed immediately by a planning activity in which key implementation aspects are 

addressed, namely, risk tracking and control, including 

risk mitigation if necessary. Also shown conceptually on 

Figure 6.4-5 is the interface between risk management 

and other technical and programmatic processes.

Risk Analysis, Performing Trade Studies and 

Ranking

The goal of this step is to carry out the kinds and amounts 

of analysis needed to characterize the risk for two purposes: ranking risk alternatives, and performing the 

“identify” and “analyze” steps of CRM. 

Figure 6.4-4 Continuous risk management

Communicate,

Deliberate, and

Document

Control

Identify

Analyze

Track

Plan
6.4 Technical Risk Management

NASA Systems Engineering Handbook  143

To support ranking, trade studies may be performed. 

TPMs that can affect the decision outcome are quantified including uncertainty as appropriate. 

To support the “identify” and “analyze” steps of CRM, 

the risk associated with the preferred alternative is analyzed in detail. Refer to Figure 6.4-6. Risk analysis can 

take many forms, ranging from qualitative risk identification (essentially scenarios and consequences, without 

performing detailed quantification of likelihood using 

techniques such as Failure Mode and Effects Analysis 

(FMEA) and fault trees), to highly quantitative methods 

such as PRA. The analysis stops when the technical 

case is made; if simpler, more qualitative methods suffice, then more detailed methods need not be applied. 

The process is then identified, planned for, and continuously checked. Selection and application of appropriate 

methods is discussed as follows.

6.4.2.3 Selection and Application of 

Appropriate Risk Methods

The nature and context of the problem, and the specific 

TPMs, determine the methods to be used. In some projects, qualitative methods are adequate for making decisions; in others, these methods are not precise enough to 

appropriately characterize the magnitude of the problem, 

or to allocate scarce risk reduction resources. The technical team needs to decide whether risk identification 

and judgment-based characterization are adequate, or 

whether the improved quantification of TPMs through 

more detailed risk analysis is justified. In making that determination, the technical team must balance the cost of 

risk analysis against the value of the additional information to be gained. The concept of “value of information” 

is central to making the determination of what analysis 

is appropriate and to what extent uncertainty needs to be 

quantified. 

CRM Process

Technical Risk Management

Formulation of Objectives

Hierarchy and TPMs

Risk-Informed Decision

Analysis

Decisionmaking

and

Implementation

of Decision

Alternative

Proposing and/or

Identifying Decision

Alternatives

Risk Analysis of Decision

Alternatives, Performing

Trade Studies and Ranking

Deliberating and

Recommending a

Decision Alternative

Risk Analysis of Decision

Alternatives, Performing

Trade Studies and Ranking

Stakeholder

Expectation,

Requirements

Definition/

Management

Design Solution,

Technical Planning

Design Solution,

Technical Planning,

Decision Analysis

Technical Planning,

Decision Analysis

Decision Analysis,

Lessons Learned,

Knowledge

Management

Tracking and Controlling

Performance Deviations

Communicate,

Deliberate, and

Document

Control

Identify

Analyze

Track

Plan

Figure 6.4-5 The interface between CRM and risk-informed decision analysis
144  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

A review of the lessons learned files, data, and reports 

from previous similar projects can produce insights and 

information for hazard identification on a new project. 

This includes studies from similar systems and historical 

documents, such as mishap files and near-miss reports. 

The key to applying this technique is in recognizing 

what aspects of the old projects and the current project 

are analogous, and what data from the old projects are 

relevant to the current project. In some cases the use of 

quantitative methods can compensate for limited availability of information because these techniques pull the 

most value from the information that is available.

Types of Risk

As part of selecting appropriate risk analysis methods, 

it is useful to categorize types of risk. Broadly, risk can 

be related to cost, schedule, and technical performance. 

Many other categories exist, such as safety, organizational, management, acquisition, supportability, political, and programmatic risk, but these can be thought of 

as subsets of the broad categories. For example, programmatic risk refers to risk that affects cost and/or schedule, 

but not technical. 

In the early stages of a risk analysis, it is typically necessary to screen contributors to risk to determine the 

drivers that warrant more careful analysis. For this purpose, conservative bounding approaches may be appropriate. Overestimates of risk significance will be 

corrected when more detailed analysis is performed. 

However, it can be misleading to allow bounding estimates to drive risk ranking. For this reason, analysis will 

typically iterate on a problem, beginning with screening 

estimates, using these to prioritize subsequent analysis, 

and moving on to a more defensible risk profile based on 

careful analysis of significant contributors. This is part of 

the iteration loop shown in Figure 6.4-6.

Qualitative Methods

Commonly used qualitative methods accomplish the 

following:

z Help identify scenarios that are potential risk contributors,

z Provide some input to more quantitative methods, 

and

z Support judgment-based quantification of TPMs.

Is the

ranking/

comparison

robust?

Analyze

Preliminary Risk

& Performance

Measurement

Results

Identify

Identify

Analyze

Decision

Alternatives for

Analysis 

Iteration

Net

benecial to reduce

uncertainty?

Deliberation and

Recommending a

Decision Alternative 

Yes

No

No

Scoping &

Determination of

Methods to Be

Used 

Additional Uncertainty Reduction if Necessary per Stakeholders

Risk &

Performance

Measurement

Results

Risk Analysis

Techniques Spectrum of Available Techniques

Examples of Decisions 

� Architecture A vs. Architecture B vs. Architecture C � Making changes to existing systems

� Extending the life of existing systems � Responding to operational occurrences in real time

� Contingency Plan A vs. Contingency Plan B � Technology A vs. Technology B

� Changing requirements � Prioritization

� Launch or no launch

Qualitative

Techniques 

Quantitative

Techniques 

Figure 6.4-6 Risk analysis of decision alternatives
6.4 Technical Risk Management

NASA Systems Engineering Handbook  145

These qualitative methods are discussed briefly below.

Risk Matrices

“NxM” (most commonly 5x5) risk matrices provide assistance in managing and communicating risk. (See Figure 6.4-7.) They combine qualitative and semi-quantitative measures of likelihood with similar measures of 

consequences. The risk matrix is not an assessment tool, 

but can facilitate risk discussions. Specifically, risk matrices help to:

z Track the status and effects of risk-handling efforts, 

and

z Communicate risk status information. 

When ranking risk, it is important to use a common 

methodology. Different organizations, and sometimes 

projects, establish their own format. This can cause confusion and miscommunication. So before using a ranking system, the definitions should be clearly established 

and communicated via a legend or some other method. 

For the purposes of this handbook, a definition widely 

used by NASA, other Government organizations, and 

industry is provided.

z Low (Green) Risk: Has little or no potential for increase in cost, disruption of schedule, or degradation of performance. Actions within the scope of the 

planned program and normal management attention 

should result in controlling acceptable risk.

z Moderate (Yellow) Risk: May cause some increase in 

cost, disruption of schedule, or degradation of perExample Sources of Risk

In the “identify” activity, checklists such as this can 

serve as a reminder to analysts regarding areas in 

which risks have been identified previously. 

z Unrealistic schedule estimates or allocation

z Unrealistic cost estimates or budget allocation

z Inadequate staffing or skills

z Uncertain or inadequate contractor capability

z Uncertain or inadequate vendor capability

z Insufficient production capacity

z Operational hazards

z Issues, hazards, and vulnerabilities that could adversely affect the program’s technical effort

z Unprecedented efforts without estimates

z Poorly defined requirements

z No bidirectional traceability of requirements

z Infeasible design

z Inadequate configuration management

z Unavailable technology

z Inadequate test planning

z Inadequate quality assurance

z Requirements prescribing nondevelopmental products too low in the product tree

z Lack of concurrent development of enabling products for deployment, training, production, operations, support, or disposal

Likelihoo

d

Consequences

1

5

4

3

1

2

HIGH

LOW

2 3 5 4

MODERATE

Figure 6.4-7 Risk matrix

Limitations of Risk Matrices

z Interaction between risks is not considered. Each 

risk is mapped onto the matrix individually. (These 

risks can be related to each item using FMECA or a 

fault tree.)

z Inability to deal with aggregate risks (i.e., total risk).

z Inability to represent uncertainties. A risk is assumed to exist within one likelihood range and 

consequence range, both of which are assumed to 

be known.

z Fixed tradeoff between likelihood and consequence. Using the standardized 5x5 matrix, the significance of different levels of likelihood and consequence are fixed and unresponsive to the context 

of the program.
146  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

formance. Special action and management attention 

may be required to handle risk.

z High (Red) Risk: Likely to cause significant increase 

in cost, disruption of schedule, or degradation of performance. Significant additional action and high-priority management attention will be required to handle 

risk.

FMECAs, FMEAs, and Fault Trees

FMEA; Failure Modes, Effects, and Criticality Analysis 

(FMECA); and fault trees are methodologies designed to 

identify potential failure modes for a product or process, 

to assess the risk associated with those failure modes, to 

rank the issues in terms of importance, and to identify 

and carry out corrective actions to address the most serious concerns. These methodologies focus on the hardware components as well as processes that make up the 

system. According to MIL-STD-1629, Failure Mode and 

Effects Analysis, FMECA is an ongoing procedure by 

which each potential failure in a system is analyzed to 

determine the results or effects thereof on the system, 

and to classify each potential failure mode according to 

its consequence severity. A fault tree evaluates the combinations of failures that can lead to the top event of interest. (See Figure 6.4-8.)

Quantitative and Communication Methods

PRA is a comprehensive, structured, and logical analysis 

method aimed at identifying and assessing risks in complex technological systems for the purpose of cost-effectively improving their safety and performance. 

Risk management involves prevention of (reduction of 

the frequency of) adverse scenarios (ones with undesirable consequences) and promotion of favorable scenarios. 

This requires understanding the elements of adverse scenarios so that they can be prevented and the elements of 

successful scenarios so that they can be promoted. 

PRA quantifies risk metrics. “Risk metric” refers to the 

kind of quantities that might appear in a decision model: 

such things as the frequency or probability of consequences of a specific magnitude or perhaps expected 

consequences. Risk metrics of interest for NASA include 

probability of loss of vehicle for some specific mission 

type, probability of mission failure, and probability of 

large capital loss. Figures of merit such as system failure 

probability can be used as risk metrics, but the phrase 

“risk metric” ordinarily suggests a higher level, more 

consequence-oriented figure of merit. The resources 

needed for PRA are justified by the importance of the 

consequences modeled or until the cost in time and resources of further analysis is no longer justified by the 

expected benefits. 

The NASA safety and risk directives determine the scope 

and the level of rigor of the risk assessments. NPR 8715.3, 

NASA General Safety Program Requirements assigns the 

project a priority ranking based on its consequence category and other criteria. NPR 8705.5, Probabilistic Risk AsSingular event

Event that results from a

combination of singular

events

“And” logic symbol

“Or” logic symbol

Legend:

T

E1

A

C

I

F

G H

Basic

Failure Event

Intermediate

Failure

Event

Top

Event

Leak Not Detected

Controller Fails

Pressure

Transducer 1

Fails

E3

B E5

E2

E4

Figure 6.4-8 Example of a fault tree
6.4 Technical Risk Management

NASA Systems Engineering Handbook  147

sessment (PRA) Procedures for NASA Programs and Projects then determines the scope and the level of rigor and 

details for the assessment based on the priority ranking 

and the level of design maturity.

Quantification

TPMs are quantified for each alternative and used to 

quantify an overall performance index or an overall 

measure of effectiveness for each alternative. These results are then used for ranking alternatives.

Bounding approaches are often used for initial screening 

of possible risk contributors. However, realistic assessments must ultimately be performed on the risk drivers. 

Bounding approaches are inappropriate for ranking alternatives because they bias each TPM in which they are 

applied, and are very difficult to do at a quantitatively 

consistent level from one analysis to the next. 

Because different tools employ different simplifications 

and approximations, it is difficult to compare analysis 

results in a consistent manner if they are based on different tools or done by different analysts. These sources 

of inconsistency need to be considered when the work 

is planned and when the results are applied. Vetting risk 

and TPM results with these factors in mind is one benefit 

of deliberation (discussed below).

Consideration of Uncertainty Reduction 

Measures 

In some cases, the preliminary ranking of alternatives 

will not be robust. A “robust” ranking is one that is not 

sensitive to small changes in model parameters or assumptions. As an example, suppose that differences in 

TPMs of different decision alternatives are sufficiently 

small that variations of key parameters within the stated 

uncertainty bounds could change the ranking. This 

could arise in a range of decision situations, including 

architecture decisions and risk management decisions 

for a given architecture. In the latter case, the alternatives 

result in different risk mitigation approaches. 

In such cases, it may be worthwhile to invest in work to 

reduce uncertainties. Quantification of the “value of information” can help the decisionmaker determine whether 

uncertainty reduction is an efficient use of resources.

Deliberation and Recommendation of Decision 

Alternative

Deliberation 

Deliberation is recommended in order to make use of 

collective wisdom to promote selection of an alternative for actual implementation, or perhaps, in the case 

of complex and high-stakes decisions, to recommend a 

final round of trade studies or uncertainty reduction efforts, as suggested by the analysis arrow in Figure 6.4-9.

Capturing the Preferred Alternative and the 

Basis for Its Selection

Depending on the level at which this methodology is 

being exercised (project level, subtask level, etc.), the 

technical team chooses an alternative, basing the choice 

on deliberation to the extent appropriate. The decision 

itself is made by appropriate authority inside of the systems engineering processes. The purpose of calling out 

Figure 6.4-9 Deliberation

Analysis

No No

Yes

Present

preliminary

results to

stakeholders 

Need for

additional

uncertainty

reduction? 

Yes

Decisionmaking and

implementation of

decision alternative

Need to

refine/adjust

decision

alternatives? 

Risk and TPM

Results 

Selection

� Furnish recommendation

to decisionmaker

� Capture basis

� Develop/update risk

management plan

� Refine metrics and develop

monitoring thresholds
148  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

this step is to emphasize that key information about the 

alternative needs to be captured and that this key information includes the perceived potential program vulnerabilities that are input to the “planning” activity within 

CRM. By definition, the selection of the alternative is 

based at least in part on the prospective achievement of 

certain values of the TPMs. For purposes of monitoring 

and implementation, these TPM values help to define 

success, and are key inputs to the determination of monitoring thresholds.

Planning Technical Risk Management of the 

Selected Alternative

At this point, a single alternative has been chosen. During analysis, the risk of each alternative will have been 

evaluated for purposes of TPM quantification, but detailed risk management plans will not have been drawn 

up. At this stage, detailed planning for technical risk 

management of the selected alternative takes place and 

a formal risk management plan is drafted. In the planning phase: 

z Provisional decisions are made on risk control actions 

(eliminate, mitigate, research, watch, or accept);

z Observables are determined for use in measurement 

of program performance;

z Thresholds are determined for the observables such 

that nonexceedance of the thresholds indicates satisfactory program performance;

z Protocols are determined that guide how often observables are to be measured, what to do when a threshold 

is exceeded, how often to update the analyses, decision authority, etc.; and

z Responsibility for the risk tracking is assigned.

General categories of risk control actions from NPR 

8000.4, Risk Management Procedural Requirements are 

summarized here. Each identified and analyzed risk can 

be managed in one of five ways:

z Eliminate the risk,

z Mitigate the risk,

z Research the risk,

z Watch the risk, or

z Accept the risk.

Steps should be taken to eliminate or mitigate the risk if 

it is well understood and the benefits realized are commensurate with the cost. Benefits are determined using 

the TPMs from the program’s objectives hierarchy. The 

consequences of mitigation alternatives need to be analyzed to ensure that they do not introduce unwarranted 

new contributions to risk.

If mitigation is not justified, other activities are considered. Suppose that there is substantial uncertainty regarding the risk. For example, there may be uncertainty 

in the probability of a scenario or in the consequences. 

This creates uncertainty in the benefits of mitigation, 

such that a mitigation decision cannot be made with 

confidence. In this case, research may be warranted to 

reduce uncertainty and more clearly indicate an appropriate choice for the control method. Research is only an 

interim measure, eventually leading either to risk mitigation or to acceptance.

If neither risk mitigation nor research is justified and the 

consequence associated with the risk is small, then it may 

need to be accepted. The risk acceptance process considers the likelihood and the severity of consequences. 

NPR 8000.4 delineates the program level with authority 

to accept risk and requires accepted risk to be reviewed 

periodically (minimum of every 6 months) to ensure 

that conditions and assumptions have not changed requiring the risk acceptance to be reevaluated. These reviews should take the form of quantitative and qualitative analyses, as appropriate.

The remaining cases are those in which neither risk mitigation nor research are justified, and the consequence associated with the risk is large. If there is large uncertainty 

in the risk, then it may need to be watched. This allows 

the uncertainty to reduce naturally as the program progresses and knowledge accumulates, without a research 

program targeting that risk. As with research, watching 

is an interim measure, eventually leading either to risk 

mitigation or to acceptance, along guidelines previously 

cited.

Effective Planning

The balance of this subsection is aimed primarily at ensuring that the implementation plan for risk monitoring 

is net beneficial.

A good plan has a high probability of detecting significant deviations from program intent in a timely fashion, 

without overburdening the program. In order to accomplish this, a portfolio of observables and thresholds 

needs to be identified. Selective plan implementation 

then checks for deviations of actual TPM values from 
6.4 Technical Risk Management

NASA Systems Engineering Handbook  149

planned TPM values, and does so in a way that adds net 

value by not overburdening the project with reporting 

requirements. Elements of the plan include financial and 

progress reporting requirements, which are somewhat 

predetermined, and additional program-specific observables, audits, and program reviews.

The selection of observables and thresholds should have 

the following properties:

z Measurable parameters (direct measurement of the 

parameter or of related parameters that can be used 

to calculate the parameter) exist to monitor system 

performance against clearly defined, objective thresholds;

z The monitoring program is set up so that, when a 

threshold is exceeded, it provides timely indication of 

performance issues; and

z The program burden associated with the activity is 

the minimum needed to satisfy the above.

For example, probability of loss of a specific mission 

cannot be directly measured, but depends on many 

quantities that can be measured up to a point, such as 

lower level reliability and availability metrics.

Monitoring protocols are established to clarify requirements, assign responsibility, and establish intervals for 

monitoring. The results of monitoring are collected and 

analyzed, and responses are triggered if performance 

thresholds are exceeded. These protocols also determine 

when the analyses must be updated. For example, technical risk management decisions should be reassessed 

with analysis if the goals of the program change. Due 

to the long lead time required for the high-technology 

products required by NASA programs, program requirements often change before the program completes its 

life cycle. These changes may include technical requirements, budget or schedule, risk tolerance, etc.

Tracking and Controlling Performance 

Deviations

As shown in Figure 6.4-10, tracking is the process by 

which parameters are observed, compiled, and reported 

according to the risk management plan. Risk mitigation/

control is triggered when a performance threshold is exceeded, when risk that was assumed to be insignificant 

is found to be significant, or when risk that was not addressed during the analyses is discovered. Control may 

also be required if there are significant changes to the 

program. The need to invoke risk control measures in 

light of program changes is determined in the risk management plan. Alternatives are proposed and analyzed, 

and a preferred alternative is chosen based on the performance of the alternatives with respect to the TPM, sensitivity and uncertainty analyses, and deliberation by the 

stakeholders. The new preferred alternative is then subjected to planning, tracking, and control.

During the planning phase, control alternatives were 

proactively conceived before required. Once a threshold 

is triggered, a risk control action (as described in Subsection 6.4.2.3) is required. At this point, there may be 

considerably more information available to the decisionmaker than existed when the control alternatives were 

proposed. Therefore, new alternatives or modifications 

of existing alternatives should be considered in addition 

to the existing alternatives by iterating this technical risk 

management process. 

Figure 6.4-11 shows an example of tracking and controlling performance by tracking TPM margins against predetermined thresholds. At a point in time corresponding 

with the vertical break, the TPM’s margin is less than 

the required margin. At this point, the alternative was 

changed, such that the margin and margin requirement 

increased.

Thresholds or Other 

Metrics and Thresholds

From Plan

Execution of

Chosen Decision

Alternative 

Identify

Iterate continuous

risk management

process

Intervene if

performance

thresholds are

exceeded 

Control

Track

Monitor

performance

based on TPMs and

decision rules 

Figure 6.4-10 Performance monitoring and 

control of deviations
150  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Technical risk management is not exited until the program terminates, although the level of activity varies 

according to the current position of the activity in the 

life cycle. The main outputs are the technical risk reports, including risk associated with proposed alternatives, risk control alternatives, and decision support 

data. Risk control alternatives are fed back to technical 

planning as more information is learned about the alternatives’ risk. This continues until the risk management plan is established. This learning process also produces alternatives, issues, or problems and supporting 

data that are fed back into the project. Once a project 

baseline is chosen, technical risk management focuses 

on measuring the deviation of project risk from this 

baseline, and driving decision support requests based 

on these measurements. 

Margin

Original Ma

Req

rgin

uirement

New Margin Requirement

TPM Margin +

-

0

Current Date

Time t Replanning Occurred Here

Discontinuity

Induced by Shift

to New Allocation

Figure 6.4-11 Margin management method
NASA Systems Engineering Handbook  151

Configuration Management is a management discipline 

applied over the product’s life cycle to provide visibility 

into and to control changes to performance and functional and physical characteristics. CM ensures that the 

configuration of a product is known and reflected in 

product information, that any product change is beneficial and is effected without adverse consequences, and 

that changes are managed.

CM reduces technical risks by ensuring correct product 

configurations, distinguishes among product versions, 

ensures consistency between the product and information about the product, and avoids the embarrassment of 

stakeholder dissatisfaction and complaint. NASA adopts 

the CM principles as defined by ANSI/EIA 649, NASA 

methods of implementation as defined by NASA CM 

professionals, and as approved by NASA management. 

When applied to the design, fabrication/assembly, system/

subsystem testing, integration, operational and sustaining 

activities of complex technology items, CM represents the 

“backbone” of the enterprise structure. It instills discipline and keeps the product attributes and documentation consistent. CM enables all stakeholders in the technical effort, at any given time in the life of a product, to 

use identical data for development activities and decisionmaking. CM principles are applied to keep the documentation consistent with the approved engineering, and to 

ensure that the product conforms to the functional and 

physical requirements of the approved design.

6.5.1 Process Description

Figure 6.5-1 provides a typical flow diagram for the Configuration Management Process and identifies typical inputs, 

outputs, and activities to consider in addressing CM. 

6.5.1.1 Inputs

The required inputs for this process are:

z CM plan,

z Work products to be controlled, and

z Proposed baseline changes.

6.5.1.2 Process Activities

There are five elements of CM (see Figure 6.5-2):

6.5 Configuration Management 

From project

From Requirements

Management and Interface

Management Processes

To Technical Data

Management Process

To applicable

technical processes 

To project and

Technical Data

Management Process

From Stakeholder

Expectation Denition,

Logical Decomposition, and

Technical Planning Processes

Expectation, 

Requirements, and

Interface Documents 

Engineering Change

Proposals

Project Conguration

Management Plan 

List of Conguration

Items Under

Control

Conguration

Management

Work Products

Current

Baselines

Conguration

Management

Reports 

Approved

Requirements

Baseline Changes

Prepare a strategy to conduct

conguration management

Identify baseline to be under

conguration control 

Maintain the status of conguration

documentation 

Manage conguration change control

Conduct conguration audits

Capture work products from

conguration management activities Designated

Conguration Items

to Be Controlled

Figure 6.5-1 CM Process
152  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

z Configuration planning and management

z Configuration identification,

z Configuration change management,

z Configuration Status Accounting (CSA), and

z Configuration verification.

Configuration Identification

Configuration identification is the systematic process of 

selecting, organizing, and stating the product attributes. 

Identification requires unique identifiers for a product 

and its configuration documentation. The CM activity 

associated with identification includes selecting the 

Configuration Items (CIs), 

determining CIs’ associated 

configuration documentation, determining the appropriate change control 

authority, issuing unique 

identifiers for both CIs 

and CI documentation, releasing configuration documentation, and establishing 

configuration baselines.

NASA has four baselines, each of which defines a distinct phase in the evolution of a product design. The 

baseline identifies an agreed-to description of attributes of a CI at a point in time and provides a known 

configuration to which changes are addressed. Baselines are established by agreeing to (and documenting) 

the stated definition of a CI’s attributes. The approved 

“current” baseline defines the basis of the subsequent 

change. The system specification is typically finalized 

following the SRR. The functional baseline is established at the SDR and will usually transfer to NASA’s 

control at that time.

The four baselines (see Figure 6.5-3) normally controlled 

by the program, project, or Center are the following:

z Functional Baseline: The functional baseline is the 

approved configuration documentation that describes 

a system’s or top-level CI’s performance requirements 

(functional, interoperability, and interface characteristics) and the verification required to demonstrate 

the achievement of those specified characteristics. The 

functional baseline is controlled by NASA.

z Allocated Baseline: The allocated baseline is the approved performance-oriented configuration documentation for a CI to be developed that describes the 

functional and interface characteristics that are allocated from a higher level requirements document 

or a CI and the verification required to demonstrate 

achievement of those specified characteristics. The allocated baseline extends the top-level performance 

Configuration

Verification

Configuration

Status

Accounting

Configuration

Change

Management

Configuration

Identification

Configuration

Planning and

Management

CONFIGURATION

MANAGEMENT

Figure 6.5-2 Five elements of configuration management

CM Planning and Management

CM planning starts at a program’s or project’s inception. 

The CM office must carefully weigh the value of prioritizing resources into CM tools or into CM surveillance 

of the contractors. Reviews by the Center Configuration 

Management Organization (CMO) are warranted and 

will cost resources and time, but the correction of systemic CM problems before they erupt into losing configuration control are always preferable to explaining why 

incorrect or misidentified parts are causing major problems in the program/project.

One of the key inputs to preparing for CM implementation is a strategic plan for the project’s complete CM 

process. This is typically contained in a CM plan. See Appendix M for an outline of a typical CM plan.

This plan has both internal and external uses: 

z Internal: It is used within the project office to guide, 

monitor, and measure the overall CM process. It describes both the CM activities planned for future acquisition phases and the schedule for implementing 

those activities.

z External: The CM plan is used to communicate the 

CM process to the contractors involved in the program. It establishes consistent CM processes and 

working relationships.

The CM plan may be a stand-alone document, or it may 

be combined with other program planning documents. 

It should describe the criteria for each technical baseline 

creation, technical approvals, and audits.
6.5 Configuration Management

NASA Systems Engineering Handbook  153

requirements of the functional baseline to sufficient 

detail for initiating manufacturing or coding of a CI. 

The allocated baseline is usually controlled by the design organization until all design requirements have 

been verified. The allocated baseline is typically established at the successful completion of the PDR. Prior 

to CDR, NASA normally reviews design output for 

conformance to design requirements through incremental deliveries of engineering data. NASA control 

of the allocated baseline occurs through review of the 

engineering deliveries as data items.

z Product Baseline: The product baseline is the approved technical documentation that describes the 

configuration of a CI during the production, fielding/

deployment, and operational support phases of its life 

cycle. The established product baseline is controlled as 

described in the configuration management plan that 

was developed during Phase A. The product baseline 

is typically established at the completion of the CDR. 

The product baseline describes:

▶ Detailed physical or form, fit, and function characteristics of a CI;

▶ The selected functional characteristics designated 

for production acceptance testing; and

▶ The production acceptance test requirements.

z As-Deployed Baseline: The as-deployed baseline 

occurs at the ORR. At this point, the design is considered to be functional and ready for flight. All 

changes will have been incorporated into the documentation.

Mission Need

Statement

FUNCTIONAL

BASELINE

Major Architecture

Aspects of Design

Complete

ALLOCATED

BASELINE

Implementation

Aspects of Design

Complete 

PRODUCT

BASELINE

Realization Aspects of 

Design Complete; Fabrication

and Text Complete 

AS-DEPLOYED

BASELINE

Operational Capability

Demonstrate

MDR

Concept

Partial

Analysis Engineering

Items

System Spec

Complete

Analysis

Manuals

SDR

SRR

PDR

ORR

SAR

CDR

Qualication

Items

Product

System 

End

Items

Procedures

Program

Plan

Plan

Design

Disclosure

Segment Spec

Prime Item

Design-to-Spec

End Item

Design-to-Spec

End Item

Build-to-Spec

End Item

Design-to-Spec

End Item

Design-to-Spec

Segment Spec Segment Spec

Prime Item

Design-to-Spec

Prime Item

Design-to-Spec

Figure 6.5-3 Evolution of technical baseline
154  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Configuration Change Management

Configuration change management is a process to 

manage approved designs and the implementation of 

approved changes. Configuration change management 

is achieved via the systematic proposal, justification, and 

evaluation of proposed changes, followed by incorporation of approved changes and verification of implementation. Implementing configuration change management in a given program requires unique knowledge 

of the program objectives and requirements. The first 

step establishes a robust and well-disciplined internal 

NASA Configuration Control Board (CCB) system, 

which is chaired by someone with program change authority. CCB members represent the stakeholders with 

authority to commit the team they represent. The second 

step creates configuration change management surveillance of the contractor’s activity. The CM office advises 

the NASA program or project manager to achieve a balanced configuration change management implementation that suits the unique program/project situation. See 

Figure 6.5-4 for an example of a typical configuration 

change management control process.

Configuration Status Accounting

Configuration Status Accounting (CSA) is the recording 

and reporting of configuration data necessary to manage 

CIs effectively. An effective CSA system provides timely 

and accurate configuration information such as:

z Complete current and historical configuration documentation and unique identifiers. 

z Status of proposed changes, deviations, and waivers 

from initiation to implementation. 

z Status and final disposition of identified discrepancies 

and actions identified during each configuration audit. 

Some useful purposes of the CSA data include:

z An aid for proposed change evaluations, change decisions, investigations of design problems, warranties, 

and shelf-life calculations.

z Historical traceability.

z Software trouble reporting.

z Performance measurement data. 

The following are critical functions or attributes to consider if designing or purchasing software to assist with 

the task of managing configuration.

z Ability to share data real time with internal and external stakeholders securely;

z Version control and comparison (track history of an 

object or product);

z Secure user checkout and check in;

z Tracking capabilities for gathering metrics (i.e., time, 

date, who, time in phases, etc.);

z Web based;

z Notification capability via e-mail;

z Integration with other databases or legacy systems;

z Compatible with required support contractors and/or 

suppliers (i.e., can accept data from a third party as 

required);

z Integration with drafting and modeling programs as 

required;

z Provide neutral format viewer for users;

z License agreement allows for multiple users within an 

agreed-to number;

z Workflow and life-cycle management;

z Limited customization;

z Migration support for software upgrades;

z User friendly;

z Consideration for users with limited access;

Types of Configuration Change 

Management Changes

z Engineering Change: An engineering change is 

an iteration in the baseline (draft or established). 

Changes can be major or minor. They may or may 

not include a specification change. Changes affecting an external interface must be coordinated and 

approved by all stakeholders affected.

▶ A “major” change is a change to the baseline configuration documentation that has significant impact (i.e., requires retrofit of delivered products 

or affects the baseline specification, cost, safety, 

compatibility with interfacing products, or operator, or maintenance training).

▶ A ”minor” change corrects or modifies configuration documentation or processes without impact 

to the interchangeability of products or system 

elements in the system structure.

z Waiver: A waiver is a documented agreement intentionally releasing a program or project from 

meeting a requirement. (Some Centers use deviations prior to Implementation and waivers during 

Implementation.) Authorized waivers do not constitute a change to a baseline.
6.5 Configuration Management

NASA Systems Engineering Handbook  155

z Ability to attach standard format files from desktop

z Workflow capability (i.e., route a CI as required based 

on a specific set of criteria); and

z Capable of acting as the one and only source for released information.

Configuration Verification

Configuration verification is accomplished by inspecting 

documents, products, and records; reviewing procedures, processes, and systems of operations to verify that 

the product has achieved its required performance reFigure 6.5-4 Typical change control process

ORIGINATOR

CONFIGURATION

MANAGEMENT

ORGANIZATION EVALUATORS

RESPONSIBLE

OFFICE

CONFIGURATION

CONTROL

BOARD ACTIONEES

7.

Chair signs final

directive

9.

Updates

document,

hardware, or

software

11.

Releases

document per

directive

Stores and

distributes as

required

10.

Performs final

check on

documents

1.

Prepares

change request 

and sends to

configuration

management

organization

3.

Evaluate

change

package

4.

Consolidates

evaluations

Formulates

recommended

disposition

Presents to CCB

2.

Checks format

and content

Assigns number

and enters into 

CSA

Determines

evaluators

(with originator)

Schedules CCB

date if required

Prepares CCB

agenda

6.

Finalizes CCB

directive

Updates CSA

Creates CCB

minutes

Tracks action

items

5.

Chair

dispositions

change request

Chair assigns

action items

if required

8.

Complete

assigned actions
156  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

quirements and functional attributes; and verifying that 

the product’s design is documented. This is sometimes 

divided into functional and physical configuration audits. (See Section 6.7 for more on technical reviews.)

6.5.1.3 Outputs

NPR 7120.5 defines a project’s life cycle in progressive 

phases. Beginning with Pre-Phase A, these steps in turn 

are grouped under the headings of Formulation and Implementation. Approval is required to transition between 

these phases. Key Decision Points (KDPs) define transitions between the phases. CM plays an important role in 

determining whether a KDP has been met. Major outputs of CM are procedures, approved baseline changes, 

configuration status, and audit reports.

6.5.2 CM Guidance

6.5.2.1 What Is the Impact of Not Doing CM?

The impact of not doing CM may result in a project being plagued by confusion, inaccuracies, low productivity, and unmanageable configuration data. During the 

Columbia accident investigation, the Columbia Accident Investigation Board found inconsistencies related 

to the hardware and the documentation with “unincorWarning Signs/Red Flags (How Do You Know When You’re in Trouble?)

General warning signs of an improper implementation of CM include the following:

z Failure of program to define the “top-level” technical requirement (“We don’t need a spec”).

z Failure of program to recognize the baseline activities that precede and follow design reviews.

z Program office reduces the time to evaluate changes to one that is impossible for engineering, SMA, or other CCB 

members to meet.

z Program office declares “there will be no dissent in the record” for CCB documentation.

z Contract is awarded without CM requirements concurred with by CMO supporting the program office.

z Redlines used inappropriately on production floor to keep track of changes to design.

z Material Review Board does not know the difference between critical, major, and minor nonconformances and the 

appropriate classification of waivers.

z Drawings are not of high quality and do not contain appropriate notes to identify critical engineering items for configuration control or appropriate tolerancing.

z Vendors do not understand the implication of submitting waivers to safety requirements as defined in engineering.

z Subcontractors/vendors change engineering design without approval of integrating contractor, do not know how to 

coordinate and write an engineering change request, etc.

z Manufacturing tooling engineering does not keep up with engineering changes that affect tooling concepts. Manufacturing tools lose configuration control and acceptability for production.

z Verification data cannot be traced to released part number and specification that apply to verification task.

z Operational manuals and repair instructions cannot be traced to latest released part number and repair drawings that 

apply to repair/modification task.

z Maintenance and ground support tools and equipment cannot be traced to latest released part number and specification that applies to equipment.

z Parts and items cannot be identified due to improper identification markings.

z Digital closeout photography cannot be correlated to the latest release engineering.

z NASA is unable to verify the latest released engineering through access to the contractor’s CM Web site.

z Tools required per installation procedures do not match the fasteners and nuts and bolts used in the design of CIs.

z CIs do not fit into their packing crates and containers due to losing configuration control in the design of the shipping and packing containers.

z Supporting procurement/fabrication change procedures do not adequately involve approval by originating engineering organization.
6.5 Configuration Management

NASA Systems Engineering Handbook  157

porated documentation changes” that led to failure. No 

CM issues were cited as a cause of the accident. The 

usual impact of not implementing CM can be described 

as “losing configuration control.” Within NASA, this 

has resulted in program delays and engineering issues, 

especially in fast prototyping developments (X-37 Program) where schedule has priority over recording what 

is being done to the hardware. If CM is implemented 

properly, discrepancies identified during functional and 

physical configuration audits will be addressed. The following impacts are possible and have occurred in the 

past:

z Mission failure and loss of property and life due to improperly configured or installed hardware or software,

z Mission failure to gather mission data due to improperly configured or installed hardware or software,

z Significant mission delay incurring additional cost 

due to improperly configured or installed hardware 

or software, and

z Significant mission costs or delay due to improperly 

certified parts or subsystems due to fraudulent verification data.

If CM is not implemented properly, problems may occur 

in manufacturing, quality, receiving, procurement, etc. 

The user will also experience problems if ILS data are 

not maintained. Using a shared software system that 

can route and track tasks provides the team with the resources necessary for a successful project. 

6.5.2.2 When Is It Acceptable to Use Redline 

Drawings?

“Redline” refers to the control process of marking up 

drawings and documents during design, fabrication, production, and testing that are found to contain errors or inaccuracies. Work stoppages could occur if the documents 

were corrected through the formal change process. 

All redlines require the approval of the responsible hardware manager and quality assurance manager at a minimum. These managers will determine whether redlines 

are to be incorporated into the plan or procedure.

The important point is that each project must have a 

controlled procedure for redlines that specifies redline 

procedures and approvals.

Redlines Were identified as One of the Major Causes of the NOAA N-Prime Mishap

Excerpts from the NOAA N-Prime Mishap Investigation Final Report:

“Several elements contributed to the NOAA N-PRIME incident, the most significant of which were the lack of proper 

TOC [Turn Over Cart] verification, including the lack of proper PA [Product Assurance] witness, the change in schedule 

and its effect on the crew makeup, the failure of the crew to recognize missing bolts while performing the interface surface wipe down, the failure to notify in a timely fashion or at all the Safety, PA, and Government representatives, and the 

improper use of procedure redlines leading to a difficult-to-follow sequence of events. The interplay of the several elements allowed a situation to exist where the extensively experienced crew was not focusing on the activity at hand. 

There were missed opportunities that could have averted this mishap.

“In addition, the operations team was utilizing a heavily redlined procedure that required considerable ‘jumping’ from 

step to step, and had not been previously practiced. The poorly written procedure and novel redlines were preconditions to the decision errors made by the RTE [Responsible Test Engineer].

“The I&T [Integration and Test] supervisors allowed routine poor test documentation and routine misuse of procedure 

redlines.

“Key processes that were found to be inadequate include those that regulate operational tempo, operations planning, procedure development, use of redlines, and GSE [Ground Support Equipment] configurations. For instance, the operation 

during which the mishap occurred was conducted using extensively redlined procedures. The procedures were essentially 

new at the time of the operation—that is, they had never been used in that particular instantiation in any prior operation. 

The rewritten procedure had been approved through the appropriate channels even though such an extensive use of redlines was unprecedented. Such approval had been given without hazard or safety analyses having been performed.”
158  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

The Technical Data Management Process is used to plan 

for, acquire, access, manage, protect, and use data of a technical nature to support the total life cycle of a system. Data 

Management (DM) includes the development, deployment, 

operations and support, eventual retirement, and retention 

of appropriate technical, to include mission and science, 

data beyond system retirement as required by NPR 1441.1, 

NASA Records Retention Schedules. 

DM is illustrated in Figure 6.6-1. Key aspects of DM for 

systems engineering include:

z Application of policies and procedures for data identification and control,

z Timely and economical acquisition of technical data,

z Assurance of the adequacy of data and its protection,

z Facilitating access to and distribution of the data to 

the point of use,

z Analysis of data use,

z Evaluation of data for future value to other programs/

projects, and

z Process access to information written in legacy software.

6.6.1 Process Description

Figure 6.6-1 provides a typical flow diagram for the Technical Data Management Process and identifies typical 

inputs, outputs, and activities to consider in addressing 

technical data management. 

6.6.1.1 Inputs

Inputs include technical data, regardless of the form or 

method of recording and whether the data are generated 

by the contractor or Government during the life cycle of 

the system being developed. Major inputs to the Technical Data Management Process include: 

z Program DM plan,

z Data products to be managed, and

z Data requests.

6.6.1.2 Process Activities

Each Center is responsible for policies and procedures 

for technical DM. NPR 7120.5 and NPR 7123.1 define 

the need to manage data, but leave specifics to the individual Centers. However, NPR 7120.5 does require that 

DM planning be provided as either a section in the program/project plan or as a separate document. The program or project manager is responsible for ensuring that 

the data required are captured and stored, data integrity 

is maintained, and data are disseminated as required. 

Other NASA policies address the acquisition and storage 

of data and not just the technical data used in the life 

cycle of a system. 

Role of Data Management Plan

The recommended procedure is that the DM plan be a 

separate plan apart from the program/project plan. DM 

issues are usually of sufficient magnitude to justify a separate plan. The lack of specificity in Agency policy and 

procedures provides further justification for more detailed DM planning. The plan should cover the following 

major DM topics:

6.6 Technical Data Management

Figure 6.6-1 Technical Data Management Process

From all technical

processes and contractors

To all technical processes

and contractors 

To project and all

technical processes 

Technical Data

Products to Be

Managed

Technical Data

Requests 

Technical Data

Electronic Exchange

Formats 

Form of Technical

Data Products 

Delivered Technical

Data

From project and all

technical processes 

Prepare for technical data

management implementation 

Collect and store required

technical data

Provide technical data to authorized

parties

Maintain stored technical data
6.6 Technical Data Management

NASA Systems Engineering Handbook  159

z Identification/definition of data requirements for all 

aspects of the product life cycle.

z Control procedures—receipt, modification, review, 

and approval.

z Guidance on how to access/search for data for users.

z Data exchange formats that promote data reuse and 

help to ensure that data can be used consistently 

throughout the system, family of systems, or system 

of systems.

z Data rights and distribution limitations such as export-control Sensitive But Unclassified (SBU).

z Storage and maintenance of data, including master 

lists where documents and records are maintained 

and managed.

Technical Data Management Key Considerations 

Subsequent activities collect, store, and maintain technical data and provide it to authorized parties as required. 

Some considerations that impact these activities for implementing Technical Data Management include:

z Requirements relating to the flow/delivery of data to 

or from a contractor should be specified in the technical data management plan and included in the Request for Proposal (RFP) and contractor agreement. 

z NASA should not impose changes on existing contractor data management systems unless the program 

technical data management requirements, including 

data exchange requirements, cannot otherwise be 

met. 

z Responsibility for data inputs into the technical data 

management system lies solely with the originator or 

generator of the data. 

z The availability/access of technical data will lie with 

the author, originator, or generator of the data in conjunction with the manager of the technical data management system. 

z The established availability/access description and list 

should be baselined and placed under configuration 

control.

z For new programs, a digital generation and delivery 

medium is desired. Existing programs must weigh the 

cost/benefit trades of digitizing hard copy data.

General Data Management Roles

The Technical Data Management Process provides the 

basis for applying the policies and procedures to identify and control data requirements; to responsively and 

economically acquire, access, and distribute data; and to 

analyze data use. 

Adherence to DM principles/rules enables the sharing, 

integration, and management of data for performing 

technical efforts by Government and industry, and ensures that information generated from managed technical data satisfies requests or meets expectations.

The Technical Data Management Process has a leading 

role in capturing and organizing technical data and providing information for the following uses: 

z Identifying, gathering, storing and maintaining the 

work products generated by other systems engineering technical and technical management processes as well as the assumptions made in arriving at 

those work products;

z Enabling collaboration and life-cycle use of system 

product data;

z Capturing and organizing technical effort inputs, as 

well as current, intermediate, and final outputs;

z Data correlation and traceability among requirements, designs, solutions, decisions, and rationales;

z Documenting engineering decisions, including procedures, methods, results, and analyses;

z Facilitating technology insertion for affordability improvements during reprocurement and post-production support; and 

z Supporting other technical management and technical processes, as needed.

Data Identification/Definition 

Each program/project determines data needs during the 

life cycle. Data types may be defined in standard documents. Center and Agency directives sometimes specify 

content of documents and are appropriately used for 

in-house data preparation. The standard description is 

modified to suit program/project-specific needs, and 

appropriate language is included in SOWs to implement actions resulting from the data evaluation. “Data 

suppliers” may be a contractor, academia, or the Government. Procurement of data from an outside supplier 

is a formal procurement action that requires a procurement document; in-house requirements may be handled in a less formal method. Below are the different 

types of data that might be utilized within a program/

project:
160  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

z Data

▶ “Data” is defined in general as “recorded information regardless of the form or method of recording.” 

However, the terms “data” and “information” are 

frequently used interchangeably. To be more precise, data generally must be processed in some 

manner to generate useful, actionable information.

▶ “Data,” as used in SE DM, includes technical data; 

computer software documentation; and representation of facts, numbers, or data of any nature that can 

be communicated, stored, and processed to form 

information required by a contract or agreement to 

be delivered to, or accessed by, the Government. 

▶ Data include that associated with system development, modeling and simulation used in development or test, test and evaluation, installation, parts, 

spares, repairs, usage data required for product sustainability, and source and/or supplier data. 

▶ Data specifically not included in Technical Data 

Management would be data relating to general 

NASA workforce operations information, communications information (except where related to 

a specific requirement), financial transactions, personnel data, transactional data, and other data of a 

purely business nature. 

z Data Call: Solicitation from Government stakeholders (specifically Integrated Product Team (IPT) 

leads and functional managers) identifies and justifies 

their data requirements from a proposed contracted 

procurement. Since data provided by contractors have 

a cost to the Government, a data call (or an equivalent 

activity) is a common control mechanism used to ensure that the requested data are truly needed. If approved by the data call, a description of each data item 

needed is then developed and placed on contract.

z Information: Information is generally considered as 

processed data. The form of the processed data is dependent on the documentation, report, review formats, or templates that are applicable.

z Technical Data Package: A technical data package is 

a technical description of an item adequate for supporting an acquisition strategy, production, engineering, and logistics support. The package defines 

the required design configuration and procedures to 

ensure adequacy of item performance. It consists of 

all applicable items such as drawings, associated lists, 

specifications, standards, performance requirements, 

quality assurance provisions, and packaging details.

z Technical Data Management System: The strategies, 

plans, procedures, tools, people, data formats, data 

exchange rules, databases, and other entities and descriptions required to manage the technical data of a 

program.

Inappropriate Uses of Technical Data

Examples of inappropriate uses of technical data include:

z Unauthorized disclosure of classified data or data 

otherwise provided in confidence;

z Faulty interpretation based on incomplete, out-ofcontext, or otherwise misleading data; and

z Use of data for parts or maintenance procurement 

for which at least Government purpose rights have 

not been obtained.

Ways to help prevent inappropriate use of technical 

data include the following:

z Educate stakeholders on appropriate data use and

z Control access to data.

Initial Data Management System Structure 

When setting up a DM system, it is not necessary to 

acquire (that is, to purchase and take delivery of) all 

technical data generated on a project. Some data may 

be stored in other locations with accessibility provided on a need-to-know basis. Data should be purchased only when such access is not sufficient, timely, 

or secure enough to provide for responsive life-cycle 

planning and system maintenance. Data calls are a 

common control mechanism to help address this 

need.

Data Management Planning 

z Prepare a technical data management strategy. This 

strategy can document how the program data management plan will be implemented by the technical effort or, in the absence of such a program-level plan, 

be used as the basis for preparing a detailed technical 

data management plan, including:

▶ Items of data that will be managed according to 

program or organizational policy, agreements, or 

legislation; 

▶ The data content and format; 
6.6 Technical Data Management

NASA Systems Engineering Handbook  161

▶ A framework for data flow within the program 

and to/from contractors including the language(s) 

to be employed in technical effort information exchanges;

▶ Technical data management responsibilities and 

authorities regarding the origin, generation, capture, archiving, security, privacy, and disposal of 

data products; 

▶ Establishing the rights, obligations, and commitments regarding the retention of, transmission of, 

and access to data items; and

▶ Relevant data storage, transformation, transmission, and presentation standards and conventions 

to be used according to program or organizational 

policy, agreements, or legislative constraints.

z Obtain strategy/plan commitment from relevant 

stakeholders. 

z Prepare procedures for implementing the technical 

data management strategy for the technical effort 

and/or for implementing the activities of the technical 

data management plan. 

z Establish a technical database(s) to use for technical 

data maintenance and storage or work with the program staff to arrange use of the program database(s) 

for managing technical data. 

z Establish data collection tools, as appropriate to the 

technical data management scope and available resources. (See Section 7.3.) 

z Establish electronic data exchange interfaces in accordance with international standards/agreements and 

applicable NASA standards.

z Train appropriate stakeholders and other technical 

personnel in the established technical data management strategy/plan, procedures, and data collection 

tools, as applicable.

z Expected outcomes: 

▶ A strategy and/or plan for implementing technical 

data management;

▶ Established procedures for performing planned 

Technical Data Management activities;

▶ Master list of managed data and its classification by 

category and use;

▶ Data collection tools established and available; and

▶ Qualified technical personnel capable of conducting 

established technical data management procedures 

and using available data collection tools.

Key Considerations for Planning Data 

Management and for Tool Selection

z All data entered into the technical data management 

system or delivered to a requester from the databases 

of the system should have traceability to the author, 

originator, or generator of the data.

z All technical data entered into the technical data 

management system should carry objective evidence 

of current status (for approval, for agreement, for information, etc.), version/control number, and date.

z The technical data management approach should be 

covered as part of the program’s SEMP.

z Technical data expected to be used for reprocurement 

of parts, maintenance services, etc., might need to be 

reviewed by the Center’s legal counsel.

Careful consideration should be taken when planning 

the data access and storage of data that will be generated 

from a project or program. If a system or tool is needed, 

many times the CM tool can be used with less formality. 

If a separate tool is required to manage the data, refer to 

the section below for some best practices when evaluating a data management tool. Priority must be placed 

on being able to access the data and ease of inputting the 

data. Second priority should be the consideration of the 

value of the specific data to current project/program, future programs/projects, NASA’s overall efficiency, and 

uniqueness to NASA’s engineering knowledge.

The following are critical functions or attributes to consider if designing or purchasing software to assist with 

the task of managing data:

z Ability to share data with internal and external stakeholders securely;

z Version control and comparison, to track history of 

an object or product;

z Secure user updating;

z Access control down to the file level;

z Web based;

z Ability to link data to CM system or elements;

z Compatible with required support contractors and/or 

suppliers, i.e., can accept data from a third party as 

required;

z Integrate with drafting and modeling programs as required;

z Provide neutral format viewer for users;

z License agreement allows for multiuser seats;
162  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

z Workflow and life-cycle management is a suggested 

option;

z Limited customization;

z Migration support between software version upgrades;

z User friendly;

z Straightforward search capabilities; and

z Ability to attach standard format files from desktop.

Value of Data

Storage of engineering data needs to be planned at the 

beginning of a program or project. Some of the data 

types will fall under the control of NPR 1441.1, Records 

Retention Schedules; those that do not will have to be addressed. It is best to evaluate all data that will be produced and decide how long it is of value to the program 

or project or to NASA engineering as a whole. There are 

four basic questions to ask when evaluating data’s value:

z Do the data describe the product/system that is being 

developed or built?

z Are the data required to accurately produce the 

product/system being developed or built? 

z Do the data offer insight for similar future programs 

or projects?

z Do the data hold key information that needs to be 

maintained in NASA’s knowledge base for future engineers to use or kept as a learning example?

Technical Data Capture Tasks

Table 6.6-1 defines the tasks required to capture technical data.

Protection for Data Deliverables

All data deliverables should include distribution statements and procedures to protect all data that contain 

critical technology information, as well as to ensure that 

limited distribution data, intellectual property data, or 

proprietary data are properly handled during systems 

engineering activities. This injunction applies whether 

the data are hard copy or digital. 

As part of overall asset protection planning, NASA has 

established special procedures for the protection of 

Critical Program Information (CPI). CPI may include 

components; engineering, design, or manufacturing 

processes; technologies; system capabilities and vulnerabilities; and any other information that gives a system 

its distinctive operational capability.

CPI protection should be a key consideration for the 

Technical Data Management effort and is part of the 

asset protection planning process, as shown in Appendix Q.

6.6.1.3 Outputs

Outputs include timely, secure availability of needed data 

in various representations to those authorized to receive 

it. Major outputs from the Technical Data Management 

Process include (refer to Figure 6.6-1):

z Technical data management procedures,

z Data representation forms,

z Data exchange formats, and

z Requested data/information delivered.

6.6.2 Technical Data Management 

Guidance

6.6.2.1 Data Security and ITAR

NASA generates an enormous amount of information, much of which is unclassified/nonsensitive in nature with few restrictions on its use and dissemination. 

NASA also generates and maintains Classified National 

Security Information (CNSI) under a variety of Agency 

programs, projects, and through partnerships and collaboration with other Federal agencies, academia, and 

private enterprises. SBU markings requires the author, 

distributor, and receiver to keep control of the sensitive 

Data Collection Checklist

z Have the frequency of collection and the points 

in the technical and technical management processes when data inputs will be available been determined? 

z Has the timeline that is required to move data from 

the point of origin to storage repositories or stakeholders been established? 

z Who is responsible for the input of the data? 

z Who is responsible for data storage, retrieval, and 

security? 

z Have necessary supporting tools been developed 

or acquired?
6.6 Technical Data Management

NASA Systems Engineering Handbook  163

document and data or pass the control to an established 

control process. Public release is prohibited, and a document/data marked as such must be transmitted by secure 

means. Secure means are encrypted e-mail, secure fax, 

or person-to-person tracking. WebEx is a nonsecure environment. Standard e-mail is not permitted to transmit 

SBU documents and data. A secure way to send SBU information via e-mail is using the Public Key Infrastructure 

(PKI) to transmit the file(s). PKI is a system that manages 

keys to lock and unlock computer data. The basic purpose 

of PKI is to enable you to share your data keys with other 

people in a secure manner. PKI provides desktop security, as well as security for desktop and network applications, including electronic and Internet commerce.

Data items such as detailed design data (models, drawings, presentations, etc.), limited rights data, source selection data, bid and proposal information, financial 

data, emergency contingency plans, and restricted computer software are all examples of SBU data. Items that 

Table 6.6‐1 Technical Data Tasks

Description Tasks Expected Outcomes

Technical 

data capture

Collect and store inputs and technical effort outcomes from the technical 

and technical management processes, including:

z results from technical assessments; 

z descriptions of methods, tools, and metrics used; 

z recommendations, decisions, assumptions, and impacts of technical 

efforts and decisions; 

z lessons learned; 

z deviations from plan; 

z anomalies and out-of-tolerances relative to requirements; and 

z other data for tracking requirements

Perform data integrity checks on collected data to ensure compliance with 

content and format as well as technical data check to ensure there are no 

errors in specifying or recording the data.

Report integrity check anomalies or variances to the authors or generators of 

the data for correction.

Prioritize, review, and update data collection and storage procedures as part 

of regularly scheduled maintenance.

Sharable data needed to 

perform and control the 

technical and technical 

management processes is 

collected and stored.

Stored data inventory.

Technical 

data maintenance

Implement technical management roles and responsibilities with technical 

data products received.

Manage database(s) to ensure that collected data have proper quality and 

integrity; and are properly retained, secure, and available to those with 

access authority.

Periodically review technical data management activities to ensure consistency and identify anomalies and variances.

Review stored data to ensure completeness, integrity, validity, availability, 

accuracy, currency, and traceability.

Perform technical data maintenance, as required.

Identify and document significant issues, their impacts, and changes made 

to technical data to correct issues and mitigate impacts.

Maintain, control, and prevent the stored data from being used inappropriately.

Store data in a manner that enables easy and speedy retrieval.

Maintain stored data in a manner that protects the technical data against 

foreseeable hazards, e.g., fire, flood, earthquake, etc.

Records of technical data 

maintenance.

Technical effort data, 

including captured work 

products, contractordelivered documents 

and acquirer-provided 

documents, are controlled 

and maintained.

Status of data stored is 

maintained, to include: 

version description, 

timeline, and security 

classification.

 (continued)
164  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

are deemed SBU must be clearly marked in accordance 

with NPR 1600.1, NASA Security Program Procedural Requirements. Data or items that cannot be directly marked, 

such as computer models and analyses, must have an attached copy of NASA Form 1686 that indicates the entire 

package is SBU data. Documents are required to have a 

NASA Form 1686 as a cover sheet. SBU documents and 

data should be safeguarded. Some examples of ways to 

safeguard SBU data are: access is limited on a need-toknow basis, items are copy controlled, items are attended 

while being used, items are properly marked (document 

header, footer, and NASA Form 1686), items are stored 

in locked containers or offices and secure servers, transmitted by secure means, and destroyed by approved 

methods (shredding, etc.). For more information on 

SBU data, see NPR 1600.1.

International Traffic in Arms Regulations (ITAR) implement the Arms Export Control Act, and contain the 

United States Munitions List (USML). The USML lists 

articles, services, and related technical data that are 

designated as “defense articles” and “defense services,” 

pursuant to Sections 38 and 47(7) of the Arms Export 

Control Act. The ITAR is administered by the U.S. Department of State. “Technical data” as defined in the 

ITAR does not include information concerning general 

scientific, mathematical, or engineering principles commonly taught in schools, colleges, and universities or information in the public domain (as that term is defined 

Description Tasks Expected Outcomes

Technical 

data/

information 

distribution

Maintain an information library or reference index to provide technical data 

availability and access instructions. 

Receive and evaluate requests to determine data requirements and delivery 

instructions.

Process special requests for technical effort data or information according to 

established procedures for handling such requests.

Ensure that required and requested data are appropriately distributed to 

satisfy the needs of the acquirer and requesters in accordance with the 

agreement, program directives, and technical data management plans and 

procedures.

Ensure that electronic access rules are followed before database access is 

allowed or any requested data are electronically released/transferred to the 

requester.

Provide proof of correctness, reliability, and security of technical data 

provided to internal and external recipients.

Access information (e.g., 

available data, access 

means, security procedures, time period for 

availability, and personnel 

cleared for access) is readily available.

Technical data are 

provided to authorized 

requesters in the appropriate format, with the appropriate content, and by a 

secure mode of delivery, as 

applicable.

Data 

management 

system 

maintenance

Implement safeguards to ensure protection of the technical database and of 

en route technical data from unauthorized access or intrusion.

Establish proof of coherence of the overall technical data set to facilitate 

effective and efficient use.

Maintain, as applicable, backups of each technical database.

Evaluate the technical data management system to identify collection and 

storage performance issues and problems; satisfaction of data users; risks 

associated with delayed or corrupted data, unauthorized access, or survivability of information from hazards such as fire, flood, earthquake, etc. 

Review systematically the technical data management system, including the 

database capacity, to determine its appropriateness for successive phases of 

the Defense Acquisition Framework.

Recommend improvements for discovered risks and problems:

z Handle risks identified as part of technical risk management. 

z Control recommended changes through established program change 

management activities.

Current technical data 

management system.

Technical data are appropriately and regularly 

backed up to prevent data 

loss. 

Table 6.6‐1 Technical Data Tasks (continued)
6.6 Technical Data Management

NASA Systems Engineering Handbook  165

in 22 CFR 120.11). It also does not include basic marketing information on function and purpose or general 

system descriptions. For purposes of the ITAR, the following definitions apply:

z “Defense Article” (22 CFR 120.6): A defense article 

is any item or technical data on the USML. The term 

includes technical data recorded or stored in any physical form, models, mockups, or other items that reveal 

technical data directly relating to items designated in 

the USML. Examples of defense articles included on 

the USML are (1) launch vehicles, including their specifically designed or modified components, parts, accessories, attachments, and associated equipment; 

(2) remote sensing satellite systems, including ground 

control stations for telemetry, tracking, and control 

of such satellites, as well as passive ground stations if 

such stations employ any cryptographic items controlled on the USML or employ any uplink command 

capability; and (3) all components, parts, accessories, 

attachments, and associated equipment (including 

ground support equipment) that is specifically designed, modified, or configured for such systems. (See 

22 CFR 121.1 for the complete listing.) 

z “Technical Data” (22 CFR 120.10): Technical data 

are information required for the design, development, 

production, manufacture, assembly, operation, repair, 

testing, maintenance, or modification of defense articles. This includes information in the form of blueprints, drawings, photographs, plans, instructions, 

and documentation. 

z Classified Information Relating to Defense Articles 

and Defense Services: Classified information is covered by an invention secrecy order (35 U.S.C. 181 et 

seq.; 35 CFR Part 5). 

z Software Directly Related to Defense Articles: Controlled software includes, but is not limited to, system 

functional design, logic flow, algorithms, application 

programs, operating systems, and support software 

for design, implementation, test, operations, diagnosis, and repair related to defense articles. 
166  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Technical assessment is the crosscutting process used to help 

monitor technical progress of a program/project through 

Periodic Technical Reviews (PTRs). It also provides status 

information to support assessing system design, product realization, and technical management decisions. 

6.7.1 Process Description

Figure 6.7-1 provides a typical flow diagram for the 

Technical Assessment Process and identifies typical inputs, outputs, and activities to consider in addressing 

technical assessment.

6.7.1.1 Inputs

Typical inputs needed for the Technical Assessment Process would include the following:

z Technical Plans: These are the planning documents 

that will outline the technical reviews/assessment 

process as well as identify the technical product/process measures that will be tracked and assessed to determine technical progress. Examples of these plans 

will be the SEMP, review plans, and EVM plan.

z Technical Measures: These are the identified technical measures that will be tracked to determine technical progress. These measures are also referred to as 

MOEs, MOPs, and TPMs.

z Reporting Requirements: These are the requirements 

on the methodology in which the status of the technical measures will be reported in regard to risk, cost, 

schedule, etc. The methodology and tools used for reporting the status will be established on a project-byproject basis.

6.7.1.2 Process Activities

As outlined in Figure 6.7-1, the technical plans (e.g., 

SEMP, review plans) provide the initial inputs into the 

Technical Assessment Process. These documents will 

outline the technical reviews/assessment approach as 

well as identify the technical measures that will be tracked 

and assessed to determine technical progress. An important part of the technical planning is determining what is 

needed in time, resources, and performance to complete 

a system that meets desired goals and objectives. Project 

To Decision Analysis Process

Analysis Support 

Requests

Work Products From

Technical Assessment 

To Technical Data

Management Process

To Technical Planning, 

Requirements Management, and

Interface Management Processes

Corrective Action

Recommendations

Technical Cost and Schedule

Status Reports

Product Measurements

Decision Support

Recommendations and

Impacts 

From Product Verication and

Product Validation Processes

From Decision Analysis Process 

Product and Process

Measures 

Technical Plans

From Technical

Planning Process

From project

Risk Reporting

Requirements

Technical Review

Reports 

To project and Technical Data

Management Process

Assessment Results/

Findings

To Technical Planning, 

Technical Risk Management, and 

Requirements Management Processes

Prepare strategy for conducting

technical assessments

Assess technical work productivity

(measure progress against plans)

Conduct horizontal and vertical progress

technical reviews

Assess technical product quality

(measure progress against requirements)

Capture work products from technical

assessment activities

Figure 6.7-1 Technical Assessment Process

6.7 Technical Assessment
6.7 Technical Assessment

NASA Systems Engineering Handbook  167

managers need visibility into the progress of those plans 

in order to exercise proper management control. Typical 

activities in determining progress against the identified 

technical measures will include status reporting and assessing the data. Status reporting will identify where the 

project stands in regard to a particular technical measure. 

Assessing will analytically convert the output of the status 

reporting into a more useful form from which trends can 

be determined and variances from expected results can be 

understood. Results of the assessment activity will then 

feed into the Decision Analysis Process (see Section 6.8) 

where potential corrective action is necessary.

These activities together form the feedback loop depicted 

in Figure 6.7-2. 

Regular, periodic (e.g., monthly) tracking of the technical measures is recommended, although some measures should be tracked more often when there is rapid 

change or cause for concern. Key reviews, such as PDRs 

and CDRs, are points at which technical measures and 

their trends should be carefully scrutinized for early 

warning signs of potential problems. Should there be indications that existing trends, if allowed to continue, will 

yield an unfavorable outcome, corrective action should 

begin as soon as practical. Subsection 6.7.2.2 provides 

additional information on status reporting and assessment techniques for costs and schedules (including 

EVM), technical performance, and systems engineering 

process metrics.

The measures are predominantly assessed during the 

program and project technical reviews. Typical activities 

performed for technical reviews include (1) identifying, 

planning, and conducting phase-to-phase technical reviews; (2) establishing each review’s purpose, objective, and entry and success criteria; (3) establishing the 

makeup of the review team; and (4) identifying and resolving action items resulting from the review. Subsection 6.7.2.1 summarizes the types of technical reviews 

typically conducted on a program/project and the role 

of these reviews in supporting management decision 

processes. It also identifies some general principles for 

holding reviews, but leaves explicit direction for executing a review to the program/project team to define. 

The process of executing technical assessment has close 

relationships to other areas, such as risk management, 

decision analysis, and technical planning. These areas 

may provide input into the Technical Assessment Process or be the benefactor of outputs from the process.

6.7.1.3 Outputs

Typical outputs of the Technical Assessment Process 

would include the following:

z Assessment Results, Findings, and Recommendations: This is the collective data on the established 

measures from which trends can be determined and 

variances from expected results can be understood. 

Results will then feed into the Decision Analysis Process where potential corrective action is necessary.

z Technical Review Reports/Minutes: This is the collective information coming out of each review that 

captures the results, recommendations, and actions in 

regard to meeting the review’s success criteria.

(Re-)

Planning

Status

Reporting Assessing Decisionmaking

Status Not OK

Status OK

Execute

Figure 6.7-2 Planning and status reporting

feedback loop

This loop takes place on a continual basis throughout 

the project life cycle. This loop is applicable at each level 

of the project hierarchy. Planning data, status reporting 

data, and assessments flow up the hierarchy with appropriate aggregation at each level; decisions cause actions to be taken down the hierarchy. Managers at each 

level determine (consistent with policies established at 

the next higher level of the project hierarchy) how often, and in what form, reporting data and assessments 

should be made. In establishing these status reporting 

and assessment requirements, some principles of good 

practice are:

z Use an agreed-upon set of well-defined technical 

measures. (See Subsection 6.7.2.2.)

z Report these technical measures in a consistent format 

at all project levels.

z Maintain historical data for both trend identification 

and cross-project analyses.

z Encourage a logical process of rolling up technical measures (e.g., use the WBS for project progress status).

z Support assessments with quantitative risk measures.

z Summarize the condition of the project by using 

color-coded (red, yellow, and green) alert zones for all 

technical measures. 
168  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

6.7.2 Technical Assessment Guidance

6.7.2.1 Reviews, Audits, and Key Decision Points 

To gain a general understanding of the various technical reviews called out in Agency policy (e.g., NPR 

7120.5 and NPR 7123.1), we need to examine the intent 

of the policy within each of the above-mentioned documents. These reviews inform the decision authority. 

