apollo experience report crew station integration volume ii crew station displays and controls

8/8/2019 Apollo Experience Report Crew Station Integration Volume II Crew Station Displays and Controls

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N A S A T ECHN I CA L NO T E NASA TN 0-7919

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APOLLO EXPERIENCE REPORT -CREW STATION INTEGRATIONVolume I1 - Crew Station Displays and ControlsWillium A, Lungdoc and Dale A . NztssmanLyndon B . Johnson Spuce CenterHouston, Texus 77058

N A T I O N A L A E R O N A U T I C S A N D S PA CE A D M I N I S T R A T I O N W A S H I N G T O N , D. C. A P R I L 19


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1. Repor t No.NASA TN D-7919A P O L L O E X P E R I E N C E R E P O R TCREW STATION INTEGRATION: VOLUME II-

2. Government Accession No. 3. Recipient's Catalog No.

A p r i l 19756. Performing Organization Code

4. Ti t le and Subt i t l e

CREW STATION DISPLAYS AND CON TROLS I JSC-085785. Report Date

7. Author (s )Will iam A . Langdoc and Dale A. Nussman9. Performing Organization Name and Address

~~ ~~

8. Performing Organization Rep ort No,JS C S-42010. Work Unit No .924-23-65-01 -72

National Ae ronaut ics and Space Adm inis t rat ionWashington, D. C. 20546

Lyndon B. Johnson Space CenterHouston, Texas 770582. Sponsor ing Agency Name and Address

14. Sponsor ing kgency code

~~ ~

11 . Contrac t or Grant No.

13. Type of Report and Per iod CoveredTechnical Note

I15. Supplementary Notes

17. Key Words (Suggested by Author (s ) ).Fl igh t Sys tems' Status Indicators' Swi tches' M e t e r s' I n s t ru m en t P a n e l s

6. Abstract

18. Dis t r ibut ion StatementSTAR Subject Category:1 2 (Astronaut ics , General)

In this re po r t , the funct ional require me nts fo r the Apollo displays and controls sys te m a r eprese nted ; the conf iguration of the displays , controls , and pan els for both the command moduleand the luna r module ar e desc r ibed ; and the des ign development and opera t iona l exper ienceof the d i sp lays and cont ro l s sys tem a r e d i s cus sed . Per t inen t r ecomm endat ions fo r fu tured i sp lays and cont ro l s sys te m des ign e f for t s a r e made .

19. Secu r i ty Classi f. (of this rep ort)Unclass i f ied

20. Secur i ty Classi f. (of this page) 21. No . of Pages 22. Price'Unclassified 39 $3 . 75

'For sale by the Na tional Technical Informa tion Service, Spr ingfield, Virginia 22151


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APOLLO EXPERIENCE REPORTEDITORIAL COMMITTEE

The mate rial submitted fo r the Apollo Experience Report s(a series of NASA Technical Notes) was reviewed and ap-proved by a NASA Editorial Review Board at the Lyndon B.Johnson Space Center consisting of the following m em be rs :Scott H. Simpkinson (Chai rman) , Richard R. Baldwin,Jam es R. Bate s, William M. Bland, J r . , Aleck C. Bond,Robert P. Burt, Ch ri s C. C ritzo s, John M. Eggleston,E. M. Fields, Donald T. Gregory, Edward B. Hamblett, J r . ,Kenneth F. Hecht, David N. Holman (Editor/Secretary),and Carl R. Hu ss . The prime reviewer for this reportwas Richard R. Baldwin.


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FOREWORD

This technical note documents experience gained in the a re a of space craft crewstation design and operations during the Apollo Pr og ra m. Empha sis is given to thetime period ranging from ea rly 1964 up to , and including, the Apollo 11 lunar-landingmission of July 1969- n era that covers three important phases of the Apollo Pro-gra m: the design phase, h ardwa re construction, and miss ion operations.This technical note cons is ts of five volumes. Volume I, "Crew Station Designand Development, '' gives an overview of th e total crew station integration task.Volumes 11, 111, IV , and V a r e speciali zed volumes, each of which is devoted to a basicfunctional a r e a within the Apollo crew station. The subject of each volume is indicatedby its title, as follows.Volume 11, "Crew Station Displays and Controls"Volume 111, ''Spacecraft Hand Contr oller Development''Volume IV, ''Stowage and the Support Team Concept"Volume V, "Lighting Considerations"

Lou is D. AllenLyndon B. Johnson Space Center

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CONTENTS

SectionABBREVIATIONS AND ACRONYMS . . . . . . . . . . . . . . . . . . . . . . . .SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .DESIGN PHILOSOPHIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .CONFIGURATION DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . .

Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Displays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DESIGN DEVELOPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Command Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Lunar Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Standardization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

OPERATIONAL EXPERIENCE . . . . . . . . . . . . . . . . . . . . . . . . . .Apollo 7 Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Apollo 8 Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Apollo 9 Mission . . . . . . . . . . . . . . . . . . . . . . . : . . . . . . . .Apollo 10 Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Apollo 11 Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CONCLUDING REMARKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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FIGURES

Figure PagThe Block II CM crew station arrange ment . . . . . . . . . . . . . . . .The LM crew station arrangement . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . .3 The LM main panelsThe CM main display console . . . . . . . . . . . . . . . . . . . . . . .

5 Control panel showing lever- lock switches . . . . . . . . . . . . . . . . 16 Wickets guarding the C M toggle switches . . . . . . . . . . . . . . . . . 1

theCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Standardized ro tar y control knobs used in both the LM and8 Recesse d panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Barrier guards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10 Entry monitor syste m . . . . . . . . . . . . . . . . . . . . . . . . . . .11 Apollo display and keyboard . . . . . . . . . . . . . . . . . . . . . . . .12 The LM data entry and display assembl y . . . . . . . . . . . . . . . . .13 The ORDEAL assembly . . . . . . . . . . . . . . . . . . . . . . . . . .14 Supplemental de ca ls . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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ABBREVIATIONS AND ACRONYMS

AGSCDRCMC&WD&CDEDADSKYECSELEMSEVAEVVAFDA1G&NJSCLEBLMLMPLORMDCMSCORDEALPGNCSPLSS

abort guidance sys temcommandercommand modulecaution and warningdisplays and controlsdata entry and display assemblydisplay and keyboardenvironmental control systemelectroluminescententry monitor systemextravehicular activityextravehicular vi sor assemblyflight dire cto r attitude indicatorguidance and navigationLyndon B. Johnson Space Centerlower equipment baylunar modulelunar module pilotlunar orbit rendezvousmain display consoleManned Spacecraft Centerorbita l-rate drive, Earth and lunarprimary guidance, navigation, and control sys temportable life- support s y s ern

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RAI roll attitude indicatorRCS reaction control syste mRL radioluminescentSI Syst&meInternational d'Unit6s

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APOL LO EX PER l ENCE REPORTCREW STAT1 ON INTEGR ATION:

VOLUME I I - CREW STATION DISPLAYS AND CONTROLSB y W i l l i a m A. L a ng d oc a n d D a le A . N u s s m a n

L y n d o n B. J o h n s o n Space C e n t e rS U M M A R Y

The Apollo displays and contr ols sys tem includes such devices as mete rs andswitche s that enable the flight crew to monitor and control the ope rations of the space-cra ft. The Apollo displays and contro ls sys tem was based on design pra ctic es andoperation principles established during previous aircr aft and spacecraft progr ams.Except fo r sev er al unique devices developed fo r special applications, displays andcontro ls sys tem components were conventional i n design and operation. The designdevelopment of the displays and contro ls sys tem w a s evolutionary, and most designchanges resulted from alterations in the interfacing subsystems o r fro m the identifica-tion of new requiremen ts. The Apollo displays and contro ls perfor med well under allmissio n conditions and met al l design objectives.

I N T R O D U C T I O NThe d iscussi on i n this volume primar ily pertai ns to t he Apollo command module(CM) and lunar module ( L M ) displays and controls (D&C)requirements, configurations,and operations, as opposed to the detailed design and development of D&C hardware.Throughout the development of the Apollo spacecraft, the engineering responsibilityfo r the D&C subsystem w a s essentially divided into two pa rts : requir ements andhardwar e.Require ments responsib ility consis ted of the definition and implementation ofma dm ac hi ne interface requirements; for example, control deflection charact eristic s,

display fo rm at s, and integ ration of controls and displayed information. A flight-crew-support organization had the prim ary responsibility in this area. Hardware responsi-bility cons ist ed of detailed component design, qualification testing, and te st checkout.An engineering and development organization was res ponsib le for this are a.Requ irements responsibili ty fo r the portions of t he Apollo D&C subsys tems fro mthe "panel out" is the ar e a emphasized in this report. Because the two efforts

(req uire ment s and hardware) cannot be separated entirely, some hardware discussion


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is included for clarity and completeness. No attempt is made to document in deta ilthe D&C component designs, development histories, or qualification tes ts ; however,such information may be found in the othe r volumes of thi s se ri es . This brief docu-mentation of what the Apollo D&C configuration w a s , how it was developed and operated ,and how it could have been improved is intended to benefit others faced with si mil arproblems.

