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DESIGN AND MANUFACTURE OF A COMPOSITE OVERWRAPPEDPRESSURANT TANK ASSEMBLY

Walter H Tam and Paul S GriffinPressure Systems Inc

and

Arthur C JacksonJackson Consulting

ABSTRACT

A titanium-lined composite overwrappedpressure vessel (COPV) for helium pressurantstorage was designed for a commercial

spacecraft This tank has a nominal propellantvolume of 814 liters (4967 cubic inches) and anominal weight of 117 kg (258 pounds) Themaximum expected operating pressure is 331bar (4800 psi) Proof pressure requirement is414 bar (6000 psi) and the minimum burstpressure is 497 bar (7200 psi)

The pressurant tank design is based on a flight-qualified pressurant tank to take advantage of its design and flight heritage To minimize riskthe pressurant tank is designed to use onlyexisting manufacturing technology processes

and procedures Manufacturing cost isminimized by using existing tooling to the fullestextent

Nonlinear material and geometric modelingtechniques were used to analyze this tankStress analysis showed positive margins of safety for pressure cycle fatigue vibrationfatigue and minimum burst pressure over thedesign requirements Qualification testingverified the design margins and showed thedesign analyses to be conservative

The liner is constructed from commercially puretitanium This material was chosen due to

heritage and for its superb manufacturabilityrelative high strength excellent corrosion andoxidation resistance characteristics good lowand high cycle fatigue characteristics andcompetitive manufacturing cost

The overwrap consists of high strength ToraycaT1000G carbon fiber and Epon 826 cured resinsystem Several composite layers are appliedincluding helical and hoop wraps

A complete qualification program wasconducted to verify the tank design including adestructive burst pressure test The tanksuccessfully completed qualification testing on03 April 2002 The production program is inprogress Over 10 flight tanks have beenmanufactured to date

INTRODUCTION

A Helium pressurant storage pressure vesselwith unique characteristics is needed for acommercial spacecraft This tank must be highperformance light-weight and designed towithstand severe operational loads Additionally this tank must be built with existingtechnology to minimize manufacturing cost andprogram risk A titanium-lined carbon fiber overwrapped tank was designed andmanufactured to meet such a need A sketch

of this tank is shown in Figure 1

Copyright 983209 2002 by Pressure Systems Inc Publishedby American Institute of Aeronautics amp Astronautics withpermission

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This tank was also designed to withstand shockand vibration loads All design requirementswere verified by either analysis or qualificationtesting

DESIGN HERITAGE

PSI has designed three titanium lined COPVrsquosthat were similar in design and construction ndashone a high-pressure helium tank

1 the second a

high-pressure conical Xenon tank2

and thethird a high-pressure cylindrical Xenon tank

3

All three tanks are titanium lined and T1000carbon fiber overwrapped Additionally thehelium tank of reference 1 was redesigned toeliminate the two end fitting-to-dome welds Todate dozens of these COPVs have beendelivered The new pressurant tank draws itsheritage from all these programs Themanufacturing technology established by theseprograms has matured and this new pressuranttank program did not attempt to establish anynew technology The focus of the tank designwas mainly to minimize cost and risk

To maximize design and flight heritage thedesign of the new pressurant tank blind andported heads are nearly identical to theprevious blind and ported heads of the heliumpressurant tank including the mountingfeatures See Figure 2 Additionally both liner center sections have the same wall thickness

and have identical method of construction Acomparison of the two tanks is provided inTable 2

The liner material is CP titanium identical tothe previous COPV helium pressurant tankThe selection of CP titanium was made tomaintain heritage The filament wrap remainsthe same T1000 carbon fiber

DESIGN ANALYSES

The basic approach in designing the pressurant

tank was to maximize heritage by maintainingas many design features from the previouspressurant tank as possible while enhancingthe manufacturability of the liner and overwrapTo minimize risk only existing manufacturingtechnology was used

Figure 2 Design Heritage of the Pressurant Tank

Table 2 Comparison of the Two Cylindrical Pressurant Tanks

Previous He Tank New He Tank

Dimension 41 cm dia x 66 cm long 42 cm dia x 74 cm long

MEOP 310 bar (4500 psi) 331 bar (4800 psi)

Volume MEOP 673 liter (4105 in3) 814 liter (4967 in3)

Actual burst 546 bar (7919 psig) 572 bar (8297 psig)

Weight of qual tank 101 kg (2232 lb) 117 kg (2573 lb)

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Several analyses were conducted to designand analyze the pressurant tank including

bull Finite element analysis to conduct the liner material study

bull Nonlinear axisymmetric analysis to design

the pressurant tank ported and blind headsFigure 3 shows the ported head as modeledby the analysis The blind head is similarlyanalyzed

Figure 3 Nonlinear AxisymmetricFinite Element Models

bull Three-dimensional finite element model for the modal analysis The analysis isconducted to predict the natural frequenciesof the pressurant tank The actualfrequency of the tank is determined at

vibration test Figure 4a shows the first axialmode and Figure 4b shows the first lateralmode

Figure 4a First Axial Mode

Figure 4b First Lateral Mode

bull Random vibration analysis to determinestress and fatigue effects of randomvibration on the vessel See Figure 5a and5b For conservatism only the qualificationlevel power spectral density was analyzed

bull Shock analysis to determine stressresponses due to shock See Figure 6 Thesame finite element model for the modalanalysis is used on the shock analysis

bull Fatigue analysis to determine the cumulativedamage factor due to fatigue The fatiguelife requirements for the pressurant tank

liner consists of 1 sizing (autofrettage) cycleand 4 design service lifetimes includingproof pressure cycles and operatingpressure cycles

LINER DESIGN AND FABRICATION

To maintain heritage this pressurant tank wasdesigned to have the same CP titanium liner asthe previous pressurant tank Typical of mostCOPVrsquos the composite overwrap for thepressure vessel is designed to provide most of the strength for the tank The liner is a low

load-bearing part of the tank shell that servesas a container to carry the helium pressurantand provides a defined shape to apply thefilament overwrap To minimize weight the liner wall is kept as thin as practical whilemaintaining manufacturability However thedesign of the liner also takes into account thehigh vibration and shock loads during launchThe high strength low weight CP titanium isideal for this application

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Figure 5a Vibration Analysis Lateral Random Stress Response of Liner

Figure 5b Vibration Analysis Axial Random Stress Response of Liner

Figure 6 Liner Shock Response Axial and lateral

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Other factors that contribute to the selection of titanium include

l Good corrosion and oxidation resistancel Not susceptible to pitting and stress

corrosion

l High strength-to-weight ratiol Good galvanic compatibility with carbon

fiberl Good low cycle fatigue performancel Good high cycle fatigue performancel Good manufacturabilityl Good weld propertiesl Good performance characteristics

The pressurant tank liner is a four-piececonstruction that consists of two heads acylinder and an outlet tube The threecomponents of the liner body are shown in

Figure 7 This simplified approach minimizedthe number of components to handle andassemble

Figure 7 Components of thePressurant Tank Liner

The pressurant tank liner was designed tomirror the construction of the previouspressurant tank liner Although it has a slightlylarger diameter a forging was designed suchthat all four heads from these two tanks can bemachined from the same forging configurationThe forging is made from CP 70 titanium barFigure 8 below shows a liner head beingmachined

Figure 8 Machining of a Liner Head

The outlet tube is made from 953 mm (0375inch) outside diameter tubing The center section is fabricated from 05 mm (0020 inch)

thick CP-3 titanium sheet rolled formed andwelded into a cylinder with one longitudinalseam weld This cylinder is manufacturedusing the same manufacturing technique as theprevious helium pressurant tank center section

The liner is assembled with two girth welds anda tube assembly weld using the same weldtechnique and weld schedule as the previoushelium pressurant tank Each weld isradiographic and penetrant inspected for acceptance The completed liner is leak testedprior to the filament wrap operation Acompleted liner is shown in Figure 9

Figure 9 A Completed PressurantTank Liner

Outlet tube

Cylinder

Blind head

Ported head

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Page 7

COMPOSITE OVERWRAP DESIGN ANDFABRICATION

The pressurant tank composite overwrapcontains several layers of high angle helicaland hoop wraps The same wet filamentwinding technique used on the previouspressurant tank is applied to this pressuranttank This process utilizes dry fiber roving thatis in-process impregnated with a low-viscosityresin The materials used in the compositeoverwrap include Torayca T-1000G highperformance carbon fiber and EPON 826 epoxyresin system The basic resin system hasyears of commercial heritage and offersexcellent characteristics including lowviscosity reasonable pot life high strain-to-failure capability good chemical and moistureresistance and low toxicity Thousands of COPVrsquos have been wrapped using this resin

system

The resin system has a 107degC (225degF) curetemperature The glass transition temperature

(Tg) of the cured system is 99degC (210degF)providing a comfortable margin over the tankrsquos

maximum operating temperature of 60degC

(140degF)

A computer-controlled filament windingmachine is used to perform the compositeoverwrap operation See Figure 10 Acomputer code was generated to wrap the

pressurant tank The entire wrap process wasautomated to insure quality and repeatability

Figure 10 Automated Filament Winding

The filament wrap is bonded to the liner by athin layer of adhesive This adhesive is appliedto the liner immediately prior to the filamentwrap operation After filament wrap the vesselis placed in an oven and the resin is gelled andcured

WEIGHT DISTRIBUTION

The pressurant tank weight distribution issummarized in Table 3 below

Table 3 Pressurant Tank WeightDistribution

Item NominalWeight (kg)

NominalWeight (lbm)

Liner 37 81

Composite 80 177

TOTAL 117 258

The qualification tank was slightly above thenominal weight However most flight tanksfabricated were slightly below nominal weight

TANK GROWTH

The pressurant tank undergoes expansion as itis being pressurized The tank expansion datafor the Qualification tank is summarized in

Table 4 The measured tank growth closelymatches the predicted values

TANK SIZING

The pressurant tank is subjected to a sizingoperation (autofrettage) after the tank iswrapped and the resin system is cured Theautofrettage pressure is selected during tankanalysis This pressurization cycle isconsidered part of the manufacturing processand is not included in the pressure cyclehistory Autofrettage is performed immediately

prior to acceptance proof pressure testing

Table 4 Pressurant Tank Growth Data

Pressure Linear Growth Radial Growth Volume Growth

MEOP (331 bar4800 psi) 96 mm 0376 inch 20 mm 0078 inch 31 liters (1914 in3)

Proof Pressure (414 bar6000 psi) 108 mm 0427 inch 24 mm 0093 inch 40 liters (2441 in3)

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Page 8

QUALIFICATION TEST PROGRAM

A Qualification Tank was fabricated for thequalification test program The qualificationtesting consists of a series of tests intended toverify the pressurant tank design in thefollowing areas

l Physical properties such as volume andweight

l Tank shell integrityl Low cycle fatiguel High cycle fatiguel Shock fatiguel Burst margin

PassFail criteria consisted of acceptance typeexternal leak tests conducted at intervalsthroughout the test program After the tankpassed the final external leak test it underwent

a destructive burst pressure test Thesuccessful burst certified the tank for flight use

The Qualification Tank was subjected to thefollowing qualification tests

l Volumetric capacityl Proof pressure testl Volumetric capacity at ambientl Volumetric capacity at MEOPl Pressure cyclesl External leakagel Pressurized pyrotechnic shock

l External leakagel Sinusoidal and random vibrationl External leakagel Final examinationl Destructive burst pressure test

Volumetric Capacity Examination Thevolumetric capacity of the pressurant tank wasmeasured using the weight of water method atambient condition Deionized (DI) water wasused to conduct this test The tank volumesbefore and after the proof pressure test weremeasured to verify that the tank volume met the

specification requirement and that the proof pressure test did not significantly change thetank volume As an example the internalvolume of the Qualification Tank did notincrease after the proof pressure test signifyingthat the pressurant tank was manufacturedsuccessfully

Proof Pressure Test The hydrostatic proof pressure test was conducted at 414 bar (6000psig) for a pressure hold period of 5 minutesSuccessful completion of the proof pressuretest and the subsequent volumetric growth andleakage verification indicated that the tank wasmanufactured successfully

Pressure Cycles The pressurant tank isdesigned to accommodate a minimum of 8proof pressure cycles and 50 operatingpressure cycles As a practice severaloperating pressure cycles were added for contingency A total of 8 proof cycles and 52MEOP cycles were conducted at this pressurecycle testing Additionally the QualificationTank experienced another operating pressurecycle during shock test 3 operating pressurecycles for the 3 external leakage tests and 5more operating pressure cycles during vibration

testing The cumulative total of operatingpressure cycles is 61 or 11 cycles over theminimum requirement A picture of thepressure test setup is shown in Figure 11

Figure 11 Pressure Test Setup

External Leak Test The external leak testverifies the integrity of the tank shell and alsoserves to validate the previous series of pressure testing The tank is placed in a

vacuum chamber which is evacuated to under 02 microns of mercury and helium pressurizedto MEOP for 30 minutes The helium leak ratecannot exceed 1 x 10

-6 std cc per second after

a 30-minute stabilization period For examplethe leak rate of the Qualification Tank was 23 x10

-8 sccsec

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Page 9

During pressurization the compressed gasheats up thus heating up the tank To preventoverheating four thermocouples are attachedto the tank shell to monitor and control thepressurization rate and the tank temperatureduring pressurization The tank temperature

cannot exceed 140degF throughout the duration

of the test

Pressurized Pyrotechnic Shock TestPyrotechnic shock testing was performed onthe Qualification Tank Prior to testing apathfinder tank was mounted to the test fixturefor equalization of the shock system and todemonstrate the achievable level of input shockresponse spectrum The Qualification Tankwas then installed in the fixture and pressurizedto 4800 psig The test consisted of subjectingthe tank loaded with 4800 psig of gaseoushelium to two metal-to-metal impact shock

impulses The impulses had an input shockresponse spectrum of 7000g Both thelongitudinal axis (X axis) and the lateral axis (Zaxis) were excited simultaneously by the twoqualification level metal-to-metal impact shockimpulses The shock spectrum is presented inTable 5 A picture of the shock test setup isshown in Figure 12

Figure 12 Shock Test Setup

Vibration Test Sinusoidal and RandomQualification level sinusoidal and random

vibration tests were performed on theQualification Tank in each of the three principalaxes The vibration test requirements areshown in Tables 6 and 7

The vibration test fixture is designed to simulatethe tank-to-spacecraft installation interfacesand orientation It is also sufficiently stiff to be

considered rigid for the test frequencies Apreliminary test fixture evaluation wasconducted prior to Qualification Tankinstallation to insure the fixture meets thetesting requirements

