May 2013

NASA/TM2013-217990

NESC-RP-10-00685

 

Composite Crew Module (CCM) 

Permeability Characterization

Michael T. Kirsch/NESC

Langley Research Center, Hampton, Virginia
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May 2013

NASA/TM2013-217990

NESC-RP-10-00685

 

Composite Crew Module (CCM) 

Permeability Characterization

Michael T. Kirsch/NESC

Langley Research Center, Hampton, Virginia
Available from:

NASA Center for AeroSpace Information

7115 Standard Drive

Hanover, MD 21076-1320

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Composite Crew Module (CCM) Permeability Characterization

March 14, 2013
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Report Approval and Revision History 

NOTE: This document was approved at the March 14, 2013, NRB. This document was 

submitted to the NESC Director on March 20, 2013, for configuration control.

Approved: Original Signature on File 3/21/13

NESC Director Date

Version Description of Revision Office of Primary 

Responsibility Effective Date

1.0 Initial Release Mr. Michael Kirsch, 

NESC Principal 

Engineer, Langley 

Research Center

3/14/13
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Table of Contents

Technical Assessment Report

1.0 Notification and Authorization........................................................................................ 5

2.0 Signature Page................................................................................................................... 6

3.0 Team List ..................................................................................................................... 7

4.0 Executive Summary .......................................................................................................... 8

5.0 Assessment Plan .............................................................................................................. 11

6.0 Problem Description and Scope..................................................................................... 11

7.0 Testing ................................................................................................................... 11

7.1 Leak Measurements.............................................................................................. 11

7.2 Coupon Testing..................................................................................................... 12

7.3 Full-scale Leak Testing......................................................................................... 16

7.3.1 Test Article Condition and Preparation ................................................................ 16

7.3.2 Vacuum Bag Usage............................................................................................... 22

7.3.3 3MTM 5004 Film Application................................................................................. 28

7.3.4 Full-Scale System Leak Rate Results................................................................... 32

8.0 Findings and NESC Recommendations........................................................................ 35

8.1 Findings................................................................................................................. 35

8.2 NESC Recommendations...................................................................................... 36

9.0 Alternate Viewpoint........................................................................................................ 36

10.0 Other Deliverables.......................................................................................................... 36

11.0 Lessons Learned.............................................................................................................. 36

12.0 Recommendations for NASA Standards and Specifications ...................................... 36

13.0 Definition of Terms......................................................................................................... 37

14.0 Acronyms List ................................................................................................................. 38

15.0 References ................................................................................................................... 38
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List of Figures

Figure 7.2-1. Coupon Leak Test Configuration Setup ............................................................... 13

Figure 7.2-2. 7-inch × 7-inch Coupon Leak Test (helium containment bag not shown) ........... 14

Figure 7.2-3. Coupon Leak Rate versus Impact ......................................................................... 15

Figure 7.3-1. CCM Design Features........................................................................................... 17

Figure 7.3-2. Vacuum Sealant Tape (i.e., vacuum putty) Installed on a CCM Hatch Cover on 

the Outside Flange Next to the O-ring.................................................................. 20

Figure 7.3-3. Closeup of the Vacuum Putty Placed Outside the Hatch Cover O-ring ............... 21

Figure 7.3-4. Positioning the Main Hatch Cover........................................................................ 21

Figure 7.3.5. Docking Tunnel Hatch Cover Installation ............................................................ 22

Figure 7.3-6. Schematic Illustrating the Features that were Measured Using the Vacuum 

Bag Technique (indicated in red).......................................................................... 23

Figure 7.3-7. Example Vacuum Bag Installation ....................................................................... 24

Figure 7.3-8. Vacuum Bag Installation around an SM/ALAS Fitting........................................ 24

Figure 7.3-9. Installed Hatch Vacuum Bags Attached to a Mass Spectrometer......................... 25

Figure 7.3-10. Total Leak Rate Test............................................................................................. 26

Figure 7.3-11. CCM Outside the V-20 Vacuum Chamber........................................................... 27

Figure 7.3-12. 3MTM 5004 Film Application over spools.............................................................. 29

Figure 7.3-13. Technician Starts to Apply the 3MTM 5004 Film around CCM IML Features ...... 30

Figure 7.3-14. Technician Uses a Plastic Tool to Help Avoid Wrinkles and Bubbles................. 30

Figure 7.3-15. Technician Finalizes 3MTM 5004 Film Application............................................... 31

Figure 7.3-16. Completed 3MTM 5004 Film Application .............................................................. 31

Figure 7.3-17. 3MTM 5004 Film Inspection in Docking Tunnel .................................................... 32

Figure 7.3-18. Leak Rate versus Test Date for Full-scale CCM (blue diamond), Spools 

(red square), and Repair #1 (green circle) (modifications are identified)............. 33

Figure 7.3-19. Local Leak Rate versus Feature............................................................................ 34

Figure 7.3-20. Global Leak Rate of 1.1e-1 sccs (separated by contribution)............................... 35

List of Tables

Table 7.2-1. Coupon Billet Layup............................................................................................. 12

Table 7.2-2. Coupon Test Matrix .............................................................................................. 13

Table 7.3-1. List of Individual Full-scale Tests ........................................................................ 18

Table 7.3-2. High-Potential Leak Sources ................................................................................ 19
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Technical Assessment Report

1.0 Notification and Authorization 

Mr. Michael Kirsch, NASA Engineering and Safety Center (NESC) Principal Engineer at the 

NASA Langley Research Center (LaRC), was selected to lead this assessment, which was the 

result of the Composite Crew Module (CCM) Primary Structure assessment (NESC-RP-06-019). 

The assessment plan was approved by the NESC Review Board (NRB) on December 14, 2010.

