November 2010 

NASA/TM-2010-216868/Volume II 

NESC-RP-08-00487 

 

Constellation Program (CxP) 

Crew Exploration Vehicle (CEV) 

Parachute Assembly System (CPAS) 

Independent Design Reliability Assessment 

Appendices 

Michael J. Kelly/NESC 

Langley Research Center, Hampton, Virginia 
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November 2010 

NASA/TM-2010-216868/Volume II 

NESC-RP-08-00487 

 

Constellation Program (CxP) 

Crew Exploration Vehicle (CEV) 

Parachute Assembly System (CPAS) 

Independent Design Reliability Assessment 

Appendices 

Michael J. Kelly/NESC 

Langley Research Center, Hampton, Virginia 
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 

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National Aeronautics and Space Administration. 
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NRB Review Date: August 26, 2010
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Table of Contents

Volume II: Appendices (Stand-alone Volume)

Appendix A. Stakeholder Request (November 2008)

Appendix B. 

B.1 Stakeholder Outbrief of Interim Recommendations 1 (April 2009)

B.2 Supporting Addendum of Team Assessment for Stakeholder Outbrief of Interim 

Recommendations 1

Appendix C. 

C.1 Stakeholder Outbrief of Interim NESC Recommendations 2 (September 2009)

C.2 Supporting Frequently-Asked-Questions for Stakeholder Outbrief of Interim 

NESC Recommendations 2

Appendix D. 

D.1 Stakeholder Outbrief of Interim NESC Recommendations 3 (April 2010)

D.2 Supporting Example of Reliability Growth Trending 

D.3 Supporting Example of Potential Problems with OFAT Testing
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Appendix B.1. Stakeholder Outbrief of Interim Recommendations 1 

(April 2009)

The attached version of Stakeholder Outbrief 1 differs slightly from that which was approved by 

the NRB. Figures included to facilitate board member understanding were removed in the 

stakeholder package.
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Appendix B.2. Supporting Addendum of Team Assessment for 

Stakeholder Outbrief of Interim Recommendations 1

This Addendum contains a list of 336 factual statements (FS) and 96 experience-based

observations (EO) from the NESC team‘s first review period (RP-1) which culminated in 

Outbrief 1 in April 2009.

During RP-1, the CPAS project and its contracted affiliates were working very hard during this 

time, given a complex design integration problem to converge on an architecture that would 

result in a robust and reliable system. Design details and requirements evolved rapidly during 

RP-1. During this dynamic time the assessment team rapidly evaluated a great many design 

details and project work products. 

The NESC parachute subteam members and reliability subteam members were active teaching 

each other pertinent factual aspects of their respective crafts. In an effort to compile and organize 

all of the assessed information in a manner that would facilitate the creation of its first set of 

findings, observations and interim NESC recommendations, the team created the following list 

of FS and EO. 

The list is reproduced in this Appendix to provide the reader insight into the many team 

discussions that resulted in the first set of findings, observations and interim NESC 

recommendations. Some of the items in this list may appear to be elementary or obvious 

statements of fact. These were deliberately captured as building blocks to aid technical 

understanding across the subteams and to create logical foundations for the team findings, which 

were derived later. 

The list is organized into groups of factual statements and experience-based observations 

according to the following categories:
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Organizational Communication ................................................................................................ 67

Fault Tree Analyses, Reliability Estimates, Uncertainty, and Reliability Budgets .............. 68

Applicability of Apollo Geometry for CPAS Near-Field Contact Estimates ........................ 74

Applicability of SRB Data for CPAS Near-Field Contact Estimates..................................... 75

Main Parachute Deployment Bags and Packing Issues .......................................................... 77

Pack Retention ............................................................................................................................ 79

Volume Budget............................................................................................................................ 79

Forward Bay Cover .................................................................................................................... 81

Drogue Deploy Envelope ............................................................................................................ 83

Drogue and Main Parachute Construction and Failure Risks............................................... 83

Parachute Attach Fittings .......................................................................................................... 88

Deployment Bag Handles and Energy Modulators ................................................................. 89

Kicker Straps............................................................................................................................... 90

Rotation Torque Limiter............................................................................................................ 90

Stowage Container...................................................................................................................... 92

Drogue Mortars........................................................................................................................... 93

Apportionment of Parachute System Components in the Forward Bay Sectors.................. 94

Project Technical Requirements Specification (PTRS)........................................................... 97

Analysis, General ........................................................................................................................ 99

Analysis, Specific Issues............................................................................................................ 100

Testing, General ........................................................................................................................ 104

Testing, Specific Issues ............................................................................................................. 105

Testing, Drogues Development ................................................................................................ 111

Testing, Mains Development.................................................................................................... 112

Trigger Logic............................................................................................................................. 112

Environmental........................................................................................................................... 113

Pad Abort................................................................................................................................... 113
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Organizational Communication

FS-1: Airborne Systems North America (Airborne, aka Irvin Aerospace) is contracted by Jacobs 

Engineering and Science Contract Group (Jacobs ESCG, aka Jacobs), to provide development 

data, design data, test hardware, and test data to the CPAS Project.

FS-2: The CPAS Project will deliver the Airborne development data, design data, test hardware, 

and test data as Government-Furnished Equipment (GFE), to Lockheed Martin (LM).

FS-3: The CPAS team members from NASA Johnson Space Center (JSC), Jacobs, and LM are 

located in Texas. Airborne is located in California.

FS-4: JSC/Department EA3 and Jacobs share primary System Engineering and Integration 

(SE&I) responsibilities for the project. JSC/Department EA2 has adjunct SE&I responsibilities. 

Airborne also has a System Engineering Lead.

FS-5: A chart presented at the December 2008 Initial Design Review (IDR) identified an 

individual as the ―Project Engineer/SE&I IPT Lead‖ (Integrated Product Team Lead) for 

Airborne.

FS-6: Jacobs has primary Safety and Mission Assurance (S&MA) responsibilities for the project 

and JSC/Department NT has adjunct S&MA responsibility. 

FS-7: Airborne provides reliability estimates for parachute structures to Jacobs for use in S&MA 

Fault Tree Analysis (FTA).

FS-8: LM and NASA coordinate program decisions via a Technical Integration Team (TIT).

FS-9: The inclusion of Airborne in the functional organization adds organizational complexity by 

creating an extended, matrixed organization that is also geographically dispersed.

FS-10: The CPAS functional organization is complex. 

FS-11: Organization charts show the Analysis Team to be connected to the project by dotted 

lines.

EO-1: Dotted lines on organization charts can suggest limited oversight.

FS-12: Organization charts show that LM and NASA have sufficient review boards and panels 

for assessment of CPAS Project decisions.

FS-13: From December 2008 through March 2009, S&MA fault trees and reliability estimates 

lagged behind in their representation of the evolving baseline design architecture. 

EO-2: Inherent difficulties with communication across a complex, extended, matrixed 

organization may have contributed to S&MA fault trees and reliability work products that lagged 

behind design decisions between December 2008 and March 2009.
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EO-3: Prior to the December 2008 IDR, preliminary reliability estimates were communicated to 

Constellation Program (CxP) decision makers, apparently without caution or explanation about 

the limitations of their foundation. 

EO-4: From December 2008 through February 2009, it appeared that the reliability assessment 

was seen as a separate task instead of an integrated discipline that improves design decisions. 

EO-5: In March 2009, it appeared that coordination between the S&MA Team and the Design 

team was improving.

FS-14: Operation of CPAS will involve a complex network of events, some serial and some in 

parallel, that involve numerous system components that must interact with each other different 

ways during different events. These interactions will vary by choice of architecture.

FS-15: CPAS components will interface with other systems; these interfaces will vary by choice 

of architecture.

FS-16: Systems with which CPAS interfaces are being designed by teams in various places in the 

matrixed organization.

EO-6: CPAS architectural design definition would be expected to be iterative during the time 

leading up to PDR.

FS-17: Minimal interface control documentation was provided for review between December 

2008 and March 2009.

EO-7: The complexity of communicating across an extended matrixed organization can hinder 

thorough investigation of system component interfaces with other systems, which may lead to 

poor design decisions.

FS-18: PTRS and reviewed documents make no mention of using NASA SP-2007-6105, NASA 

Systems Engineering Handbook or NPR 7123.1A, NASA Systems Engineering Processes and 

Requirements. 

Fault Tree Analyses, Reliability Estimates, Uncertainty, and 

Reliability Budgets

EO-8: FTA is a well-established methodology that uses Boolean logic to reduce the Fault Tree 

structure into the combinations of events (Minimal Cut Sets) leading to failure of a system. 

Probabilities are computed for individual Minimal Cut Sets, forming the basis for their ranking 

by importance with respect to their reliability and safety impact. FTA is especially useful when 

analyzing large and complex systems where manual methods of fault isolation and analysis are 

not viable. 
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EO-9: FTA top level events must be described precisely. 

 Defining a top event too broadly leads to an open-ended tree, showing no specific cause 

or causes for failure. 

 Defining a top event too narrowly leads to possible cause omissions. 

EO-10: An FTA needs to include all possible weaknesses, faults or failures present in the system 

that could cause safety hazards or reliability problems. Hardware, software, and human 

components of the system must be included in the FTA. All interactions between the system 

components and elements must be fully described in the FTA.

FS-19: IDR presentation stated that the FMECA, PRA and FTA are three independent 

deliverable requirements for the CPAS program. 

 Preliminary results of FTA and PRA were presented in IDR. 

 FMECA results were not presented at IDR. 

FS-20: The methodology being employed by the CPAS S&MA Team in March 2009 showed 

exclusive emphasis on the top-down/functional FTA. Consequentially, the Fault Tree is 

repetitive and lacks specificity at places (e.g., the near identical chute reefing failure modes were 

repeated seven times for Drogue, Main and Auxiliary chutes). 

EO-11: The arrangement between Airborne and Jacobs for performing various reliability 

analyses and other design assurance functions appears to violate the fundamental reliability 

principle that reliability is a part of the design process. It has to be built in at the beginning to be 

most effective and it has to be a real time, interactive and iterative process. 

EO-12: It appears that the various Project reliability analyses are being used principally as 

documentation/verification function after-the-fact, rather than as a design tool to continuously 

assess and improve the system reliability. The S&MA approach appears to be seeking a static 

design, which is inconsistent with the level of maturity in the design process with ongoing 

configuration changes.

EO-13: The current format and functional nature of the FTA makes it difficult to correlate the 

failure modes to the specific hardware. This makes it difficult to identify where additional 

analysis and/or testing could be strategically employed to reduce uncertainty in the reliability 

estimates. 

FS-21: Although FTA is a tool to detect the potential system weakness in a complex system, the 

FMECA (―bottom-up‖ approach) could be a better tool to qualitatively analyze and scrutinize the 

CPAS component design. 

FS-22: S&MA is maintaining two fault trees, a simple tree with narrative definitions to specify 

the precise failures included in each box, and a more detailed tree with sub-trees.
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EO-14: Some events in the CPAS deployment sequence will be dependent on other events, some 

will be independent. The reliability of CPAS will be dependent on the probability of the 

successful outcome of each event. The probability of the successful outcome of each event will 

be dependent on the reliability of the system components that participate during each event. 

Ultimately, design component reliability will drive system reliability. 

EO-15: The detailed FTA that can trace failures down to component level is the more valuable 

version of the two S&MA FTAs. 

EO-16: The shortened  ̳PowerPoint‘ version of the FTA with a definitions page attached, has 

limited utility except for a communication tool, and it presents risks of miscommunication.

EO-17: Reliability estimates change and evolve as systems are developed.

FS-23: Lockheed is maintaining a fault tree with integrated risks that include CPAS failures, 

with the intention to plug in the CPAS tree to the Lockheed tree after CPAS PDR. 

FS-24: S&MA has placeholders for integrated failures that relate to systems outside of the CPAS 

system, including CEV systems.

FS-25: The project S&MA Team FTA starts with undesired events (failures) and builds from the 

top, down. The S&MA Team plans to develop the PRA data by testing.

EO-18: The Lockheed FTA was reported in a March 2009 teleconference to start with 

component data and build from the bottom, up.

EO-19: There is value in doing FMEA in addition to PRA.

 PRA process using FTA is a deductive (top down) method useful for analyzing failures 

 FMEA is an inductive (bottom up) method 

 FTA and FMEA complement each other. FTA could be qualitative or quantitative 

whereas FMEA is qualitative 

 Note: FMECA could be qualitative or quantitative. Mostly NASA does FMEA with an 

exception of JPL which does FMECA

FS-26: The S&MA fault tree refers to main parachutes A, B, C, which are stowed in sectors 

identified by Lockheed as B, C, and E, respectively. 

FS-27: Between December 2008 and March 2009, the project has occasionally discussed 

relocating parachutes to other stowage sectors.

EO-20: Asymmetry of main parachute stowage could lead to special risks for individual 

parachutes. For example, side-by side mains stowed in sectors B and C might be more likely to 

pose risk to each other during deployment (entanglement, contact, etc) than they do to the main 

stowed in sector E. Or, the energy modulators attached to the same FBC beam (above Gusset 
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120, between sectors B and C), may interfere with each other, posing reliability risks not present 

with the d-bag in sector E.

FS-28: The CPAS reliability estimate of 1:217 for more than one main parachute contacting 

CEV structure during deployment was communicated by S&MA analysts without an estimated 

or calculated uncertainty or a statement regarding the applicability of SRB data. An estimated 

value for uncertainty for this risk would have been large, owing to the geometric inapplicability 

of the SRB data to the CEV system.

EO-21: Communicating reliability estimates without quantitative uncertainties or qualitative 

uncertainties (e.g., reference system similarity), for the purpose of comparing competing 

architecture alternatives, can lead to poor design decisions. 

EO-22: Communicating inapplicable reliability estimates can result in poor design decisions that 

can adversely affect system reliability.

FS-29: The CPAS reliability estimate of 1:217 for more than one main parachute contacting 

CEV structure during deployment was communicated by S&MA analysts without an estimated 

or calculated uncertainty, through the NASA and Lockheed chains of authority. 

FS-30: A Lockheed Engineering Review Board (ERB) assessed that the CPAS system was 

driving the overall reliability for Orion, by including the CPAS reliability estimate of 1:217 for 

more than one main parachute contacting CEV structure during deployment. 

FS-31: The JSC Director of Engineering asked for this NESC team to conduct an assessment of 

CPAS reliability estimates (among other objectives), citing the Lockheed ERB finding that the 

CPAS reliability estimate of 1:217 for more than one main parachute contacting CEV structure 

during deployment was driving overall Orion reliability.

FS-32: Reliability estimates for drogue and main parachute structural component failures were 

created by Airborne.

FS-33: Some reliability estimates presented at the IDR in December 2008, were said to have 

been based on Army, Apollo, Soyuz, and Space Transportation System (STS) SRB data, but that 

document did not include the lineage and derivation of each estimate.

FS-34: Reliability estimates for drogue and main parachute structural components that were 

presented at the IDR in December 2008, were said to have come from drop test data, vendor 

component data, and prediction. Fifteen out of twenty-three estimates were said to have been ―by 

prediction.‖ 

FS-35: Some predicted reliability estimates that were presented at the IDR in December 2008 

were computed using a reliability estimation method, wherein a pertinent material strength 

distribution would be compared to an applied loads distribution. The unreliability of the 

component is calculated from the area of intersection of these two distributions. 
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EO-23: The reliability estimates that were computed by Airborne using the distributionintersection estimation method may underestimate the risk of failure of those components. 

FS-36: The CPAS Project has not proposed the development of test plans to show how reliability 

estimates based on prediction would be verified/validated.

EO-24: Some reliability estimates were based on results from simulation codes for which it was 

not clear if rigorous V&V had been accomplished. 

FS-37: Reliability estimates for drogue and main parachute structural components that were 

presented at the IDR in December 2008, included five items with failure rates of 1:10,000 or 

worse. Three of these were determined by test and two were estimated by prediction. 

Determined by test:

 Failure of a drogue parachute with a root cause in some aspect of the packing 

(1:10,000) 

 Failure of a main parachute with a root cause in some aspect of the packing 

(1: 10,000)

 Failure of a drogue parachute with a proximal cause in some aspect of the parachute 

failing to extract from the d-bag (1:3,333)

Estimated by prediction:

 Failure of a main parachute with a proximate cause of failure of an unspecified 

number of attachment joints between skirt structural elements and suspension lines. 

(1:806)

 Failure of a main parachute with a proximate cause of failure of an unspecified 

number of vent line attachments. (1:8446)
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FS-38: The following table of failure mode estimates was received from the S&MA team on 

March 3, 2009.

Failure Mode

Estimate 

(1/x)

Prediction 

(1/x) Rationale

Main / Drogue Confluence Failure >10M - Low number due to proof testing and subsequent 

post packing X-ray inspections.

Environment Induced Failure >10M - Low chemical concentrations not expected to affect 

parachutes. Vibration could change the shape of 

bags causing contact issue. Low number due to 

vibration qualification.

Rigging Error (Main + Drogue) 100,000 - Conservative number due to decreased complexity 

compared to parachute packing.

Far-Field Contact 70,000 - Failure due to 2 auxiliary failures.

Near-Field Contact 15,696 - From SRB data for 3 contact chute failures. 

Nominal case assumed for independent events due 

to testing activities.

Main Chute Entanglement 1,000,000 - Estimated 2/3rds of a twist from 2–3 seconds for 

deployment supports low number.

Drogue / Auxiliary Entanglement 1,000,000 - Low number due to minimum twist due to fast 

deployment.

Skipped Reefing Stage Failure 200,000 - Low number due to remote chance of packing 

error, broken reefing line or X-ray test escape from 

high packing density. 

