Apollo Experience Report Guidance and Control Systems Lunar Module Mission Programer

8/8/2019 Apollo Experience Report Guidance and Control Systems Lunar Module Mission Programer

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N A S A T E C H N I C A L N O T E NASA TN D-794

o*w=OI

APOLLO EXPERIENCE REPORT -G U I D A N C E A N D C O N T R O L S Y S T E M S :LUNAR MODULE MISSION PROGRAMER

Jesse A. V e r n o nLyl~douB . Johnson Space CenterHouston, T e x a s 77058N 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. Report No.N ASA T N 0-7949

19. S ecurity Classif. (o f this r epo r t )U n c l a s s i f i ed

2. Government Accession No.I

20. Security Classif. (of this page) 21 . NO . of Pages 22. Price1 2 $3.25nclas s i f i ed

4 . Ti t le and Subt i t leA P O L L O E X P E R I E N C E R E P O R TGUIDANCE AND CONTROL SYSTEMS:LUNAR MODULE MISSION PROGRAMER7. Author(s )Jesse A. Vernon9. Performing Organization Name and AddressLyndon B. J o h n s o n S p ace C en t e rH o u s t o n , T ex as 77058

12. Sponsoring Agency Name and AddressN at i on a l A e r o n au t i c s an d S p ace A d m i n i st r a ti o nWashing ton , D. C. 20546

3. Recipient's Catalog hb.

5. Report DateA p r i l 13756. Performing Organizat ion Code

8. Performing Organizat ion Report No.JSC S-41410. Work Uni t No.

914 -50 -00 -00-7211. Contract or Grant No.

13. Type of Report and Period CoveredT ech n i ca l N o te

14. Sponsoring Agency Code

15. Supplementary Notes

16. AbstractA r ev i ew of t h e co n cep t, o p e r a t i o n a l r eq u i r em en t s , d e s i g n , an d d ev e l o p m en t of t h e l u n a r m o d u l em i s s io n p r o g r a m e r is p r e s en t ed , f o ll o w ed b y a r ev i ew of co m p o n en t an d s u b s y s t em p e r f o r m an ced u r i n g d e s ig n - f ea s ib i l it y , d e s i g n - v e ri f ic a t i o n , an d q u a li f ic a t io n t e s t s p e r f o r m ed i n t h e l ab o r a t o r y .T h e s y s t em w as f u r t h e r p r o v ed o n t h e u n m an ned A po llo 5 m i s s i o n .d e t ec t ed , an d s a t i s f ac t o r y s o l u ti o n s w e r e f ou nd .t h e c o r r e c t i v e a c ti o n t a k en is discus sed . Sugges t ions are g i v en f o r p r o c ed u r a l ch an g es t o b e u s edif f u t u r e g u i d an ce an d co n t r o l s y s t em s of t h i s t y p e are t o b e d ev e lo p ed .

S e v e r a l a n o m a l ie s w e r eT h es e p r o b l em s are def ined and examined , and

17. Key Words (Suggested by Author(s) 18. Dis t r ibut ion Statement'A u t o m a t i o nC h eck o u t* R e m o t e C o n t r o ls


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APOLLO EXPERIENCE REPORTGU IDANCE AND CONTROL SYSTEMS:L U N A R M O DU LE M I S S I O N P RO G R AM E R

By J es se A . V e r n o nL y n d o n B. J o h n s o n S pace C e n t e r

S U M M A R YThe lunar module m ission pro gra mer w a s designed to enable the l unar module

to meet the req uirem ents for unmanned near-E arth orbiting mis sio ns and to be adapt-abl e to re st ri ct ed unmanned lunar landing missions within the capability of the ult ra -high -frequency/very -high-frequency communication lin ks if adequate command andse rv ic e module t ran smi ssi on capability wer e provided.missi on pro gr am er would not preclude a manned mission involving two crewmembers.An onboard lunar module

The missio n pr og ra me r was used for sequencing functions in an unmanned s pac e-cr af t to prove pro per functioning of the sys tem and to ensur e spacec raft rea dines s fo rmanned flights.functional components: (1) a program reader assembly, (2 ) a digital command ass em -bly, (3) a progr am coupler assembly, and (4)a power distribution assembly.

