apollo experience report command module crew-couch restraint and load-attenuation systems

8/8/2019 Apollo Experience Report Command Module Crew-Couch Restraint and Load-Attenuation Systems

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- 31748N A S A T E C H N IC A L N O T E NASA TN 0-7440

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APOLLO EXPERIENCE REPORT -COMMAND MODULE CREW-COUCH/RESTRAINTA N D L O A D - A T T E N U A T IO N SYSTEM S

by Ra&b E. Drexel a n d Howard N.HunterLyndon B. Johnson Space CenterHozrston, Texas 77058N A TION A L A E R ONA U TIC S A N D S PA CE A D MIN IS TR A T ION W A S H IN GTON , D. C. SEPTEMBER 1973


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1. Report No. 1 2. Government Accession No. 1 3. Recipient's Catalog No. IASA TN D- 7440 I4 Title and SubtitleAPOLLO EXPERIENCE REPORTCOMMAND MODULE CREW-COUCH/RESTRAINT

5. Report DateSeptember 19736. Performing Organization Code

AND LOAD-ATTENUATION SYSTEMS7. Author(s1 8. Performing Organization Report No.

Ralph E. Drexel and Howard N. Hunter, JSC9. Performing Organization Name and Address

JSC S- 37910. Work Unit No.

9 14-50-DJ-96-72Lyndon B. Johnson Space CenterHouston, Texas 77058

2. Sponsoring Agency Name and Address

6. Abstract

11. Contract or Grant No.

13. Type of Repon and Period CoveredTechnical Note

National Aeronautics and Space AdministrationWashington, D.C. 20546

The Apollo command module crew-couch/restra.int and load-attenuation sys tem was requir ed tosupport and rest ra in the crewman during mission phases and to limit the load imposed on thecrewman during landing. Component designs evolved when requirements changed and te st s wereconducted. Advancement in the st ate of the ar t for energy-absorbing devices and changes in re-straint philosophies for impact protection resulted from the efforts and experiences presented.

14. Sponsoring Agency Code

7. Key Words (Suggested by Author(s))'Couches 'Absorbers'Seats 'Shock Absorbers'Attenuators'Mechanical Load Attenuation

5. Supplementary NotesThe JSC Director waived the use of the International System of Units (SI) for th is Apollo Expe-rience Report, because, in his judgment, use of SI units would impair the usefulness of the re..port or resul t in-excessive cost.

18. Distribut ion Statement

-

*For sale by the National Technical Information Service, Springfield, Virginia 22151

I19. Security Classif. (of this report )

None21. No. of Pages

2020. Security Classif. (of thi s page)

None22. Price*Domestic, $2.75Foreign, $5.25


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CONTENTS

Section PageSUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2DESIGN REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 .

Couch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Attenuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

DESIGN CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Couch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Attenuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

SYSTEM DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Block I. Apollo 7 Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

. . . . . . . . . . . . . . . . . . .lock 11. Apollo 8 and Subsequent Missions 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .EST PROGRAMS 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .asic-Criteria Tes ts 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .evelopment Te st s 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ertification Te st s 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .LIGHT EXPERIENCE 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .ONCLUDING REMARKS 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .EFERENCES 16 .

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FIGURES

Figure PageOrientation of the CM crew-couch/restraint system . . . . . . . . . . . 4Universal integrated couch/restraint syst em . . . . . . . . . . . . . . 5Prototype Apollo unitized couch . . . . . . . . . . . . . . . . . . . . . 5Apollo unitized-couch flight design . . . . . . . . . . . . . . . . . . . . 5Res tra int -harnes s components of the Apollo unitized couch . . . . . . . 5Apollo foldable-couch flight design . . . . . . . . . . . . . . . . . . . . 6Passive heel restraint . . . . . . . . . . . . . . . . . . . . . . . . . . 6Block I load-attenuation levels . . . . . . . . . . . . . . . . . . . . . . 7Aluminum-honeycomb-core load attenuator . . . . . . . . . . . . . . . 7Strut lockout(a) Unlocked position . . . . . . . . . . . . . . . . . . . . . . . . . . . 8(b) Locked position . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Cyclic stru t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Ramp-loaded attenuator st ru t assembly . . . . . . . . . . . . . . . . . 9