Chute Deployment Failure - 2.00E+04 Historical Data (lower bound) dominated by 

parachute packing.

Lead Lag Failure >10M Low number due to treatment as structural failure.

Inflation Failure 1,000,000 - Given successful deployment and vehicle stability, 

inflation failures historically have been non-issues. 

Reefing Cutter Fails to Disreef 4.00E+04 With redundancy (0.995 ea).

EO-25: The project has broadly assessed that chemical concentrations will be low, and so the 

risk to the parachutes will be low, but the allowable chemical concentration would depend on the 

specific chemical compound.

FS-39: The project recognizes the risk of vibration changing the shape of d-bags and causing 

contact with the FBC IML, and expects to mitigate the risk by vibration qualification testing.

FS-40: The project has estimated that the probability of a single parachute contacting CEV or 

FBC structure is 1:15,696. This is a revised number from the 1:8,205 presented at the 

December 2008 IDR.
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FS-41: The project estimates that the CM can roll 240 degrees (―2/3rds of a twist‖) relative to the 

drogue-suspended FBC, during the estimated 2–3 seconds between FBC release and line stretch, 

and uses this to support an estimate of Main Chute Entanglement of 1:1,000,000.

FS-42: The project estimates that the risk of drogue chutes or auxiliary chutes entangling with 

themselves or which each other during deployment is low, because they are deployed and 

inflated fast.

FS-42b: Theo Knacke report states ―Wind tunnel tests and free fall tests of a full-scale 

dynamically-similar CM indicated instability in all 3 axis. A preferred short-duration attitude of 

the CM was nose down at about 135 degrees to the take off (zero degree) attitude‖

FS-43: The project estimates the risk of skipped reefing stage at 1:200,000, in part because of a 

―remote‖ chance of failing to detect a damaged reefing ring or prematurely triggered cutter using 

X-ray non destructive evaluation, even at high-packed densities.

F-44: The project lower-bounds the probability of chute deployment failure at 1:20,000 based on 

historical data. Packing errors are said to be predominantly responsible for deployment failures.

FS-45: Lead/lag failures, the risk of one main parachute beating its cluster mates to the moment 

of line stretch and inflation so much earlier that it‘s loads exceed margins and it fails, is said to 

be treated as a structural failure, so the probability is set arbitrarily low in this table.

EO-26: The condition of lead/lag could be a design loads driver that could affect both the CM 

and the parachute. It would not be the results of a failure or an out of spec condition. 

EO-27: The probability of a lead/lag deployment event was high for Apollo Block II ELS main 

parachutes, because they were mortar deployed in different directions. The probability of a 

lead/lag deployment event may be less for CPAS than for Apollo, for all three architectural main 

deployment options, because all three main parachutes are deployed in the same direction.

EO-28: The project has assessed inflation failure to be a low risk, with a stable vehicle, but 

stability is not assured during deployment.

FS-46: The project has predicted that two reefing cutters have a combined reliability to cut a 

reefing line of 0.995.

Applicability of Apollo Geometry for CPAS Near-Field Contact 

Estimates

FS-47: Parachute systems in use for aircraft deceleration or aircraft recovery are deployed from 

stowage spaces that are not geometric similar to the CPAS forward bay. 

FS-48: Parachute systems in use for weapons systems are deployed from stowage spaces that are 

not geometric similar to the CPAS forward bay. 
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FS-49: The Apollo CM forward bay had four gussets, equally spaced around the Docking Tunnel 

which provided four bays. The three main parachute packs were stowed in three of the bays 

along with its related pilot parachute mortar assembly. The fourth bay contained the drogue 

parachute mortars and the parachute attach/disconnect fitting. The CEV forward bay is 

geometrically analogous to the Apollo forward bay in general arrangement, but is divided into 

six individual sectors rather than four.

FS-50: Each Apollo main d-bag was lifted from its stowed sector by a force provided by an 

inflated pilot parachute. 

EO-29: If deployed in a nominal vehicle attitude, each Apollo main d-bag was extracted from its 

stowage sector by its inflated pilot parachute in a direction up and slightly away from the

docking tunnel wall. The initial velocity vector for main chute extraction was dependant on the 

attitude of the CM and its relationship with the associated pilot chute when the pilot chute load 

was applied.

FS-51: For the loosely-attached-pilot-deployed mains architecture option, each CPAS main 

d-bag will be lifted from its stowed sector by a force provided by a pilot parachute. 

EO-30: For the loosely-attached-pilot-deployed mains architecture option, each CPAS main 

d-bag will be lifted by its inflated pilot parachute in a direction parallel to the tunnel wall. 

Applicability of SRB Data for CPAS Near-Field Contact Estimates

FS-52: At the December 2008 IDR, the probability of occurrence of more than one main 

parachute contacting CM structure during deployment, while being lifted in their d-bags from 

their stowed locations (for the architecture configuration with main d-bags loosely-attached to 

the FBC underside with two bag handles each, with integrated energy modulators), was 

presented as 1:217. This estimate was shown to have been derived from Space Transportation 

System (STS) Solid Rocket Booster (SRB) data that showed 3 occurrences out of 651 

opportunities, of a single SRB parachute failing from contacting the Main Parachute Support 

System (in its frustum) or the frustum edge. 

FS-53: The probability of a single SRB parachute component being damaged by contact (drag 

across, slide along or strike against) the Main Parachute Support System (in its frustum) or the 

frustum edge, reduced over time due to mitigating actions taken by the SRB project. The 651 

opportunities that were considered to calculate the 1:217 value is not a true representation of one 

specific configuration, nor any configuration that suitably represents CEV.

FS-54: The CPAS FBC is analogous in function to the SRB frustum, but differs geometrically in 

significant ways. 

FS-55: The CPAS FBC has six radial beam structures on its underside. These are not large 

enough to extend down between stowed main parachutes. 
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FS-56: The SRB frustum has three deep isogrid panels and three bipod struts on its underside. 

This assembly, known as the SRB Main Parachute Support Structure, separates the three stowed 

main parachute d-bags from each other. 

FS-57: For all three principal CPAS main parachute deployment architectural configurations, 

CPAS main parachute d-bags are lifted from their stowed positions to begin the deployment of 

their packed contents from the bottom. There is no comparable ―lifting‖ event for SRB 

deployment. SRB main parachutes deploy directly from d-bags that are rigidly attached inside 

the frustum.

FS-58: For all three principal CPAS main parachute deployment architectural configurations, any 

CPAS main parachute d-bag may physically contact (drag across, slide along or strike against) 

the CEV tunnel, up to two CEV gussets, and up to two LAS Wells. This risk only exists for a 

short time while a d-bag is being lifted from its stowed location, until it has cleared the top of the 

tunnel. The top surface of the SRB rocket has no structures analogous to the CEV tunnel, gusset 

or LAS Well.

FS-59: For all three principal CPAS main parachute deployment architectural configurations, as 

a main parachute‘s riser begins to play out of its d-bag, it can physically contact (drag across, 

slide along or strike against) the CEV tunnel, a CEV gusset, or a LAS Well. The top surface of 

the SRB rocket has no structures analogous to the CEV tunnel, gusset or LAS Well. 

FS-60: The SRB reliability data of 1:217 is not applicable to the risk for CPAS of main 

parachute d-bags contacting the CEV tunnel, gussets or LAS Wells during extraction from their 

stowed position.

FS-61: The SRB reliability data of 1:217 is not applicable to the risk for CPAS of main 

parachute risers contacting the CEV tunnel, gussets or LAS Wells during deployment from their 

d-bags.

FS-62: The SRB reliability data of 1:217 is not applicable to the risk for CPAS of main 

parachute components contacting the underside of the FBC, in the ―loosely attached‖ main 

parachute deployment architectural configuration.

FS-63: The SRB reliability data of 1:217 is not applicable to the risk for CPAS of main 

parachute components contacting the underside of the FBC, in the ―pilot chutes loosely attached‖ 

main parachute deployment architectural configuration.

FS-64: The SRB reliability data of 1:217 is somewhat applicable to the risk for CPAS of main 

parachute components contacting the underside of the FBC, only in the ―rigidly attached‖ main 

parachute deployment architectural configuration.

 This applicability may be limited by consideration of differences between the Orion 

CM‘s dynamic behavior relative to the FBC after separation, compared to the STS 

Shuttle SRB‘s dynamic behavior relative to its frustum after separation. 
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Main Parachute Deployment Bags and Packing Issues

FS-65: The main deployment bags (d-bags) have an irregular shape, with concavities and sharp 

corners, which could be a factor in packing the parachutes at high densities without inflicting 

damage.

FS-66: The main d-bags closure flaps are on the bottom, facing the deck when stowed, which 

could have an effect on parachute packing since they will be packed into a sloping surface. 

FS-67: The shape of the main d-bag poses risks of non-homogeneous density and difficulty in 

achieving consistent results from pack to pack.

FS-68: It may be necessary to imbed stiffeners in the main d-bags to help them maintain their 

shape.

FS-69: In March 2009, the project discussed an optional pack shape that replaced the concavity 

feature with a faceted corner. This was being coordinated with Lockheed who would have to 

redesign the shape of the LAS Wells to accommodate it.

FS-70: The system requirement is 38 lb/ft3 maximum pack density for the main parachute pack 

assembly. 

 [JSC64335, I.CM.CPAS.101] - The CM will provide volume to ensure CPAS main 

parachute packing density is less than or equal to 609 kg/m3(38 lbm/ft3). Rationale: 

This general requirement requires CPAS to fit within the volume defined by the forward 

bulkhead and FBC. The volume provided by CM will not require packing the mains to 

the density of more than 609 kg/m3 (38 lb/ft3).

FS-71: The projected pack density for the main parachute is in the high 40 pounds per cubic ft 

range, for all architectural options under consideration.

EO-31: There is expert consensus that pack density over 40 lb/ft3creates added reliability risks. 

FS-72: Reliability risks associated with high packing density can include damage to both the 

hardware items and the soft materials in the parachute pack assembly. This damage can result in 

weaknesses in the system leading to failures at less than design limit loads or parachute inflation 

malfunctions that can that exceed the design limit loads for the system, either of which can result 

in catastrophic failures in the parachute system. These risks include:

 A bent reefing ring than can cut a reefing line and result in a skipped reefing stage

 A bent reefing ring than can damage and weaken a reefing line and result in premature 

disreefing 

 A bent reefing ring than can damage other textile material packed adjacent to it, and 

result in suboptimal canopy performance 
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 A damaged reefing line cutter that cuts a reefing line, and results in a skipped reefing 

stage

 Two damaged reefing line cutters on one reefing line that cannot actuate, and prevents 

disreefing of that stage (or any subsequent stage)

 Damaged textiles during extraction from their d-bag, due to heat from friction

 Reduced probability of detection (POD) of X-ray inspection for damaged pack contents

FS-73: According to the Apollo ELS Experience Report, during development of the Apollo 

Block II ELS, as the density of the parachute packs increased, the amount of damage to the 

parachutes increased.

EO-32: Pack density in the high 40 pounds per cubic ft at this stage of the system development 

program leaves no room for error, design growth or vehicle growth (with associated parachute 

growth), all which occurred during Apollo. 

EO-33: Allowing for a 45lb/ft3density at this stage of the design could paint the designers into a 

corner. It appears a challenge for CPAS to achieve the reliability necessary for a manned system 

with the volume currently provide for three main parachutes, below the required pack density.

FS-74: Apollo ELS engineers developed a successful method for verification of intact reefing 

lines prior to flight. A strong monofilament witness line (aka  ̳catgut‘) was carefully measured 

and routed through each reefing cutter during the packing operation. One end was left accessible 

on the outside of the d-bag. Prior to parachute installation the witness line was removed and 

measured. If it was less than the pre-installed length, the pack was rejected. The program always 

packed four chutes for each mission, in case one was to fail the catgut test (or swell inspection, 

stitch inspection or other pre-flight inspection). The method proved to be successful. Apollo ran 

a comprehensive test and qualification program for the catgut procedure, because of their 

recognition that loss of more than one main chute would result in LOC.

FS-75: Apollo ELS reliability was highly dependent on quality inspection and the skill and 

experience of the inspectors. The skill levels and the procedures were developed and proven 

during the ELS development and qualification program and imposed through the operational 

program. Procedure developers, who had helped develop the inspection techniques, later 

performed operational inspections. 

FS-76: The NASA Engineering network, lessons learned database, entry 0836, submitted in 

1994, documents that to mitigate observed abrasive damage to SRB main parachute canopies 

during deployment, the SRB parachute packing procedure was revised from a ―zigzag‖ pattern to 

a ―circular‖ pattern.
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Pack Retention 

FS-77: For the loosely-attached mains architectural option, The Main Parachute retention system 

is comprised of two donut ties and two electrically initiated cutters, either one of which can cut 

both ties. The two cords retain the packed main parachutes on its upper surface at six points. The 

six points are ends of six retention straps whose other ends are attached to the CM structure at 

locations beneath the pack and behind it on the tunnel. The retention scheme does not appear to 

allow for growth due to handling, thermal and humidity cycles. A failure at one of the retention 

points will result in the loss of 50 percent of the overall retention capability. The release of the 

retention system is based upon actively initiating two electrically initiated cutters. The failure to 

release the retention system will result in locking a packed main parachute into its stowage 

sector, consequently resulting in failure to deploy one main parachute. 

FS-78: The Apollo retention system was a quick release system that fully covered the packed 

main parachute, retaining it every couple of inches along the perimeter. 

FS-79: For the pilot-deployed mains architectural option, the project redesigned the retention 

release concept to eliminate the electrically initiated cord cutters, and replaced them with a pair 

of redundant cut-knives. 

Volume Budget

FS-80: Apollo Block II ELS main parachutes were nominally 83.5 ft diameter inflated, compared 

to 116 ft for CPAS main chutes. Dimensions are approximately in proportion for vehicle size.

FS-81: Apollo Block II ELS main suspension lines were nominally 120 ft long, compared to 133 

ft for CPAS main suspension lines. Dimensions are approximately in proportion for vehicle size.

FS-82: Apollo Block II ELS main risers were nominally 7.8 ft long (6.5 ft steel and 1.3 ft fabric), 

with 3.5 ft fabric bridle legs. This compares to 113 ft for CPAS main risers (97 ft suspension 

lines plus 16 ft harness length). The total trailing distance of the Apollo main chute skirt behind 

the C/M is approximately 131 feet versus the 113 feet for the CPAS. This can have an effect on 

both the inflation characteristics and the stability of the inflated canopies. 

FS-83: Apollo ELS Block II devoted 75% of forward bay volume to its three main packed d-bags 

(including most of the riser lengths) and the three pilot parachute mortars for deploying the 

mains.

FS-84: Apollo ELS Block II devoted 25% of forward bay for its two drogue mortars, its singlepoint attach fixture (also known as the  ̳flower pot‘), and other hardware not related to ELS. 

EO-34: An estimated allocation of forward bay volume for Apollo Block II ELS components 

other than d-bags is 5% (of total) for each of two mortars, and 5% (of total) for flower pot fitting. 
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FS-85: If the ―5% for each mortar and 5% for flower pot‖ estimate is accurate, then the Apollo 

vehicle used approximately ( 75 + 5 + 5 + 5 = ) 90% of total available volume of forward bay for 

the Block II ELS, and 10% of available volume for other hardware not directly associated with 

the ELS.

FS-86: All of the Orion CPAS architectural options under consideration between December 2008 

and March 2009 devoted 50% of the forward bay volume (sectors B, C and E) for the three main 

packed d-bags (including much of the riser lengths but excluding components in the stowage 

container). None of the architectural options under consideration had pilot parachute mortars for 

deploying the mains.

FS-87: All of the CPAS architectural options under consideration between December 2008 and 

March 2009 used a portion of two sectors for two drogue mortars (one each, in sectors A and F). 

EO-35: An estimated allocation of forward bay volume for each of two CPAS mortars for CEV, 

is 10% (of total), regardless of CPAS architectural option.

FS-88: The harnessed-mains CPAS architectural option uses a portion of Sector D, for a stowage 

container for one confluence fitting, one rotation torque limiter, excess lengths of three main 

risers, and for the three main harness legs. 

EO-36: For the harnessed-mains CPAS architectural option, an estimated allocation of forward 

bay volume for the CPAS stowage container and its contents is 5 percent (of total).

EO-37: The single-point-attach CPAS architectural option may require one or more small storage 

containers for excess lengths of the three main risers and for one rotation torque limiter. Risers 

will be longer in this option to account for lost length of harness legs. 

EO-38: An estimated allocation of forward bay volume for the CPAS stowage container and its 

contents is 5% of total, for the single-point attached mains architectural option

FS-89: Orion CEV uses approximately (100 – 50 – 20 – 10 = ) 20 percent of available volume 

for other hardware not directly associated with CPAS and approximately 80 percent of available 

volume for CPAS.

EO-39: Compared to Apollo in terms of percent of available volume in the forward bay, 

assuming scalability, Orion is using approximately twice as much volume for items not 

associated with its parachute recovery system. The parachute recover system is a critical system 

for crew survival. 

FS-90: All of the CPAS architectural options apportion components among 4 sectors, B, C, D, 

and E.

FS-91: CPAS Project charts indicate previous discussion of moving main d-bags from current 

bays (B, C, and E) to three other bays, suggesting some decisional control remains with respect 

to the Lockheed CEV forward bay arrangement. 
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FS-92: Concern with ―geometric lock‖ during extraction (d-bag physical contact with tunnel, 

gussets, and LAS Wells that is so significant as to prevent extraction) is cited in project charts as 

the principal reason to not consider alternative bays for main d-bag stowage. 

