apollo experience report command and service module controls and displays subsystem

8/8/2019 Apollo Experience Report Command and Service Module Controls and Displays Subsystem

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N A S A TECHN ICAL NOTE NASA TN 0-8301c0mzc

APOLLO EXPERIENCE REPORT -C O M M A N D AND SERVICE MODULECONTROLS A N D DISPLAYS SUBSYSTEMA ar on B. Olsen and Robert J. SwintLyndon B. Johnson Space CenterHouston, Texas 77058NATIONAL AERONAUTICS AND SPACE ADM IN ISTRATION W A S H I N G T O N , 0. C. SEPTEMBER 1976


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1. Report No. 2. Government Accession No.N A S A T N D-8301

4. T i t le and Subt i t leAPOLLOEXPERIENCEREPORTCOMMAND AND SERVICE MODULEZgNTRGLS A h 3 DISPLAYS SUBSYSTEM7. Author(s)

Aaron B. Olsen and Robert J. Swint9. Performing Organization Name and Address

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

National Aeronautics and Space AdministrationWashington, D. C. 205465. Supplementary Notes

3. Recipient's Catalog No.

5. Report DateSeptember 19766. Performing Organization Code

JSC-075838. Performing Organization Report No.

S- 46310. Work Un i t No.

914- 13- 0- 00- 7211. Contract or Grant No.

13. Type of Report and Period CoveredTechnical Note

14. Sponsoring Agency Code

6. A m a c tA review of the command and se rvi ce module controls and displays subsystem is presented.The subsystem is described, and operational requirements, component history, problems andsolutions, and conclusions and recommendations for the subsystem are included.

7. Key Words (Suggested by Author(s1)Display sys tems Circuit protectionCommand modules In-flight monitoringLens design Flight safetyExtravehicu lar activity BellowsElectroluminescent lightsource

18. Distr ibut ion StatementSTAR Subject Category:12 (Astronautics, General)

For sale by the National Technical Information Service, Springfield, Virgin ia 22161

19. Security Classif. (of th is repor t ) 20. Security Classif. (o f this page1 21. NO. of PagesUnclassified Unclassified 24

22. Price'$3.50


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CONTENTS

SectionSUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .DEVELOPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .COM PONENT HISTORY . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Caution and Warning Sub system . . . . . . . . . . . . . . . . . . . . . . .M i s s i o n T i m e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Digital Event Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Elec tr ica l Indicating M eter s . . . . . . . . . . . . . . . . . . . . . . . . .Event Indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .P o tentiom eter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Rotary Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Pushbutton Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Toggle Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Other Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

CONCLUDING REMARKS AND RECOMMENDATIONS . . . . . . . . . . . . .

page111221215161717171719192121

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TABLETable

I BLOCKIICDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figure123

4567891011121314

FIGURES

The CDS panels . . . . . . . . . . . . . . . . . . . . . . . . . . . .Panel lighting schematic (integral and numerics) . . . . . . . . . .The command module integral and numer ics illuminationsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Tunnel lighting schemat ic . . . . . . . . . . . . . . . . . . . . . . .The CSM docking. extravehicular activity. and external lightsSchematic of C&WS power distribution

. . .. . . . . . . . . . . . . . . .The C&WS MA schematic . . . . . . . . . . . . . . . . . . . . . . .Apollo 1 5 DET anomaly . . . . . . . . . . . . . . . . . . . . . . . .Idler gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Rotary switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Pushbutton switch plunger cutaway . . . . . . . . . . . . . . . . . .Toggle- switch problem . . . . . . . . . . . . . . . . . . . . . . . .Momentary switches . . . . . . . . . . . . . . . . . . . . . . . . . .Toggle switch(a) Cutaway view . . . . . . . . . . . . . . . . . . . . . . . . . . .(b) Detailed view . . . . . . . . . . . . . . . . . . . . . . . . . . .

iv

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1010101314161618192020

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APOLLO EXP ERIENCE REPORTC O M M A N D A N D SERV ICE MODULE

C ON TR OL S A N D D I S P L A Y S S U B S Y S T E MB y A a r o n B. O l s e n a n d R o b e r t J. S w i n tLyndon B. Jo hn so n Space C en t e r

S U M M A R YThe command and se rv ic e module controls and displays subsystem provided theinterface between the c rew and the spacecraft. This interface allowed the crew to man-ually operate the spacecraf t under normal o r contingency conditions, to safely shutdown all equipment, to monitor subsystem conditions and energy res ources , to recog-nize malfunctions and imminent hazardous conditions, and to adjust o r select al ternatesubsys tem operating modes. The equipment required to accomplish these functions isdiscussed in this report.