Control accelerometers were placed on the

vibration test fixture near each end fitting tocontrol the vibration input Responseaccelerometers were placed on theQualification Tank to measure the tankresponses The placements of the responseaccelerometers were selected to record thetank responses at locations of maximum stressas predicted in the analytical model

The vibration test included fixture survey fulllevel sinusoidal and full level random runs Thesame tests were conducted in all three axes All testing was conducted with the tank

pressurized to 4800 psi with helium Aphotograph of the vibration test setup is shownin Figure 13

Figure 13 Pressurant Tank QualificationVibration Test Setup

Destructive Burst After the completion of thepressure cycles shock and vibration testingthe Qualification Tank was subjected to a finaldestructive burst pressure test TheQualification Tank burst at 572 bar (8297 psi)

providing a 152 margin on burst pressureThis data represents a burst factor of 173 to 1and a performance efficiency rating (Pressure xVolume Weight) of 157 x 10

6 inches This

high efficiency factor represents the mostefficient pressure vessel ever designed by PSIFigure 14 shows the Qualification Tank after burst

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Page 10

Figure 14 Qualification Tank After Qualification Burst Pressure Test

Table 5 Shock Test Spectrum

Axes Frequency (Hz) Shock response

spectrum input (g)

100 80 plusmn 6 dB

1500 7000 plusmn 6 dB

3000 7000 plusmn 6 dB

6000 7000 + 9 dB -6 dB

Longitudinal and one

lateral axis

10000 7000 + 9 dB -6 dB

Shock response spectrum based on Q=10

Table 6 Qualification Level Sinusoidal Vibration Test Environment

Axes Frequency (Hz) Input Level (G) Sweep Rate

X Y and Z 5 - 24

24 - 65

65 - 100

05 in DA

15

7

2 octmin

Table 7 Qualification Level Random Vibration Test Environment

Axes Frequency

(Hz)

PSD Input

Level

Overall Level

(Grms)

Duration

(sec)

X Y and Z 20 ndash 100

100 ndash 1000

1000 - 2000

+3 dBoct

02 g2Hz

-3 dBoct

181 120

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Page 11

Qualification Tank Pressure Log Insummary the Qualification Tank hasundergone the pressure cycles listed in Table8 The successful completion of thequalification test program is an excellentdemonstration of the tankrsquos robust design

ACCEPTANCE TESTING

The following acceptance tests are performedon a flight tank prior to delivery

l Preliminary examinationl Pre-proof volumetric capacityl Ambient proof pressurel Post-proof volumetric capacityl Volumetric capacity at MEOPl External leakagel Weld quality inspectionl Final examinationl

Cleanliness measurement

Cleanliness Verification After the finalexternal leak test each flight tank is cleaned tothe cleanliness level specified in Table 9

Table 9 Pressurant Tank CleanlinessLevel

Particle Size Range(Microns)

Maximum Allowedper 100 ml

5 to 10 140

11 to 25 2026 to 50 5

51 to 100 1

Over 100 0

Photograph of a completed tank is shown inFigure 15

Figure 15 A completed PressurantTank

Table 8 Summary of Qualification Tank Pressure Cycles

Pressure Actual of Cycles

RequiredCycles

Description

331 bar (4800 psig)Operating pressure 61 50 52 operating cycles3 external leaks1 shock test5 pressurization cycles during vibration testing

414 bar (6000 psig)Proof pressure

8 8 1 proof test7 proof cycles

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CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

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NOTES

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This tank was also designed to withstand shockand vibration loads All design requirementswere verified by either analysis or qualificationtesting

DESIGN HERITAGE

PSI has designed three titanium lined COPVrsquosthat were similar in design and construction ndashone a high-pressure helium tank

1 the second a

high-pressure conical Xenon tank2

and thethird a high-pressure cylindrical Xenon tank

3

All three tanks are titanium lined and T1000carbon fiber overwrapped Additionally thehelium tank of reference 1 was redesigned toeliminate the two end fitting-to-dome welds Todate dozens of these COPVs have beendelivered The new pressurant tank draws itsheritage from all these programs Themanufacturing technology established by theseprograms has matured and this new pressuranttank program did not attempt to establish anynew technology The focus of the tank designwas mainly to minimize cost and risk

To maximize design and flight heritage thedesign of the new pressurant tank blind andported heads are nearly identical to theprevious blind and ported heads of the heliumpressurant tank including the mountingfeatures See Figure 2 Additionally both liner center sections have the same wall thickness

and have identical method of construction Acomparison of the two tanks is provided inTable 2

The liner material is CP titanium identical tothe previous COPV helium pressurant tankThe selection of CP titanium was made tomaintain heritage The filament wrap remainsthe same T1000 carbon fiber

DESIGN ANALYSES

The basic approach in designing the pressurant

tank was to maximize heritage by maintainingas many design features from the previouspressurant tank as possible while enhancingthe manufacturability of the liner and overwrapTo minimize risk only existing manufacturingtechnology was used

Figure 2 Design Heritage of the Pressurant Tank

Table 2 Comparison of the Two Cylindrical Pressurant Tanks

Previous He Tank New He Tank

Dimension 41 cm dia x 66 cm long 42 cm dia x 74 cm long

MEOP 310 bar (4500 psi) 331 bar (4800 psi)

Volume MEOP 673 liter (4105 in3) 814 liter (4967 in3)

Actual burst 546 bar (7919 psig) 572 bar (8297 psig)

Weight of qual tank 101 kg (2232 lb) 117 kg (2573 lb)

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Page 4

Several analyses were conducted to designand analyze the pressurant tank including

bull Finite element analysis to conduct the liner material study

bull Nonlinear axisymmetric analysis to design

the pressurant tank ported and blind headsFigure 3 shows the ported head as modeledby the analysis The blind head is similarlyanalyzed

Figure 3 Nonlinear AxisymmetricFinite Element Models

bull Three-dimensional finite element model for the modal analysis The analysis isconducted to predict the natural frequenciesof the pressurant tank The actualfrequency of the tank is determined at

vibration test Figure 4a shows the first axialmode and Figure 4b shows the first lateralmode

Figure 4a First Axial Mode

Figure 4b First Lateral Mode

bull Random vibration analysis to determinestress and fatigue effects of randomvibration on the vessel See Figure 5a and5b For conservatism only the qualificationlevel power spectral density was analyzed

bull Shock analysis to determine stressresponses due to shock See Figure 6 Thesame finite element model for the modalanalysis is used on the shock analysis

bull Fatigue analysis to determine the cumulativedamage factor due to fatigue The fatiguelife requirements for the pressurant tank

liner consists of 1 sizing (autofrettage) cycleand 4 design service lifetimes includingproof pressure cycles and operatingpressure cycles

LINER DESIGN AND FABRICATION

To maintain heritage this pressurant tank wasdesigned to have the same CP titanium liner asthe previous pressurant tank Typical of mostCOPVrsquos the composite overwrap for thepressure vessel is designed to provide most of the strength for the tank The liner is a low

load-bearing part of the tank shell that servesas a container to carry the helium pressurantand provides a defined shape to apply thefilament overwrap To minimize weight the liner wall is kept as thin as practical whilemaintaining manufacturability However thedesign of the liner also takes into account thehigh vibration and shock loads during launchThe high strength low weight CP titanium isideal for this application

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Page 5

Figure 5a Vibration Analysis Lateral Random Stress Response of Liner

Figure 5b Vibration Analysis Axial Random Stress Response of Liner

Figure 6 Liner Shock Response Axial and lateral

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Page 6

Other factors that contribute to the selection of titanium include

l Good corrosion and oxidation resistancel Not susceptible to pitting and stress

corrosion

l High strength-to-weight ratiol Good galvanic compatibility with carbon

fiberl Good low cycle fatigue performancel Good high cycle fatigue performancel Good manufacturabilityl Good weld propertiesl Good performance characteristics

The pressurant tank liner is a four-piececonstruction that consists of two heads acylinder and an outlet tube The threecomponents of the liner body are shown in

Figure 7 This simplified approach minimizedthe number of components to handle andassemble

Figure 7 Components of thePressurant Tank Liner

The pressurant tank liner was designed tomirror the construction of the previouspressurant tank liner Although it has a slightlylarger diameter a forging was designed suchthat all four heads from these two tanks can bemachined from the same forging configurationThe forging is made from CP 70 titanium barFigure 8 below shows a liner head beingmachined

Figure 8 Machining of a Liner Head

The outlet tube is made from 953 mm (0375inch) outside diameter tubing The center section is fabricated from 05 mm (0020 inch)

thick CP-3 titanium sheet rolled formed andwelded into a cylinder with one longitudinalseam weld This cylinder is manufacturedusing the same manufacturing technique as theprevious helium pressurant tank center section

The liner is assembled with two girth welds anda tube assembly weld using the same weldtechnique and weld schedule as the previoushelium pressurant tank Each weld isradiographic and penetrant inspected for acceptance The completed liner is leak testedprior to the filament wrap operation Acompleted liner is shown in Figure 9

Figure 9 A Completed PressurantTank Liner

Outlet tube

Cylinder

Blind head

Ported head

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Page 7

COMPOSITE OVERWRAP DESIGN ANDFABRICATION

The pressurant tank composite overwrapcontains several layers of high angle helicaland hoop wraps The same wet filamentwinding technique used on the previouspressurant tank is applied to this pressuranttank This process utilizes dry fiber roving thatis in-process impregnated with a low-viscosityresin The materials used in the compositeoverwrap include Torayca T-1000G highperformance carbon fiber and EPON 826 epoxyresin system The basic resin system hasyears of commercial heritage and offersexcellent characteristics including lowviscosity reasonable pot life high strain-to-failure capability good chemical and moistureresistance and low toxicity Thousands of COPVrsquos have been wrapped using this resin

system

The resin system has a 107degC (225degF) curetemperature The glass transition temperature

(Tg) of the cured system is 99degC (210degF)providing a comfortable margin over the tankrsquos

maximum operating temperature of 60degC

(140degF)

A computer-controlled filament windingmachine is used to perform the compositeoverwrap operation See Figure 10 Acomputer code was generated to wrap the

pressurant tank The entire wrap process wasautomated to insure quality and repeatability

Figure 10 Automated Filament Winding

The filament wrap is bonded to the liner by athin layer of adhesive This adhesive is appliedto the liner immediately prior to the filamentwrap operation After filament wrap the vesselis placed in an oven and the resin is gelled andcured

WEIGHT DISTRIBUTION

The pressurant tank weight distribution issummarized in Table 3 below

Table 3 Pressurant Tank WeightDistribution

Item NominalWeight (kg)

NominalWeight (lbm)

Liner 37 81

Composite 80 177

TOTAL 117 258

The qualification tank was slightly above thenominal weight However most flight tanksfabricated were slightly below nominal weight

TANK GROWTH

The pressurant tank undergoes expansion as itis being pressurized The tank expansion datafor the Qualification tank is summarized in

Table 4 The measured tank growth closelymatches the predicted values

TANK SIZING

The pressurant tank is subjected to a sizingoperation (autofrettage) after the tank iswrapped and the resin system is cured Theautofrettage pressure is selected during tankanalysis This pressurization cycle isconsidered part of the manufacturing processand is not included in the pressure cyclehistory Autofrettage is performed immediately

prior to acceptance proof pressure testing

Table 4 Pressurant Tank Growth Data

Pressure Linear Growth Radial Growth Volume Growth

MEOP (331 bar4800 psi) 96 mm 0376 inch 20 mm 0078 inch 31 liters (1914 in3)

Proof Pressure (414 bar6000 psi) 108 mm 0427 inch 24 mm 0093 inch 40 liters (2441 in3)

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Page 8

QUALIFICATION TEST PROGRAM

A Qualification Tank was fabricated for thequalification test program The qualificationtesting consists of a series of tests intended toverify the pressurant tank design in thefollowing areas

l Physical properties such as volume andweight

l Tank shell integrityl Low cycle fatiguel High cycle fatiguel Shock fatiguel Burst margin

PassFail criteria consisted of acceptance typeexternal leak tests conducted at intervalsthroughout the test program After the tankpassed the final external leak test it underwent

a destructive burst pressure test Thesuccessful burst certified the tank for flight use

The Qualification Tank was subjected to thefollowing qualification tests

l Volumetric capacityl Proof pressure testl Volumetric capacity at ambientl Volumetric capacity at MEOPl Pressure cyclesl External leakagel Pressurized pyrotechnic shock

l External leakagel Sinusoidal and random vibrationl External leakagel Final examinationl Destructive burst pressure test

Volumetric Capacity Examination Thevolumetric capacity of the pressurant tank wasmeasured using the weight of water method atambient condition Deionized (DI) water wasused to conduct this test The tank volumesbefore and after the proof pressure test weremeasured to verify that the tank volume met the

specification requirement and that the proof pressure test did not significantly change thetank volume As an example the internalvolume of the Qualification Tank did notincrease after the proof pressure test signifyingthat the pressurant tank was manufacturedsuccessfully

Proof Pressure Test The hydrostatic proof pressure test was conducted at 414 bar (6000psig) for a pressure hold period of 5 minutesSuccessful completion of the proof pressuretest and the subsequent volumetric growth andleakage verification indicated that the tank wasmanufactured successfully

Pressure Cycles The pressurant tank isdesigned to accommodate a minimum of 8proof pressure cycles and 50 operatingpressure cycles As a practice severaloperating pressure cycles were added for contingency A total of 8 proof cycles and 52MEOP cycles were conducted at this pressurecycle testing Additionally the QualificationTank experienced another operating pressurecycle during shock test 3 operating pressurecycles for the 3 external leakage tests and 5more operating pressure cycles during vibration

testing The cumulative total of operatingpressure cycles is 61 or 11 cycles over theminimum requirement A picture of thepressure test setup is shown in Figure 11

Figure 11 Pressure Test Setup

External Leak Test The external leak testverifies the integrity of the tank shell and alsoserves to validate the previous series of pressure testing The tank is placed in a

vacuum chamber which is evacuated to under 02 microns of mercury and helium pressurizedto MEOP for 30 minutes The helium leak ratecannot exceed 1 x 10

-6 std cc per second after

a 30-minute stabilization period For examplethe leak rate of the Qualification Tank was 23 x10

-8 sccsec

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AIAA 2002-4349

Page 9

During pressurization the compressed gasheats up thus heating up the tank To preventoverheating four thermocouples are attachedto the tank shell to monitor and control thepressurization rate and the tank temperatureduring pressurization The tank temperature

cannot exceed 140degF throughout the duration

of the test

Pressurized Pyrotechnic Shock TestPyrotechnic shock testing was performed onthe Qualification Tank Prior to testing apathfinder tank was mounted to the test fixturefor equalization of the shock system and todemonstrate the achievable level of input shockresponse spectrum The Qualification Tankwas then installed in the fixture and pressurizedto 4800 psig The test consisted of subjectingthe tank loaded with 4800 psig of gaseoushelium to two metal-to-metal impact shock

impulses The impulses had an input shockresponse spectrum of 7000g Both thelongitudinal axis (X axis) and the lateral axis (Zaxis) were excited simultaneously by the twoqualification level metal-to-metal impact shockimpulses The shock spectrum is presented inTable 5 A picture of the shock test setup isshown in Figure 12