EO-40: Relocating main d-bags to other sectors is likely constrained by design decisions made 

by the Orion CEV project that are unrelated to CPAS, but these were not included in the material 

reviewed by the NESC team. 

FS-94: The size of the CPAS main parachutes is principally driven by pad abort loads and 

vehicle weight. The volume of the packed main parachutes d-bags is dependent the size of the 

parachute and the density to which it is packed.

FS-95: Throughout the development of Apollo, changes being made to vehicle systems and 

structures required continuous improvement in volumetric efficiency of the ELS main parachute 

packs. Demands increased but available volume did not.

EO-41: Unknown issues during ongoing development of the CPAS system may result in 

increases in the main parachute volume needs.

FS-96: Unknown issues during ongoing development of the CEV by Lockheed may adversely 

affect the volume available 

FS-97: In the single point attach architectural option, stowage of excess main risers in Sector D, 

with attachment on the 0o gusset, poses riser routing challenges that may affect the reliability of 

deployment. 

Forward Bay Cover 

FS-98: The NASA Engineering Network, Lessons-Learned database, entry number 0836 

submitted in 1994, indicated that abrasive damage was observed to have occurred to SRB main 

parachute canopies during deployment, from contact with the frustum and MPSS. Early in the 

STS program, TPS material was installed around the perimeter on the underside of the SRB 

frustums, to fill the volumes between the two lowest frustum ring frames, to provide a smooth 

contact surface should the main chutes contact the frustum during deployment. Later, this TPS 

material was replaced with a fabric curtain, to perform the same function. Foam material was 

also added to the MPSS bipod struts, to prevent damage from parachute components contacting 

the MPSS during deployment.

EO-42: Apollo engineers assessed risks of abrasion, friction damage, hang-up objects and sharp 

edges and addressed each one by proving it did not exist or by incorporating abrasion protection. 

EO-43: Parachute components that are deployed from a d-bag that is rigidly attached inside a 

FBC can contact the sides of the FBC during deployment, and this contact can be exasperated by 

the dynamic behavior of the two bodies during separation.
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FS-99: Standoff distance and/or insulation is required between FBC and the various parachute 

system components in the forward compartment to protect against damage due to thermal 

environment during reentry.

FS-100: Standoff distance is required between LAS Wells and main d-bags to protect against 

damage due to thermal environment during reentry.

FS-101: Intentionally blank. Superseded by revision to F-99. 

FS-102: Main d-bag restraint system is complex, due to complex main d-bag volumetric shape. 

FS-103: Vibration during launch or other dynamic events that occur prior to or during reentry 

can cause stowed d-bag surfaces to enter the stand-off volume and remain there for reentry, if 

restraint systems are insufficient. This poses risk of damage to the d-bag and its contents 

(canopy, suspension lines, risers) due to thermal environment during reentry.

FS-104: Vibration during launch or other dynamic events that occur prior to or during reentry 

can cause stowed and restrained risers and harness legs to enter the stand-off volume and remain 

there for reentry, if the main d-bags have moved.

FS-105: Commercially available polyimide foam has insulation qualities, mechanical and 

thermal performance and is light weight. These make polyimide foams candidate materials for 

installation between FBC and main d-bags, to act as TPS and as supplemental restraint. 

FS-106: Commercially available polyimide foam has insulation qualities, mechanical and 

thermal performance and is light weight. These make polyimide foams candidate materials for 

installation between LAS Well and main d-bags, to act as TPS and supplemental restraint.

FS-107: Aluminized fiberglass sleeves have insulation qualities and light weight that make it 

candidate TPS material for protection of textile risers and harness legs that are stowed beneath 

the FBC that may become at risk of damage due to thermal environment near the FBC IML 

during reentry, if d-bags have shifted.

FS-108: The Ares I-X flight test project wrapped aluminized fiberglass around first stage risers 

and riser attach spools to protect them from expected thermal environments associated with its 

skirt extension / forward skirt separation event. 

EO-44: Curtains installed for protection of d-bags against physical damage could become a 

hindrance to d-bag extraction unless it is securely attached to the FBC, and therefore removed 

from the forward bay at FBC release.

EO-45: TPS installed for protection of d-bags against thermal damage could become a hindrance 

to d-bag extraction unless it is securely attached to the FBC, and therefore removed from the 

forward bay at FBC release.
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FS-109: A review of CPAS preliminary design details reveal a risk of heat damage to main 

parachute risers from high temperatures at the FBC IML during reentry - if the bottom ends of 

the risers are stowed on CEV gussets in close proximity to the FBC IML.

FS-110: A review of CPAS preliminary design details reveal a risk of heat damage to main 

parachute risers from high temperatures transmitted from the LAS wells during reentry - if the 

bottom ends of the risers are stowed on CEV gussets in close proximity to the LAS wells. 

Drogue Deploy Envelope

FS-111: CPAS drogue deploy envelope was developed using Monte Carlo simulations.

FS-112: The drogue deploy envelope is comprised of overlapping zones for pad abort, ascent 

abort, and nominal reentry.

FS-113: The drogue deploy envelope Points 4 and 5 were relocated in March 2009. Point 4 was 

moved from 53,000 ft at 99 psf to 45,000 ft at 150 psf. Point 5 was moved from 32,000 ft at 

167 psf to 32,000 ft at 150 psf.

FS-114: The drogue deploy envelope zones are dissimilar from those for the Apollo drogue 

deploy envelope.

EO-46: The drogue deploy envelope establishes candidate flight test data points.

Drogue and Main Parachute Construction and Failure Risks

FS-115: The CPAS drogue parachutes are variable porosity conical ribbon chutes. The Drogue 

Parachute Drag Surface incorporates ―Rip-Stops‖ to preclude tear propagation. 

FS-116: The CPAS drogue canopies are nominally 23 ft diameter. According to Project analysts, 

the CPAS drogue size is driven by high altitude aborts, with high q and high weight.

EO-46b: Drogue size may be driven by CM stabilization and deceleration requirements 

throughout the recovery system operating envelope. The rate of descent on the drogues will vary 

depending on the altitude. The basic requirement is to stabilize the CM and bring it into the 

acceptable conditions for main parachute deployment. 

FS-117: According to Project analysts, the CPAS drogue size was determined by q=45 psf at 

terminal rate of descent 9(33 fps) with 18k load under on drogue chute.

FS-118: The CPAS drogue canopies‘ drag coefficient are nominally 0.57

FS-119: The drogue riser and harness legs are constructed from multiple plies of Kevlar®

webbing (project infers that this improves reliability).

FS-120: The drogue harness legs are nominally 16 ft. long.
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FS-121: IDR charts (revised Feb 2009) show the Drogue risers are nominally 65.4 ft. long.

FS-122: CEV-LRS-08-004 Rev A (Jan 2009), ―ODAC-3 Parachute Model Memo‖ pg 10, shows 

the riser lengths to be 48.8 ft long

FS-123: IDR (Feb 2009) and CEV-LRS-08-004 Rev A (Jan 2009) are not consistent with respect 

to drogue riser length.

FS-124: The CPAS drogue suspension lines are nominally 34.5 ft. long.

FS-125: The length of a Drogue harness leg plus a Drogue riser plus a Drogue suspension line is 

of sufficient total length to meet the wake rule of thumb of four to six times the forebody 

diameter, cited from Section 5.2.2 from Knacke page 5-21.

FS-126: The table of drogue parachute margins presented in the IDR charts indicates the use of a 

variety of textile materials of various strengths for a variety of parachute components. Nylon 

Ribbon, Kevlar®Tape, and Kevlar® Cord are conventional materials for parachute systems. 

Vectran Cord has been used in parachute systems, but is a more recently developed material; it is 

indicated for use as ―soft links.‖ 

FS-127: Vectran is a thermotropic (melt spun) liquid crystal copolyester fiber produced by 

Kuraray Co., Ltd. (Fort Mill, SC). With comparable yarn tenacity to Kevlar®29, it has better 

flex-crack/abrasion resistance. Kevlar®fibers are more readily damaged by flexing and sliding 

against themselves, when a fabric is folded. While Kevlar®offers more strength retention at 

higher temperatures than Vectran, Vectran retains its full strength upon cooling and actually gets 

stronger at low temperatures. (ref- Development and evaluation of the mars pathfinder inflatable 

airbag landing system)

FS-128: Vectran offers less strength retention at high temperatures than Kevlar®.
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DROGUE 

COMPONENT Plies IDR – DECEMBER 2008 Plies FEB - 2009

Crown Ribbons 1 PIA-T-5608 2" 300-lb Nylon Ribbon 1 PIA-T-5608 2" 300-lb Nylon Ribbon

Mid Ribbons 1 PIA-T-5608 2" 300-lb Nylon Ribbon 1 PIA-T-5608 2" 200-lb Nylon Ribbon

Skirt Ribbons 1 PIA-T-5608 2" 300-lb Nylon Ribbon 1 PIA-T-5608 2" 200-lb Nylon Ribbon

Verticals 1 PIA-T-5608 0.63" 90-lb Nylon Ribbon 1 PIA-T-5608 0.63" 90-lb Nylon Ribbon

Radials 1 PIA-T-87130 1" 4K Kevlar® Tape 1 PIA-T-87130 1" 4K Kevlar® Tape

Vent Band 2 PIA-T-87130 1" 6K Kevlar® Tape 2 PIA-T-87130 1" 6K Kevlar® Tape

Skirt Band 1 PIA-T-87130 1" 4K Kevlar® Tape 1 PIA-T-87130 1" 4K Kevlar® Tape

1st Stage Reef Line 1 PIA-C-87129 4K Kevlar® Cord 1 PIA-C-87129 5K Kevlar® Cord

2nd Stage Reef Line 1 PIA-C-87129 5K Kevlar® Cord 1 PIA-C-87129 4K Kevlar® Cord

Suspension Line 1 PIA-C-87129 4K Kevlar® Cord 1 PIA-C-87129 4K Kevlar® Cord

Soft Links 4 4,500-lb Vectran Cord 4 4,500-lb Vectran Cord

Riser 8 PIA-T-87130 1.75" 20K Kevlar® Tape 8 PIA-T-87130 1.75" 20K Kevlar® Tape

Harness 8 PIA-T-87130 1.75" 20K Kevlar® Tape 6 PIA-T-87130 1.75" 20K Kevlar® Tape

FS-129: Between December 2008 and March 2009 updates to this data, analysts increased the 

required strength of the first stage drogue reefing line, decreased the strength of the second stage 

drogue reefing line, and decreased the numbers of plies required in the drogue harness legs. 

FS-130: The main parachutes are quarter-spherical ring sail parachutes. The Main Parachute 

Drag Surface incorporates Leading and Trailing Edge reinforcement on all of the individual 

panels. These reinforcements act as ―Rip-Stops‖ to preclude tear propagation. 

FS-131: The Main canopies are nominally 116 ft diameter. The size is driven by pad aborts, 

point 7 on the drogue deploy envelope, wherein drogues are released along with the FBC while 

the drogues are still at the first reefing stage. (Low altitude, low q, high Mach.)

FS-132: Charts from the IDR (briefed Dec 8, 2008 and revised in Feb 2009) and charts from the 

ERB Orion-09-0355 (Mar 12, 2009) show the main canopies‘ combined drag coefficient as 0.94 

for 2 chutes and 0.97 for 3 chutes. 

FS-133: The ODAC-3 Parachute Model Memo, CEV-LRS-08-004 Rev A (Jan 2009), pg 11, 

shows the main canopies‘ combined drag coefficient 0.718 for 2 chutes and 0.896 for 3 chutes.

FS-134: IDR (Feb 2009) and ERB charts are not consistent with CEV-LRS-08-004 Rev A (Jan 

2009), with respect to main chute drag coefficients

FS-135: The main parachutes Riser and Harness Legs are constructed from multiple plies of 

Kevlar® webbing.

FS-136: The Main three harness legs are two at 19 ft long, and one at 16 ft. long.
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FS-137: the Main risers are nominally 97 ft for the harnessed-mains architectural option. The 

Main risers will be longer length for the single-point attachment architectural option, but not 

known.

FS-138: The Main suspension lines are nominally 133 ft. long.

FS-139: The length of a Main harness leg plus a Main riser plus a Main suspension line is of 

sufficient total length to meet the wake rule of thumb of four to six times the fore-body diameter, 

cited from Section 5.2.2 from Knacke page 5-21.

FS-140: The table of main parachute margins presented in the IDR charts indicates the use of a 

variety of textile materials of various sizes and strengths, for a variety of parachute components. 

Nylon rip-stop cloth, Kevlar®Tape, Nylon Webbing, and Kevlar® Cord are conventional 

materials for parachute systems. Vectran Cord has been used in parachute systems, but is a more 

recently developed material; Vectran cord is indicated for soft links and vent hoops.

FS-141: Vectran offers less strength retention at high temperatures than Kevlar®. (repeat)

MAIN COMPONENT Plies IDR – DECEMBER 2008 Plies FEB - 2009

Crown Rings 1 PIA-C-7350 150-200 CFM 3.5-oz Cloth 1 PIA-C-7350 150-200 CFM 3.5-oz Cloth

Mid Rings and Sails 1 III 820201 25 CFM 2.25-oz Cloth 1 III 820208 80-120 CFM 1.1-oz Cloth

Skirt Sails 1 III 820200 40 CFM 1.17-oz Cloth 1 III 820208 80-120 CFM 1.1-oz Cloth

Radials 1 PIA-T-87130 1" 1.5K Kevlar® Tape 1 PIA-T-87130 1" 1.5K Kevlar® Tape

Vent Hoop 3 5,250-lb Vectran Cord 3 5,250-lb Vectran Cord

Vent Band 1 PIA-W-4088 1" 2.5K Nylon Webbing 1 PIA-W-4088 1" 2.5K Nylon Webbing

Skirt Band 1 III 119000 1" 1K Kevlar® Tape 1 PIA-T-87130 1" 1.5K Kevlar® Tape

1st Stage Reef Line 1 PIA-C-87129 4K Kevlar® Cord 1 PIA-C-87129 5K Kevlar® Cord

2nd Stage Reef Line 1 PIA-C-87129 4K Kevlar® Cord 1 PIA-C-87129 4K Kevlar® Cord

Suspension Line 1 PIA-C-87129 1.5K Kevlar® Cord 1 PIA-C-87129 1.5K Kevlar® Cord

Soft Links 4 4,500-lb Vectran Cord 4 4,500-lb Vectran Cord

Riser 8 PIA-T-87130 1.75" 15K Kevlar® Tape 8 PIA-T-87130 1.75" 20K Kevlar® Tape

Harness 14 PIA-T-87130 1.75" 20K Kevlar® Tape 18 PIA-T-87130 1.75" 20K Kevlar® Tape

FS-142: Permeability of cloth is measured in units of cubic feet of air per minute per square foot, 

abbreviated CFM.

FS-143: Between December 2008 and March 2009, project analysts apparently reduced the 

required weight of the cloth for the mid rings, mid sails and skirt sails; increased the required 

strength of the skirt band and the first stage main reefing line; and increased the numbers of plies 

required in the main harness legs from 14 to 18. 
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FS-144: Information presented at the December 2008 IDR indicated that the parachute design 

methodology will be:

1. Begin with the Gen-1 Drogue and Main parachute designs as basis for the Gen-2 designs.

2. Develop parachute loads from trajectories.

3. Distribute the loads across parachute elements.

4. Apply Design Factors (DF) to loads to determine required element strength.

5. Select elements from known available webbings, cords and cloths based on required 

element strength.

a. Consider that custom material specifications could be more mass efficient.

6. Build up parachute weight using material specification weights.

FS-145: Information presented at the December 2008 IDR indicated that the Design Team would 

apply a Safety Factor (SF) of 1.6 to all components except those whose failure ―could result in 

catastrophic failure.‖ These critical elements have a 2.0 SF:

 Soft links

 Drogue vent band

 Main vent hoop

 All reefing lines

 All risers

 Main harness legs

FS-146: Knacke Parachute Recovery Systems Design Manual, Table 6-7, recommends a Safety 

Factor (SF) of at least 1.6 and a Design Factor (DF) of 2.21, for all elements of parachute 

assemblies used for manned vehicles.

FS-147: The Irvin Recovery Systems Design Guide, Table 8.6, recommends a SF of 1.35 and a 

DF of 2.3 for manned systems.

FS-148: The DF is equal to the SF divided by the Allowable Strength Factor (Ap). According to 

the Irvin Design Guide, AFFDL-TR-78-151, page 413-414, the Ap is the product of seven 

individual allowable strength factors, all multiplied by the cosine of the line or riser convergence 

angle from the axis of loading.

 Joint or seam efficiency

 Abrasion and wear
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 Moisture absorption due to humidity, etc

 Fatigue due to repeated loading or use

 Temperature

 Vacuum

 Asymmetrical or unequal loading

FS-149: The Table of Main Parachute Margins presented at the IDR in December 2008 showed 

the Main Vent Band DF of 2.21, which meets the Knacke guideline, but does not meet the Irvin 

guideline. 

EO-47: Joint efficiency is a critical component of the Allowable Strength Factor calculation.

FS-150: Information presented at the December 2008 IDR indicated that the Design Team 

assesses that many Gen-1 joint efficiencies assessed to be below 80% could ―be improved to at 

least 80%.‖ 

FS-151: Information presented at the December 2008 IDR indicated that the Design Team 

assesses that the main riser and the main harness joint efficiencies cannot be improved to at least 

80%, because they are driven by pin loads. 

EO-48: O: Demonstrating V&V for drogue and main parachute structures could result in a 

significant amount of testing. If all joints are tested, this could tax test facilities.