The lunar module miss ion pr og ra me r was composed of the following

The functional components of the mission programer were subjected to design-The units successfu lly com -easibility, design-verification, and qualification tests.pleted all te st s with only minor probl ems. However, fr om the beginning of the pr og ra m,the prog ram coupler as sembl y was plagued with relay p roble ms, many of whichwere a di re ct re su lt of contamination inside the sea led relay can.plained - o contamination o r other c aus es of failu res were e ver found.Others w ere unex-

The lunar module miss ion progr ame r performed all the required functionsthroughout the Apollo 5 mission.fl ight, the progra mer was operated in the primary mode with the guidance computer incontrol; then the backup mode was activated, and the prog ra me r controlled all sequenc-ing throughout the mission.one mission. A modified mission prog ram er, the asc ent -engine armin g assembly, wasflown on the Apollo 9 and 10 missi ons. This assembly perm itted the ascen t engine tobe armed after crew depa rture and to be fi red to fuel depletion after the ascent stagewas sep ara ted from the command and se rvice module.

From lift-off until 6 minutes 10 secon ds into the

The lunar module mission programer was flown on only


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INT RODUCT IONElec tric al and ele ctro nic equipment h as been used in many areas to performfunctions previously performed by man.

automated techniques and have extended the scope to include the sequencing of functioin an unmanned sp acec raft to prove p rope r functioning of t he s yst em and to en su respacecraft readiness for manned flights. The lunar module mission pr ogr ame r (LMis one such device.are described in this rep ort.module 1 (LM-1) ) and performed all requ ired functions when it was activated 6 minu10 seconds after lift-off.

Technologists have continued to develop

The LMP concept, design, development, and flight perf orma nceThe LMP w a s flown on only one m is si on (Apollo 5/lu na

A s an aid to the read er, where necessary the original units of m eas ure havebeen converted to the equivalent value in the SystGme International d'UnitGs (SI). ThSI units are written firs t, and the original units are written parenthetically thereafte

CONCEPTThe LMP was designed to enable the LM to me et the re qui rem ent s for unmann

nea r -Earth orbiting mis sio ns and to be adaptable to res tr ic te d unmanned lunar landinmiss io ns within the capability of the ultra-high-frequency (uhf )/v ery -high -frequency(vhf) communications links i f adequate command and s er vi ce module (CSM) tr an sm ission capability we re provided. An onboard L MP would not prec lud e a manned missioinvolving two crewmembers.

OPERATIONAL REQU IREMENTSThe operational req uir em ent s of the LMP we re as follows:1. Noncontingency mi ssi on perf orm anc e without ground-command con tro l ofunmanned flights2 . Nonsimultaneous manned and LMP syst em operat ion on the s am e fli ht(manned operation pos sible bef ore LMP activati on and after LMP deactivation3 . Control of LM subsystems as req uir ed to cont rol functions in an optimum

manner to meet flight tes t objectives

o r in the pr im ar y mode (within the capacity of the LM guidance com pute r (LGC))4 . Ground-command sele ctio n of alt ern ate te st sequ ence s in the backup mode

5. Pri ori ty of ground command over onboard command6 . One LMP configuration compatible with all unmanned mi ssio n operations

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EQU l PMENT D ESC RIPTIO NThe LMP consisted of the following functional components: (1) a program reader

assembly (PRA), (2 ) a digital command assembly (DCA), (3 ) a progr am couplerassembly (PCA), and (4 ) a power distribution assembly (PDA).a contingency prog ram to be us ed i f the primary mode failed or i f special subsystemcontingency oper atio ns bec ame nec ess ary . The DCA provided an uplink capability sothat ground comm ands could be rou ted to the LGC, the PRA, o r the PCA. The PCAprovided coupling of the LGC, PRA, and cert ain DCA comman ds to cont rol the basicLM subs yste ms. The PDA provided the dc power distribut ion and curr en t protectio nfor the LM components.

The PRA contained

P r o g r a m R e ad e r A ss e m b lyThe P R A was programed to contain commands to provide open-loop backup

sequencing if a failu re was detected by the pri mar y guidance, navigation, and controlsystem (PGNCS).LM subs yst ems for LM testing after a primary-mode failure. It did not providevehicle guidance o r attitude information.(1) a power supply subassem bly, (2 ) a tape reader subassembly, and (3 ) a programcontrol subassembly.