Figure 12 Shock Test Setup

Vibration Test Sinusoidal and RandomQualification level sinusoidal and random

vibration tests were performed on theQualification Tank in each of the three principalaxes The vibration test requirements areshown in Tables 6 and 7

The vibration test fixture is designed to simulatethe tank-to-spacecraft installation interfacesand orientation It is also sufficiently stiff to be

considered rigid for the test frequencies Apreliminary test fixture evaluation wasconducted prior to Qualification Tankinstallation to insure the fixture meets thetesting requirements

Control accelerometers were placed on the

vibration test fixture near each end fitting tocontrol the vibration input Responseaccelerometers were placed on theQualification Tank to measure the tankresponses The placements of the responseaccelerometers were selected to record thetank responses at locations of maximum stressas predicted in the analytical model

The vibration test included fixture survey fulllevel sinusoidal and full level random runs Thesame tests were conducted in all three axes All testing was conducted with the tank

pressurized to 4800 psi with helium Aphotograph of the vibration test setup is shownin Figure 13

Figure 13 Pressurant Tank QualificationVibration Test Setup

Destructive Burst After the completion of thepressure cycles shock and vibration testingthe Qualification Tank was subjected to a finaldestructive burst pressure test TheQualification Tank burst at 572 bar (8297 psi)

providing a 152 margin on burst pressureThis data represents a burst factor of 173 to 1and a performance efficiency rating (Pressure xVolume Weight) of 157 x 10

6 inches This

high efficiency factor represents the mostefficient pressure vessel ever designed by PSIFigure 14 shows the Qualification Tank after burst

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Page 10

Figure 14 Qualification Tank After Qualification Burst Pressure Test

Table 5 Shock Test Spectrum

Axes Frequency (Hz) Shock response

spectrum input (g)

100 80 plusmn 6 dB

1500 7000 plusmn 6 dB

3000 7000 plusmn 6 dB

6000 7000 + 9 dB -6 dB

Longitudinal and one

lateral axis

10000 7000 + 9 dB -6 dB

Shock response spectrum based on Q=10

Table 6 Qualification Level Sinusoidal Vibration Test Environment

Axes Frequency (Hz) Input Level (G) Sweep Rate

X Y and Z 5 - 24

24 - 65

65 - 100

05 in DA

15

7

2 octmin

Table 7 Qualification Level Random Vibration Test Environment

Axes Frequency

(Hz)

PSD Input

Level

Overall Level

(Grms)

Duration

(sec)

X Y and Z 20 ndash 100

100 ndash 1000

1000 - 2000

+3 dBoct

02 g2Hz

-3 dBoct

181 120

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Page 11

Qualification Tank Pressure Log Insummary the Qualification Tank hasundergone the pressure cycles listed in Table8 The successful completion of thequalification test program is an excellentdemonstration of the tankrsquos robust design

ACCEPTANCE TESTING

The following acceptance tests are performedon a flight tank prior to delivery

l Preliminary examinationl Pre-proof volumetric capacityl Ambient proof pressurel Post-proof volumetric capacityl Volumetric capacity at MEOPl External leakagel Weld quality inspectionl Final examinationl

Cleanliness measurement

Cleanliness Verification After the finalexternal leak test each flight tank is cleaned tothe cleanliness level specified in Table 9

Table 9 Pressurant Tank CleanlinessLevel

Particle Size Range(Microns)

Maximum Allowedper 100 ml

5 to 10 140

11 to 25 2026 to 50 5

51 to 100 1

Over 100 0

Photograph of a completed tank is shown inFigure 15

Figure 15 A completed PressurantTank

Table 8 Summary of Qualification Tank Pressure Cycles

Pressure Actual of Cycles

RequiredCycles

Description

331 bar (4800 psig)Operating pressure 61 50 52 operating cycles3 external leaks1 shock test5 pressurization cycles during vibration testing

414 bar (6000 psig)Proof pressure

8 8 1 proof test7 proof cycles

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Page 12

CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

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AIAA 2002-4349

Page 13

NOTES

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AIAA 2002-4349

Page 3

This tank was also designed to withstand shockand vibration loads All design requirementswere verified by either analysis or qualificationtesting

DESIGN HERITAGE

PSI has designed three titanium lined COPVrsquosthat were similar in design and construction ndashone a high-pressure helium tank

1 the second a

high-pressure conical Xenon tank2

and thethird a high-pressure cylindrical Xenon tank

3

All three tanks are titanium lined and T1000carbon fiber overwrapped Additionally thehelium tank of reference 1 was redesigned toeliminate the two end fitting-to-dome welds Todate dozens of these COPVs have beendelivered The new pressurant tank draws itsheritage from all these programs Themanufacturing technology established by theseprograms has matured and this new pressuranttank program did not attempt to establish anynew technology The focus of the tank designwas mainly to minimize cost and risk

To maximize design and flight heritage thedesign of the new pressurant tank blind andported heads are nearly identical to theprevious blind and ported heads of the heliumpressurant tank including the mountingfeatures See Figure 2 Additionally both liner center sections have the same wall thickness

and have identical method of construction Acomparison of the two tanks is provided inTable 2

The liner material is CP titanium identical tothe previous COPV helium pressurant tankThe selection of CP titanium was made tomaintain heritage The filament wrap remainsthe same T1000 carbon fiber

DESIGN ANALYSES

The basic approach in designing the pressurant

tank was to maximize heritage by maintainingas many design features from the previouspressurant tank as possible while enhancingthe manufacturability of the liner and overwrapTo minimize risk only existing manufacturingtechnology was used

Figure 2 Design Heritage of the Pressurant Tank

Table 2 Comparison of the Two Cylindrical Pressurant Tanks

Previous He Tank New He Tank

Dimension 41 cm dia x 66 cm long 42 cm dia x 74 cm long

MEOP 310 bar (4500 psi) 331 bar (4800 psi)

Volume MEOP 673 liter (4105 in3) 814 liter (4967 in3)

Actual burst 546 bar (7919 psig) 572 bar (8297 psig)

Weight of qual tank 101 kg (2232 lb) 117 kg (2573 lb)

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Page 4

Several analyses were conducted to designand analyze the pressurant tank including

bull Finite element analysis to conduct the liner material study

bull Nonlinear axisymmetric analysis to design

the pressurant tank ported and blind headsFigure 3 shows the ported head as modeledby the analysis The blind head is similarlyanalyzed

Figure 3 Nonlinear AxisymmetricFinite Element Models

bull Three-dimensional finite element model for the modal analysis The analysis isconducted to predict the natural frequenciesof the pressurant tank The actualfrequency of the tank is determined at

vibration test Figure 4a shows the first axialmode and Figure 4b shows the first lateralmode

Figure 4a First Axial Mode

Figure 4b First Lateral Mode

bull Random vibration analysis to determinestress and fatigue effects of randomvibration on the vessel See Figure 5a and5b For conservatism only the qualificationlevel power spectral density was analyzed

bull Shock analysis to determine stressresponses due to shock See Figure 6 Thesame finite element model for the modalanalysis is used on the shock analysis

bull Fatigue analysis to determine the cumulativedamage factor due to fatigue The fatiguelife requirements for the pressurant tank

liner consists of 1 sizing (autofrettage) cycleand 4 design service lifetimes includingproof pressure cycles and operatingpressure cycles

LINER DESIGN AND FABRICATION

To maintain heritage this pressurant tank wasdesigned to have the same CP titanium liner asthe previous pressurant tank Typical of mostCOPVrsquos the composite overwrap for thepressure vessel is designed to provide most of the strength for the tank The liner is a low

load-bearing part of the tank shell that servesas a container to carry the helium pressurantand provides a defined shape to apply thefilament overwrap To minimize weight the liner wall is kept as thin as practical whilemaintaining manufacturability However thedesign of the liner also takes into account thehigh vibration and shock loads during launchThe high strength low weight CP titanium isideal for this application

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Page 5

Figure 5a Vibration Analysis Lateral Random Stress Response of Liner

Figure 5b Vibration Analysis Axial Random Stress Response of Liner

Figure 6 Liner Shock Response Axial and lateral

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Page 6

Other factors that contribute to the selection of titanium include

l Good corrosion and oxidation resistancel Not susceptible to pitting and stress

corrosion

l High strength-to-weight ratiol Good galvanic compatibility with carbon

fiberl Good low cycle fatigue performancel Good high cycle fatigue performancel Good manufacturabilityl Good weld propertiesl Good performance characteristics

The pressurant tank liner is a four-piececonstruction that consists of two heads acylinder and an outlet tube The threecomponents of the liner body are shown in

Figure 7 This simplified approach minimizedthe number of components to handle andassemble

Figure 7 Components of thePressurant Tank Liner

The pressurant tank liner was designed tomirror the construction of the previouspressurant tank liner Although it has a slightlylarger diameter a forging was designed suchthat all four heads from these two tanks can bemachined from the same forging configurationThe forging is made from CP 70 titanium barFigure 8 below shows a liner head beingmachined

Figure 8 Machining of a Liner Head

The outlet tube is made from 953 mm (0375inch) outside diameter tubing The center section is fabricated from 05 mm (0020 inch)

thick CP-3 titanium sheet rolled formed andwelded into a cylinder with one longitudinalseam weld This cylinder is manufacturedusing the same manufacturing technique as theprevious helium pressurant tank center section

The liner is assembled with two girth welds anda tube assembly weld using the same weldtechnique and weld schedule as the previoushelium pressurant tank Each weld isradiographic and penetrant inspected for acceptance The completed liner is leak testedprior to the filament wrap operation Acompleted liner is shown in Figure 9

Figure 9 A Completed PressurantTank Liner

Outlet tube

Cylinder

Blind head

Ported head

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Page 7

COMPOSITE OVERWRAP DESIGN ANDFABRICATION

The pressurant tank composite overwrapcontains several layers of high angle helicaland hoop wraps The same wet filamentwinding technique used on the previouspressurant tank is applied to this pressuranttank This process utilizes dry fiber roving thatis in-process impregnated with a low-viscosityresin The materials used in the compositeoverwrap include Torayca T-1000G highperformance carbon fiber and EPON 826 epoxyresin system The basic resin system hasyears of commercial heritage and offersexcellent characteristics including lowviscosity reasonable pot life high strain-to-failure capability good chemical and moistureresistance and low toxicity Thousands of COPVrsquos have been wrapped using this resin

system

The resin system has a 107degC (225degF) curetemperature The glass transition temperature

(Tg) of the cured system is 99degC (210degF)providing a comfortable margin over the tankrsquos

maximum operating temperature of 60degC

(140degF)

A computer-controlled filament windingmachine is used to perform the compositeoverwrap operation See Figure 10 Acomputer code was generated to wrap the

pressurant tank The entire wrap process wasautomated to insure quality and repeatability

Figure 10 Automated Filament Winding

The filament wrap is bonded to the liner by athin layer of adhesive This adhesive is appliedto the liner immediately prior to the filamentwrap operation After filament wrap the vesselis placed in an oven and the resin is gelled andcured

WEIGHT DISTRIBUTION

The pressurant tank weight distribution issummarized in Table 3 below

Table 3 Pressurant Tank WeightDistribution

Item NominalWeight (kg)

NominalWeight (lbm)

Liner 37 81

Composite 80 177

TOTAL 117 258

The qualification tank was slightly above thenominal weight However most flight tanksfabricated were slightly below nominal weight

TANK GROWTH

The pressurant tank undergoes expansion as itis being pressurized The tank expansion datafor the Qualification tank is summarized in

Table 4 The measured tank growth closelymatches the predicted values

TANK SIZING

The pressurant tank is subjected to a sizingoperation (autofrettage) after the tank iswrapped and the resin system is cured Theautofrettage pressure is selected during tankanalysis This pressurization cycle isconsidered part of the manufacturing processand is not included in the pressure cyclehistory Autofrettage is performed immediately

prior to acceptance proof pressure testing

Table 4 Pressurant Tank Growth Data

Pressure Linear Growth Radial Growth Volume Growth

MEOP (331 bar4800 psi) 96 mm 0376 inch 20 mm 0078 inch 31 liters (1914 in3)

Proof Pressure (414 bar6000 psi) 108 mm 0427 inch 24 mm 0093 inch 40 liters (2441 in3)

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Page 8

QUALIFICATION TEST PROGRAM

A Qualification Tank was fabricated for thequalification test program The qualificationtesting consists of a series of tests intended toverify the pressurant tank design in thefollowing areas

l Physical properties such as volume andweight

l Tank shell integrityl Low cycle fatiguel High cycle fatiguel Shock fatiguel Burst margin

PassFail criteria consisted of acceptance typeexternal leak tests conducted at intervalsthroughout the test program After the tankpassed the final external leak test it underwent

a destructive burst pressure test Thesuccessful burst certified the tank for flight use

The Qualification Tank was subjected to thefollowing qualification tests

l Volumetric capacityl Proof pressure testl Volumetric capacity at ambientl Volumetric capacity at MEOPl Pressure cyclesl External leakagel Pressurized pyrotechnic shock

l External leakagel Sinusoidal and random vibrationl External leakagel Final examinationl Destructive burst pressure test

Volumetric Capacity Examination Thevolumetric capacity of the pressurant tank wasmeasured using the weight of water method atambient condition Deionized (DI) water wasused to conduct this test The tank volumesbefore and after the proof pressure test weremeasured to verify that the tank volume met the

specification requirement and that the proof pressure test did not significantly change thetank volume As an example the internalvolume of the Qualification Tank did notincrease after the proof pressure test signifyingthat the pressurant tank was manufacturedsuccessfully

Proof Pressure Test The hydrostatic proof pressure test was conducted at 414 bar (6000psig) for a pressure hold period of 5 minutesSuccessful completion of the proof pressuretest and the subsequent volumetric growth andleakage verification indicated that the tank wasmanufactured successfully

Pressure Cycles The pressurant tank isdesigned to accommodate a minimum of 8proof pressure cycles and 50 operatingpressure cycles As a practice severaloperating pressure cycles were added for contingency A total of 8 proof cycles and 52MEOP cycles were conducted at this pressurecycle testing Additionally the QualificationTank experienced another operating pressurecycle during shock test 3 operating pressurecycles for the 3 external leakage tests and 5more operating pressure cycles during vibration

testing The cumulative total of operatingpressure cycles is 61 or 11 cycles over theminimum requirement A picture of thepressure test setup is shown in Figure 11