INTRODUCTIONThe command and se rv ic e module (CSM) ontrols and displays subsystem (CDS)was composed of various electr ica l controls and elec trically powered displays. Thecontrol types were on/off (switch) and variable (potentiometer and rheostat) . Displaytypes included the elec tri cal met er and the flag, o r lighted, indicator that displayedthe information in an EVENT, an ANALOG, or a DIGITAL format . Excluding the inte-r ior floodlighting, the exte rior lights, and the caution detection unit (CDU), all controlsand d isp lays (C&D) were mounted on panels inside the spacecraft. This ??port discuss-es the equipment that comprised the subsystem and presen ts the major problems thatoccurred during the Apollo Program.As an aid to the reader, where necessary the original units of measure have beenconverted to the equivalent value in the Systsrne International d 'Un i t 6 s (SI). The SI

units are written fir st , and the original units ar e written parenthetically thereafter.DEVELOPMENT

When the requi rements f o r the CSM CDS had been finalized and the desired meth-ods of control and display had been decided, specifications were formula ted for dis tri -bution to industry to obtain the hardware to fulfill the requi rements. To qualify, each


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component had to undergo the following tests: design feasibility (breadboard model),design verification (engineering model), qualification (flight item), acceptance (flightitem), and preinstal lation (flight item). The qualification test levels varied, dependingon the physical location of the component in the vehicle. Several it ems underwent ad-ditional qualification testing as late as 1968-1969 because the initial test levels werefound to be inadequate.The basic C&D operational requi remen ts for block I1 vehicles were very simil arto those for block I vehicles. The block 11vehicle was a redesigned block I vehicle withchanges affecting spacecraf t wiring, wiring harnes ses , and inte rnal struc ture. Theadditional C&D functions needed to accommodate the block I1 miss ion requirementsmainly affected the lighting and the panels. Block I inte rior lighting consisted entirelyof floodlights, whereas the block I1 spacecraft included in tegral lighting, backlightedpanel components, and electroluminescent (EL) lighting for panel nomenclature anddigi tal displays. Block I main display consoles (panels) consisted of sev er al as sortedsma ll panels that were consolidated into th ree l ar ge display panels in the block I1 space-craft (fig. 1).

COMPONENT H I STORYThe component, the quantity used per vehicle, the par t number, and the certif i-cation test report number of the components used in the block I1 C&D subsystem arelisted in table I. Most of the items are identical to thei r block I counterpart s; e. g.,the digita l event time r (DET) is the same as the block I unit except fo r the addition ofEL lighting to the indicator window. Some items, such as the mission timers, toggleswitches, and EL panels, were completely new on block I1 spacecraf t.

LightingThe CSM lighting system (figs. 2 to 5) provided genera l int erior lighting, panelinstrumentat ion and nomenclature illumination, tunnel lights, exte rior orientationlights, illumination fo r docking and ex travehicular activi ty (EVA), and a flashing beaconfo r vi sual recognition at distances as great as 297 kilometers (160 nautical miles). Thegeneral inter ior lighting w as provided by six fluorescent floodlights, each containingtwo separately controlled lamps (one pr im ar y and one secondary). The floodlight fix-tu re s were mounted on the head position at each side of the center couch, on the bulk-head at the head position of each side couch, and on the couch st rut s at the foot positionof th e center couch to light the lower equipment bay (LEB). The control fo r each flood-light consisted of an on/off switch, a primary/secondary selection switch, and a rheo-stat fo r varying the lamp input voltage. The lamps opera ted on direct cur re nt (dc)

voltage that was converted to alternating cu rre nt (ac) voltage by a converter inside thelam p fixture. Because of the numerous fa ilures and fa ilure modes involved, the flood-light cir cuit design was progre ssive ly changed.

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1m I 1 I I I 3 * I4 3 I 2 I 11 0 7 611 IA

LDClC\

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j Figure 1.- The CD S panels.

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Figure 1. - Concluded.


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TABLE I. - BLOCK I1 CDS~~ ~~ Component

Accelerometer indicatorEL panelCDUElectrical indicating me terEvent indicatorBarometric- pr essur eindicatorCaution and warning sub-sys tem event annunciatorAbort annunciatorSaturn V launch vehicleengine annunciatorExternal lightInte rior floodlightMiniature and dual tunnellightsPotentiometerRheostatVariable power tran sformerVariable transformer-rheostatPushbutton switchPushbutton switchEL pushbutton switch

~~QuantityPervehicle1

231

31511

2

11

1066

213322110

Part no.