The key stakeholders for this assessment are the Exploration Systems Mission Directorate and 

the NASA Office of Chief Engineer.
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2.0 Signature Page

Submitted by: 

Team Signature Page on File – 4/9/13

Mr. Michael T. Kirsch Date

Significant Contributors: 

Dr. Daniel L. Polis Date Mr. William M. McMahon Date

Mr. Steven D. Underwood Date Mr. Wade C. Jackson Date

Mr. Donald C. Hull Date

Signatories declare the findings, observations, and NESC recommendations compiled in the 

report are factually based from data extracted from program/project documents, contractor 

reports, and open literature, and/or generated from independently conducted tests, analyses, and 

inspections.
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3.0 Team List

Name Discipline Organization

Core Team

Mike Kirsch NESC Lead LaRC

Daniel Polis Deputy Lead

Sierra Nevada Corporation 

(formally GSFC)

Alvin Eidson Safety Office Team Lead MSFC

Don Hull Systems Engineer MSFC/NESC/SEO

Wade Jackson Structures Engineer LaRC

Mike Lau Instrumentation Team Lead MSFC

James Marris ETF Test Coordinator MSFC/METTS

William McMahon Material Engineer MSFC

Gerald Neal Safety Engineer Bastion Technologies

Manuel Schultz Chamber V20 Facility Lead MSFC

Morgan Simpson Test Engineer KSC

Vanessa Stroh Test Engineer KSC

Steve Underwood Test Engineer MSFC/Boeing

Pamela Throckmorton MTSO Program Analyst LaRC

Administrative Support

Teri Derby Project Coordinator LaRC/AMA

Christina Williams Technical Writer LaRC/AMA
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4.0 Executive Summary

In January 2007, the NASA Administrator chartered the NASA Engineering and Safety Center 

(NESC) to form an Agency team to design and build a composite crew module in 

18 months in order to gain hands-on experience in anticipation that future exploration systems 

may be made of composite materials. One of the conclusions from this Composite Crew Module

(CCM) Primary Structure assessment [ref. 1] was that there was a lack of understanding 

regarding the ability for composite pressure shells to contain consumable gases, which posed a 

technical risk relative to the use of a metallic design. After the completion of the CCM test 

program, the test article was used in a new program to assess the overall leakage/permeability

and identify specific features associated with high leak rates. The “International Space Station 

(ISS) to Commercial Orbital Transportation Services Interface Requirements Document”

specifies that the maximum leakage rate cannot exceed 0.01 kilograms (kg) per day of air at 

14.7 pounds per square inch differential (psid) (760 millimeters of mercury (mmHg)) while the 

crew module is mated to the ISS [ref. 2].

The CCM was built as two halves spliced together around the circumference using a double lap 

shear joint cured under vacuum bag pressure with a heater. The majority of the construction was 

honeycomb sandwich with unvented aluminum honeycomb. The unvented core was selected to 

provide double redundancy in pressure containment with the two skins of the sandwich. Six

large openings were included for windows and hatches. The minimum gage sandwich skin and 

the minimum gage laminate consisted of 4 plies and 10 plies of fabric, respectively. Metallic 

fittings bolted through the pressure shells were used for attachment points for the Service 

Module/Alternate Launch Abort System (SM/ALAS) and parachutes. An external bracket was 

attached to the sandwich structure using 20 two-piece inserts that penetrated both face sheets. In 

addition to these penetrations, two repairs were made using through bolts in the lobed bottom of 

the lower pressure shell.

An extensive mechanical test program that included 11 test conditions was conducted on the 

CCM [ref. 3]. The test program consisted of pressurizing the internal volume and applying 

mechanical loads to the metallic fittings. Each test condition consisted of a number of 

loading/unloading sequences leading up to either limit or ultimate load. Mechanical loads were 

applied to four types of metallic fittings (SM/ALAS, parachute, drogue chute, and external 

bracket) using straps attached to a hydraulic actuator, while the internal pressure was controlled. 

A damage tolerance program was included in the test program, which involved impacting the 

vehicle at 18 unique locations at 6 foot-pounds (ft-lb) followed by life cycling (four lifetimes).

In addition, five design details were taken to critical impact threat levels (reliable detection or a 

threshold energy level of 26 ft-lb) and subsequently tested to an additional four lifetimes. At the 

end of the test program, the CCM was hydraulically pressurized to failure, which occurred at 

54 psid (3.5 times the pressure limit).

The CCM did incur significant damage from the test program [ref. 4]. At failure, three of the six 
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bays contained large regions of skin-to-honeycomb debonding in the “shoulder” region (ceiling 

to conic transition), as well as core splice failures. The potting compound that was used between 

the upper and lower pressures shells was cracked extensively. Water also was observed escaping 

from the bolts used on the repair to the lower pressure shell after failure. As a result of the 

damage tolerance program, localized impact damage was scattered inside and outside the CCM. 

The impact testing near the docking ring caused a large debond in the doubler and damage to the 

pressure shell. It was unknown whether extensive microcracking developed in the fabric plies 

throughout the CCM due to the high loads during the test program.

All leak measurements were performed using helium, instead of the operational fluid (air), in 

conjunction with a mass spectrometer. This is a very common technique used in many industries 

to detect small leaks. Because of its extremely small atomic size, helium easily passes through 

small cracks. However, conversion from a helium flow rate to an air flow rate can be complex 

due to the different characteristics of the two gases. For example, the permeability of several 

types of polymeric membranes differed by over 2 orders of magnitude for helium relative to 

nitrogen [ref. 5]. The use of helium will result in conservative results for leak measurements (air 

leakage will not be greater than the measured helium leak rate). In this assessment, the helium 

leak rates were compared directly with the maximum leak rate for air.

The pristine permeability of carbon-fiber-reinforced toughened epoxy laminates, measured at the 

coupon level, is sufficient to meet vehicle-level requirements of 0.01 kg/day or 1e-1 standard 

cubic centimeters per second (sccs) of air [refs. 2 and 6]. The CCM Program and subsequent 

investigations demonstrated that composite permeability is sufficiently low under design limit 

strains [refs. 6 and 7]. In addition to the damage caused by the test program, several outstanding 

leakage risks remain that relate to the design and manufacture. These items include but are not 

limited to bolted fittings, out-of-autoclave joints, potted inserts, bolted repairs, and impact 

damage repair. The CCM was not designed and manufactured for leakage/permeation testing. 

Consequently, the aluminum frames, seals, and covers were not “flight like” and may be subject 

to leakage (e.g., single O-ring seal). Some of the covers also have through-thickness 

penetrations that could leak. 

With these leakage risks in mind, one goal of the CCM permeability characterization 

investigation was to quantify the leakage of some of these structural features that were readily 

available on the full-scale structure. The CCM enabled the quantification of the variability 

associated with these features to better understand the process control aspects of their design. 

The investigation quantified the permeability/leakage from coupons with and without impacts

and then demonstrated that a sheet appliqué liner solution could mitigate the impact leakage. 