A s an aid to the rea der , where necessary the original units of measu re have beenconverted to the equivalent value in the SystGme International d'Unit6s (SI). The SIunits are written fi rs t, and the original units are written parenthetically thereafter.

DESI GN PHI L O S O P H IESAn enumeration of the philosophies under which the displays and controls weredeveloped precedes the descript ion of the CM and the LM D&C and the discuss ion ofthe ir design and operation. The Apollo D&C requirements we.re based mostly on pre -vious spacecraft and ai rc ra ft experience and were refined, modified, and finalized asthe design evolved. The following were the most fundamental and influential requi re-

ments levied on the D&C sys tem s.1. No single display o r control fail ure would jeopardize the safety of the flightcrew o r be cause for an abort.2. The D&C design would allow a single crewman to f ly either the CM o r the LMto safety (i.e., the L M to lunar orbit or the CM to Earth).3 . Displays and controls would be provided to enable the flight crew to controlthe vehicle and to manage the subsystems during all mission phases.4. Information would be prese nted s o as to permi t rapid asses sment of cr itica l

sys tem s tatus without re sor tin g to extensive troubleshooting procedures to identifymalfunctions.5. Normal subsystem operation would not re qu ir e continuous monitoring or con-tr ol by the crewmen.6. Displays and controls that were susceptible to damage or to inadvertentactuation as a res ult of normal crew opera tions would be guarded appropriately.7. Existing proven design concep ts would be used a s much a s pract ical .8. The D&C of the CM and the LM would be s tandardized to improve crew effi-

ciency by the elimination of conflicting designs.9. A ll D&C would be designed for sati sfac tory operation by a pressure-suitedcrewman, and all D&C used during ac cel era ted flight would be designed for operationby a pressure-suit ed, fully restrain ed crewman.

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10. Pr im ar y command would be onboard the sp acecr aft. The capability wouldexist to perform the mission without dependence on ground-based information; how-eve r, the us e of ground-based information to in cr ea se reliabi lity, accu racy, o r per-formance would not be precluded.

11. Automatic s ys te ms would be used to obtain precision, to speed response, orto reli eve the crewmen of tedious task s; but all automatic contro l modes would have amanual backup.12 . Initiation of any a bort would be onboard, and the c rewmen would have theprimary responsibility.13. Annunciator disp lays would be provided to indicate c ri ti ca l malfunctions ofonboard sys te ms . Activation of thes e displays would be announced to the crewmen byboth visible and audible master alarm signals.14 . Displays and controls would be furnished to provide the L M with the capa-bility fo r a visual or an instrume nt landing.15. Crew launch-abort initiation would be based o n at lea st two cues.Within the aforementioned general philosophies, detailed design pra cti ces we reestablished. .The following pra cti ces evolved i n the final design.

1. Time -shar ed displays would be used whenever the displayed para me te rs didnot need to be monitored continuously or concurrently. This approach reduced thenumber of components require d, conserved panel space , and facilitated crew opera-tions by helping to group related information.

2. Perc enta ge readou ts would be used fo r quantity displays. Originally, con-sumables we re to be displayed in volume or ma ss uni ts, but us e of t his method wouldhave required a mental calculation by the crewman to determine how usage was progres-sing. Percentage readouts facilitated a rapid as se ss me nt of quantity status.

3. Fixed-scale, moving-pointer me te rs would be the pre fer red and generallyused type of display.4. Status ind ica tor s would be used to indicate equipment status where such

equipment was actuated by inputs fr om momentary toggle switche s.5. Where feasible, dual me te rs of the fixed-scale, moving-pointer type would

u s e a single scale that was appropriate f or both par ame ter s displayed and that wascentered between two pointers.6. Scale graduations would generally pro gr es s b y one, five, or two units, in

that ord er of preference, or by decimal multiples.7. Nonlinear display scales would be avoided.8. Nomenclature would describe "what ,** not %ow.''

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9 . A l l displ ays, contr ols, and panel nomenclature would be integrally li t s o asto be visible under darkened cabin conditions, such as during st ar sightings.10. Time would be displayed digitally. Analog clocks and ti me rs (simil ar to anaircraft 8-day clock) were originally proposed, but difficulty in reading analog clocksand ti me rs rapidly and accurately cause d the change to digital clocks.11. Display range and readout ac curacy would not exceed t he needs of the flight

cre w to manage the space craft , and display scaling would not be m or e prec is e than theacc ura cy of the input sign als .12. Status displays would indicate equipment respo nse and not me re ly contro lposition.13. Flight-control and navigation displays would have "fly to" po inters and

symbols.1 4 . Displays associated with a control would be located so as to be unambiguouslyrel ate d to the control and visible to the crewmen while i n operation.15. Related D&C would be grouped to facil ita te tra ining and opera tions .16. When operat ions followed a sequential or logical patt ern , the D&C would bearrang ed to facilitate such operations.17. When pra cti cab le, a positive indication of the l os s of display power and sig-nal would be provided.18. Switches would be provided to deadface all crew operational power connectorsto prevent the necessity fo r making o r breaking any connections while power was applied.

C O N F I G U R A T I O N DESCRIPTIONAlthough the general conf iguration of the D&C pane ls for the Apollo CM and LM

was based on design practices established for previous aircraft and spacecraft, theconfigurations were , nonetheless, unique in many aspe ct s because of the specializedmiss ion involved. The CM wa s a three-man vehicle designed to be flyable durin g lunarorbit or emergency conditions by a single crewm an. Most of th e displ ays and contr olswe re located on the main display console (MDC) above the couches. This location per -mitted easy monitoring and rap id acc es s. The MDC was designed with the left halfdevoted primar ily to fligh t-con trol- related D&C and the right half devoted to sub sys-te ms management D&C. Sever al of the spa cecra ft s ys te ms al so had additional contr olslocated elsewhere in the cabin. The guidance and navigation ( G & N ) sys tem d ispla ys an.dcontrols used in conjunction with navigation sightings and inertial plaff orm alinementswere locatedin the lower equipment bay (LEB), adjacent to the G& N telescope andsextant. Manual controls fo r the environmental control sy st em (ECS) that did notreq uir e frequent o r time-critical manipulation were located in the left-hand equipmentbay. Waste management cont rols and non-time-critical cir cui t brea ke rs were locatedin the right-hand equipment bay. The general arr an ge me nt of the CM cre w station isshown in figure 1 .4


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- ombined tunn el hatchA f l equipm ent storage bay

LLefl-han d equipment bay Right-hand equipment bayA

Figure 1 . - The Block I1 CM crew station arrang ement.The LM, like the CM, was designed to be flyable in a contingency condition by asingle crewm an. Normal operation, however, requi red a two-man crew, with thecommander (CDR) in the left position and the LM pilot (LMP) in the right position. Themain D&C panel s wer e canted forward and cente red between t he two crewmen to pe r-mit sharing and easy scanning. An alinement optical telescope between the flight st a-tions wa s provided fo r navigational opera tions . The ECS and portab le life-supportsy st em (PLSS) rec har ge stati ons we re locate d immediately behind the LMP and theCDR, respectively. The general LM crew station arrangemen t is shown in figur e 2 .A standard approach was u sed for locating and ar ra ng ing the D&C within the CMand the LM. Flight-control displays and controls, because of their inherent critical

nature and frequent us e, were located in the prime panel areas. The displ ays andcontrols for all other space craft s ys te ms were generally grouped by sy ste m and locatedaccording to criticali ty, frequency of use, crew task sharing, and the most efficientuse of avail able panel space . Assignment of D&C to (and sometimes between) particu-lar crewmen, in general, was instituted according to standard aeros pace practi ces.Fo r example, on the LM, the CDR was provided with the pri ma ry flight-critical D&C.However, cer tai n it em s were located for mutual ac ce ss by the crewmen o r were dupli-cated a t the LMP flight station to implement copilot responsibi lity. The LMP stationsal so had subsystem-management D&C that reflected the additional flight-engineerresponsibilities of the LMP. The main panels fo r the LM and CM ar e shown infigures 3 and 4, respectively. The ways in which the design philosophies were imple-mented and th e configuration that finally evolved can be se en in some de tail in the sefigures.

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Dockingwindow7 Mai n panel1 7anel 1 7 cabin floodllght Crash ba r(both s i d e s 1 7

Figure 2 . - The L M crew station arrangement.

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a

Figure 3 . - The L M main panel s.The D&C components use d on the Apollo spacecraft were, like the overall D & Csys tem s configurations, similar to those used on air cra ft and previous spacec raft.

Unique devices, such as the entry monitor system (EMS), wer e developed for specialapplications; but, generally , the components were conventional in design and opera-tions. The component vari ations that did exist were generally attributab le to the addi-tion of operational requirement s, such as the us e of cont rols while the crewman was ina pressurized suit or under zero-g conditions o r the need to monitor and control duringhigh-g or vibration conditions (or both), and to the addition of more stringent qualifica-tion r equir ement s to achieve very high reliability under sev ere environmentalconditions.Controls

The control devices used in the Apollo space cra ft included toggle switches, push-button switches, rotary switches, continuously variable controls, and circuit breakers.Toggle switches. - Toggle switches were the most f requently used control devlces.The chief factors favoring their selection were that toggle switches generally requiredless panel space, gave a positive status indication (except for momentary switches), andwer e ea sy to actuate under a variety of flight conditions. Two- and three-positionswi tches with vario us combinations of maintaining and momentary positions were used

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Figure 4 . - The C M main display console.

