NASA/TP-2014-218556

Human Integration Design 

Processes (HIDP)

Human Health and Performance

Directorate

National Aeronautics and Space Administration

International Space Station Program

Johnson Space Center

Houston, Texas

September 2014
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NASA/TP-2014-218556

Human Integration Design 

Processes (HIDP)

Human Health and Performance

Directorate

National Aeronautics and Space Administration

International Space Station Program

Johnson Space Center

Houston, Texas

September 2014
Available from:

NASA Center for AeroSpace Information National Technical Information Service

7121 Standard Drive 5285 Port Royal Road

Hanover, MD 21076-1320 Springfield, VA 22161

This report is also available in electronic form at http://ston.jsc.nasa.gov/collections/TRS
NASA/TP-2014-218556

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REVISION AND HISTORY

REV. DESCRIPTION PUB. 

DATE

- Initial Release 9/2014
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ii

ACKNOWLEDGMENTS

The following individuals comprised the team, subject matter experts, and authors who 

contributed to the HIDP. Their hard work on this document is very much appreciated

and clearly reflected in the high quality of the content.

Jurine Adolf

Abbe Barr

Janet Barzilla

Debbie Berdich

Jennifer Boyer

Jeff Beno

Paul Campbell

Johnny Conkin

Jonathan Dory

Grace Douglas

Scott England

Neta Ezer

Mike Ferrer

Yamil Garcia

Lauren Harvill

Kritina Holden

Keith Holubec

John Keller

Jane Krauhs

Kate Kubicek

Chip Litaker

Sarah Margerum

Kerry McGuire

Lauren Merkle

Deborah Neubek

Jason Norcross

Christopher Reid

Aniko Sandor

Susan Schuh

Ellen Snook

Jeff Somers

Gordon Vos

David Welsh
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iii

TABLE OF CONTENTS

PARAGRAPH PAGE

1.0 INTRODUCTION ...................................................................................................................................... 1-1

1.1 PURPOSE ................................................................................................................................................ 1-1

1.2 APPLICABILITY........................................................................................................................................ 1-1

1.3 HOW TO USE THE HIDP......................................................................................................................... 1-1

2.0 DOCUMENTS........................................................................................................................................... 2-1

2.1 APPLICABLE DOCUMENTS.................................................................................................................... 2-1

2.2 REFERENCE DOCUMENTS.................................................................................................................... 2-1

3.0 HUMAN SYSTEMS INTEGRATION PROCESS....................................................................................... 3-1

3.1 HUMAN SYSTEMS INTEGRATION (HSI)................................................................................................ 3-1

3.2 HUMAN-CENTERED DESIGN ................................................................................................................. 3-1

3.2.1 RATIONALE FOR HUMAN-CENTERED DESIGN ................................................................................... 3-1

3.2.2 PRINCIPLES OF HUMAN-CENTERED DESIGN..................................................................................... 3-2

3.2.3 HUMAN-CENTERED DESIGN ACTIVITIES............................................................................................. 3-3

3.3 ROLES AND RESPONSIBILITIES ........................................................................................................... 3-9

3.3.1 THE HUMAN-SYSTEMS INTEGRATION (HSI) TEAM............................................................................. 3-9

3.3.2 HSI TEAM BASIS IN NASA REQUIREMENTS ........................................................................................ 3-9

3.3.3 TECHNICAL SCOPE OF THE HSI TEAM.............................................................................................. 3-10

3.3.4 THE ROLE OF THE HSI TEAM.............................................................................................................. 3-10

3.3.5 HSI TEAM REVIEW OF DELIVERABLES.............................................................................................. 3-11

3.4 SUMMARY OF HIDP TECHNICAL PRODUCTS.................................................................................... 3-11

3.4.1 GENERIC TECHNICAL PRODUCTS ..................................................................................................... 3-11

3.4.2 DEFINITIONS OF GENERIC TECHNICAL PRODUCTS........................................................................ 3-12

4.0 HIDP PROCESSES.................................................................................................................................. 4-1

4.1 USER TASK ANALYSIS........................................................................................................................... 4-1

4.2 USABILITY EVALUATION........................................................................................................................ 4-7

4.3 WORKLOAD EVALUATION ................................................................................................................... 4-16

4.4 HUMAN ERROR ANALYSIS .................................................................................................................. 4-28

4.5 DESIGN FOR CREWMEMBER PHYSICAL CHARACTERISTICS AND CAPABILITIES....................... 4-30

4.5.1 INTRODUCTION .................................................................................................................................... 4-30

4.5.2 DESIGN FOR ANTHROPOMETRY........................................................................................................ 4-31

4.5.3 DESIGN FOR RANGE OF MOTION....................................................................................................... 4-50

4.5.4 DESIGN FOR STRENGTH..................................................................................................................... 4-61

4.5.5 DESIGN FOR MASS PROPERTIES, VOLUME, AND SURFACE AREA............................................... 4-72

4.5.6 BACKGROUND OF CHSIR REQUIREMENT VALUES.......................................................................... 4-82

4.5.7 DESIGN USING INTEGRATED APPROACH......................................................................................... 4-84

4.6 HANDLING QUALITIES EVALUATION.................................................................................................. 4-86

4.7 ACOUSTIC NOISE CONTROL DESIGN.............................................................................................. 4-104

4.8 RADIATION SHIELDING DESIGN ....................................................................................................... 4-114

4.9 FUNCTIONAL VOLUME DESIGN ........................................................................................................ 4-123

4.10 CREW SURVIVABILITY ASSESSMENT.............................................................................................. 4-146

4.11 METABOLIC LOADS AND ENVIRONMENTAL CONTROL LIFE SUPPORT SYSTEM DESIGN ........ 4-148
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4.12 DISPLAY FORMAT DESIGN................................................................................................................ 4-154

4.13 USER INTERFACE LABELING DESIGN ............................................................................................. 4-169

4.14 OCCUPANT PROTECTION DESIGN................................................................................................... 4-183

4.15 DESIGN FOR DECONDITIONED CREWMEMBER............................................................................. 4-198

4.16 DESIGN FOR MITIGATION OF DECOMPRESSION SICKNESS RISK............................................... 4-219

4.17 SPACE FOOD SYSTEM DESIGN........................................................................................................ 4-247

4.18 LEGIBILITY EVALUATION ................................................................................................................... 4-255

APPENDIX

A ACRONYMS AND DEFINITIONS........................................................................................................... A-1

B GLOSSARY............................................................................................................................................ B-1

C REFERENCE DOCUMENTS.................................................................................................................. C-1

D POTENTIAL FUTURE HIDP CHAPTERS .............................................................................................. D-1

TABLE

TABLE 3.2.3.1.2-1 EXAMPLE NOMINAL SCENARIO - TRAVEL TO ISS (NOTIONAL) ....................................... 3-6

TABLE 3.4.1-1 SUMMARY OF GENERIC TECHNICAL PRODUCTS................................................................. 3-12

TABLE 4.1.3-1 TASK ANALYSIS TECHNICAL PRODUCTS ................................................................................ 4-6

TABLE 4.2.7-1 USABILITY EVALUATION TECHNICAL PRODUCTS ................................................................ 4-14

TABLE 4.3.3-1 WORKLOAD EVALUATION TECHNICAL PRODUCTS.............................................................. 4-26

TABLE 4.5.2.7-1 ANTHROPOMETRY TECHNICAL PRODUCTS....................................................................... 4-46

TABLE 4.5.3.7-1 RANGE OF MOTION TECHNICAL PRODUCTS ..................................................................... 4-57

TABLE 4.5.4.7-1 STRENGTH TECHNICAL PRODUCTS.................................................................................... 4-68

TABLE 4.5.5.7-1 MASS PROPERTIES, VOLUME, AND SURFACE AREA TECHNICAL PRODUCTS.............. 4-78

TABLE 4.6.4-1 HANDLING QUALITIES EVALUATION TECHNICAL PRODUCTS........................................... 4-101

TABLE 4.7.4-1 ACOUSTIC NOISE CONTROL DESIGN TECHNICAL PRODUCTS......................................... 4-111

TABLE 4.8.3-1 RADIATION SHIELDING DESIGN TECHNICAL PRODUCTS.................................................. 4-118

TABLE 4.9.1.1-1 REFERENCE MATERIALS FOR FUNCTIONAL VOLUME DESIGN ..................................... 4-124

TABLE 4.9.3-1 UNIQUE SPACECRAFT ARCHITECTURAL DRIVERS............................................................ 4-132

TABLE 4.9.5-1 FUNCTIONAL VOLUME DESIGN TECHNICAL PRODUCTS................................................... 4-143

TABLE 4.10.3-1 CREW SURVIVABILITY TECHNICAL PRODUCTS................................................................ 4-147

TABLE 4.11.3-1 METABOLIC LOADS DESIGN TECHNICAL PRODUCTS...................................................... 4-152

TABLE 4.12.6-1 DISPLAY FORMAT DESIGN TECHNICAL PRODUCTS ........................................................ 4-166

TABLE 4.13.2.2.4-1 DDPF LABEL DRAWING DETAILS................................................................................... 4-179

TABLE 4.13.2.2.5-1 NASA-APPROVED LABELING MATERIALS.................................................................... 4-180

TABLE 4.13.3-1 USER INTERFACE LABELING DESIGN TECHNICAL PRODUCTS...................................... 4-181

TABLE 4.14.3-1 TECHNICAL PRODUCTS OF OCCUPANT PROTECTION DESIGN ..................................... 4-194

TABLE 4.15.7-1 OVERVIEW OF CREWMEMBER DECONDITIONING ............................................................ 4-212

TABLE 4.15.8-1 DECONDITIONING TECHNICAL PRODUCTS....................................................................... 4-214

TABLE 4.16.8-1 DCS MITIGATION TECHNICAL PRODUCTS......................................................................... 4-238

TABLE 4.17.6-1 SPACE FOOD SYSTEMS TECHNICAL PRODUCTS.............................................................. 4-253
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TABLE 4.18.3.2-1 EXAMPLE OF COMBINATIONS OF FACTORS TO TEST LEGIBILITY OF DISPLAY ELEMENTS

............................................................................................................................................... 4-259

TABLE 4.18.4-1 LEGIBILITY TECHNICAL PRODUCTS .................................................................................... 4-261

FIGURE

FIGURE 3.2.3-1 HUMAN-CENTERED DESIGN ACTIVITIES ............................................................................... 3-4

FIGURE 3.2.3.1.1-1 NOMINAL COMMERCIAL CREW TRANSPORT MISSION (ASSUMED FOR CHSIR) ........ 3-5

FIGURE 4.1.2.1.1-1 TASK ANALYSIS EXECUTION PROCESS .......................................................................... 4-5

FIGURE 4.3.2-1 THE BEDFORD SCALE............................................................................................................ 4-19

FIGURE 4.5.3.5.4-1 EXAMPLE OF SURFACE PENETRATION IN RAMSIS AS DEPENDENT ON SUBJECT 

ANTHROPOMETRY................................................................................................................. 4-53

FIGURE 4.6.1.3.2-1 COOPER-HARPER HANDLING QUALITIES RATING SCALE........................................... 4-89

FIGURE 4.6.3.6-1 PRIMARY COMPONENTS OF A HANDLING-QUALITIES TESTING SESSION................... 4-95

FIGURE 4.6.3.7-1 BOX-AND-WHISKER PLOTS OF THE ORBIT SCENARIO COOPER-HARPER RATINGS . 4-98

FIGURE 4.6.3.7-2 FREQUENCY SCATTER PLOTS OF THE ORBIT SCENARIO COOPER-HARPER RATINGS...

................................................................................................................................................. 4-99

FIGURE 4.6.3.7-3 HISTOGRAMS OF THE ORBIT SCENARIO COOPER-HARPER RATINGS ...................... 4-100

FIGURE 4.9.2.2.2-1 INITIAL CAD MODELING OF NHV ................................................................................... 4-128

FIGURE 4.9.2.2.2-2 HYPOTHETICAL CAD MODEL OF TASK VOLUME NEEDED BASED ON ANTHROPOMETRY 

AND RANGE OF MOTION REQUIREMENTS ....................................................................... 4-129

FIGURE 4.9.2.2.3.1-1 CAD MODELING AND LOW-FIDELITY MOCKUP EVALUATION................................. 4-130

FIGURE 4.9.4.1-1 CAD MODEL SIMULATING 4 CREWMEMBERS PERFORMING POST-INSERTION CABIN 

RECONFIGURATION TASKS................................................................................................ 4-135

FIGURE 4.9.4.1-2 DAC2 CAD MODEL SIMULATING 4 CREWMEMBERS PERFORMING THE VOLUME-DRIVING 

SUIT TASK OF DONNING AND DOFFING............................................................................ 4-136

FIGURE 4.9.4.2-1 MOCKUP EVALUATION FOR DRIVING TASKS................................................................. 4-139

FIGURE 4.9.4.2-2 MOCKUP EVALUATION FOR DYNAMIC TASKS ............................................................... 4-140

FIGURE 4.9.4.2-3 MOCKUP EVALUATION OF REDESIGNED CONFIGURATION......................................... 4-140

FIGURE 4.9.4.2-4 MEDIUM-FIDELITY MOCKUP EVALUATION...................................................................... 4-141

FIGURE 4.9.4.2-5 MEDIUM-FIDELITY MOCKUP ITERATION EVALUATION.................................................. 4-142

FIGURE 4.9.4.2-6 ENHANCED MEDIUM-FIDELITY MOCKUP ITERATION EVALUATION............................. 4-142

FIGURE 4.11.2.1-1 EXAMPLE OF MISSION TIMELINE WITH METABOLIC RATES ...................................... 4-149

FIGURE 4.11.2.1-2 EXAMPLE METABOLIC RATE PROFILE.......................................................................... 4-150

FIGURE 4.13.2.2.2.1-1 ISS HAZARDOUS TRASH IDENTIFICATION LABEL (SDG32105751)....................... 4-171

FIGURE 4.13.2.2.2.1-2 ISS CAUTION/WARNING PINCH POINTS LABEL (SDG32105057)........................... 4-171

FIGURE 4.13.2.2.2.1-3 ISS FIRE PORT LOCATION CODE (SDG32108589).................................................. 4-172

FIGURE 4.13.2.2.2.1-4 ISS PORTABLE FIRE EXTINGUISHER PANEL DOOR LABELS (SDG32107729)..... 4-172

FIGURE 4.13.2.2.2.1-5 ISS EMERGENCY DISCONNECT LABEL (SDG32106342)........................................ 4-172

FIGURE 4.13.2.2.2.2-1 ISS CREW PREFERENCE LOCATION MARKING LABELS (SDG32106315)............ 4-173

FIGURE 4.13.2.2.2.3-1 SAMPLE “LOCK” INSTRUCTION LABEL .................................................................... 4-174

FIGURE 4.13.2.2.2.3-2 SAMPLE ISS HATCH OPENING INSTRUCTION LABEL............................................ 4-174

FIGURE 4.13.2.2.2.4-1 SAMPLE ISS CONTROL-PANEL LABELING .............................................................. 4-175

FIGURE 4.13.2.2.2.5-1 ISS HARDWARE IDENTIFICATION LABEL (SDG32107015) ..................................... 4-176

FIGURE 4.13.2.2.2.6.-1 SAMPLE ISS COMBINATION IDENTIFICATION AND BARCODE LABEL (SDG32108325)

............................................................................................................................................... 4-176

FIGURE 4.13.2.2.2.7-1 SAMPLE ISS FLAG-STYLE LABEL ............................................................................. 4-177
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FIGURE 4.13.2.2.2.7-2 SAMPLE ISS BAND-STYLE LABEL............................................................................. 4-177

FIGURE 4.13.2.2.2.7-3 SAMPLE ISS ELECTRICAL CABLE LABELING.......................................................... 4-178

FIGURE 4.13.2.2.2.7-4 SAMPLE ISS FLUID HOSE LABELING ....................................................................... 4-178

FIGURE 4.14.2.3.2-1 NASA/NACA PROJECT MERCURY CONFORMAL COUCH (SEAT) ............................ 4-191

FIGURE 4.16.6.4.2-1 VISUAL EXAMPLE OF A PROSPECTIVE, SEQUENTIAL, STATISTICAL DESIGN ....... 4-233

FIGURE 4.18.3.2-1 SYMBOL HIGHLIGHTED WITH AN ORANGE BOX ON AN ELECTRONIC PROCEDURES 

SCREEN IS THE CUED ELEMENT THE SUBJECT IS ASKED TO IDENTIFY..................... 4-260
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1.0 INTRODUCTION

1.1 PURPOSE

The purpose of the Human Integration Design Processes (HIDP) document is to provide 

human-systems integration design processes, including methodologies and best 

practices that NASA has used to meet human systems and human rating requirements 

for developing crewed spacecraft. HIDP content is framed around human-centered 

design methodologies and processes in support of human-system integration 

requirements and human rating.

NASA-STD-3001, Space Flight Human-System Standard, is a two-volume set of 

National Aeronautics and Space Administration (NASA) Agency-level standards 

established by the Office of the Chief Health and Medical Officer, directed at minimizing 

health and performance risks for flight crews in human space flight programs. Volume 1 

of NASA-STD-3001, Crew Health, sets standards for fitness for duty, space flight 

permissible exposure limits, permissible outcome limits, levels of medical care, medical 

diagnosis, intervention, treatment and care, and countermeasures. Volume 2 of NASASTD-3001, Human Factors, Habitability, and Environmental Health, focuses on human 

physical and cognitive capabilities and limitations and defines standards for spacecraft 

(including orbiters, habitats, and suits), internal environments, facilities, payloads, and 

related equipment, hardware, and software with which the crew interfaces during space 

operations. The NASA Procedural Requirements (NPR) 8705.2B, Human-Rating 

Requirements for Space Systems, specifies the Agency’s human-rating processes, 

procedures, and requirements.

The HIDP was written to share NASA’s knowledge of processes directed toward

achieving human certification of a spacecraft through implementation of human-systems 

integration requirements. Although the HIDP speaks directly to implementation of 

NASA-STD-3001 and NPR 8705.2B requirements, the human-centered design, 

evaluation, and design processes described in this document can be applied to any set 

of human-systems requirements and are independent of reference missions.

1.2 APPLICABILITY

The HIDP is a reference document that is intended to be used during the development 

of crewed space systems and operations to guide human-systems development 

process activities.

1.3 HOW TO USE THE HIDP

The HIDP and NASA/SP-2010-3407 Human Integration Design Handbook (HIDH) are 

complementary reference documents. The HIDH provides background information on 

the rationale for human-system design standards, while HIDP describes the “how-to” 

processes, including methodologies and best practices that NASA has used during the 

development of crewed space systems and operations. Select processes included in 

the HIDP are based on NASA’s experiences and expertise in spacecraft design,

particularly those that are complex processes, have notable lessons learned, or have 

important considerations. Many program-specific examples are used throughout the 

HIDP to illustrate processes, methodologies, and/or best practices; they are not 
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intended to prescribe design solutions. Program-specific examples are used to illustrate 

the processes, but the chapters can be adapted for any mission.

Although the HIDP does not levy design requirements, the relevant standards, example 

program requirements, and/or NPR requirements are referenced in each process.

Additionally, suggested technical work products are identified to provide program 

managers, technical authorities, and stakeholders with insight and assessment 

throughout the systems engineering life cycle. In subject areas where NASA has 

previously documented background or supplementary information, references are made 

to the HIDH.

The HIDP is organized into stand-alone sections, which should be referenced as 

needed. Relevant information is purposely repeated in various sections, with crossreferences provided.

Chapter 3 provides over-arching information, beginning with a discussion of NASA’s 

Human Systems Integration and human-centered design (HCD) philosophies and their

approach to space system development. The HCD approach is captured in NASA-STD3001, Volume 2 as a requirement for each human space flight program. Section 3.2

describes human-centered design activities in the context of spacecraft design and the 

NASA systems engineering process. The HCD activities serve as the framework for 

each process in the HIDP document. For each milestone review, relevant technical 

products (e.g., concepts of operation, analyses and evaluations, design descriptions) 

are identified with the intent of minimizing engineering life cycle development costs 

through iterative assessment of concepts and designs. Section 3.3 describes the 

Human-Systems Integration (HSI) Team concept and the role of an HSI Team in the 

HCD process and development of crewed space vehicles. Section 3.4 summarizes the 

generic technical products that would be typical outputs of HCD activities, and their 

associated milestones.

Section 4 contains separate, stand-alone subsections describing different spacecraft 

design processes related to requirements in NASA-STD-3001 and/or NPR 8705.2B. 

Each process is explicitly tied to a requirement(s) in NASA-STD-3001 and/or NPR 

8705.2B, and is written with the intent of enabling space systems development and

certification. Each process contains a background section intended to provide just 

enough background information to understand the content of the process, with pointers 

to other documents (such as the HIDH) for more information as appropriate. To facilitate 

successful development and the ultimate achievement of requirement compliance and 

human-rating certification, each process also suggests key technical products that 

should be assessed throughout the engineering development life cycle.

A list of the sections follows. Sections 3.1 through 3.4 should be read by all audiences,

as they are a companion to each section. For convenience, each title is a hyperlink to 

that section.

3.1 Human Systems Integration (HSI)

3.2 Human-Centered Design

3.3.1 Human-Systems Integration (HSI) Team
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3.4 Summary of HIDP Technical Products

4.1 User Task Analysis

4.2 Usability Evaluation

4.3 Workload Evaluation

4.4 Human Error Analysis

4.5 Design for Crewmember Physical Characteristics and Capabilities

4.6 Handling Qualities Evaluation

4.7 Acoustic Noise Control Design

4.8 Radiation Shielding Design

4.9 Functional Volume Design

4.10 Crew Survivability Assessment

4.11 Metabolic Loads and Environmental Control Life Support System Design

4.12 Display Format Design

4.13 User Interface Labeling Design

4.14 Occupant Protection Design

4.15 Design for Deconditioned Crewmember

4.16 Design for Mitigation of DCS Risk

4.17 Space Food System Design

4.18 Legibility Evaluation

As defined in NPR 8705.2B, a crewed space system consists of all the system elements 

that are occupied by the crew during the mission and provide life-support functions for 

the crew. The crewed space system also includes all system elements that are 

physically attached to the crew-occupied element during the mission, while the crew is 

in the vehicle or system. Throughout HIDP, the terms “spacecraft” and “vehicle” are 

used synonymously to mean the system elements (e.g., orbiters, habitats, or suits) that 

are occupied by crew during any mission phase and that provide life-support functions 

for the crew. Acronyms and definitions can be found in Appendix A and Appendix B, 

respectively.

It is important to note that the processes described in HIDP do not cover all activities 

necessary to ensure effective system design. Appendix C contains a list of possible 

additional HIDP chapters. This process document may be used in addition to existing 

design methods to apply a human-centered design perspective to various subsystems 

in a way that is appropriate to the particular aspect and the overall system. All humancentered design activities identified in this document are applicable, in varying degrees, 

at any stage in system development.
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2.0 DOCUMENTS

2.1 APPLICABLE DOCUMENTS

Document Number Document 

Revision Document Title

NASA-STD-3001 March 5, 2007

NASA Space Flight Human-System 

Standard

Volume 1: Crew Health

NASA-STD-3001 January 10, 

2011

NASA Space Flight Human-System 

Standard

Volume 2: Human Factors, Habitability, 

and Environmental Health

NPR 8705.2B May 6, 2008

Human-Rating Requirements for 

Space Systems (w/change 4

dated 8/21/2012)

2.2 REFERENCE DOCUMENTS

The list of reference documents is extensive and can be found in Appendix C.
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3.0 HUMAN-SYSTEMS INTEGRATION PROCESS

3.1 HUMAN-SYSTEMS INTEGRATION (HSI)

Human-Systems Integration (HSI) is a process by which knowledge of human 

capabilities and limitations is integrated within the systems engineering life cycle. A key 

component of HSI is the concept of a human as a system, which should be integrated 

throughout the life cycle. The HSI process has a broad scope that includes a wide 

variety of technical domains and specialties, such as personnel, training, safety, 

environments, toxicology, medicine, human factors, and many more. Because HSI

requires the integration of multiple technical processes, a Human-Systems Integration 

Plan is a deliverable at the major design milestones defined in NPR 7123.1 NASA 

Systems Engineering Processes and Requirements (pending) and its supporting 

handbook (NASA-SP-2007-6105; pending).

A key component of the HSI process that is borrowed from the human factors domain is 

"human-centered design." Human-centered design is a methodology used to ensure 

that a design accommodates human capabilities and limitations. The following sections 

explain HCD in greater detail and provide guidance on how to implement the HCD 

approach in systems design. 

3.2 HUMAN-CENTERED DESIGN

3.2.1 RATIONALE FOR HUMAN-CENTERED DESIGN

This section provides an overview of a human-centered design approach based on the 

International Standards Organization (ISO) 13407: Human-Centered Design Processes 

for Interactive Systems. Human-centered design (HCD) is an approach to development 

of interactive systems that focuses on making systems usable by ensuring that the 

needs, abilities, and limitations of the human user are met. HCD is a multidisciplinary 

activity that involves a range of skills and stakeholders who collaborate on design. Most 

importantly, HCD is an iterative activity that intentionally uses data gathered from users 

and evaluations to inform designs. The benefits of the HCD approach can be realized in 

terms of cost control, mission success, and user satisfaction.

Development costs of an engineering life cycle are controlled through the iterative 

calibration of designs based on structured analyses and evaluations, which involve the 

user / customer and are measured against applicable requirements. Taking these 

iterative steps eliminates the occurrence of late design changes or rework during 

production, which have costly impacts.

Mission success is optimized when attention is paid to human interfaces that provide 

operational clarity and consistency and reduce potential for human error, performance 

failure, injury, or illness. Though not designed, the human user may be viewed as a 

functional subsystem of the greater system. Therefore, the designs that are created for 

the mission and the system must accommodate the human, within the additional 

constraints of the natural environments.
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User satisfaction is increased by involving the user in the HCD process so that users 

understand and participate in design decisions. This is especially important when the 

human user will have critical control responsibilities over the system or when user 

interaction is important to mission goals.

3.2.2 PRINCIPLES OF HUMAN-CENTERED DESIGN

The human-centered design approach is characterized by 4 principles:

 Active involvement of users and a clear understanding of user and task 

requirements

 Function allocation between users and technology

 Design iteration 

 Multidisciplinary design

3.2.2.1 ACTIVE INVOLVEMENT OF USERS AND A CLEAR UNDERSTANDING OF USER 

AND TASK REQUIREMENTS

Users provide valuable knowledge about the context of use, the tasks, and how users 

are likely to work with the future product or system. NASA users include astronauts who 

function as commanders, pilots, or technical specialists (e.g., mission specialist or 

payload specialist); ground operations personnel; mission operations personnel; 

scientists with a wealth of knowledge collected from research and studies; and 

engineers with extensive knowledge and data collected over years of experience with 

human space flight and space habitation. It is important that the user(s) be included in 

the development of a product or system. Active involvement of users allows for 

increased understanding of user needs, feedback on how they will use the product or 

system, and the demands imposed by a task. This understanding leads to the inclusion 

of proper task and system requirements, and results in improved design decisions.

3.2.2.2 FUNCTION ALLOCATION BETWEEN USERS AND TECHNOLOGY

One of the most important human-centered design principles concerns the appropriate 

allocation of function – the specification of which functions should be performed by the 

users and which by the system. These design decisions determine the extent to which a 

given job, task, function or responsibility is to be automated or assigned to human 

performance.

Designers making the decision should weigh the relative capabilities and limitations of 

the human vs. technology, and the decision should be based on many factors such as 

reliability, speed, accuracy, strength, flexibility of response, financial cost, the 

importance of successful or timely accomplishment of tasks, and user well-being. 

Decisions should not simply be based on determining which functions the technology is 

capable of performing and then simply allocating the remaining functions to users, 

relying on their flexibility to make the system work. The resulting human functions 

should form a meaningful set of tasks. Representative users should be involved in these 

decisions. 
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3.2.2.3 DESIGN ITERATION

In addition to results from modeling, analyses, and tests, feedback from the users is a 

critical source of information for iterating design solutions. Iteration, when combined with 

active user involvement, provides an effective means of minimizing the risk that a 

system does not meet user or mission requirements, including requirements that are 

hidden or difficult to specify explicitly. Iteration allows preliminary design solutions to be 

tested against “real-world” scenarios, with the results being fed back into progressively 

refined solutions.

3.2.2.4 MULTIDISCIPLINARY DESIGN

Human-centered design involves the application of a range of technical expertise to

adequately address the human aspects of the design. This means that multidisciplinary 

teams should be involved in a human-centered design process. The composition of the 

teams should reflect the relationship between the organization responsible for technical 

development and the customer. The roles can include the following:

 Customer (e.g., users such as scientists, engineers, or operations managers)

 Systems analysts, systems engineers, programmers, scientists, subject matter

experts

 User interface designers, visual designers

 Human factors and ergonomics experts, human-computer interaction specialists

 Technical writers, trainers, and support personnel

Individual team members can cover a number of different skill areas and viewpoints.

Multidisciplinary teams do not have to be large, but the team should be sufficiently 

diverse to make appropriate design tradeoff decisions.

3.2.3 HUMAN-CENTERED DESIGN ACTIVITIES

This section describes human-centered design activities tailored for NASA spacecraft 

design. In these activities, the user may be referred to as “crew” or “crewmember.” The 

HCD process comprises 3 main activities that are performed iteratively in a feedback 

loop as represented in Figure 3.2.3-1. The HCD process is conducted and iterated 

throughout the overall systems engineering life cycle. The HCD activities are shown in 

the context of the systems engineering milestones in section 3.4. The HIDP processes 

in section 4 are either structured around or a part of these activities, which are

described in paragraphs below.
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FIGURE 3.2.3-1 HUMAN-CENTERED DESIGN ACTIVITIES

3.2.3.1 UNDERSTAND THE USER AND ENVIRONMENT

Understanding the user and the operating environment is important to ensuring that 

design solutions meet the needs of the user within constraints of the operating 

environment. “Understanding the user and environment” means gaining a full 

awareness of the user (i.e., capabilities and limitations, skills and expertise), the work 

environment’s constraints and challenges (e.g., microgravity, isolation, small enclosed 

volumes), and the tasks that will be performed to accomplish the mission (e.g., piloting, 

maintenance, eating, and sleeping). Understanding is gained through conducting the 

following activities:

 Develop missions and scenarios

 Develop concept of operations

 Allocate functions between user and system

 Perform user task analysis

 Conduct requirements analysis

3.2.3.1.1 DEVELOP MISSIONS AND SCENARIOS

In accordance with NPR 8705.2B, human-rating certifications are based on programdefined reference missions, which establish the objectives and scope of the program 

and space system. Reference missions are established during the early phases of 
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spacecraft development. From these, the nominal, off-nominal, and emergency 

scenarios are defined. 

For example, the reference mission that the commercial crewed spacecraft and JSC 

65993 Commercial Human-Systems Integration Requirement (CHSIR) are based on is 

to provide ISS increment crew rotation for up to 4 NASA crewmembers. The example

nominal scenario includes the following events, which are illustrated in Figure 3.2.3.1.1-

1.

 Vehicle maintenance and processing at launch site 

 Launch 

 Up to a 3-day transit to International Space Station (ISS)

 Quiescent vehicle-docked phase of up to 210 days

 Less than 2 days for return to Earth from ISS

 Post-landing operations no greater than 2 hours 

FIGURE 3.2.3.1.1-1 NOMINAL COMMERCIAL CREW TRANSPORT MISSION (ASSUMED 

FOR CHSIR)

The off-nominal and emergency scenarios addressed in CHSIR include, but are not 

limited to:

 Emergency evacuation from ISS if it becomes uninhabitable

 Medical evacuation if one crewmember becomes ill or injured with a lifethreatening, time-critical condition beyond the medical capability to treat on ISS

 Safe haven capability for 4 United States Orbital Segment crewmembers
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3.2.3.1.2 DEVELOP CONCEPT OF OPERATIONS

The Concept of Operations (ConOps) is developed for all scenarios to describe how 

mission objectives will be accomplished using planned resources, including crew and

system. The ConOps gives an overall picture of the operation from the perspective of 

the users who will operate the system.

As a tool for developing ConOps, it may be useful to visualize each scenario in a table 

such as the example shown in Table 3.2.3.1.2-1. The example takes a notional scenario 

for travel to ISS and identifies, initially at a high level, the planned crew activities for 

each phase of the mission. The table also identifies subsystems that may be influenced 

by crew activities associated with the notional scenario, which may influence 

subsystems design. Similar tables should be created for other segments of the mission 

(e.g., quiescent vehicle docked, return to Earth, post landing) and for the off-nominal 

and emergency scenarios. As design matures, more detailed tables are created to 

break up and clearly define the mission phases. ConOps should evolve to cover the 

end-to-end system as the system capabilities, including the user, become better defined 

through the conduct of activities in the iterative human-centered design process.

TABLE 3.2.3.1.2-1 EXAMPLE NOMINAL SCENARIO - TRAVEL TO ISS (NOTIONAL)

Mission 

Phase

Crew Activities Subsystems 

Crew 1 Crew 2 Crew 3 Crew 4 Crew 5 Affected

Vehicle Boarding Ingress in suit Ingress in suit Ingress in suit Ingress in suit Ingress in suit

Architecture

ECLSS*

Lighting

Launch Prep Checklist 

procedures

Checklist 

procedures N/A N/A N/A

ECLSS

Lighting

Windows

Controls, displays

Launch Checklist 

procedures N/A N/A N/A N/A

ECLSS

Lighting

Controls, displays

Ascent Checklist 

procedures

Eat

Waste

Sleep

Eat

Waste

Sleep

Eat

Waste

Sleep

Eat

Waste

Sleep

ECLSS

Lighting

Controls, displays

Orbit

Eat

Waste

Sleep

Eat

Waste

Sleep

Eat

Waste

Sleep

Eat

Waste

Sleep

Eat

Waste

Sleep

ECLSS

Hygiene

Stowage & trash

Lighting

Proximity 

Operations

Checklist 

procedures

Checklist 

procedures N/A N/A N/A

ECLSS

Lighting

Windows

Controls, displays

Rendezvous Checklist 

procedures

Checklist 

procedures N/A N/A N/A

ECLSS

Lighting

Windows

Controls, displays

Dock/Berth Checklist

procedures

Checklist 

procedures N/A N/A N/A

ECLSS

Lighting

Windows

Controls, displays

Architecture

*Environmental Control and Life Support System (ECLSS)
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3.2.3.1.3 ALLOCATE FUNCTIONS BETWEEN USER AND SYSTEM

Function allocation significantly influences design decisions by establishing which 

functions are to be performed by the users and which by the system. Based on the 

ConOps, function allocation determines the extent to which a given activity, task, 

function, or responsibility is to be automated or assigned to humans. Function allocation 

is based on many factors, such as relative capabilities and limitations of humans and 

technology in terms of reliability, speed, accuracy, strength, flexibility of response, 

financial cost, the importance of successful or timely accomplishment of tasks, and user 

well-being. Decisions should not be based simply on determining which functions 

technologies are capable of performing and then allocating the remaining functions to 

users, relying on their flexibility to make the system work. The resulting human functions 

should form a meaningful set of tasks. Task analyses and tests may be useful in 

evaluating performance to help to determine allocations. Representative users should 

be involved in these decisions. According to NPR 8705.2B paragraph 2.3.3, 

documenting the design philosophy for utilization of the crew is an important step in 

improving safety and mission success. When unexpected conditions or failures occur, 

the capability of the crew to control the system can be used to prevent catastrophic 

events and aborts.

Function allocations evolve as the system capabilities, including the user, become 

better defined through the conduct of activities in the iterative human-centered design 

process.

3.2.3.1.4 PERFORM USER TASK ANALYSIS

The purpose of task analysis is to analyze how the user interacts with the space system 

and to define the tasks, which direct design concepts and decisions. Task analyses 

should be performed for all functions allocated to human users for the established 

mission objectives, scenarios, and ConOps. For each function allocated to human 

users, define the physical and cognitive tasks that must be accomplished and describe 

pertinent task attributes such as

 User roles and responsibilities

 Task sequence 

 Task durations and frequencies

 Environmental conditions

 Necessary clothing and equipment

 Constraints or limiting factors

 Necessary user knowledge, skills, abilities, or training

Representative users should be involved in task analysis activities. HIDP section 4.1 

provides additional details and guidance on performing user task analysis. Task 

analyses also contribute to the development of operational task procedures, which 

should be evaluated with design concepts.
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Task definitions should evolve as the system capabilities, including the user, become 

better defined through the conduct of activities in the iterative human-centered design 

process.

3.2.3.1.5 CONDUCT REQUIREMENTS ANALYSIS

As operating scenarios, function allocations, and tasks become better defined, design 

requirements should be revisited and refined, and documentation updated. A 

comparison of analyzed task requirements to program requirements may reveal 

discrepancies or gaps, perhaps due to incorrect assumptions that were made early-on 

during concept development and the establishment of program requirements. To direct 

refinement and maturity of system design, the developer may find it useful to document 

results of requirements analyses as system-interface requirements.

3.2.3.2 VISUALIZE AND PRODUCE DESIGN SOLUTIONS

In this activity, candidate design solutions should be visualized through graphical or 

physical representations based on information gathered in the activities described in 

section 3.2.3.1 Understanding the User and Environment. Design concepts may be 

communicated in many forms, depending on the maturity of the design, and may range 

from paper and pencil sketches to interactive prototypes to high-fidelity mockups or 

computer-based simulations. It is important during this activity to communicate ideas 

and involve the user in focused design reviews to gather feedback. Designs and their 

physical representations should be iteratively improved based on user feedback until 

acceptable solutions are achieved. Consider the use of available NASA design data, 

models, and equipment when producing design solutions.

3.2.3.3 EVALUATE DESIGNS AND ITERATE SOLUTIONS

This activity evolves designs by identifying areas for design improvement through the 

gathering of quantitative and qualitative data. Intentional design iteration is a 

fundamental principle of human-centered design that contributes to control of life-cycle 

development cost by helping to identify risks and issues early in the design cycle when 

they are relatively inexpensive to fix. Evaluation of design concepts and alternatives is 

crucial to achieving optimal design solutions. Evaluations begin early and continue 

throughout system design. Evaluations can include a wide variety of activities, such as 

informal reviews with subject matter experts (SMEs) or users, formal usability tests for 

gathering quantitative performance data or qualitative observations, assessments of 

design based on human-in-the-loop (HITL) evaluation (required by NPR 8705.2B 

paragraph 2.3.10), and flight simulations to assess vehicular handling qualities and 

vehicle controllability by pilots. NASA expects all evaluations with human test subject 

participation to have institutional review board (IRB) approval.

Fidelity and integration increase with maturation of the design. As the design matures, 

high-fidelity evaluations are used, progressing from computer-aided design (CAD) 

analyses to HITL evaluations in a flight simulator. Likewise, integration of the system in 

the evaluation also increases as design matures. Early in design, single-system or even 

single-component evaluations are performed. As the design matures, evaluations 

include entire subsystems, systems, and eventually integrated systems. HIDP sections 
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4.2 and 4.3 provide additional detail and guidance on usability and workload 

evaluations, respectively.

Evaluations focus on specific objectives, and plans are developed to include details 

such as

 Human-centered design goals

 Responsibility for evaluation 

 Parts of the system to be evaluated and how they’ll be evaluated (e.g., by use of 

computer simulations, mockups or prototypes, or test scenarios)

 How the evaluation is to be performed (e.g., test setup, methodology)

 The procedures to be used in the evaluation

 Resources required for evaluation and analysis, including users and test subjects

 Scheduling evaluation activities and resources, including users/test subjects and 

concrete design proposals (e.g., models, simulations, mockups)

 Intended use of results/feedback

Evaluation findings are used to reassess understanding of the user and environment

and to re-plan design solutions in an iterative, feedback loop. Therefore, as designs 

mature each successive evaluation should be performed with more complete and flightrepresentative inputs, simulations, or hardware (e.g., mockups, qualification units, etc.). 

Intentional design iteration is a fundamental principle of human-centered design that

contributes to control of life-cycle development cost by helping to identify risks and 

issues early in the design cycle when they are relatively inexpensive to fix. 

3.3 ROLES AND RESPONSIBILITIES

3.3.1 THE HUMAN-SYSTEMS INTEGRATION (HSI) TEAM

The Human-Systems Integration (HSI) Team is the group that holds authority, 

responsibility, and accountability for implementing human-centered design principles 

and processes during development of new crewed space systems. These systems may 

include integrated space vehicle systems with human interfaces for diagnostics and 

control, habitable environments, or solutions that protect crew from hostile or extreme 

environments. Ensuring effective human-systems integration across the design is 

particularly important for crewed space system design because of the increased risk,

associated with space flight, to human health and performance, as well as the reliance 

on human capability as part of total system performance. HSI considers all aspects of 

human interaction with the design. It is the role of the HSI Team to guarantee that this 

integration occurs, beginning with the earliest design concepts and continuing iteratively 

during the engineering life cycle through operations and decommission.

3.3.2 HSI TEAM BASIS IN NASA REQUIREMENTS

An HSI Team is required for NASA human rating and is described in NPR 8705.2B 

Human-rating Requirements for Space Systems paragraph 2.3.8, which states:

2.3.8 Human-System Integration Team. No later than SRR, the Program Manager shall establish a 

human-system integration team, consisting of astronauts, mission operations personnel, training 

personnel, ground processing personnel, human factors personnel, and human engineering experts, 
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with clearly defined authority, responsibility, and accountability to lead the human-system integration 

(hardware and software) for the crewed space system (Requirement).

Rationale: Past experience with cockpit development in spacecraft and military aircraft has 

shown that when a correctly staffed human-system integration team is given the authority, 

responsibility, and accountability for cockpit design and human integration, the best possible 

system is achieved within the schedule and budget constraints. This team focuses on all 

human system interfaces (crew, launch control, and ground processing) that can cause a 

catastrophic failure.

For a given NASA program, the managing program office establishes the NASA HSI 

Team, which is composed of NASA members representing various stakeholder 

disciplines, and representation from the space system developer.

3.3.3 TECHNICAL SCOPE OF THE HSI TEAM

To integrate a design across multiple disciplines, an HSI Team must have significant 

depth and breadth of technical expertise to review and evaluate a significant majority of 

design considerations. Areas of technical expertise necessary for proper HSI include, 

but are not limited to:

 Human factors and human engineering (including crew workload and usability, 

human-in-the-loop evaluation, and human error analysis)

 Crew health and countermeasures

 Environmental health (including radiation, toxicology, and other areas)

 Safety 

 Systems engineering

 Architecture

 Crew functions and habitability functions (including nutrition, acoustics, water 

quality and quantity, etc.)

 Crew interfaces and information management

 Maintenance and housekeeping

 Ground maintenance and assembly

 Extravehicular activity physiology

 Mission operations

 Training

3.3.4 THE ROLE OF THE HSI TEAM 

The NASA HSI Team provides guidance in human-centered design practices 

throughout the design process. This includes reviewing deliverables that are due at 

each Program milestone to ensure that iterative and adequate HSI design 

considerations are taking place throughout the engineering life cycle. Appropriate 

subject matter experts from the HSI Team interact with system designers between 

milestone reviews to provide guidance and expertise, ensuring that human-centered 

design issues are identified early to avoid cost and schedule impacts. The HSI Team 

has the authority to elevate issues directly to Program Management for resolution and 
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to document formal acceptance or lack of acceptance of the deliverables provided. It is 

important that the NASA HSI Team include participation by the space system developer

for effective human-centered design (HCD) implementation. Membership on the NASA 

HSI Team ensures that the developer is involved in discussions of design reviews, 

stakeholder reviews, evaluations, and other activities such as system analyses and 

design trades, to communicate information to and from appropriate subject matter

experts within the developing group or company and provide design insight as needed. 

Note that the developer may also choose to form an internal HSI Team as an interface 

with the NASA HSI Team. The mechanism by which the developer chooses to handle 

this internally would be left up to their discretion. The NASA HSI Team serves as the 

official representative body for HSI and HCD implementation, providing official positions 

to any and all developers and NASA oversight boards and panels. This level of authority 

is necessary for an HSI Team to fulfill its responsibility.

3.3.5 HSI TEAM REVIEW OF DELIVERABLES

The NASA HSI Team is involved in review of all human-rating deliverables, as detailed 

in a program’s Human-Rating Certification Plan (HRCP). The deliverables due at each 

stage of the engineering life cycle are multiple and varied. The technical products 

presented in sections 3.4 and 4 of the HIDP may or may not be required deliverables. 

The determination will be made by the managing program. The NASA HSI Team should 

have insight into design progress between milestones to facilitate review of applicable 

materials at each milestone. This reinforces the concept of early and often inclusion of 

the HSI Team as part of an HCD process. For specific details of the HRCP 

requirements and other human-rating requirements, refer to NPR 8705.2B Humanrating Requirements for Space Systems.

3.4 SUMMARY OF HIDP TECHNICAL PRODUCTS

To facilitate successful development and the ultimate achievement of requirement 

compliance and human-rating certification, each HIDP process suggests key technical 

products that should be assessed by the NASA HSI Team throughout the engineering 

development life cycle. The technical products are identified on the basis of experiences 

with other NASA programs and projects. Subject matter experts have determined these 

products to be important indicators of progress toward verification and certification 

achievement. 

3.4.1 GENERIC TECHNICAL PRODUCTS

A summary of generic technical products and the life cycle review by which they should 

be provided is presented in Table 3.4.1-1. Definitions for the products are provided 

below the table. Individual processes may have unique product details or schedules. 

Refer to the individual process sections for specific details.
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TABLE 3.4.1-1 SUMMARY OF GENERIC TECHNICAL PRODUCTS

Technical Products

Phase

A

Phase 

B

Phase 

C

Phase

D

SRR SDR PDR CDR SAR FRR

A description of each reference mission for which 

human rating is being pursued.

Required per NPR 8705.2B paragraph 2.3.1.

X --- --- --- --- ---

A description of the Human-Systems Integration 

Team and their authority within the program.

Required per NPR 8705.2B paragraph 2.3.8.

X --- --- --- --- ---

A description of the ConOps, function allocation, 

and associated crew task lists. I U U U --- ---

A summary of modeling/analysis/evaluation 

performed to date and the influence on system 

design with links to the detailed analysis results.

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10.

--- --- I U U ---

System architecture drawings (structures, 

equipment, etc.), material specifications, interface 

requirements.

--- --- I U U ---

Verification plan. --- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

3.4.2 DEFINITIONS OF GENERIC TECHNICAL PRODUCTS 

Reference Missions

Before System Requirements Review (SRR), NASA will provide a description of each 

reference mission for which human rating is being pursued. Defining reference missions 

establishes the scope of the program to be human rated and also provides a framework 

that supports, among other things, identification of crew survival strategies and 

establishment of scenarios to be used for hazard analysis and risk assessments. The 

reference missions also define the interfaces with other systems, such as mission 

control centers, that functionally interact with the crewed space systems. This 

information is required by NPR 8705.2B paragraph 2.3.1, and it is essential as input for 

products such as Concept of Operations and crew task lists.

Human-Systems Integration Team

No later than SRR, NASA programs will provide a description of the NASA HSI Team 

and their authority within the program (required by NPR 8705.2B paragraph 2.3.8). The 

description will also include how the NASA HSI Team will interface with NASA Program 

boards and the developing company’s boards, if applicable. Past experience with 

cockpit development in spacecraft and military aircraft has shown that when HSI teams 

have the expertise, authority, responsibility, and accountability for cockpit design and 

human integration throughout the project life cycle, the best possible system is 

achieved. The HSI Team focuses on human-system interfaces (crew, launch control, 

and ground processing) that can lead to a catastrophic failure if they do not work 

properly.
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Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are influenced by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of the crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures.

Summaries of Modeling, Analyses, and Evaluations

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-system integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how key and critical design 

decisions were assessed. In accordance with NPR 8705.2B, updated summaries are to 

be provided at each design review through SAR. Also, in paragraph 2.3.10, the use of 

human-in-the-loop evaluation is a required method to progressively demonstrate that 

the operational concept meets system requirements for operational safety, efficiency, 

and user interface design.

Architecture, Materials, and Interface Specifications

Specifications for drawings, materials, and interfaces provide NASA with insight into 

human-systems integration technical details throughout the design process. 

Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. For some aspects of spacecraft 

design, such as radiation shielding, the program’s approach to verification is developed 

at SRR and reflected in the verification plan.
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4.0 HIDP PROCESSES

4.1 USER TASK ANALYSIS

4.1.1 INTRODUCTION

Task analysis is a methodology used to break an event down into tasks and break tasks 

down into components. It is used to understand and thoroughly document how tasks are 

accomplished. This section explains the process for conducting a task analysis, and the 

associated decomposition of physical and mental (i.e., cognitive) activities, activity 

frequency and duration, task allocation, inter-task dependencies, task criticality and 

complexity, environmental conditions, necessary clothing and equipment, and any other 

unique factors involved in or required for one or more people to perform a given task.

A task analysis identifies system-level and subsystem-level tasks, to determine operator 

needs for established mission objectives and concepts of operation. The focus is on 

humans and how they perform the task, rather than on the system. When performed 

throughout the vehicle iterative design process, task analysis can be used to help drive 

the design of optimal human-system interfaces and to ensure that the design of vehicle 

components supports the needs of the human for all mission tasks that must be 

performed. Additional information on using task analysis in the human-systems 

integration design process can be found in chapter 3 of the NASA/SP-2010-3407 

Human Integration Design Handbook (HIDH).

This section details the task analysis process that should be used for identification of 

critical crew and space system tasks necessary for vehicle, system, and hardware 

design and verification. When used in conjunction with human factors guidelines, 

human-in-the-loop testing, and other analysis methods, task analysis can help to ensure 

that all crew-to-vehicle interfaces and operational environments provide the necessary 

physical or informational affordances for nominal and contingency tasks. HIDP section 

3.2 discusses the human-centered design approach and activities, highlighting the 

importance of task analysis throughout the design life cycle.

4.1.1.1 PURPOSE

Task analysis is an essential component of human-centered design, focused on 

providing usable systems for humans throughout a system’s entire life cycle. Although it 

is recognized as a critical function in design, task analysis is often overlooked until late 

in design phases when hardware, system, and software designs are too mature to allow 

for changes that could increase crew efficiency and task performance. Therefore, it is 

imperative that task analysis begins as early in the design process as possible and 

continues to be done frequently as design matures. An iterative approach allows the 

identification of current and future task demands that can aid in decisions, such as 

which tasks should be allocated to a human instead of an automated system, or how 

system components should be used. Task analysis also results in the identification of 

critical crew tasks, which are tasks that are absolutely required and necessary for crews

to successfully accomplish operations and meet mission objectives. Critical crew tasks 

may occur nominally or off-nominally and include tasks that are essential to crew health 

or, if done incorrectly, may lead to loss of crew, loss of mission, or undesirable vehicle 
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states. Identifying these tasks early, can enable efforts to be made to implement 

designs that reduce the probability of mishaps or errors and allow crews to perform 

tasks within expected time limits and environmental conditions. Thus, errors can be 

avoided, safety can be improved, and crew time can be optimized.

4.1.1.2 SCOPE

Task analysis is a fundamental design activity necessary for implementing many human

system requirements. In support of verification, task analysis assists in scoping the 

specific scenarios for which the verification should be performed. It is used to ensure 

that provided design solutions meet the needs of associated crew and system tasks. 

Early and iterative task analyses are recommended to avoid late and costly changes. A 

single task analysis activity may concurrently address multiple requirements. 

4.1.2 TASK ANALYSIS PROCESS OVERVIEW

Task analysis refers to a family of techniques (see Ainsworth, 2004) that involve the 

systematic identification of the tasks and subtasks involved in a process or system and 

the analysis of those tasks (e.g., who performs them, what equipment is used, under 

what conditions, the priority of the task, and dependence on other tasks). A high-level 

task analysis is one of the first steps in vehicle design. Initial definition of a task occurs 

during the Concept and Technology Development Phase, when mission, operations, 

and requirements are refined and clarified. Task definition and descriptions should 

continue to evolve as designs and plans are developed and crew utilization and 

functional allocation are defined. At later stages, the focus should be on capturing the 

lower-level crew and system interactions required for successful mission completion. 

Interactions include physical and cognitive activities, the latter of which includes 

perceptual (e.g., visual, tactile, and auditory), decision-making, comprehension, and 

monitoring activities.

As designs materialize into proposed solutions during the Preliminary Design Phase, 

evaluation of these designs should be performed using identified crew tasks. Findings 

from evaluations should be used to improve designs and to evolve and refine crew 

tasks. Thus task analysis informs the selection of tasks for other analysis methods, 

which in turn results in modified designs and enhanced knowledge that can be captured 

in subsequent task analyses. The process of iterative design, task analysis, and 

evaluation of the needs of the users should continue until a design is achieved that 

allows the user to perform all necessary tasks and operations during the course of a 

defined mission.

4.1.2.1 TASK ANALYSIS APPROACH

Both physical and cognitive tasks are addressed in a user task analysis, which is 

performed with subject matter experts (SMEs) throughout the vehicle design process. 

To provide structure to the analysis, tasks are often grouped by subsystem so that they 

are related to concepts such as food, hygiene, vehicle control and monitoring, crew 

safety and health, environment, maintenance, and other concepts that affect mission 

objectives, vehicle architecture, and interfaces. For data collected at a subsystem or 

component level, considerations need to be made for how crew and system-level tasks 
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may be affected by or have an effect on each component and the fully integrated 

vehicle. Understanding these inter-dependencies may make it possible for 

knowledgeable designers and engineers to influence the subsequent development of 

mission-related task sequences or concepts of operation. Such influence will be needed 

throughout the process of designing systems and hardware.

It is recommended that task analysis sessions be conducted, not only at the component 

or hardware level, but also by mission phase. Task analyses by mission phase can help 

determine that all of the necessary hardware and software is available to crewmembers

when it is needed throughout the mission. The analysis should generally focus on

interfaces (hardware and software) and locations within the spacecraft with which 

crewmembers have direct interaction during a mission.

4.1.2.1.1 TASK ANALYSIS EXECUTION

The task analysis execution process involves group interviews with SMEs. In 

preparation for the task analysis session, the specific objectives of the session should 

be defined. For example, the mission phase and relevant systems should be specified. 

The level of task detail (e.g., high-level tasks and goals versus low-level crew activities) 

most appropriate to the phase of design should also be determined. Objectives that are 

concise and detailed will help to ensure that consistent data are captured from session 

to session.

After the objectives are specified, the conductors of the task analysis should review 

appropriate reference documents (such as requirements, standards, and engineering 

drawings) and identify currently understood tasks, mission operations, scenarios, 

related systems, and possible operational constraints from crew, system, and vehicle 

perspectives. Task analysis conductors should also identify any specific areas of 

uncertainty or questions that specifically need to be addressed by the SMEs during the 

task analysis session.

Formal task analysis should be conducted with appropriate SMEs for each individual 

topic area based on the objectives of the task analysis. SMEs may be system 

engineers, safety representatives, mission operations experts, crewmembers, or other 

individuals with specialized knowledge about the tasks of interest. Before the task 

analysis session is conducted, briefings on related system hardware and interfaces, 

vehicle constraints, mission objectives, assumptions, relevant requirements, and other 

details should be compiled and provided to the SMEs. This should be done to ensure 

that all involved parties have a common and clear baseline understanding of the topic 

area being assessed and the objectives of the task analysis session. Providing SMEs 

with a preliminary task list is sometimes recommended to allow efficient use of time and 

resources.

During the task analysis session, one member of the task analysis team should serve 

as the moderator, while other members serve as co-moderators or note takers. The 

moderator should begin the session by reminding the participants about the objectives 

of the session and the scenario or topic area being addressed. It may be helpful to 

provide reference material, such as hardware drawings or preliminary task lists, for 
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participants to refer to. Throughout the session, the moderator’s role is to ensure 

(through appropriate queries) that the objectives of the session are met and all SMEs 

have an equal opportunity to provide input.

Data collected during the session should address multiple aspects of the task. For 

example, when conducting a task analysis regarding hygiene, it is critical to address not 

only the tasks required to perform hygiene such as unstowing crew provisioning items 

and setting up the hygiene area, but also other considerations such as the mission 

phases when hygiene should occur; how many crewmembers can conduct the hygiene 

tasks at one time; the type of hardware (restraints, mobility aids, or crew provisioning 

equipment) necessary for hygiene; and any environmental constraints. Task analysis 

data collection should include, but not be limited to, the following items for each 

scenario and individual task:

 Tasks that are required to achieve mission objectives 

 Tasks that are required for each mission phase

 Task priority and criticality

 Nominal and off-nominal crew tasks 

 Integrated human-system tasks and system interactions

 Crew monitoring activities

 Potential impacts on and impedances to crew tasks

 Vehicle, environmental, safety, operational, and crew constraints on tasks

 All human interfaces (hardware and software) with which the crew will interact to 

accomplish tasks, including tools and equipment needed to accomplish tasks

 Required communication with the ground

 Function allocation for manual and automated crew and system tasks

 Vehicle information and resources required to perform tasks

 Vehicle/system state

 Expected results of task errors or failures in task completion

 Required operator inputs

 Performance expectations

 Data related to task time (e.g., duration, frequency, limits)

 Task sequences (parallel, serial, multiple crewmembers and/or systems, 

individual crewmembers and/or systems)

o Identify when tasks are initiated, concluded, or terminated (i.e., “trigger” 

conditions)

o Identify how decisions are made within a task (e.g., decision trees)

The moderator should ensure that the data collected for each scenario and task is 

complete with regard to these aspects. Any aspects about which SMEs disagree or in 

which knowledge is incomplete should be documented.

On completion of SME interviews, members of the task analysis team should compare 

notes and then compile all crew and systems task data identified during the task 

analysis SME activities. All results from the sessions should be documented in a similar 
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fashion to promote consistency and efficiency across sessions. Separate reports, task 

lists, and documentation can, and should be, maintained for individual task analysis 

sessions; however, it is preferred that all critical crew and systems task analysis data be 

consolidated and maintained in a Master Task List (MTL). Figure 4.1.2.1.1-1 depicts the 

task analysis execution process involving group interviews with SMEs. 

FIGURE 4.1.2.1.1-1 TASK ANALYSIS EXECUTION PROCESS

4.1.2.1.2 TASK ANALYSIS RESULTS AND DESIGN IMPLICATIONS

Task analysis data collection should yield an understanding of critical crew and systems 

tasks, inter-task interactions, and vehicle interactions. These task data can be used for 

system, hardware, and vehicle design; development of modeling and simulation 

products; concept of operations development; procedure development; human reliability 

assessment; and vehicle verification.

4.1.2.1.3 TASK ANALYSIS PRODUCTS

It is suggested that data collected during all task analysis sessions be documented 

individually per topic area (in the form of a summary report and task list) and in the form 

of a completed MTL, which serves as a compilation of all task analyses and their 

findings. The MTL serves a vital role in facilitating verification because so many 

verification activities rely on task requirements identified by means of task analyses. 

The MTL provides a common document for designers and test/verification personnel to 

find task analysis data.

The summary reports and MTL products should address and document the 

aforementioned data collection objectives, including the degree to which these

objectives were met in the task analysis and the sources for the data collected, which 

can be used for future reference. It is assumed that as part of the iterative humancentered design process, the individual task lists, summary reports per topic area, and 

an updated MTL will be provided for each major milestone within the design life cycle. 

NASA will iteratively review task analysis products to ensure that identified tasks and 

design solutions provided meet the needs of the reference mission.

4.1.3 TASK ANALYSIS TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.1.3-1 are recommended.
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TABLE 4.1.3-1 TASK ANALYSIS TECHNICAL PRODUCTS

Technical Products Phase A Phase B

Phase 

C

Phase 

D

SRR SDR PDR CDR SAR FRR

Completion of “Round 1” of all task analysis sessions and 

related individual summary reports and task list. 

Master Task List (MTL) Rev A complete.

X --- --- --- --- ---

Completion of “Round 2” of all task analysis sessions and 

updates to related individual summary reports and task 

list. MTL Rev B complete.

--- X --- --- --- ---

Completion of “Round 3” of all task analysis sessions and 

updates to related individual summary reports and task 

list. MTL Rev C complete.

--- --- X --- --- ---

Task analysis sessions are complete and final versions of 

individual summary reports and task list are complete. 

Final MTL.

--- --- --- X --- ---

Hardware- and vehicle-based review of task analysis

verification based on defined crew tasks and system 

tasks. Final review of any existing concerns or needs for 

task data.

--- --- --- --- X ---

Final hardware- and vehicle-based analysis based on 

defined critical crew tasks and systems tasks. --- --- --- --- --- X

X = one-time release of item

I = initial release of item

U = updated release of item

4.1.4 REFERENCES

Ainsworth, L.K. (2004). Task analysis. In C. Sandom, R. Harvey (Eds.), Human factors 

for engineers (pp. 81–112). London: Institution of Engineering and Technology.

Loukopoulos, L. D., Dismukes, R. K., & Barshi, I. (2009). The Multitasking myth: 

handling complexity in real-world operations. Farnham, Surrey, England: Ashgate 

Publishing Limited.

Woolford, B. J., & Bond, R. L. (1999). Human factors of crewed spaceflight. In W. J. 

Larson & L. K. Pranke (Eds.), Human spaceflight: mission analysis and design (Chapter 

6). New York, NY: McGraw-Hill.
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4.2 USABILITY EVALUATION

4.2.1 INTRODUCTION

4.2.1.1 DEFINITION OF USABILITY

The International Standards Organization (ISO) defines usability as “the extent to which 

a product can be used by specified users to achieve specified goals” (ISO-9241-11, 

1998). Usability is a key element of the human-centered design (HCD) approach, and it 

has been shown to increase efficiency, effectiveness, and user satisfaction. 

Furthermore, designs with good usability can reduce errors, fatigue, training time, and 

overall life cycle costs.

4.2.1.2 HUMAN-CENTERED DESIGN

Usability is a key component of human-centered design. Human-centered design 

focuses on users’ needs to design the system based on users’ capabilities. Usability 

testing and evaluation methods provide user performance measures and subjective 

(qualitative and quantitative) comments that can be used to improve the system in 

question throughout the engineering design life cycle.

Using the HCD process provides designers and engineers with direct feedback from the 

earliest stages of design, all the way through product use and distribution. Whether in 

the conceptual phase or in final prototyping, usability evaluations can elucidate design 

optimizations for increasing functional efficiency as well as determine potential design 

issues that could cause increased error rates and potential system failures.

4.2.1.3 ITERATIVE NATURE

Usability testing and evaluation is an iterative process. Usability evaluations should be 

conducted several times during the life cycle of the system, and results should have a 

direct influence on system design, providing continuous feedback for the designers of 

the system. Usability should be part of the system development life cycle from the 

earliest stages, to make sure that users’ needs, capabilities, and limitations are 

considered from the start of design and development.

4.2.1.4 APPLICABLE REQUIREMENTS

Usability requirements are specified in NASA-STD-3001 Volume 2 section 10.0 Crew 

Interfaces. The principal requirements are the 3 listed below:

 Usability Acceptance Criteria [V2 10001]

 Crew Interface Provision [V2 10002]

 Provision of Usable Interfaces [V2 10003]

NPR 8705.2B paragraph 2.3.10 requires human-in-the-loop usability evaluations for 

human-system interfaces. The NPR-required deliverables at PDR and CDR include 

summaries of how these evaluations should be used to influence system design.
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4.2.2 CONDUCTING A USABILITY STUDY

A variety of methods and metrics may be used for the purpose of conducting a usability 

study; some of them are described in detail later in this section. Whichever methods and 

metrics are selected, a structured iterative approach based on human-centered design 

is to be used. This section provides a high-level, step-by-step approach that may be 

tailored to fit each usability study.

1. Define the purpose of the study

- Decide what features of the system are to be tested during the design phase 

(e.g., features that may be problematic or frequently used features). For 

example, the purpose of the study may be to provide a basis for selecting 

between 2 cursor control device prototypes, or it may be to evaluate a specific 

display implementation.

2. Define tasks

- Develop a list of crew and system tasks that are related to the tested features 

and define conditions that are relevant to these tasks. This procedure may 

include defining task criticality and frequency, identifying task dependencies 

and interactions, and defining operating environments (e.g., vibration, 

acceleration, lighting, suit conditions), as well as planning for associated 

resources such as personnel and equipment. For usability testing, the 

identification of potential errors that may be encountered for each task is also 

important. 

- Not all tasks can always be selected for usability testing if the number of 

possible tasks is large; therefore a subset of possible tasks may be selected. 

It is wise to select tasks that are frequently performed, tasks that are critical 

due to time constraints or potential for error, and tasks that involve a unique 

or novel type of interaction or understanding.

3. Define user sample

- The users in the usability test should be a sample of the expected user group 

for the system. Factors to take into account may include age, gender, 

anthropometry, visual acuity, or special skill sets (e.g., trained pilots).

4. Select methods and metrics to be used

- Possible methods and metrics for usability studies are discussed later in this 

section. The selection of methods and metrics depends on the purpose of the 

study, the number of subjects available, and the fidelity of prototypes or 

mockups. Gathering measures that will give you the relevant feedback for the 

design is critical; for example, if the design criteria of highest concern are time 

and errors, usability error rates would be an appropriate measure, whereas if 

user perceptions of simplicity are of highest concern, then ease of use, 

satisfaction, or aesthetics as evaluated by a survey or questionnaire may be 

more appropriate.
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5. Plan evaluation design

- Determine the appropriate number of subjects for the study. This may vary 

with the method selected. A minimum of 8-10 subjects is typically 

recommended. More subjects are needed to find less frequent design issues. 

Subjects should be representative of the user population in terms of 

experience, training, age, and other factors.

6. Collect data

- Complete the collection of data according to previous planning steps. When 

mockup hardware or prototype software is used, the level of fidelity should be 

documented and taken into consideration when analyzing results.

7. Analyze data

- The types of analyses conducted on data from usability tests depend on the 

objectives of the study. A quantitative analysis can help compare interfaces, 

determine whether error rates decreased with a new design, or compare 

efficiency of and satisfaction with the various designs. A qualitative analysis 

can point to reasons behind any usability issues and can provide information 

about user needs and preferences. The qualitative analysis looks at 

comments and observations provided by the users (e.g., the frequency with 

which different issues were mentioned).

- Depending on the measures recorded, decide what descriptive and statistical 

methods can be used. Consult Sauro and Lewis (2005) about data from a 

small sample size (n) and statistical methods for user testing. Sometimes only 

descriptive statistics are appropriate (e.g., range, mean, median, standard 

deviation), whereas at other times it is appropriate to look at pairwise 

comparisons of performance measures.

4.2.3 USABILITY EVALUATION METHODS

Many usability evaluation methods exist. Some are conducted by human factors experts 

alone (e.g., heuristic evaluation, cognitive walkthrough) and others are conducted with 

the participation of users or test subjects (e.g., user testing, knowledge elicitation). 

Which method should be selected depends on the purpose and needs of the evaluation.

4.2.3.1 HEURISTIC EVALUATION

Heuristic analysis is an assessment of how a device or system conforms to wellestablished user interface design rules, and is performed by a human factors expert or 

group of experts. 

Heuristic analysis is particularly useful early in the design process for identifying 

problematic aspects of the user interface. Also, it is useful for comparing potential 

interface designs because the assessments for each rule can be compared across 

products. This analysis method is usually quick and inexpensive. The weaknesses of 

heuristic analysis methods are that, generally, they are not applied in the actual use 

environment, and typical or expected device users are usually not involved in the 

evaluation. Heuristic analysis often yields good design insights early in the development 
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process. However, it should be used in conjunction with other techniques that acquire 

input from expected users, especially when heuristic analysis is used later in the design 

process.

Based on the ten heuristic rules (listed below) developed by Jacob Nielsen (1993), the 

method provides a high-level evaluation of a system. Such evaluations are often 

completed by only one reviewer, although having multiple reviewers is recommended. 

Furthermore, expert reviewers usually find more issues than a novice usability analyst. 

When a heuristic evaluation is performed, the following heuristics can be used to 

evaluate the design:

1. Use simple and natural dialogue

2. Speak the user’s language

3. Minimize the user’s memory load

4. Maintain consistency

5. Provide feedback

6. Clearly mark exits

7. Provide shortcuts

8. Use good error messages

9. Prevent errors

10.Provide useful help and documentation

4.2.3.2 COGNITIVE WALKTHROUGH

Cognitive walkthrough involves a structured review of user actions for performing a 

sequence of predefined tasks. It involves working through the cognitive and motor 

actions a user would take for each step, to identify the steps in which the usability of the 

interface is not optimal. This method focuses on user tasks and user goals rather than 

evaluating the interface based on general guidelines. A cognitive walkthrough early in 

the design process permits evaluation of different preliminary design concepts. Later in 

the design process, when designs have become better defined, a cognitive walkthrough 

may still be productive.

4.2.3.3 CONTEXTUAL INQUIRY AND OBSERVATION

Contextual inquiry generally involves unobtrusive observation of users performing 

relevant tasks associated with the devices or similar devices in the actual use 

environment. Observing and working with users in their actual use environment permits 

a better understanding of the relevant tasks and workflow. This method is typically used 

early in the design process (i.e., during conceptual design and requirements analysis) to 

understand users and their tasks. This technique generally does not reveal cognitive 

processes, attitudes, or opinions.

4.2.3.4 DESIGN AUDITS

In a design audit, the proposed attributes and components of the user interface are 

compared against a checklist of good design practices. The checklist itemizes 

characteristics that the user interface should possess along with some method of 

recording whether or not the interface meets the listed standards and it can be built 
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based on general standards documents such as ISO standards or the Human 

Integration Design Handbook (NASA/SP-2010-3407). Design audits are relatively quick 

and cost-effective but may yield only a superficial understanding of user interface 

issues.

4.2.3.5 DEVICE COMPARISONS AND FUNCTIONAL ANALYSIS

Alternative devices or alternative device concepts can be compared by arranging a list 

of devices and their attributes in a matrix format. The attributes of each of the device 

alternatives are assigned ratings or scored on a series of criteria. These comparisons 

can be useful for understanding which design approach best meets the user needs.

4.2.3.6 EXPERT REVIEWS

Expert reviews depend on the knowledge and experience of human factors specialists 

to identify design strengths and weaknesses and to recommend opportunities for 

improvement. Expert reviews combine the basics of heuristic evaluation and cognitive 

walkthrough. Depending on the expertise level of the evaluator, they can be very 

effective. To catch the majority of design issues, a minimum of 2 experts should 

evaluate a given interface. Expert reviews can be performed on design concept 

sketches as well as on working prototypes. Many serious design flaws can be detected 

early, without incurring costs for user testing. However, if used in isolation, this 

technique is unlikely to detect all of the design flaws.

4.2.3.7 FUNCTIONAL ANALYSIS

A functional analysis provides a representation of the functions and events required to 

meet system objectives. This type of analysis is used to determine the appropriate 

allocation of functions amongst humans and machines or automated systems. 

Numerous types of functional analyses can be performed, including operational 

sequence diagrams, the Functional Analysis Systems Technique (FAST), and computer 

simulation and modeling techniques (e.g., Systems Analysis of Integrated Network of 

Tasks [SAINT]).

4.2.3.8 INTERVIEWS

Often, it is useful to discuss design issues with a small group of users, especially when 

the goal is to generate ideas or reach consensus. Interviews can also be conducted 

individually. This method is for information gathering, not for evaluation. Structured or 

directed interviews are useful in circumstances in which the goal is to uncover answers 

to specific questions, often when designers are fairly well along in the design process. 

In contrast, unstructured interviews are useful for gaining initial insights about designs 

under conditions in which the designer wants to avoid biasing the interviewee in any 

particular direction.

4.2.3.9 PARTICIPATORY DESIGN

Participatory design provides potential users with tools that allow them to become adhoc design team members. Examples of the many tools available include 3-dimensional 

models of components that users might be asked to arrange in a preferred 
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configuration, or 2-dimensional representations that users arrange to represent their 

ideas about a product’s design. Similarly, users could be asked to direct the efforts of an 

illustrator to represent their ideas, or to manipulate options on a computer screen.

4.2.3.10 USER TESTING METHODOLOGY

Usability testing and human-in-the-loop (HITL) evaluations are methods that evaluate a 

system by testing it with its users. The testing consists of asking users to complete 

tasks related to the system and capture their performance (e.g., error, deviation from 

optimal path, time) and subjective comments.

4.2.4 USABILITY METRICS

4.2.4.1 EFFECTIVENESS, EFFICIENCY, AND SATISFACTION

Many usability metrics exist that can be used in usability studies. The most relevant 

ones are the measures of effectiveness, efficiency, and satisfaction:

Effectiveness: The accuracy and completeness with which users achieve certain 

goals. Indicators of effectiveness include the quality of the user’s 

solution and error rates. 

Efficiency: The relation between (1) accuracy and completeness with which 

users achieve certain goals and (2) resources expended in 

achieving them. Indicators of efficiency include task completion 

time and learning time. 

Satisfaction: Users' comfort with and positive attitudes toward the use of the 

system. Indicators of satisfaction include survey results and scores 

on standardized scales.

It is important to consider that efficiency, effectiveness, and satisfaction have been 

found to have low correlation among them (Hornbæk & Law, 2007; Sauro & Lewis, 

2009). Therefore, it is advisable to measure all 3 factors to get an appropriate measure 

of usability. 

4.2.4.1.1 METRICS OF EFFECTIVENESS

The most frequently used metrics of effectiveness are error rates and task/step 

success:

 Error rates 

o Error rates can be calculated in multiple ways: total number of errors on every 

step (possibly divided by the number of steps; e.g., out of 8 subjects, 5 

committed an error on a given step), total number of errors on every task 

(e.g., 50 errors), or mean number of errors (e.g., 50 errors divided by 100 

steps equals 0.5 error rate). The use of error counts across all task steps 

versus rates (where the number of steps is in the denominator, resulting in a 

ratio of errors to steps or a percentage) is at the discretion of the analyst, and 

should be guided by the specifics of the test.
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 Task/step success

o Task/step completion rates, e.g., 9 out of 10 tasks have been completed 

successfully. 

4.2.4.1.2 METRICS OF EFFICIENCY

The most frequently used metrics of efficiency:

 Step/task completion time: The time needed to complete a step or a task. 

 Deviation from the optimal path: The number of times users do not use the most 

efficient path to reach their goals

4.2.4.1.3 METRICS OF SATISFACTION

The most frequently used metrics of satisfaction include:

 Ratings of satisfaction with the interface. 

 Survey addressing satisfaction with specific aspects of the interface 

 Specific attitudes toward the interface, as measured on a standardized attitude 

questionnaire. 

o Users' satisfaction can be measured by attitude rating scales such as 

Software Usability Measurement Inventory (SUMI) or System Usability Scale 

(SUS) (Bangor, Kortum, & Miller, 2008; Kirakowski & Corbett, 1993).

4.2.4.2 SUBJECTIVE COMMENTS

Subjective comments are collected during usability studies by asking subjects to think 

aloud while completing the tasks, unless task completion time is recorded, in which 

case subjects should be asked to comment about their experience after the 

trial/step/task is complete. Subjective comments should be recorded and analyzed 

according to how many subjects mentioned each of the issues and also ranked 

according to severity. These comments help to identify various types of errors and their 

design implications.