ME 106-0023M E 181-OXXXM E 430-0006M E 430-0170M E 432-0172M E 432-0173

M E 434-0020

M E 434-0021M E 434-0043

M E 434-0041M E 434-0045M E 434-0051

M E 444-0033M E 444-0049M E 446-0034M E 446-0036M E 452-0060M E 452-0061M E 452-0092

Certification test report

2645600126456002, 02726456003, 0122630126456004, 01226312, 315264 5600526456006

01226319

0122631801226317

26456008, 02226456019, 0122631626456009, 01226319

0122631001226311264560126456012, 021, 02601126303, 01226303, 31301126303, 01226303, 31326456013

7


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TABLE I . - Concluded

Component

Rotary switchToggle switchDigital event timerE ec r ca1 conver erLight- f lashing beaconFilter-flashing beaconDocking lightMission timer

Panel assemblies 1 to 1015, 16, 100, 101, 225,226, 229, 306, 181, 162,163, 164, 230, 604, 201,227, 250, 275, 276, 277,and 278

-@ant ityPervehicle1 5

3 02111

12

31

Part no.

ME 52-0093M E 452-0102ME 56-0044ME 476-0049M E 434-0055ME 447-0043ME 434-0054LSC- 3 5-31600-or LSC-355-31600-11V36

Certification test report

01126302, 309, 264560142645602001226306, 2645601526456018264560232645602426456025Government- furnishedequipment

- -

Triggers. - Most floodlight failures were attributed to the overloading of a semi-conductor diode. Because of excessive cur rent, the unit overheated the encapsulatedcirc uitr y and caused emission of smoke and noxious odors. The fa ilu re was traced tothe thermal sensitiv ity of the three- layered semiconductor diode used as a trigger. Thesupplier confirmed that the three-layered diode could not be manufactured with adequatepara mete r controls.

--

The three-layered diode trigger was replaced with a four-layered one that couldbe manufactured wi th adequate controls. The new tr igg er maintained the requiredswitching speed over the required environmental range of vibration, temperature, pres-sure, and humidity. An improved pa rt s screen ing procedure was implemented on thenew triggers. A summary of the scr een ing tests includes the following.

1. A functional test of the trigger at its highest power setting2. A burn-in for 100 hours at 373 K (100" C) with 30 milliamperes of current

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3. A thermal stress of the unit by varying the temperature from 218 o 398 K(-55" to 125" C) for 4 hours4. A repeated functional test of the triggerTransient susceptibility. - In July and August 1966, floodlight fai lur es were attrib-uted to transient susceptibility of he lamp circuitry, which created conditions that al-lowed the lamp assembly to draw excessive current that, in turn, opened the fuse. Thecir cui try was redesigned to l imit the cu rre nt flow by the addition of an input filter, atime-delay network, and a zener diode.

Lighting numericslintegrai (RHEB 2261(Bus 1 9 + A > Nomen

t A Q NEUT 2II I

Numerics

I MDC 1 1 I MDC 3 1@ Resistors on SI C la.106, and subsequentANN annunciator G&N ouidance and navioation NUN

WlHEB 229

numerics

I LEB 122 1

> - ~AT1 attitude GPI gimbal position indicator P B pushbuttonC&W caution and war ning LHEB left- hand equipment bay PUGS prw ell ant utilizati on and gaging systemD S K Y display and keyboard MDC main display console RHEB rig ht- han d equipment bayEMS entry monitor system MSN mission SI C spacecraftEV event NEUT neutral s pS service propulsion systemFDA1 flight director attitude indicator Nomen nomencla ture SW switchT B I talkback indicator

I L 7 IhlSN timer

LHEB 3M

Figure 2. - Panel lighting schematic (integral and numerics).9


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-1 nterior liqhts- -I nt er io r lightsIntegral Flood

nff R rt Off Brt Of f Brt O ff B r t O f f Brt",, - YLEB lights-(MDC 8) Numerics Flwd Integral (MCC 51

O f f B r t O f f B r t O f f Br tILEB 100)

Figure 3 . - The command module integraland numerics illumination system.Lamp tube. - Other than problemscaused by poor handling, the greatestcau se of tube fai lur e was an inadequateamount of mercury injected into thetube. Manufacturing procedures werechanged to prevent recur rence of this dis-crepancy.Lamp moisture absorption. - To pre-vent fai lure s caused by moisture absorp-tion, improved procedures were implemen-ted fo r the application of the potting sealantto tube ends and epoxy surfaces.Silicon- controlled rect ifie r. - Althoughno failure was directly attributed to the fail-ure of a silicon-controlled rectifier, thefollowing additional screening was imple-mented t o preclude t h i s possibility.1. A burn-in for 100 hours at 1

ampere at 373 K(100" C)2. A tes t for the minimum gate turn-on current

10

\ \\ \

To docking To external spotlightsystem system

Figure 4. - Tunnel lighting schematic.