NPR 7120.5’s primary focus is to inform the decision authority as to the readiness of a program/project to proceed into the next phase of the life cycle. This is done for 

each milestone review and is tied to a KDP throughout 

the life cycle. For KDP/milestone reviews, external independent reviewers known as Standing Review Board 

(SRB) members evaluate the program/project and, in the 

end, report their findings to the decision authority. For a 

program or project to prepare for the SRB, the technical 

team must conduct their own internal peer review process. This process typically includes both informal and 

formal peer reviews at the subsystem and system level. 

This handbook attempts to provide sufficient insight and 

guidance into both policy documents so that practitioners can understand how they are to be successfully integrated; however, the main focus in this handbook will 

be on the internal review process.

The intent and policy for reviews, audits, and KDPs 

should be developed during Phase A and defined in the 

program/project plan. The specific implementation of 

these activities should be consistent with the types of reviews and audits described in this section, and with the 

NASA program and project life-cycle charts (see Figures 3.0-1 and 3.0-2). However, the timing of reviews, 

audits, and KDPs should accommodate the need of each 

specific project.

Purpose and Definition

The purpose of a review is to furnish the forum and process to provide NASA management and their contractors assurance that the most satisfactory approach, plan, 

or design has been selected; that a configuration item has 

been produced to meet the specified requirements; or that 

a configuration item is ready. Reviews help to develop a 

better understanding among task or project participants, 

open communication channels, alert participants and 

management to problems, and open avenues for solutions. Reviews are intended to add value to the project and 

enhance project quality and the likelihood of success. This 

is aided by inviting outside experts to confirm the viability 

of the presented approach, concept, or baseline or to recommend alternatives. Reviews may be program life-cycle 

reviews, project life-cycle reviews, or internal reviews.

The purpose of an audit isto provide NASA management 

and its contractors a thorough examination of adherence 

to program/project policies, plans, requirements, and 

specifications. Audits are the systematic examination of 

tangible evidence to determine adequacy, validity, and 

effectiveness of the activity or documentation under review. An audit may examine documentation of policies 

and procedures, as well as verify adherence to them.

The purpose of a KDP is to provide a scheduled event at 

which the decision authority determines the readiness of 

a program/project to progress to the next phase of the 

life cycle (e.g., B to C, C to D, etc.) or to the next KDP. 

KDPs are part of NASA’s oversight and approval process for programs/projects. For a detailed description of 

the process and management oversight teams, see NPR 

7120.5. Essentially, KDPs serve as gates through which 

programs and projects must pass. Within each phase, a 

KDP is preceded by one or more reviews, including the 

governing Program Management Council (PMC) review. Allowances are made within a phase for the differences between human and robotic space flight programs 

and projects, but phases always end with the KDP. The 

potential outcomes at a KDP include:

z Approval for continuation to the next KDP.

z Approval for continuation to the next KDP, pending 

resolution of actions.

z Disapproval for continuation to the next KDP. In such 

cases, follow-up actions may include a request for 

more information and/or a delta independent review; 

a request for a Termination Review (described below) 

for the program or the project (Phases B, C, D, and E 

only); direction to continue in the current phase; or 

redirection of the program/project.

The decision authority reviews materials submitted by the 

governing PMC, SRB, Program Manager (PM), project 

manager, and Center Management Council (CMC) in 

addition to agreements and program/project documentation to support the decision process. The decision authority makes decisions by considering a number of factors, including continued relevance to Agency strategic 

needs, goals, and objectives; continued cost affordability 

with respect to the Agency’s resources; the viability 

and the readiness to proceed to the next phase; and re-
6.7 Technical Assessment

NASA Systems Engineering Handbook  169

maining program or project risk (cost, schedule, technical, safety). Appeals against the final decision of the decision authority go to the next higher decision authority.

Project Termination

It should be noted that project termination, while usually disappointing to project personnel, may be a proper 

reaction to changes in external conditions or to an improved understanding of the system’s projected cost-effectiveness.

General Principles for Reviews

Several factors can affect the implementation plan for 

any given review, such as design complexity, schedule, 

cost, visibility, NASA Center practices, the review itself, 

etc. As such, there is no set standard for conducting a review across the Agency; however, there are key elements, 

or principles, that should be included in a review plan. 

These include definition of review scope, objectives, success criteria (consistent with NPR 7123.1), and process. 

Definition of the review process should include identification of schedule, including duration of the face-toface meeting (and draft agenda), definition of roles and 

responsibilities of participants, identification of presentation material and data package contents, and a copy of 

the form to be used for Review Item Disposition (RID)/

Request For Action (RFA)/Comment. The review process for screening and processing discrepancies/requests/

comments should also be included in the plan. The review plan must be agreed to by the technical team lead, 

project manager, and for SRB-type reviews, the SRB chair 

prior to the review.

It is recommended that all reviews consist of oral presentations of the applicable project requirements and the 

approaches, plans, or designs that satisfy those requirements. These presentations are normally provided by the 

cognizant design engineers or their immediate supervisor. 

It is also recommended that, in addition to the SRB, the 

review audience include key stakeholders, such as the science community, program executive, etc. This ensures 

that the project obtains buy-in from the personnel who 

have control over the project as well as those who benefit 

from a successful mission. It is also very beneficial to have 

project personnel in attendance that are not directly associated with the design being reviewed (e.g., EPS attending 

a thermal discussion). This gives the project an additional 

opportunity to utilize cross-discipline expertise to identify design shortfalls or recommend improvements. Of 

course, the audience should also include nonproject specialists from safety, quality and mission assurance, reliability, verification, and testing. 

Program Technical Life-Cycle Reviews 

Within NASA there are various types of programs:

z Single-project programs (e.g., James Webb Space 

Telescope Program) tend to have long development 

and/or operational lifetimes, represent a large investment of Agency resources in one program/project, 

and have contributions to that program/project from 

multiple organizations or agencies.

z Uncoupled programs (e.g., Discovery Program, Explorer) are implemented under a broad scientific 

theme and/or a common program implementation 

concept, such as providing frequent flight opportunities for cost-capped projects selected through AOs 

or NASA research announcements. Each such project 

is independent of the other projects within the program. 

z Loosely coupled programs (e.g., Mars Exploration 

Program or Lunar Precursor and Robotic Program) 

address specific scientific or exploration objectives 

through multiple space flight projects of varied 

scope. While each individual project has an assigned 

set of mission objectives, architectural and technological synergies and strategies that benefit the program as a whole are explored during the Formulation process. For instance, all orbiters designed for 

more than one year in Mars orbit are required to 

carry a communication system to support present 

and future landers. 

Termination Review

A termination review is initiated by the decision authority to secure a recommendation as to whether to 

continue or terminate a program or project. Failing to 

stay within the parameters or levels specified in controlling documents will result in consideration of a termination review.

At the termination review, the program and the 

project teams present status, including any material requested by the decision authority. Appropriate 

support organizations are represented (e.g., procurement, external affairs, legislative affairs, public affairs) 

as needed. The decision and basis of the decision are 

fully documented and reviewed with the NASA Associate Administrator prior to final implementation.
170  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

z Tightly coupled programs (e.g., Constellation Program) have multiple projects that execute portions of 

a mission or missions. No single project is capable of 

implementing a complete mission. Typically, multiple 

NASA Centers contribute to the program. Individual 

projects may be managed at different Centers. The 

program may also include other Agency or international partner contributions. 

Regardless of the type, all programs are required to undergo the two technical reviews listed in Table 6.7-1. The 

main difference lies between uncoupled/loosely coupled 

programs that tend to conduct “status-type” reviews on 

their projects after KDP I and single-project/tightly coupled programs that tend to follow the project technical 

life-cycle review process post KDP I.

After KDP I, single-project/tightly coupled programs 

are responsible for conducting the system-level reviews. 

These reviews bring the projects together and help ensure the flowdown of requirements and that the overall 

system/subsystem design solution satisfies the program 

requirements. The program/program reviews also help 

resolve interface/integration issues between projects. For 

the sake of this handbook, single-project programs and 

tightly coupled programs will follow the project life-cycle 

review process defined after this table. Best practices and 

lessons learned drive programs to conduct their “concept 

and requirements-type” reviews prior to project concept 

and requirements reviews and “program design and acceptance-type” reviews after project design and acceptance reviews. 

Project Technical Life-Cycle Reviews

The phrase “project life cycle/project milestone reviews” 

has, over the years, come to mean different things to 

various Centers. Some equate it to mean the project’s 

controlled formal review using RIDS and pre-boards/

boards, while others use it to mean the activity tied to 

RFAs and SRB/KDP process. This document will use the 

latter process to define the term. Project life-cycle reviews are mandatory reviews convened by the decision 

authority, which summarize the results of internal technical processes (peer reviews) throughout the project 

life cycle to NASA management and/or an independent 

review team, such as an SRB (see NPR 7120.5). These 

reviews are used to assess the progress and health of a 

project by providing NASA management assurance that 

the most satisfactory approach, plan, or design has been 

selected, that a configuration item has been produced to 

meet the specified requirements, or that a configuration 

item is ready for launch/operation. Some examples of 

life-cycle reviews include System Requirements Review, 

Preliminary Design Review, Critical Design Review, and 

Acceptance Review. 

Specified life-cycle reviews are followed by a KDP in 

which the decision authority for the project determines, 

based on results and recommendations from the lifecycle review teams, whether or not the project can proceed to the next life-cycle phase.

Standing Review Boards

The SRB’s role is advisory to the program/project and the 

convening authorities, and does not have authority over 

any program/project content. Its review provides expert 

assessment of the technical and programmatic approach, 

risk posture, and progress against the program/project 

baseline. When appropriate, it may offer recommendations to improve performance and/or reduce risk.

Internal Reviews 

During the course of a project or task, it is necessary 

to conduct internal reviews that present technical approaches, trade studies, analyses, and problem areas to 

a peer group for evaluation and comment. The timing, 

participants, and content of these reviews is normally 

defined by the project manager or the manager of the 

performing organization with support from the technical team. In preparation for the life-cycle reviews a 

project will initiate an internal review process as defined 

in the project plan. These reviews are not just meetings 

Table 6.7-1 Program Technical Reviews

Review Purpose

Program/

System

Requirements 

Review

The P/SRR examines the functional 

and performance requirements 

defined for the program (and its 

constituent projects) and ensures that 

the requirements and the selected 

concept will satisfy the program 

and higher level requirements. It is 

an internal review. Rough order of 

magnitude budgets and schedules are 

presented.

Program/

System 

Definition 

Review

The P/SDR examines the proposed 

program architecture and the 

flowdown to the functional elements 

of the system.
6.7 Technical Assessment

NASA Systems Engineering Handbook  171

to share ideas and resolve issues, but are internal reviews 

that allow the project to establish baseline requirements, 

plans, or design through the review of technical approaches, trade studies, and analyses. 

Internal peer reviews provide an excellent means for 

controlling the technical progress of the project. They 

should also be used to ensure that all interested parties 

are involved in the development early on and throughout 

the process. Thus, representatives from areas such as 

manufacturing and quality assurance should attend the 

internal reviews as active participants. It is also a good 

practice to include representatives from other Centers 

and outside organizations providing support or developing systems or subsystems that may interface to your 

system/subsystem. They can then, for example, ensure 

that the design is producible and integratable and that 

quality is managed through the project life cycle. 

Since internal peer reviews will be at a much greater level 

of detail than the life-cycle reviews, the team may utilize internal and external experts to help develop and assess approaches and concepts at the internal reviews. Some 

organizations form a red team to provide an internal, independent, peer review to identify deficiencies and offer recommendations. Projects often refer to their internal reviews 

as “tabletop” reviews or “interim” design reviews. Whatever 

the name, the purpose is the same: to ensure the readiness 

of the baseline for successful project life-cycle review. 

It should be noted that due to the importance of these 

reviews each review should have well-defined entrance 

and success criteria established prior to the review.

Required Technical Reviews

This subsection describes the purpose, timing, objectives, success criteria, and results of the NPR 7123.1 

required technical reviews in the NASA program and 

project life cycles. This information is intended to provide guidance to program/project managers and systems 

engineers, and to illustrate the progressive maturation of 

review activities and systems engineering products. For 

Flight Systems and Ground Support (FS&GS) projects, 

the NASA life-cycle phases of Formulation and Implementation divide into seven project phases. The checklists provided below aid in the preparation of specific 

review entry and success criteria, but do not take their 

place. To minimize extra work, review material should 

be keyed to program/project documentation.

Program/System Requirements Review

The P/SRR is used to ensure that the program requirements are properly formulated and correlated with the 

Agency and mission directorate strategic objectives.

Table 6.7‐2 P/SRR Entrance and Success Criteria

Program/System Requirements Review

Entrance Criteria Success Criteria

1. An FAD has been approved. 

2. Program requirements have been defined that support mission 

directorate requirements on the program.

3. Major program risks and corresponding mitigation strategies have 

been identified.

4. The high-level program requirements have been documented to include:

a. performance,

b. safety, and

c. programmatic requirements.

5. An approach for verifying compliance with program requirements has 

been defined.

6. Procedures for controlling changes to program requirements have 

been defined and approved.

7. Traceability of program requirements to individual projects is 

documented in accordance with Agency needs, goals, and objectives, 

as described in the NASA Strategic Plan. 

8. Top program/project risks with significant technical, safety, cost, and 

schedule impacts are identified. 

1. With respect to mission and science 

requirements, defined high-level program 

requirements are determined to be 

complete and are approved.

2. Defined interfaces with other programs 

are approved.

3. The program requirements are determined 

to provide a cost-effective program.

4. The program requirements are adequately 

levied on either the single-program project 

or the multiple projects of the program.

5. The plans for controlling program requirement changes have been approved. 

6. The approach for verifying compliance 

with program requirements has been 

approved.

7. The mitigation strategies for handling 

identified major risks have been approved. 
172  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Program/System Definition Review

The P/SDR applies to all NASA space flight programs to 

ensure the readiness of these programs to enter an approved Program Commitment Agreement (PCA). The 

approved PCA permits programs to transition from the 

program Formulation phase to the program Implementation phase. A Program Approval Review (PAR) is conducted as part of the P/SDR to provide Agency management with an independent assessment of the readiness of 

the program to proceed into implementation. 

The P/SDR examines the proposed program architecture and the flowdown to the functional elements of 

the system. The proposed program’s objectives and the 

concept for meeting those objectives are evaluated. Key 

technologies and other risks are identified and assessed. 

The baseline program plan, budgets, and schedules are 

presented. The technical team provides the technical 

content to support the P/SDR. The P/SDR examines the 

proposed program architecture and the flowdown to the 

functional elements of the system.

Table 6.7‐3 P/SDR Entrance and Success Criteria

Program/System Definition Review

Entrance Criteria Success Criteria

1. A P/SRR has been satisfactorily completed.

2. A program plan has been prepared that includes the following:

a. how the program will be managed;

b. a list of specific projects;

c. the high-level program requirements (including risk criteria);

d. performance, safety, and programmatic requirements correlated to Agency and directorate strategic 

objectives;

e. description of the systems to be developed (hardware and software), legacy systems, system interfaces, 

and facilities; and

f. identification of major constraints affecting system development (e.g., cost, launch window, required 

launch vehicle, mission planetary environment, engine design, international partners, and technology 

drivers).

3. Program-level SEMP that includes project technical approaches and management plans to implement the 

allocated program requirements including constituent launch, flight, and ground systems; and operations 

and logistics concepts. 

4. Independent cost analyses (ICAs) and independent cost estimates (ICEs).

5. Management plan for resources other than budget.

6. Documentation for obtaining the PCA that includes the following:

a. the feasibility of the program mission solution with a cost estimate within acceptable cost range,

b. project plans adequate for project formulation initiation,

c. identified and prioritized program concept evaluation criteria to be used in project evaluations,

d. estimates of required annual funding levels,

e. credible program cost and schedule allocation estimates to projects,

f. acceptable risk and mitigation strategies (supported by a technical risk assessment),

g. organizational structures and defined work assignments,

h. defined program acquisition strategies,

i. interfaces to other programs and partners,

j. a draft plan for program implementation, and

k. a defined program management system.

7. A draft program control plan that includes:

a. how the program plans to control program requirements, technical design, schedule, and cost to achieve 

its high-level requirements;

b. how the requirements, technical design, schedule, and cost of the program will be controlled;

c. how the program will utilize its technical, schedule, and cost reserves to control the baseline;

d. how the program plans to report technical, schedule, and cost status to the MDAA, including frequency 

and the level of detail; and

e. how the program will address technical waivers and how dissenting opinions will be handled.

8. For each project, a top-level description has been documented.

1. An approved 

program plan 

and management approach. 

2. Approved SEMP 

and technical 

approach. 

3. Estimated costs 

are adequate.

4. Documentation 

for obtaining 

the PCA is 

approved.

5. An approved 

draft program 

control plan.

6. Agreement that 

the program 

is aligned with 

Agency needs, 

goals, and 

objectives.

7. The technical 

approach is 

adequate.

8. The schedule is 

adequate and 

consistent with 

cost, risk, and 

mission goals. 

9. Resources other 

than budget are 

adequate and 

available.
6.7 Technical Assessment

NASA Systems Engineering Handbook  173

Table 6.7‐4 MCR Entrance and Success Criteria

Mission Concept Review

Entrance Criteria Success Criteria

1. Mission goals and objectives.

2. Analysis of alternative concepts to show 

at least one is feasible.

3. ConOps.

4. Preliminary mission descope options.

5. Preliminary risk assessment including 

technologies and associated risk 

management/mitigation strategies and 

options.

6. Conceptual test and evaluation strategy.

7. Preliminary technical plans to achieve 

next phase.

8. Defined MOEs and MOPs.

9. Conceptual life-cycle support strategies 

(logistics, manufacturing, operation, etc.).

1. Mission objectives are clearly defined and stated and are unambiguous 

and internally consistent.

2. The preliminary set of requirements satisfactorily provides a system 

that will meet the mission objectives.

3. The mission is feasible. A solution has been identified that is technically 

feasible. A rough cost estimate is within an acceptable cost range.

4. The concept evaluation criteria to be used in candidate systems evaluation have been identified and prioritized.

5. The need for the mission has been clearly identified.

6. The cost and schedule estimates are credible.

7. An updated technical search was done to identify existing assets or 

products that could satisfy the mission or parts of the mission.

8. Technical planning is sufficient to proceed to the next phase.

9. Risk and mitigation strategies have been identified and are acceptable 

based on technical assessments.

Mission Concept Review

The MCR will affirm the mission need and examine 

the proposed mission’s objectives and the concept for 

meeting those objectives. It is an internal review that 

usually occurs at the cognizant organization for system 

development. The MCR should be completed prior to 

entering the concept development phase (Phase A).

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately 

documented and a plan for resolution is prepared.

Results of Review

A successful MCR supports the determination that the 

proposed mission meets the customer need, and has 

sufficient quality and merit to support a field Center 

management decision to propose further study to the 

cognizant NASA program associate administrator as a 

candidate Phase A effort.
174  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Table 6.7‐5 SRR Entrance and Success Criteria

System Requirements Review

Entrance Criteria Success Criteria

1. Successful completion of the MCR and responses made to all MCR RFAs and 

RIDs.

2. A preliminary SRR agenda, success criteria, and charge to the board have been 

agreed to by the technical team, project manager, and review chair prior to the SRR.

3. The following technical products for hardware and software system elements 

are available to the cognizant participants prior to the review:

a. system requirements document;

b. system software functionality description;

c. updated ConOps;

d. updated mission requirements, if applicable;

e. baselined SEMP;

f. risk management plan;

g. preliminary system requirements allocation to the next lower level system;

h. updated cost estimate;

i. technology development maturity assessment plan;

j. updated risk assessment and mitigations (including PRA, as applicable);

k. logistics documentation (e.g., preliminary maintenance plan);

l. preliminary human rating plan, if applicable;

m. software development plan;

n. system SMA plan;

o. CM plan;

p. initial document tree;

q. verification and validation approach;

r. preliminary system safety analysis; and

s. other specialty disciplines, as required.

1. The project utilizes a sound 

process for the allocation 

and control of requirements 

throughout all levels, and a plan 

has been defined to complete 

the definition activity within 

schedule constraints.

2. Requirements definition is 

complete with respect to 

top-level mission and science 

requirements, and interfaces with 

external entities and between 

major internal elements have 

been defined.

3. Requirements allocation and 

flowdown of key driving requirements have been defined down 

to subsystems.

4. Preliminary approaches have 

been determined for how 

requirements will be verified 

and validated down to the 

subsystem level.

5. Major risks have been identified 

and technically assessed, and 

viable mitigation strategies have 

been defined.

System Requirements Review

The SRR examines the functional and performance requirements defined for the system and the preliminary 

program or project plan and ensures that the requirements and selected concept will satisfy the mission.The 

SRR is conducted during the concept development phase 

(Phase A) and before conducting the SDR or MDR.

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately documented and a plan for resolution is prepared.

Results of Review

Successful completion of the SRR freezes program/

project requirements and leads to a formal decision by 

the cognizant program associate administrator to proceed with proposal request preparations for project implementation.
6.7 Technical Assessment

NASA Systems Engineering Handbook  175

Mission Definition Review (Robotic Missions 

Only)

The MDR examines the proposed requirements, the 

mission architecture, and the flowdown to all functional 

elements of the mission to ensure that the overall concept is complete, feasible, and consistent with available 

resources.

MDR is conducted during the concept development 

phase (Phase A) following completion of the concept 

studies phase (Pre-Phase A) and before the preliminary 

design phase (Phase B). 

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately documented and a plan for resolution is prepared.

Results of Review

A successful MDR supports the decision to further develop the system architecture/design and any technology 

needed to accomplish the mission. The results reinforce 

the mission’s merit and provide a basis for the system acquisition strategy.

Table 6.7‐6 MDR Entrance and Success Criteria

Mission Definition Review

Entrance Criteria Success Criteria

1. Successful completion of the SRR and responses made to all SRR RFAs 

and RIDs.

2. A preliminary MDR agenda, success criteria, and charge to the board 

have been agreed to by the technical team, project manager, and review 

chair prior to the MDR.

3. The following technical products for hardware and software system elements are available to the cognizant participants prior to the review:

a. system architecture;

b. updated system requirements document, if applicable;

c. system software functionality description;

d. updated ConOps, if applicable;

e. updated mission requirements, if applicable;

f. updated SEMP, if applicable;

g. updated risk management plan, if applicable;

h. technology development maturity assessment plan;

i. preferred system solution definition including major trades and 

options;

j. updated risk assessment and mitigations (including PRA, as applicable);

k. updated cost and schedule data;

l. logistics documentation (e.g., preliminary maintenance plan);

m. software development plan;

n. system SMA plan;

o. CM plan;

p. updated initial document tree, if applicable;

q. preliminary system safety analysis; and

r. other specialty disciplines as required.

1. The resulting overall concept is reasonable, feasible, complete, responsive 

to the mission requirements, and is 

consistent with system requirements 

and available resources (cost, schedule, 

mass, and power).

2. System and subsystem design approaches and operational concepts 

exist and are consistent with the 

requirements set.

3. The requirements, design approaches, 

and conceptual design will fulfill the 

mission needs within the estimated 

costs.

4. Major risks have been identified and 

technically assessed, and viable mitigation strategies have been defined.
176  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Table 6.7‐7 SDR Entrance and Success Criteria

System Definition Review

Entrance Criteria Success Criteria

1. Successful completion of the SRR and responses made to all 

SRR RFAs and RIDs.

2. A preliminary SDR agenda, success criteria, and charge to the 

board have been agreed to by the technical team, project 

manager, and review chair prior to the SDR.

3. SDR technical products listed below for both hardware and 

software system elements have been made available to the 

cognizant participants prior to the review:

a. system architecture; 

b. preferred system solution definition including major 

trades and options;

c. updated baselined documentation, as required;

d. preliminary functional baseline (with supporting tradeoff 

analyses and data);

e. preliminary system software functional requirements;

f. SEMP changes, if any;

g. updated risk management plan;

h. updated risk assessment and mitigations (including PRA, 

as applicable);

i. updated technology development maturity assessment 

plan;

j. updated cost and schedule data;

k. updated logistics documentation;

l. based on system complexity, updated human rating plan;

m. software test plan;

n. software requirements document(s);

o. interface requirements documents (including software);

p. technical resource utilization estimates and margins;

q. updated SMA plan; and

r. updated preliminary safety analysis.

1. Systems requirements, including mission success 

criteria and any sponsor-imposed constraints, 

are defined and form the basis for the proposed 

conceptual design.

2. All technical requirements are allocated, and 

the flowdown to subsystems is adequate. The 

requirements, design approaches, and conceptual 

design will fulfill the mission needs consistent with 

the available resources (cost, schedule, mass, and 

power). 

3. The requirements process is sound and can 

reasonably be expected to continue to identify 

and flow detailed requirements in a manner timely 

for development.

4. The technical approach is credible and responsive 

to the identified requirements.

5. Technical plans have been updated, as necessary.

6. The tradeoffs are completed, and those planned 

for Phase B adequately address the option space.

7. Significant development, mission, and safety risks 

are identified and technically assessed, and a risk 

process and resources exist to manage the risks.

8. Adequate planning exists for the development of 

any enabling new technology.

9. The ConOps is consistent with proposed design 

concept(s) and is in alignment with the mission 

requirements.

System Definition Review (Human Space 

Flight Missions Only)

The SDR examines the proposed system architecture/design and the flowdown to all functional elements of the 

system. SDR is conducted at the end of the concept development phase (Phase A) and before the preliminary 

design phase (Phase B) begins.

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately documented and a plan for resolution is prepared.

Results of Review

As a result of successful completion of the SDR, the 

system and its operation are well enough understood 

to warrant design and acquisition of the end items. Approved specifications for the system, its segments, and 

preliminary specifications for the design of appropriate 

functional elements may be released. A configuration 

management plan is established to control design and 

requirement changes. Plans to control and integrate the 

expanded technical process are in place.
6.7 Technical Assessment

NASA Systems Engineering Handbook  177

Preliminary Design Review

The PDR demonstrates that the preliminary design 

meets all system requirements with acceptable risk and 

within the cost and schedule constraints and establishes 

the basis for proceeding with detailed design. It will show 

that the correct design options have been selected, interfaces have been identified, approximately 10 percent of 

engineering drawings have been created, and verification methods have been described. PDR occurs near the 

completion of the preliminary design phase (Phase B) as 

the last review in the Formulation phase.

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately documented and a plan for resolution is prepared.

Results of Review

As a result of successful completion of the PDR, the design-to baseline is approved. A successful review result 

also authorizes the project to proceed into implementation and toward final design.

Table 6.7‐8 PDR Entrance and Success Criteria

Preliminary Design Review

Entrance Criteria Success Criteria

1. Successful completion of the SDR or MDR and responses made to all 

SDR or MDR RFAs and RIDs, or a timely closure plan exists for those 

remaining open.

2. A preliminary PDR agenda, success criteria, and charge to the board 

have been agreed to by the technical team, project manager, and 

review chair prior to the PDR.

3. PDR technical products listed below for both hardware and software 

system elements have been made available to the cognizant participants prior to the review:

a. Updated baselined documentation, as required.

b. Preliminary subsystem design specifications for each configuration 

item (hardware and software), with supporting tradeoff analyses 

and data, as required. The preliminary software design specification 

should include a completed definition of the software architecture 

and a preliminary database design description as applicable.

c. Updated technology development maturity assessment plan.

d. Updated risk assessment and mitigation.

e. Updated cost and schedule data.

f. Updated logistics documentation, as required.

g. Applicable technical plans (e.g., technical performance measurement plan, contamination control plan, parts management plan, 

environments control plan, EMI/EMC control plan, payload-to-carrier integration plan, producibility/manufacturability program plan, 

reliability program plan, quality assurance plan).

h. Applicable standards.

i. Safety analyses and plans.

j. Engineering drawing tree.

k. Interface control documents.

l. Verification and validation plan.

m. Plans to respond to regulatory (e.g., National Environmental Policy 

Act) requirements, as required.

n. Disposal plan.

o. Technical resource utilization estimates and margins.

p. System-level safety analysis.

q. Preliminary LLIL.

1. The top-level requirements—including mission 

success criteria, TPMs, and any sponsor-imposed constraints—are agreed upon, finalized, stated clearly, 

and consistent with the preliminary design.

2. The flowdown of verifiable requirements is complete 

and proper or, if not, an adequate plan exists for 

timely resolution of open items. Requirements are 

traceable to mission goals and objectives.

3. The preliminary design is expected to meet the 

requirements at an acceptable level of risk.

4. Definition of the technical interfaces is consistent 

with the overall technical maturity and provides an 

acceptable level of risk.

5. Adequate technical interfaces are consistent with the 

overall technical maturity and provide an acceptable 

level of risk.

6. Adequate technical margins exist with respect to 

TPMs.

7. Any required new technology has been developed 

to an adequate state of readiness, or backup options 

exist and are supported to make them a viable 

alternative.

8. The project risks are understood and have been 

credibly assessed, and plans, a process, and resources 

exist to effectively manage them.

9. SMA (e.g., safety, reliability, maintainability, quality, 

and EEE parts) has been adequately addressed in preliminary designs and any applicable SMA products 

(e.g., PRA, system safety analysis, and failure modes 

and effects analysis) have been approved.

10. The operational concept is technically sound, 

includes (where appropriate) human factors, and 

includes the flowdown of requirements for its execution.
178  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Table 6.7‐9 CDR Entrance and Success Criteria

Critical Design Review

Entrance Criteria Success Criteria

1. Successful completion of the PDR and responses made to all PDR RFAs and RIDs, 

or a timely closure plan exists for those remaining open.

2. A preliminary CDR agenda, success criteria, and charge to the board have been 

agreed to by the technical team, project manager, and review chair prior to the CDR.

3. CDR technical work products listed below for both hardware and software 

system elements have been made available to the cognizant participants prior to 

the review:

a. updated baselined documents, as required;

b. product build-to specifications for each hardware and software configuration 

item, along with supporting tradeoff analyses and data;

c. fabrication, assembly, integration, and test plans and procedures;

d. technical data package (e.g., integrated schematics, spares provisioning list, 

interface control documents, engineering analyses, and specifications);

e. operational limits and constraints;

f. technical resource utilization estimates and margins;

g. acceptance criteria;

h. command and telemetry list;

i. verification plan (including requirements and specifications);

j. validation plan;

k. launch site operations plan;

l. checkout and activation plan;

m. disposal plan (including decommissioning or termination);

n. updated technology development maturity assessment plan;

o. updated risk assessment and mitigation;

p. update reliability analyses and assessments;

q. updated cost and schedule data;

r. updated logistics documentation;

s. software design document(s) (including interface design documents);

t. updated LLIL;

u. subsystem-level and preliminary operations safety analyses;

v. system and subsystem certification plans and requirements (as needed); and

w. system safety analysis with associated verifications.

1. The detailed design is expected to meet the 

requirements with adequate margins at an 

acceptable level of risk.

2. Interface control documents are appropriately matured to proceed with fabrication, 

assembly, integration, and test, and plans 

are in place to manage any open items.

3. High confidence exists in the product 

baseline, and adequate documentation 

exists or will exist in a timely manner to allow proceeding with fabrication, assembly, 

integration, and test.

4. The product verification and product validation requirements and plans are complete.

5. The testing approach is comprehensive, 

and the planning for system assembly, 

integration, test, and launch site and mission operations is sufficient to progress into 

the next phase.

6. Adequate technical and programmatic 

margins and resources exist to complete 

the development within budget, schedule, 

and risk constraints.

7. Risks to mission success are understood and 

credibly assessed, and plans and resources 

exist to effectively manage them.

8. SMA (e.g., safety, reliability, maintainability, quality, and EEE parts) have been 

adequately addressed in system and operational designs, and any applicable SMA plan 

products (e.g., PRA, system safety analysis, 

and failure modes and effects analysis) have 

been approved.

Critical Design Review

The purpose of the CDR is to demonstrate that the maturity of the design is appropriate to support proceeding 

with full scale fabrication, assembly, integration, and 

test, and that the technical effort is on track to complete 

the flight and ground system development and mission 

operations to meet mission performance requirements 

within the identified cost and schedule constraints. Approximately 90 percent of engineering drawings are approved and released for fabrication. CDR occurs during 

the final design phase (Phase C).

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately documented and a plan for resolution is prepared.

Results of Review

As a result of successful completion of the CDR, the 

build-to baseline, production, and verification plans 

are approved. A successful review result also authorizes 

coding of deliverable software (according to the buildto baseline and coding standards presented in the review), and system qualification testing and integration. 

All open issues should be resolved with closure actions 

and schedules.
6.7 Technical Assessment

NASA Systems Engineering Handbook  179

Production Readiness Review

A PRR is held for FS&GS projects developing or acquiring multiple or similar systems greater than three or 

as determined by the project. The PRR determines the 

readiness of the system developers to efficiently produce 

the required number of systems. It ensures that the production plans; fabrication, assembly, and integration-enabling products; and personnel are in place and ready 

to begin production. PRR occurs during the final design 

phase (Phase C).

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria.

z Ensure issues raised during the review are appropriately 

documented and a plan for resolution is prepared.

Results of Review

As a result of successful completion of the PRR, the final 

production build-to baseline, production, and verification plans are approved. Approved drawings are released 

and authorized for production. A successful review result also authorizes coding of deliverable software (according to the build-to baseline and coding standards 

presented in the review), and system qualification testing 

and integration. All open issues should be resolved with 

closure actions and schedules.

Table 6.7‐10 PRR Entrance and Success Criteria

Production Readiness Review

Entrance Criteria Success Criteria

1. The significant production engineering problems encountered 

during development are resolved.

2. The design documentation is 

adequate to support production.

3. The production plans and preparation are adequate to begin 

fabrication.

4. The production-enabling products and adequate resources are 

available, have been allocated, 

and are ready to support end 

product production.

1. The design is appropriately certified.

2. The system requirements are fully met in the final production configuration.

3. Adequate measures are in place to support production.

4. Design-for-manufacturing considerations ensure ease and efficiency of 

production and assembly.

5. Risks have been identified, credibly assessed, and characterized; and mitigation 

efforts have been defined.

6. The bill of materials has been reviewed and critical parts identified.

7. Delivery schedules have been verified.

8. Alternative sources for resources have been identified, as appropriate.

9. Adequate spares have been planned and budgeted.

10. Required facilities and tools are sufficient for end product production.

11. Specified special tools and test equipment are available in proper quantities.

12. Production and support staff are qualified.

13. Drawings are certified.

14. Production engineering and planning are sufficiently mature for cost-effective 

production.

15. Production processes and methods are consistent with quality requirements 

and compliant with occupational safety, environmental, and energy conservation regulations.

16. Qualified suppliers are available for materials that are to be procured.
180  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Table 6.7‐11 SIR Entrance and Success Criteria

System Integration Review

Entrance Criteria Success Criteria

1. Integration plans and procedures have been completed and 

approved.

2. Segments and/or components are available for integration.

3. Mechanical and electrical interfaces have been verified against the 

interface control documentation.

4. All applicable functional, unit-level, subsystem, and qualification 

testing has been conducted successfully.

5. Integration facilities, including clean rooms, ground support 

equipment, handling fixtures, overhead cranes, and electrical test 

equipment, are ready and available.

6. Support personnel have been adequately trained.

7. Handling and safety requirements have been documented.

8. All known system discrepancies have been identified and disposed 

in accordance with an agreed-upon plan. 

9. All previous design review success criteria and key issues have 

been satisfied in accordance with an agreed-upon plan.

10. The quality control organization is ready to support the integration 

effort.

1. Adequate integration plans and procedures 

are completed and approved for the system 

to be integrated.

2. Previous component, subsystem, and system 

test results form a satisfactory basis for 

proceeding to integration.

3. Risk level is identified and accepted by 

program/project leadership, as required.

4. The integration procedures and workflow 

have been clearly defined and documented.

5. The review of the integration plans, as well 

as the procedures, environment, and the 

configuration of the items to be integrated, 

provides a reasonable expectation that the 

integration will proceed successfully.

6. Integration personnel have received appropriate training in the integration and safety 

procedures.

System Integration Review

An SIR ensures that the system is ready to be integrated. 

Segments, components, and subsystems are available 

and ready to be integrated into the system. Integration 

facilities, support personnel, and integration plans and 

procedures are ready for integration. SIR is conducted 

at the end of the final design phase (Phase C) and before the systems assembly, integration, and test phase 

(Phase D) begins. 

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria.

z Ensure issues raised during the review are appropriately 

documented and a plan for resolution is prepared.

Results of Review

As a result of successful completion of the SIR, the final 

as-built baseline and verification plans are approved. Approved drawings are released and authorized to support 

integration. All open issues should be resolved with closure actions and schedules. The subsystems/systems integration procedures, ground support equipment, facilities, logistical needs, and support personnel are planned 

for and are ready to support integration.
6.7 Technical Assessment

NASA Systems Engineering Handbook  181

Test Readiness Review

A TRR ensures that the test article (hardware/software), 

test facility, support personnel, and test procedures are 

ready for testing and data acquisition, reduction, and 

control. A TRR is held prior to commencement of verification or validation testing.

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately documented and a plan for resolution is prepared.

Results of Review

A successful TRR signifies that test and safety engineers 

have certified that preparations are complete, and that 

the project manager has authorized formal test initiation.

Table 6.7‐12 TRR Entrance and Success Criteria

Test Readiness Review

Entrance Criteria Success Criteria

1. The objectives of the testing have been clearly defined and 

documented and all of the test plans, procedures, environment, 

and the configuration of the test item(s) support those objectives.

2. Configuration of the system under test has been defined and 

agreed to. All interfaces have been placed under configuration 

management or have been defined in accordance with an 

agreed-to plan, and a version description document has been 

made available to TRR participants prior to the review.

3. All applicable functional, unit-level, subsystem, system, and 

qualification testing has been conducted successfully.

4. All TRR-specific materials such as test plans, test cases, and 

procedures have been made available to all participants prior to 

conducting the review.

5. All known system discrepancies have been identified and 

disposed in accordance with an agreed-upon plan.

6. All previous design review success criteria and key issues have 

been satisfied in accordance with an agreed-upon plan.

7. All required test resources people (including a designated test 

director), facilities, test articles, test instrumentation, and other 

enabling products have been identified and are available to 

support required tests.

8. Roles and responsibilities of all test participants are defined and 

agreed to.

9. Test contingency planning has been accomplished, and all 

personnel have been trained.

1. Adequate test plans are completed and approved for the system under test.

2. Adequate identification and coordination of 

required test resources are completed.

3. Previous component, subsystem, and system 

test results form a satisfactory basis for proceeding into planned tests.

4. Risk level is identified and accepted by program/competency leadership as required.

5. Plans to capture any lessons learned from the 

test program are documented.

6. The objectives of the testing have been clearly 

defined and documented, and the review of 

all the test plans, as well as the procedures, 

environment, and the configuration of the test 

item, provide a reasonable expectation that the 

objectives will be met.

7. The test cases have been reviewed and analyzed for expected results, and the results are 

consistent with the test plans and objectives.

8. Test personnel have received appropriate training in test operation and safety procedures.
182  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Table 6.7‐13 SAR Entrance and Success Criteria

System Acceptance Review

Entrance Criteria Success Criteria

1. A preliminary agenda has been coordinated (nominally) prior to the 

SAR.

2. The following SAR technical products have been made available to the 

cognizant participants prior to the review:

a. results of the SARs conducted at the major suppliers;

b. transition to production and/or manufacturing plan;

c. product verification results;

d. product validation results;

e. documentation that the delivered system complies with the 

established acceptance criteria;

f. documentation that the system will perform properly in the 

expected operational environment;

g. technical data package updated to include all test results;

h. certification package;

i. updated risk assessment and mitigation;

j. successfully completed previous milestone reviews; and

k. remaining liens or unclosed actions and plans for closure.

1. Required tests and analyses are 

complete and indicate that the system 

will perform properly in the expected 

operational environment.

2. Risks are known and manageable.

3. System meets the established acceptance criteria.

4. Required safe shipping, handling, 

checkout, and operational plans and 

procedures are complete and ready for 

use.

5. Technical data package is complete and 

reflects the delivered system.

6. All applicable lessons learned for 

organizational improvement and system 

operations are captured.

System Acceptance Review

The SAR verifies the completeness of the specific end 

products in relation to their expected maturity level and 

assesses compliance to stakeholder expectations. The 

SAR examines the system, its end products and documentation, and test data and analyses that support verification. It also ensures that the system has sufficient 

technical maturity to authorize its shipment to the designated operational facility or launch site.

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately documented and a plan for resolution is prepared.

Results of Review

As a result of successful completion of the SAR, the 

system is accepted by the buyer, and authorization is 

given to ship the hardware to the launch site or operational facility, and to install software and hardware for 

operational use.
6.7 Technical Assessment

NASA Systems Engineering Handbook  183

Operational Readiness Review

The ORR examines the actual system characteristics and 

the procedures used in the system or end product’s operation and ensures that all system and support (flight 

and ground) hardware, software, personnel, procedures, 

and user documentation accurately reflect the deployed 

state of the system. 

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately 

documented and a plan for resolution is prepared.

Results of Review

As a result of successful ORR completion, the system is 

ready to assume normal operations.

Table 6.7‐14 ORR Entrance and Success Criteria 

Operational Readiness Review

Entrance Criteria Success Criteria

1. All validation testing has been completed.

2. Test failures and anomalies from validation testing have been 

resolved and the results incorporated into all supporting and 

enabling operational products.

3. All operational supporting and enabling products (e.g., 

facilities, equipment, documents, updated databases) that are 

necessary for the nominal and contingency operations have 

been tested and delivered/installed at the site(s) necessary to 

support operations.

4. Operations handbook has been approved.

5. Training has been provided to the users and operators on the 

correct operational procedures for the system.

6. Operational contingency planning has been accomplished, 

and all personnel have been trained.

1. The system, including any enabling products, 

is determined to be ready to be placed in an 

operational status.

2. All applicable lessons learned for organizational 

improvement and systems operations have been 

captured.

3. All waivers and anomalies have been closed.

4. Systems hardware, software, personnel, and 

procedures are in place to support operations.
184  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Flight Readiness Review

The FRR examines tests, demonstrations, analyses, and 

audits that determine the system’s readiness for a safe 

and successful flight or launch and for subsequent flight 

operations. It also ensures that all flight and ground 

hardware, software, personnel, and procedures are operationally ready. 

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately documented and a plan for resolution is prepared.

Results of Review

As a result of successful FRR completion, technical and 

procedural maturity exists for system launch and flight 

authorization and in some cases initiation of system operations.

Table 6.7‐15 FRR Entrance and Success Criteria 

Flight Readiness Review

Entrance Criteria Success Criteria

1. Receive certification that flight operations can 

safely proceed with acceptable risk. 

2. The system and support elements have been confirmed as properly configured and ready for flight. 

3. Interfaces are compatible and function as expected.

4. The system state supports a launch Go decision 

based on Go or No-Go criteria.

5. Flight failures and anomalies from previously 

completed flights and reviews have been resolved 

and the results incorporated into all supporting and 

enabling operational products.

6. The system has been configured for flight.

1. The flight vehicle is ready for flight.

2. The hardware is deemed acceptably safe for flight (i.e., meeting the established acceptable risk criteria or documented as 

being accepted by the PM and DGA).

3. Flight and ground software elements are ready to support 

flight and flight operations.

4. Interfaces are checked out and found to be functional.

5. Open items and waivers have been examined and found to 

be acceptable.

6. The flight and recovery environmental factors are within 

constraints.

7. All open safety and mission risk items have been addressed.
6.7 Technical Assessment

NASA Systems Engineering Handbook  185

Post-Launch Assessment Review

A PLAR is a post-deployment evaluation of the readiness of the spacecraft systems to proceed with full, routine operations. The review evaluates the status, performance, and capabilities of the project evident from the 

flight operations experience since launch. This can also 

mean assessing readiness to transfer responsibility from 

the development organization to the operations organization. The review also evaluates the status of the project 

plans and the capability to conduct the mission with 

emphasis on near-term operations and mission-critical 

events. This review is typically held after the early flight 

operations and initial checkout.

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately 

documented and a plan for resolution is prepared.

Table 6.7‐16 PLAR Entrance and Success Criteria 

Post-Launch Assessment Review

Entrance Criteria Success Criteria

1. The launch and early operations performance, including (when appropriate) the early propulsive maneuver results, are available.

2. The observed spacecraft and science instrument performance, including instrument calibration plans and status, are available. 

3. The launch vehicle performance assessment and mission implications, 

including launch sequence assessment and launch operations experience with lessons learned, are completed.

4. The mission operations and ground data system experience, including 

tracking and data acquisition support and spacecraft telemetry data 

analysis, are available.

5. The mission operations organization, including status of staffing, 

facilities, tools, and mission software (e.g., spacecraft analysis, and 

sequencing), is available.

6. In-flight anomalies and the responsive actions taken, including any 

autonomous fault protection actions taken by the spacecraft, or any 

unexplained spacecraft telemetry, including alarms, are documented.

7. The need for significant changes to procedures, interface agreements, 

software, and staffing has been documented.

8. Documentation is updated, including any updates originating from the 

early operations experience.

9. Future development/test plans are developed.

1. The observed spacecraft and science 

payload performance agrees with prediction, or if not, it is adequately understood 

so that future behavior can be predicted 

with confidence.

2. All anomalies have been adequately 

documented, and their impact on 

operations assessed. Further, anomalies 

impacting spacecraft health and safety 

or critical flight operations have been 

properly disposed.

3. The mission operations capabilities, 

including staffing and plans, are adequate to accommodate the actual flight 

performance.

4. Liens, if any, on operations, identified as 

part of the ORR, have been satisfactorily 

disposed.
186  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Critical Event Readiness Review

A CERR confirms the project’s readiness to execute the 

mission’s critical activities during flight operation. 

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately 

documented and a plan for resolution is prepared.

Post-Flight Assessment Review

The PFAR evaluates the activities from the flight after recovery. The review identifies all anomalies that occurred 

during the flight and mission and determines the actions 

necessary to mitigate or resolve the anomalies for future 

flights.

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately 

documented and a plan for resolution is prepared.

Table 6.7‐18 PFAR Entrance and Success Criteria

Post-Flight Assessment Review

Entrance Criteria Success Criteria

1. All anomalies that occurred 

during the mission, as well 

as during preflight testing, 

countdown, and ascent, 

identified.

2. Report on overall post-recovery condition.

3. Report any evidence of ascent 

debris.

4. All photo and video documentation available.

5. Retention plans for scrapped 

hardware completed.

6. Post-flight assessment team 

operating plan completed.

7. Disassembly activities 

planned and scheduled.

8. Processes and controls to 

coordinate in-flight anomaly 

troubleshooting and postflight data preservation 

developed.

9. Problem reports, corrective 

action requests, post-flight 

anomaly records, and final 

post-flight documentation 

completed.

10. All post-flight hardware and 

flight data evaluation reports 

completed.

1. Formal final 

report documenting flight 

performance and 

recommendations for future 

missions. 

2. All anomalies 

have been 

adequately 

documented and 

disposed. 

3. The impact of 

anomalies on 

future flight 

operations has 

been assessed. 

4. Plans for retaining assessment 

documentation 

and imaging 

have been made.

5. Reports and 

other documentation have 

been added to 

a database for 

performance 

comparison and 

trending.

Table 6.7‐17 CERR Entrance and Success Criteria

Critical Event Readiness Review

Entrance Criteria Success Criteria

1. Mission overview and 

context for the critical 

event(s).

2. Activity requirements and 

constraints.

3. Critical activity sequence 

design description 

including key tradeoffs 

and rationale for selected 

approach.

4. Fault protection strategy.

5. Critical activity operations 

plan including planned 

uplinks and criticality.

6. Sequence verification 

(testing, walk-throughs, 

peer review) and critical 

activity validation.

7. Operations team training 

plan and readiness report.

8. Risk areas and mitigations.

9. Spacecraft readiness 

report.

10. Open items and plans.

1. The critical activity 

design complies 

with requirements.

2. The preparation 

for the critical 

activity, including 

the verification 

and validation, is 

thorough.

3. The project (including all the systems, 

supporting services, 

and documentation) 

is ready to support 

the activity.

4. The requirements 

for the successful 

execution of the 

critical event(s) 

are complete and 

understood and 

have been flowed 

down to the appropriate levels for 

implementation.
6.7 Technical Assessment

NASA Systems Engineering Handbook  187

Decommissioning Review

The DR confirms the decision to terminate or decommission the system and assesses the readiness of the 

system for the safe decommissioning and disposal of 

system assets. The DR is normally held near the end of 

routine mission operations upon accomplishment of 

planned mission objectives. It may be advanced if some 

unplanned event gives rise to a need to prematurely terminate the mission, or delayed if operational life is extended to permit additional investigations. 

Objectives

The objectives of the review are to:

z Ensure a thorough review of the products supporting 

the review. 

z Ensure the products meet the entrance criteria and 

success criteria. 

z Ensure issues raised during the review are appropriately documented and a plan for resolution is prepared.

Results of Review

A successful DR completion ensures that the decommissioning and disposal of system items and processes are 

appropriate and effective.

Table 6.7‐19 DR Entrance and Success Criteria

Decommissioning Review

Entrance Criteria Success Criteria

1. Requirements associated with decommissioning and disposal are defined.

2. Plans are in place for decommissioning, 

disposal, and any other removal from 

service activities. 

3. Resources are in place to support decommissioning and disposal activities, 

plans for disposition of project assets, 

and archival of essential mission and 

project data. 

4. Safety, environmental, and any other 

constraints are described.

5. Current system capabilities are 

described. 

6. For off-nominal operations, all contributing events, conditions, and changes 

to the originally expected baseline are 

described.

1. The reasons for decommissioning disposal are documented.

2. The decommissioning and disposal plan is complete, approved by appropriate management, and compliant with applicable Agency safety, 

environmental, and health regulations. Operations plans for all potential 

scenarios, including contingencies, are complete and approved. All 

required support systems are available. 

3. All personnel have been properly trained for the nominal and contingency procedures.

4. Safety, health, and environmental hazards have been identified. Controls 

have been verified. 

5. Risks associated with the disposal have been identified and adequately 

mitigated. Residual risks have been accepted by the required management.

6. If hardware is to be recovered from orbit: 

a. Return site activity plans have been defined and approved.

b. Required facilities are available and meet requirements, including 

those for contamination control, if needed.

c. Transportation plans are defined and approved. Shipping containers 

and handling equipment, as well as contamination and environmental control and monitoring devices, are available.

7. Plans for disposition of mission-owned assets (i.e., hardware, software, 

facilities) have been defined and approved.

8. Plans for archival and subsequent analysis of mission data have been 

defined and approved. Arrangements have been finalized for the 

execution of such plans. Plans for the capture and dissemination of 

appropriate lessons learned during the project life cycle have been 

defined and approved. Adequate resources (schedule, budget, and 

staffing) have been identified and are available to successfully complete 

all decommissioning, disposal, and disposition activities.
188  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Other Technical Reviews

These typical technical reviews are some that have been 

conducted on previous programs and projects but are 

not required as part of the NPR 7123.1 systems engineering process.

Design Certification Review

Purpose

The Design Certification Review (DCR) ensures that the 

qualification verifications demonstrate design compliance with functional and performance requirements.

Timing

The DCR follows the system CDR, and after qualification tests and all modifications needed to implement 

qualification-caused corrective actions have been completed.

Objectives

The objectives of the review are to:

z Confirm that the verification results met functional 

and performance requirements, and that test plans 

and procedures were executed correctly in the specified environments.

z Certify that traceability between test article and production article is correct, including name, identification number, and current listing of all waivers.

z Identify any incremental tests required or conducted 

due to design or requirements changes made since test 

initiation, and resolve issues regarding their results.

Criteria for Successful Completion

The following items comprise a checklist to aid in determining the readiness of DCR product preparation:

z Are the pedigrees of the test articles directly traceable 

to the production units?

z Is the verification plan used for this article current 

and approved?

z Do the test procedures and environments used comply 

with those specified in the plan?

z Are there any changes in the test article configuration 

or design resulting from the as-run tests? Do they require design or specification changes and/or retests?

z Have design and specification documents been audited?

z Do the verification results satisfy functional and performance requirements?

z Do the verification, design, and specification documentation correlate?

Results of Review

As a result of a successful DCR, the end item design is 

approved for production. All open issues should be resolved with closure actions and schedules.
6.7 Technical Assessment

NASA Systems Engineering Handbook  189

Functional and Physical Configuration Audits

Configuration audits confirm that the configured 

product is accurate and complete. The two types of configuration audits are the Functional Configuration Audit 

(FCA) and the Physical Configuration Audit (PCA). The 

FCA examines the functional characteristics of the configured product and verifies that the product has met, via 

test results, the requirements specified in its functional 

baseline documentation approved at the PDR and CDR. 

FCAs will be conducted on both hardware or software 

configured products and will precede the PCA of the 

configured product. The PCA (also known as a configuration inspection) examines the physical configuration 

of the configured product and verifies that the product 

corresponds to the build-to (or code-to) product baseline documentation previously approved at the CDR. 

PCAs will be conducted on both hardware and software 

configured products.

Technical Peer Reviews

Peer reviews provide the technical insight essential to 

ensure product and process quality. Peer reviews are 

focused, in-depth technical reviews that support the 

evolving design and development of a product, including 

critical documentation or data packages. They are often, 

but not always, held as supporting reviews for technical 

reviews such as PDR and CDR. A purpose of the peer 

review is to add value and reduce risk through expert 

knowledge infusion, confirmation of approach, identification of defects, and specific suggestions for product 

improvements. 

The results of the engineering peer reviews comprise a 

key element of the review process. The results and issues that surface during these reviews are documented 

and reported out at the appropriate next higher element 

level.

The peer reviewers should be selected from outside the 

project, but they should have a similar technical background, and they should be selected for their skill and 

experience. Peer reviewers should be concerned with 

only the technical integrity and quality of the product. 

Peer reviews should be kept simple and informal. They 

should concentrate on a review of the documentation 

and minimize the viewgraph presentations. A roundtable format rather than a stand-up presentation is preferred. The peer reviews should give the full technical 

picture of items being reviewed.

Table 6.7‐20 Functional and Physical Configuration Audits 

Representative Audit Data List

FCA PCA

z Design specifications

z Design drawings and parts list

z Engineering change proposals/engineering change requests

z Deviation/waiver approval requests incorporated and pending

z Specification and drawing tree

z Fracture control plan

z Structural dynamics, analyses, loads, and models documentation

z Materials usage agreements/materials identification usage list

z Verification and validation requirements, plans, procedures, and 

reports

z Software requirements and development documents

z Listing of accomplished tests and test results

z CDR completion documentation including RIDs/RFAs and disposition reports

z Analysis reports

z ALERT (Acute Launch Emergency Restraint Tip) tracking log

z Hazard analysis/risk assessment

z Final version of all specifications

z Product drawings and parts list 

z Configuration accounting and status reports 

z Final version of all software and software documents

z Copy of all FCA findings for each product

z List of approved and outstanding engineering 

change proposals, engineering change requests, 

and deviation/waiver approval requests

z Indentured parts list

z As-run test procedures

z Drawing and specification tree

z Manufacturing and inspection “build” records

z Inspection records

z As-built discrepancy reports

z Product log books

z As-built configuration list
190  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Technical depth should be established at a level that allows the review team to gain insight into the technical 

risks. Rules need to be established to ensure consistency 

in the peer review process. At the conclusion of the review, a report on the findings, recommendations, and 

actions must be distributed to the technical team.

For those projects where systems engineering is done 

out-of-house, peer reviews must be part of the contract.

Additional guidance on establishing and conducting 

peer reviews can be found in Appendix N.

6.7.2.2 Status Reporting and Assessment

This subsection provides additional information on 

status reporting and assessment techniques for costs and 

schedules (including EVM), technical performance, and 

systems engineering process metrics. 

Cost and Schedule Control Measures

Status reporting and assessment on costs and schedules 

provides the project manager and systems engineer visibility into how well the project is tracking against its 

planned cost and schedule targets. From a management 

point of view, achieving these targets is on a par with 

meeting the technical performance requirements of the 

system. It is useful to think of cost and schedule status 

reporting and assessment as measuring the performance 

of the “system that produces the system.”

NPR 7120.5 provides specific requirements for the application of EVM to support cost and schedule management. EVM is applicable to both in-house and contracted efforts. The level of EVM system implementation 

will depend on the dollar value and risk of a project or 

contract. The standard for EVM systems is ANSI-EIA748. The project manager/systems engineer will use the 

guidelines to establish the program and project EVM 

implementation plan. 

Assessment Methods

Performance measurement data are used to assess project 

cost, schedule, and technical performance and their impacts on the completion cost and schedule of the project. 

In program control terminology, a difference between 

actual performance and planned costs or schedule status 

is called a “variance.” Variances must be controlled at the 

control account level, which is typically at the subsystem 

WBS level. The person responsible for this activity is frequently called the Control Account Manager (CAM). 

The CAM develops work and product plans, schedules, 

and time-phased resource plans. The technical subsystem manager/leads often takes on this role as part of 

their subsystem management responsibilities.

Figure 6.7-3 illustrates two types of variances, cost and 

schedule, and some related concepts. A product-oriented WBS divides the project work into discrete tasks 

and products. Associated with each task and product (at 

any level in the WBS) is a schedule and a budgeted (i.e., 

planned) cost. The Budgeted Cost for Work Scheduled

(BCWSt) for any set of WBS elements is the sum of the 

budgeted cost of all work on tasks and products in those 

elements scheduled to be completed by time t. The Budgeted Cost for Work Performed (BCWPt

), also called 

Earned Value (EVt), is the sum of the budgeted cost for 

tasks and products that have actually been produced at 

time t in the schedule for those WBS elements. The difference, BCWPt

 and BCWSt, is called the schedule variance at time t. A negative value indicates that the work is 

behind schedule.

The Actual Cost of Work Performed (ACWPt) represents the funds that have been expended up to time t on 

those WBS elements. The difference between the budgeted and actual costs, BCWPt  ACWPt

, is called the 

cost variance at time t. A negative value here indicates a 

cost overrun.

Cumulative $ 0

Time t

Cost Variance

to Date

(BCWP - ACWP)

Schedule

Variance

to Date

(BCWP - BCWS)

Forecast

of Cost

Variance at

Completion

Current

Date

Budget

EAC

BCWS

ACWP

BCWP

(or EV)

Figure 6.7-3 Cost and schedule variances
6.7 Technical Assessment

NASA Systems Engineering Handbook  191

When either schedule variance or cost variance exceeds 

preestablished control-account-level thresholds that represent significant departures from the baseline plan, the 

conditions must be analyzed to identify why the variance 

exists. Once the cause is understood, the CAM can make 

an informed forecast of the time and resources needed 

to complete the control account. When corrective actions are feasible (can stay within the BCWS), the plan 

for implementing them must be included in the analysis. 

Sometimes no corrective action is feasible; overruns or 

schedule slips may be unavoidable. One must keep in 

mind that the earlier a technical problem is identified as 

a result of schedule or cost variances, the more likely the 

project team can minimize the impact on completion.

Variances may indicate that the cost Estimate at Completion (EACt

) of the project is likely to be different 

from the Budget at Completion (BAC). The difference 

between the BAC and the EAC is the Variance at Completion (VAC). A negative VAC is generally unfavorable, 

while a positive is usually favorable. These variances may 

also point toward a change in the scheduled completion date of the project. These types of variances enable 

a program analyst to estimate the EAC at any point in 

the project life cycle. (See box on analyzing EAC.) These 

analytically derived estimates should be used only as a 

“sanity check” against the estimates prepared in the variance analysis process.

If the cost and schedule baselines and the technical scope 

of the work are not adequately defined and fully integrated, then it is very difficult (or impossible) to estimate 

the current cost EAC of the project.

Other efficiency factors can be calculated using the performance measurement data. The Schedule Performance 

Index (SPI) is a measure of work accomplishment in dollars. The SPI is calculated by dividing work accomplished 

in dollars or BCWP by the dollar value of the work scheduled or BCWS. Just like any other ratio, a value less than 

one is a sign of a behind-schedule condition, equal to one 

indicates an on-schedule status, and greater than one denotes that work is ahead of schedule. The Cost Performance Index (CPI) is a measure of cost efficiency and is 

calculated as the ratio of the earned value or BCWP for 

a segment of work compared to the cost to complete that 

same segment of work or ACWP. A CPI will show how 

much work is being accomplished for every dollar spent 

on the project. A CPI of less than one reveals negative 

cost efficiency, equal to one is right on cost, and greater 

than one is positive. Note that traditional measures compare planned cost to actual cost; however, this comparison is never made using earned value data. Comparing 

planned to actual costs is an indicator only of spending 

and not of overall project performance.

Technical Measures—MOEs, MOPs, and TPMs

Measures of Effectiveness

MOEs are the “operational” measures of success that are 

closely related to the achievement of mission or operational objectives in the intended operational environment. MOEs are intended to focus on how well mission 

or operational objectives are achieved, not on how they 

are achieved, i.e., MOEs should be independent of any 

particular solution. As such, MOEs are the standards 

against which the “goodness” of each proposed solution 

may be assessed in trade studies and decision analyses. 

Measuring or calculating MOEs not only makes it possible to compare alternative solutions quantitatively, but 

sensitivities to key assumptions regarding operational 

environments and to any underlying MOPs can also be 

investigated. (See MOP discussion below.)

In the systems engineering process, MOEs are used to:

z Define high-level operational requirements from the 

customer/stakeholder viewpoint.

z Compare and rank alternative solutions in trade 

studies.

Analyzing the Estimate at Completion

An EAC can be estimated at any point in the project 

and should be reviewed at least on a monthly basis. 

The EAC requires a detailed review by the CAM. A statistical estimate can be used as a cross-check of the 

CAM’s estimate and to develop a range to bound the 

estimate. The appropriate formula used to calculate 

the statistical EAC depends upon the reasons associated with any variances that may exist. If a variance 

exists due to a one-time event, such as an accident, 

then EAC = ACWP + (BAC – BCWP). The CPI and SPI 

should also be considered in developing the EAC.

If there is a growing number of liens, action items, or 

significant problems that will increase the difficulty 

of future work, the EAC might grow at a greater rate 

than estimated by the above equation. Such factors 

could be addressed using risk management methods 

described in the Section 6.4. 
192  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

z Investigate the relative sensitivity of the projected 

mission or operational success to key operational assumptions and performance parameters.

z Determine that the mission or operational success 

quantitative objectives remain achievable as system 

development proceeds. (See TPM discussion below.)

Measures of Performance

MOPs are the measures that characterize physical or 

functional attributes relating to the system, e.g., engine 

I

sp, max thrust, mass, and payload-to-orbit. These attributes are generally measured under specified test conditions or operational environments. MOPs are attributes 

deemed important in achieving mission or operational 

success, but do not measure it directly. Usually multiple MOPs contribute to an MOE. MOPs often become 

system performance requirements that, when met by a 

design solution, result in achieving a critical threshold 

for the system MOEs.

The distinction between MOEs and MOPs is that they 

are formulated from different viewpoints. An MOE refers to the effectiveness of a solution from the mission 

or operational success criteria expressed by the user/customer/stakeholder. An MOE represents a stakeholder 

expectation that is critical to the success of the system, 

and failure to attain a critical value for it will cause the 

stakeholder to judge the system a failure. An MOP is a 

measure of actual performance of a (supplier’s) particular design solution, which taken alone may only be indirectly related to the customer/stakeholder’s concerns.

Technical Performance Measures

TPMs are critical or key mission success or performance 

parameters that are monitored during implementation 

by comparing the current actual achievement of the parameters with the values that were anticipated for the 

current time and projected for future dates. They are 

used to confirm progress and identify deficiencies that 

might jeopardize meeting a system requirement or put 

the project at cost or schedule risk. When a TPM value 

falls outside the expected range around the anticipated 

value, it signals a need for evaluation and corrective action.

In the systems engineering process, TPMs are used to:

z Forecast values to be achieved by critical parameters 

at major milestones or key events during implementation.

z Identify differences between the actual and planned 

values for those parameters. 

z Provide projected values for those parameters in order 

to assess the implications for system effectiveness.

z Provide early warning for emerging risks requiring 

management attention (when negative margins exist).

z Provide early identification of potential opportunities to make design trades that reduce risk or cost, or 

increase system effectiveness (when positive margins 

exist).

z Support assessment of proposed design changes.

Selecting TPMs

TPMs are typically selected from the defined set of 

MOEs and MOPs. Understanding that TPM tracking requires allocation of resources, care should be exercised 

in selecting a small set of succinct TPMs that accurately 

reflect key parameters or risk factors, are readily measurable, and that can be affected by altering design decisions. In general, TPMs can be generic (attributes that are 

meaningful to each PBS element, like mass or reliability) 

or unique (attributes that are meaningful only to specific 

PBS elements). The relationship of MOEs, MOPs, and 

TPMs can be found in Figure 6.7-4. The systems engineer needs to decide which generic and unique TPMs 

are worth tracking at each level of the PBS. (See box for 

examples of TPMs.) At lower levels of the PBS, TPMs 

MOE #1 MOE #2

MOEs Derived from stakeholder expectation statements;

deemed critical to mission or operational success of 

the system

MOPs Broad physical and performance parameters; means of

ensuring meeting the associated MOEs

TPMs Critical mission success or performance attributes;

measurable; progress prole established, controlled,

and monitored

MOP #1 MOP #2 MOP #3 MOP#n

TPM #1 TPM #2 TPM #3 TPM #4 TPM #5 TPM #k

Figure 6.7-4 Relationships of MOEs, MOPs,

and TPMs
6.7 Technical Assessment

NASA Systems Engineering Handbook  193

worth tracking can be identified through the functional 

and performance requirements levied on each individual 

system, subsystem, etc. 