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Figure 4 . - Concluded.

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to actuate o r sele ct operating conditions or components. A four-position (up/down,left/ righ t) momentary switch was al so used on the LM fo r manual positioning of t herendezvous ra da r antenna. Momentary positions were used to initiate a specific actionrequiring curren t for only a short time, such as jettisoning the launch-escape tower oroperating a latching relay or valve.Maintaining switches we re used for most applications . An inherent advantage of

the maintaining-type switch is a visual indication of switch position and, t her efo re, ofsys tem and vehicle configuration. The momentary -type switch, i n which the handle isspring-loaded to retu rn to another position, does not give such inhe rent s ta tus indica-tion. For most functions initiated with momentary switches, such a s opening a latchingvalve, some type of adjacent sta tus indicator was necessar y. This requirement fo r astatu s indicator to be used with most momentary toggle switches meant that an addi-tional component and more pane l sp ace would be req uir ed than i f a maintaining-typetoggle switch wer e used. Status indicato rs provided with momentary switches,however, had the added advantage of providing the end-it em st atus of the equipmentbeing controlled, w herea s a maintaining switch, i n its elf , gave no such informat ion.Most of the toggle swi tches used on the Apollo vehic les had a wedge-shaped tab

handle that provided the crewman a large purchase ar ea with which to actuate theswitch while wearing a pre ssu riz ed glove. Toggle switches that had locking mecha-nism s incorporated into the handle to keep the switch fr om being thrown inadvertentlywer e als o used. Thes e lever-lock switches (fig. 5) had large, bat-shaped handles andwer e used extensively on the LM spacecra ft. An additional fea tur e of t he LM toggleswitches w a s a radioluminescent (RL) tip on both regu lar and lever-lock handles. TheRL ti ps enabled quick determination of the switch position even when the cabin flood-lights were dimmed. Alternate approacheswere used to guard and to illuminate C Mtoggle swit ches . Command module toggleswitches were r ece sse d within a trough andguarded with adjacent wickets (fig. 6). Thetoggle switches were li t by spill lightingfr om the edge of the electro luminescent(EL) nomenclature overlay.

The operating cha rac ter ist ics of thetoggle switches were approximately 3 to44.5 newtons (10 to 160 ounces) of actu-ating force (depending on the number ofpoles), 34" f 8" of throw fo r two-positionswitches, and 17" * 4" of throw for th ree -position switches. The for ce values wereacceptable, but a lower value for the upperlim it of actuating forc e would have beenprefe rable fr om an operational viewpoint.The possibility of i ncreasing the deflectionfor three-position switches should al so beconsidered in future designs because manyof these switches have been mistakenlymispositioned o r monitored (or both) onApollo missions.10

Figure 5. - Control panel showingleve r -lock switches.


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switc Pushbutton switches. -hes were used f or applicPushbuttonations requ ringthe rapid initiation of a function, for high-frequency-of-use situations, and for appli-cations requiring a combined control/signaldevice. Pushbutton switches we re mostwidely use d fo r applications requiring therapid ini tiation of a function. In the CM,pushbutton switches were use d mostly asmanual backup c ontr ols to initiate varioussequential events during launch and entry;in the LM, they were use d to back up mainengine commands and to shut down thedescent engine on lunar touchdown. Push-button switches, in a keyboard format,we re used to ent er data into the guidancecomputers. Mast er al ar m pushbutton/signal lights in both vehicles servi?d toindicate caution and warning (C&W) ondi-tions and to reset the ala rm circuitry. Figure 6. - Wickets guarding the CMtoggle switches.Square pushbuttons, slightly large r than those normally used in air cra ft o r in theGemini space craft , we re used f o r most applications. The la rg er s iz e (approximately2.03 centimeters.(0.8 inch) on a side) aided actuation and permitted the us e of la rg erlegends.Rectangular mas te r al ar m pushbutton lights, approximately 6.5 squ are centi-meters (1 squar e inch) in area, were used in both the CM and the LM. Pushbutton-switch operating characte rist ics were 3 to 2 1 newtons (10 to 74 ounces) of actuatingforce and 0.317 to 1.5 centimeters (0.125 to 0.6 inch) of t rave l.Rotary switches. - Rotary switches were used when fou r or mor e detent positionswer e requi red fo r dis crete functions, o r in applications that required many poles o rhigh-current capacities. In the lat ter applications, the design of a rota ry switch wasgenerally m or e suitable than the design of a toggle switch.Rotary switches were highly advantageous in accomplishing numerous switchingfunctions, but this capability in turn in creased the criticality of a failure. A mechan-ically jammed rotary switch, for example, could inhibit all the switching functionsnormally performed by the control. Therefore, the L M rotar y switches wer e posi-tioned in the most cri tic al detent positions before Earth launch; and, in later lunar

modules, missi on-cr itica l rota ry switches were replaced with (and by an additionalnumber of) toggle switches .A standardized rot ary control knob (fig. 7) was us ed i n both the Apollo vehicles.The knob w a s equipped with a circular sk i r t to allow fo r transillumination of an integral

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pointer indicium. Actuating fo rc es rangedf rom 8.5 to 85 centimeter-newtons (12 to120 inch-ounces). A standard 30" spacingbetween adjacent positions w a s used for al lrotary switches.Continuously v ariabl e controls. -

Continuously variable contro ls, such aspotentiometers, rheos tats, and variabletransfo rmers, were used for functionsrequir ing preci se control and adjustmentof system o r equipment param eter s. Someof t hese functions included the cont rol oflighting intensities , audio volume, andantenna positioning. Con inuou sly va ri ab1econ trols we re equipped with thumbwheeland rotary-switch-type knobs. Thumb-wheels were used predominantly for audiocontrols and knobs for lighting and antennacontrols. The periphery of thumbwheelswas marked with integers from one to ninefor indexing the control.

Figure 7. - Standardized rotary controlknobs used in both the L M andthe CM.A slightly different type of rot ary control knob was used to opera te a ste ppe rmotor. Because a stepper motor has little inherent friction to maintain it at the setposition, a device that would hold the control a t the s elected position w a s necessary.Thi s locking was accomplished by the use of a knob resembling the other ro ta ry con-tr ol knobs but having an internal locking mechanism. Pushing in the top portion ofthe knob unlocked the cont rol and allowed i t to be positioned fr ee ly . Releas ing theknob locked the st epp er motor in place.To opera te continuously variable con trols with rotary-switch-type knobs requir eda torque of 6 to 25 centimeter-newtons (8 to 36 inch-ounces). Failure to specify alower acceptable limit for rheostat actuating torque in the LM procurement specifica-tion resulted in the delivery of sev era l units having torq ues of le ss than 1. 4 centimete rnewtons ( 2 inch-ounces). The addition of ex ternal fric tion washer s between the contro lknob and the panel compensated for this imp rop er torque value. Thumbwheel controlsrequired 1.4 to 4 centimeter-newtons (2 to 6 inch-ounces) to operate. Early LMthumbwheels were al so delivered with improp er torque values. Because requir ementsdocumentation w a s misinte rprete d, early thumbwheel units having torques of14 centimeter-newtons (20 inch-ounces) and gr ea ter w er e delivered; but these unitswere used "as is" in nonflight applications. A standard 300" deflection was imple-mented for all continuously variable controls.Circuit breakers . - Circuit break ers were used primari ly to protect electricalcircuits. Sometimes, however, circuit bre ak ers were used as control devices; thisapplication occur red mostly on the LM, whe re weight was very cr itic al. In all theseinstan ces, though, an attempt was made to design the sys tem s so that switching actionwere limited in number and conducted under a no-load condition. Circuit br eak erswere procedurally used on both vehicles to disable c ri tic al ci rcu its during period swhen they were not required.

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The circ uit b reaker s used on the Apollo vehicles were the push/pull type and hada sm al l, black knob. An aluminum band w a s displayed when the breaker was open. Awhite band origina lly used was deleted because the paint flaked and chaffed. Somedifficulty was encountered in visually monitoring the lower con tra st silve r-coloredbands in the lower level lighting environment of the LM. This condition resulted inthe misconfiguration of cer tai n circu it breakers by the Apollo flight crew s. To avoidthis si tuation in future programs, crew station lighting simulations should be per-formed to verify altered D&C color schemes.

Circu it break ers w ere particular ly susceptible to inadvertent actuation ordamage. Thi s susceptibility w a s especially prevalent on the LM because of the amountof crew activity associ ated with lunar s urf ace operations (e.g., backpack donning anddoffing). There fore, special precautions were taken in both vehic les to protect thecircu it break ers by recessin g the panels (fig. 8) or by providing ba rr ie r gu ards(fig. 9) or by both methods.

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Figure 8. - Recessed panel. Figure 9. - Barrier guards.A ll cir cui t bre ake rs were the "trip free" type currently used on military air-craft; that is , a "tripped" breaker could not be manually overridden (closed).

Nominally, 53.4 newtons (192 ounces) of force were requi red to c lose and 27 newtons(96 ounces) to open the circu it bre ake rs. Total travel w a s approximately 0.5 centi-meter ( 0 . 2 inch).