Following that demonstration, the liner solution was partially installed on the CCM to examine 

the feasibility of full-scale implementation. The appliqué film was manually installed on the 

interior of the CCM, covering approximately 25 percent of the upper shell, the splice, and all of 

the potted inserts. Despite some difficulty in installation, the film was effective at reducing the 
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leak rate associated with the inserts. The film also appeared to reduce the leak rate associated 

with the splice, although insufficient data were collected to establish the statistical significance 

of this change. This mitigation scheme could allow for numerous low velocity impacts (i.e., 

approximately 900, assuming one-inch-diameter damage areas) without compromising the 

system leak performance. 

The leak rate associated with critical features such as bolted penetrations was quantified. The 

measurements revealed that the sealing process for the bolted fittings was not robust (i.e., similar 

fittings showed large variability in performance). However, some fittings demonstrated that low 

leak rates are achievable. This suggests that, with improved process control and/or design 

improvements, acceptable leak rates through penetrations are possible. 

The leak rate associated with the composite shell, absent of penetrations, was estimated using 

two methods: 1) scaling coupon data and 2) subtracting the critical feature leak rates from the 

global leak rate. The estimates are 2.3e-3 and 8.4e-2 sccs for methods 1 and 2, respectively. 

Method 2 required scaling the feature leak rates to the reference operating pressure of 

1 atmosphere (atm). The discrepancy in the two methods suggests that there were significant 

features or defects that were not quantified during the feature test. The coupon estimate should 

have been an upper bound since the leak rates were measured on a single, minimum gage skin. 

The CCM shell is either two skins that are at least as thick as the minimum gage skin or a solid 

laminate that is more than twice as thick. Potential leak sources that were not specifically

quantified in this study include the impact sites, three large core debonded zones from the test-tofailure, and areas of undetected damage related to the previous test program. In addition, the 

coupon tests were performed on pristine laminates, while the test article had an extensive load 

history.

In summary, the CCM permeability characterization concluded that a pressurized composite 

vehicle could meet the maximum leakage rate requirements without a liner using improved 

process controls during manufacturing. However, a liner greatly limits the amount of leakage 

caused by an impact. A brushable or sprayable coating should be pursued as an alternative to a 

manually applied appliqué film in applications that involve complex curvatures or other 

geometric complexities. In addition, process control techniques and improved designs for 

leakage should be considered for bolted penetrations to reduce variability.
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5.0 Assessment Plan

This assessment was the result of the findings and NESC recommendations contained in the 

NESC Technical Assessment Report for the Composite Crew Module: Primary Structure [ref. 1]. 

The CCM program was designed to provide NASA engineers with design, build, and test 

experience, with the expectation that future manned vehicles would utilize composites as 

pressure-containing primary structures. One of the conclusions from reference 1 was that there 

was a lack of understanding regarding the ability for composite pressure shells to contain 

consumable gases, which posed a technical risk relative to the use of a metallic design. At a 

coupon level, the pristine permeability of carbon-fiber-reinforced toughened epoxy laminates is

sufficient in meeting vehicle-level requirements of 0.01 kg/day at 14.7 psid (760 mmHg) 

[refs. 2 and 6]. In addition, CCM and subsequent investigations demonstrated that composite

permeability is sufficiently low under design limit strains [refs. 6 and 7]. However, several 

outstanding risks remain regarding the permeability/leakage of full-scale composite pressurized 

structures, particularly after impact damage. This assessment attempted to quantify the CCM 

permeability/leakage in its current as-manufactured and tested state. 

6.0 Problem Description and Scope

The goal of the CCM leak characterization assessment was to quantify leakage/permeability of 

the entire vehicle and of specific features such as bolted fittings, out-of-autoclave joints, and

potted inserts. This assessment was performed after the CCM program completed an extensive 

test program that included ultimate loads applied to fittings, extensive impact damage, life 

cycling, and, finally, pressurization to failure (3.5 times the pressure limit). The CCM enabled

the quantification of the variability associated with design features to better understand the 

process control aspects. In addition to examining bolted penetrations, the investigation

quantified permeability from coupons with and without impacts and then demonstrated that a 

sheet appliqué liner solution could mitigate the leakage caused by impact. Following that

demonstration, the liner solution was partially installed on the CCM to examine the feasibility of 

a full-scale implementation.

7.0 Testing

7.1 Leak Measurements

All leak measurements were performed using a helium mass spectrometer. Using this technique, 

one surface is in a helium environment, while a vacuum attached to the mass spectrometer is 

located on the opposite surface. The vacuum system carries the helium into the analyzer cell to 

determine the helium concentration. This technique is commonly used in many industries, 

including the aerospace industry, to locate and measure small leaks. For the Constellation

Program (CxP), the molecular size of the leak test fluid is required be equal to or less than the 

molecular size of the operational fluid [ref. 8]. However, molecules of nitrogen and oxygen are 

2 to 3 orders of magnitude larger than helium atoms. Consequently, the conversion from a 
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helium flow rate to an air flow rate can be complex and depends on many factors associated with 

the medium, gas, and test conditions. For simple viscous flow, the flow rates between helium and 

air should be similar. However, for flows through dense polymeric membranes, the 

permeabilities to helium and air/nitrogen have been reported to differ by a factor up to 600 

[ref. 5]. The use of helium results in conservative conclusions (leakage rate of air will be less 

than for helium) for leakage/permeability measurements. For the CCM assessment, the 

differences in leakage rates between helium and air were not investigated and may vary 

depending on the transport mechanisms and materials involved at specific locations. All 

measured leak rates are reported in sccm of helium. In some cases (e.g., permeability 

measurements), the total leak rate was divided by the test area to obtain a leak rate per unit area. 

The flow rates in sccm were not converted to English units such as standard cubic feet per 

minute (scfm) since the measurements were made in sccm and are commonly reported for leak 

rates.

7.2 Coupon Testing

To examine leakage after impact, coupon testing was focused on the CCM minimum gage 

sandwich skin, which is composed of four plies of CCM-SPEC-001, Type II material [ref. 9]. 

While the minimum gage solid laminate was eight plies of Type II material, the four-ply 

laminate for sandwich skin served as a bounding case for the CCM shell where a penetration or 

splice was not present. The NESC team was able to estimate an expected leak rate for the CCM 

acreage (no penetration or damage) for full-scale testing based on the coupon tests.

A four-ply laminate billet (approximately 30 inches × 30 inches), was manufactured according to 

the Type I process specified in reference 10. The layup is given in Table 7.2-1 and mimics the 

full-body plies in the pre-cured CCM inner mold line (IML) skin. 