Figure 11 Pressure Test Setup

External Leak Test The external leak testverifies the integrity of the tank shell and alsoserves to validate the previous series of pressure testing The tank is placed in a

vacuum chamber which is evacuated to under 02 microns of mercury and helium pressurizedto MEOP for 30 minutes The helium leak ratecannot exceed 1 x 10

-6 std cc per second after

a 30-minute stabilization period For examplethe leak rate of the Qualification Tank was 23 x10

-8 sccsec

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Page 9

During pressurization the compressed gasheats up thus heating up the tank To preventoverheating four thermocouples are attachedto the tank shell to monitor and control thepressurization rate and the tank temperatureduring pressurization The tank temperature

cannot exceed 140degF throughout the duration

of the test

Pressurized Pyrotechnic Shock TestPyrotechnic shock testing was performed onthe Qualification Tank Prior to testing apathfinder tank was mounted to the test fixturefor equalization of the shock system and todemonstrate the achievable level of input shockresponse spectrum The Qualification Tankwas then installed in the fixture and pressurizedto 4800 psig The test consisted of subjectingthe tank loaded with 4800 psig of gaseoushelium to two metal-to-metal impact shock

impulses The impulses had an input shockresponse spectrum of 7000g Both thelongitudinal axis (X axis) and the lateral axis (Zaxis) were excited simultaneously by the twoqualification level metal-to-metal impact shockimpulses The shock spectrum is presented inTable 5 A picture of the shock test setup isshown in Figure 12

Figure 12 Shock Test Setup

Vibration Test Sinusoidal and RandomQualification level sinusoidal and random

vibration tests were performed on theQualification Tank in each of the three principalaxes The vibration test requirements areshown in Tables 6 and 7

The vibration test fixture is designed to simulatethe tank-to-spacecraft installation interfacesand orientation It is also sufficiently stiff to be

considered rigid for the test frequencies Apreliminary test fixture evaluation wasconducted prior to Qualification Tankinstallation to insure the fixture meets thetesting requirements

Control accelerometers were placed on the

vibration test fixture near each end fitting tocontrol the vibration input Responseaccelerometers were placed on theQualification Tank to measure the tankresponses The placements of the responseaccelerometers were selected to record thetank responses at locations of maximum stressas predicted in the analytical model

The vibration test included fixture survey fulllevel sinusoidal and full level random runs Thesame tests were conducted in all three axes All testing was conducted with the tank

pressurized to 4800 psi with helium Aphotograph of the vibration test setup is shownin Figure 13

Figure 13 Pressurant Tank QualificationVibration Test Setup

Destructive Burst After the completion of thepressure cycles shock and vibration testingthe Qualification Tank was subjected to a finaldestructive burst pressure test TheQualification Tank burst at 572 bar (8297 psi)

providing a 152 margin on burst pressureThis data represents a burst factor of 173 to 1and a performance efficiency rating (Pressure xVolume Weight) of 157 x 10

6 inches This

high efficiency factor represents the mostefficient pressure vessel ever designed by PSIFigure 14 shows the Qualification Tank after burst

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AIAA 2002-4349

Page 10

Figure 14 Qualification Tank After Qualification Burst Pressure Test

Table 5 Shock Test Spectrum

Axes Frequency (Hz) Shock response

spectrum input (g)

100 80 plusmn 6 dB

1500 7000 plusmn 6 dB

3000 7000 plusmn 6 dB

6000 7000 + 9 dB -6 dB

Longitudinal and one

lateral axis

10000 7000 + 9 dB -6 dB

Shock response spectrum based on Q=10

Table 6 Qualification Level Sinusoidal Vibration Test Environment

Axes Frequency (Hz) Input Level (G) Sweep Rate

X Y and Z 5 - 24

24 - 65

65 - 100

05 in DA

15

7

2 octmin

Table 7 Qualification Level Random Vibration Test Environment

Axes Frequency

(Hz)

PSD Input

Level

Overall Level

(Grms)

Duration

(sec)

X Y and Z 20 ndash 100

100 ndash 1000

1000 - 2000

+3 dBoct

02 g2Hz

-3 dBoct

181 120

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Page 11

Qualification Tank Pressure Log Insummary the Qualification Tank hasundergone the pressure cycles listed in Table8 The successful completion of thequalification test program is an excellentdemonstration of the tankrsquos robust design

ACCEPTANCE TESTING

The following acceptance tests are performedon a flight tank prior to delivery

l Preliminary examinationl Pre-proof volumetric capacityl Ambient proof pressurel Post-proof volumetric capacityl Volumetric capacity at MEOPl External leakagel Weld quality inspectionl Final examinationl

Cleanliness measurement

Cleanliness Verification After the finalexternal leak test each flight tank is cleaned tothe cleanliness level specified in Table 9

Table 9 Pressurant Tank CleanlinessLevel

Particle Size Range(Microns)

Maximum Allowedper 100 ml

5 to 10 140

11 to 25 2026 to 50 5

51 to 100 1

Over 100 0

Photograph of a completed tank is shown inFigure 15

Figure 15 A completed PressurantTank

Table 8 Summary of Qualification Tank Pressure Cycles

Pressure Actual of Cycles

RequiredCycles

Description

331 bar (4800 psig)Operating pressure 61 50 52 operating cycles3 external leaks1 shock test5 pressurization cycles during vibration testing

414 bar (6000 psig)Proof pressure

8 8 1 proof test7 proof cycles

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Page 12

CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

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AIAA 2002-4349

Page 13

NOTES

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AIAA 2002-4349

Page 4

Several analyses were conducted to designand analyze the pressurant tank including

bull Finite element analysis to conduct the liner material study

bull Nonlinear axisymmetric analysis to design

the pressurant tank ported and blind headsFigure 3 shows the ported head as modeledby the analysis The blind head is similarlyanalyzed

Figure 3 Nonlinear AxisymmetricFinite Element Models

bull Three-dimensional finite element model for the modal analysis The analysis isconducted to predict the natural frequenciesof the pressurant tank The actualfrequency of the tank is determined at

vibration test Figure 4a shows the first axialmode and Figure 4b shows the first lateralmode

Figure 4a First Axial Mode

Figure 4b First Lateral Mode

bull Random vibration analysis to determinestress and fatigue effects of randomvibration on the vessel See Figure 5a and5b For conservatism only the qualificationlevel power spectral density was analyzed

bull Shock analysis to determine stressresponses due to shock See Figure 6 Thesame finite element model for the modalanalysis is used on the shock analysis

bull Fatigue analysis to determine the cumulativedamage factor due to fatigue The fatiguelife requirements for the pressurant tank

liner consists of 1 sizing (autofrettage) cycleand 4 design service lifetimes includingproof pressure cycles and operatingpressure cycles

LINER DESIGN AND FABRICATION

To maintain heritage this pressurant tank wasdesigned to have the same CP titanium liner asthe previous pressurant tank Typical of mostCOPVrsquos the composite overwrap for thepressure vessel is designed to provide most of the strength for the tank The liner is a low

load-bearing part of the tank shell that servesas a container to carry the helium pressurantand provides a defined shape to apply thefilament overwrap To minimize weight the liner wall is kept as thin as practical whilemaintaining manufacturability However thedesign of the liner also takes into account thehigh vibration and shock loads during launchThe high strength low weight CP titanium isideal for this application

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AIAA 2002-4349

Page 5

Figure 5a Vibration Analysis Lateral Random Stress Response of Liner

Figure 5b Vibration Analysis Axial Random Stress Response of Liner

Figure 6 Liner Shock Response Axial and lateral

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AIAA 2002-4349

Page 6

Other factors that contribute to the selection of titanium include

l Good corrosion and oxidation resistancel Not susceptible to pitting and stress

corrosion

l High strength-to-weight ratiol Good galvanic compatibility with carbon

fiberl Good low cycle fatigue performancel Good high cycle fatigue performancel Good manufacturabilityl Good weld propertiesl Good performance characteristics

The pressurant tank liner is a four-piececonstruction that consists of two heads acylinder and an outlet tube The threecomponents of the liner body are shown in

Figure 7 This simplified approach minimizedthe number of components to handle andassemble

Figure 7 Components of thePressurant Tank Liner

The pressurant tank liner was designed tomirror the construction of the previouspressurant tank liner Although it has a slightlylarger diameter a forging was designed suchthat all four heads from these two tanks can bemachined from the same forging configurationThe forging is made from CP 70 titanium barFigure 8 below shows a liner head beingmachined

Figure 8 Machining of a Liner Head

The outlet tube is made from 953 mm (0375inch) outside diameter tubing The center section is fabricated from 05 mm (0020 inch)

thick CP-3 titanium sheet rolled formed andwelded into a cylinder with one longitudinalseam weld This cylinder is manufacturedusing the same manufacturing technique as theprevious helium pressurant tank center section

The liner is assembled with two girth welds anda tube assembly weld using the same weldtechnique and weld schedule as the previoushelium pressurant tank Each weld isradiographic and penetrant inspected for acceptance The completed liner is leak testedprior to the filament wrap operation Acompleted liner is shown in Figure 9

Figure 9 A Completed PressurantTank Liner

Outlet tube

Cylinder

Blind head

Ported head

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AIAA 2002-4349

Page 7

COMPOSITE OVERWRAP DESIGN ANDFABRICATION

The pressurant tank composite overwrapcontains several layers of high angle helicaland hoop wraps The same wet filamentwinding technique used on the previouspressurant tank is applied to this pressuranttank This process utilizes dry fiber roving thatis in-process impregnated with a low-viscosityresin The materials used in the compositeoverwrap include Torayca T-1000G highperformance carbon fiber and EPON 826 epoxyresin system The basic resin system hasyears of commercial heritage and offersexcellent characteristics including lowviscosity reasonable pot life high strain-to-failure capability good chemical and moistureresistance and low toxicity Thousands of COPVrsquos have been wrapped using this resin

system

The resin system has a 107degC (225degF) curetemperature The glass transition temperature

(Tg) of the cured system is 99degC (210degF)providing a comfortable margin over the tankrsquos

maximum operating temperature of 60degC

(140degF)

A computer-controlled filament windingmachine is used to perform the compositeoverwrap operation See Figure 10 Acomputer code was generated to wrap the

pressurant tank The entire wrap process wasautomated to insure quality and repeatability

Figure 10 Automated Filament Winding

The filament wrap is bonded to the liner by athin layer of adhesive This adhesive is appliedto the liner immediately prior to the filamentwrap operation After filament wrap the vesselis placed in an oven and the resin is gelled andcured

WEIGHT DISTRIBUTION

The pressurant tank weight distribution issummarized in Table 3 below

Table 3 Pressurant Tank WeightDistribution

Item NominalWeight (kg)

NominalWeight (lbm)

Liner 37 81

Composite 80 177

TOTAL 117 258

The qualification tank was slightly above thenominal weight However most flight tanksfabricated were slightly below nominal weight

TANK GROWTH

The pressurant tank undergoes expansion as itis being pressurized The tank expansion datafor the Qualification tank is summarized in

Table 4 The measured tank growth closelymatches the predicted values

TANK SIZING

The pressurant tank is subjected to a sizingoperation (autofrettage) after the tank iswrapped and the resin system is cured Theautofrettage pressure is selected during tankanalysis This pressurization cycle isconsidered part of the manufacturing processand is not included in the pressure cyclehistory Autofrettage is performed immediately

prior to acceptance proof pressure testing

Table 4 Pressurant Tank Growth Data

Pressure Linear Growth Radial Growth Volume Growth

MEOP (331 bar4800 psi) 96 mm 0376 inch 20 mm 0078 inch 31 liters (1914 in3)

Proof Pressure (414 bar6000 psi) 108 mm 0427 inch 24 mm 0093 inch 40 liters (2441 in3)

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AIAA 2002-4349

Page 8

QUALIFICATION TEST PROGRAM

A Qualification Tank was fabricated for thequalification test program The qualificationtesting consists of a series of tests intended toverify the pressurant tank design in thefollowing areas

l Physical properties such as volume andweight

l Tank shell integrityl Low cycle fatiguel High cycle fatiguel Shock fatiguel Burst margin

PassFail criteria consisted of acceptance typeexternal leak tests conducted at intervalsthroughout the test program After the tankpassed the final external leak test it underwent

a destructive burst pressure test Thesuccessful burst certified the tank for flight use

The Qualification Tank was subjected to thefollowing qualification tests

l Volumetric capacityl Proof pressure testl Volumetric capacity at ambientl Volumetric capacity at MEOPl Pressure cyclesl External leakagel Pressurized pyrotechnic shock

l External leakagel Sinusoidal and random vibrationl External leakagel Final examinationl Destructive burst pressure test

Volumetric Capacity Examination Thevolumetric capacity of the pressurant tank wasmeasured using the weight of water method atambient condition Deionized (DI) water wasused to conduct this test The tank volumesbefore and after the proof pressure test weremeasured to verify that the tank volume met the

specification requirement and that the proof pressure test did not significantly change thetank volume As an example the internalvolume of the Qualification Tank did notincrease after the proof pressure test signifyingthat the pressurant tank was manufacturedsuccessfully

Proof Pressure Test The hydrostatic proof pressure test was conducted at 414 bar (6000psig) for a pressure hold period of 5 minutesSuccessful completion of the proof pressuretest and the subsequent volumetric growth andleakage verification indicated that the tank wasmanufactured successfully

Pressure Cycles The pressurant tank isdesigned to accommodate a minimum of 8proof pressure cycles and 50 operatingpressure cycles As a practice severaloperating pressure cycles were added for contingency A total of 8 proof cycles and 52MEOP cycles were conducted at this pressurecycle testing Additionally the QualificationTank experienced another operating pressurecycle during shock test 3 operating pressurecycles for the 3 external leakage tests and 5more operating pressure cycles during vibration

testing The cumulative total of operatingpressure cycles is 61 or 11 cycles over theminimum requirement A picture of thepressure test setup is shown in Figure 11

Figure 11 Pressure Test Setup

External Leak Test The external leak testverifies the integrity of the tank shell and alsoserves to validate the previous series of pressure testing The tank is placed in a

vacuum chamber which is evacuated to under 02 microns of mercury and helium pressurizedto MEOP for 30 minutes The helium leak ratecannot exceed 1 x 10

-6 std cc per second after

a 30-minute stabilization period For examplethe leak rate of the Qualification Tank was 23 x10