The PRA provided only those command s nece ssa ry to oper ate theThe PRA cons iste d of th ree subassemb lies:

The power supply suba ssembly provided the i nter nal voltages requ ired f or PRAoper atio n and supplied isolation of sign al and power g roun ds within t he PRA. It alsoprot ecte d the PRA fro m damage resulting fr om abnor mal vehicle conditions.

The tape rea der subassembly was a bidirectional rea der using programed tape.The tape w a s capable of st ori ng ama xim um of 64 000 bits of informatlon.information was sen sed by a rea d head. A tape "hole" was a binary one; a tape"no hole" was a bina ry zer o. Capability to sense the beginning and end of the tapewas inco rpor ated in the PRA.

The stored

The prog ram control subassembly was used to select, control, and issue-as a function of time -the information sto red in the PRA. Exte rnal control commandswer e provided to the PRA by me an s of uplink commands through the DCA. The pr o-gr am cont rol subass embl y placed the PRA in the standby mode or the normal (eithersea rch or readout) mode.the prog ram control subassembly provided a "compare" pulse and, in the readout mode,transmitted a 1 puls e/se c clock pulse to the ground.

To inform the ground station that the PRA was sequencing,

D i g i t a l C o m m a n d A s s e m b lyThe DCA received, aecoded, and processed commands received f ro m the ground byuhf transm issio n. These commands were sent to the LGC to accomplish limited pro -

gr am con tro l, to the PRA to enable selec tion and initiation of a segment of the PRAprogram, o r to the ground rel ay mat rix of the PCA to accomplish rea l-t ime control

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of cer ta in functions of the LM sub systems.fication capability con trolled by the Manned Space Flight Network. The DCA consi ste dof a uhf receiver, two decoders (redundant), a phase -shift -keying (PSK) dem odu lator,and a power supply.

The DCA also had a self-test and ver i-

The uhf receiver was a miniaturized solid-sta te, double -conversion, sup erh et-erodyne device that re ceived and demodulated frequency -modulation/PSK sig nal sin the uhf band.and allowed parti al mess age s from the res idue of reject ed mess age s to be receivedwithout transfe rring them to assoc iated assemb lie s. The PSK demodulator conver tedthe PSK signal from the receiver into a se ri es of digital bits fo r the decoder and alsoprovided a se t of refe ren ce clock pul ses for the decod er. The power supply providedthe regulated power and sign al ground isolation r equ ire d for DCA operatio n.

The decoder decoded digital messages from the PSK demodulator

Prog ram C o u p l e r A s s e m b lyThe PCA receiv ed commands fr om the LGC, the PRA, or the DCA and coupled

the se commands to the LM subs ys te ms by mea ns of magneti c latching rel ays . Eachrel ay contained two direction al diodes and was half- cry sta l ca n si ze . The PCA con-sis ted of a decoder subassemb ly, a power supply subassembly, and a switching sub-assembly. The decoder subassembly selecte d and decoded command words fro m theLGC or the PRA. The LGC command word contained 1 2 bits (4 address bits and 8 datbits). The PRA command word contained only 8 data bits. The power supply su ba ss embly provided the reg ulate d power req uir ed fo r PCA operatio n and for is olati on of poweand signal grounds within the PCA. The switching subas sembly contained two ma tr ic eof latching relays.man ds by mea ns of the decoder subassem bly. The se re la ys were controlled on a realtime basis.failures of the programed relays and to co rre ct o r compensate for certain LM subsystem failures. The switching su basse mbly al so contained the uplink-activated interlocking relays to allow ground-control pri ori ty i f a PCA prim e relay failed. These relayswhen activated, disabled specific control circ ui ts in the LMP prime-relay matrix.

The prim e ma tri x was controll ed by the LGC or PRA output com-The real-time command relay s were used to correc t o r compensate for

Power D t r i u on A sse m blyThe PDA provided dc power d istri butio n and cu rr en t protecti on for the DCA, the

PCA, and the PRA and provided the dc power r equ ire d fo r LMP c ontro l of the acinverters.disab led the LMP. Additional re la ys perf or me d high-power switching functionsrequired for proper LM operation. These re lay s wer e controlled by relays in the PC

The PDA contained manually oper able ci rcu it bre ak er s that enabled and

DES IGNThe LMP was designed and constructed to satisfy the individual specificationrequir ement s of struc tur al and elec tri cal design and of perf orman ce.