4.2.5 INTERPRETING AND USING THE RESULTS

The results of usability testing should be analyzed and related usability issues flagged 

for follow-up with the designers. These issues usually identify design problems such as 

unclear labeling or control identification, unintuitive task flow, and interface element 

locations that do not optimize the task flow. Such problems may result in low efficiencies 

or high error rates, or issues with physical interface design factors such as control sizing 

or orientation of movement. Use of usability results to further the design’s maturation 

can increase the efficiency and effectiveness of the interface while reducing errors and 

fatigue.

4.2.6 USABILITY EVALUATION TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.2.7-1 are recommended.
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TABLE 4.2.7-1 USABILITY EVALUATION TECHNICAL PRODUCTS

Technical Products

Phase 

A

Phase 

B

Phase 

C

Phase 

D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function allocation, 

and associated crew task lists. Includes 

identification of potential errors that can be 

encountered for each task.

I U U U --- ---

A summary of modeling/analysis/evaluation 

performed to date and the influence on system 

design with links to the detailed analysis results.

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10.

--- --- I U U ---

Verification plan. --- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are affected by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

For usability testing, task analysis must include an analysis of potential errors that can 

be encountered for each task. This information is necessary for the calculation of error 

rates, which is a required objective measure of usability.

Summaries of Modeling, Analyses, and Evaluations

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-system integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups 

with increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs 

and Iterate Solutions. It is important that summaries address how key and/or critical 

design decisions were assessed. Per the NPR 8705.2B, updated summaries are to be 

provided at each design review through the SAR. Also in paragraph 2.3.10, the use of 

HITL evaluation is a required method to progressively demonstrate that the operational 

concept meets system requirements for operational safety, efficiency, and user interface 

design.

For usability, this should include the evaluation of metrics for effectiveness, efficiency, 

and satisfaction as well as subjective data.
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Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement.

4.2.7 REFERENCES

Bangor, A., Kortum, P. T., & Miller, J. A. (2008). An empirical evaluation of the System 

Usability Scale (SUS). International Journal of Human-Computer Interaction, 24(6), 574-

594.

Hornbæk, K., & Law, E. L.-C. (2007). Meta-analysis of correlations among usability 

measures. Paper presented at the Proceedings of the SIGCHI conference on human 

factors in computing systems, April 28-May 03, 2007, San Jose, CA, USA.

ISO-9241-11. (1998). ISO/IEC 9241-11:1998. Ergonomic requirements for office work 

with visual display terminals (VDTs), Part 11: Guidance on usability.

Kirakowski, J., & Corbett, M. (1993). SUMI: the Software Usability Measurement 

Inventory. British Journal of Educational Technology, 24(3), 210-212.

Nielsen, J. (1993). Usability engineering. San Francisco, CA: Morgan Kauffman 

Publishers Inc.

Sauro, J., & Lewis, J. R. (2005). Estimating completion rates from small samples using 

binomial confidence intervals: Comparisons and recommendations. Paper presented at 

the Human Factors and Ergonomics Society Annual Meeting, Orlando, FL.

Sauro, J., & Lewis, J. R. (2009). Correlations among prototypical usability metrics: 

Evidence for the construct of usability. Paper presented at the Computer Human 

Interaction (CHI), Boston, MA.
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4.3 WORKLOAD EVALUATION

4.3.1 INTRODUCTION

Historically workload has been defined in a variety of ways. Workload has been defined 

alternately as the set of test or task demands, the effort that the subject must exert to 

meet those demands, and the resulting performance based on the task demands. 

However, in a survey of pilots, Roscoe and Ellis (1990) found that most pilots think of 

workload in terms of the effort required to meet the demands of the task. In other words, 

it is the mental and physical effort exerted by subjects to satisfy the requirements of a 

given task or scenario. 

Workload is an important component of crew interaction with systems, and designers 

must consider it when designing hardware and software with crew interfaces, 

procedures, and operations. Designers need to consider the workload of the user when 

designing and producing an interface or designing a task, as low workload levels have 

been associated with boredom and decreased attention to task, whereas high workload 

levels have been associated with increased error rates and the narrowing of attention to 

the possible detriment of other information or tasks (Sheridan, 2002). 

Evaluation of crew workload is required by NPR 8705.2B paragraph 2.3.9, which 

requires a description of how crew workload will be evaluated; and paragraph 2.4.9, 

which requires documentation of how crew workload was validated and determined 

acceptable. In space flight, the primary concern is avoiding unnecessarily high workload 

levels, given that space flight is generally a high-stress environment. Therefore, the 

process described below focuses on measuring workload with the goal of keeping 

workload at a level that does not negatively affect performance. For additional details on 

workload measures, predictors, and limits, please refer to section 5.7 in the NASA/SP2010-3407 Human Integration Design Handbook (HIDH).

Note that workload is closely linked with other human factors concepts such as handling 

qualities and usability, and that significant usability or handling qualities issues will often 

drive high workload ratings. These topics are covered in complementary HIDP sections 

along with this one, and the reader is strongly advised to review all 3 sections. The 

reader should also review the HIDP section on task analysis, as task analysis is 

required for identifying workload tasks.

4.3.1.1 APPLICABLE REQUIREMENTS

Workload requirements are specified in NASA-STD-3001, Volume 2, and further refined 

in program-level requirements documents. Volume 2 specifies in V2 5007 that 

“Cognitive workload shall be accommodated (to avoid overload or underload) in the 

design of all system elements that interface with the crew for all levels of crew capability 

and all levels of task demands”.

NPR 8705.2B requires the evaluation of crew workload (paragraph 2.3.9) and a 

description of how workload evaluation methods were validated (paragraph 2.4.9). 

Additionally, NPR 8705.2B requires human-in-the-loop (HITL) usability evaluations for 

human-system interfaces (paragraph 2.3.10). In addition, NPR-required deliverables at 
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PDR and CDR include presentations of how these evaluations were used to influence 

system design.

4.3.2 WORKLOAD ASSESSMENT PROCESS

The process of assessing the crew workload induced by the system involves the 

following:

1. Task analysis to identify the tasks and associated hardware and systems that are 

relevant to workload

2. Testing early and often in the engineering design life cycle: Testing of those 

tasks, hardware, and systems that task analysis identified as relevant to 

workload

3. Component-level through system-level testing

4. Verification

It is easier and more cost-effective to correct deficiencies in hardware or procedures 

that produce high crew workload during the early design phases rather than just before 

vehicle certification. For these reasons, workload assessments are best integrated early 

and often through the engineering design life cycle so that related design decisions can 

be made from a data-driven perspective and ensure crew safety and efficiency.

Consistent with core human-centered design philosophy, the consideration of workload 

can be done from the very earliest stages of design, though evaluation of workload does 

require a certain minimum level of design maturity. At the earliest stages of the design 

life cycle, integration of crew workload should focus on defining the various tasks that 

are relevant to workload. Task analysis is the method for identifying which crew and 

system tasks will be performed during each mission phase, the hardware associated 

with the task, and whether the task is expected to contribute to crew workload. Many of 

these considerations can be defined very early on during the vehicle specification stage, 

even before a request for proposal is released or before procurement activity. However, 

task analysis should continue to mature as the design progresses. Also, early in the 

design cycle, comparative measures of workload are effective in deciding between

design solutions, selecting the design that does not inflict high levels of workload. 

After task definitions, the next stage would be to start assessing crew workload in a 

series of simulated vehicle tasks. NASA has determined that for the current space flight 

programs (Multi Purpose Crew Vehicle Program and Commercial Crew Program),

workload should be assessed using the Bedford scale. The reasons this scale was

chosen are numerous, but arguably the most important is the ability to use the scale to 

determine whether workload is tolerable for the task. Many other types of scales (e.g., 

NASA Task Load Index, or TLX) are diagnostic or multi-dimensional, meaning that they 

allow the source of the workload to be localized. These types of scales are 

advantageous to use during the design phase, where modifications based on workload 

evaluations are possible. However, during the verification phase, the Bedford scale is 
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most appropriate. The Bedford scale is appropriate for verification because it provides 

anchors for every rating, is familiar to the crew population, and provides a decision gate 

in which ratings above this gate indicate that workload is not satisfactory without a 

reduction in spare capacity or is not tolerable. Given NASA’s decision to require that the 

Bedford scale be used for verification of current spacecraft, this section will focus on the 

Bedford scale. For a discussion of other types of scales, please refer to the HIDH, 

Chapter 5. How to assess workload is described below in paragraph 4.3.2.2 Assessing 

Workload Using the Bedford Scale, and in HIDH paragraph 5.7.3 Measures of 

Workload.

Eventually, as vehicle design maturity increases, the simulation fidelity also increases, 

and ratings achieved by means of simulation become more consistent. The value of this 

early and frequent evaluation of workload is really its direct interaction with design 

decisions, related to both hardware and procedures.

4.3.2.1 THE BEDFORD SCALE

The Bedford scale (Roscoe, 1987) was developed for and with the help of test pilots at 

the Royal Aircraft Establishment in Bedford, England. The Bedford scale is organized in 

a decision-tree format (see Figure 4.3.2-1) in which the subject starts at the bottom left 

corner and answers each question in order, to move to the next node. In this document, 

each box with a number (e.g., WL10) is called a level, and each grouping of 3 levels 

(e.g., WL7, WL8, and WL9) is called a group. For example, the subject first answers the 

question, “Was it possible to complete the task?” If the answer is “No,” the subject 

follows the branch to the right on the decision tree and reports a workload level of 10. If 

the answer is “Yes,” the subject follows the branch up to answer the next question, 

“Was workload tolerable for the task?” When the decision tree guides the subject to a 

group containing multiple workload levels, the subject selects the appropriate level on 

the basis of the descriptions. For example, if the subject answered “No” to the question 

“Was workload tolerable for the task?” he or she would evaluate their workload against 

the descriptions such as “Very little spare capacity, but maintenance of effort in the 

primary tasks not in question.” If this statement best reflects the workload, the subject 

selects WL7 for that task.
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FIGURE 4.3.2-1 THE BEDFORD SCALE

4.3.2.1.1 SPARE CAPACITY

The Bedford scale uses the concept of “spare capacity” to determine the workload level. 

The concept of “spare capacity” comes from the information processing approach to 

cognition, in which the brain is analogous to a computer with limited resources. If a 

computer has 100 MB of RAM and a task is using 50 MB, then the spare capacity of the 

system to perform another task is 50 MB. The same is true of the human system. The 

human brain has a limited capacity to perform tasks. If the primary task is using a 

certain amount of resources, then the resources left over (i.e., unused) are thought of as 

the spare capacity available to perform additional tasks. This explanation applies to both 

mental and physical resources. The workload to complete the task is the effort required 

or the amount of resources used out of the limited supply of resources available. The 

use of the concept of spare capacity in the application of the Bedford scale is discussed 

further in the next paragraph on assessing workload.
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4.3.2.2 ASSESSING WORKLOAD USING THE BEDFORD SCALE

Workload is assessed as part of a HITL evaluation. A HITL evaluation involves having 

one or more subjects perform a representative task while data are gathered from the 

subject(s) to meet an objective (e.g., task performance is measured or subjective 

feedback is provided by the subject). Workload should be assessed iteratively 

throughout the design cycle, allowing design changes to be made as necessary, in 

addition to the final verification testing. There are multiple ways to assess the workload 

of the task: physiological, performance, and subjective measures. Current NASA 

programs, MPCV and Commercial Crew program, have a requirement to assess 

workload using subjective measures. In a HITL evaluation aimed at assessing workload, 

each subject will be asked to perform a task and have an identified secondary task 

(whether mocked up for the test or just described to the subject), and the Bedford scale 

will be administered after completion of the task. Paragraph 4.3.2.2.1, below, discusses

how to administer the Bedford scale during a HITL evaluation.

It is critically important that before administering the Bedford scale in an evaluation, the 

test conductor defines the task, task steps, task duration, and what secondary 

tasks the subjects need to judge their spare capacity against. This ensures that 

each subject is exposed to the same information, which decreases the measurement 

error and leads to a more accurate measure of task workload. Additionally, each subject 

needs to understand the test setup, task, and expectations. The definition of a task is 

important because multiple steps are often required to complete a scenario, with 

possibly multiple tasks in each scenario, so subjects need to be very clear on which 

steps they should use to judge their workload. For example, if the task involves 

egressing the vehicle, subjects may be instructed that the task begins when they loosen 

their restraints to egress the seat and ends when their feet reach the floor exterior to the 

vehicle. This allows subjects to constrain the assessment of workload and exclude tasks 

that may have occurred before or after those instructed boundary points. Also, in 

defining the task steps for each subject, the test conductor is reducing the amount of 

subject variability that is introduced into the measure. Each subject in the test will base 

their workload rating on the same steps. 

The Bedford scale has been validated for administration at the end of a task and at 

specified intervals during a task. Administering Bedford at intervals during a task is 

primarily used when the Bedford scores will be correlated with some other measure of 

workload, such as heart rate, or with performance metrics. For space flight tasks, the 

Bedford scale should be administered at the end of the entire task, resulting in one 

score/rating for each subject for each task. During a task there may be peaks of high 

workload followed by periods of lower workload. It is best to advise the subject to either 

take the mental “average” or “weighted average” across those peaks and valleys to 

decide on the most representative level of workload, spanning the entire task duration. If 

task-specific testing (such as dry-run testing or development testing) has been done 

that shows short peaks of high workload, the test conductor may use the results of that 

testing to advise the subject to use some predetermined method of weighting the peaks 

of high workload when determining their overall Bedford level. 
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Every attempt should be made to make the assessment of tasks as high-fidelity and 

flight-like as possible. The test setup influences the subjects’ workload levels, and to

get a representative measure of workload for a given task, the task setup must be as 

representative as possible. Making the setup representative includes using high-fidelity 

hardware, software, test procedures, timelines, and environments, and including

multiple subjects for multiple crew scenarios. For example, if the subject’s task is to 

perform a piloting task using a display and a control, the content of the display needs to 

include everything that would be there in flight, accurately representing all details such 

as color, spacing, and labeling, and the control must be an accurate representation of 

the flight hardware, having an accurate tactile feel and shape, control characteristics 

(e.g., torque), and interaction with the display. In this example, deviations from the flightlike scenario such as too little display content or an inaccurate control would lead to an 

inaccurate measure of the workload associated with the task. Too little display content 

may lead to lower than actual workload ratings because extraneous information that 

could interfere with the task is absent, or it could lead to higher than actual workload 

ratings because not enough information is presented for the subject to complete the 

task without mental compensation. Just as the assessment of workload is contingent on 

the test setup, an accurate depiction of the workload induced by a design is contingent 

on having a high-fidelity design.

Subjects need to maintain error rates and task completion times commensurate with 

the performance requirements of the particular task. Without this stipulation, a subject 

may decide to compromise performance or the time it takes to complete the task so that 

their workload level does not increase. If this happens, the resulting workload rating will 

be an artificial representation of the actual workload necessary to complete the task. To 

maintain task performance across individuals and get a representative measure of 

workload, it is important to instruct each subject how much time they have to perform 

the task and what performance level they need to achieve. 

It is important when administering the Bedford scale to identify and describe to subjects 

what the secondary tasks may be since the Bedford scale is designed to assess 

spare capacity. Many studies have shown that people have difficulty judging their 

capacity (mental and physical) without a reference to judge that capacity against. One 

type of reference that has been shown to be helpful in making the judgment is for the 

subject to determine whether they have the capacity to perform an additional task. For 

example, if the primary task is piloting and the secondary task is talking to the copilot, 

subjects may have sufficient spare capacity to perform this secondary task and a low 

workload rating is provided (e.g., WL3). However, if the primary task is piloting and the 

secondary task is tracking a visual item around a crowded display, subjects may not 

have the spare capacity necessary to perform both tasks without a detriment in 

performance, and thus a high workload rating may be provided (e.g., WL6), even 

though the primary task demands were the same. In the latter case, the visual tracking 

task is not a good secondary task because the purpose of the secondary task is to aid 

the subject in assessing whether there is spare capacity to perform that task while 

performing the primary task. If the secondary task is so difficult that it interferes with the 

primary task, then it is not serving the purpose of assessing spare capacity, but is 
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affecting performance. If the subject is judging whether they have the capacity to 

perform an additional task, it is essential that they understand the requirements of the 

additional task. A clear understanding of the secondary task demands allows the 

subject to make the best possible decision as to his/her spare capacity. If a subject only 

has limited knowledge of the secondary task demands, then he/she may misjudge the 

amount of spare capacity because of failure to consider all of the task steps or mental 

requirements in the task and the mental/physical resources necessary to complete the 

task. Also, it is advisable to make the secondary task a realistic task identified in the 

task analysis, as these tasks may be more familiar and applicable to the user in a given 

scenario.

In space flight, both piloting and non-piloting tasks need to be assessed to ensure 

that they do not introduce unnecessary workload. Although the Bedford scale was 

created for and has been validated with pilots and piloting tasks, NASA believes that the 

Bedford scale is appropriate for verification of all space flight designs because the scale 

“provides anchors for every rating, is familiar to the crew population, and provides a 

decision gate in which ratings above this gate are indicative of workload that is not 

satisfactory without a reduction in spare capacity” (e.g., CH10003V and CH10004V). 

Even though the Bedford scale can be applied to non-piloting tasks, there are certain 

factors that may need extra attention from the test conductor when preparing for an 

evaluation of a non-piloting task, simply because there is no precedent to refer to. 

Among those factors are identifying the task steps and secondary tasks for non-piloting 

primary tasks, such as vehicle egress. In a vehicle egress task, a crewmember may 

need to talk to another crewmember to successfully egress the vehicle. The test 

conductor needs to decide and advise the subject whether talking to another 

crewmember is part of the primary task or is considered the secondary task. To do this, 

the test conductor should run through the task with the help of appropriate stakeholders 

(e.g., crew, ops, hardware designers, human engineering) before the evaluation to 

determine each task step in the primary task, and what the appropriate secondary task 

should be. Often iterative testing during the design phase serves this purpose for a 

verification test. NASA has experts who can help determine appropriate secondary 

tasks.

Several differences are expected between a nominal and an off-nominal situation, 

including new or increased troubleshooting tasks, time pressure due to an emergency 

situation, increased communication between crewmembers and/or the ground, 

performing less frequently or minimally trained actions, and so on. All of these offnominal factors have the potential to increase task workload. Thus, there should be 2

workload requirements with different acceptance criteria -- one for a nominal task and 

one for an off-nominal task (e.g., CHSIR nominal and off-nominal workload 

requirements). An off-nominal workload requirement allows higher workload ratings to 

be given for the task (up to and including WL6) than a nominal workload requirement 

allows (up to and including WL3), because workload is expected to be higher for the offnominal task than for the nominal task, due to the differences highlighted above. 

However, for the off-nominal task, a Bedford rating of WL6 or less should be required 

because ratings greater than WL6 indicate that the workload is not tolerable for the task. 
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The second question in the Bedford decision tree is “Was workload tolerable for the 

task?” and if the answer is “no,” then the subject is required to provide a rating of WL7 

or above. When designing for space flight, it is unacceptable for the workload to be 

intolerable for the subject. Even for an off-nominal task, the design should support a 

tolerable workload level. 

4.3.2.2.1 ADMINISTERING BEDFORD

Any person administering the Bedford scale in a HITL evaluation needs to be trained on 

the parameters of the scale and be able to describe workload and the scale properties 

to the subjects. 

At a HITL evaluation to measure workload, the subject will arrive at the test site, give 

informed consent, and then be briefed on:

1. The definition of workload. The experimenter needs to provide the subject with a 

definition of workload so that he/she has a concept of which mental and physical 

faculty they are judging.

2. The Bedford scale will be used to assess the amount of workload induced by the 

task, hardware, software, or procedures. Subjects should be shown a copy of the 

scale and this copy should be available throughout the entire test session for the 

subject to refer to as needed.

3. The Bedford scale assesses a combination of mental and physical workload. 

Because the Bedford scale does not dictate how those factors are combined, 

subjects need to make their own determinations of how they should be combined 

for an overall workload rating, or the experimenter can advise the subject (if there 

is some rationale why more weight should be given to either the mental or 

physical aspect).

4. The concept of spare capacity and how it relates to workload and the Bedford 

scale.

5. The primary task to be completed and the secondary task to judge spare 

capacity against. If a piece of hardware or part of a procedure should be given 

more emphasis or weight (based on some rationale), then that needs to be 

described to the subject.

6. The decision tree. It is important that the subject always walk through the 

decision tree starting on the bottom left side and answering each question to 

move up or to the right. Subjects who have experience with the scale may want 

to jump to an answer without walking through the entire tree. However, to make 

sure that the response is an accurate representation of the subjects’ workload 

and that they have not had a memory failure regarding the level wording, and to 
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keep consistency across subjects, it is important that all subjects follow the same 

procedure and walk through the entire tree before responding. The differences 

between some of the levels are subtle, so the experimenter should walk through 

the tree with the subject during the briefing to make sure that the subject 

understands the content, or what each level means, and answer any questions 

the subject may have.

7. Acceptable ratings. The Bedford scale allows the use of half ratings, even 

between groups (such as levels 3 and 4, or 6 and 7). A half rating between levels 

should be given if the subject’s workload fell somewhere between the 

descriptors. A half rating between groups should be given only if the subject 

cannot determine an answer to the question on the left distinguishing those 

groups.

After the briefing, the subject will perform the primary task. At the conclusion of the task, 

the subject should be shown the Bedford scale and asked to walk through the decision 

tree until he/she decides on a workload level. The experimenter should be present with 

the subject to answer any questions he/she may have. The subject should verbally 

provide the rating to the experimenter, who will record it. The experimenter should then 

ask the subject to verbally explain why he/she provided that rating (i.e., what is the 

rationale?). It is important to understand why each subject provides the rating that they 

do, especially in the design phase, so that changes to the design can be made as 

necessary. A Bedford workload rating alone cannot tell a designer what needs to be 

improved in a design (the Bedford scale is not diagnostic), only that the design imparted 

a certain level of workload on the subject. The dialogue with the subject is critical in 

understanding what may have induced the workload level.

Because the Bedford scale is not diagnostic, it can be beneficial, especially early in the 

design phase, to use a more diagnostic or multi-dimensional workload scale along with 

the Bedford. An example of a multi-dimensional scale is the NASA Task Load Index 

(TLX). NASA-TLX provides an estimate of overall workload based on a weighted 

average of 6 subscale ratings: Mental Demand, Physical Demand, Temporal Demand, 

Own Performance, Effort, and Frustration (Hart & Staveland, 1988). Subscale ratings, 

which range from 1 to 100 in 5-point increments, are given verbally or by selecting a 

position along a scale presented on a rating form or computer screen. In addition, raters 

quantify the relative importance of each factor in creating the workload they 

experienced. The relative importance values, which range from 0 to 5, are used to 

weight the magnitude ratings when computing the overall workload score. Diagnostic 

information is provided by variations in subscale ratings as well as the weight given to 

each factor.

4.3.2.2.2 ANALYZING AND INTERPRETING RESULTS OF THE BEDFORD SCALE

When thinking about choosing an appropriate level of workload on the Bedford scale, 

the mental distance between the levels is not predicted to be equal. In other words, the 

difference between levels 1 and 2 may not be the same as the difference between 
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levels 9 and 10; workload rated level 10 is not twice as much as workload rated level 5. 

Therefore the scale is not linear. Also, the distribution of level responses does not follow 

a standard, predictable pattern; and therefore the underlying distribution is not known. 

Because the distribution of responses is not known and the scale is not linear, the use 

of probability distribution descriptive statistics (such as mean or median) or the use of 

parametric statistics (which assume a known distribution) are not appropriate methods 

for describing or analyzing Bedford data. The most effective way of describing the data 

is using frequency tables or plots (e.g., histograms, frequency weighted scatter plots). 

The most meaningful presentation of the data shows the number of subjects who gave 

any particular rating. For example, an evaluation with 6 subjects who rated their 

workload a 1 and 2 subjects who rated their workload a 2 on the Bedford scale would 

suggest that the design induces low levels of workload. 

4.3.2.2.3 INCORPORATING WORKLOAD THROUGHOUT THE PROJECT LIFE CYCLE

To identify the tasks that are relevant to the workload requirement, a task analysis must 

be performed outlining all tasks the crew will be performing during all mission phases. 

Once the task analysis is complete, representative nominal and off-nominal tasks may 

be selected for evaluation. The task analysis should begin at the beginning of the 

program and be refined through CDR. After SDR, the developer is expected to begin 

generation of the verification task list. The verification task list should be delivered at 

PDR and CDR. 

A workload requirement needs to be flowed from the system level down to the 

component level. At the system level, NASA wants to ensure that the vehicle is usable 

by the crew without inducing unnecessary workload. Each component that makes up 

the system needs to be designed well, with crew workload in mind, in order for the 

vehicle to support adequate crew workload levels.

NASA expects the Bedford scale (along with an additional diagnostic scale, if desired) 

to be used during developmental testing of tasks (i.e., HITL evaluations) that are 

predicted to be relevant to crew workload. These tasks may not ultimately be selected 

for verification testing, but the administration of the Bedford scale during development 

allows a better understanding of the workload associated with a given task, familiarity 

with the administration of the Bedford scale, potential redesign of hardware or software

based on scale ratings, and crew feedback for associated tasks.

Products associated with workload should always include these items:

 Task analyses

 Component, subsystem, and system requirements traceability

 Implementation of the above best practices for administering and analyzing the 

Bedford scale in test plans and analysis (for developmental and verification 

testing)
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4.3.3 WORKLOAD EVALUATION TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.3.3-1 are recommended.

TABLE 4.3.3-1 WORKLOAD EVALUATION TECHNICAL PRODUCTS

Technical Product

Phase

A

Phase 

B

Phase 

C

Phase 

D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function allocation, 

and associated crew task lists. I U U U --- ---

An explanation of how crew workload will be 

evaluated for the reference missions.

Required per NPR 8705.2B paragraph 2.3.9.

--- I U U --- ---

A summary of modeling/analysis/evaluation 

performed to date and the influence on system 

design with links to the detailed analysis results.

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10.

--- --- I U U ---

Verification plan. --- --- I U U ---

A description of how crew workload for the 

reference mission was validated and determined to 

be acceptable. Required per NPR 8705.2B 

paragraph 2.4.9.

--- --- --- ---

X

(ORR)

---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are affected by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of the crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

Explanation of Workload Evaluation Plans

As required by NPR 8705.2B paragraph 2.3.9, an explanation of how crew workload will 

be evaluated for the reference missions is required at SDR, and then updated at PDR 

and CDR. Documentation of plans for workload evaluation will provide NASA with 

insight into this important aspect of human-system integration. 

Summaries of Modeling, Analyses, and Evaluations

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-system integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 
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Iterate Solutions. It is important that summaries address how key or critical design 

decisions were assessed. In accordance with NPR 8705.2B, updated summaries are to 

be provided at each design review through SAR. Also in paragraph 2.3.10 of that 

document, the use of HITL evaluation is a required method to progressively

demonstrate that the operational concept meets system requirements for operational 

safety, efficiency, and user interface design.

The use of iterative testing throughout the design is a necessary part of designing for 

workload. It is expected that the Bedford scale (along with additional metrics, as 

needed) will be used during developmental testing. NASA will provide input as needed 

concerning testing details such as appropriate secondary tasks.

Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 

Workload Validation

As required by NPR 8705.2B paragraph 2.4.9, a description of how crew workload for 

the reference mission was validated and determined to be acceptable is required at 

SAR. 

4.3.4 REFERENCES

Hart, S. G., & Staveland, L. E. (1988) Development of NASA-TLX (Task Load Index): 

Results of empirical and theoretical research. In P. A. Hancock & N. Meshkati (Eds.), 

Human mental workload (pp. 139-183). Amsterdam: North Holland. 

Roscoe, A. H. (1987). Inflight assessment of workload using pilot ratings and heart rate. 

In A. H. Roscoe (Ed.) The practical assessment of pilot workload (AGARD-AG-282) (pp. 

78-82). Neuilly-sur-Seine, France: Advisory Group for Aerospace Research and 

Development.

Roscoe, A.H., & Ellis, G.A. (1990). A subjective rating scale for assessing pilot workload 

in flight: A decade of practical use (Technical Report TR 90019). Farnborough, UK:

Royal Aerospace Establishment.

Sheridan, T. (2002). Humans and automation: Systems design and research issues.

New York: Wiley.
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4.4 HUMAN ERROR ANALYSIS

4.4.1 INTRODUCTION

Human error is a broad classification of effects that may be the result of action or 

inaction by a pilot or human operator in the control of a vehicle or vehicle system. Errors 

of this sort can be the result of many different causes, which may range from 

inadvertent actions or usability- or interface-induced errors to errors related to fatigue 

and various forms of confusion, to name just a few. The intent of conducting the Human 

Error Analysis (HEA) is to determine the likely or possible errors that could occur in the 

operation or use of a vehicle, system, or component, so that the design can be modified 

to reduce or eliminate errors and reduce their likelihood to an acceptable threshold.

4.4.2 APPLICABLE REQUIREMENTS

NASA’s philosophy behind HEA for spacecraft systems requires that iterative human 

error analyses be conducted, the results of which are to be used for making design 

decisions. These analyses are supposed to cover all mission phases, including 

operations planned as responses to system failures. This philosophy is best 

represented by NPR 8705.2B Human-Rating Requirements for Space Systems, most 

notably in paragraphs 2.3.11 and 2.3.11.1 (the primary HEA sections), as well as in 

paragraphs 2.2.3, 2.3.1, 2.3.6, 2.3.12, and 3.2.4. Additional requirements associated 

with HEA are included in NPR 8715.3 NASA General Safety Program Requirements 

and NPR 8705.5 Technical Probabilistic Risk Assessment (PRA) Procedures for Safety 

and Mission Success for NASA Programs and Projects.

4.4.3 HUMAN ERROR ANALYSIS METHODS

This document is intended to join together industry standard methods for HEA within the 

framework of human-system integration (HSI). The use of HSI processes in aviation is 

well established, as is the implementation of human error analysis. Many HEA 

approaches are described in the literature, and the vehicle, system, or component 

developer must consider the most appropriate method for any given analysis. 

Numerous tools are associated with the analysis of human error and are driven by a 

variety of factors including the inherent variation in individual performance capabilities 

from person to person, the difficulties in forecasting possible errors and probabilities 

before they occur, and the needs of accident investigators to retroactively deduce the 

factors associated with an incident.

Note that human error analysis is closely linked with other human factors concepts such 

as workload and usability, and that significant usability issues or excessive workload 

demands will often be associated with an increased incidence of human errors. Indeed 

usability errors are a specific subset of human error referred to as “interface induced 

errors,” alluding to the fact that poor interface design was a direct cause of an error. 

Usability and workload considerations are covered in complementary HIDP sections as 

well as this one, and the reader is strongly advised to review all 3 processes.

4.4.4 RESERVED
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4.4.5 HUMAN ERROR ANALYSIS TECHNICAL PRODUCTS

Reserved
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4.5 DESIGN FOR CREWMEMBER PHYSICAL CHARACTERISTICS AND CAPABILITIES

4.5.1 INTRODUCTION

The NASA-STD-3001, Volume 2 NASA Spaceflight Human-System Standard section 4 

Physical Characteristics and Capabilities includes requirements to ensure that the entire 

crew population can physically be accommodated within the spacecraft and integrated 

human-systems interfaces. This process document describes the philosophy and 

approach of including the parameters of anthropometry, range of motion, strength, body 

surface area, body volume, and body mass in the design process, and to evaluate the 

spacecraft design against requirements. The process also details the various factors 

that will affect successful accommodation of the population within the design and how to 

account for their effects. The anticipated technical products needed to assess whether 

the design is on track during the course of the engineering life cycle are also discussed 

in the context of this design process. The purpose of the process for each parameter of 

anthropometry, range of motion, strength, body surface area, body volume, and body 

mass for any space vehicle design is to ensure accommodation and physical 

incorporation of the crew within the design so that the entire crew population can fit, 

reach, and perform tasks while maintaining a safe and successful mission. Additional 

information on anthropometry, biomechanics, and strength can be found in chapter 4 of 

the NASA/SP-2010-3407 Human Integration Design Handbook (HIDH).

4.5.1.1 HOW TO USE THESE GUIDELINES

Section 4.5 describes processes for critically evaluating a proposed design by using 

approaches based on anthropometry, range of motion, body surface area, body volume, 

body mass, and strength. Each approach’s methodology is outlined from initial design 

concept to final verification. Most of the processes are iterative, using a combination of 

analytical, computer-based, and/or physical human-in-the-loop (HITL) task evaluations. 

The end goal is to provide a basic framework that space flight programs and developers

can use as a guide to identify population characteristics, set appropriate assumptions, 

conduct testing and analysis, and outline the expected technical products in the 

engineering design life cycle.

4.5.1.2 THE INTEGRATED APPROACH

An integrated approach examines the design across all possible physical characteristics 

and evaluation methodologies at various stages in the design process. It is 

recommended that an integrated approach is used to understand how the primary 

physical characteristics and capability aspects relate to each other within a design to 

ensure that, for each aspect and across aspects, the entire population meets design 

compliance. More information on design using the integrated approach is given in 

paragraph 4.5.7.

4.5.1.3 ADDITIONAL CONSIDERATIONS AND NASA ASSISTANCE

NASA has unique experience in suit design and accommodation for space missions. It 

is anticipated that spacecraft developers who include use of Launch, Entry, Abort (LEA) 

suits for crewmembers may have questions about suit implementation and design 
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criteria, specifically on how to incorporate or account for suit effects in their design. 

Additionally, needs may arise for designs to place the crew in postures or dynamic 

activities that differ from standard conventions. For these circumstances or questions on 

the application of requirements, suit factors, or accommodation due to suit usage, 

NASA is available to facilitate interpretation and work with developers to assist their 

successful design efforts.

4.5.2 DESIGN FOR ANTHROPOMETRY

4.5.2.1 INTRODUCTION

The purpose of the design requirements is to ensure that all vehicle, vehicle-suit 

hardware, and interfaces are operable by the entire anticipated crew population. NASA 

requires and expects that all crewmembers are provided with hardware that they all can 

handle, operate, and use for mission success and crew safety. Thus it is necessary that 

the designers and developers verify and validate, by means of analysis, modeling, and 

physical testing, each design against the anthropometric requirements set forth in 

NASA-STD-3001, Volume 2 section 4.

4.5.2.2 APPLICABLE REQUIREMENTS

The following NASA-STD-3001, Volume 2 requirements are applicable to 

anthropometry:

 Data Sets [V2 4001]

 Data Set Characteristics [V2 4002]

 Population Definition [V2 4003]

 Data Set Assumptions [V2 4004]

 Body Lengths Data [V2 4005]

 Changes in Body Lengths [V2 4006]

4.5.2.3 SELECTION OF AN ANTHROPOMETRIC DATA SET

The NASA-STD-3001 NASA Spaceflight Human-System Standard Requirement V2 

4001 specifies that an anthropometric data set for the crewmember population must be 

selected and implemented in the design, and V2 4004 specifies that age, gender, and 

physical condition shall also be included in this data set. Furthermore, Requirement V2 

4003 requires that the definition of the population ranges for the physical dimensions 

that the system is intended to accommodate shall also be included. 

Proper selection of the data set to represent the crewmember population is of critical 

importance. First, the data set itself must reflect the physical range of the anticipated 

crew population. If the general public will be expected to be accommodated in the 

design, then a data set that reflects a general population should be selected. For the

NASA astronaut crew, the anticipated population is akin to a military population, which 

is more restrictive over a comparable measurement range than a general population. 

The NASA anthropometry data set for Space Shuttle, Space Station, Constellation, and 
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Commercial Crew is based on military Anthropometric Survey (ANSUR) data. 

Requirements (e.g., anthropometry limits, strength limits) for each of those programs 

were selected using the NASA data set and modified according to program needs such 

as changes in selection criteria for future crew populations. Secondly, the selected data

set must include the measurements that are critical to the design to ensure proper 

accommodation. Requirement V2 4005 specifically names body lengths as critical to be 

incorporated into an anthropometric data set. If the data set consists of only height and 

weight, it does not capture the critical design parameters or the variation present in the 

population. For example, individuals may have nearly identical stature but some may 

have long torsos and short legs whereas others have short torsos and long legs. 

Including body segment parameters and their variations is critical when examining the 

way the human fits into a complex, confined space. With proper data set selection, one 

can ensure that the critical dimensions integral to the design of a vehicle and suit are 

representative of the range of anthropometry within the crewmember population.

This crewmember population data set is not only used to select measurements and 

accommodation ranges, but it is also used for all aspects of population analysis. One 

cannot always have the full range of the population represented in test subjects; thus 

the data set is used for analyses to determine the extent of the population 

accommodated and to place test subjects within the population to classify and quantify 

their clearance and accommodation within the space. 

4.5.2.4 ANTHROPOMETRY GENERAL OVERVIEW

The evaluation of designs is a multiphase process that depends on the stages of the 

design life cycle. In the preliminary stages of design, robust analytical and computeraided design (CAD) modeling should be used at a minimum, to identify the worst-case 

scenarios and the critical dimensions of interest, and to determine accommodation of 

the design. The assumptions of posture, suit effects, and other human interface 

variables must be documented so they can be verified with future HITL testing. HITL 

testing will either validate those assumptions or disprove them. If the assumptions are 

disproven, the analytical and CAD modeling work can be reanalyzed with the corrected 

information and the design can be iteratively analyzed and verified using HITL testing. 

As the design matures within the design cycle, the evaluation of the design against the 

selected anthropometric data set must move from the theoretical to the physical using 

HITL testing. 

Additional discussion of HITL testing for anthropometry, biomechanics, and strength 

assessments can be found in HIDH section 4.2.4.2 Enhancement of Human-in-the-Loop 

Testing.

In general, the flow of any anthropometric design evaluation for space flight-related 

designs, whether low-fidelity analytical analysis or high-fidelity HITL testing, contains the 

same backbone of required steps:

1. Identify test objectives – which include but are not limited to accounting for

unsuited and suited operations, gravity condition (1g, micro-g, hyper-g, etc.), 

group effects, test configuration fidelity, and so on.
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2. Identify the critical measurements from the crewmember population that 

influence the ability of a human to interact with the design and the surrounding 

environment. These critical measurements can be population-based and/or 

derived dimensions.

3. Account for suit, posture, and microgravity factors.

4. Identify worst-case scenarios involving dimensions based on the critical tasks.

5. Evaluate the design using analytical analysis, CAD modeling, and/or HITL testing 

at the appropriate stage of the design cycle, and determine what segments of the 

population are not accommodated and what adjustments are necessary to 

accommodate the entire user population.

6. Make changes to the design to increase anthropometric accommodation

7. Repeat Steps 1-6 until the design meets the requirements set forth for the 

selected population data set and the design is in the final stages of the design 

cycle.

4.5.2.5 METHODOLOGY

4.5.2.5.1 IDENTIFY TEST OBJECTIVES

Preparation for evaluations starts with a very clear idea of the test objectives; these are 

critical to a successful evaluation of the design. Test objectives are developed by 

identifying the tasks crewmembers are expected to perform, assumptions owing to the 

design fidelity and/or the concepts of operations, the context of the surrounding 

environment, and any areas of concern. For instance, if the focus of the design 

evaluation is on a hypothetical seated crewmember at a console, the primary objectives 

would be to ensure that the seat can fit all crewmembers and the console can be 

reached by all crewmembers, both suited and unsuited. Secondary objectives could 

examine whether the seat can accommodate the population within the overall vehicle 

context, such as the ability of all crewmembers to ingress and egress the seat for a 

given seat configuration, with other vehicle components acting as obstacles. It is critical 

to examine the design as both an individual piece and part of the larger overall vehicle

and interface design at all steps of the design cycle.

4.5.2.5.2 IDENTIFY CRITICAL MEASUREMENTS

Various anthropometric measurements should be evaluated throughout the design’s 

lifecycle, as dictated by design and evaluation needs. Measurements that are unique to 

a particular design may be critical to a proper evaluation. Examples of such 

measurements are functional measurements used to reconstruct a body posture, 

unique measurements derived from the combination of 2 or more established 

measurements, or clearances between the human and hardware. The measurements 

selected should include those specifically tailored to the task; these incorporate all 

critical subject body posture configurations for proper subject classification within the 

population. At a minimum, one should select task-specific measurements for unsuited 

crewmembers, to place measurements in the context of the population and to 

understand the impact of posture. Task-specific measurements for suited 

crewmembers should be selected as appropriate to understand the impact of the suit.
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Compliance requires that a design meet the minimum and maximum as defined by the 

limits selected from the data set range of dimensions for a given design. However,

measurements may not be available for every task-specific and posture-specific design. 

Measurements may have to be derived analytically and then verified through HITL 

testing. For example, if the focus of the design evaluation is on a hypothetical seated,

unsuited crewmember at a console, the seated posture will influence the hip angle of 

the person. The chair itself must still accommodate the maximum to minimum buttockto-knee distance; however, when the distance of the chair from the console is 

evaluated, the hip angle’s impact on buttock-to-knee length must be accounted for to 

accurately predict the clearance between the human and interface.

4.5.2.5.3 ACCOUNTING FOR SUIT, POSTURE, AND MICROGRAVITY FACTORS

4.5.2.5.3.1 SUIT FACTORS

Changes to overall suited body shape caused by the suit, called suit factors, have 

ramifications across all levels of design and must be accounted for, if applicable, when 

allotting and interpreting the space needed to fit the expected population. NASA-STD3001 Requirement V2 4002 includes the spacesuits and suit pressurization as 

characteristics that must be included in the definition of a data set. Suit factors are 

classified as the ratio between the unsuited and suited anthropometric measurements of 

an individual, and take into account not only the added material of the suit and its 

components but also the small changes in posture that are inherent in the body-to-suit 

interface. 

The estimated suit anthropometry is obtained by modifying the unsuited measurement 

using a suit factor to result in a derived suited measurement. Each individual 

measurement taken for a subject will have a corresponding suit factor since the suit 

affects different parts of the body in different ways and each suit may have different 

design attributes that affect posture, stature, and other aspects of body shape. Ideally, 

suit factors are derived for a specific suit, in a specific configuration, in a standardized 

baseline posture, and are applicable only under the same or very similar conditions. For 

example, the suit factor determined for a subject’s stature in an Extravehicular Mobility

Unit (EMU) suit will be different from the stature suit factor for an ACES suit. Likewise 

the hardware will affect the suit factors; the suit factor for stature in an ACES suit with a 

bailer bar will be different from the stature suit factor for an ACES suit without a bailer 

bar. A bailer bar is an external locking mechanism of the helmet that rotates to the top 

of the head when the face shield of the helmet is open, and latches near the chin when 

closed and locked. 

The suit will have an impact on the overall body size and posture of individuals and 

must be incorporated into a design to ensure that the population is accommodated. 

These suit factors allot a certain amount of clearance for the suit and provide a standard 

that the suit designers must adhere to and the vehicle and hardware designers must 

account for within their respective designs. Ideally, a suit factor would be a known 

element, clearly defined for every dimension of interest. However, this is not the case, 

and suit factors must be quantified and the design must demonstrate incorporation of 

suit effects before full verification can occur. 
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Questions have previously arisen about how to handle suit factors for subjects falling in 

the middle range between the maximum and minimum values. These questions are 

based on scenarios in which the worst-case body configurations do not occur at the 

extremes but rather near the middle of the population or during human-based testing 

with subjects of varied anthropometry. 

Take for example, a hypothetical test subject who has a 25th-percentile male stature 

value or the equivalent 96th-percentile female stature value: should the suit factor used 

to derive the minimum anthropometry value or the suit factor used to derive the 

maximum anthropometry value be used to evaluate the subject’s accommodation within 

the vehicle? If the subject is male, the analyst should apply the suit factor used to 

derive the maximum value. If the subject is female, the analyst should apply the suit 

factor used to derive the minimum value, with the exception of hip breadth where the 

situation is reversed. For more complicated cases between the minimum and maximum 

values in an anthropometry data set, the developer is advised to seek support from 

NASA.

4.5.2.5.3.2 POSTURAL FACTORS

Measurements will also be influenced during testing by posture effects, induced by the 

hardware, that change the standard body position of the human. NASA-STD-3001 

Requirement V2 4002 includes external-interfacing equipment and gravity environments 

as characteristics that must be included in the definition of a data set, and V2 4006 

specifies that changes to body posture be included in reduced-gravity environments. 

Essentially posture factors account for the variation between the baseline, unsuited 

posture and the unsuited task-specific posture. The measurements in the NASA 

crewmember anthropometric data set were collected in a laboratory environment with 

distinct, standardized anthropometric data collection postures. Vehicle or system design 

and the effects of gravity may necessitate that crewmembers assume postures that 

differ significantly from the prescribed and standardized measurement postures 

reflected in the requirements. These postural effects need to be quantified and 

accounted for, to analyze the impact of the design on the entire population. 

In the preliminary stages of design, the posture factors can be estimated using 

assumptions about body posture for the analytical or CAD modeling methods. The 

posture factor can be initially calculated by using trigonometry to quantify the impact of 

body joint angles on anthropometry and then determining the ratio between the adjusted 

and standardized posture. The suit and posture factors can be combined at that stage 

to provide a preliminary impact of the suited human interacting with the interface of 

interest. An error will be associated with this estimation of the posture factors, as well as 

a secondary error of the interaction effects between the suit and posture that will also 

negatively influence the robustness of the results. The assumptions of the impact of 

posture effects on the human body unequivocally must be verified during HITL testing to 

ensure that the assumptions are valid or to modify the analysis as appropriate. At the 

stage of HITL testing, the ratio of a standard unsuited body measurement to the 

posture-based unsuited body measurement in the human-system interface can be 
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determined, compared to the previous estimated factors, and integrated into the overall 

analysis in a fashion similar to the suit factors.

4.5.2.5.3.3 COMBINED POSTURAL AND SUIT EFFECTS

In the preliminary stages of design, the posture and suit factors can be estimated using 

anthropometric data set values and assumptions about body posture for the analytical 

or CAD modeling methods. These estimates can be used to determine the 

accommodation of the design, but they have inherent error, which must be verified 

during HITL testing. As the design process moves into HITL testing, it follows that if a 

combination of posture and suit is influencing the human-system interface, the actual 

values must be collected and compared to the assumed effects. The easiest way to do 

this is to measure subjects in the unsuited standard configuration and the suited 

subjects in the posture-specific position. The ratio between the suited, posture-specific

value and the unsuited standard value becomes a combined suit factor, incorporating 

the effects of both posture and suit. When this factor is iteratively applied back into 

analytical or CAD modeling, this combined effect automatically accounts for both the 

posture and suit and can be applied directly to the unsuited standard value. 

Alternatively, the combined factor can be broken down into its respective values, but 

that requires additional data gathering to capture the unsuited standard, unsuited 

posture-specific, and suited posture-specific values to quantify each piece of the puzzle.

4.5.2.5.3.4 MICROGRAVITY SPINAL ELONGATION

When analyzing tasks that will be performed in microgravity or will be influenced by 

microgravity effects, spinal elongation must be incorporated into the assessment. 

NASA-STD-3001 Requirement V2 4006 specifies that changes to lengths be included in 

reduced-gravity environments. The most prominent and well-documented change in 

length due to reduced gravity is spinal elongation. Spinal elongation is the straightening 

of the spinal curve due to the lack of vertebral compression, bone loss, and body fluid 

shifts in microgravity. Historically, it has been found that the spine straightens in 

microgravity, resulting in a 3% growth in stature. This elongation affects anthropometric 

dimensions involving the spine (such as seated height and eye height). These 

dimensions must be increased by 3% for spinal elongation due to microgravity 

exposure. For example, spinal elongation needs to be included when analyzing fit or 

accommodation to determine whether a crewmember will properly fit within the seat for 

landing after being exposed to microgravity. To properly determine whether the 

crewmember is accommodated, 3% of the stature needs to be added to the seated 

height or any other measurement that incorporates the length of the spine (Equation 1). 

This holds true for all crewmembers returning from a low Earth orbit mission, such as a 

mission to the International Space Station. 

Equation 1 
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Spinal elongation must be calculated on an individual subject basis for the population. It 

cannot be applied mathematically to the maximum/minimum values of the selected 

anthropometric data set, as those values are set limits that have been mathematically 

derived from the entire population. From a mathematical perspective, the maximum 

stature and maximum sitting height cannot be input into Equation 1 to derive the 

maximum sitting height with spinal elongation because it is not representative of a 

“realistic” human; it must be done on an individual basis. Designers are advised to apply 

spinal elongation on a per-subject basis for the measurement of interest, and then 

statistically examine the resulting impact on population values to evaluate compliance.

4.5.2.5.3.5 MICROGRAVITY FLUID SHIFT

Crewmembers experience significant changes to their body, especially in the regions of 

hands, legs, torso, and face, as a result of the shifting of body fluid distribution. To date, 

no empirical data exist on the amount of fluid shift in these regions and how it may 

affect crew anthropometry. Since NASA-STD-3001 Requirement V2 4006 specifies that 

changes to circumferences be included for reduced-gravity environments, designers are 

advised to take into consideration the possibility that changes in circumference could 

occur that may negatively affect the design.

4.5.2.5.4 IDENTIFY WORST-CASE SCENARIOS

Identification of the worst-case scenarios essentially focuses the analysis to highlight 

the segments of the population affected most by the design. The worst case is not 

always the largest male value or smallest female value, and the multivariate nature of 

anthropometry may obscure the ability to determine the worst case with only a cursory 

overview of the design. The best approach is to analytically model the problem at hand 

using the entire population from the selected anthropometric data set to identify 

individuals within the population who have issues with the restrictions imposed by 

design or who are an “at risk” group with respect to anthropometric compliance. The 

range of anthropometry of those individuals indicates the worst-case scenarios. 

Identification of worst cases is important for 3 reasons: 1) it quickly highlights the 

changes that need to be made to the design by examining or accounting for the 

population as a whole; 2) It identifies the segments of the population to be focused on 

during modeling and testing who are “at risk,” who potentially may have clearance or fit 

issues; and 3) it helps to define the problematic measurements that can be verified with 

modeling or HITL testing, given the current stage of the design. 

Note: Often the alternative to the derivation of realistic worst cases presented above is 

to use a “large” male or “small” female manikin representation. It is inappropriate to use 

the largest male in all dimensions or smallest female in all dimensions for an analysis. 

For example, it is physiologically and numerically impossible for a single person to have 

the maximal crotch height, maximal sitting height, and maximum stature of the 

population. The percentile values of specific attributes of the expected user population 

cannot be mathematically manipulated. For example, if you add maximum segment 

lengths together to derive a stature value, that stature value will exceed the maximum 

population stature. Such a configuration is unrealistic, skews the results of the analysis, 

and masks the portions of the population who are truly affected by the design. Although 
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modeling a “large” male or “small” female could be useful for visualization purposes, 

verification should use the anthropometric values identified by the worst-case analysis 

to feed into modeling or analytical analyses. 

4.5.2.6 EVALUATE THE DESIGN USING POPULATION ANALYSIS

Several factors go into the interpretation of results from anthropometric data collection,

and the method of interpretation is heavily dependent on the ultimate end goals of the 

test. A key principle of the interpretation phase for any anthropometric analysis is the 

following:

Population analysis, which minimally means placing the design factors under 

consideration within the context of the entire population of interest, should be 

applied to all anthropometric evaluations. 

Population analysis may consist of defining test subjects based on a percentile analysis, 

comparing to the extremes of the expected population, or comparing hardware 

dimensions with a large sample from a population data set of potential users. Whichever 

approach is used, the end result is quantification of subject accommodation for the 

purposes of compliance evaluation. No one-size-fits-all population analysis method 

applies to all situations; therefore, it is important to select a method that is appropriate to 

the problem being solved. The following sections provide details on various population 

analysis methods, associated pros and cons, and the benefits of combining more than 

one method to use during various life-cycle phases.

4.5.2.6.1 ANALYTICAL EVALUATION

The analytical evaluation method is the simplest “on paper” analysis used to compare 

the human requirements against the design. The complexity of the analytical method is 

driven by the number of measurements involved, the posture, and the specific focus of 

the analysis. The benefits of this analysis are that it provides a quick analysis of the 

data to ensure that the design meets the criteria, it identifies the worst-case scenarios, 

and it is relatively quick and simple to do before any other analysis. To understand this 

method further, take an example of a basic seat. 

For individual measurements with a direct one-to-one match between the requirement 

dimensions and an identical posture, the analysis is very simple: meet the maximum 

and minimum for the design for the unsuited and suited conditions, as applicable. Using 

the example of a seat, the seat pan depth must not exceed the minimum buttock-topopliteal length, the seat pan width must meet the maximum hip breadth sitting value, 

and the seat back length must meet the maximum sitting height to fully accommodate 

the entire population for the ranges as defined with the requirements. Thus, the 

recommended analytical method for a simplistic measurement case is to compare the 

design’s measurements against the maximum and minimum, as applicable, to ensure 

that the entire population can fit within the design specifications. This is the most 

simplistic scenario one would encounter, and does not account for anticipated changes 

in posture due to the vehicle/suit interface. 
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For singular measurements influenced by posture, the analytical method must be 

adjusted to account for the difference in posture for the body measurement of interest. 

The measurement must be mathematically adjusted to reflect the change in body 

posture. The recommended analytical method is to break the body into body planes 

(sagittal, frontal, and transverse), use trigonometry to mathematically adjust the body 

posture to the anticipated postural changes, and evaluate the resulting measurement. 

Using the example of a seat design, if the hip angle of the chair is adjusted from 90 

degrees to 75 degrees, the seat pan depth must still not exceed the minimum buttockto-popliteal length; however, the clearance of the human in relation to the surrounding 

environment has changed. In this case, the knee distance from the seat back is no 

longer the buttock-to-knee length; it is the buttock-to-knee length adjusted by an 

estimated hip angle of 75 degrees. For singular measurements and simple body posture 

changes, these transformations can be applied directly to the maximum and minimum 

values and the resulting derived measurement can be compared with the design. The 

proviso to this analytical analysis is that the estimation of the actual body angle must be 

verified through HITL testing to achieve confidence in the results.

For multivariate measurements influenced by posture, a whole-body-posture-based 

analysis (WBPBA) should be used (Rajulu, 2010; Gonzalez, 2003). The analysis is used

to determine a derived measurement composed of several other measurements 

spanning body segments. The methodology behind the WBPBA involves using fixed 

joint angles or body segment locations and the multiple measurements that compose 

the posture of interest to run a simulation with each member of the selected 

anthropometric data set to calculate the range of the derived body dimension needed to 

accommodate the population. A hypothetical example is the total length a seated 

person spans from foot to top of head, or “seated clearance” for the purposes of this 

example. The worst-case scenarios are the smallest (1st-percentile female) and largest 

(99th-percentile male) calculated seated clearance values. The recommended way to 

perform this analysis is to first determine the correct seated posture, including hip and 

knee angles, for the seated position. Using the combination of the hip and knee angles, 

knee height, upper thigh length, and sitting height, the geometry of the seated individual 

can be examined in the 2-D sagittal plane, and the seated clearance can be calculated 

analytically for all members of the selected population. Determination of the mean and 

standard deviation values of that calculated measurement will yield the percentile 

values and allow verification that the design constraints can accommodate the NASA 

crew population.

The analytical models discussed above can also be used to determine group effects. 

Group effects are the impact of the surrounding environment on the ability to 

accommodate multiple crewmembers. Ideally, a designer would account for the space 

that multiple crewmembers occupy in a design, but often design constraints are 

prohibitive. For example, the minimum spacing between 2 seats can be set using the 

maximum suited male forearm-to-forearm breadth, as this would ensure that there will 

be enough elbow room for any seated crewmember. In less-than-ideal states, where 

total space and free volume are at a premium, design constraints may force that 

spacing to be smaller than ideal. This can be justified with assertions that instances are 
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rare where 2 males with maximum forearm-to-forearm breadth will fly together. The 

quantification of group effects using a Monte Carlo simulation can be used to determine 

statistically just how much of the resulting population is accommodated in the less-thanideal spacing as well as evaluate the probability that random selection of any 2

crewmembers would result in an accommodation issue. A Monte Carlo simulation is a 

numerical simulation technique that relies on large numbers of repeated random 

samplings to compute results. In the context of human factors design, the Monte Carlo 

can provide information about multi-crew, single anthropometric measurement design 

issues (Margerum, 2008). A standard or derived dimension can be used to fuel a Monte 

Carlo simulation, and the output of a Monte Carlo is essentially a new population of the 

grouped measurement of interest. For the above example of forearm-to-forearm 

breadth, one can randomly sample 2 people from a gender-weighted population and 

total the combined forearm-to-forearm breadth. Repeating this random sampling over 

thousands of iterations yields a new population of derived total forearm-to-forearm 

breadth for 2 people. The design constraints can be compared with the new population 

to determine what percentiles are not accommodated and how much more space is 

required to accommodate the majority, and even to evaluate the probability that 

crewmembers will have to be reselected based on the measurement constraints. It is 

also important to note that although the Monte Carlo can assess accommodation of the 

population in a restricted space, it does not account for performance, and HITL testing 

should be used to assess the impacts of the restricted environment in conjunction with 

group effects (Thaxton, 2008).

4.5.2.6.2 CAD MODELING AND SIMULATION

Modeling is the 3-D representation of the human in the surrounding environment. The 

utility of modeling for verification is driven by the configurability of the human model and 

the operator’s ability to accurately represent the real-life postures of the models of 

interest. The benefits of modeling are that it is an extremely useful tool for visualizing a 

particular scenario and for determining initial limitations of the design. The major 

drawback of modeling is that it provides only a snippet of the entire spectrum of the 

population and the multivariate interplay of all the measurements. Modeling follows the 

old programming axiom of “garbage in, garbage out,” and caution must be used in 

evaluations based on modeling to ensure that the entire population spectrum is 

accounted for. Modeling is similar to preliminary analytical analyses; both involve 

assumptions for suit factors, postures, and body measurement configurations. Like 

analytical analyses, the assumptions and conclusions drawn from the CAD model must 

be validated with HITL testing. 

Ideally, a CAD program would have the capability of adjusting any measurement of the 

human model to any value set by the user, allow modeling of clothing effects, and 

account for variations in anthropometry caused by changes in posture. Unfortunately, 

off-the-shelf CAD modeling programs are not advanced enough to be the sole tool used 

for a human factors analysis. Thus, it is important to recognize the limitations of CAD 

programs and use proper analysis methods. The CAD model must account for the 

actual impact of the suit on the anthropometry, not by modifying the human model 

dimensions, but by adding on the suit effect as an external shell or clothing effect to the 
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model. If the model is unable to add on the suit effects, then they must be accounted for 

mathematically when calculating clearance or interference issues from the CAD model. 

In addition the model must account for differences in postural changes between the 

analytical analysis method and the model, as well as differences in body 

measurements.

It is recommended that designers use the analytical analysis method to identify the 

worst-case scenarios and preliminary issues with the design before moving to a CADbased analysis. By the time modeling is used, the concept of how the design fits or does 

not fit the population should be understood. In this regard, the CAD modeling becomes 

a preliminary visualization tool for the results witnessed in the analytical method and 

allows a 3-D overview of the design’s impact on the surrounding structure. 

The test methodology for CAD modeling should consist of identifying the worst-case 

scenarios using the analytical analysis and developing manikins that match the 

identified measurements. For individual measurements, a manikin that matches just the 

measurement of interest is sufficient. The group effects of multiple crewmembers can 

be modeled similarly to individual measurements by just adding a second manikin. 

However, when the analysis involves multivariate measurements influenced by posture, 

the WBPBA should be used to capture the worst-case individual’s anthropometry 

(Rajulu, 2010; Gonzalez, 2003) and the corresponding values should be used to drive 

the CAD manikin sizing. In this manner, the modeling will use realistic custom-tailored 

manikins that have been identified as problematic to analyze in 3 dimensions against 

the design. As previously noted in paragraph 4.5.2.5.4 Identify Worst-Case Scenarios, 

one should not use a “large” or “small” manikin, which has all the maximum or minimum 

measurements entered for all the possible customizable manikin dimensions, for 

verification purposes. The percentile values are not additive or subtractive, and the 

maximum and minimum manikins do not represent realistic configurations of a human. 

Relying on 1 or 2 erroneous manikins to show that the entire population spectrum is 

accommodated is not the proper method for evaluating the design.

By entering the worst-case manikins identified from the analytical analysis, designers 

can initially use the CAD representation of the human-to-design interface to verify the 

analysis assumptions. For example, the distances from hardware to hardware or human 

to hardware can be examined and compared to the analytical analysis, which may or 

may not have fully captured or explored the complexity of the design. Once the potential 

interference or clearance issues identified by the analytical analysis have been 

confirmed, the CAD model can then be used to mitigate those issues, either through 

design changes to the surrounding structure or postural changes to the human model. If 

changes are made, the analytical analysis should be re-run to ensure that a different 

segment of the population is not influenced by the modified design. 

This iterative process results in an optimized methodology, in which the analytical model 

is used to identify problem areas, the modeling is used to explore those problems and 

make design changes, and the process starts over until a design is ready for the 

prototype stage. By not relying solely on 1 method, a designer can ensure that the 

entire population is mathematically accommodated within the complexity of the overall 
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human-systems interface while accounting for the assumptions used in both methods. 

Modeling only the worst-case scenarios reduces the cost associated with developing 

and tweaking each human model while ensuring that no segments of the population 

remain unaccounted for in the design.

4.5.2.6.3 HUMAN-IN-THE-LOOP TESTING

NPR 8705.2B paragraph 2.3.10 requires HITL evaluations for human-system interfaces. 

In the context of this document, HITL testing is a physical simulation involving a human 

operator. The benefits of HITL testing are that it allows a designer to test a mockup or 

prototype with a human and determine whether the assumptions about the posture 

and/or hardware issues are consistent. The major drawbacks of HITL testing are the 

time consumption, limited subject pool availability, and reliance on mockups of 

appropriate fidelity. HITL testing should be performed iteratively throughout design and 

as the final step in verification of the design against the requirements. Technical 

products provided for PDR and CDR should include presentations of how HITL 

evaluations were used to influence system design. 

The value of HITL testing depends on the fidelity of the mockup to the proposed design. 

The lower the mockup fidelity, the more mathematical assumptions will have to be 

incorporated into the analysis to account for the differences between the mockup and

the actual design. HITL testing for anthropometric evaluation requires a concrete plan 

for the measurements that will be collected, quantification of test subjects’ 

anthropometry, and the data analysis that will be done to verify the design. 

Analytical analysis and modeling should be used as previously discussed to identify 

worst-case-scenario body configurations and drive specific data collection during the 

HITL testing. These previous methods should also inform the posture, suit, and 

microgravity factors to be addressed in the analysis.

Ideally, the subjects selected for HITL testing should cover the full spectrum of the 

population for each critical measurement of interest. In practice, however, subjects are 

usually limited to a select group that does not represent the entire anthropometric 

range. Regardless, anthropometry corresponding to the identified task-specific critical 

dimensions must be gathered from each subject. 

The data analysis associated with HITL testing for anthropometric evaluation has 

several basic goals. The first goal is simply validation of the assumptions used for 

analytical and CAD modeling. Facets of this validation include whether the actual 

posture is the same as the assumed posture, whether the actual restrictions and 

limitations on the dimensions of the human are the same as those previously 

anticipated based on analytical and modeled scenarios, and whether any additional 

issues are faced by a person at the human-system interface. If differences are found 

between the actual and the previously calculated or modeled work, then the previous

analytical analysis and CAD model must be updated to reflect the observed differences 

and once again tested for population accommodation. For example, in a scenario with 

knee clearance between the seat back and the kneecap, the hip angle of the seat 

hardware is angled at 85 degrees. During HITL testing, it is observed that the hip angle 
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of the human does not match the seat hardware angle, and instead it ranges from 80 to 

90 degrees. The previous work must then be updated to determine the impact on the 

population as a whole of using this new number range.

Ideally, during HITL testing the subject will have no observed issues with clearance or 

restrictions with the interface based on the background analytical and modeling work. 

Situations will occur where this is not the case. Thus, a second goal of the data analysis 

is to identify these unanticipated restrictions and quantify them with respect to the 

population as a whole to determine the root of the problem, be it subject-specific, 

posture-specific, or design-specific. One method of quantifying the subject in terms of 

the population uses percentile analysis. The basic steps for this analysis are to identify 

the subject’s percentile value in the gender-specific population, evaluate where the 

subject falls within the population, and then determine how much of the population is 

affected by the particular issue for a given measurement. Each measurement’s mean 

(μ), standard deviation (σ), and z-score (k) can be used to determine each subject’s 

percentile value (X) using Equation 2 below.

Equation 2

If one subject has an issue where another does not, evaluation of the percentiles can 

help identify the root cause of the problem and the impact on accommodation of the 

population (Rajulu, 2010: Population Analysis). Take as an example an individual 

seated in a chair. The analytical analysis and CAD modeling both indicate that all 

subjects should be accommodated within the seat; however, during HITL testing one 

female subject complains that the edge of the seat pan is painfully digging into the back 

of her knee. On subsequent percentile analysis you determine that she has a 20th-

percentile female buttock-to-popliteal length and has the smallest value of all subjects in 

the HITL test. This indicates that women ranging from the 1st to the 20th percentile may 

have a similar issue with the edge of the seat pan. Perhaps the impingement is caused 

by postural differences between small women and the rest of the population, perhaps 

the ability to conform to the seat pan is different for smaller women, or perhaps the foot 

rest adjustability dropped the thigh closer than ideal to the seat pan. Regardless, a 

segment of the population is now identified as “at risk,” a designation that requires 

further follow-up and analysis. 

The third goal of the HITL data analysis is to classify whether the worst-case scenarios 

pass or fail the anthropometric requirements, by extrapolating from HITL test subjects 

who may not be the worst cases from both an accommodation and performance 

perspective. In the ideal situation, where the subjects tested in the HITL study have no 

observed issues with clearance or restrictions with the interface, the subjects must still 

be classified in terms of the overall population using percentiles. The basis for this 

classification is to determine the human-to-hardware clearance values, and extrapolate 

to determine whether individuals who were identified as the “worst cases” of that 

measurement will have an issue. As an example of an extrapolation population analysis 

scenario, consider the task of walking through an entryway while wearing a suit. 
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Hypothetically speaking, the critical dimensions of interest would be identified as 

bideltoid breadth and stature, and the 2 worst-case scenarios would be the largest 

values (i.e., 99th-percentile male in both bideltoid breadth and stature). Before testing, 

the scenario is analytically examined and the entryway seems to accommodate a suited 

99th-percentile male in both bideltoid breadth and stature, but it is not yet verified as 

meeting the requirements at this stage. The motion of walking involves 2 aspects that 

must be accounted for in the population analysis: a swinging motion of the arms, 

resulting in a higher width requirement, and the height variations observed during 

walking, which may increase the amount of head clearance required. For this example, 

a group of subjects ranges from 20th- to 80th-percentile male bideltoid breadth and 60th-

to 95th-percentile male stature. During testing, all subjects were able to walk through the 

door, but the total clearance was only about 2 inches for the men who had the largest 

bideltoid breadth and 1 inch for stature. Collecting unsuited data from the subject pool 

and comparing each subject’s values and the actual observed clearance will cause the 

analysis to yield the anticipated postural effects (see paragraph 4.5.2.5.3.2 Postural 

Factors). By extrapolating the observed postural effects to the 99th-percentile male 

values for both dimensions, designers can determine the required entryway dimensions 

and compare them to the actual mockup or design. As a result, this hypothetical 

population analysis identifies the necessary requirements the design must meet, given 

the worst-case scenario for this selected task. 

The HITL test will be used to examine the worst-case manikins identified from the 

analytical analysis and CAD modeling, validate the assumptions from the previous 

analysis, and identify any unforeseen issues in the design. If the previous analysis 

assumptions are determined to be incorrect, the analytical analysis and CAD modeling 

must be re-run with the updated assumptions in place to evaluate compliance of the 

design. If the design is determined to be noncompliant with the anthropometric 

requirements, the issues must be mitigated by making appropriate design changes. If 

changes are made, the analytical analysis and CAD modeling should be re-run to 

ensure that a different segment of the population is not affected by the modified design. 

Finally, if the design is compliant according to the HITL test, designers should continue 

conducting HITL testing using mockups at a higher fidelity level until the final stage of 

design is reached. Strategically placed iterative HITL tests will ensure that differences 

between the low-fidelity and high-fidelity stages of the design will not result in 

accommodation issues and that seemingly minor changes to a design will not result in 

major issues in the end product. 

This iterative process results in an optimized methodology, in which the HITL test is 

used to validate design assumptions and identify problem areas, the modeling and 

analytical analyses are used to explore those problems, evaluate the population, and 

make design changes, and the process repeats until a design is ready for the prototype 

stage. By not relying solely on one method, a designer can ensure that the entire 

population is both mathematically and functionally accommodated within the complexity 

of the overall human-systems interface while validating the assumptions by using actual 

human data. 
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Additional discussion of HITL testing for anthropometry, biomechanics, and strength 

assessments can be found in HIDH section 4.2.4.2 Enhancement of Human-in-the-Loop 

Testing.

4.5.2.6.4 PERCENTILE ANALYSIS

Percentile analysis can be used at all levels of analytical, modeling, and HITL analyses. 

In the most simplistic terms, anthropometric verification and validation is a comparison 

of the design against the maximum and minimum critical dimensions. As the complexity 

of the analysis increases, the percentile analysis becomes a critical tool for evaluation of 

the design. As discussed throughout this section, the selected anthropometric data set 

in conjunction with percentiles can be used to derive atypical measurements, and 

evaluate multivariate posture-based body configurations and group effects. The 

percentile analysis can be used to place the design constraints in the context of the 

population, evaluate HITL subjects in relation to worst-case subjects, assist with 

extrapolation of the results to the worst cases, and even yield the accommodation 

restrictions of the design. It is highly recommended that designers use this tool during 

the design process, using the basic mathematical equation (Equation 2) or using the 

more complex variations, adding in the microgravity aspect (Equation 1) or the suited 

aspect (Margerum, 2008: Case Study #2) to assist with validation and verification of the 

design.

4.5.2.6.5 USE OF THE MINIMUM AND MAXIMUM POPULATION ACCOMMODATION 

VALUES

A design may not specifically require both the maximum and minimum values, but care 

must be taken to account for both of them in the context of the overall vehicle design. 

Both the maximum and minimum values must be considered even if a design 

specifically uses only one of the critical values. Using a basic seat example, the seat 

pan width must meet the maximum hip breadth value to ensure that all crewmembers 

are supported, but examination of the minimum should be considered in terms of crew 

safety or comfort. If the crew is jostled on launch and landing, the smaller women may 

shift around on the seat plan, which could cause discomfort and potential injury. Thus,

although the seat pan width is driven by the maximum and supports the entire 

population range, a factor of adjustability for that dimension is driven by the combination 

of the maximum and minimum. Consideration of this adjustability factor is essential for 

crew comfort and safety.

4.5.2.7 ANTHROPOMETRY TECHNICAL PRODUCTS

Verification and validation of a given design requires that the entire population range is 

accounted for in the design. At a minimum, the design must meet the relevant maximum 

and minimum ranges for the selected set of critical dimensions set forth by Requirement 

V2 4003 and tied to the data set used for satisfaction of V2 4001. The design must 

prove through analytical, modeling, and HITL methods that the entire population 

spectrum between the maximum and minimum values has been accounted for within 

the design. Designs in which multiple critical dimensions interact, such as posturebased clearance measurements, must use the relevant analysis methods to 
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accommodate the population as a whole. Successful verification for these multi-variable 

scenarios would mean that the design accounts for the entire range between the 

minimum and maximum values for the given measurements of interest using the entire 

selected anthropometric data set. 

For each of the major milestones of the design life cycle, the technical products in Table 

4.5.2.7-1 are recommended for review by the NASA customer.

TABLE 4.5.2.7-1 ANTHROPOMETRY TECHNICAL PRODUCTS

Technical Products

Phase 

A

Phase 

B

Phase 

C

Phase 

D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function allocation, 

associated crew task lists, and the selected 

anthropometric data set and its associated critical 

measurement ranges. Includes list of tasks 

considered to be design-driving for anthropometry 

requirements as well as definition of factors 

influencing anthropometry.

I U U U --- ---

A summary of modeling/analysis/evaluation (i.e., 

CAD, human modeling, and population analysis) 

performed to date and the influence on system 

design with links to the detailed analysis results.

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10.

--- --- I U U ---

System architecture drawings (structures, 

equipment, etc.), material specifications, interface 

requirements.

--- --- I U U ---

Verification plan. --- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are affected by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of the sequence of crew activities, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

For anthropometry requirements, it is important to determine what tasks may be designdriving. Tasks or uses of hardware that represent challenges for anthropometric 

extremes will be particularly important for system-level analysis and testing. Factors that 

may influence anthropometry include suit conditions, posture, gravity conditions, and 

group effects.
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Modeling, Analysis, and Evaluation Summaries

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into technical details of human-systems integration throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how key and critical design 

decisions were assessed. According to the NPR 8705.2B, updated summaries are to be 

provided at each design review through SAR. Also, in paragraph 2.3.10, the use of HITL

evaluation is a required method to progressively demonstrate that the operational 

concept meets system requirements for operational safety, efficiency, and user interface 

design.

For anthropometric analyses, as appropriate for each design phase, reports should 

detail CAD model work and progressively higher fidelity human model work in addition 

to analysis of HITL evaluations. Population analysis ensures that findings extend to the 

entire crew population and consider worst-case scenarios.

Architecture, Materials, and Interface Specifications

Drawings, materials, and interface specifications provide NASA with insight into humansystems integration technical details throughout the design process. 

Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 

System Requirements Review (SRR)

Suggested developer technical products:

 Selected anthropometric data set and its associated critical measurement ranges

 Overall plan for meeting anthropometric design compliance

 Definition of human-related major systems and what anthropometric 

requirements are applicable 

 High-level analytical analyses examining the impact of anthropometric 

requirements on the design

 Plans for mitigation efforts if high-level analyses indicate that design does not 

meet requirements

NASA Involvement:

 Review overall plan, give feedback

 Review major systems and applicable requirements, give feedback

 Review analytical analysis results for consistency and methodology and plans for 

mitigation, give feedback

System Definition Review (SDR)

Suggested developer technical products:

 Reports detailing analytical analyses for all major subsystems, to prove that 

concept designs meet anthropometric requirements and account for assumptions 
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 If available, reports detailing preliminary CAD model work based on previous

analytical analyses to prove that concept designs meet anthropometric 

requirements and account for assumptions

 Plans for mitigation efforts if analyses indicate that design does not meet 

requirements

NASA Involvement:

 Review reports and mitigation plans, provide feedback 

Preliminary Design Review (PDR)

Suggested developer technical products:

 Reports on detailed analyses (analytical, modeling, and HITL) examining the 

impact of anthropometric requirements on the human-systems interface design, 

with any limitations and assumptions addressed

 Plans for mitigation efforts if analyses indicate that design does not meet 

requirements

 Plan for verification of requirements

NASA Involvement:

 Review detailed analysis results for consistency and methodology, provide 

feedback

 Review plans, provide feedback

Critical Design Review (CDR)

Suggested developer technical products:

 Reports detailing HITL testing to examine the impact of anthropometric 

requirements on the design; plans for mitigation efforts if analyses indicate that 

design does not meet requirements

 Reports on updated analyses (analytical and modeling) based on results of HITL 

testing to examine the impact of anthropometric requirements on the humansystems interface design; plans for mitigation efforts if analyses indicate that 

design does not meet requirements

 Final plans for anthropometric verification testing

NASA Involvement:

 Review reports, provide feedback

 Review verification plan, provide feedback

 Review design for consistency and methodology, provide feedback on final 

prototype design

Test Readiness Review (TRR)

Suggested developer technical products:

 Demonstration of adherence to overall plan for meeting human-systems design 

compliance and justification for necessary plan changes

 All testing completed and mitigation efforts incorporated into the design
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NASA Involvement:

 Review report, give feedback

System Acceptance Review (SAR) 

Suggested developer Company technical products:

 Demonstration of design compliance and all anthropometric requirements met

NASA Involvement:

 Review of design relative to levied anthropometric requirements

4.5.2.8 ANTHROPOMETRY REFERENCES

Churchill, E. & McConville, J. (1976). Sampling and data gathering strategies for future 

USAF anthropometry, Appendix II-A. Air Force Systems Command, Wright Patterson 

Air Force Base, OH.