As TPMs are intended to provide an early warning of 

the adequacy of a design in satisfying selected critical 

technical parameter requirements, the systems engineer 

should select TPMs that fall within well-defined (quantitative) limits for reasons of system effectiveness or mission feasibility. Usually these limits represent either a 

firm upper or lower bound constraint. A typical example 

of such a TPM for a spacecraft is its injected mass, which 

must not exceed the capability of the selected launch 

vehicle. Tracking injected mass as a high-level TPM is 

meant to ensure that this does not happen. A high-level 

TPM like injected mass must often be “budgeted” and 

allocated to multiple system elements. Tracking and reporting should be required at these lower levels to gain 

visibility into the sources of any variances. 

In summary, for a TPM to be a valuable status and assessment tool, certain criteria must be met:

z Be a significant descriptor of the system (e.g., weight, 

range, capacity, response time, safety parameter) that 

will be monitored at key events (e.g., reviews, audits, 

planned tests). 

z Can be measured (either by test, inspection, demonstration, or analysis). 

z Is such that reasonable projected progress profiles can 

be established (e.g., from historical data or based on 

test planning).

TPM Assessment and Reporting Methods

Status reporting and assessment of the system’s TPMs 

complement cost and schedule control. There are a 

number of assessment and reporting methods that have 

been used on NASA projects, including the planned profile method and the margin management method. 

A detailed example of the planned profile method 

for the Chandra Project weight TPM is illustrated in 

Figure 6.7-5. This figure depicts the subsystem contributions, various constraints, project limits, and management reserves from project SRR to launch.

A detailed example of the margin management method 

for the Sojourner mass TPM is illustrated in Figure 6.7-6 

This figure depicts the margin requirements (horizontal 

straight lines) and actual mass margins from project SRR 

to launch. 

Relationship of TPM Assessment Program to the 

SEMP

The SEMP is the usual document for describing the project’s TPM assessment program. This description should 

include a master list of those TPMs to be tracked, and the 

measurement and assessment methods to be employed. 

If analytical methods and models are used to measure 

Examples of Technical Performance 

Measures 

TPMs from MOEs

z Mission performance (e.g., total science data volume returned)

z Safety (e.g., probability of loss of crew, probability 

of loss of mission)

z Achieved availability (e.g., (system uptime)/(system 

uptime + system downtime))

TPMs from MOPs

z Thrust versus predicted/specified

z I

sp versus predicted/specified

z End of Mission (EOM) dry mass

z Injected mass (includes EOM dry mass, baseline 

mission plus reserve propellant, other consumables and upper stage adaptor mass)

z Propellant margins at EOM

z Other consumables margins at EOM

z Electrical power margins over mission life 

z Control system stability margins

z EMI/EMC susceptibility margins 

z Onboard data processing memory demand

z Onboard data processing throughput time

z Onboard data bus capacity

z Total pointing error

z Total vehicle mass at launch

z Payload mass (at nominal altitude or orbit)

z Reliability 

z Mean time before refurbishment required

z Total crew maintenance time required

z System turnaround time

z Fault detection capability

z Percentage of system designed for on-orbit crew 

access
194  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

certain high-level TPMs, then these need to be identified. The reporting frequency and timing of assessments 

should be specified as well. In determining these, the systems engineer must balance the project’s needs for accurate, timely, and effective TPM tracking against the cost 

of the TPM tracking program. 

The TPM assessment program plan, which may be a part 

of the SEMP or a stand-alone document for large programs/projects, should specify each TPM’s allocation, 

time-phased planned profile or margin requirement, 

and alert zones, as appropriate to the selected assessment 

method.

A formal TPM assessment program should be fully 

planned and baselined with the SEMP. Tracking TPMs 

should begin as soon as practical in Phase B. Data to 

support the full set of selected TPMs may, however, 

not be available until later in the project life cycle. As 

the project life cycle proceeds through Phases C and D, 

the measurement of TPMs should become increasingly 

more accurate with the availability of more actual data 

about the system. 

For the WBS model in the system structure, typically the 

following activities are performed:

z Analyze stakeholder expectation statements to establish a set of MOEs by which overall system or product 

effectiveness will be judged and customer satisfaction 

will be determined. 

Figure 6.7-5 Use of the planned profile method for the weight TPM with rebaseline in Chandra Project

Chandra Project: Weight Changes

NASA Reserve

(Includes FPSI

Reserves)

Propellant 

(Less MUPS)/

Pressurant/

IUS Adapter/

System Reserve

Science

Instruments

Contractor Margin

Observatory

Contingency +

S/C, T/S, and SIM

Reserves

Contractor Reserve

Weight (lb)

Projected Basic Weight

PDR CDR

13,000 IICD Weight

Control Weight

Observatory +

Science Instruments

Observatory Contractor

Spec Weight

Observatory

Projected Weight

Observatory

Current Weight +

Subsystem Reserves

Observatory Basic

Weight (Planned)

Tolerance Band

Observatory Basic

Weight (Estimated)

8,000

10,000

SRR Launch

9,587

9,907

10,533

10,560

12,930

9,994

Figure 6.7-6 Use of the margin management 

method for the mass TPM in Sojourner

Note: Current Margin Description: Microrover System (Rover + 

Lander-Mounted Rover Equipment (LMRE)) Allocation = 16.0 kg; 

Microrover System (Rover + LMRE) Current Best Estimate = 

15.2 kg; Microrover System (Rover + LMRE) Margin = 0.8 kg (5.0%).

1% Margin Level

CDR Value

15% Margin Level

Month

Mass Margin (kg)

3.0

2.5

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

July ‘93

Oct. ‘93

Jan. ‘94

Apr. ’94

July ‘94

Oct. ‘94

Jan. ‘95

Apr. ’95

July ‘95

Oct. ‘95

Jan. ‘96

Apr. ’96

July ‘96

Oct. ‘96

Jan. ‘97

5% Margin Level

10% Margin Level
6.7 Technical Assessment

NASA Systems Engineering Handbook  195

z Define MOPs for each identified MOE.

z Define appropriate TPMs and document the TPM assessment program in the SEMP.

Systems Engineering Process Metrics

Status reporting and assessment of systems engineering 

process metrics provide additional visibility into the performance of the “system that produces the system.” As 

such, these metrics supplement the cost and schedule 

control measures discussed in this subsection.

Systems engineering process metrics try to quantify 

the effectiveness and productivity of the systems engineering process and organization. Within a single 

project, tracking these metrics allows the systems engineer to better understand the health and progress of that 

project. Across projects (and over time), the tracking of 

systems engineering process metrics allows for better 

estimation of the cost and time of performing systems 

engineering functions. It also allows the systems engineering organization to demonstrate its commitment to 

continuous improvement.

Selecting Systems Engineering Process 

Metrics

Generally, systems engineering process metrics fall into 

three categories—those that measure the progress of 

the systems engineering effort, those that measure the 

quality of that process, and those that measure its productivity. Different levels of systems engineering management are generally interested in different metrics. 

For example, a project manager or lead systems engineer may focus on metrics dealing with systems engineering staffing, project risk management progress, and 

major trade study progress. A subsystem systems engineer may focus on subsystem requirements and interface 

definition progress and verification procedures progress. 

It is useful for each systems engineer to focus on just a 

few process metrics. Which metrics should be tracked 

depends on the systems engineer’s role in the total systems engineering effort. The systems engineering process metrics worth tracking also change as the project 

moves through its life cycle.

Collecting and maintaining data on the systems engineering process is not without cost. Status reporting and 

assessment of systems engineering process metrics divert 

time and effort from the activity itself. The systems engineer must balance the value of each systems engineering 

process metric against its collection cost. The value 

of these metrics arises from the insights they provide 

into the activities that cannot be obtained from cost and 

schedule control measures alone. Over time, these metrics 

can also be a source of hard productivity data, which are 

invaluable in demonstrating the potential returns from investment in systems engineering tools and training. 

Examples and Assessment Methods

Table 6.7-21 lists some systems engineering process metrics to be considered. This list is not intended to be exhaustive. Because some of these metrics allow for different interpretations, each NASA Center needs to define 

them in a common-sense way that fits its own processes. 

For example, each field Center needs to determine what 

is meant by a “completed” versus an “approved” requirement, or whether these terms are even relevant. As part 

of this definition, it is important to recognize that not all 

requirements, for example, need be lumped together. It 

may be more useful to track the same metric separately 

for each of several different types of requirements.

Quality-related metrics should serve to indicate when 

a part of the systems engineering process is overloaded 

and/or breaking down. These metrics can be defined and 

tracked in several different ways. For example, requirements volatility can be quantified as the number of newly 

identified requirements, or as the number of changes to 

already approved requirements. As another example, 

Engineering Change Request (ECR) processing could be 

tracked by comparing cumulative ECRs opened versus 

cumulative ECRs closed, or by plotting the age profile 

of open ECRs, or by examining the number of ECRs 

opened last month versus the total number open. The 

systems engineer should apply his or her own judgment 

in picking the status reporting and assessment method.

Productivity-related metrics provide an indication of 

systems engineering output per unit of input. Although 

more sophisticated measures of input exist, the most 

common is the number of systems engineering hours dedicated to a particular function or activity. Because not all 

systems engineering hours cost the same, an appropriate 

weighing scheme should be developed to ensure comparability of hours across systems engineering personnel.

Schedule-related metrics can be depicted in a table or 

graph of planned quantities versus actuals, for example, 

comparing planned number of verification closure notices against actual. This metric should not be confused 
196  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Table 6.7‐21 Systems Engineering Process Metrics

Function Metric Category

Requirements 

development and 

management

Requirements identified versus completed versus approved S

Requirements volatility Q

Trade studies planned versus completed S

Requirements approved per systems engineering hour P

Tracking of TBAs, TBDs, and TBRs (to be announced, determined, or resolved) resolved 

versus remaining 

S

Design and developmentSpecifications planned versus completed S

Processing of engineering change proposals (ECPs)/engineering change requests (ECRs) Q

Engineering drawings planned versus released S

Verification and 

validation

Verification and validation plans identified versus approved S

Verification and validation procedures planned versus completed S

Functional requirements approved versus verified S

Verification and validation plans approved per systems engineering hour P

Processing of problem/failure reports Q

Reviews Processing of RIDs Q

Processing of action items Q

S = progress or schedule related; Q = quality related; P = productivity related

with EVM described in this subsection. EVM is focused 

on integrated cost and schedule at the desired level, 

whereas this metric focuses on an individual process or 

product within a subsystem, system, or project itself.

The combination of quality, productivity, and schedule 

metrics can provide trends that are generally more important than isolated snapshots. The most useful kind of 

assessment method allows comparisons of the trend on 

a current project with that for a successfully completed 

project of the same type. The latter provides a benchmark against which the systems engineer can judge his 

or her own efforts.
NASA Systems Engineering Handbook  197

The purpose of this section is to provide a description 

of the Decision Analysis Process, including alternative 

tools and methodologies. Decision analysis offers individuals and organizations a methodology for making 

decisions; it also offers techniques for modeling decision problems mathematically and finding optimal decisions numerically. Decision models have the capacity 

for accepting and quantifying human subjective inputs: 

judgments of experts and preferences of decisionmakers. 

Implementation of models can take the form of simple 

paper-and-pencil procedures or sophisticated computer 

programs known as decision aids or decision systems. 

The methodology is broad and must always be adapted 

to the issue under consideration. The problem is structured by identifying alternatives, one of which must 

be decided upon; possible events, one of which occurs 

thereafter; and outcomes, each of which results from a 

combination of decision and event. Decisions are made 

throughout a program/project life cycle and often are 

made through a hierarchy of panels, boards, and teams 

with increasing complementary authority, wherein each 

progressively more detailed decision is affected by the 

assumptions made at the lower level. Not all decisions 

need a formal process, but it is important to establish a 

process for those decisions that do require a formal process. Important decisions as well as supporting information (e.g., assumptions made), tools, and models must 

be completely documented so that new information can 

be incorporated and assessed and past decisions can be 

researched in context. The Decision Analysis Process 

accommodates this iterative environment and occurs 

throughout the project life cycle. 

An important aspect of the Decision Analysis Process is 

to consider and understand at what time it is appropriate 

or required for a decision to be made or not made. When 

considering a decision, it is important to ask questions 

such as: Why is a decision required at this time? For how 

long can a decision be delayed? What is the impact of 

delaying a decision? Is all of the necessary information 

available to make a decision? Are there other key drivers 

or dependent factors and criteria that must be in place 

before a decision can be made?

The outputs from this process support the decisionmaker’s difficult task of deciding among competing alternatives without complete knowledge; therefore, it is critical 

to understand and document the assumptions and limitation of any tool or methodology and integrate them 

with other factors when deciding among viable options.

Early in the project life cycle, high-level decisions are 

made regarding which technology could be used, such 

as solid or liquid rockets for propulsion. Operational 

scenarios, probabilities, and consequences are determined and the design decision made without specifying 

the component-level detail of each design alternative. 

Once high-level design decisions are made, nested systems engineering processes occur at progressively more 

detailed design levels flowed down through the entire 

system. Each progressively more detailed decision is affected by the assumptions made at the previous levels. 

For example, the solid rocket design is constrained by 

the operational assumptions made during the decision 

process that selected that design. This is an iterative process among elements of the system. Also early in the life 

cycle, the technical team should determine the types of 

data and information products required to support the 

Decision Analysis Process during the later stages of the 

project. The technical team should then design, develop, 

or acquire the models, simulations, and other tools that 

will supply the required information to decisionmakers. 

In this section, application of different levels and kinds 

of analysis are discussed at different stages of the project 

life cycle.

6.8.1 Process Description

The Decision Analysis Process is used to help evaluate 

technical issues, alternatives, and their uncertainties to 

support decisionmaking. A typical process flow diagram 

is provided in Figure 6.8-1, including inputs, activities, 

and outputs. 

Typical processes that use decision analysis are:

z Determining how to allocate limited resources (e.g., 

budget, mass, power) among competing subsystem 

interests to favor the overall outcome of the project; 

z Select and test evaluation methods and tools against 

sample data;

z Configuration management processes for major 

change requests or problem reports;

z Design processes for making major design decisions 

and selecting design approaches;

6.8 Decision Analysis
198  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Note: Studies often deal in new territory, so it is important to test whether there are sufficient data, needed 

quality, resonance with decision authority, etc., before diving in, especially for large or very complex decision trade spaces.

z Key decision point reviews or technical review decisions (e.g., PDR, CDR) as defined in NPR 7120.5 and 

NPR 7123.1;

z Go or No-Go decisions (e.g., FRR):

▶ Go—authorization to proceed or

▶ No-Go—repeat some specific aspects of development or conduct further research.

z Project management of major issues, schedule delays, 

or budget increases;

z Procurement of major items;

z Technology decisions;

z Risk management of major risks (e.g., red or yellow);

z SMA decisions; and

z Miscellaneous decisions (e.g., whether to intervene in 

the project to address an emergent performance issue).

Decision analysis can also be used in emergency situations. Under such conditions, process steps, procedures, 

and meetings may be combined, and the decision analysis documentation may be completed at the end of the 

process (i.e., after the decision is made). However, a decision matrix should be completed and used during the decision. Decision analysis documentation must be archived 

as soon as possible following the emergency situation.

6.8.1.1 Inputs

Formal decision analysis has the potential to consume 

significant resources and time. Typically, its application 

to a specific decision is warranted only when some of the 

following conditions are met:

From all technical

processes 

Work Products From

Decision Analysis

To Technical Data

Management Process 

Decision Need,

Alternatives, Issues, or 

Problems and

Supporting Data To Technical

Assessment Process

Decision Support

Recommendations and

Impacts

To all technical processes

Alternative Selection

Recommendations and

Impacts

From Technical

Assessment Process 

Analysis Support

Requests

Establish guidelines to determine

which technical issues are subject to a

formal analysis/evaluation process

Identify alternative solutions to

address decision issues

Select evaluation methods and tools

Dene the criteria for evaluating

alternative solutions

Evaluate alternative solutions with

the established criteria and

selected methods

Select recommended solutions from

the alternatives based on the

evaluation criteria

Report analysis results with 

recommendations, impacts, and

corrective actions 

Capture work products from

decision analysis activities

Figure 6.8-1 Decision Analysis Process
6.8 Decision Analysis

NASA Systems Engineering Handbook  199

z High Stakes: High stakes are involved in the decision, 

such as significant cost, safety, or mission success criteria. 

z Complexity: The actual ramifications of alternatives 

are difficult to understand without detailed analysis.

z Uncertainty: Uncertainty in key inputs creates substantial uncertainty in the ranking of alternatives and 

points to risks that may need to be managed. 

z Multiple Attributes: Greater numbers of attributes 

cause a greater need for formal analysis. 

z Diversity of Stakeholders: Extra attention is warranted to clarify objectives and formulate TPMs when 

the set of stakeholders reflects a diversity of values, 

preferences, and perspectives.

Satisfaction of all of these conditions is not a requirement 

for initiating decision analysis. The point is, rather, that 

the need for decision analysis increases as a function of 

the above conditions. When the Decision Analysis Process is triggered, the following are inputs:

z Decision need, identified alternatives, issues, or problems and supporting data (from all technical management processes).

z Analysis support requests (from Technical Assessment Process).

z High-level objectives and constraints (from the program/project).

6.8.1.2 Process Activities

For the Decision Analysis Process, the following activities typically are performed.

Establish Guidelines to Determine Which 

Technical Issues Are Subject to a Formal Analysis/

Evaluation Process

This step includes determining: 

z When to use a formal decisionmaking procedure, 

z What needs to be documented,

z Who will be the decisionmakers and their responsibilities and decision authorities, and 

z How decisions will be handled that do not require a 

formal evaluation procedure. 

Decisions are based on facts, qualitative and quantitative 

data, engineering judgment, and open communications 

to facilitate the flow of information throughout the hierarchy of forums where technical analyses and evaluations are presented and assessed and where decisions are 

made. The extent of technical analysis and evaluation required should be commensurate with the consequences 

of the issue requiring a decision. The work required to 

conduct a formal evaluation is not insignificant and applicability must be based on the nature of the problem to 

be resolved. Guidelines for use can be determined by the 

magnitude of the possible consequences of the decision 

to be made.

For example, the consequence table from a risk scorecard can be used to assign numerical values for applicability according to impacts to mission success, flight 

safety, cost, and schedule. Actual numerical thresholds 

for use would then be set by a decision authority. Sample 

values could be as shown in Table 6.8-1. 

Table 6.8‐1 Consequence Table

Numerical Value Consequence Applicability

Consequence = 5, 4 High Mandatory

Consequence = 3 Moderate Optional

Consequence = 1, 2 Low Not required

Define the Criteria for Evaluating Alternative 

Solutions

This step includes identifying:

z The types of criteria to consider, such as customer expectations and requirements, technology limitations, 

environmental impact, safety, risks, total ownership 

and life-cycle costs, and schedule impact; 

z The acceptable range and scale of the criteria; and 

z The rank of each criterion by its importance. 

Decision criteria are requirements for individually assessing options and alternatives being considered. Typical decision criteria include cost, schedule, risk, safety, 

mission success, and supportability. However, considerations should include technical criteria specific to the 

decision being made. Criteria should be objective and 

measurable. Criteria should also permit distinguishing 

among options or alternatives. Some criteria may not be 

meaningful to a decision; however, they should be documented as having been considered. Identify criteria that 

are mandatory (i.e., “must have”) versus the other criteria (i.e., “nice to have”). If mandatory criteria are not 

met, that option should be disregarded. For complex 

decisions, criteria can be grouped into categories or ob-
200  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

jectives. (See the analytical hierarchy process in Subsection 6.8.2.6.)

Ranking or prioritizing the criteria is probably the 

hardest part of completing a decision matrix. Not all criteria have the same importance, and ranking is typically 

accomplished by assigning weights to each. To avoid 

“gaming” the decision matrix (i.e., changing decision 

outcomes by playing with criteria weights), it is best to 

agree upon weights before the decision matrix is completed. Weights should only be changed with consensus 

from all decision stakeholders.

For example, ranking can be done using a simple approach like percentages. Have all the weights for each 

criterion add up to 100. Assign percents based on how 

important the criterion is. (The higher the percentage, 

the more important, such as a single criterion worth 50 

percent.) The weights need to be divided by 100 to calculate percents. Using this approach, the option with the 

highest percentage is typically the recommended option. 

Ranking can also be done using sophisticated decision 

tools. For example, pair-wise comparison is a decision 

technique that calculates the weights using paired comparisons among criteria and options. Other methods include:

z Formulation of objectives hierarchy and TPMs;

z Analytical hierarchy process, which addresses criteria 

and paired comparisons; and

z Risk-informed decision analysis process with 

weighting of TPMs.

Identify Alternative Solutions to Address 

Decision Issues

This step includes considering alternatives in addition to 

those that may be provided with the issue.

Almost every decision will have options to choose from. 

Brainstorm decision options, and document option 

summary names for the available options. For complex 

decisions, it is also a best practice to perform a literature search to identify options. Reduce the decision options to a reasonable set (e.g., seven plus or minus two). 

Some options will obviously be bad options. Document 

the fact that these options were considered. The use of 

mandatory criteria also can help reduce the number of 

options. A few decisions might only have one option. It 

is a best practice to document a decision matrix even for 

one option if it is a major decision. (Sometimes doing 

nothing or not making a decision is an option.) 

Select Evaluation Methods and Tools

Select evaluation methods and tools/techniques based 

on the purpose for analyzing a decision and on the availability of the information used to support the method 

and/or tool. 

Typical evaluation methods include: simulations; weighted 

tradeoff matrices; engineering, manufacturing, cost, and 

technical opportunity of trade studies; surveys; extrapolations based on field experience and prototypes; user review and comment; and testing.

Tools and techniques to be used should be selected based 

on the purpose for analyzing a decision and on the availability of the information used to support the method 

and/or tool. 

Additional evaluation methods include:

z Decision matrix (see Figure 6.8-2);

z Decision analysis process support, evaluation methods, 

and tools; 

z Risk-informed decision analysis process; and 

z Trade studies and decision alternatives.

Evaluate Alternative Solutions with the 

Established Criteria and Selected Methods

Regardless of the methods or tools used, results must include:

z Evaluation of assumptions related to evaluation criteria and of the evidence that supports the assumptions, and 

z Evaluation of whether uncertainty in the values for alternative solutions affects the evaluation. 

Alternatives can be compared to evaluation criteria via 

the use of a decision matrix as shown in Figure 6.8-2. 

Evaluation criteria typically are in the rows on the left 

side of the matrix. Alternatives are typically the column 

headings on the top of the matrix (and to the right top). 

Criteria weights are typically assigned to each criterion. 

In the example shown, there are also mandatory criteria. 

If mandatory criteria are not met, the option is scored at 

0 percent. 

When decision criteria have different measurement 

bases (e.g., numbers, money, weight, dates), normalization can be used to establish a common base for mathematical operations. The process of “normalization” is 

making a scale so that all different kinds of criteria can 
6.8 Decision Analysis

NASA Systems Engineering Handbook  201

be compared or added together. This can be done informally (e.g., low, medium, high), on a scale (e.g., 1-3-9), 

or more formally with a tool. No matter how normalization is done, the most important thing to remember is 

to have operational definitions of the scale. An operational definition is a repeatable, measurable number. For 

example, “high” could mean “a probability of 67 percent 

and above.” “Low” could mean “a probability of 33 percent and below.” For complex decisions, decision tools 

usually provide an automated way for normalization. Be 

sure to question and understand the operational definitions for the weights and scales of the tool.

Select Recommended Solutions from the 

Alternatives Based on the Evaluation Criteria

This step includes documenting the information, including 

assumptions and limitations of the evaluation methods 

used, that justifies the recommendations made and gives 

the impacts of taking the recommended course of action.

The highest score (e.g., percentage, total score) is typically the option that is recommended to management. 

If a different option is recommended, an explanation 

must be provided as to why the lower score is preferred. 

Usually, if a lower score is recommended, the “risks” 

or “disadvantages” were too great for the highest score. 

Sometimes the benefits and advantages of a lower or 

close score outweigh the highest score. Ideally, all risks/

benefits and advantages/disadvantages would show up 

in the decision matrix as criteria, but this is not always 

possible. Sometimes if there is a lower score being recommended, the weighting or scores given may not be 

accurate.

Report the Analysis and Evaluation Results and 

Findings with Recommendations, Impacts, and 

Corrective Actions

Typically a technical team of subject matter experts 

makes a recommendation to a NASA decisionmaker 

(e.g., a NASA board, forum, or panel). It is highly recommended that the team produce a white paper to document all major recommendations to serve as a backup to 

Figure 6.8-2 Example of a decision matrix 

Decision Matrix

Example for Battery 

ENTER SCORES

Extend Old Battery LifeBuy New BatteriesCollect Experient Data WithAlternative ExperimentCancelled Experiment

CRITERIA Mandatory (Y=1/N=0)? Weight SCALE

Mission Success (Get

Experiment Data) 1 30 3 = Most Supportive

1 = Least Supportive

2 3 3 0

Cost per Option 0 10 3 = Least Expensive

1 = Most Expensive

1 2 3 1

Risk (Overall Option Risk) 0 15 3 = Least Risk

1 = Most Risk 2 1 2 3

Schedule 0 10 3 = Shortest Schedule

1 = Longest Schedule

3 2 1 3

Safety 1 15 3 = Most Safe

1 = Least Safe 2 1 2 3

Uninterrupted Data Collection 0 20 3 = Most Supportive

1 = Least Supportive

3 1 2 1

WEIGHTED TOTALS in % 100% 3 73% 60% 77% 0%

SCALE 1-3

Note: Completing the decision matrix can be thought 

of as a default evaluation method. Completing the 

decision matrix is iterative. Each cell for each criterion 

and each option needs to be completed by the team. 

Use evaluation methods as needed to complete the 

entire decision matrix.
202  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

any presentation materials used. A presentation can also 

be used, but a paper in conjunction with a decision matrix is preferred (especially for complex decisions). Decisions are typically captured in meeting minutes, but can 

be captured in the white paper.

Capture Work Products from Decision Analysis 

Activities

This step includes capturing: 

z Decision analysis guidelines generated and strategy 

and procedures used; 

z Analysis/evaluation approach, criteria, and methods 

and tools used; 

z Analysis/evaluation results, assumptions made in arriving at recommendations, uncertainties, and sensitivities of the recommended actions or corrective actions; and 

z Lessons learned and recommendations for improving 

future decision analyses.

Typical information captured in a decision report is 

shown in Table 6.8-2.

6.8.1.3 Outputs

Decision analysis continues throughout the life cycle. 

The products from decision analysis include:

z Alternative selection recommendations and impacts 

(to all technical management processes);

z Decision support recommendations and impacts (to 

Technical Assessment Process);

Table 6.8‐2 Typical Information to Capture in a Decision Report 

# Section Section Description

1 Executive Summary Provide a short half-page executive summary of the report:

z Recommendation (short summary—1 sentence)

z Problem/issue requiring a decision (short summary—1 sentence)

2 Problem/Issue 

Description

Describe the problem/issue that requires a decision. Provide background, history, the 

decisionmaker(s) (e.g., board, panel, forum, council), and decision recommendation team, etc.

3 Decision Matrix 

Setup Rationale

Provide the rationale for setting up the decision matrix:

z Criteria selected

z Options selected

z Weights selected

z Evaluation methods selected

Provide a copy of the setup decision matrix.

4 Decision Matrix 

Scoring Rationale

Provide the rationale for the scoring of the decision matrix. Provide the results of populating the 

scores of the matrix using the evaluation methods selected.

5 Final Decision 

Matrix

Cut and paste the final spreadsheet into the document. Also include any important snapshots of 

the decision matrix.

6 Risk/Benefits For the final options being considered, document the risks and benefits of each option.

7 Recommendation 

and/or Final 

Decision

Describe the recommendation that is being made to the decisionmaker(s) and the rationale for 

why the option was selected. Can also document the final decision in this section.

8 Dissent If applicable, document any dissent with the recommendation. Document how dissent was 

addressed (e.g., decision matrix, risk, etc.).

9 References Provide any references.

A Appendices Provide the results of the literature search, including lessons learned, previous related decisions, 

and previous related dissent. Also document any detailed data analysis and risk analysis used for 

the decision. Can also document any decision metrics.
6.8 Decision Analysis

NASA Systems Engineering Handbook  203

z Work products of decision analysis activities (to Technical Data Management Process); and

z Technical risk status measurements (to Technical Risk 

Management Process).

z TPMs, Performance Indexes (PIs) for alternatives, the 

program- or project-specific objectives hierarchy, and 

the decisionmakers’ preferences (to all technical management processes).

6.8.2 Decision Analysis Guidance

The purpose of this subsection is to provide guidance, 

methods, and tools to support the Decision Analysis 

Process at NASA. 

6.8.2.1 Systems Analysis, Simulation, and 

Performance

Systems analysis can be better understood in the context 

of the system’s overall life cycle. Systems analysis within 

the context of the life cycle is responsive to the needs of 

the stakeholder at every phase of the life cycle, from prePhase A through Phase B to realizing the final product 

and beyond (See Figure 6.8-3.) 

Systems analysis of a product must support the transformation from a need into a realized, definitive product; 

be able to support compatibility with all physical and 

functional requirements; and support the operational 

Figure 6.8-3 Systems analysis across the life cycle

Concept

Collaboration,

Assessment, and

Feedback to Design 

Virtual Prototyping Detailed, Focused Development

Requirements Understanding/Filtering Architectures Selection/Analysis Execution

60–90% of life-cycle

cost locked in (but not

necessarily known) Needs Identication

Requirements Analysis

System Feasibility Analysis

Cost/Benet Analysis

Operational Requirements Analysis

Establish MOEs, TPMs

Functional Systems Analysis and Allocation

Analysis, Synthesis, and Evaluation

Feasible Technology Applications Evaluation

Technical Approach Selection 

Functional Denition of System

System Planning

Alternative Architectures

Top-Level Architecture

Functional Analysis

Requirements Allocation

Trade Studies and Decision Analysis

Input Data Required

Denitions

Functional Baseline

Selection Evaluation Techniques

Select Model(s)

Identication of Design-Dependent Parameters

 Reevaluation of Established MOEs/TPMs

Acquire Input Data

Evaluate Each Candidate

Tradeo and Decision Analysis

Sensitivity Analysis

Design Renement

Recommendations

 Condence Levels

 Tradeos

 Breakeven Points

 Sensitivities—Risks and Uncertainties

 MOEs Associated With Decision Alternatives

Design to Baseline or Allocated Baseline

Renement of Synthesis/Evaluation for System

 and Subsystem Levels

Evaluation in Terms of Requirements

Continuation of Iterations

Sensitivity and Contingency Analysis

Update Analysis and Models With New Data

Build-to Product Baseline

Evaluation and Selection of Dierent Technologies

Evaluation and Selection of Dierent Materials

Alternative System Packaging and Wiring

Alternative Diagnostics

Alternative Instrumentation Concepts

Evaluation and Selection of COTS Items

Alternative Maintenance and Support Concepts

Evaluation of Autonomous vs. Human Facilitation

Acquisition Plans

 Contracting

Program Implementation

Major Suppliers and Supplier Activities

Subsystem Component Design

Trade Studies and Evaluation of Decision Alternatives

Development of Engineering and Prototype Models

Verication of Manufacturing and Production Processes

Developmental Test and Evaluation

Supplier Activities

 Alternative Manufacture/Producibility Concepts

 Alternative Logistics Support Concepts

 Alternative System/Material Disposal Concepts

Update Analysis and Models With New Data

As-Built Product Baseline

Production and/or Construction of System Components

Supplier Production Activities

 Acceptance Testing

System Distribution and Operation

Developmental/Operational Test and Evaluation

Interim Contractor Support

Update Analysis With New Data

As-Deployed Baseline

 System Operation in User Environment

Sustaining Maintenance & Logistic Support

Operational Testing

 System Modications for Improvement

 Contractor Support

 System Assessment/Field Data Collection

 and Analysis

Update Analysis and Models 

Phase E:

Operations and

Sustainment 

Phase D:

System Assembly,

Integration & Test, Launch

Pre-Phase A:

Concept Studies

Phase B:

Preliminary Design and

Technology Completion

Phase A:

Concept & Technology

Development 

Phase C:

Final Design and

Fabrication

Process/Product

Assessment, and

Renement

Operations
204  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

scenarios in terms of reliability, maintainability, supportability, serviceability, and disposability, while maintaining performance and affordability. 

Systems analysis support is provided from cradle to 

grave of the system. This covers the product design, verification, manufacturing, operations and support, and 

disposal. Viewed in this manner, life-cycle engineering 

is the basis for concurrent engineering. 

Systems analysis should support concurrent engineering. 

Appropriate systems analysis can be conducted early in 

the life cycle to support planning and development. The 

intent here is to support seamless systems analysis optimally planned across the entire life cycle. For example, 

systems engineering early in the life cycle can support 

optimal performance of the deployment, operations, and 

disposal facets of the system. 

Historically, this has not been the case. Systems analysis 

would focus only on the life cycle that the project occupied at that time. The systems analyses for the later 

phases were treated serially, in chronological order. This 

resulted in major design modifications that were very 

costly in the later life-cycle phases. Resources can be 

used more efficiently if the requirements across the life 

cycle are considered concurrently, providing results for 

decisionmaking about the system. 

Figure 6.8-3 shows a life-cycle chart that indicates how 

the various general types of systems analyses fit across 

the phases of the life cycle. The requirements for analysis 

begin with a broader scope and more types of analysis 

required in the early phases of the life cycle and funnel 

or narrow in scope and analysis requirements as decisions are made and project requirements become clearer 

as the project proceeds through its life cycle. Figure 6.8-4 

presents a specific spaceport example and shows how 

specific operational analysis inputs can provide analysis result outputs pertinent to the operations portion of 

the life cycle. Note that these simulations are conducted 

across the life cycle and updated periodically with the 

new data that is obtained as the project evolves.

Figure 6.8-4 Simulation model analysis techniques

From: Lockheed Martin presentation to KSC, November 2003, Kevin Brughelli, Lockheed Martin Space Systems Company; Debbie Carstens, 

Florida Institute of Technology; and Tim Barth, KSC.

SEE IMPACTS HERE

Program Schedules

Date

Landing ops

Hangar ops

PPF ops

VIF ops

Pad ops

Flight ops

Personnel Utilization Manhours

Worked Paid

Preventive Maint.

Unplanned Work

Planned Work

Straight Time

Overtime

Facility Utilization Utilization

Hangar VIF PPF Pad

Simulation Model Outputs

MAKE CHANGES HERE

Mission Model

� Annual Launches for Each Vehicle 

Configuration

Process Flow

� Task Duration, Sequence

� Resource Requirements

ConOps

� Work Shifts and Priorities

� Weather, Range, Safety Constraints

� Extended Maintenance

Probabilistic Events

� Weather and Range Events

� Unplanned Work

� Equipment Downtime (MTBF 

and MTTR)

� Process Time Variability and 

Learning Effects

� Loss of Vehicle

Resources

� Launch Vehicle Quantity

� Facilities and Equipment

� Personnel Quality and Skills

Simulation Model Inputs

Sensitivity Analyses Sensitivity Analyses Customized Analyses

Unlimited Customized

Analyses per Specific

Program Needs 

Flight H/W Reliability

Optimum

Turnaround

Personnel Quantity

Optimum

Launch Rate

Schedule Dependability Frequency

Launch Delay (days)

01234567

mean= 1.0

Personnel Utilization

Date

Available Pool

Utilization

vehicle

2

vehicle

1

vehicle

1

Stationized Cost Manhours

Sys1 Sys2

Landing ops

Hangar ops

PPF ops

VIF ops Pad ops

Flight ops

Turnaround Frequency

Turnaround (days)

16 17 18 19 20 21 22 23

mean = 18.2

Launch Rate Launch Rate Sys1 Sys2 Sys3

Optimization

=n =y

Optimum

Nonrecurring $ Simulation Model Iterations

Meets all req’mts 
6.8 Decision Analysis

NASA Systems Engineering Handbook  205

During the early life-cycle phases, inputs should include a plan for collecting the quantitative and qualitative data necessary to manage contracts and improve 

processes and products as the project evolves. This plan 

should indicate the type of data necessary to determine 

the cause of problems, nonconformances, and anomalies, and propose corrective action to prevent recurrence. 

This closed-loop plan involving identification, resolution, and recurrence control systems is critical to producing actual reliability that approaches predicted reliability. It should indicate the information technology 

infrastructure and database capabilities to provide data 

sorting, data mining, data analysis, and precursor management. Management of problems, nonconformances, 

and anomalies should begin with data collection, should 

be a major part of technical assessment, and should provide critical information for decision analysis.

6.8.2.2 Trade Studies

The trade study process is a critical part of systems engineering. Trade studies help to define the emerging system 

at each level of resolution. One key message of this subsection is that to be effective, trade studies require the 

participation of people with many skills and a unity of 

effort to move toward an optimum system design.

Figure 6.8-5 shows the trade study process in simplest 

terms, beginning with the step of defining the system’s 

goals and objectives, and identifying the constraints it 

must meet. In the early phases of the project life cycle, 

the goals, objectives, and constraints are usually stated in 

general operational terms. In later phases of the project 

life cycle, when the architecture and, perhaps, some aspects of the design have already been decided, the goals 

and objectives may be stated as performance requirements that a segment or subsystem must meet. 

At each level of system resolution, the systems engineer 

needs to understand the full implications of the goals, 

objectives, and constraints to formulate an appropriate 

system solution. This step is accomplished by performing 

a functional analysis. “Functional analysis” is the process 

of identifying, describing, and relating the functions a 

system must perform to fulfill its goals and objectives 

and is described in detail in Section 4.4.

Figure 6.8-5 Trade study process

Define/Identify

Goals/Objectives

and Constraints 

Perform Functional

Analysis 

Define

Selection

Rule

Make a

tentative

selection

(decision)

Is tentative

selection

acceptable?*

Yes

No

Proceed to further

resolution of

system design, or to

implementation

 *The following questions

should be considered:

� Have the goals/objectives and

constraints been met?

� Is the tentative selection robust?

� Is more analytical refinement

needed to distinguish among

alternatives?

� Have the subjective aspects of

the problem been addressed?

Define measures and

measurement methods for:

� System effectiveness

� System performance or

technical attributes

� System cost

Collect data on

each alternative

to support

evaluation by

selected

measurement

methods 

� Compute an estimate of system effectiveness,

performance or technical attributes, and cost

for each alternative

� Compute or estimate uncertainty ranges

� Perform sensitivity analyses

Analytical Portion of Trade Studies

Define

Plausible

Alternatives
206  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

Closely related to defining the goals and objectives and 

performing a functional analysis is the step of defining 

the measures and measurement methods for system effectiveness (when this is practical), system performance 

or technical attributes, and system cost. (These variables 

are collectively called outcome variables, in keeping with 

the discussion in Section 2.3. Some systems engineering 

books refer to these variables as decision criteria, but this 

term should not be confused with “selection rule,” described below. Sections 2.5 and 6.1 discuss the concepts of 

system cost and effectiveness in greater detail.) Defining 

measures and measurement methods begins the analytical portion of the trade study process, since it suggests the 

involvement of those familiar with quantitative methods.

For each measure, it is important to address how that 

quantitative measure will be computed—that is, which 

measurement method is to be used. One reason for 

doing this is that this step then explicitly identifies those 

variables that are important in meeting the system’s goals 

and objectives. 

Evaluating the likely outcomes of various alternatives 

in terms of system effectiveness, the underlying performance or technical attributes, and cost before actual fabrication and/or programming usually requires the use of 

a mathematical model or series of models of the system. 

So a second reason for specifying the measurement 

methods is to identify necessary models. 

Sometimes these models are already available from previous projects of a similar nature; other times, they need 

to be developed. In the latter case, defining the measurement methods should trigger the necessary system modeling activities. Since the development of new models 

can take a considerable amount of time and effort, early 

identification is needed to ensure they will be ready for 

formal use in trade studies. Defining the selection rule 

is the step of explicitly determining how the outcome 

variables will be used to make a (tentative) selection 

of the preferred alternative. As an example, a selection 

rule may be to choose the alternative with the highest 

estimated system effectiveness that costs less than x dollars (with some given probability), meets safety requirements, and possibly meets other political or schedule 

constraints. Defining the selection rule is essentially deciding how the selection is to be made. This step is independent from the actual measurement of system effectiveness, system performance or technical attributes, 

and system cost.

Many different selection rules are possible. The selection 

rule in a particular trade study may depend on the context in which the trade study is being conducted—in particular, what level of system design resolution is being addressed. At each level of the system design, the selection 

rule generally should be chosen only after some guidance from the next higher level. The selection rule for 

trade studies at lower levels of the system design should 

be in consonance with the higher level selection rule. 

Defining plausible alternatives is the step of creating 

some alternatives that can potentially achieve the goals 

and objectives of the system. This step depends on understanding (to an appropriately detailed level) the system’s 

functional requirements and operational concept. Running an alternative through an operational timeline or 

reference mission is a useful way of determining whether 

it can plausibly fulfill these requirements. (Sometimes it 

is necessary to create separate behavioral models to determine how the system reacts when a certain stimulus 

or control is applied, or a certain environment is encountered. This provides insights into whether it can plausibly 

fulfill time-critical and safety requirements.) Defining 

plausible alternatives also requires an understanding 

of the technologies available, or potentially available, 

at the time the system is needed. Each plausible alternative should be documented qualitatively in a description sheet. The format of the description sheet should, 

at a minimum, clarify the allocation of required system 

functions to that alternative’s lower level architectural or 

design components (e.g., subsystems).

One way to represent the trade study alternatives under 

consideration is by a trade tree.

During Phase A trade studies, the trade tree should contain 

a number of alternative high-level system architectures to 

avoid a premature focus on a single one. As the systems 

engineering process proceeds, branches of the trade tree 

containing unattractive alternatives will be “pruned,” and 

greater detail in terms of system design will be added to 

those branches that merit further attention. The process 

of pruning unattractive early alternatives is sometimes 

known as doing “killer trades.” (See trade tree box.)

Given a set of plausible alternatives, the next step is to 

collect data on each to support the evaluation of the measures by the selected measurement methods. If models 

are to be used to calculate some of these measures, then 

obtaining the model inputs provides some impetus and 
6.8 Decision Analysis

NASA Systems Engineering Handbook  207

direction to the data collection activity. By providing 

data, engineers in such disciplines as reliability, maintainability, producibility, integrated logistics, software, 

testing, operations, and costing have an important supporting role in trade studies. The data collection activity, 

however, should be orchestrated by the systems engineer. 

The results of this step should be a quantitative description of each alternative to accompany the qualitative.

Test results on each alternative can be especially useful. 

Early in the systems engineering process, performance 

and technical attributes are generally uncertain and must 

be estimated. Data from breadboard and brassboard testbeds can provide additional confidence that the range of 

values used as model inputs is correct. Such confidence 

is also enhanced by drawing on data collected on related, 

previously developed systems.

The next step in the trade study process is to quantify the 

outcome variables by computing estimates of system effectiveness, its underlying system performance or technical attributes, and system cost. If the needed data have 

been collected and the measurement methods (for example, models) are in place, then this step is, in theory, 

mechanical. In practice, considerable skill is often needed 

to get meaningful results.

In an ideal world, all input values would be precisely 

known and models would perfectly predict outcome 

variables. This not being the case, the systems engineer 

should supplement point estimates of the outcome variables for each alternative with computed or estimated 

uncertainty ranges. For each uncertain key input, a 

range of values should be estimated. Using this range 

of input values, the sensitivity of the outcome variables 

An Example of a Trade Tree for a Mars Rover

The figure below shows part of a trade tree for a robotic Mars rover system, whose goal is to find a suitable manned landing site. Each layer represents some aspect of the system that needs to be treated in a trade study to determine the best 

alternative. Some alternatives have been eliminated a priori because of technical feasibility, launch vehicle constraints, 

etc. The total number of alternatives is given by the number of end points of the tree. Even with just a few layers, the 

number of alternatives can increase quickly. (This tree has already been pruned to eliminate low-autonomy, large rovers.) As the systems engineering process proceeds, branches of the tree with unfavorable trade study outcomes are discarded. The remaining branches are further developed by identifying more detailed trade studies that need to be made. 

A whole family of (implicit) alternatives can be represented in a trade tree by the continuous variable. In this example, 

rover speed or range might be so represented. By treating a variable this way, mathematical optimization techniques 

can be applied. Note that a trade tree is, in essence, a decision tree without chance nodes.

Mars Rover

Small

(–10 kg) 

Large

(–1,000 kg)

Size

Number

Mobility

Medium

(–100 kg)

50 20 10 10 5 2 1

Low High Low High Low High Low Semi High Semi High Wheels Legs Wheels Wheels Legs Wheels Wheels Legs Wheels Wheels Legs Wheels Wheels Legs Wheels Legs Wheels Legs

Low Semi High Wheels Legs Wheels Wheels Legs

Low Semi High Wheels Legs Wheels Wheels Legs

Autonomy
208  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

can be gauged and their uncertainty ranges calculated. 

The systems engineer may be able to obtain meaningful 

probability distributions for the outcome variables using 

Monte Carlo simulation, but when this is not feasible, 

the systems engineer must be content with only ranges 

and sensitivities. See the risk-informed decision analysis 

process in Subsection 6.8.2.8 for more information on 

uncertainty.

This essentially completes the analytical portion of the 

trade study process. The next steps can be described as 

the judgmental portion. Combining the selection rule 

with the results of the analytical activity should enable 

the systems engineer to array the alternatives from most 

preferred to least, in essence making a tentative selection.

This tentative selection should not be accepted blindly. In 

most trade studies, there is a need to subject the results 

to a “reality check” by considering a number of questions. Have the goals, objectives, and constraints truly 

been met? Is the tentative selection heavily dependent 

on a particular set of input values to the measurement 

methods, or does it hold up under a range of reasonable 

input values? (In the latter case, the tentative selection 

is said to be robust.) Are there sufficient data to back up 

the tentative selection? Are the measurement methods 

sufficiently discriminating to be sure that the tentative 

selection is really better than other alternatives? Have the 

subjective aspects of the problem been fully addressed?

If the answers support the tentative selection, then the 

systems engineer can have greater confidence in a recommendation to proceed to a further resolution of the 

system design, or to the implementation of that design. 

The estimates of system effectiveness, its underlying performance or technical attributes, and system cost generated during the trade study process serve as inputs 

to that further resolution. The analytical portion of the 

trade study process often provides the means to quantify 

the performance or technical (and cost) attributes that 

the system’s lower levels must meet. These can be formalized as performance requirements.

If the reality check is not met, the trade study process returns to one or more earlier steps. This iteration may result in a change in the goals, objectives, and constraints; 

a new alternative; or a change in the selection rule, based 

on the new information generated during the trade study. 

The reality check may lead instead to a decision to first 

improve the measures and measurement methods (e.g., 

models) used in evaluating the alternatives, and then to 

repeat the analytical portion of the trade study process.

Controlling the Trade Study Process

There are a number of mechanisms for controlling the 

trade study process. The most important one is the SEMP. 

The SEMP specifies the major trade studies that are to be 

performed during each phase of the project life cycle. It 

should also spell out the general contents of trade study 

reports, which form part of the decision support packages (i.e., documentation submitted in conjunction with 

formal reviews and change requests).

A second mechanism for controlling the trade study process is the selection of the study team leaders and members. Because doing trade studies is part art and part science, the composition and experience of the team is an 

important determinant of a study’s ultimate usefulness. 

A useful technique to avoid premature focus on a specific technical design is to include in the study team individuals with differing technology backgrounds.

Trade Study Reports

Trade study reports should be prepared for each 

trade study. At a minimum, each trade study report 

should identify:

z The system under analysis

z System goals and objectives (or requirements, as 

appropriate to the level of resolution), and constraints

z The measures and measurement methods (models) used

z All data sources used

z The alternatives chosen for analysis

z The computational results, including uncertainty 

ranges and sensitivity analyses performed

z The selection rule used

z The recommended alternative.

Trade study reports should be maintained as part of 

the system archives so as to ensure traceability of decisions made through the systems engineering process. Using a generally consistent format for these 

reports also makes it easier to review and assimilate 

them into the formal change control process.
6.8 Decision Analysis

NASA Systems Engineering Handbook  209

Another mechanism is limiting the number of alternatives that are to be carried through the study. This 

number is usually determined by the time and resources 

available to do the study because the work required in 

defining additional alternatives and obtaining the necessary data on them can be considerable. However, focusing on too few or too similar alternatives defeats the 

purpose of the trade study process.

A fourth mechanism for controlling the trade study process can be exercised through the use (and misuse) of 

models. Lastly, the choice of the selection rule exerts a 

considerable influence on the results of the trade study 

process. See Appendix O for different examples of how 

trade studies are used throughout the life cycle. 

6.8.2.3 Cost-Benefit Analysis

A cost-benefit analysis is performed to determine the 

advantage of one alternative over another in terms of 

equivalent cost or benefits. The analysis relies on the addition of positive factors and the subtraction of negative 

factors to determine a net result. Cost-benefit analysis 

maximizes net benefits (benefits minus costs). A costbenefit analysis finds, quantifies, and adds all the positive 

factors. These are the benefits. Then it identifies, quantifies, and subtracts all the negatives, the costs. The difference between the two indicates whether the planned 

action is a preferred alternative. The real trick to doing 

a cost-benefit analysis well is making sure to include all 

the costs and all the benefits and properly quantify them. 

A similar approach, used when a cost cap is imposed 

externally, is to maximize effectiveness for a given level 

of cost. Cost-effectiveness is a systematic quantitative 

method for comparing the costs of alternative means of 

achieving the same equivalent benefit for a specific objective. A project is cost-effective if, on the basis of lifecycle cost analysis of competing alternatives, it is determined to have the lowest costs expressed in present value 

terms for a given amount of benefits.

Cost-effectiveness analysis is appropriate whenever it is 

impractical to consider the dollar value of the benefits 

provided by the alternatives. This is the scenario whenever each alternative has the same life-cycle benefits expressed in monetary terms, or each alternative has the 

same life-cycle effects, but dollar values cannot be assigned to their benefits. After determining the scope of 

the project on the basis of mission and other requirements, and having identified, quantified, and valued 

the costs and benefits of the alternatives, the next step is 

to identify the least-cost or most cost-effective alternative to achieve the purpose of the project. A comparative analysis of the alternative options or designs is often 

required. This is illustrated in Figure 4.4-3. In cases in 

which alternatives can be defined that deliver the same 

benefits, it is possible to estimate the equivalent rate between each alternative for comparison. Least-cost analysis aims at identifying the least-cost project option for 

meeting the technical requirements. Least-cost analysis involves comparing the costs of the various technically feasible options and selecting the one with the 

lowest costs. Project options must be alternative ways of 

achieving the mission objectives. If differences in results 

or quality exist, a normalization procedure must be applied that takes the benefits of one option relative to another as a cost to the option that does not meet all of 

the mission objectives to ensure an equitable comparison. Procedures for the calculation and interpretation 

of the discounting factors should be made explicit, with 

the least-cost project being identified by comparing the 

total life-cycle costs of the project alternatives and calculating the equalizing factors for the difference in costs. 

The project with the highest equalizing factors for all 

comparisons is the least-cost alternative.

Cost-effectiveness analysis also deals with alternative 

means of achieving mission requirements. However, 

the results may be estimated only indirectly. For example, different types of systems may be under consideration to obtain science data. The effectiveness of 

each alternative may be measured through obtaining 

science data through different methods. An example 

of a cost-effectiveness analysis requires the increase in 

science data to be divided by the costs for each alternative. The most cost-effective method is the one that 

raises science data by a given amount for the least cost. 

If this method is chosen and applied to all similar alternatives, the same increase in science data can be obtained for the lowest cost. Note, however, that the most 

cost-effective method is not necessarily the most effective method of meeting mission objectives. Another 

method may be the most effective, but also cost a lot 

more, so it is not the most cost-effective. The cost-effectiveness ratios—the cost per unit increase in science 

data for each method—can be compared to see how 

much more it would cost to implement the most effective method. Which method is chosen for implementation then depends jointly on the desired mission ob-
210  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

jectives and the extra cost involved in implementing the 

most effective method.

There will be circumstances where project alternatives 

have more than one outcome. To assess the cost-effectiveness of the different alternatives, it is necessary to devise a testing system where the results for the different 

factors can be added together. It also is necessary to decide on weights for adding the different elements together, reflecting their importance in relation to the objectives of the project. Such a cost-effectiveness analysis is 

called weighted cost-effectiveness analysis. It introduces 

a subjective element, the weights, into the comparison of 

project alternatives, both to find the most cost-effective 

alternative and to identify the extra cost of implementing 

the most effective alternative.

6.8.2.4 Influence Diagrams

An influence diagram (also called a decision network) is 

a compact graphical and mathematical representation of 

a decision state. (See Figure 6.8-6.) Influence diagrams 

were first developed in the mid-1970s within the decision analysis community as an intuitive approach that is 

easy to understand. They are now adopted widely and 

are becoming an alternative to decision trees, which 

typically suffer from exponential growth in number of 

branches with each variable modeled. An influence diagram is directly applicable in team decision analysis 

since it allows incomplete sharing of information among 

team members to be modeled and solved explicitly. Its 

elements are:

z Decision nodes, indicating the decision inputs, and 

the items directly influenced by the decision outcome;

z Chance nodes, indicating factors that impact the 

chance outcome, and items influenced by the chance 

outcome;

z Value nodes, indicating factors that affect the value, 

and items influenced by the value; and 

z Arrows, indicating the relationships among the elements.

An influence diagram does not depict a strictly sequential process. Rather, it illustrates the decision process at 

a particular point, showing all of the elements important to the decision. The influence diagram for a particular model is not unique. The strength of influence diagrams is their ability to display the structure of a decision 

problem in a clear, compact form, useful both for communication and to help the analyst think clearly during 

problem formulation. An influence diagram can be 

transformed into a decision tree for quantification. 

6.8.2.5 Decision Trees

Like the influence diagram, a decision tree portrays a decision model, but a decision tree is drawn from a point 

of view different from that of the influence diagram. The 

decision tree exhaustively works out the expected consequences of all decision alternatives by discretizing all 

“chance” nodes, and, based on this discretization, calculating and appropriately weighting all possible consequences of all alternatives. The preferred alternative is then 

identified by summing the appropriate outcome variables 

(MOE or expected utility) from the path end states. 

A decision tree grows horizontally from left to right, 

with the trunk at the left. Typically, the possible alternatives initially available to the decisionmaker stem from 

the trunk at the left. Moving across the tree, the decisionmaker encounters branch points corresponding to 

probabilistic outcomes and perhaps additional decision 

nodes. Thus, the tree branches as it is read from left to 

right. At the far right side of the decision tree, a vector 

of TPM scores is listed for each terminal branch, representing each combination of decision outcome and 

chance outcome. From the TPM scores, and the chosen 

selection rule, a preferred alternative is determined. 

Consequences

Forecast Hurricane Path

Hits

Misses

Decision Table:

Decision\

Hurricane Path

Will Hit

Will Miss

Evacuate

Stay Decision 

Elements of Influence Diagrams

Chance 

Decision 

Value

Value

Decision node: represents

alternatives

Chance node: represents

events (states of nature)

Value node: represents

consequences, objectives,

} or calculations

Figure 6.8-6 Influence diagrams
6.8 Decision Analysis

NASA Systems Engineering Handbook  211

In even moderately complicated problems, decision trees 

can quickly become difficult to understand. Figure 6.8-7 

shows a sample of a decision tree. This figure only shows 

a simplified illustration. A complete decision tree with 

additional branches would be expanded to the appropriate level of detail as required by the analysis. A commonly employed strategy is to start with an equivalent 

influence diagram. This often aids in helping to understand the principal issues involved. Some software packages make it easy to develop an influence diagram and 

then, based on the influence diagram, automatically furnish a decision tree. The decision tree can be edited if 

this is desired. Calculations are typically based on the decision tree itself.

6.8.2.6 Multi-Criteria Decision Analysis

Multi-Criteria Decision Analysis (MCDA) is a method 

aimed at supporting decisionmakers who are faced with 

making numerous and conflicting evaluations. These 

techniques aim at highlighting the conflicts in alternatives and deriving a way to come to a compromise in 

a transparent process. For example, NASA may apply 

MCDA to help assess whether selection of one set of 

software tools for every NASA application is cost effective. MCDA involves a certain element of subjectiveness; 

the bias and position of the team implementing MCDA 

play a significant part in the accuracy and fairness of decisions. One of the MCDA methods is the Analytic Hierarchy Process (AHP).

The Analytic Hierarchy Process

AHP was first developed and applied by Thomas Saaty. 

AHP is a multi-attribute methodology that provides a 

proven, effective means to deal with complex decisionmaking and can assist with identifying and weighting 

selection criteria, analyzing the data collected for the 

criteria, and expediting the decisionmaking process. 

Many different problems can be investigated with the 

mathematical techniques of this approach. AHP helps 

capture both subjective and objective evaluation measures, providing a useful mechanism for checking the 

consistency of the evaluation measures and alternatives 

suggested by the team, and thus reducing bias in decisionmaking. AHP is supported by pair-wise comparison techniques, and it can support the entire decision 

process. AHP is normally done in six steps:

Figure 6.8-7 Decision tree

Alternative

B

Alternative

A

100%

100 Hours 

None

Localized

Widespread

Cost

0.0

None

Localized

Widespread

ContaminationCrew

Hours

Cost

0.0 0.0

0.0 0.0

0.1

0.1

0.1

0.1 0.1

0.9

0.9 0.9

0.8

0.3 0.3

0.7 0.7

100%

120%

110%

110%

120%

100 Hours 

150 Hours 

150 Hours 

200 Hours 

200 Hours 

Crew

Hours

Contamination

Alternative

Selection 

Alternative

C
212  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

1. Describe in summary form the alternatives under 

consideration.

2. Develop a set of high-level objectives.

3. Decompose the high-level objective from general to 

specific to produce an objectives hierarchy.

4. Determine the relative importance of the evaluation objectives and attributes by assigning weights 

arrived at by engaging experts through a structured 

process such as interviews or questionnaires.

5. Have each expert make pair-wise comparisons of 

the performance of each decision alternative with 

respect to a TPM. Repeat this for each TPM. Combine the results of these subjective evaluations mathematically using a process or, commonly, an available software tool that ranks the alternatives.

6. Iterate the interviews/questionnaires and AHP evaluation process until a consensus ranking of the alternatives is achieved.

If AHP is used only to produce the TPM weights to be 

used in a PI or MOE calculation, then only the first four 

steps listed above are applicable.

With AHP, consensus may be achieved quickly or several 

feedback rounds may be required. The feedback consists 

of reporting the computed ranking, for each evaluator 

and for the group, for each option, along with the reasons 

for differences in rankings, and identified areas of divergence. Experts may choose to change their judgments on 

TPM weights. At this point, divergent preferences can be 

targeted for more detailed study. AHP assumes the existence of an underlying preference vector with magnitudes and directions that are revealed through the pairwise comparisons. This is a powerful assumption, which 

may at best hold only for the participating experts. The 

ranking of the alternatives is the result of the experts’ 

judgments and is not necessarily a reproducible result. 

For further information on AHP, see references by Saaty, 

The Analytic Hierarchy Process.

Flexibility and Extensibility Attributes

In some decision situations, the selection of a particular 

decision alternative will have implications for the long 

term that are very difficult to model in the present. In 

such cases, it is useful to structure the problem as a series 

of linked decisions, with some decisions to be made in 

the near future and others to be made later, perhaps on 

the basis of information to be obtained in the meantime. 

There is value in delaying some decisions to the future, 

when additional information will be available. Some 

technology choices might foreclose certain opportunities that would be preserved by other choices. 

In these cases, it is desirable to consider attributes such 

as “flexibility” and “extensibility.” Flexibility refers to the 

ability to support more than one current application. Extensibility refers to the ability to be extended to other applications. For example, in choosing an architecture to 

support lunar exploration, one might consider extensibility to Mars missions. A technology choice that imposes a hard limit on mass that can be boosted into a 

particular orbit has less flexibility than a choice that is 

more easily adaptable to boost more. Explicitly adding 

extensibility and flexibility as attributes to be weighted 

and evaluated allows these issues to be addressed systematically. In such applications, extensibility and flexibility are being used as surrogates for certain future performance attributes. 

6.8.2.7 Utility Analysis

“Utility” is a measure of the relative value gained from 

an alternative. Given this measure, the team looks at increasing or decreasing utility, and thereby explain alternative decisions in terms of attempts to increase their utility. 

The theoretical unit of measurement for utility is the util.

The utility function maps the range of the TPM into the 

range of associated utilities, capturing the decisionmaker’s preferences and risk attitude. It is possible to imagine 

simply mapping the indicated range of values linearly 

onto the interval [0,1] on the utility axis, but in general, 

this would not capture the decisionmaker’s preferences. 

The decisionmaker’s attitude toward risk causes the 

curve to be convex (risk prone), concave (risk averse), or 

even some of each. 

The utility function directly reflects the decisionmaker’s 

attitude toward risk. When ranking alternatives on the 

basis of utility, a risk-averse decisionmaker will rank an 

alternative with highly uncertain performance below an 

alternative having the same expected performance but 

less uncertainty. The opposite outcome would result for 

a risk-prone decisionmaker. When the individual TPM 

utility functions have been assessed, it is important to 

check the result for consistency with the decisionmaker’s 

actual preferences (e.g., is it true that intermediate values 

of TPM1 and TPM2 are preferred to a high value of TPM1

and a low value of TPM2). 
6.8 Decision Analysis

NASA Systems Engineering Handbook  213

An example of a utility function for the TPM “volume” 

is shown in Figure 6.8-8. This measure was developed 

in the context of design of sensors for a space mission. 

Volume was a precious commodity. The implication of 

the graph is that low volume is good, large volume is bad, 

and the decisionmaker would prefer a design alternative 

with a very well-determined volume of a few thousand 

cc’s to an alternative with the same expected volume but 

large uncertainty. 

Sometimes the expected utility is referred to as a PI. An 

important benefit of applying this method is that it is the 

best way to deal with significant uncertainties when the 

decisionmaker is not risk neutral. Probabilistic methods 

are used to treat uncertainties. A downside of applying 

this method is the need to quantify the decisionmaker’s 

risk attitudes. Top-level system architecture decisions are 

natural examples of appropriate applications of MAUT. 

6.8.2.8 Risk-Informed Decision Analysis 

Process Example

Introduction

A decision matrix works for many decisions, but the decision matrix may not scale up to very complex decisions 

or risky decisions. For some decisions, a tool is needed 

to handle the complexity. The following subsection describes a detailed Decision Analysis Process that can be 

used to support a risk-informed decision.

In practice, decisions are made in many different ways. 

Simple approaches may be useful, but it is important to 

recognize their limitations and upgrade to better analysis when this is warranted. Some decisionmakers, when 

faced with uncertainty in an important quantity, determine a best estimate for that quantity, and then reason as 

if the best estimate were correct. This might be called the 

“take-your-best-shot” approach. Unfortunately, when 

the stakes are high, and uncertainty is significant, this 

best-shot approach may lead to poor decisions. 

The following steps are a risk-informed decision analysis 

process:

1. Formulation of the objectives hierarchy, TPMs.

2. Proposing and identifying decision alternatives. 

Alternatives from this process are combined with 

the alternatives identified in the other systems engineering processes including the Design Solution 

Definition Process, but also including verification 

and validation as well as production.

3. Risk analysis of decision alternatives and ranking of 

alternatives. 

4. Deliberation and recommendation of decision alternatives.

5. Followup tracking of the implementation of the decision.

These steps support good decisions by focusing first on 

objectives, next on developing decision alternatives with 

those objectives clearly in mind and/or using decision alFigure 6.8-8 Utility function for a “volume” 

performance measure

2,000 4,000 6,000 8,000 10,000 12,000

0.8

0.6

0.4

0.2

Utility

Volume (ccm) 

Value functions can take the place of utility functions 

when a formal treatment of risk attitude is unnecessary. 

They appear very similar to utility functions, but have 

one important difference. Value functions do not consider the risk attitude of the decisionmaker. They do not 

reflect how the decisionmaker compares certain outcomes to uncertain outcomes.

The assessment of a TPM’s value function is relatively 

straightforward. The “best” end of the TPM’s range is assigned a value of 1. The “worst” is assigned a value of 

0. The decisionmaker makes direct assessments of the 

value of intermediate points to establish the preference 

structure in the space of possible TPM values. The utility 

function can be treated as a value function, but the value 

function is not necessarily a utility function. 

One way to rank alternatives is to use a Multi-Attribute, 

Utility Theory (MAUT) approach. With this approach, 

the “expected utility” of each alternative is quantified, and 

alternatives are ranked based on their expected utilities. 
214  NASA Systems Engineering Handbook

6.0 Crosscutting Technical Management

ternatives that have been developed under other systems 

engineering processes. The later steps of the Decision 

Analysis Process interrelate heavily with the Technical 

Risk Management Process, as indicated in Figure 6.8-9. 

These steps include risk analysis of the decision alternatives, deliberation informed by risk analysis results, and 

recommendation of a decision alternative to the decisionmaker. Implementation of the decision is also important.

Objectives Hierarchy/TPMs

As shown in Figure 6.8-9, risk-informed decision analysis starts with formulation of the objectives hierarchy. 

Using this hierarchy, TPMs are formulated to quantify 

performance of a decision with respect to the program 

objectives. The TPMs should have the following characteristics:

z They can support ranking of major decision alternatives. 

z They are sufficiently detailed to be used directly in the 

risk management process. 

z They are preferentially independent. This means that 

they contribute in distinct ways to the program goal. 

This property helps to ensure that alternatives are 

ranked appropriately. 

An example of an objectives hierarchy is shown in 

Figure 6.8-10. Details will vary from program to program, but a construct like Figure 6.8-10 is behind the 

program-specific objectives hierarchy.