Spotlight (whale Floodlights Q)5.4 lmlm2 (0.5 fclaimed 45" to X-aXiS

K n d e z v o u s eacon brightnessSeen by eye at 111 km (60 . mi.) or bytelescope at 297 km a60 n. mi.): 1 flashlsec ( 1 flashlsecl

Figure 5. - The CSM docking, ext rave-hicular activity, and exte rnal lights.


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Circuit protection. - The power distribution circuit was examined to determinethe feasibility of improving the overcurr ent protection by reducing circuit b reak er rat-ings. It w a s determined that the existing brea kers were sized to protect the power dis-tribution wiring and that the reduction of these ra tings to provide protec tion for eachlight assembly would resul t in the loss of other lights o r system elements on that samecir cui t breaker . The final correct ive action adopted was to add a fuse in each powerinput ci rcui t of each light assembly.Transient protection. - To protect against the effect s of switch contact bounce,the input filter chokes were replaced with 0.25-ohm resistors, and the 6.8-microfaradinput filter capacitance was incr eased to 68 microfarads. Also, a 102-millisecondtime-constant delay network and a zener diode were added to lim it the maximum voltagethat could be applied to the tri gge r circuit.

Lens strength. - During spacecraft checkout, the plast ic lenses of the floodlightswere found to be susceptible to breakage and dislodgment with normal checkout handling.This susceptibility disclosed the possibility that mer cury could be released in toxicamounts into the command module (CM) interior if fluorescent lamps inside the flood-light should become cracked o r broken. An investigation revealed that this suscepti-bility was caused by inadequate strength of the lenses and lens attachment to the flood-light cases. Lenses and lens- case attachments were redesigned. Thicker, more rug-ged lenses of high-impact p las tic were used. Lenses were produced by machining andoptical polishing. The previously used adhesive- bonding technique for lens attachmentto the case was replaced by a mechanical fastening. These changes provided gr ea te rlens- case strength and, consequently, improved lamp protection. The redesigned lens-es met the following requirements: st re ss of 890 newtons (200 pounds) applied on 6.45square centimeters (1 squ are inch) of the lens surface; stress of 1334 newtons (300pounds) applied on 25.8 squ are cent ime ters (4 square inches) of the len s surface ; andimpact by a 7-kilogram (15 pound) disk (38 centimeters (15 inches) in diameter by 1.3centimeters (0. inch) thick) moving at 0.6 m/sec (2 ft/sec).

To make the CM interior more fireproof, the high-impact plastic lens was re-placed by a len s of laminated glass. Because the gla ss len s could spl in ter on hard im-pact, it was overlaid with a thin (approximately 0.008 centimeter (0.003 inch)) coatingof fluorinated ethylene propylene Teflon to prevent in jury to any crewmember shouldsplintering occur.Fluorescent tube protection. - To prevent leakage of mercury vapor in case offluorescent tube fail ure (cr ack or break), a protective coating of Teflon was added tothe tube, and the tube ends were encapsulated to provide a seal.Noise. - Rotation of the floodlight- brightness- cont rol rheos tat f or the pr imaryfloodlights caused a high-pitched noise. The rheostat w as encapsulated in a new con-figuration, using a hard- shelled room- temperature-vulcanizing (RTV) adhesive.Electroluminescent lighting. - The panel nomenclature and instrumentation digitalreadouts w ere illuminated by EL panels. The EL lighting operated on 115-volt ac,400-hertz power. The EL lighting was relatively trouble free throughout the program.