. . . . . . . . . . . . . . . . . . . . . .oldable-couch flight positions 11. . . . . . . . . . . . . . . . . .yclic-strut load/time characteristic 12Combined cyclic-stru t and low-onset-device load/time. . . . . . . . . . . . . . . . . . . . . . . . . . . . .haracteristic 12. . . . . . . . . . . . . . . . .amp-loading device load/stroke curve 13. . . . . . . . . . . . . . . . . . . . . .lock II load-attenuation levels 14


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APOLLO EXPERIENCE REPORTCOM MAN D MODULE CREW-COUCHIRESTRAI NT

AND LOAD-ATTENUATI ON SY STEMSB y R a l p h E. D r e x el a n d H o w a r d N . H u n t e rL y n d o n B . J o h n s o n S pa ce C e n t e r

S U M M A R Y

The development of the crew-couch/restra.int system and the crew load-attenuationsys tem for the Apollo command module re sulted in a significant advancement in the sta teof the art. During the Apollo Program, changes in program requirements causeda change in system requirements. These changes, together with res earch and testing,resulted i n the design and flight of various couch, res tra int , and attenuation syste ms.The pre-Apollo impact-loading restraint philosophy dictated a requirement forcomplete re str ain t and support of the body that resu lted in cumbersome st raps and mas-sive, individually contoured couches. The development effort for the Apollo Programresulted in a couch that accommodates al l size crewmen, is self-adjusting to the con-tour of the crewman, and can be disassembled, folded, and reassembled in flight by asuited crewman without the use of tools. The restr ain t system that was developed forthe Apollo Program is a six-point suspension system incorporating an easily actuated

single-point release. This couch/restraint system allows the crewman the necessarymobility for spacecraft operations and affords him adequate restr ain t during landingimpact.The load attenuators available during the ea rly stages of the Apollo Progra m metthe specified spacecraft requiremen ts, but could not meet the controlled-load andreve rsib le-s troke requirements of the final Apollo Pro gra m definitions. The couchload-attenuation system developed for the spacecraft to protect the crewman primarilyduring land landing us es two methods of energy absorption: frict ion and two fo rm s ofcyclic deformation of material. The spacecraft couch load-attenuation system is com-pact, will absorb energy in both compress ion and tension stroking , and can be cycledwith an accumulative life of approximately 100 inches of stroking without load degrada-tion. The long stroking life and repeatability of the load levels made possib le a pre-

acceptance load/stroke te st that allowed the determination of the actual stroking loadvalue before installation in the spacecraft.


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The Apollo crew-couch/restraint system was designed to support and res trainth ree crewmen during all phases of the mission from launch to landing. The load-attenuation system was designed to control the impact loads imposed on the crew duringlanding, and to remain nonfunctional during any other phase of the mission.

The functional and physical design requirements, the evolution of the design, andthe command module (CM) interfaces of the crew-couch/restraint and load-attenuationsystems a r e discussed in this report . A brief description of the s ystems and some ofthe problems encountered during development and flight a r e also included.The development of the crew-couch/restraint and load-attenuation sys tem was a5-year effort. During this time , philosophies and program requirements changed whichresulted i n different generations of equipment and in the use of more than one design inthe program.

DE S IGN REQU I EMENTS

The following a re the final design requirements for the Apollo crew-couch/res tra int and load-attenuation system. Since al l the requirements were not imposedinitially or recognized in the ea rly stages of the Apollo Pr ogra m, the evolution of thedesign and requirements is described in the text. The abor t mission requirement ofland landing the CM had the greatest influence on finalizing the crew-couch/restraintand load-attenuation system requirements.

CouchFinal design requirements for the Apollo crew-couch/restraint system a re asfollows.1. Support: The couch shal l support the crewman during al l mission phases.2 . Restraint : The crewman shal l be rest rained, when necessary, during themission.3. Mobility: The crewman shall be allowed adequate freedom, while res tra ined,to perform spacecraft operations.4. Accommodation: The couch shall accommodate any size crewman between

the 10th- and 90th-percentile dimensions a s defined in reference 1. No tools or specialequipment shall be required for positioning the couch during flight.5. Operation: Operation of the couch shall be compatible with a crewman in apressurized space suit.


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6. Disassembly: The couch shal l be foldable and stowable in flight to incr easethe inter ior working volume of the CM for mission operations.7. Strength: Structura lly, the couch shall be adequate to support a crewmanunder loads imposed by the attenuator system.