The TPMs in this figure are meant to be generically important for many missions. Depending on the mission, 

these TPMs are further subdivided to the point where 

they can be objectively measured. Not all TPMs can be 

measured directly. For example, safety-related TPMs are 

Figure 6.8-9 Risk-informed Decision Analysis Process

Technical Risk Management

Formulation of Objectives

Hierarchy and TPMs

Decision Analysis

Decisionmaking

and

Implementation

of Decision

Alternative

Proposing and/or

Identifying Decision

Alternatives

Risk Analysis of Decision

Alternatives, Performing

Trade Studies and Ranking

Deliberating and

Recommending a

Decision Alternative

Risk Analysis of Decision

Alternatives, Performing

Trade Studies and Ranking

Stakeholder

Expectation,

Requirements

Definition/

Management

Design Solution,

Technical Planning

Design Solution,

Technical Planning,

Decision Analysis

Technical Planning,

Decision Analysis

Decision Analysis,

Lessons Learned,

Knowledge

Management

Tracking and Controlling

Performance Deviations

Recognition

of Issues

or

Opportunities
6.8 Decision Analysis

NASA Systems Engineering Handbook  215

Figure 6.8-10 Example of an objectives hierarchy

Mission Success

Affordability

Meet

Budget

Constraints 

Decision

Alternative

Technical Performance Measures 

Design/

Development 

Cost

Overrun

OBJECTIVES HIERARCHY PERFORMANCE MEASURES

(representative measures are shown)

Economics and

Schedule Models

Models to Assess LifeCycle Cost and

Schedule Performance

Schedule

Slippage

Operation

Cost

Overrun

...

Loss of

Mission

Function x

Mass/

Cargo

Capacity

Reliability/

Availability/

QA

Effectiveness

Commercial

Extensibility

Loss of 

Support

Capability x

Loss of

Flight

Systems

Loss of

Public

Property

Planetary

Contamination

Earth

Contamination

Astronaut

Death or

Injury

Public

 Death

or Injury

Science

Community

Support

Public

Support

...

Meet

Schedules 

Safety Other Stakeholders’

Support 

Technical Objectives

and Performance 

� Models Quantifying Capability Metrics Relating to Mission Requirements (Mass,

Thrust, Cargo Capacity)

� Models Quantifying Metrics Relating to Probability of Loss of Mission-Critical 

System/Function (e.g., PRA)

� Models Quantifying Metrics Relating to Frequency or Probability of Failure to Meet

High-Level Safety Objectives (e.g., PRA)

Models Quantifying Technical Performance Measures

Stakeholder

Models 

Achieve

MissionCritical

Functions 

Enhance

Effectiveness/

 Performance

Provide

Extensibility/

Supportability

Protect

Workforce

& Public

Health

Protect

Environment

Protect

Mission

& Public

Assets

Realize

Other

Stakeholders’

Support

MODEL-BASED

QUANTIFICATION

OF PERFORMANCE

MEASURES 

defined in terms of the probability of a consequence type 

of a specific magnitude (e.g., probability of any general 

public deaths or injuries) or the expected magnitude of 

a consequence type (e.g., the number of public deaths 

or injuries). Probability of Loss of Mission and Probability of Loss of Crew (P(LOM) and P(LOC)) are two 

particularly important safety-related TPMs for manned 

space missions. Because an actuarial basis does not suffice for prediction of these probabilities, modeling will 

be needed to quantify them. 

NASA Systems Engineering Handbook  217

The topics below are of special interest for enhancing 

the performance of the systems engineering process or 

constitute special considerations in the performance 

of systems engineering. The first section elucidates the 

process of how the systems engineering principles need 

to be applied to contracting and contractors that implement NASA processes and create NASA products. 

7.0 Special Topics

Applying lessons learned enhances the efficiency of the 

present with the wisdom of the past. Protecting the environment and the Nation’s space assets are important 

considerations in the design and development of requirements and designs. Integrated design can enhance the efficiency and effectiveness of the design 

process.

7.1.1 Introduction, Purpose, and Scope

Historically, most successful NASA projects have depended on effectively blending project management, systems engineering, and technical expertise among NASA, 

contractors, and third parties. Underlying these successes are a variety of agreements (e.g., contract, memorandum of understanding, grant, cooperative agreement) between NASA organizations or between NASA 

and other Government agencies, Government organizations, companies, universities, research laboratories, and 

so on. To simplify the discussions, the term “contract” is 

used to encompass these agreements. 

This section focuses on the engineering activities pertinent to awarding a contract, managing contract performance, and completing a contract. However, interfaces 

to the procurement process will be covered, since the engineering technical team plays a key role in development 

and evaluation of contract documentation.

Contractors and third parties perform activities that supplement (or substitute for) the NASA project technical 

team accomplishment of the common technical process 

activities and requirements. Since contractors might be 

involved in any part of the systems engineering life cycle, 

the NASA project technical team needs to know how to 

prepare for, perform, and complete surveillance of technical activities that are allocated to contractors.

7.1.2 Acquisition Strategy

Creating an acquisition strategy for a project is a collaborative effort among several NASA HQ offices that 

7.1 Engineering with Contracts

leads to approval for project execution. The program 

and project offices characterize the acquisition strategy 

in sufficient detail to identify the contracts needed to execute the strategy. Awarding contracts at the project level 

occurs in the context of the overall program acquisition 

strategy. 

While this section pertains to projects where the decision 

has been made to have a contractor implement a portion of the project, it is important to remember that the 

choice between “making” a product in-house by NASA 

or “buying” it from a contractor is one of the most crucial decisions in systems development. (See Section 5.1.) 

Questions that should be considered in the “make/buy” 

decision include the following:

z Is the desired system a development item or more off 

the shelf?

z What is the relevant experience of NASA versus potential contractors?

z What are the relative importance of risk, cost, schedule, 

and performance?

z Is there a desire to maintain an “in-house” capability?

As soon as it is clear that a contract will be needed to 

obtain a system or service, the responsible project manager should contact the local procurement office. The 

contracting officer will assign a contract specialist to 

navigate the numerous regulatory requirements that affect NASA procurements and guide the development 

of contract documentation needed to award a contract. 

The contract specialist engages the local legal office as 

needed.
218  NASA Systems Engineering Handbook

7.0 Special Topics

tegration, and details of product support. Similarly, the 

technical team provides corporate knowledge to identify 

and evaluate risks of acquiring the desired product, especially regarding the proposed contract type and particular contract elements. 

7.1.2.2 Acquisition Life Cycle

Contract activities are part of the broader acquisition life cycle, which comprises the phases solicitation, 

source selection, contract monitoring, and acceptance. 

(See Figure 7.1-1.) The acquisition life cycle overlaps 

and interfaces with the systems engineering processes 

in the project life cycle. Acquisition planning focuses on 

technical planning when a particular contract (or purchase) is required. (See Section 6.1.) In the figure below, 

requirements development corresponds to the Technical Requirements Definition Process in the systems 

engineering engine. (See Figure 2.1-1.) The next four 

phases—solicitation, source selection, contract monitoring, and acceptance—are the phases of the contract 

activities. Transition to operations and maintenance represents activities performed to transition acquired products to the organization(s) responsible for operating 

and maintaining them (which could be contractor(s)). 

Acquisition management refers to project management 

activities that are performed throughout the acquisition 

life cycle by the acquiring organization.

7.1.2.3 NASA Responsibility for Systems 

Engineering

The technical team is responsible for systems engineering 

throughout the acquisition life cycle. The technical team 

contributes heavily to systems engineering decisions and 

results, whatever the acquisition strategy, for any combination of suppliers, contractors, and subcontractors. The 

technical team is responsible for systems engineering 

whether the acquisition strategy calls for the technical 

team, a prime contractor, or some combination of the 

two to perform system integration and testing of products from multiple sources. 

This subsection provides specific guidance on how to assign responsibility when translating the technical processes onto a contract. Generally, the Technical Planning, 

7.1.2.1 Develop an Acquisition Strategy

The project manager, assisted by the assigned procurement and legal offices, first develops a project acquisition 

strategy or verifies the one provided. The acquisition 

strategy provides a business and technical management 

outline for planning, directing, and managing a project 

and obtaining products and services via contract.

In some cases, it may be appropriate to probe outside 

sources in order to gather sufficient information to formulate an acquisition strategy. This can be done by issuing a Request for Information (RFI) to industry and 

other parties that may have interest in potential future 

contracts. An RFI is a way to obtain information about 

technology maturity, technical challenges, capabilities, 

price and delivery considerations, and other market information that can influence strategy decisions.

The acquisition strategy includes:

z Objectives of the acquisition—capabilities to be provided, major milestones;

z Acquisition approach—single step or evolutionary 

(incremental), single or multiple suppliers/contracts, 

competition or sole source, funding source(s), phases, 

system integration, Commercial-Off-the-Shelf 

(COTS) products;

z Business considerations—constraints (e.g., funding, 

schedule), availability of assets and technologies, applicability of commercial items versus internal technical product development;

z Risk management of acquired products or services—

major risks and risk sharing with the supplier;

z Contract types—performance-based or level of effort, 

fixed-price or cost reimbursable; 

z Contract elements—incentives, performance parameters, rationale for decisions on contract type; and

z Product support strategy—oversight of delivered 

system, maintenance, and improvements.

The technical team gathers data to facilitate the decisionmaking process regarding the above items. The technical 

team knows about issues with the acquisition approach, 

determining availability of assets and technologies, applicability of commercial items, issues with system inFigure 7.1-1 Acquisition life cycle 

Acceptance

Contract

Monitoring

Source

Selection Solicitation Requirements 

Development

Acquisition 

Planning

Transition to

Operations &

Maintenance 
7.1 Engineering with Contracts

NASA Systems Engineering Handbook  219

Interface Management, Technical Risk Management, 

Configuration Management, Technical Data Management, Technical Assessment, and Decision Analysis processes should be implemented throughout the project 

by both the NASA team and the contractor. Stakeholder 

Expectations Definition, Technical Requirements Definition, Logical Decomposition, Design Solution Definition, Product Implementation and Integration, Product 

Verification and Validation, Product Transition, and Requirements Management Processes are implemented by 

NASA or the contractor depending upon the level of the 

product decomposition. 

Table 7.1-1 provides guidance on how to implement the 

17 technical processes from NPR 7123.1. The first two 

columns have the number of the technical process and 

the requirement statement of responsibility. The next 

column provides general guidance on how to distinguish who has responsibility for implementing the process. The last column provides a specific example of the 

application of how to implement the process for a particular project. The particular scenario is a science mission where a contractor is building the spacecraft, NASA 

assigns Government-Furnished Property (GFP) instruments to the contractor, and NASA operates the mission.

7.1.3 Prior to Contract Award

7.1.3.1 Acquisition Planning

Based on the acquisition strategy, the technical team 

needs to plan acquisitions and document the plan 

in developing the SEMP. The SEMP covers the technical team’s involvement in the periods before contract award, during contract performance, and upon 

contract completion. Included in acquisition planning 

are solicitation preparation, source selection activities, contract phase-in, monitoring contractor performance, acceptance of deliverables, completing the contract, and transition beyond the contract. The SEMP 

focuses on interface activities with the contractor, including NASA technical team involvement with and 

monitoring of contracted work.

Often overlooked in project staffing estimates is the 

amount of time that technical team members are involved in contracting-related activities. Depending on 

the type of procurement, a technical team member involved in source selection could be consumed nearly full 

time for 6 to 12 months. After contract award, technical 

monitoring consumes 30 to 50 percent, peaking at full 

time when critical milestones or key deliverables arrive. 

Keep in mind that for most contractor activities, NASA 

staff performs supplementary activities.

The technical team is intimately involved in developing 

technical documentation for the acquisition package. The 

acquisition package consists of the solicitation (e.g., Request for Proposals (RFPs) and supporting documents. 

The solicitation contains all the documentation that is 

advertised to prospective contractors (or offerors). The 

key technical sections of the solicitation are the SOW (or 

performance work statement), technical specifications, 

and contract data requirements list. Other sections of 

the solicitation include proposal instructions and evaluation criteria. Documents that support the solicitation 

include a procurement schedule, source evaluation plan, 

Government cost estimate, and purchase request. Input 

from the technical team will be needed for some of the 

supporting documents.

It is the responsibility of the contract specialist, with 

input from the technical team, to ensure that the appropriate clauses are included in the solicitation. The contract specialist is familiar with requirements in the Federal Acquisition Regulation (FAR) and the NASA FAR 

Supplement (NFS) that will be included in the solicitaSolicitations

The release of a solicitation to interested parties is 

the formal indication of a future contract. A solicitation conveys sufficient details of a Government need 

(along with terms, conditions, and instructions) to allow prospective contractors (or offerors) to respond 

with a proposal. Depending on the magnitude and 

complexity of the work, a draft solicitation may be 

issued. After proposals are received, a source evaluation board (or committee) evaluates technical and 

business proposals per its source evaluation plan 

and recommends a contractor selection to the contracting officer. The source evaluation board, led by a 

technical expert, includes other technical experts and 

a contracting specialist. The source selection process 

is completed when the contracting officer signs the 

contract. 

The most common NASA solicitation types are RFP 

and Announcement of Opportunity (AO). Visit the online NASA Procurement Library for a full range of details regarding procurements and source selection.
220  NASA Systems Engineering Handbook

7.0 Special Topics

Table 7.1-1 Applying the Technical Processes on Contract

# NPR 7123.1 Process

General Guidance on Who 

Implements the Process Application to a Science Mission

1 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for the definition of stakeholder expectations for the applicable 

WBS model.

If stakeholders are at the contractor, then the contractor should 

have responsibility and vice versa.

Stakeholders for the mission/project are within NASA; stakeholders 

for the spacecraft power subsystem 

are mostly at the contractor.

2 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for definition of the 

technical requirements from the set of 

agreed-upon stakeholder expectations for 

the applicable WBS model.

Assignment of responsibility 

follows the stakeholders, e.g., if 

stakeholders are at the contractor, 

then requirements are developed 

by the contractor and vice versa.

NASA develops the high-level 

requirements, and the contractor 

develops the requirements for the 

power subsystem.

3 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for logical decomposition 

of the validated technical requirements of 

the applicable WBS.

Follows the requirements, e.g., if 

requirements are developed at 

the contractor, then the decomposition of those requirements is 

implemented by the contractor 

and vice versa.

NASA performs the decomposition 

of the high-level requirements, and 

the contractor performs the decomposition of the power subsystem 

requirements.

4 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for designing product 

solution definitions within the applicable 

WBS model that satisfy the derived technical requirements.

Follows the requirements, e.g., if 

requirements are developed at the 

contractor, then the design of the 

product solution is implemented 

by the contractor and vice versa.

NASA designs the mission/project, 

and the contractor designs the 

power subsystem.

5 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for implementation of 

a design solution definition by making, 

buying, or reusing an end product of the 

applicable WBS model.

Follows the design, e.g., if the 

design is developed at the contractor, then the implementation 

of the design is performed by the 

contractor and vice versa.

NASA implements (and retains 

responsibility for) the design for the 

mission/project, and the contractor 

does the same for the power 

subsystem.

6 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for the integration of 

lower level products into an end product 

of the applicable WBS model in accordance with its design solution definition.

Follows the design, e.g., if the 

design is developed at the 

contractor, then the integration of 

the design elements is performed 

by the contractor and vice versa.

NASA integrates the design for the 

mission/project, and the contractor 

does the same for the power 

subsystem.

7 The Center Directors or designees establish 

and maintain a process to include activities, 

requirements, guidelines, and documentation for verification of end products 

generated by the Product Implementation 

Process or Product Integration Process 

against their design solution definitions.

Follows the product integration, 

e.g., if the product integration is 

implemented at the contractor, 

then the verification of the product is performed by the contractor 

and vice versa.

NASA verifies the mission/project, 

and the contractor does the same 

for the power subsystem.

 (continued)
7.1 Engineering with Contracts

NASA Systems Engineering Handbook  221

# NPR 7123.1 Process

General Guidance on Who 

Implements the Process Application to a Science Mission

8 The Center Directors or designees establish 

and maintain a process to include activities, 

requirements, guidelines, and documentation for validation of end products 

generated by the Product Implementation 

Process or Product Integration Process 

against their stakeholder expectations.

Follows the product integration, 

e.g., if the product integration is 

implemented at the contractor, 

then the validation of the product 

is performed by the contractor 

and vice versa.

NASA validates the mission/project, 

and the contractor does the same 

for the power subsystem.

9 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for transitioning end 

products to the next-higher-level WBS 

model customer or user.

Follows the product verification and 

validation, e.g., if the product verification and validation is implemented 

at the contractor, then the transition 

of the product is performed by the 

contractor and vice versa.

NASA transitions the mission/project to operations, and the contractor transitions the power subsystem 

to the spacecraft level.

10 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for planning the technical 

effort.

Assuming both NASA and the 

contractor have technical work 

to perform, then both NASA and 

the contractor need to plan their 

respective technical efforts.

NASA would plan the technical 

effort associated with the GFP 

instruments and the launch and operations of the spacecraft, and the 

contractor would plan the technical 

effort associated with the design, 

build, verification and validation, 

and delivery and operations of the 

power subsystem.

11 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for management of 

requirements defined and baselined 

during the application of the system 

design processes.

Follows process #2.

12 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for management of 

the interfaces defined and generated 

during the application of the system 

design processes.

Interfaces should be managed 

one level above the elements 

being interfaced.

The interface from the spacecraft 

to the project ground system 

would be managed by NASA, while 

the power subsystem to attitude 

control subsystem interface would 

be managed by the contractor.

13 The Center Directors or designees establish 

and maintain a process to include activities, 

requirements, guidelines, and documentation for management of the technical risk 

identified during the technical effort. 

NPR 8000.4, Risk Management Procedural 

Requirements is to be used as a source 

document for defining this process; and 

NPR 8705.5, Probabilistic Risk Assessment 

(PRA) Procedures for NASA Programs and 

Projects provides one means of identifying 

and assessing technical risk.

Technical risk management 

is a process that needs to be 

implemented by both NASA and 

the contractor. All elements of the 

project need to identify their risks 

and participate in the project risk 

management process. Deciding 

which risks to mitigate, when, at 

what cost is generally a function of 

NASA project management.

NASA project management should 

create a project approach to risk 

management that includes participation from the contractor. Risks 

identified throughout the project 

down to the power subsystem level 

and below should be identified 

and reported to NASA for possible 

mitigation.

 (continued)

Table 7.1-1 Applying the Technical Processes on Contract (continued)
222  NASA Systems Engineering Handbook

7.0 Special Topics

# NPR 7123.1 Process

General Guidance on Who 

Implements the Process Application to a Science Mission

14 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for CM.

Like risk management, CM is a 

process that should be implemented throughout the project 

by both the NASA and contractor 

teams.

NASA project management should 

create a project approach to CM 

that includes participation from 

the contractor. The contractor’s 

internal CM process will have to be 

integrated with the NASA approach. 

CM needs to be implemented 

throughout the project down to the 

power subsystem level and below.

15 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for management of the 

technical data generated and used in 

the technical effort.

Like risk management and CM, 

technical data management is 

a process that should be implemented throughout the project 

by both the NASA and contractor 

teams.

NASA project management should 

create a project approach to 

technical data management that 

includes participation from the 

contractor. The contractor’s internal 

technical data process will have to 

be integrated with the NASA approach. Management of technical 

data needs to be implemented 

throughout the project down to the 

power subsystem level and below.

16 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for making assessments 

of the progress of planned technical ef‐

fort and progress toward requirements 

satisfaction.

Assessing progress is a process 

that should be implemented 

throughout the project by both 

the NASA and contractor teams.

NASA project management should 

create a project approach to 

assessing progress that includes 

participation from the contractor. 

Typically this would be the project 

review plan. The contractor’s internal review process will have to be 

integrated with the NASA approach. 

Technical reviews need to be implemented throughout the project 

down to the power subsystem level 

and below.

17 The Center Directors or designees establish and maintain a process to include 

activities, requirements, guidelines, and 

documentation for making technical 

decisions.

Clearly technical decisions are 

made throughout the project 

both by NASA and contractor personnel. Certain types of decisions 

or decisions on certain topics may 

best be made by either NASA or 

the contractor depending upon 

the Center’s processes and the 

type of project.

For this example, decisions affecting 

high-level requirements or mission 

success would be made by NASA 

and those at the lower level, e.g., 

the power subsystem that did not 

affect mission success would be 

made by the contractor.

Table 7.1-1 Applying the Technical Processes on Contract (continued)

tion as clauses in full text form or as clauses incorporated by reference. Many of these clauses relate to public 

laws, contract administration, and financial management. Newer clauses address information technology security, data rights, intellectual property, new technology 

reporting, and similar items. The contract specialist stays 

abreast of updates to the FAR and NFS. As the SOW and 

other parts of the solicitation mature, it is important for 

the contract specialist and technical team to work closely 

to avoid duplication of similar requirements.
7.1 Engineering with Contracts

NASA Systems Engineering Handbook  223

7.1.3.2 Develop the Statement of Work

Effective surveillance of a contractor begins with the development of the SOW. The technical team establishes 

the SOW requirements for the product to be developed. 

The SOW contains process, performance, and management requirements the contractor must fulfill during 

product development.

As depicted in Figure 7.1-2, developing the SOW requires 

the technical team to analyze the work, performance, 

and data needs to be accomplished by the contractor. 

The process is iterative and supports the development of 

other documentation needed for the contracting effort. 

The principal steps in the figure are discussed further in 

Table 7.1-2.

After a few iterations, baseline the SOW requirements 

and place them under configuration management. (See 

Section 6.5.)

Use the SOW checklist, which is in Appendix P, to help 

ensure that the SOW is complete, consistent, correct, unambiguous, and verifiable. Below are some key items to 

require in the SOW:

z Technical and management deliverables having the 

highest risk potential (e.g., the SEMP, development 

and transition plans); requirements and architecture 

specifications; test plans, procedures and reports; 

metrics reports; delivery, installation, and maintenance documentation.

z Contractual or scheduling incentives in a contract 

should not be tied to the technical milestone reviews. 

These milestone reviews (for example, SRR, PDR, CDR, 

etc.) enable a critical and valuable technical assessment 

to be performed. These reviews have specific entrance 

criteria that should not be waived. The reviews should 

be conducted when these criteria are met, rather than 

being driven by a particular schedule.

z Timely electronic access to data, work products, and 

interim deliverables to assess contractor progress on 

final deliverables.

z Provision(s) to flow down requirements to subcontractors and other team members.

z Content and format requirements of deliverables in 

the contract data requirements list. These requirements are specified in a data requirements document 

Organize

SOW

Dene 

Performance 

Standards

Dene 

Scope

Step 1: Analyze 

Work

Step 2: Analyze 

Performance

Step 3: Analyze 

Data

Write SOW

Requirements 

Document

Rationale

Dene 

Deliverables

Front-End

Analysis Baseline

SOW

Requirements 

Identify

Standards

� Dene Product

� Specify Standards

� Prepare Quality Assurance

Surveillance Plan

� Dene Incentives

NEED

Other Related

Documentation 

�

Figure 7.1-2 Contract requirements development process
224  NASA Systems Engineering Handbook

7.0 Special Topics

or data item description, usually as an attachment. 

Remember that you need to be able to edit data deliverables.

z Metrics to gain visibility into technical progress for 

each discipline (e.g., hardware, software, thermal, 

optics, electrical, mechanical). For guidance on metrics to assess the contractor’s performance and to assess adherence to product requirements on delivered 

products, refer to System and Software Metrics for Performance-Based Contracting.

z Quality incentives (defect, error count, etc.) to reduce risk of poor quality deliverables. Be careful because incentives can affect contractor behavior. For 

example, if you reward early detection and correction 

of software defects, the contractor may expend effort 

correcting minor defects and saving major defects for 

later.

z A continuous management program to include a periodically updated risk list, joint risk reviews, and 

vendor risk approach.

z Surveillance activities (e.g., status meetings, reviews, 

audits, site visits) to monitor progress and production, especially access to subcontractors and other 

team members.

z Specialty engineering (e.g., reliability, quality assurance, cryogenics, pyrotechnics, biomedical, waste 

management) that is needed to fulfill standards and 

verification requirements.

z Provisions to assign responsibilities between NASA 

and contractor according to verification, validation, 

or similar plans that are not available prior to award.

z Provisions to cause a contractor to disclose changing 

a critical process. If a process is critical to human 

safety, require the contractor to obtain approval from 

Table 7.1-2 Steps in the Requirements Development Process 

Step Task Detail

Step 1: 

Analyze the 

Work

Define scope Document in the SOW that part of the project’s scope that will be contracted. 

Give sufficient background information to orient offerors.

Organize SOW Organize the work by products and associated activities (i.e., product WBS).

Write SOW requirements Include activities necessary to:

z Develop products defined in the requirements specification; and

z Support, manage, and oversee development of the products.

Write SOW requirements in the form “the Contractor shall.” 

Write product requirements in the form “the system shall.”

Document rationale Document separately from the SOW the reason(s) for including requirements 

that may be unique, unusual, controversial, political, etc. The rationale is not 

part of the solicitation.

Step 2: 

Analyze 

Performance

Define performance 

standards

Define what constitutes acceptable performance by the contractor. Common 

metrics for use in performance standards include cost and schedule. For 

guidance on metrics to assess the contractor’s performance and to assess 

adherence to product requirements on delivered products, refer to System and 

Software Metrics for Performance-Based Contracting.

Step 3: 

Analyze Data

Identify standards Identify standards (e.g., EIA, IEEE, ISO) that apply to deliverable work products 

including plans, reports, specifications, drawings, etc. Consensus standards 

and codes (e.g., National Electrical Code, National Fire Protection Association, 

American Society of Mechanical Engineers) that apply to product development 

and workmanship are included in specifications.

Define deliverables Ensure each deliverable data item (e.g., technical data—requirements specifications, design documents; management data—plans, metrics reports) has a 

corresponding SOW requirement for its preparation. Ensure each product has a 

corresponding SOW requirement for its delivery.
7.1 Engineering with Contracts

NASA Systems Engineering Handbook  225

the contracting officer before a different process is implemented.is simplified because the contract already establishes baseline requirements for execution. First-time users need to 

understand the scope of the contract and the degree to 

which delivery and reporting requirements, performance 

metrics, incentives, and so forth are already covered. 

Task contracts offer quick access (days or weeks instead 

of months) to engineering services for studies, analyses, 

design, development, and testing and to support services 

for configuration management, quality assurance, maintenance, and operations. Once a task order is issued, the 

technical team performs engineering activities associated 

with managing contract performance and completing a 

contract (discussed later) as they apply to the task order.

7.1.3.4 Surveillance Plan

The surveillance plan defines the monitoring of the contractor effort and is developed at the same time as the 

SOW. The technical team works with mission assurance 

personnel, generally from the local Safety and Mission Assurance (SMA) organization, to prepare the surveillance 

plan for the contracted effort. Sometimes mission assurance is performed by technical experts on the project. 

In either case, mission assurance personnel should be 

engaged from the start of the project. Prior to contract 

award, the surveillance plan is written at a general level 

to cover the Government’s approach to perceived programmatic risk. After contract award, the surveillance 

plan describes in detail inspection, testing, and other 

quality-related surveillance activities that will be performed to ensure the integrity of contract deliverables, 

given the current perspective on programmatic risks. 

Recommended items to include in the surveillance plan 

follow:

z Review key deliverables within the first 30 days to ensure adequate startup of activities.

z Conduct contractor/subcontractor site visits to monitor production or assess progress.

z Evaluate effectiveness of the contractor’s systems engineering processes.

Drafting the surveillance plan when the SOW is developed promotes the inclusion of key requirements in the 

SOW that enable activities in the surveillance plan. For 

example, in order for the technical team to conduct site 

visits to monitor production of a subcontractor, then the 

SOW must include a requirement that permits site visits, 

combined with a requirement for the contractor to flow 

down requirements that directly affect subcontractors.

Note: If you neglect to require something in the SOW, 

it can be costly to add it later.

The contractors must supply a SEMP that specifies their 

systems engineering approach for requirements development, technical solution definition, design realization, 

product evaluation, product transition, and technical 

planning, control, assessment, and decision analysis. It 

is best to request a preliminary SEMP in the solicitation. The source evaluation board can use the SEMP to 

evaluate the offeror’s understanding of the requirements, 

as well as the offeror’s capability and capacity to deliver 

the system. After contract award, the technical team can 

eliminate any gaps between the project’s SEMP and the 

contractor’s SEMP that could affect smooth execution of 

the integrated set of common technical processes.

Often a technical team has experience developing technical requirements, but little or no experience developing SOW requirements. If you give the contractor a 

complex set of technical requirements, but neglect to include sufficient performance measures and reporting requirements, you will have difficulty monitoring progress 

and determining product and process quality. Understanding performance measures and reporting requirements will enable you to ask for the appropriate data or 

reports that you intend to use.

Traditionally, NASA contracts require contractors to satisfy requirements in NASA policy directives, NASA procedural requirements, NASA standards, and similar documents. These documents are almost never written in 

language that can be used directly in a contract. Too often, 

these documents contain requirements that do not apply 

to contracts. So, before the technical team boldly goes 

where so many have gone before, it is a smart idea to understand what the requirements mean and if they apply to 

contracts. The requirements that apply to contracts need 

to be written in a way that is suitable for contracts.

7.1.3.3 Task Order Contracts

Sometimes, the technical team can obtain engineering 

products and services through an existing task order contract. The technical team develops a task order SOW and 

interacts with the contracting officer’s technical representative to issue a task order. Preparing the task order SOW 
226  NASA Systems Engineering Handbook

7.0 Special Topics

7.1.3.5 Writing Proposal Instructions and 

Evaluation Criteria

Once the technical team has written the SOW, the Government cost estimate, and the preliminary surveillance 

plan and updated the SEMP, the solicitation can be developed. Authors of the solicitation must understand the 

information that will be needed to evaluate the proposals 

and write instructions to obtain specifically needed information. In a typical source selection, the source selection board evaluates the offerors’ understanding of 

the requirements, management approach, and cost and 

their relevant experience and past performance. This information is required in the business and technical proposals. (This section discusses only the technical proposal.) The solicitation also gives the evaluation criteria 

that the source evaluation board will use. This section 

corresponds one-for-one to the items requested in the 

proposal instructions section.

State instructions clearly and correctly. The goal is to 

obtain enough information to have common grounds 

for evaluation. The challenge becomes how much information to give the offerors. If you are too prescriptive, the proposals may look too similar. Be careful not 

to level the playing field too much, otherwise discriminating among offerors will be difficult. Because the 

technical merits of a proposal compete with nontechnical items of similar importance (e.g., cost), the technical team must wisely choose discriminators to facilitate the source selection.

The source evaluation board evaluates nontechnical 

(business) and technical items. Items may be evaluated 

by themselves, or in the context of other technical or 

nontechnical items. Table 7.1-3 shows technical items 

to request from offerors and the evaluation criteria with 

which they correlate.

Evaluation Considerations

The following are important to consider when evaluating 

proposals:

z Give adequate weight to evaluating the capability of 

disciplines that could cause mission failure (e.g., hardware, software, thermal, optics, electrical, mechanical).

z Conduct a preaward site visit of production/test facilities that are critical to mission success.

z Distinguish between “pretenders” (good proposal 

writers) and “contenders” (good performing organizations). Pay special attention to how process descriptions match relevant experience and past performance. 

While good proposals can indicate good future performance, lesser quality proposals usually predict lesser 

quality future work products and deliverables.

z Assess the contractor’s SEMP and other items submitted with the proposal based on evaluation criteria 

that include quality characteristics (e.g., complete, unambiguous, consistent, verifiable, and traceable).

The cost estimate that the technical team performs as 

part of the Technical Planning Process supports evaluation of the offerors’ cost proposals, helping the source 

evaluation board determine the realism of the offerors’ 

technical proposals. (See Section 6.1.) The source evaluation board can determine “whether the estimated 

proposed cost elements are realistic for the work to be 

performed; reflect a clear understanding of the requirements; and are consistent with the unique methods of 

performance and materials described in the offeror’s 

technical proposal.”1

7.1.3.6 Selection of COTS Products

When COTS products are given as part of the technical 

solution in a proposal, it is imperative that the selection 

of a particular product be evaluated and documented 

by applying the Decision Analysis Process. Bypassing 

this task or neglecting to document the evaluation suf1

FAR 15.404-1(d) (1).

Source Evaluation Board

One or more members of the technical team serve as 

members of the source evaluation board. They participate in the evaluation of proposals following applicable NASA and Center source selection procedures. 

Because source selection is so important, the procurement office works closely with the source evaluation board to ensure that the source selection process 

is properly executed. The source evaluation board develops a source evaluation plan that describes the 

evaluation factors, and the method of evaluating the 

offerors’ responses. Unlike decisions made by systems 

engineers early in a product life cycle, source selection decisions must be carefully managed in accordance with regulations governing the fairness of the 

selection process.
7.1 Engineering with Contracts

NASA Systems Engineering Handbook  227

ficiently could lead to a situation where NASA cannot 

support its position in the event of a vendor protest. 

7.1.3.7 Acquisition-Unique Risks 

Table 7.1-4 identifies a few risks that are unique to acquisition along with ways to manage them from an engineering perspective. Bear in mind, legal and procurement aspects of these risks are generally covered in 

contract clauses.

There may also be other acquisition risks not listed in 

Table 7.1-4. All acquisition risks should be identified and 

handled the same as other project risks using the Continuous Risk Management (CRM) process. A project can 

also choose to separate out acquisition risks as a risk-list 

subset and handle them using the risk-based acquisition 

management process if so desired.

When the technical team completes the activities prior 

to contract award, they will have an updated SEMP, the 

Government cost estimate, an SOW, and a preliminary 

surveillance plan. Once the contract is awarded, the 

technical team begins technical oversight.

7.1.4 During Contract Performance

7.1.4.1 Performing Technical Surveillance 

Surveillance of a contractor’s activities and/or documentation is performed to demonstrate fiscal responsibility, 

ensure crew safety and mission success, and determine 

award fees for extraordinary (or penalty fees for substandard) contract execution. Prior to or outside of a contract award, a less formal agreement may be made for the 

Government to be provided with information for a trade 

study or engineering evaluation. Upon contract award, 

it may become necessary to monitor the contractor’s adherence to contractual requirements more formally. (For 

a greater understanding of surveillance requirements, 

see NPR 8735.2, Management of Government Quality Assurance Functions for NASA Contracts.)

Under the authority of the contracting officer, the technical team performs technical surveillance as established 

in the NASA SEMP. The technical team assesses technical work productivity, evaluates product quality, and 

conducts technical reviews of the contractor. (Refer to 

the Technical Assessment Process.) Some of the key activities are discussed below.

Table 7.1‐3 Proposal Evaluation Criteria

Item Criteria

Preliminary contractor SEMP. How well the plan can be implemented given the resources, processes, 

and controls stated. Look at completeness (how well it covers all 

SOW requirements), internal consistency, and consistency with other 

proposal items. The SEMP should cover all resources and disciplines 

needed to meet product requirements, etc.

Process descriptions, including subcontractor’s 

(or team member’s) processes.

Effectiveness of processes and compatibility of contractor and subcontractor processes (e.g., responsibilities, decisionmaking, problem 

resolution, reporting).

Artifacts (documents) of relevant work 

completed. Such documentation depicts the 

probable quality of work products an offeror 

will provide on your contract. Artifacts provide 

evidence (or lack) of systems engineering 

process capability.

Completeness of artifacts, consistency among artifacts on a given project, consistency of artifacts across projects, conformance to standards.

Engineering methods and tools. Effectiveness of the methods and tools. 

Process and product metrics. How well the offeror measures performance of its processes and quality 

of its products.

Subcontract management plan (may be part of 

contractor SEMP).

Effectiveness of subcontract monitoring and control and integration/

separation of risk management and CM.

Phase-in plan (may be part of contractor SEMP). How well the plan can be implemented given the existing workload of 

resources.
228  NASA Systems Engineering Handbook

7.0 Special Topics

z Develop NASA-Contractor Technical Relationship:

At the contract kick-off meeting, set expectations for 

technical excellence throughout the execution of the 

contract. Highlight the requirements in the contract 

SOW that are the most important. Discuss the quality 

of work and products to be delivered against the technical requirements. Mutually agree on the format of 

the technical reviews and how to resolve misunderstandings, oversights, and errors.

z Conduct Technical Interchange Meetings: Start early 

in the contract period and meet periodically with the 

contractor (and subcontractors) to confirm that the 

Table 7.1‐4 Risks in Acquisition

Risk Mitigation

Supplier goes bankrupt prior to 

delivery

The source selection process is the strongest weapon. Select a supplier with a proven 

track record, solid financial position, and stable workforce. As a last resort, the Government may take possession of any materials, equipment, and facilities on the work site 

necessary for completing the work in-house or via another contract.

Supplier acquired by another 

supplier with different policies

Determine differences between policies before and after the acquisition. If there is a 

critical difference, then consult with the procurement and legal offices. Meet with the 

supplier and determine if the original policy will be honored at no additional cost. If 

the supplier balks, then follow the advice from legal.

Deliverables include software to 

be developed

Include an experienced software manager on the technical team. Monitor the 

contractor’s adherence to software development processes. Discuss software progress, issues, and quality at technical interchange meetings.

Deliverables include COTS products (especially software)Understand the quality of the product:

z Look at test results. When test results show a lot of rework to correct defects, then 

users will probably find more defects.

z Examine problem reports. These show whether or not users are finding defects 

after release.

z Evaluate user documentation.

z Look at product support.

Products depend on results from 

models or simulations

Establish the credibility and uncertainty of results. Determine depth and breadth of 

practices used in verification and validation of the model or simulation. Understand 

the quality of software upon which the model or simulation is built. For more information, refer to NASA-STD-(I)-7009, Standard for Models and Simulations.

Budget changes prior to delivery 

of all products (and contract 

was written without interim 

deliverables)

Options include:

z Remove deliverables or services from the contract scope in order to obtain key 

products.

z Relax the schedule in exchange for reduced cost.

z Accept deliverables “as is.”

To avoid this situation, include electronic access to data, work products, and interim 

deliverables to assess contractor progress on final deliverables in the SOW.

Contractor is a specialty supplier 

with no experience in a particular 

engineering discipline; for example, the contractor produces 

cryogenic systems that use alarm 

monitoring software from another 

supplier, but the contractor does 

not have software expertise

Mitigate risks of COTS product deliverables as discussed earlier. If the contract is for 

delivery of a modified COTS product or custom product, then include provisions in 

the SOW to cover the following:

z Supplier support (beyond product warranty) that includes subsupplier support

z Version upgrade/replacement plans

z Surveillance of subsupplier

If the product is inexpensive, simply purchasing spares may be more cost effective 

than adding surveillance requirements.
7.1 Engineering with Contracts

NASA Systems Engineering Handbook  229

contractor has a correct and complete understanding 

of the requirements and operational concepts. Establish day-to-day NASA-contractor technical communications.

z Control and Manage Requirements: Almost inevitably, new or evolving requirements will affect a 

project. When changes become necessary, the technical team needs to control and manage changes and 

additions to requirements proposed by either NASA 

or the contractor. (See Section 6.2.) Communicate 

changes to any project participants that the changes 

will affect. Any changes in requirements that affect 

contract cost, schedule, or performance must be conveyed to the contractor through a formal contract 

change. Consult the contracting officer’s technical 

representative.

z Evaluate Systems Engineering Processes: Evaluate 

the effectiveness of defined systems engineering processes. Conduct audits and reviews of the processes. 

Identify process deficiencies and offer assistance with 

process improvement.

z Evaluate Work Products: Evaluate interim plans, reports, specifications, drawings, processes, procedures, 

and similar artifacts that are created during the systems engineering effort.

z Monitor Contractor Performance Against Key Metrics: Monitoring contractor performance extends beyond programmatic metrics to process and product 

metrics. (See Section 6.7 on technical performance 

measures.) These metrics depend on acceptable 

product quality. For example, “50 percent of design 

drawings completed” is misleading if most of them 

have defects (e.g., incorrect, incomplete, inconsistent). The amount of work to correct the drawings affects cost and schedule. It is useful to examine reports 

that show the amount of contractor time invested in 

product inspection and review.

z Conduct Technical Reviews: Assess contractor progress and performance against requirements through 

technical reviews. (See Section 6.7.)

z Verify and Validate Products: Verify and validate 

the functionality and performance of products before 

delivery and prior to integration with other system 

products. To ensure that a product is ready for system 

integration or to enable further system development, 

perform verification and validation as early as practical. (See Sections 5.3 and 5.4.)

7.1.4.2 Evaluating Work Products

Work products and deliverables share common attributes that can be used to assess quality. Additionally, relationships among work products and deliverables can 

be used to assess quality. Some key attributes that help 

determine quality of work products are listed below:

z Satisfies content and format requirements,

z Understandable,

z Complete,

z Consistent (internally and externally) including terminology (an item is called the same thing throughout 

the documents, and

z Traceable.

Table 7.1-5 shows some typical work products from the 

contractor and key attributes with respect to other documents that can be used as evaluation criteria.

7.1.4.3 Issues with Contract-Subcontract 

Arrangements

In the ideal world, a contractor manages its subcontractors, each subcontract contains all the right requirements, and resources are adequate. In the real world, the 

technical team deals with contractors and subcontractors 

that are motivated by profit, (sub)contracts with missing 

or faulty requirements, and resources that are consumed 

more quickly than expected. These and other factors 

cause or influence two key issues in subcontracting: 

z Limited or no oversight of subcontractors and

z Limited access to or inability to obtain subcontractor 

data.

These issues are exacerbated when they apply to second- 

(or lower) tier subcontractors. Table 7.1-6 looks at these 

issues more closely along with potential resolutions.

Scenarios other than those above are possible. Resolutions might include reducing contract scope or deliverables in lieu of cost increases or sharing information 

technology in order to obtain data. Even with the adequate flowdown requirements in (sub)contracts, legal 

wrangling may be necessary to entice contractors to satisfy the conditions of their (sub)contracts.

Activities during contract performance will generate 

an updated surveillance plan, minutes documenting 

meetings, change requests, and contract change orders. 

Processes will be assessed, deliverables and work 

products evaluated, and results reviewed. 
230  NASA Systems Engineering Handbook

7.0 Special Topics

7.1.5 Contract Completion 

The contract comes to completion with the delivery of 

the contracted products, services, or systems and their 

enabling products or systems. Along with the product, 

as-built documentation must be delivered and operational instructions including user manuals.

7.1.5.1 Acceptance of Final Deliverables

Throughout the contract period, the technical team reviews and accepts various work products and interim 

deliverables identified in the contract data requirements 

list and schedule of deliverables. The technical team also 

participates in milestone reviews to finalize acceptance 

of deliverables. At the end of the contract, the technical 

team ensures that each technical deliverable is received 

and that its respective acceptance criteria are satisfied. 

The technical team records the acceptance of deliverables against the contract data requirements list and the 

schedule of deliverables. These documents serve as an 

inventory of items and services to be accepted. Although 

rejections and omissions are infrequent, the technical 

team needs to take action in such a case. Good data 

management and configuration management practices 

facilitate the effort.

Acceptance criteria include:

z Product verification and validation completed successfully. The technical team performs or oversees verification and validation of products, integration of products 

into systems, and system verification and validation. 

z Technical data package is current (as-built) and complete.

Table 7.1‐5 Typical Work Product Documents

Work Product Evaluation Criteria

SEMP Describes activities and products required in the SOW.

The SEMP is not complete unless it describes (or references) how each activity and product 

in the SOW will be accomplished.

Software management/

development plan

Consistent with the SEMP and related project plans. 

Describes how each software-related activity and product in the SOW will be accomplished.

Development approach is feasible.

System design Covers the technical requirements and operational concepts. 

System can be implemented.

Software design Covers the technical requirements and operational concepts. 

Consistent with hardware design. 

System can be implemented.

Installation plans Covers all user site installation activities required in the SOW. 

Presents a sound approach. 

Shows consistency with the SEMP and related project plans.

Test plans Covers qualification requirements in the SOW. 

Covers technical requirements. 

Approach is feasible.

Test procedures Test cases are traceable to technical requirements.

Transition plans Describes all transition activities required in the SOW. 

Shows consistency with the SEMP and related project plans.

User documentation Sufficiently and accurately describes installation, operation, or maintenance (depending on 

the document) for the target audience.

Drawings and documents 

(general)

Comply with content and format requirements specified in the SOW.
7.1 Engineering with Contracts

NASA Systems Engineering Handbook  231

z Transfer of certifications, spare parts, warranties, etc., 

is complete.

z Transfer of software products, licenses, data rights, intellectual property rights, etc., is complete.

z Technical documentation required in contract clauses 

is complete (e.g., new technology reports).

It is important for NASA personnel and facilities to be 

ready to receive final deliverables. Key items to have prepared include:

z A plan for support and to transition products to operations;

z Training of personnel;

z Configuration management system in place; and

z Allocation of responsibilities for troubleshooting, repair, and maintenance.

7.1.5.2 Transition Management

Before the contract was awarded, a product support 

strategy was developed as part of the acquisition strategy. 

The product support strategy outlines preliminary notions regarding integration, operations, maintenance, 

improvements, decommissioning, and disposal. Later, 

after the contract is awarded, a high-level transition plan 

Table 7.1‐6 Contract-Subcontract Issues

Issue Resolution

Oversight of subcontractor is 

limited because requirement(s) 

missing from contract

The technical team gives the SOW requirement(s) to the contracting officer who adds 

the requirement(s) to the contract and negotiates the change order, including additional 

costs to NASA. The contractor then adds the requirement(s) to the subcontract and 

negotiates the change order with the subcontractor. If the technical team explicitly 

wants to perform oversight, then the SOW should indicate what the contractor, its 

subcontractors, and team members are required to do and provide.

Oversight of subcontractor is 

limited because requirement(s) 

not flowed down from contractor to subcontractor

It is the contractor’s responsibility to satisfy the requirements of the contract. If the 

contract includes provisions to flow down requirements to subcontractors, then the 

technical team can request the contracting officer to direct the contractor to execute the 

provisions. The contractor may need to add requirements and negotiate cost changes 

with the subcontractor. If NASA has a cost-plus contract, then expect the contractor to 

bill NASA for any additional costs incurred. If NASA has a fixed-price contract, then the 

contractor will absorb the additional costs or renegotiate cost changes with NASA.

If the contract does not explicitly include requirements flowdown provisions, the 

contractor is responsible for performing oversight.

Oversight of second-tier subcontractor is limited because 

requirement(s) not flowed 

down from subcontractor to 

second-tier subcontractor

This is similar to the previous case, but more complicated. Assume that the contractor 

flowed down requirements to its subcontractor, but the subcontractor did not flow 

down requirements to the second-tier subcontractor. If the subcontract includes provisions to flow down requirements to lower tier subcontractors, then the technical team 

can request the contracting officer to direct the contractor to ensure that subcontractors 

execute the flowdown provisions to their subcontractors.

If the subcontract does not explicitly include requirements flowdown provisions, the 

subcontractor is responsible for performing oversight of lower tier subcontractors.

Access to subcontractor data 

is limited or not provided 

because providing the data is 

not required in the contract

The technical team gives the SOW requirement(s) to the contracting officer who adds 

the requirement(s) to the contract and negotiates the change order, including additional 

costs to NASA. The contractor then adds the requirement(s) to the subcontract and negotiates the change order with the subcontractor. If the technical team explicitly wants 

direct access to subcontractor data, then the SOW should indicate what the contractor, 

its subcontractors, and team members are required to do and provide.

Access to subcontractor data 

is limited or not provided 

because providing the data is 

not required in the subcontract

It is the contractor’s responsibility to obtain data (and data rights) necessary to satisfy 

the conditions of its contract, including data from subcontractors. If the technical 

team needs direct access to subcontractor data, then follow the previous case to add 

flowdown provisions to the contract so that the contractor will add requirements to the 

subcontract.
232  NASA Systems Engineering Handbook

7.0 Special Topics

that expands the product support strategy is recorded in 

the SEMP. Details of product/system transition are subsequently documented in one or more transition plans. 

Elements of transition planning are discussed in Section 5.5.

Transition plans must clearly indicate responsibility for 

each action (NASA or contractor). Also, the contract 

SOW must have included a requirement that the contractor will execute responsibilities assigned in the transition plan (usually on a cost-reimbursable basis).

Frequently, NASA (or NASA jointly with a prime contractor) is the system integrator on a project. In this 

situation, multiple contractors (or subcontractors) will 

execute their respective transition plans. NASA is responsible for developing and managing a system integration plan that incorporates inputs from each transition plan. The provisions that were written in the SOW 

months or years earlier accommodate the transfer of 

products and systems from the contractors to NASA.

7.1.5.3 Transition to Operations and Support

The successful transition of systems to operations and 

support, which includes maintenance and improvements, depends on clear transition criteria that the 

stakeholders agree on. The technical team participates 

in the transition, providing continuity for the customer, 

especially when a follow-on contract is involved. When 

the existing contract is used, the technical team conducts 

a formal transition meeting with the contractor. Alternatively, the transition may involve the same contractor 

under a different contract arrangement (e.g., modified or 

new contract). Or the transition may involve a different 

contractor than the developer, using a different contract 

arrangement.

The key benefits of using the existing contract are that 

the relevant stakeholders are familiar with the contractor and that the contractor knows the products and 

systems involved. Ensure that the contractor and other 

key stakeholders understand the service provisions (requirements) of the contract. This meeting may lead to 

contract modifications in order to amend or remove service requirements that have been affected by contract 

changes over the years.

Seeking to retain the development contractor under a 

different contract can be beneficial. Although it takes 

time and resources to compete the contract, it permits 

NASA to evaluate the contractor and other offerors 

against operations and support requirements only. The 

incumbent contractor has personnel with development 

knowledge of the products and systems, while service 

providers specialize in optimizing cost and availability 

of services. In the end, the incumbent may be retained 

under a contract that focuses on current needs (not several years ago), or else a motivated service provider will 

work hard to understand how to operate and maintain 

the systems. If a follow-on contract will be used, consult 

the local procurement office and exercise the steps that 

were used to obtain the development contract. Assume 

that the amount of calendar time to award a follow-on 

contract will be comparable to the time to award the development contract. Also consider that the incumbent 

may be less motivated upon losing the competition.

Some items to consider for follow-on contracts during 

the development of SOW requirements include:

z Staff qualifications;

z Operation schedules, shifts, and staffing levels;

z Maintenance profile (e.g., preventive, predictive, runto-fail);

z Maintenance and improvement opportunities (e.g., 

schedule, turnaround time);

z Historical data for similar efforts; and

z Performance-based work.

The transition to operations and support represents a 

shift from the delivery of products to the delivery of services.

Service contracts focus on the contractor’s performance 

of activities, rather than development of tangible products. Consequently, performance standards reflect customer satisfaction and service efficiency, such as:

z Customer satisfaction ratings;

z Efficiency of service;

z Response time to a customer request;

z Availability (e.g., of system, Web site, facility);

z Time to perform maintenance action;

z Planned versus actual staffing levels;

z Planned versus actual cost;

z Effort and cost per individual service action; and

z Percent decrease in effort and cost per individual service action.

For more examples of standards to assess the contractor’s performance, refer to System and Software Metrics 

for Performance-Based Contracting.
7.1 Engineering with Contracts

NASA Systems Engineering Handbook  233

7.1.5.4 Decommissioning and Disposal

Contracts offer a means to achieve the safe and efficient 

decommissioning and disposal of systems and products 

that require specialized support systems, facilities, and 

trained personnel, especially when hazardous materials 

are involved. Consider these needs during development 

of the acquisition strategy and solidify them before the 

final design phase. Determine how many contracts will 

be needed across the product’s life cycle.

Some items to consider for decommissioning and disposal during the development of SOW requirements:

z Handling and disposal of waste generated during the 

fabrication and assembly of the product.

z Reuse and recycling of materials to minimize the disposal and transformation of materials.

z Handling and disposal of materials used in the product’s operations.

z End-of-life decommissioning and disposal of the 

product.

z Cost and schedule to decommission and dispose of 

the product, waste, and unwanted materials.

z Metrics to measure decommissioning and disposal of 

the product. 

z Metrics to assess the contractor’s performance. (Refer 

to System and Software Metrics for Performance-Based 

Contracting.)

For guidelines regarding disposal, refer to the Systems 

Engineering Handbook: A “What To” Guide for all SE 

Practitioners.

7.1.5.5 Final Evaluation of Contractor 

Performance

In preparation for closing out a contract, the technical 

team gives input to the procurement office regarding the 

contractor’s final performance evaluation. Although the 

technical team has performed periodic contractor performance evaluations, the final evaluation offers a means 

to document good and bad performance that continued 

throughout the contract. Since the evaluation is retained 

in a database, it can be used as relevant experience and 

past performance input during a future source selection 

process.

This phase of oversight is complete with the closeout 

or modification of the existing contract, award of the 

follow-on contract, and an operational system. Oversight continues with follow-contract activities.
234  NASA Systems Engineering Handbook

7.0 Special Topics

7.2.1 Introduction 

Concurrent Engineering (CE) and integrated design is a 

systematic approach to integrated product development 

that emphasizes response to stakeholder expectations 

and embodies team values of cooperation, trust, and 

sharing. The objective of CE is to reduce the product development cycle time through a better integration of activities and processes. Parallelism is the prime concept in 

reducing design lead time and concurrent engineering 

becomes the central focus. Large intervals of parallel 

work on different parts of the design are synchronized 

by comparatively brief exchanges between teams to produce consensus and decisions.1

 CE has become a widely 

accepted concept and is regarded as an excellent alternative approach to a sequential engineering process.

This section addresses the specific application of CE and 

integrated design practiced at NASA in Capability for 

Accelerated Concurrent Engineering (CACE) environments. CACE is comprised of four essential components: 

people, process, tools, and facility. The CACE environment typically involves the collocation of an in-place 

leadership team and core multidisciplinary engineering 

team working with a stakeholder team using well defined 

processes in a dedicated collaborative, concurrent engineering facility with specialized tools. The engineering 

and collaboration tools are connected by the facility’s integrated infrastructure. The teams work synchronously 

for a short period of time in a technologically intensive 

physical environment to complete an instrument or mission design. CACE is most often used to design space 

instruments and payloads or missions including orbital 

configuration; hardware such as spacecraft, landers, 

rovers, probes, or launchers; data and ground communication systems; other ground systems; and mission operations. But the CACE process applies beyond strict instrument and/or mission conceptual design.

Most NASA centers have a CACE facility. NASA CACE 

is built upon a people/process/tools/facility paradigm 

that enables the accelerated production of high-quality 

engineering design concepts in a concurrent, collaborative, rapid design environment. (See Figure 7.2-1.)

1

From Miao and Haake “Supporting Concurrent Design 

by Integrating Information Sharing and Activity Synchronization.”

Although CACE at NASA is based on a common philosophy and characteristics, specific CACE implementation varies in many areas. These variations include level 

of engineering detail, information infrastructure, knowledge base, areas of expertise, engineering staffing approach, administrative and engineering tools, type of facilitation, roles and responsibilities within CACE team, 

roles and responsibilities across CACE and stakeholder 

teams, activity execution approach, and duration of session. While primarily used to support early life-cycle 

phases such as pre-Formulation and Formulation, the 

CACE process has demonstrated applicability across the 

full project life cycle.

7.2.2 CACE Overview and Importance

CACE design techniques can be an especially effective 

and efficient method of generating a rapid articulation of 

concepts, architectures, and requirements. 

The CACE approach provides an infrastructure for brainstorming and bouncing ideas between the engineers and 

stakeholder team representatives, which routinely results 

in a high-quality product that directly maps to the customer needs. The collaboration design paradigm is so 

successful because it enables a radical reduction in decision latency. In a non-CACE environment, questions, 

issues, or problems may take several days to resolve. If 

a design needs to be changed or a requirement reevaluated, significant time may pass before all engineering 

team members get the information or stakeholder team 

members can discuss potential requirement changes. 

These delays introduce the possibility, following initial 

evaluation, of another round of questions, issues, and 

7.2 Integrated Design Facilities

Figure 7.2-1 CACE people/process/tools/facility 

paradigm
7.2 Integrated Design Facilities

NASA Systems Engineering Handbook  235

changes to design and requirements, adding further delays. 

The tools, data, and supporting information technology 

infrastructure within CACE provide an integrated support environment that can be immediately utilized by 

the team. The necessary skills and experience are gathered and are resident in the environment to synchronously complete the design. In a collaborative environment, questions can be answered immediately, or key 

participants can explore assumptions and alternatives 

with the stakeholder team or other design team members and quickly reorient the whole team when a design 

change occurs. The collaboration triggers the creativity 

of the engineers and helps them close the loop and rapidly converge on their ideas. Since the mid-1990s, the 

CACE approach has been successfully used at several 

NASA Centers as well as at commercial enterprises to 

dramatically reduce design development time and costs 

when compared to traditional methods. 

CACE stakeholders include NASA programs and projects, scientists, and technologists as well as other Government agencies (civil and military), Federal laboratories, 

and universities. CACE products and services include:

z Generating mission concepts in support of Center 

proposals to science AO;

z Full end-to-end designs including system/subsystem 

concepts, requirements, and tradeoffs;

z Focused efforts assessing specific architecture subelements and tradeoffs;

z Independent assessments of customer-provided reports, concepts, and costs;

z Roadmapping support; and

z Technology and risk assessments.

As integrated design has become more accepted, collaborative engineering design efforts expanded from the 

participation of one or more Centers in a locally executed 

activity; to geographically distributed efforts across a few 

NASA Centers with limited scope and participation; to 

true OneNASA efforts with participation from many 

NASA integrated design teams addressing broad, complex architectures. 

The use of geographically distributed CACE teams is a 

powerful engineering methodology to achieve lower risk 

and more creative solutions by factoring in the best skills 

and capabilities across the Agency. Using a geographically 

distributed process must build upon common CACE elements while considering local CACE facility differences 

and the differences in the local Center cultures.

7.2.3 CACE Purpose and Benefits

The driving forces behind the creation of NASA’s early 

CACE environments were increased systems engineering efficiency and effectiveness. More specifically, the 

early CACE environments addressed the need for:

z Generating more conceptual design studies at reduced cost and schedule, 

z Creating a reusable process within dedicated facilities 

using well-defined tools,

z Developing a database of mission requirements and 

designs for future use,

z Developing mission generalists from a pool of experienced discipline engineers, and

z Infusing a broader systems engineering perspective 

across the organization.

Additional resulting strategic benefits across NASA included:

z Core competency support (e.g., developing systems 

engineers, maturing and broadening of discipline engineers, training environment, etc.);

z Sensitizing the customer base to end-to-end issues 

and implications of requirements upon design;

z Test-bed environment for improved tools and processes;

z Environment for forming partnerships;

z Technology development and roadmapping support;

z Improved quality and consistency of conceptual designs; and

z OneNASA environment that enables cooperative rather 

than competitive efforts among NASA organizations.

7.2.4 CACE Staffing

A management or leadership team, a multidisciplinary 

engineering team, a stakeholder team, and a facility support team are all vital elements in achieving a successful 

CACE activity.

A CACE team consists of a cadre of engineers, each representing a different discipline or specialty engineering 

area, along with a lead systems engineer and a team lead 

or facilitator. As required, the core engineering team is 

supplemented with specialty and/or nonstandard engi-
236  NASA Systems Engineering Handbook

7.0 Special Topics

neering skills to meet unique stakeholder needs. These 

supplementary engineering capabilities can be obtained 

either from the local Center or from an external source. 

The team lead coordinates and facilitates the CACE activity and interacts with the stakeholders to ensure that 

their objectives are adequately captured and represented. 

Engineers are equipped with techniques and software 

used in their area of expertise and interact with the team 

lead, other engineers, and the stakeholder team to study 

the feasibility of a proposed solution and produce a design for their specific subsystem. 

A CACE operations manager serves as the Center advocate and manager, maintaining an operational capability, 

providing initial coordination with potential customers 

through final delivery of CACE product, and infusing 

continuous process and product improvement as well as 

evolutionary growth into the CACE environment to ensure its continued relevance to the customer base.

A CACE facility support team maintains and develops the 

information infrastructure to support CACE activities.

7.2.5 CACE Process

The CACE process starts with a customer requesting 

engineering support from CACE management. CACE 

management establishes that the customer’s request is 

within the scope of the team capabilities and availability 

and puts together a multidisciplinary engineering team 

under the leadership of a team lead and lead systems engineer collaborating closely with the customer team. The 

following subsections briefly describe the three major 

CACE activity phases: (1) planning and preparation, 

(2) execution, and (3) wrap-up. 

7.2.5.1 Planning and Preparation

Once a customer request is approved and team lead 

chosen, a planning meeting is scheduled. The key experts attending the planning meeting may include the 

CACE manager, a team lead, and a systems engineer 

as well as key representatives from the customer/stakeholder team. Interactions with the customer/stakeholder 

team and their active participation in the process are integral to the successful planning, preparation, and execution of a concurrent design session. Aspects addressed 

include establishing the activity scope, schedule, and 

costs; a general agreement on the type of product to be 

provided; and the success criteria and metrics. Agreements reached at the planning meeting are documented 

and distributed for review and comment. 

Products from the planning and preparation phase include the identification of activities required by the customer/stakeholder team, the CACE team, or a combination of both teams, as well as the definition of the 

objectives, the requirements, the deliverables, the estimated budget, and the proposed schedule. Under 

some conditions, followup coordination meetings are 

scheduled that include the CACE team lead, the systems engineer(s), a subset of the remaining team members, and customer/stakeholder representatives, as appropriate. The makeup of participants is usually based 

on the elements that have been identified as the activity 

drivers and any work identified that needs to be done before the actual design activity begins. 

During the planning and preparation process, the stakeholder-provided data and the objectives and activity 

plan are reviewed, and the scope of the activity is finalized. A discussion is held of what activities need to be 

done by each of the stakeholders and the design teams. 

For example, for planning a mission design study, the 

customer identifies the mission objectives by defining 

the measurement objectives and the instrument specifications, as applicable, and identifying the top-level requirements. A subset of the CACE engineering team 

may perform some preliminary work before the actual 

study (e.g., launch vehicle performance trajectory analysis; thrust and navigation requirements; the entry, descent, and landing profile; optical analysis; mechanical 

design; etc.) as identified in the planning meetings to 

further accelerate the concurrent engineering process in 

the study execution phase. The level of analysis in this 

phase is a function of many things, including the level of 

maturity of the incoming design, the stated goals and objectives of the engineering activity, engineer availability, 

and CACE scheduling. 

7.2.5.2 Activity Execution Phase

A typical activity or study begins with the customer presentation of the overall mission concept and instrument 

concepts, as applicable, to the entire team. Additional 

information provided by the customer/stakeholders includes the team objectives, the science and technology 

goals, the initial requirements for payload, spacecraft 

and mission design, the task breakdown between providers of parts or functions, top challenges and concerns, 

and the approximate mission timeline. This information 

is often provided electronically in a format accessible to 

the engineering team and is presented by the customer/
7.2 Integrated Design Facilities

NASA Systems Engineering Handbook  237

stakeholder representatives at a high level. During this 

presentation, each of the subsystems engineers focuses 

on the part of the overall design that is relevant to their 

subsystem. The systems engineer puts the high-level 

system requirements into the systems spreadsheets and/

or a database that is used throughout the process to track 

engineering changes. These data sources can be projected 

on the displays to keep the team members synchronized 

and the customer/stakeholders aware of the latest developments.

The engineering analysis is performed iteratively with the 

CACE team lead and systems engineer playing key roles 

to lead the process. Thus, issues are quickly identified, so 

consensus on tradeoff decisions and requirements redefinition can be achieved while maintaining momentum. 

The customer team actively participates in the collaborative process (e.g., trade studies, requirements relaxation, 

clarifying priorities), contributing to the rapid development of an acceptable product. 

Often, there are breakout sessions, or sidebars, in which 

part of the team discusses a particular tradeoff study. 

Each subsystem has a set of key parameters that are used 

for describing its design. Because of the dependencies 

among the various subsystems, each discipline engineer 

needs to know the value of certain parameters related to 

other subsystems. These parameters are shared via the 

CACE information infrastructure. Often, there are conflicting or competing objectives for various subsystems. 

Many tradeoff studies, typically defined and led by the 

team systems engineer, are conducted among subsystem 

experts immediately as issues occur. Most of the communication among team members is face to face or live 

via video or teleconference. Additional subject matter 

experts are consulted as required. In the CACE environment, subsystems that need to interact extensively are 

clustered in close proximity to facilitate the communication process among the experts.

The team iterates on the requirements, and each subsystem expert refines or modifies design choices as 

schedule allows. This process continues until an acceptable solution is obtained. There may be occasions where 

it is not possible to iterate to an acceptable solution prior 

to the scheduled end of the activity. In those cases, the 

available iterated results are documented and form the 

basis of the delivered product. 

In each iteration, activities such as the following take 

place, sometimes sequentially and other times in parallel. The subsystem experts of science, instruments, 

mission design, and ground systems collaboratively define the science data strategy for the mission in question. 

The telecommunications, ground systems, and command and data-handling experts develop the data-return 

strategy. The attitude control systems, power, propulsion, 

thermal, and structure experts iterate on the spacecraft 

design and the configuration expert prepares the initial 

concept. The systems engineer interacts with all discipline 

engineers to ensure that the various subsystem designs fit 

into the intended system architecture. Each subsystem expert provides design and cost information, and the cost 

expert estimates the total cost for the mission.

While design activity typically takes only days or weeks 

with final products available within weeks after study 

completion, longer term efforts take advantage of the 

concurrent, collaborative environment to perform more 

detailed analyses than those performed in the shorter 

duration CACE exercises. 

7.2.5.3 Activity Wrap-Up 

After the completion of a CACE study, the product is delivered to the customer. In some CACE environments, 

the wrap-up of the product is completed with minimal 

additional resources: the engineers respond to customer/stakeholder feedback by incorporating additional 

refinements or information emphasizing basic cleanup. In other CACE environments, significant time is expended to format the final report and review it with the 

customer/stakeholders to ensure that their expectations 

have been addressed adequately. 

Some CACE environments have standardized their 

wrap-up activities to address the customer/stakeholder 

feedback and develop products that are structured and 

uniform across different ranges of efforts. 