Gonzalez, L. J., & Rajulu, S. L. (2003, June) Posture-based whole body anthropometric 

analysis – A case study, Paper presented at the meeting Digital Human Modeling for 

Design and Engineering Conference and Exhibition, Montreal, Canada.

Gordon, C. C., Bradtmiller, B., Churchill, T., Clauser, C. E., McConville, J. T., Tebbetts. 

I., & Walker, R. A. (1989, September). 1988 Anthropometric Survey of U.S. Army 

Personnel (ANSUR): Methods and summary statistics (NATICK/TR-89/044). Natick, 

MA: U.S. Army Natick RD&E Center.

Margerum, S., & Rajulu, S. (2008). Human factors analysis of crew height and weight 

limitations in space vehicle design. Human Factors and Ergonomics Society Annual 

Meeting Proceedings, 52(1), 114-118.

McConville, J., & Tillman, B. (1991). Year 2015 astronaut population anthropometric 

calculations for NASA-STD-3000. Houston, TX: Johnson Space Center.

U.S. Department of Health and Human Services. (2004, October). NHANES (National 

Health and Nutrition Examination Survey) Mean Body Weight, Height, and Body Mass 

Index, United States 1960–2002. Rockville, MD: Author.

Rajulu, S., Margerum, S., Young, K., & Blackledge, C. (2010). Anthropometric 

processes for population analysis, suit factor generation, and a NASA recommended 

set of practices essential for data collection and analysis for verification and validation of 

vehicle, suit, and vehicle-suit interface requirements. (JSC 65851). Houston, TX: 

Johnson Space Center.

Thaxton, S., & Rajulu, S. (2008). Population analysis: Communicating about 

anthropometry in context. Human Factors and Ergonomics Society Annual Meeting 

Proceedings, 52(1), 119-123(5).
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4.5.3 DESIGN FOR RANGE OF MOTION

4.5.3.1 INTRODUCTION

The NASA-STD-3001, Volume 2 NASA Spaceflight Human-System Standard, section 4 

Physical Characteristics and Capabilities, includes requirements to accommodate crew 

ranges of motion (ROM) and reach. The purpose of mobility design requirements is to 

ensure that all developed hardware is operable by all potential NASA crewmembers. 

Accordingly, all designers and developers of space systems will need to demonstrate 

compliance with the verification requirement using a variety of methodologies including 

analysis, modeling, and HITL testing.

4.5.3.2 APPLICABLE REQUIREMENTS

The following NASA-STD-3001, Volume 2 requirements are applicable to range of 

motion:

 Data Sets [V2 4001]

 Data Set Characteristics [V2 4002]

 Population Definition [V2 4003]

 Data Set Assumptions [V2 4004]

 Range of Motion Data [V2 4007]

 Reach Data [V2 4008]

4.5.3.3 SELECTION OF A RANGE-OF-MOTION DATA SET

The NASA-STD-3001 NASA Spaceflight Human-System Standard Requirement V2 

4001 specifies that a biomechanics data set for the crewmember population must be 

selected and implemented in the design for range of motion (V2 4007) and reach (V2 

4008) Requirement V2 4004 specifies that age, gender, and physical condition shall 

also be included in this data set. Furthermore, Requirement V2 4003 requires the 

definition of the population ranges for the physical dimensions that the system is 

intended to accommodate, and V2 4002 requires these values to include suited 

conditions. 

ROM of a joint is measured by using the maximum observed angle of a joint during a 

specified task or posture. ROM is referenced in terms of rotation of a child entity with 

respect to a parent entity, and the exact rotation definitions depend on what type of 

coordinate system (e.g.., Cartesian, spherical) or transformation (e.g., Euler, fixed) is 

used by a program. Proper representation of the crewmember population with ROM for 

both unsuited and suited tasks can be done with a combination of literature surveys and 

data collection. No data set of ROM values is available as there is with anthropometry; 

however, a variety of technical papers detail ROM values for particular tasks. The 

particular joints selected for each requirement would be those identified as important 

through a task analysis, for example, only upper body, only lower body, or entire body 

for certain tasks. If the program uses data collection to gather the ROM data, the limits 
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should be determined by using the minimum of the maximum ROM data of the test 

subject pool. Using information that is in the public domain and data collected from 

unsuited and suited subjects, a designer can determine the anticipated ROM of the 

population, as well as the impact of the suit on ROM values, using a crew task to drive 

the selection of the requirement limits. The ROM requirements specified in HSIR and 

CHSIR were determined through a study of tasks, specific to suited crewmembers, that 

focused on the functional ROM. The unsuited and suited motion data were compared 

across multiple subjects and were summarized first by task; then the tasks were 

compiled into an overall set of requirements delineated by joint.

4.5.3.4 RANGE OF MOTION GENERAL OVERVIEW

Unfortunately there is no single, simple test to verify that a design will meet mobility 

requirements for any crewmember. A systematic approach must be taken to conduct 

progressively more vigorous testing to ensure that a crewmember in the worst-case 

configuration (see section 4.5.3.5.2 ROM in the worst-case configuration) (e.g., 

restrained, seated, and suited at various gravitational states with a full contingent of 

crew in place) can still perform all required operations. Analytical and CAD-based 

modeling may be implemented as a part of initial concept testing to identify key areas of 

concern. HITL testing may then be conducted with progressively higher fidelity 

hardware and tests to ensure that all mobility requirements are met. Initial HITL testing 

may involve a single test subject in a low-fidelity hardware mockup at 1g. Final phases 

of testing should involve a full complement of test subjects in flight configuration 

(including high-fidelity flight hardware and pressure suits, if planned), performing all 

required operations, and when feasible and appropriate, at simulated relevant 

gravitational states. Relevant nominal and contingency operations should be tested as 

well. As test hardware progresses to more closely resemble flight hardware, greater 

efforts must be made to include test subjects that represent the entire crewmember 

population with associated crew protection devices (e.g., pressure suits, seat restraints)

As with other human factors-driven evaluations, a logical and iterative progression 

should be made from low-fidelity to high-fidelity test conditions. Generally these steps 

are involved:

1. State objectives – depending on the phase of the project life cycle, objectives 

may focus on evaluating hardware, crew accommodation, contingency 

operations, or other highly specialized tests.

2. Identify critical metrics – these key measurements dictate how the test should be 

set up and may be related to specific requirements.

3. Identify and compensate for appropriate test conditions – initial tests may be 

acceptable with a single modeled test subject to demonstrate that hardware can 

be operated within an accepted ROM of the test subject, whereas final testing 

should consider gravitational state, suited condition (if appropriate), possibly 

deconditioned crewmembers, and any other relevant conditions.
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4. Recognize critical operations – some comprehensive testing may require testing 

every possible configuration of the hardware, or earlier testing may be 

acceptable with just worst-case scenarios. 

5. Evaluate the design – evaluate the hardware design using the appropriate fidelity 

of testing.

6. Review and redesign as necessary – interpret the results of the test to verify that 

the design met the designated requirements, and improve the design to increase 

accommodation if necessary.

Repeat and finalize - Repeat steps 1-6 with progressively higher fidelity hardware and 

more representative subject range until all requirements are met and the design is 

finalized.

4.5.3.5 METHODOLOGY

4.5.3.5.1 IDENTIFY OBJECTIVES

Evaluating mobility constraints on designs of flight hardware for human accommodation 

can be a difficult process that depends highly on maturity of the hardware being 

evaluated. Early in the project life cycle the design may exist only as CAD models, but 

as the design matures, low- to high-fidelity mockups become available, and eventually 

flight hardware is available for testing. Initial objectives should focus on ensuring that 

the tasks(s) can be successfully performed, judging by human-system interaction with 

respect to the ROM. Initial objectives should also incorporate common problems 

associated with mobility in human-systems integration such as operability of hardware 

and use of translation paths by a generic crewmember. Eventual human testing with 

hardware mockups allows identification of issues associated with a diverse population 

of test subjects. Human models typically create an idealized test subject, but inclusion 

of live human test subjects introduces idiosyncrasies such as bilateral asymmetry 

(dominant limbs may have different ROM than non-dominant limbs), subject motivation, 

and training. Use of models may be appropriate to save time early in the design cycle,

but HITL testing is necessary to verify that a mature design satisfies all requirements.

4.5.3.5.2 IDENTIFY CRITICAL METRICS

Before designing an experiment, it is important to consider what the goals of the study 

are and to design the test accordingly. Typical motion is described in terms of jointangle ROMs tied to specific tasks. A task analysis must be performed to ensure that the 

ROM is relevant to planned operations. The results of the task analysis should be 

compared and aligned with the corresponding ROM requirements determined from the 

selected ROM data set. Ultimately, the goal is to prove that the design configuration 

satisfactorily allows a mission to succeed for all tasks rather than to verify that body 

movements fall just within required ranges. Recognizing these critical mobility metrics 

that influence the ability of a crewmember to successfully complete the mission enables 

the design of tests to prove that requirements are met. 
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4.5.3.5.3 IDENTIFY TEST CONDITIONS

As the scope of the test becomes clear, it is important to anticipate issues that may 

affect the accuracy and fidelity of testing. Mobility and other biomechanical 

investigations can become complex, and therefore the issues detailed in this document 

are not all-inclusive. New issues may be identified and novel solutions may be 

developed to account for test factors that otherwise would negatively affect the fidelity of 

testing.

4.5.3.5.4 HUMAN MODELING

If the goal of the test is, for example, to determine whether a seated and restrained 

crewmember can reach an emergency control, a carefully crafted human model may 

work adequately. However, care must be taken to ensure that all constraints are 

realistically applied and that no obvious errors exist in the model, such as surface 

penetration, or postures that may be physically possible for some subjects but not 

others. For example, care must be taken in applying generic ROM limits on human 

models. As shown in Figure 4.5.3.3.4-1, 2 human models with identical ROM limits but 

different anthropometry yield a feasible arm position for a larger man (left) but surface 

penetration of the arm into the chest for a smaller woman (right).

FIGURE 4.5.3.5.4-1 EXAMPLE OF SURFACE PENETRATION IN RAMSIS AS DEPENDENT 

ON SUBJECT ANTHROPOMETRY

Although most human modeling packages come with the ability to control subject sizes 

and limitations on ROM, it can be prohibitively time-consuming to check large numbers 

of simulated operations with many sizes of test subjects. A critical issue that must be 

addressed for any suited operation is that most human modeling packages have no way 

of dealing with restrictions to motion, visibility, and comfort stemming from the presence 

of spacesuits. Some software permits editing of certain parameters, and this editing 
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may partially permit an attempt at simulating a spacesuit, but the fidelity of such 

simulations currently is questionable, at best. Despite these specific limitations, human 

modeling holds the most promise early in the design cycle, when designs are immature 

and it may be prohibitively expensive to build physical mockups of all design 

permutations. Additionally, once some HITL data are acquired, human modeling may be 

an appropriate intermediary step after acquisition of preliminary input and before 

physical fabrication of new hardware.

4.5.3.5.5 HUMAN-IN-THE-LOOP TESTING

After the initial evaluation of hardware designs with human modeling, generally the next 

step would be to create physical mockups of the vehicle and hardware with appropriate 

fidelity to determine capabilities and accommodation of the design. These mockups may 

be simple simulations made out of foam core and cardboard, or they may be elaborate 

prototypes constructed of flight-grade materials capable of interfacing with reducedgravity analogs.

Relatively late in the design cycle, as HITL testing of higher fidelity is being performed, it 

may be necessary to use a variety of means for simulating altered-gravity states. These 

simulators, which include NASA’s parabolic flight Reduced-Gravity Aircraft, the Neutral 

Buoyancy Lab (NBL), the hydraulically offloading partial gravity simulator (POGO), the 

precision air-bearing floor (PABF) and others, represent various degrees of microgravity 

simulation fidelity and associated restrictions in cost and custom hardware needed for 

testing. Each simulator carries very unique conditions and as such should be dealt with 

on a case-by-case basis.

Once physical mockups or components of flight hardware have been fabricated for 

testing, HITL testing may proceed at 2 levels of detail. The first may call for discrete 

yes/no answers to the question, “Could the subject satisfactorily complete the task?” 

with possible subjective feedback from the test subject. The second level of detail 

provides for the collection of quantitative data, primarily through the use of motion 

capture or some analogous technology as an objective means of determining if 

requirements have been met. This quantitative approach for HITL testing allows very 

clear verification of requirements compliance, but the process of collecting and 

analyzing the data may be rather involved.

Mobility data can be acquired through a wide variety of methods, which differ in 

markers, analysis techniques, and even principles of physics that influence how the

motion data are collected. For instance there are picture-based methods 

(stereophotogrammetry), simple video analysis tools, multi-camera video-based 

systems, passive marker motion systems, active marker motion systems, 

electrogoniometry systems, and even systems based on accelerometers and inertia. 

Each system has benefits and limitations depending on the surrounding environment, 

the test setup, occlusion issues, and on what motion data are output from the specific 

method. When collecting mobility data, care must be taken to ensure that the data 

collection hardware can operate in the required test settings. Many active and passive, 

camera-based motion-capture systems have minimal operable volume requirements 

that prevent data collection in small, enclosed spaces like some crew capsule mockups. 
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Systems based on electrogoniometry often run into problems with drift and interference 

from electrical or magnetic fields. These problems can often be mitigated with 

appropriate planning, but they may add to the technical difficulties of validating mobility 

requirements for flight systems.

The number of subjects to be used in a mobility study is always an issue, and the 

answer depends on the maturity of the system being studied and the degree of 

verification being sought. Early in the project life cycle, when proof-of-concept studies 

are more prevalent than final requirements validation, having a relatively small number 

of subjects may be appropriate to demonstrate the effectiveness of the hardware or 

system, either through modeling or HITL testing. Human modeling opens the door for 

evaluating specifically crafted test subjects designed to verify against some 

anthropometric extreme; however, care must be taken to ameliorate the concerns 

presented previously. For HITL testing, one must balance the time investment of 

collecting many test subjects with confidence in the determined results. The relevant 

population must be considered; if verification includes the need to accommodate the full 

range of crewmembers, then every effort should be made to include test subjects who 

represent the full spectrum of crewmembers. In unsuited tests this may be difficult, but 

when suits are involved, it may be nearly impossible to include subjects of extreme 

dimensions for whom spacesuit sizes may not be available until the design is verified. In 

these cases, it may be necessary to develop a metric of performance difference, for 

example some percentage of unsuited mobility that a spacesuit permits. Applying this 

ratio to unsuited data for extremes of anthropometry may be a necessary step in initially 

verifying a design’s success. However, the system would still need to be reviewed with 

the final design of the spacesuit for these extreme test subjects, as the metric of 

performance difference may change with suit size. 

Additional discussion of HITL testing for anthropometry, biomechanics, and strength 

assessments can be found in HIDH section 4.2.4.2 Enhancement of Human-in-the-Loop 

Testing.

4.5.3.5.6 RECOGNIZE CRITICAL OPERATIONS

Recognizing critical operations essentially involves identifying what crew tasks with 

which subjects are likely to result in a failure to complete the mission. Although

additional conditions should be investigated, it is important to ensure that the most likely 

modes of failure are specifically verified and explored. It is important to note that the 

worst-case mobility scenario with the smallest subject is not always the point of failure. 

The worst-case mobility is not synonymous with the worst-case anthropometry; they are 

2 distinct scenarios. Points of interference are likely to be discovered with large or 

intermediately sized subjects performing tasks in ways not anticipated. An analysis 

should examine a range of anthropometry matched to the “worst-case” mobility to verify 

the design. 

4.5.3.6 EVALUATE THE DESIGN

In the initial stages of design, the anticipated ROM values from the requirements data 

set can be entered into the CAD model to assess the ability of the modeled 
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crewmember to reach the various devices and controls. This first step ensures that the 

theoretical crewmember’s motions fall within the ROM requirements. The CAD model 

can be iteratively updated with the results of HITL testing, capturing the differences 

between the modeled and actual performance as development progresses, and 

improving the design progressively as needed. 

To assess that a mobility requirement has been met, kinematic data for multiple 

subjects must be collected across the entire population for all conditions through HITL 

testing. As the design fidelity increases, HITL testing should be used to gather subjects’ 

unsuited ROM outside of the design, the unsuited ROM within the design, and suited 

ROM, as applicable. The evaluation of a hardware design through initial HITL testing 

may provide a preliminary assessment of mobility information before the data are even 

processed. For example, if a test subject can successfully complete a task, the level of 

mobility used by the test subject should be acceptable. However, one must be cautious 

about the scope of that assessment, because it applies only to the subset of the 

population represented by the specific subjects who completed the test. 

In preliminary design stages, it is acceptable to have a smaller representative subject 

range for HITL testing and extrapolate to the entire population. To extrapolate collected 

data to other conditions and test subjects, it is necessary to collect many test subjects 

and determine the performance degradation due to the test conditions (assuming 

unsuited, 1g mobility is ideal) using a performance difference metric. This metric is the 

percentage of unrestrained, unsuited mobility relative to the ROM required to use the 

designed hardware or system in completion of a specific task. Applying this 

performance metric to unsuited data for extremes of anthropometry may be a necessary 

step in initially assessing a design’s success. 

For example, if cockpit design is verified to meet mobility requirements for unsuited 

crewmembers of all sizes and the design is then tested with average-sized 

crewmembers in pressurized suits, a fair first step would be to apply the same ratio of 

degradation in mobility that was experienced by average crewmembers wearing suits to 

the mobility exhibited by very small test subjects. However, the cockpit design would not 

be verified for all sizes of test subjects in pressurized suited conditions until a pressure 

suit is available to test with very small or very large subjects and the requirement is 

verified experimentally through HITL testing. 

As the hardware moves into the final design stages, the range of test subjects should be 

increased to fully encompass the entire population, specifically including those who 

have been identified as problematic by the CAD modeling work. Performance 

degradation ratios may be applied to data input into various human models to help 

ensure a design is on track, but verification must come down to successful performance 

of HITL testing in relevant conditions across the entire anticipated population.

4.5.3.6.1 REVIEW AND REDESIGN AS NECESSARY

As the evaluation of the design is completed, the opportunity exists to enact positive 

change on the design to increase accommodation of the hardware based on the results 

of mobility testing. Additional risks to successful verification of the hardware should be 
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identified and any necessary extra analysis of the collected data should be completed 

before following through to the next step in the process. Special attention should be 

paid to potential performance limitations in the evaluation of the design. For example,

significant effort may be needed to test hardware in a micro- or hypergravity 

environment (such as on the reduced-gravity aircraft or in a centrifuge) to assess the 

performance limitations of a reduced-gravity state. Likewise, issues presented with 

contingency conditions may require extra attention to be paid to critical operations of the 

hardware.

4.5.3.6.2 REPEAT AND FINALIZE

With the iterative process identified earlier, continue the cycle of designing and testing 

with progressively higher fidelity hardware, test subjects, and testing environments until 

the hardware is verified to satisfy all requirements.

4.5.3.7 RANGE-OF-MOTION TECHNICAL PRODUCTS

Developer companies must be able to demonstrate that they have satisfactorily met 

mobility requirements as identified through careful selection of the data set and 

associated test conditions and critical operations. Initially, the designer may report what 

mobility was required to operate the hardware based on human modeling, but final 

verification will necessitate high-fidelity HITL tests.

For each of the major milestones of the design life cycle, the technical products in Table 

4.5.3.7-1 are recommended for review by the NASA customer.

TABLE 4.5.3.7-1 RANGE OF MOTION TECHNICAL PRODUCTS

Technical Products

Phase 

A

Phase

B

Phase 

C

Phase 

D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function allocation, 

associated crew task lists, and the selected rangeof-motion data set critical limits. Includes list of tasks 

considered to be design-driving for range-of-motion 

requirements as well as definition of test conditions 

and critical operations affecting range of motion.

I U U U --- ---

A summary of modeling/analysis/evaluation (i.e., 

CAD, human modeling, and population analysis) 

performed to date and the influence on system 

design with links to the detailed analysis results.

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10.

--- --- I U U ---

System architecture drawings (structures, 

equipment, etc.), material specifications, interface 

requirements.

--- --- I U U ---

Verification plan. --- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item
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Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are affected by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

For ROM requirements, it is important to determine what tasks may be design-driving. 

Tasks that require large ranges of motion will be particularly important for system-level 

analysis and testing. Factors that may influence ROM include suit conditions, posture, 

gravity conditions, and group effects.

Summaries of Modeling, Analysis, and Evaluation

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-systems integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how key and critical design 

decisions were assessed. According to the NPR 8705.2B, updated summaries are to be 

provided at each design review through SAR. Also in paragraph 2.3.10, the use of HITL 

evaluation is a required method to progressively demonstrate that the operational 

concept meets system requirements for operational safety, efficiency, and user interface 

design. 

For ROM analyses, as appropriate for each design phase, reports should detail CAD 

model work and progressively higher fidelity human model work in addition to analysis 

of HITL evaluations. Population analysis ensures that findings extend to the entire crew 

population and consider worst-case scenarios.

Architecture, Materials, and Interface Specifications

Drawings, materials, and interface specifications provide NASA with insight into humansystems integration technical details throughout the design process. 

Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 

System Requirements Review (SRR)

Suggested developer technical products:

 Selected ROM limits for an applicable task list.

 Overall plan for meeting human-systems design compliance for mobility
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 Definition of human-related major systems and which mobility requirements are 

applicable 

 High-level analytical analyses examining the impact of mobility requirements on 

the design

 Plans for mitigation efforts if high-level analyses identify risks of design not 

meeting requirements for all conditions

NASA Involvement:

 Review overall plan, provide feedback

 Review major systems and applicable requirements, provide feedback

 Review analytical methodologies, analysis results, and plans for mitigation, 

provide feedback

System Definition Review (SDR)

Suggested developer technical products:

 Reports detailing analytical analyses for all major subsystems to prove that 

concept designs meet designated mobility requirements and account for 

assumptions 

 If available, reports detailing preliminary CAD model work or low-fidelity human 

model work based on previous analytical analyses to prove that concept designs 

meet designated mobility requirements and account for assumptions

 Plans for mitigation efforts if analyses indicate that design does not meet 

requirements

NASA Involvement:

 Review reports and mitigation plans, provide feedback on areas of concern, 

especially any anticipated impingements on crewmember mobility 

Preliminary Design Review (PDR)

Suggested developer technical products:

 Reports on detailed analyses (analytical, human modeling, and HITL) examining 

the impact of designated mobility requirements on the human-system interface 

design, with any limitations and assumptions addressed 

 Plans for mitigation efforts if analyses indicate that design does not meet 

requirements for all crewmember configurations (i.e., the entire population, 

under all design constraints)

 Plan for verification of requirements

NASA Involvement:

 Review detailed analysis results for accommodation and issues with integration 

of results, provide feedback

 Review plans, provide feedback

Critical Design Review (CDR)

Suggested developer Company technical products:
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 Reports detailing advanced human modeling and HITL testing examining the 

impact of mobility requirements on the design; plans for mitigation efforts if 

analyses indicate that design does not meet requirements

 Reports on updated analyses (analytical and modeling) based on results of HITL 

testing examining the impact of designated mobility requirements on the humansystem interface design; plans for mitigation efforts if analyses indicate that 

design does not meet requirements

 Final Plans for verification of mobility requirements

NASA Involvement:

 Review reports, provide feedback

 Review verification plan, provide feedback

 Review design for accommodation and issues with integration of results, provide 

feedback on final prototype design

Test Readiness Review (TRR)

Suggested developer technical products:

 Demonstration of adherence to overall plan for meeting human-systems design 

compliance and justification for necessary plan changes

 Demonstration of readiness to perform HITL testing to verify that mobility 

requirements are met for contingency operations and multi-point failures, or 

suitable plans are in place

 All required testing completed and mitigation efforts incorporated into the design

NASA Involvement:

 Review overall report, provide feedback

 Review potential contingency plans, provide feedback

System Acceptance Review (SAR) 

Suggested developer Company technical products:

 Demonstration of design compliance and all mobility requirements met for all 

crewmembers in all conditions

NASA Involvement:

 Review of design relative to levied requirements

4.5.3.8 RANGE OF MOTION REFERENCES

England, S. A., Benson, E. A. and Rajulu, S. L. (2010, May) Functional mobility testing: 

Quantification of functionally utilized mobility among unsuited and suited subjects

(NASA/TP-2010-216122). Houston, TX: Johnson Space Center.
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4.5.4 DESIGN FOR STRENGTH

4.5.4.1 INTRODUCTION

The NASA-STD-3001, Volume 2 NASA Spaceflight Human-System Standard section 4 

Physical Characteristics and Capabilities includes requirements to accommodate 

crewmember strength and deconditioning. See HIDP section 4.15 Deconditioned 

Crewmember for discussion of muscle deconditioning and its impact on strength. The 

purpose of the human strength requirements is to ensure that hardware is operable by 

all potential crewmembers. Accordingly, all designers and developers of space systems 

must demonstrate by means of analysis, modeling, and HITL testing that verification 

and validation of the design has been satisfactorily achieved against the requirements. 

The intent of this design process is to provide users with methodologies and best 

practices that should be implemented to ensure that adherence to the human-systems 

integration requirements set forth by NASA with respect to strength is satisfactory. The 

hardware design should involve careful consideration for interactions between humans 

and interfaces when humans are performing tasks, including consideration for the 

weakest crewmember, hardware integrity, and performance decrements due to 

physiological adaptations to space flight. 

4.5.4.2 APPLICABLE REQUIREMENTS

The following NASA-STD-3001, Volume 2 requirements are applicable to strength:

 Data Sets [V2 4001]

 Data Set Characteristics [V2 4002]

 Population Definition [V2 4003]

 Data Set Assumptions [V2 4004]

 Strength Data [V2 4012]

 Muscle Effects [V2 4013]

 Operational Strength [V2 4014]

4.5.4.3 SELECTION OF STRENGTH DATA SET

The NASA-STD-3001 NASA Spaceflight Human-System Standard Requirement V2 

4001 specifies that a strength data set for the crewmember population must be selected 

and V2 4012 states that this strength data set must be applied to the design. In addition,

requirement V2 4004 specifies that age, gender, and physical condition shall also be 

included within this data set, specifically V2 4013 requires that the effects of 

deconditioning of the astronaut are included in the system design and V2 4002 requires 

that characteristics unique to space travel also be factored into the design. Furthermore, 

requirement V2 4003 requires definition of the population ranges for the strength values 

that the system is intended to accommodate, and V2 4014 requires that the system is 

operable at the lowest anticipated strength. 
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No data set of strength values is available as are values for anthropometry; however, a 

variety of technical papers detail strength values for particular tasks. Using information 

in the public domain, a designer can determine the anticipated strength limits of the 

population. Specific crew operational loads associated with movements could be 

identified by matching the movement to the design using a task analysis. The strength 

requirements in HSIR and CHSIR were determined by conducting a task analysis to 

determine the anticipated motions that would be important to crew strength, and then 

literature surveys were performed to identify existing unsuited strength data. The suit’s 

effects on strength were estimated by comparing unsuited to suited strength for a range 

of functional tasks. Deconditioning effects depend on the duration of exposure to 

reduced gravity and prescribed countermeasures. Because of limited data availability, 

deconditioning in HSIR and CHSIR was applied by taking a minimum strength limit 

during a specified movement and applying a safety factor of 2.

4.5.4.3.1 DEFINITION OF HUMAN STRENGTH

Strength refers to a person’s ability to generate force. Applying strength requirements 

will result in a minimum and a maximum applied crew load to be used for operational 

and hardware design. The minimum load pertains to operational strength that 

accommodates the weakest person whereas the maximum load represents the force 

the hardware must be able to withstand without failure. It is important to note that these 

definitions apply to intentional forces applied by the crewmember. Hardware design 

should be performed in a human-centered manner, with analysis of expected crew 

operations used to drive the design of such human-machine interfaces. Analyses should 

evaluate and define activities and tasks in terms of criticality and required postures. The 

strength limits established by each program must consider physiological deconditioning 

effects on crewmembers of extended space flight, which could affect their ability to 

perform necessary tasks. 

4.5.4.3.2 APPLICABILITY TO SPACE FLIGHT SCENARIOS

Launch, Flight, and Reentry

Higher gravitational forces, as would be experienced during launch and reentry, will 

affect the successful application of human strength to perform a given task (that is, 

higher gravitational forces may result in a decrement in the force a crewmember is able 

to apply for completion of a given task). Strength value selection should be carefully 

considered when designing hardware and tasks for scenarios with higher gravitational 

force, as the inability to perform a given task under these conditions may result in loss 

of life, vehicle, or mission. Similarly, tasks that are performed under microgravity 

conditions (i.e., during flight) may be subject to decreased application forces by users. 

This may be the result of crewmembers being unable to attain a posture that allows 

compensation for any reaction forces applied back on the human by the tool or interface 

used (e.g., torque reaction force from a wrench). Therefore, the posture used, as well as 

available braces or handholds, should be taken into consideration to ensure successful 

completion of tasks performed under microgravity conditions. This subject is further 

addressed in paragraph 4.5.4.5.3.2 Posture Variability.
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Decrement Caused by Space Flight

Decrement(s) that reflect the deconditioning effects of space adaptation on 

crewmembers must be applied to strength limits. Deconditioning includes bone loss, 

muscle atrophy (including loss of strength and mass), and other physiological 

decrements associated with long-duration space flight. It can have notable effects on a 

crewmember’s ability to apply the necessary force or torque to complete a given 

mission task or operation. As deconditioning will affect each human in different ways, 

values for muscle strength decrements will vary. See HIDP section 4.15 for discussion 

of crewmember deconditioning.

4.5.4.4 STRENGTH GENERAL OVERVIEW

The evaluation of the design is a multi-phase process that depends on the stages of the 

design life cycle. In the preliminary stages of design, robust analytical analysis and 

modeling at a minimum should be used to identify the worst-case scenarios and the 

postures of interest, and to determine accommodation of the design. Any assumptions 

of posture, fatigue, and other human interface variables must be documented to verify 

them by future HITL testing. As the design matures within the design cycle, the 

evaluation of the design against the limits set forth by the requirements must move from 

the theoretical to the actual use of HITL. 

In general, any design evaluation, whether it is low-fidelity analytical analysis or highfidelity HITL testing, contains the same basic sequence of required steps in the flow of 

the design process:

1. Identify test objectives, which include but are not limited to accounting for the 

following: unsuited and suited operations, gravity condition (e.g., 1g, micro-g, 

hyper-g), postural effects, muscle fatigue effects, and test configuration fidelity.

2. Identify factors that influence the ability of a human to interact with the design 

and the surrounding environment. 

3. Account for applicable factors affecting human strength, such as posture 

variability across the population, muscle fatigue, and gravity conditions.

4. Identify worst-case scenarios (i.e., criticalities, weakest crewmembers, and 

deconditioning effects on ability to generate force/strength).

5. Evaluate the design using analytical analysis, modeling techniques, or HITL 

testing at the appropriate stage of the design cycle and determine what 

segments of the population are not accommodated and what adjustments are 

necessary to accommodate the entire user population.

6. Make changes to the design based on evaluation findings to ensure 

accommodation of those using hardware to perform tasks or operations.

7. Repeat steps 1-6 until the design meets the limits set forth by the requirements,

and the design is in the final stages of the design cycle.
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4.5.4.5 METHODOLOGY

4.5.4.5.1 IDENTIFY TEST OBJECTIVES

Evaluation of the strength characteristics of a design is highly dependent on hardware 

maturity and requires very clear test objectives; these are critical to a successful 

evaluation of the design. Initial objectives in the early stages of the design life cycle 

must focus on ensuring operability of the design by the full range of crewmembers. As 

the design life cycle progresses, the objectives focused on human-centered testing 

allow identification of issues associated with a diverse population of test subjects and 

postures. For example, if the focus of a particular design evaluation is on a hatch lever 

that requires hand grip and elbow flexion to operate, the primary objective would be to 

ensure that the lever can be successfully operated by all crewmembers, from strongest 

to weakest, and the required force to actuate the lever allows all deconditioned 

crewmembers to still successfully operate it in both nominal and emergency situations. 

Secondary objectives may examine whether the hatch lever can accommodate the 

population of strengths given a set location within the overall vehicle context, such as 

the ability of larger crewmembers to bend down and actuate the lever or smaller 

crewmembers to reach up and operate the lever, with other vehicle components acting 

as obstacles. It is critical to examine the design as both an individual piece and part of 

the larger overall vehicle-human-interface design at all steps of the design cycle. 

4.5.4.5.2 IDENTIFY INFLUENCING FACTORS

Using the defined test objectives, the next step would be to match the assumed posture 

needed to perform the task (e.g., a pushing motion at an oblique angle using a handle, 

hand grip, and elbow flexion) to corresponding postures determined from the strength 

requirements data set and resolve the posture into all necessary and applicable 

strength components. This analysis will aid in the identification of postural factors that 

may affect the subject’s ability to apply the necessary force or torque to perform a given 

task or operation. These steps will help determine whether the requirements for an 

assumed posture are reasonable and applicable to the human-system interface in 

question, while identifying the necessary test metrics and accounting for any 

assumptions or influencing factors associated with the design.

4.5.4.5.3 ACCOUNT FOR SUIT, POSTURE, AND GRAVITY EFFECTS

4.5.4.5.3.1 SUIT EFFECTS

For the Constellation Program and the Commercial Crew Program, NASA has 

measured and/or estimated suit effects on crewmember strength. The crewmember 

strength datasets for those programs can be found in HSIR Appendix B4 and CHSIR 

Appendix D4. Strength data are provided for unsuited, suited pressurized, and suited 

unpressurized conditions. The forces required to operate a given designed humansystem interface must be within the strength range of the weakest anticipated 

crewmember for the worst-case pressure differential anticipated (e.g., unsuited, suitedunpressurized, or suited-pressurized). The HSIR and CHSIR set forth very specific 

postures for application of human strength and it is possible that a posture required to 

perform a specific, yet-to-be-determined task, may not directly correspond with any one 
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posture in the strength data tables. Under such circumstances, programs should consult 

with NASA for direction on how to apply the appropriate combination of postures and 

associated strength values, or whether an additional validation is necessary for a 

particular posture and strength combination. This will ensure that the appropriate 

measures are implemented to protect both crewmembers and vehicle.

4.5.4.5.3.2 POSTURE VARIABILITY

During testing, strength measurements will be directly influenced by posture effects, and 

therefore the strength requirements compiled and set forth in the strength requirements 

data set are valid at only at the postures given. The assumption of a specific posture is 

highly dependent on the population and the location of the hardware design within the 

environment. If the design is placed in a location where smaller individuals will adopt a 

posture different from that of larger individuals, this variability must be accounted for 

and should be validated separately. Although data for the analytical and modeling 

stages of design are limited, the performance changes can be identified through HITL 

testing. Thus, it is critical to perform HITL testing on a wide variety of subject types to 

address postural variability in the population and determine its impacts on strength 

performance. The assumptions for the impact of posture effects on the human body 

must be unequivocally verified during HITL testing to ensure that the assumptions are 

valid or to modify the analysis as appropriate.

4.5.4.5.3.3 GRAVITY EFFECTS

Microgravity conditions present an interesting challenge to crewmembers when they are 

actuating a hardware interface or performing a task or operation requiring the 

application of force or torque. In this environment, it is much more difficult to apply the 

necessary force or torque because reaction forces (i.e., the forces acting back on the 

body when a human force is applied) are lacking, and therefore tasks performed under 

such conditions should be evaluated carefully and the appropriate strength values 

should be applied for the other conditions applicable to the situation (e.g., suited or 

unsuited conditions). For instance, the posture used by the crewmember, as well as any 

available braces or handholds, should be accounted for and the appropriate strength 

values applied. This will work to ensure that human operators are able to successfully 

perform any in-flight tasks requiring the application of force or torque.

For conditions involving hypergravity (e.g., launch, reentry), worst-case scenarios (e.g., 

deconditioning effects, safety factors, weakest crewmember) should be applied to 

ensure safe operation of human-system interfaces and the avoidance of any failures 

that may lead to loss of crew, vehicle, or mission. The task should be carefully analyzed 

and the appropriate strength value be applied.

4.5.4.5.4 IDENTIFY WORST-CASE SCENARIOS

Identification of the worst-case scenarios for human strength focuses the minimum 

strength values for a given population in a given posture for a selected criticality to 

protect all members of that population who will be affected by the design. 
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4.5.4.6 EVALUATE THE DESIGN

Several factors go into the interpretation of results from human strength data collection,

and the method of interpretation is heavily dependent on the ultimate end goals of the 

test. For example, comparison of the strength requirements associated with a design to 

the strength levied in a specific posture will require analyses of adopted posture(s) 

during force production, as well as a determination of the scenarios in which the 

designed hardware will be used. For example, if a given piece of hardware is used in all 

phases of flight and potentially under any circumstances, nominal or 

contingency/emergency, then the appropriate space flight-related factors must be 

considered. A comparison of the force or torque values of the hardware to the 

standardized strength values for a given posture will determine compliance of the 

design.

4.5.4.6.1 PRELIMINARY ANALYSIS

The preliminary analytical analysis method is a simplistic “on paper” analysis to 

compare the human strength requirements against the strength demands of the 

hardware design. The use of free-body diagrams can be implemented to account for the 

force or torque requirements of the hardware design. These can then be compared to 

human strength requirements found in the strength requirements data set to determine 

whether further examination, analysis, and/or testing are warranted.

4.5.4.6.2 MODELING

As the design matures, more than likely the design will be placed into a CAD model. 

The designer should use dynamic models or other defendable, validated modeling 

techniques to determine the force or torque requirements of the hardware design. 

Compare the results to the human strength requirements to determine whether the 

weakest crewmember can apply the necessary force or torque to the hardware interface 

to successfully perform a task or operation.

4.5.4.6.3 HITL TESTING

HITL testing in the context of this document is a physical simulation involving a human 

operator. The benefits of HITL testing are that it allows a designer to test a mockup or 

prototype with a human and determine whether the assumptions about the posture, 

strength required to perform a task, and/or hardware issues are consistent. Some 

challenges associated with HITL testing are cost, time consumption, subject availability 

and participation, and the need for mockups of appropriate fidelity. HITL testing is the 

final step in validation of the design against the requirements. When HITL testing is 

conducted for evaluation of strength, multiple subjects will be needed to validate the 

posture assumptions, and if a variation occurs, the performance improvement or 

degradation can be determined by comparing subjects. Testing must include a range of 

subject sizes to properly scope the population. Ideally, a mockup of the human-system 

interface would be used with instrumentation capable of measuring human-applied 

forces and torques. This would allow a one-to-one comparison of actual hardware 

forces and torques to those being estimated, as well as to applicable strength 

requirements. Other scenarios, though less than ideal, may include obtaining unsuited 
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strength data for the functional posture in question using a strength dynamometer to 

see where subjects fall in the population, and comparing performance on that 

dynamometer to actuating the hardware. However, if no dynamometer is available, it 

may be feasible to test the designed hardware in “ideal” configuration (i.e., outside a 

mockup, shirt-sleeved, unencumbered, in the location matching the posture selected 

from the strength requirements), and compare test results from this configuration with 

results from performing the task in the mockup given the postural issues and identifying 

all other influencing factors. The appropriate performance metrics (e.g., quantification of 

force decrement, postural analyses) should be used to characterize any differences 

between the 2 conditions and to provide recommendations on how to proceed with the 

human-system interface design.

Additional discussion of HITL testing for anthropometry, biomechanics, and strength 

assessments can be found in HIDH section 4.2.4.2 Enhancement of Human-in-the-Loop 

Testing.

4.5.4.6.4 FINALIZE THE DESIGN

Evaluate the design using analytical analysis, modeling techniques, or HITL testing at 

the appropriate stage of the design cycle and determine what segments of the 

population are not accommodated and what adjustments are necessary to 

accommodate the entire user population (i.e., the weakest crewmember). If overall 

failure of the user-interface interaction (i.e., inability of the weakest crewmember to 

actuate or operate hardware for task completion) occurs, then re-evaluation of the 

design is required and the appropriate testing steps must be taken to ensure 

accommodation of the entire user population.

4.5.4.7 STRENGTH TECHNICAL PRODUCTS

The reporting of human strength values should involve incorporation of worst-case 

scenarios as identified through careful selection of the data set and associated test 

conditions. These should be implemented to ensure the protection of all crewmembers, 

and of the hardware, vehicle, and mission completion. In the realm of human strength 

testing, worst-case scenarios manifest in the form of minimum values. Mean strength 

values can provide valuable information about the strength of a group of individuals, but 

do not provide end-users with information about the protection of weaker subjects (i.e., 

those with strength values lower than the mean). Inclusion of minimum strength values 

(i.e., strength values of the weakest individual) ensures that all other members of that 

tested population are able to effectively apply the force of the weakest subject. In sum, 

the reporting of minimum values provides users with guidelines for system design to 

protect the weakest crewmember who may operate a given hardware component or 

interface. This information will apply to HITL testing as well, and it is crucial for any 

developer’s HITL testing to include an appropriate number of subjects so as to provide 

the necessary statistical confidence in results and testing-derived strength requirements

and recommendations. 
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Reporting maximum strength values for human-system interfaces provides users 

guidelines for protecting hardware from the strongest crewmembers who may operate a 

given hardware component or interface.

For each of the major milestones of the design life cycle, the technical products in Table 

4.5.4.7-1 are recommended for review by the NASA customer.

TABLE 4.5.4.7-1 STRENGTH TECHNICAL PRODUCTS

Technical Products

Phase 

A

Phase 

B

Phase 

C

Phase 

D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function allocation, 

associated crew task lists, and the selected strength 

critical limits. Includes list of tasks considered to be 

design-driving for strength requirements as well as 

definition of factors that influence strength.

I U U U --- ---

A summary of modeling/analysis/evaluation (i.e., 

CAD, human modeling, and population analysis) 

performed to date and the influence on system 

design, with links to the detailed analysis results.

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10.

--- --- I U U ---

System architecture drawings (structures, 

equipment, etc.), material specifications, interface 

requirements.

--- --- I U U ---

Verification plan. --- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are influenced by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

For strength requirements, it is important to determine what tasks may be designdriving. Tasks or uses of hardware that represent challenges for weaker individuals will 

be particularly important for system-level analysis and testing. Factors that may affect 

strength include suit conditions, posture, gravity conditions, and group effects. 

Modeling, Analysis, and Evaluation Summaries

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into technical details of human-systems integration throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 
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increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how key and critical design 

decisions were assessed. According to NPR 8705.2B, updated summaries are to be 

provided at each design review through SAR. Also, in paragraph 2.3.10, the use of HITL

evaluation is a required method to progressively demonstrate that the operational 

concept meets system requirements for operational safety, efficiency, and user interface 

design.

For strength analyses, as appropriate for each design phase, reports should detail CAD 

model work and progressively higher fidelity human model work in addition to analysis 

of HITL evaluations. CAD and HITL analyses are necessary to define postures and 

actions used for each task. Population analysis ensures that findings extend to the 

entire crew population and consider worst-case scenarios. 

Architecture, Materials, and Interface Specifications

Drawings, materials, and interface specifications provide NASA with insight into humansystem integration technical details throughout the design process. 

Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 

System Requirements Review (SRR)

Suggested developer technical products:

 Selected strength limits for an applicable task list.

 Overall plan for meeting human-systems design compliance

 Definition of human-related major systems and what strength requirements are 

applicable 

 High-level analytical analyses examining the impact of requirements on the 

design

NASA Involvement:

 Review overall plan, give feedback

 Review major systems and applicable requirements, give feedback

 Review analytical analysis results for consistency and methodology, give 

feedback

System Definition Review (SDR)

Suggested developer technical products:

 Reports detailing analytical analyses for all major subsystems, to prove that 

concept designs meet designated strength requirements and any assumptions 

are accounted for 

NASA Involvement:

 Review reports, give feedback on strength requirements as well as any 

assumptions made about human strength in the design process
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Preliminary Design Review (PDR)

Suggested developer technical products:

 Continued development of overall plan for meeting human-systems design 

compliance

 Detailed analyses (e.g., modeling) examining the impact of designated strength 

requirements on the human-system interface design, with any limitations and 

assumptions addressed

NASA Involvement:

 Review overall plan, provide feedback

 Review major systems and applicable requirements, provide feedback

 Review detailed analysis results for consistency and methodology, provide 

feedback

Critical Design Review (CDR)

Suggested developer technical products:

 Continued development of overall plan for meeting human-systems design 

compliance

 Demonstration of design maturity and readiness for fabrication of final design 

prototype

NASA Involvement:

 Review overall plan, provide feedback

 Review design for consistency and methodology, provide feedback on final 

prototype design

Test Readiness Review (TRR)

Suggested developer technical products:

 Demonstration of adherence to overall plan for meeting human-systems design 

compliance and justification for necessary plan changes

 Demonstration of readiness to perform HITL testing to verify and validate 

strength requirements

 Definition of human-related major systems and designated strength requirements 

applicable to the HITL testing to be performed

NASA Involvement:

 Review overall plan, give feedback

 Review major systems and applicable requirements, give feedback

 Review analytical analysis results for consistency and methodology, give 

feedback

System Acceptance Review (SAR)

Suggested developer technical products:

 Demonstration of design compliance
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NASA Involvement:

 Review of design relative to levied requirements

4.5.4.8 STRENGTH REFERENCES

Chaffin, D. B., Andersson, G. B. J., Martin, B. J. (1999). Occupational biomechanics. 

New York: J. Wiley & Sons. 

MIL-STD-1472. (1968 and ff.) Department of Defense human engineering design 

criteria for military systems, equipment, and facilities.(initial, with revisions through F). 

Washington, D.C.: U.S. Department of Defense.
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4.5.5 DESIGN FOR MASS PROPERTIES, VOLUME, AND SURFACE AREA

4.5.5.1 INTRODUCTION

Requirements for ROM, anthropometry, and strength are provided to ensure that any 

crewmember can safely operate and manipulate the selected human-system interface 

of interest, but considerations for mass properties, volume, and surface area differ in 

their direct applicability to the design. The contributions of mass properties, volume, and 

surface area serve as inputs for other design factors, such as dynamic calculations of 

mass and moment of inertia of the vehicle, the functional volume design of the cabin, 

and radiation exposure calculations. The intent of this process is to provide designers 

with methodologies and best practices for implementing crew body mass properties, 

volume, and surface area requirements.

4.5.5.2 APPLICABLE REQUIREMENTS

The following NASA-STD-3001, Volume 2 requirements are applicable to mass 

properties, volume, and surface area:

 Data Sets [V2 4001]

 Data Set Characteristics [V2 4002]

 Population Definition [V2 4003]

 Data Set Assumptions [V2 4004]

 Body Surface Area Data [V2 4009]

 Body Volume Data [V2 4010]

 Body Mass Data [V2 4011]

4.5.5.3 SELECTION OF VOLUME, MASS, AND AREA DATA SETS

The NASA-STD-3001 NASA Spaceflight Human-System Standard Requirement V2 

4001 specifies that a biomechanics data set for the crewmember population must be 

selected, and specifically that volume (V2 4010), mass (V2 4011) and surface area (V2 

4009) must be applied to the design. In addition, requirement V2 4004 specifies that 

age, gender, and physical condition shall also be included in this data set, and V2 4002 

requires that characteristics unique to space travel also be factored into the design. And 

V2 4003 requires the definition of the population ranges for the associated values of 

volume, mass, and area that the system is intended to accommodate.

No data set of volume, mass, and area values is available as one is for anthropometry; 

however, a variety of technical papers detail those values for different populations. 

Using information in the public domain, a designer can determine the anticipated limits 

of the population for volume, mass, and area respectively. 
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4.5.5.3.1 WHOLE-BODY AND BODY-SEGMENT MASS PROPERTIES

The requirement in NASA-STD-3001 for whole-body and body-segment mass 

properties data sets (V2 4011) is included specifically for the purposes of propulsion 

calculations and to ensure the structural integrity of human-system interfaces. Accurate 

data regarding the full range of crewmember mass is critical in analyzing potential 

forces imparted by a crewmember under all acceleration and gravity environments. 

Forces exerted by the whole body or body segment create reactions that depend on the 

mass properties. The mass, center of mass (COM) position, and moment of inertia 

(MOI) of the body and/or segments greatly affect the degree and severity of possible 

injuries during acceleration. Thus, accounting for mass properties of the crewmembers 

is a critical component of crew safety.

4.5.5.3.2 WHOLE-BODY AND BODY-SEGMENT VOLUME

The requirement in NASA-STD-3001 for development and implementation of wholebody and body-segment volume data (V2 2010) is included as a resource for analysis, 

potentially applicable to cabin or suit volume displacement. Quantifiable volumetric 

values for the users may also be useful in determining the functional volume design 

estimates. 

4.5.5.3.3 WHOLE-BODY SURFACE AREA

The requirement in NASA-STD-3001 for development and implementation of a wholebody surface area data set (V2 4009) is included as a resource for analysis, potentially 

applicable to estimating radiation or thermal exposure. For example, body surface area 

may aid in the estimation of body heat production for thermal environmental control or in 

the estimation of radiation dosimetry. 

4.5.5.4 MASS PROPERTIES, VOLUME, AND SURFACE AREA GENERAL OVERVIEW

Unfortunately, the exact mass properties, volume, and surface area of a given human 

body are not directly measurable by conventional means. Historically, cadaver studies 

were performed to quantify the exact physical characteristics of mass, volume, and 

surface area (DuBois and DuBois, 1916; Gehan et al., 1970; Martin et al., 1984). The 

regression equations used by the cited references (McConville et al., 1980, and Young 

et al., 1983) all compromise to this fact and are a means of determining the estimated 

specific volume, area, and mass properties of a unique individual. The lack of readily 

available measurement tools places heavy emphasis on the analytical and modeling 

aspects of design with respect to mass properties, volume, and surface area, with 

limited value to HITL testing. Below is a suggested approach that places focus on 

analytical and modeling aspects for the majority of design work, using human-based

testing to verify assumptions made in the earlier stages of design. In general, the flow of 

any design evaluation, whether low-fidelity analytical analysis or high-fidelity HITL 

testing, contains the same basic sequence of steps:

1. Determine the objectives of the analysis 

2. Account for any impacts of suit, posture, group, and gravitational effects

3. Identify possible worst-case scenarios for the proposed objectives 
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4. Evaluate the design: use the volume, surface area, and mass properties 

information in the relevant analysis. Evaluate and revise the design to ensure 

accommodation of the user population.

5. Repeat steps 1-4 until the design meets the requirements set forth and the 

design is in the final stages of the design cycle.

4.5.5.5 METHODOLOGY

4.5.5.5.1 IDENTIFY ANALYSIS OBJECTIVES

The necessity for an evaluation of the volume, surface area, and/or mass properties of 

the design is based on their applicability to the design, given the relevant vehicle 

conditions and exposure concerns of the crewmember. Not every human-system 

interface design will require such an analysis, so the first step is to identify the relevance 

of an analysis of volume, surface area, or mass properties to the design, given the 

stage of the design cycle. For example, launch and landing scenarios will focus heavily 

on the mass properties data related to the seat. The evaluators will require a solid 

understanding of the proposed seat design and structural properties of the seat 

components to perform an evaluation. Low Earth orbit (LEO) scenarios may involve 

body volume and body surface area characteristics, but inclusion of these in analysis 

may not be required until the layout of the vehicle design has been fully determined. 

After analysis of relevance, the second step in utilization of the volume, surface area, 

and mass properties information is to scope the contingency scenarios and the 

associated safety impact on the crewmembers. For example, an off-nominal landing 

scenario will require a separate dynamic analysis involving the mass properties 

information. Essentially, consider the various situations that a crewmember may be 

exposed to and where the mass properties, volume, and surface area requirements are 

applicable, to ensure crew safety and health.

4.5.5.5.2 ACCOUNT FOR SUIT, POSTURE, GROUP, AND GRAVITY EFFECTS

4.5.5.5.2.1 SUIT EFFECTS

Information about spacesuits and their impact on humans in relation to volume, surface 

area, and mass properties is limited, but if possible, include suit effects in the analysis. 

For example, in a dynamic evaluation of landing, if a crewmember is wearing a suit, the 

helmet, boots, crew survival equipment, and other gear will affect the mass and inertia 

profiles of the analysis. This addition of any mass to the body of the user will adversely 

influence the mass properties and must be accounted for in the analysis. Previous 

NASA studies have shown how to account for suit mass and subject anthropometry on 

the whole-body center of mass of a seated crewmember (Blackledge, 2010), and the 

same principles can be applied to body moment-of-inertia analyses. 

The suit will also affect the analyses related to the volume and body surface area. The 

addition of the suit components adds to the total body volume, influencing functional 

volume design calculations. The addition of the suit components also influences the 

surface area of the body in relation to radiation dosimetry and associated protection and 
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shielding. All of these examples are potential applications of suit effects. If possible, 

attempt to incorporate aspects of the suit into the analysis when they are applicable.

4.5.5.5.2.2 POSTURE EFFECTS

Whereas volume and body surface area values are, for the most part, independent of 

posture, analysis of mass properties requires posture information to perform dynamic 

calculations. The whole-body mass properties in most existing literature are related only 

to a standing position, and deviation from this body position requires recalculation of the 

whole-body mass properties. For given task posture, the user’s body segment positions 

must be factored in calculating segmental mass effects on whole-body mass properties, 

such as center of mass and moment of inertia. If the developer needs to derive posturebased mass properties, they are advised to use the anthropometric data set developed 

from section 4.5.2 Design for Anthropometry coupled with the regression equations from 

literature. For example, NASA explored the combination of suit and posture effects on 

the location of the center of mass for a given set of seated recumbent postures in a 

Blackledge (2010) paper. In this study, regression equations from McConville (1980) 

and Young (1983) coupled with a suited center of mass (COM) methodology yielded 

information on the COM changes across the entire population. After this analysis is 

performed, the assumptions of posture and associated body angles must be evaluated 

through HITL testing to ensure that the calculations are accurate.

4.5.5.5.2.3 GROUP EFFECTS

A group of users may influence the analyses associated with mass properties and 

volume, specifically group mass and functional volume design. Group effects reflect a 

mixture of multiple users across the user population and need to be accounted for to 

identify any scenarios that may have a negative impact on the system’s capability for

complying with requirements. 

Group effects for mass have been addressed in the past using a Monte Carlo 

simulation. As previously discussed in the anthropometry section, a Monte Carlo 

simulation is a numerical simulation technique that relies on repeated random 

samplings to compute results. In the context of mass, the total mass of the crew may 

preclude taking other objects into space, because of restrictions in the total mass that 

can be flown. For example, there is a low likelihood that multiple men in the 99th

percentile for mass will fly simultaneously. Instead, random sampling of the weight or 

mass of the entire selected population can be used to derive whole-body crew mass.

The details on the derivation of these values are given in Margerum and Rajulu (2008). 

A total crew mass value may be used to establish individual mass limits for selecting 

crew, within the range of allowable individual mass limits. The Monte Carlo simulation 

can also be expanded for calculations requiring distributions of crew mass during launch 

and landing and the associated impacts on the vehicle dynamics.

Group effects also need to be accounted for in the functional volume provided to all 

users for performing their tasks. As users vary in body size, their body volume also 

varies and the group effects compound this variation in volume. Consideration for a 

multi-sized crew is essential to functional volume calculations; for example, consider the 
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volume of a crew of 4 that is composed of 3 large crewmembers and one small 

crewmember instead of the volume of 3 medium crewmembers and one small 

crewmember. The variances apparent in the population will influence these calculations,

and thus the designer should consider group effects in their analyses.

4.5.5.5.2.4 GRAVITY EFFECTS

Gravity deconditioning affects crew body volume, mass properties, and surface area. 

However, no empirical data exists on the amount of change in these body parameters.

4.5.5.5.3 IDENTIFY WORST-CASE SCENARIOS

Typically for radiation exposure analyses or functional volume design calculations, the 

worst-case whole-body values are typically the largest and smallest values available in 

the dataset. However, it is recommended that designers critically evaluate the design 

and the analysis objectives to determine whether these values should be used for 

worst-case scenarios. Caution must be used in determining the worst-case scenario,

and designers should not assume that applying all maximum or minimum values to the 

given body segments will produce the worst case. For example, examination of the 

worst-case dynamic profiles using mass properties will be influenced by posture and 

anthropometry, and adding suit or crew survival equipment will affect it further. It is 

suggested that, to properly determine a posture-specific COM, designers should identify 

worst cases by the procedure specified in the Blackledge (2010) paper.

4.5.5.6 EVALUATE THE DESIGN

The suggested approach is to focus on analytical and modeling aspects for the majority 

of design work, using human-based testing to verify assumptions made in the earlier 

stages of design. Using the defined objectives of the analysis, incorporating the suit, 

posture, group and gravity effects, and focusing on the worst-case scenarios will assist 

designers in evaluating their design with respect to mass properties, volume, and 

surface area. The end goal is to ensure that the full population has been considered in

the design.

4.5.5.6.1 ANALYTICAL EVALUATION

Early in the design process, the mass properties, body volume, and body surface area 

can be incorporated into the designs using a simplistic analytical analysis. 

Mass properties representing the worst-case scenarios can be incorporated into freebody diagrams of the design to evaluate its kinetic behavior. For example, the forces at 

the hip joint of a recumbent chair during hypergravity situations are influenced by the 

mass properties of the seat pan, seat legs, crewmember legs and feet, and their 

associated positioning with respect to the loading forces. Thus the mass properties of 

the section of the population with the heaviest and longest legs will drive the maximal 

loading at the hip joint of the seat. Estimations of COM locations and moment of inertia 

can be coupled with anthropometry and a whole-body posture-based analysis (WBPBA) 

to derive the leg mass properties and the forces imparted to the hip joint of the chair for 

the entire population (Blackledge, 2010). 
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Volume can provide information about anticipated space required by the crewmember in 

relation to the design. Similarly, area and volume can be used in initial calculations for 

radiation dosimetry or other related analyses. Group and suit effects can be factored 

into the analysis as well, to ensure that the entire user population is considered in the 

design.

4.5.5.6.2 CAD MODELING AND SIMULATION

As the design stage shifts toward modeling the worst-case scenarios identified in the 

analytical analysis, models can be loaded into the relevant CAD modeling tool for 

estimation and visualization. These individually based, anthropometrically based values 

for mass properties, volume, and surface area can be incorporated into the applicable 

design for further analysis. The entire population should be factored into the analysis 

utilizing the available tools at hand, whether the analysis relates to the evaluation of 

dynamic loading or to estimations of radiation dosimetry.

4.5.5.6.3 HUMAN-IN-THE-LOOP TESTING

HITL for mass properties, volume, and surface area can be used to verify assumptions 

used in the analytical and CAD modeling analyses. Specifically this pertains to the mass 

properties work that depends on posture. HITL testing can be used to verify that the 

assumed postures used in the previous analyses are correct, and if not, those analyses 

can be updated with the actual values. For volume, body surface area, and mass 

properties, the HITL testing can be used to tie an actual subject’s data into previous

analysis work, and by doing so account for potential variations not accounted for in the 

previous analyses. The assumptions of group, suit, or postural effects can also be 

confirmed through HITL testing, ensuring that the entire population has been considered 

for the analysis that uses these parameters and that all assumptions have been 

validated. In scenarios where HITL testing is required but unsafe, mannequins or crash 

test dummies should be used as substitutes for the human body (i.e., mannequin-in-theloop testing). Mannequin-in the loop testing would follow HITL testing parameters and 

methodology, except that the data would be collected from mannequins instead of 

humans. An example of this is flight testing the center of gravity of the manned vehicle 

using representative mannequins instead of actual crewmembers.

4.5.5.6.4 ADDITIONAL INFORMATION

The developer is advised to acquire copies of the McConville (1980), Young (1983), and 

Gehan and George (1970) papers for access to the regression equations for calculation 

of volume, surface area, and mass properties on a per-subject basis.

4.5.5.7 MASS PROPERTIES, VOLUME, AND SURFACE AREA TECHNICAL PRODUCTS

Evaluating a design requires unique phases that depend on the various stages of the 

design life cycle. As previously mentioned, during the preliminary stages of design, 

analytical and CAD modeling should be used to identify worst-case scenarios, the 

critical human dimensions of interest, and a general accommodation level of the design. 

HITL testing can be valuable for verifying assumptions about the body properties of 

mass, volume, or body surface area used in analytical and modeling analyses. 
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For each of the major milestones of the design life cycle, the technical products in Table 

4.5.5.7-1 are recommended for review by the NASA customer.

TABLE 4.5.5.7-1 MASS PROPERTIES, VOLUME, AND SURFACE AREA TECHNICAL 

PRODUCTS

Technical Products

Phase

A

Phase 

B

Phase 

C

Phase

D

SRR SDR PDR CDR SRR SDR

A description of the ConOps, function allocation, 

associated crew task lists, and the selected mass, 

volume, and area critical limits. Includes list of tasks 

considered to be design-driving for mass properties, 

volume, and surface area requirements as well as 

definition of factors affecting these properties.

I U U U --- ---

A summary of modeling/analysis/evaluation (i.e., 

CAD, human modeling, and population analysis) 

performed to date and its influence on system 

design with links to the detailed analysis results.

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10.

--- --- I U U ---

System architecture drawings (structures, 

equipment, etc.), material specifications, interface 

requirements.

--- --- I U U ---

Verification plan. --- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are affected by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

For mass properties, volume, and surface area requirements, it is important to 

determine what tasks may be design-driving. Factors that may influence these 

properties include suit conditions, posture, gravity conditions, and group effects.

Summaries of Modeling, Analysis, and Evaluation

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into technical details of human-systems integration throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how key and critical design 
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decisions were assessed. According to NPR 8705.2B, updated summaries are to be 

provided at each design review through SAR. 

For mass properties, volume, and surface area analyses, as appropriate for each 

design phase, reports should detail CAD model work and progressively higher fidelity 

human model work in addition to analysis of human-in-the-loop evaluations. Population 

analysis ensures that findings extend to the entire crew population and consider worstcase scenarios. 

Architecture, Materials, and Interface Specifications

Drawings, materials, and interface specifications provide NASA with insight into 

technical details of human-systems integration throughout the design process. 

Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 

System Requirements Review (SRR)

Suggested developer technical products:

 Selected mass, volume, and area limits

 Definition of human-related systems and what mass property, body volume, and 

body surface area requirements are applicable 

 Overall plan for meeting mass property, body volume, and body surface area 

design compliance

 High-level analytical analysis depicting method and implementation for meeting 

requirements based on mass property, body volume, and body surface area

NASA Involvement:

 Review overall plan, give feedback

 Review analytical analysis methods and results for consistency, give feedback

System Definition Review (SDR)

Suggested developer technical products:

 Reports detailing analytical analyses and/or modeling work (area, volume, mass) 

for all major subsystems, detailing compliance with the specifications given in the 

designated requirements.

 Plans for mitigation efforts if analyses indicate that design does not meet 

requirements

NASA Involvement:

 Review reports, give feedback

Preliminary Design Review (PDR)

Suggested developer technical products:

 Reports detailing analytical analyses and/or modeling work (area, volume, mass) 

for the design, detailing compliance with the specifications given in the 

designated requirements.
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 Plans for mitigation efforts if analyses indicate that design does not meet 

requirements

 Plan for verification of requirements

NASA Involvement:

 Review detailed analysis results for consistency and methodology, provide 

feedback

 Review plans, provide feedback

Critical Design Review (CDR)

Suggested developer technical products:

 Reports detailing analytical, modeling, and HITL analyses (area, volume, mass) 

for all major subsystems, detailing compliance with the specifications given in the 

designated requirements; plans for mitigation efforts if analyses indicate that 

design does not meet requirements

 Reports on updated analyses (analytical and modeling) based on results of HITL 

testing examining the impact of anthropometric requirements on the humansystem interface design; plans for mitigation efforts if analyses indicate that 

design does not meet requirements

 Final plans for body surface area, volume, and mass properties verification 

testing

NASA Involvement:

 Review reports, give feedback

 Review final verification plan, give feedback 

Test Readiness Review (TRR)

Suggested developer technical products:

 Demonstration of adherence to overall plan for meeting human-systems design 

compliance and justification for necessary plan changes

 All testing completed and mitigation efforts incorporated into the design

NASA Involvement:

 Review reports, give feedback 

System Acceptance Review (SAR)

Suggested developer technical products:

 Demonstration of design compliance and all anthropometric requirements met for 

area, volume, and mass 

NASA Involvement:

 Review of design relative to levied requirements
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4.5.5.8 MASS PROPERTIES, VOLUME, AND SURFACE AREA REFERENCES

Blackledge, C., Margerum, S., Ferrer, M., Morency, R., & Rajulu, S. (2010). Modeling 

the impact of space suit components and anthropometry on the center of mass of a 

seated crewmember. Applied Human Factors and Ergonomics, Electronic Proceedings.

DuBois, D., & DuBois, E. F. (1916). A formula to estimate the approximate surface area 

if height and weight be known. Archives of Internal Medicine, 17, 863–871. 

Gehan, E. A., & George, S. L. (1970). Estimation of human body surface area from 

height and weight. Cancer Chemotherapy Reports Part I, 54(4), 225-235.

Margerum, S., & Rajulu, S. (2008). Human factors analysis of crew height and weight 

limitations in space vehicle design. Human Factors and Ergonomics Society Annual 

Meeting Proceedings, 52(1), 114-118(5).

Martin, A. D., Drinkwater, D. T., & Clarys, J. P. (1984). Human body surface area: 

validation of formulae based on cadaver study. Human Biology, 56(3), 475-485.

McConville, J., et al. (1980). Anthropometric relationships of body and body segment 

moments of inertia (AFAMRL-TR-80-119). Wright-Patterson Air Force Base, Ohio: Air 

Force Aerospace Medical Research Laboratory, Aerospace Medical Division, Air Force 

Systems Command.

Young, J.W., et al. (1983). Anthropometrics and mass distribution characteristics of the 

adult female (AD-A143096). Oklahoma City, Oklahoma: FAA Civil Aeromedical Institute, 

Federal Aviation Administration.
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4.5.6 BACKGROUND OF CHSIR REQUIREMENT VALUES

4.5.6.1 ANTHROPOMETRY

The anthropometric measurements and limits selected for inclusion in the Commercial 

Human Systems Integration Requirements (CHSIR) were determined through work with 

NASA cockpit, seat, and suit teams to generate a consolidated list of dimensions 

integral to the design of hardware for the space program. The CHSIR anthropometric 

data set is based on the Natick Anthropometry Survey of Army Personnel (ANSUR), an 

Army-based anthropometric data set (Gordon et al., 1989). This data set represents the 

anticipated body type of the astronaut corps more closely than more general population 

data sets that are available. The data set was age-truncated to between 30 and 51 

years to encompass the representative age range of the astronaut corps. It was also 

height-adjusted to align with Air Force population height and to correspond to projected 

growth trends to the year 2015 (Churchill et al., 1976; McConville et al., 1991; NHANES 

2004). This truncated data set is more appropriate than a more generalized population 

data set because it minimizes the anticipated anthropometric ranges while ensuring that 

the astronaut corps can be accommodated. 

The minimum and maximum values in CHSIR represent the 1st-percentile-female to 

99th-percentile-male range for each critical dimension. This percentile range was 

selected to accommodate the astronaut corps (as of 2004) as well as minimize the 

impact on future crew selection and accommodation. Although a 1st- to 99th-percentile

range may initially seem high, it is an age-truncated, specifically tailored population as 

opposed to corresponding values from a generic population data set. Analyses were 

performed to investigate reducing this 1st-percentile female to 99th-percentile male range 

to a smaller range of values, but it was determined that blanket reductions in the 

anthropometric ranges would result in a large detriment to crew accommodation with 

low payoff for the design, because of the relatively poor correlations between 

anthropometric dimensions and the large number of dimensions. This truncated and 

height-adjusted CHSIR anthropometric data set should be the data set used by the 

Commercial Crew Transportation (CCT) Company for the majority of population 

analyses that rely on a data set. Generation of the suited anthropometric values in 

CHSIR is discussed in a later section (see paragraph 4.5.3.2.2.3.1 Suit Factors).

Additional examples of HITL testing and population analysis methods as they have 

been applied to the space program can be found in the process document JSC 65851

Anthropometric Processes for Population Analysis, Suit Factor Generation, and a NASA 

Recommended set of Practices Essential for Data Collection and Analysis for 

Verification and Validation of Vehicle, Suit, and Vehicle-Suit Interface Requirements.

4.5.6.2 RANGE OF MOTION

The details of testing from which the CHSIR ROM tables were generated can be found 

in NASA Technical Paper 2010-216122 (England et al., 2010). Data interpreted from 

that report provides a single value for each suited state.
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4.5.6.3 STRENGTH

The strength limit values in the CHSIR were developed from extensive review of 

literature as well as from human strength testing performed at NASA facilities under 

unsuited, suited unpressurized, and suited pressurized conditions. The literature review 

included an extensive collection of journal articles associated with human strength data. 

In addition, other references, such as the MIL-STD-1472 and the Occupational 

Biomechanics textbook (Chaffin et al., 1999), were used to set a standard for very 

specific strength data such as lifting, pushing, and pulling strengths. The strength data 

in the tables of CHSIR Appendix D5 represent static (i.e., isometric) force applied by 

subjects in specific postures (involving segment postures as well as whole-body 

postures) that were determined to be relevant and applicable to a wide range of 

possible mission tasks that may include both suited (e.g., launch, entry, extravehicular 

activities) and unsuited operations. 

4.5.6.4 WHOLE-BODY AND BODY-SEGMENT MASS PROPERTIES

To calculate whole-body and body-segment mass properties for the CHSIR, regression 

equations were used that were based on 2 anthropometric dimensions, stature and 

weight. Both female and male anthropometric parameters for stature and weight were 

used from the CHSIR anthropometric data set. These regression equations are sourced 

from McConville et al. (1980) and Young et al. (1983). These studies have been 

historically used to compute the whole-body and body-segment volumes. Whole-body 

and body-segment mass were calculated from these equations by assuming that the 

density of human flesh was homogeneous and had a density value of 1 g/cm3. With a 

value of unity for the density, the mass values were numerically equal to their 

corresponding volume values. The COM and moment of inertia (MOI) were also 

captured from the McConville et al. (1980) and Young et al. (1983) studies. 

The COM locations for the whole body and body segments were also determined from 

McConville et al. (1980) and Young et al. (1983). Determination of the COM in those 

studies was based on the assumption that human flesh is homogeneous and the 

assumption that the center of volume is at the COM location. Both McConville et al. 

(1980) and Young et al. (1983) provided ranges for the location of the center of volume 

for men and women, respectively, in their studies. Unique values for the locations of the 

center of mass with respect to the anatomical axes were captured from each study for 

the range in CHSIR. Specifically, the upper range value was specific to the male 95th-

percentile stature and weight upper range values, and the lower range value was 

specific to the female 5th-percentile stature and weight lower range values. 

Whole-body and body-segment MOI values were captured from regression equations in 

McConville et al. (1980) and Young et al. (1983). Each of these studies contained 

regression equations based on using the stature and weight parameters. The data in 

the CHSIR anthropometric data set was used for identifying the lower (i.e., 5th-

percentile) and upper (i.e., 95th-percentile) range values for the MOI locations. However, 

the MOIs presented are about the principal axes, XP, YP, and ZP.
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4.5.6.5 WHOLE-BODY AND BODY-SEGMENT MASS VOLUME

Regression equations from the McConville et al. (1980) and Young et al. (1983) studies 

were used to compute the whole-body and body-segment volumes. As previously 

mentioned, the regression equations used 2 independent parameters, stature and 

weight. The whole-body and body-segment volumes were determined for each gender 

by using the input parameters from the entire CHSIR population. An average and 

standard deviation was acquired from each set of data to calculate the minimum and 

maximum values. The maximum whole-body and body-segment values pertained to the 

acquired maximum value from the male data and the minimum whole-body and bodysegment values from the minimum female data calculated from the regression 

equations.

4.5.6.6 WHOLE-BODY SURFACE AREA

Historically, whole-body surface area was calculated as a function of stature and weight. 

DuBois and DuBois (1916) devised an algorithm for determining the whole-body surface 

area and Martin et al. (1984) validated the results. The minimum and maximum wholebody surface area values pertain to the values calculated using this algorithm in 

conjunction with the CHSIR female and male stature and weight data. The minimum 

and maximum whole-body surface area values in CHSIR were captured from the female 

data and from the male data, respectively.

4.5.7 DESIGN USING INTEGRATED APPROACH

4.5.7.1 INTRODUCTION

An integrated approach examines the design across all possible physical characteristics 

using evaluation methodologies at various stages in the design process. Early in the 

design process, assessments often focus on univariate concerns (e.g., just strength, 

just ROM, or just anthropometry). As the design matures, it is beneficial to begin 

examining the design from a multivariate perspective. The individual process sections in 

this document and their methodologies are univariate but can be leveraged in unison 

once the design has matured adequately. It is this multivariate approach that is referred 

to as the integrated approach. 

It is recommended that developers use an integrated approach as soon as possible in 

the design life cycle, to understand how the primary physical characteristics and 

capabilities interact with one another. At a minimum, the integrated approach should be 

performed for PDR and CDR to ensure that the individual methodologies, when 

combined, will still accommodate the entire population. The main benefit of the 

integrated approach is an understanding of how the 3 primary aspectsanthropometry, 

strength, and ROMrelate to each other within a design, because they interrelate in the 

execution of static and dynamic tasks. Such a multivariate approach can uncover 

unanticipated problems that are not identified in early univariate assessments. Each 

aspect may have different issues, meaning that a larger segment of the population is “at 

risk” for accommodation, and this overall picture would otherwise go unnoticed. These 

accommodation and performance issues may possibly be coupled together, indicating 

that a general flaw exists in the design if the design is used by a certain segment of the 
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population. If the 3 aspects are evaluated together, overall design compliance can be 

assessed. A secondary benefit of the integrated approach is the cost benefit. Testing 

multiple aspects at once will reduce overall subject time, evaluator time, and test time 

relative to the time and costs required to assess each factor in multiple, independent 

tests.

4.5.7.2 IDENTIFY WORST-CASE SCENARIOS

The identification of worst-case scenarios uses the same methodologies outlined in the 

strength, ROM, and anthropometry sections. Similar to the individual sections, 

identification of the worst-case scenarios essentially focuses the analysis to highlight 

the segments of the population most affected by the design. For example, a larger 

individual may fit, anthropometrically speaking, in the seat and reach all the controls; 

however, a small person seated next to a larger person may have a portion of their 

ROM blocked by the bulk of the person sitting next to them. Similarly, a larger individual 

may be able to articulate a lever at their extreme range of motion, but a similarly 

positioned small person would be unable to both grasp the device fully and induce 

enough leverage to fully operate the device. Designers should consider how the 

combination of various factors can place segments of the population at risk. 