EO-49: Review of Gen 1 test reports suggests that in 2007 and 2008 there was a lack of a 

systematic process in establishing the basis for and the conduct of testing.

Parachute Attach Fittings

FS-152: The Apollo  ̳flower pot‘ fitting attached to the CM at 0o (the ‘crew heads up‘ direction), 

mid-way between two gussets (45o and 315o). The fitting reacted drogue and main parachute 

loads.

EO-50: Six CEV CM LAS Wells are sized for substantial loads from launch abort conditions. 

FS-153: LAS Wells are located at the base of each of the six forward bay gussets.

FS-154: Six CEV CM forward bay gussets (Al-Li) are FSW welded along two orthogonal sides, 

to the forward bay bulkhead (monolithic integrally machined Al-Li structure) and to the tunnel 

(monolithic integrally machined Al-Li structure). 

FS-155: For all CPAS architectural options, the drogue parachute loads are transmitted through 

the FBC and reacted by the CM gussets at 60o, 180o, and 300o. 
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FS-156: For the CPAS harnessed-mains architectural option, main parachute loads are reacted at 

the base of CM gussets at 0o, 120 o, and 240 o.

FS-157: For the CPAS single-point attach main architectural option, three main parachute attach 

fittings are integrated into the CM‘s 0o gusset, midway up its length.

EO-50b: Integrating three main parachute attach fittings are into the CM‘s 0o gusset, midway up 

its length may not allow for sufficient riser excursion during parachute deployment.

FS-158: For the CPAS single-point attach main architectural option, CPAS assumes load share 

main attach fitting load share of 50% / 25% / 25%.

EO-50c: The CPAS load share assumption on main attach fittings of 50% / 25% / 25% will have 

to be verified by appropriate main chute cluster tests.

FS-159: According to Airborne charts from a Feb 3, 2009 presentation, Apollo designed main 

attach fittings (flowerpot assembly) to the assumed load share of 40% - 40% - 20%.

EO-50d: The Apollo load share assumption on main attach fittings of 40% - 40% - 20% were 

verified by instrumented aerial drop tests.

EO-51: For the CPAS single-point attach main architectural option, if main risers have wrapped 

more than one complete turnaround each other during deployment, the loads from multiple 

inflating canopies may all react though one riser beneath the twist point. This could affect torque 

limiter function and could result in high loads on just one attach fitting.

EO-52: If significant design changes are required for to the CEV CM 0o Gusset to accommodate 

the CPAS single-point attach architectural option, detailed coordination with Lockheed designers 

and analysts is essential to recognize integration issues as soon as possible. The 0o Gusset may 

need to be assessed as Design for Minimum Risk (DFMR).

Deployment Bag Handles and Energy Modulators

FS-160: In the loosely-attached mains architectural option described in the December 2008 IDR, 

each main d-bag is attached to the FBC by four bag handles of 20,000 lb Kevlar® Tape each, 

two on each side of the d-bag.

FS-161: In the loosely-attached mains architectural option described in the December 2008 IDR, 

Energy Modulators are incorporated into the bag handles, to reduce snatch forces. 

EO-53: The geometry of the d-bags suggests that the d-bags centers of gravity will be offset 

outboard (radially, away from the tunnel) from the attach locations of the four bag handles. If the 

d-bags centers of gravity are outboard from the handles, then the extraction forces acting on the 

d-bag handles as the bags are lifted, would impart a pitching moment on the bags. This moment 

may be sufficient for the lower back edge of all of bags to contact (slide along or strike against) 
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the tunnel during extraction. This could be a common cause source of damage to all three main 

d-bags.

FS-162: Energy modulators are sewn-together double-lengths of fabric that as they are loaded, 

tear apart. The tearing spreads the energy of a rapidly applied force over a longer period of time. 

FS-163: Energy modulators are incorporated into d-bag bag handles for the loosely-attached 

mains architectural option.

FS-164: The effectiveness of energy modulators in this application may be reduced if a d-bag‘s 

extraction from its stowed location is delayed by contact (drag across, slide along or strike 

against) with CM structure.

Kicker Straps

FS-165: Kicker strap concepts were shown that use kinetic energy from the separation of the 

FBC away from the CM after release, provided by drogue parachute forces, to impart energy to 

main d-bags in a radial direction while they are being extracted, for FBC-deployed main 

parachute architectural options.

FS-166: Kicker straps as envisioned for FBC-deployed main parachute architectural options may 

reduce the risk of near field contact (drag across, slide along or strike against) of main d-bags 

with CM tunnel and gussets during extraction from their stowed locations.

FS-167: Kicker straps as envisioned for FBC-deployed main parachute architectural options may 

not reduce the risk of near field contact (drag across, slide along or strike against) of main d-bags 

with CM LAS Wells during extraction from their stowed locations.

FS-168: Kicker straps as envisioned for FBC-deployed main parachute architectural options may 

increase the risk of near field contact of main d-bags with FBC structure, by imparting a pitching 

moment as they impel d-bags radially away from the CM, with the FBC still proximal.

EO-53b: Kicker Strap concepts that use some of the energy from the force provided by the pilot 

parachute at inflation, to impart energy to main d-bags in a radial direction while they are being 

extracted should be physically conceivable. 

Rotation Torque Limiter

FS-169: The PTRS requires CPAS to limit the torque required to roll the CM about the gravity 

vector prior to landing while suspended by its main parachute system, to less than 450 ft-lbs., to 

allow the RCS to maintain the crew‘s feet oriented towards the horizontal direction of travel 

prior to landing. 

FS-170: For the harnessed-mains architectural option, a rotation torque limiter would stow 

beneath the confluence fitting in a stowage container attached to the CM in sector D. 
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FS-171: For the harnessed-mains architectural option, when the three harness legs deploy, the 

torque limiter would ride up to its functional height, restrained from going higher by restraining 

cords. The section of the three harness legs between the confluence fitting (on top) and the 

torque limiter (on bottom) would be allowed to twist up and untwist, depending on the 

commands from the RCS. According to information communicated at the December 2008 IDR, 

this distance would be nominally 6 ft. This would be the effective length of harness that would 

be allowed to twist up in response to RCS commands. 

EO-54: The remaining harness leg lengths from the torque limiter to the CM attach points would 

be nominally 10 feet each.

FS-172: The torque limiter system includes restraining cords that are nominally 20 feet long 

(twice the length of remaining harness leg lengths), and are intended to assure that after 

deployment, the three harness legs lengths from the torque limiter to the CM attach points would 

all be the same length.

FS-173: The torque limiter system includes securing ties to hold three harness legs in a ―triangle‖ 

arrangement while deployed. 

EO-55: Failure of restraining cords and securing ties are possible during deployment, from 

contact (dragging across, sliding along or striking against) with CEV structure.

FS-174: Failure of two torque limiter restraining cords is necessary for one harness leg remaining 

length to deviate from nominal. This feature provides redundancy against loss of intended 

function.

FS-175: Failure of one torque limiter securing tie could allow one harness leg to become 

unseated from its place in the torque limiter, if the assembly is twisted. This feature has no 

redundancy against loss of intended function.

EO-56: The team was unaware of systems that included hardware similar in function to the 

described rotation torque limiter.

FS-176: The ICD drawing of the rotation torque limiter showed a version that was sized with 

recesses in which tapes would seat that are two inches wide including a 0.25 inch radius on each 

side, and with a harness installation clearance of 1.063 inches. This design appears to 

accommodate three tapes (harness legs or riser) with a maximum size of two-inch wide by oneinch thick. The drawing also showed hole provisions for routing securing ties across the inner 

surfaces of all three tapes. It also showed hole provisions for routing restraining cords. Various 

versions of the torque limiter could be manufactured. 

EO-57: Installation of Kevlar® tapes (harness legs or risers) would allow a space between the 

inner surface corners of adjacent tapes, in the untwisted condition. This space would close as 

twists are added. The number of twists at which the spaces close to zero will be a function of the 

width and thickness of the tapes, and the dimensions of the torque limiter.
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FS-177: In the single-point attach architectural option, the stowage location for the torque limiter 

was not specified. 

EO-58: In the single-point attach architectural option, the restraining cord feature cannot 

maintain the torque limiter at its intended height for proper function. When the three risers 

deploy, the torque limiter would have to ―be‖ at its functional height. 

EO-59: Assuming the upper limiter would be retained at its functional height by another method, 

the section of the three risers between the upper limiter and the lower limiter (at the gusset) 

would be allowed to twist up and untwist, depending on the commands from the RCS. This 

distance was not found in information reviewed by the NESC team, but is probably 6 ft by 

similarity with the other architectural option. 

FS-178: If CPAS utilizes a set of two rotation torque limiters for the single-point attach 

architectural option, with a lower torque limiter integrated into a CM gusset, and a flying upper 

torque limiter, deployment of the upper torque limiter may contact (strike against) CEV structure 

as it is extracted from its stowed location. Riser routing may limit the location of a stowage box 

for the upper torque limiter to sectors A or F, the two sectors that are adjacent to the 0o gusset. 

These two sectors contain the drogue mortars, one in each.

EO-60: In the single-point attach architectural option, if a main riser fails, the failure of a second 

riser may not be an independent event, given the confluence and arrangement of the three risers 

passing through the rotation torque limiter. One slack Kevlar® tape may bind or interfere with 

the two remaining taut tapes still under tension, causing their unexpected shifting in the torque 

limiter, and consequently damaging a second tape.

EO-61: In the harnessed-mains architectural option, if a main harness leg fails, the failure of a 

second harness leg may not be an independent event, given the confluence and arrangement of 

the three harness legs passing through the rotation torque limiter. One slack Kevlar® tape may 

bind or interfere with the two remaining tapes still under tension, causing their unexpected 

shifting in the torque limiter, and consequently damaging a second tape.

Stowage Container

EO-62: In the harnessed-mains architectural option, there are risks of disorderly extraction of the 

contents of the stowage container installed in sector D. The container contents (confluence 

fitting, torque limiter, harness legs), could be damaged by contact (drag across, slide along or 

strike against) with the CM structure. The container contents could be hindered or prevented 

from being deployed.

EO-63: In the single-point attach architectural option, the rotation torque limiter may be stowed 

in a container in Sector A or Sector F (the sectors nearest the 0° Gusset attach location), or may 

be stowed in a forward bay location without a container. If stowed in a container, there is a risk 
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that the torque limiter could be hindered or prevented from being deployed. Whether stowed in a 

container or not, there is a risk of the torque limiter contacting CM structure.

EO-64: Failure of the torque limiter will prevent CEV roll control prior to splashdown.

Drogue Mortars

FS-179: All of the CPAS architectural options have two drogue mortars - one each, in sectors A 

and F of the CM forward bay.

FS-180: The mortars will be provided to Airborne by a subcontractor.

FS-181: An ICD drawing provided showed the mortars to be 1.13 ft diameter with 1.58 cubic ft 

of volume. (depth 1.4 ft)

FS-182: The mortars have two initiators and two bridge wires, providing redundancy.

FS-183: The mortars are attached to the FBC and remain with the FBC after FBC/CM 

separation.

FS-184: Apollo conducted tests to characterize mortar propellant degradation with age, and with 

exposure to full mission environmental conditions including thermal cycles.

FS-185: The CPAS project explained at a February 2009 teleconference that they also would 

conduct tests to characterize mortar propellant degradation with age, and with exposure to 

thermal cycles.

FS-186: Packing the confluence ring inside the drogue mortar, on top of the riser and drogue 

parachute, complicates successful expulsion of the contents of the mortar.

EO-64b: Packing the confluence ring inside the drogue mortar, on top of the riser and drogue 

parachute might result in more controlled motion of the ring during deployment.

FS-187: Apollo coiled their (steel) drogue risers and encased them in foam disk to improve 

reliability of expulsion from mortar, eliminating the possibility of developing kinks in the cables.

FS-188: The project calculates the drogue pack density to include the confluence ring mass. This 

is unnecessarily conservatively and misrepresents the risk of damage to drogue structural 

components from high density packing.

FS-189: According to information discusses at a March 2009 ERB, the project recognizes the 

risks associated with a mortar having insufficient energy to eject all of its contents from the 

mortar with sufficient velocity to inject the drogue d-bag (―last out‖) far enough into the air 

stream to begin inflating.

FS-190: Vehicle attitude relative to direction of travel and wind direction can introduce an 

additional hindrance to successful extraction of drogue mortar contents. 
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EO-65: A weak-fired mortar poses a risk of a failure to fully extract a drogue d-bag from the 

mortar tube, leaving its confluence ring potentially impacting against the side of the CM, or 

worse, becoming an entanglement hazard for other CPAS components as they deploy from 

adjacent sectors.

EO-66: There may be risk of a metallic confluence ring contacting the mortar tube‘s edge on its 

way out, causing surface damage that subsequently damages a d-bag during its exit.

Apportionment of Parachute System Components in the Forward 

Bay Sectors

FS-191: Parachute growth capacity is limited due to confined space.

FS-192: The Apollo design stowed a variety of landing and retrieval hardware and equipment in 

the four sectors of its forward bay, including but not limited to: 

 three main parachute d-bags each with a canopy, suspension lines, and some lengths of a 

riser inside

 various lengths of three main parachute risers outside the d-bags

 three main parachute pilot chute mortars

 two drogue parachute mortars each with a sabot, a d-bag, a canopy, suspension lines, and 

some lengths of a riser inside; the riser was coiled and encased in a foam disc.

 two equal lengths of two drogue parachute risers outside the mortars

 a so-called  ̳flower-pot‘ parachute fitting attached to the CM between two gussets (45o 

and 315o with 0o being the ‘crew heads up‘ direction) where drogue and main parachute 

riser loads were transferred to the CM structure

 CM uprighting system

 Antennas and location aids

FS-193: The CEV design architectures under consideration by the project between 

December 2008 and March 2009 each also allocated stowage for a variety of hardware and 

equipment in the six sectors of its forward bay. Assuming the dual drogue harness architectural 

option, and excluding retention hardware, these stowed items include but are not limited to:

Three-leg-harness main parachute CPAS architectural option

 three main parachute d-bags each with a canopy, suspension lines, and some lengths of a 

riser inside

 various lengths of three main parachute risers outside the d-bags
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 one metallic main parachute rotation torque limiter

 one metallic main parachute confluence fitting

 two 19-ft harness legs, and one 16-ft harness leg

 one large stowage container for rotation torque limiter, confluence fitting, and excess 

riser and harness legs

 (no main parachute pilot chute mortars for either architectural option)

 two drogue parachute mortars each with a sabot, a d-bag, a canopy, suspension lines, and 

some lengths of a riser inside, plus a metallic confluence ring and a short length of one 

harness leg

 (remaining lengths of drogue parachute harness legs are routed from the mortar tubes 

outside the FBC, and stowed outside on top of the FBC)

 three main parachute attach fittings attached to the CM at the lower extremity of three of 

the six gussets (0o, 120o, 240o with 0o being the  ̳crew heads up‘ direction) 

 three pilot parachute packs and extraction lines – if pilot-deployed-mains architectural 

option

 CM uprighting system (presumed)

 Antennas and location aids (presumed)

Single-point-attach main parachute CPAS architectural option

 three main parachute d-bags each with a canopy, suspension lines, and some lengths of a 

riser inside

 various lengths of three main parachute risers outside the d-bags

 one metallic main parachute rotation torque limiter 

 one smaller stowage container for rotation torque limiter and excess riser lengths

 (no main parachute pilot chute mortars for either architectural option)

 two drogue parachute mortars each with a sabot, a d-bag, a canopy, suspension lines, and 

some lengths of a riser inside, plus a metallic confluence ring and a short length of one 

harness leg 

 (remaining lengths of drogue parachute harness legs are routed from the mortar tubes 

outside the FBC, and stowed outside on top of the FBC)
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 a second metallic rotation torque limiter, integrated halfway up the CM‘s 0o gusset ( ̳crew 

heads up‘ direction), three main risers pass through one hole, the three belt-cross section 

risers making a 120o angle with each other.

 three main parachute attach fittings integrated into the CM‘s 0o gusset, at three places 

beneath the gusset-pass-through location.

 three pilot parachute packs and extraction lines – if pilot-deployed-mains architectural 

option

 CM uprighting system (presumed)

 Antennas and location aids (presumed)

FS-194: Apollo used approximately 75% of the available volume of its forward bay – three of 

four sectors (each sector defined by a pair of gussets) – as stowage volumes for three main 

parachutes. Each of these three volumes also contained one main pilot parachute mortar and one 

CM uprighting bag. The fourth sector in the Apollo design contained two drogue mortars, one 

flower-pot attach fitting, and much of all the remaining hardware stowed in the forward bay. 

FS-195: As reviewed between December 2008 and March 2009, the Orion CEV allocates 50% of 

the available volume of its forward bay – three of six sectors defined by pairs of gussets – as 

stowage bays for three main parachutes. 

FS-196: Assuming all things are scaleable, the CPAS Project is being asked to achieve a 33% 

reduction in the stowed volume of its main parachutes – from 75% of available volume to 50% 

of available volume.

EO-67: Advances in parachute design and materials technology since the development of the 

Apollo ELS could possibly achieve a 33% reduction in required volume for the parachute packs 

(proportionally compared to Apollo), but if not, an overaggressive reduction may introduce new 

reliability risks for CPAS that may adversely affect the overall probability of LOC. 

FS-197: Apollo used portions of its remaining sector for stowage space for short lengths of 

drogue risers, short lengths of main risers and two drogue mortars, of which the latter used the 

majority, proportionally. Apollo mortar sizes were increased during vehicle development due to 

CM weight increases and subsequent increases in drogue parachutes. 