A t t e n u a t o r sFinal design requirements fo r the Apollo load-attenuation system a re a s follows.1. Stroking level: The stroking level of the attenuator s shal l limi t the loads im-posed on the crewman during landing. The attenuato rs sha ll not allow the couch tomove during any mission phase other than landing.2. Stroking distance : The attenuators shall absorb the landing energy transmi ttedto the couch within the stroking distance allowed in the CM.3. Reversibility : The attenuators sha ll absorb energy in both tension and com-pression stroking.

DESI GN CONSI DERATIONS

Although support and rest ra in t of the crewmen during all mission phases was aprimary couch requirement fo r Proje ct Mercury and for the Gemini and Apollo Pro -gram s, some progra m differences that influenced the design and development of thecouch and load-attenuation syste ms did exist. The differences in the program require-ments a r e listed in the following paragraphs.1. Mobility: Mobility within the spacecraft was not a requirement in Pr ojec tMercury and the Gemini Program . In the Apollo Pro gra m, an intravehicular mobilityrequirement made it necessary to design a folding couch.2. Launch abort: In both Pro jec t Mercury and the Apollo Pro gra m, an escapetower was provided for separation of the spacecraft from the booster in the event of alaunch abort , during which the crewmen would remain in the spacecraft. In the GeminiPro gra m, individual ejection sea ts were provided for pad and low-altitude aborts.3. Landing: Although al l thr ee programs had a pri mary water-landing capability,design of the Mercury and Apollo spacecraft required incorporation of a secondaryland-landing capability in cas e of a pad o r very-low-altitude abort . Landing-load at- .tenuation was provided externally on the Mercury capsule, but i t was provided internally

on the Apollo CM. The requirement fo r a land-landing capability with inte rna l attenua-tion was a primary facto r in the design of the Apollo couch load-attenuation system.The orientation of the couch, rest ra in t, and attenuation sy stem s within the CM isshown i n figure 1.


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Y -Y struts 1bearing plateFigure 1.- Orientat ion of the CM crew-couch/restraint system.

During the Apollo Program, two mis-sion designations were made, which resu ltedin a Block I and a Block I1 CM. The Block Ivehicle was used for an earth-orbital mis-sion only, and the Block I1 vehicle was usedfo r the lunar-landing mission. The CM re-quirements were redefined for the Block 11mission, which resulted in a change inspacecraft equipment. The redefinitionrequirements resulted in changes to thecrew-couch/restraint and load-attenuationsystems design considerations that a re iden-tified later in this report.

CouchThe Apollo Block I crew-couch assem-

bly was required to provide comfortablesupport in the proper operating position and,during all mission phases, to provide ade-quate res train t fo r crewmen in both theventilated- and pressurized-space-sui t conditions. The crew-couch assembly was re -quired to allow inflight position adjustment fo r all specified mission operating require-ments and to provide mounting space for rotational and translational flight controls.The original couch design was influenced strongly by the human factor s (that is,size, reach, mobility), by the biodynamic requirements for impact protection, and bya lack of knowledge about the landing character is tics of the spacecraft. A requirementthat the crewman must be rest rained completely to survive the landing impact was dic-tated by these fac tor s. A need for fur the r investigation of crew impact , with considera-

tion given to spacecraft operational-requirement trade-offs, became evident from thecouch design shown in figure 2. This design resu lted fr om a study conducted by an in-dependent contrac tor very early in the Apollo Program. The criterion used for thestudy was the existing human-impact-protection philosophy. The crew support and re-stra int system that resulted from this study was entirely too cumbersome, complex,and massive.The fi r s t prototype of the Apollo couch assembly , built by the pr ime contractor

- to meet the ea rly program requirements, is shown i n figure 3 . After a review of thiscouch, impairment of the inflight mobility of the crewman, both by the massiveness ofthe couch and by the complexity of the restr ain t harness , was apparent.As a result of the review, research and human-impact testing were conducted to

maximize inflight crewman mobility and to maintain adequate impact protection. Theresu lts of human-impact testing reduced the requirement fo r complete rest ra in t of thecrewman within the deceleration loads specified fo r the Apollo CM crew couch.The advancement of the support and res traint philosophy resul ted in changing thecouch design from the individualized, contoured-seat concept that was used in the


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Figure 2. - Universal integrated couch/restraint system.

Figure 4. - Apollo unitized-couchflight design.