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The calculated reliability goal for a DCA was met through the us e of redundancyin the digital deco der sectio n only. A self-checking and fai l-s afe fea tur e was includedto prevent a n invalid messa ge f rom performing a function.used wher eve r possib le in designing the DCA because of t he ir high rel iabi lity , lowpower consumption, sm al l si ze , and light weight. Dis cre te components were used inthose ar ea s in which the circ uit con stra ints precluded the use of i ntegrated circ uits .

Integrated circu its were

The PCA design goal wa s to achieve high reliability. To accomplish thi s goal,numerous broad-based design objectives- uch as minimum weight, optimum thermaldesign, high packaging den sit y, and adaptability to des ign changes -were met ear lyin the PCA design.

The minimization of weight was a pri me consideration.concepts were us ed to fulfill the ri goro us environmental and operational requi reme ntseffectively while maintaining the concept of minimum weight.

The following design

Integrated circuits we re used instead of discr ete components where practical.A single flatpack per for med the ta sk of approximately 34 discrete components withobvious weight -saving res ult s. Welded-wire cordwood ass emb lie s were use d, wher eprac tica l, ra th er than conventional sold er. This proce dure added reliability to theele ctr ica l junction and provided substantial weight savings. All pa rt s used represe ntedthe st at e -of -the -art high-reliability versions of products being manufactured at thetime.

To provide th e best poss ible ther mal path fr om heat -dissipating pa rt s to themounting flange, al l parts and components were bonded directly to the module webwith an adhe sive having high the rm al conductivity. All cordwood asse mb li es we recompletely encapsulated.which resulted in a further reduction in thermal resistanc e.

The encapsulant then paralleled the path of the part lead,

Every effort was made to design a package that incorporated high-density designconcepts. In many cas es , the elect rica l requirements and the available pa rt s limitedthe miniaturization effort (i.e. , transformers, chokes, capacitors, relays, etc. ).Be ca us e of the na tu re and functions of the PCA, the conceptual design within the

PCA and the se ve ra l interfacing electronic ass emb lie s changed.the PCA to accept these changes w a s difficult,inclusion of s pa re ter min als on each module to provide the s impl est mea ns for exe -cuting changes are examples of the adaptability to design changes.multilayer o r printed circ uit board (mother board) had been used, a complete redesig nwould have been nec ess ary to incorpo rate a change in module interwiring.

Therefore, designingThe use of flexible ha rn es s and the

If a hardwired

The PRA had an integra ted plan ar photodiode a r r a y , which was used to rea ddigital data store d on 35 -millimeter photographic film.was advanced by a simple step servosystem that req uired a minimum number ofmoving pa rt s and gea rs. The tape-transpor t system , drive sproc kets, and supplyand takeup spools were identical in concept to the components and system used inspace-flight-proven programers. The programed film was, for all practical pur -pose s, indestructible. Thi s was not tru e for magnetic-tape and magnetic-c ore sy st em sin which the data can be inadvertently erase d. The decision to us e a photoelectric

The tape (photographic film)

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performed in two separ ate phases: (1) the design-limit te st (equipment subjected tote st -sequential, singly applied environm ents at desi gn-li mit conditions), and (2) theendurance t es t (equipment subject ed to one operational cycl e and one subsequentmission cycle at nominal m iss ion conditions).

P r o g r a m R e a de r A s s e m b l yThe PRA, pa rt num ber LSC -300-72, had the following phys ical param et er s:

weight, 6.24 ki lograms (13. 75 pounds); length, 24. 64 cen ti me te rs (9. 7 inches); width,13 cen time ter s (5.12 inches); and height, 17. 8 cen time ter s (7.0 inches). The PRAwas subjected to the qualification test in accordance with the t es t plan (CertificationTest Requireme nt (CTR) LCQ-300-005). Each of the qua lif ica tion-t est pr og ra ms(design lim it and endurance) was successfu lly implemented in accordance with theapplicable specifi ed req uir eme nts and was approved with no deviation or waiverrequested or issue d. Data gene rated during the per for man ce of the qualification-test programs indicated that each PRA successfully completed all the requirementsspecified f or operation and perfo rmanc e during acceptance tes ting with no waivers ordeviations.