-8 sccsec

8132019 AIAA2002-4349 Astrolink Pres

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AIAA 2002-4349

Page 9

During pressurization the compressed gasheats up thus heating up the tank To preventoverheating four thermocouples are attachedto the tank shell to monitor and control thepressurization rate and the tank temperatureduring pressurization The tank temperature

cannot exceed 140degF throughout the duration

of the test

Pressurized Pyrotechnic Shock TestPyrotechnic shock testing was performed onthe Qualification Tank Prior to testing apathfinder tank was mounted to the test fixturefor equalization of the shock system and todemonstrate the achievable level of input shockresponse spectrum The Qualification Tankwas then installed in the fixture and pressurizedto 4800 psig The test consisted of subjectingthe tank loaded with 4800 psig of gaseoushelium to two metal-to-metal impact shock

impulses The impulses had an input shockresponse spectrum of 7000g Both thelongitudinal axis (X axis) and the lateral axis (Zaxis) were excited simultaneously by the twoqualification level metal-to-metal impact shockimpulses The shock spectrum is presented inTable 5 A picture of the shock test setup isshown in Figure 12

Figure 12 Shock Test Setup

Vibration Test Sinusoidal and RandomQualification level sinusoidal and random

vibration tests were performed on theQualification Tank in each of the three principalaxes The vibration test requirements areshown in Tables 6 and 7

The vibration test fixture is designed to simulatethe tank-to-spacecraft installation interfacesand orientation It is also sufficiently stiff to be

considered rigid for the test frequencies Apreliminary test fixture evaluation wasconducted prior to Qualification Tankinstallation to insure the fixture meets thetesting requirements

Control accelerometers were placed on the

vibration test fixture near each end fitting tocontrol the vibration input Responseaccelerometers were placed on theQualification Tank to measure the tankresponses The placements of the responseaccelerometers were selected to record thetank responses at locations of maximum stressas predicted in the analytical model

The vibration test included fixture survey fulllevel sinusoidal and full level random runs Thesame tests were conducted in all three axes All testing was conducted with the tank

pressurized to 4800 psi with helium Aphotograph of the vibration test setup is shownin Figure 13

Figure 13 Pressurant Tank QualificationVibration Test Setup

Destructive Burst After the completion of thepressure cycles shock and vibration testingthe Qualification Tank was subjected to a finaldestructive burst pressure test TheQualification Tank burst at 572 bar (8297 psi)

providing a 152 margin on burst pressureThis data represents a burst factor of 173 to 1and a performance efficiency rating (Pressure xVolume Weight) of 157 x 10

6 inches This

high efficiency factor represents the mostefficient pressure vessel ever designed by PSIFigure 14 shows the Qualification Tank after burst

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AIAA 2002-4349

Page 10

Figure 14 Qualification Tank After Qualification Burst Pressure Test

Table 5 Shock Test Spectrum

Axes Frequency (Hz) Shock response

spectrum input (g)

100 80 plusmn 6 dB

1500 7000 plusmn 6 dB

3000 7000 plusmn 6 dB

6000 7000 + 9 dB -6 dB

Longitudinal and one

lateral axis

10000 7000 + 9 dB -6 dB

Shock response spectrum based on Q=10

Table 6 Qualification Level Sinusoidal Vibration Test Environment

Axes Frequency (Hz) Input Level (G) Sweep Rate

X Y and Z 5 - 24

24 - 65

65 - 100

05 in DA

15

7

2 octmin

Table 7 Qualification Level Random Vibration Test Environment

Axes Frequency

(Hz)

PSD Input

Level

Overall Level

(Grms)

Duration

(sec)

X Y and Z 20 ndash 100

100 ndash 1000

1000 - 2000

+3 dBoct

02 g2Hz

-3 dBoct

181 120

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AIAA 2002-4349

Page 11

Qualification Tank Pressure Log Insummary the Qualification Tank hasundergone the pressure cycles listed in Table8 The successful completion of thequalification test program is an excellentdemonstration of the tankrsquos robust design

ACCEPTANCE TESTING

The following acceptance tests are performedon a flight tank prior to delivery

l Preliminary examinationl Pre-proof volumetric capacityl Ambient proof pressurel Post-proof volumetric capacityl Volumetric capacity at MEOPl External leakagel Weld quality inspectionl Final examinationl

Cleanliness measurement

Cleanliness Verification After the finalexternal leak test each flight tank is cleaned tothe cleanliness level specified in Table 9

Table 9 Pressurant Tank CleanlinessLevel

Particle Size Range(Microns)

Maximum Allowedper 100 ml

5 to 10 140

11 to 25 2026 to 50 5

51 to 100 1

Over 100 0

Photograph of a completed tank is shown inFigure 15

Figure 15 A completed PressurantTank

Table 8 Summary of Qualification Tank Pressure Cycles

Pressure Actual of Cycles

RequiredCycles

Description

331 bar (4800 psig)Operating pressure 61 50 52 operating cycles3 external leaks1 shock test5 pressurization cycles during vibration testing

414 bar (6000 psig)Proof pressure

8 8 1 proof test7 proof cycles

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AIAA 2002-4349

Page 12

CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

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AIAA 2002-4349

Page 13

NOTES

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AIAA 2002-4349

Page 5

Figure 5a Vibration Analysis Lateral Random Stress Response of Liner

Figure 5b Vibration Analysis Axial Random Stress Response of Liner

Figure 6 Liner Shock Response Axial and lateral

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AIAA 2002-4349

Page 6

Other factors that contribute to the selection of titanium include

l Good corrosion and oxidation resistancel Not susceptible to pitting and stress

corrosion

l High strength-to-weight ratiol Good galvanic compatibility with carbon

fiberl Good low cycle fatigue performancel Good high cycle fatigue performancel Good manufacturabilityl Good weld propertiesl Good performance characteristics

The pressurant tank liner is a four-piececonstruction that consists of two heads acylinder and an outlet tube The threecomponents of the liner body are shown in

Figure 7 This simplified approach minimizedthe number of components to handle andassemble

Figure 7 Components of thePressurant Tank Liner

The pressurant tank liner was designed tomirror the construction of the previouspressurant tank liner Although it has a slightlylarger diameter a forging was designed suchthat all four heads from these two tanks can bemachined from the same forging configurationThe forging is made from CP 70 titanium barFigure 8 below shows a liner head beingmachined

Figure 8 Machining of a Liner Head

The outlet tube is made from 953 mm (0375inch) outside diameter tubing The center section is fabricated from 05 mm (0020 inch)

thick CP-3 titanium sheet rolled formed andwelded into a cylinder with one longitudinalseam weld This cylinder is manufacturedusing the same manufacturing technique as theprevious helium pressurant tank center section

The liner is assembled with two girth welds anda tube assembly weld using the same weldtechnique and weld schedule as the previoushelium pressurant tank Each weld isradiographic and penetrant inspected for acceptance The completed liner is leak testedprior to the filament wrap operation Acompleted liner is shown in Figure 9

Figure 9 A Completed PressurantTank Liner

Outlet tube

Cylinder

Blind head

Ported head

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AIAA 2002-4349

Page 7

COMPOSITE OVERWRAP DESIGN ANDFABRICATION

The pressurant tank composite overwrapcontains several layers of high angle helicaland hoop wraps The same wet filamentwinding technique used on the previouspressurant tank is applied to this pressuranttank This process utilizes dry fiber roving thatis in-process impregnated with a low-viscosityresin The materials used in the compositeoverwrap include Torayca T-1000G highperformance carbon fiber and EPON 826 epoxyresin system The basic resin system hasyears of commercial heritage and offersexcellent characteristics including lowviscosity reasonable pot life high strain-to-failure capability good chemical and moistureresistance and low toxicity Thousands of COPVrsquos have been wrapped using this resin

system

The resin system has a 107degC (225degF) curetemperature The glass transition temperature

(Tg) of the cured system is 99degC (210degF)providing a comfortable margin over the tankrsquos

maximum operating temperature of 60degC

(140degF)

A computer-controlled filament windingmachine is used to perform the compositeoverwrap operation See Figure 10 Acomputer code was generated to wrap the

pressurant tank The entire wrap process wasautomated to insure quality and repeatability

Figure 10 Automated Filament Winding

The filament wrap is bonded to the liner by athin layer of adhesive This adhesive is appliedto the liner immediately prior to the filamentwrap operation After filament wrap the vesselis placed in an oven and the resin is gelled andcured

WEIGHT DISTRIBUTION

The pressurant tank weight distribution issummarized in Table 3 below

Table 3 Pressurant Tank WeightDistribution

Item NominalWeight (kg)

NominalWeight (lbm)

Liner 37 81

Composite 80 177

TOTAL 117 258

The qualification tank was slightly above thenominal weight However most flight tanksfabricated were slightly below nominal weight

TANK GROWTH

The pressurant tank undergoes expansion as itis being pressurized The tank expansion datafor the Qualification tank is summarized in

Table 4 The measured tank growth closelymatches the predicted values

TANK SIZING

The pressurant tank is subjected to a sizingoperation (autofrettage) after the tank iswrapped and the resin system is cured Theautofrettage pressure is selected during tankanalysis This pressurization cycle isconsidered part of the manufacturing processand is not included in the pressure cyclehistory Autofrettage is performed immediately

prior to acceptance proof pressure testing

Table 4 Pressurant Tank Growth Data

Pressure Linear Growth Radial Growth Volume Growth

MEOP (331 bar4800 psi) 96 mm 0376 inch 20 mm 0078 inch 31 liters (1914 in3)

Proof Pressure (414 bar6000 psi) 108 mm 0427 inch 24 mm 0093 inch 40 liters (2441 in3)

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AIAA 2002-4349

Page 8

QUALIFICATION TEST PROGRAM

A Qualification Tank was fabricated for thequalification test program The qualificationtesting consists of a series of tests intended toverify the pressurant tank design in thefollowing areas

l Physical properties such as volume andweight

l Tank shell integrityl Low cycle fatiguel High cycle fatiguel Shock fatiguel Burst margin

PassFail criteria consisted of acceptance typeexternal leak tests conducted at intervalsthroughout the test program After the tankpassed the final external leak test it underwent

a destructive burst pressure test Thesuccessful burst certified the tank for flight use

The Qualification Tank was subjected to thefollowing qualification tests

l Volumetric capacityl Proof pressure testl Volumetric capacity at ambientl Volumetric capacity at MEOPl Pressure cyclesl External leakagel Pressurized pyrotechnic shock

l External leakagel Sinusoidal and random vibrationl External leakagel Final examinationl Destructive burst pressure test

Volumetric Capacity Examination Thevolumetric capacity of the pressurant tank wasmeasured using the weight of water method atambient condition Deionized (DI) water wasused to conduct this test The tank volumesbefore and after the proof pressure test weremeasured to verify that the tank volume met the

specification requirement and that the proof pressure test did not significantly change thetank volume As an example the internalvolume of the Qualification Tank did notincrease after the proof pressure test signifyingthat the pressurant tank was manufacturedsuccessfully

Proof Pressure Test The hydrostatic proof pressure test was conducted at 414 bar (6000psig) for a pressure hold period of 5 minutesSuccessful completion of the proof pressuretest and the subsequent volumetric growth andleakage verification indicated that the tank wasmanufactured successfully

Pressure Cycles The pressurant tank isdesigned to accommodate a minimum of 8proof pressure cycles and 50 operatingpressure cycles As a practice severaloperating pressure cycles were added for contingency A total of 8 proof cycles and 52MEOP cycles were conducted at this pressurecycle testing Additionally the QualificationTank experienced another operating pressurecycle during shock test 3 operating pressurecycles for the 3 external leakage tests and 5more operating pressure cycles during vibration

testing The cumulative total of operatingpressure cycles is 61 or 11 cycles over theminimum requirement A picture of thepressure test setup is shown in Figure 11

Figure 11 Pressure Test Setup

External Leak Test The external leak testverifies the integrity of the tank shell and alsoserves to validate the previous series of pressure testing The tank is placed in a

vacuum chamber which is evacuated to under 02 microns of mercury and helium pressurizedto MEOP for 30 minutes The helium leak ratecannot exceed 1 x 10

-6 std cc per second after

a 30-minute stabilization period For examplethe leak rate of the Qualification Tank was 23 x10

-8 sccsec

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 913

AIAA 2002-4349

Page 9

During pressurization the compressed gasheats up thus heating up the tank To preventoverheating four thermocouples are attachedto the tank shell to monitor and control thepressurization rate and the tank temperatureduring pressurization The tank temperature

cannot exceed 140degF throughout the duration

of the test

Pressurized Pyrotechnic Shock TestPyrotechnic shock testing was performed onthe Qualification Tank Prior to testing apathfinder tank was mounted to the test fixturefor equalization of the shock system and todemonstrate the achievable level of input shockresponse spectrum The Qualification Tankwas then installed in the fixture and pressurizedto 4800 psig The test consisted of subjectingthe tank loaded with 4800 psig of gaseoushelium to two metal-to-metal impact shock

impulses The impulses had an input shockresponse spectrum of 7000g Both thelongitudinal axis (X axis) and the lateral axis (Zaxis) were excited simultaneously by the twoqualification level metal-to-metal impact shockimpulses The shock spectrum is presented inTable 5 A picture of the shock test setup isshown in Figure 12

Figure 12 Shock Test Setup

Vibration Test Sinusoidal and RandomQualification level sinusoidal and random

vibration tests were performed on theQualification Tank in each of the three principalaxes The vibration test requirements areshown in Tables 6 and 7

The vibration test fixture is designed to simulatethe tank-to-spacecraft installation interfacesand orientation It is also sufficiently stiff to be

considered rigid for the test frequencies Apreliminary test fixture evaluation wasconducted prior to Qualification Tankinstallation to insure the fixture meets thetesting requirements

Control accelerometers were placed on the

vibration test fixture near each end fitting tocontrol the vibration input Responseaccelerometers were placed on theQualification Tank to measure the tankresponses The placements of the responseaccelerometers were selected to record thetank responses at locations of maximum stressas predicted in the analytical model

The vibration test included fixture survey fulllevel sinusoidal and full level random runs Thesame tests were conducted in all three axes All testing was conducted with the tank

pressurized to 4800 psi with helium Aphotograph of the vibration test setup is shownin Figure 13

Figure 13 Pressurant Tank QualificationVibration Test Setup

Destructive Burst After the completion of thepressure cycles shock and vibration testingthe Qualification Tank was subjected to a finaldestructive burst pressure test TheQualification Tank burst at 572 bar (8297 psi)

providing a 152 margin on burst pressureThis data represents a burst factor of 173 to 1and a performance efficiency rating (Pressure xVolume Weight) of 157 x 10

6 inches This

high efficiency factor represents the mostefficient pressure vessel ever designed by PSIFigure 14 shows the Qualification Tank after burst

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AIAA 2002-4349

Page 10

Figure 14 Qualification Tank After Qualification Burst Pressure Test

Table 5 Shock Test Spectrum

Axes Frequency (Hz) Shock response

spectrum input (g)