Table 7.2-1. Coupon Billet Layup 

Ply 

Number Orientation Warp Direction Material [ref. 9]

1 45 Up CCM-SPEC-001, Type II

2 0 Up CCM-SPEC-001, Type II

3 0 Down CCM-SPEC-001, Type II

4 45 Down CCM-SPEC-001, Type II

From this laminate billet, 15 (7 inch × 7 inch) coupons were extracted for impact testing. Note 

that a 1-inch border around the billet was removed before extracting the coupons to eliminate 

edge bleed artifacts. Nine of the 15 coupons had appliqué film (i.e., 3MTM Paint Replacement 

Tape 5004) installed on the laminate tool side prior to testing. Table 7.2-2 summarizes the 

coupon matrix, where the letter denotes either composite only (C) or composite with film (F), 

and the number represents the impact energy (ft-lb). 
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Table 7.2-2. Coupon Test Matrix 

Impact energy (ft-lb) 0 0.5 1.0 2.0 3.0 4.0 6.0 9.0 12.0

Four-ply laminate (C) C0 C0.5 C1 C2 C3 C4

Four-ply laminate w/ 

appliqué (F) F0 F0.5 F1 F2 F3 F4 F6 F9 F12

Impacts were performed with a 1-inch-diameter hemispherical tip impacter on the four-ply 

laminates resting on an aluminum honeycomb core. The laminate bag side was in contact with 

the core; therefore, the impacts occurred on the tool side, consistent with an IML impact. 

Each coupon was tested using the hood method, which consisted of a bell jar centered over the 

marked center/impact film area and connected to a helium mass spectrometer, as shown in 

Figures 7.2-1 and 7.2-2. Prior to each test series, the mass spectrometer system was calibrated to 

a known leak rate so that leak sensitivity could be established. The helium containment bag was 

centered on the opposite side (Figure 7.2-1) and a constant helium flow was injected into the bag. 

The mass spectrometer measured the helium flow rate through the sample. This rate was 

monitored until the mass spectrometer output stabilized. 

Figure 7.2-1. Coupon Leak Test Configuration Setup
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Figure 7.2-2. 7-inch × 7-inch Coupon Leak Test (helium containment bag not shown)

The appliqué film, the laminate, and the laminate with appliqué film were leak tested. A 

summary of these results is given in Figure 7.2-3. The measurement area for these coupons was 

4.9 square inches (in2), and the measured leak rate was in sccs per unit area. The pressure 

differential was 1 atm. It should be noted that the deformation on these coupons from the 

pressure differential was not specifically constrained. The deformations may affect the leakage 

rates relative to an unstressed specimen.
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Figure 7.2-3. Effect of Appliqué Film and Impact Energy on the Leak Rate per Unit Area

Figure 7.2-3 contains two reference lines: a global maximum and appliqué film leak rates. The 

global leak rate is based on the CxP leak requirement (1e-1 sccs) divided by the CCM internal 

shell surface area (400 ft2= 57600 in2). The figure shows the appliqué film is not sufficient to 

act as the sole permeability barrier on the entire 400 ft2. However, as discussed earlier, the 

permeability of the film to air may be significantly improved relative to the helium used in the 

leak measurement. 

Figure 7.2-3 shows a permeability that is largely unaffected by impacts less than 2 ft-lb. This 

result is consistent with what was reported using the nitrogen flow technique [ref. 2] (i.e., there 

appears to be an impact threshold at ~2 ft-lb). However, this technique provides quantification 

below the impact threshold. The leakage rises rapidly with impact energy so that even one 

impact of the laminate at low energy (<6 ft-lb) would produce a leak that is in excess of the 

global maximum leak rate. In contrast, the laminate with the appliqué film shows the same 

impact threshold, but rather than showing a continued rise versus impact energy, displays a 
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shallow rise and appears to approach an asymptote below the leakage rate of the pure appliqué 

film.

If it is assumed that the CCM is composed of mostly pristine laminate and sandwich (i.e., 

impacts <2 ft-lb), with several higher energy impacts (i.e., below the barely detectable threshold, 

~6 ft-lb) the question then would be: how many impacts could be tolerated before the global 

maximum leak rate is exceeded? One method to estimate the allowable impact area is equation

7.1-1: 

R = (T – x)*(P) + x*(A) (Eq. 7.1-1)

Where:

R = CxP vehicle requirement = 1e-1 sccs 

T = total shell area = 57,600 in2

P = pristine minimum gage leak rate = 4e-8 sccs/in2

A = appliqué leak rate = 1.4e-4 sccs/in2

x = allowable impact area 

The value for P was 4e-8 sccs/in2, which was obtained for F0 (see Table 7.2-2). This 

conservative value was chosen because the measurement for C0 was ~25 percent lower than that 

for F0. These results illustrate the variability in the measurements. 

Solving for x yields 700 in2(4.86 ft2) of allowable impact area. This can be thought of in terms 

of the number of tool drops or hardware bumps that could go undetected. If it is assumed that 

each impact results in a damage zone equivalent to a 1-inch-diameter open hole in the laminate, 

then the allowable impact area can be translated into almost 900 impacts. However, this number 

would be adjusted based on the estimated leak rate of other technical features such as joints and 

penetrations.

A final result from the coupon test is a leak rate estimate for the composite shell, given as T*P, 

which assumes a shell absent of any penetrations. This approach yields 2.3e-3 sccs and serves as 

an order-of-magnitude estimate for the full-scale testing. 

7.3 Full-scale Leak Testing

The goals of the full-scale testing were to determine the overall vehicle leak rate and to quantify 

the significant contributing features to the overall leak rate. 

7.3.1 Test Article Condition and Preparation

The CCM was built as two halves, an upper and lower pressure shell, and is shown in 

Figure 7.3-1. It was manufactured in an autoclave on two different male tools: one for the upper 

and one for the lower. The two shells were joined using a double lap shear joint, with 12

different internal and external doublers: 1 for each longeron and 1 for the acreage between 
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longerons. The splice cures were done under vacuum bag pressure with a purpose-built Kapton®

heater. The major openings in the CCM included two side windows, two docking windows, a 

docking tunnel cover, and a main hatch. The cutouts were machined into the side of the pressure 

shell and fit with matching aluminum frames after cure.