P o w er D i s t r i b u t i o n A s s e m b lyThe PDA, pa rt number LDW-390-28153-1, had the following phys ical par am -eters: weight, 4.08 kilo gra ms (9 pounds); length, 64.77 ce nt ime ter s (25.5 inches);width, 17.1 5 cen time ter s (6.75 inches); and height, 19.68 centi mete rs (7 . 75 inches).The PDA was subjected to the qualification tes t in accord anc e with te st planLTP-390-15 (CTR LCQ-390-015).The test ar ti cl e was initially configured with a polyurethane collar between the

The purpose of the collarircuit br ea ke r panel and the main assembly of the PDA.was to provid e vibration isolation to the MS-type cir cui t br ea ke rs . After the success-ful completion of these tests, data fro m the lunar test ar tic le 3 (LTA-3) vibrationte st indicated that significantly lower vibration lev els should have been used. Testi ngat the lower vibration l eve ls indicated tha t the vibratio n isolation provided by the poly-urethane collar was not required. In consideration of the potential fire hazard ofpolyurethane and of the reduced vibration levels, the polyurethane co llar was eli mi-nated, the circuit bre ake rs were h k d mounted, and the PDA was successfully testedin a supplemental qualification test.

P r o g r a m C o u p l e r A s s e m b lyThe PCA, par t number LSC -300 -710 - 5 , had the following physical par ame ter s:weight, 23.59 kil ogr ams (52 pounds); length, 70.49 cen tim et er s (27. 75 inches);width, 13.018 cen time ter s (5.125 inches); and height, 19.0 5 centi met ers (7.5 inches).

The PCA was subjected to the qualification test in accor dance with te st planLTP-303-20 (CTR LCQ-300-004).

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A number of relay f ail ure s occurr ed on the qualification enduran ce assem bly .Thes e were of two types: sh or ts to cas e caused by contaminants (tipoff pin) insidethe relay cas e and sho rts to ca se caused by the diode leads.

The changes incorpo rated into the high -reliabili ty -type relay to pr event thes ekinds of failures were as follows:

1. A new tipoff pin w a s used that had a head lar ge enough to prevent it fro mdropping into the relay case.2 . l b o lay ers of insulating Mylar we re put on the coil-diode as semb ly to pr e-vent possible sh or ts of diodes to the cas e.3. Different ass emb ly techniques were applied to the coil-diode unit, and more

rigid inspections were use d to elimina te any possibility of an in ter nal diode in therelay shorting to a coil.It was recommend ed that the PCA be requalified because of t he relay fa il ur esthat occurr ed during the qualification test. The requalification test ing was consisten t

with the requirem ent not to jeopardize the st atu s of the parti cula r PCA unit as a flightspare.because of two relay failures, one of which could not be explained.at the delta-qualification te st was completed with one failu re (attri buted to contami -nation). The delta -qualification te st was abbreviated to pres er ve the flight integri tyof the part icul ar PCA unit. It should be noted that th er e was never a functional fai l -u re of th is part icul ar PCA unit; that is , there was never a fail ure of a redundant relayand a primary relay that caused the los s of a function. Ther efor e, the decision wasmade that this part icul ar unit w as flight qualified.

The requalification or delta-qualification te st was abo rted on the first s t a r tThe second attempt

Dig i t a l C o m m a n d AssemblyThe DCA, pa rt number 380-0050, had the following phy sical par am et er s:

weight, 6 .2 4 kilograms (13. 75 pounds); length, 29. 85 cent imete rs (11.75 inches);width, 1 7.15 cent imet ers (6 . 75 inches); and height, 17. 78 centi met ers ( 7 . 0 inches).The CCA was subjected to the qualification test in accor danc e with te st plan LT P-4614-11 (CTR LCQ-380-005).

Each of the qualification-test pr og ra ms (design limit and endurance) was co m-pleted; however, thre e failures occurred during these tests . These failures wererelat ed in nature and wer e trace d to a workman ship problem that involved (1) an openweld connection (discov ered during vibration testing) a nd ( 2 ) a loo se cordwood (a pottedmodule) that caused break age of intercon necting leads (a lso disco vere d during vibra-tion testing). The vibration spec trum exceeded the specification level s except fo r asm al l portion in the high-frequency region. However, the te st level s a l w a y s remainedabove the actual LTA-3 vibration lev els , which wer e used to check validity of requ ire -ment s. After the two qualification models were modified, no furt her deviations we renecessary, and the tests were successful ly Completed.