Figure 3 . - Prototype Apollo unitizedcouch.Mercury and Gemini Pro gra ms to a univer-sa l couch that would fit a ll crewmen betweenthe 10th-and 90th-percentile s izes . With thenew restr ain t requirements, the crew-couch/restra int syst em was redesigned tothe configuration shown in figure s 4 and 5(unitized couch) and was flown on theApollo 7 mission.

The Block II redefinition of the ApolloProgram emphasized the requirement formore work volume i n the CM to allow in-travehicular mobility and the requirementto open a center a isle for side-hatch extra-vehicular activity (EVA) by a suited crew-man wearing a portable life support system.

Figure 5. - Restraint-harness com-ponents of the Apollo unitizedcouch.


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The side-hatch EVA requirement allows fora contingency return from the lunar module(LM) to the CM should a crewman not beable to re turn through the tunnel. Becausethese requirements could not be met with-out a major redesign of the unitized couch,a new couch that had minimum mechanicalcomplexity but maximum flexibility wasdesigned. The foldable couch (fig. 6) wasdeveloped and was used on al l mannedmissions subsequent to the Apollo 7mission.A further review of the crew-couchrequirements determined that the early r e-quirement for the couch to transla te theleft- and right-hand crewmen from thelaunch positions to the docking window wasnot necessary. This requirement was de-leted in favor of the crewman moving him-self up to the docking window without thecouch and then using the couch-restraintsystem to secure himself. Also, a s a re -sult of the review, the crewman-operatedfoot-restraint system was deleted and re-placed with a passive heel restraint (fig. 7).

Figure 6. - Apollo foldable-couchflight design.

The elimination of the functions justdescribed reduced the complexity of thecrew-couch system. The passive heel re -straint design on the foldable couch elimi-nated inaccessible mechanisms in the

Loopan &nt retaining bar

Figure 7. - Passive heel restraint.restraint system and resulted in increa sed crew safety. The passive heel restraint wasincorporated on the unitized couch just before the launch of the Apollo 7 spacecraft.Translation of the man, instead of the couch, to the docking position was verified on theApollo 7 mission because the Apollo 7 couch design allowed investigation of both methods.

Installation tools were not needed for prelaunch installation of the foldable couchand, consequently, installation time was reduced from 4 hours to 1 hour. Because thecouch was easy to remove and instal l, removal of the couch was permitted in the launch-readiness countdown to maximize the CM accessible inte rior and to minimize the t imerequired for activities (such a s stowage and repa irs ) inside the CM.

AttenuatorsIn the Apollo Program, the crew was protected from landing-impact loads by con-trolling only the loads imposed on the crewmen and the crew-couch/restraint system,not the loads imposed on the whole vehicle a s in conventional craft. In other words,the landing gear was inside the vehicle.


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The requirements imposed on the attenuators were rather simple and direct. Be-cause the CM did not have any faci liti es fo r limiting the landing impact, the a ttenuatorswere required to provide support to the crew couch during all mission phases and tolimit the energy transmitted to the crewman during landing impact. Also, the attenua-to rs were limited to a stroking distance of 16 inches.The attenuators for the Block I CM were sized theoretically to produce the strokingg levels shown in figure 8 for a single-mass (man and couch) system.Various methods of energy absorption, such a s metal cutting, meta l bending, tubeswaging, and hydraulics, were studied and tested in an effort to meet the or iginal ApolloProg ram requirements of load, stroke, and repeatability. The first load attenuatorproposed fo r the Apollo CM was an aluminum-honeycomb-core concept (fig . 9).The honeycomb-attenuator load could be predicted only by testing samples fromthe same core of honeycomb that was used in the attenuator. Furthermore, the fr ic -tional for ces of the brake, which was used for retu rn st rok es, decreased with time dndwere not predictable. The result was an attenuator with a questionable load level within

large tolerances. This attenuator met the water-landing requirements of the Block Ispacecraft and provided the lightest weight st ru t fo r the required load levels. Becausethe water-landing loads were lower than the high-g entry loads, shear pins were pro-vided to ensure that the attenuator would not stroke during entry. The attenuator de-sign remained relatively stable, but design of the lockout device was changed until acrew-operated design (fig. 10) was developed and flown on all missions except theApollo 7 mission. The honeycomb attenuator was used in al l axes on the Apollo 7 mis-sion and for the Y-axis only on all other missions.During the Block 11 redefinition, thedecision was made to provide crew protec-tion for land landing because the location ofthe launch pad and the height of the vehicle

resulted in a high probability of land landingduring a pad or very-low-altitude abor t.Because the CM could tumble during a landlanding, a requirement for load attenuationin both stroking directions was imposed.