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Other lighting. - Lighting f o r the tunnel area was provided by six incandescentfix tures, each containing two miniature 28-volt dc lamps (fig. 4). Exte rior lighting(fig. 5) consisted of a docking spotlight, eight orientation or identification lights (fouramber, two red, and two green), a rendezvous flashing beacon, and a white floodlightfor EVA'S. The docking spotlight was electr ical ly deployed on a spring-mounted doorand projected a light beam 21.3 meter s (70 feet) in diameter at a range of 61 me te rs(200 feet). The orientation lights were sma ll l amps spaced around the ser vice module(SM) f o r position identification by other vehicles. The rendezvous flashing beacon,located in t h e forward section of the SM, used a xenon tube that flashed at a rate of1 flash/sec for a duration of 20 milliseconds and was visible by telescope for 297 kil-ome ters (160 nautical miles). The beacon wa s used for long-distance identification bythe lunar module (LM) cr ew when approaching the CM. The white floodlight (EVAlight), als o located in the forward section of the SM, was s pring loaded to deploy whenthe boost protective cover was jettisoned. The floodlight was used to illuminate thehatch area and the side of the CM during EVA. The tunnel lighting and all exteriorlighting were relat ively trouble free during the ent ire program.

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Caution and Warning SubsystemThe caution and warning subsystem (C&WS) (figs. 6 and 7) monitored crit icalparamete rs of most of the spacecraft operatiunal sys tem s and alerted the crewmembersto malfunctions or out-of-tolerance conditions when they occurred in any of these sys-tems. The C&WS was composed of the CDU, system status light matrices, mast eralarm (MA) switches, and associated control switches.nent in the C&WS, was located behind panel 3. The CDU contained two redundant regu-lated *12-volt dc power supplies, high- and low- limit comparators , logic circu it ry,level detectors, lamp drive rs, and a two-level-output tone generator . When a mal-function or out- of- tolerance condition occurred, the al arm l imit s (refe rence voltages)were exceeded. These alarm-limit signals triggered voltage comparator s that acti-vated logic and lamp dri ver circui ts. These cir cui ts activated the MA, the tone gene-rator, and the appropria te sys tem sta tus light on panel 2. The MA light and the bilevel

(750 o 2000 hertz) tone were reset when the MA pushbutton switch was depressed.However, the status lights on panel 2 remained lighted as long as the malfunction o rout- of- tolerance condition existed. The status lights could be prevented fro m lightingwhen there was an out-of- tolerance condition by positioning the "normal/boost/acknowledge" switch to "acknowledge. '' When a malfunction occurred with the switchin this position, only the MA and the tone gene rator were energized, but the statuslight was lighted only while the MA was depressed. When the switch was placed in the"boost" position, the MA light adjacent to the red "abort" light on panel 1 was disabledto prevent possible confusion between the two lights. Thirty-three of the available 48mat rix status lights on panel 2 were used as sys tem inputs; some of the ligh ts had asmany as 7 separate inputs to indicate malfunctions. If there was mor e than one param-eter to a status light, the first malfunction to occur triggered the tone, the MA light,and the status light. As long as the malfunction existed, the tone and MA cir cu it s couldnot be res et for that particular channel, and any of the other para me te rs in the channelthat went out of tolerance were unable to indicate the out-of- tolerance situation throughthe C&WS. This condition, known as masking, was very undesirable. However, by thetime this condition was recognized as a problem, cor rec tion would have required a ma-jar redesign and redevelopment program on the CM C&WS. The main reason fo r notcorrecting the masking problem was that all paramete rs in question could be monitoredelsewhere during this period.

The CDU, the ma jor compo-


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I IMDC 1)

MAreset

ACK . - I

ACK acknowledgeLH left handMA master alarmMN mainNOR normalRH righ t handSM service module

To: CM systemstatus lightsI61 LH side1111 RH side

ac bus 1resetIMDC 3)Resetb

To: CM systemstatus lights12) LH sideQl RH side

T o SM systemstatus lights(91 LH side(7 ) RH side

ac bus 2reset(MDC 31,-i0

of f

0 CM

MN A(MDC 51

TO: CMfunctions(61 eventchannelsfor ACK r o d e

To: SM system To: SMfunct ions fundions-181 event 01 electr icallc hanneis mechanicalindicatorsfor ACK mode

Figure 6. - Schematic of C&WS power distribution.

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Mission T imerThe electronic miss ion timer indicated time in hours, minutes, and seconds ona seven-dig it EL panel. Maximum accumulative time was 999 hours 59 minutes 59 sec-onds. The t ime r operated on 28-volt dc and 115-volt ac, 400-hertz power, and it usedthe 10-pulse/sec signal from the centra l timing equipment (CTE) o r its own internaltuning fork as a time reference.The internal tuning fork time re ference was effective when the CTE became inop-erative. This time was indicated by a smal l lighted tuning fork symbol to the left of theseven-digit panel. Stop, start, reset, and slew controls were adjacent to each of thetwo mission time rs in the CM (one each on panels 2 and 306). The mis sion ti me r wa ssupplied to the CSM cont rac tor as Government-furnished equipment and was identicalto the one used on the LM. The init ial recorded failure on a CM w as in Febru ary 1967on CSM 101. Between Febr uary 1967 and November 1969, there were 12 fai lures, 3 ofwhich occurred during flight. An investigation revealed that the fail ure s were traceableto cracked solder joints, which were caused by internal differentia l the rma l expansionbetween the end terminal boards of th e cordwood const ruct ion and the encapsulat ing ma-