4.5.7.3 EVALUATE THE DESIGN

The integrated approach involves looking at multiple design variables simultaneously, in 

analytical analyses, CAD modeling or simulation, or HITL testing, and placing the 

results in the context of the population for each design variable of interest. This might be 

thought of as a multidimensional evaluation that examines all relevant design variables 

for all possible combinations of the population based design factors. For example, this

could involve examining the impact of the suit, posture, gravity, and group on the ability 

of a crew to perform a given task across an entire population spectrum. The integrated 

approach assists in the evaluation of apparently conflicting requirements (e.g., a need 

for application of high force combined with reduced clearancea situation where a 

larger individual may have a challenge due to clearance concerns, but the high-force 

requirement would challenge low-strength individuals). This combined approach will 

highlight design issues and challenges that may otherwise be missed after a strictly 

univariate evaluation path.
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4.6 HANDLING QUALITIES EVALUATION

4.6.1 INTRODUCTION

This section is intended to join together industry standard methods for assessment of 

vehicle handling qualities (HQ) within the framework of human-systems integration 

(HSI). The use of HSI processes in aviation is well established, as is the implementation 

of HQ assessment, though present documentation in the public domain leaves some 

ambiguity regarding a strict start-to-finish methodology for HQ assessment planning and 

execution, and integration of HQ assessment within an HSI process. The evaluation of 

handling qualities is required in accordance with NPR 8705.2B paragraph 3.4.2, which 

specifies minimal ratings on the Cooper-Harper Rating Scale during manual control of 

the spacecraft’s flight path and attitude.

Note that HQ are closely linked with other human factors concepts such as usability

and workload and that significant usability issues or excessive workload demands will 

often drive poor HQ. These topics are covered in HIDP sections 4.2 and 4.3, 

respectively. Review of all 3 processes is strongly recommended.

4.6.1.1 APPLICABLE HANDLING QUALITIES REQUIREMENTS

The evaluation of HQ is required by NASA per NPR 8705.2B paragraph 3.4.2, which 

specifies minimal ratings on the Cooper-Harper Rating Scale during manual control of 

the spacecraft’s flight path and attitude. HQ standards are also specified in the NASASTD-3001 Volume 2 section 10.1.2 Handling Qualities. These standards set minimum 

criteria for vehicle HQ as measured by the Cooper-Harper Scale.

 V2 10004 Controllability and Maneuverability

NPR 8705.2B paragraph 2.3.10.1 requires human-in-the-loop (HITL) usability 

evaluations for human-system interfaces. In addition, NPR-required technical products 

at PDR and CDR include summaries of how these evaluations were used to influence 

system design.

4.6.1.2 HISTORY OF HANDLING QUALITIES ASSESSMENT

The history of pilot evaluation and the study of aircraft HQ goes back to the very first 

flights of the Wright brothers. From then until now, the evaluation of HQ and the 

tweaking and modification of vehicle design parameters to ensure better handling has 

been an area of both active research and applied engineering solutions. 

Early assessment of HQ by pilots was highly subjective and lacked formality. Efforts to 

examine aircraft performance characteristics and pilot opinion increased from the 1930s 

through the 1960s, resulting in the development of various tools to standardize the 

assessment of HQ. These efforts culminated in the 1969 publication of the CooperHarper rating scale (NASA TND-5153) by George C. Cooper of the Ames Research 

Center and Robert P. Harper Jr. from the Cornell Aeronautical Laboratory. 

The concept of levels of HQ, as embodied by the Cooper-Harper rating scale, was 

adopted by the U.S. military (MIL-F-8785C). Though efforts have been made to create 
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new scales and derivatives of the Cooper-Harper, the original Cooper-Harper scale 

continues to be used as the industry standard for HQ assessment.

4.6.1.3 OVERVIEW OF THE COOPER-HARPER HANDLING QUALITIES SCALE

4.6.1.3.1 DEFINITION OF HANDLING QUALITIES

"Handling Qualities" are defined by Cooper and Harper in their seminal 1969 publication 

as "those qualities or characteristics of an aircraft that govern the ease and precision 

with which a pilot is able to perform the tasks required in support of an aircraft role." 

What the pilot feels (vehicle response), what the pilot sees (out the window and on

displays), and what the pilot touches (input devices) are all factors that influence and 

are related to HQ. The goal of handling-quality assessment is to categorize the 

performance of the vehicle and determine what, if any, changes may be warranted to 

improve vehicle performance. These changes may include engineering design revision, 

task simplification, control parameter tuning, and improved user interface design. 

4.6.1.3.2 COOPER-HARPER HANDLING QUALITIES SCALE

The Cooper-Harper Rating Scale is the most commonly used metric in the assessment 

of aircraft HQ. The scale associates subjective ratings of 1 through 10 on HQ to one of 

3 levels of performance through use of a decision gate chart, as shown in Figure 

4.6.1.3.2-1.

Cooper-Harper Scale Levels:

 Level 1 (ratings of 1, 2, 3): Satisfactory without improvement 

 Level 2 (ratings of 4, 5, 6): Deficiencies warrant improvement

 Level 3 (ratings of 7, 8, 9): Improvement is required

 Rating 10: Handling qualities are worse than Level 3; vehicle is uncontrollable

The Cooper-Harper decision tree begins with an assessment of the vehicle’s “Adequacy 

for Selected Tasks or Required Operation,” in which the test subject decides whether

the performance achieved in a piloting run was desired, adequate, or uncontrolled. 

These adjectives are associated with the objective or quantitative performance of the 

flight phase or specific task and are used as anchors at various locations in the scale. 

As these adjectives are involved in the core decision logic of the scale, the objective 

performance criteria associated with their definition are key drivers of the rating process. 

The phrase “desired performance” refers to the best possible objective performance 

attainable in a flight phase or in a specific flight-related task. “Adequate performance” 

is used to describe a level of success within the needs of the flight phase or specific 

task for successful completion, though better performance might have been possible 

had the vehicle handled better. The lack of desired or adequate performance suggests 

that the flight phase or task was not completed successfully or that the vehicle was 

uncontrollable.

After the initial determination of performance adequacy, the subject proceeds to the 

right of the scale into the defined categories of Level 1, 2 or 3. Next, the subject reviews 

the aircraft characteristics and the demands on the pilot, and determines the final rating.
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On a fundamental level the scale relies on the concept of pilot compensation, which is 

based on the pilot's ability to compensate for inadequacies in the vehicle design that 

result in less than ideal HQup to a point. Beyond a certain mental and physical 

threshold (based on human capability), the pilot is no longer able to compensate and 

the vehicle is rated as uncontrollable.
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FIGURE 4.6.1.3.2-1 COOPER-HARPER HANDLING QUALITIES RATING SCALE
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4.6.2 HANDLING QUALITIES DESIGN PROCESS

4.6.2.1 WHEN TO INTEGRATE HANDLING QUALITIES IN AN HSI ENGINEERING LIFE 

CYCLE

Generally speaking it is easier and more cost-effective to correct deficiencies in HQ

during the early design phases rather than just before vehicle certification. For these 

reasons, handling-quality assessments are best integrated early and often throughout 

the engineering life cycle so that design decisions related to handling qualities can be 

made from a data-driven perspective and ensure safe and effective control of the 

vehicle.

4.6.2.2 EARLY AND OFTEN

Consistent with core human-centered design philosophy, the consideration of HQ can 

be done from the very earliest stages of design, though actual evaluation of HQ does 

require a certain minimum level of design maturity. At the earliest stages of the design 

life cycle, integration of HQ should focus on activities such as these:

 defining the various operational flight phases of the vehicle (e.g., what actions 

will the vehicle be expected to perform, particularly from the standpoint of manual 

control versus automation); 

 identifying different control modes (e.g., pulse vs. continuous thrust);

 determining available pitch, yaw, and roll capabilities combined with available 

translational modes; and 

 listing potential failure modes in which manual control will be available or 

required. 

Each of the flight phases will also need to be associated with a required rating or level 

of handling quality (e.g., ratings of 1-10 or Levels 1-3). These factors will be driven by 

the vehicle’s intended mission and operational theatres. Many of these considerations 

can be defined very early during the vehicle specification stage, even pre-request for 

proposal or before procurement activity.

After flight definition, the next stage would be to start testing early aerodynamic- or 

control scheme-based prototypes by computer simulation. These simulations may 

simply be aerodynamic models of the craft with rudimentary control algorithms, and may 

benefit the program by exposing any potentially inherent aerodynamic instability that 

might drive flight-control development. This is also a good stage in which to start 

evaluating relevant early display prototypes for each flight phase, including primary flight 

displays and associated displays used for secondary piloting tasks (e.g., 

communications, navigation, or systems monitoring). 

Eventually, as vehicle design maturity increases, the simulation fidelity also increases, 

and ratings achieved through simulation become more consistent. The value of early 

and iterative evaluation of HQ is realized through direct input to design decisions related 

to both physical layout and conformation and control methodologies and algorithms. 

This also allows exposure of any flight phases in which manual control may not be 

feasible because of either system demands (e.g., required response times may be 
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below the human threshold for reaction time) or environmental constraints (e.g., gloading or vehicle vibration may make manual control impractical).

4.6.3 HANDLING QUALITIES METHODOLOGY

A key note here is that a handling-quality evaluation is an assessment of the vehicle’s 

performance related to its design and control capabilities, and not an assessment of the 

pilot’s ability. Therefore, experienced test pilots are strongly recommended as test 

subjects. Experienced test pilots have achieved a high level of proficiency in vehicle 

operation and handling, and with this experience can identify faults with the vehicle. For 

spacecraft design, the test subject pool should include test pilots or crewmembers

trained as operators who have also flown in space or rarefied atmosphere environments 

(e.g., Space Shuttle pilots and extreme-altitude reconnaissance aircraft pilots) and 

trained spacecraft pilots. 

The general methodology of conducting a Cooper-Harper-based HQ evaluation includes 

the following components, each of which is discussed in more detail in the sections to 

follow:

 Definition of flight phases, specific flight scenarios, and composite tasks to be 

tested

 Definition of adequate versus desired performance criteria for each flight 

scenario to be tested

 Selection of test conductor 

 Selection of test subject(s)

 Preparation of briefing materials

 Test execution and data collection

 Data analysis and interpretation

4.6.3.1 DEFINING PARAMETERS: FLIGHT PHASES, SUBPHASES, SCENARIOS

The first step in the assessment of HQ is definition of the vehicles’ required flight 

phases, subphases, scenarios, and crew tasks. These will be based on the design 

reference mission prescribed by NASA. The detailed identification of flight phases, 

subphases, scenarios, and crew tasks may occur as part of the development of the 

overall Concept of Operations. The Concept of Operations (ConOps) specifies crew 

activities for each mission phase and scenario and determines which subsystems are 

affected by crew activities. 

The term “flight phase” is commonly used to refer to a portion of an entire flight (i.e., 

launch to landing), and may include phases such as “launch,” “ascent,” “orbit,” 

“docking,” “entry,” and “landing.” Each of these phases is frequently divided further into 

more detailed components, referred to as “subphases.” Example subphases for a 

docking phase might include “initial approach” and “final docking.” These distinctions 

are important, as a handling-quality evaluation provides the most meaningful data when 

each subphase is rated separately, or at the even more granular level of the specific 

subphase piloting tasks. Under almost no circumstances would an entire flight be 

associated with a single rating because separate subphases (a) place different degrees 

of workload or attention on the pilot, and (b) elicit different performance characteristics 
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from the vehicle according to characteristics of the flight envelope (where flight 

envelope refers to the operational “envelope” of a vehicle based upon acceptable levels 

of variables such as airspeed, altitude, and g-loading).

The term “scenario” is often used when a subphase has multiple conditions that might 

be evaluated. For example, consider a spacecraft in an “entry” flight phase and the 

“initial deceleration” subphase in which the craft must use aerodynamic maneuvers to 

shed velocity as it reenters the atmosphere. For this example, several scenarios might 

be tested: one in which the entry profile is flown as a “ballistic” entry; another scenario in 

which it is flown as a “loads managed” return; and a final scenario referred to as “skipreturn.” Under the ballistic-entry scenario, the craft may simply be falling into the 

atmosphere at an angle preset by the pilot or autopilot (with pilot concurrence) from 

orbit. Under the loads-managed scenario, the pilot may be engaged in placing the craft 

into a rolling maneuver. The third scenario would be the “skip-return” whereby the pilot, 

after the craft initially enters the atmosphere, manages the lift vector of the craft to loft 

back out of the atmosphere for a short period, and reenter with additional roll reversals 

before a final landing. All 3 of these situations are associated with the “initial 

deceleration” subphase of an entry phase, but represent different scenarios to be 

tested.

Additionally, different initial conditions, or starting parameters, should be used for each 

test run so that the pilot does not see exactly the same starting point and conditions 

when he or she pilots a given scenario. Otherwise the lack of variability may skew the 

ratings due to a learning effect associated with repeatedly flying exactly the same 

simulation. These differing initial conditions may be as subtle as a slightly different 

coordinate starting point in the simulation, different environmental conditions (e.g., day

or night), aero properties (density, temperature, humidity), or percentage of fuel 

remaining. These differing initial conditions keep the scenarios fresh for the pilot and 

require that the pilot approach each test in a slightly different manner, but should not be 

such a significant source of variability that they present a totally different scenario to the 

pilot. These slight differences help to maintain the integrity of the ratings while also 

eliciting potential handling issues that may exist at different parameter values in the 

scenario.

4.6.3.2 DEFINING PARAMETERS: ADEQUATE VERSUS DESIRED PERFORMANCE

After scenarios have been selected for testing, it is necessary to define the minimal 

level of vehicle performance. The Cooper-Harper scale (as shown in Figure 4.6.1.3.2-1) 

is used by cognitively working through a series of 3 decision gates, any one of which 

can direct the test subject to a subset of 3 potential levels, each of which contains 3

ratings. Each rating is associated with certain aircraft characteristics as well as a set 

of demands on the pilot. Once the test subject makes a selection in the decision gates 

that directs him or her to a particular level, the subject must choose among the 3 ratings 

associated with that level. A key differentiating concept used in the demands on the pilot

component of the ratings is the subject’s objective performance in the simulation or 

flight test. The 2 adjectives associated with performance are adequate versus desired. 
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Within these words lies a subtlety of the Cooper-Harper scale. As previously mentioned, 

desired performance refers to the best possible objective performance attainable in a 

flight phase or in a specific flight-related task. Adequate performance describes a level 

of success within the needs of the flight phase or specific task for successful 

completion, though better performance might have been possible had the vehicle 

handled better. The lack of desired or adequate performance suggests that the flight 

phase or task was not completed successfully. The key is that these classes of 

performance are associated with some metric of the flight phase or task that can be 

assessed objectively, perhaps even quantitatively. 

For example, performance might be based on the percentage of fuel left when a certain 

maneuver is completed (e.g., adequate would be associated with at least 30% fuel 

remaining, whereas desired would be associated with 50% fuel remaining), or 

performance might be based on accuracy of a capsule rendezvous (a docking 

operation) with the International Space Station (e.g., no more than ± 3 cm of centerpoint for desired or within ± 9 cm for adequate, with those numbers based on the 

specifications for the docking mechanism and its design capabilities). Performance 

criteria should be established ahead of time in collaboration with subject matter experts 

such as pilots, operators, and ground control.

The importance of these terms comes most into play when the test subject is trying to 

decide between Level 1 and Level 2 ratings. Within Level 1 are 3 ratings, all of which 

include desired performance and are fairly easy to attain. Level 2, however, has 3 

ratings of which the first (Rating 4) is associated with desired performance, but note that 

it requires moderate pilot compensation, whereas ratings of 5 and 6 are associated with 

adequate performance and considerable or extensive pilot compensation. The key here 

lies in marrying the performance attained with the level of pilot compensation required to 

get there. Again, a fundamental concept of this scale is that the pilot is highly adaptable 

and can compensate for less than ideal HQ in the vehicle, but that this adaptability has 

its limits. In other words, the pilot can compensate when needed, but only so 

muchplace too many demands on the pilot and the flight phase objectives may not be 

met, or worse, an accident may occur.

Note that a test subject can attain desired performance but still provide a poor rating for 

HQ because the pilot’s required degree of compensation is the driving factor to be

considered for the rating. Even if desired performance is attained, ratings are not limited 

to the range of 1-4. Desired performance does not prohibit selection of a poor 

(numerically higher) rating, though adequate or poor performance does prohibit 

selection of a better (numerically lower) rating than the performance warrants. An 

example might include a docking maneuver for which the pilot is on the final approach 

to the docking mechanism, but is having a difficult time staying “on-center” with the 

mechanism and has to perform multiple lateral translations to correct the capsule’s 

trajectory. Even if successful docking is achieved, the pilot may give HQ a rating of 6,

given the need for extensive control inputs to perform the docking. The test conductor 

should keep track of whether the test subject achieves desired performance. The test 

conductor can advise the test subject when a rating cannot be selected because of not 

meeting performance criteria, but cannot advise on what rating to pick.
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4.6.3.3 TEST CONDUCTOR SELECTION

Critically important to the validity of the evaluations are the credentials of the test 

conductors. It is essential that the test conductors are familiar with the intricacies of the 

Cooper-Harper scale and have been mentored on proper application of a handlingquality evaluation through past assessments with experienced professionals. It is not 

enough to simply understand the scale; an effective test conductor must also 

understand testing and evaluation as an applied science, how to administer evaluations 

with human subjects, and how to brief and debrief subjects. Several federal 

organizations, including the Department of Defense, NASA, and the Federal Aviation 

Administration (FAA), can facilitate the training and mentoring of new test conductors. In 

addition, commercially available centers exist that specialize in simulations, handlingquality evaluations, and are available to conduct testing.

4.6.3.4 TEST SUBJECT SELECTION

One of the key driving factors of the evaluation is an understanding of and common 

basis of knowledge about the Cooper-Harper rating scale. Military test pilots are trained 

at Test Pilot School and have historically been considered the “gold standard” baseline 

for the rating of military flight vehicles. The justification for this is that not only do military 

test pilots have extensive classroom training on application of the Cooper-Harper scale, 

they also have been through training and may have operational experience in rating 

actual flight hardware vehicles. This level of experience, familiarity, and understanding 

far exceeds the result of any simple briefing given in a 1- to 2-hour window just before a 

simulation. For this reason, current or former military test pilots are the gold standard by 

which most if not all handling-quality evaluations are conducted. This has also been true 

in most NASA settings, where most NASA pilots are former military test pilots of either 

fixed-wing or rotary-wing aircraft. It is recommended that handling-quality assessments 

conducted in future space programs continue this tradition and use current or former 

test pilots in evaluation of their vehicles. In the circumstance where this is not possible, 

it is highly recommended that test subjects go through extensive training in use of the 

scale and are shown real-world examples of how past operational craft were rated 

under various conditions and settings to calibrate them on proper application of the 

scale. 

An additional topic related to test subject selection is the number of subjects to recruit 

for testing. Generally, a sample size of 30 or more subjects is considered an adequately 

large sample. However, recruiting of 30 test pilots is unlikely to be practical for handlingquality evaluation. On the other hand, sample populations that have less inherent 

variability can be characterized with a smaller number of samples, which is relevant to 

HQ because the preferred subjects are experienced test pilots (a population with far 

less variability in piloting skill than the larger population of general aviators). A sound 

compromise is to propose using an initial sample size of 10 to 20 pilot subjects for an 

assessment. This provides a data set of sufficient size that significant variability in the 

underlying vehicle HQ should be revealed, as should any significant consistency or 

clustering of the data. For requirement verification, NASA recommends testing with at 

least 8 crewmembers trained as operators. This sample size is acceptable because of
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the homogeneity of the subject population (highly trained crew, many with test pilot 

backgrounds). By the time verification of HQ is conducted, the crew operator population 

ought to have been regularly engaged in iterative handling-quality evaluations focused 

on systems design and manual control scenario down-selection, ensuring desired or 

adequate handling-quality performance with known and quantified flight performance 

characteristics.

4.6.3.5 PREPARATION OF BRIEFING MATERIALS

Briefing materials must be generated before the handling-quality evaluations are 

conducted. These materials should introduce the subjects to multiple topics, including

 The purpose of the evaluation

 The specific aspects of the vehicle that will be assessed

 Details of each flight phase and scenario to be tested

 The metrics to be used for determinations of desired, adequate, or failed 

performance

 A refresher on the Cooper-Harper handling-quality rating scale

The level of detail for each of the above may vary from one evaluation to the next, but 

generally all components listed should be present for any assessment. In particular, the 

desired versus adequate performance metrics are critical for the test subject to 

understand, as well as the details of what is expected of them for the assessment.

4.6.3.6 TEST EXECUTION AND DATA COLLECTION

Testing is a multi-stage process that includes a briefing session, a collection of 

familiarization runs, data runs and collection of ratings, and finally debriefing the pilot, as 

noted in Figure 4.6.3.6-1. Note that when multiple profiles are being tested, each with 

several scenarios, it is often recommended that a different test session be conducted for 

each. For example, if an organization were testing both docking and entry flight profiles, 

a test could be conducted in the morning with a briefing, familiarization period, testing, 

and debrief just for the docking profile and the various scenarios associated with it. The 

entry test session could be done that afternoon with its own specific briefing, 

familiarization, testing, and debrief. This separation of flight profiles is highly 

recommended to prevent confusion of the pilots about what is being tested and what the 

performance metrics are for each flight profile.

FIGURE 4.6.3.6-1 PRIMARY COMPONENTS OF A HANDLING-QUALITIES TESTING 

SESSION

Briefing Familiarization Testing

1) Practice Run(s)

2) Data Runs (2-3)

3) Rating and comments 

collection

Debrief

30-60 min 30-90 min 60-120 min 30-60 min
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Briefing

The briefing session may vary in length from 30 to 90 minutes, and should include both 

a refresher on the use of the Cooper-Harper scale, a presentation of the overall vehicle 

capabilities and control methods as related to the testing, and details of the planned test 

itself. For pilots who have gone through handling-quality tests recently (i.e., within the 

past few days or weeks), the Cooper-Harper refresher portion may be more streamlined 

than for pilots who have not performed an HQ assessment in several months or years. 

Familiarization

Familiarization runs are simply a set of simulation or flight passes in which the pilot is 

given time to become accustomed to the vehicle’s control schema and general handling 

characteristics, and perform several iterations of the flight profiles to be tested, but 

without the collection of any data and without rating the vehicle. This may be thought of 

as “sandbox time” for the pilot to simply become familiar with the vehicle and the tasks 

he or she is expected to perform during the test. Generally it is recommended that the 

pilot be given ample time to fly through all expected tasks and scenarios associated with 

each profile being tested. Times for this component may vary, usually ranging from 30 

to 90 minutes, depending on the number of profiles and scenarios being tested or the 

complexity of the vehicle controls. A minimum time should be planned for familiarization 

to ensure valid results.

Testing

The testing session has 3 basic components: 

 Practice run(s)

 Data runs 

 Collection of ratings and comments

The practice runs are an opportunity for the pilots to be sure they fully understand the 

profile and scenario being tested, and have their piloting methodology figured out. If 

they have spent considerable time with the familiarization runs, they may need or want 

only a single practice run. On the other hand, if multiple scenarios are being tested for 

the current flight profile, the subjects may be confused about which specific scenario 

they are piloting and want to ensure that they are flying the scenario they think they are 

flying. It may sound too conservative, but on many occasions pilots have tried jumping 

straight from familiarization time into data runs, only to make incorrect flight stick inputs 

because they were not flying the scenario they thought they were. A minimum number 

of practice runs should be planned to ensure valid results.

For data runs, the test conductor should ensure that the pilot understands which 

scenario is being tested. Often, the pilot will fly 2 runs with the ability to go ahead and 

provide their ratings and comments at the end of the second run, or proceed with a third 

data run. For these runs it is important to pay close attention to the performance criteria 

for adequate versus desired performance. Frequently the data runs may attain different 

levels of performance (e.g., run 1 is performed with desired performance, but run 2 is 

performed with adequate performance). In these cases a third data run is highly 
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recommended to determine the best performance category to assign to the collection of 

runs. The rating by the pilot should be a mental integration of all their data runs.

Once the data runs are complete, the pilot should provide the Cooper-Harper ratings 

and verbal commentary. The rating should take into consideration all of the pilot’s data 

runs, and is essentially a mental integration of those runs to provide a single rating. This 

rating is not an average of the runs, nor is it a separate rating for each run; instead it 

should rely on the pilot’s professional judgment of the vehicle’s performance across the 

2 or 3 data runs. It is extremely important to properly administer the Cooper-Harper 

scale according to its published methodology. For this, the pilot must have a visual 

representation of the scale in front of them, and they are asked to verbalize their 

thoughts as they proceed through the decision gates to the various levels, and then on 

to select a specific rating. They should be reminded of the performance attained 

(adequate versus desired), and they must resist the temptation to jump directly to a 

rating number (a tendency more prevalent in highly experienced pilots). The test 

conductor may remind the pilots that although they may have attained desired 

performance, this does not limit them to a rating of 1 to 4. However, if they attained only 

adequate performance, they are not allowed to provide a rating of 1 to 4. So desired 

performance does not prohibit selection of a poor rating, though adequate or poor 

performance does prohibit selection of a better rating than the performance warrants. 

The rating by the pilot should be a mental integration of all their data runs. This does not 

mean "average," as that would imply a measure of central tendency or blind drift to the 

median rating of the data runs. Instead, the mental integration is supposed to consider 

the significance of unexpected behaviors in the handling of a craft, even though these

behaviors may have been only a transient effect in a single run. If such a transient 

response caused a major loss of control, it could drive the overall rating more than the 

other data runs. Along with the rating, the pilot should be prompted to verbally comment 

on any noted deficiencies or things that should be improved regarding the vehicle or its 

controls, displays, or characteristics.

Debrief

After completion of testing for all scenarios in the flight profile of interest, it is important 

to regroup in a nearby office or conference room to debrief the pilot on his or her 

experience in the test. The pilots are encouraged to talk about any items of note that 

they found or experienced, and they may also be provided with a more detailed 

questionnaire or survey where they may provide additional ratings on items such as the 

physical flight displays, flight stick design, cockpit layout, software design, or any other 

component of the vehicle that they may have interacted with.

4.6.3.7 DATA ANALYSIS AND INTERPRETATION

Once testing is completed, the data must be treated as a non-parametric data set 

because of the nonlinear and categorical nature of the Cooper-Harper scale, 

compounded by the lack of any single and specific continuous latent trait that it might be 

based on. (Although cognitive or physical workload may be a reasonable underlying 

cognitive trait for pilot compensation, the dynamics of the vehicle may simply create 

poor handling characteristics, ones unrelated to workload and simply related to 
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uncontrollability, making any final selection of latent traits difficult.) Because of this, the 

simplest and often best way to examine and communicate the data is by means of

graphical methods such as histograms, box-and-whisker plots, or frequency-weighted 

scatter plots.

Examples of each graphical method are provided below, taken from the Constellation 

Program’s Orion pre-PDR Handling Qualities Evaluation led by NASA in 2008 (Figures 

4.6.3.7-1, -2, and -3). These 3 plots portray the same data set in 3 different ways (i.e., 

histogram, box-and-whisker plot, and frequency-weighted scatter plot). Illustrated are

data from a set of 2 different scenarios tested for an on-orbit attitude correction 

maneuver performed using a rotational hand controller (RHC) to reset the guidance 

system’s star-tracker after a system error. Each scenario was associated with a specific 

type of RHC control mode. The first mode was RHC Discrete Rate mode and the 

second was RHC Pulse mode. One of the goals of this particular test was to determine 

which mode would be most appropriate for piloting the craft. Each scenario tested 

included 4 tasks, resulting in a total of 8 separate ratings that needed to be 

documented. The following figures allowed the team to determine that pulse mode was 

the preferred and more controllable way to pilot the vehicle for this flight profile and 

suggested a design decision in development of the control schema for Orion.

FIGURE 4.6.3.7-1 BOX-AND-WHISKER PLOTS OF THE ORBIT SCENARIO COOPERHARPER RATINGS
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Ratings for gross acquisition (GA), maintenance (M), maintenance while rolling (MR),

and the composite (Comp) score, for both discrete rate (D) and pulse (P) cases. Median 

values are represented by the midline of each box, and the upper and lower shoulders

represent the 75th and 25th ordinal percentiles respectively. Whiskers portray data within 

1.5 x IQR (inter-quartile range) from the shoulders, with additional values greater than 

1.5 x IQR and greater than 3.0 x IQR illustrated by circles and asterisks.

Ordinal box-and-whisker plots are content-rich and allow a very detailed simultaneous 

review of data for multiple distributions. However, they may be misinterpreted by 

audiences that are less familiar with this method of data presentation. Thus, their use in 

handling-quality evaluations can be a great benefit in the analysis of findings, but is not 

advised for communicating results to a larger audience.

On the other hand, frequency scatter plots are readily communicated in a fashion that 

also allows comparison of multiple distributions simultaneously, whereas histograms are 

easily generated and understood. The only significant drawback to histograms is 

determining how to present them in such a way as to allow comparison of multiple 

distributions. Histograms are a frequently used methodology for illustrating CooperHarper ratings and their use is strongly encouraged in final presentation of results. The 

following 2 figures provide an example of each of these graphical methodologies.

FIGURE 4.6.3.7-2 FREQUENCY SCATTER PLOTS OF THE ORBIT SCENARIO COOPERHARPER RATINGS
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Ratings for gross acquisition (GA), maintenance (M), maintenance while rolling (MR),

and the composite (Comp) score, for both discrete rate (D) and pulse (P) cases. Results 

are color coded for non-pilot data, pilot data, and the combined dataset (both pilots and 

non-pilots).

FIGURE 4.6.3.7-3 HISTOGRAMS OF THE ORBIT SCENARIO COOPER-HARPER RATINGS

Ratings colored green indicate Level 1, ratings colored orange indicate Level 2, and 

ratings colored red indicate Level 3 or higher.

In circumstances where significant variability is seen in the results, likely causes that 

should be examined include the background of the test subject population (e.g., were all 

subjects military test pilots with similar backgrounds, did subjects have significant 

differences in their histories such as rotary-wing versus fixed-wing experience?), 

differences in piloting strategies, and simulation deviations. Piloting strategies can 

explain some variability in performance and ratings and should be elicited in the debrief 

for comparative assessment. Simulation deviations or off-nominal boundary conditions 

may explain variant ratings if deviations are experienced by some, but not all, of the 

subjects. Note that these are often some of the most important data points, as they may 

illustrate previously unconsidered flight conditions or scenarios on which more scrutiny 

may need to be focused. In such circumstances, additional testing may be warranted.

4.6.4 HANDLING-QUALITIES EVALUATION TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.6.4-1 are recommended for review by the NASA customer.
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TABLE 4.6.4-1 HANDLING QUALITIES EVALUATION TECHNICAL PRODUCTS

Technical Products

Phase 

A

Phase 

B

Phase 

C

Phase 

D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function allocation, 

and associated crew task lists. Includes details such 

as identification of all potential flight phases, 

subphases, related scenarios, and pilot tasks for 

which manual control is provided, as required by the 

design reference mission and as specified by 

NASA.

I U U U --- ---

Definition of control modes for each flight phase. 

Preliminary flight display concepts. I U U U U

A summary of modeling/analysis/evaluation 

performed to date and their influence on system 

design, with links to the detailed analysis results. 

Includes simulation-based HQ evaluation of each 

flight phase, based on aerodynamic models, 

preliminary control algorithms, and display 

concepts.

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10.

--- --- I U --- ---

System architecture drawings (structures, 

equipment, etc.), material specifications, interface 

requirements.

--- --- I U U ---

High-fidelity simulation-based evaluation of HQ 

based on final structural models, control algorithms, 

and final displays.

--- --- I U U

Verification plan. --- --- I U U ---

Final review of any lingering handling-quality issues 

or pilot ability concerns. --- --- --- --- I U

Hardware-based evaluation of handling qualities 

with test pilots. All flight phases should be tested. --- --- --- --- --- X

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are affected by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

Crew task list development details specific to HQ evaluations include the identification 

of all potential flight phases, subphases, related scenarios, and pilot tasks for which 

manual control is provided. By SRR, definition of flight phases and required HQ rating 
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for each phase should be defined. By SDR, control modes for each flight phase should 

be defined.

Summaries of Modeling, Analyses, and Evaluations

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-system integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how key and critical design 

decisions were assessed. According to NPR 8705.2B, updated summaries are to be 

provided at each design review through SAR. Also in paragraph 2.3.10, the use of 

human-in-the-loop evaluation is a required method to progressively demonstrate that 

the operational concept meets system requirements for operational safety, efficiency, 

and user interface design.

For HQ, a simulation-based HQ evaluation of each flight phase, based on aerodynamic 

models, preliminary control algorithms, and display concepts, should be performed by 

PDR. By CDR, a high-fidelity simulation-based evaluation of HQ, based on final 

structural models, control algorithms, and final displays, should be performed. 

Hardware-based evaluations of HQ with test pilots, testing all flight phases, should 

occur no later than SRR.

Architecture, Materials, and Interface Specifications

Drawings, materials, and interface specifications provide NASA with insight into humansystem integration technical details throughout the design process. For HQ, this 

includes providing preliminary flight display concepts at SDR.

Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 

4.6.5 CONCLUSION

The procedures and processes listed here are based on the publications of Cooper and 

Harper, including their seminal 1969 paper on HQ, the numerous follow-up publications 

they have released, military standards, common industry practice, the mentorship of 

experienced handling-quality experts from both the Ames and Langley Research 

Centers, and the testimony of numerous military test pilots and test pilot instructors who 

were also Space Shuttle pilots and commanders. These sources tie together the use of 

the Cooper-Harper scale in the assessment of HQ as it pertains to not only aviation but 

also the assessment of spacecraft. With the burgeoning development of multiple 

commercial spacecraft, the relevance of HQ has only increased in recent years and is 

set to continue increasing in the near future. The methodology discussed here is meant

to provide a sound foundation to facilitate spacecraft development by these companies 

as well as NASA and its contractors. Building on this foundation should ensure that 

future craft are safe, reliable, and controllable under all anticipated flight conditions.
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4.6.6 REFERENCES

Cooper, G. E., & Harper, R. P., Jr. (1969). The use of pilot rating in the evaluation of 

aircraft HQ (NASA-TN-D-5153). Washington, DC: National Aeronautics and Space 

Administration. 

Hart, S. G., & Staveland, L. E. (1988). Development of NASA-TLX (Task Load Index): 

Results of empirical and theoretical research. In P. A. Hancock & N. Meshkati (Eds.), 

Human mental workload (pp. 139-183). Amsterdam: North Holland. 

International Organization for Standardization. (1998). Ergonomic requirements for 

office work with visual display terminals (VDTs). Part 11: Guidance on usability

(ISO/IEC 9241-11). Geneva (Switzerland): ISO.

U.S. Military Specification: Flying qualities of piloted airplanes (MIL-F-8785C). (1980, 

November 5). 
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4.7 ACOUSTIC NOISE CONTROL PLAN DEVELOPMENT

4.7.1 INTRODUCTION

Spacecraft acoustics are a critical design consideration from the standpoint of crew 

safety, health, and mission performance. The first and foremost concern is the risk of 

temporary and permanent hearing damage caused by exposure to high noise levels 

over a relatively long duration. Also, the crew must be able to communicate among 

themselves, hear and respond to communication from the ground, and be altered by 

alarms. Finally, acoustics play a critical role in the crew’s health and stress level. Loud, 

annoying, or intermittent noise can be disruptive of restful sleep and can stimulate the 

human “fight or flight” reflex, which can contribute to the overall anxiety level of the 

crew. For further discussion of the effects of noise on human performance, see 

NASA/SP-2010-3407 Human Integration Design Handbook (HIDH) section 6.6.2 

Human Response to Noise.

The acoustic environment of a spacecraft is a critical design consideration and must be 

addressed from the outset of the design process. This extreme environment is 

discussed further in HIDH section 6.6.1 The Acoustic Environment of Spacecraft. 

Incorporating acoustic design concepts for noise control into the early stages of 

hardware development will reduce or eliminate costly re-work, design changes, 

mitigations, and associated schedule slippage, as well as potential operational 

constraints. A human-centered approach to spacecraft design is essential for achieving 

required acoustic conditions needed to ensure the safety of the crew with respect to 

acoustics and thereby attain human rating of the spacecraft.

4.7.2 APPLICABLE ACOUSTIC REQUIREMENTS

Acoustic requirements are specified in NASA-STD-3001 Volume 2, section 6.6. Mission 

phases covered by this document include launch, abort, orbit, entry, and post landing. 

ISS docked operations are covered in a separate family of SSP documents. Although 

acoustic requirements for ISS are similar to some of the NASA-STD-3001 Vol. 2

requirements, discussion of ISS-specific requirements is beyond the scope of this 

document.

The first acoustic requirement of NASA-STD-3001 Vol. 2 is the establishment of an 

Acoustic Noise Control Plan (V2 6071), which specifies documenting the plan for 

achieving spacecraft acoustic requirements. 

The following are the acoustic requirements for launch, entry, and abort phases: 

 V2 6073 Launch, Entry, and Abort Noise Exposure Limits

 V2 6074 Hazardous Noise Levels for Launch and Entry

 V2 6075 Hazardous Noise Levels for Launch Abort

 V2 6076 Launch, Entry, and Abort Impulsive Noise Limits

 V2 6085 Infrasonic Sound Pressure Limits

The following are the acoustic requirements for orbit and post-landing phases:
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 V2 6077 Hazardous Noise Limits for All Phases Except Launch, Entry, and Abort

 V2 6078 Continuous Noise Limits 

 V2 6079 Crew Sleep Continuous Limits

 V2 6080 Intermittent Noise Limits

 V2 6084 Narrow-Band Noise Limits

 V2 6082 Impulse Annoyance Limit

 V2 6083 Impulse Noise Limit

 V2 6086 Ultrasonic Noise Limits

Additionally, V2 6072 establishes the requirement for Acoustic Requirement 

Verifications, and V2 6087 & V2 6088 require mission acoustic monitoring and individual 

crew exposure monitoring, respectively.

Additionally, HIDH section 6.6.3 Human Exposure and Acoustic Environment Limits 

provides guidelines for the limits that ensure that a spacecraft provides the crew with an 

acoustic environment that will not cause injury or hearing loss, interfere with voice 

communications, cause fatigue, or degrade overall human-machine system 

effectiveness.

4.7.3 ACOUSTIC NOISE CONTROL DESIGN PROCESS

NASA-STD-3001, Vol. 2 requirement V2 6071 establishes the requirement for an 

Acoustic Noise Control Plan (ANCP). The ANCP is a document that contains an 

acknowledgment of the applicable acoustic requirements, identification of the noiseproducing systems and components, a development plan for meeting the acoustic 

requirements (e.g., criteria for planned hardware selection, efforts that will be used for 

acoustic mitigation), and a summary of the project’s acoustic requirement verification 

plan. The ANCP is a “forward-looking” plan and serves as a guide for addressing 

development of acoustic noise control. In the later stages of development, the ANCP 

becomes comprehensive documentation of the rationale behind design decisions 

affecting the acoustic environment of the vehicle. It also serves as a summary of the 

requirement verification testing and analyses performed. The ANCP is to be updated as 

subsystem designs are developed, subsystem components are selected, and analysis 

and test data are applied to improve the accuracy of the initial acoustic projections. 

Identified challenges to meeting acoustic requirements should also be documented in 

the ANCP. The ANCP is to be provided to NASA at each design review (i.e., program 

milestone) and will be assessed for progress toward meeting acoustic requirements. 

The following paragraphs highlight design steps that should be followed and 

documented in the ANCP.

4.7.3.1 DEVELOP CREW TASK LIST

Crew task lists are necessary for identifying crew locations and positions with respect to 

noise sources, potential combinations of hardware that may be operated concurrently 

(for evaluation of intermittent acoustic noise emission requirements), and configurations 

of the crew (suited, unsuited, helmeted, visor up, visor down). All of these factors are 

important for evaluating the acoustic noise emission scenarios to compare them with 

the acoustic requirements. Vehicle design for acoustic noise control should begin with 
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development of the concept of operations and scenarios for nominal, off-nominal, and 

emergency operations. For each mission phase and relevant scenario, crew roles and 

activities should be specified for the purpose of developing crew task lists and 

procedures. Off-nominal situations, such as abort scenarios, must also be considered, 

and the applicable acoustic requirement applied. See HIDP sections 3.2.3.1.2 and 4.1 

for discussion of developing concept of operations and crew task lists. 

The following general mission phases and crew configurations should be separately 

considered and compared to the applicable acoustic requirements (note that this list is 

not exhaustive and should not be considered as such):

 Launch

At launch the dominant noise sources will be the vehicle engines and the air 

interaction between the vehicle and the atmosphere, and the dominant acoustic 

path will be the vehicle structure. Vibro-acoustic analysis and testing will be 

necessary to assess the inputs to the vehicle and the resulting acoustic 

environment experienced at the crewmember’s ear. The noise reduction of the 

communications gear, spacesuit, and helmet must also be considered during this 

mission phase. Insertion loss is the decrease in sound pressure level, measured 

at the location of the receiver, when a sound insulator or a sound attenuator is 

inserted in the transmission path between the source and the receiver.

 Pad Abort and Launch Abort

In the event of either a pad or launch abort situation, the dominant noise sources 

will be the abort engines and atmosphere interaction with the vehicle. As with 

launch, vibro-acoustic analysis and testing will be necessary to assess the inputs 

to the vehicle and the resulting acoustic environment experienced at the 

crewmember’s ear. The noise reduction of the communications gear, spacesuit, 

and helmet must also be considered during this mission phase.

 On-orbit Operations

The dominant noise sources during the free-flight mission phase will need to be 

assessed according to the specified vehicle and crew configurations. Generally 

during this mission phase, the dominant noise sources will be inside the 

pressurized volume of the vehicle, including vehicle and/or spacesuit 

Environmental Control and Life Support (ECLS) systems. Acoustic transmission 

paths will be a combination of structure-born and airborne paths. Particular 

consideration must be paid to the crew configuration. It must be specified 

whether the crew is seated or free to move inside the pressurized volume, suited 

with visors down inside pressurized suits, suited with visors up and suit 

unpressurized, or unsuited. The differing noise sources and acoustic 

transmission paths for each configuration must be considered and compared to 

the applicable acoustic requirements.

 Docked Operations

If the visiting-vehicle will be docking to the ISS, the visiting-vehicle requirements 

will apply and must be considered. A complete discussion of this mission phase 
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is beyond the scope of this document. Refer to SSP 50808 for more information 

about ISS commercial visiting vehicle docked requirements.

 Undocking, Deorbit, Reentry, Landing, and Post Landing

As with launch and on-orbit operations, the configuration of the crew during 

different phases of post-docked operations must be considered. Applicable noise 

sources may include deorbit engines, aerodynamic interaction between the 

vehicle and the atmosphere, and vehicle and/or spacesuit ECLS systems. 

Acoustic transmission paths will include both structural and airborne paths. 

Different noise sources and acoustic paths may be dominant at different points of 

the mission and must be considered and compared to the applicable acoustic 

requirements. Note that acoustic requirements are applicable until the crew is 

recovered from the vehicle.

4.7.3.2 DEVELOP DESIGN SOLUTIONS

4.7.3.2.1 ACOUSTIC MODELING

The major noise-generating systems and components should be included in an 

integrated acoustic model for an accurate representation of individual sources and 

propagation paths, as well as reverberation effects. In recent years, computerized 

acoustic modeling techniques have improved, especially with respect to modeling 

complex geometries. The ANCP is to include a description of the selected acoustic 

modeling approach, noting the engineering assumptions made in the construction of the 

acoustic model. Different modeling strategies may be needed to address the separate 

acoustic requirements or frequency ranges. Finite Element Analysis (FEA) and 

Boundary Element Analysis (BEA) approaches are acceptable modeling techniques for 

low-frequency noise prediction; however, these methods can become complex and 

computationally intensive as the frequencies of interest increase. Statistical Energy 

Analysis (SEA) has been shown to be an effective and accurate analysis approach for 

mid-frequency and high-frequency predictions; however, the accuracy of SEA estimates 

may decrease in the low frequencies, where the fundamental assumptions of this 

method may not be applicable. It is expected that a hybrid acoustic modeling approach 

utilizing 2 or 3 of the noted acoustic modeling techniques will need to be applied to

bridge gaps and address the entire frequency range. A single commercial acoustic 

modeling software package that combines these 3 modeling techniques may be used, 

or separate acoustic modeling packages may be selected and combined into a coherent 

overall model result. As component, system, and vehicle designs are developed and 

modeling analyses are performed, results and design decisions are to be documented 

in the ANCP. Any acoustic issues or areas of concern and the forward plans for 

addressing, mitigating, and resolving these issues and concerns are to be documented 

for each design review. Although modeling is used to make predictions, data from 

component acoustic testing, flight testing, and ground test articles are to be used as 

inputs to the models and incorporated as early in the process as possible to verify 

assumptions and improve the accuracy of the acoustic model. Empirical and analytical 

models and techniques can also be very useful and are often necessary. These can be 
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used along with acoustic modeling or alone if needed. An example is the use of 

empirical data for first estimates of launch rocket noise.

4.7.3.2.2 NOISE SOURCE ALLOCATIONS

Acoustic allocations for each major noise source and each mission phase are to be 

identified and documented in the ANCP. The significant noise sources (e.g., engines, 

ECLS components, payload, boundary layer noise) either within or penetrating the crew 

pressurized volume should be identified and broken down into component noise 

allocations. Each noise source should then be allocated with an allowable acoustic 

emission level based on the appropriate requirement using acoustic analysis. For 

example, launch noise can be divided into (1) external noise environment, (2) interior 

vehicle noise (taking into account the attenuation provided by the vehicle), and (3) noise 

inside the spacesuit (again taking into account the attenuation provided by the 

spacesuit). This is an iterative process with the accuracy of the assessment improving 

as the design matures, major components are tested, and acoustic mitigation efforts are 

developed and implemented. The ANCP is to be updated as the design matures and 

should include summaries of how modeling and analyses influenced system design.

4.7.3.2.3 NOISE SOURCE SELECTION

Using the acoustic requirement allocations, a test-based strategy should be used to 

select or design noise-producing hardware (e.g., pumps, fans, and actuators) that have 

the lowest acoustic levels and meet the functional requirements. Allocations should be 

expressed in Sound Power Level (as opposed to sound pressure level) for the highest 

accuracy. Sound power levels indicate the total propagating acoustic energy created by 

the source, and do not depend on source directivity or the distance from the noise 

source (as with sound pressure levels). Preliminary acoustic testing results should also 

be used as model inputs to make early estimates of the integrated hardware acoustic 

noise levels. These results should be compared to the acoustic allocations and the 

overall acoustic requirements to verify that the vehicle will be able to meet the acoustic 

requirements and to identify where acoustic mitigation efforts will need to be developed.

4.7.3.2.4 DESIGN ITERATION OF NOISE SOURCES

Trade studies should be conducted to balance the functional requirements with a 

component’s acoustic emissions. Selection of components that have capabilities in 

excess of functional requirements or extra engineering margin should not come at the 

expense of elevated acoustic emissions that put the overall acoustic requirements at 

risk. The results of these trade studies and the resulting design decisions are to be 

documented in the ANCP. Operating fans and pumps at reduced speeds is effective at 

lowering noise levels while maintaining performance margin for contingencies.

Consider an example trade study for a fan, which is a typical spacecraft noise source. 

Generally, higher fan speeds lead to higher acoustics emissions. Therefore, one should 

design or select fans that operate most efficiently at the speed necessary to meet the 

flow and pressure requirements for its role. This is an iterative process in which 

tradeoffs between performance and acoustics are made between many noise-producing 

systems. One important consideration when selecting and designing “prime mover” fans 
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is to include an estimate of pressure loss from inline mufflers (as necessary). See 

4.7.3.2.7 on component-level noise controls.

4.7.3.2.5 FURTHER NOISE SOURCE REDUCTION

Once components are optimized for required performance and acoustics, the remaining 

noise sources must be addressed individually for noise source reduction measures. 

Applying the previous example of a fan, once the fan speed is selected based on the 

functional requirements, it may be necessary to look at noise source treatments such as 

optimized balancing of the fan or vibration isolation to reduce the noise source 

emissions of the unit to acceptable limits. If noise source treatments cannot be applied, 

this fact should be documented in the ANCP along with the rationale. 

One of the most important design activities for reduction of noise sources is early testing 

of noise sources and measurements of radiated noise levels at realistic installed 

conditions. For example, a flow restrictor may be used to impose the right pressure loss 

for measuring fan noise. The measured sound power levels for early testing of noise 

source data should be input into the acoustic model to update the accuracy of the model 

predictions. Early testing will give an early indication of possible problems; this is 

extremely important. These updates should be noted and documented in the ANCP.

4.7.3.2.6 DESIGN OF SYSTEM-LEVEL NOISE TREATMENTS

Meeting the acoustic requirements is not just the responsibility of the noise-making 

system, but is an integrated vehicle design endeavor. To incorporate more broadly 

applied noise controls, system-level treatments such as barriers, gap-sealing elements, 

and absorbers, as part of the hardware or inside the crew pressurized volume (for 

vehicles), may be applied and incorporated in the acoustic model. The needed insertion 

loss of system-level noise treatments are to be documented in the ANCP as well as

model results showing the acoustic impacts of proposed mitigation efforts. 

An example is the case of a fan that has a sound pressure level of 60 dB in the 250-Hz 

octave band. To meet the acoustic requirement allocation, assume that the required 

acoustic emissions for the fan in the 250 Hz octave band must not exceed 50 dB. In this 

simple example, the “needed insertion loss” would be 10 dB in the 250 Hz octave band 

in order to meet the requirement. Assume further that a muffler is designed for the fan, 

and when the fan and muffler are tested together, the insertion loss in the 250-Hz 

octave band is only 7 dB. This would result in an exceedance to the acoustic 

requirement allocation of 3 dB, and the exceedance could roll up to the overall vehicle 

acoustic requirement. In this case, a possible solution could be application of absorption 

treatments inside the cabin to reduce the reverberation and resulting noise levels by 3 

dB. 

Note that this iterative analysis process is necessary over the entire frequency range of 

the acoustic requirements and all the associated operating conditions for each of the 

defined mission phases. The use of an acoustic model will greatly simplify the analysis 

process, assist in the identification of acoustic challenges, and allow the virtual 

evaluation of potential acoustic mitigation efforts to be performed quickly and efficiently.
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4.7.3.2.7 DESIGN OF COMPONENT-LEVEL (END-ITEM) NOISE TREATMENTS

Once the noise source levels have been measured and the system-level noise 

treatments are designed (at least preliminarily), the noise-reduction requirements for 

component-level treatments can be determined to meet the noise source’s allocation. 

Designs for component-level reductions may include such items as component mufflers 

and acoustic covers. Also, tradeoffs between the component-level noise treatments and 

system-level noise treatments can be addressed when the projected component-level 

reductions are predicted and applied to the global model to predict system-level 

compliance with acoustic requirements. The predicted results of these component-level 

noise treatments are to be documented in the ANCP.

Also note that consideration of structure-born noise is very important and the use of 

vibration isolation as component noise control can be very effective at reducing this 

effect. Broader control of structure-born noise or identification of structural resonance 

may need to be approached as system-level noise control efforts.

4.7.3.3 TEST AND EVALUATION

Iterative tests and evaluations should be performed to assess the acoustic emission 

characteristics of the hardware selected for use in the vehicle. The results of the initial 

component-level noise and treatment testing are applied as inputs to the acoustic model 

to assess progress in meeting the acoustic requirements. Additionally, data from 

spacecraft external noise sources are applied, as needed. As the system design 

matures, the ANCP is to be updated and include summaries of how tests and 

evaluations influenced design decisions.

4.7.3.3.1 TESTING OF COMPONENT-LEVEL NOISE TREATMENTS

Component-level treatments are to be mocked up, fabricated, and tested so that their 

performance is known. Integrated treatments are tested at component level to be used 

as inputs to the acoustic model. Examples of methods to use include 1) insertion-loss 

measurements for mufflers and silencers (or components that act as such), and 2) 

impedance tube absorption and transmission-loss measurements for acoustic materials 

and layups. Actual measured results of component-level noise treatment performance 

are to be documented in the ANCP.

4.7.3.3.2 TESTING OF SPACECRAFT EXTERNAL ENVIRONMENTS

Test data from spacecraft external noise sources (e.g., engines, aerodynamic boundary 

layer noise) are to be applied as inputs to acoustic modeling. External noise sources 

should be characterized through all mission phases including launch, abort, and 

descent, and testing must be used as the basis for estimates. For this, static rocket 

firings, wind- tunnel tests, and flight tests are to be used. Data are to be included from 

pad abort testing, launch abort testing, and unmanned flight testing, and these data are

essential for the human rating of the space vehicle.
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4.7.3.3.3 VERIFICATION TEST PLAN

The ANCP is to include, or point to, a complete acoustic verification plan and schedule 

with pass/fail criteria for component verification testing (sound power, acoustic 

emissions testing), static system verification testing (ground test article test plan), and 

development flight testing (pad abort tests, aerial abort tests, unmanned flight tests). 

Validation of pressure shell, blast protective cover, and spacesuit attenuation of launch 

and abort acoustic loading must be performed through testing at expected noise levels. 

Acoustic verification is to include modeling analysis of the interior noise environment 

and flight-test data before the first manned test flight. The ANCP is to include all 

verification results.

4.7.4 ACOUSTIC NOISE CONTROL DESIGN TECHNICAL PRODUCTS

An updated version of the ANCP is to be provided at each program milestone for 

review. It is important to emphasize that the ANCP is a “living document” that will evolve 

over the project design life to reflect the current project strategy at each review phase. 

The ANCP will both document the overall process and update NASA on the course and 

expected results of future development. Recommended activities and products for each 

program milestone review are outlined in the following paragraphs. A summary table of 

technical products is provided in Table 4.7.4-1.

TABLE 4.7.4-1 ACOUSTIC NOISE CONTROL DESIGN TECHNICAL PRODUCTS

Technical Products

Phase 

A

Phase B Phase C Phase 

D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function allocation, 

and associated crew task lists. I U U U --- ---

Acoustic model. --- I U U --- ---

An Acoustic Noise Control Plan (ANCP) that 

includes statement of applicable acoustic 

requirements, identification of noise sources, 

external environment definition, modeling analyses, 

component acoustic testing results, external 

environment test results, verification plan, 

verification results, and any remedial actions 

needed to address requirement non-conformance).

--- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are influenced by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of the sequence of crew activities, and 
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identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

Preliminary Design Review (PDR)

The initial ANCP is to be prepared for PDR and provided to NASA for review. It is to 

contain restatement of the applicable acoustic requirements, identification of the major 

noise-producing systems (e.g., ECLS, Payload), and an initial allocation of the acoustic 

requirements to appropriate systems. 

To understand the proposed system architecture, an acoustic model of the pressurized 

volume is to be prepared and the model assumptions, inputs, findings, and projections

documented in the ANCP. Modeling analyses should demonstrate the progress of the 

system design toward meeting acoustic allocations for all mission phases. Areas of 

concern are to be identified and documented in the ANCP with forward plans for 

addressing the issues. Plans for acoustic testing of component noise sources (such as 

fans, blowers, and pumps) and selection criteria for flight hardware are to be included in 

the ANCP. 

Preliminary design and effects of system-level noise treatments are to be documented. 

Components are to be specified along with sound power level allocations that meet the 

overall acoustic requirements previously specified. The acoustic model is to be updated 

to reflect the component-level acoustic contributions to the applicable systems and the 

overall acoustic environment. An initial definition of the spacecraft external 

environments for launch, descent, and abort is to be presented, and inputs are to be 

included in the acoustic model. The acoustic model is to be updated to reflect the 

results of any completed component tests before the PDR, and the results are to be 

documented in the ANCP. Necessary component noise controls and their expected 

contributions are also to be accounted for in the model and documented in the ANCP.

The initial acoustic verification plan is to be prepared for the PDR. The acoustic 

verification plan is to include a schedule and pass/fail criteria for component verification 

testing (sound power, acoustic emissions testing), static system verification testing 

(ground test article test plan), and development flight testing (pad abort tests, aerial 

abort tests, unmanned flight tests). 

NASA will review the updated ANCP and upon successful completion of the PDR, will 

give authorization to proceed into implementation and final design.

Critical design review (CDR)

At the CDR stage, the ANCP is updated to reflect the results of already completed 

component qualification testing, and a comprehensive plan and schedule for incomplete 

qualification testing are to be presented. Component-level noise treatment design 

requirements are to be specified. The acoustic model is updated to reflect the results of 

the completed component acoustic qualification testing. In addition, the ANCP is 

updated to reflect the results of ground and flight testing completed to date and the 

spacecraft exterior launch, descent, and abort environments. Risks to the overall 

acoustic requirements identified by the acoustic model are to be highlighted in the 

ANCP as well as a comprehensive forward plan for mitigation. 
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The acoustic requirement verification plan is to be updated with the results of completed 

tests and analyses, and the schedule for remaining tests is to be identified. Flight test 

objectives for acoustic requirement verification are to be defined clearly, and a forward 

plan for acquisitions activities is to be presented.

NASA will review the updated ANCP, and upon successful completion of the CDR, will 

give authorization to proceed with system qualification testing and integration activities.

Test Readiness Review (TRR)

A TRR is to be conducted before each verification test involving acoustics design

requirements. An updated ANCP is not a necessary input for the TRR; however, a 

formal acoustic test plan is to be submitted for review at least 1 month before the 

scheduled TRR. The acoustic test plan is to include a summary of the applicable 

acoustic requirements that the test is intended to verify, a list of measurement locations 

with instrumentation details (transducer type and traceable calibration record, 

placement of transducer, data acquisition parameters), intended post-processing 

analysis planned for the measurement data, and expected results relating to the 

acoustic requirements. 

The acoustic test plan is to be reviewed by NASA and inputs submitted to the flight 

article team. Upon successful completion of the TRR, approval will be given to conduct 

the test. After the test is completed, a test report is to be provided. Updates should be 

made to the ANCP with the findings of the test and a forward plan to address any 

acoustic requirement exceedances identified in the test results.

System Acceptance Review (SAR)

A SAR is to be conducted upon the successful completion of all acoustic verification 

testing, submittal of the respective test reports, and the ANCP updated to reflect the 

results of all testing. Verification documentation will be reviewed for requirement 

closure. Therefore, it is not necessary to include all verification documentation in its 

entirety. It is expected that a synopsis statement for each verification test conducted, as 

well as a cross-reference to the test documentation, will be included in the ANCP. All 

acoustic requirements are to be met or their nonconformances documented and 

approved by NASA.

Upon successful completion of the SAR, acoustic flight certification of the vehicle will be 

granted for crewed space flight.
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4.8 RADIATION SHIELDING DESIGN

4.8.1 INTRODUCTION

Radiation shielding is an important aspect of vehicle design that is incorporated during 

the various design phases of a spacecraft. Radiation shielding is designed to protect the 

crew from radiation exposure so that effective dose (tissue averaged) is consistent with 

the “as low as reasonably achievable” (ALARA) principle, as specified in NASA-STD3001 Volume 2 section 6.8.1 Ionizing Radiation. 

The following process is intended to guide the spacecraft developer by describing the 

NASA radiation shielding design process to facilitate successful design verifications and 

support achievement of spacecraft human rating.

4.8.1.1 BACKGROUND

Radiation sources in space consist of galactic cosmic rays (GCR), trapped radiation, 

and solar particle events (SPEs). Limits for both short-term and career exposure are 

established on the basis of assessments of projection models and a reasonable “worstcase” space environment to be encountered on specific missions. Although specific 

exposure limits are identified according to mortality risk, all decisions concerning 

vehicle, habitat, and mission design are made such that resulting crew radiation 

exposures are ALARA. Additional information about ionizing and non-ionizing radiation 

can be found in the NASA/SP-2010-3407 Human Integration Design Handbook (HIDH) 

sections 6.8 and 6.9, respectively.

Crewmembers’ mission risk of radiation exposure varies with age and gender of the 

astronaut, and the variation of solar activity during the approximately 11-year solar 

cycle. The likelihood of SPEs is higher near solar maximum and the GCR doses are 

higher at solar minimum. Shielding against radiation can substantially reduce SPE 

doses and provide modest protection from GCR. Career exposure to radiation is limited 

to not exceed 3% risk of exposure-induced death (REID) for fatal cancer. NASA 

ensures that this risk limit is not exceeded at a 95% confidence level by using a 

statistical assessment of the uncertainties in the risk projection calculations to limit the 

cumulative effective dose received by an astronaut throughout his or her career. Refer 

to NASA-STD-3001 Volume 1 for more information on dose limits, and HIDH section 

6.8.3 Physiological Effects of Ionizing Radiation Exposure for information on the 

physiological effects of radiation exposure.

The ALARA principle is both a legal and a recognized NASA requirement intended to 

ensure astronaut safety. An important function of ALARA is to ensure that astronauts do 

not approach radiation limits and that such limits are not considered “tolerance values.” 

Mission programs resulting in radiation exposures to astronauts are required to find 

cost-effective approaches to implement ALARA. At the present time, acute risks are a 

concern with SPEs; therefore, protection against these events must be incorporated into 

the vehicle design. The impracticalities involved in shielding for the higher GCR 

energies, as well as the large uncertainties in GCR risk projections, must be considered 

in exposure projections and mitigation. Risk uncertainties for SPEs are smaller than for 
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GCR; therefore, application of the ALARA principle through shielding design and related 

mass distributions is more practical.

4.8.1.2 RADIATION SHIELDING DESIGN APPLICABLE REQUIREMENTS

NASA-STD-3001 Volume 2 requirement [V2 6097] Design Approach specifies that the 

vehicle shall be designed using the ALARA principle to limit crew radiation exposure. A 

mitigation plan to protect crewmembers in the event that shielding is inadequate should 

also be provided.

4.8.2 RADIATION SHIELDING DESIGN PROCESS

4.8.2.1 DEVELOP CONCEPT OF OPERATIONS AND CREW TASK LIST

Vehicle design for radiation shielding should begin with development of the concept of 

operations and scenarios for nominal, off-nominal, and emergency operations. For each 

mission phase and relevant scenario, crew roles and activities need to be specified and 

crew task lists developed. Crew task lists are necessary for identifying crew locations 

and positions with respect to radiation sources and/or varying levels of shielding within 

the vehicle. See HIDP sections 3.2.3.1.2 and 4.1 for discussion of developing concept 

of operations and crew task lists.

4.8.2.2 DEVELOP DESIGN SOLUTIONS

Methods of protection from radiation exposure include development of effective 

shielding materials, provision for radiation safe haven, solar proton event warning 

systems, scheduling of missions and tasks to reduce exposure, and development of 

dietary or pharmaceutical countermeasures (e.g., chemopreventives and 

radioprotectants). For more information see HIDH section 6.8.5 Protection from Ionizing 

Radiation.

Achievement of ALARA is an iterative process of integrating radiation protection into the 

design process and ensuring optimization of the design to afford the most protection 

possible, within other constraints of the vehicle systems. The protection from radiation 

exposure is ALARA when the expenditure of further resources would be resource 

prohibitive relative to the reduction in exposure that would be achieved. Radiation 

protection for humans in space differs from that on Earth because of the distinct types of 

radiation, the small population of workers, and the remote location of astronauts during 

space flight. The National Council on Radiation Protection and Measurements (NCRP) 

has set a limit for crew exposure in Low-Earth Orbit (LEO) as defined in NCRP Report 

No. 132, Radiation Protection Guidance for Activities in Low-Earth Orbit. The definition 

of the worker population (i.e., NASA astronaut population) is incorporated into the 

design limit. The radiation sources in spaceGCR, trapped particles, and SPEs have 

physically and biologically damaging properties different from those of terrestrial 

radiation, and the spectrum and energy of concern for humans differ from those for 

electronics. Radiation protection for the crew must consider this environment and these 

concerns. Nominal mission exposure will be covered by the legal limit as established in 

NCRP Report No. 132.
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4.8.2.3 DESIGN EVALUATION AND VALIDATION

Design evaluations will be a collaborative effort between the spacecraft developer and 

NASA. Throughout the iterative process of vehicle design, evaluation of the vehicle 

radiation shielding is to be performed by the developer using standard analysis tools 

and an integrated set of models. These models will be initially provided by NASA or the 

developer at SRR. Those models provided by the developer should be approved by 

NASA before use. The integrated set of models used to perform analysis of the vehicle 

design includes components such as design environment, biological components, 

transport code, and vehicle geometry. These models should be specified in programlevel requirements, as in Commercial Human-Systems Integration Requirements 

(CHSIR) CH6054V, for example. 

As materials are selected, design solutions are implemented, and vehicle system 

configuration layouts are determined, models are updated for iterative analyses. All 

elements of the radiation shielding analyses, to include input data and calculations, are 

to be provided to NASA to confirm the developer’s findings. Input data includes CAD 

models, mass distributions, and material compositions. NASA insight into 

developmental analyses can be beneficial for checking assumptions and assessing 

progress toward meeting adequate radiation shielding. 

To validate that the ALARA principle has been met, monitoring with passive radiation 

area monitors is included during vehicle flight tests and crewed missions. Although the 

major phases of the vehicle design have been completed before the flight tests, the data 

obtained from these monitors are used to validate the shielding provided, verify model 

results, and identify areas that have a relatively high exposure rate (e.g., avoidance 

areas) by providing a spatial distribution of radiation exposure within the spacecraft. 

Spacecraft design must accommodate passive radiation monitoring, which continues 

during the operational flight phase of the vehicle. Levels of exposure rate will continue 

to vary with solar activity and vehicle stowage configuration changes, and must be 

continuously monitored and assessed. Continual monitoring and assessment, using real 

time or near-real-time data, are important for enabling crew health and should be part of 

a mission plan.

The spacecraft developer provides locations for no fewer than 6 radiation area monitors 

to be mounted within the vehicle. NASA provides the dosimeters and uses the results of 

radiation exposure analyses provided by the developer to help determine the ideal 

quantity and best locations for the monitors within the vehicle. The developer verifies 

that the attachment method for the passive radiation monitors is sufficient to withstand 

anticipated loads to the vehicle structure during all mission phases, including launch 

and landing. The concept of operations document includes the installation of radiation 

area monitors inside the vehicle just before launch. The ground operations Interface 

Requirement Document (IRD) contains requirements for installation and recovery of 

dosimeters immediately before and after a mission, respectively. NASA supports postlanding collection and analysis of samples. . The data obtained from these passive 

radiation area monitors will be used to evaluate total mission ioniziong radiation 

exposure from the various locations within the vehicle. It may also be used as part of 
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the individual crewmember exposure results, if the individual crewmember worn passive 

dosimeter becomes lost or misplaced.

4.8.3 RADIATION SHIELDING DESIGN TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.8.3-1 are suggested for review by the NASA customer.
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TABLE 4.8.3-1 RADIATION SHIELDING DESIGN TECHNICAL PRODUCTS

Technical Products

Phase

A

Phase 

B

Phase 

C

Phase

D

SRR SDR PDR CDR SAR ORR/F

RR

A description of the ConOps, function allocation, 

and associated crew task lists. I U U U U ---

Integrated set of models used to perform analysis of 

vehicle design with radiation shielding. 

I U U U --- ---

Radiation instrument specifications and drawings. I U U U U ---

Verification approach and plans for radiation 

shielding and area monitoring. I U U U U ---

System architecture drawings (structures, 

equipment, etc.), material specifications, interface 

requirements.

--- I U U U ---

Specifications for vehicle construction w/ shielding. --- I U U U ---

Radiation shielding tests and analyses. --- I U U U --

IRDs for vehicle and portable equipment and cargo, 

vehicle and ground systems, vehicle and mission 

systems, vehicle and ISS.

--- I U U U ---

Mounting and recovery procedures for dosimeters

and radiation area monitors.

--- --- I U U U

Flight plan, flight rules, space weather environment, 

projected radiation dose, flight data file procedures, 

system operations data file procedures.

-- --- --- --- --- X

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are influenced by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

Architecture, Materials, and Interface Specifications

Drawings, materials, and interface specifications provide NASA with insight into humansystem integration technical details throughout the design process. 

Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 

System Requirements Review (SRR)

NASA technical products:
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 Desired design reference mission (DRM)

 Program Medical Operations Requirement Document

 Program Human-Systems Integration Requirements Document

 NASA-STD-3001 Volumes 1 and 2

 NPR 8705.2B 

 Radiation instrumentation specifications

Suggested developer technical products:

 Initial ConOps addressing radiation requirements 

 Preliminary analysis plan and verification & validation (V&V) approach for 

shielding analyses

 Preliminary analysis plan and V&V approach for radiation area monitor 

installation

NASA or Developer Technical Products:

 Integrated set of models used to perform analysis of vehicle design

System Definition Review (SDR) 

NASA technical products:

 Updates to previous documentation, as available

 Changes to radiation instrumentation specifications

Suggested developer technical products:

 Revisions of ConOps 

 Definition of system architecture (structures, portable equipment, cargo) 

 IRDs for vehicle/equipment/cargo, vehicle/ground systems, vehicle/mission 

systems, vehicle/ISS

 Specifications for vehicle construction and shielding

o Final analysis plan/V&V approach 

o Preliminary analysis results 

o Input data and calculations used in shielding analysis

o Preliminary mitigation plan if shielding is inadequate

 Methods for mounting dosimeter to vehicle

o Updated analysis plan/V&V approach

o Preliminary assessment of maximum loads

NASA or Developer technical products:

 Updates to integrated set of models used to perform analysis of vehicle design

Preliminary Design Review (PDR) 

NASA technical products:

 Updates to previous documentation, as available

 Changes to radiation instrumentation specifications, as available
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Suggested developer technical products:

 Revisions of ConOps 

 Updates to definition of system architecture (structures, portable equipment, 

cargo) 

 IRDs for vehicle/equipment/cargo, vehicle/ground systems, vehicle/mission 

systems, vehicle/ISS

 Updated analysis plan/ V&V approach for shielding analyses

 Updated analysis plan/V&V approach for radiation area monitor installation

 Specifications for vehicle construction and shielding

o Updated analysis results 

o Input data and calculations used in shielding analysis

o Updated mitigation plan if shielding is inadequate

 Methods for mounting dosimeter to vehicle

o Updated load assessment

NASA or developer technical products:

 Updates to integrated set of models used to perform analysis of vehicle design

Critical Design Review (CDR) 

NASA technical products:

 Updates to previous documentation, as available

 Changes to radiation instrumentation specifications, as available

Suggested developer technical products:

 Final ConOps 

 System architecture (structures, portable equipment, cargo)

 Final IRDs for vehicle/equipment/cargo, vehicle/ground systems, vehicle/mission 

systems, vehicle/ISS

 Final analysis plan/V&V approach for analyses of shielding 

 Final analysis plan/V&V approach for installing radiation area monitor 

 Specifications for vehicle construction and shielding

o Final analysis results 

o Input data and calculations used in shielding analysis

o Final mitigation plan

 Methods for mounting dosimeters to a minimum of 6 locations in vehicle

o Final load assessment

NASA or developer technical products:

 Updates to integrated set of models used to perform analysis of vehicle design

System Integration Review (SIR) (if scheduled) 

NASA technical products:

 Updates to previous documentation, as available

 Changes to radiation instrumentation specifications, as available
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Suggested developer technical products:

 Final ConOps, IRDs. 

Test Readiness Review (TRR) 

NASA technical products:

 Changes to radiation instrumentation specifications, as available

 Operational constraints for hardware

Suggested developer technical products:

 Specifications and drawings for vehicle

o Updates to shielding analysis, as available

o Input data and calculations used in shielding analysis, as available 

o Changes to shielding mitigation plan, as required

o Testing results

 A minimum of 6 dosimeter mounting locations in vehicle

o Updates to analyzed maximum loads, as available

o Testing results

System Acceptance Review (SAR)

NASA technical products:

 Changes to radiation instrumentation specifications, as available

 Operational constraints for hardware

Suggested developer technical products:

 Documentation that vehicle will provide adequate shielding

 Documentation that no fewer than 6 dosimeters will be mounted to vehicle

Operational Readiness Review (ORR)

NASA technical products:

 Preliminary flight plan

 Preliminary flight rules (vehicle specific and ISS/vehicle, Space Environment 

section)

 Preliminary flight data file procedures

 Preliminary system operations data file procedures

 Final specifications for radiation instrumentation

 Operational constraints for hardware

Suggested developer technical products:

 Specifications for vehicle construction and shielding

o Final analysis results 

o Input data and calculations used in shielding analysis. 

o Final mitigation plan as required

 Methods for mounting dosimeters to a minimum of 6 locations in vehicle

o Final assessment of maximum loads
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Flight Readiness Review (FRR)

NASA technical products:

 Final flight plan

 Final flight rules (vehicle specific and ISS/vehicle, Space Environment section)

 Current and expected space weather environment

 Projected crew radiation dose

 Final flight data file procedures

 Final system operations data file procedures

Suggested developer technical products:

 Plan to attach and recover radiation area monitors
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4.9 FUNCTIONAL VOLUME DESIGN

4.9.1 INTRODUCTION

Functional volume, also referred to as net habitable volume (NHV), is the accessible 

volume available to crewmembers in which they can perform required mission tasks. 

The use of a structured iterative design and evaluation process to define, calculate, and 

preserve functional volume helps to ensure that crewmembers are provided adequate 

volume within which to perform these tasks and optimally function in their environment. 

Several methods and processes are used to drive designs and assess the functional 

volume of systems and vehicles. Although the specific methods may vary, proper 

assessment requires careful consideration of human operational needs during the 

mission.Some of the questions to consider are how crewmembers will move or translate 

from task to task throughout the course of a mission, as well as how multiple 

crewmembers may perform simultaneous tasks. Functional volume design is thus a 

core component of a system’s iterative human-centered design process. Additional 

information on how to ensure that crewmembers have enough room to safely and 

effectively perform mission tasks can be found in section 8.2.4 of the NASA/SP-2010-

3407 Human Integration Design Handbook (HIDH), Internal Size and Shape of 

Spacecraft.

4.9.1.1 APPLICABLE REQUIREMENTS

The following requirements for functional volume design and evaluation are specified in 

NASA-STD-3001, Volume 2:

 Volume Allocation [V2 8001]

 Volume for Crewmember Accommodation [V2 8002]

 Volume for Mission Accommodation [V2 8003]

 Volume for Behavioral Health [V2 8004]

Collectively, these requirements specify that the system provide defined and sufficient 

functional volumes for crew to perform tasks, for the expected number of crewmembers

and mission days. 

The intent of these requirements is for the system to provide sufficient volume for the 

crew to work, sleep, eat, ingress, egress, and perform all other necessary tasks safely 

and effectively.