FS-198: CPAS has been allocated portions of the CEV‘s remaining three (of six) sectors in its 

forward bay, for stowage space for main harness legs, medium lengths of main risers, a 

confluence fitting, a torque limiter, a storage box, and two drogue mortars. In some architectural 

options under consideration by the project between December 2008 and March 2009, the harness 

legs and confluence fitting has been deleted.
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EO-68: Orion CEV might have a requirement that demands more of the available volume of the 

forward bay (proportionally compared to Apollo), for hardware that is not related to CPAS. If 

this is true, then if these systems are not related to crew survival, design trades between these 

items and CPAS components should not be made if they introduce new reliability risks for CPAS 

that may adversely affect the overall probability of LOC. 

EO-69: Using four of six sectors on the CEV forward bay for four main parachutes would 

provide 66% of the available volume for packed parachutes. Assuming all things are scaleable, 

this would provide for at least a 12% improvement based on advances in parachute design and 

materials technology since the development of the Apollo ELS (from 75% of available volume to 

66% of available volume). 

EO-70: A CPAS architecture with four main parachutes instead of three, could introduce new 

reliability risks for CPAS that may adversely affect the overall probability of LOC. Technical 

assessment is necessary to establish the merits and demerits of such an architecture.

EO-71: One architectural option that addresses many of the NESC team‘s recommendations 

comprehensively would include:

 Four main parachutes in four d-bags stowed in sectors B, C, D, and E, that could be 

smaller, less dense, and possess volume reserve.

 Total 4-pack volume that could be 20% greater than the assessed 3-pack total volume, 

representing 60% of total forward bay volume, rather than 50%.

 This would be achieved with a 5% growth in total parachute mass, a 5% decrease in the 

size of each pack, a 5% decrease in pack density, and still retain a 5% volume reserve 

going into PDR.

 One failed main would represent 75% capability rather than 66% capability.

 Smaller main pack shapes can be simplified, possibly avoiding wrapping around the LAS 

Wells.

 Redundant Kicker straps.

 Single point attach at Gusset 0. Gusset assessed as DFMR.

 One DFMR steel riser, one DFMR confluence fitting, and four fabric risers.

 No torque limiter. The steel riser will twist-up to minimize rotation torque, between the 

gusset attach and the confluence fitting.

Project Technical Requirements Specification (PTRS)
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FS-199: A preliminary draft of CPAS Requirements (Project Technical Requirements 

Specification, PTRS) was published in October, 2008, and provided to the NESC team at the 

IDR in December 2008.

FS-200: The PTRS and an associated document called the ―Assumptions document‖ got final 

signatures in January 2009 (double check), and both were provided to the NESC team.

FS-201: Significant changes were made to the PTRS and assumptions documents between 

December 2008 and March 2009.

FS-202: The initial conditions for drogue mortar firing defined in the PTRS for CPAS are 

incomplete.

FS-203: Appropriate and validated parachute analysis tools will be critical to the design of CPAS 

and the verification of requirements.

FS-204: [I.CPAS.CM.006] CPAS shall limit the vertical descent rate of the CM to less than 

10.07 m/s (33.0 ft/s) at standard sea-level conditions (as defined in NASA-TM-X-74335, U.S. 

Standard Atmosphere, 1976) for a maximum CM mass of 9,464.2 kg (20,865.0 lbm). (PTRS, 

October 2008)

FS-205: It will be difficult to statistically verify requirement since it is written in absolute terms. 

[I.CPAS.CM.006].

FS-206: [R.CPAS.018] CPAS shall meet all functional and performance requirements of this 

specification when subject to one drogue parachute and one main parachute failure. Rationale: 

This requirement refers to a complete loss of one drogue and one main parachute on the same 

landing event. Each subcomponent of CPAS (drogues and mains) should be one fault tolerant.

(PTRS, October 2008)

FS-207: Requirement [R.CPAS.018] does not explicitly include the possibility that one drogue 

parachute will fail without the subsequent failure of one main parachute.

FS-208: [I.CPAS.CM.011] CPAS shall limit the peak total parachute load (3-sigma) to less than 

the peak loads defined in Table 3.3-1, Parachute Peak Loads, under all fault conditions defined in 

[R.CPAS.018], [R.CPAS.017], and [R.CPAS.129]. Rationale: These peak loads define the 

extreme load to which the CM design will be based. While the CPAS is not required to design 

the parachutes to survive the skipped reefing stages defined in [R.CPAS.018], these failures must

not impart more load into the CM and load-carrying structures than listed here to prevent the 

failure from propagating into a catastrophic failure. (PTRS, October 2008)

FS-209: Requirement [I.CPAS.CM.011] does not specify a limit peak parachute load under the 

(most likely) nominal condition where there is no fault in the system.

FS-210: Requirement [I.CPAS.CM.011] does not limit the direction in which the parachute peak 

loads are applied.
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FS-211: [R.CPAS.012] CPAS shall design to meet or exceed the load dispersions for each fault 

case defined in Table 3.3-2, Parachute Load Dispersions. Rationale: Load dispersions result from 

Monte Carlo analyses which vary performance parameters. Designing for 3-sigma dispersions in 

low likelihood cases drives up mass for very little return in overall reliability. For the purposes of 

this requirement, the analyses will vary all relevant parachute performance parameters (drag 

area, opening shock, cutter times, etc.), and all initial conditions defined in [R.CPAS.005], 

[I.CPAS.CM.128], [I.CPAS.CM.129], [I.CPAS.CM.132], [I.CPAS.CM.133], [I.CPAS.CM.134], 

[I.CPAS.CM.135] and [I.CPAS.CM.139]. The analyses results assume the use of 3 main and 2 

drogue parachutes in the CPAS configuration. Trajectory conditions will be assumed at the edges 

of the deploy trajectory envelope defined in [R.CPAS.005] and use NASA-TM-X-74335, U.S. 

Standard Atmosphere, 1976. (PTRS, October 2008)

FS-212: Requirements [R.CPAS.012] is silent on whether the parachute that had a skipped 

reefed stage remains operational or not.

F-213: Using multiples of ―sigma‖ in specifying requirement [R.CPAS.012] may yield an 

unacceptable percentile of cases that exceed the specified loads since this percentile depends not 

just on ―sigma,‖ but also in the probability distribution, which is not known up front.

FS-214: PTRS fig 3.1-1 is not clear whether ―roll rate‖ refers to wind or body axis. (PTRS, 

October 2008)

FS-215: Project is using Monte Carlo dispersions generated by DSS simulations to set the 

Requirement for CEV attitude at drogue deployment at +/- 70°.

Analysis, General

EO-72: Appropriate and validated parachute analysis tools will be critical to the design of CPAS 

and the verification of requirements.

FS-216: A tool called Decelerator Dynamics (DCLDYN) is an in-house FORTRAN analysis tool 

used by Airborne for two-body dynamic analysis of a parachute and an item of cargo suspended

beneath the parachute. The two simulated bodies are connected by a nonlinear spring 

representing the riser, the suspension lines, and the canopy‘s radials. Each body is modeled with 

3 DOF: vertical (along the axis between the two bodies), horizontal (perpendicular to that axis), 

and pitch. Roll and yaw cannot be analyzed. 

FS-217: DCLDYN models represent other parachute-specific features, such as drag and mass as 

a function of time; disreefing schedules; parachute opening parameters; parachute shape and time 

parameters.

EO-73: DCLDYN appears to be the Design Team‘s principal analysis tool.
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FS-218: It is not clear how DCLDYN has been validated for use to compute numbers that are 

used to justify significant design decisions.

FS-219: Design Team analysts use DCLDYN to account for a phenomenon wherein a percentage 

of parachute mass reaccelerates towards the cargo velocity at line stretch.

FS-220: DCLDYN analysis accounts for apparent mass effects wherein a parachute mass 

increases during inflation, as the mass of air  ̳inside‘ it increases.

FS-221: DCLDYN cannot model a cluster of multiple parachutes. Spreadsheet simulations are 

constructed to model multiple parachutes. The spreadsheet simulations do not include a 

nonlinear spring parameter to represent the riser/lines/radials. Ratios determined from the 

spreadsheet simulation are used in a subsequent DCLDYN simulations. 

FS-222: During a teleconference with the NESC team in February 2009, the project lead 

indicated an intention to run a NASA analysis tool, Dynamic System Simulator (DSS) for checks 

of DCLDYN.

FS-223: DSS is a NASA high-fidelity code that can be used for dynamic analysis of parachutes 

and items of cargo.

FS-224: A review of Gen-1 test reports revealed that DCLDYN mispredicted opening load and 

inflation time of the pilots, drogues, and mains.

FS-225: A review of Gen-1 test reports revealed that results from both DCLDYN and DSS were 

used by the project but no direct comparison of DSS and DCLDYN results were ever shown. 

Results from one analysis tool were always presented independently from the other.

FS-226: A review of Gen-1 test reports revealed that a migration by the Design team from using 

predominantly DCLDYN in CY 2007, and increased use of both DCLDYN and DSS in CY 

2008. 

FS-227: During a teleconference with the NESC team in February 2009, the project indicated an 

intention to run a less-detailed analysis tool known as OSIRIS for verification analysis and 

requirements closure. (Integrated GNC Design and Data book, Section 9.1.4.)

FS-228: POST is a generalized point mass, discrete parameter targeting and optimization 

program that provides the capability to target and optimize point mass trajectories for multiple 

powered or unpowered vehicles near an arbitrary rotating, oblate planet. POST is supported by 

NASA LaRC.

EO-74: Using two different codes, such as DCLDYN and DSS or POST and DSS, has in 

previous projects resulted in revelation of shortcomings of each code, and improved confidence 

in results.

Analysis, Specific Issues
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EO-75: Validation, verification, and/or calibration are planned by CPAS to support uncertainty 

estimates on results that feed into the reliability estimates.

FS-229: LS-DYNA is an advanced general-purpose multiphysics simulation software package 

that is actively developed by the Livermore Software Technology Corporation (LSTC).

FS-230: The project has used LS-DYNA to determine preliminary Kevlar® harness hysteresis 

curves, to establish the appropriate main harness leg lengths that would provide the required 

hang angle at landing.

FS-231: According to charts prepared for a brief by CPAS to a Lockheed Engineering Review 

Board in March 2009, the project intends to use LS-DYNA for simulation of separation of the 

FBC from the CM.

FS-232: Project analysts have run Monte Carlo analyses with DCLDYN for stochastic 

nondeterministic problems. 

FS-233: Results from DCLDYN Monte Carlo analyses of drogue parachute loads were presented 

at the December 2008 IDR. Results represented all seven points of the deployment envelope, and 

included analyses of an aggressive disreefing schedule for deployment after pad abort.

FS-234: Results from DCLDYN Monte Carlo analyses of drogue parachute loads presented at 

the December 2008 IDR indicated that input dispersion for the analysis included 5 parameters for 

the CM, and between 16 and 19 parameters for a parachute that was modeled to represent two 

drogue parachutes as one.

FS-235: The DCLDYN Monte Carlo analyses of drogue parachute loads presented at the 

December 2008 IDR showed all input dispersions were based on Gen-1 data.

FS-236: The DCLDYN Monte Carlo analyses of drogue parachute loads presented at the 

December 2008 IDR used uniform dispersions for all parameters. Presented charts indicated a 

plan to review the distribution types for future analyses.

FS-237: The CPAS IDR charts showed the Monte Carlo analysis used uniform dispersions for 

the dispersed parameters. Design requirements state analysis will show CPAS performance to 

meet the requirements to a specified sigma value, assuming normal distributions. Monte Carlo 

results using uniform dispersions will likely not fit a normal distribution well, given the 

parameter space shown in the IDR.

FS-238: The CPAS IDR charts showed a mass reduction for not having the skipped reefing stage 

requirement. There was no skipped reefing stage requirement for Apollo. To protect for this, 

extra reefing lines and cutters were incorporated into the design. These extra reefing lines were 

however required to meet Apollo reliability requirements (pg 23, ―The Apollo Parachute 

Landing System,‖ Knacke).
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FS-239: There are only 2 simulations apparently being used in making design decisions, 

DCLDYN and DSS. The 2 simulations are working closely and not independently.

FS-240: System definitions and data are provided across a broad range of documents. 

Configuration documents have been found in PDF, Word, and PowerPoint format. Some of the 

documents contradict each other (dispersions).

FS-241: DCLDYN Monte Carlo analyses were also run to assess drogue and main riser loads 

sensitivities to other parameters.

FS-242: Limit load requirement for drogues is 55,000 lb (either or both drogues). 

FS-243: Results from DCLDYN Monte Carlo analyses of main parachute loads presented at the 

December 2008 IDR indicated that some design load requirements were exceeded for that 

preliminary look.

FS-244: Peak drogue riser load at initial opening to 1st stage, was found to be most sensitive to 

 Initial pitch angle of vehicle

 1

st stage reefing ratio

 1

st stage fill constant

 1

st stage Ck

FS-245: Peak drogue riser load at disreef from 1st stage to 2nd stage, was found to be most 

sensitive to 

 2

nd stage reefing ratio

 2

nd stage Ck

 1

st stage reefing ratio

FS-246: Peak drogue riser load at disreef from 2

nd stage to full open, was found to be most 

sensitive to 

 3

rd stage Ck

 2

nd stage reefing ratio

FS-247: Peak main riser load at initial opening to 1st stage, was found to be most sensitive to 

 1st stage fill constant

FS-248: Peak main riser load at disreef from 1st stage to 2nd stage, was found to be most 

sensitive to 

 2nd stage reefing ratio
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FS-249: Peak main riser load disreef from 2nd stage to full open, was found to be most sensitive 

to 

 2nd stage reefing ratio
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Testing, General

FS-50: Prior to October 2008, Airborne performed demonstration testing of various elements of a 

―Generation 1‖ parachute system to develop data that was expected to have utility for CPAS 

development. 

FS-251: The system architecture briefed in December 2008, is so-called  ̳Generation-2,‘ differed 

in significant ways from the Generation-1 architecture.

FS-252: Some Gen-1 test data is applicable to the Generation-2 system.

EO-76: A great deal of developmental ground and flight testing will be necessary to qualify 

any of the CPAS architectural options that were reviewed by the NESC Team between 

December 2008 and March 2009. 

EO-77: Testing conducted by the project between December 2008 and March 2009, appeared to 

lack a methodological approach. 

EO-78: Testing conducted between December 2008 and March 2009 appeared to be principally 

for the means of evaluating design concepts.

FS-253: No Gen-2 verification and validation testing was accomplished between December 2008 

and March 2009.

FS-254: Between December 2008 and March 2009, a test matrix was not available for the NESC 

team to review.

FS-255: The project‘s draft V&V Plan will not be available until near PDR.

EO-79: All testing conducted, including development, should be done in support of the design 

effort, building confidence in the design, and eventually qualification.

EO-80: The Verification and Validation matrix should address all requirements set forth in the 

ICD and the PTRS. 

EO-81: The project has not clearly identified what is required to pass through the gate of PDR. 

EO-82: Given the broad range of initial/boundary conditions on the CPAS performance envelope 

for the CPAS and the expense of testing, the final certification of CPAS is likely be highly 

dependent upon modeling and simulation results. Modeling and simulation results are only valid 

after the model(s) is(are) thoroughly understood, the application limits have been established, 

have been deemed valid for use in the application, and have been verified by test data and/or 

comparison to other models and we have heard very little of any plans for such a V&V program. 

A rigorous review process must be applied for the validation and verification test program used 

to certify a modeling based approach.

FS-256: Revision of PTRS in March 2009 changed the following:
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 An update to the CPAS drogue deploy envelope was made.

 The pad abort, main parachute deployment initiation requirement was deleted.

 The CM hang angle requirement was deleted.

 Requirements were reworded to be better defined.

 Drogue parachute pack mass was stipulated to be 31.5 kg (69.5 lbm).

 Operational temperature bounds were changed from -54 C (-65 F) to -83 C (-117 F).

 The gaseous methane and oxygen requirements were deleted.

 Main and drogue parachute failure tolerance requirements were revised for nominal entry 

and pad aborts.

Testing, Specific Issues

EO-83: The Apollo Experience Report – Earth Landing System (ELS), NASA TN D-7437, 

(1973), illustrates the extent of the testing that was necessary to demonstrate the overall 

reliability of the ELS system, to make it suitable for manned flight. It also illustrated the need for 

thorough systems integration and compatibility verification.

FS-257: The Apollo Experience Report – ELS does not contain data useful for creating reliability 

estimates. 

FS-258: Some quantitative Apollo data useful for creating reliability estimates is in the Knacke 

Book.

FS-259: The Northrop Venture report 4040, Apollo Earth Landing System, report of reliability 

Analysis (1968) could not be located by individuals at Northrop who are contracted with the 

NESC for other purposes. 

FS-260: Developmental test data from Apollo Earth Landing System that might be useful to 

CPAS reliability assessments is not readily available. 

FS-261: The Gen-1 forward bay full-scale mockup shown in pictures in IDR charts lacks 

significant geometric details including LAS Wells, integrally machined features on the tunnel, 

and features on the gussets.

FS-262: The project‘s first draft Test Matrix is not expected until after March 2009.