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DisplaysSeveral different types of displays and signal devices were used i n the Apollo

spacec raft. Among these wer e D'Arsonval me ter s, numeric displays, event indi-cators, annunciator lights, and several special flight instruments.D'Arsonval meters. - The D'Arsonval met er w a s the predominant displayinstrument used in the Apollo CM spacecraft . A modified vers ion of th is type ofmeter, incorporating a feedback loop and ter med a servometric meter, w a s used

the meter, its compatibility with conventional analog transducers and signal condi-tione rs , and the extensive experience with the D'Arsonval-type movement were theprimary factors in its selection as the general type of display.

extensively on the LM. The basic simplicity and inherent respon se cha ract eri sti cs of

Although the servometric meter provided improved accuracy and minimizedvibration-induced pointer movement, the mechanism had cer tain undesirable featu res .One such fea ture, the necess ity of providing a sep arat e power input in addition to thesigna l input, r equ ired additional power, weight, wiring, and circuit breakers.Implementation of the requirem ent to provide a positive indication of m ete r failure orlo ss of input w a s als o mor e difficult. The standard D'Arsonval meter inherentlymoves off sca le with los s of signal and thus giv es a positive fai lure indication. Withthe serv ometric meter , however, lo ss of the additional power input (o r internalpower) leaves the pointer at i ts last position. Unless the crewmen have anothersou rce of information, they a r e led to believe that the parame ter is unchanged. Thisproblem was circumvented in the L M by the addition of a small signal light above cer-tain critical displays. This light illuminated whenever meter input power w a s inter-rupted. In future pro grams, the standard D'Arsonval movement should be used,where possible, instead of the servom etr ic design. Servometric displays, when used,should be designed to provide a positive indication for both los s of signal and power .

The types of D'Arsonval and servom etr ic m et er s used in the Apollo crew sta -tions included single- and dual-scale vertical met er s, single- scale cir cular met ers ,dual-scale semicir cular meter s, and cross-p ointer indicators. Minimization ofpanel space and crew preference for vertical met ers wer e the primary factor s in theselection of the type of met ers to be used. To conserv e panel sp ace (and to reduceweight and electrical connections), dual-movement me te rs were used, where possible,for the d i s p l a y of rel ated par amet ers . Crew commen ts about the poor readability ofthe dual-scale, semici rcular meter configuration resulted in i ts omission from theLM design. For the purpose of standardizati on, ci rcu la r me te rs were used to displaycommunications and electric al power sy stem s par am ete rs in both vehicles.

The dial faces of all D'Arsonval me te rs were tran sillu minate d by the us e of ELlighting. This type of meter face provided readability under a wide range of lightingconditions but did not lend itself to modification. The transilluminated markings onCM meters were produced by an etching technique, whereas a film overlay was usedon the L M met ers. Construction of new dial fa ce s by eithe r technique requi red a longlead time. When transilluminated mete rs a r e required fo r future applications, a flex-ible method for constructing dial fac es should be adopted. Consideration should als obe given to an improved method of implement ing me te r color bands. Color bands thatdenoted operating range s, lim its , and conditions we re located directly on the meter

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dial fac e in Apollo spacecra ft. Thi s method had two undesirable char acter istic s:meter disassembly w a s req uir ed to modify the color bands, and the paint on ear ly LMmet ers flaked.Numeric displays . Numeric displays of both the electromech anical rotatingdrum and the electroni c EL-segment type were used for c ert ain applications in which

precise quantitative data were required and trend information w a s not of primaryimpo rtanc e. Among the applications we re the display of mission and event times ,propellant quantities, and guidance-computer param ete rs. Early CM numeric indi-cat ors , except the display and keyboard (DSKY) assembly, were primarily electro-mechanical. When EL lighting was sel ected for the la te r CM and LM designs, thedecision was made to us e EL nume ric indicators exclusively i n the LM and to sub-stitute EL indicators in the CM where possible.

Event indicators. - Electromecha nical event indi cato rs, mor e popularly knownas "flags, ( ( were used to show the st atus of components or sys tem elements. Gen-erally, these flags were used as indi cator s of di scr ete , norm al events such as a valveopening or closing; but, in a few applications, they wer e used as malfunctionindicators.

Event indicat ors used D'Arsonval- type mete r movements consisti ng of a signalfla g attached to the end of a pivot ar m. The flag would appe ar in view when the devicewas in one energy s ta te and would deflect fro m view when in the othe r. Two-positionindic ators wer e predominantly use d throughout both vehicles. A second, three-positionconfiguration w a s als o used for special applications requ iring the display of thr ee sep-arate status indications (e.g. , off, on, or failure indications). In thi s configuration, agray flag meant that a monitored element was operating or was not inhibited fromoperating (valve open, power on, etc . ), a black-and-white str ipe d indication meant thatthe element was deactivated or inhibited from operating (valve closed, power off, etc.),and a re d indication meant that a monitored element had failed. Three-position flagswere use d on the L M to monitor the status of the reaction co ntrol sy stem (RCS) thru st-chamber valves. A gray flag indicated an open valve; str ipe d, a closed valve; andred, a faile d jet . Flag s wer e also classified according to the type of e lec tri cal actua-tion used . One type of indicato r displayed a gray flag when energized and a stripedflag when no power w a s applied. Another type of indicato r worked in re ve rs e. Thetype of fla g indicator chosen fo r a particular application w a s normally the one thatrequired the le ss er operating power for the duration of the mission. For example, a"gray deenergized" flag indicato r would be use d to monitor a valve that was openthroughout most of the miss ion. Although power is conserved, this scheme is opera-tionally disadvantageous i n that a deenergized indicator fails to give a positive failureindication.

In most ca se s in which a flag indicator wa s used to monitor the condition of pro-pellant valves, the power to the flag was routed in se ri es through valve-position-indi cato r sw itches of both the fuel and oxidizer sy ste ms. If the flag received power inthe gray position, the conclusion w a s that both the fuel and oxidizer valves were"positively open. '' If the flag received power in the str ipe d position, the conclusionwas that both valves were "positively closed. ?' Using thi s type of wiring logic, apositive-open flag could not provide a positive-closed indication; that is, removal ofpower a nd display of a stri ped flag could resul t from one of t hr ee conditions: fuel

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valve closed, oxidizer valve closed, o r both fuel and oxidizer valves closed, Theopposite situation exis ted with positive-closed wiring logic. When missio n plans andprocedure s began to fo r m midway into the Apollo development, the indication was that ,fo r cer tain case s, the ambiguities in determining actual valve configurations could notbe tolerated. As a result , a considerable amount of rewiring was made in both the CMand the L M to interchange positive-open and posit ive-c losed wiring logic. In futureefforts, flag indic ators should be powered i n each active display position, where pos si-ble, to provide positive sta tus information. When thi s proce dure is not possible, theoperational ramif ications of the flag-indicator wiring logic should be carefullyscrutinized.

Flags were us ed on Apollo spa cecraf t in prefere nce t o annunciator lights fo rgener al status indications. The ir us e conserved power, facilitated dark-adaptedoperations ( s u c h as star sightings), and helped to eliminate an objectionable"Christmas tree" effect. Unfortunately, the inconspicuousness of flags could al soeasily allow an abnormal change in the st ate of the monitored element to go undetectedby the crewmen. The ref ore , flags wer e generally used as sta tus indic ators and not ascaution o r warning indi cator s.

Annunciator lights. - Annunciator lights w er e used when a discrete, attention-getting display was require d. On Apollo spac ecr aft , annunciator lights we re generallyused to provide subsys em or component malfunction in format ion in asso cia tion withthe C&W system, but they were occasionally used as event indicators. The amb ercaution and red warning lights on both vehicles were grouped i n a matrix and centrallylocated for easy visibility by all crewmembers. A mast er ala rm light and an auditoryal ar m operated in conjunction with these lights. The se al ar ms were activated si mul-taneously with the pertinent C &W light whenever an out-of -tolerance condition existedamong the monitored pa ra me te rs . To distinguish between CM and LM fa ilures , twodifferent auditory sig nals we re used. The CM use d a dual-frequency (750 and2000 her tz) alternating tone; the LM, a single-frequency (3000 her tz ) tone. The LMadditionally used component caution light s, subordinate to the C&W lights, that showedwhich of severa l subsys tem elements gated into a single C&W light had malfunctioned.The CM used flags f or a simi la r function.

To avoid the dis tracti on of constan tly illuminated annunciato rs, both vehicles we reprovided with annunciator extinguishment con tro ls. This function was accomplished inthe CM by using an operat ing mode (acknowledge mode) that removed the lighting powerfro m the entire C&W lamp assembly, except when the m as te r a la rm was depr essed.When a C&W al ar m occurred, the m ast er a la rm light and auditory al ar m would acti-vate as usual. By res ett ing the ma st er ala rm , the crewmen al so enabled the C&Wlam p power and could then obser ve which C&W lig hts were ac tivated. An acknowledge-mode technique was not used in the LM; instead, sep ara te contr ols were used to re setor inhibit the dedicated logic within the C&W elec tron ics that enabled the power to aspecific C&W annunciator.Problems were experienced with nui sance tr igg ering of C &W annunciators onboth vehicles. Some of the fa ls e al ar ms were e limina ted before flight by the incorpo-ration of increas ed time delays within the C&W electr onics. In other cases, the C&Wlogic of t roublesome lights was completely di sab led as a minimum-impact modifica-tion i f alternate sy stem information channels wer e available. The experience gained

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in the area of Apollo C&W design ind ica tes that the i dea l C&W sy st em s for f uturespa cecraf t would have the following capabilities : an acknowledge mode, dedicatedresets/inhibits for each C&W channel, a memory or latching s ys te m for identifyingthe source of short- term abnormalities, a variable time delay fo r screening transient sin individual C&W channels, and the capability to alter the alar m limits easily. Forthe last two fea tur es, trade-off studi es should be perf ormed to dete rmine the advantagesbetween onboard and ground adjustment schemes.