terial used to protect the inte rnal elec tronic components against shock and vibration.Unsuccessful attempts were made to open the hermetical ly seal ed units, to re solder theterminals, to reseal the units, and to reuse them. Finally, in 1969, the decision w asmade to redesign the units, using integrated ci ri ai ts and welded connections instead ofthe cordwood construction and soldering, which had been dictated by the use of d is cret ecomponents.Several problem s were encountered wi th the redesigned timer. The EL digitalpanels, reused from earlier ti me rs made by a previous vendor, were not as bright asdes ired. However, the lack of light intensity was not as great a problem as a defectin the original EL panels made by the new vendor; these panels would not withstand thevoltage (115-volt ac, 400 hertz). Thus, a second new vendor for the EL panels had to

be found. The la te r EL units wer e relatively trouble fr ee .While testing the timer , it was found that the combination of electrical parametersat several temperature values reduced the gain to a point where the new oscil la tor wouldnot restart every time it was stopped. Circuit analysis indicated that the problem wasin the integrated-circu it logic gates. Substitution of tran sist ors fo r the logic gatessolved the problem.Several procurement problems were experienced with printed circuit boards andintegrated circui ts, but these problems were solved by locating new supply sources.The insulation resistance of the input filter inductor was a problem on the earlier re-designed timer s, but a better filter inductor was found after se ve ra l months of sea rch -ing. The new mission timer experienced three fail ures, one light input filter capacitoron CSM 112 (Apollo 15) and an EL segment on each of the t imers on CSM 114 (Apollo 17).To correct the se problems, the time r ac input circuits were fused, and the capacitorrated voltage wa s increased.Delivery delays were caused by additional paperwork required because one initialpr im e cont ractor did not have dir ect ac cess to the vendor but instead had to deal direc t-ly with a second prime contractor.

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Digital Event T i m erThe DET was an electromechanicaldevice that counted up o r down in minutesand seconds to a maximum of 59 minutes59 seconds, The re were two DET's oneach CM: one on panel 1 or flight controland one on panel 306 or navigational pur-

poses. The DET would reset to z ero andbegin counting up when a lift-off o r anabort signal occurred. Timer controls tostop, start, count up and down, and sleweach digit were on the s am e panel with thetimer. Of the 22 failures that occurred, 5were electrical, and the remaining 17 werecaused by mechanical problems in thecounting-wheel mechanism. Only four ofthes e failures occurred during flight (oneeach on CSM 106 and CSM 113 and two onCSM 112). Although the electri cal prob-lems were varied (EL lighting, timer fail-ing to stop on "reset, ( ( and broken wire),they were not difficult to correct.The mechanical problems consistedof interference between the gear and thecounter wheels and contamination of thebrushes and the sliprings. These problemswere f ir st attributed to the looseness of thedimensional tolerances , which allowed theidler gear (figs. 8 and 9) to ru b against the

number wheel and dislodge paint particlesfrom it. Being nonconductive, the paintparticles would adhere to the slipring andprevent the brush from making contact,which, in turn, would prevent the countingpulse fr om being transmitt ed to the nextcounter wheel. When brass shims, insert-ed between the idler gear and the spacerson the shaft to provide more clearance, didnot cor rect the problem, a more thorough

Motor plate(magnesium)

Slipring

Motor platelmagnesiuml

Interfermc e areaShaft(stainless s t e e l )

Spacer(stainless steel)

Shims 1brass)J L S h i m s brass1Idler gear

Figure 8.- Apollo 15 DET anomaly.

bearing p i n t s 1Normal IO. 040 n. Abnormal

Figure 9.- Idler gear,investigation was made. During this investigation, it was found that the stainless-steel shaf t on which the idler gear turned was not fastened securely to the magnesiummoto r plates. This slack allowed the shaft to turn, and the smal l moment applied toth e end of the shaft by the idler gear eroded the shaft hole to an oval shape. The end-plate erosion was sufficient to allow the shaft to move and to cause the idler gear to rubthe paint off the number wheel. Because the time r was not mission crit ical and becauseonly one flight remained in which the ti me r would be used very often, the decision wasmade to visually inspect the ti mer s before flight rath er than to attempt a redesign andrefurbishment program.