Figure 7.3-1. CCM Design Features 

The CCM leak integrity approach was to use predominantly sandwich systems with unvented

cores. The approach provided two barriers against through-thickness permeability: the IML skin 

and the outer mold line (OML) skin. The skins in the acreage areas consisted of four plies of 

fabric. It was shown that exceedingly low impact damage (less than 2 ft-lb) could cause leakage 

and would not be detectable visibly or with NDE techniques. Given the extensive subsystem 

integration both on the inside and the outside of the CCM, there was a possibility of undetected 

damage coincident on the inside and outside that could provide an undetected leak path. Some 

areas of solid laminates were also used in the design, specifically the tunnel, the backbone cap, 

and the pan down regions where metallic fittings such as parachute fittings and SM/ALAS

interface fittings were bolted through the shell. Although higher impact energies are required to 

damage these regions, there is no redundancy to prevent leakage.

The full-scale CCM mechanical test program [ref. 3] consisted of 11 test conditions (Table

7.3-1). Each test condition consisted of a number of loading/unloading sequences leading up to 

the maximum intended load. Mechanical loads were applied to three types of metallic fittings 
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(SM/ALAS, parachute, and drogue chute) using straps attached to a hydraulic actuator while the 

CCM was pressurized. Mechanical loads were also applied to an external bracket attached to the 

sandwich structure using 20 two-piece aluminum inserts that were potted into the core and 

penetrated both skins. 

Table 7.3-1. List of Individual Full-scale Tests

Test Test Description Number of 

Runs

1 Internal pressure to limit load 5

2 SM/ALAS fitting pull to limit load 4

3 Main parachute fitting to limit load 4

4 Internal pressure to ultimate load 6

5 External bracket/insert pull to ultimate load 2

6 Drogue chute to limit (no pressure) 1

7 Internal pressure to ultimate load after 6-ft-lb impacts 2

8 Main parachute fitting to ultimate after 6-ft-lb impacts 5

9 Four-lifetime cyclic test to 110%* limit load after 6 ft-lb 5**

10 Four-lifetime cyclic test to 110%* limit load after 26 ft-lb 4**

11 Internal pressure to failure using water 2

* The 110 percent corresponds to a life enhancement factor of 1.1 times the limit load. This is explained in 

more detail in the sections describing the cyclic tests.

** Here, one run corresponds to one lifetime, which is equal to 22 load/unload pressure cycles 

plus 9 load/unload main-parachute pull cycles.

A full-scale damage tolerance program was included in the test program to demonstrate that the 

CCM could meet the intent of current NASA requirements with minimal design changes. This 

included impacting the vehicle at 18 unique locations at 6 ft-lb, defined as the allowable threat 

level. Following these impacts, the test article was taken through two critical design ultimate 

load cases followed by life cycling (four lifetimes). Subsequently, five design details were 

impacted at critical threat levels (reliable detection or threshold energy of 26 ft-lb) and then

tested to an additional four life times. In all cases, no detrimental growth of damage was shown.

Following the damage tolerance testing, the CCM was pressurized to failure using water. Water 

was used instead of air to limit the amount of damage that occurred at failure. A structural 

failure was detected at 54 psi, which was 3.5 times the pressure limit, and resulted in a small 

drop in pressure. After the CCM was drained, three large regions were discovered where the 

core debonded from the face sheets [ref. 4]. All three debonded regions were located on the 

upper pressure shell in the shoulder region between the conic and the ceiling. Of the six bays, 

the debonded regions were located in every other bay and covered most of the bay width.

Prior to leak testing, potential sources were identified that may have high leak rates 

(Table 7.3-2). The CCM frames, covers/hatches, and associated penetrations were not flight-like 

designs and, therefore, did not possess the necessary characteristics to minimize leakage. The 

NESC team had a concern that the single O-ring hatch seals would be insufficient to meet the 
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leak requirements for the testing. The splice was cured out of the autoclave using a prepreg that 

was formulated for an autoclave. The splice showed a 3- to 4-percent void content that made it a 

concern for leakage [ref. 6]. In addition, the potting between the two pressure shells was cracked 

extensively [ref. 4]. Given these two conditions, a leak path could be present between the IML 

and OML. Two bolted repairs were made to the lobed bottom of the lower pressure shell to 

attach the backbone after the pi joint failed to position correctly during a secondary bonding 

procedure. These repairs used 55 bolts to secure the backbone to the lobed bottom. After the 

CCM test-to-failure, water was observed on the OML in one of the repair areas. 

Table 7.3-2. High-Potential Leak Sources

1 Cutout frames and seals

2 Covers for cutouts

3 Splice 

4 Bolted repairs to lower pressure shell

5 Bolts for fittings (SM/ALAS, parachute)

6 Potted inserts (20)

7 Impact sites

8 Debonded bays

Each parachute and SM/ALAS fitting was installed using 14 0.25-inch bolts and 

32 0.25-inch bolts, respectively. For fastener penetrations through the pressure shell, the design 

baselined the use of polysulfide sealant, wet installed with the fasteners, as the method for 

managing leak integrity around the penetrations. The polysulfide passed the NASA Test 

Standard 6001 for compatibility but presented an odor problem. It is believed that an alternative 

that preserves the advantages of polysulfide, without the obnoxious odor, could be identified and

demonstrated if a composite pressure shell was adopted for a human spaceflight program. 

Twenty potted inserts were installed into the pressure shell midway through the full-scale test 

program. Previously in the CCM test program, the leakage around these inserts was investigated 

at the coupon level using a bottled nitrogen test method [refs. 3 and 6]. No leakage was found on 

any of the 18 inserts in the test specimens prior to testing. After testing, one insert that had been 

tested to failure was found to leak through the hole used for the potting installation. 

During the damage tolerance program, the CCM received nearly 30 impacts. While impact 

damage located on one side of a sandwich structure should not result in a through-shell leak, 

others locations may be susceptible to leakage from the damage. The CCM pressurization-tofailure test caused three large debonded regions to form in the shoulder-to-ceiling region. With 

the core no longer bonded to the face sheets, a leakage path could be created between any of the 

IML and OML skins in that region. Previously, a leak path could only be created by having 

damage on each end of a honeycomb cell. In addition, the strains that may have occurred in the 

skins during the test as a result of the failure are unknown. 
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Prior to leak testing, six distinct openings had to be sealed: one docking tunnel cover, one main 

entry hatch, two docking windows, and two side windows. The single O-ring hatch seals were

not expected to be sufficient to meet the leak requirements; additional sealing was provided with 

vacuum putty. The putty was placed around the inside of the hatch seals just outside the O-rings. 