Piston/--Honeycomb/-

Note: arrows denote the direction of the force applied to the man.

Figure 8. - Block I load-attenuationlevels. Figure 9. - Aluminum-honeycomb- coreload attenuator .


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Attenuator piston (inne r cylinder)

+

0

t ~ t t e n u a t o rylinder (outer)1 h /- Attenuator piston (inner wlinderl

(a) Unlocked position. (b) Locked position.Figure 10. - Strut lockout.

The higher energy levels of land landing and the limited stroking distance also resultedin a requirement f or an attenuator that would stroke a t a predictable level within closetolerance.A double-acting, repeatable attenuator (cyclic strut) (fig. 11)was developed thatfulfilled the spacecraft land-landing cri te ria. The cyclic st rut is based on a uniqueconcept of cyclic deformation of metal to absorb energy (refs . 2 and 3). Simply stated,energy absorption is accomplished by rolling a ring of metal between two surfaces thatare located less than the diameter of the ring apa rt, resulting in continual deformationof the ring as it rolls.Because the cyclic st ru t is a constant-load device, load overshoot at the init ialstroke of the strut (breakout) is an inherent problem. Because of the small differencebetween the strut load value necessary to meet the allowable stroking distance and thecrew tolerance in the Z-axis, this overshoot could not be tolerated.

The couch and man represent a two-mass system with the couch attached to thestrut; therefore, the overshoot results ina secondary impact of the man on the couch.Because the couch mass is one-third of thetotal suspended mass, i t does not impose ahigh enough load on the st ru t to initiatestroking; a s a result, the man impacts therelatively stationary couch with approxi-mately the same velocity a s the landingspacecraft. This secondary impact,coupled with the breakout load of the st rut ,results in a g level that is higher than thestroking level that is designed for a single-Figure 11.- Cyclic strut . mass system. Although this initial-impact


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g level was not considered dangerous, a softening of the secondary impact was desirablein the Z-axis to decrease the probability of spinal injury.To reduce the secondary impact level, couch stroking had to star t before the sec-ondary impact. This early stroking of the couch was produced by controlling the onset

ra te of loading that was imposed on the couch system. A low-onset device was devel-oped to control the rate of loading (ref. 3). When this device was added to a Z-axiscyclic stru t (fig. 12), the combination stru t started stroking at a lower level than thepure cyclic stru t, and the rat e of loadingfrom breakout to nominal s troke load wasWashers controllable. With this application, the/- -Q.A maximum load imposed on the crew wasnever higher thanthe nominal stroke load,and the secondary impact level was reduced.I 1 1 1 1 1 1 1 1 1 1 1 1 1 n 1 1 1 1 1 1 3 The low-onset device incorporates the con-I I cept of metal-to-metal friction for energyabsorption with the frictional load being in-

Rings creased incrementally a s the st rut strokes.Figure 12. - Ramp-loaded attenuator Cyclic attenuators were used for thestrut assembly. X-ax i s on all missions starting with theApollo 8 mission. Cyclic attenuators wereused for the Z- ax i s on the Apollo 8 and 9missions. On the Apollo 10 and subsequent missions, the Z-axis cyclic attenuatorwas replaced by the combination attenuator.

SYSTEM DESCRIPTI ONBecause of the changes in requirements for the Block I and Block I1 CM and be-

cause different equipment was flown on the two command modules, a description of eachsystem is presented.Block I, Apollo 7 Mission

Couch. - The Block I couch consisted of a unitized, box-beam-construction, three-man plafform for the back support. The headres t and the seat/leg-pan assembly foreach crewman were attached to this plafform. The body of the crewman was restra inedby a six-point suspension restraint harness with a single-point-release system. Aninstep stra p that was tightened and released by means of a mechanism actuated by aD-ring located on the sea t pan (fig. 4) rest rained the feet. This device was replacedby a passive heel restraint (fig. 7) ust before the Apollo 7 mission.The Block I couch headrest was adjustable in flight for two conditions: pressur-ized suit and nonpressurized suit . Adjustment for crewman size had to be made on theground before launch. Essentially, the seat/leg-pan assembly was a single unit thatpivoted about the hip joint for couch ingress and egress.