A speciai-purpose bank of annunciator lights was used on the CM to display thestatus of the launch vehicle during boost. Eight ligh ts, grouped within a 5.72- by8.26-centimeter (2.25 by 3.25 inch) ar ea adjacent to the commander 's flight ins tru -merits, provided the fundamental booster s tatus information requ ired by the crewmem-be rs during launch. By means of thi s display, the crew memb ers could deter minewhether o r not each booster engine was developing enough thru st , whether or not thebooster guidance was functioning proper ly, and whether or not the staging sequencew a s proper.A unique annunciator was the LM lunar-contact light , which illuminated when3-meter (10 foot) long pro bes on the L M landing g ear contacted th e lunar surfac e to

alert the flight crew to shut down the descent engine. The se two light s, insta lled oneac h side of the panel, were als o provided to compensate fo r a possible loss of externalvision because of the format ion of a dustcloud caused by the landing engine thrust.Each light was round and approximately 2.5 centimeters (1 inch) in diameter . Fo rdistinction fro m all other annunciators, each light was equipped with a blue lens.

Special flight instr uments . - Several unique displays were developed especiallyfo r Apollo spac ecraft . Among these we re the CM and LM flight direc tor at titudeindicator (FDAI) devices, the CM EMS, the LM range/ ran ge- rate me te r, and theDSKY combinations for the prim ary guidance, navigation, and control syst em (PGNCS)computers.Flight direc tor attitude indic ator: The FDAI, the pri ma ry flight display in boththe LM and the CM, integ rated into a single ins tru ment the display of veh icle attitude,rotation ra te , and attitude er ro r. The display design was similar to that used forair cra ft attitude and flight direct or indicators, except that attitude, er ro rs , and rat eswere displayed for al l three vehicle axes. Attitude wa s displayed on a sphere markedin an "inside looking out" fashion. E r r o r s and rat es we re displayed with "fly to"needles. Attitude could be displayed to 1" , and the scaling for the e rr or and rateneedles could be changed to suit the flight situation.Numerous changes wer e made to the attitude indica tors before and during pro-duction and aft er the initial Apollo flights. Changes were made for a variety of rea-sons. To obtain mor e pr eci se monitoring of vehicle attitude during active maneuvers,

5" yaw markings and 1" pitch markings were added. This requirement fo r improvedattitude resoluti on res ult ed fr om Gemini reentry-targeting experience. A t approxi-mately the same time, as a result of recently ac quired e xperie nce in both CM and LMflight simulations, astron auts expressed the desire to eliminate unnecessary dissimi-larities i n attitude sp he re markings. The indicators in both vehicl es wer e changedaccordingly. Lat er , changes wer e made to the LM FDAI e rr or and rat e needle scaling

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as a re sul t of e arl y Apollo flight experience. Lat er miss ions verifi ed the belief thatincr eas ed meter sensitivity would re sul t in improved vehicle-control perfo rman ce and,correspondingly, i n l e s s fuel consumption.One of the changes made to the LM FDAI stemmed fr om ambiguities in int erfacecontrol documents. A s a re sul t, the FDAI units we re mistakenly mi swired f or "flyfrom" needle operat ion ins tead of the standard "fly to" relat ionship. Fortunately ,thi s situation could be, and was , corre cted by interchanging the two signal ref erenc eleads to the display. In future prog rams , generic functional requir ements should beidentified and c learly delineated at t he earliest possible date. The end-to-end res pons ebetween vehicle movement and display movement should be descr ibed and illust rat edwithin pertinent program documentation.Entry monitor system: The CM EMS was mor e than just a speci al display. The

EMS was, i n fact, a self-contained guidance package that allowed the crewmen tomonitor, independently, the performa nce of the automatic PGNCS during entry andthrust ing maneuvers. The EM S als o displayed sufficient information to enable per -for manc e of a manual entry i f a PGNCS failu re oc cur red.The EMS assem bly (fig. 10) contained five sep ara te displays. An entry thr esh-

hold annunciator light illuminated at 0 . 0 5 ~o show that atmospher ic dec elerat ion hadbeen sensed. A roil attitude indicator(RAI) , a circula r met er with a movingpointer, displayed roll attitude and, thus,lift-vector position throughout the entry.Two entry- corrid or-ver ificat ion annunci-ators wer e integral to the MI. ne ofthe se two lights would illumina te approxi-mately 10 seconds after the s ta rt of entryto indicate t h e necessity of having the lif tvector up or down to accomplish a suc-cessful entry. If the upper light illumi-nated, the lift vec tor had to be up; if thelower light illuminated, the lift vector hadto be down. A delta-velocity/range-to-goindica tor, which w a s an EL numeric read-out, ser ved one of th ree functions depend-ing on the positions of the mode andfunction switches controll ing the EMS.During entry, the indicator displayed theine rti al flightpath distance in nauticalmiles to the predicted splashdown point.For thrusting maneuvers, the indicatordisplayed velocity change in fee t pe r second;

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8 -I-,-Figure 10. - Entry monitor system.igure 10. - Entry monitor system.

or rendezvous, it displayed the range tothe LM in hundredths of a nautical mile. The fifth EM S display w a s a scr oll assemblythat provided a scrib ed tr ac e of acce lerati on as a function of inertial velocity through-out entry. The scr ol l had printed contour guidelines that allowed the cre wme mbe rs tomonitor o r control the s pacecra ft acceleration profile and range potential.

Range/range-rate meter : The LM range/r ange-ra te mete r displayed rad ar- andguidance-sensed ranges and rang e rat es between the LM and the CM and between the

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LM and the lunar surf ace. The display w a s a dual-scale, fixed-pointer, moving-tapeindicato r. Range was displayed on a moving tape located to the left of a centrallypositioned fixed pointer . The range-rate tape w a s to the right of the pointer. Thistype of display w a s selected so that the requirements for a larg e data range and reso-lution plus trend information could be met. The indicato r was one of the most complexdisplay devices used on the Apollo spac ecra ft and contained approximately 500 elec-tronic flat packs plus the mechanical drive for moving the tape. The la rg e amount ofelectronic circuitry w a s needed to condition the vari ous digital and analog input s igna lscoming from s ever al different sources and to provide malfunction-detection cir cui tryto monitor all signal and power inputs. A s with servometric meters, special circuitrywas required to provide a positive indication of loss of input power. Each of the twodisplay tape s was approximately 3 . 6 meters (12 feet) long. Digital encoding with agold-plated "gray code" on the back of the tapes provided feedback information forimproved display accuracy.

Display and keyboard assembly: The displays used to communicate with the CMand LM PGNCS computer s wer e pa rt of an integrated DSKY assembly (fig. ll), a pieceof equipment common to both Apollo vehi-cles. The CM had two DSKY assembliesthat operated in parallel; one DSKY w a slocated in the MDC and the other at the LEBG&N station. The LM contained a singleDSKY located between the two crewmen.The DSKY consisted of two groups of dis-plays: on the left was a group of annunci-ator lights that showed computer status o rcaution conditions; on the right were an ELnumeric display and a computer-activityannunciator. The numeric display fulfilledthree bas ic functions: display of computeddata on both one-time and periodic updatebases; display of data being loaded for ver-ificati on by the crewman; and display ofthe operation (verb), the operand (noun),and the majo r mode ( prog ram) under whichthe computer w a s working. c

The data being entered into or read Figure 11. - Apollo display andkeyboard.ro m the computers were displayed onthr ee five-digit regi ster s. The verb, noun,and programdisplays were two- digit- r ad- .outs showing the code numbers for the action being performed. For example, pro-gram 52 w a s used to realine the inertial platform; verb 25 meant load the data inregisters 1 to 3; and noun 35 w a s the time from an event in hours (register l ) , minutes(register 2 ) , and seconds (reg iste r 3 ) . The EL-segmented alphanumeric displays wereused for the data registers.

The LM included a dedicated keyboard for communication with the abort guidancesy st em (AGS) and the AGS computer . Whereas the P G N C S DSKY w a s intended anddesigned for general use, the AGS data entry and display assembly (DEDA) w a s designed

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as a special-purpose device to be limitedto the displaying and process ing of AGSabort-related param eters . Therefore, asingle-address register, a data register,and an "operator er ro r" annunciator lightwer e adequate. An LM DEDA is illus-trated i n figure 1 2 .