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E l e c t r i c a l I d i c a t in g M e t e r sThe panel me ter s were of the D'Arsonval or moving-coil type and varied in scaletypes from single to dual and from circular to elongated. No in-flight panel-meterfai lures occur red. Most fai lures occurred during vendor acceptance checkout and werecaused by out- of-tolerance pr es su re leakage, by inadequate o r excessive play in jewel-pivot end joints, by inaccurate calibrations, or by foreign par ti cle s interfering with

coil rotation. The high leakage rate was corrected by adding a secondary seal of epoxycement overlaying the solder seals. The inadequate or exces sive play in the jewel-pivot end joints, the inaccurate calibrations, and the interior contamination problemswere corrected by readjustment, recalibration, and an internal cleaning proces s in thevendor's facility before retest and shipment.E v e n t In d i c a t o r s

The event indicator is an electromagnetic device that drives a drum o r shutter-type display. The manner of display depends on the type of se ns or driving it. In avalve position, if the valve-actuating device gives a proportional signal to the indicator,the varying position of the valve is shown by the indicator. No known flight fai lures ofthe event indicator occurred. Failures in the vendor acceptance and vehicle test pro-gra ms were primar ily caused by mishandling or by poor workmanship. These fail uresconsisted of foreign par ticles, out-of-adjustment o r out-of-socket j ewe l and pivot, andexcessive flag excursion. The excess ive flag excursion was caused by improper j ewe land pivot adjustment and was the result of poor workmanship. To correct these prob-lems, the vendor reworked and reevaluated each unit before delivery.

P o t e n t i o m e t e rThe potentiometer, a hermetically sealed unit with a carbon element and a brush,was used in the CM for volume and squelch control in the communication syst em andfo r cabin heat control in the environmental control system. The shaft was connectedto the internal element through a sea led bellows assembly. The potentiometer wasmounted behind the panel so that the shaft was parallel to the panel surface and thethumbwheel control protruded through the panel surface. Because of the side loadingon the shaft, the brush elements were overriding the stop and breaking inside the her-metically sealed unit. This problem was solved by installing a bearing support f or theouter end of the shaft with an external mechanical stop. Some prob lems with shaftbinding in the bearing surface still remained; however, these problems were solvedwith better alinement and some dry lubricant. No known flight failures occurred, andalmost all the r eported fai lures in the vendor acceptance, the panel checkout, and the

spacecraft test phases were attributable t o side loads on the shaft and overriding of theinternal stop as a result of excessive loads.

R o t a r y S w i t c he sRotary switches were used as selector switches when there were more than tworequired selections. The switches used on the CM varied in capacity from 2 to 10 poles,from 2 to 1 2 positions, and fr om 1 to 5 decks. The switches had a very successful

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To remedy the extra detent problem, the vendor lowered the ramp angle on thecontact buttons and improved tole rances by changing the tooling jigs. The spacecraft012 deliveries were the first to have these modifications.

Pushbutton SwitchesPushbutton switches were used as backup contro ls f o r the initiation of events thatwould normally occur as automatic functions and as the C&WS MA reset. No flight fail-ur es we re recorded, but several failure s occurred during vehicle testing. One of thesefailures, which forced the removal of approximately 57 switches from vehicles pro-duced after CSM 107, resulted from the vendor's use of a paraffin-type ma teri al in agrinding operation to avoid the entry of ground-off pa rt ic le s around the actuation but-tons on the contact port ions of the switch. The ma te rial hardened and prevented switchactuation. Another vehicle failure resulted from a switch miss ing one of the manufac-Mring proc ess steps, which was to have crimped the pushbutton plunger base over theinsulation board of the EL lamp lead. The problem occurred in the environmentallysealed por tion of the switch. When the external ambienkp ressu re was reduced in thealtitude chamber, the plunger, which had been held in by the strength of the EL leadwires as long as the pressures remained equal, pushed the face of the switch out s othat it was protruding from the surface of panel 1 (fig. 11).

Toggle SwitchesToggle switches, used as manual con-trol elements on the CM, were configuredin one to four poles and in two o r three po-sitions and were of a maintained, momen-tary , o r lock type, depending on the use.