Additional putty was placed in gaps around the hatch IML once installed. Figures 7.3-2 through 

7.3-5 show the various stages of the hatch installation.

Figure 7.3-2. Vacuum Sealant Tape (i.e., vacuum putty) Installed on a CCM Hatch Cover on the 

Outside Flange Next to the O-ring 
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Figure 7.3-3. Close-up of the Vacuum Putty Placed Outside the Hatch Cover O-ring

Figure 7.3-4. Positioning the Main Hatch Cover
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Figure 7.3.5. Docking Tunnel Hatch Cover Installation

7.3.2 Vacuum Bag Usage

To measure leak rates across a specific CCM feature, a hybrid leak test method was devised that

involved placing an active vacuum bag on the feature’s external surface and then measuring the

helium migration while the CCM was pressurized. This technique was used to measure leak 

rates on the closed hatch covers and the permanently attached fittings (e.g., six parachute attach 

points and six SM/ALAS fittings). A schematic of the CCM in shown in Figure 7.3-6; each 

detail that was measured with an external vacuum bag is labeled in the figure. 
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Figure 7.3-6. Schematic Illustrating the Features that were Measured Using the Vacuum Bag 

Technique (indicated in red)

Sealing the vacuum bags to the CCM exterior around the complex fittings was more labor 

intensive than initially envisioned. There were strain gages and wires that had to be removed or 

relocated. In addition, the outside surface was scrubbed/lightly abraded with Scotch-BriteTM

pads and abrasive paper to remove paint and resin ridges. Figures 7.3-7 through 7.3-9 show the 

CCM vacuum bag installation. 
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Figure 7.3-7. Example Vacuum Bag Installation 

Figure 7.3-8. Vacuum Bag Installation around an SM/ALAS Fitting

Port for 

leak helium 

leak 

calibration

Port for 

vacuum 

source

Vacuum 

sealant 

tape
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Figure 7.3-9. Installed Hatch Vacuum Bags Attached to a Mass Spectrometer 

The details of the full-scale leak testing can be found in reference 11, with excerpts contained 

herein. All the leak rate tests were conducted in the Marshall Space Flight Center (MSFC) V-20 

vacuum chamber located in Building 4619. The setup is shown in Figure 7.3-10. 
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 Figure 7.3-10. Schematic for Measuring the Total Leak Rate of the CCM

In all cases, helium leak rate measurements were conducted using a mass spectrometer. The

tests were conducted in one of two scenarios: 1) the CCM was at 1 atm while the vacuum 

chamber was evacuated or 2) the CCM was at 2 atm while the chamber was at 1 atm. 

Figure 7.3-11 shows the CCM sitting outside the vacuum chamber. 
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Figure 7.3-11. CCM Outside the V-20 Vacuum Chamber

In the first scenario, the mass spectrometer was connected to the vacuum chamber to measure the 

CCM total leak rate. In the second scenario, feature vacuum bags were evacuated and the 

helium leak rates were measured on each bag. The shell strains were maintained within the

1-atm limit pressure (CCM pressure – vacuum chamber pressure). 

One of the complicated details of the vacuum bag measurements was that the leak rates were 

determined under a pressure differential of 2 atm (shell pressure – vacuum bag 

pressure = 2 atm), rather than the reference pressure differential of 1 atm. Since pressure 

differential directly impacts permeability/leak rates, the raw measurements needed to be scaled 

for comparison to the global measurements that were performed at a differential pressure 

of 1 atm. Many factors affect how the leak rates scale with pressure and include medium 

characteristics, gas properties, absolute pressure, flow behavior, and flow paths. 

Poiseuille's equation for laminar flow of a compressible fluid is often used to scale flow rates

during leak measurements [ref. 12]. Using this equation, the measured leak rates are reduced by 
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25 percent to coincide with the reference pressure condition of 1 atm on the interior and 

0 atm on the exterior. In reference 6, leak rates were measured using nitrogen for an insert 

loaded to failure and were found to vary linearly with pressure. Also in this reference, leakage 

rates for impacted four-ply laminates (CCM minimum-gage skins) with various coatings were

measured with impact damage. The leak rates were reduced by 44 to 60 percent when the 

pressure difference was reduced from 2 to 1 atm. Since Poiseuille's equation provided the most 

conservative estimate of flow reduction, the CCM feature measurements were reduced by 25

percent to the reference pressure differential.

In several instances, a high leak rate guided the NESC team to modify or improve a feature to 

demonstrate understanding of the leakage mechanism and to bring it within compliance at the 

vehicle level. In these instances, measurements were performed before and after the 

modifications to evaluate the modification effectiveness. The following modifications were 

made during testing:

1. Appliqué film installed over the out-of-autoclave splice and the upper eight inserts (fullscale leak test before and after). 

2. Appliqué film installed over the lower eight spools (local leak test before and after).

3. Bolts removed from repair #1 and polysulfide added (local leak test before and after).

4. Full-scale leak test after modifications 1, 2, and 3.

7.3.3 3MTM 5004 Film Application

Any through penetrations are at risk of being a leak source during testing and use. The 

composite structure acreage will have a baseline permeability. The 3MTM 5004 film was 

suggested as a leak barrier. In practice, the 5004 film was easier to install on the CCM acreage, 

less so when applying to/over IML joints/fittings. FiberSIM software was used to aid in film 

placement and sizing. Figure 7.3-12 shows the 3M

TM 5004 film (grey color) applied over inserts 

(spools) embedded in the CCM wall. The upper two rows of inserts were covered with 

5004 film while the bottom three rows were not.
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Figure 7.3-12. 3MTM 5004 Film Application over spools

Figures 7.3-13 through 7.3-17 show the various stages of the manual application of the 3MTM

5004 film. 