As part of activity followup, customer/stakeholder feedback is requested on processes, whether the product 

met their needs, and whether there are any suggested 

improvements. This feedback is factored back into the 

CACE environment as part of a continuous improvement process.

7.2.6 CACE Engineering Tools and 

Techniques 

Engineering tools and techniques vary within and across 

CACE environments in several technical aspects (e.g., 

level of fidelity, level of integration, generally available 
238  NASA Systems Engineering Handbook

7.0 Special Topics

commercial applications versus custom tools versus customized knowledge-based Excel spreadsheets, degree of 

parametric design and/or engineering analysis). For example, mechanical design tools range from white-board 

discussions to note pad translations to computer-aided 

design to 3D rapid design prototyping.

Important factors in determining which tools are appropriate to an activity include the purpose and duration of 

the activity, the engineers’ familiarity or preference, the 

expected product, the local culture, and the evolution of 

the engineering environment. Factors to be considered 

in the selection of CACE tools and engineering techniques should also include flexibility, compatibility with 

the CACE environment and process, and value and ease 

of use for the customer after the CACE activities.

Engineering tools may be integrated into the CACE infrastructure, routinely provided by the supporting engineering staff, and/or utilized only on an activity-byactivity basis, as appropriate. As required, auxiliary 

engineering analysis outside of the scope of the CACE 

effort can be performed external to the CACE environment and imported for reference and incorporation into 

the CACE product.

7.2.7 CACE Facility, Information 

Infrastructure, and Staffing 

Each CACE instantiation is unique to the Center, program, or project that it services. While the actual implementations vary, the basic character does not. Each 

implementation concentrates on enabling engineers, 

designers, team leads, and customer/stakeholders to be 

more productive during concurrent activities and communication. This subsection focuses on three aspects of 

this environment: the facility, the supporting information infrastructure, and the staff required to keep the facility operational.

7.2.7.1 Facility

The nature of communication among discipline specialists working together simultaneously creates a somewhat 

chaotic environment. Although it is the duty of the team 

lead to maintain order in the environment, the facility itself has to be designed to allow the participants to maintain order and remain on task while seeking to increase 

communication and collaboration. To do this effectively 

requires a significant investment in infrastructure resources. 

The room needs sufficient space to hold active participants from the disciplines required, customer/stakeholder representatives, and observers. CACE managers 

encourage observers to show potential future CACE 

users the value of active CACE sessions. 

It is also important to note that the room will get reconfigured often. Processes and requirements change, and 

the CACE facility must change with that. The facility 

could appear to an onlooker as a work in progress. Tables, chairs, computer workstations, network connections, electrical supplies, and visualization systems will 

continually be assessed for upgrades, modification, or 

elimination.

CACE requirements in the area of visualization are 

unique. When one subject matter expert wants to communicate to either a group of other discipline specialists 

or to the whole group in general, the projection system 

needs to be able to switch to different engineering workstations. When more than one subject matter expert 

wants to communicate with different groups, multiple 

projection systems need to be able to switch. This can 

typically require three to six projection systems with 

switching capability from any specific workstation to 

any specific projector. In addition, multiple projection 

systems switchable to the engineering workstations need 

to be mounted so that they can be viewed without impacting other activities in the room or so that the entire 

group can be refocused as required during the session. 

The ease of this reconfiguration is one measure of the efficacy of the environment.

7.2.7.2 Information Infrastructure

A CACE system not only requires a significant investment in the facility but relies heavily on the information 

infrastructure. Information infrastructure requirements 

can be broken down into three sections: hardware, software, and network infrastructure.

The hardware portion of the information infrastructure 

used in the CACE facility is the most transient element 

in the system. The computational resources, the communication fabric, servers, storage media, and the visualization capabilities benefit from rapid advances in technology. A CACE facility must be able to take advantage 

of the economy produced by those advances and must 

also be flexible enough to take advantage of the new capabilities. 
7.2 Integrated Design Facilities

NASA Systems Engineering Handbook  239

One of the major costs of a CACE infrastructure is 

software. Much of the software currently used by engineering processes is modeling and simulation, usually 

produced by commercial software vendors. Infrastructure software to support exchange of engineering data; 

to manage the study archive; and to track, administer, 

and manage facility activities is integral to CACE success. One of the functions of the CACE manager is to determine how software costs can be paid, along with what 

software should be the responsibility of the participants 

and customers.

The network infrastructure of a CACE facility is critical. 

Information flowing among workstations, file servers, 

and visualization systems in real time requires a significant network infrastructure. In addition, the network 

infrastructure enables collaboration with outside consultants, external discipline experts, and intra-Center 

collaboration. The effective use of the network infrastructure requires a balance between network security 

and collaboration and, as such, will always be a source 

of modification, upgrade, and reconfiguration. A natural 

extension of this collaboration is the execution of geographically distributed CACE efforts; therefore it is essential that a CACE facility have the tools, processes, and 

communications capabilities to support such distributed 

studies.

7.2.7.3 Facility Support Staff Responsibilities

A core staff of individuals is required to maintain an operational CACE environment. The responsibilities to be 

covered include end-to-end CACE operations and the 

management and administration of the information infrastructure. 

CACE information infrastructure management and administration includes computer workstation configuration; network system administration; documentation 

development; user help service; and software support to 

maintain infrastructure databases, tools, and Web sites.

7.2.8 CACE Products 

CACE products are applicable across project life-cycle 

phases and can be clearly mapped to the various outputs 

associated with the systems engineering activities such 

as requirements definition, trade studies, decision analysis, and risk management. CACE products from a typical design effort include a requirements summary with 

driving requirements identified; system and subsystem 

analysis; functional architectures and data flows; mass/

power/data rackups; mission design and ConOps; engineering trades and associated results; technology maturity levels; issues, concerns, and risks; parametric and/or 

grassroots cost estimates; engineering analyses, models, 

and applicable tools to support potential future efforts; 

and a list of suggested future analyses.

CACE product format and content vary broadly both 

within and across CACE environments. The particular 

CACE environment, the goals/objectives of the supported 

activity, whether the activity was supported by multiple 

CACE teams or not, the customer’s ultimate use, and the 

schedule requirements are some aspects that factor into 

the final product content and format. A primary goal in 

the identification and development of CACE products 

and in the packaging of the final delivery is to facilitate 

their use after the CACE activity.

Products include in-study results presentation, PowerPoint packages, formal reports and supporting computer-aided design models, and engineering analysis. 

Regardless of format, the CACE final products typically 

summarize the incoming requirements, study goal expectation, and study final results.

CACE environment flexibility enables support activities 

beyond that of a traditional engineering design study 

(e.g., independent technical reviews, cost validation, risk 

and technology assessments, roadmapping, and requirements review). Product contents for such activities might 

include feasibility assessment, technical recommendations, risk identification, recosting, technology infusion 

impact and implementation approach, and architectural 

options. 

In addition to formal delivery of the CACE product to 

the customer team, the final results and planning data 

are archived within the CACE environment for future 

reference and for inclusion in internal CACE cross-study 

analyses.

7.2.9 CACE Best Practices

This subsection contains general CACE best practices 

for a successful CACE design activity. Three main topic 

areas—people, process, technologies—are applicable 

to both local and geographically distributed activities. 

Many lessons learned about the multi-CACE collaboration activities were learned through the NASA Exploration Design Team (NEDT) effort, a OneNASA 
240  NASA Systems Engineering Handbook

7.0 Special Topics

multi-Center distributed collaborative design activity 

performed during FY05.

7.2.9.1 People

z Training: Individuals working in CACE environments benefit from specialized training. This training 

should equip individuals with the basic skills necessary for efficient and effective collaboration. Training 

should include what is required technically as well as 

orientation to the CACE environment and processes.

z Characteristics: Collaborative environment skills include being flexible, working with many unknowns, 

and willingness to take risks. Ability and willingness 

to think and respond in the moment is required as 

well as the ability to work as part of a team and to 

interact directly with customer representatives to negotiate requirements and to justify design decisions. 

Supporting engineers also need the ability to quickly 

and accurately document their final design as well as 

present this design in a professional manner. In addition, the CACE team leads or facilitators should have 

additional qualities to function well in a collaborative 

design environment. These include organizational 

and people skills, systems engineering skills and background, and broad general engineering knowledge.

7.2.9.2 Process and Tools

z Customer Involvement: Managing customer expectations is the number one factor in positive study outcome. It is important to make the customers continuously aware of the applications and limitations of the 

CACE environment and to solicit their active participation in the collaborative environment. 

z Adaptability: The CACE environments must adapt 

processes depending on study type and objectives, as 

determined in negotiations prior to study execution. 

In addition to adapting the processes, engineers with 

appropriate engineering and collaborative environment skills must be assigned to each study. 

z Staffing: Using an established team has the benefit of 

the team working together and knowing each other 

and the tools and processes. A disadvantage is that a 

standing army can get “stale” and not be fluent with 

the latest trends and tools in their areas of expertise. 

Supporting a standing army full time is also an expensive proposition and often not possible. A workable 

compromise is to have a full-time (or nearly full-time) 

leadership team complemented by an engineering 

team. This engineering team could be composed of 

engineers on rotational assignments or long-term detail to the team, as appropriate. An alternative paradigm is to partially staff the engineering team with 

personnel provided through the customer team.

z Tools and Data Exchange: In general, each engineer 

should use the engineering tools with which he or she 

is most familiar to result in an effective and efficient 

process. The CACE environment should provide an 

information infrastructure to integrate resulting engineering parameters.

z Decision Process: Capturing the decisionmaking 

and design rationale is of great interest and of value 

to CACE customers as well as being a major challenge 

in the rapid engineering environment. The benefit of 

this is especially important as a project progresses and 

makes the CACE product more valuable to the customer. Further along in the life cycle of a mission or 

instrument, captured decisions and design rationale 

are more useful than a point-design from some earlier time. 

z Communication: CACE environments foster rapid 

communication among the team members. Because 

of the fast-paced environment and concurrent engineering activities, keeping the design elements “in 

synch” is a challenge. This challenge can be addressed 

by proactive systems engineers, frequent tag-ups, additional systems engineering support and the use of 

appropriate information infrastructure tools.

z Standards Across CACE Environments: Establishing 

minimum requirements and standard sets of tools 

and techniques across the NASA CACE environment 

would facilitate multi-Center collaborations.

z Planning: Proper planning and preparation are crucial for efficient CACE study execution. Customers 

wanting to forgo the necessary prestudy activity or 

planning and preparation must be aware of and accept the risk of a poor or less-than-desired outcome.

7.2.9.3 Facility

z Communication Technologies: The communication 

infrastructure is the backbone of the collaborative 

CACE environment. Certain technologies should be 

available to allow efficient access to resources external 

to a CACE facility. It is important to have “plug and 

play” laptop capability, for example. Multiple phones 

should be available to the team and cell phone access 

is desirable.
7.2 Integrated Design Facilities

NASA Systems Engineering Handbook  241

z Distributed Team Connectivity: Real-time transfer of 

information for immediate access between geographically distributed teams or for multi-Center activities can 

be complicated due to firewall and other networking issues. Connectivity and information transfer methods 

should be reviewed and tested before study execution.
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7.0 Special Topics

7.3 Selecting Engineering Design Tools

NASA utilizes cutting-edge design tools and techniques 

to create the advanced analyses, designs, and concepts 

required to develop unique aerospace products, spacecraft, and science experiments. The diverse nature of the 

design work generated and overseen by NASA requires 

use of a broad spectrum of robust electronic tools such 

as computer-aided design tools and computer-aided systems engineering tools. Based on the distributed and 

varied nature of NASA projects, selection of a single suite 

of tools from only one vendor to accomplish all design 

tasks is not practical. However, opportunities to improve 

standardization of design policy, processes, and tools remain a focus for continuous improvement activities at all 

levels within the Agency.

These guidelines serve as an aid to help in the selection 

of appropriate tools in the design and development of 

aerospace products and space systems and when selecting tools that affect multiple Centers.

7.3.1 Program and Project Considerations

When selecting a tool to support a program or project, 

all of the upper level constraints and requirements must 

be identified early in the process. Pertinent information 

from the project that affects the selection of the tools will 

include the urgency, schedule, resource restrictions, extenuating circumstances, and constraints. A tool that 

does not support meeting the program master schedule 

or is too costly to be bought in sufficient numbers will not 

satisfy the project manager’s requirements. For example, 

a tool that requires extensive modification and training 

that is inconsistent with the master schedule should not 

be selected by the technical team. If the activity to be 

undertaken is an upgrade to an existing project, legacy 

tools and availability of trained personnel are factors to 

be considered.

7.3.2 Policy and Processes

When selecting a tool, one must consider the applicable 

policies and processes at all levels, including those at the 

Center level, within programs and projects, and at other 

Centers when a program or project is a collaborative effort. In the following discussion, the term “organization” 

will be used to represent any controlling entity that establishes policy and/or processes for the use of tools in the design or development of NASA products. In other words, 

“organization” can mean the user’s Center, another collaborating Center, a program, a project, in-line engineering groups, or any combination of these entities.

Policies and processes affect many aspects of a tool’s 

functionality. First and foremost, there are policies that 

dictate how designs are to be formally or informally controlled within the organization. These policies address 

configuration management processes that must be followed as well as the type of data object that will be formally controlled (e.g., drawings or models). Clearly this 

will affect the types of tools that will be used and how 

their designs will be annotated and controlled.

The Information Technology (IT) policy of the organization also needs to be considered. Data security and 

export control (e.g., International Traffic in Arms Regulations (ITAR)) policies are two important IT policy 

considerations that will influence the selection of a particular design tool.

The policy of the organization may also dictate requirements on the format of the design data that is produced 

by a tool. A specific format may be required for sharing 

information with collaborating parties. Other considerations are the organizations’ quality processes, which 

control the versions of the software tools as well as their 

verification and validation. There are also policies on 

training and certifying users of tools supporting critical 

flight programs and projects. This is particularly important when the selection of a new tool results in the transition from a legacy tool to a new tool. Therefore, the quality 

of the training support provided by the tool vendor is an 

important consideration in the selection of any tool.

Also, if a tool is being procured to support a multi-Center 

program or project, then program policy may dictate 

which tool must be used by all participating Centers. If 

Centers are free to select their own tool in support of a 

multi-Center program or project, then consideration of 

the policies of all the other Centers must be taken into 

account to ensure compatibility among Centers.

7.3.3 Collaboration

The design process is highly collaborative due to the complex specialties that must interact to achieve a successful 

integrated design. Tools are an important part of a suc-
7.3 Selecting Engineering Design Tools

NASA Systems Engineering Handbook  243

cessful collaboration. To successfully select and integrate 

tools in this environment requires a clear understanding 

of the intended user community size, functionality required, nature of the data to be shared, and knowledge 

of tools to be used. These factors will dictate the number 

of licenses, hosting capacity, tool capabilities, IT security requirements, and training required. The sharing of 

common models across a broad group requires mechanisms for advancing the design in a controlled way. Effective use of data management tools can help control 

the collaborative design by requiring common naming 

conventions, markings, and design techniques to ensure 

compatibility among distributed design tools.

7.3.4 Design Standards

Depending on the specific domain or discipline, there 

may be industry and Center-specific standards that must 

be followed, particularly when designing hardware. This 

can be evident in the design of a mechanical part, where 

a mechanical computer-aided design package selected to 

model the parts must have the capability to meet specific 

standards, such as model accuracy, dimensioning and 

tolerancing, the ability to create different geometries, and 

the capability to produce annotations describing how to 

build and inspect the part. However, these same issues 

must be considered regardless of the product.

7.3.5 Existing IT Architecture

As with any new tool decision, an evaluation of defined 

Agency and Center IT architectures should be made that 

focuses on compatibility with and duplication of existing 

tools. Typical architecture considerations would include 

data management tools, middleware or integration infrastructure, network transmission capacity, design analysis tools, manufacturing equipment, approved hosting, 

and client environments.

While initial focus is typically placed on current needs, 

the scalability of the tools and the supporting IT infrastructure should be addressed too. Scalability applies to 

both the number of users and capacity of each user to 

successfully use the system over time.

7.3.6 Tool Interfaces

Information interfaces are ubiquitous, occurring whenever information is exchanged.

This is particularly characteristic of any collaborative 

environment. It is here that inefficiencies arise, information is lost, and mistakes are made. There may be an 

organizational need to interface with other capabilities 

and/or analysis tools, and understanding the tools used 

by the design teams with which your team interfaces 

and how the outputs of your team drive other downstream design functions is critical to ensure compatibility of data. 

For computer-aided systems engineering tools, users are 

encouraged to select tools that are compatible with the 

Object Management Group System Modeling Language 

(SysML) standard. SysML is a version of the Unified 

Modeling Language (UML) that has been specifically 

developed for systems engineering.

7.3.7 Interoperability and Data Formats

Interoperability is an important consideration when selecting tools. The tools must represent the designs in formats that are acceptable to the end user of the data. It is 

important that any selected tool include associative data 

exchange and industry-standard data formats. As the 

Agency increasingly engages in multi-Center programs 

and projects, the need for interoperability among different tools, and different versions of the same tool, becomes even more critical. True interoperability reduces 

human error and the complexity of the integration task, 

resulting in reduced cost, increased productivity, and a 

quality product.

When considering all end users’ needs, it is clear that interoperability becomes a difficult challenge. Three broad 

approaches, each with their own strengths and weaknesses, are: 

z Have all employees become proficient in a variety of 

different tool systems and the associated end use applications. While this provides a broad capability, it 

may not be practical or affordable.

z Require interoperability among whatever tools are 

used, i.e., requiring that each tool be capable of transferring model data in a manner that can be easily and 

correctly interpreted by all the other tools. Considerable progress has been made in recent years in the 

standards for the exchange of model data. While this 

would be the ideal solution for many, standard data 

formats that contain the required information for all 

end users do not yet exist.

z Dictate that all participating organizations use the 

same version of the same tool.
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7.0 Special Topics

7.3.8 Backward Compatibility

On major programs and projects that span several years, 

it is often necessary to access design data that are more 

than 3 to 5 years old. However, access to old design data 

can be extremely difficult and expensive, either because 

tool vendors end their support or later versions of the tool 

can no longer read the data. Strategies for maintaining 

access include special contracts with vendors for longer 

support, archiving design data in neutral formats, continuous migration of archives into current formats, and 

recreating data on demand. Organizations should select 

the strategy that works best for them, after a careful consideration of the cost and risk.

7.3.9 Platform

While many tools will run on multiple hardware platforms, some perform better in specific environments 

or are only supported by specified versions of operating 

systems. In the case of open-source operating systems, 

many different varieties are available that may not fully 

support the intended tools. If the tool being considered 

requires a new platform, the additional procurement cost 

and administration support costs should be factored in.

7.3.10Tool Configuration Control

Tool configuration control is a tradeoff between responsive adoption of the new capabilities in new versions and 

smooth operation across tool chain components. This 

is more difficult with heterogeneous (multiple vendor) 

tool components. An annual or biannual block upgrade 

strategy requires significant administrative effort. On the 

other hand, the desktop diversity resulting from usermanaged upgrade timing also increases support requirements.

7.3.11Security/Access Control

Special consideration should be given to the sensitivity 

and required access of all design data. Federal Government and Agency policy requires the assessment of all 

tools to ensure appropriate security controls are addressed to maintain the integrity of the data.

7.3.12Training

Most of the major design tools have similar capabilities 

that will not be new concepts to a seasoned designer. 

However, each design tool utilizes different techniques 

to perform design functions, and each contains some 

unique tool sets that will require training. The more 

responsive vendors will provide followup access to instructors and onsite training with liberal distribution of 

training materials and worked examples. The cost and 

time to perform the training and time for the designer to 

become proficient can be significant and should be carefully factored in when making decisions on new design 

tools. 

The disruptive aspect of training is an important consideration in adapting to a different tool. Before transitioning to a new tool, an organization must consider the 

schedule of deliverables to major programs and projects. 

Can commitments still be met in a timely fashion? It is 

suggested that organizations implement a phase-in approach to a new tool, where the old tool is retained for 

some time to allow people to learn the new tool and become proficient in its use. The transition of a fully functional and expert team using any one system, to the same 

team fully functional using another system, is a significant undertaking. Some overlap between the old tool 

and the new tool will ensure flexibility in the transition 

and ensure that the program and project work proceeds 

uninterrupted.

7.3.13Licenses

Licenses provide and control access to the various modules or components of a product or product family. Consideration of the license scheme should be taken into 

account while selecting a tool package. Licenses are 

sometimes physical, like a hardware key that plugs into 

a serial or parallel port, or software that may or may not 

require a whole infrastructure to administer. Software licenses may be floating (able to be shared on many computers on a first-come, first-served basis) or locked (dedicated to a particular computer). A well-thought-out 

strategy for licenses must be developed in the beginning 

of the tool selection process. This strategy must take into 

consideration program and project requirements and 

constraints as well as other factors such as training and 

use.

7.3.14Stability of Vendor and Customer 

Support

As in the selection of any support device or tool, vendor 

stability is of great importance. Given the significant investment in the tools (directly) and infrastructure (indirectly), it is important to look at the overall company sta-
7.3 Selecting Engineering Design Tools

NASA Systems Engineering Handbook  245

bility to ensure the vendor will be around to support the 

tools. Maturity of company products, installed user base, 

training, and financial strength can all provide clues to 

the company’s ability to remain in the marketplace with 

a viable product. In addition, a responsive vendor provides customer support in several forms. A useful venue 

is a Web-based user-accessible knowledge base that includes resolved issues, product documentation, manuals, 

white papers, and tutorials. Live telephone support can be 

valuable for customers who don’t provide support internally. An issue resolution and escalation process involves 

customers directly in prioritizing and following closure 

of critical issues. Onsite presence by the sales team and 

application engineers, augmented by post-sales support 

engineers, can significantly shorten the time to discovery 

and resolution of issues and evolving needs.
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7.0 Special Topics

7.4 Human Factors Engineering

The discipline of Human Factors (HF) is devoted to the 

study, analysis, design, and evaluation of human-system 

interfaces and human organizations, with an emphasis 

on human capabilities and limitations as they impact 

system operation. HF engineering issues relate to all aspects of the system life, including design, build, test, operate, and maintain, across the spectrum of operating 

conditions (nominal, contingency, and emergency). 

People are critical components in complex aerospace 

systems: designers, manufacturers, operators, ground 

support, and maintainers. All elements of the system 

are influenced by human performance. In the world of 

human-system interaction, there are four avenues for 

improving performance, reducing error, and making 

systems more error tolerant: (1) personnel selection; 

(2) system, interface, and task design; (3) training; and 

(4) procedure improvement. Most effective performance 

improvement involves all four avenues. People can be 

highly selected for the work they are to perform and the 

environment they are to perform it in. Second, equipment 

and systems can be designed to be easy to use, error resistant, and quickly learned. Third, people can be trained 

to proficiency on their required tasks. Fourth, improving 

tasks or procedures can be an important intervention. 

HF focuses on those aspects where people interface 

with the system. It considers all personnel who must interact with the system, not just the operator; deals with 

organizational systems as well as hardware; and examines all types of interaction, not just hardware or software interfaces. The role of the HF specialist is to advocate for the human component and to ensure that the 

design of hardware, software, tasks, and environment is 

compatible with the sensory, perceptual, cognitive, and 

physical attributes of those interacting with the system. 

The HF specialist should elucidate why human-related 

issues or features should be included in analyses, design decisions, or tests and explain how design options 

will affect human performance in ways that impact total 

system performance and/or cost. As system complexity 

grows, the potential for conflicts between requirements 

increases. Sophisticated human-system interfaces create 

conflicts such as the need to create systems that are easy 

for novices to learn while also being efficient for experts 

to use. The HF specialist recognizes these tradeoffs and 

constraints and provides guidance on balancing these 

competing requirements. The domain of application is 

anywhere there are concerns regarding human and organizational performance, error, safety, and comfort. The 

goal is always to inform and improve the design. 

What distinguishes an HF specialist is the particular 

knowledge and methods used, the domain of employment, and the goal of the work. HF specialists have expertise in the knowledge of human performance, both 

general and specific. There are many academic specialties concerned with applying knowledge of human behavior. These include psychology, cognitive science, cognitive psychology, sociology, economics, instructional 

system development, education, physiology, industrial 

psychology, organizational behavior, communication, 

and industrial engineering. Project and/or process managers should consult with their engineering or SMA directorates to get advice and recommendations on specific HF specialists who would be appropriate for their 

particular activity.

It is recommended to consider having HF specialists 

on the team throughout all the systems engineering 

common technical processes so that they can construct 

the specific HF analysis techniques and tests customized to the specific process or project. Not only do the 

HF specialists help in the development of the end items 

in question, but they should also be used to make sure 

that the verification test and completeness techniques 

are compatible and accurate for humans to undertake. 

Participation early in the process is especially important. 

Entering the system design process early ensures that 

human systems requirements are “designed in” rather 

than corrected later. Sometimes the results of analyses 

performed later call for a reexamination of earlier analyses. For example, functional allocation typically must 

be refined as design progresses because of technological 

breakthroughs, unforeseen technical difficulties in design or programming, or task analysis may indicate that 

some tasks assigned to humans exceed human capabilities under certain conditions. 

During requirements definition, HF specialists ensure 

that HF-related goals and constraints are included in 

the overall plans for the system. The HF specialist must 

identify the HF-related issues, design risks, and tradeoffs pertinent to each human-system component, and 

document these as part of the project’s requirements so 
7.4 Human Factors Engineering

NASA Systems Engineering Handbook  247

they are adequately addressed during the design phase. 

For stakeholder expectation definition from the HF perspective, the stakeholders include not only those who are 

specifying the system to be built, but also those who will 

be utilizing the system when it is put into operation. This 

approach yields requirements generated from the top 

down—what the system is intended to accomplish—and 

from the bottom up—how the system is anticipated to 

function. It is critical that the HF specialist contribute to 

the ConOps. The expectations of the role of the human in 

the system and the types of tasks the human is expected 

to perform underlie all the hardware and software requirements. The difference between a passive passenger 

and an active operator will drive major design decisions. 

The number of crewmembers will drive subsequent decisions about habitable volume and storage and about 

crew time available for operations and maintenance. 

HF specialists ensure appropriate system design that defines the environmental range in which the system will 

operate and any factors that impact the human components. Many of these factors will need to accommodate 

human, as well as machine, tolerances. The requirements 

may need to specify acceptable atmospheric conditions, 

including temperature, pressure, composition, and humidity, for example. The requirements might also address 

acceptable ranges of acoustic noise, vibration, acceleration, and gravitational forces, and the use of protective 

clothing. The requirements may also need to accommodate adverse or emergency conditions outside the range 

of normal operation.

7.4.1 Basic HF Model

A key to conducting human and organizational analysis, 

design, and testing is to have an explicit framework that 

relates and scopes the work in question. The following 

model identifies the boundaries and the components involved in assessing human impacts.

The HF interaction model (Figure 7.4-1) provides a reference point of items to be aware of in planning, analyzing, 

designing, testing, operating, and maintaining systems. 

Detailed checklists should be generated and customized 

for the particular system under development. The model 

presented in this module is adapted from David Meister’s 

Human Factors: Theory and Practice and is one depiction 

of how humans and systems interact. Environmental influences on that interaction have been added. The model 

illustrates a typical information flow between the human 

and machine components of a system.

Figure 7.4-2 provides a reference point of human factors 

process phases to be aware of in planning, analyzing, designing, testing, operating, and maintaining systems.

7.4.2 HF Analysis and Evaluation 

Techniques

Table 7.4-1 provides a set of techniques for human and 

organizational analysis and evaluation that can help to 

ensure that appropriate human and organizational factors have been considered and accommodated. These 

HF analysis methods are used to analyze systems, provide data about human performance, make predictions 

about human-system performance, and evaluate if the 

human-machine system performance meets design criteria. Most methods involve judgment and so are highly 

dependent on the skill and expertise of the analyst. In 

addition, both experienced and inexperienced operators provide valuable information about the strengths 

and weaknesses of old systems and how the new system 

might be used.

These methods are appropriate to all phases of system 

design with increasing specificity and detail as development progresses. While HF principles are often researched and understood at a generic level, their application is only appropriate when tailored to fit the design 

phase. Each type of analysis yields different kinds of information and so they are not interchangeable. The outputs or products of the analyses go into specification documents (operational needs document, ConOps, System 

Requirements Document (SRD), etc.) and formal review 

processes (e.g., ORR, SRR, SDR, PDR, CDR, PRR, PIR). 

Human Factors

Interaction Model

Machine Display

Component

Human Sensory

Component

Machine CPU

Component

Human Musculoskeletal

Component

Human Cognitive

Component

Machine Input

Device Component

Figure 7.4-1 Human factors interaction model
248  NASA Systems Engineering Handbook

7.0 Special Topics

The list shown in Table 7.4-1 is not exhaustive. The main 

point is to show examples that demonstrate the scope 

Pre-Phase A: Concept Studies/

Phase A: Concept & Tech Development

NASA Program/Project

Life Cycle 

Phase A: Concept & Tech Development/

Phase B: Prelim Design & Tech Completion

Phase C: 

Final Design & Fabrication

Phase D: System Assembly,

Integration & Test, Launch

Phase E:

Operations & Sustainment

Phase F:

Closeout

Human Factors Engineering

Process Integrating Points 

7. Track Use of the System;

Validation Testing

6. Usability Testing of Procedures &

Integration Assessment

1. Operational Analysis &

Analysis of Similar Systems

2. Preliminary Function

Allocation & Task Analysis

5. Formal Usability Testing

of Full System

4. Usability Study of

Components, Prototypes, Mockups

3. Human Factors

Requirements Denitions

Figure 7.4-2 HF engineering process and its links to the NASA program/

project life cycle

and usefulness of common methods used to evaluate 

system design and development.
7.4 Human Factors Engineering

NASA Systems Engineering Handbook  249

Table 7.4-1 Human and Organizational Analysis Techniques 

Process Human/Individual Analysis Additional Organizational Analysis

A. Operational Analysis

Definition When applied to HF, it is analysis of projected operations.

Purpose Obtain information about situations or events that may confront 

operators and maintainers using the new system. Systems 

engineers or operations analysts have typically done operational 

analyses. HF specialists should also be members of the analysis 

team to capture important operator or maintainer activities.

Inputs RFPs, planning documents, system requirements documents, and 

expert opinion.

Process Consult the systems engineer and projected users to extract 

implications for operators and maintainers.

Assess interactions and logistics 

between individuals and organizations. 

Evaluate operations under different 

types of organizations, structures, or 

distributions.

Outputs Detailed scenarios (for nominal operations, hard and soft failures, 

and emergencies) including consequences; verbal descriptions 

of events confronting operators and maintainers; anticipated 

operations (list of feasible operations and those that may overstress 

the system); assumptions; constraints that may affect system performance; environments; list of system operation and maintenance 

requirements.

New or adjusted workflows to compensate for organizational impacts as 

appropriate.

B. Similar Systems Analysis

Definition When applied to HF, it examines previous systems or systems in use 

for information useful for the new system.

Purpose To obtain lessons learned and best practices useful in planning for 

a new system. Experiences gained from systems in use is valuable 

information that should be capitalized on.

Inputs Structured observations, interviews, questionnaires, activity analysis, accident/incident reports, maintenance records, and training 

records.

Process Obtain data on the operability, maintainability, and number of 

people required to staff the system in use. Identify skills required 

to operate and maintain the system and training required to bring 

operators to proficiency. Obtain previous data on HF design problems and problems encountered by previous users of the previous 

system or system in use.

Identify the existing system’s organizational hierarchies and management 

distribution schemes (centralized versus 

decentralized).

Outputs Identification of environmental factors that may affect personnel; 

preliminary assessments of workload and stress levels; assessment 

of skills required and their impact on selection, training, and 

design; estimates of future staffing and manpower requirements; 

identification of operator and maintainer problems to avoid; 

assessment of desirability and consequences of reallocation of 

systems functions.

Evaluation of the configuration’s impact 

on performance and its potential risks.

 (continued)
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Process Human/Individual Analysis Additional Organizational Analysis

C. Critical Incident Study

Definition When applied to HF, it identifies sources of difficulties for operators or 

maintenance or in the operational systems (or simulations of them).

Purpose To analyze and hypothesize sources of errors and difficulties in a 

system. This is particularly useful when a system has been operational and difficulties are observed or suspected, but the nature 

and severity of those difficulties is not known.

Inputs Operator/maintainer accounts of accidents, near-accidents, 

mistakes, and near-mistakes.

Process Interview large numbers of operators/maintainers; categorize incidents/accidents; use HF knowledge and experience to hypothesize 

sources of difficulty and how each one could be further studied; 

mitigate or redesign to eliminate difficulty.

Trace difficulties between individuals 

and organizations and map associated 

responsibilities and process assignments.

Outputs Sources of serious HF difficulties in the operation of a system or its 

maintenance with suggested solutions to those difficulties.

Identification of potential gaps or 

disconnects based on the mapping.

D. Functional Flow Analysis

Definition When applied to HF, it is a structured technique for determining 

system requirements. Decomposes the sequence of functions or 

actions that a system must perform.

Purpose Provides a sequential ordering of functions that will achieve system 

requirements and a detailed checklist of system functions that 

must be considered in ensuring that the system will be able to 

perform its intended mission. These functions are needed for the 

solution of trade studies and determinations of their allocation 

among operators, equipment, software, or some combination of 

them. Decision-action analysis is often used instead of a functional 

flow analysis when the system requires binary decisions (e.g., 

software-oriented).

Inputs Operational analyses, analyses of similar systems, activity analyses.

Process Top-level functions are progressively expanded to lower levels 

containing more and more detailed information. If additional 

elaboration is needed about information requirements, sources of 

information, potential problems, and error-inducing features, for 

example, then an action-information analysis is also performed.

Map functional flows to associated 

organizational structures.

Outputs Functional flow diagrams. Identification of any logistics or responsibility gaps based on the integrated 

map.

E. Action-Information Analysis

Definition When applied to HF, it elaborates each function or action in 

functional flows or decision-action diagrams by identifying the 

information that is needed for each action or decision to occur. 

This analysis is often supplemented with sources of data, potential 

problems, and error-inducing features associated with each function or action.

 (continued)

Table 7.4-1 Human and Organizational Analysis Techniques (continued) 
7.4 Human Factors Engineering

NASA Systems Engineering Handbook  251

Process Human/Individual Analysis Additional Organizational Analysis

Purpose Provides more detail before allocating functions to agents.

Inputs Data from the analysis of similar systems, activity analyses, critical 

incident studies, functional flow and decision-action analyses, and 

comments and data from knowledgeable experts.

Process Each function or action identified in functional flows or decisionaction analyses is elaborated.Map associated components (function, 

action, decisions) to the responsible 

organizational structures.

Outputs Detailed lists of information requirements for operator-system interfaces, early estimates of special personnel provisions likely to be 

needed, support requirements, and lists of potential problems and 

probable solutions. Often produces suggestions for improvements 

in design of hardware, software, or procedures.

Identification of any logistics or responsibility gaps based on the integrated 

map.

F. Functional Allocation

Definition When applied to HF, it is a procedure for assigning each system 

function, action, and decision to hardware, software, operators, 

maintainers, or some combination of them.

Purpose To help identify user skill needs and provide preliminary estimates 

of staffing, training, and procedures requirements and workload 

assessments. Functional flows and decision-action analyses do 

not identify the agent (person or machine) that will execute the 

functions.

Inputs Functional flow analyses, decision-action analyses, action-information analyses, past engineering experience with similar systems, 

state-of-the-art performance capabilities of machines and 

software, and store of known human capabilities and limitations.

Process Identify and place to the side all those functions that must be 

allocated to personnel or equipment for reasons of safety, limitations of engineering technology, human limitations, or system 

requirements. List the remaining functions—those that could be 

either performed manually or by some combination of personnel 

and equipment. Prepare descriptions of implementation. Establish 

weighting criteria for each design alternative. Compare alternative 

configurations in terms of their effectiveness in performing the 

given function according to those criteria.

After initial assignment configuration 

is completed, evaluate allocations 

against relevant organizational norms, 

values, and organizational interfaces for 

logistics and management impacts.

Outputs Allocations of system functions to hardware, software, operators, 

maintainers, or some combination of them. Task analyses are then 

performed on those functions allocated to humans.

List of potential impacts with recommended modifications in either functions or management or both.

G. Task Analysis

Definition When applied to HF, it is a method for producing an ordered list of 

all the things people will do in a system.

Purpose To develop input to all the analyses that come next. A subsequent 

timeline analysis chart can provide the temporal relationship 

among tasks—sequences of operator or maintainer actions, the 

times required for each action, and the time at which each action 

should occur.

 (continued)

Table 7.4-1 Human and Organizational Analysis Techniques (continued) 
252  NASA Systems Engineering Handbook

7.0 Special Topics

Process Human/Individual Analysis Additional Organizational Analysis

Inputs Data from all the methods above supplemented with information 

provided by experts who have had experience with similar systems.

Process HF specialists and subject matter experts list and describe all tasks, 

subdividing them into subtasks with the addition of supplementary information.

Group all tasks assigned to a given 

organization and evaluate the range of 

skills, communications, and management capabilities required. Evaluate 

new requirements against existing 

organization’s standard operating 

procedures, norms, and values.

Outputs Ordered list of all the tasks people will perform in a system. Details 

on information requirements, evaluations and decisions that must 

be made, task times, operator actions, and environmental conditions.

Identify group-level workloads, 

management impacts, and training 

requirements.

H. Fault Tree Analysis

Definition When applied to HF, it determines those combinations of events 

that could cause specific system failures, faults, or catastrophes. 

Fault tree and failure mode and effects analysis are concerned with 

errors.

Purpose Anticipate mistakes that operators or maintainers might make and 

try to design against those mistakes. Limitation for HF is that each 

event must be described in terms of only two possible conditions, 

and it is extremely difficult to attach exact probabilities to human 

activities.

Inputs All outputs of the methods described above, supplemented with 

data on human reliability.

Process Construct a tree with symbols (logic gates) to represent events 

and consequences and describe the logical relationship between 

events.

Anticipate mistakes and disconnects 

that may occur in the workflow between 

individuals and organizations including 

unanticipated interactions between 

standard organization operating procedures and possible system events.

Outputs Probabilities of various undesirable workflow-related events, the 

probable sequences that would produce them, and the identification of sensitive elements that could reduce the probability of a 

mishap.

Probabilities of various undesirable 

workflow-related events arranged by 

organizational interface points for the 

workflows, the probable sequences that 

would produce them, and the identification of sensitive elements that could 

reduce the probability of a mishap.

I. Failure Modes and Effects Analysis

Definition When applied to HF, it is a methodology for identifying error-inducing features in a system.

Purpose Deduce the consequences for system performance of a failure in 

one or more components (operators and maintainers) and the 

probabilities of those consequences occurring.

 (continued)

Table 7.4-1 Human and Organizational Analysis Techniques (continued) 
7.4 Human Factors Engineering

NASA Systems Engineering Handbook  253

Process Human/Individual Analysis Additional Organizational Analysis

Inputs All outputs of methods described above, supplemented with data 

on human reliability.

Process Analyst identifies the various errors operators or maintainers may 

make in carrying out subtasks or functions. Estimates are made 

of the probabilities or frequencies of making each kind of error. 

The consequences of each kind of error are deduced by tracing its 

effects through a functional flow diagram to its final outcome.

Identify possible organizational entities 

and behaviors (i.e., political) involved 

with the system. Estimate the probabilities of occurrence and the impact of 

consequence.

Outputs List of human failures that would have critical effects on system 

operation, the probabilities of system or subsystem failures due to 

human errors, and identification of those human tasks or actions 

that should be modified or replaced to reduce the probability of 

serious system failures.

List organizational behaviors that 

would have a critical effect on the 

system operation; the probabilities of 

the system or subsystem failures due 

to the organizational behaviors; and 

those organizational values, culture, or 

actions/standard operating procedures 

that should be modified or replaced to 

reduce the probability of serious system 

failures.

J. Link Analysis

Definition When applied to HF, it is an examination of the relationships 

between components, including the physical layout of instrument 

panels, control panels, workstations, or work areas to meet certain 

objectives.

Purpose To determine the efficiency and the effectiveness of the physical 

layout of the human-machine interface.

Inputs Data from activity and task analysis and observations of functional 

or simulated systems.

Process List all personnel and items. Estimate frequencies of linkages 

between items, operators, or items and operators. Estimate the 

importance of each link. Compute frequency-importance values 

for each link. Starting with the highest link values, successively add 

items with lower link values and readjust to minimize linkages. Fit 

the layout into the allocated space. Evaluate the new layout against 

the original objectives.

Assess links at individual versus organizational levels.

Outputs Recommended layouts of panels, workstations, or work areas. Adjusted layouts of panels, 

workstations, or work areas based on 

optimum individual and organizational 

performance priorities.

K. Simulation

Definition When applied to HF, it is a basic engineering or HF method to predict 

performance of systems. Includes usability testing and prototyping.

Purpose To predict the performance of systems, or parts of systems, that do 

not exist or to allow users to experience and receive training on systems, or parts of systems, that are complex, dangerous, or expensive.

Inputs Hardware, software, functions, and tasks elucidated in task analysis, 

operating procedures.

 (continued)

Table 7.4-1 Human and Organizational Analysis Techniques (continued) 
254  NASA Systems Engineering Handbook

7.0 Special Topics

Process Human/Individual Analysis Additional Organizational Analysis

Process Users perform typical tasks on models or mockups prepared to 

incorporate some or all of the inputs.

Assess individual performance within 

possible organizational models.

Outputs Predictions about system performance, assessment of workloads, 

evaluation of alternative configurations, evaluation of operating 

procedures, training, and identification of accident- or errorprovocative situations and mismatches between personnel and 

equipment.

Predict system performance under 

varied organizational conditions, assess 

workloads, evaluate alternative configurations and operating procedures, train, 

and identify accident- or error-provocative situations and mismatches between 

personnel and equipment.

L. Controlled Experimentation

Definition When applied to HF, it is a highly controlled and structured version 

of simulation with deliberate manipulation of some variables.

Purpose To answer one or more hypotheses and narrow number of alternatives used in simulation.

Inputs From any or all methods listed thus far.

Process Select experimental design; identify dependent, independent, 

and controlled variables; set up test, apparatus, facilities, and tasks; 

prepare test protocol and instructions; select subjects; run tests; 

and analyze results statistically.

Scale to organizational levels where 

appropriate and feasible.

Outputs Quantitative statements of the effects of some variables on others 

and differences between alternative configurations, procedures, or 

environments.

Quantitative statements of the effects of 

some organizational variables on others 

and differences between alternative organizational configurations, procedures, 

or environments.

M. Operational Sequence Analysis

Definition When applied to HF, it is a powerful technique used to simulate 

systems.

Purpose To permit visualization of interrelationships between operators 

and operators and equipment, identify interface problems, and 

explicitly identify decisions that might otherwise go unrecognized. 

Less expensive than mockups, prototypes, or computer programs 

that attempt to serve the same purpose.

Inputs Data from all above listed methods.

Process Diagram columns show timescale, external inputs, operators, 

machines, external outputs. Flow of events (actions, functions, 

decisions) is then plotted from top to bottom against the timescale 

using special symbology.

After initial analysis is complete, group 

results by responsible organizations.

Outputs Time-based chart showing the functional relationships among 

system elements, the flow of materials or information, the physical 

and sequential distribution of operations, the inputs and outputs of 

subsystems, the consequences of alternative design configurations, 

potential sources of human difficulties.

Assessment of range of skills, communication processes, and management 

capabilities required. Evaluation of performance under various organizational 

structures.

 (continued)

Table 7.4-1 Human and Organizational Analysis Techniques (continued) 
7.4 Human Factors Engineering

NASA Systems Engineering Handbook  255

Process Human/Individual Analysis Additional Organizational Analysis

N. Workload Assessment

Definition When applied to HF, it is a procedure for appraising operator 

and crew task loadings or the ability of personnel to carry out all 

assigned tasks in the time allotted or available.

Purpose To keep operator workloads at reasonable levels and to ensure that 

workloads are distributed equitably among operators.

Inputs Task time, frequency, and precision data are obtained from many 

of the above listed methods supplemented with judgments and 

estimates from knowledgeable experts.

Process DOD-HDBK-763 recommends a method that estimates the time 

required to perform a task divided by the time available or allotted 

to perform it. There are three classes of methods: performance 

measures, physiological measures, and subjective workloads either 

during or after an activity.

After initial analysis is complete, group 

results by responsible organizations.

Outputs Quantitative assessments of estimated workloads for particular 

tasks at particular times.

Assessment of range of skills, communication processes, and management capabilities required. Evaluation of performance 

under various organizational structures.

O. Situational Awareness

Definition When applied to HF, it is a procedure for appraising operator and 

crew awareness of tasks and current situation.

Purpose To raise operator and maintainer awareness to maintain safety and 

efficiency.

Inputs All of the above listed analyses.

Process Different methods have been proposed including: situation awareness rating technique, situation awareness behaviorally anchored 

rating scale, situation awareness global assessment technique, 

situation awareness verification and analysis tool.

Collect organizational decisionmaking 

structures and processes and map the 

organization’s situational awareness 

profiles.

Outputs Quantitative estimates of situational awareness for particular tasks 

at particular times.

Identification of possible gaps, disconnects, and shortfalls.

P. Performance Modeling

Definition When applied to HF, it is a computational process for predicting 

human behavior based on current cognitive research.

Purpose To predict human limitations and capabilities before prototyping.

Inputs All of the above listed analyses.

Process Input results from above analyses. Input current relevant environmental and machine parameters. Can be interleaved with fast-time 

simulation to obtain frequency of error types.

Scale as appropriate to relevant organizational behaviors.

Outputs Interrelationships between operators and operators and equipment and identification of interface problems and decisions that 

might otherwise go unrecognized.

Interrelationships between individuals 

and organizations and identification 

of organizational interface problems 

and decisions that might otherwise go 

unrecognized.

Table 7.4-1 Human and Organizational Analysis Techniques (continued) 
256  NASA Systems Engineering Handbook

7.0 Special Topics

7.5.1 NEPA and EO 12114

7.5.1.1 National Environmental Policy Act

The National Environmental Policy Act (NEPA) declares 

the basic national policy for protecting the human environment. NEPA sets the Nation’s goals for enhancing 

and preserving the environment. NEPA also provides 

the procedural requirements to ensure compliance by 

all Federal agencies. NEPA compliance can be a critical 

path item in project or mission implementation. NEPA 

requires all Federal agencies to consider, before an action 

is taken, environmental values in the planning of actions 

and activities that may have a significant impact upon 

the quality of the human environment. NEPA directs 

agencies to consider alternatives to their proposed activities. In essence, NEPA requires NASA decisionmakers 

to integrate the NEPA process into early planning to ensure appropriate consideration of environmental factors, along with technical and economic ones. NEPA is 

also an environmental disclosure statute. It requires that 

available information be adequately addressed and made 

available to the NASA decisionmakers in a timely manner 

so they can consider the environmental consequences of 

the proposed action or activity before taking final action. 

Environmental information must also be made available 

to the public as well as to other Federal, state, and local 

agencies. NEPA does not require that the proposed action 

or activity be free of environmental impacts, be the most 

environmentally benign of potential alternatives, or be 

the most environmentally wise decision. NEPA requires 

the decisionmaker to consider environmental impacts as 

one factor in the decision to implement an action.

NASA activities are implemented through specific sponsoring entities, such as NASA HQ, NASA Centers (including component facilities, e.g., Wallops Flight Facility, 

White Sands Test Facility, and Michoud Assembly Facility), mission directorates, program, or mission support 

offices. The lead officials for these entities, the officials 

in charge, have the primary responsibility for ensuring 

that the NEPA process is integrated into their organizations’ project planning activities before the sponsoring 

entities implement activities and actions. The sponsoring entities also are responsible for ensuring that records management requirements are met. NEPA functions are not performed directly by lead officials. Each 

NASA Center has an Environmental Management Office (EMO), which is usually delegated the responsibility 

for implementing NEPA. The EMO performs the primary or working-level functions of the NEPA process, 

such as evaluating proposed activities, developing and/

or reviewing and approving required documentation, 

advising project managers, and signing environmental 

decision documents on projects and programs having 

little or no environmental impact. However, ultimate responsibility for complying with NEPA and completing 

the process in a timely manner lies with the program or 

project manager. Since the EMO provides essential functional support to the sponsoring entity, and because its 

implementation responsibilities are delegated, the term 

“sponsoring entity” will be used throughout to include 

the implementing NEPA organization at any NASA facility. In cases where the sponsoring entity needs to be 

further defined, it will be specifically noted. For proposals 

made by tenants or entities using services or facilities at a 

NASA Center or component facility, the sponsoring entity shall be that Center or, if such authority is delegated 

to the component facility, the component facility.

NEPA compliance documentation must be completed 

before project planning reaches a point where NASA’s 

ability to implement reasonable alternatives is effectively precluded (i.e., before hard decisions are made regarding project implementation). Environmental planning factors should be integrated into the Pre-Phase A 

concept study phase when a broad range of alternative 

approaches is being considered. In the Phase A concept 

development stage, decisions are made that could affect 

the Phase B preliminary design stage. At a minimum, 

an environmental evaluation should be initiated in the 

Phase A concept development stage. During this stage, 

the responsible project manager will have the greatest 

latitude in making adjustments in the plan to mitigate 

or avoid important environmental sensitivities and in 

planning the balance of the NEPA process to avoid unpleasant surprises later in the project cycle which may 

have schedule and/or cost implications. Before completing the NEPA process, no NASA official can take an 

action that would (1) affect the environment or (2) limit 

the choice of reasonable alternatives.

7.5 Environmental, Nuclear Safety, Planetary Protection, and Asset Protection 

Policy Compliance
7.5 Environmental, Nuclear Safety, Planetary Protection, and Asset Protection Policy Compliance

NASA Systems Engineering Handbook  257

Accommodating environmental requirements early in 

project planning ultimately conserves both budget and 

schedule. Further detail regarding NEPA compliance 

requirements for NASA programs and projects can be 

found in NPR 8580.1, Implementing The National Environmental Policy Act and Executive Order 12114.

7.5.1.2 EO 12114 Environmental Effects 

Abroad of Major Federal Actions 

Executive Order (EO) 12114 was issued “solely for the purpose of establishing internal procedures for Federal agencies to consider the significant effects of their actions on 

the environment outside the United States, its territories 

and possessions.” The EO also specifically provided that 

its purpose is to enable the decisionmakers of the Federal 

agencies to be informed of pertinent environmental considerations, and factor such considerations in their decisions; however, such decisionmakers must still take into 

account considerations such as foreign policy, national security, and other relevant special circumstances.

The NASA Office of the General Counsel (OGC), or designee, is the NASA point of contact and official NASA 

representative on any matter involving EO 12114. Accordingly, any action by, or any implementation or legal interpretation of EO 12114 requires consultations with and the 

concurrence of the designee of the OGC. The sponsoring 

entity and local EMO contemplating an action that would 

have global environmental effects or effects outside the 

territorial jurisdiction of the United States must notify the 

NASA Headquarters/Environmental Management Division (HQ/EMD). The HQ/EMD will, in turn, coordinate 

with the Office of the General Counsel, the Assistant Administrator for External Relations, and other NASA organizations as appropriate; and assist the sponsoring entity 

to develop a plan of action. (Such a plan is subject to the 

concurrence of the OGC.) Further detail regarding EO 

12114 compliance requirements for NASA programs and 

projects can be found in NPR 8580.1. 

7.5.2 PD/NSC-25

NASA has procedural requirements for characterizing 

and reporting potential risks associated with a planned 

launch of radioactive materials into space, on launch vehicles and spacecraft, during normal or abnormal flight 

conditions. Procedures and levels of review and analysis 

required for nuclear launch safety approval vary with the 

quantity of radioactive material planned for use and potential risk to the general public and the environment. 

Specific details concerning these requirements can be 

found in NPR 8715.3, NASA General Safety Program Requirements.

For any U.S. space mission involving the use of radioisotope power systems, radioisotope heating units, nuclear 

reactors, or a major nuclear source, launch approval 

must be obtained from the Office of the President per 

Presidential Directive/National Security Council Memorandum No. 25 (PD/NSC-25), “Scientific or Technological Experiments with Possible Large-Scale Adverse 

Environmental Effects and Launch of Nuclear Systems 

into Space,” paragraph 9, as amended May 8, 1996. The 

approval decision is based on an established and proven 

review process that includes an independent evaluation 

by an ad hoc Interagency Nuclear Safety Review Panel 

(INSRP) comprised of representatives from NASA, the 

Department of Energy (DOE), the Department of Defense, and the Environmental Protection Agency, with 

an additional technical advisor from the Nuclear Regulatory Commission. The process begins with development 

of a launch vehicle databook (i.e., a compendium of information describing the mission, launch system, and 

potential accident scenarios including their environments 

and probabilities). DOE uses the databook to prepare a 

Preliminary Safety Analysis Report for the space mission. 

In all, three Safety Analysis Reports (SARs) are typically 

produced and submitted to the mission’s INSRP—the 

PSAR, an updated SAR (draft final SAR), and a final SAR. 

The DOE project office responsible for providing the nuclear power system develops these documents.

The ad hoc INSRP conducts its nuclear safety/risk evaluation and documents their results in a nuclear Safety 

Evaluation Report (SER). The SER contains an independent evaluation of the mission radiological risk. DOE 

uses the SER as its basis for accepting the SAR. If the 

DOE Secretary formally accepts the SAR-SER package, 

it is forwarded to the NASA Administrator for use in the 

launch approval process.

NASA distributes the SAR and SER to the other cognizant Government agencies involved in the INSRP, and 

solicits their assessment of the documents. After receiving responses from these agencies, NASA conducts 

internal management reviews to address the SAR and 

SER and any other nuclear safety information pertinent 

to the launch. If the NASA Administrator recommends 

proceeding with the launch, then a request for nuclear 

safety launch approval is sent to the director of the Office 
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7.0 Special Topics

of Science and Technology Policy (OSTP) within the Office of the President.

NASA HQ is responsible for implementing this process 

for NASA missions. It has traditionally enlisted the Jet 

Propulsion Laboratory (JPL) to assist in this activity. 

DOE supports the process by analyzing the response 

of redundant power system hardware to the different 

accident scenarios identified in the databook and preparing a probabilistic risk assessment of the potential 

radiological consequences and risks to the public and 

the environment for the mission. KSC is responsible for 

overseeing development of databooks and traditionally 

uses JPL to characterize accident environments and integrate databooks. Both KSC and JPL subcontractors provide information relevant to supporting the development 

of databooks. The development team ultimately selected 

for a mission would be responsible for providing payload 

descriptions, describing how the nuclear hardware integrates into the spacecraft, describing the mission, and supporting KSC and JPL in their development of databooks. 

Mission directorate associate administrators, Center Directors, and program executives involved with the control 

and processing of radioactive materials for launch into 

space must ensure that basic designs of vehicles, spacecraft, and systems utilizing radioactive materials provide 

protection to the public, the environment, and users such 

that radiation risk resulting from exposures to radioactive sources are as low as reasonably achievable. Nuclear 

safety considerations must be incorporated from the PrePhase A concept study stage throughout all project stages 

to ensure that the overall mission radiological risk is acceptable. All space flight equipment (including medical 

and other experimental devices) that contain or use radioactive materials must be identified and analyzed for 

radiological risk. Site-specific ground operations and radiological contingency plans must be developed commensurate with the risk represented by the planned launch of 

nuclear materials. Contingency planning, as required by 

the National Response Plan, includes provisions for emergency response and support for source recovery efforts. 

NPR 8710.1, Emergency Preparedness Program and NPR 

8715.2, NASA Emergency Preparedness Plan Procedural 

Requirements—Revalidated address the NASA emergency 

preparedness policy and program requirements.

7.5.3 Planetary Protection

The United States is a signatory to the United Nations’ 

Treaty of Principles Governing the Activities of States 

in the Exploration and Use of Outer Space, Including 

the Moon and Other Celestial Bodies. Known as the 

Outer Space Treaty, it states in part (Article IX) that exploration of the Moon and other celestial bodies shall 

be conducted “so as to avoid their harmful contamination and also adverse changes in the environment 

of the Earth resulting from the introduction of extraterrestrial matter.” NASA policy (NPD 8020.7, Biological Contamination Control for Outbound and Inbound 

Planetary Spacecraft) specifies that the purpose of preserving solar system conditions is for future biological 

and organic constituent exploration. This NPD also establishes the basic NASA policy for the protection of 

the Earth and its biosphere from planetary and other 

extraterrestrial sources of contamination. The general 

regulations to which NASA flight projects must adhere 

are set forth in NPR 8020.12, Planetary Protection Provisions for Robotic Extraterrestrial Missions. Different 

requirements apply to different missions, depending 

on which solar system object is targeted or encountered and the spacecraft or mission type (flyby, orbiter, 

lander, sample return, etc.). For some bodies (such as 

the Sun, Moon, and Mercury), there are minimal planetary protection requirements. Current requirements 

for the outbound phase of missions to Mars and Europa, however, are particularly rigorous. Table 7.5-

1 shows the current planetary protection categories, 

while Table 7.5-2 provides a brief summary of their associated requirements. 

At the core, planetary protection is a project management responsibility and a systems engineering activity. 

The effort cuts across multiple WBS elements, and failure 

to adopt and incorporate a viable planetary protection 

approach during the early planning phases will add cost 

and complexity to the mission. Planning for planetary 

protection begins in Phase A, during which feasibility of 

the mission is established. Prior to the end of Phase A, 

the project manager must send a letter to the Planetary 

Protection Officer (PPO) stating the mission type and 

planetary targets and requesting that the mission be assigned a planetary protection category. 

Prior to the PDR, at the end of Phase B, the project manager must submit to the NASA PPO a planetary protection plan detailing the actions that will be taken to meet 

the requirements. The project’s progress and completion 

of the requirements are reported in a planetary protection pre-launch report submitted to the NASA PPO for 

approval. The approval of this report at the FRR con-
7.5 Environmental, Nuclear Safety, Planetary Protection, and Asset Protection Policy Compliance

NASA Systems Engineering Handbook  259

Table 7.5‐1 Planetary Protection Mission Categories

Planet Priorities Mission Type Category Example

Not of direct interest for understanding the 

process of chemical evolution. No protection of 

such planets is warranted (no requirements).

Any I Lunar missions

Of significant interest relative to the process 

of chemical evolution, but only a remote 

chance that contamination by spacecraft could 

jeopardize future exploration.

Any II Stardust (outbound)

Genesis (outbound)

Cassini

Of significant interest relative to the process 

of chemical evolution and/or the origin of life 

or for which scientific opinion provides a significant chance of contamination which could 

jeopardize a future biological experiment.

Flyby, Orbiter III Odyssey

Mars Global Surveyor

Mars Reconnaissance Orbiter

Lander, Probe IV Mars Exploration Rover

Phoenix

Europa Explorer 

Mars Sample Return 

(outbound)

Any solar system body. Unrestricted Earth returna V Stardust (return)

Genesis (return)

Restricted Earth returnb V Mars Sample Return (return)

a. No special precautions needed for returning material/samples back to Earth. 

b. Special precautions need to be taken for returning material/samples back to Earth. See NPR 8020.12.

Table 7.5‐2 Summarized Planetary Protection Requirements

Mission Category Summarized Requirements

I Certification of category.

II Avoidance of accidental impact by spacecraft and launch vehicle. Documentation of final disposition of launched hardware.

III Stringent limitations on the probability of impact. Requirements on orbital lifetime or requirements for microbial cleanliness of spacecraft.

IV Stringent limitations on the probability of impact and/or the contamination of the object. Microbial cleanliness of landed hardware surfaces directly established by bioassays.

V Outbound requirements per category of a lander mission to the target. Detailed restricted Earth 

return requirements will depend on many factors, but will likely include sterilization of any 

hardware that contacted the target planet before its return to Earth, and the containment of any 

returned sample.

stitutes the final planetary protection approval for the 

project and must be obtained for permission to launch. 

An update to this report, the planetary protection postlaunch report, is prepared to report any deviations from 

the planned mission due to actual launch or early mission events. For sample return missions only, additional 

reports and reviews are required: prior to launch toward 

the Earth, prior to commitment to Earth reentry, and 

prior to the release of any extraterrestrial sample to the 

scientific community for investigation. Finally, at the formally declared End of Mission (EOM), a planetary protection EOM report is prepared. This document reviews 
260  NASA Systems Engineering Handbook

7.0 Special Topics

the entire history of the mission in comparison to the 

original planetary protection plan and documents the 

degree of compliance with NASA’s planetary protection 

requirements. This document is typically reported on by 

the NASA PPO at a meeting of the Committee on Space 

Research (COSPAR) to inform other spacefaring nations 

of NASA’s degree of compliance with international planetary protection requirements.

7.5.4 Space Asset Protection

The terrorist attacks on the World Trade Center in New 

York and on the Pentagon on September 11, 2001 have 

created an atmosphere for greater vigilance on the part 

of Government agencies to ensure that sufficient security is in place to protect their personnel, physical assets, 

and information, especially those assets that contribute 

to the political, economic, and military capabilities of the 

United States. Current trends in technology proliferation, 

accessibility to space, globalization of space programs 

and industries, commercialization of space systems and 

services, and foreign knowledge about U.S. space systems increase the likelihood that vulnerable U.S. space 

systems may come under attack, particularly vulnerable 

systems. The ability to restrict or deny freedom of access 

to and operations in space is no longer limited to global 

military powers. The reality is that there are many existing capabilities to deny, disrupt, or physically destroy 

orbiting spacecraft and the ground facilities that command and control them. Knowledge of U.S. space systems’ functions, locations, and physical characteristics, 

as well as the means to conduct counterspace operations 

is increasingly available on the international market. Nations or groups hostile to the United States either possess 

or can acquire the means to disrupt or destroy U.S. space 

systems by attacking satellites in space, their communications nodes on the ground and in space, the ground 

nodes that command these satellites or process their 

data, and/or the commercial infrastructure that supports 

a space system’s operations.

7.5.4.1 Protection Policy

The new National Space Policy authorized by the President on August 31, 2006, states that space capabilities are 

vital to the Nation’s interests and that the United States 

will “take those actions necessary to protect its space capabilities.” The policy also gives responsibility for Space 

Situational Awareness (SSA) to the Secretary of Defense. 

In that capacity the Secretary of Defense will conduct 

SSA for civil space capabilities and operations, particularly human space flight activities. SSA provides an indepth knowledge and understanding of the threats posed 

to U.S., allied, and coalition space systems by adversaries 

and the environment, and is essential in developing and 

employing protection measures. Therefore, NASA’s space 

asset protection needs will drive the requirements that 

the NASA levies on DOD for SSA.

7.5.4.2 Goal

The overall space asset protection goal for NASA is to 

support sustained mission assurance through the reduction of susceptibilities and the mitigation of vulnerabilities, relative to risk, and within fiscal constraints.

7.5.4.3 Scoping

Space asset protection involves the planning and implementation of measures to protect NASA space assets 

from intentional or unintentional disruption, exploitation, or attack, whether natural or manmade. It is essential that protection is provided for all segments of a space 

system (ground, communications/information, space, and 

launch) and covers the entire life cycle of a project. Space 

asset protection includes aspects of personnel, physical, 

information, communications, information technology, 

and operational security, as well as counterintelligence activities. The role of the systems engineer is to integrate security competencies with space systems engineering and 

operations expertise to develop mission protection strategies consistent with payload classifications as defined in 

NPR 8705.4, Risk Classification for NASA Payloads.

7.5.4.4 Protection Planning

Systems engineers use protection planning processes and 

products (which include engineering trade studies and 

cost-benefit analyses) to meet NASA’s needs for acquiring, 

fielding, and sustaining secure and uncompromised space 

systems. Project protection plans are single-source documents that coordinate and integrate protection efforts and 

prevent inadvertent or uncontrolled disclosure of sensitive 

program information. Protection plans provide project 

management personnel (project manager, project scientist, mission systems engineer, operations manager, user 

community, etc.) with an overall view of the valid threats 

to a space system (both hostile and environmental), identify infrastructure vulnerabilities, and propose security 

countermeasures to mitigate risks and enhance survivability of the mission. An outline for a typical protection 

plan can be found in Appendix Q.
NASA Systems Engineering Handbook  261

7.6 Use of Metric System 

The decision whether a project or program could or 

should implement the System Internationale (SI), often 

called the “metric system,” requires consideration of a 

number of factors, including cost, technical, risk, and 

other programmatic aspects. 

The Metric Conversion Act of 1975 (Public Law 94-168) 

amended by the Omnibus Trade and Competitiveness 

Act of 1988 (Public Law 100-418) establishes a national 

goal of establishing the metric system as the preferred 

system of weights and measures for U.S. trade and commerce. NASA has developed NPD 8010.2, Use of the SI 

(Metric) System of Measurement in NASA Programs, 

which implements SI and provides specific requirements 

and responsibilities for NASA. 

However, a second factor to consider is that there are 

possible exceptions to the required implementation approach. Both EO 12770 and NPD 8010.2 allow exceptions and, because full SI implementation may be difficult, allow the use of “hybrid” systems. Consideration 

of the following factors will have a direct impact on the 

implementation approach and use of exceptions by the 

program or project.

Programs or projects must do analysis during the early 

life-cycle phases when the design solutions are being developed to identify where SI is feasible or recommended 

and where exceptions will be required. A major factor to 

consider is the capability to actually produce or provide 

metric-based hardware components. Results and recommendations from these analyses must be presented by 

SRR for approval.

In planning program or project implementation to produce metric-based systems, issues to be addressed should 

include the following:

z Interfaces with heritage components (e.g., valves, pyrotechnic devices, etc.) built to English-based units:

▶ Whether conversion from English to SI and/or interface to English-based hardware is required.

▶ The team should review design implementation to 

ensure there is no certification impact with heritage 

hardware or identify and plan for any necessary recertification efforts.

z Dimensioning and tolerancing:

▶ Can result in parts that do not fit.

▶ Rounding errors have occurred when converting 

units from one unit system to the other.

▶ The team may require specific additional procedures, steps, and drawing Quality Assurance (QA) 

personnel when converting units.

z Tooling:

▶ Not all shops have full metric tooling (e.g., drill bits, 

taps, end mills, reamers, etc.).