FS-263: the project‘s first draft Verification and Validation plan is not expected until closer to 

the project‘s PDR (NLT September 2009.)
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FS-264: According to a chart presented by the S&MA Team in February 2009, a draft plan for 

methods to generate reliability data included the following:

Function Method

Main / Drogue Confluence Fitting Cluster Test

Environment Induced Failure Historical / Test

Rigging Error (Main + Drogue) Historical Data

Far-Field Contact Auxiliary Test

Near-Field Contact Ground Testing

Main Chute Entanglement Flight Testing

Drogue / Auxiliary Entanglement Flight Testing

Skipped Reefing Stage Failure Historical Data

Chute Deployment Failure

Friction Failure Due to Rapid Extraction Historical / Test

 Disorderly Deployment Historical Data

 Inadvertent Chute Release Integrated

 Bag Cutter Failure NSI + Integrated

 Single Chute Near-Field Contact Ground Testing

 Inflation Failure Historical Data

 Failure Due to Extraction Line Load Too High Unknown

FS-265: The table indicates that the project recognizes that for the dual drogue confluence fitting 

architectural option, cluster testing is necessary to verify and validate load sharing assumptions 

and to generate data of the probability of damage to one or both confluence rings during 

deployment. 

EO-84: There is risk of damage to one or both drogue confluence rings between deployment 

from drogue mortars and line stretch from:

 Impact with the mortar while exiting the tube

 Impact with the mortar cover during or after exiting the tube

 Impact with each other 

 Impact with FBC structure

 Impact with CEV structure 
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FS-266: The table indicates that the project recognizes that for the harnessed-mains architectural 

option, cluster testing of the main confluence fitting is necessary to validate load sharing 

assumptions. 

FS-267: The table indicates that the project recognizes that environmental laboratory testing is 

necessary where test data does not already exist.

FS-268: The table indicates that the project recognizes that historical data is necessary to 

estimate the probability of failure of main or drogue inflation due to errant rigging.

FS-269: The table indicates that the project recognizes that testing is necessary to verify and 

validate the reliability of the auxiliary chute system which is intended to decelerate the FBC after 

release, so as to reduce the risk of its subsequent interference with one or more inflated main 

parachutes, main suspension lines, main risers, or main harness.

FS-270: The Apollo Block II ELS forward heat shield (FHS) incorporated a 7.2 ft auxiliary 

chute, the same one used as pilot parachutes for main chute deployment. The auxiliary chute‘s 

mortar was redesigned to fit in the available volume that was inside the heat shield adjacent to 

the top of the tunnel.

FS-271: The Apollo Block II ELS aux chute mortar was initiated by a time-delayed distanceswitch on a short lanyard that pulled tight during cover separation as the cover cleared the tunnel.

FS-272: The Apollo Block II ELS auxiliary chute was deployed laterally compared to the vehicle 

flight path, through the opening above the tunnel as the CM dropped from the FHS. Inflation of 

the chute exerted a force that redirected the cover into a separate flight path and subsequently 

slowed the rate of descent of the FHS and took it out of the wake and flight path of the 

Command Module.

EO-85: The Apollo Project recognized that premature firing of the Apollo auxiliary chute could 

have resulted in an inability to jettison the FHS. Extensive testing verified that the Apollo 

auxiliary chute reliability was sufficient so that its benefits would outweigh its risks.

FS-273: Comprehensive testing with a boilerplate vehicle was used to verify and validate the 

reliability of the Apollo Block II ELS auxiliary chute system because contact of the forward heat 

cover that damages more than one main parachute, main suspension lines, main risers, or main 

harness, was recognized to result in LOC.

FS-274: The CPAS auxiliary chutes being considered by the project are two 10 lb. ring sails, 

nominally 25.7 ft diameter. For comparison, the two drogue parachutes are nominally 23 ft in 

diameter.

FS-275: The CPAS auxiliary chutes are installed beneath the drogue mortars and fired by a gun 

simultaneously towards one side of the FBC.
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EO-86: A preliminary assessment of the CPAS auxiliary chute architectural option suggests that 

the concept of operation is principally to provide additional drag to decelerate the FBC after 

release. Suspended beneath two drogue parachutes, the force from two auxiliary parachutes 

inflating off to one side, at low speed, may not significantly redirect the FBC laterally out of the 

vehicle flight path. Their chief benefit would be to decelerate the FBC relative to the CM. 

EO-87: The FBC will decelerate rapidly after releasing the CM. 

FS-276: According to information in the IDR charts, the terminal q of the FBC suspended by two 

inflated drogues is 1.26 psf.

EO-88: As discussed in a CPAS Project teleconference in March 2009, the project appears to 

discount the risk of damage to more than one main risers from contact by an FBC that is 

suspended on only two parachutes (any combination of drogue and auxiliary chutes) and is 

falling faster than the suspended CM. The Project rationale is that that risers will be relatively 

lightly loaded at impact. 

FS-277: PTRS 3.2.4.3 requires prevention of propagation of component failures that can result in 

catastrophic hazard. 

FS-278: The table indicates that the project recognizes that ground testing is necessary to verify 

and validate that main d-bags will not suffer damage from contact with CEV structure or FBC 

structure, as they are lifted from their stowed locations.

FS-279: The table indicates that the project recognizes that ground testing is necessary to verify 

and validate that main risers will not suffer damage from contact with CEV structure or FBC 

structure, as they are deployed from their d-bags. It is not clear if the project recognizes this 

should be system-level ground testing with a geometrically accurate CM mockup. 

FS-280: The table indicates that the project recognizes that ground testing is necessary to verify 

and validate that main canopies and suspension lines will not suffer damage from contact with 

FBC structure, as they are deployed from their d-bags.

FS-281: The table indicates that the project recognizes that ground testing is necessary to verify 

and validate that for the loosely-attached mains architectural option and loosely-attached pilots 

architectural option, components that attach same to the FBC will not suffer damage from 

contact with FBC structure, as contents are deployed from the d-bags.

FS-282: The table indicates that the project recognizes that flight testing is necessary to develop 

data needed to estimate the risk of main chute entanglement, regardless of main deployment 

architectural option.

FS-283: The table indicates that the project recognizes that aerial drop flight testing is necessary 

to develop data needed to estimate the risk of entanglement between drogue parachutes and 

auxiliary parachutes.
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FS-284: The table indicates that the project recognizes that historical data is available to estimate

the risk of skipped reefing stage failure.

FS-285: The table indicates that the project recognizes that the risk of chute deployment failure 

due to burn damage from rapid extraction cannot be solely characterized with historical data, and 

that incorporation of new materials or novel applications of materials, and high packing density 

all compel extraction tests.

FS-286: For the loosely-attached mains architectural option, the extraction of a main d-bag from 

its stowage sector can be hindered by contact (drag across, slide along or strike against) with CM 

structure. Hindrance of extraction can be followed by a more rapid extraction than nominal. This 

can lead to subsequently more rapid extraction of the contents from the d-bag (riser, suspension 

lines, canopy). This rapid deployment can generate heat from friction that can damage Nylon, 

Kevlar®, and Vectran fabric materials. Vectran offers less strength retention at high 

temperatures than Kevlar®.

FS-287: The table indicates that the project recognizes that historical data exists to characterize 

the risk of failure due to disorderly deployment.

FS-288: The table indicates that the project recognizes that premature release of a chute is an 

integrated risk, but does not specify how the risk will established. 

FS-289: The table indicates that the project recognizes that the risk of a bag cutter failure can be 

characterized by available NSI data.

FS-290: The table indicates that the project recognizes that inflation failure can be characterized 

with historical data.

FS-291: v project recognizes a risk with the loosely-attached mains architectural configuration, 

of snatch loads on the main d-bags handles being high, which can lead to a physical failure 

which results in leaving a d-bag in its stowage location. Mitigations discussed by the project 

included the addition of energy modulators on the bag handles. 

FS-292: In December 2008 and February 2009 versions of the IDR charts, the main risers were 

indicated to be 1.75 inch wide Kevlar®Tape with 8 plies.

FS-293: In December 2008 and February 2009 versions of the IDR charts, the main harness legs 

were indicated to be 1.75-inch wide Kevlar®Tape. They were indicated to have 14 plies in 

December 2008 and 18 plies in February 2009.

FS-294: If a rotation torque limiter is incorporated into the main riser system for either the 

harnessed-mains architectural option or the single point attach architectural option, the three 

involved lengths of Kevlar®tape will be allowed to twist so the vehicle‘s RCS can maintain a 

CM orientation with the crew‘s feet towards the horizontal direction of travel prior to landing.
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FS-295: In December 2008, Airborne had manufactured or procured subscale harness legs for 

testing in a Tinius Olsen tensio-meter (twist fixture). The test legs were said to be quarter-scale, 

but shown in the image next to a ruler, to be approximately one inch in width.

FS-296: In December 2008, tests were being planned to measure tension in sets of subscale 

Kevlar®Tape, while twisted, to characterize strength degradation with respect to number of full 

twists, up to five twists. One twist was defined as 360o.

EO-89: Three tapes with rectangular cross sections, held in a torque limiter in a triangular 

arrangement at a 120o angle to each other (but not touching each other at the ends when 

untwisted), will touch each other along their lengths at some number of twists that will depend 

on the lengths and the widths of the tapes. Twisting beyond this point will put stresses on the 

tapes that will be difficult to predict and could pose a risk of failure. Torque limiter dimensions 

can be designed to avoid stresses that could damage the tapes, securing ties, or restraining cords.

FS-297: Between December 2008 and March 2009, stretch testing was being planned to apply 

peak loads to full-scale fabricated Kevlar® harness legs, to characterize their hysteresis curves, 

to verify completed analyses that established that one 16 ft harness leg and two 19 ft harness legs 

would provide the required hang angle at splashdown. 

FS-298: Apex forward deployment of the drogues or the mains is not a requirement.

FS-299: There are numerous opportunities for damage to Kevlar® tapes and cords expected to be 

used for drogue harness legs, risers, suspension lines, and main harness legs, risers and 

suspension lines, from contact with sharp edges on the CEV and FBC. 

FS-300: The project approach to mitigate these risks is to require large radius edges on any 

protruding or exposed CM or FBC hardware. 

FS-301: The separation of the LIDS prior to initiation of the CPAS system may present a sharp 

edge on the top of the tunnel.

FS-302: An off-nominal LAS separation could result in the LAS contacting the FBC on its way 

out.

EO-90: During a Hardware IPT in February 2009, it was noted by a participant that steel risers 

were still carried as a design alternative for CPAS. 

FS-303: According to charts prepared for a brief by CPAS to a Lockheed Engineering Review 

Board in March 2009, high altitude and high Mach tests will be performed with single-drogue 

drop tests. These will not include cluster tests of two drogues. These will not provide information 

about wake effects.

EO-91: Cannot drop test parachute test cargos from a C-17 above 20,000 ft.
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FS-304: The unmanned Ares-1Y ascent abort flight test will provide data on CPAS parachute 

performance at higher altitudes in the drogue deployment envelope.

Testing, Drogues Development

FS-305: CPAS employs 2 Drogue Parachutes, only 1 of the Drogues is required to establish 

Main Parachute deployment conditions 

FS-306: Airborne IDR chart said that the drogues to be used for flight test development unit 

(FDU) will have two-inch wide 2000 lb Nylon ripstops added to the trailing edge tapes of the 

vent, the upper shoulder, and the lower shoulder.

FS-307: Apollo drogues deployed with risers out of tube first, encased in a foam disk, then the 

packs, with the d-bag mouth facing outwards. 

FS-308: The two Apollo drogues fired at an included angle of approximately 60 degrees. The 

kick load on the Apollo CM would tend push the vehicle apex away from direction of 

deployment of the two drogues, regardless of the vehicle‘s initial attitude. From each tube, the 

steel riser came out first, encased in a foam disk, and uncoiled from its foam encasement. The 

suspension lines played out of the d-bag as the pack turned around, and the canopy came out of 

the d-bag last. ELS system designers assumed that the vehicle could be in any attitude at drogue 

line stretch. Each drogue‘s line stretch load would tend to pull the CM apex towards the 

direction of line stretch.

EO-92: The Orion CEV has two three-legged drogue harnesses and two confluence rings. The 

rings are stowed one in each mortar. The included angle between the two mortars is not known to 

the NESC team. Similar to the Apollo system, the kick load on the Orion CM would tend to 

push the vehicle apex away from the direction of deployment of the two drogues, regardless of 

the vehicle‘s initial attitude. From each tube, the confluence ring comes out first, then the 

Kevlar®tape riser, then the d-bag. When one or both harnesses go into tension (extracted from 

their stowed location on top of the FBC), the event would tend to pull the apex towards the 

direction of deployment. The suspension lines would play out of the d-bag as the pack turned 

around, and then the canopy would came out of the d-bag last. Each drogue‘s line stretch load 

would tend to pull the CM apex towards the direction of line stretch. The vehicle could be in any 

attitude at drogue line stretch.

FS-309: The project estimated a failure of 1:333 for ―drogue bag separation.‖ 

EO-93: The 1:333 estimate for ―drogue bag separation‖ failure likely refers to a d-bag not getting 

propelled far enough out to catch the free stream airflow, due to insufficient energy of the 

mortar.

FS-310: Airborne chart said - Drogues are completely independent. Failure of one drogue due to 

skipped reefing will not affect the other drogue. 
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FS-311: No FBC design detail has been made available about the drogue attach fittings. For the 

single confluence fitting architectural option, there will be one attach bolt per fitting at 60o, 180o, 

and 300o, near the top of the FBC. (crew  ̳heads up‘ is 0o). For the dual drogue confluence fitting 

architectural option, there will be two attach bolts per each fitting at the same three locations. 

The fittings will have to be protected by TPS.

FS-312: No FBC design detail has been made available about the load path through the FBC 

from drogue harness fittings to the FBC attachment to the CM. The three FBC release 

mechanisms are integrated into CM forward bay gussets at the same three locations (60o, 180o 

and 300o), to react drogue harness leg loads. 

Testing, Mains Development

FS-313: CPAS employs 3 Main Parachutes, only 2 of the 3 Mains is required to establish the 

terminal descent conditions for a safe landing

FS-314: Apollo system mains were mortar-deployed in 3 directions, 120 degrees apart, within a 

plane. If all 3 mortars fired simultaneously, the net kick load on the vehicle at mortar fire would 

be zero. If all 3 pilot parachutes pulled all 3 mains out synchronously and all 3 main parachutes 

reached line stretch simultaneously, the net force on the vehicle at line stretch would be zero. 

FS-315: Intentionally blank 

FS-316: There is a risk during main parachute deployment of one canopy becoming a leader in 

initial filling. The leader runs the risk of encountering excessive loads with the initial 

deceleration loads not being shared amongst the other two. 

Trigger Logic

FS-317: According to Lockheed document CEV-T-078005, reviewed in February 2008, GPSderived altitude and velocity are used to initiation decent and landing phase events, such as FBC 

release, drogue deployment, main deployment, depend 

FS-318: According to Lockheed document CEV-T-078005, reviewed in February 2008, IMUpropagated altitude is used as a back-up to GPS-derived altitude. 

FS-319: IMU propagated altitudes could contain altitude errors on the order of tens of thousands 

of feet.

FS-320: According to charts prepared for a brief by CPAS to a Lockheed Engineering Review 

Board in March 2009, CPAS has decided to use IMU-propagated velocity as the trigger for 

drogue mortar initiation, for ISS reentries.

FS-321: The velocity to which the CEV must slow to during reentry in order to trigger drogue 

mortar initiation is 676 feet per second (206 meters per second).
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FS-322: Based on project simulations, the target trigger velocity will result in a drogue 

deployment altitude range of between 45,000 ft down to 32,000 ft.

FS-323: The FBC release is on a timer, 82 seconds after the drogue mortars are initiated.

FS-324: A barometric altimeter option is being considered by the project as a back-up but is not 

baselined at this time.

FS-325: Apollo used a barometric altitude trigger.

FS-326: The project has not included a manual deployment capability for the initiation of drogue 

deployment or other stages. The Apollo ELS had manual backup capability. 

FS-327: According to charts prepared for a brief by CPAS to a Lockheed Engineering Review 

Board in March 2009, GPS data will be qualified for use after the vehicle becomes operational, 

and will be used for reentries from lunar missions.

Environmental 

EO-94: Ascent out-gassing could damage the TPS covering the drogue harnesses on top of the 

FBC, creating risk to the harnesses during reentry heating. 

FS-328: A review of CPAS preliminary design details reveal a risk of heat damage to the drogue 

harness legs stowed on top of the FBC covered with TPS, during normal reentry, if the TPS has 

been damaged at any time prior to or during entry insertion. A single fault can damage two 

drogue legs—one from each parachute per the routing scheme.

FS-329: Textile material properties change with age.

FS-330: Mortar propellant properties change with age.

Pad Abort

FS-331: The requirement for max terminal rate of descent at landing is 33 fps.

FS-332: The PTRS Para 3.2.1.2.3 ―Full deploy at min altitude‖ assumes no wind for pad abort.

FS-333: The PTRS Para 3.2.1.1.4 requires at most 5 seconds between drogue mortar initiation 

and the initiation of FBC release for a pad abort. IDR chart 62 says 0 to 5. Discussion later said 

2-5.

EO-95: The CM may be unstable at LAS hand-off. The project is performing trades to establish 

test points.

FS-334: Monte Carlo analyses run in March 2009 show wide attitude and load dispersions for 

pad abort. (Point 7 on the drogue deploy envelope.)

FS-335: Orion GNC requirements are one failed drogue or one failed main.
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FS-336: CPAS is changing the PTRS to align with GNC requirement – single chute fault 

tolerant.

EO-96: A failed main may not be an independent event to a failed drogue. Operation with one 

failed drogue may affect stability which may in turn affect probability of near field contact 

during FBC separation. 
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Appendix C.1. Stakeholder Outbrief of Interim NESC 

Recommendations 2 (September 2009)

The version of the Stakeholder Outbrief 2 in this Appendix differs slightly from that which was 

approved by the NRB. Figures included to facilitate board member understanding were removed 

in the stakeholder package. Also, backup material was added: a sample Functional Verification 

Matrix and a tutorial, Introduction to Design of Experiments. All are included in this Appendix.
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Appendix C.2. Supporting Frequently-Asked-Questions for 

Stakeholder Outbrief of Interim NESC Recommendations 2 

(December 2009)

The team provided the material in this Appendix and discussed it with the Project in December 

2009, to improve their understanding of material previously outbriefed during Stakeholder 

Outbrief 2 (September 2009). 