3M 5004 film covering inserts 

through the CCM wall

CCM inside surface without film 

application (note uncovered

spools)
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Figure 7.3-13. Technician Starts to Apply the 3MTM 5004 Film around CCM IML Features

Figure 7.3-14. Technician Uses a Plastic Tool to Help Avoid Wrinkles and Bubbles
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Figure 7.3-15. Technician Finalizes 3MTM 5004 Film Application

Figure 7.3-16. Completed 3MTM 5004 Film Application
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Figure 7.3-17. 3MTM 5004 Film Inspection in Docking Tunnel

7.3.4 Full-Scale System Leak Rate Results

Before addressing feature leak rates, a baseline test was conducted to obtain an overall leak rate 

before modifications. After 18 hours under vacuum, the stable leak rate was 0.35 sccs helium,

which was 3.5 times the maximum allowed rate of 0.1 sccs for air. Additional sealant was 

applied to four windows and hatches, and the overall leak test was repeated. The leak rate after 

65 hours was 0.88 sccs helium, which indicated that the additional sealing tape did not improve 

the leakage around these openings. An additional attempt was made to seal the openings 

externally with vacuum bags, but the bags detached turning testing. During this measurement, 

the leak rate was 0.57 sccs helium.

The techniques for sealing vacuum bags around the openings were further developed. To 

measure the leakage rate coming from the openings after the improvements, vacuum bags were 

installed on all the closeouts and connected to a common line. The CCM internal pressure was

increased to 14.7 psig helium, but the chamber was not evacuated. The combined leak rate for 

all of the closeouts was 7e-5 sccs helium. As previously discussed, the local pressure differential 

around the vacuum bags was 2 atm. Consequently, the flow rates were reduced by 25 percent to 

correspond to a 1-atm pressure differential. 

A similar method was used to determine the leakage rate of other CCM features. Bolted repair 
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1 (on lobed bottom) and the through-thickness inserts (spools) had leak rates that were of the 

same magnitude (i.e., 1e-1 sccs) as the overall vehicle requirement. Figure 7.3-18 shows the 

overall CCM leak rate, the insert leak rate, and the bolted repair leak rate on a time line as 

modifications were made to reduce the leak rates. Figure 7.3-18 also illustrates the effect of the 

improvements on the feature and the overall leak rate. Again, the leak rates from the feature 

tests were adjusted for the 2-atm pressure differential. After modification, these features had a 

leak rate that was lowered by at least a factor of 10. However, the rate for the bolted repair

remained higher than the rates for the other bolted fittings, suggesting that this feature was not 

appropriately prepared for managing leakage. With the modifications, the overall leak rate was 

reduced to 1.1e-1 sccs, which is close to the maximum allowable leak rate of 1e-1 sccs.

Figure 7.3-18. History of Leak Rate Measurements for Full-scale CCM and for Individual Features 

(modifications are identified)

As discussed, some local measurements were made multiple times, either to account for 

modifications or to examine repeatability. However, attention was focused on the last 

Constellation 

Leak Rate 

Requirement
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measurement that was made for each feature as this measurement incorporated the best practices 

for vacuum bagging. 

Figure 7.3-19 shows the leak rate for the local features studied with the results adjusted for a 

2-atm pressure differential. Four features are noted as being significant contributors: the bolted 

repairs and SM/ALAS fittings #1 and #2. These features are out-of-family with the other bolted 

fittings and are significant contributors to the overall vehicle leak rate. It is clear from the 

remainder of the fittings that significant improvement in the leak rate of a bolted fitting is 

possible through the adoption of sealing method process improvements. 

Figure 7.3-19. Local Leak Rate versus Feature

The magnitude of the leakage from the composite shell was estimated by subtracting the local 

leak rates, summarized in Figure 7.3-19, from the final global leak rate of 1.1e-1 sccs. The shell 

leak rate is estimated at 8.4e-2 sccs. Figure 7.3-20 shows a pie chart where the global leak rate 

of 1.1e-1 sccs is divided into the contributing leak factors. While this figure shows that the shell 

1.0E-0 7

1.0E-0 6

1.0E-0 5

1.0E-0 4

1.0E-0 3

1.0E-0 2

1.0E-0 1

Leak rate (sccs)

Constellation 

Leak Rate 

Requirement
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is the largest contributor to the overall leak rate, it suggests there may be a discrete leak source 

on the shell (i.e., the scaling of the coupon result suggests that this rate should be much lower). 

Possible sources for discrete leaks are the impact sites from the damage tolerance test 

investigation [ref. 3] that were not covered with appliqué film, the damage created by the test-tofailure, and other undetected regions of damage. 

Figure 7.3-20. Global Leak Rate of 1.1e-1 sccs (separated by contribution)

8.0 Findings and NESC Recommendations

8.1 Findings

The following findings were identified:

F-1. The overall volumetric leak rate of the CCM, measured with helium, was 10 percent 

greater than the CxP system leak rate requirement of 1 kg/day of air. With improved 

process controls while sealing around penetrations, a non-lined pressurized vehicle made 

from composite materials could meet program leakage requirements. 

F-2. The leak test investigation was able to demonstrate at a coupon level that a polymeric 

liner (appliqué film) is capable of mitigating leakage after impact damage. 

F-3. The appliqué film appeared to reduce the leak rate associated with the splice and other 

acreage features such as through inserts, although not enough data were collected to 

establish the statistical significance of this change. 

F-4. Manual application of the appliqué film on large complex or concave surfaces posed 

installation challenges; thus, a brushable or sprayable coating would be preferred from an 
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ease-of-installation perspective. 

F-5. The highest leak rates were associated with through-shell fasteners. However, the bolted 

fitting sealing method utilized was able to get to sufficiently low leak rates utilized per 

fitting, but it was not robust (i.e., similar fittings showed large variability in 

performance). 

F-6. The observed discrepancy in the leak rate estimates using the coupon data and subtracting

the critical feature leak rates from the global leak rate suggests there were significant 

features or defects that did not get quantified during the feature testing. 

8.2 NESC Recommendations

The following NESC recommendations were identified and directed toward the Exploration 

Mission Directorate:

R-1. A brushable or sprayable coating should be pursued as an alternative to the appliqué film 

in applications that involve complex curvatures or other geometric complexities. (F-4)

R-2. Process control techniques and improved designs for leakage should be considered for 

bolted penetrations to reduce variability. (F-5)

9.0 Alternate Viewpoint

There were no alternate viewpoints identified by the NESC team or the NRB quorum during the 

course of this assessment.

10.0 Other Deliverables

No unique hardware, software, or data packages, outside those contained in this report, were

disseminated to other parties outside this assessment.

11.0 Lessons Learned

No applicable lessons learned were identified for entry into the NASA Lessons Learned 

Information System (LLIS) as a result of this assessment.