▶ The team needs to inform potential contractors of 

intent to use SI and obtain feedback as to potential 

impacts.

z Fasteners and miscellaneous parts:

▶ High-strength fastener choices and availability are 

more limited in metric sizes.

▶ Bearings, pins, rod ends, bushings, etc., are readily 

available in English with minimal lead times.

▶ The team needs to ascertain availability of acceptable SI-based fasteners in the timeframe needed.

z Reference material:

▶ Some key aerospace reference materials are built 

only in English units, e.g., MIL-HDBK-5 (metallic 

material properties), and values will need to be converted when used.

▶ Other key reference materials or commercial databases are built only in SI units.

▶ The team needs to review the reference material to 

be used and ensure acceptable conversion controls 

are in place, if necessary.

z Corporate knowledge:

▶ Many engineers presently think in English units, 

i.e., can relate to pressure in PSI, can relate to material strength in KSI, can relate to a tolerance of 0.003 

inches, etc.

▶ However, virtually all engineers coming out of 

school in this day and era presently think in SI 

units and have difficulty relating to English-based 

units such as slugs (for mass) and would require retraining with attendant increase in conversion errors. 

▶ The team needs to be aware of their programor project-specific knowledge in English and SI 

units and obtain necessary training and experience.
262  NASA Systems Engineering Handbook

7.0 Special Topics

z Industry practices:

▶ Certain industries work exclusively in English units, 

and sometimes have their own jargon associated 

with English material properties. The parachute 

industry falls in this category, e.g., “600-lb braided 

Kevlar line.”

▶ Other industries, especially international suppliers, 

may work exclusively in metric units, e.g., “30-mmthick raw bar stock.”

▶ The team needs to be aware of these unique cases 

and ensure both procurement and technical design 

and integration have the appropriate controls to 

avoid errors.

z Program or project controls: The team needs to 

consider, early in the SE process, what program- or 

project-specific risk management controls (such as 

configuration management steps) are required. This 

will include such straightforward concerns as the 

conversion(s) between system elements that are in 

English units and those in SI units or other, more 

complex, issues.

Several NASA projects have taken the approach of using 

both systems, which is allowed by NPD 8010.2. For example, the Mars soil drill project designed and developed their hardware using English-based components, 

while accomplishing their analyses using SI-based units. 

Other small-scale projects have successfully used a similar approach. 

For larger or more dispersed projects or programs, a 

more systematic and complete risk management approach may be needed to successfully implement an SIbased system. Such things as standard conversion factors 

(e.g., from pounds to kilograms) should be documented, 

as should standard SI nomenclature. Many of these risk 

management aspects can be found in such documents 

as the National Institute of Standards and Technology’s 

Guide for the Use of the International System of Units (SI)

and the DOD Guide for Identification and Development 

of Metric Standards. 

Until the Federal Government and the aerospace industrial base are fully converted to an SI-based unit system, 

the various NASA programs and projects will have to address their own level of SI implementation on a case-bycase basis. It is the responsibility of each NASA program 

and project management team, however, to comply with 

all laws and executive orders while still maintaining a 

reasonable level of risk for cost, schedule, and performance.
NASA Systems Engineering Handbook  263

Appendix A: Acronyms

ACS Attitude Control Systems

ACWP Actual Cost of Work Performed

AD2 Advancement Degree of Difficulty Assessment 

AHP Analytic Hierarchy Process

AIAA American Institute of Aeronautics and Astronautics

AO Announcement of Opportunity

ASME American Society of Mechanical Engineers

BAC Budget at Completion

BCWP Budgeted Cost for Work Performed

BCWS Budgeted Cost for Work Scheduled

C&DH Command and Data Handling

CACE Capability for Accelerated Concurrent Engineering

CAIB Columbia Accident Investigation Board

CAM Control Account Manager or Cost Account 

Manager

CCB Configuration Control Board

CDR Critical Design Review

CE Concurrent Engineering

CERR Critical Event Readiness Review

CI Configuration Item

CM Configuration Management

CMC Center Management Council

CMMI Capability Maturity Model® Integration

CMO Configuration Management Organization

CNSI Classified National Security Information

CoF Construction of Facilities

ConOps Concept of Operations

COSPAR Committee on Space Research

COTS Commercial Off the Shelf

CPI Critical Program Information or Cost Performance Index

CRM Continuous Risk Management

CSA Configuration Status Accounting

CWBS Contract Work Breakdown Structure

DCR Design Certification Review

DGA Designated Governing Authority

DLA Defense Logistics Agency

DM Data Management

DOD Department of Defense

DOE Department of Energy

DODAF DOD Architecture Framework

DR Decommissioning Review

DRM Design Reference Mission

EAC Estimate at Completion

ECP Engineering Change Proposal

ECR Environmental Compliance and Restoration 

or Engineering Change Request

EEE Electrical, Electronic, and Electromechanical

EFFBD Enhanced Functional Flow Block Diagram 

EIA Electronic Industries Alliance

EMC Electromagnetic Compatibility

EMI Electromagnetic Interference

EMO Environmental Management Office

EO Executive Order

EOM End of Mission

EV Earned Value

EVM Earned Value Management

FAD Formulation Authorization Document

FAR Federal Acquisition Requirement

FCA Functional Configuration Audit

FDIR Failure Detection, Isolation, And Recovery

FFBD Functional Flow Block Diagram

FMEA Failure Modes and Effects Analysis

FMECA Failure Modes, Effects, and Criticality Analysis

FMR Financial Management Requirements

FRR Flight Readiness Review

FS&GS Flight Systems and Ground Support

GEO Geostationary

GFP Government-Furnished Property

GMIP Government Mandatory Inspection Point

GPS Global Positioning Satellite 

HF Human Factors

HQ Headquarters

HQ/EMD NASA Headquarters/Environmental Management Division

HWIL Hardware in the Loop

ICA Independent Cost Analysis

ICD Interface Control Document/Drawing

ICE Independent Cost Estimate

ICP Interface Control Plan

IDD Interface Definition Document

IEEE Institute of Electrical and Electronics Engineers

ILS Integrated Logistics Support

INCOSE International Council on Systems Engineering
264  NASA Systems Engineering Handbook

Appendix A: Acronyms

INSRP Interagency Nuclear Safety Review Panel

IPT Integrated Product Team

IRD Interface Requirements Document

IRN Interface Revision Notice

ISO International Organization for Standardization

IT Information Technology or Iteration

ITA Internal Task Agreement.

ITAR International Traffic in Arms Regulation

I&V Integration and Verification

IV&V Independent Verification and Validation

IWG Interface Working Group

JPL Jet Propulsion Laboratory

KDP Key Decision Point

KSC Kennedy Space Center

LCCE Life-Cycle Cost Estimate

LEO Low Earth Orbit or Low Earth Orbiting

LLIL Limited Life Items List

LLIS Lessons Learned Information System

M&S Modeling and Simulation

MAUT Multi-Attribute Utility Theory

MCDA Multi-Criteria Decision Analysis

MCR Mission Concept Review

MDAA Mission Directorate Associate Administrator

MDR Mission Definition Review

MOE Measure of Effectiveness

MOP Measure of Performance

MOU Memorandum of Understanding

NASA National Aeronautics and Space Administration

NEDT NASA Exploration Design Team

NEPA National Environmental Policy Act 

NFS NASA FAR Supplement

NODIS NASA On-Line Directives Information 

System 

NIAT NASA Integrated Action Team

NOAA National Oceanic and Atmospheric Administration

NPD NASA Policy Directive

NPR NASA Procedural Requirements

OCE Office of the Chief Engineer

OGC Office of the General Counsel

OMB Office of Management and Budget

ORR Operational Readiness Review

OSTP Office of Science and Technology Policy

OTS Off-the-Shelf

PAR Program Approval Review

PBS Product Breakdown Structure

PCA Physical Configuration Audit or Program 

Commitment Agreement

PD/NSC Presidential Directive/National Security 

Council

PDR Preliminary Design Review

PERT Program Evaluation and Review Technique

PFAR Post-Flight Assessment Review

PHA Preliminary Hazard Analysis

PI Performance Index/Principal Investigator

PIR Program Implementation Review

PIRN Preliminary Interface Revision Notice

PKI Public Key Infrastructure

PLAR Post-Launch Assessment Review

P(LOC) Probability of Loss of Crew

P(LOM) Probability of Loss of Mission

PMC Program Management Council

PPBE Planning, Programming, Budgeting, and Execution

PPO Planetary Protection Officer

PQASP Program/Project Quality Assurance Surveillance Plan

PRA Probabilistic Risk Assessment

PRD Project Requirements Document

PRR Production Readiness Review

P/SDR Program/System Definition Review

PSR Program Status Review

P/SRR Program/System Requirements Review

PTR Periodic Technical Reviews

QA Quality Assurance

R&T Research and Technology

RF Radio Frequency

RFA Requests for Action

RFI Request for Information

RFP Request for Proposal

RID Review Item Discrepancy

SAR System Acceptance Review or Safety Analysis Report

SBU Sensitive But Unclassified

SDR System Definition Review

SE Systems Engineering

SEE Single-Event Effects

SEMP Systems Engineering Management Plan

SER Safety Evaluation Report

SI System Internationale (metric system)

SIR System Integration Review

SMA Safety and Mission Assurance

SOW Statement of Work

SP Special Publication

SPI Schedule Performance Index

SRB Standing Review Board

SRD System Requirements Document

SRR System Requirements Review

SSA Space Situational Awareness

STI Scientific and Technical Information

STS Space Transportation System

SysML System Modeling Language

T&E Test and Evaluation
Appendix A: Acronyms

NASA Systems Engineering Handbook  265

TA Technology Assessment 

TBD To Be Determined

TBR To Be Resolved

TDRS Tracking and Data Relay Satellite

TDRSS Tracking and Data Relay Satellite System

TLA Timeline Analysis

TLS Timeline Sheet 

TMA Technology Maturity Assessment

TPM Technical Performance Measure

TRAR Technology Readiness Assessment Report 

TRL Technology Readiness Level

TRR Test Readiness Review

TVC Thrust Vector Controller

UML Unified Modeling Language

USML United States Munitions List

V&V Verification and Validation

VAC Variance at Completion

WBS Work Breakdown Structure
266  NASA Systems Engineering Handbook

Appendix B: Glossary

Term Definition/Context

Acceptable Risk The risk that is understood and agreed to by the program/project, governing authority, mission 

directorate, and other customer(s) such that no further specific mitigating action is required.

Acquisition The acquiring by contract with appropriated funds of supplies or services (including construction) by 

and for the use of the Government through purchase or lease, whether the supplies or services are already in existence or must be created, developed, demonstrated, and evaluated. Acquisition begins at 

the point when Agency needs are established and includes the description of requirements to satisfy 

Agency needs, solicitation and selection of sources, award of contracts, contract financing, contract 

performance, contract administration, and those technical and management functions directly related 

to the process of fulfilling Agency needs by contract.

Activity (1) Any of the project components or research functions that are executed to deliver a product or service or provide support or insight to mature technologies. (2) A set of tasks that describe the technical 

effort to accomplish a process and help generate expected outcomes.

Advancement Degree of Difficulty 

Assessment (AD2)

The process to develop an understanding of what is required to advance the level of system maturity.

Allocated Baseline (Phase C)The allocated baseline is the approved performance-oriented configuration documentation for a CI 

to be developed that describes the functional and interface characteristics that are allocated from a 

higher level requirements document or a CI and the verification required to demonstrate achievement 

of those specified characteristics. The allocated baseline extends the top-level performance requirements of the functional baseline to sufficient detail for initiating manufacturing or coding of a CI. 

The allocated baseline is controlled by the NASA. The allocated baseline(s) is typically established at 

the Preliminary Design Review. Control of the allocated baseline would normally occur following the 

Functional Configuration Audit.

Analysis Use of mathematical modeling and analytical techniques to predict the compliance of a design to 

its requirements based on calculated data or data derived from lower system structure end product 

validations.

Analysis of 

Alternatives

A formal analysis method that compares alternative approaches by estimating their ability to satisfy 

mission requirements through an effectiveness analysis and by estimating their life-cycle costs 

through a cost analysis. The results of these two analyses are used together to produce a cost-effectiveness comparison that allows decisionmakers to assess the relative value or potential programmatic 

returns of the alternatives.

Analytic Hierarchy 

Process

A multi-attribute methodology that provides a proven, effective means to deal with complex decisionmaking and can assist with identifying and weighting selection criteria, analyzing the data collected 

for the criteria, and expediting the decisionmaking process.

Approval Authorization by a required management official to proceed with a proposed course of action. Approvals must be documented. 

Approval (for 

Implementation)

The acknowledgment by the decision authority that the program/project has met stakeholder 

expectations and formulation requirements, and is ready to proceed to implementation. By approving 

a program/project, the decision authority commits the budget resources necessary to continue into 

implementation. 

As-Deployed 

Baseline

The as-deployed baseline occurs at the Operational Readiness Review. At this point, the design is 

considered to be functional and ready for flight. All changes will have been incorporated into the 

documentation.
Appendix B: Glossary

NASA Systems Engineering Handbook  267

Term Definition/Context

Baseline An agreed-to set of requirements, designs, or documents that will have changes controlled through a 

formal approval and monitoring process.

Bidirectional 

Traceability

An association among two or more logical entities that is discernible in either direction (i.e., to and 

from an entity).

Brassboard A research configuration of a system, suitable for field testing, that replicates both the function and 

configuration of the operational systems with the exception of nonessential aspects such as packaging.

Breadboard A research configuration of a system, generally not suitable for field testing, that replicates both the 

function but not the actual configuration of the operational system and has major differences in 

actual physical layout.

Component 

Facilities

Complexes that are geographically separated from the NASA Center or institution to which they are 

assigned.

Concept of Operations (ConOps) 

(sometimes 

Operations 

Concept)

The ConOps describes how the system will be operated during the life-cycle phases to meet stakeholder expectations. It describes the system characteristics from an operational perspective and helps 

facilitate an understanding of the system goals. It stimulates the development of the requirements 

and architecture related to the user elements of the system. It serves as the basis for subsequent 

definition documents and provides the foundation for the long-range operational planning activities.

Concurrence A documented agreement by a management official that a proposed course of action is acceptable. 

Concurrent 

Engineering

Design in parallel rather than serial engineering fashion.

Configuration 

Items

A Configuration Item is any hardware, software, or combination of both that satisfies an end use 

function and is designated for separate configuration management. Configuration items are typically 

referred to by an alphanumeric identifier which also serves as the unchanging base for the assignment 

of serial numbers to uniquely identify individual units of the CI.

Configuration 

Management 

Process

A process that is a management discipline that is applied over a product’s life cycle to provide visibility 

into and to control changes to performance and functional and physical characteristics. It ensures 

that the configuration of a product is known and reflected in product information, that any product 

change is beneficial and is effected without adverse consequences, and that changes are managed.

Context Diagram A diagram that shows external systems that impact the system being designed.

Continuous Risk 

Management

An iterative process to refine risk management measures. Steps are to analyze risk, plan for tracking 

and control measures, track risk, carry out control measures, document and communicate all risk 

information, and deliberate throughout the process to refine it.

Contract A mutually binding legal relationship obligating the seller to furnish the supplies or services (including 

construction) and the buyer to pay for them. It includes all types of commitments that obligate the 

Government to an expenditure of appropriated funds and that, except as otherwise authorized, are in 

writing.

Contractor An individual, partnership, company, corporation, association, or other service having a contract with 

the Agency for the design, development, manufacture, maintenance, modification, operation, or 

supply of items or services under the terms of a contract to a program or project.

Control Account 

Manager

The person responsible for controlling variances at the control account level, which is typically at the 

subsystem WBS level. The CAM develops work and product plans, schedules, and time-phased resource plans. The technical subsystem manager/lead often takes on this role as part of their subsystem 

management responsibilities.

Control Gate (or 

milestone)

See “Key Decision Point.”

Cost-Benefit 

Analysis

A methodology to determine the advantage of one alternative over another in terms of equivalent 

cost or benefits. It relies on totaling positive factors and subtracting negative factors to determine a 

net result.

Cost-Effectiveness 

Analysis

A systematic quantitative method for comparing the costs of alternative means of achieving the same 

equivalent benefit for a specific objective.
268  NASA Systems Engineering Handbook

Appendix B: Glossary

Term Definition/Context

Critical Design 

Review

A review that demonstrates that the maturity of the design is appropriate to support proceeding 

with full-scale fabrication, assembly, integration, and test, and that the technical effort is on track to 

complete the flight and ground system development and mission operations in order to meet mission 

performance requirements within the identified cost and schedule constraints.

Critical Event (or 

key event)

An event that requires monitoring throughout the projected life cycle of a product that will generate 

critical requirements that would affect system design, development, manufacture, test, and operations (such as with an MOE, MOP, or TPM).

Critical Event 

Readiness Review

A review that confirms the project’s readiness to execute the mission’s critical activities during flight 

operation.

Customer The organization or individual that has requested a product and will receive the product to be 

delivered. The customer may be an end user of the product, the acquiring agent for the end user, or 

the requestor of the work products from a technical effort. Each product within the system hierarchy 

has a customer.

Data Management DM is used to plan for, acquire, access, manage, protect, and use data of a technical nature to support 

the total life cycle of a system.

Decision Analysis 

Process

A process that is a methodology for making decisions. It also offers techniques for modeling decision 

problems mathematically and finding optimal decisions numerically. The methodology entails 

identifying alternatives, one of which must be decided upon; possible events, one of which occurs 

thereafter; and outcomes, each of which results from a combination of decision and event.

Decision AuthorityThe Agency’s responsible individual who authorizes the transition at a KDP to the next life-cycle phase 

for a program/project.

Decision Matrix A methodology for evaluating alternatives in which valuation criteria typically are displayed in rows 

on the left side of the matrix, and alternatives are the column headings of the matrix. Criteria “weights” 

are typically assigned to each criterion.

Decision Support 

Package

Documentation submitted in conjunction with formal reviews and change requests.

Decision Trees A portrayal of a decision model that displays the expected consequences of all decision alternatives 

by making discreet all “chance” nodes, and, based on this, calculating and appropriately weighting the 

possible consequences of all alternatives.

Decommissioning 

Review

A review that confirms the decision to terminate or decommission the system and assess the readiness for the safe decommissioning and disposal of system assets. The DR is normally held near the 

end of routine mission operations upon accomplishment of planned mission objectives. It may be 

advanced if some unplanned event gives rise to a need to prematurely terminate the mission, or 

delayed if operational life is extended to permit additional investigations.

Deliverable Data 

Item

Consists of technical data–requirements specifications, design documents, management data–plans, 

and metrics reports.

Demonstration Use of a realized end product to show that a set of stakeholder expectations can be achieved.

Derived RequirementsFor a program, requirements that are required to satisfy the directorate requirements on the program. 

For a project, requirements that are required to satisfy the program requirements on the project. 

Descope Taken out of the scope of a project.

Design Solution 

Definition Process

The process by which high-level requirements derived from stakeholder expectations and outputs of 

the Logical Decomposition Process are translated into a design solution. 

Designated Governing AuthorityThe management entity above the program, project, or activity level with technical oversight responsibility.

Doctrine of 

Successive 

Refinement

A recursive and iterative design loop driven by the set of stakeholder expectations where a strawman 

architecture/design, the associated ConOps, and the derived requirements are developed.

Earned Value The sum of the budgeted cost for tasks and products that have actually been produced (completed or 

in progress) at a given time in the schedule.
Appendix B: Glossary

NASA Systems Engineering Handbook  269

Term Definition/Context

Earned Value 

Management

A tool for measuring and assessing project performance through the integration of technical scope 

with schedule and cost objectives during the execution of the project. EVM provides quantification of 

technical progress, enabling management to gain insight into project status and project completion 

costs and schedules. Two essential characteristics of successful EVM are EVM system data integrity and 

carefully targeted monthly EVM data analyses (i.e., risky WBS elements).

Enabling Products The life-cycle support products and services (e.g., production, test, deployment, training, maintenance, and disposal) that facilitate the progression and use of the operational end product through 

its life cycle. Since the end product and its enabling products are interdependent, they are viewed as 

a system. Project responsibility thus extends to responsibility for acquiring services from the relevant 

enabling products in each life-cycle phase. When a suitable enabling product does not already exist, 

the project that is responsible for the end product may also be responsible for creating and using the 

enabling product.

Technical Cost 

Estimate

The cost estimate of the technical work on a project created by the technical team based on its 

understanding of the system requirements and operational concepts and its vision of the system 

architecture.

Enhanced Functional Flow Block 

Diagram

A block diagram that represents control flows and data flows as well as system functions and flow.

Entry Criteria Minimum accomplishments each project needs to fulfill to enter into the next life-cycle phase or level 

of technical maturity.

Environmental 

Impact

The direct, indirect, or cumulative beneficial or adverse effect of an action on the environment. 

Environmental 

Management

The activity of ensuring that program and project actions and decisions that potentially impact or 

damage the environment are assessed and evaluated during the formulation and planning phase 

and reevaluated throughout implementation. This activity must be performed according to all NASA 

policy and Federal, state, and local environmental laws and regulations. 

Establish (with 

respect to 

processes)

The act of developing policy, work instructions, or procedures to implement process activities.

Evaluation The continual, independent (i.e., outside the advocacy chain of the program/project) evaluation of the 

performance of a program or project and incorporation of the evaluation findings to ensure adequacy 

of planning and execution according to plan. 

Extensibility The ability of a decision to be extended to other applications.

Flexibility The ability of a decision to support more than one current application.

Flight Readiness 

Review

A review that examines tests, demonstrations, analyses, and audits that determine the system’s readiness for a safe and successful flight/launch and for subsequent flight operations. It also ensures that all 

flight and ground hardware, software, personnel, and procedures are operationally ready.

Flight Systems 

and Ground 

Support

FS&GS is one of four interrelated NASA product lines. FS&GS projects result in the most complex and 

visible of NASA investments. To manage these systems, the Formulation and Implementation phases 

for FS&GS projects follow the NASA project life-cycle model consisting of Phases A (concept development) through F (closeout). Primary drivers for FS&GS projects are safety and mission success.

Float Extra time built into a schedule.

Formulation 

Phase

The first part of the NASA management life cycle defined in NPR 7120.5 where system requirements 

are baselined, feasible concepts are determined, a system definition is baselined for the selected 

concept(s), and preparation is made for progressing to the Implementation phase.

Functional 

Analysis

The process of identifying, describing, and relating the functions a system must perform to fulfill its 

goals and objectives.

Functional Baseline (Phase B)The functional baseline is the approved configuration documentation that describes a system’s or 

top-level CIs’ performance requirements (functional, interoperability, and interface characteristics) and 

the verification required to demonstrate the achievement of those specified characteristics.
270  NASA Systems Engineering Handbook

Appendix B: Glossary

Term Definition/Context

Functional 

Configuration 

Audit (FCA)

Examines the functional characteristics of the configured product and verifies that the product has 

met, via test results, the requirements specified in its functional baseline documentation approved at 

the PDR and CDR. FCAs will be conducted on both hardware- or software-configured products and 

will precede the PCA of the configured product.

Functional 

Decomposition

A subfunction under logical decomposition and design solution definition, it is the examination of a 

function to identify subfunctions necessary for the accomplishment of that function and functional 

relationships and interfaces.

Functional Flow 

Block Diagram

A block diagram that defines system functions and the time sequence of functional events.

Gantt Chart Bar chart depicting start and finish dates of activities and products in the WBS.

Goal Quantitative and qualitative guidance on such things as performance criteria, technology gaps, 

system context, effectiveness, cost, schedule, and risk.

Government 

Mandatory 

Inspection Points 

Inspection points required by Federal regulations to ensure 100 percent compliance with safety/mission-critical attributes when noncompliance can result in loss of life or loss of mission.

Heritage (or 

legacy)

Refers to the original manufacturer’s level of quality and reliability that is built into the parts which 

have been proven by (1) time in service, (2) number of units in service, (3) mean time between failure 

performance, and (4) number of use cycles.

Human Factors 

Engineering

The discipline that studies human-system interfaces and provides requirements, standards, and 

guidelines to ensure the human component of an integrated system is able to function as intended.

Implementation 

Phase

The part of the NASA management life cycle defined in NPR 7120.5 where the detailed design of 

system products is completed and the products to be deployed are fabricated, assembled, integrated, 

and tested and the products are deployed to their customers or users for their assigned use or mission.

Incommensurable CostsCosts that cannot be easily measured, such as controlling pollution on launch or mitigating debris.

Influence 

Diagram 

A compact graphical and mathematical representation of a decision state.

Inspection Visual examination of a realized end product to validate physical design features or specific manufacturer identification.

Integrated Logistics SupportActivities within the SE process that ensure the product system is supported during development 

(Phase D) and operations (Phase E) in a cost-effective manner. This is primarily accomplished by early, 

concurrent consideration of supportability characteristics, performing trade studies on alternative 

system and ILS concepts, quantifying resource requirements for each ILS element using best-practice 

techniques, and acquiring the support items associated with each ILS element.

Interface Management ProcessThe process to assist in controlling product development when efforts are divided among parties 

(e.g., Government, contractors, geographically diverse technical teams) and/or to define and maintain 

compliance among the products that must interoperate.

Iterative Application of a process to the same product or set of products to correct a discovered discrepancy or 

other variation from requirements. (See “Recursive” and “Repeatable.”)

Key Decision 

Point (or milestone)

The event at which the decision authority determines the readiness of a program/project to progress 

to the next phase of the life cycle (or to the next KDP).

Key Event See “Critical Event.”

Knowledge 

Management

Getting the right information to the right people at the right time without delay while helping people 

create knowledge and share and act upon information in ways that will measurably improve the 

performance of NASA and its partners.

Least-Cost 

Analysis

A methodology that identifies the least-cost project option for meeting the technical requirements.
Appendix B: Glossary

NASA Systems Engineering Handbook  271

Term Definition/Context

Liens Requirements or tasks not satisfied that have to be resolved within a certain assigned time to allow 

passage through a control gate to proceed.

Life-Cycle Cost The total cost of ownership over the project’s or system’s life cycle from Formulation through 

Implementation. The total of the direct, indirect, recurring, nonrecurring, and other related expenses 

incurred, or estimated to be incurred, in the design, development, verification, production, deployment, operation, maintenance, support, and disposal of a project.

Logical Decomposition ModelsRequirements decomposed by one or more different methods (e.g., function, time, behavior, data 

flow, states, modes, system architecture).

Logical Decomposition ProcessThe process for creating the detailed functional requirements that enable NASA programs and 

projects to meet the ends desired by Agency stakeholders. This process identifies the “what” that must 

be achieved by the system at each level to enable a successful project. It utilizes functional analysis to 

create a system architecture and to decompose top-level (or parent) requirements and allocate them 

down to the lowest desired levels of the project.

Logistics The management, engineering activities, and analysis associated with design requirements definition, material procurement and distribution, maintenance, supply replacement, transportation, and 

disposal that are identified by space flight and ground systems supportability objectives. 

Maintain (with 

respect to 

establishment of 

processes)

The act of planning the process, providing resources, assigning responsibilities, training people, managing configurations, identifying and involving stakeholders, and monitoring process effectiveness.

Maintainability The measure of the ability of an item to be retained in or restored to specified conditions when 

maintenance is performed by personnel having specified skill levels, using prescribed procedures and 

resources, at each prescribed level of maintenance.

Margin The allowances carried in budget, projected schedules, and technical performance parameters (e.g., 

weight, power, or memory) to account for uncertainties and risks. Margin allocations are baselined in 

the Formulation process, based on assessments of risks, and are typically consumed as the program/

project proceeds through the life cycle. 

Measure of 

Effectiveness

A measure by which a stakeholder’s expectations will be judged in assessing satisfaction with products or systems produced and delivered in accordance with the associated technical effort. The MOE is 

deemed to be critical to not only the acceptability of the product by the stakeholder but also critical to 

operational/mission usage. An MOE is typically qualitative in nature or not able to be used directly as a 

design-to requirement.

Measure of 

Performance

A quantitative measure that, when met by the design solution, will help ensure that an MOE for a 

product or system will be satisfied. These MOPs are given special attention during design to ensure 

that the MOEs to which they are associated are met. There are generally two or more measures of 

performance for each MOE.

Metric The result of a measurement taken over a period of time that communicates vital information about 

the status or performance of a system, process, or activity. A metric should drive appropriate action.

Mission A major activity required to accomplish an Agency goal or to effectively pursue a scientific, technological, or engineering opportunity directly related to an Agency goal. Mission needs are independent 

of any particular system or technological solution. 

Mission Concept 

Review

A review that affirms the mission need and examines the proposed mission’s objectives and the 

concept for meeting those objectives. It is an internal review that usually occurs at the cognizant 

organization for system development.

Mission Definition 

Review

A review that examines the functional and performance requirements defined for the system and the 

preliminary program or project plan and ensures that the requirements and the selected concept will 

satisfy the mission.

NASA LifeCycle Phases (or 

program life-cycle 

phases)

Consists of Formulation and Implementation phases as defined in NPR 7120.5.
272  NASA Systems Engineering Handbook

Appendix B: Glossary

Term Definition/Context

Objective Function (sometimes 

Cost Function)

A mathematical expression that expresses the values of combinations of possible outcomes as a single 

measure of cost-effectiveness.

Operational 

Readiness Review

A review that examines the actual system characteristics and the procedures used in the system or 

product’s operation and ensures that all system and support (flight and ground) hardware, software, 

personnel, procedures, and user documentation accurately reflects the deployed state of the system.

Optimal Solution A feasible solution that minimizes (or maximizes, if that is the goal) an objective function.

Other Interested 

Parties (Stakeholders)

A subset of “stakeholders,” other interested parties are groups or individuals who are not customers 

of a planned technical effort but may be affected by the resulting product, the manner in which the 

product is realized or used, or have a responsibility for providing life-cycle support services.

Peer Review Independent evaluation by internal or external subject matter experts who do not have a vested 

interest in the work product under review. Peer reviews can be planned, focused reviews conducted 

on selected work products by the producer’s peers to identify defects and issues prior to that work 

product moving into a milestone review or approval cycle.

Performance 

Index 

An overall measure of effectiveness for each alternative.

Performance 

Standards

Common metrics for use in performance standards include cost and schedule.

Physical Configuration Audits (or 

configuration 

inspection)

The PCA examines the physical configuration of the configured product and verifies that the product 

corresponds to the build-to (or code-to) product baseline documentation previously approved at the 

CDR. PCAs will be conducted on both hardware- and software-configured products.

Post-Flight Assessment ReviewA review that evaluates the activities from the flight after recovery. The review identifies all anomalies 

that occurred during the flight and mission and determines the actions necessary to mitigate or 

resolve the anomalies for future flights.

Post-Launch Assessment ReviewA review that evaluates the status, performance, and capabilities of the project evident from the flight 

operations experience since launch. This can also mean assessing readiness to transfer responsibility 

from the development organization to the operations organization. The review also evaluates the 

status of the project plans and the capability to conduct the mission with emphasis on near-term 

operations and mission-critical events. This review is typically held after the early flight operations and 

initial checkout.

Precedence 

Diagram

Workflow diagram that places activities in boxes, connected by dependency arrows; typical of a Gantt 

chart.

Preliminary 

Design Review

A review that demonstrates that the preliminary design meets all system requirements with acceptable risk and within the cost and schedule constraints and establishes the basis for proceeding with 

detailed design. It will show that the correct design option has been selected, interfaces have been 

identified, and verification methods have been described.

Process A set of activities used to convert inputs into desired outputs to generate expected outcomes and 

satisfy a purpose.

Producibility A system characteristic associated with the ease and economy with which a completed design can be 

transformed (i.e., fabricated, manufactured, or coded) into a hardware and/or software realization.

Product A part of a system consisting of end products that perform operational functions and enabling 

products that perform life-cycle services related to the end product or a result of the technical efforts 

in the form of a work product (e.g., plan, baseline, or test result).

Product Baseline 

(Phase D/E)

The product baseline is the approved technical documentation that describes the configuration of 

a CI during the production, fielding/deployment, and operational support phases of its life cycle. 

The product baseline describes detailed physical or form, fit, and function characteristics of a CI; the 

selected functional characteristics designated for production acceptance testing; the production 

acceptance test requirements.
Appendix B: Glossary

NASA Systems Engineering Handbook  273

Term Definition/Context

Product Breakdown StructureA hierarchical breakdown of the hardware and software products of the program/project.

Product 

Implementation 

Process

The first process encountered in the SE engine, which begins the movement from the bottom of the 

product hierarchy up toward the Product Transition Process. This is where the plans, designs, analysis, 

requirement development, and drawings are realized into actual products.

Product Integration ProcessOne of the SE engine product realization processes that make up the system structure. In this process, 

lower level products are assembled into higher level products and checked to make sure that the 

integrated product functions properly. It is the first element of the processes that lead from realized 

products from a level below to realized end products at a level above, between the Product Implementation, Verification, and Validation Processes.

Product RealizationThe act of making, buying, or reusing a product, or the assembly and integration of lower level realized products into a new product, as well as the verification and validation that the product satisfies its 

appropriate set of requirements and the transition of the product to its customer.

Product Transition 

Process

A process used to transition a verified and validated end product that has been generated by product 

implementation or product integration to the customer at the next level in the system structure for 

integration into an end product or, for the top-level end product, transitioned to the intended end 

user.

Product Validation ProcessThe second of the verification and validation processes conducted on a realized end product. While 

verification proves whether “the system was done right,” validation proves whether “the right system 

was done.” In other words, verification provides objective evidence that every “shall” was met, whereas 

validation is performed for the benefit of the customers and users to ensure that the system functions 

in the expected manner when placed in the intended environment. This is achieved by examining the 

products of the system at every level of the structure.

Product Verification ProcessThe first of the verification and validation processes conducted on a realized end product. As used in 

the context of systems engineering common technical processes, a realized product is one provided 

by either the Product Implementation Process or the Product Integration Process in a form suitable for 

meeting applicable life-cycle phase success criteria.

Production Readiness ReviewA review that is held for FS&GS projects developing or acquiring multiple or similar systems greater 

than three or as determined by the project. The PRR determines the readiness of the system developers to efficiently produce the required number of systems. It ensures that the production plans; 

fabrication, assembly, and integration-enabling products; and personnel are in place and ready to 

begin production.

Program A strategic investment by a mission directorate (or mission support office) that has defined goals, objectives, architecture, funding level, and a management structure that supports one or more projects.

Program/System 

Definition Review 

A review that examines the proposed program architecture and the flowdown to the functional 

elements of the system. The proposed program’s objectives and the concept for meeting those 

objectives are evaluated. Key technologies and other risks are identified and assessed. The baseline 

program plan, budgets, and schedules are presented.

Program/System 

Requirements 

Review

A review that is used to ensure that the program requirements are properly formulated and correlated 

with the Agency and mission directorate strategic objectives.

Programmatic 

Requirements

Requirements set by the mission directorate, program, project, and PI, if applicable. These include 

strategic scientific and exploration requirements, system performance requirements, and schedule, 

cost, and similar nontechnical constraints. 

Project (1) A specific investment having defined goals, objectives, requirements, life-cycle cost, a beginning, 

and an end. A project yields new or revised products or services that directly address NASA’s strategic 

needs. They may be performed wholly in-house; by Government, industry, academia partnerships; 

or through contracts with private industry. (2) A unit of work performed in programs, projects, and 

activities.

Project Plan The document that establishes the project’s baseline for implementation, signed by the cognizant 

program manager, Center Director, project manager, and the MDAA, if required. 
274  NASA Systems Engineering Handbook

Appendix B: Glossary

Term Definition/Context

Project Technical 

Team

The whole technical team for the project.

Solicitation The vehicle by which information is solicited from contractors to let a contract for products or services.

Prototype Items (mockups, models) built early in the life cycle that are made as close to the flight item in form, fit, 

and function as is feasible at that stage of the development. The prototype is used to “wring out” the 

design solution so that experience gained from the prototype can be fed back into design changes 

that will improve the manufacture, integration, and maintainability of a single flight item or the 

production run of several flight items.

Quality Assurance An independent assessment needed to have confidence that the system actually produced and 

delivered is in accordance with its functional, performance, and design requirements. 

Realized Product The desired output from the application of the four product realization processes. The form of this 

product is dependent on the phase of the product-line life cycle and the phase success criteria.

Recursive Value is added to the system by the repeated application of processes to design next lower layer system products or to realize next upper layer end products within the system structure. This also applies 

to repeating application of the same processes to the system structure in the next life-cycle phase to 

mature the system definition and satisfy phase exit criteria.

Relevant StakeholderSee “Stakeholder.”

Reliability The measure of the degree to which a system ensures mission success by functioning properly over 

its intended life. It has a low and acceptable probability of failure, achieved through simplicity, proper 

design, and proper application of reliable parts and materials. In addition to long life, a reliable system 

isrobust and fault tolerant.

Repeatable A characteristic of a process that can be applied to products at any level of the system structure or 

within any life-cycle phase.

Requirement The agreed-upon need, desire, want, capability, capacity, or demand for personnel, equipment, facilities, or other resources or services by specified quantities for specific periods of time or at a specified 

time expressed as a “shall” statement. Acceptable form for a requirement statement is individually 

clear, correct, feasible to obtain, unambiguous in meaning, and can be validated at the level of the 

system structure at which stated. In pairs of requirement statements or as a set, collectively, they are 

not redundant, are adequately related with respect to terms used, and are not in conflict with one 

another.

Requirements 

Allocation Sheet

Documents the connection between allocated functions, allocated performance, and the physical 

system.

Requirements 

Management 

Process

A process that applies to the management of all stakeholder expectations, customer requirements, 

and technical product requirements down to the lowest level product component requirements.

Risk The combination of the probability that a program or project will experience an undesired event 

(some examples include a cost overrun, schedule slippage, safety mishap, health problem, malicious 

activities, environmental impact, or failure to achieve a needed scientific or technological breakthrough or mission success criteria) and the consequences, impact, or severity of the undesired event, 

were it to occur. Both the probability and consequences may have associated uncertainties.

Risk Assessment An evaluation of a risk item that determines (1) what can go wrong, (2) how likely is it to occur, 

(3) what the consequences are, and (4) what are the uncertainties associated with the likelihood and 

consequences. 

Risk Management An organized, systematic decisionmaking process that efficiently identifies, analyzes, plans, tracks, 

controls, communicates, and documents risk and establishes mitigation approaches and plans to 

increase the likelihood of achieving program/project goals. 

Risk-Informed 

Decision Analysis 

Process

A five-step process focusing first on objectives and next on developing decision alternatives with 

those objectives clearly in mind and/or using decision alternatives that have been developed under 

other systems engineering processes. The later steps of the process interrelate heavily with the Technical Risk Management Process.
Appendix B: Glossary

NASA Systems Engineering Handbook  275

Term Definition/Context

Safety Freedom from those conditions that can cause death, injury, occupational illness, damage to or loss of 

equipment or property, or damage to the environment.

Search Space (or 

Alternative Space)

The envelope of concept possibilities defined by design constraints and parameters within which 

alternative concepts can be developed and traded off.

Software As defined in NPD 2820.1, NASA Software Policy.

Specification A document that prescribes completely, precisely, and verifiably the requirements, design, behavior, 

or characteristics of a system or system component.

Stakeholder A group or individual who is affected by or is in some way accountable for the outcome of an undertaking. The term “relevant stakeholder” is a subset of the term “stakeholder” and describes the people 

identified to contribute to a specific task. There are two main classes of stakeholders. See “Customers” 

and “Other Interested Parties.”

Stakeholder 

Expectations 

A statement of needs, desires, capabilities, and wants that are not expressed as a requirement (not 

expressed as a “shall” statement) is to be referred to as an “expectation.” Once the set of expectations 

from applicable stakeholders is collected, analyzed, and converted into a “shall” statement, the 

expectation becomes a requirement. Expectations can be stated in either qualitative (nonmeasurable) 

or quantitative (measurable) terms. Requirements are always stated in quantitative terms. Expectations can be stated in terms of functions, behaviors, or constraints with respect to the product being 

engineered or the process used to engineer the product.

Stakeholder 

Expectations 

Definition Process

The initial process within the SE engine that establishes the foundation from which the system is designed and the product realized. The main purpose of this process is to identify who the stakeholders 

are and how they intend to use the product. This is usually accomplished through use-case scenarios, 

design reference missions, and operational concepts.

Standing Review 

Board

The entity responsible for conducting independent reviews of the program/project per the life-cycle 

requirements. The SRB is advisory and is chartered to objectively assess the material presented by the 

program/project at a specific review. 

State Diagram A diagram that shows the flow in the system in response to varying inputs.

Success Criteria Specific accomplishments that must be satisfactorily demonstrated to meet the objectives of a 

technical review so that a technical effort can progress further in the life cycle. Success criteria are 

documented in the corresponding technical review plan.

Surveillance 

(or Insight or 

Oversight)

The monitoring of a contractor’s activities (e.g., status meetings, reviews, audits, site visits) for progress 

and production and to demonstrate fiscal responsibility, ensure crew safety and mission success, and 

determine award fees for extraordinary (or penalty fees for substandard) contract execution. 

System (1) The combination of elements that function together to produce the capability to meet a need. The 

elements include all hardware, software, equipment, facilities, personnel, processes, and procedures 

needed for this purpose. (2) The end product (which performs operational functions) and enabling 

products (which provide life-cycle support services to the operational end products) that make up a 

system.

System Acceptance ReviewA review that verifies the completeness of the specific end item with respect to the expected maturity 

level and to assess compliance to stakeholder expectations. The SAR examines the system, its end 

items and documentation, and test data and analyses that support verification and validation. It also 

ensures that the system has sufficient technical maturity to authorize its shipment to the designated 

operational facility or launch site.

System Definition 

Review

A review that examines the proposed system architecture/design and the flowdown to all functional 

elements of the system.

System Integration ReviewA review that ensures that the system is ready to be integrated; segments, components, and 

subsystems are available and ready to be integrated; and integration facilities, support personnel, and 

integration plans and procedures are ready for integration. SIR is conducted at the end of the final 

design phase (Phase C) and before the systems assembly, integration, and test phase (Phase D) begins.

System Requirements ReviewA review that examines the functional and performance requirements defined for the system and the 

preliminary program or project plan and ensures that the requirements and the selected concept will 

satisfy the mission.
276  NASA Systems Engineering Handbook

Appendix B: Glossary

Term Definition/Context

System Safety 

Engineering 

The application of engineering and management principles, criteria, and techniques to achieve acceptable mishap risk within the constraints of operational effectiveness and suitability, time, and cost, 

throughout all phases of the system life cycle.

System Structure A system structure is made up of a layered structure of product-based WBS models. (See “Work 

Breakdown Structure.”)

Systems Analysis The analytical process by which a need is transformed into a realized, definitive product, able to 

support compatibility with all physical and functional requirements and support the operational 

scenarios in terms of reliability, maintainability, supportability, serviceability, and disposability, 

while maintaining performance and affordability. Systems analysis is responsive to the needs of the 

customer at every phase of the life cycle, from pre-Phase A to realizing the final product and beyond.

Systems Approach The application of a systematic, disciplined engineering approach that is quantifiable, recursive, 

iterative, and repeatable for the development, operation, and maintenance of systems integrated into 

a whole throughout the life cycle of a project or program.

Systems Engineering EngineThe technical processes framework for planning and implementing the technical effort within 

any phase of a product-line life cycle. The SE engine model in Figure 2.1-1 shows the 17 technical 

processes that are applied to products being engineered to drive the technical effort.

Systems Engineering Management PlanThe SEMP identifies the roles and responsibility interfaces of the technical effort and how those 

interfaces will be managed. The SEMP is the vehicle that documents and communicates the technical 

approach, including the application of the common technical processes; resources to be used; and key 

technical tasks, activities, and events along with their metrics and success criteria.

Tailoring The documentation and approval of the adaptation of the process and approach to complying with 

requirements underlying the specific program or project.

Technical Assessment ProcessThe crosscutting process used to help monitor technical progress of a program/project through 

periodic technical reviews. It also provides status information in support of assessing system design, 

product realization, and technical management decisions.

Technical Data 

Management 

Process

The process used to plan for, acquire, access, manage, protect, and use data of a technical nature to 

support the total life cycle of a system. This includes its development, deployment, operations and 

support, eventual retirement, and retention of appropriate technical data beyond system retirement 

as required by current NASA policies.

Technical Data 

Package

An output of the Design Solution Definition Process, it evolves from phase to phase, starting with conceptual sketches or models and ending with complete drawings, parts list, and other details needed 

for product implementation or product integration.

Technical 

Measures

An established set of measures based on the expectations and requirements that will be tracked and 

assessed to determine overall system or product effectiveness and customer satisfaction. Common 

terms for these measures are MOEs, MOPs, and TPMs. 

Technical Performance Measures The set of critical or key performance parameters that are monitored by comparing the current actual 

achievement of the parameters with that anticipated at the current time and on future dates. Used 

to confirm progress and identify deficiencies that might jeopardize meeting a system requirement. 

Assessed parameter values that fall outside an expected range around the anticipated values indicate 

a need for evaluation and corrective action. Technical performance measures are typically selected 

from the defined set of MOPs.

Technical Planning ProcessThe first of the eight technical management processes contained in the SE engine, the Technical Planning Process establishes a plan for applying and managing each of the common technical processes 

that will be used to drive the development of system products and associated work products. This 

process also establishes a plan for identifying and defining the technical effort required to satisfy the 

project objectives and life-cycle-phase success criteria within the cost, schedule, and risk constraints 

of the project.

Technical 

Requirements 

Definition Process

The process used to transform the stakeholder expectations into a complete set of validated technical 

requirements expressed as “shall” statements that can be used for defining a design solution for the 

PBS model and related enabling products.
Appendix B: Glossary

NASA Systems Engineering Handbook  277

Term Definition/Context

Technical Risk Risk associated with the achievement of a technical goal, criterion, or objective. It applies to undesired 

consequences related to technical performance, human safety, mission assets, or environment.

Technical Risk 

Management 

Process

The process for measuring or assessing risk and developing strategies to manage it, an important 

component of managing NASA programs under its charter to explore and expand knowledge. Critical 

to this process is the proactive identification and control of departures from the baseline program, 

project, or activity.

Technical Team A group of multidisciplinary individuals with appropriate domain knowledge, experience, competencies, and skills assigned to a specific technical task.

Technology 

Readiness Assessment Report 

A document required for transition from Phase B to Phase C/D demonstrating that all systems, subsystems, and components have achieved a level of technological maturity with demonstrated evidence 

of qualification in a relevant environment.

Technology 

Assessment

A systematic process that ascertains the need to develop or infuse technological advances into a 

system. The technology assessment process makes use of basic systems engineering principles and 

processes within the framework of the PBS. It is a two-step process comprised of (1) the determination 

of the current technological maturity in terms of technology readiness levels and (2) the determination of the difficulty associated with moving a technology from one TRL to the next through the use of 

the AD2. 

Technology 

Development 

Plan

A document required for transition from Phase A to Phase B identifying technologies to be developed, 

heritage systems to be modified, alternative paths to be pursued, fallback positions and corresponding performance descopes, milestones, metrics, and key decision points. It is incorporated in the 

preliminary project plan.

Technology Maturity AssessmentThe process to determine a system’s technological maturity via TRLs.

Technology 

Readiness Level 

Provides a scale against which to measure the maturity of a technology. TRLs range from 1, Basic 

Technology Research, to 9, Systems Test, Launch, and Operations. Typically, a TRL of 6 (i.e., technology 

demonstrated in a relevant environment) is required for a technology to be integrated into an SE 

process.

Test The use of a realized end product to obtain detailed data to validate performance or to provide sufficient information to validate performance through further analysis.

Test Readiness 

Review

A review that ensures that the test article (hardware/software), test facility, support personnel, and test 

procedures are ready for testing and data acquisition, reduction, and control.

Traceability A discernible association among two or more logical entities such as requirements, system elements, 

verifications, or tasks. 

Trade Study A means of evaluating system designs by devising alternative means to meet functional requirements, 

evaluating these alternatives in terms of the measures of effectiveness and system cost, ranking the 

alternatives according to appropriate selection criteria, dropping less promising alternatives, and 

proceeding to the next level of resolution, if needed.

Trade Study 

Report

A report written to document a trade study. It should include: he system under analysis; system goals, 

objectives (or requirements, as appropriate to the level of resolution), and constraints; measures and 

measurement methods (models) used; all data sources used; the alternatives chosen for analysis; 

computational results, including uncertainty ranges and sensitivity analyses performed; the selection 

rule used; and the recommended alternative.

Trade Tree A representation of trade study alternatives in which each layer represents some system aspect that 

needs to be treated in a trade study to determine the best alternative.

Transition The act of delivery or moving of a product from the location where the product has been implemented or integrated, as well as verified and validated, to a customer. This act can include packaging, 

handling, storing, moving, transporting, installing, and sustainment activities.

Utility A measure of the relative value gained from an alternative. The theoretical unit of measurement for 

utility is the util.
278  NASA Systems Engineering Handbook

Appendix B: Glossary

Term Definition/Context

Validated 

Requirements 

A set of requirements that are well formed (clear and unambiguous), complete (agree with customer 

and stakeholder needs and expectations), consistent (conflict free), and individually verifiable and 

traceable to a higher level requirement or goal.

Validation Testing, possibly under simulated conditions, to ensure that a finished product works as required.

Validation (of a 

product)

Proof that the product accomplishes the intended purpose. Validation may be determined by a 

combination of test, analysis, and demonstration.

Variance In program control terminology, a difference between actual performance and planned costs or 

schedule status.

Verification The process of proving or demonstrating that a finished product meets design specifications and 

requirements.

Verification (of a 

product) 

Proof of compliance with specifications. Verification may be determined by test, analysis, demonstration, or inspection.

Waiver A documented agreement intentionally releasing a program or project from meeting a requirement. 

(Some Centers use deviations prior to Implementation and waivers during Implementation).

WBS Model Model that describes a system that consists of end products and their subsystems (which perform 

the operational functions of the system), the supporting or enabling products, and any other work 

products (plans, baselines) required for the development of the system.

Work Breakdown 

Structure (WBS)

A product-oriented hierarchical division of the hardware, software, services, and data required to 

produce the program/project’s end product(s) structured according to the way the work will be 

performed, reflecting the way in which program/project costs, schedule, technical, and risk data are to 

be accumulated, summarized, and reported.

Workflow 

Diagram

A scheduling chart that shows activities, dependencies among activities, and milestones.
NASA Systems Engineering Handbook  279

Appendix C: How to Write a Good Requirement

Use of Correct Terms

z Shall = requirement

z Will = facts or declaration of purpose

z Should = goal

Editorial Checklist

Personnel Requirement

1. The requirement is in the form “responsible party shall perform such and such.” In other words, use the active, 

rather than the passive voice. A requirement must state who shall (do, perform, provide, weigh, or other verb) followed by a description of what must be performed.

Product Requirement

1. The requirement is in the form “product ABC shall XYZ.” A requirement must state “The product shall” (do, perform, provide, weigh, or other verb) followed by a description of what must be done.

2. The requirement uses consistent terminology to refer to the product and its lower level entities.

3. Complete with tolerances for qualitative/performance values (e.g., less than, greater than or equal to, plus or minus, 

3 sigma root sum squares).

4. Is the requirement free of implementation? (Requirements should state WHAT is needed, NOT HOW to provide 

it; i.e., state the problem not the solution. Ask, “Why do you need the requirement?” The answer may point to the 

real requirement.)

5. Free of descriptions of operations? (Is this a need the product must satisfy or an activity involving the product? Sentences like “The operator shall...” are almost always operational statements not requirements.)

Example Product Requirements

z The system shall operate at a power level of...

z The software shall acquire data from the...

z The structure shall withstand loads of...

z The hardware shall have a mass of...

General Goodness Checklist

1. The requirement is grammatically correct.

2. The requirement is free of typos, misspellings, and punctuation errors.

3. The requirement complies with the project’s template and style rules.

4. The requirement is stated positively (as opposed to negatively, i.e., “shall not”).

5. The use of “To Be Determined” (TBD) values should be minimized. It is better to use a best estimate for a value 

and mark it “To Be Resolved” (TBR) with the rationale along with what must be done to eliminate the TBR, who is 

responsible for its elimination, and by when it must be eliminated.

6. The requirement is accompanied by an intelligible rationale, including any assumptions. Can you validate (concur 

with) the assumptions? Assumptions must be confirmed before baselining.

7. The requirement is located in the proper section of the document (e.g., not in an appendix).
280  NASA Systems Engineering Handbook

Appendix C: How to Write a Good Requirement

Requirements Validation Checklist

Clarity

1. Are the requirements clear and unambiguous? (Are all aspects of the requirement understandable and not subject 

to misinterpretation? Is the requirement free from indefinite pronouns (this, these) and ambiguous terms (e.g., “as 

appropriate,” “etc.,” “and/or,” “but not limited to”)?)

2. Are the requirements concise and simple?

3. Do the requirements express only one thought per requirement statement, a standalone statement as opposed to 

multiple requirements in a single statement, or a paragraph that contains both requirements and rationale?

4. Does the requirement statement have one subject and one predicate?

Completeness

1. Are requirements stated as completely as possible? Have all incomplete requirements been captured as TBDs or 

TBRs and a complete listing of them maintained with the requirements?

2. Are any requirements missing? For example have any of the following requirements areas been overlooked: functional, performance, interface, environment (development, manufacturing, test, transport, storage, operations), 

facility (manufacturing, test, storage, operations), transportation (among areas for manufacturing, assembling, delivery points, within storage facilities, loading), training, personnel, operability, safety, security, appearance and 

physical characteristics, and design.

3. Have all assumptions been explicitly stated?

Compliance

1. Are all requirements at the correct level (e.g., system, segment, element, subsystem)? 

2. Are requirements free of implementation specifics? (Requirements should state what is needed, not how to provide it.)

3. Are requirements free of descriptions of operations? (Don’t mix operation with requirements: update the ConOps 

instead.)

Consistency

1. Are the requirements stated consistently without contradicting themselves or the requirements of related systems?

2. Is the terminology consistent with the user and sponsor’s terminology? With the project glossary?

3. Is the terminology consistently used through out the document?

4. Are the key terms included in the project’s glossary?

Traceability

1. Are all requirements needed? Is each requirement necessary to meet the parent requirement? Is each requirement 

a needed function or characteristic? Distinguish between needs and wants. If it is not necessary, it is not a requirement. Ask, “What is the worst that could happen if the requirement was not included?”

2. Are all requirements (functions, structures, and constraints) bidirectionally traceable to higher level requirements 

or mission or system-of-interest scope (i.e., need(s), goals, objectives, constraints, or concept of operations)?

3. Is each requirement stated in such a manner that it can be uniquely referenced (e.g., each requirement is uniquely 

numbered) in subordinate documents?

Correctness

1. Is each requirement correct?

2. Is each stated assumption correct? Assumptions must be confirmed before the document can be baselined.

3. Are the requirements technically feasible?
Appendix C: How to Write a Good Requirement

NASA Systems Engineering Handbook  281

Functionality

1. Are all described functions necessary and together sufficient to meet mission and system goals and objectives?

Performance

1. Are all required performance specifications and margins listed (e.g., consider timing, throughput, storage size, latency, accuracy and precision)?

2. Is each performance requirement realistic?

3. Are the tolerances overly tight? Are the tolerances defendable and cost-effective? Ask, “What is the worst thing that 

could happen if the tolerance was doubled or tripled?”

Interfaces

1. Are all external interfaces clearly defined?

2. Are all internal interfaces clearly defined?

3. Are all interfaces necessary, sufficient, and consistent with each other?

Maintainability

1. Have the requirements for system maintainability been specified in a measurable, verifiable manner?

2. Are requirements written so that ripple effects from changes are minimized (i.e., requirements are as weakly coupled as possible)?

Reliability

1. Are clearly defined, measurable, and verifiable reliability requirements specified?

2. Are there error detection, reporting, handling, and recovery requirements?

3. Are undesired events (e.g., single event upset, data loss or scrambling, operator error) considered and their required responses specified?

4. Have assumptions about the intended sequence of functions been stated? Are these sequences required?

5. Do these requirements adequately address the survivability after a software or hardware fault of the system from the 

point of view of hardware, software, operations, personnel and procedures?

Verifiability/Testability

1. Can the system be tested, demonstrated, inspected, or analyzed to show that it satisfies requirements? Can this be 

done at the level of the system at which the requirement is stated? Does a means exist to measure the accomplishment of the requirement and verify compliance? Can the criteria for verification be stated?

2. Are the requirements stated precisely to facilitate specification of system test success criteria and requirements?

3. Are the requirements free of unverifiable terms (e.g., flexible, easy, sufficient, safe, ad hoc, adequate, accommodate, 

user-friendly, usable, when required, if required, appropriate, fast, portable, light-weight, small, large, maximize, 

minimize, sufficient, robust, quickly, easily, clearly, other “ly” words, other “ize” words)?

Data Usage

1. Where applicable, are “don’t care” conditions truly “don’t care”? (“Don’t care” values identify cases when the value 

of a condition or flag is irrelevant, even though the value may be important for other cases.) Are “don’t care” conditions values explicitly stated? (Correct identification of “don’t care” values may improve a design’s portability.)
282  NASA Systems Engineering Handbook

Appendix D: Requirements Verification Matrix

When developing requirements, it is important to 

identify an approach for verifying the requirements. 

This appendix provides the matrix that defines how 

all the requirements are verified. Only “shall” requirements should be included in these matrices. The matrix should identify each “shall” by unique identifier 

and be definitive as to the source, i.e., document from 

which the requirement is taken. This matrix could be 

divided into multiple matrices (e.g., one per requirements document) to delineate sources of requirements 

depending on the project. The example is shown to 

provide suggested guidelines for the minimum information that should be included in the verification matrix.
Requirement No. a Documentb Paragraphc Shall Statementd Verification Suc‐ cess Criteriae

Verification 

Methodf

Facility 

or Labg Phaseh

Acceptance 

Requirement?i

Preflight 

Acceptance?j

Performing 

Organizationk Resultsl

P-1 xxx 3.2.1.1 

Capability: Support Uplinked Data (LDR)

System X shall provide a max. groundto-station uplink of...

1. System X locks to forward link at the min and max data rate tolerances2. System X locks to the forward link at the min and max operating frequency tolerances 

Test xxx 5 xxx TPS xxxx

P-i xxx Other 

paragraphs

Other “shalls” in PTRS

Other criteria xxx xxx xxx xxx Memo xxx

S-i or other unique designator

xxxxx (other specs, ICDs, etc.)

Other paragraphs 

Other “shalls” in specs, ICDs, etc.

Other criteria xxx xxx xxx xxx Report xxx

a. Unique identifier for each System X requirement.b. Document number the System X requirement is contained within.c. Paragraph number of the System X requirement.d. Text (within reason) of the System X requirement, i.e., the “shall.”e. Success criteria for the System X requirement.f. Verification method for the System X requirement (analysis, inspection, demonstration, or test).g. Facility or laboratory used to perform the verification and validation.h. Phase in which the verification and validation will be performed: (1) Pre-Declared Development, (2) Formal Box-Level Functional, (3) Formal Box-Level Environmental, (4) Formal SystemLevel Environmental, (5) Formal System-Level Functional, (6) Formal End-to-End Functional, (7) Integrated Vehicle Functional, (8) On-Orbit Functional.i. Indicate whether this requirement is also verified during initial acceptance testing of each unit.j. Indicate whether this requirement is also verified during any pre-flight or recurring acceptance testing of each unit.k. Organization responsible for performing the verificationl. Indicate documents that contain the objective evidence that requirement was satisfied

Table D-1 Requirements Verification Matrix
284  NASA Systems Engineering Handbook

Appendix E: Creating the Validation Plan 

(Including Validation Requirements Matrix)

Validation 

Product # Activity Objective

Validation 

Method

Facility or 

Lab Phase

Performing 

Organization Results

Unique 

identifier 

for 

validation 

product

Describe 

evaluation 

by the customer/sponsor that will 

be performed

What is to be 

accomplished 

by the 

customer/ 

sponsor 

evaluation

Validation 

method for 

the System X 

requirement 

(analysis, 

inspection, 

demonstration, 

or test)

Facility or 

laboratory 

used to 

perform 

the validation

Phase in 

which the 

verification/ 

validation 

will be 

performeda

Organization 

responsible for 

coordinating 

the validation 

activity

Indicate 

the 

objective 

evidence 

that 

validation 

activity 

occurred

1 Customer/

sponsor will 

evaluate the 

candidate 

displays

1. Ensure 

legibility is 

acceptable

2. Ensure overall appearance 

is acceptable

Test xxx Phase A xxx

a. Example: (1) during product selection process, (2) prior to final product selection (if COTS) or prior to PDR, (3) prior to CDR, (4) during 

box-level functional, (5) during system-level functional, (6) during end-to-end functional, (7) during integrated vehicle functional, 

(8) during on-orbit functional.

When developing requirements, it is important to identify a validation approach for how additional validation 

evaluation, testing, analysis or other demonstrations will 

be performed to ensure customer/sponsor satisfaction. 

This validation plan should include a validation matrix with the elements in the example below. The final 

column in the matrix below uses a display product as a 

specific example.

Table E-1 Validation Requirements Matrix
NASA Systems Engineering Handbook  285

Appendix F: Functional, Timing, and State Analysis 

Functional Flow Block Diagrams

Functional analysis can be performed using various 

methods, one of which is Functional Flow Block Diagrams (FFBDs). FFBDs define the system functions and 

depict the time sequence of functional events. They identify “what” must happen and do not assume a particular 

answer to “how” a function will be performed. They are 

functionally oriented, not solution oriented. 

FFBDs are made up of functional blocks, each of which 

represents a definite, finite, discrete action to be accomplished. The functional architecture is developed using a 

series of leveled diagrams to show the functional decomposition and display the functions in their logical, sequential relationship. A consistent numbering scheme is 

used to label the blocks. The numbers establish identification and relationships that carry through all the diagrams 

and facilitate traceability from the lower levels to the top 

level. Each block in the first- (top-) level diagram can be 

expanded to a series of functions in the second-level diagram, and so on. (See Figure F-1.) Lines connecting functions indicate function flow and not lapsed time or intermediate activity. Diagrams are laid out so that the flow 

direction is generally from left to right. Arrows are often 

used to indicate functional flows. The diagrams show both 

input (transfer to operational orbit) and output (transfer 

to STS orbit), thus facilitating the definition of interfaces 

and control process.

Each diagram contains a reference to other functional 

diagrams to facilitate movement between pages of the 

diagrams. Gates are used: “AND,” “OR,” “Go or No-Go,” 

sometimes with enhanced functionality, including exclusive OR gate (XOR), iteration (IT), repetition (RP), or 

loop (LP). A circle is used to denote a summing gate and 

is used when AND/OR is present. AND is used to indicate parallel functions and all conditions must be satisfied 

to proceed (i.e., concurrency). OR is used to indicate that 

alternative paths can be satisfied to proceed (i.e., selection). G and G—are used to denote Go and No-Go conditions. These symbols are placed adjacent to lines leaving 

a particular function to indicate alternative paths. For 

examples of the above, see Figures F-2 and F-3.

Enhanced Functional Flow Block Diagrams (EFFBDs) 

provide data flow overlay to capture data dependencies. 

EFFBDs (shown in Figure F-4) represent: (1) functions, 

(2) control flows, and (3) data flows. An EFFBD specification of a system is complete enough that it is executable 

as a discrete event model, capable of dynamic, as well as 

static, validation. EFFBDs provide freedom to use either 

control constructs or data triggers or both to specify execution conditions for the system functions. EFFBDs 

graphically distinguish between triggering and nontriggering data inputs. Triggering data are required before 

a function can begin execution. Triggers are actually 

data items with control implications. In Figure F-4, the 

data input shown with a green background and doubleheaded arrows is a triggering data input. The nontriggering data inputs are shown with gray backgrounds and 

single-headed arrows. An EFFBD must be enabled by: 

(1) the completion of the function(s) preceding it in the 

control construct and (2) triggered, if trigger data are 

identified, before it can execute. For example, in Figure F-4, “1. Serial Function” must complete and “Data 

3” must be present before “3. Function in Concurrency” 

can execute. It should be noted that the “External Input” 

data into “1. Serial Function” and the “External Output” 

data from “6. Output Function” should not be confused 

with the functional input and output for these functions, 

which are represented by the input and the output arrows 

respectively. Data flows are represented as elongated ovals 

whereas functions are represented as rectangular boxes.

Functional analysis looks across all life-cycle processes. 

Functions required to deploy a system are very different 

from functions required to operate and ultimately dispose of the system. Preparing FFBDs for each phase of 

the life cycle as well as the transition into the phases 

themselves is necessary to draw out all the requirements. 

These diagrams are used both to develop requirements 

and to identify profitability. The functional analysis also 

incorporates alternative and contingency operations, 

which improve the probability of mission success. The 

flow diagrams provide an understanding of total operation of the system, serve as a basis for development of 

operational and contingency procedures, and pinpoint 
286  NASA Systems Engineering Handbook

Appendix F: Functional, Timing, and State Analysis

TOP LEVEL

1.0

Ascent Into

Orbit Injection

(6.0) Ref.

Transfer to

STS Orbit

(3.0) Ref.

Transfer to

OPS Orbit 

AND

 (4.10) Ref.

Transmit Payload & Subsystem Data 

(4.7) Ref.

Store/Process

Command

OR

THIRD LEVEL

SECOND LEVEL

2.0

Check Out

and Deploy

3.0

Transfer to

OPS Orbit

5.0

Contingency

Operations

6.0

Transfer to

STS Orbit

7.0

Retrieve

Spacecraft

8.0

Reenter and

Land

4.1

Provide

Electric Power

4.2

Provide

Attitude

Stabilization

4.3

Provide

Thermal

Control

4.4

Provide Orbit

Main

4.5

Receive

Command

4.6

Receive Command (Omni)

4.7

Store/Process

Command

4.8

Acquire

Payload Data

4.0

Perform

Mission

Operations

4.10

Transmit Payload & Subsystem Data

OR

4.9

Acquire

Subsystem

Status Data

4.11

Transmit

Subsystem

Data

4.8.1

Compute TDRS

Pointing

Vector

4.8.2

Slew to

and Track

TDRS

4.8.3

Radar to

Standby

4.8.4

Compute LOS

Pointing

Vector

4.8.5

Slew S/C

to LOS

Vector

4.8.6

Command 

ERP PW

Radar On

4.8.7

Process Receiving Signal

and Format

4.8.8

Radar to

Standby

4.8.9

Radar O

OR OR

OR

Figure F-1 FFBD flowdown

areas where changes in operational procedures could 

simplify the overall system operation. This organization will eventually feed into the WBS structure and ultimately drive the overall mission organization and cost. 