DE S IGN DEVELOPMENTGenerally, the D&C design develop-ment was an evolutionary pro ce ss that fol-lowed the development of the overa ll CMand LM vehicles. After the initial designswer e completed, most of the fa ctor s thatshaped and modified the D&C were gener-ated outside the subsystem, prima rily fro mchanges in interfacing subsy stems o r from

rev ise d operational techniques. The devel-

Figure 12. - The L M data entry anddisplay assembly.opment paths and milestones for both the CM and the LM D&C were similar (althoughon different schedules) , and the chronologies of both vehicles we re essential ly thesame as fo r the respective crew stations.

Command ModuleEarly in the Apollo Pro gr am , pushbutton switches wer e proposed for extensiveus e in the CM; however, pushbuttons we re not used as the general switch type fo r anumber of reasons . One rea son was that , for a two-state function, a pushbuttongenerally required mor e panel spa ce than a toggle switch, Second, the desig ns of

pushbutton switches wer e mo re complicated than the designs of toggle switches. Thi rd,the design of a maintaining type of pushbutton was additionally complica ted because thepushbutton require d the use of a relatively complicated internal o r external latchingmechanism o r the us e of external latching rel ays . A fourth disadvantage of pushbuttonswitches was the problem of a "Chris tmas tre e" effect cr ea te d by pushbuttons equippedwith integral statu s lights. Constantly illuminated signal lights ar e distr actin g, tend tomask other important signal lights, and res ult in unwanted reflections i n the space-cra ft windows. The ref ore , the toggle switch, ins tead of the pushbutton, was chosena s the general switch type for Apollo spac ecraf t.At the time of the initial CM design, the decision to use the lunar or bit rendez-vous (LOR) mode of operation had not been made. After the selection of the LOR mode

with a separate L M , the CM had to be provided with the added capab ilit ies fo r dockingand crew transfer. A s the design development proceeded, the need aro se to reducethe CM weight, to improve reliability, and to incorpor ate nu merous sys tem modifica-tions that early experience had shown to be nec ess ary . The lunar -miss ion space craftthat incorporated all these changes and added capabilities we re designated Block 11space craft . The initial Block I design w a s continued, but strictly a s research anddevelopment spacecraft for Earth-orbital tests.20


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The Block I1 design point w a s one of the few time s that truly major changes wer emade in the CM D&C configuration. Because weight had to be reduced and because theconcept of in-fligh t maintenance had been deleted, the panel st ru ct ur e and wiring we retotally revis ed. The 20 smal l, sheet metal panels making up the MDC on Block I wererepla ced by 3 la rg e, machined panels for Block 11, and the servi ce loops on the panelwiring har ne ss es were eliminated. (Subsequent experience has shown that retainingthe se rvi ce loops or having rear se rv ic e access t o the panel s would have been a majorbenefit to ground modifications and checkout operations. ) The EL inte gral panel anddisplay lighting were also added for Block II; only the FDAI (which was incandescent)in Block I was integrally lit. The layout of the D&C was als o r evi sed extensively toaccommodate t he numerous sub sys tem s changes.

The following detail changes to the D&C configurations res ulted fr om theBlock 11 redesign.1. The FDAI was redesigned and repackaged to incorporate EL integral lightingand a single ref ere nce index. (The Block I FDAI had two refe rence symbo ls becausethe v ehicle and navigation ax es did not coincide. ) A second FDAI w a s als o added for

redundancy ana operational flexibility.2 . Displays and cont rol s were added to accommodate the newly a cqu ire d high-gain antenna and docking-probe systems.3 . The c rew control of the stabilization and control sy st em was changed froma mode-selection scheme to a function- selection arr ang eme nt,ove ral l s yst em reliability and provided additional operational flexibility.switch es wer e r equir ed fo r function selection because t his s che me allowed manualand alte rnate selection of individual sys tem components o r functions. For example,the e ar li er mode- selection schem e had automatic FDAI err or- nee dle scaling on thebas is of pr ese lec ted values. However, the function- selection arran gement inco rpora -ted a scalin g switch that permitted the crewmen to se lect the sc aling desire d fo r apar tic ula r operation. Although function selection unquestionably gave grea te r flexibil-ity, the approach also had two undesirable side effects. First, this approachin cr ea se d the number of s witches that had to be positioned and monitored; second,inc rea sin g the number of switches inc rea sed task tim es, complicated training, andra is ed the possibility of inadver tent o r improp er switch combinations. The princ ipal

advantage of the function-selection scheme may have been it s capability to accommo-date change s in vehicle flying techniques.select ion sche me we re hardwired into the system.

This change improvedMore

By con tras t, most fea tu re s of the mode-

4. Flag event ind ica tors that worked in conjunction with switches were movedf ro m below the switch to above the switch s o that the operator's hand did not blockvisibility during operations.5. Th e EMS development was continued s tr ic tly as a Block II item, and thedevice w a s deleted fr om Block I spacecraft.The deletion of the in-flight-maintenance concept als o meant that an elabora tein-flight te st sys tem would no longer be require d; theref ore, the syst em was reducedto a single voltmeter and two multiposition switches. This sy ste ms test met er, as i t

came to be called, w a s used to check out certa in equipment and monitor p ar am eters2 1


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that had low criticality or that required a very low checking frequency. The posit ionsof one rotary switch were identified with le tt er s and the other with numbe rs. Themet er displayed tes t valu es between 0 and 5 volts. A decal that identified (1) thepar ame ter displayed with a given switch position; (2) the nominal, maximum, andminimum meter readings; and (3 ) the corresponding engineering units for the voltagereadou ts was provided for us e with the sy ste ms test panel.After the Apollo CM fire, many changes were made in a relatively s hort time.The primary impact on the D&C was that cert ain ECS controls we re r elocat ed toimprove crew acce ss. Holes were added to most D&C panels as ports for insertion ofa fi re extinguisher nozzle in the unlikely event that a fire erupted behind the panel.The flammable plastic control knobs were also replace d with metal knobs.Severa l individual changes in the D & C occurred as the design evolved. The

fi rs t change involved t h e nucleonics quantity measuring system developed for theservice module and LM reaction contro l system . This gaging system consisted ofmany sm all radioactive sou rc es placed exte rnally on one side of an RCS ank and ascintillator-photomultiplier counter placed on the other side. The idea w a s that thepropellant would scatter o r absorb radiation at a rat e proportional to the quantityremaining in the tank. This quantity would then be displayed on a digital readout. ANixie tube display was baselined for the CM- he only space cra ft application of sucha display. Unfortunately, problem s were encountered in the development prog ram;the cost increased, and the system was canceled. A s a resu lt, an indirec t quantitygaging sys tem had to be used. A pressur e/temper ature ratio transdu cer monitoredthe RCS helium tank that supplied propel lant pres sur iza tion. The output of t his tr ans -ducer drove an analog mete r that was calibrated to read the corresponding propellantquantity .

Prob lems i n the development of toggle switches caused changes in ven dors,redesigns, and numerous refinements in screening proc ess es. One result of theseproble ms was a requir ement to provide redundant pa rall el switche s, each havingredundant contacts wired in se ri es parall el fashion, fo r the most cri tica l pyrotechnicfunctions on the command and ser vi ce module spacecr aft.

Another significant D&C development was the addition of the orbi tal -rate dr iv e,Earth and lunar (ORDEAL), assembly to the C M and the LM. Beca use the Apollospacecraft was conceived primarily as a nonorbital vehicle, its guidance and controlscheme was based on a strict ly inert ial re fe ren ce sys tem without any capability fo r alocal-vertical or a local-horizontal orbita l mode. Gemini exp erience , however,showed that the crewmen required a rapid and accurate method for determining theangle between the relative line of sight and the loca l horizontal d urin g rendezvousmaneuve rs. When the require ment w as firmly established, the CM and LM designshad progress ed too far to enable incorporati ng the requ ire ment easi ly o r cheaply intothe existing syst ems. To fulfill this need, the ORDEAL was designed as a black boxwith integra l controls that could litera lly b e hung on the w a l l and wired to dr ive theFDA1 at a n orbita l rat e. The ORDEAL box instal led in the CM is illustrated infigure 13 .

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L u n a r M o d u l eAfter the initial design was finalized,the LM did not undergo a major redesignsuch as the CM block changes. The majordevelopment change to the LM D&C con-sisted of replac ement of fuel cel ls and

associated cryogenic supplies with bat-ter ies. The displays and controls associ-ated with a battery a r e much less numerousthan those fo r a fuel cell and cryogenicsyst em; thus, the net resu lt of th is changewas to simplify the LM D&C.

Figure 13. - The ORDEAL assembly. An intere st ing LM D&C componentdevelopment was that of the cro ss-p oin terindicator. This instrument provided simul-taneous display of forward and lat eral vel oc-it ie s during landing and of line-of-sight azimuth and elevation angles fo r rendezvous.The initial proposal was that the display be an EL grid and that the drive sign als bedigital. Advantages of this implementation were improved syst em accuracy andelimination of parall ax. Afte r much study, however, the analog-meter c ro ss pointerwas retained because of the impact of converting to an all-digital system.