12.0 Recommendations for NASA Standards and Specifications

No recommendations for NASA standards and specifications were identified as a result of this 

assessment.
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13.0 Definition of Terms 

Corrective Actions Changes to design processes, work instructions, workmanship practices, 

training, inspections, tests, procedures, specifications, drawings, tools, 

equipment, facilities, resources, or material that result in preventing, 

minimizing, or limiting the potential for recurrence of a problem. 

Finding A relevant factual conclusion and/or issue that is within the assessment 

scope and that the team has rigorously based on data from their 

independent analyses, tests, inspections, and/or reviews of technical 

documentation.

Lessons Learned Knowledge, understanding, or conclusive insight gained by experience 

that may benefit other current or future NASA programs and projects. The 

experience may be positive, as in a successful test or mission, or negative, 

as in a mishap or failure.

Observation A noteworthy fact, issue, and/or risk, which may not be directly within the 

assessment scope, but could generate a separate issue or concern if not 

addressed. Alternatively, an observation can be a positive 

acknowledgement of a Center/Program/Project/Organization’s operational 

structure, tools, and/or support provided.

Problem The subject of the independent technical assessment.

Proximate Cause The event(s) that occurred, including any condition(s) that existed 

immediately before the undesired outcome, directly resulted in its 

occurrence and, if eliminated or modified, would have prevented the 

undesired outcome.

Recommendation A proposed measurable stakeholder action directly supported by specific 

Finding(s) and/or Observation(s) that will correct or mitigate an identified 

issue or risk.

Root Cause One of multiple factors (events, conditions, or organizational factors) that 

contributed to or created the proximate cause and subsequent undesired 

outcome and, if eliminated or modified, would have prevented the 

undesired outcome. Typically, multiple root causes contribute to an 

undesired outcome.

Supporting Narrative A paragraph, or section, in an NESC final report that provides the detailed 

explanation of a succinctly worded finding or observation. For example, 

the logical deduction that led to a finding or observation; descriptions of 

assumptions, exceptions, clarifications, and boundary conditions. Avoid 

squeezing all of this information into a finding or observation
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CCM Permeability Characterization

Page #:

38 of 39

NESC Request No.: TI-10-00685

14.0 Acronyms List

ALAS Alternate Launch Abort System

atm atmosphere

C composite

CCM Composite Crew Module

COTS Commercial Orbital Transportation Services

CxP Constellation Program

F film

ft-lb foot-pound

GSFC Goddard Space Flight Center

IML Inner Mold Line

ISS International Space Station

kg kilogram

LaRC Langley Research Center

mmHg millimeters of mercury

MSFC Marshall Space Flight Center

NESC NASA Engineering and Safety Center

NRB NESC Review Board

OML Outer Mold Line

psid pounds per square inch differential

sccs standard cubic centimeters per second

scfm standard cubic feet per minute

SM Service Module

15.0 References

1. “Composite Crew Module: Primary Structure,” NESC-RP-06-019, also referenced as 

NASA/TM–2011-217185, November 2011.

2. “The International Space Station (ISS) to Commercial Orbital Transportation Services 

(COTS) Interface Requirements Document,” Rev. C, SSP 50808, November 2011.

3. “Composite Crew Module: Test,” NESC-RP-06-019, also referenced as NASA/TM–

2011-217190, November 2011.

4. “Composite Crew Module: Nondestructive Evaluation Report,” NESC-RP-06-019, also 

referenced as NASA/TM–2011-217191, November 2011.

5. Tremblay, P.; Savard, M.; Vermette, J.; and Paquin, R.: Gas Permeability, Diffusivity 

and Solubility of Nitrogen, Helium, Methane, Carbon Dioxide and Formaldehyde in 

Dense Polymeric Membranes using a New On-line Permeation Apparatus, Journal of 

Membrane Science, Vol. 282, 2006.
NASA Engineering and Safety Center 

Technical Assessment Report 

Document #:

NESC-RP10-00685

Version:

1.0

Title:

CCM Permeability Characterization

Page #:

39 of 39

NESC Request No.: TI-10-00685

6. “Composite Crew Module: Materials and Process,” NESC-RP-06-019, also referenced 

as NASA/TM–2011-217187, November 2011.

7. Stokes, E. H.: “Hydrogen Permeability of Polymer Based Composites under Bi-axial 

Strain and Cryogenic Temperatures,” AIAA-2004-1858, April 2004.

8. “Constellation Program Environmental Qualification and Acceptance Testing 

Requirements (CEQATR),” Rev C, CxP 70036, October 2009.

9. “Material Specification, Pre-impregnated Carbon Fiber Reinforced Resin Tape And 

Fabric,” Rev. B, CCM-SPEC-001.

10. “Process Requirements For Carbon Fiber Reinforced Epoxy Laminates, 350oF 

Curing,” Rev. B, CCM-SPEC-002.

11. Boeing Final Leak Test Report for NESC CCM, NDT12-00020REP.

12. Nondestructive Testing Handbook, Third Edition: Volume 1, Leak Testing, The 

American Society of Nondestructive Testing, 1997.
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

2. REPORT TYPE 

Technical Memorandum

 4. TITLE AND SUBTITLE

Composite Crew Module (CCM) Permeability Characterization

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Kirsch, Michael T.

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center

Hampton, VA 23681-2199

 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

 8. PERFORMING ORGANIZATION

 REPORT NUMBER

L-20258 NESC-RP-10-00685

10. SPONSOR/MONITOR'S ACRONYM(S)

NASA

13. SUPPLEMENTARY NOTES

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category 16-Space Transportation and Safety

Availability: NASA CASI (443) 757-5802

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email: help@sti.nasa.gov)

14. ABSTRACT

In January 2007, the NASA Administrator chartered the NASA Engineering and Safety Center (NESC) to form an Agency 

team to design and build a composite crew module in 18 months in order to gain hands-on experience in anticipation that 

future exploration systems may be made of composite materials. One of the conclusions from this Composite Crew Module 

Primary Structure assessment was that there was a lack of understanding regarding the ability for composite pressure shells to 

contain consumable gases, which posed a technical risk relative to the use of a metallic design. After the completion of the 

Composite Crew Module test program, the test article was used in a new program to assess the overall leakage/permeability 

and identify specific features associated with high leak rates. This document contains the outcome of the leakage assessment.

15. SUBJECT TERMS

Composite Crew Module; NASA Engineering and Safety Center; Service Module; Alternate Launch Abort System; 

International Space Station

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December 2010 - March 2013

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869021.05.07.07.29

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NASA/TM-2013-217990

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