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Attenuators. - The Block I attenuators consisted of a cylinder and a piston with analuminum-honeycomb core placed between the piston and cylinder ends. The loads ap-plied to the piston rod were limited to the crushing strength of the honeycomb core, andenergy was absorbed by material deformation. Because implementation of this conceptwould limit the load and would result i n energy absorption in the in itial stroking direc-tion only, a friction brake was installed on the X- and Z-axis attenuators to provide alimited amount of load attenuation for the re tu rn and subsequent stroking and to hold thecouch stable after stroking. Because the Y-axis attenuators acted as bumpers betweenthe couch and the CM sidewall and, therefore, stroked in one direction only, a frictionbrake was not required.

To prevent stroking during high-g ent rie s that would resul t in attenuator loads. higher than the stroking load, a passive lockout was installed. The ini tial couch load-ing had to be higher than the breakout level of the lockout before the attenuator wouldstroke.Block I I , Apollo 8 and SubsequentMissions

Couch. - The Block I1 couch consisted of three individual body supports that wereattached by pip pins and clamps to a supporting framework. The body supports could befolded at the hip joint and knee joint, had provisions for locking the seat pan at twoangles other than that of the folded position, were capable of being folded at approxi-mately the shoulder position, and could be detached from the framework fo r storage(fig. 13). The body supports also could be detached and folded in flight by a crewmanin a pressurized space suit. As in the case of side-hatch EVA, the center body supportis detached and stowed under the couch of the spacecraft commander. The headrestwas adjustable in flight for any size crewman and for any pressure-suit condition. Thebackpan portion of the body support was constructed of Teflon-coated fiber glass, whichwould conform to the crewman for comfortable support. Restraint of the crewman wasthe same a s in the Apollo 7 couch with the six-point harness and the passive heelrestraint.Attenuators. - The Block I1 attenuators (X- and Z-axis) were double-acting orcyclic st ru ts that used the concept of mater ial deformation in the plastic range toachieve energy absorption. Material is deformed by rolling a ring of metal (reactionring) between an inner and outer tube (fig. 11). When the space between the tubes isle ss than the diameter of the ring, the ring is forced out of round, thus absorbing energya s it rolls. Because the ring is free to ro ll in ei ther direction, load attenuation occurs. for compression, for tension, and at any position of the st rut. The reaction load wascontrolled by varying the number of reaction rings installed. Heat-treated, high-strength bearing rings are located at each end of the gang of reaction rings to maintain. concentricity of the tubes and to control the deflection of the reaction rings. The finaldesign of the cyclic strut was held to a breakout load of 10 percent over nominal and astroking load of ~t percent of nominal.

For the Apollo 10 and subsequent missions, the Z-axis cyclic attenuator was re-placed by a combination cyclic attenuator, which was basically a cyclic attenuator incombination with a low-onset device. The low-onset device consists of a slender, hardrod of very uniform diameter onto which a seri es of washers has been pressed. Thewashers are forced onto the straight portion of the rod, thus causing the washer to be


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Seat positions

Outboard armrest,left couchFor EV A egress and ingress

Figure 13. - Foldable-couch flight positions.deformed plastically and thereby maintaining a squeeze on the rod. When the washeris forced to slide along the rod, drag occurs from metal-to-metal friction and energyis absorbed.

The total load (or total energy consumed) is the cumulative effect of al l the wash-e rs stroking along the rod. If spaces a re left between the washers , the load is in-creased each time a washer is picked up and pushed along the rod. This incrementalloading produces an approximate ramp function of the applied force, which, fo r a givenmass, reduces the deceleration-onset ra te . Thus, the deceleration-onset ra te of amass can be controlled by selecting the appropriate washer spacing, and the magnitudeof the deceleration can be controlled by selecting the proper number of washers. Char-acter istic load curves for the cyclic st ru t and combined s trut a re shown in figures 14and 15, respectively. The ramp-loading effect is produced only during the initialstroke of the attenuator, and the attenuator remains a lower level cyclic attenuator forsubsequent stroking.Because a reversible loading in the Y-axis for the Block I1 vehicle was not needed,the same honeycomb-type attenuator that was used on the Apollo 7 mission was used forall missions.


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Breakout

IYllillllllllilFigure 14. - Cyclic-strut load/time Figure 15.- Combined cyclic-strut andcharacteristic. low-onset-device load/timecharacteristic.