In certain cases, alternative FFBDs may be used to represent various means of satisfying a particular function 

until data are acquired, which permits selection among 

the alternatives. For more information on FFBDs and 

EFFBDs, see Jim Long’s Relationships between Common 

Graphical Representations in Systems Engineering.

Requirements Allocation Sheets

Requirements allocation sheets document the connection 

between allocated functions, allocated performance, and 

the physical system. They provide traceability between 

Technical Requirements Definition functional analysis 

activities and Logical Decomposition and Design Solution Definition activities and maintain consistency between them, as well as show disconnects. Figure F-5 provides an example of a requirements allocation sheet. The 
Appendix F: Functional, Timing, and State Analysis

NASA Systems Engineering Handbook  287

Figure F-2 FFBD: example 1

Ref 9.2, Provide Guidance

9.2.1

AND

9.2.4

9.2.3

9.2.2

3.5 Ref AND

OR

System

Malfunction 

Parallel Functions 

Alternate Functions 

Functional

Description

Function

Number

Summing

Gate

Leader

Note

Go Flow

No Go Flow

1.1.2 Ref

AND

OR

Ref 11.3.1

See Detail Diagram

See Detail

Diagram

See Detail Diagram

OR G

G

_

OR

Tentative

Function

Scope Note: _________________

____________________________

____________________________ Functional Flow Block

Diagram Format Title Block and Standard Drawing Number

2nd Level

Flow-Level Designator

Interface Reference

Block (used on firstand lower level

functional diagrams 

only)

Figure F-3 FFBD showing additional control constructs: example 2

Multiple Exit Function Iterate

Loop

Concurrency Select

Completion Criterion

Branch Annotation

Replicate

1

Function in a

Concurrency

2

Second

Function in a

Concurrency

4

Multi-Exit

Function

5

Function on

Exit Branch

7

Function in a

Replicate

6

Function on

a Coordinate

Branch

AND LP

RP RP

Domain set for iterate

Loop annotation

Domain set for

replicate with

coordination

Annotation

Branch #2

Branch #3

CC #2

CC #1

Ref AND OR LP OR Ref

3

Function in

an Iterate

IT IT

OR
288  NASA Systems Engineering Handbook

Appendix F: Functional, Timing, and State Analysis

Figure F-4 Enhanced FFBD: example 3

2

Multi-Exit

Function

3

Function in

Concurrency

4

Function in

Multi-Exit

Construct

AND

3 times

AND

OR

5

Function in

Iterate

IT IT

Data 1 Data 2

Data 3

Data 4

Data 5

External

Output

6

Output

Function

External

Input

1

Serial

Function

IT

CC #2

CC #1

reference column to the far right indicates the function 

numbers from the FFBDs. Fill in the requirements allocation sheet by performing the following: 

1. Include the functions and function numbers from 

the FFBDs.

2. Allocate functional performance requirements and 

design requirements to the appropriate function(s) 

(many requirements may be allocated to one function, or one requirement may be allocated to many 

functions).

3. All system-level requirements must be allocated to 

a function to ensure the system meets all system requirements (functions without allocated requirements 

should be eliminated as unnecessary activities).

4. Allocate all derived requirements to the function 

that spawned the requirement.

5. Identify the physical equipment, configuration item, 

facilities, and specifications that will be used to meet 

the requirements.

(For a reference on requirements allocation sheets, see 

DOD’s Systems Engineering Fundamentals Guide.)

N2 Diagrams

An N-squared (N2) diagram is a matrix representation 

of functional and/or physical interfaces between elements of a system at a particular hierarchical level. The 

N2 diagram has been used extensively to develop data interfaces, primarily in the software areas. However, it can 

also be used to develop hardware interfaces as shown in 

Figure F-6. The system components are placed on the diagonal. The remainder of the squares in the NxN matrix 

represent the interfaces. The square at the intersection of 

a row and a column contains a description of the interface between the two components represented on that 

row and that column. For example, the solar arrays have 

a mechanical interface with the structure and an electrical interface and supplied service interface with the 

voltage converters. Where a blank appears, there is no 

interface between the respective components. 

The N2 diagram can be taken down into successively 

lower levels to the hardware and software component 

functional levels. In addition to defining the data that 

must be supplied across the interface, by showing the 
Appendix F: Functional, Timing, and State Analysis

NASA Systems Engineering Handbook  289

ID DESCRIPTION REQUIREMENT TRACED 

FROM

PERFORMANCE MARGIN COMMENTS REF

M1 Mission Orbit 575 +/-15 km Sun-synchronous dawn-dusk orbit S3, S11, P3 Complies NA Pegasus XL with HAPS

provides required launch 

injection dispersion accuracy

F.2.c

M2 Launch Vehicle Pegasus XL with HAPS P2, P4 Complies NA F.2.c

M3 Observatory Mass The observatory total mass shall not exceed

 241 kg

M1, M2 192.5 kg 25.20% F.5.b

M4 Data Acquisition

Quality 

The mission shall deliver 95% data with 

better than 1 in 100,000 BER

P1 Complies NA Standard margins and

systems baselined; formal 

system analysis to be

completed by PDR 

F.7

M5 Communication

Band 

The mission shall use S-band SQPSK at 5 Mbps for 

spacecraft downlink and 2 kbps uplink

S12, P4 Complies NA See SC27, SC28, and G1, G2 F.3.f,

F.7

M7 Tracking MOC shall use NORAD two-line elements for 

observatory tracking 

P4 Complies NA F.7

M8 Data Latency Data latency shall be less than 72 hours P12 Complies NA F.7

M9 Daily Data Volume Accommodate average daily raw science data 

volume of 10.8 Gbits 

P1, S12 Complies 12% Margin based on funded 

ground contacts

F.3.e,

F.7

M10 Ground Station The mission shall be compatible with the

Rutherford Appleton Laboratory Ground Station 

and the Poker Flat Ground Station

P1 Complies NA F.7

M11 Orbital Debris

(Casualty Area) 

Design observatory for demise upon 

reentry with <1/10,000 probability of injury

P3 1/51,000 400% See Orbital Debris Analysis in 

Appendix M-6

F.2.e,

App.6

M12 Orbital Debris

(Lifetime)

Design observatory for reentry <25 years 

after end of mission 

P3 <10 years 15 years See Orbital Debris Analysis in 

Appendix M-6

F.2.e,

App.6

Figure F-5 Requirements allocation sheet

Figure F-6 N2 diagram for orbital equipment 

Note: From NASA Reference Publication 1370, Training Manual for Elements of Interface Definition and Control.

Structure

Fuel

Pods

Thrusters

Solar

Arrays

Heat

Converters

Voltage

Converters

Antenna

A

Antenna

B

Experiment

1

Experiment

2

Experiment

3

Gyros

Mechanical/Physical Interface

Electrical/Functional Interface

Supplied Services

Legend:
290  NASA Systems Engineering Handbook

Appendix F: Functional, Timing, and State Analysis User

Wait Access

Wait Card

Idle

Access Card

System

No Card

Has Card

Code

Start OK {t...t+3}

Idle

User Accepted

[d...3*d]

0...13

Idle Wait Card Wait Access

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

[d...3*d]

Figure F-7 Timing diagram example

data flows the N2 chart pinpoints areas where conflicts 

could arise in interfaces, and highlights input and output 

dependency assumptions and requirements. 

Timing Analysis

There are several methods for visualizing the complex 

timing relationships in a system. Two of the more important ones are the timing diagram and the state transition diagram. The timing diagram (see Figure F-7) defines the behavior of different objects within a timescale. 

It provides a visual representation of objects changing 

state and interacting over time. Timing diagrams can be 

used for defining the behavior of hardware-driven and/

or software-driven components. While a simple timeline 

analysis is very useful in understanding relationships 

such as concurrency, overlap, and sequencing, state diagrams (see Figure F-8) allow for even greater flexibility 

in that they can depict events such as loops and decision processes that may have largely varying timelines. 

Timing information can be added to an FFBD to create 

a timeline analysis. This is very useful for allocating resources and generating specific time-related design requirements. It also elucidates performance characteristics and design constraints. However, it is not complete. 

State diagrams are needed to show the flow of the system 

in response to varying inputs. 

The tools of timing analysis are rather straightforward. 

While some Commercial-Off-the-Shelf (COTs) tools are 

available, any graphics tool and a good spreadsheet will 

do. The important thing to remember is that timeline 

analysis is better for linear flows while circular, looping, 

multi-path, and combinations of these are best described 

with state diagrams. Complexity should be kept layered 

and track the FFBDs. The ultimate goal of using all these 

techniques is simply to force the thought process enough 

into the details of the system that most of the big surprises can be avoided.

State Analysis

State diagramming is another graphical tool that is most 

helpful for understanding and displaying the complex 

timing relationships in a system. Timing diagrams do 

not give the complete picture of the system. State diagrams are needed to show the flow of the system in response to varying inputs. State diagrams provide a sort of 

simplification of understanding on a system by breaking 

complex reactions into smaller and smaller known re-
Appendix F: Functional, Timing, and State Analysis

NASA Systems Engineering Handbook  291

Figure F-8 Slew command status state diagram

Ready

Slewing

Complete Settled

Rejected

Good

Slew 

Command

“Bad”

Slew 

Command

Slew 

Command

Timer Expire

Initialize

End of 

Slew

End of

Settling

Slew 

Command

Timer Expire

Slew 

Command

Timer Expire

Slew 

Command

Timer 

Expired?

No

Yes

Minor 

Cycle

Slew 

Command

Timer Expire

“Any”

Slew 

Command

“Any”

Slew 

Command

“Any”

Slew 

Command

sponses. This allows detailed requirements to be developed and verified with their timing performance.

Figure F-8 shows a slew command status state diagram 

from the James Webb Space Telescope. Ovals represent 

the system states. Arcs represent the event that triggers the 

state change as well as the action or output taken by the 

system in response to the event. 

Self-loops are permitted. In the example in Figure F-8 the slew states can loop until they arrive at 

the correct location, and then they can loop while 

they settle. 

When it is used to represent the behavior of a sequential 

finite-state machine, the state diagram is called a state 

transition diagram. A sequential finite-state machine is 

one that has no memory, which means that the current 

output only depends on the current input. The state transition diagram models the event-based, time-dependent 

behavior of such a system.
292  NASA Systems Engineering Handbook

Appendix F: Functional, Timing, and State Analysis

Context Diagrams

When presented with a system design problem, the systems engineer’s first task 

is to truly understand the problem. That means understanding the context in 

which the problem is set. A context diagram is a useful tool for grasping the system to be built and the external domains that are relevant to that system and 

which have interfaces to the system. The diagram shows the general structure 

of a context diagram. The system is shown surrounded by the external systems 

which have interfaces to the system. These systems are not part of the system, 

but they interact with the system via the system’s external interfaces. The external systems can impact the system, and the system does impact the external 

systems. They play a major role in establishing the requirements for the system. 

Entities further removed are those in the system’s context that can impact the system but cannot be impacted by the 

system. These entities in the system’s context are responsible for some of the system’s requirements.

Defining the boundaries of a system is a critical but often neglected task. Using an example from a satellite project, one 

of the external systems that is impacted by the satellite would be the Tracking and Data Relay Satellite System (TDRSS). 

The TDRSS is not part of the satellite system, but it defines requirements on the satellite and is impacted by the satellite since it must schedule contacts, receive and transmit data and commands, and downlink the satellite data to the 

ground. An example of an entity in the context of the satellite system that is not impacted by the satellite system is the 

Global Positioning Satellite (GPS) system. The GPS is not impacted in any way by the satellite, but it will levy some requirements on the satellite if the satellite is to use the GPS signals for navigation.

Reference: Diagram is from Buede, The Engineering Design of Systems, p. 38.

System

External Systems

Context

Are impacted by the system

Impacts, but not impacted by, the system 
NASA Systems Engineering Handbook  293

Appendix G: Technology Assessment/Insertion

Introduction, Purpose, and Scope

The Agency’s programs and projects, by their very nature, frequently require the development and infusion 

of new technological advances to meet mission goals, 

objectives, and resulting requirements. Sometimes the 

new technological advancement being infused is actually a heritage system that is being incorporated into a 

different architecture and operated in different environment from that for which it was originally designed. In 

this latter case, it is often not recognized that adaptation 

of heritage systems frequently requires technological advancement and as a result, key steps in the development 

process are given short shrift—often to the detriment of 

the program/project. In both contexts of technological 

advancement (new and adapted heritage), infusion is a 

very complex process that has been dealt with over the 

years in an ad hoc manner differing greatly from project 

to project with varying degrees of success. 

Frequently, technology infusion has resulted in schedule 

slips, cost overruns, and occasionally even to cancellations or failures. In post mortem, the root cause of such 

events has often been attributed to “inadequate definition of requirements.” If such were indeed the root cause, 

then correcting the situation would simply be a matter of 

requiring better requirements definition, but since history seems frequently to repeat itself, this must not be 

the case—at least not in total. 

In fact there are many contributors to schedule slip, cost 

overrun, and project cancellation and failure—among 

them lack of adequate requirements definition. The 

case can be made that most of these contributors are 

related to the degree of uncertainty at the outset of the 

project and that a dominant factor in the degree of uncertainty is the lack of understanding of the maturity of 

the technology required to bring the project to fruition 

and a concomitant lack of understanding of the cost and 

schedule reserves required to advance the technology 

from its present state to a point where it can be qualified and successfully infused with a high degree of confidence. Although this uncertainty cannot be eliminated, 

it can be substantially reduced through the early application of good systems engineering practices focused on 

understanding the technological requirements; the maturity of the required technology; and the technological 

advancement required to meet program/project goals, 

objectives, and requirements.

A number of processes can be used to develop the appropriate level of understanding required for successful 

technology insertion. The intent of this appendix is to 

describe a systematic process that can be used as an example of how to apply standard systems engineering 

practices to perform a comprehensive Technology Assessment (TA). The TA comprises two parts, a Technology Maturity Assessment (TMA) and an Advancement Degree of Difficulty Assessment (AD2

). The 

process begins with the TMA which is used to determine technological maturity via NASA’s Technology 

Readiness Level (TRL) scale. It then proceeds to develop an understanding of what is required to advance 

the level of maturity through AD2. It is necessary to 

conduct TAs at various stages throughout a program/

project to provide the Key Decision Point (KDP) products required for transition between phases. (See Table G-1.)

The initial TMA provides the baseline maturity of 

the system’s required technologies at program/project 

outset and allows monitoring progress throughout development. The final TMA is performed just prior to 

the Preliminary Design Review. It forms the basis for 

the Technology Readiness Assessment Report (TRAR), 

which documents the maturity of the technological advancement required by the systems, subsystems, and 

components demonstrated through test and analysis. 

The initial AD2 assessment provides the material necessary to develop preliminary cost and to schedule plans 

and preliminary risk assessments. In subsequent assessment, the information is used to build the technology 

development plan in the process identifying alternative 

paths, fallback positions, and performance descope options. The information is also vital to preparing milestones and metrics for subsequent Earned Value Management (EVM). 
294  NASA Systems Engineering Handbook

Appendix G: Technology Assessment/Insertion

.1: Integ MPS

.2: LH System

.3: O2 Fluid Sys.

.4: Pressure &

Pneumatic Sys.

.5: Umbilicals & 

Disconnect 

Crew Launch

Vehicle

1.3

Launch

Vehicle

1.3.8

First Stage

1.3.8.1

Upper Stage

1.3.8.2

Upper Stage

Engine

1.3.8.3

...

MPS

1.3.8.2.4

...

US RCS

1.3.8.2.5

FS RCS

1.3.8.2.6

TVCS

1.3.8.2.7

Avionics

1.3.8.2.8

Software

1.3.8.2.9

...

Integrated

Test H/W

1.3.8.2.10

...

.1: Integ RCS

.2: Integ Energy

Support

.1: Integ RCS .1: Integ TVCS

.2: Actuator

.3: Hydraulic

Power

.4: APU

.1: Integ Avionics

.2: C&DH System

.3: GN&C H/W

.4: Radio Frequency

System

.5: EPS

.6: Electrical Integration

.7: Develop Flight Instrument

.8: Sensor & Instrument System

.9: EGSE

.10: Integ CLV Avionics System

Element Testing

.11: Flight Safety System

.1: Integ S/W

System

.2: Flight S/W

.1: MPTA

.2: GVT

.3: STA

.4: US for DTF-1

.5: US for VTF-2

.6: US for RRF-3

.7: Struc. Thermal

Component Test

Figure G-1 PBS example

Table G-1 Products Provided by the TA as a Function of Program/Project Phase

Gate Product

KDP A—Transition from 

Pre-Phase A to Phase A

Requires an assessment of potential technology needs versus current and planned technology 

readiness levels, as well as potential opportunities to use commercial, academic, and other 

government agency sources of technology. Included as part of the draft integrated baseline.

KDP B—Transition from 

Phase A to Phase B

Requires a technology development plan identifying technologies to be developed, heritage 

systems to be modified, alternative paths to be pursued, fall-back positions and corresponding 

performance descopes, milestones, metrics, and key decision points. Incorporated in the 

preliminary project plan.

KDP C—Transition from 

Phase B to Phase C/D

Requires a TRAR demonstrating that all systems, subsystems, and components have achieved 

a level of technological maturity with demonstrated evidence of qualification in a relevant 

environment.

Source: NPR 7120.5.

The TMA is performed against the hierarchical breakdown of the hardware and software products of the program/project PBS to achieve a systematic, overall understanding at the system, subsystem, and component 

levels. (See Figure G-1.)
Appendix G: Technology Assessment/Insertion

NASA Systems Engineering Handbook  295

Figure G-2 Technology assessment process

Identify systems, subsystems, and components

per hierarchical product

breakdown of the WBS 

Assign TRL to subsystems

based on lowest TRL of

components and TRL 

state of integration 

Assign TRL to all

components based on

assessment of maturity

Assign TRL to systems

based on lowest TRL of

subsystems and TRL 

state of integration 

Identify all components,

subsystems, and systems

that are at lower TRLs

than required by program

Baseline technology

maturity assessment

Perform AD2 on all

components, subsystems,

and systems that are below

requisite maturity level

Technology Development Plan

Cost Plan

Schedule Plan

Risk Assessment

Inputs/Entry Criteria

It is extremely important that a TA process be defined 

at the beginning of the program/project and that it be 

performed at the earliest possible stage (concept development) and throughout the program/project through 

PDR. Inputs to the process will vary in level of detail according to the phase of the program/project, and even 

though there is a lack of detail in Pre-Phase A, the TA will 

drive out the major critical technological advancements 

required. Therefore, at the beginning of Pre-Phase A, the 

following should be provided:

z Refinement of TRL definitions.

z Definition of AD2.

z Definition of terms to be used in the assessment process.

z Establishment of meaningful evaluation criteria and 

metrics that will allow for clear identification of gaps 

and shortfalls in performance.

z Establishment of the TA team.

z Establishment of an independent TA review team.

How to Do Technology Assessment

The technology assessment process makes use of basic 

systems engineering principles and processes. As mentioned previously, it is structured to occur within the 

framework of the Product 

Breakdown Structure (PBS) 

to facilitate incorporation of 

the results. Using the PBS 

as a framework has a twofold benefit—it breaks the 

“problem” down into systems, subsystems, and components that can be more 

accurately assessed; and it 

provides the results of the 

assessment in a format that 

can readily be used in the 

generation of program costs 

and schedules. It can also be 

highly beneficial in providing 

milestones and metrics for 

progress tracking using 

EVM. As discussed above, 

it is a two-step process comprised of (1) the determination of the current technological maturity in terms of 

TRLs and (2) the determination of the difficulty associated with moving a technology from one TRL to the 

next through the use of the AD2. The overall process 

is iterative, starting at the conceptual level during program Formulation, establishing the initial identification of critical technologies and the preliminary cost, 

schedule, and risk mitigation plans. Continuing on into 

Phase A, it is used to establish the baseline maturity, the 

technology development plan and associated costs and 

schedule. The final TA consists only of the TMA and 

is used to develop the TRAR which validates that all 

elements are at the requisite maturity level. (See Figure G-2.) 

Even at the conceptual level, it is important to use the formalism of a PBS to avoid having important technologies 

slip through the crack. Because of the preliminary nature 

of the concept, the systems, subsystems, and components 

will be defined at a level that will not permit detailed assessments to be made. The process of performing the assessment, however, is the same as that used for subsequent, 

more detailed steps that occur later in the program/project 

where systems are defined in greater detail. 

Once the concept has been formulated and the initial 

identification of critical technologies made, it is nec-
296  NASA Systems Engineering Handbook

Appendix G: Technology Assessment/Insertion

Figure G-4 Technology readiness levels

TRL 1 Basic principles observed and reported

TRL 2 Technology concept and/or application formulated

 __

TRL 3 Analytical and experimental critical function and/or

 __ characteristic proof-of-concept

TRL 4 Component and/or breadboard validation in laboratory 

 __ environment 

TRL 5 Component and/or breadboard validation in relevant

 __ environment

TRL 6 System/subsystem model or prototype demonstration

 __ in a relevant environment (ground or space)

TRL 7 System prototype demonstration in a 

target/space environment

 __

TRL 8 Actual system completed and “ight qualied” through

 __ test and demonstration (ground or ight)

TRL 9 Actual system “ight proven” through successful

 __ mission operations

System test, launch, 

and operations

System/subsystem

development

Technology

demonstration

Technology

development

Research to prove

feasibility

Basic technology

research

essary to perform detailed architecture studies with 

the Technology Assessment Process intimately interEstablishing TRLs

TRL is, at its most basic, a description of the performance history of a given system, subsystem, or component relative to a set of levels first described at NASA 

HQ in the 1980s. The TRL essentially describes the state 

of the art of a given technology and provides a baseline 

from which maturity is gauged and advancement defined. (See Figure G-4.) Even though the concept of TRL 

has been around for almost 20 years, it is not well understood and frequently misinterpreted. As a result, we 

often undertake programs without fully understanding 

either the maturity of key technologies or what is needed 

to develop them to the required level. It is impossible 

to understand the magnitude and scope of a development program without having a clear understanding of 

the baseline technological maturity of all elements of the 

system. Establishing the TRL is a vital first step on the 

Figure G-3 Architectural studies and technology 

development

Requirements

TRL/AD2 Assessment

Architectural

Studies

Technology Maturation 

Concepts System

Design

woven. (See Figure G-3.) The purpose of the architecture studies is to refine end-item system design to meet 

the overall scientific requirements of the mission. It is 

imperative that there be a continuous relationship between architectural studies 

and maturing technology 

advances. The architectural 

studies must incorporate 

the results of the technology 

maturation, planning for 

alternative paths and identifying new areas required 

for development as the architecture is refined. Similarly, it is incumbent upon 

the technology maturation 

process to identify requirements that are not feasible 

and development routes 

that are not fruitful and to 

transmit that information to 

the architecture studies in a 

timely manner. Similarly, it 

is incumbent upon the architecture studies to provide 

feedback to the technology 

development process relative to changes in requirements. Particular attention 

must be given to “heritage” 

systems in that they are 

often used in architectures 

and environments different 

from those in which they 

were designed to operate. 
Appendix G: Technology Assessment/Insertion

NASA Systems Engineering Handbook  297

way to a successful program. A frequent misconception 

is that in practice it is too difficult to determine TRLs and 

that when you do it is not meaningful. On the contrary, 

identifying TRLs can be a straightforward systems engineering process of determining what was demonstrated 

and under what conditions was it demonstrated. 

At first blush, the TRL descriptions in Figure G-4 appear to be straightforward. It is in the process of trying 

to assign levels that problems arise. A primary cause of 

difficulty is in terminology—everyone knows what a 

breadboard is, but not everyone has the same definition. 

Also, what is a “relevant environment”? What is relevant 

to one application may or may not be relevant to another. 

Many of these terms originated in various branches of engineering and had, at the time, very specific meanings to 

that particular field. They have since become commonly 

used throughout the engineering field and often take differences in meaning from discipline to discipline, some 

subtle, some not so subtle. “Breadboard,” for example, 

comes from electrical engineering where the original use 

referred to checking out the functional design of an electrical circuit by populating a “breadboard” with components to verify that the design operated as anticipated. 

Other terms come from mechanical engineering, referring primarily to units that are subjected to different 

levels of stress under testing, i.e., qualification, protoflight, and flight units. The first step in developing a 

uniform TRL assessment (see Figure G-5) is to define 

the terms used. It is extremely important to develop and 

use a consistent set of definitions over the course of the 

program/project. 

Having established a common set of terminology, it 

is necessary to proceed to the next step—quantifying 

“judgment calls” on the basis of past experience. Even 

with clear definitions there will be the need for judgment calls when it comes time to assess just how similar 

a given element is relative to what is needed (i.e., is it 

close enough to a prototype to be considered a prototype, or is it more like an engineering breadboard?). Describing what has been done in terms of form, fit, and 

function provides a means of quantifying an element 

based on its design intent and subsequent performance. 

The current definitions for software TRLs are contained 

in NPR 7120.8, NASA Research and Technology Program 

and Project Management Requirements.

A third critical element of any assessment relates to the 

question of who is in the best position to make judgment 

calls relative to the status of the technology in question. 

For this step, it is extremely important to have a wellbalanced, experienced assessment team. Team members 

do not necessarily have to be discipline experts. The primary expertise required for a TRL assessment is that the 

Figure G-5 The TMA thought process

Has an identical unit been successfully

operated/launched in identical

configuration/environment?

Has an identical unit in a different configuration/

system architecture been successfully operated

in space or the target environment or launched?

If so, then this initially drops to TRL 5 until

differences are evaluated.

Has an identical unit been flight qualified but

not yet operated in space or the target

environment or launched?

Has a prototype unit (or one similar enough to be

considered a prototype) been successfully operated

in space or the target environment or launched?

Has a prototype unit (or one similar enough 

to be considered a prototype) been

demonstrated in a relevant environment?

Has a breadboard unit been demonstrated in 

a relevant environment?

Has a breadboard unit been demonstrated in 

a laboratory environment?

Has analytical and experimental

proof-of-concept been demonstrated?

Has concept or application

been formulated?

Have basic principles been observed

and reported?

RETHINK POSITION REGARDING

THIS TECHNOLOGY!

NO

NO

NO

NO

NO

NO

NO

NO

NO

NO

TRL 9 YES

TRL 5 YES

TRL 2 YES

TRL 1 YES

TRL 3 YES

TRL 4 YES

TRL 5 YES

TRL 6 YES

TRL 7 YES

TRL 8 YES
298  NASA Systems Engineering Handbook

Appendix G: Technology Assessment/Insertion

Figure G-6 TRL assessment matrix

TRL ASSESSMENT Developmental Model Breadboard Brassboard Prototype

Concept

Demonstration Units Environment

Flight Qualied

Relevant EnvironmentSpace Environment

Labor

Space/Launch Operation

atory Environment

Overall TRL

Unit Description Form Fit Function

Appropriate Scale

Red = Below TRL 3

Yellow = TRL 3,4 & 5

Green = TRL 6 and above

White = Unknown

X Exists

1.0 System

 1.1 Subsystem X

 1.1.1 Mechanical Components

 1.1.2 Mechanical Systems

 1.1.3 Electrical Components X X X X X

 1.1.4 Electrical Systems

 1.1.5 Control Systems

 1.1.6 Thermal Systems X X X

 1.1.7 Fluid Systems X

 1.1.8 Optical Systems

 1.1.9 Electro-Optical Systems

 1.1.10 Software Systems

 1.1.11 Mechanisms X

 1.1.12 Integration 

 1.2 Subsystem Y

 1.2.1 Mechanical Components

Developmental ModelBreadboardBrassboard

Prototype

Concept

Flight Qualied

Relevant EnvironmentSpace Environment

Labor

Space/Launch Operation

atory Environment

Overall TRLFormFitFunctionAppropriate Scale

systems engineer/user understands the current state of the 

art in applications. Having established a set of definitions, 

defined a process for quantifying judgment calls, and assembled an expert assessment team, the process primarily 

consists of asking the right questions. The flowchart depicted in Figure G-5 demonstrates the questions to ask to 

determine TRL at any level in the assessment. 

Note the second box particularly refers to heritage systems. If the architecture and the environment have 

changed, then the TRL drops to TRL 5—at least intially. 

Additional testing may need to be done for heritage systems for the new use or new environment. If in subsequent analysis the new environment is sufficiently close to 

the old environment, or the new architecture sufficiently 

close to the old architecture then the resulting evaluation 

could be then TRL 6 or 7, but the most important thing 

to realize is that it is no longer at a TRL 9. Applying this 

process at the system level and then proceeding to lower 

levels of subsystem and component identifies those elements that require development and sets the stage for the 

subsequent phase, determining the AD2. 

A method for formalizing this process is shown in Figure G-6. Here, the process has been set up as a table: the 

rows identify the systems, subsystems, and components 

that are under assessment. The columns identify the categories that will be used to determine the TRL—i.e., what 

units have been built, to what scale, and in what environment have they been tested. Answers to these questions determine the TRL of an item under consideration. The TRL 

of the system is determined by the lowest TRL present in 

the system; i.e., a system is at TRL 2 if any single element in 

the system is at TRL 2. The problem of multiple elements 

being at low TRLs is dealt with in the AD2 process. Note 

that the issue of integration affects the TRL of every system, 

subsystem, and component. All of the elements can be at a 

higher TRL, but if they have never been integrated as a unit, 

the TRL will be lower for the unit. How much lower depends on the complexity of the integration. 
NASA Systems Engineering Handbook  299

Appendix H: Integration Plan Outline

Purpose

The integration plan defines the integration and verification strategies for a project interface with the system design and decomposition into the lower level elements.1

The integration plan is structured to bring the elements 

together to assemble each subsystem and to bring all of 

the subsystems together to assemble the system/product. 

The primary purposes of the integration plan are: (1) to 

describe this coordinated integration effort that supports 

the implementation strategy, (2) to describe for the participants what needs to be done in each integration step, 

and (3) to identify the required resources and when and 

where they will be needed.

Questions/Checklist

z Does the integration plan include and cover integration of all of the components and subsystems of the 

project, either developed or purchased?

z Does the integration plan account for all external systems to be integrated with the system (for example, 

communications networks, field equipment, other 

1

The material in this appendix is adapted from Federal 

Highway Administration and CalTrans, Systems Engineering 

Guidebook for ITS, Version 2.0. 

complete systems owned by the government or owned 

by other government agencies)?

z Does the integration plan fully support the implementation strategy, for example, when and where the 

subsystems and system are to be used?

z Does the integration plan mesh with the verification 

plan?

z For each integration step, does the integration plan 

define what components and subsystems are to be integrated?

z For each integration step, does the integration plan 

identify all the needed participants and define what 

their roles and responsibilities are?

z Does the integration plan establish the sequence and 

schedule for every integration step?

z Does the integration plan spell out how integration 

problems are to be documented and resolved?

Integration Plan Contents

Table H-1 outlines the content of the integration plan by 

section.
300  NASA Systems Engineering Handbook

Appendix H: Integration Plan Outline

Section Contents

Title page The title page should follow the NASA procedures or style guide. At a minimum, it should contain 

the following information:

z INTEGRATION PLAN FOR THE [insert name of project] AND [insert name of organization]

z Contract number

z Date that the document was formally approved

z The organization responsible for preparing the document

z Internal document control number, if available

z Revision version and date issued

1.0 Purpose of DocumentA brief statement of the purpose of this document. It is the plan for integrating the components 

and subsystems of the project prior to verification.

2.0 Scope of Project This section gives a brief description of the planned project and the purpose of the system to be 

built. Special emphasis is placed on the project’s deployment complexities and challenges.

3.0 Integration 

Strategy

This section informs the reader what the high-level plan is for integration and, most importantly, 

why the integration plan is structured the way it is. The integration plan is subject to several, 

sometimes conflicting, constraints. Also, it is one part of the larger process of build, integrate, verify, 

and deploy, all of which must be synchronized to support the same project strategy. So, for even 

a moderately complex project, the integration strategy, based on a clear and concise statement 

of the project’s goals and objectives, is described here at a high, but all-inclusive, level. It may also 

be necessary to describe the analysis of alternative strategies to make it clear why this particular 

strategy was selected. 

The same strategy is the basis for the build plan, the verification plan, and the deployment plan. 

This section covers and describes each step in the integration process. It describes what components are integrated at each step and gives a general idea of what threads of the operational capabilities (requirements) are covered. It ties the plan to the previously identified goals and objectives 

so the stakeholders can understand the rationale for each integration step. This summary-level 

description also defines the schedule for all the integration efforts.

4.0 Phase 1 IntegrationThis, and the following sections, define and explain each step in the integration process. The intent 

here is to identify all the needed participants and to describe to them what they have to do.

In general, the description of each integration step should identify:

z The location of the activities.

z The project-developed equipment and software products to be integrated. Initially this is just a 

high-level list, but eventually the list must be exact and complete, showing part numbers and 

quantity. 

z Any support equipment (special software, test hardware, software stubs, and drivers to simulate 

yet-to-be-integrated software components, external systems) needed for this integration step. 

The same support equipment is most likely needed for the subsequent verification step.

z All integration activities that need to be performed after installation, including integration with 

on-site systems and external systems at other sites.

z A description of the verification activities, as defined in the applicable verification plan, that 

occur after this integration step.

z The responsible parties for each activity in the integration step.

z The schedule for each activity.

5.0 Multiple Phase 

Integration Steps (1 

or N steps)

This, and any needed additional sections, follow the format for Section 3.0. Each covers each step in 

a multiple step integration effort.

Table H-1 Integration Plan Contents
NASA Systems Engineering Handbook  301

Appendix I: Verification and Validation Plan 

Sample Outline

1. Introduction

1.1 Purpose and Scope

1.2 Responsibility and Change Authority

1.3 Definitions

2. Applicable and Reference Documents

2.1 Applicable Documents

2.2 Reference Documents

2.3 Order of Precedence

3. System X Description

3.1 System X Requirements Flow Down

3.2 System X Architecture

3.3 End Item Architectures

 3.3.1 System X End Item A

 3.3.n System X End Item n

3.4 System X Ground Support Equipment

3.5 Other Architecture Descriptions

4. Verification and Validation Process

4.1 Verification and Validation Management Responsibilities

4.2 Verification Methods

 4.2.1 Analysis

 4.2.2 Inspection

 4.2.3 Demonstration

 4.2.4 Test

 4.2.4.1 Qualification Testing

 4.2.4.2 Other Testing

4.3 Validation Methods

4.4 Certification Process

4.5 Acceptance Testing

5. Verification and Validation Implementation

5.1 System X Design and Verification and Validation Flow

5.2 Test Articles

5.3 Support Equipment

5.4 Facilities

6. System X End Item Verification and Validation

6.1 End Item A

 6.1.1 Developmental/Engineering Unit Evaluations

 6.1.2 Verification Activities

 6.1.2.1 Verification Testing

 6.1.2.1.1 Qualification Testing

 6.1.2.1.2 Other Testing
302  NASA Systems Engineering Handbook

Appendix I: Verification and Validation Plan Sample Outline

 6.1.2.2 Verification Analysis

 6.1.2.2.1 Thermal Analysis

 6.1.2.2.2 Stress Analysis

 6.1.2.2.3 Analysis of Fracture Control

 6.1.2.2.4 Materials Analysis

 6.1.2.2.5 EEE Parts Analysis

 6.1.2.3 Verification Inspection

 6.1.2.4 Verification Demonstration

 6.1.3 Validation Activities

 6.1.4 Acceptance Testing

6.n End Item n

7. System X Verification and Validation

7.1 End-Item-to-End-Item Integration

 7.1.1 Developmental/Engineering Unit Evaluations

 7.1.2 Verification Activities

 7.1.2.1 Verification Testing

 7.1.2.2 Verification Analysis

 7.1.2.3 Verification Inspection

 7.1.2.4 Verification Demonstration

 7.1.3 Validation Activities

7.2 Complete System Integration

 7.2.1 Developmental/Engineering Unit Evaluations

 7.2.2 Verification Activities

 7.2.2.1 Verification Testing

 7.2.2.2 Verification Analysis

 7.2.2.3 Verification Inspection

 7.2.2.4 Verification Demonstration

 7.2.3 Validation Activities

8. System X Program Verification and Validation

8.1 Vehicle Integration

8.2 End-to-End Integration

8.3 On-Orbit V&V Activities

9. System X Certification Products

Appendix A: Acronyms and Abbreviations

Appendix B: Definition of Terms

Appendix C: Requirement Verification Matrix

Appendix D: System X Validation Matrix
NASA Systems Engineering Handbook  303

Appendix J: SEMP Content Outline

SEMP Content

The SEMP is the foundation document for the technical and engineering activities conducted during the 

project. The SEMP conveys information on the technical 

integration methodologies and activities for the project 

within the scope of the project plan to all of the personnel. Because the SEMP provides the specific technical 

and management information to understand the technical integration and interfaces, its documentation and 

approval serves as an agreement within the project of 

how the technical work will be conducted. The technical 

team, working under the overall program/project plan, 

develops and updates the SEMP as necessary. The technical team works with the project manager to review the 

content and obtain concurrence. The SEMP includes the 

following three general sections:

z Technical program planning and control, which describes the processes for planning and control of the 

engineering efforts for the design, development, test, 

and evaluation of the system.

z Systems engineering processes, which includes specific tailoring of the systems engineering process as 

described in the NPR, implementation procedures, 

trade study methodologies, tools, and models to be 

used.

z Engineering specialty integration describes the integration of the technical disciplines’ efforts into the 

systems engineering process and summarizes each 

technical discipline effort and cross references each of 

the specific and relevant plans.

Purpose and Scope

This section provides a brief description of the purpose, 

scope, and content of the SEMP. The scope encompasses 

the SE technical effort required to generate the work 

products necessary to meet the success criteria for the 

product-line life-cycle phases. The SEMP is a plan for 

doing the project technical effort by a technical team for 

a given WBS model in the system structure and to help 

meet life-cycle phase success criteria.

Applicable Documents

This section of the SEMP lists the documents applicable 

to this specific project and its SEMP implementation and 

describes major standards and procedures that this technical effort for this specific project needs to follow. Specific implementation of standardization tasking is incorporated into pertinent sections of the SEMP.

Provide the engineering standards and procedures to be 

used in the project. Examples of specific procedures could 

include any hazardous material handling, crew training 

for control room operations, special instrumentation 

techniques, special interface documentation for vehicles, 

and maintenance procedures specific to the project. 

Technical Summary

This section contains an executive summary describing 

the problem to be solved by this technical effort and the 

purpose, context, and products of the WBS model to be 

developed and integrated with other interfacing systems 

identified.

System Description

This section contains a definition of the purpose/mission/objective of the system being developed, a brief 

description of the purpose of the products of the WBS 

models of the system structure for which this SEMP applies, and the expected scenarios for the system. Each 

WBS model includes the system end products and their 

subsystems and the supporting or enabling products and 

any other work products (plans, baselines) required for 

the development of the system. The description should 

include any interfacing systems and system products, 

including humans, with which the WBS model system 

products will interact physically, functionally, or electronically. 

Identify and document system constraints, including 

cost, schedule, and technical (for example, environmental, design).
304  NASA Systems Engineering Handbook

Appendix J: SEMP Content Outline

System Structure

This section contains an explanation of how the WBS 

models will be developed, how the resulting WBS model 

will be integrated into the project WBS, and how the 

overall system structure will be developed. This section 

contains a description of the relationship of the specification tree and the drawing tree with the products of the 

system structure and how the relationship and interfaces 

of the system end products and their life-cycle-enabling 

products will be managed throughout the planned technical effort.

Product Integration

This subsection contains an explanation of how the 

product will be integrated and will describe clear organizational responsibilities and interdependencies whether 

the organizations are geographically dispersed or managed across Centers. This includes identifying organizations—intra- and inter-NASA, other Government agencies, contractors, or other partners—and delineating 

their roles and responsibilities.

When components or elements will be available for integration needs to be clearly understood and identified on 

the schedule to establish critical schedule issues.

Planning Context

This subsection contains the product-line life-cycle 

model constraints (e.g., NPR 7120.5) that affect the planning and implementation of the common technical processes to be applied in performing the technical effort. 

The constraints provide a linkage of the technical effort 

with the applicable product-line life-cycle phases covered by the SEMP including, as applicable, milestone decision gates, major technical reviews, key intermediate 

events leading to project completion, life-cycle phase, 

event entry and success criteria, and major baseline and 

other work products to be delivered to the sponsor or 

customer of the technical effort.

Boundary of Technical Effort

This subsection contains a description of the boundary 

of the general problem to be solved by the technical effort. Specifically, it identifies what can be controlled by 

the technical team (inside the boundary) and what influences the technical effort and is influenced by the technical effort but not controlled by the technical team (outside the boundary). Specific attention should be given to 

physical, functional, and electronic interfaces across the 

boundary.

Define the system to be addressed. A description of the 

boundary of the system can include the following: definition of internal and external elements/items involved 

in realizing the system purpose as well as the system 

boundaries in terms of space, time, physical, and operational. Also, identification of what initiates the transitions of the system to operational status and what initiates its disposal is important. The following is a general 

listing of other items to include, as appropriate:

z General and functional descriptions of the subsystems,

z Document current and established subsystem performance characteristics,

z Identify and document current interfaces and characteristics,

z Develop functional interface descriptions and functional flow diagrams,

z Identify key performance interface characteristics, and

z Identify current integration strategies and architecture.

Cross References

This subsection contains cross references to appropriate 

nontechnical plans and critical reference material that 

interface with the technical effort. It contains a summary 

description of how the technical activities covered in 

other plans are accomplished as fully integrated parts of 

the technical effort.

Technical Effort Integration

This section contains a description of how the various 

inputs to the technical effort will be integrated into a coordinated effort that meets cost, schedule, and performance objectives.

The section should describe the integration and coordination of the specialty engineering disciplines into the 

systems engineering process during each iteration of the 

processes. Where there is potential for overlap of specialty efforts, the SEMP should define the relative responsibilities and authorities of each. This section should contain, as needed, the project’s approach to the following:

z Concurrent engineering,

z The activity phasing of specialty engineering,

z The participation of specialty disciplines,

z The involvement of specialty disciplines,
Appendix J: SEMP Content Outline

NASA Systems Engineering Handbook  305

z The role and responsibility of specialty disciplines,

z The participation of specialty disciplines in system 

decomposition and definition,

z The role of specialty disciplines in verification and 

validation,

z Reliability,

z Maintainability,

z Quality assurance,

z Integrated logistics,

z Human engineering,

z Safety,

z Producibility,

z Survivability/vulnerability,

z National Environmental Policy Act compliance, and

z Launch approval/flight readiness.

Provide the approach for coordination of diverse technical 

disciplines and integration of the development tasks. For 

example, this can include the use of integrated teaming 

approaches. Ensure that the specialty engineering disciplines are properly represented on all technical teams and 

during all life-cycle phases of the project. Define the scope 

and timing of the specialty engineering tasks.

Responsibility and Authority

This subsection contains a description of the organizing 

structure for the technical teams assigned to this technical 

effort and includes how the teams will be staffed and managed, including (1) what organization/panel will serve as 

the designated governing authority for this project and, 

therefore, will have final signature authority for this SEMP; 

(2) how multidisciplinary teamwork will be achieved; 

(3) identification and definition of roles, responsibilities, 

and authorities required to perform the activities of each 

planned common technical process; (4) planned technical 

staffing by discipline and expertise level, with human resource loading; (5) required technical staff training; and 

(6) assignment of roles, responsibilities, and authorities to 

appropriate project stakeholders or technical teams to ensure planned activities are accomplished.

Provide an organization chart and denote who on the 

team is responsible for each activity. Indicate the lines 

of authority and responsibility. Define the resolution authority to make decisions/decision process. Show how 

the engineers/engineering disciplines relate.

The systems engineering roles and responsibilities need 

to be addressed for the following: project office, user, 

Contracting Office Technical Representative (COTR), 

systems engineering, design engineering, specialty engineering, and contractor.

Contractor Integration

This subsection contains a description of how the technical effort of in-house and external contractors is to be 

integrated with the NASA technical team efforts. This 

includes establishing technical agreements, monitoring 

contractor progress against the agreement, handling 

technical work or product requirements change requests, 

and acceptance of deliverables. The subsection will specifically address how interfaces between the NASA technical team and the contractor will be implemented for 

each of the 17 common technical processes. For example, it addresses how the NASA technical team will be 

involved with reviewing or controlling contractor-generated design solution definition documentation or how 

the technical team will be involved with product verification and product validation activities.

Key deliverables for the contractor to complete their 

systems and those required of the contractor for other 

project participants need to be identified and established 

on the schedule.

Support Integration

This subsection contains a description of the methods 

(such as integrated computer-aided tool sets, integrated 

work product databases, and technical management information systems) that will be used to support technical 

effort integration.

Common Technical Processes 

Implementation

Each of the 17 common technical processes will have a 

separate subsection that contains a plan for performing 

the required process activities as appropriately tailored. 

(See NPR 7123.1 for the process activities required and 

tailoring.) Implementation of the 17 common technical 

processes includes (1) the generation of the outcomes 

needed to satisfy the entry and success criteria of the 

applicable product-line life-cycle phase or phases identified in D.4.4.4 and (2) the necessary inputs for other 

technical processes. These sections contain a description 

of the approach, methods, and tools for: 

z Identifying and obtaining adequate human and nonhuman resources for performing the planned process, 
306  NASA Systems Engineering Handbook

Appendix J: SEMP Content Outline

developing the work products, and providing the services of the process.

z Assigning responsibility and authority for performing 

the planned process, developing the work products, 

and providing the services of the process.

z Training the technical staff performing or supporting 

the process, where training is identified as needed.

z Designating and placing designated work products of 

the process under appropriate levels of configuration 

management.

z Identifying and involving stakeholders of the process.

z Monitoring and controlling the process.

z Identifying, defining, and tracking metrics and success. 

z Objectively evaluating adherence of the process and 

the work products and services of the process to the 

applicable requirements, objectives, and standards 

and addressing noncompliance.

z Reviewing activities, status, and results of the process 

with appropriate levels of management and resolving 

issues.

This section should also include the project-specific 

description of each of the 17 processes to be used, including the specific tailoring of the requirements to the 

system and the project; the procedures to be used in 

implementing the processes; in-house documentation; 

trade study methodology; types of mathematical and/or 

simulation models to be used; and generation of specifications.

Technology Insertion

This section contains a description of the approach and 

methods for identifying key technologies and their associated risks and criteria for assessing and inserting 

technologies, including those for inserting critical 

technologies from technology development projects. 

An approach should be developed for appropriate level 

and timing of technology insertion. This could include 

alternative approaches to take advantage of new technologies to meet systems needs as well as alternative 

options if the technologies do not prove appropriate in 

result or timing. The strategy for an initial technology 

assessment within the scope of the project requirements should be provided to identify technology constraints for the system. 

Additional SE Functions and 

Activities

This section contains a description of other areas not 

specifically included in previous sections but that are essential for proper planning and conduct of the overall 

technical effort.

System Safety

This subsection contains a description of the approach 

and methods for conducting safety analysis and assessing 

the risk to operators, the system, the environment, or the 

public.

Engineering Methods and Tools

This subsection contains a description of the methods 

and tools not included in the technology insertion section that are needed to support the overall technical effort and identifies those tools to be acquired and tool 

training requirements.

Define the development environment for the project, including automation and software tools. If required, develop and/or acquire the tools and facilities for all disciplines on the project. Standardize when possible across 

the project, or enable a common output format of the 

tools that can be used as input by a broad range of tools 

used on the project. Define the requirements for information management systems and for using existing elements. Define and plan for the training required to use 

the tools and technology across the project.

Specialty Engineering

This subsection contains a description of engineering 

discipline and specialty requirements that apply across 

projects and the WBS models of the system structure. 

Examples of these requirement areas would include 

planning for safety, reliability, human factors, logistics, 

maintainability, quality, operability, and supportability. 

Estimate staffing levels for these disciplines and incorporate with the project requirements. 

Integration with the Project Plan and 

Technical Resource Allocation

This section contains how the technical effort will integrate with project management and defines roles and responsibilities. It addresses how technical requirements 
Appendix J: SEMP Content Outline

NASA Systems Engineering Handbook  307

will be integrated with the project plan to determinate 

the allocation of resources, including cost, schedule, and 

personnel, and how changes to the allocations will be coordinated. 

This section describes the interface between all of the 

technical aspects of the project and the overall project 

management process during the systems engineering 

planning activities and updates. All activities to coordinate technical efforts with the overall project are included, such as technical interactions with the external 

stakeholders, users, and contractors. 

Waivers

This section contains all approved waivers to the Center 

Director’s Implementation Plan for SE NPR 7123.1 requirements for the SEMP. This section also contains a 

separate subsection that includes any tailored SE NPR 

requirements that are not related and able to be documented in a specific SEMP section or subsection.

Appendices

Appendices are included, as necessary, to provide a glossary, acronyms and abbreviations, and information published separately for convenience in document maintenance. Included would be: (1) information that may 

be pertinent to multiple topic areas (e.g., description of 

methods or procedures); (2) charts and proprietary data 

applicable to the technical efforts required in the SEMP; 

and (3) a summary of technical plans associated with the 

project. Each appendix should be referenced in one of 

the sections of the engineering plan where data would 

normally have been provided.

Templates

Any templates for forms, plans, or reports the technical 

team will need to fill out, like the format for the verification and validation plan, should be included in the appendices.

References

This section contains all documents referenced in the 

text of the SEMP.

SEMP Preparation Checklist

The SEMP, as the key reference document capturing the 

technical planning, needs to address some basic topics. 

For a generic SEMP preparation checklist, refer to Systems Engineering Guidebook by James Martin.
308  NASA Systems Engineering Handbook

Appendix K: Plans

Activity Plan.......................................................................................................................... 187

Baseline Plan......................................................................................................................... 111

Build Plan.............................................................................................................................. 300

Closure Plan.......................................................................................................................... 178

Configuration Management Plan.............................................................................. 176, 311

Cost Account Plan............................................................................................................... 121

Data Management Plan....................................................................................................... 158

Deployment Plan ................................................................................................................. 300

Earned Value Management Plan....................................................................................... 166

Engineering Plan.................................................................................................................. 307

Implementation Plan........................................................................................................... 148

Installation Plan ................................................................................................................... 230

Integration Plan.................................................................................................................... 299

Interface Control Plan........................................................................................................... 81

Launch and Early Orbit Plan ............................................................................................... 35

Life-Cycle Cost Management Plan.................................................................................... 129

Logistics Support Plan........................................................................................................... 26

Mission Operations Plan ...................................................................................................... 26

Operations Plan...................................................................................................................... 35

Production Plan ..................................................................................................................... 25

Program Plan.......................................................................................................................... 19

Project Plan........................................................................................................................... 112

Project Protection Plan ............................................................................................... 260, 321

Quality Control Plan............................................................................................................. 24

Requirements Management Plan...................................................................................... 134

Review Plan........................................................................................................................... 169

Risk Control Plan................................................................................................................. 142

Risk Management Plan ....................................................................................................... 140

Risk Mitigation Plan............................................................................................................ 295

Software Development Plan............................................................................................... 104

Software IV&V Plan............................................................................................................ 105

Source Evaluation Plan ....................................................................................................... 219

Strategic Plan ........................................................................................................................ 152

Surveillance Plan.................................................................................................................. 225

System and Subsystem Test Plans ....................................................................................... 42

Systems Decommissioning/Disposal Plan........................................................................... 7

Systems Engineering Management Plan (SEMP)................................................... 113, 303

Technology Development Plan.......................................................................................... 277

Test Plan ................................................................................................................................ 230

Time-Phased Resource Plan .............................................................................................. 190

Transition Plan ..................................................................................................................... 230

Transportation Plan............................................................................................................. 187

Validation Plan............................................................................................................. 100, 284

Verification Plan..................................................................................................................... 83
NASA Systems Engineering Handbook  309

Appendix L: Interface Requirements 

Document Outline

1.0 Introduction 

1.1 Purpose and Scope. State the purpose of this document and briefly identify the interface to be defined. (For 

example, “This IRD defines and controls the interface(s) requirements between ______ and _____.”) 

1.2 Precedence. Define the relationship of this document to other program documents and specify which is 

controlling in the event of a conflict. 

1.3 Responsibility and Change Authority. State the responsibilities of the interfacing organizations for development of this document and its contents. Define document approval authority (including change approval 

authority). 

2.0 Documents

2.1 Applicable Documents. List binding documents that are invoked to the extent specified in this IRD. The 

latest revision or most recent version should be listed. Documents and requirements imposed by higher–level 

documents (higher order of precedence) should not be repeated. 

2.2 Reference Documents. List any document that is referenced in the text in this subsection. 

3.0 Interfaces 

3.1 General. In the subsections that follow, provide the detailed description, responsibilities, coordinate systems, 

and numerical requirements as they relate to the interface plane. 

3.1.1 Interface Description. Describe the interface as defined in the system specification. Use tables, figures, or drawings as appropriate.

3.1.2 Interface Responsibilities. Define interface hardware and interface boundary responsibilities to depict the interface plane. Use tables, figures, or drawings as appropriate. 

3.1.3 Coordinate Systems. Define the coordinate system used for interface requirements on each side of the 

interface. Use tables, figures, or drawings as appropriate.

3.1.4 Engineering Units, Tolerances, and Conversions. Define the measurement units along with tolerances. If required, define the conversion between measurement systems.

3.2 Interface Requirements. In the subsections that follow, define structural limiting values at the interface, such 

as interface loads, forcing functions, and dynamic conditions.

3.2.1 Interface Plane. Define the interface requirements on each side of the interface plane. 

3.2.1.1 Envelope 

3.2.1.2 Mass Properties. Define the derived interface requirements based on the allocated requirements contained in the applicable specification pertaining to that side of the interface. For example, this subsection should cover the mass of the element.

3.2.1.3 Structural/Mechanical. Define the derived interface requirements based on the allocated requirements contained in the applicable specification pertaining to that side of the interface. 

For example, this subsection should cover attachment, stiffness, latching, and mechanisms.

3.2.1.4 Fluid. Define the derived interface requirements based on the allocated requirements contained in the applicable specification pertaining to that side of the interface. For example, this 

subsection should cover fluid areas such as thermal control, O2 and N2, potable and waste 

water, fuel cell water, and atmospheric sampling.
310  NASA Systems Engineering Handbook

Appendix L: Interface Requirements Document Outline

3.2.1.5 Electrical (Power). Define the derived interface requirements based on the allocated requirements contained in the applicable specification pertaining to that side of the interface. For example, this subsection should cover various electric current, voltage, wattage, and resistance 

levels.

3.2.1.6 Electronic (Signal). Define the derived interface requirements based on the allocated requirements contained in the applicable specification pertaining to that side of the interface. 

For example, this subsection should cover various signal types such as audio, video, command 

data handling, and navigation. 

3.2.1.7 Software and Data. Define the derived interface requirements based on the allocated requirements contained in the applicable specification pertaining to that side of the interface. For example, this subsection should cover various data standards, message timing, protocols, error 

detection/correction, functions, initialization, and status.

3.2.1.8 Environments. Define the derived interface requirements based on the allocated requirements contained in the applicable specification pertaining to that side of the interface. For 

example, cover the dynamic envelope measures of the element in English units or the metric 

equivalent on this side of the interface. 

3.2.1.8.1 Electromagnetic Effects

3.2.1.8.1.a Electromagnetic Compatibility. Define the appropriate electromagnetic compatibility requirements. For example, end-item-1-toend-item-2 interface shall meet the requirements [to be determined] 

of systems requirements for electromagnetic compatibility.

3.2.1.8.1.b Electromagnetic Interference. Define the appropriate electromagnetic interference requirements. For example, end-item-1-to-enditem-2 interface shall meet the requirements [to be determined] of 

electromagnetic emission and susceptibility requirements for electromagnetic compatibility.

3.2.1.8.1.c Grounding. Define the appropriate grounding requirements. For 

example, end-item-1-to-end-item-2 interface shall meet the requirements [to be determined] of grounding requirements.

3.2.1.8.1.d Bonding. Define the appropriate bonding requirements. For example, end-item-1-to-end-item-2 structural/mechanical interface 

shall meet the requirements [to be determined] of electrical bonding 

requirements.

3.2.1.8.1.e Cable and Wire Design. Define the appropriate cable and wire design requirements. For example, end-item-1-to-end-item-2 cable 

and wire interface shall meet the requirements [to be determined] 

of cable/wire design and control requirements for electromagnetic 

compatibility. 

3.2.1.8.2 Acoustic. Define the appropriate acoustics requirements. Define the acoustic noise 

levels on each side of the interface in accordance with program or project requirements. 

3.2.1.8.3 Structural Loads. Define the appropriate structural loads requirements. Define 

the mated loads that each end item must accommodate. 

3.2.1.8.4 Vibroacoustics. Define the appropriate vibroacoustics requirements. Define the 

vibroacoustic loads that each end item must accommodate. 

3.2.1.9 Other Types of Interface Requirements. Define other types of unique interface requirements 

that may be applicable. 
NASA Systems Engineering Handbook  311

Appendix M: CM Plan Outline

Section Description

1.0 Introduction This section includes:

z The purpose and scope of the CM plan and the program phases to which it applies

z Brief description of the system or top-level configuration items

2.0 Applicable and Reference 

Documents

This section includes a list of the specifications, standards, manuals, and other documents, referenced in the plan by title, document number, issuing authority, revision, 

and as applicable, change notice, amendment, and issue date.

3.0 CM Concepts and Organization This section includes:

z CM objectives

z Information needed to support the achievement of objectives in the current and 

future phases

z Description and graphic portraying the project’s planned organization with 

emphasis on the CM activities

4.0 CM Process

z CM Management and Planning

z Configuration Identification

z Configuration Control

z Configuration Status Accounting

z Configuration Audits

This section includes a description of the project’s CM process for accomplishing the 

five CM activities, which includes but is not limited to: 

z CM activities for the current and future phases

z Baselines

z Configuration items

z Establishment and membership of configuration control boards

z Nomenclature and numbering

z Hardware/software identification

z Functional configuration audits and physical configuration audits

5.0 Management of Configuration 

Data

This section describes the methods for meeting the CM technical data requirements.

6.0 Interface Management This section includes a description on how CM will maintain and control interface 

documentation.

7.0 CM Phasing and Schedule This section describes milestones for implementing CM commensurate with major 

program milestones.

8.0 Subcontractor/Vendor Control This section describes methods used to ensure subcontractor/vendors comply with 

CM requirements.

A typical CM plan should include the following:

Table M-1 CM Plan Outline
312  NASA Systems Engineering Handbook

Appendix N: Guidance on Technical Peer 

Reviews/Inspections 

Introduction

The objective of technical peer reviews/inspections is to 

remove defects as early as possible in the development 

process. Peer reviews/inspections are a well defined review process for finding and fixing defects, conducted by 

a team of peers with assigned roles, each having a vested 

interest in the work product under review. Peer reviews/inspections are held within development phases, 

between milestone reviews, on completed products or 

completed portions of products. The results of peer reviews/inspections can be reported at milestone reviews. 

Checklists are heavily utilized in peer reviews/inspections to improve the quality of the review. 

Technical peer reviews/inspections have proven over 

time to be one of the most effective practices available for 

ensuring quality products and on-time deliveries. Many 

studies have demonstrated their benefits, both within 

NASA and across industry. Peer reviews/inspections improve quality and reduce cost by reducing rework. The 

studies have shown that the rework effort saved not only 

pays for the effort spent on inspections, but also provides 

additional cost savings on the project. By removing defects at their origin (e.g., requirements and design documents, test plans and procedures, software code, etc.), 

inspections prevent defects from propagating through 

multiple phases and work products, and reduce the 

overall amount of rework necessary on projects. In addition, improved team efficiency is a side effect of peer reviews/inspections (e.g., by improving team communication, more quickly bringing new members up to speed, 

and educating project members about effective development practices).

How to Perform Technical Peer 

Reviews/Inspections 

Figure N-1 shows a diagram of the peer review/inspection stages, and the text below the figure explains how to 

perform each of the stages. (Figure N-2, at the end of the 

Third Hour

 = Process Stage

= Person

= Stage Transition

= Form

Overview

Modera Meeting tor

Planning

Author

= Optional Stage

Moderator

Moderator

Author

Rework

Author

Follow-Up

Moderator

Author

Author

Others

Inspectors

Preparation

Moderator

Inspectors

Inspection

Meeting 

Moderator

Author

Reader

Recorder

Inspectors

Inspectors

Inspection

Announcement

Individual

Preparation

Logs

Detailed

Inspection

Report

Inspection

Summary

Report

Inspection

Defect

List

Figure N-1 The peer review/inspection process
Appendix N: Guidance on Technical Peer Reviews/Inspections

NASA Systems Engineering Handbook  313

appendix, summarizes the information as a quick reference guide.)

It is recommended that the moderator review the Planning Inspection Schedule and Estimating Staff Hours, 

Guidelines for Successful Inspections, and 10 Basic 

Rules of Inspections in Figure N-2 before beginning the 

planning stage. (Note: NPR 7150.2, NASA Software Engineering Requirements defines Agency requirements on 

the use of peer reviews and inspections for software development. NASA peer review/inspection training is offered by the NASA Office of the Chief Engineer.)

A. Planning

The moderator of the peer review/inspection performs 

the following activities.1

1. Determine whether peer review/inspection entrance 

criteria have been met.

2. Determine whether an overview of the product is 

needed.

3. Select the peer review/inspection team and assign 

roles. For guidance on roles, see Roles of Participants 

in Figure N-2 at the end of this appendix. Reviewers 

have a vested interest in the work product (e.g., they 

are peers representing areas of the life cycle affected 

by the material being reviewed).

4. Determine if the size of the product is within the 

prescribed guidelines for the type of inspection. (See 

Meeting Rate Guidelines in Figure N-2 for guidelines on the optimal number of pages or lines of 

code to inspect for each type of inspection.) If the 

product exceeds the prescribed guidelines, break the 

product into parts and inspect each part separately. 

(It is highly recommended that the peer review/inspection meeting not exceed 2 hours.)

5. Schedule the overview (if one is needed).

1

Langley Research Center, Instructional Handbook for 

Formal Inspections. This document provides more detailed instructions on how to perform technical peer reviews/inspections. It also provides templates for the forms used in the peer 

review/inspection process described above: inspection announcement, individual preparation log, inspection defect 

list, detailed inspection report, and the inspection summary 

report.

6. Schedule peer review/inspection meeting time and 

place.

7. Prepare and distribute the inspection announcement 

and package. Include in the package the product to 

be reviewed and the appropriate checklist for the 

peer review/inspection.

8. Record total time spent in planning.*

B. Overview Meeting

1. Moderator runs the meeting, and the author presents background information to the reviewers. 

2. Record total time spent in the overview.* 

C. Peer Review/Inspection Preparation

1. Peers review the checklist definitions of defects.

2. Examine materials for understanding and possible 

defects.

3. Prepare for assigned role in peer review/inspection.

4. Complete and turn in individual preparation log to 

the moderator.

5. The moderator reviews the individual preparation 

logs and makes Go or No-Go decision and organizes 

inspection meeting.

6. Record total time spent in the preparation.* 

D. Peer Review/Inspection Meeting

1. The moderator introduces people and identifies 

their peer review/inspection roles. 

2. The reader presents work products to the peer review/

inspection team in a logical and orderly manner.

3. Peer reviewers/inspectors find and classify defects 

by severity, category, and type. (See Classification of 

Defects in Figure N-2.)

4. The recorder writes the major and minor defects on 

the inspection defect list (for definitions of major 

and minor, see the Severity section of Figure N.2).

5. Steps 1 through 4 are repeated until the review of the 

product is completed.

6. Open issues are assigned to peer reviewers/inspectors if irresolvable discrepancies occur.

7. Summarize the number of defects and their classification on the detailed inspection report. 

8. Determine the need for a reinspection or third hour. 

Optional: Trivial defects (e.g., redlined documents) 

can be given directly to the author at the end of the 

inspection.

Note: Where activities have an *, the moderator records the time on the inspection summary report.
314  NASA Systems Engineering Handbook

Appendix N: Guidance on Technical Peer Reviews/Inspections

9. The moderator obtains an estimate for rework time 

and completion date from the author, and does the 

same for action items if appropriate.

10. The moderator assigns writing of change requests 

and/or problem reports (if needed).

11. Record total time spent in the peer review/inspection meeting.* 

E. Third Hour

1. Complete assigned action items and provide information to the author. 

2. Attend third hour meeting at author’s request.

3. Provide time spent in third-hour to the moderator.*

F. Rework

1. All major defects noted in the inspection defect list 

are resolved by the author.

2. Minor and trivial defects (which would not result in 

faulty execution) are resolved at the discretion of the 

author as time and cost permit. 

3. Record total time spent in the rework on the inspection defect list.

G. Followup

1. The moderator verifies all major defects have been 

corrected and no secondary defects have been introduced.

2. The moderator ensures all open issues are resolved 

and verifies all success criteria for the peer review/

inspection are met.

3. Record total time spent in rework and followup.*

4. File the inspection package.

5. The inspection summary report is distributed.

6. Communicate that the peer review/inspection has 

been passed.
Appendix N: Guidance on Technical Peer Reviews/Inspections

NASA Systems Engineering Handbook  315

Classification of Defects

Severity

Major

• An error that would cause a malfunction or

prevents attainment of an expected or specified

result. 

• Any error that would in the future result in an 

approved change request or failure report.

Minor

• A violation of standards, guidelines, or rules

that would not result in a deviation from

requirements if not corrected, but could result in

difficulties in terms of operations, maintenance,

or future development .