Simila rly, feasibility s tudi es and simulations we re conducted to analyze thedesira bility of using digitally driven attitude indica tors. Pr obl ems of attitude- sp her erespons e and information lag wer e identified, and th is concept was therefo re dismissed.Apollo software, it should be noted, was generally li mited to outputting information ata ra te of 10 times per second. W i t h the miniaturiza tion of so ftware logic, the state-of-the-art "refresh" techniques, and the advances in display desig ns that cur rent ly exi st,digital displays would now poss ibly be feasible.Special prob lems we re encountered with the LM engine-stop pushbutton switch.On seve ral oc casion s during ground checkout operations, this switch w a s inadvertentlyreset f rom the "on" st at e (engine off) to the "off" state (engine on). If th is conditionhad occ urr ed during lunar touchdown, the result could have been catastrophic . To avoidsuch a catast rophe, an external "positive actuation device" was added to the push-button to hold the switch in the internally latched position. Unfortunately, numerousproblem s wer e experienced with the device itself, but these w ere resolved before thefirst lunar landing. In fu tur e effort s, the use of maintaining-type pushbuttons fo raccomplishing c ri ti cal switching functions should generally be avoided.

Standardizat ionThe principles of commonality and standard ization of equipment recei ved muchemphasi s ear ly in the Apollo P rogr am. A s a resu lt, commonality studies wer e con-ducted to examine the feasibili ty of using Gemini ha rdware o r other common hardwar e(or both) in both Apollo vehicles. The result s of t hes e studie s indicated that the dif-fere nt development schedules and different environment requi rem ents of the thre evehicles eliminated the use of most common hardware. Therefore, the initial CM and

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LM D&C designs did not include a single piece of equipment that was common to bothvehicles. Later in the pro gram , however, the operational advantage of a stFndardDSKY configuration became apparent, and a common (although not interchangeable)DSKY was procured f o r us e in both the CM and the LM. For s im il ar re asons , when therequir ement fo r the ORDEAL was la ter identified, common equipment was proc uredf rom a single socr ce. Later in the program , toggle switches, circuit break ers, andmission t ime rs a lso became common equipment because of problems i n the hardwarebeing procured from Apollo vendors.

The goal of functional standardizat ion w a s ultimately achieved by two methods.Fi rs t, interfa ce control documents w ere established among the prim e vehicle contrac-tors, the G& N sy st em s contr acto r, and the NASA Lyndon B. Johnson Space Center(JSC) (formerly the Manned Spacecraft Center (MSC)). These documents formal lydefined and standardized the basic D& C functional requirements to eliminate conflictingdesign feature s. Among the it em s standardized were panel controls, display faces,annunciators and fla g indicators, nomenclature, marking s and colo rs, and lighting.Thes e documents established a.basic compatib ility "ballpark" in which detail design-ing could be done. The second fac tor in achieving standardiza tion- ess formal thanthe first but just a s important and effective, especially in day-to-day work in speci ficdetails- as that the D&C efforts for both the CM and the LM were monitored by thesa me group at MSC. Th is arrange ment encouraged and--facilitated constant communica-tion between the cognizant eng ineers and helped to achieve fu rther compatibility in theCM and L M D&C designs.

For future efforts, a se t of D&C functional r equi rem ent s sp'ecifications has beenprep ared . These documents, based on manned spacecraft experien ce to date, includea compilation of require ments fro m the Apollo interfa ce control documents and applica-ble military standards. The intent of these specifications is to identify basic consider-ations, c riteria, parameter s, and values ?f benefit to D&C sys tem s desig ners , and tomaximize crew efficiency by standard izing functional ch ar ac te ri st ic s and thereby reduc-ing the possibility of ambiguity. These specif ications co-ver the bas ic ent iti es of di s-plays and contro ls including lighting; nomenc lature , markings, and col or ; abbreviations;displays; and controls.

O P E R A T I O N A L E X P E R 1 ENCEThe fi rs t five manned Apollo miss ions (Apollo 7 to 11) provided mo re than

1000 hour s of flight operations: the D&C subs yst ems, as a whole, worked well and metall design objectives during these. missions. Flight crew s reporte d that the displaysprovided the required information and wer e rea d easi ly even under the mos t s ev er eenvironmental conditions, that the markings and nomenclature were satisfactory, andthat the controls gave the needed command capabilities and were operated easily. Manyof the D&C anomalies reported on Apollo flights we re not directl y attrib utable to th eD&C equipment itself but to anomali es within inte rfacing equipment (e. g. , instrumenta-tion). Discussions of these types of anomali es have generally been omitted in thisreport.

In a sens e, operational exper ience with the D&C sys tem began well before t hef ir st manned Apollo fligh ts. Valuable knowledge of D&C subsyst em perfo rma nce was24


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gained both f ro m unmanned orbi tal flights and from manned thermal-vacuum chambertest s. Unmanned developmental command modules we re equipped with sequenceca me ras tha t photographed po rtions of the MDC and obtained forward-window viewsduring some of the cri tic al mis sion phases (such as entry). Verification of the flightperf orman ce of c ert ain cr itic al displays was believed to be a contributing fac tor tomanned Apollo missions.Mission AS-202 w as one of the earl y unmanned flights that provided ope rationalexperience. Postflight examination of telemetry data and of in-flight motion pic ture sof the panels rev ealed that most of the displays operated normally. The data also indi-cated that those displays that did not respond as expected wer e actually only reflec tingprob lems in the subsystems. Fo r example, an improp er FDA1 attitude indication that

existed throughout the flight was caused by an alinement er r o r in the platfo rm, and afuel cell C&W annunciator illuminated because of a low oxygen flow rate.Because LM vehicles could not be recovered, the LM panels were not photo-graphed in flight. A study conducted to dete rmi ne the feas ibilit y of using the Apollotelevision c ame ra fo r re al-tim e D&C asses sment proved this approach to be impr ac-tical, pr imar ily bec ause of the unavailability of communications channels and rece iving

stations.Manned thermal-vacuum chamber tests were pe rformed fo r both the CM and theLM by using special tes t spacecraft. These te st s permitted a combined environ-

men tal and operational asse ssment of the Apollo D&C. In conjunction with the pr im ar yduty of man-rating the spacec raft , astronauts manning the vehicles during these te st sas se ss ed the following D&C areas: readability of d isp lays and accessib ility of con-tr ols , torques and forc es required to actuate contr ols, inter fere nce with D&C panelsduring norma l operations, comparison of onboard display readin gs with teleme try andcontr ol-ro om read ings , operation of the C &W sys tem , and gene ral acceptability oflighting. With few exceptions, the displays and cont rols for both vehicles we re foundto be acceptable. These tes ts were especially helpful because they enabled determina-tion of operational quirks within the D&C and vehicle subs yst ems . Numerous prob-lem s with transient and false C&W al ar ms were encountered. A s a result, significantchanges we re made to C&W syst em s within the flight vehic les. In other cases, pro-cedur al workarounds w ere established.

Apollo 7 MissionThe pr im ary purpose of the Apollo 7 mission, the fi rs t manned CM flight, wasto check out and gain experience with the spacecraft systems. A t the postflight debrief-ing, the c rew mem ber s reported that, in general, the D&C configuration and operationswere very satisfactory. Control for ces and torques were found to be s atisf acto ry underall the diffe ring accele ration conditions and wer e gr eat enough to preclude inadvertentcontrol actuations. The displays were readable, but sev era l met ers were found to beless ac cu ra te than had been anticipated. A problem with washout of the EL readoutsof the EMS, the DSKY, and the missi on timer w a s als o experienced. Sun shafting,

par ticula rly through the sid e hatch window, occasionally made these disp lays unread-able. A s corre ctive action, portable shades we re provided to shield these displays onlater missio ns. The panel nomenclature and markings wer e reported to be satisfac-tor y, and the EL pan els provided excellent readability even in a darkened cabin.

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The Apollo 7 flight crew found that the frequency of timing opera tions warrantedan additional ti me r for use by the crewman who occupied the right-hand couch. Theus e of either another event tim er o r a "kitchen timer" w a s suggested. An evaluationof the impact of adding another event time r resu lted in provision of a kitchen-typetime r f or subsequent missions. A new nonflammable case was made, and the tim erw a s tested to ensur e that the re w a s no harmful outgassing. Thi s modified householdtime r proved to be especially useful because of i ts portability, lack of in ter fac es, andbuilt-in signal bell.

Two D&C hardware failures were experienced on the Apollo 7 mission. A crackdeveloped i n the optical gla ss window of both mission timers, and the EMS delta-velocity/range-to-go display malfunctioned before lift-off. Fortunate ly, the mission-tim er gla ss did not come loose, and tim er operation was unaffected. Postflightinvestigations revealed that the cracking resulted fr om s tr es s induced in the gl assduring manufacturing. The nature of the fa ilu re did not warrant redesign of the t imers ;but, to compensate fo r this type of fai lure on la te r miss ions, trans parent tape wasinsta lled over the display windows of both mission t im er s to prevent the rel ea se ofglass particles within the crew compartment. Loose particles constitute a specialdanger in a zero -g condition because the se par ticl es float freely within the cabin andcan ea sily be ingested by the crewmen. Investigations after the mission disclosed thatthe EMS failure was apparently caused by a poor so lder connection and a poor wire-cr im p connection within the EMS.