TEST PROGRAMS

The following types of te sts were conducted on the crew-couch/restraint and load-attenuation systems.Basic -Cr i te r i a Tests

Couch. - Before the couch could be designed, certain basic questions had to beanswered. Crew/couch interface exerci ses were conducted to determine the couch sizethat was required to accommodate a crewman in ei ther a pressurized or a ventilatedspace suit . The location of arm rest s, hand-controller supports, headrests, andrestraint-harness attachments and routings had to be determined. In addition, thecouch had to accommodate men ranging in s ize from the 10th to the 90th percentile witha minimum of adjustments. Also, a s part of the basic cri te ri a, human-impact test swere necessary to determine sea t angles, methods of rest raint, and the g-level toler-ance of humans in various directions for the proposed designs.

Before a design could be completed, crewman/couch/spacecraft interface tests. were required to determine the mobility of the crewman inside the spacecraft with thecouch installed and to determine the capability of the crewman to operate a ll couch con-trols and to perform the functions necessary for folding and dismantling the couch.

Attenuators. - The basic design requirement for attenuators is a determination ofthe load level at which the st rut must stroke. This load level is determined from thehuman tolerance resulting from the couch design coupled with the attenuator geometrywithin the spacecraft and from the distance the st rut is allowed to s troke within thespacecraft. With the basic design requirement in mind, attenuator concepts were r e-viewed and tested to determine the design that had the best functional performance andthe smallest weight-to- load ratio.


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Development TestsCouch. - The development testing of the crew couch consisted primarily ofcomponent-structural test s, life-cycle tests, and crew-interface tes ts . As a resul t ofdevelopment testing, some design changes were incorporated. The most significant of

these changes were the heel rest raint and the headrest.The snap-in-type heel restraint used on the Gemini spacecraft was determined tobe inadequate for the Apollo load conditions and was redesigned to a side-entry, slide-in-type heel restraint that offered better retention. The slide-in-type heel-restraintconcept also has been employed in the Skylab Program for restraining a crewmanduring extravehicular work.The large, foldable-type headrest that was used on the early Apollo couch was re-designed to a low-profile-type headrest that reduced interference with the crewmanduring ingress and egress .Attenuators . During the development of the cyclic attenuators, test results

proved (1) that the inner and outer tubes had to be sized properly to obtain the exactamount of squeeze on the r ings to prevent slippage or fatigue, (2) that par ts had to beheld to very close tolerances to obtain a constant load/stroke curve, (3) that the ringand tube surfaces had to be grit blasted to prevent any slippage, and (4) that spacersseparating the rings had to be incorporated to prevent interference between the rings .Results of the corrosion-contaminants test proved that, although the materials usedwere stainless steel , the attenuators had to be sealed to prevent corrosion. A flexiblefluorocarbon boot seal that tor e away at a force of 100 pounds was designed for themoving end of the attenuator. The attenuator was flushed with nitrogen, and the bootwas installed in a 100-percent-nitrogen atmosphere. Also, the sea l kept out foreignparticles that might have interfered with the rolling rings.One significant program milestone was the availability of a complete CM to per-

fo rm a s er ies of drop tes ts to understand better the CM dynamics and the dynamics ofthe couch and attenuation system within the CM. The understanding of the dynamicsand test simulation on a drop tower with afull couch/attenuator system permitted re-finement of the initial-impact load to anacceptable rate of acceleration fo r crewtolerance.The final load/stroke design curvefor the low-onset device is shown in fig-ur e 16. The load-attenuation levels foreach axis flight st ru ts a re shown in fig-ure 17.By using the land-landing g-timecurves that were determined from the full-scale-CM impact tests, a serie s of drop-tower te st s with the complete couch/attenuation system was performed to de-termine the load value of the attenuators

maximumIoad. IIIIIIItIIIIIIStroke, in.

Figure 16. - Ramp-loading deviceload/stroke curve.


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Note: arrows denote the direct ion of the force appliedh he man.

Figure 17. Block 11 load-attenuationlevels.

that would resu lt i n the lowest g level forthe crewman within the stroking distanceallowed in the CM. Results of the full-system drop te st s were invaluable in deter-mining the attenuator load value that wasrequired for the spacecraft, that is , tuningthe sys tem. A comparison of figure 17 tofigure 8 eveals the reduction in load im-posed on the crew that was accomplished.