100 80 plusmn 6 dB

1500 7000 plusmn 6 dB

3000 7000 plusmn 6 dB

6000 7000 + 9 dB -6 dB

Longitudinal and one

lateral axis

10000 7000 + 9 dB -6 dB

Shock response spectrum based on Q=10

Table 6 Qualification Level Sinusoidal Vibration Test Environment

Axes Frequency (Hz) Input Level (G) Sweep Rate

X Y and Z 5 - 24

24 - 65

65 - 100

05 in DA

15

7

2 octmin

Table 7 Qualification Level Random Vibration Test Environment

Axes Frequency

(Hz)

PSD Input

Level

Overall Level

(Grms)

Duration

(sec)

X Y and Z 20 ndash 100

100 ndash 1000

1000 - 2000

+3 dBoct

02 g2Hz

-3 dBoct

181 120

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AIAA 2002-4349

Page 11

Qualification Tank Pressure Log Insummary the Qualification Tank hasundergone the pressure cycles listed in Table8 The successful completion of thequalification test program is an excellentdemonstration of the tankrsquos robust design

ACCEPTANCE TESTING

The following acceptance tests are performedon a flight tank prior to delivery

l Preliminary examinationl Pre-proof volumetric capacityl Ambient proof pressurel Post-proof volumetric capacityl Volumetric capacity at MEOPl External leakagel Weld quality inspectionl Final examinationl

Cleanliness measurement

Cleanliness Verification After the finalexternal leak test each flight tank is cleaned tothe cleanliness level specified in Table 9

Table 9 Pressurant Tank CleanlinessLevel

Particle Size Range(Microns)

Maximum Allowedper 100 ml

5 to 10 140

11 to 25 2026 to 50 5

51 to 100 1

Over 100 0

Photograph of a completed tank is shown inFigure 15

Figure 15 A completed PressurantTank

Table 8 Summary of Qualification Tank Pressure Cycles

Pressure Actual of Cycles

RequiredCycles

Description

331 bar (4800 psig)Operating pressure 61 50 52 operating cycles3 external leaks1 shock test5 pressurization cycles during vibration testing

414 bar (6000 psig)Proof pressure

8 8 1 proof test7 proof cycles

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AIAA 2002-4349

Page 12

CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1313

AIAA 2002-4349

Page 13

NOTES

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 613

AIAA 2002-4349

Page 6

Other factors that contribute to the selection of titanium include

l Good corrosion and oxidation resistancel Not susceptible to pitting and stress

corrosion

l High strength-to-weight ratiol Good galvanic compatibility with carbon

fiberl Good low cycle fatigue performancel Good high cycle fatigue performancel Good manufacturabilityl Good weld propertiesl Good performance characteristics

The pressurant tank liner is a four-piececonstruction that consists of two heads acylinder and an outlet tube The threecomponents of the liner body are shown in

Figure 7 This simplified approach minimizedthe number of components to handle andassemble

Figure 7 Components of thePressurant Tank Liner

The pressurant tank liner was designed tomirror the construction of the previouspressurant tank liner Although it has a slightlylarger diameter a forging was designed suchthat all four heads from these two tanks can bemachined from the same forging configurationThe forging is made from CP 70 titanium barFigure 8 below shows a liner head beingmachined

Figure 8 Machining of a Liner Head

The outlet tube is made from 953 mm (0375inch) outside diameter tubing The center section is fabricated from 05 mm (0020 inch)

thick CP-3 titanium sheet rolled formed andwelded into a cylinder with one longitudinalseam weld This cylinder is manufacturedusing the same manufacturing technique as theprevious helium pressurant tank center section

The liner is assembled with two girth welds anda tube assembly weld using the same weldtechnique and weld schedule as the previoushelium pressurant tank Each weld isradiographic and penetrant inspected for acceptance The completed liner is leak testedprior to the filament wrap operation Acompleted liner is shown in Figure 9

Figure 9 A Completed PressurantTank Liner

Outlet tube

Cylinder

Blind head

Ported head

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 713

AIAA 2002-4349

Page 7

COMPOSITE OVERWRAP DESIGN ANDFABRICATION

The pressurant tank composite overwrapcontains several layers of high angle helicaland hoop wraps The same wet filamentwinding technique used on the previouspressurant tank is applied to this pressuranttank This process utilizes dry fiber roving thatis in-process impregnated with a low-viscosityresin The materials used in the compositeoverwrap include Torayca T-1000G highperformance carbon fiber and EPON 826 epoxyresin system The basic resin system hasyears of commercial heritage and offersexcellent characteristics including lowviscosity reasonable pot life high strain-to-failure capability good chemical and moistureresistance and low toxicity Thousands of COPVrsquos have been wrapped using this resin

system

The resin system has a 107degC (225degF) curetemperature The glass transition temperature

(Tg) of the cured system is 99degC (210degF)providing a comfortable margin over the tankrsquos

maximum operating temperature of 60degC

(140degF)

A computer-controlled filament windingmachine is used to perform the compositeoverwrap operation See Figure 10 Acomputer code was generated to wrap the

pressurant tank The entire wrap process wasautomated to insure quality and repeatability

Figure 10 Automated Filament Winding

The filament wrap is bonded to the liner by athin layer of adhesive This adhesive is appliedto the liner immediately prior to the filamentwrap operation After filament wrap the vesselis placed in an oven and the resin is gelled andcured

WEIGHT DISTRIBUTION

The pressurant tank weight distribution issummarized in Table 3 below

Table 3 Pressurant Tank WeightDistribution

Item NominalWeight (kg)

NominalWeight (lbm)

Liner 37 81

Composite 80 177

TOTAL 117 258

The qualification tank was slightly above thenominal weight However most flight tanksfabricated were slightly below nominal weight

TANK GROWTH

The pressurant tank undergoes expansion as itis being pressurized The tank expansion datafor the Qualification tank is summarized in

Table 4 The measured tank growth closelymatches the predicted values

TANK SIZING

The pressurant tank is subjected to a sizingoperation (autofrettage) after the tank iswrapped and the resin system is cured Theautofrettage pressure is selected during tankanalysis This pressurization cycle isconsidered part of the manufacturing processand is not included in the pressure cyclehistory Autofrettage is performed immediately

prior to acceptance proof pressure testing

Table 4 Pressurant Tank Growth Data

Pressure Linear Growth Radial Growth Volume Growth

MEOP (331 bar4800 psi) 96 mm 0376 inch 20 mm 0078 inch 31 liters (1914 in3)

Proof Pressure (414 bar6000 psi) 108 mm 0427 inch 24 mm 0093 inch 40 liters (2441 in3)

8132019 AIAA2002-4349 Astrolink Pres

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AIAA 2002-4349

Page 8

QUALIFICATION TEST PROGRAM

A Qualification Tank was fabricated for thequalification test program The qualificationtesting consists of a series of tests intended toverify the pressurant tank design in thefollowing areas

l Physical properties such as volume andweight

l Tank shell integrityl Low cycle fatiguel High cycle fatiguel Shock fatiguel Burst margin

PassFail criteria consisted of acceptance typeexternal leak tests conducted at intervalsthroughout the test program After the tankpassed the final external leak test it underwent

a destructive burst pressure test Thesuccessful burst certified the tank for flight use

The Qualification Tank was subjected to thefollowing qualification tests

l Volumetric capacityl Proof pressure testl Volumetric capacity at ambientl Volumetric capacity at MEOPl Pressure cyclesl External leakagel Pressurized pyrotechnic shock

l External leakagel Sinusoidal and random vibrationl External leakagel Final examinationl Destructive burst pressure test

Volumetric Capacity Examination Thevolumetric capacity of the pressurant tank wasmeasured using the weight of water method atambient condition Deionized (DI) water wasused to conduct this test The tank volumesbefore and after the proof pressure test weremeasured to verify that the tank volume met the

specification requirement and that the proof pressure test did not significantly change thetank volume As an example the internalvolume of the Qualification Tank did notincrease after the proof pressure test signifyingthat the pressurant tank was manufacturedsuccessfully

Proof Pressure Test The hydrostatic proof pressure test was conducted at 414 bar (6000psig) for a pressure hold period of 5 minutesSuccessful completion of the proof pressuretest and the subsequent volumetric growth andleakage verification indicated that the tank wasmanufactured successfully

Pressure Cycles The pressurant tank isdesigned to accommodate a minimum of 8proof pressure cycles and 50 operatingpressure cycles As a practice severaloperating pressure cycles were added for contingency A total of 8 proof cycles and 52MEOP cycles were conducted at this pressurecycle testing Additionally the QualificationTank experienced another operating pressurecycle during shock test 3 operating pressurecycles for the 3 external leakage tests and 5more operating pressure cycles during vibration

testing The cumulative total of operatingpressure cycles is 61 or 11 cycles over theminimum requirement A picture of thepressure test setup is shown in Figure 11

Figure 11 Pressure Test Setup

External Leak Test The external leak testverifies the integrity of the tank shell and alsoserves to validate the previous series of pressure testing The tank is placed in a

vacuum chamber which is evacuated to under 02 microns of mercury and helium pressurizedto MEOP for 30 minutes The helium leak ratecannot exceed 1 x 10

-6 std cc per second after

a 30-minute stabilization period For examplethe leak rate of the Qualification Tank was 23 x10

-8 sccsec

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 913

AIAA 2002-4349

Page 9

During pressurization the compressed gasheats up thus heating up the tank To preventoverheating four thermocouples are attachedto the tank shell to monitor and control thepressurization rate and the tank temperatureduring pressurization The tank temperature

cannot exceed 140degF throughout the duration

of the test

Pressurized Pyrotechnic Shock TestPyrotechnic shock testing was performed onthe Qualification Tank Prior to testing apathfinder tank was mounted to the test fixturefor equalization of the shock system and todemonstrate the achievable level of input shockresponse spectrum The Qualification Tankwas then installed in the fixture and pressurizedto 4800 psig The test consisted of subjectingthe tank loaded with 4800 psig of gaseoushelium to two metal-to-metal impact shock

impulses The impulses had an input shockresponse spectrum of 7000g Both thelongitudinal axis (X axis) and the lateral axis (Zaxis) were excited simultaneously by the twoqualification level metal-to-metal impact shockimpulses The shock spectrum is presented inTable 5 A picture of the shock test setup isshown in Figure 12

Figure 12 Shock Test Setup

Vibration Test Sinusoidal and RandomQualification level sinusoidal and random

vibration tests were performed on theQualification Tank in each of the three principalaxes The vibration test requirements areshown in Tables 6 and 7

The vibration test fixture is designed to simulatethe tank-to-spacecraft installation interfacesand orientation It is also sufficiently stiff to be

considered rigid for the test frequencies Apreliminary test fixture evaluation wasconducted prior to Qualification Tankinstallation to insure the fixture meets thetesting requirements

Control accelerometers were placed on the

vibration test fixture near each end fitting tocontrol the vibration input Responseaccelerometers were placed on theQualification Tank to measure the tankresponses The placements of the responseaccelerometers were selected to record thetank responses at locations of maximum stressas predicted in the analytical model

The vibration test included fixture survey fulllevel sinusoidal and full level random runs Thesame tests were conducted in all three axes All testing was conducted with the tank

pressurized to 4800 psi with helium Aphotograph of the vibration test setup is shownin Figure 13

Figure 13 Pressurant Tank QualificationVibration Test Setup

Destructive Burst After the completion of thepressure cycles shock and vibration testingthe Qualification Tank was subjected to a finaldestructive burst pressure test TheQualification Tank burst at 572 bar (8297 psi)

providing a 152 margin on burst pressureThis data represents a burst factor of 173 to 1and a performance efficiency rating (Pressure xVolume Weight) of 157 x 10

6 inches This

high efficiency factor represents the mostefficient pressure vessel ever designed by PSIFigure 14 shows the Qualification Tank after burst

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1013

AIAA 2002-4349

Page 10

Figure 14 Qualification Tank After Qualification Burst Pressure Test

Table 5 Shock Test Spectrum

Axes Frequency (Hz) Shock response

spectrum input (g)

100 80 plusmn 6 dB

1500 7000 plusmn 6 dB

3000 7000 plusmn 6 dB

6000 7000 + 9 dB -6 dB

Longitudinal and one

lateral axis

10000 7000 + 9 dB -6 dB

Shock response spectrum based on Q=10

Table 6 Qualification Level Sinusoidal Vibration Test Environment

Axes Frequency (Hz) Input Level (G) Sweep Rate

X Y and Z 5 - 24

24 - 65

65 - 100

05 in DA

15

7

2 octmin

Table 7 Qualification Level Random Vibration Test Environment

Axes Frequency

(Hz)

PSD Input

Level

Overall Level

(Grms)

Duration

(sec)

X Y and Z 20 ndash 100

100 ndash 1000

1000 - 2000

+3 dBoct

02 g2Hz

-3 dBoct

181 120

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httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1113

AIAA 2002-4349

Page 11

Qualification Tank Pressure Log Insummary the Qualification Tank hasundergone the pressure cycles listed in Table8 The successful completion of thequalification test program is an excellentdemonstration of the tankrsquos robust design

ACCEPTANCE TESTING

The following acceptance tests are performedon a flight tank prior to delivery

l Preliminary examinationl Pre-proof volumetric capacityl Ambient proof pressurel Post-proof volumetric capacityl Volumetric capacity at MEOPl External leakagel Weld quality inspectionl Final examinationl

Cleanliness measurement

Cleanliness Verification After the finalexternal leak test each flight tank is cleaned tothe cleanliness level specified in Table 9

Table 9 Pressurant Tank CleanlinessLevel

Particle Size Range(Microns)

Maximum Allowedper 100 ml

5 to 10 140

11 to 25 2026 to 50 5

51 to 100 1

Over 100 0

Photograph of a completed tank is shown inFigure 15

Figure 15 A completed PressurantTank

Table 8 Summary of Qualification Tank Pressure Cycles

Pressure Actual of Cycles

RequiredCycles

Description

331 bar (4800 psig)Operating pressure 61 50 52 operating cycles3 external leaks1 shock test5 pressurization cycles during vibration testing

414 bar (6000 psig)Proof pressure

8 8 1 proof test7 proof cycles

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AIAA 2002-4349

Page 12

CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

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AIAA 2002-4349

Page 13

NOTES

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AIAA 2002-4349

Page 7

COMPOSITE OVERWRAP DESIGN ANDFABRICATION

The pressurant tank composite overwrapcontains several layers of high angle helicaland hoop wraps The same wet filamentwinding technique used on the previouspressurant tank is applied to this pressuranttank This process utilizes dry fiber roving thatis in-process impregnated with a low-viscosityresin The materials used in the compositeoverwrap include Torayca T-1000G highperformance carbon fiber and EPON 826 epoxyresin system The basic resin system hasyears of commercial heritage and offersexcellent characteristics including lowviscosity reasonable pot life high strain-to-failure capability good chemical and moistureresistance and low toxicity Thousands of COPVrsquos have been wrapped using this resin

system

The resin system has a 107degC (225degF) curetemperature The glass transition temperature