The purpose of this section is to elaborate on the processes and methodologies used 

for functional volume design assessments. Additional reference materials on functional 

volume design are listed in Table 4.9.1.1-1.
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TABLE 4.9.1.1-1 REFERENCE MATERIALS FOR FUNCTIONAL VOLUME DESIGN

Document 

Number

Document 

Revision Document Title

JSC 63557 10/2008 Net Habitable Volume Verification Method

NASASTD-3001 4/2009 NASA Space Flight Human-System Standard Volume 2: 

Human Factors, Habitability, and Environment Health

NASA/SP2010-3407 1/2010 Human Integration Design Handbook (HIDH)

ISO 13407 6/1999 International Standard for Human-Centred Design 

Processes for Interactive Systems

NPR 

8705.2B 5/2008 NASA Procedural Requirements for Human-Rating Requirements for Space Systems

NPR 8705.2B, paragraph 2.3.10.1, requires human-in-the-loop (HITL) evaluations for 

human-system interfaces. NPR-required deliverables at PDR and CDR include 

summaries of how these evaluations were used to influence system design.

4.9.1.2 FUNCTIONAL VOLUME DEFINITION

Providing adequate and appropriate functional volume in a vehicle or habitat is 

necessary for ensuring mission success. Historically, mass and volume constraints 

associated with factors such as vehicle lift capability, structural requirements, 

environmental support, and other required technical equipment have defined the 

amount of space left over and allocated to the crew. Redefining the human as a system 

has allowed vehicles and habitats to be designed to fit the needs of the crew rather than 

forcing the crew to fit the design. To protect against the mass and volume of various 

systems encroaching into the mass and volume needed by the crew, it is important to 

consider the functional volume required by the crew from the earliest phases in the 

spacecraft design life cycle.

HIDH describes 3 spacecraft volumes that the vehicle designer must consider:

 Pressurized volume – the total volume within the pressure shell.

 Habitable volume – the volume remaining within the pressurized volume after 

accounting for all installed hardware and systems (sometimes known as “sand 

volume”).

 Net habitable volume (NHV) – the functional volume made available to the crew 

after accounting for the loss of volume due to deployed equipment, stowage, 

trash, and any other structural inefficiencies and gaps or unusable volume that 

decrease the functional volume. Items such as the crewmember’s body volume 

or temporarily deployed equipment required for a task are not considered a 

deduction to NHV.

Any space vehicle design will have a certain number of cavities and voids, which are 

deducted from the overall habitable volume. JSC-63557, Net Habitable Volume 

Verification Method, defines cavities as “regions extending off the main volume that are 
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too small or poorly shaped to count as habitable.” Voids, on the other hand, are defined 

as “empty volumes completely separated from the habitable volume” (NASA, 2008a). 

An example of a void might be a volume behind a bulkhead or wall that is totally 

inaccessible by the crew. The following lists provide some additional guidance for 

determining the habitability of a given volume.

A volume is considered habitable if

 A human body can be placed completely inside it

 It consists of cavities that are touching or connected to the vehicle’s main volume 

and are nominally accessible

 A human body cannot completely fit inside the volume (e.g., it is too small), but a 

human limb can be placed in that volume while the rest of the body is contained 

within a contiguous, adjacent volume

A volume is not considered habitable if

 It is unreasonable for a crewmember to nominally place a body part inside a 

volume produced by cavities between stowage, equipment, etc., during the 

execution of a nominal task

 It is taken up by physical systems or hardware (e.g., seats, structure, electrical or 

electronic systems, hygiene systems, waste management systems)

 It consists of voids

 It is within stowage volumes

 It is inaccessible inside a gravity field (e.g., lunar gravity)

4.9.2 FUNCTIONAL VOLUME DESIGN PROCESS

4.9.2.1 HUMAN-CENTERED DESIGN APPROACH

A human-centered design (HCD) process supports development of an effective, 

efficient, productive, and safe design by linking task, crew, and design requirements. 

Consistent with core HCD philosophy, the consideration of functional volume should be 

done from the very earliest stages of the design life cycle. As the design matures, 

functional volume assessments should be performed iteratively to drive design 

decisions, understand changes to crew functional volume, and compare design volumes 

with task-required volumes. Performing assessments throughout the design process 

ensures that required functional volumes are preserved. Further information on HCD 

can be found in HIDP section 3.2.

The HCD approach to functional volume design includes both computer-aided design 

(CAD) modeling and testing with physical mockups. CAD modeling is used to define 

volumes, visualize concepts, investigate volume with crewmembers of a range of 

anthropometric sizes, and evaluate body positions within static physical volumes (also 

see paragraph 4.5.2 Anthropometry). Physical testing, in mockups of increasing fidelity, 

allows designers to conduct HITL evaluations involving dynamic tasks, translations, and 

coordination between crewmembers. HITL evaluations are critical for providing 

information on how volumes affect crew task efficiency, effectiveness, and satisfaction. 

CAD analyses and HITL evaluations each provide important information about the 

sufficiency of functional volume; thus both of them should be performed iteratively as 
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the design matures. This approach can save time and money by catching potential 

volumetric issues early in the design cycle.

4.9.2.2 TASK ANALYSIS, MODELING, AND EVALUATION

The functional volume design process begins with understanding the vehicle and 

mission. This includes understanding mission requirements (objectives and associated 

crew tasks, duration, crew size, location, and so on), overall vehicle or habitat 

configuration, interior module design, and facility design (e.g., windows, hygiene area). 

Information can be obtained from requirements, design reference mission 

documentation, and concept of operations. Existing and historic systems can provide 

information on how similar missions were accomplished in the past and the lessons 

learned from those missions. More information about the architecture analysis process 

and development of the vehicle configuration and mission requirements can be found in 

the HIDH section 8.2.5, Module Layout and Arrangement.

Throughout the vehicle design process, 3 major activities are involved in designing for 

and assessing functional volume design:

 Task analysis: Define the tasks that crewmembers will perform, both nominally 

and off-nominally, and the context in which they will perform them (mission 

phase, vehicle configuration, time constraints, number of crewmembers, and so 

on)

 Modeling: Use CAD models to represent and assess static crew body positions 

for the various tasks identified in the task analysis. Modeling should be driven by 

anthropometric and biomechanical requirements.

 HITL evaluation: Use physical mockups with crew subjects to simulate tasks 

and evaluate provided volume under mission-like circumstances (as per NPR 

8705.2B paragraph 2.3.10).

Task analyses, modeling, and HITL evaluations each provide unique information about 

the tasks that crewmembers need to perform, potential postures for crewmembers of a 

range of anthropometric sizes, and acceptable volume for dynamic tasks and 

translations. Each component of the functional volume process also informs the others. 

For example, tasks and scenarios identified in a task analysis may be modeled using 

CAD software to provide guidance on how much volume is needed per task, which may 

then be validated with crew subjects in a HITL evaluation, or vice versa. Thus, it is 

crucial that all 3 componentstask analysis, modeling, and HITL evaluationsbe used 

throughout the functional volume design and analysis process. More detailed 

information about each is provided below.

4.9.2.2.1 TASK ANALYSIS

Task analysis is used to produce a list of tasks that crewmembers will need to perform 

and the relevant information about those tasks, such as mission phase, vehicle 

configuration, task criticality, time for tasks, concurrent tasks, crew interfaces, and crew 

clothing. Section 4.1 User Task Analysis provides information about the general task 

analysis process. For functional volume design, these tasks are examined to determine 

which of them are expected to have the greatest effects on required volume. It is 
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important to consider mission phase and interior vehicle configuration, as these will 

affect the volume available to the crew. For example, some tasks may require 

rearrangement of hardware (such as seats) or stowage; other tasks may require keepout zones because of privacy, contamination, or safety issues. When critical tasks need 

to be performed in a short time, faster task performance may take priority over vehicle 

rearrangement for additional volume. 

To illustrate the selection of volume-driving scenarios, consider an event involving 4

crewmembers who need to don suits in a short period of time. The amount of volume 

required for this activity will likely be more than that needed for a single crewmember to 

don a suit. A task analysis may help determine whether all crewmembers will need to 

don suits at the same time or if they can assist one another, determine the expected 

configuration of the vehicle interior (including interfaces used to accomplish the task), 

and determine whether enough time is available to relocate stowage to provide more 

volume. The task analysis is used to identify the task that requires the greatest amount 

of volume (e.g., 4 suits donned at the same time) and the context of that task, so that 

appropriate volume is allocated for it and all related tasks that require less volume. At 

other times multiple crewmembers may be performing concurrent smaller tasks, such as 

reviewing procedures, preparing food, and performing hygiene activities. The volume 

allocated for these tasks would need to be considered all at once because the volume 

required for one activity (e.g., hygiene) may limit the amount available for another 

activity (e.g., food preparation). Additionally, crewmembers may need to be given 

functional volume that allows them to translate between the areas where these tasks 

occur. 

Several scenarios have proved to be volume-driving for NASA vehicles. These include, 

but are not limited to, the following:

 Suit donning and doffing

 Cabin reconfiguration

 Separating meal and hygiene areas

 Vehicle ingress and egress

 Exercise operations

 Medical event operations

Section 2.5 of JSC 63557 provides additional information on how to determine volumedriving tasks.

4.9.2.2.2 MODELING

After the volume-driving tasks have been identified, CAD modeling can be used to 

assess the amount of available volume, given current or proposed designs, and the 

bounding volume required for these tasks across a range of anthropometric sizes. 

Determining net habitable volume is not as simple as subtracting the volume of 

components in the vehicle from the full volume of the vehicle. First, simple solids 

(spheres, cones, cylinders) are used to represent and calculate, by summing all these 

solids, the gross amount of volume available (Figure 4.9.2.2.2-1). Using Boolean or 

equivalent operations, the model is refined to remove nonfunctional volumes that 
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intersect or are completely enclosed within the full volume. This includes removing 

volumes taken up by mechanical, electric, or life-support systems, architectural 

components such as struts, hardware such as seats and display units, stowage, and 

volumes that are too small to be considered habitable. Several models may need to be 

developed to account for various vehicle interior configurations or competing design 

concepts. The final model should represent the overall available volume in an accurate 

shape (not just the volume of a simple solid or rectangular prism). Additional information 

on how to calculate functional volume, using cubic feet or meters, can be found in JSC 

63557 Appendix A.1.

FIGURE 4.9.2.2.2-1 INITIAL CAD MODELING OF NHV

The image on the left shows the first step of defining the simple solids. The image on 

the right shows a compilation of many simple solids, used to create an Orion model.

Models of the human body within the overall available volume can be used to generate 

functional volume needs for each workstation and associated tasks. Modeling the 

human body should be based on the anthropometric dimensions, range of motion, and 

body volume (Figure 4.9.2.2.2-2). Bodies can be modeled so that they assume 

expected positions for accomplishing the task, as determined by historic systems or 

HITL evaluations. For example in determining ways that 2 crewmembers could fit into a 

volume designed for radiation shielding, several possible configurations for 2 large male

crewmembers may be explored (e.g., back to back, both sitting with legs crossed, or 

one laying and one sitting). The amount of required functional volume can be estimated 

again by using simple solids to represent and calculate the minimum amount of volume 

needed for the task. This modeling can be used to further develop HITL scenarios or 

suggest design changes to hardware.
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FIGURE 4.9.2.2.2-2 HYPOTHETICAL CAD MODEL OF TASK VOLUME NEEDED BASED 

ON ANTHROPOMETRY AND RANGE OF MOTION REQUIREMENTS

When modeling the functional volume of related or simultaneous tasks, it is important to 

note that these volumes cannot be simply added together to yield a total functional 

volume, as it is expected that a volume might be shared among several workstations. 

CAD modeling is also useful for analyzing volumes required for tasks that are difficult to 

perform in 1g, such as docked operations. Task analysis and HITL evaluations can be 

used to drive the scenarios, but the posture and accommodation will have to be 

analyzed using a model.

Another benefit of modeling is that it allows frequent analysis. Often small design 

changes can be checked for feasibility using modeling, much faster and cheaper than 

performing a HITL evaluation. A HITL evaluation should still be performed in conjunction 

with the modeling, but may need to be postponed until several design changes are 

complete and mockup upgrades have been made.

Although CAD modeling provides critical information about the available versus needed 

functional volume for various vehicle configurations and body positions, CAD does have 

some limitations, which HITL evaluations can make up for. CAD analysis may not be 

able to capture the adaptability and flexibility of the human body to attain various 

postures and orientations. In a HITL evaluation, crew subjects may come up with 

alternative body positions and orientations not anticipated by biomechanics engineers, 

designers, or CAD developers, to accomplish a given task. Additionally, HITL 

evaluations may reveal comfort levels, pain, or fatigue associated with various body 

positions or orientations and how these positions and orientations are related to the 

ability to accomplish the task effectively and efficiently. Results of HITL evaluations may 

be integrated into the next iterative phase of CAD modeling by introducing new possible 

body or hardware placements or eliminating ones that are unacceptable.

CAD modeling should be used after a HITL evaluation to capture the postures and 

motions used by the HITL test subjects, so that assessment of the task across the 

anthropometric distribution can be performed. This assessment has a 2-fold purpose: 

(1) to provide evidence that the required range of crew sizes is accommodated, not just 

the sizes of the subjects in the HITL evaluation, and (2) to integrate and measure 

volume from the physical mockup into the CAD model. Take, for example, a 
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hypothetical capsule designed to seat 2 crewmembers. The capsule program may 

require that the capsule be able to seat, side by side, 2 fully suited men with 99th-

percentile bideltoid breadth. A HITL evaluation is performed using 2 men, one with an 

84th-percentile bideltoid breadth and another with a 90th-percentile bideltoid breadth,

and both subjects are able to accomplish all expected mission tasks within the volume 

provided. An analysis could then be performed with CAD modeling in which 2 men with 

99th-percentile bideltoid breadth and a set of other critical dimensions are modeled in 

the seats through the volume-driving tasks to confirm that the HITL findings extrapolate 

to the expected anthropometric distribution.

4.9.2.2.3 HUMAN-IN-THE-LOOP EVALUATIONS

Task analysis and CAD modeling can both be used to develop HITL evaluation 

scenarios and parameters, which are used to judge the acceptability and adequacy of 

the provided volume for a task. HITL evaluations involve having human subjects 

perform the identified volume-driving tasks in a representative mockup. HITL 

evaluations with low- and medium-fidelity mockups are discussed below. High-fidelity 

testing would take place in a qualification or flight vehicle.

4.9.2.2.3.1 CAD MODELING AND HITL WITH LOW-FIDELITY MOCKUPS

To help validate and refine CAD analysis, a physical mockup should be constructed to 

evaluate movements, dynamic tasks, translations, and coordination between 

crewmembers during HITL evaluations. A low-fidelity mockup can be constructed from 

simple materials such as wood or foam-core, with printed faceplates, volumetrically 

representing all the subsystems (see Figure 4.9.2.2.3.1-1). This will aid the test subjects 

in visualizing the volume and interacting with the required hardware while acting out the 

task. Data should be collected on obstructions to the task, major reconfigurations, 

whether the hardware is configured to support task flow, whether the subjects have the 

required volume to perform the task, whether that volume is sufficient to successfully 

accomplish the task, and anything else identified as relevant. 

FIGURE 4.9.2.2.3.1-1 CAD MODELING AND LOW-FIDELITY MOCKUP EVALUATION

The image on the left is a CAD representation of the Orion Crew Exploration Vehicle 

(CEV). The image on the right is the low-fidelity physical mockup of the CAD model with 

human participants (Kallay et al., 2006).
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This type of physical mockup is key to determining which human task(s) absorb the 

largest amount of habitable volume and which vehicle configuration best supports 

successful completion of the volume-driving tasks. Simulating the tasks in a physical 

mockup can also help in defining the driving tasks that require simultaneous operations 

and/or choreography among all or some crewmembers.

To assess the adequacy of the functional volume during a HITL evaluation, an evaluator 

(i.e., test conductor) should plan to collect the following data:

 Real-time measurements: Real-time measurements may be collected on range 

of motion, joint angles, anthropometry, distance from the body to a surface, 

clearances, and so on to document the available volume as well as feed future 

CAD models

 Interferences: The evaluator should document when a subject bumps or hits an 

interface, when a protrusion interferes with the task, when fit is not adequate, and 

anything related to the subjects’ ability to successfully accomplish the tasks.

 Subjective measures: Subjective measures such as acceptability, fatigue, and 

workload should be collected during or after a task. Subjective feedback from the 

subject is important in making design decisions and identifying areas for

improvement.

Comments: Subject comments during and after a task should be documented to better 

understand the operations of the task and subject requirements, such as effort, avoiding 

obstacles, and choreography.

4.9.2.2.3.2 CAD MODELING AND HITL WITH MEDIUM-FIDELITY MOCKUPS

Leveraging the data and lessons learned from HITL testing using a low-fidelity mockup, 

designers should integrate any redesign decisions into the project’s CAD models. Once 

the CAD models are updated, the design can be tested again in a medium-fidelity 

mockup. The medium-fidelity mockup should represent the baseline functional vehicle, 

and may contain some limited functionality in the human interaction components. 

Incorporation of subsystem prototypes is encouraged. A functional mockup that is as 

realistic as possible will aid the test subject in providing quality data. The subject will be 

able to effectively simulate hardware interactions, obstacles, necessary volume, 

timeline, and so on. The designers and test subjects are shown how hardware use may 

affect the interior habitable volume and drive crew interactions. 

Factors that increase task and mockup fidelity include but are not limited to the 

following:

 Hardware: Inclusion of hardware with as high a fidelity as possible increases the 

realism and allows the identification of representative issues. Also, having 

hardware present that was not available during previous HITL testing is 

important. For example, incorporation of increasingly higher fidelity suits into the 

suit-doffing task increases the quality of data such as time on task, difficulty, 

obstructions, and acceptability.
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 Environmental Conditions: Simulating the task under the anticipated 

environmental conditions (e.g., noise levels) will provide realism and increase the 

potential for identifying NHV-related issues. 

 Timeline: Performing a simulated mission in which subjects spend their days and 

nights working a simulated mission timeline, including activities such as 

exercising, sleep, and meal preparation, may reward the design team with higher 

quality volumetric data than previous mockups or CAD modeling. Behavioral 

assessments of how the crew perceives the volume while working and living in 

the vehicle, under a representative timeline, can focus the task analysis, human 

performance, and movement within the vehicle mockup. This type of testing is 

usually rare, but definitely beneficial.

As mission tasks and crew expectations are refined, design or volume changes are 

made, and the design cycles advance, it is important to repeat the steps in this 

processtask analysis, CAD modeling, and HITL testingto ensure that adequate 

functional volume is provided to perform all identified tasks. Functional volume design is 

a key component of the system design life cycle. 

4.9.3 DESIGN DRIVERS

When the functional volumes of space environments are being evaluated, several 

unique design drivers should be taken into account. These drivers may be associated 

with the number of crewmembers, the number of mission and contingency days; the 

crewmembers’ behavioral health, body dimensions, postural factors, and movement 

capabilities; gravity; environmental factors; and tasks associated with both nominal and 

off-nominal (e.g., emergency) operations. Table 4.9.3-1 provides some specific 

examples of these unique design drivers.

TABLE 4.9.3-1 UNIQUE SPACECRAFT ARCHITECTURAL DRIVERS

Drivers Description

The gravity environment

Crews in 0g are not constrained in any one 

orientation and they have the ability to move 

about freely in 3-dimensional space.

Mission objectives

The mission objectives are all affected by the 

reference mission, crew size, duration of 

mission, and the operational gravity 

environment of the crew and vehicle.

Size and number of crew

The design will have to accommodate the 

maximum number of expected crew, the range 

of physical dimensions, and the range of 

motions. Crew interaction during planned 

mission tasks should be addressed, so that 

infringement on another crewmember’s 

volume is avoided to the best extent possible. 

Limitations of mass and volume

The internal volume must ensure the safety, 

efficiency, and effectiveness of the crew to 

perform the functions necessary for a 

successful mission.
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Mission duration

As the duration of a mission increases, so 

does the physical volume required to 

accommodate the personal needs of the crew 

and the mission tasks. Long-duration missions 

can affect the crews’ behavioral health, due to 

the confinement, stress, and isolation. The 

psychological needs of a long-duration mission 

may drive additional space and privacy 

requirements.

4.9.3.1 MEDICAL CAPABILITIES

An example spacecraft design driver includes design for medical capabilities. The 

vehicle design needs to accommodate operations associated with use of the medical kit 

and use of NASA-specified HMS hardware for specific medical conditions. NASA 

identifies space medical conditions and prioritizes each by likeliness to occur and 

treatability in NASA/TP-2010-216118 Space Medicine Exploration Medical (ExM) 

Condition List. Diagnosis and treatment procedures associated with each condition are 

described in JSC 65973 Medical Conditions Concept of Operations.

Design to accommodate the volume required for medical tasks involves the same 

iterative 3-step process described above: task analysis, CAD modeling, and HITL 

evaluations. The difference is the incorporation of government-furnished equipment 

(GFE) and procedures for diagnosis and treatment. Design solutions to accommodate 

crew tasks for addressing medical conditions involves incorporating considerations for 

the medical treatment area, patient and caregiver area and volume, and needed 

equipment and resources (e.g., oxygen, power). For example, diagnosis of most 

conditions calls for measurement of crewmember vital signs including temperature, 

blood pressure, pulse, respiratory rate, oxygen saturation, and auscultation along with 

verbal intake of medical history and symptoms. To supplement the content below, refer 

to NASA/SP-2010-3407 Human Integration Design Handbook (HIDH) section 7.6 

Medical for additional information on the design and layout of a medical area in a 

spacecraft, including the overall size, medical interfaces, and stowage.

Identifying the area(s) of the vehicle where medical care will be provided is one of the 

first steps in accommodating functional volume for the medical system. When designing 

functional volume for patient and caregiver, ensure that task analysis has considered 

the number of crewmembers involved, the equipment needed including interface 

location and size constraints, and any nonmedical (e.g., vehicle system operations) 

tasks that may be occurring in adjacent or overlapping volumes or areas. The medical 

care area needs to have adequate volume and surface area to provide care to a patient 

and allow access for the medical care provider and medical equipment. 

For in-flight medical diagnosis and treatment, restraint of the patient is needed to 

prevent motion of the patient’s arms and legs, and allow stabilization of the 

crewmember’s head, neck, and spine in a fully supine position from hips to head. In 

addition, the capability to restrain the caregiver and medical equipment needed for 

diagnosis and treatment is to be provided. The medical restraints design should 

consider multiple and/or moveable restraints so that equipment can be positioned where
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it is needed or so the caregiver can access or move around the patient from any side. 

Furthermore, electrical isolation capability may be built into the patient restraint system 

for treatment involving advanced life support (ALS) procedures.

The vehicle needs to accommodate NASA-defined medical hardware and procedures in 

locations that are easily accessible to the medical care area or point of use. All required 

vehicle medical resources (e.g., power, data, potable water, pressurized oxygen), 

specified in JSC 65973 Medical Conditions Concept of Operations document (according 

to medical condition), should be easily accessible within the medical care area. NASA 

will provide NASA medical hardware specifications upon request.

Design activities for medical equipment stowage and accessibility should be performed 

in conjunction with design of overall stowage needs (food, crew equipment) and 

stowage restraint. 

4.9.4 EXAMPLES FROM NASA PROGRAMS AND PROJECTS

Several specific examples exist of how NASA projects have addressed functional 

volume design, and they are given in the following paragraphs. These include examples 

from the Orion project and the Lunar Surface Systems project of the Constellation 

Program. These examples describe how specific projects chose to pursue iterative 

functional volume design at different design phases and are an excellent demonstration 

of how CAD and HITL testing concepts are integrated into their respective engineering 

life cycles. These examples are provided as guides, and by no means imply that these 

are the only ways to execute the process. There is a great deal of flexibility in how 

functional volume design can be performed, and developers are encouraged to be 

innovative while taking advantage of the lessons learned at NASA over the course of 

many programs and projects. 

4.9.4.1 THE ORION PROJECT

DAC1

Orion’s design process is divided into cycles, called design and analysis cycles (DACs). 

The first cycle, DAC1, began the 3-step NHV process of task analysis, CAD modeling, 

and HITL evaluations for the vehicle. The task analysis sessions in DAC1 were 

initialized using the current DRM and ConOps, and were organized according to

hardware needs. For example, one task analysis session would be devoted to 

assessing the operational needs and tasks associated with the food warmer, and 

another session would be devoted to assessing the tasks associated with the hatch. 

The assumptions and critical driving tasks were identified for all crew systems’ 

hardware, and some associated hardware such as hatches (structures) that the crew is 

required to interact with for a successful mission. 

The DAC1 task analysis identified several volume-driving tasks:

 Nominal ingress

 Post-insertion operations

 Post-sleep operations
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 Rendezvous and docking

 EVA preparation and contingency EVA 

The identified driving scenarios were further developed in CAD, to identify the volume 

needs based on the anthropometry and range-of-motion data provided in the 

requirements tables (of the HSIR). The CAD model was used to represent performing 

these tasks to identify any design or volume issues. Figure 4.9.4.1-1 shows a CAD 

model of 4 crewmembers performing post-insertion cabin reconfiguration tasks. 

Additionally, CAD modeling was used to assess the amount of NHV in cubic 

feet/meters, to determine how much NHV Orion was providing relative to the NHV 

requirement. Note, at that time the requirement for NHV was quantified in cubic 

feet/meters. The Lockheed Martin and NASA teams each performed a CAD analysis 

measuring NHV, and then compared their measurements to check whether cubic 

feet/meters was a valid way of measuring NHV. Formal HITL evaluations were not 

conducted in DAC1, as a need for further analytical work was identified before mockups 

were to be built.

FIGURE 4.9.4.1-1 CAD MODEL SIMULATING 4 CREWMEMBERS PERFORMING POSTINSERTION CABIN RECONFIGURATION TASKS

DAC2

The task analysis sessions in DAC2 were similar to those in DAC1 in that they were 

hardware based, but they expanded on the information gathered, the knowledge gained, 

and the design changes made during DAC1. CAD modeling was used to ensure that the 

recommended design changes from DAC1 did not impinge on the NHV allocated for 

volume-driving tasks, and to provide an updated model to feed HITL mockup 

refinements. DAC2 HITL evaluations resulted in important design changes intended to 

increase crew operability.

The DAC2 task analysis identified several additional volume-driving tasks to be 

evaluated in CAD and HITL evaluations. For example, increased knowledge about the 
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operations associated with the exercise device, such as an outstretched elbow motion, 

added the exercise task as a potential volume driver.

 DAC1 list:

o Nominal ingress

o Post-insertion operations

o Post-sleep operations

o Rendezvous and docking

o EVA preparation and contingency EVA (suit donning and doffing)

 DAC2 additions:

o Exercise

o Suit donning and doffing for ISS and lunar missions

The increased fidelity of the CAD modeling in DAC2 (Figure 4.9.4.1-2) increased

confidence in the results of the simulation, increased the probability of identifying 

obstructions to the task, and helped scope the protocol for the HITL testing.

FIGURE 4.9.4.1-2 DAC2 CAD MODEL SIMULATING 4 CREWMEMBERS PERFORMING 

THE VOLUME-DRIVING TASK OF SUIT DONNING AND DOFFING

An NHV HITL evaluation was performed during DAC2 to examine performing the NHV 

volume-driving tasks within the CEV Crew Module low-fidelity mockup. The objectives of 

the test were to

 Identify NHV impacts of volume-intensive tasks in the baseline configuration

 Review system and subsystem concepts with scripts generated to best 

approximate context and fidelity within the mockup

 Determine the value of HITL as part of a verification process
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 Identify activities that could not be performed in the mockup, for future 

evaluations in higher fidelity mockups or microgravity environments, and future 

watch items

The caveats were that this testing was being performed early in the design cycle, the 

data were not to be used to update any requirements, no crew performance/time 

measures were taken at this level of fidelity, and the full anthropometric range was not 

represented. Within the CEV mockup, subjects enacted scripted scenarios with 

volumetric representations of suits, seat stowage, and other crew cabin equipment, 

performing tasks to the level of available fidelity. The tasks included these:

 Post-insertion cabin configuration (crew of 6)

o Crewmembers performing in-space stowage of seats and suits, setup and 

use of Waste Management System (WMS), and access to stowed items. 

 Group meet and eat, galley food preparation (crew of 6)

 Medical event with use of medical seat (crew of 6)

 Exercise activity (crew of 4)

 Radiation event – no activity, discussion only (crew of 4) 

 Suit donning

 Suit doffing

 Vehicle ingress

 Vehicle egress

The evaluators collected video, audio, still images, real-time human engineering 

observations, real-time subject comments, and comments on a post-evaluation 

questionnaire. The main findings of the evaluation were these:

 Pallet interference with WMS operations 

 Potential strut interference in area of food preparation activity

 Strut interference with window viewing (of Earth, vehicle photo opportunities) and 

armrests

 Display console view not available unless floating into that space 

 Display console keypad protrusion consistently bumped 

 HITL evaluation of tasks can be used as both a validation of CAD analysis and 

as an independent method to demonstrate that volume-driving crew tasks can be 

performed in the available NHV.

The design issues identified in this evaluation resulted in changes to the pallet to reduce 

interference with WMS operations and relocation of the struts to prevent interferences. 

The other displays and controls related issues were unavoidable at this time because of

other design constraints. As a result of these evaluations, additional recommendations 

on cabin stowage and space management were recorded and applied to ConOps, 

specifications, and later to mission planning.

The CAD and HITL activities of DAC2 shifted the focus of the NHV requirement from a 

cubic feet/meters-based verification to include a task-based verification. The HITL 

evaluations highlighted that the NHV measurement should not only meet a number, but 

also constitute a volume that is usable space for all the NHV-driving tasks the crew 
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must perform. The creation of JSC 63557 established a dual-phased verification 

method, with phase 1 including calculation of the vehicle’s NHV (CAD model volume 

measurement and mockup physical measurement) and phase 2 including verification

that NHV is usable space through task analysis and demonstration. Phase 2 should 

include CAD model analyses of tasks difficult to perform in 1g and allow more frequent 

analysis as well as task analysis and task demonstration performed by human subjects 

in a physical mockup.

DAC3

DAC3 task analysis and CAD modeling followed the same process as DAC2 by 

expanding the knowledge base and incorporating design changes. An Orion DAC3 NHV 

evaluation was conducted to evaluate the NHV with a crew of 4 for ISS and lunar 

missions and identify NHV impacts of volume-intensive tasks in the baseline 

configuration. The evaluation took place in an updated CEV low-fidelity mockup, 

simulating hardware to the current configuration. The evaluation focused on specific 

suited and unsuited volume-driving tasks, acted out by the subjects to exercise the 

volume configuration. The volume-driving tasks included these: 

 Suit doffing and stowage

 Contingency suit donning

 On-orbit stowage including umbilical stowed layout

 WMS and hygiene tasks

 Sleep layout

 Exercise operations

 Medical event operations

 Radiation shelter setup and inhabitance

Vehicle ingress and egress were evaluated during DAC3 in a separate evaluation, not 

as part of the NHV assessment. Also, rendezvous and docking was removed from the 

list of volume-driving tasks. It was determined that the tasks in the list above were larger 

volume drivers than ingress/egress and rendezvous/docking. 

The CEV low-fidelity mockup was complemented with volumetric mockups to represent 

suits, seats, suit stowage bags, and emergency medical kits. Every attempt was made 

to acquire the highest fidelity possible. These items were used to facilitate discussion of 

potential volume impacts. Oral and written comments, anthropometric data, and audio 

and video were collected for analysis.

Overall in the evaluation the volume was deemed adequate to perform the key driving 

tasks. The changes to the pallet and WMS area from DAC2 led to satisfactory ratings 

during the DAC3 evaluation. Design changes were identified for

 Stowage restraints

 Seat removal

 Restraints to perform medical procedure on patient

 Radiation shelter, ventilation, lighting, and communication
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Work followed the evaluation to mature the detailed component operations and crew 

procedures, particularly with respect to the EVA suit interfaces and choreography to 

develop the operational timelines.

The efforts of DAC1-3 highlighted the importance of including HITL evaluation of 

volume-driving tasks in the design life cycle, and using the results of task analysis, 

CAD, and HITL evaluations to iterate the design.

4.9.4.2 LUNAR SURFACE SYSTEMS

After task analysis sessions, the Lunar Surface Systems team built a low-fidelity 

mockup of the Altair Lunar Lander and the Lunar Rover. 

The low-fidelity mockup of the Altair was developed with simulated foam-core boxes 

and representative volume to simulate the identified volume-driving tasks, such as suit 

donning and meal preparation. The HITL evaluation identified the driving tasks that 

required “choreography” among crewmembers and helped to refine hardware and 

configurations affecting the tasks (see Figure 4.9.4.2-1).

FIGURE 4.9.4.2-1 MOCKUP EVALUATION FOR DRIVING TASKS

Using a low-fidelity mockup of the Altair Lunar Lander, both suited and unsuited tasks 

were tested in the proposed design volume. The image on the left illustrates connecting 

an umbilical to a mockup spacesuit. The image on the right is the full crew eating dinner 

in the vehicle’s volume. Note the foam-core boxes, representing all the subsystem 

hardware, on the walls around the crew (Litaker et al., 2008; Thompson et al., 2010). 

The Lunar Rover has gone through 2 different configurations since its inception. Figure 

4.9.4.2-2 shows the low-fidelity mockup of the first configuration considered, built based 

on a CAD model. Human factors engineers conducted an initial NHV HITL evaluation of 

16 tasks in this low-fidelity mockup using simple subjective scales, subjects’ comments, 

field analysis, frequency of movement, reconfiguration patterns and frequencies, and 

anthropometric analysis, using dynamic tasks that were baselined by the Program. After 

the analysis of the NHV data, as well as other dynamic data, it was concluded that a 

new cabin design was needed because of excessive reconfiguration and a change in 

the vehicle’s center of gravity (CG).
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FIGURE 4.9.4.2-2 MOCKUP EVALUATION FOR DYNAMIC TASKS

The first configuration of the Lunar Rover as a low-fidelity mockup. The image on the 

left is the cabin mockup with investigators collecting NHV data. The image on the right 

shows test subjects reconfiguring for sleeping (Litaker et al., 2008).

This initial HITL evaluation was able to identify volume limitations during the cabin 

reconfiguration task, not identified by the CAD model. Taking the knowledge gained 

about the rover’s NHV during the initial HITL test, the designers updated the cabin 

configuration in the model and then built another mockup. Figure 4.9.4.2-3 shows the 

low-fidelity mockup used for the NHV testing of the updated design. Human factors 

investigators asked the test subjects to perform the same 16 tasks used in the initial 

HITL test to judge the required functional volume. 

FIGURE 4.9.4.2-3 MOCKUP EVALUATION OF REDESIGNED CONFIGURATION

The left image was the new redesigned-configuration, low-fidelity mockup that was used 

for testing the NHV. The image on the right shows test subjects discussing the visibility 

of the front window with the side displays. The blue-taped box at the far right of the 

photo represents a side window (Litaker et al., 2008).

The lunar rover’s second configuration benefited from iterative NHV analyses and 

evaluations, which provided the project team an enhanced ability to make an informed 

decision on how to mature the design and create a medium-fidelity mockup of the 

second configuration. Figure 4.9.4.2-4 shows the functional Cabin 1A medium-fidelity 

mockup. 
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The medium-fidelity mockup has been used in 2 field trials during the Desert Research 

and Technology Studies (DRATS) at the Black Point Lava Flow in Arizona. During the 

first field trial in 2008, a crew of 2 worked and lived in the functional mockup for 3 days,

interfacing with all the interior and exterior systems. Human factors engineers, along

with vehicle design engineers, collected data on the volumetric acceptability of the 

vehicle, the acceptability of the task accomplished, and the engineering data associated 

with operating such a prototype vehicle in a real-world simulation (Litaker, Thompson, 

Howard, Szabo, Conlee, & Twyford, 2008). 

FIGURE 4.9.4.2-4 MEDIUM-FIDELITY MOCKUP EVALUATION

The top image shows the medium-fidelity functional rover Cabin 1A during engineering 

test runs before the 3-day field trial. The bottom left image shows the Cabin 1A cockpit 

interior with functional system computers and controls. The bottom right image shows 

Cabin 1A from the perspective of the suitports in the aft section of the vehicle. With the 

front seats in the down position, the cabin is being configured for crew sleep.

The data gathered during the 3-day test proved to be invaluable to the vehicle 

designers. Several modifications to the design were made, including adding stowage 

areas, adding an environment enclosure for the spacesuits, and redesigning the cockpit 

layout for increased efficiency. Using these HITL lessons learned from the Cabin 1A 

mockup, another medium-fidelity functional mockup was built with the added 

modifications (Figure 4.9.4.2-5).
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FIGURE 4.9.4.2-5 MEDIUM-FIDELITY MOCKUP ITERATION EVALUATION

The left image is the modified Cabin 1B with suit enclosure and added side hatch. The 

right image shows the modified Cabin 1B cockpit display arrangement and added 

overhead stowage.

With the earlier data showing confidence in the vehicle’s NHV, a 14-day simulated 

mission was planned with Cabin 1B during the 2009 DRATS field trials. Using the same 

tasks as in the earlier test, but with more mission fidelity added, investigators collected 

data not only on the vehicle’s volumetric and habitability design configuration but also 

on how the volume affected the crewmembers’ behavioral health (Figure 4.9.4.2-6). The 

increased fidelity and representative timeline allows increased confidence in the results 

of the volumetric assessment, and possibly validation of some functional volume 

allocations in the vehicle (depending on the phase of the design process). Data of this 

caliber gives the design team stronger knowledge of the characteristics of the vehicle’s 

habitable volume, which in turn becomes a valuable asset in updating the design. 

FIGURE 4.9.4.2-6 ENHANCED MEDIUM-FIDELITY MOCKUP ITERATION EVALUATION

The image on the left shows a crewmember both using the control stick and interacting 

with edge keys on the display during a 14-day mission. The image on the right shows 

both crewmembers during off-working hours. The crewmember in the background is 

doing exercises while the crewmember in the foreground is having a snack. Both 

images were made in the Cabin 1B mockup vehicle and show how various dynamic 

tasks were testing the NHV (Litaker et al., 2010).
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For the rover team, the lessons learned from these simulated missions, the quantity and 

quality of data collected, and the use of multiple mockups of varying fidelity reduced the 

needed amount of iterative testing considerably. In fact, through this NHV process, the 

rover design team (at the time of this writing: September, 2010) felt confident about 

pushing forward to develop a next-generation vehicle to bring the project closer to a 

pressurized flight-like vehicle with realistic online subsystems. This will allow flight-like 

vehicle testing of all volumetric parameters of the configuration, and provide interface 

interaction data that will facilitate finalization of the design as well as evaluation of other 

factors such as workload and usability. 

4.9.5 FUNCTIONAL VOLUME DESIGN TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.9.5-1 are recommended for review by the NASA customer.

TABLE 4.9.5-1 FUNCTIONAL VOLUME DESIGN TECHNICAL PRODUCTS

Technical Products

Phase 

A

Phase 

B

Phase 

C

Phase 

D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function allocation, 

and associated crew task lists. Includes 

identification of volume-driving tasks and 

identification of equipment and configurations that 

will be present in crew work and habitation areas.

I U U U --- ---

A summary of modeling/analysis/evaluation 

performed to date and their influence on system 

design with links to the detailed analysis results.

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10. Includes analysis of 

volume-driving tasks based on CAD and human-inthe-loop.

--- --- I U --- ---

System architecture drawings (structures, 

equipment, etc.), material specifications, interface 

requirements. Includes provision of vehicle CAD for 

use in analyses.

--- --- I U U ---

Verification plan. --- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations (ConOps) and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are influenced by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 
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ConOps and crew task list development for functional volume includes the identification 

of expected volume-driving tasks such as work, sleep, eating, medical care, translation, 

egress, ingress, pressure-suit donning, and other tasks. In addition, they include the 

identification of equipment and configurations that will be present in crew work and 

habitation areas.

Summaries of Modeling, Analyses, and Evaluations

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-system integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how critical design decisions 

were assessed. According to NPR 8705.2B, updated summaries are to be provided at 

each design review through SAR. Also in paragraph 2.3.10, the use of HITL evaluation 

is a required method to progressively demonstrate that the operational concept meets 

system requirements for operational safety, efficiency, and user interface design. 

For functional volume, analysis of volume-driving tasks should occur in CAD and HITL

evaluations, with increasing fidelity of models beginning at SDR and continuing to SAR.

Architecture, Materials, and Interface Specifications

Drawings, materials, and interface specifications provide NASA with insight into humansystem integration technical details throughout the design process.

Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 

4.9.6 REFERENCES

Kallay, A., Harvey, C., Byrne, V., DeSantis, L., Maida, J., Szabo, R., & Whitmore, M. 

(2006, August). Crew exploration vehicle (CEV) net habitable volume assessments for 

6-crew missions (NASA TDS CEV-05-002). Houston, TX: Johnson Space Center.

Litaker, H. L., Jr., Howard, R., Ferrer, M., & Young, K. (2008, January). Lunar rover 

habitability volume evaluation on configuration one. Houston, TX: Johnson Space 

Center. Internal NASA Document.

Litaker, H. L., Jr., Thompson, S., Howard, R., Szabo, R., Baldwin, T., Conlee, C., 

Twyford, E., Nguyen, A., & Ward, M. (2008, February). Suited and unsuited habitable 

volume evaluation for Altair lunar lander DAC-2 configuration. Houston, TX: Johnson 

Space Center. Internal NASA Document, September 2008. 

Litaker, H. L., Jr., Thompson, S., Howard, R., Szabo, R., Conlee, C., & Twyford, E. 

(2008). Habitable volume evaluation for the lunar sortie habitat Altair: Configuration one. 

NASA/Johnson Space Center. Internal NASA Document.
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Litaker, H. L., Thompson, S., Howard, R., Szabo, R., Conlee, C., & Twyford, E. (2008, 

December). Small Pressurized Rover (SPR) three day desert trial: A human factors 

assessment. Houston, TX: Johnson Space Center. Internal NASA Document.

Litaker, H. L., Jr., Thompson, S., Howard, R., Szabo, R., Conlee, C., Green, S., & 

Twyford, E. (2010, February). A human factors assessment of the Lunar Electric Rover 

(LER) during a 14-day desert trial. Houston, TX: Johnson Space Center. Internal NASA 

Document.

National Aeronautics and Space Administration. (2008a, October). Net habitable volume 

verification method (JSC 63557 Draft, October 30, 2008). Internal NASA Document.

National Aeronautics and Space Administration. (2010a, January 27). Human 

integration design handbook (HIDH) (NASA/SP-2010-3407). Washington, DC: Author.

Thompson, S., Litaker, Jr., H.L., Szabo, R., Howard, R., & North, D. (2010, January). 

Evaluation of the Altair lunar lander DAC-3 interior volume configuration. Houston, TX: 

Johnson Space Center. Internal NASA Document.
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4.10 CREW SURVIVABILITY ASSESSMENT

4.10.1 INTRODUCTION

According to NPR 8705.2B Human-Rating Requirements for Space Systems, one of the 

key elements to be included in a human-rating certification plan is the system’s 

implementation of crew survival strategies for each phase of the reference mission. For 

each reference mission it is important to identify potential operational risks and 

accompanying mitigation strategies to enhance crew survival. The risks should include 

system failures and emergencies (such as fire, collision, toxic atmosphere, decreasing 

atmospheric pressure, and medical emergencies) with specific mitigation capabilities 

(such as abort, safe haven, rescue, emergency egress, emergency systems, and 

emergency medical equipment or access to emergency medical care) identified to 

protect the crew. Crew survivability assessment is the process of identifying potential 

crew survivability methods for all potential catastrophic hazards expected to occur 

during each phase of the reference mission. This process should be integrated 

throughout system design and be iteratively performed as missions, operations, and 

tasks mature. 

4.10.2 PROCESS 

Reserved

4.10.3 CREW SURVIVABILITY ASSESSMENT TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.10.3-1 are suggested for review by the NASA customer.
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TABLE 4.10.3-1 CREW SURVIVABILITY TECHNICAL PRODUCTS

Technical Products

Phase

A

Phase 

B

Phase 

C

Phase

D

SRR SDR PDR CDR SAR FRR

A description of each reference mission for which 

human rating is being pursued.

Required per NPR 8705.2B paragraph 2.3.1.

X --- --- --- --- ---

A description of the ConOps, function allocation, 

and associated crew task lists. I U U U --- ---

Establishment of scenarios to be used for hazard 

analysis and risk assessments. I U --- --- --- ---

A description of the design philosophy that will be 

followed to develop a system that utilizes the crew’s 

capabilities to execute the reference missions, 

prevent aborts, and prevent catastrophic events. 

Required per NPR 8705.2B paragraph 2.3.3 

Documenting the Design Philosophy for Utilization 

of the Crew. 

X --- --- --- --- ---

A description of the crew survival strategy for all 

phases of the reference missions and the system 

capabilities required to execute the strategy. A 

description of the implementation of the identified 

survival capabilities. Required per NPR 8705.2B 

paragraph 2.3.2 Identifying System Capabilities for 

Crew Survival.

--- I U U U U

A description of the implementation of the crew 

survival capabilities and a clear traceability to the 

highest level of program documentation. Required

per NPR 8705.2B paragraph 2.3.4 Incorporating 

Capabilities into the System Design.

--- I U U --- ---

A summary of how the safety analysis activities 

related to loss of crew were used to understand the 

relative risks and uncertainties within the design and 

subsequently influence decisions related to the 

system design and application of testing. Required 

per NPR 8705.2B paragraph 2.3.6 Designing to 

Control Hazards and Reduce Risk.

--- I U U U ---

X = one-time release of item

I = initial release of item

U = updated release of item
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4.11 METABOLIC LOADS AND ENVIRONMENTAL CONTROL LIFE SUPPORT SYSTEM 

DESIGN

4.11.1 INTRODUCTION

Crewmembers’ metabolic loads are one important contributor to the design and sizing of 

the spacecraft Environmental Control and Life Support (ECLS) system capacity. An 

effective ECLS system is critical to provide and maintain cabin atmospheric conditions 

necessary to ensure the health and performance of the crewmembers. Taking the 

human-centered approach to spacecraft design will help the designer to achieve 

required environmental conditions needed to sustain crews and attain human-rating 

certification.

Although human response to physical and environmental stimuli is individual and 

variable, NASA has developed data and requirements that reflect the best knowledge to 

date regarding space flight physiological response. Integrated analysis of crew system 

metabolic loads in conjunction with other vehicle system loads early in the vehicle 

design process will ensure that the ECLS system design is adequate to meet the 

vehicle environmental limits. The NASA-STD-3001 requirements relevant to metabolic 

loads and ECLS design include the following::

 V2 6003 O2 Partial Pressure Range for Crew Exposure

 V2 6006 Total Pressure Tolerance Range for Crew Exposure

 V2 6010 Relative Humidity

 V2 6011 Suited and Post-Landing Relative Humidity

 V2 6012 Comfort Zone

 V2 6013 Temperature Range

 V2 6014 Crewmember Heat Storage

The contributions of metabolic loads are one important aspect of ECLS design that is 

discussed in this section. The following process describes the “how to,” assumptions, 

critical components, and data that are relevant to the development and utilization of an 

appropriate representation of crew-induced metabolic loads. Additional discussion can 

be found in NASA/SP-2010-3407 Human Integration Design Handbook (HIDH) section 

6.2.3.1.4 Expected Metabolic Loads.

4.11.2 METABOLIC LOADS DESIGN PROCESS

4.11.2.1 DEVELOP CREW ACTIVITIES LIST AND METABOLIC RATE PROFILES

To maintain required spacecraft internal temperature range, relative humidity, and air 

composition, crewmember metabolic rate profiles are necessary to quantify the 

crewmember contributions to total vehicle heat load and metabolic gas exchange during 

the mission phases. Establishing crew metabolic rate profiles for a given design 

reference mission should begin with development of the concept of operations and 

scenarios for nominal, off-nominal, and emergency operations. For each mission phase 

and relevant scenario, specify and sequence crew roles and activities (see HIDP

sections 3.2.3.1.2 Develop Concept of Operations and 4.1 User Task Analysis).
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Comprehensive analysis of crew activities in establishing metabolic rate profiles is 

critical for ensuring that the ECLS system is designed to accommodate nominal and 

peak transient thermal loads and metabolic byproducts without compromising the cabin 

environment. Figures 4.11.2.1-1 and 4.11.2.1-2 provide examples for developing 

metabolic rate profile. Figure 4.11.2.1-1 illustrates the breakdown of metabolic rates for 

each crewmember by mission phase and activity for a nominal scenario that includes 

spacesuit doffing. The contributions of each crewmember must be considered, 

especially if crewmember activities differ significantly during a given mission phase.

Phase Activity Duration 

(hours)

Elapsed 

Time 

(hours)

Met Rate (BTU/hr)

Crew Activities

Operator 1 Operator 2 Operator 3 Operator 4

Ascent Ascent 0.41 0.41 1600 1600 1600 1600

First Stage ignition until 

Circulation Burn 

complete

LEO Config Post-insertion 1.5 1.91 550 550 550 550 Go for On-orbit Ops, PSA 

activation

LEO RPOD Ops Coast to NC1 Burn 

until Docking 7.5 9.41 550 550 550 550

NC1 Burn, NPC Burn, NC2 

Burn, NH Burn, NSR Burn, 

TPI Burn, Proximity Ops, 

Docking.

Earth Orbit Operations

Post-Docking 

Activities 1 10.41 550 550 550 550

Deconfig from 

suited ops

0.5 10.91 800 800 650 650

O2 Reconfiguration, Doff 

and Stow suit. Avg

between don/doff (800) 

and assist (650) 0.5 11.41 650 650 800 800

Pre-Sleep 2 13.41 449 449 449 449

Sleep 8.5 21.91 300 300 300 300

Post-Sleep 3 24.91 449 449 449 449

FD1/FD2 Timeline

FIGURE 4.11.2.1-1 EXAMPLE OF MISSION TIMELINE WITH METABOLIC RATES

Metabolic rate timelines will provide the spacecraft developer with a tool to determine 

the system’s efficiency in managing human metabolic loads early in the design process. 

The developer must also determine the ability of the system to support peak loads while 

maintaining the 24-hour and 1-hour limits for atmospheric constituents during the 

different phases of the mission. For example, ascent and entry phases are expected to 

induce increased metabolic rates due to vibration, g-loads, and excitatory state of the 

crew. Figure 4.11.2.1-2 illustrates cumulative crew metabolic rate breakdown for launch 

phase and the use of a time-elapsed chart to show a representative metabolic rate 

timeline.
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Phase Duration 

(minutes)

Phase Elapsed Time 

(minutes)

Met Rate 

(BTU/hr) Crew Activities

Launch Suit Donning

Launch Operations 120 120 450 L-2 hours crew ingress vehicle

Ascend – part 1 15 135 1600 § First Stage ignition until Circulation Burn complete

Ascend – part 2 15 150 550

LEO Configuration 15 165 550 Go for On-orbit Ops, PSA activation

LEO Loiter 140 305 450

Transition fron Ascent to Orbits Ops Config until Suit Doff (two crew doffing 

at the same time)

Suit Doffing 800

§ 1600 BTU agreed to in Space Medicine EVA Working Group due to multi-axis acceleration/vibration, G-forces and neurosensory issues (i.e., stress, excitement)

300

400

500

600

700

800

900

1000

0 50 100 150 200 250 300 350

Metabolic Rate (BTU/hr)

Phase Elapsed Time (minutes)

Conceptual Crewmember Metabolic Rate Trend for Trans-Lunar Injection (TLI) Phase 

Elapsed Time (Preliminary)

Conceptual Metabolic Rate Trends

13

FIGURE 4.11.2.1-2 EXAMPLE OF METABOLIC RATE PROFILE

For the Commercial Crew and Multi-Purpose Crew Vehicle Programs, NASA provides 

metabolic load values for unsuited and suited activities in Appendix tables. Those 

values are based on a set of environmental conditions and crewmember assumptions, 

which are detailed in each Appendix. If the spacecraft conditions or crewmember 

characteristics vary from the assumptions, metabolic loads will differ from values in the 

tables and should be captured in the metabolic rate profile. For example, if pressurized 

suits are worn instead of shirtsleeves, insulation and convection properties must be 

adjusted accordingly. 

Where metabolic rate data are not available, the developer should use an evidencebased approach in determining values that accurately represent the crew’s physiological 

response during a particular mission phase. Resources available for this process 

include published in-flight data, space flight analog data, or applicable ground-based 

data from NASA laboratories or other aerospace physiology laboratories. NASA can 

provide assistance with adjusting values for metabolic loads or developing metabolic 

profiles. Failure to reassess metabolic loads may result in potential shortfalls of the 

ECLS system, thereby increasing the risk for loss of mission and/or loss of crew.

4.11.2.2 DEVELOP DESIGN SOLUTIONS

4.11.2.2.1 MODEL THERMAL LOADS

Throughout ECLS system design, human thermal response modeling should be 

performed to assess the interactive effects of the spacecraft cabin environment on the 

crew. A validated human thermal model must allow variable input for key parameters 

that include crewmember metabolic rate, crewmember size, cabin gas temperature, 
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cabin gas pressure, wall temperature, dew point, cabin gas free-stream velocity, and 

gravitational forces. The output of the model must represent the crewmembers’ reaction 

to the environmental cabin conditions and the impact that it will have on the cabin’s 

environment, including CO2 production, O2 consumption, and water production. 

Historically, NASA has used the 41-Node Man or Wissler models as a validated means 

of ascertaining the human physiological response to flight environments. 

By SDR, the developer should identify the validated model that will be used to perform 

analyses throughout the design process. Input data needed for each model may vary 

from the Commercial Human-Systems Integration Requirements example. In these 

cases, NASA will work with the developer to adjust assumptions and metabolic loads 

data for use as input to the model.

4.11.2.2.2 CABIN ATMOSPHERE QUALITY

Cabin atmosphere quality limits are identified and described in NASA-STD-3001 

Volume 2. As mentioned in the preceding paragraph, metabolic loads are affected by 

these cabin conditions. It is important that these parameters be used as inputs to the 

thermal models in order for the predicted outputs to be representative of acceptable 

cabin atmosphere. For cabin atmosphere specifications, refer to the following NASASTD-3001 requirements:

 V2 6006 Total Pressure Tolerance Ranges for Crew Exposure

 V2 6003 O2 Partial Pressure Tolerance Ranges for Crew Exposure

 V2 6013 Temperature Range

 V2 6010 Relative Humidity 

4.11.2.3 ITERATIVE AND INTEGRATED ANALYSES

Modeling analyses should be performed iteratively, as design concepts and crew 

activities are defined or modified. NASA insight into developmental analyses can be 

beneficial for checking assumptions and assessing progress toward meeting cabin 

atmosphere requirements. By CDR, an integrated analysis should be performed to 

include other life support hardware and actual metabolic loads.

4.11.3 METABOLIC LOADS DESIGN TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.11.3-1 are recommended for review by the NASA customer.
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TABLE 4.11.3-1 METABOLIC LOADS DESIGN TECHNICAL PRODUCTS

Technical Products

Phase 

A

Phase 

B

Phase 

C

Phase 

D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function allocation, 

and associated crew task lists. I U U U --- ---

Metabolic load timelines/profiles. --- I U U --- ---

A summary of modeling/analysis/evaluation 

performed to date, including human thermal 

modeling analyses and integrated metabolic loads 

analyses, and the influence on system design with 

links to the detailed analysis results.

Required per NPR 8705.2B. The validated 

metabolic model should be identified by SDR.

--- I U U --- ---

Integrated analysis of all subsystems demonstrating 

design capacity to manage human metabolic loads 

throughout all mission phases.

--- --- I U U ---

Verification plan. --- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are influenced by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

Summaries of Modeling, Analyses, and Evaluations

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-system integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how critical design decisions 

were assessed. According to NPR 8705.2B, updated summaries are to be provided at 

each design review through SAR. 

Architecture, Materials, and Interface Specifications

Drawings, materials, and interface specifications provide NASA with insight into humansystem integration technical details throughout the design process. 
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Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 
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4.12 DISPLAY FORMAT DESIGN

4.12.1 INTRODUCTION

Designing a spacecraft that features a glass cockpit presents many challenges, such as 

determining appropriate information architecture for limited display real estate; 

allocating functions to hardware versus software controls; and finding intuitive ways to 

manage a variety of input devices (e.g., cursor control devices, keypads, edge keys, or 

other console-based controls). These spacecraft cockpits often involve many unknowns: 

systems that have never before existed, hardware and software functions that have yet 

to be defined, and only a very small population of users and experts who have the 

experience to address design questions. Only rarely does a wealth of tried and true 

design solutions exist that can be mimicked. The designer is faced with developing 

software to meet the user’s needs, when it is unclear what those needs are and which 

design solutions are even possible. All of these challenges pose a risk to information 

availability in the cockpit, which can result in errors and ultimate threats to mission 

success and crew safety. 

Software displays, also referred to as “display formats,” provide the primary interface for 

a crewmember in a glass cockpit to command subsystems and monitor subsystem 

health and status data. Display formats must provide situational awareness, reduce 

crew workload, and enhance crew safety by providing readily understood graphical and 

textual subsystem information in a timely manner. This chapter describes the processes 

and activities that should be undertaken in the development of display formats and 

display standards to ensure human rating of vehicles and habitats.

The term “display standards” is used here to mean a set of user-interface specifications 

and guidelines developed and implemented to ensure a common design framework for 

all computer interfaces (i.e., all flight and system displays) used by crewmembers. 

These standards establish a consistent look and feel across all interfaces and specify 

consistent behaviors across all user-interface components of the same type. The 

purpose of the standards is to promote ease of learning, crew productivity, and mission 

safety by supporting a simple and consistent user environment. It is expected that crew 

transportation companies will develop, modify, and enforce display standards 

throughout the display development process.

4.12.2 ESTABLISHING A DISPLAY FORMAT DESIGN AND STANDARDS TEAM

Designing usable software systems requires multiple areas of expertise. The display 

format design team should be a multidisciplinary team, including individuals who (1) 

have content or domain expertisee.g., vehicle subsystems experts, (2) have process 

and design expertisee.g., human factors specialists, (3) have technical 

implementation expertisee.g., software developers, or (4) are users or representative 

usersideally crewmembers with space flight experience. It is important that all 

participants are able to openly offer their ideas and concerns, and that no one team 

member owns all the decision-making power. The work of the team should be a 

collaboration in which all team members’ viewpoints are valued and respectfully 

considered. The size of this team is an important consideration. A team that is too small 
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may not have the relevant representation and will not have the breadth of community 

buy-in of a larger team. A larger team can be difficult to manage and inefficient. 

Although the display format design team should perform the core display format design 

work, the process should ensure proper review and participation by other stakeholders 

as welle.g., management, vehicle integration groups, safety, training, procedure 

developers.

The development of display formats involves multiple phases, including definition of the 

display format layout and behavior, implementation of the formats, and final verification 

of the formats in flight software. These activities may be performed by the same or 

different organizations.

4.12.3 DOCUMENTS SUPPORTING THE DISPLAY FORMAT DESIGN EFFORT

The efforts of the display format design team should be supported by the following types 

of documents:

 Display development process document – a project-specific process document 

describing activities, including flows and timelines, roles and responsibilities of 

the various parties, review milestones, and final technical products.

o Some of the information in this document could be used to create a process 

document

 Program-level requirements document – requirements to ensure human rating, 

and safe and productive integration of the human and the system

o Derived from NASA-STD-3001

 Display format standards document – describes the design standards, templates, 

software component “look and feel,” colors, fonts, and so on, to promote 

consistency, ease of learning, and ease of use.

 Display format definition document (“dictionary”) – describes the detailed layout 

and behavior of each display format.

 Software requirements specification – detailed specifications for developing 

display formats; may contain the format dictionaries; points to the display 

standards document.

 Software development plan – describes the method of implementation of the 

display formats

 Other resources – human factors design guidelines documents, standard 

templates, icon libraries

4.12.4 HUMAN-CENTERED DESIGN ACTIVITIES FOR DISPLAY FORMAT DESIGN

Working within a design space where there are many unknowns means that iteration, 

revision, and refocusing are a necessary part of the process. Project goals, functions, 

designs, and standards may need to be revisited throughout the process as more 

information becomes available. Thus, special processes, methods, and policies are 

required when applying human-centered design to software user interfaces in a 

spacecraft.

Section 3.2 describes the Human-Centered Design process that should be followed in 

the development of all hardware or software products for human-rated vehicles and 
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habitats. The subsections that follow elaborate this process as applied to display format 

design.

4.12.4.1 FUNCTIONAL REQUIREMENTS DEFINITION

Given the unique nature of designing display formats for new spacecraft, functional 

requirements are not likely to be complete at the beginning of a project. Potential 

users/crew may assist in this definition process, but sometimes they themselves have 

had no previous experience in using this unique software. Software developers may be 

unsure about the functionality they will be able to provide through the display formats,

as system design often is still immature early in the life cycle. Thus, efforts to define 

functional requirements must begin early. 

Requirements should evolve throughout the design process, particularly once

prototypes are built. When crewmembers are able to see the capabilities in a concrete 

format within a scenario, they can see the potential of the system. They can begin to 

think of functions that may have been left out or need to be modified. Functional 

requirements should be allowed to mature throughout design instead of being locked in 

for implementation too early. 

Task analyses should progress throughout the design cycle, and the outcomes should 

be used to establish requirements for the displays. During requirements development, 

the focus should be crew needs and understanding the variety of ways in which the 

system may be used by crewmembers. The development and use of scenarios can be 

helpful in discussing and defining these requirements.

4.12.4.2 SCENARIO DEVELOPMENT

Scenario development often begins with an operational concept definition. This 

describes the working environment and typical activities involved in performing the tasks 

planned for various missions. Scenarios can begin as simple narratives, and evolve to 

include embedded display designs. Scenarios can be important and useful for designing 

usability evaluations. At a minimum, scenarios should be developed that address 

nominal or frequent operations, particularly difficult or troublesome tasks, and expected 

emergency or contingency situations. Make sure all members of the display format 

design team review and concur with the scenarios developed, as it is not uncommon for 

team members working in different domains to have very different ideas about expected 

scenarios. 

4.12.4.2.1 EXAMPLE QUESTIONS TO CONSIDER

With respect to display formats, examples of some challenging questions that might be 

considered during task analysis, scenario development, and concepts of operation 

include these:

 What will be accomplished by means of software versus hardware controls?

 How much automation is involved and what role does the crew play?

 Will all display formats be available on each display device?
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 Will there be default configurations (i.e., predefined sets of formats) for different 

tasks?

 How will crewmembers interact with the display formats and how will control of a 

format be shared, if it is shared?

 Are multiple instances of a display format possible? If so, how will real-time data 

updates and commands be handled?

 What insight will the crew have into system states and faults?

 How will system cautions and warnings be handled?

4.12.4.2.2 NUMBER AND TYPES OF DISPLAY FORMATS

Once decisions have been made about display device hardware, input devices, and 

software platform, it is important to scope the display format design effort by 

determining how many display formats will be needed and which categories of formats 

will be needed (e.g., summary formats, detailed subsystem formats, electronic 

procedures). Again, it will be important to first understand basic concepts of operation, 

i.e., how the crewmembers will work independently or in teams to monitor and 

command by means of display formats. It is prudent to begin work on a small subset of 

display formats that provide basic capabilities. Much will be learned from the initial 

design effort that can be applied to all remaining efforts for greatest efficiency.

4.12.4.3 TASK ANALYSIS

Section 4.1 describes task analysis, and many documented methods are available to 

accomplish this activity. Task analysis results become critical for interpreting many 

requirements and for developing procedures to be used in evaluations and in real-time 

operations. The challenge with display formats is that unlike in some of the more 

standard hardware task analyses, documenting many of the software-driven tasks may 

require prediction because, as previously mentioned, the planned tasks and capabilities 

may have never before existed; “experts” may have to make educated guesses.

4.12.4.4 CONCEPT PROTOTYPING

The human-centered design activities outlined in section 3.2.3 describe concept 

prototyping as part of the Visualize and Produce Design Solutions activity. Early 

concept prototyping is a method for visualizing, exploring, or demonstrating aspects of a 

software system. One of the initial goals of prototyping is to capture multiple ideas in a 

visual form so that they can be reviewed and discussed. The greatest benefit of 

prototypes is that they are concrete and tangible, thus making design discussions much 

easier.

Important aspects of early concept prototyping are (1) iteration and (2) increasing fidelity

of prototypes over time. Large amounts of time should not be spent on initial prototypes, 

because their purpose is short-lived and many changes will be made early on. For this 

reason, it is good practice to develop early prototypes with a rapid prototyping tool or a 

tool such as Microsoft PowerPoint. The first goal is to get the concept on paper so that it 

can be discussed and evolved. Time spent by developers on perfecting these early 

prototypes, or on building in interactivity or system models, is time wasted as the 

designs may quickly become obsolete. It is important to select prototyping tools that can 
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be used to make changes rapidly and easily. It is also beneficial if the prototyping tool 

can produce usable code, which saves software implementation time. 

Prototypes should progress in fidelity from early concept prototypes to integration 

prototypes as described below:

 Early concept prototype (“paper” prototype): static sketch used to illustrate design 

layouts and basic functions. These are often fragmentary, illustrating 

representative display formats or portions of formats.

 Interactive prototype: dynamic prototype with the ability for key functions to be 

demonstrated through user interaction. Still typically incomplete in functionality.

 Operational prototype: highly interactive prototype that may have some system 

models running in the background to enhance realism.

 Integration prototype: suite of high-fidelity, interactive prototype display formats 

integrated into an operational environment. Often used in high-fidelity simulations 

for training or verification.

Prototypes should be made available to all members of the design team and to 

stakeholders, for review and comment throughout the process. This helps ensure early 

buy-in, and no surprises late in the development life cycle that could result in costly 

redesigns.

When a custom software platform is being used, prototyping and display standards 

development must often occur somewhat in parallel. Standards should define the basic 

template and high-level standards. A standard template is important for ensuring a 

consistent approach to display format design. Prototypes should demonstrate and prove 

the standards; and finally, prototyping and evaluation results will lead to the need to 

document new standards or modify existing ones. In addition to a standard, 

documented template, an icon library should be established for the collection and use of 

a single, standard set of icons and symbols. This will avoid time being wasted by 

developers recreating common display objects, and will ensure a consistent “look and 

feel.”

4.12.4.5 HEURISTIC EVALUATION

Once prototypes are mature enough for evaluation to begin, a heuristic evaluation 

should be performed. This type of evaluation involves a human factors specialist 

reviewing the display format with respect to established program display format 

standards, and usability guidelines and principles. The result of this evaluation is a list of 

issues and redesign recommendations. Ideally, a heuristic evaluation should be 

performed before any crew-in-the-loop testing, as crew time is typically limited and 

should be reserved for feedback related to operational concerns, rather than obvious 

design issues and standards violations. Once the recommendations from a heuristic 

evaluation have been incorporated into the prototype, crew evaluations can proceed.

4.12.4.6 HUMAN-IN-THE-LOOP EVALUATION

The purpose of these evaluations is to determine the usability of the display formats in 

terms of the following: (1) Does the format support task performance? (2) Does it 
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promote efficiency? (3) Does it optimize workload and minimize errors? This part of the 

process is intended to be highly iterative. The design-evaluate-redesign approach 

ensures that problems are identified early, when the design is more changeable.

Human-in-the-loop evaluations, required per NPR 8705.2B paragraph 2.3.10.1, should 

be conducted in much the same way as a standard usability test. This testing is the core 

of the development process – an opportunity for the display formats to be used and 

evaluated within the context of a real-world task, and the opportunity to collect objective 

data in a structured way, instead of relying on subjective opinions. This testing can also 

be used to discover any issues with the concept of operations, written procedures, or 

the hardware involved in the task. It may also offer some preliminary task timeline 

information.

4.12.4.6.1 SCENARIO-BASED TESTING

Test sessions should be set up for one crewmember at a time. With very mature, 

simulation-level prototypes, crew-in-the-loop testing can involve teams. Testing should 

be scenario-based, whereby the subject completes a list of procedures designed to 

“exercise” all of the key human interface components and functions. Testing should 

include nominal, contingency, and/or particularly problematic scenarios.

4.12.4.6.2 PROCEDURES

Procedures should be developed specifically for the purpose of the test. Relevant team 

members should contribute to development of these test procedures to ensure that they 

are semi-realistic and formatted correctly. It will not be possible to test all components, 

functions, options, and so on, so it is important to work within the multidisciplinary team 

to select the subset of functions to be tested. Although procedures should be somewhat 

realistic, it is more important that the procedures require the crewmember to work 

through or exercise all of the preselected display components, functions, or operations. 

This may have a negative impact on realism, and you may receive some comments 

from subjects about this, but it is more important that all of the key functions be 

exercised. A decision will have to be made about use of paper versus electronic 

procedures, depending on the concept of operations, scenarios tested, and maturity of 

the electronic procedures.

4.12.4.6.3 TEST METHODOLOGY

A standard usability testing approach should be used. The goal in the test plan should 

be to have the crewmember/subject work through the display formats to perform semirealistic tasks. The evaluation should focus on all aspects of the format, including spatial 

layout, use of icons, proper terminology, consistency, and methods of interaction. 

Everything may not be functional, and inoperable functions can be skipped or simulated. 

Timing sessions is sometimes useful, but its usefulness may depend on the level of 

maturity of the prototypes. Tests of immature prototypes using subjects who are not 

familiar with the display formats will result in much more interaction between the test 

conductor and the subject, thus making completion times invalid. Later sessions with 

trained subjects and more mature prototypes can be timed. This information may help 

with mission planning and timelining. Completion times can also serve as meaningful 
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data if they can be compared to task completion times from previous vehicle designs. 

Automated data collection should be used where possible to capture errors during the 

session. 

After completing the task, crewmembers should be asked to complete a questionnaire 

or rating scale about various aspects of their experience with the interface. Subjects are 

often videotaped to capture frustration, confusion, fluctuations in their attention, and

verbal comments during their participation. A technique called “Verbal Protocol 

Analysis” (or “think aloud” method) is useful for collecting additional data. In this 

technique, subjects are asked to verbalize (i.e., speak their thoughts), while they are 

performing the task. This allows identification of points of confusion and frustration in 

the format or procedures. Once a crew-in-the-loop evaluation has been completed, the 

problems identified should be addressed through design iteration, as discussed in 

section 3.2.3 Human-Centered Design Activities. Results and recommendations for 

display format or prototype redesign will be documented in a report, and provided to the 

design team for use in the next iteration of the prototype. Comments or results related to 

standards will be forwarded to the format standards team or committee.

4.12.4.6.4 FREQUENCY OF TESTING

Crew-in-the-loop-testing should be done in an iterative fashion, with multiple tests being 

completed during development. As formats and scenarios mature, testing can become 

more structured, and error rates and completion times should begin to be calculated 

and tracked. Assessments of the path to compliance should be made with early checks 

regarding ability to meet the Human-Systems Integration Requirements and the Display 

Standards with the display formats designed. Testing should be performed on individual 

display formats early in the design process, and then testing should be done on 

integrated suites of display formats as the designs mature. A final “run for the record” 

test will need to be performed for verification of many of the requirements related to 

display formats. Once the display formats have been implemented in the spacecraft, a 

plan should be developed for post-deployment evaluation. This plan is to be developed 

to enable identification of any issues in the real-time operations environment that may 

be able to be addressed for the next vehicle block upgrade.

4.12.5 DISPLAY FORMAT STANDARDS

The key to ensuring consistency within and among display formats is the creation and 

use of display format standards. Consistency in display formats can increase usability 

(see section 4.2 Usability Evaluation), reduce workload (see section 4.3 Workload 

Evaluation), decrease learning time for users, and increase mission safety. For display 

designers and developers, the development of standards can reduce work time by 

providing a common set of templates and widgets. 

4.12.5.1 STANDARDS DEVELOPMENT PROCESS

The development of display standards uses an iterative process that begins before any 

design work is started; standards are updated and revised as displays are being 

developed. The display standards process consists of the following steps:
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 Determine the purpose of the standards

 Create a display standards committee with appropriate stakeholders

 Perform research and task analyses

 Develop standards and evaluate them

 Draft a display standards document and use an iterative process to refine and 

update standards 

 Perform a stakeholder review

 Implement standards and perform checks to verify that displays comply with 

standards

4.12.5.2 DETERMINE THE PURPOSE OF THE STANDARDS

The first step in developing display standards is to determine the purpose of the 

standards and their scope. Display standards can provide general guidelines based on 

good design and human factors principles, or they can explicitly call out rules and 

requirements that ensure absolute consistency among displays. In general, the larger 

the design team and number of displays, the more specific the display standards should 

be. Furthermore, it should be determined whether the standards will be specified at the 

user interface level for display designers, or at the programming (code) level for display 

programmers. Display standards without a clear purpose and audience may suffer from 

an unmanageable amount of information, leading to noncompliance. 

4.12.5.3 CREATE A DISPLAY STANDARDS COMMITTEE WITH APPROPRIATE 

STAKEHOLDERS

A display standards committee is responsible for making decisions about display 

standards, and for documenting, disseminating, and enforcing these standards. A 

committee creates a single point of contact for the determination and interpretation of 

standards. Having a single point of contact can minimize confusion and allow standards 

updates to flow down to design teams. Thus, it is important for all stakeholders to be 

represented on the display standards committee. The committee should include the 

following representatives:

 Crew 

 Human factors experts

 Safety experts

 Software developers

 Mission control and operations

 Procedure writers

Committee members need to be fully committed to the display standards process. 

Support of the process may include attending standing meetings, bringing standards 

issues to the committee for decisions to be made by the committee, helping with 

documentation and review, assisting with producing templates and common widgets, 

and disseminating information to design teams. Ideally, committee members will also be 

part of a design team, giving them an opportunity to record any problems with the 

current standards and to enforce standards. 
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Once the display standards committee is formed, the members should decide the 

methods for establishing standards, including how disagreements between committee 

members will be handled (e.g., two-thirds vote). The committee should also determine 

how new, recommended standards will be flowed to the committee, and then flowed 

down to design teams. For example, the committee can decide to create a master 

spreadsheet of all known standards issues that is updated according to feedback from 

design team leads. The committee can create and maintain a shared network folder that 

includes all standards documentation and templates. The method chosen by the 

committee for determining standards should be transparent to display designers; they 

should have easy access to documented standards. Committee members should 

decide how standards will be enforced. For example, the committee can hold standard 

compliance checks at various points in the display design process. During these 

checks, the design of displays can be compared against the standards, and any 

mismatches can be fed back to the designers. Lastly, the committee should establish 

goal dates for draft completion. This will ensure that the standards will be available 

when needed for display development. These and other process decisions of the 

committee should be documented and agreed on.

4.12.5.4 PERFORM RESEARCH AND TASK ANALYSIS

The process of developing new standards should begin by gathering information about 

users and their tasks, existing standards and guidelines, and hardware. It is important to 

understand users’ existing knowledge and experience because standards that conflict 

with user expectations may reduce the usability of displays. For example, certain 

symbols, colors, or terminologies may have familiar meanings to users that are based 

on their cockpit experience or other display interactions (e.g., the International Space 

Station). Users may be familiar with other standards documents from, for example, the 

Federal Aviation Administration, Department of Transportation, Military Standards, 

Institute of Electrical and Electronics Engineers, or other organizations, or the 

committee may draw on general human factors principles.

It is critical to understand the tasks that users will be asked to perform using the 

displays, and the environmental or situational requirements of those tasks. For example, 

displays that crewmembers need to interact with during dynamic phases of flight may 

need to have a larger font size than those used during nondynamic phases. Results 

from a task analysis (see section 4.1 User Task Analysis) should be used to make 

reasonable predictions as to how many displays will be needed and the type of 

information needed on each. 