NESC CPAS team discussion at the Project MVP Tag-up

As an extension/reiteration of NESC CPAS assessment team recommendations approved by the 

NESC Review Board and communicated to the project in September 2009, the team suggests

that all test planning (for verification or development) be started with a clear definition of the 

technical knowledge to be obtained about system performance, rather than starting with a predetermined idea of what testing is acceptable within budget or schedule constraints. 

Test matrices should be based on technical objectives, not perceived resource constraints. 

We recognize the practical constraints that will be necessarily imposed on the magnitude of the 

test programs, and therefore a strategic, efficient testing approach should be developed. This 

approach should defend the resource requirements and quantitatively define the confidence (or 

risk) as a function of test resources.

To facilitate productive discussion, the team has prepared a list of six FAQs that address issues 

that have been discussed at recent CPAS MVP Tag-up meetings.

1. ―Why not drop it once under worst case conditions?‖

The determination of worst-case conditions requires (1) an analytical determination of the 

settings of the controllable factors (e.g., altitude), (2) measurement of the uncontrollable 

factors (e.g., atmospheric, winds), and (3) traceability that the test article is representative 

of the actual flight unit. If those conditions are met, then the first drop provides a single 

statistical sample of the worst case with no information about variability in the 

responses (e.g., descent rate) observed. Without multiple samples a data-driven estimate 

of variability cannot be obtained, and therefore a data-driven statement about confidence

(inversely proportional to variability) in the results is not possible.

With multiple drops, we obtain replicates of the factor settings (controllable and 

uncontrollable) with multiple test articles to estimate experimental variability, which is 

the variability in the response (e.g., descent rate) when the settings are identical (identical 

within the experimental system‘s ability to control and measure). In contrast, repeated

measurements are obtained from a single setting of the factors on a single test article. 
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Repeats, or sub-samples, provide the ability to estimate measurement noise, which is a 

component of experimental variability (usually a very small component).

______________________________________________________

2. ―Why not partition a single drop to obtain multiple samples?‖

Partitioning a single drop test provides sub-samples, not replicates, and therefore the 

variability of the test article and factor settings will most likely be underestimated 

resulting in an inflated confidence level. Underestimating the variability can result in an 

inferential error (i.e., conclusion drawn from data) in which we declare that the 

requirement has been met when in fact it is not.

Employing partitioning a single drop as a data analysis method can provide other 

valuable information, but it is not a replacement for experimental replication.

_________________________________________________________

3: ―Does the CPAS need to perform across a range of values or only at an extreme 

value?‖

Several requirements, such as I.CPAS.CM.133, listed in JSC-63497 refer only to extreme 

values, i.e., max and min values along a range. Listing only the extreme values assumes 

that values falling within the extremes are not dangerous. It also assumes that interactions 

between variables are not consequential. 

Failure to test non-extremes could result in an increase in the probability of mission loss. 

Further, testing only extreme values is akin to one-factor-at-a-time testing (OFAT). 

OFAT is an inefficient method for determining the effect of a factor on the system. 

Performing OFAT correctly requires an exorbitant amount of testing resources and fails 

to account for the interactions of one factor with another. Factorial experiments (DOE) 

are the only way to detect interactions.

For example, the CPAS may perform under an extreme condition for each of two 

variables. However, the CPAS may fail when two variables are jointly set at some values 

below their respective extremes. Given that failure can occur at any value within a range 

of values; all requirements should specify a range of values that the CPAS must perform 

within. 

__________________________________________________________

4: ―Why include probability measures for each of the requirements?‖

JSC-63497 does not specify a probability threshold for compliance with the requirements 

listed. This leaves the contractor to interpret how well and how often the CPAS must 

meet a given requirement. 
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_________________________________________________________

5: ―Why not center the MVP testing strategy around verification activities?‖

The current MVP testing strategy centers around verification activities. As a result, the 

number of verification activities and types of verification activities are determining 

testing resources. Focus on verification activities as a generator of test runs neglects the 

actual causes of failure for CPAS. Verification activities provide a context and scenario 

for testing the CPAS but are not necessarily linked to the factors that affect CPAS 

performance. 

MVP testing strategy should focus on the factors that affect the ability of the CPAS to 

perform against its requirements. Verification activities should be a secondary concern 

for providing a context in which the performance factors can be varied through their 

required sample space. Care should be taken to minimize the number of verification 

activities while maximizing the number of factors stressed in each verification activity.

_________________________________________________

6: ―Can the MVP testing strategy meet all of the CPAS requirements within budget?‖

Documentation for the MVP testing strategy does not have a planning matrix listed. 

Without a planning matrix it is unclear as to how verification testing will meet all of the 

requirements within their resources and within their schedule.

The planning matrix should list, at a minimum: the requirement, CPAS function under 

test, and number of runs. After the planning matrix is built, a DOE matrix could easily 

follow from this construct. An example matrix adopted from ―A Systematic Approach to 

Planning for a Designed Industrial Experiment‖ by Montgomery & Coleman is below.

Requirement Response 

Variable

CPAS 

Function

Hold-constant 

factors

Nuisance 

factors

Control 

factors

Number of 

runs

[I.CPAS.CM.13

4]

Probability 

of successful 

release

forward bay 

cover (FBC) 

release

Altitude Temp

Wind Speed

CM total angle 

of attack

XXX
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Appendix D.1. Stakeholder Outbrief of Interim NESC 

Recommendations 3 (April 2010)

Stakeholder Outbrief

of Interim NESC Recommendations

Rev 01, 04/12/10

Project Assessment between

September 2009 and March 2010

Crew Exploration Vehicle (CEV)

Parachute Assembly System (CPAS) 

Independent Reliability Assessment

(TI-08-00487)

April 12, 2010

Mr. Michael Kelly

NESC Principal Engineers Office
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November 2008—Stakeholder Request

“Review the reliability analysis of the CPAS in the context of the existing design and planned 

development program and make recommendations for improving either (the design or the planned 

development program), if appropriate. Identify design and/or process improvement opportunities to 

increase the overall reliability of the CPAS as well as to ensure the success of the integrated (CPAS) 

system. Of particular interest is the planned development test program due to its value in uncovering 

design flaws contrasted with the cost and resources required. Striking the proper balance between 

reliability enhancing tests and total project cost and schedule is important for the success of the 

Program.” - Steve Altemus

Notes to Stakeholder

The 23 Interim NESC Recommendations herein (R-33 through R-55) are directed towards the 

CPAS project, unless otherwise indicated. These are interim recommendations, consistent with 

the scope of the request. Those considered top-priority are underlined. 

All previous findings, observations, and interim NESC Recommendations are included in 

backup material.

A final report will be delivered in June, 2010. Bulleted information seen throughout this 

document is provided for stakeholder clarity, and will ultimately appear within narrative in the 

final report.
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I. DESIGN-DEVELOPMENT-RELATED INTERIM NESC 

RECOMMENDATIONS

F-24: The project choice of segmenting the Forward Bay Cover (FBC) into six airbag-jettisoned 

panels appears to have been made without detailed consideration of certain key aspects.

 Fail-safe requirements

 Airbag load reaction on the main packs

 Panel separation line features

 Volumetric requirements

 Panel release velocity uncertainties

 The effect of residuals from mild detonating cord (MDC) detonation on susceptible 

components in the compartment.

F-25: FBC panel post-jettison trajectory analyses did not include important effects.

 Variation in airbag thrust vector direction

 Air flow around the CM at off-nominal CM attitudes 

 Panel tumbling and rolling 

 The range of potential panel ballistic coefficients resulting from a variety of airbag 

inflated shapes or shape differences of the panels that cover the drogue mortar bays

F-26: An analysis model of undemonstrated validity was used with a set of simplistic

assumptions to provide translational trajectory predictions of jettisoned FBC panels to support 

design trade decisions and conclusions:

 The change from a monolithic FBC to a six-panel, segmented FBC

 The preference of six panels versus fewer, larger panels

 The conclusion that the panels‘ terminal velocity would be ~92 ft/sec

 The conclusion that the panels‘ required jettison velocity was 100 ft/sec

F-27: FBC panel trajectory analyses were conducted for nominal reentry but not for aborts. 

F-28: No multi-body trajectory analyses were conducted of dispersed relative trajectories of FBC 

panels, drogue chutes, pilot chutes, main chutes or other liberated components.

F-29: The risk and consequences of near-field contact between FBC panels and parachutes have

not been rigorously assessed.

 During descent after reentry, a short interval is planned between FBC panels‘ jettison and 

drogue mortars‘ firing to reduce the risk of CM angular-rate buildup, but this may 

introduce the risk of a drogue parachute being fired into and contacting a jettisoned panel.

 Following launch abort system (LAS) handoff after an abort, a short interval is planned 

between FBC panels‘ jettison and pilot mortars‘ firing to reduce the risk of CM angularrate buildup. However, this may introduce a risk of a pilot parachute being fired into and 

contacting a jettisoned panel.
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F-30: The risk and consequence of far-field contact of FBC panels with parachutes have not been 

rigorously assessed.

 FBC panel jettison airbags must provide positive separation of all six panels from the 

CM, drive them outside the deployment radius of any of the parachutes, and set them on 

flight paths that will not intercept the CM on its parachutes.

 Jettison may occur in a complex air stream that is highly dependent upon capsule 

orientation relative to the wind vector.

 The probability of any one jettisoned panel (out of a set of six) contacting a parachute is 

greater than the probability of a single monolithic cover contacting a parachute. 

O-27: Analysis tools used by the military to assess aircraft survivability in hostile environments 

may be helpful for analysis of far-field contact.

 Reference: The Fundamentals of Aircraft Combat Survivability Analysis and Design, 2nd 

Edition, Robert E. Ball, Naval Postgraduate School, American Institute of Aeronautics 

and Astronautics (AIAA) Education Series C 2003, 2nd Edition, 889 pages, mixed media, 

ISBN-10: 1-56347-582-0, ISBN-13: 978-1-56347-582-5. 

 http://aircraft-survivability.com/

R-33: Assess the risks (likelihood/consequences) of near-field re-contact from firing a 

drogue or pilot parachute into a jettisoned FBC panel, and of far-field re-contact of a panel 

with any drogue, pilot, or main parachute component, by conducting a comprehensive 

development test and analysis program. (F-24, F-25, F-26, F-27, F-28, F-29, F-30, O-27) 

F-31: Project analyses of the risks and consequences of unsuccessful panel jettison due to either 

MDC fail or airbag fail were not shown.

 A failure of one of the panels on a drogue mortar sector to jettison may result in the 

improper deployment, or failure to deploy, of one drogue parachute and the improper 

deployment of, or failure to deploy, of one pilot parachute (and consequently one main 

parachute). 

 A failure of the panel to jettison from the sector with the CM Uprighting System (CMUS) 

tanks may result in the improper deployment, or failure to deploy, of one pilot parachute 

(and consequently one main parachute).

 A failure of one panel to jettison from one of three sectors with main parachutes may 

result in the improper deployment, or failure to deploy, of one main parachute; if in this 

event the pilot riser physically releases the stuck panel at line stretch, this would pose 

increased risk of main parachute damage.
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 Retained FBC panels are apparently not designed to break away or fail by drogue or pilot 

parachute deployment.

O-28: Aircraft ejection-seat escape systems that rely on MDC to rupture a cockpit canopy often 

include physical strikers mounted on the upper-most position of the seat as a fail-safe feature. 

R-34: Assess the risks (likelihood/consequences) of any FBC panel failing to separate from 

the CM by conducting a comprehensive development test and analysis program. (F-31, 

O-28)

F-32: Computer algorithms for panel jettison and subsequent firing of mortars are poorly 

defined.

 The timing sequence and control of FBC panel deployment should be considered a risk 

mitigation design parameter.

 Algorithms must be sufficiently defined to enable project engineers to understand the 

event sequence. 

O-29: Initial trajectories and motions of FBC panels will be sensitive to variations that will be 

inherent in several closely sequenced initial events. 

 MDC detonation events

 Initiation of airbag inflation

 Rate of airbag inflation

 Push-off force

R-35: Consider implementing an error margin budget that is derived by Monte Carlo 

simulation, in the FBC deployment design and analysis effort. (F-32, O-29) 

 An FBC deployment error margin budget could include (with example values):

o Timing mismatch between FBC separation and airbag inflation (ultimately 

effective delta-v from airbags) (e.g., 0 + 0.05 sec 3-sigma, Gaussian distribution).

o Airbag inflation rate and panel stability (e.g., 5 +/ 0.10 m3/sec 3-sigma, Gaussian 

distribution).

o Time allowed in free-fall between FBC jettison and chute deploy (e.g., 1 +/ 0.1 

sec 3-sigma, Gaussian distribution).

o Atmospheric density (e.g., +/ 0.001 kg/m33-sigma, Gaussian distribution).

o CM attitude at FBC separation and chute deploy (e.g., 180 +/ 50 deg 3-sigma, 

Gaussian distribution).
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 An error budget could be interrogated:

o Do the budgeted dispersions (uncertainties) meet the design requirement?

o Can the design requirement (e.g., acceptable range from FBC at parachute deploy) 

be changed to accommodate the budgeted dispersions (uncertainties)?

 Mars Science Laboratory (MSL) Entry, Descent, and Landing (EDL) designers employed 

an error margin budget to various operational phases, as described in: Mars Science 

Laboratory Entry, Descent, and Landing Triggers, Kipp, D., et al. (2006), Institute of 

Electrical and Electronics Engineers Aerospace Conference (IEEEAC) paper #1445, 

Version 2, Updated 2006:12:27.

R-36: Validate the aerodynamic trajectory analysis by conducting appropriate wind 

tunnel, ground, and/or flight tests. (F-26, F-28) 

 Consider subjecting a family of test panels that envelopes a best-guess range of panel 

dimensions, to vertical wind tunnel testing or free fall from an aircraft; investigate panels 

with variously deflated airbags in this same manner.

 Characterize the nature of terminal descent of the six panels (stable, metastable, 

unstable).

 Verify the assumptions/analysis of flight stability and ballistic coefficients.

 Conduct full 3D multi-body Monte Carlo trajectory analyses using dispersed 

aerodynamic parameters that encompass the FBC panel testing campaign‘s derived 

uncertainty.

F-33: The CPAS main parachute stowage bay geometry is more restrictive of unhindered 

extraction than was the heritage Apollo Earth landing system (ELS).

 The CPAS forward bay gusset geometry provides a 60-degree sweep of unhindered 

extraction, compared to 90 degrees for the ELS.

 The ramp on the upper back side of the three CPAS main-deployment bags will hinder 

upward extraction above the angle of the ramp. 

F-34: The project decision to classify the risk of deployment bag contact with forward bay 

features during extraction as ―off scope‖ in the development test matrix was not based on test 

data.

 Consequences could include deployment bag extraction failure or extraction delay and

damage to packed main parachute components.

R-37: Assess the risks (likelihood/consequences) arising from main parachute pack 

assembly contact with CM features during extraction by performing analysis and 
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conducting a comprehensive development test and analysis program using a representative

forward bay mock-up. (F-33, F-34)

F-35: Some of the main parachute retention options being considered expose the daisy-chain 

locking loops and their associated lanyards to risks of abrasion and heat damage. 

F-36: The latest reviewed main parachute retention system (March 2010) exhibits rigging 

complexity that introduces new risks of failed or delayed extraction of a main parachute pack. 

 No mechanism was shown for the left/right pilot riser halves to impart forces to unzip 

their associated daisy-chain loops; risers would require one-for-one integration with each 

locking loop to pull each loop through its associated grommet. This concept has no 

apparent precedent. 

O-30: Parachute extraction, deployment, and inflation have historically required testing because 

these events are difficult to analyze.

R-38: Conduct development ground testing to assess retention system options before

submitting the preliminary design to aerial drop tests. (F-35, F-36, O-30) 

 Ground tests could include a series of static and dynamic strip tests at various pull angles 

on a representative forward bay mock-up.

F-37: The system of corsets and beckets on the outer deployment bag surface of the current 

iteration of the main parachute retention may insufficiently support the convex-curved upperouter edge of the main parachute pack. 

O-31: Inertial forces may shift a pack in its retention system, altering its top and outer surfaces 

and particularly affecting its curved upper-outer edge. Such movement or distortion could allow 

contact of the deployment bag with the FBC inner mold line (IML), consequently damaging 

parachute components.

O-32: The lock/loop release concept on the current iteration of the main parachute retention 

system appears unnecessarily complex in that it requires pilot risers to un-loop each link during 

deployment.

 Diverges from the Apollo model by restraining the packs along their side edges instead of 

along their top and bottom edges.

R-39: Assess design options and risks (likelihood/consequences) of failure of the main 

parachute deployment bag corset-and-becket restraints by conducting development tests of 

a variety of restraint schemes under vibration and shock. (F-37, O-31, O-32) 

 Pay particular attention to risks along the convex-curved upper-outer edge of the main 

parachute deployment bags and consider incorporation of stiffening material.
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O-33: Movement internal to a main parachute pack can result in premature reefing line cutter 

initiation, as may have contributed proximally to the Ares 1-X test parachute performance 

anomaly. 