(Tg) of the cured system is 99degC (210degF)providing a comfortable margin over the tankrsquos

maximum operating temperature of 60degC

(140degF)

A computer-controlled filament windingmachine is used to perform the compositeoverwrap operation See Figure 10 Acomputer code was generated to wrap the

pressurant tank The entire wrap process wasautomated to insure quality and repeatability

Figure 10 Automated Filament Winding

The filament wrap is bonded to the liner by athin layer of adhesive This adhesive is appliedto the liner immediately prior to the filamentwrap operation After filament wrap the vesselis placed in an oven and the resin is gelled andcured

WEIGHT DISTRIBUTION

The pressurant tank weight distribution issummarized in Table 3 below

Table 3 Pressurant Tank WeightDistribution

Item NominalWeight (kg)

NominalWeight (lbm)

Liner 37 81

Composite 80 177

TOTAL 117 258

The qualification tank was slightly above thenominal weight However most flight tanksfabricated were slightly below nominal weight

TANK GROWTH

The pressurant tank undergoes expansion as itis being pressurized The tank expansion datafor the Qualification tank is summarized in

Table 4 The measured tank growth closelymatches the predicted values

TANK SIZING

The pressurant tank is subjected to a sizingoperation (autofrettage) after the tank iswrapped and the resin system is cured Theautofrettage pressure is selected during tankanalysis This pressurization cycle isconsidered part of the manufacturing processand is not included in the pressure cyclehistory Autofrettage is performed immediately

prior to acceptance proof pressure testing

Table 4 Pressurant Tank Growth Data

Pressure Linear Growth Radial Growth Volume Growth

MEOP (331 bar4800 psi) 96 mm 0376 inch 20 mm 0078 inch 31 liters (1914 in3)

Proof Pressure (414 bar6000 psi) 108 mm 0427 inch 24 mm 0093 inch 40 liters (2441 in3)

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AIAA 2002-4349

Page 8

QUALIFICATION TEST PROGRAM

A Qualification Tank was fabricated for thequalification test program The qualificationtesting consists of a series of tests intended toverify the pressurant tank design in thefollowing areas

l Physical properties such as volume andweight

l Tank shell integrityl Low cycle fatiguel High cycle fatiguel Shock fatiguel Burst margin

PassFail criteria consisted of acceptance typeexternal leak tests conducted at intervalsthroughout the test program After the tankpassed the final external leak test it underwent

a destructive burst pressure test Thesuccessful burst certified the tank for flight use

The Qualification Tank was subjected to thefollowing qualification tests

l Volumetric capacityl Proof pressure testl Volumetric capacity at ambientl Volumetric capacity at MEOPl Pressure cyclesl External leakagel Pressurized pyrotechnic shock

l External leakagel Sinusoidal and random vibrationl External leakagel Final examinationl Destructive burst pressure test

Volumetric Capacity Examination Thevolumetric capacity of the pressurant tank wasmeasured using the weight of water method atambient condition Deionized (DI) water wasused to conduct this test The tank volumesbefore and after the proof pressure test weremeasured to verify that the tank volume met the

specification requirement and that the proof pressure test did not significantly change thetank volume As an example the internalvolume of the Qualification Tank did notincrease after the proof pressure test signifyingthat the pressurant tank was manufacturedsuccessfully

Proof Pressure Test The hydrostatic proof pressure test was conducted at 414 bar (6000psig) for a pressure hold period of 5 minutesSuccessful completion of the proof pressuretest and the subsequent volumetric growth andleakage verification indicated that the tank wasmanufactured successfully

Pressure Cycles The pressurant tank isdesigned to accommodate a minimum of 8proof pressure cycles and 50 operatingpressure cycles As a practice severaloperating pressure cycles were added for contingency A total of 8 proof cycles and 52MEOP cycles were conducted at this pressurecycle testing Additionally the QualificationTank experienced another operating pressurecycle during shock test 3 operating pressurecycles for the 3 external leakage tests and 5more operating pressure cycles during vibration

testing The cumulative total of operatingpressure cycles is 61 or 11 cycles over theminimum requirement A picture of thepressure test setup is shown in Figure 11

Figure 11 Pressure Test Setup

External Leak Test The external leak testverifies the integrity of the tank shell and alsoserves to validate the previous series of pressure testing The tank is placed in a

vacuum chamber which is evacuated to under 02 microns of mercury and helium pressurizedto MEOP for 30 minutes The helium leak ratecannot exceed 1 x 10

-6 std cc per second after

a 30-minute stabilization period For examplethe leak rate of the Qualification Tank was 23 x10

-8 sccsec

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 913

AIAA 2002-4349

Page 9

During pressurization the compressed gasheats up thus heating up the tank To preventoverheating four thermocouples are attachedto the tank shell to monitor and control thepressurization rate and the tank temperatureduring pressurization The tank temperature

cannot exceed 140degF throughout the duration

of the test

Pressurized Pyrotechnic Shock TestPyrotechnic shock testing was performed onthe Qualification Tank Prior to testing apathfinder tank was mounted to the test fixturefor equalization of the shock system and todemonstrate the achievable level of input shockresponse spectrum The Qualification Tankwas then installed in the fixture and pressurizedto 4800 psig The test consisted of subjectingthe tank loaded with 4800 psig of gaseoushelium to two metal-to-metal impact shock

impulses The impulses had an input shockresponse spectrum of 7000g Both thelongitudinal axis (X axis) and the lateral axis (Zaxis) were excited simultaneously by the twoqualification level metal-to-metal impact shockimpulses The shock spectrum is presented inTable 5 A picture of the shock test setup isshown in Figure 12

Figure 12 Shock Test Setup

Vibration Test Sinusoidal and RandomQualification level sinusoidal and random

vibration tests were performed on theQualification Tank in each of the three principalaxes The vibration test requirements areshown in Tables 6 and 7

The vibration test fixture is designed to simulatethe tank-to-spacecraft installation interfacesand orientation It is also sufficiently stiff to be

considered rigid for the test frequencies Apreliminary test fixture evaluation wasconducted prior to Qualification Tankinstallation to insure the fixture meets thetesting requirements

Control accelerometers were placed on the

vibration test fixture near each end fitting tocontrol the vibration input Responseaccelerometers were placed on theQualification Tank to measure the tankresponses The placements of the responseaccelerometers were selected to record thetank responses at locations of maximum stressas predicted in the analytical model

The vibration test included fixture survey fulllevel sinusoidal and full level random runs Thesame tests were conducted in all three axes All testing was conducted with the tank

pressurized to 4800 psi with helium Aphotograph of the vibration test setup is shownin Figure 13

Figure 13 Pressurant Tank QualificationVibration Test Setup

Destructive Burst After the completion of thepressure cycles shock and vibration testingthe Qualification Tank was subjected to a finaldestructive burst pressure test TheQualification Tank burst at 572 bar (8297 psi)

providing a 152 margin on burst pressureThis data represents a burst factor of 173 to 1and a performance efficiency rating (Pressure xVolume Weight) of 157 x 10

6 inches This

high efficiency factor represents the mostefficient pressure vessel ever designed by PSIFigure 14 shows the Qualification Tank after burst

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1013

AIAA 2002-4349

Page 10

Figure 14 Qualification Tank After Qualification Burst Pressure Test

Table 5 Shock Test Spectrum

Axes Frequency (Hz) Shock response

spectrum input (g)

100 80 plusmn 6 dB

1500 7000 plusmn 6 dB

3000 7000 plusmn 6 dB

6000 7000 + 9 dB -6 dB

Longitudinal and one

lateral axis

10000 7000 + 9 dB -6 dB

Shock response spectrum based on Q=10

Table 6 Qualification Level Sinusoidal Vibration Test Environment

Axes Frequency (Hz) Input Level (G) Sweep Rate

X Y and Z 5 - 24

24 - 65

65 - 100

05 in DA

15

7

2 octmin

Table 7 Qualification Level Random Vibration Test Environment

Axes Frequency

(Hz)

PSD Input

Level

Overall Level

(Grms)

Duration

(sec)

X Y and Z 20 ndash 100

100 ndash 1000

1000 - 2000

+3 dBoct

02 g2Hz

-3 dBoct

181 120

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AIAA 2002-4349

Page 11

Qualification Tank Pressure Log Insummary the Qualification Tank hasundergone the pressure cycles listed in Table8 The successful completion of thequalification test program is an excellentdemonstration of the tankrsquos robust design

ACCEPTANCE TESTING

The following acceptance tests are performedon a flight tank prior to delivery

l Preliminary examinationl Pre-proof volumetric capacityl Ambient proof pressurel Post-proof volumetric capacityl Volumetric capacity at MEOPl External leakagel Weld quality inspectionl Final examinationl

Cleanliness measurement

Cleanliness Verification After the finalexternal leak test each flight tank is cleaned tothe cleanliness level specified in Table 9

Table 9 Pressurant Tank CleanlinessLevel

Particle Size Range(Microns)

Maximum Allowedper 100 ml

5 to 10 140

11 to 25 2026 to 50 5

51 to 100 1

Over 100 0

Photograph of a completed tank is shown inFigure 15

Figure 15 A completed PressurantTank

Table 8 Summary of Qualification Tank Pressure Cycles

Pressure Actual of Cycles

RequiredCycles

Description

331 bar (4800 psig)Operating pressure 61 50 52 operating cycles3 external leaks1 shock test5 pressurization cycles during vibration testing

414 bar (6000 psig)Proof pressure

8 8 1 proof test7 proof cycles

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AIAA 2002-4349

Page 12

CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1313

AIAA 2002-4349

Page 13

NOTES

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 813

AIAA 2002-4349

Page 8

QUALIFICATION TEST PROGRAM

A Qualification Tank was fabricated for thequalification test program The qualificationtesting consists of a series of tests intended toverify the pressurant tank design in thefollowing areas

l Physical properties such as volume andweight

l Tank shell integrityl Low cycle fatiguel High cycle fatiguel Shock fatiguel Burst margin

PassFail criteria consisted of acceptance typeexternal leak tests conducted at intervalsthroughout the test program After the tankpassed the final external leak test it underwent

a destructive burst pressure test Thesuccessful burst certified the tank for flight use

The Qualification Tank was subjected to thefollowing qualification tests

l Volumetric capacityl Proof pressure testl Volumetric capacity at ambientl Volumetric capacity at MEOPl Pressure cyclesl External leakagel Pressurized pyrotechnic shock

l External leakagel Sinusoidal and random vibrationl External leakagel Final examinationl Destructive burst pressure test

Volumetric Capacity Examination Thevolumetric capacity of the pressurant tank wasmeasured using the weight of water method atambient condition Deionized (DI) water wasused to conduct this test The tank volumesbefore and after the proof pressure test weremeasured to verify that the tank volume met the

specification requirement and that the proof pressure test did not significantly change thetank volume As an example the internalvolume of the Qualification Tank did notincrease after the proof pressure test signifyingthat the pressurant tank was manufacturedsuccessfully

Proof Pressure Test The hydrostatic proof pressure test was conducted at 414 bar (6000psig) for a pressure hold period of 5 minutesSuccessful completion of the proof pressuretest and the subsequent volumetric growth andleakage verification indicated that the tank wasmanufactured successfully

Pressure Cycles The pressurant tank isdesigned to accommodate a minimum of 8proof pressure cycles and 50 operatingpressure cycles As a practice severaloperating pressure cycles were added for contingency A total of 8 proof cycles and 52MEOP cycles were conducted at this pressurecycle testing Additionally the QualificationTank experienced another operating pressurecycle during shock test 3 operating pressurecycles for the 3 external leakage tests and 5more operating pressure cycles during vibration

testing The cumulative total of operatingpressure cycles is 61 or 11 cycles over theminimum requirement A picture of thepressure test setup is shown in Figure 11

Figure 11 Pressure Test Setup

External Leak Test The external leak testverifies the integrity of the tank shell and alsoserves to validate the previous series of pressure testing The tank is placed in a

vacuum chamber which is evacuated to under 02 microns of mercury and helium pressurizedto MEOP for 30 minutes The helium leak ratecannot exceed 1 x 10

-6 std cc per second after

a 30-minute stabilization period For examplethe leak rate of the Qualification Tank was 23 x10

-8 sccsec

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 913

AIAA 2002-4349

Page 9

During pressurization the compressed gasheats up thus heating up the tank To preventoverheating four thermocouples are attachedto the tank shell to monitor and control thepressurization rate and the tank temperatureduring pressurization The tank temperature

cannot exceed 140degF throughout the duration

of the test

Pressurized Pyrotechnic Shock TestPyrotechnic shock testing was performed onthe Qualification Tank Prior to testing apathfinder tank was mounted to the test fixturefor equalization of the shock system and todemonstrate the achievable level of input shockresponse spectrum The Qualification Tankwas then installed in the fixture and pressurizedto 4800 psig The test consisted of subjectingthe tank loaded with 4800 psig of gaseoushelium to two metal-to-metal impact shock

impulses The impulses had an input shockresponse spectrum of 7000g Both thelongitudinal axis (X axis) and the lateral axis (Zaxis) were excited simultaneously by the twoqualification level metal-to-metal impact shockimpulses The shock spectrum is presented inTable 5 A picture of the shock test setup isshown in Figure 12

Figure 12 Shock Test Setup

Vibration Test Sinusoidal and RandomQualification level sinusoidal and random

vibration tests were performed on theQualification Tank in each of the three principalaxes The vibration test requirements areshown in Tables 6 and 7

The vibration test fixture is designed to simulatethe tank-to-spacecraft installation interfacesand orientation It is also sufficiently stiff to be

considered rigid for the test frequencies Apreliminary test fixture evaluation wasconducted prior to Qualification Tankinstallation to insure the fixture meets thetesting requirements

Control accelerometers were placed on the

vibration test fixture near each end fitting tocontrol the vibration input Responseaccelerometers were placed on theQualification Tank to measure the tankresponses The placements of the responseaccelerometers were selected to record thetank responses at locations of maximum stressas predicted in the analytical model

The vibration test included fixture survey fulllevel sinusoidal and full level random runs Thesame tests were conducted in all three axes All testing was conducted with the tank

pressurized to 4800 psi with helium Aphotograph of the vibration test setup is shownin Figure 13