Finally, information about vehicle hardware and software should be collected to 

understand the capabilities and limitations of the system. At a minimum, the size of the 

display device and software processing speed should be gathered.

4.12.5.5 DEVELOP STANDARDS AND EVALUATE

After initial task analyses, the next step is to start developing and documenting 

standards. Of course, task analysis should be ongoing as standards are developed and 

evaluated. Any updated knowledge about the vehicle, tasks, and crew should be 
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incorporated into iterations of the standards, as appropriate. As a reminder, the purpose 

of display standards is to ensure consistency between display formats used by 

crewmembers, by providing a common design framework. At a minimum, standards 

should specify a common template or templates, common design elements, and 

common methods of interaction. The intent of standards is not to provide rigid rules that 

reduce the usability of displays; rather, standards should provide regularity in how 

display elements are shown and interacted with to reduce learning time and errors. 

Standards can and should be updated if evidence becomes available, from task 

analysis, evaluation, or display development, that better implementations are available. 

A standards document should be developed hand-in-hand with development of 

prototype templates and widgets. These prototypes help to communicate the 

implementation and intent of standards. Widgets that can be duplicated and reused (i.e., 

copy-and-paste) provide display designers an easy method to replicate common design 

elements and maintain consistency.

The appropriateness of novel display standards (e.g., new symbols) should be 

evaluated to ensure that they contribute to the usability of displays, and do not lead to 

user errors (see section 4.2 Usability Evaluation for information on how to calculate 

error rates). 

4.12.5.5.1 DISPLAY FORMAT STANDARDS DOCUMENT CONTENT

Once a set of standards is established, the standards should be officially documented to 

ensure a single source of written information on standards decisions. The following is a 

suggested list of what should be included in the standards document.

Interaction with hardware. The standards document should include an overview of how 

hardware (e.g., physical buttons, cursor control devices, keypads, and other input 

devices) interface with display formats. Typically this section is intended to provide 

sufficient foundational information to document how users’ interaction with hardware 

affects software. The level of detail in this section will likely correspond to the “newness” 

of the hardware device. For example, if a standard computer mouse and keyboard are 

used, less information will likely need to be included than the information needed for a 

new type of control or interaction device. If different types of hardware are used during 

different phases of flight (e.g., dynamic phases above 3g versus on-orbit phases), this 

should be documented as well.

Cockpit configuration. An overview of how the cockpit is configured should be included 

in the display standards document. This will provide display design teams with 

information such as the number of displays available, their size and orientation, and the 

number of crewmembers who can interact with the displays at any one time. 

Definitions and common terms. All terms related to display components and modes of 

operation should be clearly defined to ensure that all display teams and software 

developers use a common language. Definitions may include names and descriptions of 

different types of keys or buttons, title bars, cursors, display regions, focus areas, and 

input/command-able areas.
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Interaction with displays. It is important to provide a description of how crewmembers

will interact with displays. For example, how crewmembers will input values or 

commands (e.g., through data entry fields, popups, or virtual keypads) should be 

documented. Other standards may describe cursor movement, navigation between 

displays, and error handling.

Automation and procedures. Documentation should be provided describing how 

automation (e.g., electronic procedures) interacts with display elements, if applicable. If 

crewmembers are able to control the level of automation or are able to inhibit automatic 

processes, this should be documented as well.

Common template. To have a unified look and feel, display formats should be built on

one or a few related common templates. Elements in templates can include the 

appearance and location of display format titles, time, navigational menus, and system 

health and status items. 

Static versus dynamic information, and areas for crew input or action. The standards 

document should specify how display elements that are dynamic (e.g., telemetry of 

vehicle states and data values) are distinguished from those that are static (e.g., 

reference information or labels). The document should specify how display elements 

that crewmembers can manipulate or change are distinguished visually from elements 

that cannot be changed by crewmembers. 

Colors. The display standards document should specify available colors, the use of 

which should be limited to a small set of highly distinguishable values. Color should not 

be used as the sole indicator of a state, because of potential issues with perception of 

color under different lighting conditions or crew visual abilities. Redundant information 

can be provided to supplement color (e.g., symbols, text, or other design features), and 

the standards document can specify these. A color table with a clear description of uses 

of color, and a method to produce the colors (e.g., red/green/blue values) is 

recommended. Existing color standards and conventions exist and should be followed 

unless there is a significant rationale for not following them. Example conventions 

include

 Yellow – caution or cautionary state

 Red – warning or emergency

 Blue or cyan – advisory

 Gray – unavailable function

 White – available / dynamic information

 Green – available information or normal state (noncautionary)

Icons. Icons are a common set of symbols that represent vehicle components (e.g., 

valves, switches, batteries, and tanks). The display standards document should specify 

common icons and their definitions. An icon table with images of icons and their 

meanings is recommended. Industry standard and conventional icons should be used 

wherever possible.
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Graphical elements. Standards should include specifications for available graphical 

elements and their behaviors, if applicable. Examples include line widths, the look and 

behavior of virtual buttons, and graphics used to group common elements together.

Time. A standard way to display and/or enter time values should be specified.

Data Display. Standards should specify how data are displayed; for example, units of 

measure, significant digits, and rate of change. Human-factors principles should be 

followed. For example, numerical data should be decimal aligned, units of measure 

displayed, and leading zeros suppressed for numbers greater than one. There should 

also be standards for displaying missing information.

Additional standards. The above items are not an exhaustive list of possible standards. 

All applicable standards that support consistency of displays should be included in the 

display standards document.

General rules for a well-written standards document:

 Write in simple and concise language

 Provide examples through images

 Provide a clear organization to the document

4.12.5.6 USE AN ITERATIVE PROCESS TO REFINE AND UPDATE STANDARDS 

DOCUMENT

As displays are being designed, new standards issues or need for clarifications may 

arise. An iterative process should be used to incorporate any updates, changes, or 

clarifications into the standards document and supporting materials such as prototype 

templates and widgets.

4.12.5.7 PERFORM STAKEHOLDER REVIEW

All relevant stakeholders should be given an opportunity to review and comment on the 

display standards draft document before it is released as an official document. 

4.12.5.8 IMPLEMENT STANDARDS AND PERFORM CHECKS TO VERIFY THAT 

DISPLAYS COMPLY WITH STANDARDS

After an official display standards document is released, all displays should be designed 

to comply with the standards set forth in the document. A checklist that lists all display 

standards can be a helpful tool in determining whether designs comply with the 

standards. Verification by inspection should be performed on all displays before their 

implementation on a spacecraft. Any inconsistencies between a display design and 

display standards will need to be resolved by a redesign of the display, or a waiver with 

appropriate rationale. 

4.12.6 DISPLAY FORMAT DESIGN TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.12.6-1 are recommended for review by the NASA customer.
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NASA personnel can assist with any or all of these activities, as facilities, expertise, and 

recent vehicle design experience are all in place (e.g., rapid prototyping lab, library of 

display components and templates, display standards, preliminary flight system 

designs, data collection tools, and human engineering expertise). 

TABLE 4.12.6-1 DISPLAY FORMAT DESIGN TECHNICAL PRODUCTS

Technical Products

Phase A Phase 

B

Phase 

C

Phase D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function allocation, 

operational use scenarios, and associated crew task 

lists.

I U U U --- ---

A summary of modeling/analysis/evaluation 

performed to date and the influence on system 

design with links to the detailed analysis results.

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10.

--- --- I U --- ---

Software Development Plan I U U --- --- ---

Display Format Standards Document, including icon 

library and display dictionaries I U U --- --- ---

Verification plan. --- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are influenced by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

Summaries of Modeling, Analysis, and Evaluation

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-system integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how critical design decisions 

were assessed. According to NPR 8705.2B, updated summaries are to be provided at 

each design review through SAR. Also in paragraph 2.3.10, the use of human-in-theloop evaluation is a required method to progressively demonstrate that the operational 

concept meets system requirements for operational safety, efficiency, and user interface 

design. 
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Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 

Before the System Requirements Review (SRR)

 Draft of Software Development Plan

 Concept(s) of Operation

 Operational and Use Scenarios

 Early task lists and task flows

 User and system function allocation tables

 Commercial trade studies

 Preliminary “paper” prototypes 

 Preliminary templates

 Prototype reviews

 White papers

 Draft of display format development process document, referenced by the 

Software Development Plan

 Early draft of display format standards document, including plans for an icon 

library

 Report on proof-of-concept / pathfinder display format design effort after draft 

process plan

 Draft requirements verification strategies

SRR through Preliminary Design Review (PDR)

 Final Software Development Plan

 Updated draft of display format standards document 

 Icon library

 Updated Concepts of Operation

 Revised operational and use scenarios

 Updated task lists and task flows

 Updated function allocation tables

 Interactive prototypes

 Draft procedures

 Prototype reviews

 Commercial trade studies

 White papers

 Reports from human-in-the-loop evaluations of single interactive display formats

 Draft display dictionaries
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PDR through Critical Design Review (CDR)

 Updated Concepts of Operation

 Task lists and task flows

 Updated function allocation tables

 High-fidelity prototypes

 Evaluation reports

 White papers

 Reports from human-in-the-loop evaluations of integrated suites of mature 

display formats

 Reports from phase-based human-in-the-loop evaluations of integrated suites of 

operational display formats

 Final display dictionaries

CDR

 Updated Concepts of Operation

 Vehicle display formats

 Verification activities related to display formats

Post Delivery

 In situ surveys and Reports

 Post-mission questionnaires, debriefs and interviews

 Lessons learned

4.12.7 REFERENCES

Holden, K. L, Malin, J. T., & Thronesbery, C. (1998). Guide to designing usable software 

systems in advanced technology environments (JSC Technical Report JSC-28517).

Houston, TX: Johnson Space Center.

Turner, S., Bockman, M. Cain, L., Morgan, J., & Barber, D. (2009). CEV Display Format 

Development Process (Draft).
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4.13 USER INTERFACE LABELING DESIGN

4.13.1 INTRODUCTION

Labels are an essential component of a user interface. They provide identifying or 

instructional information to the operator for activities such as finding items, following 

procedures, avoiding hazards, locating emergency equipment, and orienting to their 

environment. It is important that labels support recognition, identification, and operation; 

provide operationally relevant and consistent information; and be readable to the 

intended user in the design environment. Additional information about labeling can be 

found in NASA/SP-2010-3407 Human Integration Design Handbook (HIDH) section 

10.7 Labels.

4.13.1.1 PURPOSE

This section provides an overview of the International Space Station (ISS) crew 

interface labeling process and is intended to aid the implementation of labeling 

requirements in NASA-STD-3001. This overview is to serve as a guide for spacecraft 

and equipment developers to facilitate design of labeling for user interfaces, through the 

use of the human-centered design process and ISS labeling examples. Additional 

examples from the Constellation Program can be found in CxP 70152 Constellation 

Program Crew Interface Labeling Standard.

4.13.1.2 BACKGROUND

The ISS crew interface labeling process is a collaborative effort between the hardware 

developers, procedure writers, mission operations personnel, crew office, and Flight 

Crew Integration. ISS standards have been established to promote consistency in 

labeling style, content, and operational nomenclature. To facilitate usability by NASA 

crewmembers, the developer is encouraged to use the ISS standards described in this 

process.

4.13.2 USER INTERFACE LABELING PROCESS

4.13.2.1 DEVELOP CONCEPT OF OPERATIONS AND CREW TASK LIST

Crew task lists are necessary for identifying crew operational interfaces and related 

labeling needs. Spacecraft crew interface designs should begin with development of the 

concept of operations and scenarios for nominal, off-nominal, and emergency 

operations. For each mission phase and relevant scenario, specify crew roles and 

activities and develop crew task lists. See HIDP sections 3.2.3.1.2 and 4.1 for 

description of concept of operations and developing crew task lists. 

4.13.2.2 DEVELOP DESIGN SOLUTIONS

4.13.2.2.1 LABELING DESIGN PLAN

As crew tasks and equipment/system interfaces are defined, labeling designs should be 

planned and documented in a Labeling Design Plan. The Labeling Design Plan should 

contain detailed descriptions and illustrations or photos of all necessary user interface 
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labels. Descriptions are to include label information such as text content, text size and 

font style, colors, dimensions, materials, location and placement on the equipment or 

system, and orientation with respect to the equipment/system and expected user 

working orientation. Label design for user interfaces should consider the item being 

labeled, the task at hand, adjacent or concurrent tasks and interfaces, and any need to 

distinguish interfaces. Equipment and system labels must also be consistent with 

operational procedures that identify controls to be operated, displays to be monitored, 

and so on. Text size should be in accordance with NASA-STD-3001, Volume 2 and be 

sans serif style for optimum readability. The preferred font styles used on the ISS are 

Helvetica and Arial.

The content of the Labeling Design Plan depends on the size of the hardware project. 

Information for a single piece of hardware may be contained on a single label drawing, 

or on one single top-level assembly drawing. For larger hardware projects, such as an 

entire vehicle, the information may be a consolidated package of several label drawings 

and charts identifying label locations, orientations, content, and design, or could be a 

document that details where the label information is depicted in a hardware project’s 

drawing package.

4.13.2.2.2 CREW INTERFACE LABEL TYPES

An approach for organizing a Labeling Design Plan is to organize by label types. To 

facilitate implementation, NASA categorizes labels into types based on their function:

 Hazard, Caution and Warning, Emergency Use

 Location Coding and Orientation

 Instructional

 Control and Display Panel

 Equipment Identification

 Inventory Management System (IMS) Barcode

 Cable and Hose Connector-end

By virtue of the intended label function, each type of label has unique design 

considerations that are described in the following paragraphs. For commonality with the 

ISS, and to minimize training and risk of error, NASA standards for panel labeling and 

operational nomenclature are recommended. Refer to SSP 50783 Labeling of 

Intravehicular International Space Station Hardware: Design Development Process, 

SSP 50005 International Space Station Flight Crew Integration Standard section 9.5 for 

NASA labeling standards, and SSP 50254 Operations Nomenclature.

4.13.2.2.2.1 HAZARD, CAUTION AND WARNING, EMERGENCY USE LABELING

Hazard, caution and warning, and emergency use labels are intended to convey critical 

information in an appropriate context. Hazard labels should be applied to equipment or 

components that may be hazardous to crew or equipment. Examples of hazards include 

biohazards, electrical shock hazards, and trash containing toxic or otherwise hazardous 

waste to which crewmembers may be exposed. Space vehicles designed for NASA 

crew use should comply with ISS label design standards for hazard, caution and 

warning, and emergency use. The commonality reduces training time and minimizes 
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confusion or error because NASA crewmembers are familiar with the design. Figure 

4.13.2.2.2.1-1 is an example hazardous waste label that can be found in JSC 27260 

Decal Process Document and Catalog and satisfies the requirement in V2 7069 

Labeling of Hazardous Waste.

FIGURE 4.13.2.2.2.1-1 ISS HAZARDOUS TRASH IDENTIFICATION LABEL (SDG32105751)

Caution and warning labels should be used to indicate special circumstances, such as

keep-out zones, reduced clearance, sensitivity to electrostatic discharge, stored energy, 

or an unprotected hot surface that may cause startle reaction. Generally, caution and 

warning labels are distinguished by the use of yellow and black diagonal striping for 

intravehicular activity (IVA) applications. Gold and black are used for extravehicular 

activity (EVA) applications. Specifications for the striping pattern can be found in SSP 

50005 ISS Flight Crew Integration Standards paragraph 9.5.3.1.13 Caution and 

Warning Labels Design Requirements. Figure 4.13.2.2.2.1-2 is an example 

caution/warning label that can be found in JSC 27260 Decal Process Document and 

Catalog.

FIGURE 4.13.2.2.2.1-2 ISS CAUTION/WARNING PINCH POINTS LABEL (SDG32105057)

Emergency use labels should be used to identify special-use items such as fire 

extinguishers, fire ports, emergency exits, and connectors that are to be disconnected in 

an emergency. Emergency-use labels are distinguished by the use of red and white 

diagonal striping. Specifications for the striping pattern can be found in SSP 50005 ISS 

Flight Crew Integration Standards paragraph 9.5.3.1.13 Caution and Warning Labels 

Design Requirements. Figures 4.13.2.2.2.1-3, -4, and -5 are example emergency-use 

labels that can be found in JSC 27260 Decal Process Document and Catalog.
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FIGURE 4.13.2.2.2.1-3 ISS FIRE PORT LOCATION CODE (SDG32108589)

FIGURE 4.13.2.2.2.1-4 ISS PORTABLE FIRE EXTINGUISHER PANEL DOOR LABELS 

(SDG32107729)

FIGURE 4.13.2.2.2.1-5 ISS EMERGENCY DISCONNECT LABEL (SDG32106342)

For commonality with ISS to minimize training and risk of error, NASA standard or 

conventional hazard labels or icons are recommended. Refer to JSC-27260 Decal 

Process Document and Catalog for NASA standard labels that can be produced by the 

Decal Design and Production Facility (DDPF). 

4.13.2.2.2.2 LOCATION AND ORIENTATION LABELING

Location coding and orientation labels are intended to provide location and direction 

information. On the ISS, location coding is an alphanumeric coding system used to 

uniquely identify internal locations to facilitate identification of equipment location, 

stowage areas, or emergency-use equipment location. See SSP 30575 Space Station 

Interior and Exterior Operational Location Coding System for guidance on location 
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coding. Orientation labels provide needed position cues to crew in the absence of 

gravity. When attached to the ISS, interior visiting vehicle orientation should correspond 

with the ISS reference orientation, which can be found in applicable Interface 

Requirement Documents or in SSP 30575. Figure 4.13.2.2.2.2-1 is an example of 

orientation placards used on the ISS and available from DDPF.

FIGURE 4.13.2.2.2.2-1 ISS CREW PREFERENCE LOCATION MARKING LABELS 

(SDG32106315)

4.13.2.2.2.3 INSTRUCTIONAL LABELING

Instructional labels are useful for providing cues on how to operate hardware, or 

augmenting operational procedures to which crewmembers have been trained or that 

must be performed quickly in an emergency situation. Instructional labels range from 

one-line cues, such as “Lock” or “Press to Activate,” to step-by-step instructions for 

hatch operation. Iterative design and evaluation by representative users performing the 

intended operations should be used in developing instruction labels. Figure 

4.13.2.2.2.3-1 shows a sample “Lock” cue and Figure 4.13.2.2.2.3-2 shows a sample 

ISS hatch instruction label.
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FIGURE 4.13.2.2.2.3-1 SAMPLE “LOCK” INSTRUCTION LABEL

FIGURE 4.13.2.2.2.3-2 SAMPLE ISS HATCH OPENING INSTRUCTION LABEL
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4.13.2.2.2.4 CONTROL AND DISPLAY PANEL LABELING

Control and display panel labels are intended to convey operationally relevant 

information about function or usage. All input and output devices that crewmembers

may operate or monitor are to be clearly and succinctly labeled. Figure 4.13.2.2.2.4-1 is 

a sample control panel illustrating how power switches are to be labeled with the 

equipment/system controlled and the “ON” and “OFF” positions, and how connector 

ports are to be labeled with the connecting cable type (e.g., power, 1553 data, Ethernet) 

and port identification code (e.g., J11). The sample also illustrates the ISS convention 

for labeling circuit breakers using the acronym “CB” and the positions “OPEN,” 

“CLOSE,” and “TRIP” to provide clear indication of the circuit breaker status. One power 

switch is reserved for emergency use, as indicated by the red and white striping around 

the control and labeling. One indicator light display is labeled with its function for smoke 

indication. Note that labels are typically located above and centered with respect to the 

control or display and that all text is consistently oriented with respect to the operator’s 

expected working orientation. Grouping lines are used to visually distinguish related and 

unrelated controls and displays.

FIGURE 4.13.2.2.2.4-1 SAMPLE ISS CONTROL-PANEL LABELING

4.13.2.2.2.5 EQUIPMENT IDENTIFICATION LABELING

Equipment labels are intended to identify operationally and functionally relevant pieces 

of hardware, equipment, subsystems, or components that crewmembers may operate. 

Registered operational nomenclature should be used to identify hardware and 

equipment; see paragraph 4.13.2.2.3 Operational Nomenclature. Equipment labeling 

should be sized and located so that crewmembers can easily see, recognize, and 

distinguish items when they are needed. Identification labeling is used to identify control 

panels (such as in Figure 4.13.2.2.2.4-1), cables and hoses (such as in Figures 

4.13.2.2.2.7-1, -2, and -3), and equipment, as shown in Figure 4.13.2.2.2.5-1. For 

hardware and equipment, including cables and hoses, identification labeling includes 

part number and serial number to further identify the item.
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FIGURE 4.13.2.2.2.5-1 ISS HARDWARE IDENTIFICATION LABEL (SDG32107015)

4.13.2.2.2.6 INVENTORY MANAGEMENT SYSTEM BARCODE LABELING

Typically, items that are transferred to the ISS are registered in the established ISS 

inventory management system (IMS) for inventory and/or on-orbit tracking purposes. 

The IMS is used to track items that may be replaced, resupplied, or temporarily stored 

on the ISS. The IMS is also used to catalog and track items that are on board the ISS. 

Therefore, items that are transferred to the ISS are registered in the ISS IMS system for 

a unique tracking number and have an IMS barcode label applied. IMS barcode labels 

can be separate from or combined with equipment identification labeling. Figure 

4.13.2.2.2.6-1 shows a combination identification and IMS barcode label that is 

available from the DDPF.

FIGURE 4.13.2.2.2.6.-1 SAMPLE ISS COMBINATION IDENTIFICATION AND BARCODE 

LABEL (SDG32108325)

4.13.2.2.2.7 CABLE AND HOSE CONNECTOR-END LABELING

Connector-end labels are intended to provide clear and succinct information needed by 

crewmembers to correctly match mating connector ends. Connector-end labels are to 

be implemented on all cables and hoses that may be connected or disconnected by 

crewmembers. Flag-style labels, as shown in Figure 4.13.2.2.2.7-1, are easier to see 

and read and are preferred, especially for use on connector ends that crewmembers will 

operate regularly or nominally, or will need to locate, identify, and operate during 

emergencies. Alternatively, band-style labels (shown in Figure 4.13.2.2.2.7-2) which 

completely wrap around, are acceptable on cables and hoses that are for nonemergency use or are operated infrequently, such as utility cables installed behind 

equipment racks that may be operated only when equipment is replaced.
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FIGURE 4.13.2.2.2.7-1 SAMPLE ISS FLAG-STYLE LABEL

FIGURE 4.13.2.2.2.7-2 SAMPLE ISS BAND-STYLE LABEL

Figures 4.13.2.2.2.7-3 and 4.13.2.2.2.7-4 illustrate ISS connector-end labeling 

conventions for an electrical cable and a fluid hose, respectively. Generally, 3 lines of 

text are used.

Line 1: Identifies either the name of the hardware that the cable or hose is part of or a 

connector identification code. Use of the hardware name is recommended on long 

cables or hoses where the connector end may be far from the base hardware, such as 

long utility cables connecting equipment to power. When a connector identification code 

is used with electrical cables, the cable end plugs are coded with “P” and a number, and 

the hardware receptacles are coded with “J” and a matching number. Electrical 

connector gender (pins or sockets) is immaterial to connector coding. Within a given 

hardware system, ensure that unique connector identification code numbers are used 

for each connector. Hose connectors are coded with “F” on the female end and “M” on 

the male end.

Line 2: Identifies the hardware that the connector end will connect to. Registered 

operational nomenclature should be used to identify the hardware; see paragraph 

4.13.2.2 Operational Nomenclature.

Line 3: Identifies the receptacle on the hardware that the connector end will connect to. 

The connect-to text is to match the labeling text on the hardware receptacle. Electrical 

connector receptacles are coded with “J” and a number that matches the connector end 

number. “P” and “J” coding are to be used only with electrical connectors and 

receptacles.
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FIGURE 4.13.2.2.2.7-3 SAMPLE ISS ELECTRICAL CABLE LABELING

FIGURE 4.13.2.2.2.7-4 SAMPLE ISS FLUID HOSE LABELING

4.13.2.2.3 OPERATIONAL NOMENCLATURE

For operational consistency, NASA and the ISS use a managed set of operational 

nomenclature and a defined process to assign operationally relevant nomenclature to 

equipment and systems. The OpNom process also manages standardized 

abbreviations, including acronyms. If needed, NASA will assist the developer in 

obtaining OpNom through the OpNom process. Registered OpNom is used on ISS 

labels for identifying hardware and software, in procedures, on displays, and in 

communications between flight crew and ground support. Equipment, controls, and 

displays with which the NASA crew will interface are to be identified in accordance with 

SSP 50254 Operations Nomenclature (CH10008).

4.13.2.2.4 LABEL DRAWINGS

The NASA DDPF produces flight-certified labels for the ISS. If the developer chooses to 

request DDPF production of flight labels, the labels must be ordered from the JSC27260 Decal Process Document and Catalog or engineering drawings of labels must be 

provided with the DDPF request. The engineering drawings for DDPF label production 
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must contain the information in Table 4.13.2.2.4-1. Drawings for custom labels to be 

produced by DDPF should be provided to NASA for inspection at design reviews. 

Engineering drawings of labels in the decal catalog may be requested from NASA. If 

needed, NASA will assist with preparation and submittal of NASA DDPF label orders on 

JSC Form 733 Decal Design and Production Facility Support Request.

TABLE 4.13.2.2.4-1 DDPF LABEL DRAWING DETAILS

Label Drawing Details Notes

Material

See JSC-27260 paragraph 5.2.1.1 Recommended 

Decal or Placard Base Material for IVA Applications 

or 5.2.1.2 Recommended Decal or Placard Base 

Material for EVA Applications

Adhesive DDPF uses 3M #966 or NASA-approved equivalent

Color Specified per FED-STD-595

Character Style and Size Specify font style (Helvetica or Arial preferred), size

Dimensions Specify in drawing

Text and/or Graphics Details Specify in drawing 

4.13.2.2.5 LABELING MATERIALS

The JSC-27260 Decal Process Document and Catalog paragraph 5.1 provides material 

safety requirements and recommended flight-certified material for intravehicular labels. 

To be approved for flight to the ISS, labeling materials must meet requirements and 

restrictions for flammability, odor, toxic off-gassing, fungus, and polyvinyl chloride. Refer 

to JSC-27260 for material specifications. 

If the developer chooses to request label production from DDPF, the materials in Table 

4.13.2.2.5-1 are available and approved for flight use and on the ISS in accordance with

SSP 30233 Space Station Requirements for Materials and Processes as implemented 

by JSC 27301 Materials Control Plan for JSC Space Station GFE. Note that there may 

be restrictions on use of some materials because of environmental or other use 

considerations.
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TABLE 4.13.2.2.5-1 NASA-APPROVED LABELING MATERIALS

Materials Notes

Aluminum, photosensitive Metalphoto, Dye-N-Seal

Nomex

HT 90-40, HT10-41

When using Nomex labels with adhesive 

backing (non-sewn labels) the DDPF will 

cut the labels using a laser or heat knife to 

prevent fraying of edges. In the event that 

the laser or heat knife is not available, 

approved fray-check material will be 

applied to prevent fraying of edges. DDPF 

customers should include this information 

as a note on new engineering drawings for 

Nomex labels (non-sewn).

Polycarbonate Lexan 8A35-112, 8A13-112

Polycarbonate laminated photosensitive 

polyester 

3M or NASA-approved equivalent with 

label guard 3M # 821

Polycarbonate (Lexan) laminated paper

Hammermill or Canon laser color, or 

Cardstock/K-10, etc., laminated with ID 

Mark Polycarbonate P/N 8794

Vinyl Gerber Scotchcal 220, Starliner

Polyester Brady, Intermec, and Tedlar

Polyolefin Cryo-Babies

If the DDPF is not used for label production, materials used to fabricate flight decals and 

placards must be certified for flammability, toxic off-gassing, odor, fungus resistance, 

and thermal vacuum stability for uses with short-term low Earth orbit (LEO) exposure, 

and for thermal vacuum stability, atomic oxygen and ultraviolet resistance, and thermal 

cycling for uses with long-term LEO exposure. 

Decal materials typically used on the ISS include paper stocks, vinyl (2 - 4 mil), 

polyester film, photosensitive films, and Nomex cloth. Placard materials include Lexan, 

acrylic, and polyester-based transparent films. Aluminum, sheet metals, stainless steel, 

and various plastics can also be used to manufacture placards for more harsh 

environments.

4.13.2.3 ITERATE DESIGNS, TEST, AND EVALUATE

Labeling designs should be evaluated by representative users performing 

representative operations and in conjunction with related usability evaluations, workload 

assessments, task analyses, or error analyses. Labeling evaluations are primarily 

subjective and should focus on assessing clarity and accuracy of the labels for their 

intended operational purpose. Operational procedures should be evaluated along with 

labeling to ensure consistency where labeled items are referenced. Evaluation results 
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should be used to iteratively improve designs, and changes should be updated in the 

Labeling Design Plan. 

4.13.3 USER INTERFACE LABELING DESIGN TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table

4.13.3-1 are suggested for review by the NASA customer. 

TABLE 4.13.3-1 USER INTERFACE LABELING DESIGN TECHNICAL PRODUCTS

Technical Products

Phase 

A

Phase 

B

Phase 

C

Phase 

D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function allocation, 

and associated crew task lists. I U U U --- ---

User interface Labeling Design Plan. I U U U --- ---

Operational nomenclature proposals/requests. I U U U --- ---

Operational nomenclature approvals/registration. I U U --- ---

A summary of modeling/analysis/evaluation 

performed to date and the influence on system 

design with links to the detailed analysis results.

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10.

--- --- I U --- ---

Verification plan. --- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are influenced by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

Summaries of Modeling, Analyses, and Evaluations

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-system integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how critical design decisions 

were assessed. According to NPR 8705.2B, updated summaries are to be provided at 

each design review through SAR. In accordance with the requirements in NPR 8705.2B 

paragraph 2.3.10, the use of human-in-the-loop evaluation is a method required for 

progressively demonstrating that the operational concept meets system requirements 

for operational safety, efficiency, and user interface design. 
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Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 
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4.14 OCCUPANT PROTECTION DESIGN

4.14.1 INTRODUCTION

Occupant protection focuses on crewed spacecraft features designed to control hazards 

and limit injury risks presented by excessive loads to crewmembers due to transient 

accelerations (≤0.5 second) or insufficient crew restraint during dynamic phases of the 

mission such as ascent abort and Earth landing. It is important that the occupants be 

protected from injury without excessive design implementations that lead to 

unnecessary vehicle weight and complexity. Approaches to ensure safety, such as 

those used in the commercial aviation and automotive industries, provide a foundation 

for occupant protection in human-rated space vehicles; however, their application to 

crewed spacecraft requires modification to meet NASA human-systems standards 

(NASA-STD-3001) that are applicable to all NASA human space flight (HSF) programs.

Proper support and restraint of body components can reduce the risk of injury and must 

be addressed by designers of the vehicle and the pressure suit system (if included). 

Many factors affect the likelihood of injury during dynamic flight events. Extrinsic factors 

include vehicle-specific factors (G-loading, velocity change, rate of acceleration onset, 

acceleration profile, load paths, load distribution, deflection of spacecraft structure, and 

collapse of habitable volume) and crew factors (bone and soft-tissue compression, 

tension, joint extension, flexion, shear-force magnitudes and directions, deflections of 

body components). Intrinsic factors relating to the crew include age, gender, physical 

condition, deconditioning due to space flight, and degree of muscle tension. Reliable 

injury-predictive tools and injury criteria are required to ensure that human-rated 

spacecraft be designed with the appropriate level of occupant protection.

4.14.1.1 APPLICABLE REQUIREMENTS

Occupant protection requirements are specified in NASA-STD-3001 Volume 2, section 

6.5. These requirements are in place to control hazards and limit injury risk presented 

by excessive crew loads due to high accelerations or insufficient crew restraint, 

particularly during abort and landing scenarios. 

 Acceleration Injury Prevention [V2 6069]

 Injury Risk Criterion [V2 6070]

Additional information that supports system design for occupant protection is provided 

by section 6.5 of the NASA Human Integration Design Handbook (HIDH), NASA/SP2010-3407.

4.14.2 OCCUPANT PROTECTION DESIGN PROCESS

Designing a spacecraft to carry humans into low Earth orbit or beyond and returning 

them safely to Earth presents unique challenges because of the varying environments 

they must withstand during the ascent, descent, and landing phases of flight. Vehicle 

design solutions may range from a winged to lifting body, a biconic to a capsule shape
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with a wide range of nominal and off-nominal trajectories, cross-range capabilities, 

deceleration means, and landing modes (e.g., land, water, rocket, airbag). Ascent abort 

methods include puller and pusher rockets that may be used at various points from the 

launch pad to high atmospheric altitudes. During all phases of flight, the crew will be 

exposed to accelerations of widely varying intensity, duration, and orientation. 

Therefore, simple adoption of standardized methodologies of injury assessment from 

other industries (such as commercial aircraft) is not feasible for many spacecraft. Each 

vehicle’s design solution results in a unique set of transient acceleration loadings on the 

flight crew, and thus necessitates unique methods to achieve occupant protection to 

NASA’s human-systems standards. This section is intended to provide a guide to the 

process that may be used to evaluate compliance with NASA standards on occupant 

protection, but it is not an exhaustive description of the methods needed to implement 

the process.

4.14.2.1 RECOMMENDED BEST PRACTICES

The reader should identify industry best practices to use during design and testing. A list 

is provided by NASA in the HIDH.

Crewmembers may be subjected to forces and accelerations during mission scenarios 

such as nominal, off-nominal, and contingency landing and ascent aborts, that may 

cause serious injury if not adequately mitigated. By utilizing methods for evaluating 

occupant protection system designs, predictions of injuries for acceleration load cases, 

seat designs, and seat locations can be developed. These predictions can be used to 

formulate recommendations to improve the spacecraft design to prevent or mitigate 

these injuries to the acceptable levels described by NASA human-systems standards. 

4.14.2.2 DEFINE LANDING CONDITIONS AND LANDING LOADS

Because of the complexity and cost of manufacturing a new spacecraft, much of the 

design work for assessing and controlling accelerations and determining the effects on 

structural integrity and crew safety during contingency, nominal and off-nominal landing 

scenarios, and aborts may be based on analytical methods. As a result of the inherent 

uncertainty and natural variation of environmental factors affecting impact conditions, 

landing assessments are often performed using a probabilistic approach, including 

consideration of vehicle-specific worst-case scenarios. This section provides a highlevel overview of the process that may be used to establish landing conditions due to 

environmental factors and the subsequent down-selection process to a subset of cases 

for detailed crew injury assessment. 

4.14.2.2.1 ENVIRONMENTAL CONDITIONS AND LANDING DISTRIBUTION DEFINITION

Parameters that affect vehicle landing orientation and relative velocity should be 

included in landing probabilistic analysis to accurately predict landing probabilities. 

Some of the parameters that factor into the analysis are parachute performance, hang 

angle, wind speed, and sea state (e.g., wave height, frequency, angle, shape, direction) 

or terrain (e.g., slope, soil conditions). Because some of the parameters are correlated 

(i.e., horizontal wind speed and sea state), a probabilistic approach may be preferable 

to reduce the number of possible conditions for landing. The output of this analysis 
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describes the initial conditions of the vehicle orientation and dynamics in relation to the 

water or land surface. These parameters should include normal velocity; relative angle 

of impact; roll, pitch, and yaw angles; and horizontal and vertical velocities. This process 

will need to be conducted for all nominal and for select off-nominal and contingency 

landing environments and vehicle landing conditions based on program-specific 

requirements for design and verification. The off-nominal and contingency landing 

environments may include parachute-out conditions, loss of guidance or roll control, 

failure of air bags or other landing systems, off-target landing locations, pad- and 

ascent-abort landing conditions, and so on.

4.14.2.2.2 CRITICAL LANDING CASE SELECTION METHODOLOGY

Once a distribution of landing parameters is generated, a systematic method for 

selecting critical landing cases for further analysis is necessary. Many methods exist for 

determining the selected cases. Two methods will be discussed here: the Boundary 

Selection Method and the Response Surface Selection Method. For either method, 

success criteria will be developed on the basis of the probability of occurrence and 

acceptance of risk under each condition. 

4.14.2.2.2.1 BOUNDARY SELECTION METHOD

The intention of this selection method is to define a boundary along the distribution that 

defines the acceptable and unacceptable landing cases for factors such as system 

failures, horizontal and vertical landing velocity, impact angle, wave state, and soil 

condition. An initial boundary is defined that includes the majority of landing conditions 

based on a probabilistic distribution, with variables assessed either independently (such 

is the case for random failures) or dependently (for conditions such as wave state, wind, 

and horizontal velocity, which are highly correlated). Typically, goals such as 3-sigma 

dispersions are established to define the certified boundary. The system will then be 

designed in such a way that all cases on one side of the boundary will be acceptable 

and meet all the crew injury requirements and the cases on the other side will not be 

certified cases and may be controlled by means of operational controls on flight 

operations (i.e., placards) or accepted as residual risk. Additional analysis must be 

conducted to show that the cases inside the boundary satisfactorily meet the occupant 

protection requirements, else either the design must be modified or the offending 

environmental conditions controlled through placards to prevent the system from 

operating outside of the certified conditions.

Once this boundary is defined satisfactorily, cases near the boundary on each side are 

selected for further analysis. The method for selecting the cases should be justified and 

the number of cases should be justified statistically. After analysis, the boundaries may 

have to be modified to capture a broader distribution of landing cases based on injury 

criteria. The conditions defining the certified landing distribution may then be used to 

refine the design or be used as derived requirements for conditions such as landing 

velocity or flight environment placards.
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4.14.2.2.2.2 RESPONSE SURFACE SELECTION METHOD

An alternate approach to selecting cases to analyze may be used separately or may be 

used to define the boundary in the previous method. In this method, a statistically 

significant number of cases are selected uniformly from the entire distribution. These 

cases are modeled as described below in the following sections. The results of these 

analyses are used to estimate the injury response of all of the landing cases, using a 

response surface. See NASA/TM-2009-215704 for additional information about the 

method. Once this analysis has been conducted, additional critical landing cases can be 

selected that may be near the threshold of failing the requirements. This procedure 

may be used to more accurately define the certified landing condition boundary. The 

conditions defining the certified landing distribution may then be used to refine the 

design or be used as derived requirements for conditions such as landing velocity or

flight environment placards.

4.14.2.2.3 LANDING DYNAMICS MODELING

Once critical landing cases have been selected, landing simulations of the entire vehicle 

are conducted by numerical analysis (e.g., by dynamic finite element modeling). These

simulations provide the necessary information about loads and dynamics that is needed 

to drive the crew interface subsystem model, which includes the crew, seats, and 

restraints, as well as anything in the direct load path, such as pressure suits, and the 

accelerations the crew experiences. The designers consider the effects of impact, 

vehicle structural deformation, and impact attenuation systems such as landing gear, 

airbags, retrorockets, and seat support structures and mechanisms. The numerical 

analysis and the subsystem model may have increasing levels of fidelity with increasing 

levels of design maturity, allowing more detailed results to be obtained in each 

subsequent design phase.

4.14.2.2.4 CREW INTERFACE AND CREW RESPONSE MODELING

After the vehicle landing dynamics are estimated, the next step is to model the crew

interfaces (i.e., crew positions). As before, this is an evolutionary process in which lowfidelity models may be used early in the design process and are then replaced by higher 

fidelity models as the design matures. Using these models, crew responses will be 

simulated by driving the model using information from the loads and dynamics obtained 

from the critical landing cases.

Initial low-fidelity models should, at a minimum, allow evaluation of the Brinkley 

Dynamic Response criteria. To accomplish this evaluation, the model must account for 

gross accelerations at the vehicle level and simulate energy attenuation, to accurately 

predict the accelerations at each crewmember location. Ideally, this level of analysis 

occurs no later than between SRR and PDR. 

Once the gross performance of the vehicle accelerations is known, more detailed 

modeling of the crew-vehicle interface is needed, including the seat and any additional 

energy-attenuation systems inherent to the crew-seat interface. This fidelity model also 

requires a human surrogate (i.e., Anthropomorphic Testing Device [ATD]) finite element 

model to be restrained in the seat. Models of the suit, if applicable, should be included, 
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even if they may have low fidelity at this point. This level of simulation should inform the 

design no later than between PDR and CDR.

4.14.2.2.5 MODEL VALIDATION TESTING

Because the above analysis is only of Finite Element (FE) models, physical testing is 

required to support the validity of the analysis. The physical test data are obtained to 

correlate the model responses with the real performance of the system. Testing should 

begin as early as possible in the developmental cycle to inform the design, build 

confidence in the FE models, and reduce cost of the ultimate verification events. 

Developmental and validation testing potentially includes parachute testing to validate 

deceleration onset rate and landing velocity, drop testing of full and subscale vehicles in 

various wave conditions and soil types as applicable to determine vehicle-level impact 

accelerations, drop testing of load attenuation subsystems such as crew pallet and 

stroking seat or strut assemblies, and finally drop or sled testing of seat assemblies and 

restraints, including ATDs or human (volunteer or post mortem) test subjects. 

Developmental testing transitions into validation testing when the tested system moves 

toward flight-like systems and subsystems. Test data can therefore be used to validate 

the analytical modeling results. 

4.14.2.3 INJURY ASSESSMENT

An initial overall injury assessment can be performed after the modeling activities 

described above are completed. All injury metrics except the Brinkley Dynamic 

Response Criteria are to be calculated as described in SAE J211/1. The results are 

then compared with the Injury Assessment Reference Values (IARV) detailed below.

4.14.2.3.1 BRINKLEY DYNAMIC RESPONSE MODEL

4.14.2.3.1.1 HISTORY OF THE BRINKLEY DYNAMIC RESPONSE MODEL

The multi-axial dynamic response criteria, referred to by NASA as the Brinkley Dynamic 

Response Model, have been used in numerous research and development applications. 

These include the investigation of the Challenger accident; the development, test, and 

evaluation of the Crew Escape Technologies (CREST) escape system demonstration 

ejection seat, among others.

The Brinkley Dynamic Response criteria were developed as a result of an evolutionary 

process to define the human dynamic response to and exposure limits for short-duration 

accelerations associated with spacecraft landing and emergency escape system 

performance. During the development of the NASA Mercury, Gemini, and Apollo crew 

modules (as well as the B-58, XB-70, and F/B-111 aircraft escape systems), the 

established acceleration limits specified the acceleration rate of onset, acceleration 

amplitude, and duration for areas known to be within voluntary tolerance and those 

known to cause moderate to severe injury. These acceleration limits were based on the 

research of John P. Stapp and his contemporaries using military volunteers, animal 

surrogates, and the results of accidental exposures of humans. Additional information 

related to the Brinkley Dynamic Response Criteria can be found in AGARD CP-472, 
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Development of Acceleration Exposure Limits for Advanced Escape Systems and in the 

HIDH Chapter 6.5.

4.14.2.3.1.2 ASSUMPTIONS AND LIMITATIONS FOR THE BRINKLEY DYNAMIC 

RESPONSE MODEL

As with any model, the Brinkley Dynamic Response Model has assumptions and 

limitations. The model will be accurate only for systems meeting the following criteria:

 Accelerations must be less than or equal to 0.5 seconds (e.g., during liftoff, 

launch abort, landing impacts, and parachute deployments).

 Seat padding or cushions should preclude amplification of transient linear 

accelerations transmitted to the occupant. Excessive padding will result in 

dynamic overshoot, amplifying rather than attenuating accelerations.

 Crewmembers must be restrained by a system that includes, at a minimum, 

pelvic restraints, torso restraints, and anti-submarining restraints that provide 

occupant restraint no less than that of a conventional 5-point harness during all 

events.

 The restraint system must be adequately pre-tensioned to eliminate slack. 

 Proper crewmember fit and restraint must be ensured such that there is no gap 

between the subject and the seating support surfaces Any gap between the seat 

and subject, including gaps created by rigid elements within suits (if applicable), 

will increase the risk of injury and cannot be predicted by the Brinkley Dynamic 

Response Model.

 The suit may not change the natural frequency or damping of the body.

 The GX axis limits presume that the seat occupant's head is protected by a flight 

helmet weighing less than 2.3 kg, with a liner adequate to pass the test 

requirements of American National Standards Institute (ANSI) Z-90 (latest 

edition) or equivalent. 

 All crewmembers are similarly restrained during all events that require the 

application of the Brinkley model.

Resulting qualifications and uncertainties on the valid use of this model include the 

following:

 The Brinkley model predicts risk of generic “injury” but not the severity or location 

of injury. This inability to predict the severity and location of an injury limits the 

ability to assess the integrated medical consequences of different injuries under 

different landing operation conditions. For example, a post-mortem human 

subject study of the placement of rigid suit elements proved that the Brinkley was 

inefficient in predicting injury (McFarland, 2011). The addition of the elements 

drastically increased the probability of injury, but the increase was not predicted 

using the Brinkley.
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 The model does not predict risk of injury based on subject’s gender, age, weight, 

or space flight deconditioning.

 In the development of the original model, a generic seat was used along with the 

assumptions listed above. Another seat configuration would need the 

development of a new model. Thus, the probability of crew injury may be lesser

or greater than the prediction given by the Brinkley.

 The dynamic response model cannot predict injury caused by localized blunt 

trauma or localized point loading (i.e., point loading due to rigid suit elements or 

interference with restraints). Blunt trauma due to rigid suit elements invalidates 

the risk prediction.

 The model assumes a minimally supported head mass in the risk estimate. 

Heavier space flight helmets may increase risk of neck injury but may not be 

predicted by the model.

 The natural frequency of the body could be changed by the suit and helmet. The 

model was originally developed without the use of a pressure suit. The additional 

mass from the suit and helmet, along with the fact that the mass would not be 

evenly distributed, would have an effect on the dampening parameters of the 

human. 

 The Dynamic Response Index (DRI) was developed for a defined single-axis 

pulse shape, which may not apply to landing pulses of complex spacecraft. For 

example, the DRI primarily predicts thoracolumbar spine injury in the +GZ axis. 

Other axis limits are not well defined with the model. 

o NATO recommends using the Brinkley model only for the +GZ axis. The 

U.S. Army, on the other hand, does not use the Brinkley Model due 

because of its limitations. 

 Along with the defined pulse, valid application requires the spine to be aligned 

within 5° of the load vector. An application greater than 5° drastically increases 

the risk of injury.

4.14.2.3.1.3 BRINKLEY DYNAMIC RESPONSE MODEL APPLICATION

The Brinkley Dynamic Response model may be applied only if all of the assumptions 

are met and the limitations are accepted. If these criteria are met, the Brinkley Dynamic 

Response Model is valid to apply and the injury risk criterion, β, is calculated according 

to the Brinkley Dynamic Response Model with Dynamic Response Limits, DRlim. 

The appropriate risk level for the Brinkley assessment will be determined in coordination 

with NASA Health and Medical Technical Authority (HMTA) and the specific HSF 

vehicle development program. The desired Dynamic Response limits are low (about

0.5%) for all cases. If occupant protection principles are not properly applied and/or 

multiple off-nominal failures occur, loads could impart risks in the medium risk (about

5%) and high risk (about 50%) categories for risk of sustaining a serious or 

incapacitating injury.
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To calculate the injury risk criterion, β, see HIDH section 6.5.

In this model, it is assumed that the total body mass that acts on the vertebrae to cause 

deformation can be represented by a single mass. Using the Dynamic Response Model 

limits for accelerations of less than or equal to 0.5 second (e.g., during nominal liftoff, 

launch abort, landing impact, and parachute deployment) provides the proper margins 

of safety for a healthy conditioned crewmember. Prediction of injury risk for 

deconditioned crewmembers with 6-month space flight exposures can be achieved by 

applying the model with modified Dynamic Response Limits. For either crew condition, 

the Dynamic Response Model will provide a general injury risk assessment for either 

nominal or off-nominal failure or multiple failures, given an input acceleration profile. 

Appropriately used, the Brinkley Dynamic Response Model can provide an early 

assessment of general injury potential for a new vehicle design. More specific 

evaluation of injury likelihood and consequence is expected to require physical 

Anthropomorphic Test Device (ATD) testing in conjunction with Finite Element (FE) 

modeling.

For further detail, the Brinkley Dynamic Response Model is documented in the Advisory 

Group for Aerospace Research and Development (AGARD) publication CP-472, 

"Development of Acceleration Exposure Limits for Advanced Escape Systems" as well 

as in NASA TM-2008-215198.

4.14.2.3.2 LIMITATION OF SPECIFIC CREW INJURY TYPES

NASA-STD- 3001 V2 6069 requires protection from injury caused by accelerations, 

including blunt-force trauma, point loads impact, and flail injury, and injurious loads to 

the head and neck. Protection can be achieved in a variety of ways, and verification that 

this requirement is met can be achieved by inspection of the design and the analysis, 

supported by test data.

Blunt-force trauma is one of the leading impact injury modes in terrestrial accidents, 

including aviation and automotive crashes. Trauma occurs when the structural failure 

associated with acceleration and resulting forces causes the occupant to strike 

surrounding structure, the structure itself to fail resulting in a collapse of the occupant’s 

survivable volume or in impingement into the volume from structures deforming or 

becoming ballistic. To prevent this injury mode, designers need to ensure that the 

volume surrounding the occupant is sufficient to prevent crewmembers from impacting 

the structure when they are subjected to accelerations, including consideration of 

uncontrolled flailing of limbs. Further, structural designers and analysts must ensure that 

safety factors are such that the structure does not yield and deform into the survivable 

volume or fail and strike the occupants. 

Accelerations are best tolerated by the human body when they are distributed evenly 

over a large body surface area. To prevent point loads in the design of seats and 

restraints, seats should conform to the human body to the extent possible in any 

direction that is designed to provide support, particularly at the buttocks, back, legs, 

shoulders, and head, and should provide large, uniform surfaces to distribute the loads 

in these directions. A variety of design approaches exist, including individually molded 
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seat liners as provided by the Russian Soyuz or United States Mercury vehicles (shown 

in Figure 4.13.2.3.2-1); taut fabric seat back, seat, and leg pan as provided by the 

United States Apollo; as well as rigid metal seat back with minimal padding as provided 

by the United States Gemini and Orion vehicles and common to many aircraft ejection 

seats. Conformal supports should be considered for both the nominal and off-nominal 

load directions of seats. For instance, many capsule designs concentrate nominal loads 

in the x and z axes, but provide lateral support to prevent injury in the case of 

unexpected off-nominal loads in the y axis. Any locations on the seats or restraints 

where the load is supported unevenly by only a small area will concentrate the loads 

and increase the injurious effects of accelerations. The occupant protection crew 

interfaces system should be free of any such points, including those generated by 

interference with restraints and the flight suit, or by any rigid part of the flight suit (if 

applicable).

FIGURE 4.14.2.3.2-1 NASA/NACA PROJECT MERCURY CONFORMAL COUCH (SEAT)

During high-acceleration phases with rapid onset rates, the human body, and in 

particular the limbs and extremities, may be unable to resist the accelerations and will 

consequently flail relative to the cabin without design features to act as flail 

countermeasures. Limb flail can cause injury when flailing limbs collide with structures

or when a limb of one crewmember collides with the body of another crewmember. Limb 

flail may also result in hyperextension or hyperflexion, injuring joints of the limb. System 

designers should consider the effects of limb flail in the design, and provide design 

countermeasures. To the degree possible, structures should be kept away from the 

occupant with the exception of controls. Additionally, designers may limit the magnitude 

of crew flail by providing limb restraints for all dynamic mission phases. Limb restraints 

include boot clips to fully restrain the foot, and elbow or wrist restraints to prevent arm 

flail beyond the designed reach area. Additionally, inserts within the helmet should 
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prevent the crew from experiencing head and neck flail within the helmet itself. Care 

should be taken to ensure that any restraints do not preclude unassisted egress or 

prevent crewmembers from reaching critical controls.

To evaluate specific injury types, in terms of both likelihood and consequence, NASA is 

developing a suite of tools and measures. The Operationally Relevant Injury Scale 

(ORIS) describes injuries in terms of their relation to space flight crew tasking and 

functional needs that may be negatively affected by injuries. 

A standard for acceptable risk of injury from transient acceleration is also being defined, 

on the basis of flight crew injury data from historically acceptable space flight systems 

and by comparison to acceptable risk in other relevant human transportation systems. 

In addition to the Brinkley Dynamic Response Model, recent advances in the automotive 

industry have provided additional tools for assessing injury risk during impact and 

dynamic loads. In determining what NASA’s posture on injury risk should be, NASA has 

found it is helpful to review the risk postures of other industries. 

Currently, NASA is using human surrogate data and additional data mining to develop 

injury risk functions. A set of Injury Assessment Reference Values (IARV) are being 

derived that specify loading limits on various portions of the human body that 

correspond to acceptable risk of injury. These IARVs are expected to focus on load 

limits such as these, for both conditioned and deconditioned crewmembers in both 

nominal and off-nominal situations:

 Head Injury Criteria (HIC)

 Rotational Brain Injury Criteria (BRIC) 

 Peak upper neck axial tension force [N]

 Peak upper neck axial compression force [N]

 Maximum chest compression displacement [mm]

 Lateral shoulder force [N] 

 Lateral shoulder deflection [mm]

 Lumbar axial compression force [N]

 Peak ankle dorsiflexion moment [Nm]

 Peak ankle inversion/eversion moment [Nm]

 Contact force [N]

Once they have been established, the IARVs must not be exceeded in any dynamic 

phase of flight. For additional information on the application and derivation of these 

values, see Somers, et al. (2012). 
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In addition, a deconditioning factor must be added for cases when the crew has been 

exposed to reduced gravity. See HIDP section 4.15 Deconditioned Crewmember for a 

description of space flight deconditioning effects. Each injury metric was evaluated at 

each injury class at the specified risk level, and the lowest IARV was chosen so as to be 

conservative.

Refer to the HIDH section 6.5 for more information about calculating the IARVs. These 

descriptions will be updated as NASA human research provides new information to 

inform the IARVs. This proposed method is currently under development, but other 

methods, with approval by NASA, may be used to evaluate and verify a minimal 

probability of risk to the crewmembers. 

4.14.3 OCCUPANT PROTECTION DESIGN TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.14.3-1 are recommended for review by the NASA customer.
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TABLE 4.14.3-1 TECHNICAL PRODUCTS OF OCCUPANT PROTECTION DESIGN 

Technical Products

Phase 

A

Phase 

B

Phase 

C

Phase 

D

SRR SDR PDR CDR SIR FRR

A description of the ConOps, function allocation, and 

associated crew task lists. Includes identification of 

potential errors that can be encountered for each task.

I U U U --- ---

Definitions of environmental conditions I U U U --- ---

Monte Carlo distribution of probabilities for nominal and 

off-nominal landings --- I U U --- ---

Definition of boundary cases for landing, and full landing 

FE model run for each case --- I U U --- ---

Finite element subsystem models with ATD, including 

seat and energy attenuation system. Model fidelity should 

increase for each milestone review.

--- I U U --- ---

Brinkley Analysis

Perform Brinkley Dynamic Response Model analysis --- I U U U ---

ATD Testing 

ATD testing --- --- I --- --- ---

ATD verification testing --- --- --- --- I ---

Biodynamic Results from FE Modeling

Model correlation with ATD testing results --- --- I --- --- ---

Assessment of finite element (FE) model --- --- I --- --- ---

Initial biodynamic results of FE modeling --- --- I --- --- ---

Final design results of FE modeling --- --- --- U --- ---

Results of FE modeling after verification testing --- --- --- --- U ---

A summary of modeling/analysis/evaluation performed to 

date and their influence on system design, with links to 

the detailed analysis results

Required per NPR 8705.2B, and HITL evaluations 

required per paragraph 2.3.10

--- --- I U --- ---

System architecture drawings (structures, equipment, 

etc.), material specifications, interface requirements. --- --- I U U ---

Verification plan --- --- I U ---

Report on biodynamic response, crew injury limitation, 

and spinal alignment verification X

X = one-time release of item

I = initial release of item

U = updated release of item

4.14.3.1 CONCEPT OF OPERATIONS AND CREW TASK LISTS

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are influenced by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of the sequence of crew activities, and 

identification of critical tasks. For occupant protection considerations, the Concept of 

Operations should address such factors as seat deployment, restraint don and doff for 

both nominal and off-nominal situations, a description of critical tasks to be performed 
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during restrained or partially restrained operations including reach to critical controls, 

and any manual tasks associated with activating the occupant protection system such 

as tightening restraints at key mission phases, or activating, arming, or disarming 

aspects of the crew impact attenuation system, parachutes, or landing system. 

Designers should ensure their conops and tasks lists are used to help define tasks that 

need to be modeled in the occupant protection systems.

4.14.3.2 SUMMARIES OF MODELING, ANALYSES, AND EVALUATIONS

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-system integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how critical design decisions 

were assessed. In accordance with NPR 8705.2B, updated summaries are to be 

provided at each design review through System Integration Review (SIR). Also in NPR 

8705.2B paragraph 2.3.10, the use of human-in-the-loop (HITL) evaluation is a required 

method to progressively demonstrate that the operational concept meets system 

requirements for operational safety, efficiency, and user interface design. For occupant 

protection considerations, the HITL evaluations should include crew seated tasks and 

ingress and egress from seats including don and doff of restraints, to demonstrate that 

the occupant protection system does not prevent successful activation of critical 

controls or crew egress in emergency scenarios, and to demonstrate seat fit and 

function for the design population in the suited configuration (if applicable). The HITL

testing may also include tests of the seat and restraints with volunteer human subjects 

under simulated landing and abort acceleration pulses. 

4.14.3.3 ARCHITECTURE, MATERIALS, AND INTERFACE SPECIFICATIONS

Drawings, materials, and interface specifications provide NASA with insight into humansystem integration technical details throughout the design process. 

4.14.3.4 VERIFICATION PLAN

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 

4.14.4 REFERENCES

Association for the Advancement of Automotive Medicine. (2005). Abbreviated Injury 

Scale 2005. Barrington, IL.

Brinkley, J. W., & Specker, L. J. (1989). Development of Acceleration Exposure Limits 

for Advanced Escape Systems (Proceedings No. 472). Presented at the meeting of 

AGARD NATO Conference.

U.S. Department of Transportation, Research and Innovative Technology 

Administration, (2007). Trends in Personal Income and Passenger Vehicle Miles. 

(Bureau of Transportation Statistics Publication No. SR-006).
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Dub, M. O., & McFarland, S. M. (2010). Suited Occupant Injury Potential during 

Dynamic Spacecraft Flight Phases. NASA Johnson Space Center. Houston, TX: 

Duma, S., Boggess, B., Bass, C., & Crandall, J. (2003). Injury Risk Functions for the 5th 

percentile Female Upper Extremity. In D. Holt (Ed.), Recent Developments in 

Automotive Safety Technology (pp. 93-101). Warrendale, Pennsylvania: Society of 

Automotive Engineers.

Duma, S., Schreiber, P., McMaster, J., Crandall, J., Bass, C., & Pilkey, W. (1999). 

Dynamic injury tolerances for long bones of the female upper extremity. Journal of 

Anatomy, 194, 463-471.

Horta, L. G., Mason, B. H., & Lyle, K. H. (2009). A Computational Approach for 

Probabilistic Analysis of Water Impact Simulations. (NASA TM-2009-215704). Houston, 

TX: NASA Johnson Space Center.

Lawrence, C., Fasanella, E. L., Tabiei, A., Brinkley, J. W., & Shemwell, D. M. (2008). 

The Use of a Vehicle Acceleration Exposure Limit Model and a Finite Element Crash 

Test Dummy Model to Evaluate the Risk of Injuries During Orion Crew Module 

Landings. (NASA-TM-2008-215198). Houston, TX: NASA Johnson Space Center.

Kuppa, S., Wang, J., Haffner, M., & Eppinger, R. (2001). Lower Extremity Injuries and 

Associated Injury Criteria. 17th ESV Conference Paper No. 457. 

United States Air Force. (2006). Mapes, P. USAF Helicopter Mishap Data. (The Human 

Effectiveness Directorate No. AFRL-WS 06-2221).

McFarland, S. M. (2011). Injury Potential Testing of Suited Occupants during Dynamic 

Spaceflight Phases. American Institute of Aeronautics and Astronautics.

Mertz, H. J., Prasad, P., & Irwin, A. L. (1997). Injury Risk Curves for Children and Adults 

in Frontal and Rear Collisions (SAE 973318). (pp. 13-30)Presented at the Forty-First 

Stapp Car Crash Conference.

National Highway Traffic Safety Administration. (2012). Motorcycle Helmets (Federal 

Motor Vehicle Safety Standard No. 218). 

National Aeronautics and Space Administration. NASA Space Flight Human-System 

Standard Volume 2: Human Factors, Habitability, and Environmental Health, January 

2011.

National Aeronautics and Space Administration, Human Integration Design Handbook, 

NASA/SP-2010-3407, January 2010.
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National Center for Statistics and Analysis. (2009). Motor Vehicle Traffic Crash Fatality 

Counts and Estimates of People Injured for 2007. DOT HS 811 034, U.S. Department of 

Transportation, National Highway Traffic Safety Administration, Washington, D.C.

National Highway Traffic Safety Administration. (1995). Final Economic Assessment, 

FMVSS No. 201, Upper Interior Head Protection.

Nightingale, R. W., McElhaney, J. H., Richardson, W. J., & Myers, B. S. (1996). 

Dynamic responses of the head and cervical spine to axial impact loading. Journal of 

Biomechanics, 29 (3), 307-318.

Federal Aviation Administration. (2011). Philippens, M., Forbes, P., Wismans, J., 

DeWeese, R., & Moorcroft, D. Neck Injury Criteria for Side Facing Aircraft Seats.

(Federal Aviation Administration Final Report No. DOT/FAA/AR-09/41).

Somers, J., Granderson, B., & Scheuring, R. (2010). Occupant Protection at NASA. 

JSC-CN-21380, Houston, TX: NASA Johnson Space Center.

Somers, J., Lawrence, C., Granderson, B., Jones, J., Scheuring, R., Ridella, S., et al. 

(2012). Recommended changes to NASA's occupant protection standards and 

requirements. In Press.

Somers, J., Melvin, J., Tabiei, A., Lawrence, C., Ploutz-Snyder, R., Granderson, B., et 

al. (2011). Development of head injury assessment reference values based on NASA 

injury modeling. Stapp Car Crash Journal, 55.

Takhounts, E., Hasija, V., Ridella, S., Rowson, A., & Duma, S. (2011). Kinematic 

Rotational Brain Injury Criterion (BRIC) (11-0263). Presented at the 22nd International 

ESV Conference.
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4.15 DESIGN FOR DECONDITIONED CREWMEMBER

4.15.1 INTRODUCTION

Deconditioning refers to the decreased performance capacity of crewmembers who

have been exposed to space flight. The effects of deconditioning are measurable and 

observable in decrements to sensorimotor function, aerobic capacity, and orthostatic 

tolerance, and in loss of muscle and bone strength. The occurrence of deconditioning 

and reduced abilities of the deconditioned crewmember must be considered in the 

design of spacecraft and space systems. Additionally, countermeasures must be 

incorporated into the concept of operations for use during space flight and post landing 

to effectively mitigate or manage the effects of deconditioning and ensure the health 

and performance of the crewmembers. Although individual responses to space flight 

vary, all organ systems are affected to some degree by the space flight environment. 

NASA has gathered data and developed requirements that reflect the best knowledge to 

date about responses to space flight. 

Many tasks are affected by crew deconditioning. This chapter will highlight some of 

those areas, but will focus the design process considerations on post-landing 

unassisted (emergency) egress. The act of emergency egress includes, but is not 

limited to, rapid motor control tasks (including fine motor tasks such as object 

manipulation, and gross motor tasks such as opening a hatch), visual acuity tasks, and 

ambulation, as well as maintenance of spatial orientation and postural stability to

escape safely. 

4.15.2 APPLICABLE REQUIREMENTS

NASA standards for protecting the health and performance of crewmembers are 

captured in NASA Standard 3001 Volume 1 (Crew Health) and Volume 2 (Human 

Factors, Habitability, and Environmental Health). Deconditioning effects have 

implications for designs based on the following standards:

 For the musculoskeletal system: V2 8022, V2 8025, V2 8040, and V2 8041

 For the cardiovascular system: V2 7042

 For the sensorimotor system: V2 8015, V2 8016, V2 8018, V2 8019, V2 8020, V2 

8021, V2 8024, and V2 11002, and Volume 1, section 4.2.4

These standards are based on the best available scientific and clinical evidence as well 

as operational experience acquired during Apollo, Skylab, Shuttle, Shuttle-Mir, and 

International Space Station (ISS) programs. 

4.15.3 BACKGROUND

Two key factors play into crewmember deconditioning: gravity unloading and gravity 

transitions. With direct exposure to space flight, crewmembers experience changes in 

anatomy and physiology. Initially upon entering the space flight environment, 
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crewmembers experience sensorimotor dysfunction and space motion sickness (SMS) 

due to a mismatch between vestibular and visual signals. The normal gravity cues 

sensed by the vestibular system (providing terrestrial humans with a spatial orientation) 

are misinterpreted once the gravitational vector is removed. The sensorimotor system 

will adapt to the new cues, but until that adaptation has fully taken place, a mismatch in 

cues leads to sensorimotor dysfunction and SMS. Sensorimotor disturbances typically 

resolve within the first few days of flight. Additionally, gravitational unloading leads to a 

cephalad fluid shift and loss of load-bearing forces on the body. Over time, this leads to 

progressive changes in the cardiovascular and musculoskeletal systems. 

Crewmembers experience bone demineralization and decreased strength and aerobic 

capacity due to gravity unloading. Even though countermeasures are used, they are not 

yet fully protective.

On landing, crewmembers experience new sensorimotor disturbances (gait dysfunction, 

decreased visual acuity, and postural stability disturbances), motion sickness, impaired 

strength and aerobic capacity, and orthostatic intolerance (which is characterized by a 

variety of symptoms that occur on standing, including lightheadedness, increase in 

heart rate, altered blood pressure, and in some cases fainting). Because of these 

physiological disturbances, careful consideration should be given to the deconditioned 

crewmember specifically during vehicle egress. The result of space flight adaptation on 

the human body, if not mitigated in full or in part by countermeasures, includes muscle 

atrophy, reduced orthostatic tolerance, reduced aerobic capacity, sensorimotor 

dysfunction (including gait instability and altered dynamic visual acuity), decreased bone 

mineral density, and changes in bone architecture. The following sections describe 

deconditioning and what should be considered in spacecraft design with respect to the 

sensorimotor, musculoskeletal (muscle and bone), and cardiovascular (aerobic capacity 

and orthostatic intolerance) systems. 

4.15.4 SENSORIMOTOR ADAPTATION 

4.15.4.1 BACKGROUND

The occurrence of sensorimotor dysfunction varies by individual, but is most prominent 

within the first 72 hours of space flight after gravitational transitions (entry into 

microgravity and landing). The spacecraft designer must consider the impacts of 

gravitational transitions on human performance when developing the concept of 

operations, crew tasks, and crew interfaces. The plasticity of the human central 

nervous system allows individuals to adapt to altered stimulus conditions encountered in 

space flight. However, until some level of adaptation is achieved, many astronauts 

experience space motion sickness (SMS), disturbances in gait and eye-hand 

coordination, unstable vision, and illusory motion of the self, the visual scene, or both

(Reschke et al., 1998; Clement and Reschke, 2008). 
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Sensorimotor impairments can present as sudden performance decrements or failures, 

such as diminished visual acuity, decreased strength, impaired gait, symptoms of SMS, 

transient illusions, impaired gaze control, oscillopsia, or disturbances in postural 

equilibrium. See Paloski et al., 2008 for a complete description of the sensorimotor 

performance disturbances. The NASA Standard 3001, Volume 1 section 4.2.4 Fitness 

for Duty Sensorimotor Standards should be used to mitigate decrements in 

sensorimotor function, so that successful performance of all required duties is possible, 

including egress. 

A common sensorimotor difficulty encountered upon entering the space flight 

environment is SMS. Symptoms of SMS can vary from mild to moderate nausea, 

headaches, and disorientation, to vomiting and intense discomfort. Although the 

symptoms are similar to terrestrial motion or sea sickness, the mechanisms are 

different. Current NASA countermeasures for SMS on the ISS include pharmaceuticals 

and minimization of crew tasks during ascent and the first few days of flight, and before 

reentry. The drug promethazine is part of the ISS medical kit and is prescribed either 

prophylactically or within the first 72 hours of flight as treatment for SMS. Additionally, 

since many sensorimotor disturbances are caused by mismatched visual-vestibular 

cues (which happens when individuals make independent eye, head, and trunk 

movements), a reduced or minimized list of tasks is often prescribed for crewmembers 

affected by SMS until adaptation takes place and SMS symptoms resolve. 

Upon reentry and landing on Earth, crewmembers encounter a unique set of 

neurovestibular symptoms with functional consequences that must be considered in the 

design of crew egress procedures and interfaces (e.g., seat egress, translation paths, 

mobility aids, and emergency equipment). The probability and the duration of the 

impairment after any gravity transition will be related to both the magnitude of the 

gravitational transition and mission duration. Missions of longer duration typically 

require longer recoveries.

Water landings present additional environmental challenges to sensorimotor 

deconditioned crewmembers. For safety and operational reasons, returning 

crewmembers may need to egress the vehicle within a few minutes after a water 

landing under various sea state conditions. Exposure to even low frequency motions 

(0.2-2.0 Hz) induced by sea conditions surrounding a vessel can cause significant fine 

and gross motor control problems that can affect critical tasks. Furthermore, the 

modulation of otolith-mediated responses are frequency dependent, in that lowfrequency linear acceleration may be misinterpreted as tilt and high-frequency 

acceleration may be misinterpreted as translation. The ambiguity of otolith-mediated 

information is greatest in the mid-frequency region where tilt and translation otolith 

mediated responses cross over. This frequency range is also the common frequency 

range of wave action. The minimum wave periods corresponding to different sea states 

(Sea States 1-7) indicate frequencies ranging from 0.125-0.5 Hz. The ambiguity of 
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inertial motion cues is greatest in the frequency region where tilt and translation 

responses cross over (0.1-0.5 Hz).

Full sensorimotor recovery is expected within 15-30 days after landing. Recent data 

indicate that astronauts returning from long-duration space flight (6 months) experience 

altered locomotor function with a 48% increase in the time to complete an obstacle

course on the day after landing (or return, R+1). These data indicate that a typical 

subject would recover to 95% of his/her pre-flight level at about 15 days post-flight 

(Mulavara et al. 2010). Similar recovery curves for posturography during pitch head 

movements have been observed after 6-month expeditions on the ISS (Wood et al.

2011). 

4.15.4.2 IMPACT ON DESIGN

Physiological changes have a significant effect on crewmember ambulation during 

egress, and such changes should be considered and accounted for in the design of new 

vehicles. It is likely that crewmembers will experience impaired ability to control the 

spacecraft during landing and impaired ability to immediately egress after a landing on a 

planetary surface (Earth or other). Additionally, astronauts may (1) experience the 

sensation of turning while attempting to walk a straight path, (2) encounter sudden loss 

of postural stability, especially when rounding corners, (3) perceive exaggerated pitch 

and roll of head movements when walking, (4) experience sudden loss of orientation in 

unstructured visual environments, and/or (5) experience significant oscillopsia (a visual 

disturbance in which objects in the visual field appear to oscillate) during locomotion. 

Muscle activation patterns around heel strike and toe-off are altered after flight (Layne 

et al., 1998), and head pitch and vertical trunk movements are significantly reduced 

(Bloomberg et al., 1997). Returning crewmembers compensate for the potential loss of 

stability by adopting a wide base of support, taking shorter strides, and using their arms 

more than they did before flight. These adaptations serve to maintain stability, but 

walking speed is reduced and more steps are needed to cover a specified distance. The 

altered muscle activation patterns can mean a failure to achieve the proper toe 

clearance and result in tripping, which increases the risk of post-flight injury.

Hatch openings and egress pathways should be designed so that a space flightadapted crewmember would be able to egress safely from a vehicle while meeting 

NASA Standard 3001, Volume 2 requirements. These requirements include 

configuration of egress pathways so that the adapted crewmember can egress within 

the time required (V2 8013 and 8014) and while in a suit (V2 8015). Since postural 

stability is compromised and crewmembers may be disoriented, egress pathways 

should be large enough to tolerate sway without injury to the crewmembers, contain 

handholds for balance, free of interference (V2 8016), and designed to prevent 

exposure to hazards or obstacles (V2 8018; e.g., crewmembers should not have to step 

over large objects). Additionally, since visual acuity is diminished and oscillopsia is 

usually present, markings and interfaces should be prominently displayed for egress 
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tasks such as restraint release, egress pathways, and egress equipment location and 

operations (V2 8019). 

In the challenging situation that a water egress will demand, space flight-adapted, 

deconditioned crewmembers will need additional time to resolve the ambiguity of inertial 

motion cues. These motion frequencies coupled with the varying sea state conditions 

(e.g., Sea State 6 results in wave heights of 4-6 meters) could cause performance 

deficits by affecting the efficacy of skills that depend on motor and visual acuity in tasks 

critical to emergency egress activities, such as visual monitoring of displays, actuating 

discrete controls, operating auxiliary equipment, and communicating with Mission 

Control and recovery teams.

Egress activities can also be impaired by post-flight motion sickness. The probability

will increase with moderate to large wave activity. Thus, the sensorimotor disturbances 

caused by crewmembers’ adaptation to space flight may disrupt the ability to perform 

emergency egress tasks during the initial introduction to Earth’s gravity after longduration space flight. Therefore, tasks should be designed to be as simple as possible,

with ample performance time planned for the adapted crew. Additionally, crew access 

to motion-sickness bags without requiring ambulation or excessive head motion is 

essential.

4.15.5 ORTHOSTATIC INTOLERANCE

4.15.5.1 BACKGROUND

Orthostatic intolerance is an abnormal response to standing upright that results from 

decreased blood pressure (an inability to maintain arterial pressure) and inadequate 

blood flow to the brain (inadequate cerebral perfusion), and it is frequently seen in 

crewmembers returning from space flight. It is also one of the most important 

physiological changes that have a negative impact on flight operations and crew safety, 

especially if it progresses to presyncope or syncope. Symptoms of orthostatic 

intolerance are elevated heart rate, decreased stroke volume, pallor, sweating, and a 

drop in blood pressure or orthostatic hypotension. All of the orthostatic intolerance 

symptoms are acceptable to some degree provided orthostatic hypotension does not 

occur. Due to this fact, orthostatic intolerance countermeasures are geared toward 

preventing orthostatic hypotension. Symptoms and consequences of orthostatic 

hypotension include dizziness, confusion, and loss of consciousness. Without proper 

mitigation of orthostatic hypotension, a crewmember suffering from the effects of this 

condition post flight could not achieve safe and successful descent and landing (if in an 

upright posture), or post-landing tasks. These effects may result in an inability to 

operate controls, complete required tasks (such as landing the vehicle), and egress 

from the vehicle unassisted. 