Trivial

• Editorial errors such as spelling, punctuation, and

grammar that do not cause errors or change

requests. Recorded only as redlines. Presented

directly to author.

Author is required to correct all major defects 

and should correct minor and trivial defects as

time and cost permit.

Category

• Missing • Wrong • Extra

Type

Types of defects are derived from headings on

checklist used for the inspection. Defect types can

be standardized across inspections from all phases 

of the life cycle. A suggested standard set of defect

types are:

• Clarity

• Completeness

• Compliance

• Consistency

• Correctness/

Logic

• Data Usage

• Fault Tolerance 

• Functionality

• Interface

• Level of Detail

• Maintainability

• Performance

• Reliability

• Testability

• Traceability

• Other

EXAMPLE

The following is an example of a defect classification

that would be recorded on the Inspection Defect List:

Description Classification

Type

Minor Defect Wrong

Open Issue Extra

Major Defect X Missing

X 

Data Usage

Origin

Line 169 – While counting

the number of leading 

spaces in variable NAME, 

the wrong “I” is used to

calculate “J.”

Roles of Participants

Moderator

Responsible for conducting inspection process and

collecting inspection data. Plays key role in all stages

of process except rework. Required to perform special

duties during an inspection in addition to inspector’s

tasks.

Inspectors

Responsible for finding defects in work product from

a general point of view, as well as defects that

affect their area of expertise.

Author

Provides information about work product during all 

stages of process. Responsible for correcting all 

major defects and any minor and trivial defects that 

cost and schedule permit. Performs duties of an

inspector.

Reader

Guides team through work product during inspection

meeting. Reads or paraphrases work product in 

detail. Should be an inspector from same (or next) 

life-cycle phase as author. Performs duties of an 

inspector in addition to reader’s role. 

Recorder

Accurately records each defect found during

inspection meeting on the Inspection Defect List. 

Performs duties of an inspector in addition to

recorder’s role. 

Guidelines for Successful Inspections

• Train moderators, inspectors, and managers

• No more than 25% of developers’ time should be

devoted to inspections

• Inspect 100% of work product

• Be prepared

• Share responsibility for work product quality

• Be willing to associate and communicate

• Avoid judgmental language

• Do not evaluate author

• Have at least one positive and negative input

• Raise issues; don’t resolve them

• Avoid discussions of style

• Stick to standard or change it

• Be technically competent

• Record all issues in public

• Stick to technical issues

• Distribute inspection documents as soon as possible

• Let author determine when work product is ready

for inspection

• Keep accurate statistics

Based on JCK/LLW/SSP/HS: 10/92

10 Basic Rules of Inspections

• Inspections are carried out at a number of points 

inside phases of the life cycle. Inspections are not 

substitutes for milestone reviews. 

• Inspections are carried out by peers representing 

areas of life cycle affected by material being 

inspected (usually limited to 6 or fewer people). 

All inspectors should have a vested interest in the

work product.

• Management is not present during inspections. 

Inspections are not to be used as a tool to evaluate 

workers.

• Inspections are led by a trained moderator.

• Trained inspectors are assigned roles. 

• Inspections are carried out in a prescribed series of 

steps. 

• Inspection meeting is limited to 2 hours. 

• Checklists of questions are used to define task and 

to stimulate defect finding.

• Material is covered during inspection meeting within 

an optional page rate, which has been found to give 

maximum error-finding ability. 

• Statistics on number of defects, types of defects, and 

time expended by engineers on inspections are kept.

Peer Reviews/Inspections

QUICK REFERENCE

GUIDE

1. 1-day minimum

2. 5-day minimum, when included

3. 3- to 5-day minimum for inspectors to fit preparation time into normal 

work schedule

4. 3- to 5-day minimum for inspectors to fit preparation time into normal

work schedule

5. 4 hour minimum prior to inspection meeting 

6. Immediate: Rework can begin as soon as inspection meeting ends 

7. 1 day recommended 

8. Minimum possible time 

9. 1-week maximum from end of Inspection meeting 

10. 2-week maximum

1

PLANNING PREPARATION REWORK FOLLOW-UP

Planning Inspection Schedule* 

and Estimating Staff Hours

THIRD HOUR

(Use on approx. 

17% of total 

inspections.)

2 5

8

9

10

 TRANSITION TIMES** 

staff hours 

= 1 to 3 

hours 

OVERVIEW

MEETING

INSPECTION 

MEETING

staff hours

= 5 to 20

 hours

3

6

 ** Entire inspection process should be completed from start to finish within a 3-week period.

staff hours

= 0.5 hour 

x # inspectors

(Author)

 * Historically, complete inspections have averaged 30.5 total staff hours for 5-person teams.

(Use on approx. 6% 

of total inspections.) (All inspectors) (All inspectors)

SYMBOLS

= TIME REFERENCE

= STAGE TRANSITION

 = PROCESS STAGE

= OPTIONAL STAGE

(Author & 

Moderator)

staff hours 

= 1 hour x 

# inspectors 

staff hours 

= 2 hours x 

# inspectors

(Author & 

Moderator)

staff hours 

= 2 hours 

x # inspectors

 staff hours 

= 1 to 3

hours 

Meeting Length

• Overview* 0.5 to 1hrs

• Inspection 2 hrs Max.

• Third Hour 1 to 2 hrs

*Author Preparation for Overview:

3 to 4 hrs over 3 to 5 working days

+ author

 prep time

7

4 Types of Inspections

SY1 System Requirements

SY2 System Design

SU1 Subsystem Requirements

SU2 Subsystem Design

R1 Software Requirements

I0 Architectural Design

I1 Detailed Design

I2 Source Code

IT1 Test Plan

IT2 Test Procedures & Functions

Meeting* Rate Guidelines

for Various Inspection Types

Inspection Meeting

Target per 2 Hrs Range per 2 Hrs

20 pages 10 to 30 pages

20 pages 10 to 30 pages

30 pages 20 to 40 pages

35 pages 25 to 45 Pages

500 lines of

source code**

400 to 600 lines

of source code**

30 pages 20 to 40 pages

35 pages 25 to 45 pages

* Assumes a 2-hour meeting. Scale down planned

meeting duration for shorter work products.

** Flight software and other highly complex code

segments should proceed at about half this rate.

Type

R 0

R1

I0

I1

I2

IT1

IT2

Figure N-2 Peer reviews/inspections quick reference guide
316  NASA Systems Engineering Handbook

Appendix O: Tradeoff Examples

Table O-1 Typical Tradeoffs for Space Systems

Development Related Operations and Support Related

z Custom versus commercial-off-the-shelf

z Light parts (expensive) versus heavy parts (less expensive)

z On-board versus remote processing

z Radio frequency versus optical links

z Levels of margin versus cost/risk

z Class S versus non-class S parts

z Radiation-hardened versus standard components

z Levels of redundancy

z Degrees of quality assurance

z Built-in test versus remote diagnostics

z Types of environmental exposure prior to operation

z Level of test (system versus subsystem)

z Various life-cycle approaches (e.g., waterfall versus spiral 

versus incremental)

z Upgrade versus new start

z Manned versus unmanned

z Autonomous versus remotely controlled

z System of systems versus stand-alone system

z One long-life unit versus many short-life units

z Low Earth orbit versus medium Earth orbit versus geostationary orbit versus high Earth orbit

z Single satellite versus constellation

z Launch vehicle type (e.g., Atlas versus Titan)

z Single stage versus multistage launch

z Repair in-situ versus bring down to ground

z Commercial versus Government assets

z Limited versus public access

z Controlled versus uncontrolled reentry

Table O-2 Typical Tradeoffs in the Acquisition Process

Acquisition Phase Trade Study Purpose

Mission needs analysis Prioritize identified user needs

Concept exploration (concept and technology development)1. Compare new technology with proven concepts

2. Select concepts best meeting mission needs

3. Select alternative system configurations

4. Focus on feasibility and affordability

Demonstration/validation 1. Select technology

2. Reduce alternative configurations to a testable number

Full-scale development (system development and demonstration1. Select component/part designs

2. Select test methods

3. Select operational test and evaluation quantities

Production 1. Examine effectiveness of all proposed design changes

2. Perform make/buy, process, rate, and location decisions

Table O-3 Typical Tradeoffs Throughout the Project Life Cycle

Pre-Phase A Phase A Phase B Phases C&D Phases D&E Phases E&F

z Problem selection

z Upgrade versus 

new start

z On-board 

versus ground 

processing

z Low Earth orbit 

versus geostationary orbit

z Levels of 

redundancy

z Radio frequency 

links versus 

optical links

z Single source 

versus multiple 

suppliers

z Level of testing

z Platform STS-28 

versus STS-3a

z Launch goahead (Go or 

No-Go)

z Adjust orbit 

daily versus 

weekly

z Deorbit now 

versus later
NASA Systems Engineering Handbook  317

Appendix P: SOW Review Checklist

Editorial Checklist

1. Is the SOW requirement in the form “who” shall “do what”? An example is, “The Contractor shall (perform, provide, develop, test, analyze, or other verb followed by a description of what).”

 Example SOW requirements:

z The Contractor shall design the XYZ flight software...

z The Contractor shall operate the ABC ground system...

z The Contractor shall provide maintenance on the following...

z The Contractor shall report software metrics monthly ...

z The Contractor shall integrate the PQR instrument with the spacecraft...

2. Is the SOW requirement a simple sentence that contains only one requirement? 

Compound sentences that contain more than one SOW requirement need to be split into multiple simple sentences. (For example, “The Contractor shall do ABC and perform XYZ” should be rewritten as “The Contractor 

shall do ABC” and “The Contractor shall perform XYZ.”)

3. Is the SOW composed of simple, cohesive paragraphs, each covering a single topic? Paragraphs containing many 

requirements should be divided into subparagraphs for clarity.

4. Has each paragraph and subparagraph been given a unique number or letter identifier? Is the numbering or lettering correct? 

5. Is the SOW requirement in the active rather than the passive voice? Passive voice leads to vague statements. (For 

example, state, “The Contractor shall hold monthly management review meetings” instead of “Management review 

meeting shall be held monthly.”)

6. Is the SOW requirement stated positively as opposed to negatively? (Replace statements such as, “The Contractor 

shall not exceed the budgetary limits specified” with “The contractor shall comply with the budgetary limits specified.”)

7. Is the SOW requirement grammatically correct?

8. Is the SOW requirement free of typos, misspellings, and punctuation errors?

9. Have all acronyms been defined in an acronym list or spelled out in the first occurrence?

10. Have the quantities, delivery schedules, and delivery method been identified for each deliverable within the SOW 

or in a separate attachment/section?

11. Has the content of documents to be delivered been defined in a separate attachment/section and submitted with 

the SOW?

12. Has the file format of each electronic deliverable been defined (e.g., Microsoft—Project, Adobe—Acrobat PDF, National Instruments—Labview VIs)?

Content Checklist

1. Are correct terms used to define the requirements?

z Shall = requirement (binds the contractor)

z Should = goal (leaves decision to contractor; avoid using this word)

z May = allowable action (leaves decision to contractor; avoid using this word)
318  NASA Systems Engineering Handbook

Appendix P: SOW Review Checklist

z Will = facts or declaration of intent by the Government (use only in referring to the Government)

z Present tense (e.g., “is”) = descriptive text only (avoid using in requirements statements; use “shall” instead)

z NEVER use ”must”

2. Is the scope of the SOW clearly defined? Is it clear what you are buying?

3. Is the flow and organizational structure of the document logical and understandable? (See LPR 5000.2 “Procurement Initiator’s Guide,” Section 12, for helpful hints.) Is the text compatible with the title of the section it’s under? 

Are subheadings compatible with the subject matter of headings? 

4. Is the SOW requirement clear and understandable?

z Can the sentence be understood only one way? 

z Will all terminology used have the same meaning to different readers without definition? Has any terminology 

for which this is not the case been defined in the SOW? (E.g., in a definitions section or glossary.)

z Is it free from indefinite pronouns (“this,” “that,” “these,” “those”) without clear antecedents (e.g., replace statements such as, “These shall be inspected on an annual basis” with “The fan blades shall be inspected on an annual basis”)?

z Is it stated concisely?

5. Have all redundant requirements been removed? Redundant requirements can reduce clarity, increase ambiguity, 

and lead to contradictions.

6. Is the requirement consistent with other requirements in the SOW, without contradicting itself, without using the 

same terminology with different meanings, without using different terminology for the same thing?

7. If the SOW includes the delivery of a product (as opposed to just a services SOW): 

z Are the technical product requirements in a separate section or attachment, apart from the activities that the 

contractor is required to perform? The intent is to clearly delineate between the technical product requirements 

and requirements for activities the contractor is to perform (e.g., separate SOW statements “The contractor 

shall” from technical product requirement statements such as “The system shall” and “The software shall”).

z Are references to the product and its subelements in the SOW at the level described in the technical product requirements? 

z Is the SOW consistent with and does it use the same terminology as the technical product requirements? 

8. Is the SOW requirement free of ambiguities? Make sure the SOW requirement is free of vague terms (for example, 

“as appropriate,” “any,” “either,” “etc.,” “and/or,” “support,” “necessary,” “but not limited to,” “be capable of,” “be able 

to”).

9. Is the SOW requirement verifiable? Make sure the SOW requirement is free of unverifiable terms (for example, 

“flexible,” “easy,” “sufficient,” “safe,” “ad hoc,” “adequate,” “accommodate,” “user-friendly,” “usable,” “when required,” 

“if required,” “appropriate,” “fast,” “portable,” “lightweight,” “small,” “large,” “maximize,” “minimize,” “optimize,” 

“sufficient,” “robust,” “quickly,” “easily,” “clearly,” other “ly” words, other “ize” words).

10. Is the SOW requirement free of implementation constraints? SOW requirements should state WHAT the contractor is to do, NOT HOW they are to do it (for example, “The Contractor shall design the XYZ flight software” 

states WHAT the contractor is to do, while “The Contractor shall design the XYZ software using object-oriented 

design” states HOW the contractor is to implement the activity of designing the software. In addition, too low a 

level of decomposition of activities can result in specifying how the activities are to be done, rather than what activities are to be done).

11. Is the SOW requirement stated in such a way that compliance with the requirement is verifiable? Do the means 

exist to measure or otherwise assess its accomplishment? Can a method for verifying compliance with the requirement be defined (e.g., described in a quality assurance surveillance plan)?

12. Is the background material clearly labeled as such (i.e., included in the background section of the SOW if one is 

used)?
Appendix P: SOW Review Checklist

NASA Systems Engineering Handbook  319

13. Are any assumptions able to be validated and restated as requirements? If not, the assumptions should be deleted 

from the SOW. Assumptions should be recorded in a document separate from the SOW.

14. Is the SOW complete, covering all of the work the contractor is to do?

z Are all of the activities necessary to develop the product included (e.g., system, software, and hardware activities for the following: requirements, architecture, and design development; implementation and manufacturing; 

verification and validation; integration testing and qualification testing.)?

z Are all safety, reliability, maintainability (e.g., mean time to restore), availability, quality assurance, and security 

requirements defined for the total life of the contract? 

z Does the SOW include a requirement for the contractor to have a quality system (e.g., ISO certified), if one is 

needed?

z Are all of the necessary management and support requirements included in the SOW (for example, project 

management; configuration management; systems engineering; system integration and test; risk management; 

interface definition and management; metrics collection, reporting, analysis, and use; acceptance testing; NASA 

Independent Verification and Validation (IV&V) support tasks.)?

z Are clear performance standards included and sufficient to measure contractor performance (e.g., systems, software, hardware, and service performance standards for schedule, progress, size, stability, cost, resources, and 

defects)? See Langley’s Guidance on System and Software Metrics for Performance-Based Contracting for more 

information and examples on performance standards.

z Are all of the necessary service activities included (for example, transition to operations, operations, maintenance, database administration, system administration, and data management)?

z Are all of the Government surveillance activities included (for example, project management meetings; decision 

points; requirements and design peer reviews for systems, software, and hardware; demonstrations; test readiness reviews; other desired meetings (e.g., technical interchange meetings); collection and delivery of metrics for 

systems, software, hardware, and services (to provide visibility into development progress and cost); electronic 

access to technical and management data; and access to subcontractors and other team members for the purposes of communication)?

z Are the Government requirements for contractor inspection and testing addressed, if necessary? 

z Are the requirements for contractor support of Government acceptance activities addressed, if necessary?

15. Does the SOW only include contractor requirements? It should not include Government requirements.

16. Does the SOW give contractors full management responsibility and hold them accountable for the end result?

17. Is the SOW sufficiently detailed to permit a realistic estimate of cost, labor, and other resources required to accomplish each activity?

18. Are all deliverables identified (e.g., status, financial, product deliverables)? The following are examples of deliverables that are sometimes overlooked: management and development plans; technical progress reports that identify 

current work status, problems and proposed corrective actions, and planned work; financial reports that identify 

costs (planned, actual, projected) by category (e.g., software, hardware, quality assurance); products (e.g., source 

code, maintenance/user manual, test equipment); and discrepancy data (e.g., defect reports, anomalies). All deliverables should be specified in a separate document except for technical deliverables (e.g., hardware, software, prototypes), which should be included in the SOW.

19. Does each technical and management deliverable track to a paragraph in the SOW? Each deliverable should have 

a corresponding SOW requirement for its preparation (i.e., the SOW identifies the title of the deliverable in parentheses after the task requiring the generation of the deliverable).

20. Are all reference citations complete?

z Are the complete number, title, and date or version of each reference specified?

z Does the SOW reference the standards and other compliance documents in the proper SOW paragraphs? 
320  NASA Systems Engineering Handbook

Appendix P: SOW Review Checklist

z Is the correct reference document cited and is it referenced at least once?

z Is the reference document either furnished with the SOW or available at a location identified in the SOW?

z If the referenced standard or compliance document is only partially applicable, does the SOW explicitly and unambiguously reference the portion that is required of the contractor?
NASA Systems Engineering Handbook  321

Appendix Q: Project Protection Plan Outline

The following outline will assist systems engineers in preparing a project protection 

plan. The plan is a living document that will be written and updated as the project progresses through major milestones and ultimately through end of life.

1. Introduction

1.1 Protection Plan Overview

1.2 Project Overview

1.3 Acquisition Status

2. References

2.1 Directives and Instructions

2.2 Requirements

2.3 Studies and Analyses

3. References

3.1 Threats: Hostile Action

 3.1.1 Overview

 3.1.2 Threat Characterization

 3.1.2.1 Cyber Attack

 3.1.2.2 Electronic Attack

 3.1.2.3 Lasers

 3.1.2.4 Ground Attack

 3.1.2.5 Asymmetric Attack on Critical Commercial Infrastructure

 3.1.2.6 Anti-Satellite Weapons

 3.1.2.7 High-Energy Radio Frequency Weapons

 3.1.2.8 Artificially Enhanced Radiation Environment

3.2 Threats: Environmental

3.2.1 Overview

 3.2.2 Threat Characterization

 3.2.2.1 Natural Environment Storms

 3.2.2.2 Earthquakes

 3.2.2.3 Floods

 3.2.2.4 Fires

 3.2.2.5 Radiation Effects in the Natural Environment

 3.2.2.6 Radiation Effects to Spacecraft Electronics

4. Protection Vulnerabilities

4.1 Ground Segment Vulnerabilities

4.1.1 Command and Control Facilities

 4.1.2 Remote Tracking Stations

 4.1.3 Spacecraft Simulator(s)

 4.1.4 Mission Data Processing Facilities

 4.1.5 Flight Dynamic Facilities

 4.1.6 Flight Software Production/Verification/Validation Facilities
322  NASA Systems Engineering Handbook

Appendix Q: Project Protection Plan Outline

4.2 Communications/Information Segment Vulnerabilities

 4.2.1 Command Link

 4.2.2 Telemetry Link (Mission Data)

 4.2.3 Telemetry Link (Engineering Data)

 4.2.4 Ground Network

4.3 Space Segment Vulnerabilities

 4.3.1 Spacecraft Physical Characteristics

 4.3.2 Spacecraft Operational Characteristics

 4.3.3 Orbital Parameters

 4.3.4 Optical Devices (Sensors/Transmitters/Receivers)

 4.3.5 Communications Subsystem

 4.3.6 Command and Data Handling Subsystem

 4.3.7 Instruments

4.4 Launch Segment Vulnerabilities

 4.4.1 Launch Parameters

 4.4.2 Launch Site Integration and Test Activities

4.5 Commercial Infrastructure Vulnerabilities

 4.5.1 Electrical Power

 4.5.2 Natural Gas

 4.5.3 Telecommunications

 4.5.4 Transportation

5. Protection Countermeasures

5.1 Protection Strategy

5.2 Mission Threat Mitigation

5.3 Mission Restoration Options

5.4 Mission Survivability Characteristics

6. Debris Mitigation

6.1 Design Guidelines

6.2 End-Of-Life Mitigation Procedures

6.3 Collision Avoidance

7. Critical Program Information and Technologies

7.1 Critical Program Information Elements

7.2 Critical Information Program

8. Program Protection Costs

8.1 System Trade Analyses

8.2 Cost/Benefit Analyses
NASA Systems Engineering Handbook  323

References

This appendix contains references that were cited in the 

sections of the handbook and sources for developing the 

material in the indicated sections. See the Bibliography 

for complete citations.

Section 2.0 Fundamentals of Systems 

Engineering

Griffin, Michael D., “System Engineering and the Two 

Cultures of Engineering.” 2007.

Rechtin, Eberhardt. Systems Architecting of Organizations: Why Eagles Can’t Swim. 2000. 

Section 3.4 Project Phase A: Concept and 

Technology Development

NASA. NASA Safety Standard 1740.14, Guidelines and 

Assessment Procedures for Limiting Orbital Debris. 1995. 

Section 4.1 Stakeholder Expectations 

Definition

ANSI. Guide for the Preparation of Operational Concept 

Documents. 1992.

Section 4.2 Technical Requirements Definition

NASA. NASA Space Flight Human System Standard. 2007.

Section 4.3 Logical Decomposition

Institute of Electrical and Electronics Engineers. Standard Glossary of Software Engineering Terminology.

1999.

Section 4.4 Design Solution

Blanchard, Benjamin S. System Engineering Management. 2006.

DOD. MIL-STD-1472, Human Engineering. 2003.

Federal Aviation Administration. Human Factors Design 

Standard. 2003.

International Organization for Standardization. Quality 

Systems Aerospace—Model for Quality Assurance in Design, Development, Production, Installation, and Servicing. 1999.

NASA. NASA Space Flight Human System Standard. 2007.

NASA. Planning, Developing, and Maintaining and Effective Reliability and Maintainability (R&M) Program. 

1998. 

U. S. Army Research Laboratory. MIL HDBK 727, Design 

Guidance for Producibility. 1990.

U.S. Nuclear Regulatory Commission. Human-System 

Interface Design Review Guidelines. 2002.

Section 5.1 Product Implementation

American Institute of Aeronautics and Astronautics. 

AIAA Guide for Managing the Use of Commercial Off the 

Shelf (COTS) Software Components for Mission-Critical 

Systems. 2006.

International Council on Systems Engineering. Systems 

Engineering Handbook. 2006.

NASA. Off-the-Shelf Hardware Utilization in Flight Hardware Development. 2004.

Section 5.3 Verification

Electronic Industries Alliance. Processes for Engineering 

a System. 1999.

Institute of Electrical and Electronics Engineers. Standard for Application and Management of the Systems Engineering Process. 1998.

International Organization for Standardization. Systems 

Engineering—System Life Cycle Processes. 2002. 

NASA. Project Management: Systems Engineering & 

Project Control Processes and Requirements. 2004.

U.S. Air Force. SMC Systems Engineering Primer and 

Handbook. 2005. 

Section 5.4 Validation

Electronic Industries Alliance. Processes for Engineering 

a System. 1999.

Institute of Electrical and Electronics Engineers. Standard for Application and Management of the Systems Engineering Process. 1998.
324  NASA Systems Engineering Handbook

References

International Organization for Standardization. Systems 

Engineering—System Life Cycle Processes. 2002.

NASA. Project Management: Systems Engineering & 

Project Control Processes and Requirements. 2004.

U.S. Air Force. SMC Systems Engineering Primer and 

Handbook. 2005.

Section 5.5 Product Transition

DOD. Defense Acquisition Guidebook. 2004.

Electronic Industries Alliance. Processes for Engineering 

a System. 1999. 

International Council on Systems Engineering. Systems 

Engineering Handbook. 2006.

International Organization for Standardization. Systems 

Engineering—A Guide for the Application of ISO/IEC 

15288. 2003.

—. Systems Engineering—System Life Cycle Processes. 2002.

Naval Air Systems Command. Systems Command SE 

Guide: 2003. 2003. 

Section 6.1 Technical Planning

American Institute of Aeronautics and Astronautics. 

AIAA Guide for Managing the Use of Commercial 

Off the Shelf (COTS) Software Components for Mission-Critical Systems. 2006.

Institute of Electrical and Electronics Engineers. Standard for Application and Management of the Systems Engineering Process. 1998.

Martin, James N. Systems Engineering Guidebook: A Process for Developing Systems and Products. 1996.

NASA. NASA Cost Estimating Handbook. 2004.

—. Standard for Models and Simulations. 2006.

Section 6.4 Technical Risk Management

Clemen, R., and T. Reilly. Making Hard Decisions with 

DecisionTools Suite. 2002.

Dezfuli, H. “Role of System Safety in Risk-Informed Decisionmaking.” 2005.

Kaplan, S., and B. John Garrick. “On the Quantitative 

Definition of Risk.” 1981.

Morgan, M. Granger, and M. Henrion. Uncertainty: A 

Guide to Dealing with Uncertainty in Quantitative Risk 

and Policy Analysis. 1990.

Stamelatos, M., H. Dezfuli, and G. Apostolakis. “A Proposed Risk-Informed Decisionmaking Framework for 

NASA.” 2006.

Stern, Paul C., and Harvey V. Fineberg, eds. Understanding Risk: Informing Decisions in a Democratic Society. 1996. 

U.S. Nuclear Regulatory Commission. White Paper on 

Risk-Informed and Performance-Based Regulation. 1998.

Section 6.5 Configuration Management

American Society of Mechanical Engineers. Engineering 

Drawing Practices. 2004.

—. Types and Applications of Engineering Drawings. 

1999.

DOD. Defense Logistics Agency (DLA) Cataloging Handbook.

—. MIL-HDBK-965, Parts Control Program. 1996.

—. MIL-STD-881B, Work Breakdown Structure 

(WBS) for Defense Materiel Items. 1993.

DOD, U.S. General Services Administration, and NASA. 

Acquisition of Commercial Items. 2007.

—. Quality Assurance, Nonconforming Supplies or 

Services. 2007.

Institute of Electrical and Electronics Engineers. EIA 

Guide for Information Technology Software Life Cycle 

Processes—Life Cycle Data. 1997.

—. IEEE Guide to Software Configuration Management. 1987.

—. Standard for Software Configuration Management Plans. 1998.

International Organization for Standardization. Information Technology—Software Life Cycle Processes Configuration Management. 1998.

—. Quality Management—Guidelines for Configuration 

Management. 1995.

NASA.NOAA-N Prime Mishap Investigation Final Report. 

2004.

National Defense Industrial Association. Data Management. 2004.

—. National Consensus Standard for Configuration 

Management. 1998.
References

NASA Systems Engineering Handbook  325

Section 6.6 Technical Data Management

National Defense Industrial Association. Data Management. 2004.

—. National Consensus Standard for Configuration 

Management. 1998.

Section 6.8 Decision Analysis

Blanchard, Benjamin S. System Engineering Management. 2006.

Blanchard, Benjamin S., and Wolter Fabrycky. Systems 

Engineering and Analysis. 2006.

Clemen, R., and T. Reilly. Making Hard Decisions with 

DecisionTools Suite. 2002.

Keeney, Ralph L. Value-Focused Thinking: A Path to Creative Decisionmaking. 1992.

Keeney, Ralph L., and Timothy L. McDaniels. “A Framework to Guide Thinking and Analysis Regarding Climate Change Policies.” 2001.

Keeney, Ralph L., and Howard Raiffa. Decisions with Multiple Objectives: Preferences and Value Tradeoffs. 1993.

Morgan, M. Granger, and M. Henrion. Uncertainty: A 

Guide to Dealing with Uncertainty in Quantitative Risk 

and Policy Analysis. 1990.

Saaty,Thomas L. The Analytic Hierarchy Process. 1980.

Section 7.1 Engineering with Contracts

Adams, R. J., S. Eslinger, P. Hantos, K. L. Owens, et al. 

Software Development Standard for Space Systems. 2005.

DOD, U.S. General Services Administration, and NASA. 

Contracting Office Responsibilities. 2007.

Eslinger, Suellen. Software Acquisition Best Practices for 

the Early Acquisition Phases. 2004.

Hofmann, Hubert F., Kathryn M. Dodson, Gowri S. Ramani, and Deborah K. Yedlin. Adapting CMMI® for Acquisition Organizations: A Preliminary Report. 2006.

International Council on Systems Engineering. Systems 

Engineering Handbook: A “What To” Guide for all SE 

Practitioners. 2004.

The Mitre Corporation. Common Risks and Risk Mitigation Actions for a COTS-Based System. 

NASA. Final Memorandum on NASA’s Acquisition Approach Regarding Requirements for Certain Software Engineering Tools to Support NASA Programs. 2006.

—. The SEB Source Evaluation Process. 2001.

—. Solicitation to Contract Award. 2007.

—. Standard for Models and Simulations. 2006.

—. Statement of Work Checklist. 

—. System and Software Metrics for PerformanceBased Contracting.

Naval Air Systems Command. Systems Engineering 

Guide. 2003.

Section 7.2 Integrated Design Facilities

Miao, Y., and J. M. Haake. “Supporting Concurrent Design by Integrating Information Sharing and Activity 

Synchronization.” 1998.

Section 7.4 Human Factors Engineering

Blanchard, Benjamin S., and Wolter Fabrycky. Systems 

Engineering and Analysis. 2006.

Chapanis, A. “The Error-Provocative Situation: A Central Measurement Problem in Human Factors Engineering.” 1980.

DOD. Human Engineering Procedures Guide. 1987.

—. MIL-HDBK-46855A, Human Engineering Program Process and Procedures. 1996.

Eggemeier, F. T., and G. F. Wilson. “Performance and 

Subjective Measures of Workload in Multitask Environments.” 1991.

Endsley, M. R., and M. D. Rogers. “Situation Awareness 

Information Requirements Analysis for En Route Air 

Traffic Control.” 1994.

Fuld, R. B. “The Fiction of Function Allocation.” 1993. 

Glass, J. T., V. Zaloom, and D. Gates. “A Micro-Computer-Aided Link Analysis Tool.” 1991.

Gopher, D., and E. Donchin. “Workload: An Examination of the Concept.” 1986.

Hart, S. G., and C. D. Wickens. “Workload Assessment 

and Prediction.” 1990.

Huey, B. M., and C. D. Wickens, eds. Workload Transition. 1993.

Jones, E. R., R. T. Hennessy, and S. Deutsch, eds. Human 

Factors Aspects of Simulation. 1985.

Kirwin, B., and L. K. Ainsworth. A Guide to Task Analysis. 1992.
326  NASA Systems Engineering Handbook

References

Kurke, M. I. “Operational Sequence Diagrams in System 

Design.” 1961. 

Meister, David. Behavioral Analysis and Measurement 

Methods. 1985.

—. Human Factors: Theory and Practice. 1971.

Price, H. E. “The Allocation of Functions in Systems.” 

1985.

Shafer, J. B. “Practical Workload Assessment in the Development Process.” 1987.

Section 7.6 Use of Metric System

DOD. DoD Guide for Identification and Development of 

Metric Standards. 2003.

Taylor, Barry. Guide for the Use of the International System 

of Units (SI). 2007. 

Appendix F: Functional, Timing, and State 

Analysis

Buede, Dennis. The Engineering Design of Systems: 

Models and Methods. 2000.

Defense Acquisition University. Systems Engineering 

Fundamentals Guide. 2001.

Long, Jim. Relationships Between Common Graphical 

Representations in Systems Engineering. 2002.

NASA. Training Manual for Elements of Interface Definition and Control. 1997.

Sage, Andrew, and William Rouse. The Handbook of Systems Engineering and Management. 1999.

Appendix H: Integration Plan Outline

Federal Highway Administration and CalTrans. Systems 

Engineering Guidebook for ITS. 2007.

Appendix J: SEMP Content Outline

DOD. MIL-HDBK-881, Work Breakdown Structures for 

Defense Materiel Systems. 2005.

DOD Systems Management College. Systems Engineering 

Fundamentals. 2001.

Martin, James N. Systems Engineering Guidebook: A Process for Developing Systems and Products. 1996.

NASA. NASA Cost Estimating Handbook. 2004.

The Project Management Institute®. Practice Standards 

for Work Breakdown Structures. 2001.
NASA Systems Engineering Handbook  327

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—. NASA-STD-3001, NASA Space Flight Human 

System Standard Volume 1: Crew Health. Washington, 

DC, 2007.

—. NASA-STD-(I)-7009, Standard for Models and 

Simulations. Washington, DC, 2006.

—. NASA-STD-8719.13, Software Safety Standard, 

NASA Technical Standard, Rev B. Washington, DC, 2004.

—. NASA-STD-8729.1, Planning, Developing, and 

Maintaining and Effective Reliability and Maintainability 

(R&M) Program. Washington, DC, 1998.

—. NOAA N-Prime Mishap Investigation Final Report. 

Washington, DC, 2004.

—. NPD 2820.1, NASA Software Policy. Washington, 

DC, 2005.

—. NPD 8010.2, Use of the SI (Metric) System of Measurement in NASA Programs. Washington, DC, 2007.

—. NPD 8010.3, Notification of Intent to Decommission or Terminate Operating Space Systems and Terminate 

Missions. Washington, DC, 2004.

—. NPD 8020.7, Biological Contamination Control 

for Outbound and Inbound Planetary Spacecraft. Washington, DC, 1999.

—. NPD 8070.6, Technical Standards. Washington, 

DC, 2003.

—. NPD 8730.5, NASA Quality Assurance Program 

Policy. Washington, DC, 2005.

—. NPR 1441.1, NASA Records Retention Schedules.

Washington, DC, 2003.

—. NPR 1600.1, NASA Security Program Procedural 

Requirements. Washington, DC, 2004.

—. NPR 2810.1, Security of Information Technology.

Washington, DC, 2006.

—. NPR 7120.5, NASA Space Flight Program and 

Project Management Processes and Requirements. Washington, DC, 2007.

—. NPR 7120.6, Lessons Learned Process. Washington, DC, 2007.

—. NPR 7123.1, Systems Engineering Processes and 

Requirements. Washington, DC, 2007.

—. NPR 7150.2, NASA Software Engineering Requirements. Washington, DC, 2004.

—. NPR 8000.4, Risk Management Procedural Requirements. Washington, DC, NASA Office of Safety and 

Mission Assurance, 2007.

—. NPR 8020.12, Planetary Protection Provisions for 

Robotic Extraterrestrial Missions. Washington, DC, 2004.

—. NPR 8580.1, Implementing The National Environmental Policy Act and Executive Order 12114. Washington, DC, 2001.

—. NPR 8705.2, Human-Rating Requirements for 

Space Systems. Washington, DC, 2005.

—. NPR 8705.3, Probabilistic Risk Assessment Procedures Guide for NASA Managers and Practitioners. 

Washington, DC, 2002.
330  NASA Systems Engineering Handbook

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332  NASA Systems Engineering Handbook

Index

acceptance verification, 91

acknowledgment of receipt of system, 82

acquisition, product, 129, 175, 217–227, 316

action-information analysis for HF, 250–251

activity-on-arrow diagram, 115, 116

actual cost of work performed (ACWP), 190

advancement degree of difficulty assessment (AD2), 293

agreements, 120, 125, 172

(see also contracting)

AHP (analytic hierarchy process), 211–212

allocated baseline, CI, 152, 153

analogous cost models, 128

analysis validation type, 100

analysis verification type, 86

analytic hierarchy process (AHP), 211–212

anomaly resolution and maintenance operations, 39

approval phase, 19, 20, 21

(see also formulation)

architecture

IT, 243

modeling of, 49–51

system, 56

and technology assessment, 296

as-deployed baseline, CI, 153

assembly, product, 78, 79–82

(see also Phase D)

assessments

(see also performance; reviews)

TA, 62, 293–298

technical, 5, 61, 166–170, 190–196, 222

workload assessment for HF, 68

audits, 91, 154, 157, 168, 189

authority

CM, 152, 154

decision analysis, 199

and KDPs, 19

mission, 34

requirements management, 134, 135

stakeholder, 35

and standards, 48

technical assessments, 168–170

and technical planning, 120, 122

BAC (budget at completion), 191

backward compatibility of engineering tools, 244

baselines

configuration identification, 152–153

design solution, 61

and life cycle phases, 24

requirements, 134

system design processes, 32

BCWP (budgeted cost of work performed), 190

BCWS (budgeted cost of work scheduled), 122, 190

beta curve in cost estimate, 129

bidirectional traceability of requirements, 132

bounding approaches to quantification of risk, 147

budget at completion (BAC), 191

budget considerations in technical planning, 117, 118

budget cycle, 29–30

budgeted cost of work performed (BCWP), 190

budgeted cost of work scheduled (BCWS), 122, 190

CAMs (cost account managers), 121, 190

capability for accelerated concurrent engineering (CACE), 

234–241

CCB (configuration control board), 133, 154, 155

CDR (Critical Design Review), 25, 77, 178

CE (concurrent engineering), 234–241

CERR (Critical Event Readiness Review), 186

certification, model, 104

Chandra project, 193–194

CIs (configuration items), 152

classified national security information (CNSI), 162–163

closeout, project (see Phase F)

CM (configuration management) (see configuration management (CM))

CMO (configuration management organization), 152, 155

CM topic evaluators list, 133

CNSI (classified national security information), 162–163

coding/making end products, 73–74

collaboration design paradigm, 234–241, 242–243

Columbia disaster investigation, 156–157

Committee on Space Research (COSPAR), 260

compatibility analysis and product integration, 81

concept development (see Phase A)

concept of operations (ConOps) (see ConOps (concept of operations))

concept studies (Pre-Phase A), 7, 8, 22

concurrent engineering (CE), 234–241

configuration audits, 189

configuration change management, 154

configuration control board (CCB), 133, 154, 155

configuration inspection (PCA), 189

configuration items (CIs), 152

configuration management (CM)

and contracting, 222

and data management, 161

identification, 152–153

planning, 152, 311

and requirements changes, 133–134
Index

NASA Systems Engineering Handbook  333

in technical management process, 111, 122, 151–157

configuration management organization (CMO), 152, 155

configuration status accounting (CSA), 154

configuration verification, 91, 155–156

ConOps (concept of operations)

HF participation in, 247

in product realization, 88

in requirements definition, 41, 42–43

SE role of, 9–13, 15

in stakeholder expectations definition, 35–37

in system design processes, 35–36, 37–38, 41

constraints in system design processes, 35, 41

context diagrams, 44, 291

contingency planning, technical, 114

continuous risk management (CRM), 142–143, 227

contracting

acquisition strategy, 217–219

completion, 230–233

introduction, 217

performance, 227–230

planning and preparation, 219–227

contractor off-the-shelf (COTS) products, 226, 227

contractors, working with, 159, 217

contract specialist, 219

contract WBS (CWBS), 123

controlled experimentation and HF analysis, 254

COSPAR (Committee on Space Research), 260

cost account managers (CAMs), 121, 190

cost account plans, 121–122

cost aspects of SE

cost-effectiveness, 16–17, 21, 44, 58, 209–210

estimates, 119, 126, 127, 128–129, 226

system architecture, 50

technical assessment, 190–191

technical planning, 115, 117, 118–119, 121, 125, 126–129

validation, 100

verification, 89

cost-benefit analysis, 209–210

cost cap, 118–119

cost performance index (CPI), 191

cost risk, 139, 144

COTS (contractor off-the-shelf) products, 226, 227

CPI (cost performance index), 191

criteria

(see also reviews)

acceptance for contracted deliverables, 230

decision, 199–201

and design solution definition, 57

MCDA, 211–212

performance, 41

proposal evaluation, 227

success, 31, 34, 35, 57–59

Critical Design Review (CDR), 25, 77, 178

Critical Event Readiness Review (CERR), 186

critical incident study, HF, 250

critical path sequence, 115

CRM (continuous risk management), 142–143, 227

crosscutting processes, 111

(see also technical management processes)

CSA (configuration status accounting), 154

cumulative average curve approach, 129

customers in system design processes, 33–34

(see also stakeholders)

CWBS (contract WBS), 123

data, definition, 160

data call, 160

data capture requirements, 47, 48, 159

data formats and interoperability, 243

data management (DM), 122, 158–165, 222

DCR (Design Certification Review), 188

debris, space, limitation of, 29

decision analysis

and contracting, 222

and product validation, 102

and product verification, 87

risk-informed, 142, 143–148

in system design processes, 31

in technical management processes, 197–215

decision networks, 210

decision trees, 210–211

decommissioning, 28, 233

Decommissioning Review (DR), 187

defense article, and ITAR, 165

demonstration validation type, 100

demonstration verification type, 86

deployment

as-deployed baseline, 153

in launch operations, 39

verification of, 91–92

design

(see also Phase B; system design processes)

CDR, 25, 77, 178

collaboration paradigm for, 234–241, 242–243

integrated facilities for, 234–241

in life cycle phases, 22, 24–25, 26

process metrics for, 196

and qualification verification, 91

realization processes for, 71, 73–82

solution definition for, 31, 55–69, 81, 234–241

tool selection, 242–245

and verification vs. validation, 83

Design Certification Review (DCR), 188

design drivers, 34, 35

design-to-life-cycle cost, 127–128

deterministic safety requirements, 45

development phase and ILS, 65

(see also Phase D)

discrepancies, product, and verification, 88

disposal process, 28, 39, 92, 187, 233

DM (data management), 122, 158–165, 222

DR (Decommissioning Review), 187

EAC (estimate at completion), 191

earned value management (EVM), 121–122, 190, 196
334  NASA Systems Engineering Handbook

Index

Echo balloons, 17

EFFBDs (enhanced functional flow block diagrams), 285

effectiveness vs. cost for SE, 16

efficient solutions, 16

EMO (Environmental Management Office), 256, 257

emulators and interface verification, 82

enabling products, 60–61, 79, 102

end of mission (EOM), planetary protection report, 259–260

end-to-end system testing, 93–96

engineering (see systems engineering (SE))

engineering (grassroots) cost models, 128

enhanced functional flow block diagrams (EFFBDs), 285

entrance criteria (see reviews)

environmental compliance and restoration (ECR), 195

environmental considerations

and HF, 247

NEPA compliance, 256–267

planetary protection policy, 258–260

and product realization, 76, 87, 102, 109

radioactive materials management, 257–258

and technical requirements, 41, 44–45

Environmental Management Office (EMO), 256, 257

EO (executive order) 12114, 257

EOM (end of mission), planetary protection report, 259–260

estimate at completion (EAC), 191

estimates, cost, 119, 126, 127, 128–129, 226

evaluation

(see also assessments; validation; verification)

and contracting, 226, 227, 234

decision analysis methods and tools, 200–201

human factors engineering, 68, 247–255

overview, 71

PERT chart, 115

safety, 257

T&E, 100

event sequence diagrams/event trees, 63

EVM (earned value management), 121–122, 190, 196

executive order (EO) 12114, 257

exploration projects, 36

extensibility attributes in decision analysis, 212

fabrication (see Phase C)

facilities, integrated design, 234–241

FAD (formulation authorization document), 19, 125

failure modes and effects, and criticality analyses (FMECAs), 146

failure modes and effects analyses (FMEAs), 63–64, 146, 252–

253

fault trees, 146, 252

FCA (functional configuration audit), 189

fixed-cost profile, 118–119

flexibility attributes in decision analysis, 212

Flight Readiness Review (FRR), 25, 184

Flight Systems and Ground Support (FS&GS), 19

FMEAs (failure modes and effects analyses), 63–64, 146, 252–

253

FMECAs (failure modes and effects, and criticality analyses), 146

formulation

activities of, 19, 21, 125

life cycle role of, 20

overview, 7, 8

and system architecture, 50

formulation authorization document (FAD), 19, 125

FRR (Flight Readiness Review), 25, 184

FS&GS (Flight Systems and Ground Support), 19

functional allocation, HF, 251

functional analysis

FFBDs, 52–54, 285–288

requirements allocation sheets, 286–287, 289

system architecture, 49–51

and trade study process, 205–206

functional baseline, CI, 152, 153

functional configuration audit (FCA), 189

functional flow analysis, HF, 250

functional flow block diagram (FFBD), 52–54, 285–288

functional needs requirements, 41–44

funding issues

BAC, 191

BCWS, 122, 190

budget cycle, 29–30

in technical planning, 117, 118

Gantt chart, 117, 118

geostationary (GEO) satellites, 29

goal setting in system design processes, 35

Government mandatory inspection points (GMIPs), 65

grassroots cost estimates, 128

hardware-in-the-loop (HWIL) testing, 96–97, 115

hazard analysis, 64

hazard vs. risk, 139

heritage products, 76–77, 89

human error, 68

human factors (HF) engineering, 45, 67–69, 246–255

human reliability analysis, 64, 68

human spaceflight projects, 36, 45, 176

HWIL (hardware-in-the-loop) testing, 96–97, 115

ICD (interface control document/drawing), 81, 137–138

ICP (interface control plan), 138

IDD (interface definition document), 138

identification, configuration, 152–153

ILS (integrated logistics support), 65, 66

implementation

activities of, 21

and integration, 80

life cycle role, 20

overview, 7, 8

product, 73–77, 80

and transition, 108

influence diagrams, 210

information, data definition, 160

information infrastructure for CACE, 238–239

information technology (IT) architectures, 243

in-orbit checkout in launch operations, 39

in-process testing, 91
Index

NASA Systems Engineering Handbook  335

inspections

configuration, 189

GMIPs, 65

and product integration, 82

of purchased products, 74–75

inspection validation type, 100

inspection verification type, 86

INSRP (Interagency Nuclear Safety Review Panel ), 257

integrated design facilities, 234–241

integrated logistics support (ILS), 65, 66

integration

(see also Phase D)

components of, 39

and design solution, 81, 234–241

and interface management, 137

plan outline, 299–300

product, 78–82

and SEMP content outline, 303–307

SIR, 180

Interagency Nuclear Safety Review Panel (INSRP), 257

interface control document/drawing (ICD), 81, 137–138

interface control plan (ICP), 138

interface definition document (IDD), 138

interface requirements document (IRD), 81, 137

interfaces

defining, 82

and end-to-end testing, 94

and HF, 246–255

information, 243

management of, 54, 81–82, 111, 136–138, 221

N2 diagrams, 52, 54, 288, 289–290

and product integration, 79, 80–81

requirements, 41, 44, 81, 137, 309–310

verification, 82

interface working group (IWG), 136–137

internal task agreement (ITA), 120

international environmental considerations, 257

International Traffic in Arms Regulations (ITAR), 164–165

interoperability and engineering tool selection, 243

IRD (interface requirements document), 81

ITA (Internal Task Agreement), 120

ITAR (International Traffic in Arms Regulations), 164–165

iterative processes, 5–15

IT (information technology) architectures, 243

IWG (interface working group), 136–137

Jet Propulsion Laboratory (JPL), 258

Kennedy Space Center (KSC), 258

key decision points (KDPs), 19, 20, 21, 111, 168

launch, product, 39

(see also Phase D)

launch vehicle databook, 257–258

layers, definition, 8

LCCE (life-cycle cost estimate), 119

learning curve concept and cost estimates, 129

least-cost analysis, 209

LEO (low Earth orbiting) missions, 29

lessons learned in technical planning, 129–130

levels, definition, 8

license schemes for engineering tools, 244

life cycle

(see also phases)

acquisition, 218

budget cycle, 29–30

CACE, 234

CM role in, 155

cost considerations, 126–129

decision analysis, 197

environmental considerations, 256

functional analysis in, 285

HF in, 248

overview, 6, 7

phase overview, 19–29

planetary protection considerations, 258–259

planning and status reporting feedback loop, 167

product realization, 71–72, 78–79, 80, 89–90, 103, 106, 108

systems analysis, 203–205

technical planning, 112–113

technology assessment, 293–295

tradeoffs during, 316

WBS, 124–125

life-cycle cost estimate (LCCE), 119

link analysis and HF, 253

logical decomposition, 31, 49–54, 120

loosely coupled programs, 169

low Earth orbiting (LEO) missions, 29

maintainability, product/design, 65, 66, 110

making/coding end products, 73–74, 75

margin risk management method, 149–150, 194

maturity, system, 6, 56–58, 62

MAUT (multi-attribute utility theory), 213

MCDA (multi-criteria decision analysis), 211–212

MCR (Mission Concept Review), 173

MDAA (mission directorate associate administrator), 21

MDR (Mission Definition Review), 175

measures and measurement methods, defining, 205

measures of effectiveness (MOEs), 120, 191–192, 193

measures of performance (MOPs), 120, 192, 193

memorandum of understanding (MOU), 120

metric system usage, 261–262

milestone reviews, 170

mission

in life cycle phases, 22, 28

and stakeholder expectations, 34

mission assurance, 225

mission authority, 34

Mission Concept Review (MCR), 173

Mission Definition Review (MDR), 175

mission directorate associate administrator (MDAA), 21

mitigation of risk, 148, 149

modeling

of architecture, 49–51
336  NASA Systems Engineering Handbook

Index

certification, 104

cost, 128, 129

HF, 68

logic, 64

scenario-based hazard, 141

simulations, 68, 96, 104, 204–205, 253–254

validation, 104

verification, 96–97

modeling and simulation (M&S), 96–97, 103

MOEs (measures of effectiveness), 120, 191–192, 193

MOPs (measures of performance), 120, 192, 193

MOU (memorandum of understanding), 120

M&S (modeling and simulation), 96–97, 103

multi-attribute utility theory (MAUT), 213

multi-criteria decision analysis (MCDA), 211–212

N2 diagrams (N x N interaction matrix), 52, 54, 288, 289–290

NASA, contracting responsibilities, 232

National Environmental Policy Act (NEPA), 256–257

National Space Policy (2006), 260

network infrastructure for CACE, 239

network scheduling systems, 115–117

NOAA N-Prime mishap, 157

nominal testing, 101

nondominated solutions, 16

nuclear materials management, 257–258

objectives, mission, 34

objectives hierarchy, 213, 214–215

Office of General Counsel (OGC), 257

off-nominal testing, 101

off-the-shelf (OTS) products, 76–77

Operational Readiness Review (ORR), 153, 183

operations

(see also Phase E)

analysis of, 249, 254, 285–286

objectives for, 34, 35

phases of, 39, 65, 232

and requirements, 43

verification of, 92

ORR (Operational Readiness Review), 153, 183

OTS (off-the-shelf) products, 76–77

outcome variables in trade studies, 205, 207–208

Outer Space Treaty, 258

parallelism in design integration, 234

parametric cost models, 128, 129

payload classification and verification, 89

PBS (product breakdown structure) (see product breakdown 

structure (PBS))

PCA (physical configuration audit), 189

PCA (program commitment agreement ), 125, 172

PDR (Preliminary Design Review), 25, 77, 177

peer reviews, 59–60, 87, 170–171, 189–190, 312–315

performance

(see also evaluation; technical performance measures 

(TPMs))

assessment of contractor, 232, 233

HF evaluation of, 255

requirements for, 41–42, 43, 133, 152, 153, 224, 227

periodical technical reviews (PTRs), 166

(see also reviews)

PERT (program evaluation and review technique) chart, 115

PFAR (Post Flight Assessment Review), 186

PHA (preliminary hazard analysis), 64

Phase A

activities of, 22, 23

life cycle role of, 19, 20

overview, 7, 8–9

Phase B

activities of, 24

life cycle role of, 19, 20

overview, 7, 8, 14–15

Phase C

activities of, 25, 26

life cycle role of, 19, 20

overview, 6, 7, 8, 14–15

Phase D

activities of, 25, 27, 65

life cycle role of, 19, 20

overview, 6, 7, 8, 14–15

Phase E

activities of, 28

life cycle role of, 19, 20

overview, 6, 7, 8, 14

Phase F

activities of, 28–29

life cycle role of, 19, 20

overview, 6, 7, 8, 14

phases

(see also formulation; implementation; Phase C; Phase D; 

Phase E; Phase F)

A, 7, 8–9, 19, 20, 22, 23

B, 7, 8, 14–15, 19, 20, 24

life cycle role of, 20

overview and example, 6–15

Pre-Phase A, 7, 8, 22

physical configuration audit (PCA), 189

PKI (public key infrastructure), 163

planetary protection officer (PPO), 258

planetary protection policy, 258–260

planning, programming, budgeting, and execution (PPBE), 

29

PLAR (Post Launch Assessment Review), 185

PMC (Program Management Council), 168

PM (program manager), 19

policy compliance issues, 242, 256–260

Post Flight Assessment Review (PFAR), 186

Post Launch Assessment Review (PLAR), 185

PPBE (planning, programming, budgeting, and execution), 

29

PPO (planetary protection officer), 258

PQASP (program/project quality assurance surveillance 

plant), 65

PRA (probabilistic risk assessment), 139, 146

precedence diagrams, 115–116
Index

NASA Systems Engineering Handbook  337

pre-launch verification stage, 91–92

preliminary design (see Phase B)

Preliminary Design Review (PDR), 25, 77, 177

preliminary hazard analysis (PHA), 64

Pre-Phase A, 7, 8, 22

probabilistic risk assessment (PRA), 139, 146

probabilistic structural analysis, 64

process metrics, 195–196

procurement process and contracts, 217

producibility and system design, 66–67

product baseline, CI, 153

product breakdown structure (PBS)

logical decomposition, 52

in systems design processes, 40

in technology assessment, 294, 295

and WBS, 123, 124, 125, 126

Production Readiness Review (PRR), 179

productivity-related process metrics, 195

product management and contracts, 219

product realization processes

acquisition, 129, 175, 217–227, 316

example, 12–14

implementation, 73–77, 80

integration, 78–82

overview, 5, 71–72

transition, 71, 106–110

validation, 98–105

verification, 83–97

products, systems analysis of, 203–205

program commitment agreement (PCA), 125, 172

program evaluation and review technique (PERT) chart, 115

Program Management Council (PMC), 168

program manager (PM), 19

programmatic risk, 139, 144

program/project quality assurance surveillance plant (PQASP), 

65

programs, 4, 169–170

(see also life cycle; phases)

Program/System Definition Review (P/SDR), 170, 172

Program/Systems Requirements Review (P/SRR), 170, 171

project protection plan, 260, 321–322

projects, 4, 119, 169–170

(see also life cycle; phases)

proposal, contract solicitation, 226, 227

PRR (Production Readiness Review), 179

P/SDR (Program/System Definition Review), 170, 172

P/SRR (Program/Systems Requirements Review), 170, 171

PTRs (periodical technical reviews), 166

(see also reviews)

public key infrastructure (PKI), 163

purchasing end products, 73, 74–75, 76

qualification verification, 91

qualitative logic models, 64

quality assurance (QA), 64–65, 90, 229, 230

quality-related process metrics, 195

quantitative logic models, 64

radioactive materials management, 257–258

R&D (research and development), 107

realization processes (see product realization processes)

recursive processes, 5–15

redline drawings and CM, 157

reengineering and validation discrepancies, 103

reengineering and verification discrepancies, 88

reliability

human, 64, 68

requirements for, 43, 44–45

in system design process, 63–65

reliability block diagrams, 64

reports

decision analysis, 201–203

EOM, 259–260

life cycle feedback loop, 167

risk management, 150

SARs, 257

and SEMP, 120

SER, 257

in technical assessment, 167, 190, 195–106

technical planning types, 117

trade study, 208

TRAR, 293, 295

validation, 102–103

verification, 93

request for information (RFI), 218

request for proposal (RFP), 159

requirements

allocation of, 45–46, 47

composition guidance, 279–281

and contracts, 218, 221, 223–225, 229

data capture, 47, 48, 159

decomposition of, 45–46

definition processes, 5, 31, 40–48, 246–247

and design solution, 59

engineering tools, 242

and HF, 68

and integration, 79

interface, 41, 44, 81, 137, 309–310

management of, 131–135, 166

obsolescence of, 93

OTS products, 77

performance, 41–42, 43, 133, 152, 153, 224, 227

process metrics for, 196

product transition, 108, 110

and resource leveling, 117

system, 24, 174

and system design processes, 32, 33

traceability of, 132

validation of, 46, 132–133, 280–281, 284

verification of, 47, 48, 282–283

requirements allocation sheets, 286–287, 289

requirements “creep,” 134

research and development (R&D), 107

resource leveling, 117

reusing end products, 73–74, 75, 89
338  NASA Systems Engineering Handbook

Index

reviews

CDR, 25, 77, 178

CERR, 186

configuration audits, 189

and configuration verification, 91

DCR, 188

DR, 187

FRR, 25, 184

heritage, 76–77

internal, 170–171

life cycle overview, 20, 21, 23, 24, 25, 26–27, 28

MCR, 173

MDR, 175

ORR, 153, 183

PDR, 25, 77, 177

peer reviews, 59–60, 87, 170–171, 189–190, 312–315

PFAR, 186

PLAR, 185

pre-verification, 87

process metrics for, 196

PRR, 179

P/SDR, 170, 172

P/SRR, 170, 171

PTRs, 166

QA for product verification, 90

SAR, 91, 182

SDR, 176

SIR, 180

SRR, 174

technical assessment role of, 167–170

TRR, 92, 181

RFI (request for information), 218

RFP (request for proposal), 159

risk-informed decision analysis, 213–214

risk-informed safety requirements, 45

risk matrices, 145–146

risk metrics, 146

risk/risk management

and CM, 151

and contracting, 221, 227, 228

and cost-effectiveness, 17

definition, 139

and design alternatives, 58

levels of, 145–146

process of, 139–150

and requirements changes, 133

sources of, 145

and system design process, 63–65

and technical assessment, 166

types of risk, 139, 144

and verification, 89

robotic missions, 175

safe-hold operations, 39

safety, 41, 43, 45, 63–64, 110

safety analysis reports (SARs), 257

safety and mission assurance (SMA) organization, 225

safety evaluation report (SER), 257

SARs (safety analysis reports), 257

SAR (System Acceptance Review), 91, 182

satellites, disposal of, 29

SBU (sensitive but unclassified) information, handling of, 

162–164

scenario-based modeling of hazards, 141

schedule performance index (SPI), 191

schedule-related process metrics, 195–196

schedule risk, 139, 144

scheduling, 17, 50, 89, 115–117, 190–191

science projects, 35–37, 39, 46–47

SDR (System Definition Review), 176

security

data, 162–165, 244

space asset protection, 260

SE engine, 5, 6–15, 59

selection rule, defining, 206

SEMP (system engineering management plan)

content outline, 303–307

and contracting process, 219, 225

product realization role, 74, 85, 111, 113, 119–120, 122, 

208

and TPM assessment, 193–194

sensitive but unclassified (SBU) information, handling of, 

162–164

SER (safety evaluation report), 257

service contracts, 232

SE (systems engineering) (see systems engineering (SE))

shall statements in technical requirements definition, 40, 41

similar systems analysis, HF, 249

simulations, 68, 96, 104, 204–205, 253–254

single-project programs, 169, 170

SIR (System Integration Review), 180

SI (System Internationale) (metric system), 261

situational awareness and HF, 255

SMA (safety and mission assurance) organization, 225

software

CACE tools, 239

in contingency planning, 114

data management, 161–162

security of, 165

verification and validation, 104–105

solicitation of contract, 219, 222–227

source evaluation board, 226

SOW (statement of work), 223, 224–225, 232, 317–320

space asset protection, 260

space situational awareness (SSA), 260

space systems tradeoffs, 316

space transportation system (STS), 8–15

sparing/logistics models, 64

specialty engineering, 62–63

specialty requirements, 42, 43

specifications, design, 61

SRB (standing review board), 168, 170

SRR (System Requirements Review), 174

SSA (space situational awareness), 260

stakeholders
Index

NASA Systems Engineering Handbook  339

CACE process, 234, 235–236, 240

and CCB, 154

and CM, 151

commitment to technical plan, 120–121

expectations definition, 31, 33–39

and HF, 67, 247

identifying, 33–34

importance of ongoing communication, 40

and MOEs, 192

and requirements management, 131

and SAR, 182

and validation, 98, 99, 100, 103

standards, 47, 48, 224, 240, 243

standing review board (SRB), 168, 170

state diagrams, 290–291

statement of work (SOW), 223, 224–225, 232, 317–320

state transition diagrams, 290, 291

status accounting, configuration, 154

status reporting in technical assessment, 167, 190, 195–196

STS (space transportation system), 8–15

subcontractors, working with, 229, 231

subsystem elements, verification of, 82

success criteria, 34, 35, 57–59

surveillance of contractor operations, 225, 227

sustainment (see Phase E)

system, definition, 3

System Acceptance Review (SAR), 91, 182

System Definition Review (SDR), 176

system design processes

design solution, 31, 55–69, 81, 234–241

example, 8–12

and HF, 68

and interface management, 54

logical decomposition, 31, 49–54, 120

overview, 4, 5, 6, 31–32

requirements definition, 5, 31, 40–48, 246–247

stakeholder expectations definition, 31, 33–39

System Integration Review (SIR), 180

System Internationale (SI) (metric system), 261

system-of-systems, 51

System Requirements Review (SRR), 174

systems, verification of elements, 82

systems analysis, 203–205

systems engineer

CACE role of, 237

and QA, 64–65

responsibilities of, 3–4

systems engineering (SE)

definition, 3

fundamentals of, 3–17

overview, 1

process metrics, 195–196

and project/program life cycle, 19

SE engine, 5, 6–15, 59

specialty integration into, 62–63

task analysis for HF, 68, 251–252

task order contracts, 225

TA (technology assessment), 62, 293–298

teams, mission development

and CACE process, 234, 235–236, 240–241

contract development role, 218–219, 223, 225

contractor evaluation role, 234

and decision solution definition, 57

HF specialists on, 246

importance of technical management processes, 111

inspection of purchased products, 74–75

requirements validation role, 133

risk management role, 63, 143

surveillance of contractor operations, 227, 228–229

trade study leadership, 208

technical assessment process, 5, 62, 166–170, 190–196, 222

(see also reviews)

technical data package, 160

technical management processes

(see also configuration management (CM); decision analysis; reviews; risk/risk management)

assessment, 5, 62, 166–196, 222

and contracts, 218–219, 220–222

data management, 122, 158–165, 222

interface management, 54, 81–82, 111, 136–138, 221

overview, 5–6, 111

planning, 112–130

requirements management, 131–135, 166

technical performance measures (TPMs)

objectives hierarchy, 214–215

purpose of, 192–195

quantification of, 147

and risk management, 139, 148–149

and safety requirements, 45

utility and value functions of, 213

technical processes overview, 4–6

(see also product realization processes; system design processes; technical management processes)

technical readiness level (TRL) scale, 293, 295, 296–298

technical requirements definition, 31, 40–48

(see also requirements)

technical risk, 139, 144

technical solution definition processes

design solution definition, 31, 55–69, 81, 234–241

and HF, 68

logical decomposition, 31, 49–54, 120

overview, 5

technical work directives and planning, 121

technology assessment (TA), 62, 293–298

technology development, 56, 62

(see also Phase A; Phase B)

technology infusion assessment, 293–298

technology maturity assessment (TMA), 293, 294, 297

technology readiness assessment report (TRAR), 293, 295

termination review, 169

test and evaluation (T&E), 100

testing

(see also Phase D)
340  NASA Systems Engineering Handbook

Index

components of, 39

integration, 81

post-transition to end user, 109

in product realization processes, 72

validation, 98

verification, 83, 85, 91–92, 93–97, 98

testing verification type, 86

Test Readiness Review (TRR), 92, 181

test validation type, 100

T&E (test and evaluation), 100

tiers, definition, 8

tightly coupled programs, 170

timeline analyses (TLAs), 52, 54

timelines, operation, 37–38, 68

timeline sheets (TLSs), 54

timing analysis, 290–291

TLAs (timeline analyses), 52, 54

TLSs (timeline sheets), 54

TMA (technology maturity assessment), 293, 294, 297

TPM (technical performance measures) (see technical performance measures (TPMs))

traceability of requirements, 132

tradeoffs, summary of types, 316

trade study process, 57, 59, 128, 142–143, 205–209

training and engineering tool selection, 244

transition process, 71, 106–110, 231–233

transportability requirements, 110

TRAR (technology readiness assessment report), 293, 295

triggering data and functional flow analysis, 285

TRL (technical readiness level) scale, 293, 295, 296–298

TRR (test readiness review), 92, 181

uncertainty, 64, 147

(see also risk/risk management)

uncoupled programs, 169

unit curve approach, 129

United States Munitions List (USML), 164

usability evaluation and design, 68

utility analysis, 212–213

VAC (variance at completion), 191

validation

(see also testing)

design solution, 60, 62

and interface management, 137

in life cycle phases, 25

planning, 100, 284, 301–302

process metrics for, 196

product, 71, 72, 75, 98–105

of requirements, 46, 132–133, 280–281, 284

vs. verification, 15, 83, 88, 98

variance at completion (VAC), 191

variances, control of project, 190–191

vendor stability and engineering tool selection, 245

verification

(see also inspections; testing)

configuration, 91, 155–156

design solution, 59–60

and HF, 68

of interfaces, 82, 137

in life cycle phases, 25

planning, 84–86

process metrics for, 196

product, 71, 72, 75, 82, 83–97

program guidance, 89

of requirements, 47, 48, 282–283

sample plan outline, 301–302

software tools, 104–105

and system design processes, 32

vs. validation, 15, 83, 88, 98

waivers, 154

weighted cost-effectiveness analysis, 210

work breakdown structure (WBS)

and cost/schedule control measures, 190

and logical decomposition, 52

and technical measures, 194–195

in technical planning, 116–117, 122–125, 126

workflow diagrams, technical planning, 115

workload assessment for HF, 68, 255
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