Because the ramp- loading assemblywas essential ly a friction device, a numberof te sts had to be conducted to determinethe proper lubricant to be used in assembly.As a friction device, the assembly was ve-locity sensit ive, and development stroke-load tes ts were programed carefully toproduce the proper velocity/time profile.

Certification TestsCouch. - The CM impact te st s and thefull-system drop tes ts were invaluable incertifying the crew couch. Structurally, the couch was designed to the early theore ticalattenuator loads when applied statically, but st ructu ral failures of the couch were en-countered when impact tes ts were conducted at those theoretical values. Because theattenuator loads were reduced as a result of the full-scale tests, the decision was madeto certify the couch to the actual attenuator loads instead of incorporating design changesthat would have been required to satisfy the theoretical loads.

Attenuators. - The major certification requirement for the attenuators was tocertify that the attenuators would function at the levels established in the full-scale droptests. Certification was accomplished by stroking each attenuator in both tension andcompression on a load/stroke machine and by verifying that the attenuators strokedwithin * 5 percent of the nominal load value.FLIGHT EXPER IENCE

The CM crew-couch/restraint system has functioned satisfactori ly during launch,flight, entry, water- landing, and recovery operations. The folding, stowing, and re -assembling of the couch in flight have been achieved without problems on all missionsexcept the Apollo 9 mission. The Apollo 9 crewmen experienced some difficulty inreassembling the center body support of the couch. This difficulty proved to be a couchinstallation problem. When the couch was installed, clearance between the Y-axis-attenuator rubbing pads and the CM sidewalls did not allow for the change in the CMshape in orbit . The decrease in the distance between the CM sidewalls after launch


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caused a pinching action on the couch st ructure, making reassembly difficult. A couch-sidewall clea rance of 0.040 inch was adequate to eliminate this problem.No occasion has ar isen during any Apollo flight fo r an evaluation of the CM crew-couch/rest raint and load-attenuation sy stems under abort o r land-landing conditions.The two-parachute water landing of the Apollo 15 CM resulted in sufficient crewman/couch loading to stroke the X-axis foot attenuators 0.1 inch. From analysis of dataderived from the design qualification and attenuator acceptance test s, an acceleration*ofat l eas t 15g on the crew was determined to cause the st ru t to stroke.

C O N C L U D I N G REMARKS

The most difficult couch-development problem was the compromise that had to bemade to provide adequate crew protection for a land landing and to satisfy the operationalrequirements , simultaneously. The couch, res tra int , and attenuation interfaces in-volved controls and displays, pre ssure- suit connections, helmet and boot- heel designs,human tolerances to impact loads in a ll directions, human tolerance to prolongedeyeballs-in (forward) acceleration, stowage-compartment configurations to accommo-date couch motions on impact, rapid emergency egress for pad abort, inflight stowagefor access to the lower equipment bay, and str uctura l integrity for flight and abortconditions.The use of a full -scale vehicle to determine the landing dynamics of the totalcouch/attenuation/vehicle system proved to be invaluable in tuning a crew impact- loadattenuation system to protect the crewman adequately.The interface problems that must be considered in the design of crew-couch,res tra int-harness, and load-attenuation devices dictate that these components shouldbe considered as an integral subsystem. In addition, the design of the system shouldnot be completed until the most significant interfaces with the vehicle are defined be-cause the basic design concept is limited by the tolerance of the human body to impactloads.

Lyndon B. Johnson Space CenterNational Aeronautics and Space AdministrationHouston, Texas, July 12, 1973914- 50-DJ-96- 72


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REFERENCES

1. Hertzberg, H. T. B. ; Daniels, G. S. ; and Churchill, E. : Anthropometry of FlyingPersonnel- 950. Wright Air Development Center Rep. TR- 52-32 1 (ASTIANo. AD-47953), U. S. Air Force Aero Medical Laboratory, Dayton, Ohio, andAntioch College, Yellow Springs, Ohio, Sept. 19 54.

2. Platus, David L. : Cyclic Deformation Crew Attenuator Str uts fo r the Apollo Com-mand Module. Shock and Vibration Bull. no. 38, part III, Nov. 1968.3 . Wesselski, Clarence J. ; and Drexel, Ralph E. : Apollo Couch Energy Absorbers.Proceedings of the 7th Aerospace Mechanisms Symposium, NASA TM X-58106,1972, pp. 157-167.

apollo experience report command module crew-couch restraint and load-attenuation systems

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