Orthostatic hypotension affects about 20%-30% of crewmembers who fly short-duration 

(4-18 days) missions (Fritsch-Yelle et al., 1996; Waters et al., 2002; Meck et al., 2004)

and 83% of astronauts who fly long-duration (129-190 days) missions (Meck et al., 
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2001). The etiology of orthostatic hypotension is complicated and not completely 

understood. Factors include a decrease in plasma volume secondary to the cephalad 

fluid shift that occurs in space. Additional impacts may arise from dysfunction of the 

sympathetic nervous system, the renin-angiotensin-aldosterone system, and/or cardiac 

atrophy resulting in decreased stroke volume. A description of these mechanisms can 

be found in the Human Research Program Evidence Book on the Risk of Orthostatic 

Intolerance During Re-exposure to Gravity (HRP-47072). 

4.15.5.2 IMPACT ON DESIGN

Mitigation strategies are required in accordance with NASA-STD-3001, V2 7042. Those 

used during Space Shuttle and ISS missions included

 Fluid- and salt-loading regimens before reentry to partially counteract space 

flight-induced losses of plasma volume

 Compression garments to prevent blood pooling in the lower body and abdomen

 Liquid cooling garments to prevent heat stress-induced orthostatic hypotension 

and to maintain crewmember comfort

 Recumbent crewmember seating to minimize the effects of acceleration along 

the long axis of the body 

A fluid-loading protocol is used to partially counteract space flight-induced losses of 

blood plasma volume. NASA Space Shuttle flight rules stipulated that for each deorbit 

attempt, crewmembers must consume 48 oz of water with 12 salt tablets, or an 

alternate approved isotonic drink solution, during the 2-hour period before landing 

(Space Shuttle Operational Flight Rules, NSTS 12820 Vol A, section 13: Aeromedical: 

13-57, 1996). If one orbit wave-off occurred and the fluid-loading protocol was 

completed, one half (24 oz) of the protocol was repeated. If the wave-off was greater 

than one orbit, the entire protocol (48 oz) was repeated. 

Orthostatic hypotension is also counteracted by use of graduated pressure compression 

garments from the feet to the thorax to improve venous blood return. The mean 

compression provided by these countermeasure garments should be between 40 and

80 mmHg. These levels are similar to pressures provided by the NASA Anti-Gravity Suit 

and the Russian Kentavr, which are donned for reentry, and have been efficacious 

during Space Shuttle and Soyuz landings. Compression should be provided during 

reentry and during the period immediately post landing. Graded compression garments 

may be advantageous and, if used, must apply the highest pressure at the foot and

ankle, lower pressures up the leg, and the lowest pressure over the abdomen to the 

level of the diaphragm. 

Heat load (increased core temperature) and the resultant skin vasodilation can 

exacerbate orthostatic hypotension by causing a decrease in blood pressure. 

Therefore, control of body temperature through cooling or other means of dissipating

metabolic heat loads is a key component of orthostatic protection. NASA crewmembers 

currently wear liquid cooling garments to prevent heat stress-induced orthostatic 

hypotension and to maintain crewmember comfort. 
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Another method for minimizing lower-body blood pooling during reentry is the use of 

recumbent seating to position crewmembers in the feet-up orientation to minimize the 

effects of acceleration along the long axis of the body. Note that if crewmembers 

reenter in feet-up orientation, lower-body compression is contraindicated until post

landing when crewmembers attempt to move to a vertical, head-up orientation on the 

ground.

Because the greatest risk of hypotension is to the deconditioned crewmember, 

countermeasures are not required early in a mission, and do not apply before the start 

of ISS docked operations. Moreover, judging by existing NASA data, it should be 

assumed that most crewmembers on future exploration missions will experience postflight orthostatic hypotension, and appropriate countermeasure garments should be 

allocated for all crewmembers. 

Given that orthostatic hypotension produces dizziness, confusion, and/or loss of 

consciousness, the following factors should be considered in the design:

 Reliance on automation during descent and landing, to counter the crew’s 

potential inability to operate controls

 If a crewmember is unconscious, provisions need to be made for safe egress of 

that crewmember. This may include placing appropriate handholds on the suit,

allowing other crewmembers to easily grab the unconscious crewmember, or 

providing slide paths for dragging the incapacitated crewmember out of the 

vehicle.

 Clearly outlined procedures or diagrams posted near required equipment, to 

counter confusion and avoid errors.

 A clear egress pathway, free of obstacles and/or obtrusions that may cause 

injury.

Refer to HRP-47072 Human Research Program Evidence Book: Risk of Orthostatic 

Intolerance During Re-exposure to Gravity, and NASA/SP-2010-3407 Human 

Integration Design Handbook (HIDH) paragraphs 6.5.2.2 and 6.5.2.4, for information on 

cardiovascular deconditioning and orthostatic intolerance caused by space flight, and 

for details of extensive research performed by NASA on protective garments.

4.15.6 MUSCLE, BONE, AND AEROBIC CAPACITY DECONDITIONING

4.15.6.1 MUSCLE DECONDITIONING

4.15.6.1.1 BACKGROUND

Successful egress in an emergency scenario requires that designers of egress 

interfaces take muscle deconditioning into consideration. Muscle deconditioning 

decreases crewmember strength, or the ability to generate force. Skeletal muscle 

adaptations to space flight affect both the structure and function of the muscle. The 

muscles involved in maintenance of posture (antigravity muscles) in terrestrial gravity 

are the most susceptible to space flight-induced adaptations, as these muscles endure 
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nearly continuous levels of self-generated and environmentally generated mechanical 

loading on Earth and are not extensively used during space flight. NASA-STD- 3001, 

Volume 1 section 4.2.8 Fitness for Duty Muscle Strength Standards provides the 

standards for pre-, in-, and post-flight muscle strength, which are required so that 

successful performance of all duties is achievable, including egress. Section 4.5.4 of 

this document addresses the design process for operational strength to ensure that 

space flight equipment and interfaces are operable by all potential crewmembers. 

Long-duration space flight results in a loss of muscle strength that poses both safety 

and performance risks, particularly during emergency egress. The risks associated with 

the loss of skeletal muscle mass, strength, and endurance depend not only on the level 

of loss but also on the starting fitness of the individual crewmember. Thus, an 

operational need exists to determine the amount of strength needed to perform a task, 

and then attempt to maintain that strength during flight as much as possible. The goal is 

to prevent functional strength from falling below the level needed to complete critical 

mission tasks after deconditioning occurs on orbit. Crewmembers’ physical 

requirements for the completion of tasks should be known and within strength limits 

specified for crewmembers. 

Space flight crewmember operational force limits were developed by NASA for 

Constellation (now MPCV) and Commercial Crew Programs on the basis of post-flight 

measurements and estimated strength decrement due to deconditioning. Minimum and 

maximum operational load limits, based on average estimated post-flight strength 

decrement, were established for these programs and can be found in MPCV 70024 

Human-Systems Integration Requirements (HSIR), JSC-65993 Commercial HumanSystems Integration Requirements (CHSIR), and as reference in the HIDH (Appendix 

B).

The performance and medical risks associated with deconditioning stem from

decreases in skeletal muscle size and function, which have been reported since the 

beginning of human space flight (Kakurin et al., 1971). Space flight results in the loss of 

lean body mass as determined by body composition measurements and decreased 

lower-limb circumference. Data from space flight studies indicate significant loss of 

muscle mass/volume and strength despite use of exercise countermeasures, even on 

short-duration missions. After an 8-day Shuttle mission, LeBlanc et al. (2000) showed 

significant losses in muscle volume relative to pre-flight levels in the 

soleus/gastrocnemius (-6%), hamstrings (-8%), quadriceps (-6%), back (-10%), and 

anterior calf (-4%). After longer missions of 16-28 weeks on Mir, quadriceps (-12%), 

hamstrings (-16%), back (-20%), gastrocnemius (-24%), soleus (-20%), and anterior calf 

(-16%) muscle volumes were reduced. Reduced muscle strength accompanies the loss 

in muscle volume, but the magnitude of changes seems to be greater than can be 

explained by muscle volume alone. Greenisen et al. (1999) showed a 12% reduction in 

knee extensor strength and a 23% reduction in trunk flexor strength after Space Shuttle 

missions lasting up to 16 days. Knee extensor and flexor strength losses in long-
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duration (greater than 30 days) crewmembers after flights on board Mir and the ISS 

were 23% and 25% respectively (S. Lee, personal communication). Additionally, recent 

data from ISS crewmembers show that mean isokinetic strength declined 8-17% after

space flight of 163 ± 38 days (mean ± SD; unpublished data). Finally, the majority of 

losses occur in the lower body, as these muscles are highly active in 1g posture and 

ambulation and less active in 0g. Upper-body strength losses are generally much less 

than lower-body losses. 

4.15.6.1.2 COUNTERMEASURES

Mitigation strategies for strength loss include both physiological and engineering 

countermeasures. Resistance exercise using high-load protocols are an effective 

mitigation strategy to protect against loss of muscle mass and function during unloading 

conditions like bed rest (Alkner & Tesch, 2004; Trappe et al., 2004; Trappe et al., 2007; 

Trappe et al., 2007; Trappe et al., 2008). NASA-STD-3001 requires that the space 

system provide countermeasures to mitigate muscle loss (V2 7038). 

Exercise countermeasures should provide sufficient stimuli to help mitigate the effects 

of microgravity on the human body. For optimal and generalizable results, resistive 

exercise hardware should be able to accommodate performance of a variety of 

exercises to protect against muscle atrophy and loss of strength, and to protect postural 

muscles. These exercises may include squats, deadlift, calf raise, hip flexor/extensor, 

hip abduction/adduction, upright row, bent-over row, lateral raise, front raise, rear raise, 

shoulder press, biceps curl, triceps extension, side bend, side bend (neck), neck 

extension, neck flexion, and bench-press capabilities. 

A needs analysis should be performed to determine the hardware capabilities required 

as well as the exercise regime. After the needs analysis is completed, the developer 

should review current literature, current ISS hardware, and current available technology 

to devise a new concept. Some design features to address include 

 Type of muscle movement – It is recommended that the hardware provide both 

concentric (muscle shortening under tension) and eccentric (muscle lengthening 

under tension) capabilities to most closely emulate terrestrial resistance 

exercise. Eccentric exercise training is important, as it results in greater strength 

gains than concentric exercise alone (Hilliard-Robertson et al., 2003). 

 Load increments – Load increments should be adjustable to accommodate 

various crewmember capabilities.

 Minimum and maximum loads – The load levels should be determined during the 

needs analysis to accommodate various crewmember capabilities.

 Speed of movement – The literature suggests that speed of exercise movement 

has an effect on muscle strength and bone mineral density (BMD). Therefore, 

moderate loads at high speed (power training) may provide similar or better 

effects than high loads at slow speeds (von Stengel et al., 2007). 

 Crew usage – If a crewmember will be exercising alone, then the hardware 

should be designed so that a single crewmember can perform all configurations, 

load setting adjustments, and exercises without assistance.
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Currently NASA ISS protocols provide for resistance exercise countermeasures on all 

space flight missions that last longer than 7 days and include the core set of squat, 

deadlift, and heel-raise exercises. The primary device used for these exercises is the 

Advanced Resistive Exercise Device (ARED). The ARED uses vacuum cylinders to 

provide concentric loading up to 272 kg (600 lb), an eccentric-concentric ratio of ~90%, 

constant force throughout the range of motion, and inertial flywheels. The flywheels 

require the subject to overcome inertia to initially move the load. Strength losses have 

been reduced, but not eliminated, in crewmembers who have flown after ARED was 

deployed as the primary in-flight resistance exercise hardware. Two hours of exercise 

is built into the crewmember daily schedule for the un-stowing of hardware, 

performance of resistive and aerobic exercise (based on whatever is prescribed that 

day by the ASCR, or Astronaut Strength, Conditioning and Rehabilitation staff), stowing

of hardware, and crewmember hygiene and clean-up.

4.15.6.2 BONE DECONDITIONING

4.15.6.2.1 BACKGROUND

Bone mineral loss occurs in space flight primarily because of unloading of the skeletal 

system. The average loss rates are about 1.0%-1.5% per month, according to the 

results of pre- and post-flight evaluations. Bone resorption (demineralization or bone 

loss) targets weight-bearing skeletal sites and results in deficits in areal bone mineral 

density (aBMD) that can range from 3 to 9% of pre-flight BMD over a typical 180-day 

mission. LeBlanc et al. (2000) conducted dual-energy x-ray absorptiometry (DXA) BMD 

measurements of crewmembers (n=16 to 18) before and after they served on the Mir 

spacecraft (mission duration varied from 4 to 14 months) and reported a BMD change 

over an entire mission. However, because of the wide range of mission lengths during 

this data collection period, BMD losses were normalized as percentage change per 

month to report an average loss of 1.0 to 1.5% on a monthly basis. BMD losses were 

greater in the lower limbs and the weight-bearing sites of the central skeleton. These 

sites included the hip and spine, sites that have a high incidence of osteoporotic 

fractures. It is unclear whether BMD stabilizes at a lower level early in space flight, or if 

it continues to diminish throughout the entire expedition. It is unknown whether 

fractional gravity, present on the moon and Mars, would mitigate the loss. Evidence 

from crewmembers flown on space missions greater than 30 days suggests that the 

adaptations of the skeletal system to mechanical unloading (i.e., bone mineral loss 

during flight) predisposes crewmembers to accelerated premature onset of osteoporosis 

after they return to Earth. Refer to section 4.14 Occupant Protection of this document 

for more information on this risk. In those calculations, a deconditioning factor is 

applied to account for crewmember bone deconditioning.

Declines in volumetric BMD in the proximal femur significantly reduce compressive 

strength, bending strength, and hip strength. In the event of a post-flight emergency 

vehicle egress, reduced muscular strength and endurance, and sensorimotor adaptation 
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increase the risk of fall. This increased risk combined with reduced bone strength 

increases the risk of bone fracture during this critical task.

Understanding whether any bone is at risk for fracture requires evaluating its strength, 

that is, its capacity to resist failure under an applied mechanical loading (such as 

landing and vehicle egress). For the human skeleton, the measurement of areal bone 

mineral density [aBMD, g/cm2] by DXA is a widely applied surrogate for bone strength. It 

is used clinically as a surrogate endpoint for “fragility fractures” and for the diagnosis of 

osteoporosis. However, in recognition that DXA measures reflect only bone density and 

not bone strength, NASA is working on development of new bone strength measures 

using finite element analysis of QCT (quantitative computerized tomography) hip scans 

to better estimate bone changes caused by space flight. Additionally, the Bone Fracture 

Risk Module [BFxRM] of the Integrated Medical Model [IMM] is a predictive model 

developed at the NASA Glenn Research Center. In the absence of any fracture 

incidence data, this model uses biomechanical algorithms, knowledge of mission 

operations and tasks, and the declines in astronaut BMD in space to estimate fracture 

probability. This module can be used to increase the understanding of bone injury and 

fracture risk during design for egress. The model supplies data that can be important 

for designing egress tasks within strength and time limits to reduce bone fracture risk. 

4.15.6.2.2 COUNTERMEASURES

Attempts should be made to maintain bone mass during flight. Several factors 

pertaining to the development and capabilities of exercise countermeasures are 

important to maintaining bone mass: (1) high magnitude and rate of strain (higher strain 

rates provide greater bone formation responses), (2) diverse strain distributions (bone 

formation is specific to muscle activation and applied external loads), (3) repetition (the 

minimal number of repetitions depends on the load, and higher loads require fewer 

repetitions), and (4) rest intervals (bone sensitizes to mechanical loading stimuli, so rest 

intervals allow restoration of the mechanosensitivity). Newly designed exercise 

hardware for exploration missions should be developed on the basis of these factors, to 

properly maintain bone and reduce fracture risk during egress. 

NASA is currently researching 2 countermeasures to bone demineralization: exercise 

protocols and pharmaceuticals. Exercise protocols use resistive exercise hardware to 

impart a load on the bone across various body segments and at varying intensities, and 

it is primarily this loading that assists in the maintenance of bone and bone formation. 

NASA is investigating a high-intensity-interval training protocol to be used during flight 

to determine the efficacy of the exercise for helping to maintain bone mass during longduration missions. Design features to enhance usability, increase loading, and increase 

speed greatly improve the effectiveness of exercise countermeasures at preserving 

bone mass. Additionally, NASA is testing the effectiveness of an anti-resorptive 

pharmaceutical to prevent bone demineralization by inhibiting osteoclast-mediated bone 

resorption. The pharmaceutical (alendronate) is being tested as a prophylactic 
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countermeasure to bone loss during flight. Further work is required to validate this drug 

as an effective bone countermeasure. 

4.15.6.3 AEROBIC DECONDITIONING

4.15.6.3.1 BACKGROUND

Crewmember aerobic capacity decreases during space flight. This phenomenon is

known as aerobic deconditioning, and is the result of reduced daily activity and cardiac 

stress. Aerobic deconditioning results in a diminished ability to perform strenuous 

physical tasks, and this condition affects the capability of a crewmember to perform an 

egress. Therefore, design of unassisted egress procedures and aids must take into 

account a decrease in crewmember aerobic capacity. 

The impact of aerobic deconditioning on crewmembers needs to be minimized by 

having crewmembers maintain upright exercise capability during missions, in full or 

partial gravity. Maintaining upright exercise capability is operationally important to the 

success of a mission and perhaps to crew survival (Lee et al., 2007; Watenpaugh et al., 

2000). Emergency egress represents a significant metabolic (>2.5 l•min-1) and 

cardiovascular (>160 beats•min-1) stress in normal ambulatory subjects (Bishop et al., 

1999) and is a much greater challenge after long-duration missions of 6 months or 

more. 

The gold standard measure of aerobic capacity is maximum oxygen uptake (VO2max), 

which is directly related to the physical working capacity of an individual (ACSM, 2009; 

Astrand, 2003). VO2max is the maximal level of oxygen utilization that can be attained 

during exercise requiring a large muscle mass (McArdle et al., 2004). Many 

physiological factors influence aerobic capacity. Decreased plasma volume seems to 

have a strong influence on aerobic capacity (Stegemann et al.; 1997), and is the most 

rapidly occurring adaptation to space flight. Convertino (1997) reported that 70% of the 

variability in VO2max after bed rest deconditioning, which is an analog of space flight,

can be explained by a decreased plasma volume. Reduced circulating plasma volume 

may negatively affect exercise stroke volume, the delivery of oxygen and nutrients to 

working muscles, and the removal of metabolic waste products. After landing, a reduced 

plasma volume is even more problematic, as upright exercise or activity can cause

increased pooling of blood in the abdomen and lower body, thus degrading

crewmembers’ ability to perform demanding tasks such as suit donning or doffing and 

vehicle egress.

The NASA-STD-3001, Volume 1, section 4.2.3 Fitness for Duty Aerobic Capacity 

Standard requires that aerobic capacity be maintained to support successful 

performance of all required duties, including egress. Recent data from ISS 

crewmembers shows that aerobic capacity decreases initially during flight, but then 

increases toward pre-flight levels during the mission with exercise. Crewmembers had 

their aerobic capacity measured before and after flight, and performed graded exercise 

tests during flight approximately every 30 days. Results showed elevated heart rate 
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early in flight during each exercise stage, and reduced oxygen pulse relative to pre-flight 

levels (unpublished data). Additionally, an elevated heart rate response and reduced 

oxygen pulse occurred soon after landing. Aerobic capacity declined in the early postflight period and then recovered to pre-flight levels by 30 days after landing. These data 

show that aerobic deconditioning likely occurs in the initial in-flight period, but 

moderates as flight duration increases, presumably because of the use of exercise 

countermeasures. The elevated heart rate and reduced oxygen pulse in the early postflight period is likely due to a combination of relative hypovolemia and cardiac atrophy 

but recovers within 30 days after landing. These data indicate that crewmembers have 

compromised aerobic capacity in the early in-flight and early post-flight timeframe. 

Total crewmember deconditioning depends on the initial fitness level of the 

crewmember at launch, the overall capabilities of the exercise hardware (whether the 

hardware can provide adequate load and speed), the motivation or ability of the 

crewmember to complete prescribed exercise protocols (taking into consideration 

interruptions in exercise due to docked operations, visiting vehicles, EVA, and so on), 

and the capability of the food system to provide adequate calories and nutrients for 

crewmember health during flight.

4.15.6.3.2 COUNTERMEASURES

Mitigation strategies for aerobic deconditioning include both physiological and 

engineering countermeasures. High-intensity aerobic exercise, such as treadmill 

running and cycling, or rowing ergometry, can be used to partially mitigate the loss of 

aerobic capacity during space exploration. Mitigation has been demonstrated during 

flight analog bed rest studies (that impair aerobic performance), as well as during space 

flight missions (Guinet et al., 2009; Lee et al., 2007; Lee et al., 2009). 

The current exercise hardware suite on the ISS that is used to mitigate decreased 

aerobic capacity is the second-generation treadmill (T2) and the Cycle Ergometer with 

Vibration Isolation and Stabilization (CEVIS) ergometer. The equipment supports 

continuous exercise for 30 minutes at 75% of the crewmember’s aerobic capacity for 

each crewmember, for several days each week, as well as high-intensity interval 

training, with maximal aerobic efforts for at least 30 seconds and up to 4 minutes. 

4.15.6.4 IMPACTS ON DESIGN

Even with current exercise countermeasures, strength losses of 5-25% can occur, and 

aerobic capacity is compromised early in the post-flight timeframe. Therefore, the 

design of the egress tasks, markings, and interfaces, such as restraint release, egress 

pathways, and egress equipment location and operation, need to (1) adhere to strength 

limits, such as those specified in HIDH Appendix B for the deconditioned crewmember, 

and (2) provide support functions for the egressing crewmember. Support functions for 

crew egress include clear egress pathways (NASA-STD-3001, V2 8014), hand-holds, 

foot-steps and ladders to aid egress, and optimized mechanisms. Crew survival 

equipment should be operable within the strength requirements for a deconditioned 

crewmember, in the expected posture (e.g., lightweight, easily deployable life raft). 
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Egress pathways need to be free of obstructions (e.g., snags, protrusions, stowed 

items), clearly marked, and illuminated for emergency operations, and the number of 

the operations required for passage should be minimized (such as awkward turns or 

multiple hatch operations; V2 8014). Hatch coverings and door-opening mechanisms 

should also be designed so that the force required to open the mechanism is within the 

range of a deconditioned crewmember (that is, minimal; NASA-STD-3001, V2 8025) 

and the crew can egress safely within the time required (NASA-STD-3001, V2 8014 and 

V2 8024). 

The combination of decreased strength, endurance, and sensorimotor adaptation puts 

the crew at increased risk of falling. This increased risk of falling, combined with 

reduced BMD and decreased bone strength, puts the crew at increased risk of fracture 

post landing. As the exact amount of bone loss, and thus the functional implications, 

cannot be predicted ahead of the flight, the design must attempt to reduce the 

probability of falling and the occurrence of fracture. This involves removing egress 

obstacles, not requiring crewmembers to perform strenuous tasks or tasks that put them

in awkward postures, and preventing heavy loading on the bone. Utilizing the same 

support functions outlined for muscle and aerobic deconditioning should also prevent 

loss of bone strength.

Consideration must be given to the design and scheduling of crew tasks. In terms of 

muscle deconditioning, this is important to ensure that (1) crewmembers have reserve 

capacity to perform contingency or emergency response procedures, and (2) the 

composite task can be completed safely and effectively. For example, it is possible that 

a crewmember can complete any given task, nominal or off-nominal, individually, but 

the composite task combined with deconditioning may exceed the capabilities of the 

deconditioned crewmember. 

4.15.7 SUMMARY

This chapter addressed some of the major physiological changes induced by space 

flight deconditioning. The effects of deconditioning are measurable and observable in 

decrements to sensorimotor function, aerobic capacity, and orthostatic tolerance, and in 

loss of muscle and bone strength. The result of space flight adaptation by the human 

body at landing, if not mitigated in full or in part by in-flight countermeasures, includes 

muscle atrophy, reduced orthostatic tolerance, reduced aerobic capacity, sensorimotor 

dysfunction (including gait instability and altered dynamic visual acuity), decreased bone 

mineral density, and changes in bone architecture. Table 4.15.7-1 provides an 

overview of crewmember deconditioning symptoms, effects, and design impacts during 

flight and during the descent and landing mission phases.
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TABLE 4.15.7-1 OVERVIEW OF CREWMEMBER DECONDITIONING

In-flight Descent & Landing

Symptoms Effects Design

Impacts Symptoms Effects DesignImpacts

Sensorimotor SMS (early in flight )

Nausea or vomiting, 

malaise, headache

Restricted 

movements, 

reduced activity

Minimize activity;

provide easy access 

to sickness bags 

and medical kit; 

provide mobility aids

SMS

Nausea or vomiting, 

malaise, headache

Decreased dynamic 

visual acuity, nausea 

or vomiting, gait and/or 

eye-hand coordination 

disturbances, ataxia, 

reduced performance

Openings and walkways that 

accommodate unsteady, deconditioned 

crewmembers; assisted egress; provide 

hand-holds, minimize activity and wholebody and head movements; increased 

task time

Muscle Reduced strength N/A Exercise hardware Fatigue, exhaustion Decreased muscle 

mass, strength, and 

endurance; reduced 

performance

Openings and walkways that 

accommodate unsteady, deconditioned 

crewmembers; provide hand-holds and 

ladders for stability; minimize lifting; 

minimize force required of mechanisms; 

assisted egress

Bone N/A N/A Exercise hardware None Decreased bone 

density, altered bone 

architecture, increased 

fracture risk

Remove obstructions to egress; provide 

hand-holds and ladders for stability;

provide assisted egress

Orthostatic 

Hypotension

N/A N/A Compression 

garments and 

exercise hardware

Presyncope or 

syncope, swelling of 

the lower extremities

Incapacitated 

crewmember Provide compression garments for egress; 

provide fluids and salt for fluid-loading 

reentry protocol; provide cooling; provide 

recumbent seating; provide assisted 

egress

Aerobic

Capacity

Reduced endurance, 

fatigue

N/A Exercise hardware Fatigue, exhaustion Decreased endurance, 

reduced performance

Openings and walkways that 

accommodate unsteady, deconditioned 

crewmember; provide hand-holds and 

ladders for stability; minimize force 

required of mechanisms; assisted egress
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In general, crewmembers should not be required to egress their seats unassisted for 

any reason post landing. In the event of an emergency, such as an unassisted egress, 

the crew should not be required to make sudden movements, lift heavy objects, or 

assume awkward postures. Egress pathways need to be clear of obstructions (with 

appropriate toe clearances, and free of snags, protrusions, stowed items, and other 

obstructions), clearly marked, illuminated for emergency operations, and the number of 

the operations required for passage should be minimized. Several design 

countermeasures should be in place throughout the flight and/or before landing to 

reduce the effects of deconditioning on post-landing operations, including exercise 

hardware and protocols, compression garments, and fluid loading.

For complete scientific summaries of the space flight-induced physiological changes, 

see the Human Research Program’s Evidence Books 

(http://humanresearchroadmap.nasa.gov/evidence/). The evidence books provide the 

current record of the state of knowledge from research and operations for each of the 

defined human health and performance risks for future NASA exploration missions.

4.15.8 TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.15.8-1 are recommended.
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TABLE 4.15.8-1 DECONDITIONING TECHNICAL PRODUCTS

Technical Product Phase A

Phase 

B

Phase 

C

Phase D

SRR SDR PDR CDR SAR FRR

A description of the ConOps. I U U U --- ---

A description and justification of chosen deconditioning

mitigation strategies and/or countermeasures for the 

defined ConOps and scenarios.

--- I U U --- ---

A summary of how deconditioning has been 

accommodated in the design.

--- --- I U U ---

An assessment of efficacy of the deconditioning 

countermeasures in appropriate flight analogs. --- --- I U U ---

Verification plan, including how deconditioning mitigations 

will be assessed.

--- --- I U U ---

Validation of efficacy of selected deconditioning 

countermeasures.

--- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations 

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of the mission objectives, mission duration, and number of intended EVAs. 

Justification for Proposed Mitigation Strategy

The developer is expected to consider all mitigation strategies and propose the method 

most suitable to the design reference mission. Justification of why this method is the 

most suitable is required.

Summaries of Modeling, Analyses, and Evaluations

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-system integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how critical design decisions 

were assessed. Modeling, analysis, and/or evaluation are required to progressively 

demonstrate that the operational concept meets system requirements for operational 

safety, efficiency, and user interface design.

Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 

Validation of Method

A summary of the validation performed is required, to determine that the selected 

mitigation strategy will ensure crew safety and efficiency.
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4.15.9 REFERENCES

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Bishop, P. A., Lee, S. M., Conza, N. E., Clapp, L. L., Moore, A. D., Jr., Williams, W. J.,

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Fritsch-Yelle, J. M., Whitson, P. A., Bondar, R. L., & Brown, T. E. (1996). Subnormal 

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Lee, S. M., Schneider, S. M., Boda, W. L., Watenpaugh, D. E., Macias, B. R., Meyer, R. 

S., & Hargens, A. R. (2009). LBNP exercise protects aerobic capacity and sprint speed 

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Trappe, T. A., Burd, N. A., Louis, E. S., Lee, G. A., & Trappe, S. W. (2007). Influence of 

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4.16 DESIGN FOR MITIGATION OF DECOMPRESSION SICKNESS RISK

4.16.1 INTRODUCTION

Life on Earth exists under Earth-normal atmospheric pressure (14.7 psia, 101.3 kPa, 

760 mmHg) and Earth-normal gravity (1g). Earth-normal atmospheric pressure is just 

one pressure in a range of higher and lower pressures at which humans can 

comfortably exist. It is the rapid transition from a high to a low pressure that is the 

concern for decompression sickness (DCS). These transitions occur at different stages 

for diving and space flight. A diver experiences DCS after completing tasks at depth 

(higher pressure) and then returning to the Earth-normal atmospheric pressure at the 

surface. By contrast, an astronaut performing an extravehicular activity (EVA) in a 

spacesuit is afflicted with DCS because of the decrease in pressure from the spacecraft 

cabin to the spacesuit. Although DCS is a significant health risk in both settings, it is 

space flight DCS that can compromise crew health, EVA success, and ultimately the 

success of a mission. DCS in astronauts is both a medical and a productivity concern,

and both aspects must be considered in the definition of an acceptable risk level and 

development of a mitigation process.

Preventing DCS is preferred over treating the resulting signs and symptoms. Complete 

prevention is possible, but at significant cost, whereas management of DCS risk is often 

the practical approach used by a mitigation process. The overall scope of this section is 

to discuss DCS mitigation for planned decompressions. Decompression occurs most 

commonly during an EVA, but some of the mitigation strategies described are also 

applicable when the vehicle cabin is depressed as part of a staged decompression 

strategy to reduce the overall risk of DCS in preparation for phases of operations that 

have a higher frequency of EVAs.

4.16.2 DCS SIGNS AND SYMPTOMS

DCS signs and symptoms are historically classified as Type I, Type II, and skin bends. 

At JSC, Type I symptoms are described as “pain only” DCS symptoms localized in 

muscle(s) or joint(s) and can include localized paresthesia and simple skin bends. Type 

I symptoms can result in an EVA termination or abort and jeopardize mission success. If 

not treated, Type I symptoms can eventually become incapacitating and jeopardize 

recovery of an EVA crewmember. 

Type II symptoms are systemic, generally neurological, involving the central nervous 

system; or cardiopulmonary, resulting in pulmonary “chokes,” circulatory collapse, 

shock, and even death; and may include multiple site paresthesias. Type II symptoms 

require immediate EVA abort and jeopardize both mission success and crewmember

health. Type II symptoms may or may not be preceded by Type I symptoms and may 

be life-threatening, especially in the EVA environment, if not abated by an increase in 

pressure and adjunctive treatment.
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Cutis marmorata is a type of skin bends, more serious than Type I skin bends, in which 

the skin has a marbled or mottled appearance. At JSC, this serious type of skin bends 

is categorized separately from Type I and Type II DCS. 

DCS is also associated with gas embolism (the presence of gas bubbles in the vascular 

system), both venous gas emboli (VGE) and arterial gas emboli (AGE). Most physicians 

prefer not to allow for circulating VGE, with or without a patent foramen ovale (PFO), 

which is a hole in the wall separating the right and left atria of the heart. A PFO is a 

remnant of life in the womb, where oxygenated blood from the placental circulation is 

shunted away from the pulmonary circulation of the fetus. This connection closes in 

most newborns, but about 25% of the adult population has some small patency (hole) 

that allows oxygenated and deoxygenated blood to mix, potentially putting them at 

greater risk for DCS. If denitrogenation is not effective, either because of inadequate 

vehicle design or inadequate operational prebreathe (PB) protocols, then the resulting 

presence of VGE during an EVA could cross through a patient PFO under particular 

conditions and become arterialized. A high number of VGE entering the pulmonary 

circulation can put astronauts at high risk of arterializing VGE that are normally filtered 

out by a healthy lung. AGE put the astronaut at risk of vascular blockages and resulting 

ischemic damage to the brain or other organs.

4.16.3 BACKGROUND

Space flight DCS can occur as a result of moving from a higher atmospheric pressure to 

a lower pressure. This pressure change most often happens during an EVA, but could 

happen during a reduction in cabin pressure in preparation for EVA activities, or during 

an emergency. A fundamental axiom of DCS is that a transient gas supersaturation, 

also called over-pressure or pressure difference (ΔP), exists in a tissue region. The 

sum of all gas partial pressures in that region is greater than the ambient pressure, 

causing the release of the gas. Expressed as an equation, supersaturation exists when 

ΔP is positive:

 n

P =  (Pi - P2), Eq. 1

 i = 1

where Pi = the summed dissolved gas tensions of oxygen (O2), carbon dioxide (CO2), 

nitrogen (N2), and water vapor (H2O) in the tissue; and P2 = the ambient pressure after 

depressurization. The potential for bubble nucleation and rate of bubble growth are a 

function of supersaturation.

Gas supersaturation in the tissue is not in itself harmful, but it is a thermodynamically 

unstable condition between the tissue and the surrounding environment. The difference 

between tissue gas partial pressure and ambient pressure is easily resolved with a 

phase transition, and some of the excess mass (moles) of gas in the form of bubbles 

may be accommodated by the tissue and cause no symptoms. However, when a gas 

space is formed because of partial or complete desaturation of a supersaturated tissue, 
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there is a probability of DCS (P(DCS); Weathersby, Homer, & Flynn, 1984). A 

necessary but insufficient condition for DCS is the formation of a gas phase in the 

tissue, which may result in pain. The assumption that due to evolved gas, pain results 

from the deformation of tissue past a critical point may not account for symptoms other 

than pain-only DCS, but evolved gas is certainly the primary insult for all subsequent 

signs and symptoms. It is not the presence or even the volume of evolved gas in the 

tissue that is important in pain-only DCS; it is the pressure difference between the gas 

space and the tissue that is important. The pressure difference is termed “deformation 

pressure” (Nims, 1951).

Multiple strategies can be used to prevent DCS. The first strategy would be to prevent a 

change in the atmospheric pressure. This could be done by providing sufficient ambient 

gas pressure around the body by means of a mechanical structure. The use of Earthnormal atmospheric pressure (14.7 psia) inside the spacecraft, habitat, or spacesuit 

eliminates DCS risk.

A second strategy exposes the body to a hypobaric (lower pressure) environment but 

reduces ambient pressure at a rate that avoids or limits the formation of bubbles in the 

tissues, as denitrogenation occurs during the slow depressurization. However, when an 

astronaut transitions to a hypobaric environment, the amount of inert (nonphysiological) 

gas in excess of what can be held in solution at the new, lower pressure has the 

potential to come out of solution to form gas spaces that can displace or otherwise 

damage tissues. 

Displacement of tissue by trapped gas spaces or disruption of metabolic function by 

embolic obstruction of blood flow can cause a wide range of signs and symptoms. To 

avoid this, an effective third strategy is to perform an O2 PB, either resting or during 

exercise, before a transition to a hypobaric environment. Current suit technology, 

especially in the design of gloves, limits operation at higher suit pressures without an 

increase in crew fatigue and reduced mobility. So, reducing the risk of DCS by operating 

at a higher suit pressure during EVA has significant operational limitations. Therefore, 

NASA’s current primary mitigation strategy is through denitrogenation, which can be 

achieved in several ways, dictated by the constraints of EVA operations. 

Denitrogenation is the process of removing inert tissue nitrogen from the body and is 

most often accomplished through breathing 100% O2 (an O2 PB or PB). O2 PB can be 

accomplished through a tight-fitting oronasal mask or in the EVA suit. Both methods 

have some associated difficulties. Using a mask requires a break in PB to don the EVA 

suit, and performing O2 PB in the EVA suit requires extending the time in the suit. 

Denitrogenation protocols are effective in reducing VGE and AGE, as well as the 

P(DCS). After denitrogenation, an astronaut has reduced tissue N2. The amount of 

dissolved N2 that transforms into evolved gas under a modest supersaturation after a 

PB is very small, but is significant because of volume expansion (Boyle’s Law) at the 

new lower pressure. The denitrogenization strategy is not as safe as maintaining Earthnormal atmosphere, but increases the efficiency of a PB protocol to perform EVAs.
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4.16.4 APPLICABLE REQUIREMENTS

The following NASA-STD-3001, Volume 2 requirements are related to the mitigation of 

DCS:

 Decompression Sickness Risk Identification [V2 6008]

 Decompression Sickness Capability [V2 6009]

 Suit Decompression Sickness Treatment Capability [V2 11008]

4.16.5 DEVELOPMENT OF A DCS MITIGATION PROCESS

New space flight programs will need to either select and modify an existing DCS 

mitigation strategy or develop a new strategy, in conjunction with vehicle design. It is 

wise to consider the strategy options early in the design life cycle to save potential 

redesign costs later. Several of the strategies outlined below have significant impacts on 

design, requiring consideration of EVA frequency and the mitigation of DCS risk early in 

the design life cycle. 

4.16.5.1 DEFINE LEVEL OF ACCEPTABLE RISK

In future revisions of NASA-STD-3001, Volume 1, a standard will define the acceptable 

risk for space flight DCS for nominal EVAs. Nominal EVAs shall be performed using 

validated protocols that allow crewmembers to perform an EVA with a total risk of DCS 

≤ 15% and Grade IV VGE ≤ 20% per person with 95% statistical confidence, and no 

reports of Type II DCS. The rationale is that when Type I DCS is reported at ≤ 15%, 

there have been no reported cases of Type II DCS. Beyond this standard, the P(DCS) 

may need to be reduced further to ensure mission success. Considerations include the 

importance of a successful EVA for a particular mission scenario, the available crew to 

perform EVA in the event DCS removes an astronaut from the EVA rotation, the 

association between the P(DCS) and the severity of symptoms (Allen, Maio, & Bancroft, 

1971), and the availability of effective DCS treatment capability in a remote location. It is 

forward work to establish the level of acceptable risk for vehicle planned 

decompressions, but until then all decompressions should meet the limits established 

for EVAs.

4.16.5.2 DEVELOP CONCEPT OF OPERATIONS AND CHARACTERIZE EVA

An evaluation of the Concept of Operations (ConOps) should including a clear 

understanding of the mission objectives, cabin atmosphere, number of intended EVAs, 

frequency of EVAs, time to prepare for EVA, the activities required during EVAs, and 

the goals of each EVA. EVAs are the primary driver for selection of a DCS mitigation 

strategy. It is unlikely that the current protocols for ISS will be sufficient to support 

anticipated exploration mission EVAs, as they require significant crew time and 

consumable usage. For exploration missions, it is expected that the time to prepare for 

EVA will need to be minimized, especially if EVA durations are short and frequent. The 

physical activity on the surface of an asteroid, planet, or moon must be understood 

since the type, intensity, and duration of exercise during an EVA significantly influences 
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the P(DCS). Also, a mitigation strategy for contingency EVA operations must be 

defined. 

As described below, if the frequency of EVAs is high for a mission, then a staged 

decompression combined with an EVA suit that is both easy to don and doff and a 

quick-access entrance/exit from the vehicle will be the best design solution, given 

current knowledge. If the EVA preparation time is minimal, then multiple EVAs are 

possible within 1 day, taking advantage of the physiology of intermittent recompression.

However, if EVAs will be relatively infrequent (e.g., once per month, or even once per 

week), a staged decompression is advantageous, but a PB protocol and an airlock 

entrance/exit strategy may be sufficient to prevent DCS. Preferable mitigation strategies 

cannot be determined solely on the basis of the frequency of EVAs. There must be an 

appropriate balance between cost, consumable usage (and weight), crew workload, and 

other factors.

4.16.5.3 DEVELOP MITIGATION SOLUTIONS

Once acceptable risk is determined and the EVA and overall mission objectives are 

understood, the next step is to develop a DCS mitigation strategy. DCS mitigation can 

be accomplished through engineering design solutions in concert with operational 

procedures. The 4 protocols currently available for use on the ISS all rely primarily on 

operational procedures. The Space Shuttle staged protocol is a good example of a 

combined design solution using a partial decompression of the shuttle cabin in 

conjunction with a reduced operational in-suit PB time. 

It is assumed that a nominal vehicle cabin atmosphere is 14.7 psia. Therefore, 

transitions from this atmosphere require consideration of a DCS risk mitigation strategy. 

However, even lower nominal cabin pressures (e.g., 10.2 psia) will require mitigation of 

DCS if the crew will be transitioning to another pressure, such as that supported by an 

EVA suit. The Extravehicular Mobility Unit (EMU) currently operates at 4.3 psia, but 

other suit pressures are possible. For example, the Apollo suit operated at 3.75 psia, 

which was determined to be as low as possible with a safety margin to prevent hypoxia. 

Considerations for selection of a nominal suit pressure include several factors. 

Crewmember effort to overcome the stiffness of the suit is considered to decrease as 

the suit pressure decreases, but the lowest achievable suit pressure is bounded by 

hypoxia mitigation. The length and complexity of the denitrogenation process is based 

on the difference between the cabin atmosphere and the suit pressure. To minimize this 

difference, an EVA suit that operates at higher pressure or a staged decompression 

protocol, which lowers the nominal cabin pressure, can be used. Lowering cabin 

pressure to reduce ambient N2 partial pressure likely includes an increase in O2

concentration to mitigate hypoxia and to further reduce N2 partial pressure. This 

approach certainly has an impact on vehicle design, as reducing tissue N2 partial 

pressure to minimize the final in-suit PB time introduces a new risk of increased 

flammability and the cost of selection of compatible materials. 
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The following sections will detail several mitigation strategies to reduce P(DCS). The 

selective use of any or all of these strategies depends on the EVA and mission 

objectives in combination with the available resources.

4.16.5.3.1 MINIMIZE PRESSURE REDUCTION

Avoiding or minimizing transition to a hypobaric (lower pressure) environment avoids or 

limits the formation of bubbles in the tissues. Therefore, the first logical mitigation 

approach is to minimize pressure reduction. However, if an EVA must be performed, the 

crew will need to transition to a hypobaric environment because high-pressure suits,

operating between 8 and 10 psia, that minimize the need for a PB are not yet practical, 

due to restricted mobility. However, higher pressure EVA suits may be used in the 

future to achieve the approximate threshold pressure to eliminate DCS (about 9.0 psia). 

Even a modest increase from the current EMU pressure of 4.3 psia reduces the PB 

(denitrogenation) time significantly. For instance, the Russian Space Agency uses the 

Orlan suit at 5.8 psia after an effective PB of about 60 min, so a higher pressure suit is a 

possible solution.

4.16.5.3.2 DEVELOP PREBREATHE PROTOCOL

If an EVA must be performed, then a denitrogenation protocol must be used. A PB 

protocol at 14.7 psia is an advantageous option for missions requiring a low frequency 

of EVAs. In general, PBs take several hours to complete, and thus may not be 

operationally efficient for missions requiring a higher frequency of EVAs.

The first step in defining a new PB protocol is to justify the operational need for a new 

protocol. At present 4 PB protocols are used on the International Space Station (ISS), 

each with advantages and disadvantages depending on the planned EVA. Mission 

managers and crewmembers weigh several factors, such as availability of consumables 

and crew time, functionality of available equipment (exercise equipment, PB masks, O2

monitors), and crew preference, when making a choice of PB protocol. The protocols 

are acceptable for use because ground testing and analysis and operational 

implementation have shown the protocols to be safe and reliable. 

The following are PB considerations:

 It is important to define the minimum PB durations that protect the greatest 

number of EVA astronauts, whether they are male or female and given a 

reasonable range of body types. In general, the amount of N2 in the fat tissues of 

women is greater than in men, and the amount of N2 in lean tissues of men is 

slightly greater than in lean tissues of women. Given enough PB time, the same 

total volume of N2 would be removed from both genders. As PB time is always 

limited, the kinetics of N2 elimination and the relative contributions of N2 from the 

fat and lean tissues during a limited PB must be considered. 

 Given that PB time is limited, it is possible to reduce the DCS risk by limiting the 

exposure time and physical activity after the decompression. Although these 

methods are effective, they are not acceptable as mitigation approaches for most 

applications that require EVA. 
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 Some evidence exists that certain people may be resistant to DCS (Kumar, 

Waligora, & Gilbert, 1992; Weathersby, 1989; Webb, Pilmanis, Balldin, & Fischer, 

2005). Certain factors have been evaluated including age (Conkin, Klein, & 

Acock, 2003; Eckenhoff, Olstad, & Carrod, 1990; Cameron, Olstad, Clark, 

Gelfand, Ochroch, & Eckenhoff, 2007; Sulaiman, Pilmanis, & O’Connor, 1997; 

Carturan, Boussuges, Vanuxem, Bar-Hen, Burnet, & Gardette, 2002), gender 

(Vann, Denoble, Emmerman, & Corson, 1993; Webb, Kannan, & Pilmanis, 2003; 

Conkin, 2010; Thompson, Chhikara, & Conkin, 2003), aerobic fitness (Dujic, 

Duplancic, Marinovic-Terzic, Bakovic, Ivancev, Valic, Eterovic, Petri, Wisloff, & 

Brubakk, 2004; Dujic, Valic, & Brubakk, 2008; Carturan, Boussuges, Burnet, 

Fondaral, Vanuxem, & Gardette, 1999), hydration (Fahlman & Dromsky, 2006) 

and patent foramen ovale (PFO; Saary & Gray, 2001; Foster, Boriek, Butler, 

Gernhardt, & Bove, 2003). Selecting for natural resistance is problematic and is 

not required if efficient denitrogenation protocols are available. Therefore, 

denitrogenation is a practical means of including the greatest number of 

astronauts in an EVA program. 

 Denitrogenation time can be reduced by incorporating exercise during the PB. 

Sequencing, duration, and intensity of the exercise are factors that need to be 

considered and merit further investigation. 

 Denitrogenation through staged decompression is also practical (see below). 

Although it takes a longer time, a significant portion of denitrogenation can occur 

while the astronaut sleeps, which reduces impact on operational activities. 

 The mechanism for delivering the O2 during a PB and minimizing a break in PB 

need to be considered. Delivery options include a tight-fitting facemask, the EVA 

suit, or possibly an airlock certified to operate with enriched O2. Use of the EVA 

suit is currently the only way to ensure that there is no break in PB. Any maskbased PB will eventually require some break in PB to transition into the EVA suit 

and knowledge about the consequences of a break in PB is inadequate. An 

airlock that supports 100% O2 is an unlikely option for PB delivery as there are 

flammability concerns as well as a large amount of unused O2 that might be 

wasted if it was not reclaimed with another system. An airlock compatible with 

partial O2 enrichment may be a viable option to mitigate concerns with break in 

PB.

4.16.5.3.2.1 CONTROL OF TISSUE MICRONUCLEI INTO GROWING BUBBLES

In addition to reducing the amount of tissue N2, DCS prevention also includes hindering 

the transformation of tissue micronuclei into growing bubbles (Tikuisis & Gerth, 2003; 

Blatteau, Sourauld, Gempp, & Boussuges, 2006). The presence of gaseous micronuclei 

in the tissues permits DCS to occur under modest depressurizations (Weathersby, 

Homer, & Flynn, 1982). Application of a short-duration high-pressure spike while 

breathing 100% O2 is an accepted means to reduce the number and size of micronuclei 

(or change the distribution), as is evident from fewer bubbles or cases of DCS after a 

subsequent depressurization (Evans & Walder, 1969; Ikles, 1970; Vann, Grimstad, & 

Neilson, 1980). A high-pressure spike before EVA, possibly during the PB, is one 

possible intervention to reduce the size distribution of micronuclei in the tissue. 
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However, the difficulty of providing the technology to create the pressure spike may 

prohibit the application of this mitigation strategy. Also, normal physical activity 

establishes a size distribution of micronuclei within tissues that can be modified by 

changing activity or by adaptation to microgravity. Operationally, NASA handles this by 

recognizing that the timing of exercise countermeasures will be important for frequent 

EVA missions. On days when both EVAs and exercise sessions are required, exercise 

should be performed after the day’s EVAs have been completed. Also, if an exercise PB 

is used, the high-intensity phase should be done early in the PB protocol. 

4.16.5.3.2.2 AIR BREAK DURING PREBREATHE

Oxygen PB can be accomplished by means of either a tight-fitting oronasal mask or an 

EVA suit. If a mask is used, eventually a transition from the mask to the suited 

environment must be accomplished. A lengthy break in PB is an operational reality that 

could compromise an otherwise safe denitrogenation procedure and jeopardize a 

scheduled EVA. Current NASA Aeromedical Flight Rules define O2 payback time on the 

basis of the phase and duration of a simple air break during a PB. Payback time is the 

number of minutes of additional PB time needed to compensate for an interruption in 

the original PB time. For air breaks during resting PB, the payback time on 100% O2 is 

2 times the duration of the air break. For an air break that occurs early in an exercise 

PB protocol, the payback time is 4 times the duration of the air break. A break in PB 

that lasts longer than 10 min requires that the PB be repeated from the start, or that the 

crew switch to an alternative PB. 

Various methods to preserve the quality of, and confidence in, the PB during the 

transition from mask to suit have been evaluated at JSC, and all were found to be 

inadequate (Bateman, 1951; Clarke, Humm, & Nims, 1945; Cooke, 1976; Adams, 

Theis, & Stevens, 1977; Horrigan, Wells, Hart, & Goodpasture, 1979; Dixon, Adams, 

Olson, & Fitzpatrick, 1980; Barer, Vakar, Vorob’yev, Iseyev, Filipenkov, & Chadov, 

1983; Pilmanis, Webb, Balldin, Conkin, & Fischer, 2010). Thus, payback time is 

required. In effect, the inability to avoid a potentially long air break in PB at 14.7 psia 

and uncertainty of the consequences of an air break during PB were responsible for the 

development of the staged denitrogenation protocols on the Shuttle and the ISS 

(Powell, Horrigan, Waligora, & Norfleet, 1994; Horrigan & Waligora, 1980). Use of a 

mitigation strategy other than, or in conjunction with, a PB is necessary if a long air 

break is anticipated. Any design of an EVA system should minimize the chance of an 

interrupted PB, an interruption that renitrogenates tissues. For example, removing the 

O2 mask while at 10.2 psia and breathing a 26.5% O2 atmosphere during the Shuttle 

staged protocol, the ISS campout, and ISLE PB protocols is an acceptable break in PB 

since denitrogenation, and not renitrogenation, continues albeit at a reduced rate. The 

crew can take the required time to complete suit donning without rushing to reestablish 

the final in-suit denitrogenation. 

4.16.5.3.3 STAGED DECOMPRESSION

For mission phases that have a high-frequency EVA requirement, a staged 

decompression strategy is the most efficient solution since it minimizes in-suit PB time, 
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minimizes the impact of an air break during PB, and provides the opportunity to partially 

denitrogenate without interfering with crew activities. A staged decompression involves 

reducing the overall cabin pressure (e.g., from 14.7 to 10.2 psia) for a predetermined 

amount of time (such as 24 hours) and then completing the O2 PB required for suit 

donning. Since the cabin pressure was decreased before suit donning, the final in-suit 

PB time is also reduced (allowing more frequent EVAs). Once the EVAs are complete, 

the cabin pressure is returned to normal operating pressure (e.g., 14.7 psia). 

The Shuttle staged protocol is a successful example. The orbiter cabin was maintained 

at a setpoint of 10.2 psia and 26.5% O2 until all the EVAs for the mission were 

completed. Recent discussions have proposed a cabin environment of 8.0 psia and 

32% O2 (NASA, 2010) and more recently 8.2 psia and 34% O2 (for new vehicle/habitat 

designs). Once the blood is saturated with O2 at this environment for 24-36 hours, the 

O2 PB requirements are reduced to only what is required to complete the suit-donning 

process. When this environment is coupled with a rapid suit-donning process, such as 

the use of a rear-entry EVA suit with a suitport, the transition from the cabin to EVA 

could be as short as 15 min.

One challenge with a staged decompression protocol is the cost-benefit trade process. 

Reduction of the ambient pressure reduces the DCS risk, by decreasing the inspired 

partial pressure of N2 (PIN2) from the initial Earth-normal PIN2 (Maio, Allen, & Bancroft, 

1970; Allen, Maio, Beard, & Bancroft, 1969; Cook & Robertson, 1974; Horrigan & 

Waligora, 1980; Waligora, Horrigan, Hadley, & Conkin, 1983). To minimize hypoxia, the 

staged depressurization approach requires an increase in O2 concentration, which 

further reduces PIN2. However, O2 can be enriched only to a certain point before 

flammability concerns may limit any further increase. Therefore, a balance must be 

achieved between the increased risk of fire at higher O2 concentration and the 

decreased risk of DCS as PIN2 is reduced. The concentration of O2 and, therefore, the 

risk of fire for a given ambient pressure, can be reduced further if PIO2 is less than 150 

mmHg, but not so low as to cause significant hypoxia (Conkin & Wessel, 2008). 

Denitrogenation may be effective to reduce the P(DCS), but even effective PB protocols 

may be associated with an incidence of VGE; many more subjects have VGE than 

report DCS, even in protocols with low DCS incidence. Significant VGE insult of the 

lungs at 4.3 psia increases the chance of transporting VGE through the pulmonary 

vasculature or through a PFO (Foster, Boriek, Butler, Gernhardt, & Bove, 2003; Moon, 

2000; Pilmanis, Meissner, & Olson, 1996). Designers of a future habitat atmosphere 

should consider a low PIN2 to shorten or eliminate the PB time. One practical approach 

to reduce the PIN2 is to increase the PIO2 while also reducing the ambient pressure 

(Allen, Maio, Beard, & Bancroft, 1969; Cooke, 1974; Horrigan & Waligora, 1980). The 

atmosphere for Skylab achieved a working balance between risk and reward. The 

science and medical community accepted 70% O2 at 5.0 psia, since the Earthequivalent PIO2 would be 150 mmHg, and the risk of atelectasis was minimized 

because the atmosphere was 30% N2. Scientists on Earth did not have to provide a 

hypoxic or hyperoxic environment as part of their ground-based control studies, so μg 

was the only experimental variable. No dedicated PB was needed before EVAs were 

undertaken from Skylab in spacesuits pressurized to 3.7 psia since the tissues would 
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eventually equilibrate to a PIN2 of no more than 1.2 psia, far below the suit pressure. 

Various restrictions, such as uncomfortable flame-retardant polybenzimidazole clothing, 

were imposed because of the serious risk of fire in a 70% O2 atmosphere. Skylab was a 

success, and the need to confront several technical issues early in the mission showed 

that an effective EVA capability is critical to the success of long-duration missions.

Another concern with a staged decompression protocol is that the initial pressure 

reduction likely transforms a subpopulation of tissue micronuclei into “silent” 

(asymptomatic) bubbles in some astronauts, so a 60-min PB with a mask was 

performed before the initial modest reduction in ambient pressure to 10.2 psia for the 

Shuttle staged protocol occurred (Degner, Ikels, & Allen, 1965; Waligora, Horrigan, 

Conkin, & Hadley, 1984; Damato, Highly, Hendler, & Michel, 1963; Vann & TorreBueno, 1984; Hills, 1985). Some form of this initial PB would also take place with a 

staged decompression to an 8.0-psi cabin pressure.

Staged decompression is the preferred strategy for missions requiring frequent EVAs 

(e.g., more than once per week), because of concern over the PB time required and the 

length of the break in PB for suit donning. A staged decompression protocol requires 

that the vehicle be designed (from early in the design life cycle) to ensure compatibility 

with the lower pressure and the O2-enriched environment, and to accomplish these 

transitions in a controlled manner so that DCS risk can be minimized during the first 

transition from 14.7 psia to the incremental pressure. The hardware and systems must 

be designed to function safely at the various predetermined pressures and oxygen 

concentrations. Designers must also consider how the EVA crewmember will enter and 

exit the vehicle, as the benefit of a reduced PB will not be realized if the EVA suit 

preparation process takes an excessive amount of time. 

4.16.5.3.4 INTERMITTENT RECOMPRESSION

Intermittent recompression is a technique that reverses the growth of bubbles during a 

staged decompression or even during future exploration EVAs by an exposure to a 

higher pressure for a short period. A recompression step while the EVA crewmember is 

in the suit is more effective because the crewmember is breathing 100% O2, but it is 

also effective when the crewmember is returning to the vehicle/habitat pressure and 

breathing environment. The intermittent recompression pressure is an increase in 

pressure, but is smaller and longer than the “spike” pressure discussed above. The 

rationale for the maneuver is based on the physics of gas exchange between tissue and 

bubbles when pressure is applied during the time of bubble growth (Gernhardt, 1991; 

Abercromby, Gernhardt, & Conkin, 2008; Conkin, Gernhardt, Abercromby, & Dervay, 

2008). During this recompression, the increased O2 window (Van Liew, Conkin, & 

Burkard, 1993) and the benefit of surface tension on very small bubbles temporarily 

reverse the N2 diffusion gradient so that N2 leaves the bubble and is transported in a 

dissolved state. When the decompression resumes, less N2 is available to move into a 

smaller size distribution of bubbles. The net effect is to reduce the opportunity for 

evolved gas in silent bubbles to reach a threshold that initiates signs and symptoms of 

DCS. This technique is already part of the operational PB protocols on the ISS and 

may be used in future exploration EVAs. 
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Examples of intermittent recompression in the existing ISS protocols include the return 

to 14.7 psia after a short suit-donning period at 10.2 psia in both the Exercise and the 

In-suit Light Exercise (ISLE) PB protocols and 2 returns to 14.7 psia over the course of 

the longer campout PB. These intermittent recompressions likely reduced the 

subsequent P(DCS) by removing silent bubbles. These bubbles have the potential to 

form from a limited number of large-radius micronuclei during the initial depressurization 

to 10.2 psia. After the bubbles are formed and then reabsorbed during the 

repressurization to 14.7 psia while breathing 100% O2, tissues are temporarily left with a 

smaller range of micronuclei radii from which to grow bubbles during the final 

depressurization to 4.3 psia. Research showed that cumulative DCS was not a concern 

in repetitive hypobaric depressurizations (Conkin, Edwards, Waligora, Stanford, Gilbert, 

& Horrigan, 1990; Cooke, Bollinger, & Richardson, 1975; Pilmanis, Webb, Kannan, & 

Balldin, 2002). 

Intermittent recompression might be used even more frequently if the PB time and EVA 

suit preparation time were reduced so that EVAs could be done as required, which is 

the expectation for exploration missions with the Multi-Mission Space Exploration 

Vehicle (MMSEV) (see below), which combines the 8.2 psia / 34% O2 environment with 

a rear-entry suit and suitport operations for rapid suit and vehicle egress and ingress. 

Intermittent recompression is a bonus companion to the staged decompression 

protocol, needed when multiple EVAs are planned within a 24- to 48-hour period. 

Instead of one long daily EVA, as currently performed on the ISS, an astronaut could 

perform several short EVAs, undergoing several recompressions throughout the day 

and an overall reduction in P(DCS). The design of the vehicle would optimize methods 

for ingress and egress from the EVA suit into the vehicle. 

4.16.5.3.5 PROTOCOL CONSIDERATIONS

Designers must consider several factors before selecting a DCS mitigation strategy and 

beginning vehicle design:

 What are the EVA needs from the vehicle? – When frequent EVAs are part of the 

mission architecture, then a DCS mitigation strategy that minimizes crew time 

and especially the PB time and break in PB time is the preferred strategy. 

 What is the vehicle exit strategy? – The design of the vehicle will be greatly 

affected by the choice of an airlock, suitlock, suitport, or depressurizable cabin. 

Airlocks are well understood and were the choice for the Shuttle program and the 

ISS. A depressurizable cabin was the method used by the Apollo program 

because it had low mass requirements and a low-pressure habitat, but it offers 

minimal dust mitigation and planetary protection. A suitport offers direct access 

from the vehicle to the EVA suit and is the most rapid ingress/egress solution, but 

it relies on an EVA suit that can be pressurized nominally to the cabin pressure. 

There also is a suitlock, a hybrid of a suitport and airlock, which keeps the suit 

isolated from the cabin, but protected in a closed environment when it is not in 

use. 
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 How fast does the crew need to get out of the vehicle? – For missions requiring 

single-person, frequent, or unplanned EVAs, the crew may need to exit the 

vehicle in a relatively fast, efficient manner. If the crew needs to exit the vehicle 

quickly, a solution that has no break in PB and that minimizes PB time, suitdonning time, and habitat gas loss is the preferred strategy. 

 Reclamation of gas – For efficiency purposes, consideration should be given to 

the reclamation of gases expelled during the pressure transition and suit-purging 

process. The most efficient strategy is to reclaim the gas in the vehicle 

environment. However, the size of the vehicle has an impact on how much gas 

can be reclaimed, as the overall O2, N2, and CO2 concentrations must be 

relatively stable and within human health limits.

 Target work efficiency index – A target work efficiency index (WEI) is useful in 

planning for EVAs. Currently, the index NASA uses is: EVA time (out of the 

vehicle) / EVA preparation time. ISS-based work efficiency is currently less than 

0.5. Architectures for which a higher WEI of 2-3 is desired would need a 

combination of a staged denitrogenation protocol with efficient suit 

donning/doffing and vehicle ingress/egress.

 Suit donning – Suits should be designed to be donned quickly. The break in PB 

is a serious concern for cases where the mask PB is the primary method of 

denitrogenation. Additionally, missions requiring frequent EVAs will require 

efficient suit donning and doffing procedures.

 Pressure and O2 concentration – A robust, high-frequency EVA program will 

likely need to use a staged denitrogenation strategy that has the crew live in a

lower pressure, O2-enriched environment during the EVA stages of a mission. All 

vehicle elements will need to be compatible with or isolated from this 

environment. Examples of this include the Shuttle operating at 10.2 psia and 

26.5% O2, and the more recent environments discussed, including 8 psia and 

32% O2 (NASA, 2010), which was adjusted to 8.2 psia and 34% O2 (HMTA 

memo). 

The Exploration Atmospheres Working Group final report (NASA, 2010) provides a 

good example of a trade study conducted for an alternative to an Earth-normal 

atmosphere, including all of the factors for designers to consider. Refer to this report, in 

addition to this HIDP section, when selecting a DCS mitigation strategy or conducting 

an atmospheric trade analysis.

4.16.5.3.5.1 EXAMPLE VEHICLE

The MMSEV is an example of a vehicle that had DCS mitigation and high EVA 

capability as key initial drivers for the vehicle design. The MMSEV will be designed to 

operate at environments known to be compatible with other space flight vehicles.

Characteristics of these environments include cabin atmospheres at 14.7 psia (21% O2) 

and 10.2 psia (26.5% O2). In addition, the MMSEV will be designed to operate at 8.2 

psia / 34% O2 during the EVA stages of a mission. The MMSEV has multiple entry 

points including 2 suitports and 2 hatches, and is capable of a full depressurization

during an emergency, if needed. The MMSEV uses suitports as the nominal 
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ingress/egress strategy. The combination of suit ingress, operation checkout, suitport 

operation, and PB is expected to be about 15 min. The EVA suit used with the MMSEV 

will be a variable-pressure suit, compatible with the cabin environment up to 8.2 psia, 

but nominally expected to be used around 4.3 psia. The variable-pressure suit can be 

quickly repressurized to 8.2 psia in the case of a DCS incident, allowing near-immediate 

treatment and quick resolution of any DCS symptoms. 

4.16.5.4 PROTOCOL VALIDATION

The traditional standard approach is to validate any protocol that affects crew health, 

performance, and safety. Empirical validation through testing is preferred over 

validation through analysis. Until high confidence is attained through mathematical 

modeling of DCS, there will always be a requirement to empirically validate a new PB 

protocol.

4.16.5.4.1 PROBABILISTIC DCS MODELING

NASA uses a suite of DCS prediction models for different scenarios, but no combination 

of these models is currently considered robust enough for validation of a new PB 

protocol. These models are used as tools to generate potential PB protocol options, but 

these protocols then require a ground-based hypobaric chamber validation test. Models 

are excellent tools for evaluating subtle changes in parameters critical to P(DCS) such 

as depressurization time or O2 PB time. Therefore, a small proposed operational 

change can be evaluated by modeling in conjunction with expert opinion and may not 

require ground validation testing. A more thorough discussion of DCS probabilistic 

modeling can be found in a recent review by Conkin (2011).

Statistical descriptions of DCS and VGE outcomes from hypobaric exposures, using 

logistic regression and survival analysis as well as biophysical modeling of tissue 

bubble dynamics, have made significant advances in the last 20 years. The integration 

of the 2 approaches has produced sophisticated probabilistic models. Simple 

descriptions of decompression dose, such as tissue ratio (TR) or ΔP, approximate the 

true dose (Conkin, 1994; Weathersby, Homer, & Flynn, 1982) whereas models 

concerning tissue bubble dynamics strive to define true dose through diffusion-based 

physics and consideration of mass-balance (Srinivasan, Gerth, & Powell, 2003; Epstein 

& Plesset, 1950; Van Liew & Hlastala, 1969; Gernhardt, 1991; Gerth & Vann, 1997; 

Thalmann, Parker, Survanshi, & Weathersby, 1997; Srinivasan, Gerth, & Powell, 2002; 

Nickolaev, 2008). Those referenced, and many others as well (Ball, Himm, Homer, & 

Thalmann, 1995; Tikuisis, Gault, & Nishi, 1994; Vann, 1982; Wienke, 1991), may 

contribute to a single evolving model to describe the P(DCS), in both diving and altitude 

depressurizations, by invoking multiple tissue compartments, multiple finitely diffusible 

gases, and a distribution of bubble nuclei that begin to grow at different times during 

depressurization.
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4.16.5.4.2 EMPIRICAL TESTING

Prospective, sequential, statistically driven ground testing using subjects that represent 

the physical characteristics of astronauts is the optimal approach. Integral to this 

approach are accept and reject criteria for a PB protocol. Advancement in 

denitrogenation protocol selection is contingent on establishing a priori success criteria 

for validation trials. Validation trials should be aimed at assessment of the protocol for 

incidence of DCS. 

A sequential design was used to good effect by Kumar et al. (Kumar, Powell, & 

Waligora, 1994) as a means by which to discontinue a trial when statistical significance 

was achieved, thus minimizing risk to research subjects. A sequential design concept 

was applied to the PB protocol selection for the ISS. First, an assessment of the 

maximum impact that a case of DCS would have on the completion of ISS assembly, 

balanced with an ability to effectively treat DCS on orbit, created 3 “accept” conditions 

for validation trials. A PB protocol was acceptable in validation trials for ISS EVA 

operations if no serious case (Type II) of DCS was observed, if the incidence of painonly DCS was ≤15%, and if the incidence of Grade IV VGE was ≤20% (Gernhardt, 

Conkin, Foster, Pilmanis, Butler, & Fife, 2000). Second, the “accept” region during 

sequential trials was set at 95% statistical confidence with the “reject” region set at 70% 

statistical confidence, which avoided continued testing of ineffective protocols. Figure 

4.16.6.4.2-1 is a visual example of how one particular prospective, sequential, statistical 

design was implemented. The area between the 70% reject and 95% accept regions

defines a zone where continued testing is valid. As testing continues, the results trend 

toward the true incidence of Type I DCS. After 40 exposures and 2 cases of DCS the 

protocol was validated, but testing continued so as to reduce the chance of type II

statistical error. The testing was stopped after 47 tests and the protocol was validated 

for mitigating DCS. 
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FIGURE 4.16.6.4.2-1 VISUAL EXAMPLE OF A PROSPECTIVE, SEQUENTIAL, 

STATISTICAL DESIGN. It can be used to limit the true incidence of Type I DCS to < 15% 

at 95% statistical confidence. Two cases in 47 trials means that one is confident that 

P(DCS) is < 15% at 95% confidence. 

For the exercise-enhanced PB protocols, in 50 exposures the observed DCS could not 

exceed 3 cases (6%) and the observed Grade IV VGE could not exceed 5 cases (10%) 

to meet the accept conditions. One of these trials (the current Exercise PB protocol on 

the ISS) met accept criteria with no DCS and only 3 occurrences of Grade IV VGE in 45 

exposures. Another trial (the current ISLE exercise protocol on the ISS) met accept 

criteria with 2 cases of Type I DCS and did not meet either accept or reject criteria with 

8 occurrences of Grade IV VGE in 48 exposures. These protocols were considered 

acceptable for flight after extensive peer review of the research and with the realization 

that operational implementation of an operational PB has always included more PB than 

during ground testing. This will not necessarily be the case for exploration-class 

missions.

4.16.5.5 POST VALIDATION

Once a PB protocol is validated and approved by NASA for operational use, a 

significant effort is expended to operationalize the protocol. This includes documenting 

the detailed steps, procuring and certifying any special equipment, establishing a crew 

training protocol for the PB, developing a treatment response in the event DCS occurs, 

updating Aeromedical Flight Rules, and educating flight surgeons and mission 

managers about the new protocol.

 

For any approved and validated PB protocol, pre-flight crew training needs to be 

completed. The steps to execute a PB are documented, trained, and simulated before 

0 10 20 30 40 50 60 70 80

exposures

0

2

4

6

8

10

12

14

16

18

20

DCS cases

reject at 70%

accept at 95%

47th test
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the first operational use. PB protocols based on individual characteristics, like aerobic 

fitness in the case of the Exercise PB, require that the crew train on the exercise 

devices and that a pre-flight exercise prescription be developed and provided to the 

crew. Information about DCS symptom recognition, levels of impact, and how to 

respond to a case of DCS are also provided to the crew during pre-flight training. 

Training is often conducted in space flight analog environments. Policies and 

procedures are followed that minimize the P(DCS) after hyperbaric suited exposures in 

the U.S. Neutral Buoyancy Laboratory (NBL) and the Russian Space Agency’s 

Hydrolab, during suited exposures in hypobaric chambers, and after diving activities 

from the NASA Extreme Environment Mission Operations (NEEMO) underwater habitat. 

Objectives of an EVA are choreographed on flight-like hardware submerged in 40 feet 

of fresh water (FFW) at the NBL. Training emulates actual EVA scenarios and can last 

for 6 hours. To avoid DCS after long exposures to a maximum physiological depth of 50 

FFW (pool depth plus suit pressure), astronauts breathe nitrox, a mixture of 46% O2 and 

54% N2. At this extreme, the equivalent air depth is 23 FFW. Breathing nitrox eliminates 

the need for staged depressurization at the end of a long training session (Fitzpatrick & 

Conkin, 2003). Astronauts also train and maintain proficiency in operating the spacesuit 

by exposure to vacuum in various altitude chambers at JSC. In some cases, astronauts 

are required to fly in the T-38 aircraft to complete another training activity or may fly on 

a commercial aircraft for personal reasons shortly after a hyperbaric or hypobaric 

exposure. In these cases, specific directives, based on best available research 

(Horrigan, LaPinta, & Conkin, 1989; Vann, Denoble, Emmerson, & Corson, 1993; 

Pollock & Fitzpatrick, 2004), dictate the proper surfacing intervals and PB procedures 

that minimize the P(DCS) on a subsequent hypobaric exposure. 

Procedures and equipment are available to treat DCS on orbit and after training 

activities, and a disposition policy returns astronauts to flight status after they undergo a 

successful treatment regimen. Adherence to these policies, procedures, and 

Aeromedical Flight Rules, which undergo periodic review and update, minimizes the 

chance that DCS will become a medical concern to the astronaut or hinder the 

completion of training or safe execution of an EVA.

4.16.6 CURRENT DCS MITIGATION PROCESSES

Knowledge of ISS and Shuttle operational PB protocols is helpful to appreciate the 

complexity that even simple notions of denitrogenation achieve when they are 

implemented. This section outlines the techniques NASA uses to mitigate the risk of 

DCS when an astronaut transitions from an Earth-normal 14.7 psia spacecraft or habitat 

to the low-pressure EVA environment, which is conducive to evolved gas.

4.16.6.1 PROCESS 1: 4 HOURS IN SUIT 

Shuttle astronauts had the option of an in-suit denitrogenation strategy, for which the 

astronaut simply donned the suit and breathed 100% O2 for 3.5 - 4 hours before an 

EVA. The type and amount of work done in the suit and the duration of decompression 

set the final PB time to achieve an acceptable risk of DCS (Conkin, Waligora, Horrigan, 
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& Hadley, 1987). The operational challenge was to balance the length of the PB with an 

acceptable low incidence of DCS (Waligora, Horrigan, & Conkin, 1987). Waligora, 

Horrigan, Conkin, and Hadley (1984) describe tests of 3.5- and 4-hr PBs at JSC. The 

first of several PB protocols were evaluated with male volunteers in August 1982, and 

DCS was reported after the first 3.5-hr PB in one subject and one Doppler technician 

(Conkin, Powell, & Gernhardt, 2003; Conkin, Edwards, Waligora, Stanford, Gilbert, & 

Horrigan, 1990). A 4-hr PB while resting compared to a 3.5-hr resting PB reduced the 

incidence of DCS from 42% to 21% and the incidence of VGE from 71% to 46% in men 

who ambulated as part of exercise at 4.3 psia (Waligora, Horrigan, Conkin, & Hadley, 

1984; Conkin, Edwards, Waligora, Stanford, Gilbert, & Horrigan, 1990). 

4.16.6.2 PROCESS 2: SHUTTLE STAGED 

The protocol that ultimately became the preferred PB for the Shuttle was achieved in 3 

steps as follows. The first step was an initial 60-min PB by mask, of which 45 min were 

completed before the Shuttle atmosphere was depressurized from 14.7 to 10.2 psia and 

the air was enriched to 26.5% O2 to provide an inspired partial pressure of O2 (PIO2) of 

127 mmHg. The second step was a minimum stay of 12 hr at this intermediate 

pressure. And the third was an in-suit PB before a final depressurization to 4.3 psia, 

lasting 40 to 75 min depending on the time spent at 10.2 psia. Astronauts donned their 

suits at 10.2 psia and performed a final 40- to 75-min in-suit PB before final 

depressurization to 4.3 psia. For Shuttle missions, the cabin was typically depressurized 

on flight day 2 from 14.7 psia to 10.2 psia, and the cabin remained at 10.2 psia until the 

last EVA was completed. 

Optimization of the final Shuttle 10.2 psia staged depressurization protocol took months 

of planning and years of validation. The first critical step was to certify the Shuttle for 

operations at a reduced pressure with an enriched O2 atmosphere, as the vehicle was 

not planned to operate under these conditions. Several interacting variables were 

evaluated in isolation or combination: rate of ascent to intermediate pressure, the 

intermediate pressure itself (equipment cooling issues; Horrigan, Waligora, & Nachtwey, 

1985), the partial pressure of O2 (ppO2) and ppN2 at the intermediate pressure, hypoxia 

and flammability issues (Waligora, Horrigan, Bungo, & Conkin, 1982), length of stay 

(Waligora, Horrigan, Hadley, & Conkin, 1983; Damato, Highly, Hendler, & Michel, 1963),

likelihood of silent bubbles, final suit pressure, duration of EVA, work performed in the 

suit, final in-suit PB time before final ascent, and balancing the acceptable risk of DCS 

during EVA with limited treatment options (Waligora, Horrigan, Conkin, & Hadley, 1984; 

Adams, Dixon, Olson, Bassett, & Fitzpatrick, 1981).