Figure 13 Pressurant Tank QualificationVibration Test Setup

Destructive Burst After the completion of thepressure cycles shock and vibration testingthe Qualification Tank was subjected to a finaldestructive burst pressure test TheQualification Tank burst at 572 bar (8297 psi)

providing a 152 margin on burst pressureThis data represents a burst factor of 173 to 1and a performance efficiency rating (Pressure xVolume Weight) of 157 x 10

6 inches This

high efficiency factor represents the mostefficient pressure vessel ever designed by PSIFigure 14 shows the Qualification Tank after burst

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1013

AIAA 2002-4349

Page 10

Figure 14 Qualification Tank After Qualification Burst Pressure Test

Table 5 Shock Test Spectrum

Axes Frequency (Hz) Shock response

spectrum input (g)

100 80 plusmn 6 dB

1500 7000 plusmn 6 dB

3000 7000 plusmn 6 dB

6000 7000 + 9 dB -6 dB

Longitudinal and one

lateral axis

10000 7000 + 9 dB -6 dB

Shock response spectrum based on Q=10

Table 6 Qualification Level Sinusoidal Vibration Test Environment

Axes Frequency (Hz) Input Level (G) Sweep Rate

X Y and Z 5 - 24

24 - 65

65 - 100

05 in DA

15

7

2 octmin

Table 7 Qualification Level Random Vibration Test Environment

Axes Frequency

(Hz)

PSD Input

Level

Overall Level

(Grms)

Duration

(sec)

X Y and Z 20 ndash 100

100 ndash 1000

1000 - 2000

+3 dBoct

02 g2Hz

-3 dBoct

181 120

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1113

AIAA 2002-4349

Page 11

Qualification Tank Pressure Log Insummary the Qualification Tank hasundergone the pressure cycles listed in Table8 The successful completion of thequalification test program is an excellentdemonstration of the tankrsquos robust design

ACCEPTANCE TESTING

The following acceptance tests are performedon a flight tank prior to delivery

l Preliminary examinationl Pre-proof volumetric capacityl Ambient proof pressurel Post-proof volumetric capacityl Volumetric capacity at MEOPl External leakagel Weld quality inspectionl Final examinationl

Cleanliness measurement

Cleanliness Verification After the finalexternal leak test each flight tank is cleaned tothe cleanliness level specified in Table 9

Table 9 Pressurant Tank CleanlinessLevel

Particle Size Range(Microns)

Maximum Allowedper 100 ml

5 to 10 140

11 to 25 2026 to 50 5

51 to 100 1

Over 100 0

Photograph of a completed tank is shown inFigure 15

Figure 15 A completed PressurantTank

Table 8 Summary of Qualification Tank Pressure Cycles

Pressure Actual of Cycles

RequiredCycles

Description

331 bar (4800 psig)Operating pressure 61 50 52 operating cycles3 external leaks1 shock test5 pressurization cycles during vibration testing

414 bar (6000 psig)Proof pressure

8 8 1 proof test7 proof cycles

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1213

AIAA 2002-4349

Page 12

CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

8132019 AIAA2002-4349 Astrolink Pres

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AIAA 2002-4349

Page 13

NOTES

8132019 AIAA2002-4349 Astrolink Pres

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AIAA 2002-4349

Page 9

During pressurization the compressed gasheats up thus heating up the tank To preventoverheating four thermocouples are attachedto the tank shell to monitor and control thepressurization rate and the tank temperatureduring pressurization The tank temperature

cannot exceed 140degF throughout the duration

of the test

Pressurized Pyrotechnic Shock TestPyrotechnic shock testing was performed onthe Qualification Tank Prior to testing apathfinder tank was mounted to the test fixturefor equalization of the shock system and todemonstrate the achievable level of input shockresponse spectrum The Qualification Tankwas then installed in the fixture and pressurizedto 4800 psig The test consisted of subjectingthe tank loaded with 4800 psig of gaseoushelium to two metal-to-metal impact shock

impulses The impulses had an input shockresponse spectrum of 7000g Both thelongitudinal axis (X axis) and the lateral axis (Zaxis) were excited simultaneously by the twoqualification level metal-to-metal impact shockimpulses The shock spectrum is presented inTable 5 A picture of the shock test setup isshown in Figure 12

Figure 12 Shock Test Setup

Vibration Test Sinusoidal and RandomQualification level sinusoidal and random

vibration tests were performed on theQualification Tank in each of the three principalaxes The vibration test requirements areshown in Tables 6 and 7

The vibration test fixture is designed to simulatethe tank-to-spacecraft installation interfacesand orientation It is also sufficiently stiff to be

considered rigid for the test frequencies Apreliminary test fixture evaluation wasconducted prior to Qualification Tankinstallation to insure the fixture meets thetesting requirements

Control accelerometers were placed on the

vibration test fixture near each end fitting tocontrol the vibration input Responseaccelerometers were placed on theQualification Tank to measure the tankresponses The placements of the responseaccelerometers were selected to record thetank responses at locations of maximum stressas predicted in the analytical model

The vibration test included fixture survey fulllevel sinusoidal and full level random runs Thesame tests were conducted in all three axes All testing was conducted with the tank

pressurized to 4800 psi with helium Aphotograph of the vibration test setup is shownin Figure 13

Figure 13 Pressurant Tank QualificationVibration Test Setup

Destructive Burst After the completion of thepressure cycles shock and vibration testingthe Qualification Tank was subjected to a finaldestructive burst pressure test TheQualification Tank burst at 572 bar (8297 psi)

providing a 152 margin on burst pressureThis data represents a burst factor of 173 to 1and a performance efficiency rating (Pressure xVolume Weight) of 157 x 10

6 inches This

high efficiency factor represents the mostefficient pressure vessel ever designed by PSIFigure 14 shows the Qualification Tank after burst

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AIAA 2002-4349

Page 10

Figure 14 Qualification Tank After Qualification Burst Pressure Test

Table 5 Shock Test Spectrum

Axes Frequency (Hz) Shock response

spectrum input (g)

100 80 plusmn 6 dB

1500 7000 plusmn 6 dB

3000 7000 plusmn 6 dB

6000 7000 + 9 dB -6 dB

Longitudinal and one

lateral axis

10000 7000 + 9 dB -6 dB

Shock response spectrum based on Q=10

Table 6 Qualification Level Sinusoidal Vibration Test Environment

Axes Frequency (Hz) Input Level (G) Sweep Rate

X Y and Z 5 - 24

24 - 65

65 - 100

05 in DA

15

7

2 octmin

Table 7 Qualification Level Random Vibration Test Environment

Axes Frequency

(Hz)

PSD Input

Level

Overall Level

(Grms)

Duration

(sec)

X Y and Z 20 ndash 100

100 ndash 1000

1000 - 2000

+3 dBoct

02 g2Hz

-3 dBoct

181 120

8132019 AIAA2002-4349 Astrolink Pres

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AIAA 2002-4349

Page 11

Qualification Tank Pressure Log Insummary the Qualification Tank hasundergone the pressure cycles listed in Table8 The successful completion of thequalification test program is an excellentdemonstration of the tankrsquos robust design

ACCEPTANCE TESTING

The following acceptance tests are performedon a flight tank prior to delivery

l Preliminary examinationl Pre-proof volumetric capacityl Ambient proof pressurel Post-proof volumetric capacityl Volumetric capacity at MEOPl External leakagel Weld quality inspectionl Final examinationl

Cleanliness measurement

Cleanliness Verification After the finalexternal leak test each flight tank is cleaned tothe cleanliness level specified in Table 9

Table 9 Pressurant Tank CleanlinessLevel

Particle Size Range(Microns)

Maximum Allowedper 100 ml

5 to 10 140

11 to 25 2026 to 50 5

51 to 100 1

Over 100 0

Photograph of a completed tank is shown inFigure 15

Figure 15 A completed PressurantTank

Table 8 Summary of Qualification Tank Pressure Cycles

Pressure Actual of Cycles

RequiredCycles

Description

331 bar (4800 psig)Operating pressure 61 50 52 operating cycles3 external leaks1 shock test5 pressurization cycles during vibration testing

414 bar (6000 psig)Proof pressure

8 8 1 proof test7 proof cycles

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1213

AIAA 2002-4349

Page 12

CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1313

AIAA 2002-4349

Page 13

NOTES

8132019 AIAA2002-4349 Astrolink Pres

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AIAA 2002-4349

Page 10

Figure 14 Qualification Tank After Qualification Burst Pressure Test

Table 5 Shock Test Spectrum

Axes Frequency (Hz) Shock response

spectrum input (g)

100 80 plusmn 6 dB

1500 7000 plusmn 6 dB

3000 7000 plusmn 6 dB

6000 7000 + 9 dB -6 dB

Longitudinal and one

lateral axis

10000 7000 + 9 dB -6 dB

Shock response spectrum based on Q=10

Table 6 Qualification Level Sinusoidal Vibration Test Environment

Axes Frequency (Hz) Input Level (G) Sweep Rate

X Y and Z 5 - 24

24 - 65

65 - 100

05 in DA

15

7

2 octmin

Table 7 Qualification Level Random Vibration Test Environment

Axes Frequency

(Hz)

PSD Input

Level

Overall Level

(Grms)

Duration

(sec)

X Y and Z 20 ndash 100

100 ndash 1000

1000 - 2000

+3 dBoct

02 g2Hz

-3 dBoct

181 120

8132019 AIAA2002-4349 Astrolink Pres

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AIAA 2002-4349

Page 11

Qualification Tank Pressure Log Insummary the Qualification Tank hasundergone the pressure cycles listed in Table8 The successful completion of thequalification test program is an excellentdemonstration of the tankrsquos robust design

ACCEPTANCE TESTING

The following acceptance tests are performedon a flight tank prior to delivery

l Preliminary examinationl Pre-proof volumetric capacityl Ambient proof pressurel Post-proof volumetric capacityl Volumetric capacity at MEOPl External leakagel Weld quality inspectionl Final examinationl

Cleanliness measurement

Cleanliness Verification After the finalexternal leak test each flight tank is cleaned tothe cleanliness level specified in Table 9

Table 9 Pressurant Tank CleanlinessLevel

Particle Size Range(Microns)

Maximum Allowedper 100 ml

5 to 10 140

11 to 25 2026 to 50 5

51 to 100 1

Over 100 0

Photograph of a completed tank is shown inFigure 15

Figure 15 A completed PressurantTank

Table 8 Summary of Qualification Tank Pressure Cycles

Pressure Actual of Cycles

RequiredCycles

Description

331 bar (4800 psig)Operating pressure 61 50 52 operating cycles3 external leaks1 shock test5 pressurization cycles during vibration testing

414 bar (6000 psig)Proof pressure

8 8 1 proof test7 proof cycles

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1213

AIAA 2002-4349

Page 12

CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1313

AIAA 2002-4349

Page 13

NOTES

8132019 AIAA2002-4349 Astrolink Pres

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AIAA 2002-4349

Page 11

Qualification Tank Pressure Log Insummary the Qualification Tank hasundergone the pressure cycles listed in Table8 The successful completion of thequalification test program is an excellentdemonstration of the tankrsquos robust design

ACCEPTANCE TESTING

The following acceptance tests are performedon a flight tank prior to delivery

l Preliminary examinationl Pre-proof volumetric capacityl Ambient proof pressurel Post-proof volumetric capacityl Volumetric capacity at MEOPl External leakagel Weld quality inspectionl Final examinationl

Cleanliness measurement

Cleanliness Verification After the finalexternal leak test each flight tank is cleaned tothe cleanliness level specified in Table 9

Table 9 Pressurant Tank CleanlinessLevel

Particle Size Range(Microns)

Maximum Allowedper 100 ml

5 to 10 140

11 to 25 2026 to 50 5

51 to 100 1

Over 100 0

Photograph of a completed tank is shown inFigure 15

Figure 15 A completed PressurantTank

Table 8 Summary of Qualification Tank Pressure Cycles

Pressure Actual of Cycles

RequiredCycles

Description

331 bar (4800 psig)Operating pressure 61 50 52 operating cycles3 external leaks1 shock test5 pressurization cycles during vibration testing

414 bar (6000 psig)Proof pressure

8 8 1 proof test7 proof cycles

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1213

AIAA 2002-4349

Page 12

CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1313

AIAA 2002-4349

Page 13

NOTES

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1213

AIAA 2002-4349

Page 12

CONCLUSION

The pressurant tank development programhas successfully concluded qualificationtesting without failure The qualificationtesting shows the pressurant tank having

comfortable margins over all the operationalrequirements The production programsuccessfully fabricated several flight tanks

The pressurant tank is high performancelight weight and easy to manufacture Thecomposite overwrap and the liner components are made from commerciallyavailable materials The liner assembly andfilament winding are accomplished usingstandard manufacturing processes andprocedures Special material and processesare not required

This tank is also lighter than a typical all-metal tank of the same capacity andcapability The manufacturing cycle isseveral months shorter than a comparableall-metal tank Acceptance testing is simpler or equivalent to an all-metal pressurant tank

The pressurant tank maintains excellentdesign and flight heritage Its overall designand method of manufacturing are derivedfrom several prior COPV programs Thedesign of this pressurant tank is extremelyconservative and all manufacturing methods

are based upon existing technology

Most importantly the successful qualificationof this tank marks the milestone in which aderivative COPV pressurant tank is designedand manufactured efficiently andinexpensively using existing technology

ACKNOWLEDGMENT

Our sincere appreciation to all that made thisprogram a success Special thanks areexpressed to Mr Paul Chapman Mr Mark

Drey Mr Mike Hersh Mr Jeff Jean MrMarvin Josephson Mr Gary Kawahara MrJerry Kuo Ms Leonita Pistor Ms MarileeSoden Ms Quyen Tran and Mr Lee Truongfor their dedication and hard work on thisprogram

ABOUT THE AUTHORS

Mr Walter Tam and Mr Paul Griffin areProgram Managers at Pressure SystemsInc Mr Art Jackson is a stress analyst DBAJackson Consulting

REFERENCE

1 G Kawahara S McCleskey ldquoTitanium-Lined Carbon Composite OverwrappedPressure Vesselrdquo AIAA 96-2751

2 W H Tam I Ballinger J Kuo W LayS McCleskey P Morales Z Taylor SEpstein Design and Manufacture of aComposite Overwrapped Xenon ConicalPressure Vessel AIAA 96-2752

3 W H Tam A C Jackson E Nishida YKasai A Tsujihata K Kajiwara ldquoDesignand Manufacture of the ETS VIII XenonTankrdquo AIAA 2000-3677

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1313

AIAA 2002-4349

Page 13

NOTES

8132019 AIAA2002-4349 Astrolink Pres

httpslidepdfcomreaderfullaiaa2002-4349-astrolink-pres 1313

AIAA 2002-4349

Page 13

NOTES