Apo l lo 8 MissionThe Apollo 8 mission w a s the second manned flight and the fi rs t manned lunarorbit mission. Again, the cre wmembers repo rted that the displays and controls wer every satisfactory. The kitchen-type ti mer recommended aft er the Apollo 7 missionproved to be very useful, parti cular ly for timing fuel cel l purges. However, the panelshades that were provided to prevent washout of the EL nu mer ics wer e gene rallyineffective. The best solution was to shade the displays with one hand during the

occasional periods when washout occu rre d.Before the flight, the Apollo 8 crewmembers wrote various supplemental systemsinformation on the D&C panels. Thi s additional information proved to be very u sef ulto the crewm embers during the flight. A s a result , a sys tem was established for sub-

sequent missions in which, shortly before flight, operational informa tion of a supple-mental o r "memory jogger" nature was collected fro m the crewme mbers and wasverif ied, documented, and placed on metal foil decal s that were then added to thespace craf t panels. Examples of these decals are i l lustrated in figure 1 4 .Only one D&C-associated hardware p roble m occ urr ed during this flight- ourtime s during the mission, abnor mal indications existed on the delta-velocity counter

or the scroll display. Postflight investigations disclosed a bubble in the acce lerome terthat could have caused some of the prob lems. The remai nde r of the anoma lies resu ltedfr om using the EMS to monitor sma ll acc rue d velocities , a job for which it was notdesigned. However, a procedural workaround was developed so that, on subsequentmissi ons, the EMS could be used fo r such monitoring, i f desired.

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Apollo 9 Mission

Figure 14. - Supplemental decals.

The Apollo 9 mission, the firstmanned LM flight and the first joint CM andLM mission, was intended both to qualifythe LM spacecraft and to demonstrate, inEarth orbit, combined LM/CM operations.Although the D&C for both vehic les func-tioned satisfactorily, seve ral problemsoccurred, chiefly in the CM.

During the fi rs t scheduled LM/CMsepara tion (undocking), the "probe extend/releas e" switch was actuated, but the vehi-cles did not physically unlatch until thethird attempt. Then, on retracting th eprobe in preparation for redocking, thestat us indicators showed that the probe latches were not cocked fo r docking. Cyclingthe docking probe produced the proper indications, and docking was completed satis-factorily. Indications wer e that these anomalies did not resu lt f ro m any control o rprobe failure but fro m a procedural problem caused by not holding the probe switch inthe "extend/release" position long enough to complete the release and latch-cockingsequences. Fo r subsequent flights, the operational procedures were changed toreflect this operating time, and the problem w a s not repeated.

Some of the Apollo 9 docking proble ms could have possibly been avoided i f thecrewmembers had been provided with additional docking system information. A two-position (gray/striped) flag indicator w a s used to monitor all docking-probe operations.Thi s approach inherently limited the amount of information that could be displayed andeasily led to confusion because the meaning of the displayed indication w a s different atdifferent times in the operating sequence. In the future, if status information is neededto monitor docking or othe r multiposition mechanical sy ste ms, consideration should begiven to providing a discrete indicator f o r each event in the system operating sequence.

Several C&W sys tem anom alies occurred during the Apollo 9 mission. On threeoccasions, a C&W ma st er al ar m occur red without the illumination of any C&W annun-cia tor and without the identi fication of any out-of - olerance condition. In-flight andpostflight analysis revealed that these unexplained al ar ms we re probably caused byexternally induced transients rather than by malfunctions within the C&W electronics.A problem was also encountered with certain se rvi ce propulsion system C&W circ uits .On eight occasions during the th ree firin gs of the service propulsion engine, a C&Wlight indicated an excess ive unbalance i n the propellant quantities. Two of the eightfai lu re indications were found to be caused by actual unbalances, but the remainderwere attributed to either an unexpectedly long propellant settling time or a bias in thequantity measurin g syst em. Analysis of all the flight data showed that balancing thepropellant usage w a s not as crit ical as had been antic ipated. To avoid numerousnuisance alarms, this C&W function w a s disabled on succeeding spacecr aft.

One minor problem experienced on the Apollo 9 mission w a s directly attributableto an e r r o r in panel markings. Problems i n repressuri zing the surge tank resulted

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f rom a 20" misa linement between the ECS panel markings and the control-valve detentposition. The control position indexes had simply been mislocated during manufactur-ing, and the e r r o r was not detected before flight.A s on earlier missions, a problem with the Apollo 9 EMS was experienced. Thescr oll assembly failed to sc rib e a tr ac e of acceler ation as a function of inertial veloc-ity during entry. Postflight testing disclosed that the environmental seal for thescroll assembly had a large leak. The scr oll coating was susceptible to moisture , anda subsequent slow drying would cause the coat to harden. Apparently, ambient airleaking through the broken s ea l provided the m oistu re, and the 10-day m ission at a

34 470-N/m ( 5 psia) cabin pr es su re provided a slow vacuum drying that hardened thecoating so that the s cr ib e did not provide a tr ac e. Special photographic techniquesrevealed that the stylus had traced properly on the film.2

Three D&C-related problems occur red i n the LM used f or the Apollo 9 mission.Because the LM did not re tu rn to the Ea rth , as did the CM, a rig oro us postflightanalysis sim ila r to the type conducted fo r the CM was not poss ible. Pr ec is e identi-fication of the cause of an anomaly was therefor e often impo ssibl e. Pro ble ms wer eexperienced with the AGS keyboard , the C&W syst em, and the range indica tor. Whenthe "clear" pushbutton on the AGS keyboard was operate d, the oper ator -e rr or lightilluminated on a number of occasions.then requi red to extinguish the light. (The light would extinguish momentarily witheach subsequent switch activation. ) This problem wa s attributed to the improperoperation of one of the two microswitches contained in the pushbutton. Simultaneousactivation of both switches w a s required to extinguish an ope rat or- err or light. Theconditian was accepted on the Apollo 10 mission. However, for Apollo 11 and subse-quent missions, a wiring change was made so that activation of eit her switch withinthe "clear" pushbutton would deactivate the op er ator -e rr or light.

Four o r five additional switch activations wer e

A second L M problem w a s the illumination of a n AGS failure light. Subsequentsyste m performance and the normalcy of instrumented sy ste m pa ra me te rs reduced theprobabil ity of a n actua l AGS fa ilure. The conclusion was that the a la rm wa s probablycaused either by a shor t-cir cuit ed o r broken wir e between the AGS, signal conditioning,and C&W equipment o r by a fa il ure in the sig nal conditioning o r C&W equipment.

The L M range indicator also caused some problem s, not because it faile d butbecause it behaved differently than the me te rs on which the cr ew me mb er s had trainedin the mission simulator s. In flight, the tape responded in irregular steps, whereasthe simulator displays exhibited a smooth slewing of the tape. The action of the flightdisplay w a s normal and w a s cause d by two fac to rs : the digital natu re of the inputsignals and drive mechanism and, the mor e influencing fac tor , the us e of differentscale units among the four input sourc es to the mete r. The internal scale fac tor wasapplied according to both the so ur ce sele cted and the portion of the range tape beingused. The simulator displays wer e basically analog instr ument s and, because ofexisting software limitations, had not been programed to respond like the actual units.Unfortunately, because of the limited number of opportunitie s to obser ve integr atedrange-indicator operation before flight, the Apollo 9 crewmen initially interpreted thedigital respo nse of the range indicator to be abnormal . To avoid this situation infuture efforts , a list describing any stati c o r dynamic diff erences that e xist betweenflight vehicles, crew tra ine rs, and simula tors should be maintained.

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Apol lo 10 MissionThe Apollo 10 mission, the fi r s t lunar flight of the complete Apollo system, wa sintended to verify all aspe cts of the lunar-landing mission , except fo r the actual LMlanding, lunar surface. operat ions, and ascent . The D&C of both vehicles again per -formed well with only a few minor proble ms.Thr ee D&C-related problems wer e encountered in the CM. The launch vehicleannunciator assembly operated intermittent ly during prelaunch checkout. Each of theeight status lights in the annunciator assembly had two redundant lamps, and one lampin each of four different indica tors operated intermittently. Results of postflightanalysis showed that each of these lamps had cold s older joints.A second problem existed with the digital event ti me r. On one occasion, thetimer advanced 2 minutes; on other occasions, the tim er failed to advance the tens-of-seconds count. The failur e of the event tim er i n the tens-o f-second s count w a s foundto be caused by contamination of an electr ica l contact when a motor g ear rubbed againsta display wheel and flaked the paint. The 2-minute jump could not be reproduced and

was thought to have been caused by e lect rical noise to which the t im er had proved t obe sensitive.The third CM D & C fail ure concerned the EMS. After success ful completion ofthe pree ntry te st, the stylus of the scro ll assembly stopped scribing. When the scr ol lwas slewed back and forth, the stylus cut through the emulsion and then performednormally throughout en try. Investigations disclosed that the bas e of the emulsionused on the scrol l w a s a latex rubber and soap mixture. The formula for the com-

mercial ly pr epar ed soap used in the mixture had been changed, and the new form ulacaus ed a chem ica l reaction with the film and hardened the emulsion. Lack of t imeprevented making any change for the next mission; however, a decision was madethat, for succeeding vehicl es, either the s crol l emulsion bas

apollo experience report crew station integration volume ii crew station displays and controls

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