The block I toggle switch was an environ-mentally sealed unit with a low failure rate.After the block I1 requirements were estab-lished for a hermetically sealed switch, itwas determined that the block I vendor didnot manufacture one and did not choose tomanufacture one. Consequently, the ini-tial block I1 toggle switch was a hermeti-cally se aled plunger- type unit with an un-sealed toggle mechanism fo r switch actua-tion. Ear ly in the block TI program, switchproblems became apparent. Fail urescaused by high contact resistance, by me-chanical lockup, and by nonfunction at higho r low pressure resulted in a change to the

r1witch case assembly7.034cm(0.407in.l I B e l l o w s Pushbutton

1.237(0 .4 a i

Normal Pushbutton plungerrolloverSerial noconditionFigure 11. - Pushbutton switch plunger

cutaway.pre sen t completely hermetically sgaled switch. This swi tch had many seri ous prob-lems (figs. 1 2 to 14), such as internal solder balls, extra parts and pieces insideswitches, contact buttons welded to a terminal post in an inverted position, defectivecontact- button welds, auxi liary contact-plate welds, momentary shorting of contactarm with spring, cracked toggle block assembly and bellows, annealing and displacement

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aStationary terminal

Silver cadmium oxideNickel-plated st

Weld projections---/

Figure 12. - Toggle-switch problem.

Common

Figure 13.- Momentary switches.

Bellows to togqle arm

Solder jointsMomentary slide blockspassage of large solderparticles from kllowslyokearea into contact area.(Maximum opening pastslide i s approximately0.076 cm (0.030 n. )

Minimum opencontact (gap is0.2% cm

'Momentary slide0 I n 1202 and 1208switches 6-66.5-96, 5-110, and5-111. panel 2.tower jettison

1 and 2, andCMlSM separation)10.093 in.1 0 Not i n 1201 switch6-44. anel 1.Earth -landing-subsystem logic1

Solder ball = 0.081 cmIO. 032 in. I diametercan cause short fromfixed contact to caseif lodged in terminals leeve

(a) Cutaway view.

Gap 0.076 cmL10.OMin. l rFirst restriction onsolder particle s ize0.2% by 0.505 cmIO. 093 by 0.199 in. I

,--Toggle block(not shown)Momentary slide

Momentary springCover plate

Mounting bushingCover -plate assemb lyoggle a r m 1Bellows assembly

(b) Detailed view.Figure 14 . - Toggle switch.

of the momentary r eturn spring, spring shorting to contact a r m during sinusoidal vibra-tion, and high contact resistance.Most of these problems were correc ted by the addition of inspection stat ions dur-ing manufacturing, by bette r workmanship, by a ltering some of the weld processes,and by adding several additional steps to the acceptance test procedure (ATP). One ofthe most valuable additions was the requirement for multiaxis X-ray exposures. De-spite the poor performance during ATP and vehicle tes t, only one flight fai lur e was

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recorded. On the Apollo 15 (CSM 112) mission, the differential-velocity thrust switchprovided a groundpath through a small strand of wire f rom the switch interna l braidand lighted the entry-monitor thrust lamp. The faul t could have been seri ous had itbeen on the engine-valve power input of the se rvi ce propulsion system solenoids.

O t h e r C om p o n e n tsThe variable trans forme r, variable transformer- rheostat, rheostat, accelerom-eter, barometric-pressure indicator, and engine annunciator each had a low fai lur erate during vehicle testing and had no flight failures.

CONCL UDING REMARKS AND RECOMMENDAT IONSThe mission requirements for the command and service module controls anddisplays subsystem were satisfied very wel l during the Apollo Program. Failures

were numerous and costly, but a very thorough quali fication and test program pre-vented any catastrophic incidents. The failures were costly because the time requiredfor component removal and replacement in the panel was long and the retest wa s ex-tensive.The following recommendations should be considered $or futur e spacecraft.1. Display panels containing control elements should be simple to remove as aunit or, whenever possible, the individual control elements should be modular plug-ins.2. When ther e is a choice between the ele ctr ica l or mechanical accomplishmentofa function, the electrical method has been shown to be superior in this subsystem.3 . When the same component is used by mor e than one prime contractor o r onmore than one vehicle, the component should be procured f ro m a single vendor usingidentical specifications, i f at all possible.4. Government-furnished equipment should be de livered di rect ly to the user fromthe Government installation or fro m the vendor rather than fro m one prime contractorto another.5. Crewmembers have on se veral occasions expressed a desire for switchesthat are lighted in some manner to indicate location and status during darkened opera-tions and sleep periods.

Lyndon B. Johnson Space CenterNational Aeronautics and Space AdministrationHouston, Texas, July 2, 1976914- 3-00-00-72

apollo experience report command and service module controls and displays subsystem

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