4.16.6.3 PROCESS 3: ISS CAMPOUT 

A modification of the Shuttle staged decompression protocol, which is called the 

campout protocol, is now used on the ISS. Because the entire atmospheric pressure in 

the ISS cannot be reduced to 10.2 psia and enriched to 26.5% O2, 2 astronauts must 

“camp out” at 10.2 psia and 26.5% O2 in the ISS airlock. For various operational 

reasons, the time at 10.2 psia is limited to 8 hr and 40 min, most of which is spent 

sleeping. The lack of food preparation and restroom facilities in the airlock means that a 
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repressurization to 14.7 psia is needed so that crewmembers can use the bathroom and 

prepare food. During this break, the astronauts breathe 100% O2 by means of hose and

mask for a minimum of 70 min. On return to 10.2 psia the masks are removed, the 

crewmembers eat, and the suit-donning process is completed. The airlock is then repressurized to 14.7 psia, after the astronauts don their spacesuits to allow an assistant 

to exit at 14.7 psia, and then the astronauts complete a 50-min in-suit PB before final 

depressurization of the airlock to the vacuum of space. After extensive review, the 

similarity of the campout PB to the Shuttle staged PB, along with good operational 

experience with the Shuttle PB, negated an empirical validation (ground testing) of the 

campout PB. 

4.16.6.4 PROCESS 4: EXERCISE PB AND ISLE PB

After the ISS airlock was delivered on STS-104.7A in July 2001 and before the campout 

protocol was available in September 2006, an option to perform exercise-enhanced 

denitrogenation on the ISS became available. Because the elimination and uptake of 

N2 is a perfusion-limited process, the use of exercise during the PB allows accelerated 

denitrogenation. An exercise PB protocol was needed to avoid scheduling constraints 

on EVAs performed from the ISS, in addition to the ambitious goal of reducing the 4-hr 

in-suit PB by about half. Before the delivery of the Quest airlock, EVAs to support ISS 

construction were performed with hatches closed between ISS and Shuttle so that 

Shuttle staged 10.2-psia PB could be used. The first use of exercise PB was to 

complete the installation of the ISS airlock. The complexity of adding an effective 

interval of exercise during PB must be balanced with the rewards (less total PB time 

and greater reduction in the P(DCS) from an alternative resting PB), or the option is not 

acceptable to the astronaut. In addition, although exercise is an effective 

denitrogenation enhancement, it is also problematic in that exercise is known to affect 

tissue micronuclei. Therefore exercise has both positive and negative effects on the 

P(DCS) and should be properly managed if used during O2 PB.

Two exercise PB protocols that are deemed acceptable for operations on the ISS are 

briefly described. The first of these is the Exercise PB protocol, which uses the cycle 

ergometer with vibration isolation and stabilization (CEVIS) device; and the second is 

the In-suit Light Exercise (ISLE) PB protocol, which uses the Extravehicular Mobility 

Unit (EMU) as a resistive exercise device.

Exercise PB (CEVIS)

For the Exercise PB protocol an astronaut, months before launch, performs a peak O2

consumption test (VO2 peak test) using cycle ergometry, and a linear regression of VO2

vs. watts (workload) is created. An exercise prescription is produced that distributes the 

appropriate workload between the upper body (12%) and the lower body (88%). Before 

performing an EVA, the astronaut breathes O2 from a mask and performs 3 min of 

incremental exercise on the CEVIS at about 75 rpm using a prescription that increases 

work from 37.5% to 50.0% and then to 62.5% of VO2 peak while also rhythmically 

pulling against elastic surgical tubing to include upper body activity. The exercise 

prescription is completed after 7 min at 75% of VO2 peak. After waiting an elapsed time 

of 50 min while still breathing 100% O2 from the mask, the astronauts and an assistant 
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depressurize to 10.2 psia for 30 min in the ISS airlock. During this depressurization, the 

astronauts don the liquid cooling garment and the lower portion of the spacesuit. Once 

the airlock O2 concentration stabilizes at 26.5%, the astronauts and the assistant 

remove the masks and finish donning the upper torso of the spacesuit. Thus, for a good 

portion of the PB time, the astronaut is actively engaged in the suit-donning process. A 

leak check and then purge with 100% O2 to remove N2 from the suit completes the suitdonning procedure. In-suit PB starts in conjunction with a 5-min airlock repressurization 

back to 14.7 psia, where the remaining 55 min of in-suit PB are performed and the 

assistant exits the airlock. The final depressurization to 4.3 psia in the suit and to the 

vacuum of space takes 30 min.

ISLE

For the ISLE PB protocol, the astronaut does not engage in a short bout of intense PB 

exercise on the CEVIS before suit donning at 10.2 psia but instead performs a longer 

bout of mild exercise in the EMU. The ISLE PB protocol shares many steps with the 

Exercise PB protocol but differs from the latter in that 40 min are spent breathing 100% 

O2 by mask followed by a 20-min depressurization to 10.2 psia. Once the astronaut has 

completed suit donning, arm and leg motions are performed in segments of 4 min 

followed by 1 min of rest, in conjunction with a 5-min airlock repressurization back to 

14.7 psia. This mild exercise pattern continues for 50 min and achieves a minimum VO2

of 6.8 ml•kg

-1

•min-1. An additional 50 min of resting in-suit PB completes the protocol,

followed by a 30-min depressurization of the airlock to vacuum (Gernhardt & Pollock, 

2006).

4.16.7 SUMMARY

DCS occurs as a result of changing from a higher to a lower pressure. For astronauts, 

the primary concern is transitioning from the cabin atmosphere to the suit. Because 

space flight DCS can compromise EVA success and ultimately the success of a 

mission, prevention of DCS is crucial. Multiple strategies can be used to prevent DCS. 

The first strategy would be to prevent a change in the atmospheric pressure. A second 

strategy exposes the body to a hypobaric (lower pressure) environment but reduces 

ambient pressure at a rate that avoids or limits the formation of bubbles in the tissues. 

Third, to avoid emboli or embolic obstruction of blood flow, transitions to a hypobaric 

environment are most often coupled with O2 PB to initiate the denitrogenation process 

before depressurization occurs. Four PB protocols are currently available to use on the 

ISS. Development of a new mitigation strategy, such as a PB protocol, involves 

assessment of the level of acceptable risk and the concept of operations, development 

of the mitigation strategy (as described above), validation, operationalization, and 

training.

4.16.8 TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.16.8-1 are recommended.
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TABLE 4.16.8-1 DCS MITIGATION TECHNICAL PRODUCTS

Technical Product Phase A

Phase 

B

Phase 

C

Phase D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, cabin atmosphere, and 

number and frequency of EVAs. I U U U --- ---

A description of DCS mitigation strategies for the defined 

ConOps and scenarios, including cabin depressurization 

(nominal and contingency) and EVA.

--- I U U --- ---

A summary of the DCS mitigation strategy analyses 

performed to date. --- --- I U U ---

Verification plan. --- --- I U U ---

A description of how the selected DCS mitigation strategy 

for the reference mission was validated and determined to 

be acceptable. 

--- --- --- I U ---

I = initial release of item

U = updated release of item

Concept of Operations 

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of the mission objectives, cabin atmosphere, number of intended EVAs, 

frequency of EVAs, and the goals of the EVA. It is unlikely that the current protocols for 

the ISS will be sufficient to support anticipated exploration-mission EVAs, as they all 

require significant crew time and consumable usage. For exploration missions, it is 

expected that the time to prepare for EVA will need to be minimized, especially if EVA 

durations are short and frequent. The physical activity on the surface of an asteroid, 

planet, or moon must be understood because the type, intensity, and duration of 

exercise during an EVA significantly influences the P(DCS). Also, a mitigation strategy 

for contingency EVA operations must be defined. 

Justification for Proposed Mitigation Strategy

The developer is expected to consider all mitigation strategies and propose the method 

most suitable to the design reference mission. Justification of why this method is the 

most suitable is required.

Summaries of Modeling, Analyses, and Evaluations

Iterative summaries of modeling, analyses, and evaluations provide NASA with insight 

into human-system integration technical details throughout the design process. As 

designs mature, modeling, analyses, and evaluations should use inputs and mockups of 

increasingly higher fidelity, as discussed in paragraph 3.2.3.3 Evaluate Designs and 

Iterate Solutions. It is important that summaries address how critical design decisions 

were assessed. Modeling, analysis, and/or evaluation are required to progressively 

demonstrate that the operational concept meets system requirements for operational 

safety, efficiency, and user interface design.

Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement. 
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Validation of Method

A summary of the validation performed is required, to determine that the selected 

mitigation strategy will ensure crew safety and efficiency.

4.16.9 REFERENCES

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4.17 SPACE FOOD SYSTEM DESIGN

4.17.1 INTRODUCTION

The space food system must provide food that is safe, nutritious, and acceptable to the 

crew, to maintain crew health and performance during space flight. Provisioning of a 

space food system begins with qualified personnel, facilities, and equipment. The food 

system must be developed according to the requirements outlined in the NASA-STD3001. The food system is complex, and consideration must be given to multiple factors 

including menu development, suitability in microgravity, acceptability, packaging, safety, 

and stowage. This section describes how to consider these factors when developing a 

food system and provides examples and lessons learned from NASA’s food system. 

More detail on factors that must be considered during food system development can be 

found in the NASA Human Integration Design Handbook (HIDH) section 7.2. 

4.17.2 APPLICABLE REQUIREMENTS

The following requirements from NASA-STD-3001, Volume 2 are applicable to the 

space food system:

 Spacecraft maximum allowable concentrations (SMAC) for airborne 

contaminants [V2 6004; V2 6005; V2 6050]

 Food Quality [V2 7001]

 Food Acceptability [V2 7002]

 Food Caloric Content [V2 7003]

 EVA Food Caloric Content [V2 7004]

 Food Macronutrients [V2 7005]

 Food Micronutrients [V2 7006]

 Food Microorganism Levels [V2 7007]

 Food Preparation [V2 7008]

 Food Preparation and Cleanup [V2 7009]

 Food Contamination Control [V2 7010]

 Food and Beverage Heating [V2 7011]

4.17.3 FOOD DEVELOPMENT

Foods must be developed to be safe, nutritious, and acceptable, and to meet mission 

requirements. To do this, food scientists choose a variety of foods to develop that are 

commonly eaten on Earth, meet the daily caloric needs of the astronauts (per NASASTD-3001), and provide a variety of macronutrients and micronutrients. The current 

space food system contains more than 200 foods, comprising commercially available 

products and foods developed specifically to meet space flight requirements, which 

include meats, side dishes, vegetables, fruits, breads, snacks, and drinks. Currently, 

foods are shipped and stored at room temperature, so they are thermostabilized, 

irradiated, freeze-dried, or low-moisture foods to ensure shelf stability. As processing 

methods in industry advance, other methods may be used to increase food quality in the 

future. Provisioning of condiments such as mayonnaise, mustard, ketchup, and hot 

sauce reduces the monotony of the restricted food variety. Fresh foods also may be 

provided on a limited basis for consumption within the first few days after a resupply 

mission. Fresh food provisioning depends on the ability to stow these foods 
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immediately before launch (and the length of transit time to the crew). More 

information about the various types of foods can be found in the NASA Human 

Integration Design Handbook (HIDH) section 7.2.3.4.

4.17.3.1 MISSION REQUIREMENTS

Before food development, mission and system requirements need to be determined. 

These mission requirements include generic information found in the concept of 

operations, such as mission duration, and information more specific to the food system, 

such as menu cycle length and considerations and limitations of system and 

infrastructure. Often the food system-specific requirements are derived from the mission 

requirements, by relying on historical lessons learned and expertise. 

Mission duration is a key factor in food development. During missions up to 3 days in 

length the resources required to support certain types of foods, such as rehydratables

and heated foods, may not be available because of mass and power constraints. Shelfstable commercially available foods may be provided if they meet space food system 

requirements, including complete nutrition requirements. However, these foods may 

require repackaging for suitability in a microgravity environment. For missions longer 

than 3 days the resources required to rehydrate and heat foods in various packaging 

sizes must be provided to support crew health throughout the mission. As mission 

length increases, more foods that meet requirements will need to be developed, as 

variety promotes healthy eating habits and maintains crew health and performance.

Menu cycle length is another key factor in food development. Currently on the ISS,

NASA provides an 8-day menu cycle for 3 crewmembers and Russia provides an 8-day 

menu cycle for 3 crewmembers. The current NASA food system contains over 200 

foods, but the number of foods needed increases as mission length increases (to be 

greater than the typical ISS mission) and more variety is required to maintain 

consumption. Crews have commented that the current menu cycle is not adequate for 

6-month ISS missions, but the ability to share food (e.g., between astronauts and 

cosmonauts) at crewmembers’ discretion increases the variety and acceptability of the 

cycle length. As mission length increases over 6 months, menu cycle length must 

increase (to be greater than 8 days) to provide variety, which promotes consumption. 

System and infrastructure considerations and limitations must be assessed for food 

development. Rehydration (both hot and cold water) and heating abilities are required 

for missions longer than 3 days. Without rehydration and heating, the variety of food is 

reduced, which decreases consumption, which can lead to health problems. The ability 

to rehydrate and heat foods requires mass, power, and volume. Providing both hot and 

cold water to rehydrate foods allows preparation of freeze-dried foods, powdered 

beverages, and coffees. Providing the ability to heat foods increases the palatability of 

many thermostabilized and irradiated foods that may not be acceptable cold. 

On missions up to 3 days, the capability to rehydrate and heat foods may not be 

provided because of mass, volume, and power constraints. The current food system 

supplies 1.83 kg (0.00472 m3; data determined by measurement) of food and packaging 
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per crewmember per day. This amount, which provides 3000 kcal per day, meets the 

nutritional requirements in NASA-STD-3001. These numbers do not include the mass 

and volume of stowage containers or protective materials, which are determined when 

stowage configuration is determined (see below) because the required number of 

containers and number and type of protective materials varies with the vehicle’s 

stowage configuration.

4.17.3.2 DEVELOPMENT OF FOOD PRODUCTS

Once mission requirements are determined, food products are developed with 

consideration for nutritional content, safety, and acceptability. The food system typically 

contains a mixture of commercial off-the-shelf foods and foods developed specifically 

for space flight by a food scientist. After foods are developed to meet the nutritional 

requirements and are determined to be safe, they are analyzed for sensory acceptability 

(e.g., palatability). Foods that meet safety, nutritional, and acceptability standards are 

included in the space food system. 

The food system must provide the full caloric and nutritional complement outlined in the 

NASA- STD-3001 V2 7003-7006. Currently, foods are tested for macronutrients and a 

few micronutrients through laboratory testing (currently at the NASA JSC Water and 

Food Analysis Laboratory (WAFL), but can be outsourced). Most micronutrients are 

determined through a computer program that uses a food database. Food Processor 

SQL (ESHA Research, Salem, OR) is one of several food programs that will provide 

nutritional estimates. For long-duration missions it will be important to select foods that 

will maintain their macro- and micronutrient content throughout the mission. This may 

require empirical measurement of nutritional content throughout shelf life to ensure that 

food system requirements are continually met, although this may be financially difficult 

for large food systems. 

Each food production lot (each time the food is produced), including commercial foods 

repackaged in flight-approved packaging, must be tested for microbiological safety in 

accordance with SD-T-0252 Microbiological Specification and Testing Procedure for 

Commercially Sterile Foods and SD-T-0251 Microbiological Specification and Testing 

Procedure for Foods Which Are Not Commercially Sterile, as described in NASA-STD3001 V27007 and the NASA Human Integration Design Handbook (HIDH) section 

7.2.3.1.2. 

To ensure that the crew consumes the nutrition and calories required to maintain 

optimum physical and cognitive performance, the food must be acceptable and usable 

during space missions (NASA-STD-3001 V2 7002). Provisioning of nutritious foods that 

are unacceptable will lead to underconsumption, nutritional deficiencies, weight loss, 

reduced cognitive function, reduced physical performance, and even illness (Friedl and 

Hoyt, 1997).

After they are tested for nutritional content and microbiological safety, all potential flight 

foods must be evaluated for acceptability by volunteer panelists in a food evaluation 

session (as described in the NASA Human Integration and Design Handbook (HIDH)
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section 7.2.2.1). A quantitative 9-point hedonic scale, ranging from (9) “like extremely” 

to (1) “dislike extremely,” is used to evaluate multiple food quality factors, such as 

appearance and flavor. Given that statistical power changes with the number of 

panelists (Meilgaard, Civille, & Carr, 1999), it is best to use a large subject sample when 

testing acceptability. Currently 30 panelists are used to evaluate each new food. Items 

that receive an overall score of 6.0 or higher are included in the space food system (6 is 

the lowest “like” score). After a food is included in the space food system, each

production lot for all internally produced and commercial foods needs to be evaluated by 

at least 4 panelists, generally space food system laboratory personnel, before space 

flight. Crewmembers similarly evaluate all flight food options before their missions. This 

information may be used during menu development, described below.

In addition to nutritional content, safety, and acceptability of food items, other factors are 

important to consider during food development. The first of these additional factors is 

the storage duration (based on mission duration plus the time required to process, test, 

and ship the foods for launch) and shelf life (based on each food’s composition and 

preparation method). When selecting and developing foods, the food scientist must 

consider the mission duration and whether resupply will be available. For long-duration 

missions, foods with a long shelf life should be developed and selected. The methods 

used to provide shelf-stable foods either process the foods to commercial sterility 

(thermostabilized and irradiated foods) or reduce the water activity to the extent that 

microorganisms are not able to proliferate (freeze-dried and low-moisture foods). These 

foods deteriorate in quality over time, so shelf-life testing is needed to determine their

nutritional content and acceptability after various durations. The foods should remain 

safe to consume unless the package is damaged. 

The second additional factor to be considered is food packaging. Use of an appropriate 

packaging type is essential for maintaining the safety, nutritional quality, and 

acceptability of a food throughout its shelf life. Food packaging must meet safety and 

gaseous pollutant specifications (NASA-STD-3001 V26004; V2 6005; V2 6050).

Packaging contributes significant mass and volume to the food system, and must be 

considered for stowage, launch mass, and waste disposal mass and volume. Flexible 

packaging (which may be compressed) provides savings in mass, volume, stowage, 

and waste over rigid packaging. Packaging must be easy to open, while not allowing 

contents to escape or leak in reduced-gravity environments. Foods that need to be 

rehydrated need packaging that is compatible with the rehydration equipment. More 

information on the types of food packaging currently used can be found in the NASA 

Human Integration and Design Handbook (HIDH) section 7.2.3.4.

The third factor is suitability for use in microgravity. Foods that are easily broken (such 

as potato chips) are difficult to eat in space and should be avoided. Foods that produce 

crumbs (such as crackers) should be provided in bite-sized pieces to minimize debris. 

Meal items should contain enough moisture to stay in the package or on a utensil 

through surface tension. Foods should be packaged in single-serving sizes to eliminate 

the need to transfer food and the need for additional tableware. Consideration should be 

given to variety, food familiarity, preparation time, meal scheduling, galley location, 
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flavor changes in microgravity, and other human factors that affect food acceptability (as 

described in the HIDH section 7.2.2.1). This information has been mostly determined 

through experience and crew debriefs from previous missions. 

4.17.4 MENU DEVELOPMENT

Menus can be developed in multiple ways. Two types of menu systems have been 

used in the NASA Space Food Systems Laboratory at Johnson Space Center: 

personal-preference menus and standard menus. Both types of menus require a 

preapproved list of flight foods. 

Personal-preference menus are developed individually for each crewmember using 

scores from food evaluation sessions. Foods on which a crewmember scores 6.0 or 

higher on the hedonic scale are entered into a nutrient database program (such as the 

Food Processor SQL; ESHA Research, Salem, OR) by a dietitian. The computer 

program includes a database with nutritional information for individual foods and 

ingredients. This information is necessary for menu development to ensure adequate 

amounts of required nutrients. A dietitian may add foods necessary to fulfill the 

nutritional requirements if crewmember preferences are limiting. Personal-preference 

menus are popular with crewmembers but have proven unfeasible for the ISS due to 

variable resupply schedules. Resupply schedules for ISS are so variable that 

sometimes crewmembers’ preferred food items cannot be delivered in time to coincide 

with their increments. Personal-preference menus could be considered again for 

missions that do not involve crew rotation and/or food resupply. 

To generate a standard menu, a registered dietitian enters the flight foods into a nutrient 

database program, which (1) has a database of commercial food products and 

ingredients, (2) can calculate the nutritional content of the formulated food, and (3) uses 

these calculations of nutritional content to determine the daily nutritional content for a 

given crewmember. The dietitian selects foods with the proper balance of macro- and 

micronutrients to meet the nutritional requirements of each crewmember. This leads to a 

menu that all crewmembers use that provides the required level of nutrition for the 

mission. The length of the menu cycle should be adjusted for mission duration, with 

longer menu cycles for missions of longer duration. Menus may be supplemented with 

bonus containers that include crewmember-requested shelf-stable commercial foods or 

food items developed for space flight that the crew selects during acceptability 

evaluations before flight. Currently, each crewmember receives 0.11 m3 of bonus food 

storage for a 6-month ISS mission.

4.17.4.1 FOOD STOWAGE

Food may be stowed in various configurations, as long as the packages are protected 

from puncture or damage. Two types of stowage that may be used are (1) stowage by 

type of food and (2) stowage by meal. When food is stowed by type (e.g., meats, side

dishes, drinks, snacks), also known as pantry style, crewmembers can assemble their 

own meal choices according to what food is available and are not restricted to the menu 

cycle. When food is stowed by meal, crewmembers eat meals in a predetermined menu 
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cycle. Historically, for longer missions pantry style has been preferred. For shorter 

missions, either stowage configuration can be used and is decided on by the food 

system designer in collaboration with the stowage team or the crew. Stowage by meal 

requires that all foods required for a given meal be stowed together or in close proximity 

to one another to ease mealtime preparations.

4.17.5 EXPERTISE, FACILITIES, AND EQUIPMENT

To provide a food system suitable for use in microgravity, specific expertise, facilities, 

and equipment are necessary.

4.17.5.1 EXPERTISE

Food scientists are needed to develop specifications for food items, including 

ingredients, formulations, and processing conditions; develop new foods and determine 

food processing methods; determine sensory acceptability, confirm food safety, 

determine storage conditions, confirm shelf life, and confirm suitability for use in 

microgravity. Registered dietitians are needed to develop menus and confirm nutritional 

content. Packaging engineers are needed to determine the functionality of food 

packaging, confirm the suitability of packaging for use in microgravity, develop 

packaging parameters (including sealing and vacuum), and test the package integrity of 

packaged foods. Logistics specialists are needed to develop stowage procedures and 

monitor food inventory. A programmer is needed to develop and maintain database 

specifications for foods, and a food system engineer is required in the event that food 

processing equipment is designed in-house, including equipment to rehydrate and heat 

food.

4.17.5.2 FACILITIES AND EQUIPMENT

An analytical laboratory should provide a texture analyzer for assessing food texture 

profiles and the physical properties of packaging materials, a moisture analyzer and 

water activity analyzer for assessing the water properties of the food, a moisture 

sorption isotherm analyzer to estimate shelf life, a viscometer to determine fluid 

behavior, and a headspace analyzer to determine the oxygen content remaining in 

packaged foods.

A food processing pilot plant or test kitchen includes a freeze-dryer, a retort, a blast 

freezer, and general food production pilot plant equipment, such as a steam-jacketed 

kettle.

A sensory facility is used for acceptability testing and includes evaluation booths and a 

computerized sensory analysis program. 

The packaging room includes vacuum sealers with gas flush capability and packaging 

equipment for specialty microgravity packaging, such as sealing of a septum into a 

pouch to enable rehydration of food in the package.
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The stowage room should include areas to perform stowage and controlled storage for 

food until it is shipped for launch.

Office space is also needed for use by the members of the food laboratory for 

development of formulas, development of menus, computerized nutrition analysis, and 

other logistics, such as maintenance of inventory and specifications. 

4.17.6 TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 4.17.6-

1 are recommended for review by the NASA customer.

TABLE 4.17.6-1 SPACE FOOD SYSTEMS TECHNICAL PRODUCTS

Technical Products Phase A Phase B

Phase 

C

Phase 

D

SRR SDR PDR CDR SAR FRR

Concept of Operations X --- --- --- --- ---

Mission menu --- X --- --- ---

Rehydration and warming hardware capability --- --- I U U U

Food hardware testing results --- --- I U U U

Food safety and testing procedures --- --- X --- --- ---

Evidence of adequate stowage volume for food --- --- I U U U

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations

The ConOps, described in paragraph 3.2.3.1.2, provides information such as 

identification of crew activities and determination of which subsystems are influenced by 

crew activities. The ConOps is required to determine the type of food that will need to 

be flown for a given mission duration and the menu cycle length.

Mission Menu

The mission menu must be delivered, showing compliance with the nutritional and 

acceptability standards in NASA-STD-3001.

Rehydration and Warming Hardware Capability

If the mission duration requires rehydratable and hot food, evidence must be shown that 

the hardware is compatible with the food packaging.

Food Safety and Testing Procedures

Evidence that proper food safety and testing procedures are in place for all production 

lots needs to be delivered for NASA review at PDR. NASA expects that all foods to be 

delivered for the mission comply with the procedures specified in the evidence report.

Stowage Volume

Evidence is required that stowage volume for the food and packaging required for a 

given mission duration are adequate.
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4.17.7 REFERENCES

Friedl, K. E, & Hoyt, R. W. (1997). Development and biomedical testing of military 

operational rations. Annual Review of Nutrition, 17, 51-75.

Meilgaard, M., Civille, G. V., & Carr, B. T. (1999). Sensory evaluation techniques (3

rd

ed.) Boca Raton, FL: CRC Press.
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4.18 LEGIBILITY EVALUATION

4.18.1 INTRODUCTION

Legibility is a key component of interface usability. Interfaces should be designed so 

that crewmembers can easily and quickly recognize and read text, numbers, and any 

labels. During space flight, many tasks involve prompt responses and commands that 

require quick identification of display elements. Without legible fonts, numbers, and 

symbols, task times will be longer and the chance of error will increase, causing delays 

and, in extreme cases, task failure. 

4.18.2 BACKGROUND

4.18.2.1 DEFINITION OF LEGIBILITY

Legibility refers to the perceptual clarity of visual elements that allows discrimination of 

the details of a visual stimulus to such a degree that it can be recognized 

(Sheedy, Subbaram, Zimmerman, Hayes, 2005). Legibility is influenced by the method 

of display generation, application of human factors guidelines for correct depiction of the 

object in relation to the task requirements, the environmental conditions, and eyesight 

standards. Legibility of text is often defined in terms of readability: the relative ease with 

which text can be read and understood when characters are arranged in words, 

sentences, and paragraphs.

4.18.2.2 APPLICABLE REQUIREMENTS

The following requirements from NASA-STD-3001, Volume 2 are applicable to legibility:

 Visual Display Legibility [V2 10047]

 Visual Display Parameters [V2 10048]

 Visual Display Character Parameters [V2 10049]

 Display Font [V2 10050]

 Label Display Standards [V2 10062]

 Label Font Height [V2 10066]

4.18.2.3 FACTORS AFFECTING LEGIBILITY

The most important factors affecting legibility are related to the font used, such as type 

and size. However, environmental factors such as lighting conditions, vibration, and 

wearing a suit or helmet, which change visibility and the visual field, are also relevant. 

Font characters are complex graphic elements that vary in width and height. The size of 

a character is usually given by the height of the uppercase letter H. In a comprehensive 

series of studies, Legge and colleagues (Legge, Pelli, Rubin, & Schleske, 1985)

investigated reading rate as a function of letter size, contrast, font, color, and other 

variables. They varied character width and letter size of a fixed-width font. Maximum 

reading rates were achieved for characters of 0.3-2° of visual angle. There was a 

relatively rapid decline in reading rate for letters smaller than 0.3°. Furthermore, there 

was a gradual decline for letters larger than 2° (Legge et al., 1985). NASA-STD-3001, 

Volume 2, requires that font height be 0.4° or greater for labels and a minimum of 0.25°
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for visual display characters (with 0.4 degrees preferred). In addition to type and size, 

stroke width, character spacing, line spacing, and other characteristics of fonts also 

need to be considered for legibility (McNeese & Katz, 1987).

4.18.2.4 MEASURING LEGIBILITY

In practice, legibility is often defined by the criteria and methodologies that are used to 

investigate it. In his review of legibility research, Pyke (1926) surveyed more than 100

studies published between 1825 and 1926, and discovered 15 different methods used

by researchers for measuring legibility. The methods described were speed of reading 

(by the time threshold and amount read), the distance threshold (direct and peripheral), 

“eye-span,” “illumination threshold,” focus threshold, fatigue, number of eye pauses, 

number of eye re-fixations, regularity of eye movements, reading rhythm, “legibility 

coefficient,” “specific legibility,” size of letters, “judgment of the trained human eye,” and 

aesthetic merits. 

In Legibility of Print, published in 1963, Tinker presented a more condensed list of 

investigative criteria, representative of those most commonly used: 

1. Speed of perception: The speed and accuracy with which characters can be 

perceived in a short period of exposure.

2. Perceptibility at a distance: The distance from the eyes at which characters can be 

accurately perceived.

3. Perceptibility in peripheral vision: The distance from a given “fixation point” at which 

a character can be accurately perceived in the periphery.

4. Visibility: A measure of the point at which characters can be perceived when viewed 

through a visual apparatus that uses rotating filters to obscure and clarify those 

characters.

5. The reflex blink technique: Frequency of blinking when reading text with different 

typographical characteristics.

6. Rate of work, includes such measures as “speed of reading, amount of reading 

completed in a set time limit, time taken to find a telephone number, time taken to 

look up a power or root in mathematical tables, and work output in a variety of 

situations which involve visual discrimination.” It is a measure of the speed of 

reading, controlling for comprehension.

7. Eye movements: Measure of the movements of the eyes when reading, using 

methods such as corneal reflection and electrical signals.

8. Fatigue in reading: Measures of fatigue in reading. This measure has not been 

demonstrated to be a valid method for measuring legibility. 

However, no single one of these methods (or criteria, depending on how they are 

described) is adequate for measuring legibility in all of its aspects. Each has to be 

understood and considered on its own merits as contributing to a broader notion of 

legibility.

Based on the listed criteria, 3 major categories can be used to group the legibility 

methods , as follows:
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1. Size thresholds (visual acuity) for letter identification, measured with 5-letter 

strings presented on a video monitor, using an up-down staircase method (Levitt, 

1971) with 0.05 log unit size steps. Size (or, inversely, distance) thresholds are 

probably the most common method for assessing text legibility (Tinker, 1963), 

and are widely used in applied settings such as highway signage, with lower size 

thresholds indicating higher legibility. Studies may use different kinds of stimuli: 

random strings of all lowercase, all uppercase, and randomly selected case; and 

5-letter words, all upper- or all lowercase, randomly selected from the 2110 most 

frequent 5-letter words in English (Francis, Kucera, & Mackie, 1982).

2. Reading speeds using Rapid Serial Visual Presentation (RSVP). Higher legibility, 

by this criterion, allows faster reading. RSVP involves presenting a stimulus 

(word, letter) one at a time for a brief time interval. Reading speed is a less 

common measure of legibility but it is perhaps more representative of ordinary 

reading than is size threshold. Because RSVP can support extremely high rates 

of reading, it has the potential to be more sensitive to subtle differences in 

legibility. RSVP reading was tested with individual sentences, whose speed was 

varied to determine the speed that supported a 50% (of words) correct reading 

rate.

3. Reading speeds using continuous reading of text passages taken from 

standardized tests (9th-grade level). 

The ergonomic requirements for office work with visual display terminals (VDTs) - Part 

11 (ISO 9241-11) also describes an approach recommended to measure legibility: Ask 

users to read system messages and instructions displayed on a screen using a range of 

illumination levels from 50 lux to 5000 lux. At a normal viewing distance (typically 20′′

from eye to screen), 98% of words used in system messages and instructions should be 

read correctly.

4.18.3 LEGIBILITY EVALUATION AND VERIFICATION PROCESS WITH RSVP 

The following section describes a process of measuring and verifying legibility, given the 

following assumptions:

 The display viewing distance is 20′′ measured from the eyes of the participant to 

the display

 There may be several viewing angles defined based on task analysis that need 

to be considered. For example, if 3 displays are used, and 2 of these are canted, 

3 viewing angles would be evaluated.

 The design complies with the general human factors standards and guidelines for 

workstations, such as font size, brightness, and contrast (e.g., NASA-STD-3001). 

Standards and guidelines provide information for a good baseline design; 

however, they do not replace usability and legibility testing in representative 

conditions with representative tasks.

 The font size, spacing, and other properties of the design are based on 

recommendations and requirements from vibration and acceleration studies and 
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take into account the minimal font size, contrast, and other specifications for 

these conditions. Again, these guidelines provide a good baseline, but do not 

replace assessments and evaluations.

The recommended legibility evaluation process is completed in 3 phases:

1. Iterative, brief legibility assessments during the development phase in the context 

of iterative usability testing

2. Integrated, in-depth legibility evaluations using RSVP during development phase 

3. Final legibility verification 

The first 2 phasesassessing legibility as part of a usability study and integrated 

legibility evaluationare complementary and are usually completed in an iterative 

fashion. The last phasefinal legibility verificationis done at the end of the design 

process together with other verifications. The next sections will describe these phases 

in more detail.

This legibility evaluation process is specific to software interfaces. However, it can be 

applied to hardware labels and placards with slight modifications, such as measuring 

reading time instead of using RSVP. This method may be applied to evaluate legibility 

under other environmental conditions as well, such as during exposure to vibration and 

acceleration. To increase efficiency and save time, when it is feasible a legibility 

evaluation may be combined with other assessments and verifications, such as usability 

and workload (see HIDP section 4.2, Usability and 4.3, Workload) in integrated testing 

conditions. 

The selected process and verification method are easy to implement because they do 

not need special equipment or specialized software, and it can be used in applied 

settings and various environments.

4.18.3.1 ITERATIVE BRIEF LEGIBILITY ASSESSMENT DURING DEVELOPMENT 

ALONG WITH USABILITY TESTING

Iterative usability testing (see HIDP section 4.2, Usability) is usually completed on a 

large number of interfaces during the design and development phase. As part of 

usability testing, the test conductor should ask questions about the legibility of specific 

interface elements (e.g., during the familiarization phase). The legibility of the following 

interface elements should be queried: text, numbers, symbols, icons, and graphics.

Comments and observations regarding legibility of interface elements should be 

recorded and analyzed. Changes to improve legibility should be made according to the 

feedback received. This will help ensure that if there are legibility issues in the early 

phases of design, they will be identified early and corrected by the time of requirement 

verification. If there are questions or concerns about the legibility of a particular 

interface, the usability test should include a legibility performance test similar to that 

described for legibility verification.
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4.18.3.2 INTEGRATED LEGIBILITY EVALUATION USING RSVP DURING 

DEVELOPMENT 

An integrated legibility evaluation is performed on integrated interface suites as designs 

mature. In the case of interfaces that are one of many similar in a set, (e.g., display 

formats) the test planner should define a number of categories they can be grouped in, 

such as: mostly text based formats, schematic based formats, and flight display formats. 

Several formats that are representative of each category should be selected for testing. 

If the interface is one-of-a-kind, it should be selected for testing.

Testing should be accomplished for a reasonable number of possible lighting conditions 

and viewing angles. These conditions have to be defined based on task analysis 

conducted during the development phase to make sure that they cover the most 

relevant combinations of conditions. The test procedure should involve having the test 

conductor ask the participant to identify selected portions of each interface, querying 

text, numbers, symbols, icons, and graphics.

Identification accuracy should be collected for all or the most relevant combinations of 

factors as illustrated in the Table 4.18.3.2-1 example. 

TABLE 4.18.3.2-1 EXAMPLE OF COMBINATIONS OF FACTORS TO TEST 

LEGIBILITY OF DISPLAY ELEMENTS

Display type

Text display 

(test text)

Schematic display

(test object)

Flight display

(test symbol)

Lighting 1 Viewing angle 1 Viewing angle 1 Viewing angle 1

Viewing angle 2 Viewing angle 2 Viewing angle 2

Viewing angle 3 Viewing angle 3 Viewing angle 3

Lighting 2 Viewing angle 1 Viewing angle 1 Viewing angle 1

Viewing angle 2 Viewing angle 2 Viewing angle 2

Viewing angle 3 Viewing angle 3 Viewing angle 3

Lighting 3 Viewing angle 1 Viewing angle 1 Viewing angle 1

Viewing angle 2 Viewing angle 2 Viewing angle 2

Viewing angle 3 Viewing angle 3 Viewing angle 3

The method used for the testing should be based on rapid presentations of the items to 

the participants and asking them to identify a cued/highlighted element on the screen 

(see Figure 4.18.3.2-1 for an example). Presentation times for the highlighted item on 

the display should be 1 second for simple items such as words, numbers, or symbols. 

This timing is based on the cognitive psychology literature: simple stimuli, such as 

common words presented alone on a display are perceived in about 200 - 250 ms 

(Becker, 2011). In a cluttered display, such as an electronic procedures display shown 

in Figure 1, to perceive an element, one needs to do a visual search as well; therefore, 

the time needed to identify an element increases. Nevertheless, within 1 second, one 
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should be able to identify an element on a cluttered display. In this brief amount of time, 

accuracy should be around 98% for all elements using the ISO 9241-11 criterion.

FIGURE 4.18.3.2-1 SYMBOL HIGHLIGHTED WITH AN ORANGE BOX ON AN ELECTRONIC 

PROCEDURES SCREEN IS THE CUED ELEMENT THE SUBJECT IS ASKED TO IDENTIFY.

The display elements should be presented with the rest of the display covered or the 

area of interest highlighted. The subject should be prompted to look at the highlighted 

area for the item to be identified. Responses can be called out and recorded by the 

evaluator or entered on the computer by the subject. If the interface elements are 

legible, accuracy should be 98%.

4.18.3.3 LEGIBILITY VERIFICATION

For verification, the RSVP method using the criterion of 98% accuracy should be 

applied, as described in the previous section. A limited set of representative displays 

and display elements in a limited set of worst-case conditions (e.g., reduced visibility, 

small viewing angle) should be selected. The sets should be determined based on task 

analysis taking into account criticality, representativeness, and frequency of use.

The 3-phased iterative approach for measuring and verifying legibility described in this 

document will help ensure that problems are caught and corrected early, and that a 

standard, time-efficient, and objective method is followed for formal verification of 

legibility.

4.18.3.3.1 LEGIBILITY VERIFICATION EVALUATION USING READING TIMES

The RSVP methodology can be modified to fit evaluation conditions when RSVP cannot 

be used, such as legibility of hardware labels or when modifying the software to 

accommodate RSVP is not feasible. In these cases, overall reading time can be 

measured and used to calculate how long it takes to read the individual elements on the 

display. In this case, participants are asked to read all the words, symbols, and numbers 

line-by-line, top to bottom displayed on the screen as they would read a book. Reading 

time for each element is calculated by dividing total reading time for the part of the 

display by the number of elements in that part. Reading times for each element should 

be under 1s and accuracy above 98%, just as in the case of RSVP, to pass verification.
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4.18.4 LEGIBILITY TECHNICAL PRODUCTS

For each of the major milestones of the design life cycle, the technical products in Table 

4.18.4-1 are recommended.

TABLE 4.18.4-1 LEGIBILITY TECHNICAL PRODUCTS

Technical Products

Phase A Phase 

B

Phase 

C

Phase D

SRR SDR PDR CDR SAR FRR

A description of the ConOps, function 

allocation, and associated crew task lists 

and crew interfaces. 

I U U U --- ---

A summary of modeling/analysis/evaluation 

performed to date showing legibility of 

displays at 98%.

--- --- I U U ---

Verification plan. --- --- I U U ---

X = one-time release of item

I = initial release of item

U = updated release of item

Concept of Operations and Crew Task Lists

The ConOps, described in paragraph 3.2.3.1.2 provides information such as 

identification of crew activities and determination of which subsystems are impacted by 

crew activities. Function allocation, described in paragraph 3.2.3.1.3, establishes the 

extent to which an activity is to be automated or assigned to humans. The crew task list, 

described in section 4.1 User Task Analysis, documents details including allocation of 

function between crew and systems, definition of crew activities sequence, and 

identification of critical tasks. As the crew task list evolves through the design cycle, its 

final iteration should become crew procedures. 

For legibility testing, task analysis must include an analysis of the possible conditions 

under which displays should be legible.

Summaries of Modeling, Analyses, and Evaluations

Iterative summaries of modeling, analyses, and evaluations provide insight into humansystem integration technical details throughout the design process. As designs mature, 

modeling, analyses, and evaluations should use increasingly higher fidelity inputs and 

mockups, as discussed in paragraph 3.2.3.3 Evaluate Designs and Iterate Solutions. It 

is important that summaries address how critical design decisions were assessed. Per 

the NPR 8705.2B, updated summaries are to be provided at each design review 

through SAR. Also in paragraph 2.3.10, the use of human-in-the-loop evaluation is a 

required method to progressively demonstrate that the operational concept meets 

system requirements for operational safety, efficiency, and user interface design.

For usability, this should include the evaluation of displays, and results showing that 

elements on the displays are legible with 98% accuracy.
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Verification Plan

The verification plan is a formal document describing the specific methodologies to be 

used to show compliance with each requirement.

4.18.5 BIBLIOGRAPHY

ASTM D 7298. Standard Test Method for Measurement of Comparative Legibility by 

Means of Polarizing Filter Instrumentation.

Becker SI (2011) Determinants of Dwell Time in Visual Search: Similarity or Perceptual 

Difficulty? PLoS ONE 6(3)

Francis. W. N., Kucera, H., & Mackie, A. W. (1982). Frequency Analysis of English 

Usage: Lexicon and Grammar. Houghton Mifflin, Boston, MA.

ISO 9241-11. Ergonomic requirements for office work with visual display terminals 

(VDTs) – Part 11- Guidance on Usability

Legge, Pelli, Rubin, & Schleske, (1985). Psychophysics of reading. Normal vision. 

Vision Res, 25(2), 239-252.

Levitt, H. (1971). Transformed Up-Down Methods in Psychoacoustics. The Journal of 

the Acoustical Society of America, 49, 467.

McNeese, M. D., & Katz, L. (1987). Legibility evaluation of a large screen display

system under medium ambient illumination. Proceedings of the Society for Information 

Display, 28 (1), 59-65.

Pyke, R. L. (1926). Report on the legibility of print, Medical Research Council, Special 

Research Series. London, UK.

Sheedy, J. E., Subbaram, M., V., Zimmerman, A. B., Hayes, R. J. (2005). Text legibility 

and the letter superiority effect. Human Factors: The Journal of the Human Factors and 

Ergonomics Society, (47)4, 797–815.

Tinker, M.A. (1963). Legibility of print. Iowa State University Press, Ames, IA.
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APPENDIX A ACRONYMS AND DEFINITIONS

ABF

Anthropometry and 

Biomechanics Facility

NASA’s Space and Life Sciences Directorate, Habitability 

and Human Factors Branch, Anthropometry and 

Biomechanics Facility

ACES Advanced Crew 

Escape Suit

ACLS Advanced Cardiac Life

AGARD

Advisory Group for 

Aerospace Research 

and Development

ALARA

As Low As 

Reasonably 

Achievable

ANCP Acoustic Noise Control 

Plan

ANSI American National 

Standards Institute

ANSUR Anthropometry Survey 

of Army Personnel

NATICK document

ATD Anthropomorphic 

Testing Device

BEA Boundary Element 

Analysis

BMD Bone Mineral Density

BTE Barrier Thickness 

Evaluator

CAD Computer Aided/ 

Assisted Design

CCT Commercial Crew 

Transportation

CDR

Critical Design Review Review during project life cycle Phase C Final Design and 

Fabrication. Follows PDR and precedes SIR. May be 

conducted with PRR.

CEV Crew Exploration 

Vehicle

CG Center of Gravity

CHSIP

Commercial Human 

Systems Integration 

Processes

JSC-65995

CHSIR

Commercial HumanSystems Integration 

Requirements

JSC-65993

CMORD

Commercial Medical 

Operations 

Requirements 

Document

JSC-65994

COM Center of Mass

ConOps Concept of Operations

COTS Commercial Orbital 

Transport Services 

CREST Crew Escape 

Technologies

dB decibels
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DDPF Decal Design and 

Production Facility

NASA label design and production facility

DRATS Desert Research and 

Technology Studies

DRM

Design Reference 

Mission

End-to-end description of reference mission including # 

crew, # days, nominal and emergency, recovery, aborts, 

medical, etc.

ECLSS

Environmental Control 

and Life Support 

Systems

EMU Extravehicular Mobility 

Unit

ESPO Extravehicular Activity 

Systems Project Office

EVA Extra-Vehicular 

Activity

ExMC Exploration Medical 

Capability

FAA Federal Aviation 

Administration

FAST Functional Analysis 

Systems Technique

FCI Flight Crew Integration NASA’s Space and Life Sciences Directorate, Habitability 

and Human Factors Branch, Flight Crew Integration

FE Finite Element

FEA Finite Element 

Analysis

FMEA Failure Mode Effect 

Analysis

FRR Flight Readiness 

Review

Review at end of project life cycle Phase D System 

Assembly, Integration & Test, Launch. Follows ORR.

g Gravity Gravitational Force

GCR Galactic Cosmic Rays

GFE Government 

Furnished Equipment

H&M Health and Medical 

HCD Human-Centered 

Design

HEA Human Error Analysis

HIC Head Injury Criteria

HIDH Human Integration 

Design Handbook

NASA/SP-2010-3407 Human Integration Design Handbook 

(HIDH)

HITL

Human-in-the-Loop Human-in-the-Loop usability evaluation is required per NPR 

8705.2B paragraph 2.3.10 for the human-system interfaces 

and integrated human-system performance testing, with 

human performance criteria, for critical system and 

subsystem operations involving human performance

HRCP Human Rating 

Certification Plan

HQ Handling Qualities

HSI Human Systems 

Integration

HZ hertz
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IARV

Injury Assessment 

Reference Values

IMS Inventory 

Management System

IRD

Interface 

Requirements 

Document

ISO

International 

Standards 

Organization

ISS International Space 

Station

IVA Intra-Vehicular Activity

JSC Johnson Space 

Center

LEA Launch, Entry, Abort A type of astronaut suit worn during launch, entry, and abort 

mission phases.

LEO Low Earth Orbit

LET Linear Energy 

Transfer

MOI Moment of Inertia

MPCV Multi Purpose Crew 

Vehicle

MTL Master Task List

NASA

National Aeronautics 

and Space 

Administration

NASA-TLX NASA Task Load 

Index

NBL Neutral Buoyancy Lab

NCRP

National Council on 

Radiation Protection 

and Measurements

NHV Net Habitable Volume

NPR NASA Procedural 

Requirements

OpsCon Operations Concept

OpNom

Operational 

Nomenclature

Review during project life cycle Phase D System Assembly, 

Integration & Test, Launch. Follows SAR and precedes 

Flight Readiness Review.

ORR Operational 

Readiness Review

Review during project life cycle Phase D System Assembly, 

Integration & Test, Launch.

PABF Precision Air-Bearing 

Floor

PDR

Preliminary Design 

Review

Review during project life cycle Phase B Preliminary Design 

and Technology Completion. Follows SDR and precedes 

CDR.

PEPC Portable Equipment 

Payload and Cargo

POGO

Hydraulically 

offloading partial 

gravity simulator

PRA Probabilistic Risk 

Assessment
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PRR Production Readiness 

Review

Review during project life cycle Phase C Final Design and 

Fabrication. Follows PDR and precedes SIR. 

RAMSIS 3D CAD manikin RAMSIS is a simulation software program 

used for design and construction analyses.

REID Risk of ExposureInduced Death

RHC Rotational Hand 

Controller

RID Review Item 

Discrepancy

ROM Range of Motion

RPOD Rendezvous Proximity 

Operations & Docking

SAINT

Systems Analysis of 

Integrated Network of 

Tasks

SAR

System Acceptance 

Review

Review during project life cycle Phase D System Assembly, 

Integration & Test, Launch. Follows TRR and precedes 

ORR.

SDR System Definition 

Review

Review during project life cycle Phase A Concept and 

Technology Development. Follows SRR and precedes PDR.

SEA Statistical Energy 

Analysis

SIR System Integration 

Review

Review during project life cycle Phase C Final Design and 

Fabrication. Follows CDR/PRR and precedes TRR.

SME Subject Matter Expert

SMEMCL

Space Medicine 

Exploration Medical 

Condition List

SPE Solar Particle Events

SRAG Space Radiation 

Analysis Group

NASA Space Radiation Analysis Group

SRR System Requirements 

Review

Review during project life cycle Phase A Concept and 

Technology Development. Follows MCR and precedes SDR.

S&MA Safety and Mission 

Assurance

TA Technical Authority

THC Translational Hand 

Controller

TLX

Task Load Index NASA Task Load Index (TLX) is a diagnostic or multidimensional workload scale that can be used along with the 

Bedford. NASA-TLX provides an estimate of overall 

workload based on a weighted average of 6 subscale 

ratings: Mental Demand, Physical Demand, Temporal 

Demand, Own Performance, Effort, and Frustration (Hart & 

Staveland, 1988)

TRR

Test Readiness 

Review

Review during project life cycle Phase D System Assembly, 

Integration & Test, Launch. Follows CDR/PRR & SIR and 

precedes SAR.

V&V Verification and 

Validation

WBPBA Whole Body Posture 

Based Analysis
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APPENDIX B GLOSSARY

Term Definition 

Abort 

Early termination of the mission or mission phase before reaching the mission 

destination due to a failure or other condition that endangers the crew. At the 

moment an Abort is declared, the focus of the operation switches from flying 

the planned mission to saving the crew. A successful Abort ultimately places 

the crew in the portion of the space flight system normally used for reentry, and 

in a safe situation suitable for successful return and rescue. Aborts include 

scenarios where the vehicle is damaged or not recovered. 

Accessible 

An item is considered accessible when it can be operated, manipulated, 

serviced, removed, or replaced by the suitably clothed and equipped user with 

applicable body dimensions conforming to the anthropometric range and 

database specified by the procuring activity. Applicable body dimensions are 

those dimensions that are design-critical to the operation, manipulation, 

removal, or replacement task. 

Advisory A message that indicates a safe or normal configuration, operation of essential 

equipment, or imparts information for routine action purposes. 

Analysis 

Determination that requirements have been satisfied and results documented 

through the use of analytical techniques and tools. These techniques and tools 

may include computer and hardware simulations, analog and digital modeling, 

similarity and heritage assessments, validation of records, and the evaluation 

of results of multiple tests and analyses at a lower level applied to a higher 

level of assembly. 

Anthropometry The science of measuring the human body and its parts and functional 

capabilities. Includes lengths, circumferences, body mass, etc. 

Assembly 

A testable functional item that is viewed as a complete and separate entity for 

purposes of requirement allocation, manufacturing, maintenance, and record 

keeping. Examples: Large electronics box consisting of a chassis within which 

are housed separate smaller electrical/electronic units or a large docking ring 

attached to which are other discreet units, wire harnesses, or subassemblies. 

An assembly is testable as-configured item against its own development 

specification. It contains families of units, slices or subassemblies where all the 

lower-level units are individually qualified and electronically stressed screened 

that meet, at a minimum, the unit test requirements 

Automatic Pertaining to a function, operation, process, or device that, under specified 

conditions, functions without intervention by the crew. 

Capability Having attributes (such as physical or cognitive) required for performance. 

Catastrophic Hazard A condition that may cause the loss of life, permanently disabling injury, or a 

loss of flight assets. 

Caution An event that needs attention, but not immediate action. 

Contamination The act of rendering unfit for use by the introduction of unwholesome or 

undesirable elements. 

Countermeasures A means to offset undesirable physical, physiological, and psychological effects 

of space flight on crewmembers 

Crew 

Human onboard the spacecraft or space system during a mission. This 

includes USOS crewmembers and CCT company users or commercial 

customers (space tourists).

Crew Interface 

Any part of a vehicle through which information is transferred between the crew 

and the vehicle, whether by sight, sound, or touch. Usable, well-designed crew 

interfaces are critical for crew safety and productivity, and minimize training 

requirements. 
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Crew-In-The-Loop 

An evaluation that includes a crewmember, whether in an active or passive 

capacity in the subject role. The active crew-in-the-loop means that the 

crewmember’s actions are being evaluated in some capacity. The crewmember 

as subject means that the human is providing the data in which case human 

performance can be captured. 

Crew Survival 

Ability to keep the crew alive using capabilities such as abort, escape, safe 

haven, emergency egress, and rescue in response to an imminent catastrophic 

condition 

Criticality 1 Involve tasks where the possibility of a single failure could result in loss of life 

or vehicle.

Criticality 2 Involve tasks where the possibility of a single failure could result in loss of 

mission alone.

Critical Dimensions A key characteristic that establishes critical fit tolerances between other 

components or assemblies. 

Data Accuracy 

The degree to which information in a digital database matches true or accepted 

values. Accuracy is an issue pertaining to the quality of data and the number of 

errors contained in a dataset. 

Data Fidelity Data qualities that include accuracy, precision, reliability, latency (data 

freshness), resolution, and completeness. 

Data Precision 

The level of measurement and exactness of description in a database. Precise 

location data may measure position to a fraction of a unit. Precise attribute 

information may specify the characteristics of features in great detail. Note that 

precise data, no matter how carefully measured, may be inaccurate. 

Data Reliability The degree to which data is the same when sampled repeatedly. 

Deconditioned Crew 

Decreased functionality of physiological systems, for example, 

musculoskeletal, cardiovascular, vestibular and nervous systems, related to 

adaptation to reduced gravity. 

Demonstration 

Determination that qualitative or Boolean (Y/N) requirements have been 

satisfied by exhibition of functional performance (for example, serviceability, 

accessibility, transportability or human engineering features) usually 

accomplished with only instrumentation and equipment inherent in the item 

evaluated. 

Display 

A display is anything that provides visual, auditory and/or haptic information to 

crewmembers (for example, label, placard, tone, or display device). The term 

"display" includes text-based user interfaces, as well as Graphical User 

Interfaces (GUIs). 

Display Device 

The hardware used to present visual, aural, and tactile information to the crew 

or ground operations personnel. Display devices include computer monitors 

and Personal Digital Assistants (PDAs). 

Emergency Time critical warning event that requires immediate action and crew survival 

procedures. Each type of emergency requires a unique aural tone. 

Emergency 

Equipment 

A set of components (hardware and/or software) used to mitigate or control 

hazards, after occurrence, which present an immediate threat to the crew or 

crewed spacecraft. Examples include fire suppression systems and 

extinguishers, emergency breathing devices, and crew escape systems (NPR 

8705.2, Human-Rating Requirements for Space Systems). 

Emergency 

Evacuation 

The scenario in which ISS becomes uninhabitable and all crewmembers are 

forced to evacuate. 

Emergency Return 

The scenario in which a crewmember becomes ill and/or injured and the 

condition is life-threatening, time-critical, and/or beyond the medical capabilities 

of ISS 

Error 

Either an action that is not intended or desired by the person or a failure on the 

part of the person to perform a prescribed action within specified limits of 

accuracy, sequence, or time that does not produce the expected result and has 

led or has the potential to lead to an unwanted consequence. 
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Escape 

In-flight removal of crew from the portion of the space system normally used for 

reentry, due to rapidly deteriorating and hazardous conditions, thus placing 

them in a safe situation suitable for survivable return or recovery Escape 

includes, but is not limited to, those capabilities that use a portion of the original 

space system for the removal (for example, pods, modules, or foreign bodies). 

(NPR 8705.2A, Human-Rating Requirements for Space Systems) 

EVA Operations performed by suited crew outside the pressurized environment of a 

flight vehicle or habitat (during space flight or on a destination surface). 

Flight-like 

Non-flight component built, inspected and tested to flight component 

specifications used in flight operating conditions and built with manufacturing 

processes that are identical to those used for flight equipment. 

Ground Human team of one or more members supporting a mission from the ground 

during pre-flight, in-flight, surface, and post-flight operations. 

Habitability The state of being fit for occupation or dwelling. Meeting occupant needs of 

health, safety, performance, and satisfaction. 

Hardware Individual components of equipment including but not limited to, fasteners, 

panels, plumbing, switches, switch guards, and wiring. 

Hatch 

An opening with an operable, sealable cover that separates 2 adjoining 

environments and allows physical passage of people and/or material from one 

environment to the other (such as between 2 separate pressurized spacecraft 

when they are mated or from the inside to the outside of a spacecraft or vice 

versa). A hatch is composed of 2 components: a hatchway (the opening itself) 

and a hatch cover (the piece that closes the hatchway and provides structural 

support to the spacecraft). A pressure hatch is one in which the atmospheric 

pressure on one side of the hatch can be different from that on the opposite 

side of the hatch when the hatch cover is closed. Sometimes, the term “hatch” 

is used in place of hatch cover. In this document, however, the word “hatch 

cover” is used. 

Housekeeping 

Actions performed by the crew during a mission to maintain a healthy and 

habitable environment within the spacecraft. Examples of housekeeping 

activities include biocide wiping of spacecraft interior surfaces, cleaning or 

servicing of food preparation or hygiene facilities, and trash management. 

Human-centered 

Design 

The certification that a system has been developed and is capable of being 

operated in a manner appropriate for use by human crews at minimal risk. 

Human-rated certification includes: (1) human safety; (2) human performance 

(both nominal and degraded states of operation); and (3) human health 

management and care as applicable. 

Impulse Noise A burst of noise that is at least 10 dB above the background noise, which exists 

for one second or less. 

Information 

Management 

The act of performing functions with electronic data, including data input, 

organization, internal processing, storage, distribution, saving, and disposal of 

information about the system. Information management functions are typically 

performed by crew and ground personnel using displays on display devices. 

Inspection 

A method of verification of physical characteristics that determines compliance 

of the item with requirements without the use of special laboratory equipment, 

procedures, test support items, or services. Inspection uses standard methods 

such as visuals, gauges, etc., to verify compliance with requirements. 

Hardware may be inspected for the following: (1) Construction; (2) 

Workmanship; (3) Physical condition; (4) Specification and/or drawing 

compliance. 

Integrated 

The merger or combining of one or more components, parts, or configuration 

items into a higher level system for ensuring that the logical and physical 

interfaces can be satisfied and the integrated system satisfies its intended 

purpose. 
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Ionizing Radiation 

Radiation that converts impacted items wholly or partly into ions (electrically 

charged particles). The particulate radiation component includes all subatomic 

particles, such as protons, neutrons, electrons, atomic nuclei stripped of orbital 

electrons, mesons, etc. 

Intravehicular 

Activity (IVA) 

Operations performed by crew within the pressurized environment of a 

spacecraft during a mission. 

Legibility The extent to which alphanumeric characters and symbols are sufficiently 

distinct to be easily perceived, deciphered, or recognized. 

Linear Acceleration The rate of change of velocity of a mass, the direction of which is kept 

constant. 

Maintenance 

All actions necessary for retaining material in (or restoring it to) a serviceable 

condition. Maintenance includes servicing, repair, modification, modernization, 

overhaul, inspection, condition determination, corrosion control, and initial 

provisioning of support items. Reference - from MIL-HDBK-1908B, Definitions 

of Human Factors Terms 

Monitoring 

Includes checking for quality or fidelity; testing to determine whether a signal 

comes within limits; watching and observing for a specific signal or purpose; 

keeping track of, regulating, or controlling. 

Operator A crewmember serving the role of pilot or commander. 

Net Habitable 

Volume 

The functional volume left available to on a spacecraft after accounting for the 

loss of volume caused by deployed equipment, stowage, trash, and any other 

items that decrease the functional volume. 

Nominal Within operational limits or in accordance with planned operational concepts 

Noise 

Sound in the auditory range (15 Hz to 20,000 Hz) that is hazardous, undesired, 

and/or inappropriate to the intended use of the space. The word "noise" is used 

interchangeably with “sound” and is not intended to convey any relative or 

absolute degree of hazard or other acoustical characteristic. 

Non-Ionizing 

Radiation 

Includes 3 categories of electromagnetic radiation: radio frequency (RF) 

radiation, lasers, and incoherent electromagnetic radiation. 

Off-Nominal Outside of expected, acceptable operational limits or not in accordance with 

planned operational concepts; anomalous, unsatisfactory (aerospace usage). 

Override To halt, manually or automatically, operation of a function in progress. 

Placard

In the context of occupant protection, placards are operational controls on flight 

operations. For example, if a design is not certified to launch or abort in certain 

conditions such as wave state, or winds that would blow an abort capsule back 

toward land, placards would prevent the vehicle from launching in those 

conditions. Placards allow a design to be certified, even if it cannot meet 

requirements for all conditions, by accepting the impact to operations.

Population Analysis 

Population analysis uses statistical or mathematical tools to interpret results of 

the testing of a representative sample of subjects. Measures such as fit, reach, 

and strength are extrapolated or interpolated for comparisons against the entire 

range of potential crewmembers to ensure an adequate selection test of 

subjects has been made, and to determine whether the design successfully 

accommodates the extremes of the crew population. 

Provision 

The ancillary flight component provided for the CCT company. This includes 

pyrotechnic devices and equipment (spacesuits, camera systems, tools, 

clothing and food) primarily for crew provisioning and use. GFE is also any 

hardware/software (including documentation) provided as a finished product to 

a contractor for the contractor's use in meeting contractual requirements. 

Privacy 

Having an acceptable level of control over the extent of sharing oneself 

(physically, behaviorally, or intellectually) with others. Acceptable level is 

dependent on an individual’s background and training. 

Readily Accessible 

Immediately visible and accessible without being blocked or constrained by 

other equipment. Unimpeded Access is important for Emergency Systems and 

other critical items. 
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Recovery Generally, a recovery is a nominal post-landing operation involving the crew in 

the crew module. 

Rotational 

Acceleration The rate of change of angular velocity. 

Subject

A subject is an individual about whom an investigator conducting research or 

evaluations obtains data such as identifiable private information, physical 

measurements, responses, preferences, and/or whose performance is 

measured. A subject may be inclusive of a participant.

Suited 

Wearing clothing that is designed to protect the crewmember from differences 

in environment, such as pressure, atmosphere, acceleration, or temperature. 

“Suited” can refer to both a pressurized and unpressurized pressure suits. 

System 

Physical entities that have functional capabilities allocated to them necessary 

to satisfy Architecture-level mission objectives. Systems can perform all 

allocated functions within a mission phase. 

Task Analysis 

Task analysis is an activity that breaks a task down into its component levels. It 

involves 1) the identification of the tasks and subtasks involved in a process or 

system, and 2) analysis of those tasks (for example, who performs them, what 

equipment is used, under what conditions, the priority of the task, dependence 

on other tasks). The focus is on the human and how they perform the task, 

rather than the system. Results can help determine the displays or controls that 

should be developed/used for a particular task, the ideal allocation of tasks to 

humans vs. automation, and the criticality of tasks, which will help drive design 

decisions. 

Test 

Determination that requirements have been satisfied through measurement of 

parameters during and/or after the controlled application of functional and 

environmental stimuli using laboratory equipment, recorded data, procedures, 

test support items, or services beyond that provided by the tested unit itself. 

Transient 

Acceleration 

Acceleration event, linear or rotational, with a duration of less than or equal to 

0.5 seconds. 

Unsuited Wearing the type of clothing that is ordinarily worn in the interior of a 

spacecraft, especially a habitat, and as might be worn on Earth. 

User A user is any person who directly (physical contact) or indirectly (command, 

control, communication) interacts with the flight vehicle.

Vehicle 

A mobile or static environment with a pressurized atmosphere appropriate for 

sustained, unsuited survival and crew operations. The vehicle is a container, 

which is generally composed of multiple elements, used to transport persons or 

things to/from a location outside of Earth’s atmosphere and includes all 

hardware and equipment within or attached to the pressurized environment. 

Warning An event that requires immediate action. 

Window 

A non-electronic means for direct through-the-hull viewing using a transparent 

material; the same as and used interchangeably with window port and window 

assembly. 

Workload 

The amount of work expected in a unit of time. Physical workload refers to the 

number of individual physical activities that are conducted simultaneously or in 

close succession. Similarly, mental or cognitive workload refers to the number 

of mental operations or activities that are conducted simultaneously or in close 

succession. 

Workstation 

A place designed for a specific task or activity from where work is conducted or 

operations are directed. Workstations include cockpits, robotics control 

stations, or any work area that includes work surfaces, tools, equipment, or 

computers. 
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APPENDIX C REFERENCE DOCUMENTS

Document Number Document 

Revision Document Title

AFAMRL-TR-80-119

McConville, J. et al. (1980). Anthropometric 

Relationships of Body and Body Segment Moments 

of Inertia. Air Force Aerospace Medical Research 

Laboratory, Aerospace Medical Division, Air Force 

Systems Command, AFAMRL-TR-80-119. WrightPatterson Air Force Base, Ohio.

AGARD CP-472 April 1989

Brinkley, J. W., and Specker, L.J., "Development of 

Acceleration Exposure Limits for Advanced Escape 

Systems"

ISO/IEC 9241-11 1998

Ergonomic requirements for office work with visual 

display terminals (VDTs), Part 11: Guidance on 

Usability.

ISO 13407 1999(E) International Standard for Human-Centered Design 

Processes for Interactive Systems

JSC-27260 Decal Process Document and Catalog

JSC-27301 Materials Control Plan for JSC Space Station GFE

JSC-28517

Holden, K.L, Malin, J.T., and Thronesbery, C. 

(1998). Guide to Designing Usable Software 

Systems in Advanced Technology Environments, 

JSC Technical report: JSC-28517

JSC-63557 2008 Net Habitable Volume Verification Method

JSC-65994 Draft August 2010 Commercial Medical Operations Requirements 

Document (CMORD)

MIL-STD-1472 Revision G Department of Defense, Design Criteria Standard 

for Human Engineering

MIL-F-8785 B/C Flying Qualities of Piloted Airplanes (28 AUG 1996)

MPCV 70024 Baseline

Orion Multi Purpose Crew Vehicle

Program Human-Systems Integration

Requirements

NASA/SP-2007-6105 Rev 1 NASA Systems Engineering Handbook

NASA/SP-2010-3407 Human Integration Design Handbook
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NASA-TM-2008-215198 April 2008

Lawrence, C., Fasanella, E.L., Tabiei, A., Brinkley, 

J.W., Shemwell, D.M. The Use of a Vehicle 

Acceleration Exposure Limit Model and a Finite 

Element Crash Test Dummy Model to Evaluate the 

Risk of Injuries During Orion Crew Module 

Landings

NASA/TM-2009-215704 April 2009

Horta, L.G., Mason, B.H., Lyle, K.H. A 

Computational Approach for Probabilistic Analysis 

of Water Impact Simulations

NASA-STD-3001

Space Flight Human-systems Standard, Volume 1: 

Crew Health, and Volume 2: Habitability and 

Environmental Health

NASA-STD-5017 Design and Development Requirements for 

Mechanisms, section 4.10 Torque/Force Margins

NASA TN D-5153

“The Use of Piloted Rating In

The Evaluation Of Aircraft Handling Qualities,”

National Aeronautics and Space

Administration, Washington, D.C., April, 1969.

NASA-TM-X-62892, N79-

76319

NASA (1966). Gemini Program Mission Report of 

Gemini VII. National Aeronautics and Space 

Administration Manned Spacecraft Center, 

Houston, Texas.

NATICK/TR-89/044

1989 U.S. Army Anthropometry Survey of U.S. 

Army Personnel: Methods and Summary Statistics 

(Database Section only)

No Number

Ainsworth, L. K. (2004). Task analysis. In C. 

Sandom & R. Harvey (Eds). Human Factors for 

Engineers (pp. 81–112). London, England: 

Institution of Engineering and Technology.

No Number

Bangor, A., Kortum, P. T., & Miller, J. A. (2008). An 

empirical evaluation of the System Usability Scale 

(SUS). International Journal of Human-Computer 

Interaction, 24(6), 574-594.

No Number

Blackledge, C., Margerum, S., Ferrer, M., Morency, 

R., and Rajulu, S., (2010). Modeling the Impact of 

Space Suit Components and Anthropometry on the 

Center of Mass of a Seated Crewmember. Applied 

Human Factors and Ergonomics.

No Number

Bond, R. and Campbell, P. (1995). “Operational 

monitoring of MIR habitability,” (PIPS Database 

#810530). Internal NASA Document.

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Celentano, J.T., Amorelli, D. and Freeman, G.G. 

(1963). “Establishing a habitability index for space 

stations and planetary bases,” American Institute of 

Aeronautics and Astronautics Manned Space 

Laboratory Conference, May 2, 1963, Los Angeles, 

CA, pp. 63-139

No Number

Chaffin, D.B.; Andersson, G.B.J.; Martin, B.J. 

Occupational Biomechanics. J. Wiley & Sons, New 

York, NY 1999
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No Number

Churchill, E. and McConville, J. Sampling and Data 

Gathering Strategies for Future USAF 

Anthropometry, Appendix II-A. Air Force Systems 

Command, Wright Patterson Air Force Base, 

(1976).

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DuBois D, DuBois EF. 1916. A formula to estimate 

the approximate surface area if height and weight 

be known. Arch Intern Med 17:863–871

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Sudhakar L. Functional Mobility Testing: 

Quantification of Functionally Utilized Mobility 

among Unsuited and Suited Subjects. NASA/TP2010-216122, May 2010.

No Number Draft JSC 

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Operations 

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Gehan, E.A., George, S.L. (1970). Estimation of 

human body surface area from height and weight. 

Cancer Chemotherapy Reports Part I, 54(4), 225-

235. 11:24

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Gonzalez, L.J., Rajulu, S.L.. “Posture-Based Whole 

Body Anthropometric Analysis – A Case Study,”

Digital Human Modeling For Design And 

Engineering Conference And Exhibition, June 

2003, Montreal, Canada.

No Number

Hart, S. G. & Staveland, L. E. (1988) Development 

of NASA-TLX (Task Load Index): Results of 

empirical and theoretical research. In Human 

Mental Workload P. A. Hancock & N. Meshkati 

(Eds.). Amsterdam: North Holland, 139-183.

No Number

Hornbæk, K., & Law, E. L.-C. (2007). Meta-analysis 

of correlations among usability measures. Paper 

presented at the Proceedings of the SIGCHI 

conference on Human factors in computing 

systems, April 28-May 03, 2007, San Jose, CA, 

USA.

No Number

Kallay, A., Harvey, C., Byrne, V., DeSantis, L., 

Maida, J., Szabo, R., & Whitmore, M. (2006). Crew 

exploration vehicle (CEV) net habitable volume 

assessments for 6-crew missions. NASA TDS 

CEV-05-002, NASA/Johnson Space Center, August 

2006

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Kirakowski, J., & Corbett, M. (1993). SUMI: the 

Software Usability Measurement Inventory. British 

Journal of Educational Technology, 24(3), 210-212.

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Leiden, K., Laughery, K.R., Keller, J., French, J., 

Warwick. W., and S. Wood. A Review of Human 

Performance Models for the Prediction of Human 

Error. 2001.
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No Number

Litaker, Jr. H.L., Thompson, S., Howard, R., Szabo, 

R., Conlee, C., & Twyford, E. (2008). Habitable 

volume evaluation for the lunar sortie habitat Altair: 

Configuration one. NASA/Johnson Space Center. 

Internal NASA Document, February 2008.

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Litaker, Jr., H.L., Thompson, S., Howard, R., 

Szabo, R., Baldwin, T., Conlee, C., Twyford, E., 

Nguyen, A., & Ward, M. (2008). Suited and 

unsuited habitable volume evaluation for Altair 

lunar lander DAC-2 configuration. NASA/Johnson 

Space Center. Internal NASA Document, 

September 2008.

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Litaker, Jr., H.L., Howard, R., Ferrer, M., & Young, 

K. (2008). Lunar rover habitability volume 

evaluation on configuration one. NASA/Johnson 

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2008

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Litaker, Jr. H.L., Thompson, S., Howard, R., Szabo, 

R., Conlee, C. & Twyford, E. (2008). Small 

Pressurized Rover (SPR) three day desert trial: A 

human factors assessment. NASA/Johnson Space 

Center. Internal NASA Document, December 2008

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R., Conlee, C. Green, S., & Twyford, E. (2009). A 

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Margerum, S.; Rajulu, S. Human Factors Analysis 

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Martin, A. D., Drinkwater, D. T., Clarys, J. P., 

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McConville, J and Tillman, B. Year 2015 astronaut 

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No Number

Nielsen, J. (1993). Usability Engineering. San 

Francisco, CA: Morgan Kauffman Publishers Inc. 

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Ogden, C. L., Fryar, C. D., Carroll, M. D., & Flegal, 

K. M. (2004). Mean body weight, height, and body 

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Rajulu, S., Margerum, S., Young, K, Blackledge, C. 

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SSP 30233 Space Station Requirements for Materials and 

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SSP 30512 Space Station Ionizing Radiation Design 

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Requirements Document (IRD)
NASA/TP-2014-218556

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Appendix D Potential Future HIDP Chapters

Alignment with 

NASA-STD-3001, 

Volume 2

Chapter Topic

Chapter 3

How to determine whether a verification should be analysis, 

demonstration, test, or inspection

Chapter 3 How to plan/perform human-in-the-loop evaluations.

Chapter 3 How to plan a human-in-the-loop (HITL) type verification event, verifying 

multiple requirements in one event.

Chapter 3 Function allocation

Chapter 3 Iterative conceptual design and prototyping

Chapter 5 Design for Team performance/cohesion

Chapter 5 Evaluation of situational awareness

Chapter 6 Accounting for vibration in crew performance.

Chapter 6 Water sampling and analysis

Chapter 6 Toxicology and microbial analysis

Chapter 6 Design for heat storage

Chapter 7 Design for a stowage system and inventory management system

Chapter 7 Medical system selection

Chapter 7 Design for countermeasures

Chapter 7 Waste management design

Chapter 8 Habitat conceptual design

Chapter 9 Design for Training

Chapter 9 Design for control of human hazards, such as electrical hazards

Chapter 9 Design for long duration sustainability

Chapter 9 Equipment training 

Chapter 10 Human Robotics Interaction

Chapter 10 Design for autonomy

Chapter 10 Design for HCI

Chapter 10

Design for sharing of information between crewmembers/cock-pit 

resource management

Chapter 10 Precluding inadvertent operation

Chapter 10 Human Automation Interaction

Chapter 11 Human accommodation in suit design

Chapter 12 Mission Operational Assessment process (e.g., ISS OpsHab process)

Chapter 12 Procedures Design

Chapter 12 Concepts of operations development

Chapter 12 How to design an integrated mission plan to accommodate the human
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The purpose of the Human Integration Design Processes (HIDP) document is to provide human-systems integration design processes, 

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crewed spacecraft. Content is framed around human-centered design methodologies and processes in support of human-system 

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