R-40: Ensure the adequacy of the cutter actuation system design load safety margins to 

preclude premature reefing line cutter initiation during packing, transport, or flight, while 

ensuring actuation during the dynamic conditions of deployment. (O-33)

 Consider the cutter actuator, initiation lanyard, attachment loops, safing ties, and stowage 

procedure.

F-38: The torque limiter design feature for limiting roll torque has no precedent and can induce 

failure modes into CPAS that will require extensive deployment testing.

O-34: The requirement to use the roll control system (RCS) for touchdown roll orientation 

control appears to be a remnant from the time when the CM was being designed to withstand 

land landings. The RCS is being relied upon to limit structural loads during water landings. The 

use of the RCS after FBC jettison may adversely affect the reliability of CPAS, by introducing 

risks of burning or oxidizing damage to textile materials, especially at high CM angular rates and 

attitudes.

O-35: Integrated risks and consequences associated with the RCS do not appear to have been 

comprehensively assessed. 

R-41: The Orion Project should consider chartering an Integrated Design Assessment 

Team (IDAT) to conduct a comprehensive assessment of CM roll control effectiveness at 

limiting landing loads on the vehicle. Include representatives from all CM subsystems that 

interface with or are dependent on the RCS function, including CPAS. (F-38, O-34, O-35) 

 The assessment scope could include:

o The overall feasibility and ramifications of using the RCS for touchdown roll 

control

o Assessment of the risks (likelihood/consequence) versus benefits to CPAS and 

other subsystems

o The impact of prohibiting the use of the RCS once the FBC panels are deployed

o The impact of a requirement to not dump RCS fuel in any direction where heat, 

fuel, or oxidizer can reach any part of the parachute system 

o Inclusion of a deployable metallic torque limiter in the CPAS system
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o Design of the CM structure for water impact at worst-case combinations of watersurface conditions and vehicle-landing attitudes

o The risks of landing with fuel in the RCS tanks

o The effects of parachute oscillation

o The ability to sense CM drift direction

o The ability to sense water-surface conditions beneath the CM prior to landing 

o The methods to determine which heading to take to impact a dynamically 

changing wave slope just right 

o RCS command sequencing

o The extent and complexity of an adequate development and certification plan for 

the RCS

O-36: The 2009 IDAT outer mold line (OML) change provided increased forward-bay volume 

for packaging CPAS components, but growth during forward development should be expected. 

Main parachutes may grow in size to reduce landing loads. CM weight increases may drive 

other increases in volume requirements. Main parachute retention locking loops, flaps, 

reinforcing bars, grommets, corsets, and beckets do not appear to be included in volume accounts 

for forward bay sectors where the main parachutes are stowed. The immaturity of the routing 

scheme for the lines that will secure the inflated CMUS bags may adversely impact available 

volume for CPAS. 

Reiteration of NESC Interim Recommendation outbriefed in April 2009: 

R-3: Evaluate the use of a volume budget for the forward bay to manage main parachute 

pack volume growth before and after PDR. (F-1, F-2, O-3, O-36)
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II. PRA-RELATED INTERIM NESC RECOMMENDATIONS

F-39: Failure estimates in the CPAS Probabilistic Risk Assessment (PRA) have evolved with the 

architecture but have never completely or accurately reflected CPAS risks.

 The driving failure estimate in December 2008 was based on inapplicable data from solid 

rocket booster (SRB) experience.

 Mid-2009 failure estimates were based on engineering judgment.

 Subsequent failure estimates (and uncertainty estimates) were based on the results of a 

dubious expert elicitation exercise.

 CPAS PRA input values at all stages have been used for computations of CPAS 

contributions to Orion‘s risk of loss of crew (LOC).

F-40: Between April 2009 and March 2010, few ground tests were conducted to generate data for 

PRA estimates, as previously recommended. 

F-41: Risk-informed design decisions have been made based on PRA models that have not been 

verified and validated.

O-37: Early PRA failure estimates are predicted, not demonstrated, but they ultimately require 

some verification of driving assumptions by analysis that has been anchored by some limited 

testing.

R-42: Include the source (e.g., historical, test, analysis, expert elicitation) and a clear 

explanation of the veracity of all CPAS PRA estimates when provided to the Orion Project 

for use in overall LOC summaries. (F-39, F-40, F-41, O-37) 

R-43: The Orion Project should establish guidelines for generating PRA failure estimates 

for use on all subsystems, whether contractor-furnished equipment (CFE) or governmentfurnished equipment (GFE). (F-39, F-40, F-41, O-37)

F-42: The methodology employed in the CPAS expert elicitation exercise assumed that the 

events were all independent, but some were dependent.

F-43: The methodology employed in the CPAS expert elicitation exercise assumed that the 

events were comparable, but experts were asked to compare input events at disparate levels. 

R-44: Consider applying the Analytical Hierarchy Process (AHP) or a similar decisionranking technique, to event sets that are truly independent and comparable, in any future 

expert elicitation exercise. (F-42, F-43) 

F-44: The response data from the expert elicitation exercise exhibit large variability.

 The large variability between experts: 

o Suggests lack of agreement among the experts
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o Indicates problems with the elicitation protocol, including the collection of events and 

their precise definition, and/or the analysis approach 

o Impugns the validity and applicability of the results

o Makes the use of the results difficult to defend

F-45: Deleting PRA failure events associated with the architecture change renders the current 

expert ranking inapplicable.

 Experts used in the elicitation exercise considered the ―Harnessed Drogues and 

Monolithic FBC‖ architecture prior to the change to the ―Modified Apollo‖ architecture. 

O-38: A cache of heritage Apollo ELS test and reliability reports has been located and will soon 

be retrieved by the project. 

R-45: Discontinue using results from the existing expert elicitation exercise for CPAS 

design decisions or for PRA/LOC estimates until failure estimates are revised to reflect the 

current architecture and the cause of large variability from that process can be 

determined. (F-44, F-45)

R-46: Utilize applicable data from the geometrically similar Apollo Program ELS to 

generate estimates for applicable failure estimates or conduct tests and analyses to generate 

new PRA data. (F-44, F-45, O-38) 

O-39: CPAS may gain insight into the ―Modified Apollo‖ architecture reliability by conducting a 

reliability growth analysis of the Apollo ELS test data.

 A reliability growth analysis/trending analysis of the original Apollo ELS would provide 

a baseline for present-day development. 

 Reliability growth methods indicate progress toward system reliability goals during a 

development program and provide management with a means to detect adverse (and 

positive) trends and proactively effect programmatic adjustments. 

 A programmatic reliability growth analysis would use calendar time and programmatic 

failures (e.g., failure to meet schedule, requirements, or test objectives). 

 As CPAS components are primarily  ̳one-shot‘ devices, a growth analysis to derive 

failure or reliability data will require a different approach (e.g., plotting sequential test 

failures versus tests run for both component- and system-level tests). 
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 An example reliability growth application for a NASA space instrument is available in 

the backup material.

R-47: Consider performing a reliability growth analysis using Apollo ELS test data. (O-39)

O-40: Based on similarity, the Modified Apollo architecture will have a comparable number of 

risks driving its development program as did the Apollo Block I ELS.

 Block I (early development) aerial drop tests accounted for 76 percent of all ELS aerial 

drop tests conducted. 

 Approximately 80 percent of ELS development tests were driven by the abort conditions. 

F-46: The Project has conducted few system-development tests supporting the various design 

concepts it has vetted. 

F-47: Ground and air-drop development testing should be better integrated into the overall 

design effort. 

F-48: At IDR3, development tests were discussed for use for qualification credit. F-23

III. ANALYSES-AND-TESTING-RELATED INTERIM NESC 

RECOMMENDATIONS

F-48: At IDR3, development tests were discussed for use for qualification credit. F-23

R-48: Apply development test results for qualification credit only if the configuration 

unambiguously represents the qualification configuration and this representation has been

rigorously documented. (F-48)

F-49: The CPAS development test schedule is ambitious, with tests planned every 2–3 months 

starting late in 2010. 

O-41: Resource (cost and schedule) constraints appear to drive testing activities and may have 

adversely impacted the sufficiency of tests conducted to date. The test team appears to be onedeep in some skills, and may not be capable of meeting the test rate, or flexibly managing the 

impact of test failures (even minor failures). 

R-49: Consider reorganizing the development test conduct team to allow multiple test 

subteams to conduct parallel activities. (F-49, F-50)
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F-50: A draft DOE test plan was created by a project statistician after NESC Interim 

Recommendation R-31 was outbriefed, but the plan was not incorporated into the development 

test planning process. 

O-42: Insufficient photographic and riser loads test instrumentation hindered investigation of 

parachute failures that occurred during the Ares 1-X flight test. 

R-50: Include photographic and test instrumentation on all aerial drop tests, sufficient not 

only to meet the requirements for nominal performance, but also to assist determining 

foreseeable failure causes. (O-42)

F-51: Statistical results from parametric analyses of un-shown validity have been used to inform 

design decisions.

R-51: Recognize and convey to decision makers the maturity of analytical models and the 

resulting uncertainties prior to their use in supporting design decisions. (F-26, F-51)

F-52: DCLDYN does not have the capability to model clustered canopies as independent bodies. 

F-53: The fraction of cluster load-sharing shown at IDR3 was not correct for the system 

presented. 

 The load share fraction used was based on one Apollo mains test point, and had been 

chosen by the Hardware Integrated Product Team (IPT) (as detailed in the IDR3 backup 

charts).

O-43: The fraction of load sharing has a significant and important effect on the structural 

analysis of the parachute and the hardware connections to the CM and should be tracked during 

development. Cluster performance and load-sharing data over the range of deployment 

conditions is needed early in the design process.

O-44: Various simulation models are available for modeling parachute clusters.

 The NASA LAS team conducts multi-body MC analysis using four different simulation 

tools: Decelerator System Simulation (DSS), Program to Optimize Simulated Trajectories 

(POST), Advanced NASA Technology Architecture for Exploration Studies 

(ANTARES), and OSIRIS.

 DSS uses three degrees of freedom (3DOF) multi-body parachutes that are independent 

of the capsule and other parachutes in the cluster. The three-chute DSS cluster modeled 

during IDAT remains unvalidated. 
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 POST uses 6DOF multi-body parachutes that are independent of the capsule and other 

parachutes in the cluster. The POST simulation multi-body model has been partially 

validated per NASA TM-2002-211634. The 6DOF aerodynamics is not known for 

CPAS, and therefore POST uses scaled SRB parachute aerodynamic data.

 ANTARES and OSIRIS share common simulation frameworks and the same multi-body 

model. 

R-52: Develop a drag model to accommodate multiple bodies in a shared environment that 

represents a chute cluster such that MC runs can assess variations in inflation times and 

opening loads between chutes. (F-52, F-53, O-43, O-44)

IV. REQUIREMENTS-AND-VERIFICATION-RELATED 

INTERIM NESC RECOMMENDATIONS

F-54: The Project Technical Requirements Specification (PTRS) does not define pass/fail criteria 

quantitatively, nor require an explicit statement of test suitability, assumptions, or statistical 

confidence in the test and/or simulation data and analysis.

R-53: Revise the PTRS to unequivocally ensure verifiable pass/fail metrics that require a 

quantitative and defendable development testing approach and analysis. (F-54)

 State what needs to be known, how well it needs to be known, and how it will become 

known that it has been learned. 

 Reference EA-07-005, Verification of Probabilistic Engineering Requirements Prepared 

for Constellation Chief Engineers Forum by Verification of Probabilistic Requirements 

Team, for format of the requirements. 

 For example: ―The CPAS will ensure with XX percent statistical power at an effect size 

of X.X m/s that the CM will not exceed 10.7 m/s‖ or ―The CPAS will ensure with 90

percent confidence that the 0.3-percentile (3 sigma) of the strength of component A 

exceeds X ft-lbs.‖

F-55: The draft Master Verification Plan (MVP) appears to emphasize aerial drop tests over 

ground tests. 

 Integration of verification activities is forward work.

R-54: Implement a comprehensive verification process that is linked to the requirements 

revised per R-53. (F-55) 
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 Emphasize a bottom-up test and verification approach over system-level drop tests. 

Verification activities should be performed at the lowest level possible and built up to 

mitigate the unnecessary risk and control all external effects. For example, the riser 

assembly mechanical strength qualification can be done as a component level test versus 

during an all-up system drop test.

 Develop a test matrix based on the most probable worst-case flight conditions and 

environmental factors (on a bad day/worst case), clearly state those conditions in 

reporting the results, and restrict acceptable flight conditions as limited to those that have 

been tested. The project seeks to ―test as you fly and fly as you test‖ but it is often 

impractical to develop a test matrix that will encompass all external environmental 

variables and interactions between its subassembly components, especially for a system 

as complex as CPAS. 

 Use statistical DOEs in all testing levels (component to flight) to optimally use resources 

for requirement verification (PTRS revised per R-54).

F-56: The CPAS Project‘s use of statistical assumptions, methodology, and analyses has not 

been consistently rigorous or defendable.

R-55: Integrate statistical expertise in the decision-making process throughout the design, 

development, and testing processes. (F-50, F-56)

V. LESSONS LEARNED FOR FUTURE PROGRAMS AND

PROJECTS

O-45: The IDAT work and the Lockheed Forward Bay Technical Interchange Meeting (TIM) 

addressed many CPAS integration issues. LRS Forward Integration Team (FIT) involvement in 

CPAS integration activity will benefit the project. However, complex reporting lines, roles, and 

responsibilities that arise from CPAS being GFE may pose risks to designing a well-integrated 

and reliable subsystem. 

O-46: During Apollo, the ELS organization was responsible for the total upper deck Interface 

Control Document (ICD), allowing them to control anything that could interfere with parachute 

function.

LL-2: Developers of parachute architectures for recovery of human-rated space vehicles 

should assign control of the parachute compartment ICD to the parachute system 

development team. (O-45, O-46)
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Appendix D.2. Supporting Example of Reliability Growth Trending

The following backup material was provided to the Project with the Stakeholder Outbrief of 

Interim NESC Recommendations 3. 

BACKUP ITEM: EXAMPLE SUPPORTING INTERIM R-47

An example application for a NASA space instrument is provided that used reliability growth 

trending during development. The following graph is a Crow-AMSAA plot (so-named for Dr. 

Larry Crow and the U.S. Army Materiel Systems Analysis Activity), aka a CA plot, or a 

reliability growth plot, of this instrument during integration and test. The inflections (slope 

changes) are points at which failures occurred, fixes implemented, and testing continued. After 

several failures occurred ―post-PER,‖ the program stood down, revised their processes, and 

implemented other fix measures. The slope change from 2 (degradation, or ―negative‖ reliability 

growth) to 0.14 (excellent reliability growth) indicated that the stand-down and changes 

implemented were effective in reversing the prior adverse trend. 

The following graph is a mean-time-between-failures plot derived from the CA plot. It shows 

reliability and uncertainty trends, including confidence intervals. Similar plots for failure rate 

are also available.
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Appendix D.3. Supporting Example of Potential Problems with

OFAT Testing

The following backup material was provided to the Project with the Stakeholder Outbrief of 

Interim NESC Recommendations 3. 

BACKUP ITEM: EXAMPLE OF PROBLEMS THAT CAN ARISE 

WITH ONE-FACTOR-AT-A-TIME (OFAT) TESTING 

Consider the following experiment where the engineer is interested in determining the values of 

factors x and y that produce the highest stress. Suppose we fix factor y at 155 (the nominal 

value) and perform four tests at different levels of factor x – say, .5, 1.0, 1.5, and 2.0. The results 

are shown in Figure 1. This figure indicates that the maximum stress is achieved when factor x is 

about 1.3. 

x

Stress

0.5 1.0 1.5 2.0

0 2 4 6 8 1 0

Figure 1: Stress versus factor x with factor y constant at 155

To determine the effect of factor y fix factor x at 1.3 (the apparent optimal value) and perform 

six tests at different levels of factor y – say, 140, 150, 160, 170, 180, and 190. The results of 

these tests are plotted in Figure 2. The maximum stress occurs at about 165. Therefore we would 

conclude that the worst case stress occurs at x = 1.3 and y = 165 resulting in a stress of about 9.
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y

Stress

140 150 160 170 180 190

0 2 4 6 8 1 0

Figure 2: Stress versus factor y with factor x constant at 1.3

Figure 3 displays the contour plot of stress as a function of x and y with the one-at-a-time tests 

shown on the contours. We now see that the one-at-a-time testing has failed here, as the true 

worst case is over 50% higher (greater than 14) and occurs when x = .7 and y = 185. 

x

y

0.0 0.5 1.0 1.5 2.0 2.5 3.0

140 160 180 200

2 2

6 4

6

1 0 8

1 2

1 4

Figure 3: Stress experiment using one-factor-at-a-time method

The one-at-a-time testing has failed here because it failed to detect the interaction between the 

two factors. Factorial experiments (DOE) are the only way to detect interactions. In addition the

one-at-a-time method is inefficient; it requires more tests than a factorial, and there is no 

assurance that it will produce the correct results.
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Constellation Program (CxP) Crew Exploration Vehicle (CEV) Parachute 

Assembly System (CPAS) Independent Design Reliability Assessment

Appendices

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This document contains the Appendices to the report documenting the activities, findings, and NASA Engineering and Safety 

Center (NESC) recommendations of a multidiscipline team to independently assess the Constellation Program (CxP) Crew 

Exploration Vehicle (CEV) Parachute Assembly System (CPAS). The assessment occurred during a period of 15 

noncontiguous months between December 2008 and April 2010, prior to the CPAS Project's Preliminary Design Review 

(PDR) in August 2010. 

15. SUBJECT TERMS

NASA Engineering and Safety Center; Constellation Program; Crew Exploration Vehicle Parachute Assembly System; Crew 

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