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REL A B I L I T Y A N D Q U A L I T Y C ON TR OLA reliability and quality-control prog ram w a s established for the LMP in acc ord -

ance with NASA publications NPC-200-2 and NPC -200-3.prog ram included inspections and testin g to determine conformance of the syst em tocontr actua l and specification req uir eme nts before sub miss ion of the a rt ic le to NASAfor a cceptance. Identification and traceability we re controlled in accordance with theapproved quality -control progr am. Quality -control proce dur es we re al so implementedto ensure interchangeability, as required. A reliability program was also implementedin accordance with NASA rel iab ili ty publication NPC -250 -1 and the LM-co ntractor -approved reliability program plan (L PL -550 -1).

The implementation of this

M I S S I O N P E R F O R M A N C EThe LMP performed all required functions throughout the Apollo 5 missio n (the

FromIn

only mission on which a complete LMP, as previously described, was flown).lift-off until 06:lO:OO ground-elapsed time (GET), the L M was operated in the primarymode with the LGC in control.this mode, the LMP controlled all sequencing. Sequences 111 and V were used.Periodical ly throughout the missi on, the ground-command capability was use d; and,except for periods of abnorm al signal strength, perfo rmanc e was nominal. Abruptchanges of approximately 34 decibel s in spac ecr aft -received uhf -signal strength weredetec ted throughout the missi on. These abrupt changes in rec eived power frequentlycause d the command signal to be below the message-acceptance thresho ld. Co rr e-sponding changes did not occur in the ground-received signal strength from the vhfdata tran smit ters that share d the sa me antennas through a diplexer. Consequently,command tr ans mis sio n had to be delayed or repeated. The variations in receivedsigna l power we re consi stent with an intermitt ent condition in the DCA radiofrequencyst age, in the coaxial-cable ass emb ly connecting the diplexer and DCA, o r in the inter -nal diplexer connections.

At 06:lO:OO GET, th e backup mode was activated.

On subsequent missions (Apollo 9 and lo) , a modified LMP was used. TheApollo 9 LMP consis ted of the DCA and the ascent-engine ar min g assem bly (AEAA).The AEAA permitted the ascent engine to be armed and to be fired to fuel depletionaft er asce nt-sta ge s epara tion fr om the CSM. The Apollo 10 LMP cons isted of thedigital uplink as se mb ly , which rep laced the DCA, and an AEAA of a diffe rent config-uration. Th is AEAA pe rfo rme d the sa me function on the Apollo 10 mission that theAEAA did on the Apollo 9 mission. In addition, it contained a provision fo r switchingthe guidance fr om the PGNCS to the a bor t guidance sy ste m after the asce nt engine wassta rte d fo r the burn-to-depletion maneuver.

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CONCLUD IN G R E M A R K SData fro m the design-verification test, the qualification tes t, and the subsequentvehicle tests as w e l l as data from the missi on show that the lunar module missio nprog ramer fulfilled all design requirements.After qualification testing, the prog ram re ad er a ssemb ly had one anomaly thatmight warrant one minor design change if the unit we re to be redesigned. The prog ramtape had an end-of-tape word that, when sen sed , stopped ei ther the for war d or

rev ers e s earch mode.forward o r rev ers e searc h command issued in the sam e direct ion after the word wasfi rs t sensed could caus e the pro gra m tape to unwind from the tape spool. The co rr ec -tive action to minimize pro gra m imp act was to r epe at the end-of-tape word manytimes so that it was almos t impossible to unwind the tape f rom t he spool. If the unitis redesigned, a more positive end-of -tape sensor should be incorporated.

The end-of-tape word was repeated th ree time s; hence, a

The prog ram coupling asse mbly w a s plagued with rel ay pro blems f rom thebeginning of the prog ram. Many of the prob lems we re a di re ct res ult of contaminationinside the seale d relay can; others were unexplained problems in that no contaminationor other causes of f ailur es wer e eve r found.

Each rel ay contained two directional diodes and was hal f-cr ystal can size .Therefore, the relay complexity w a s greatly increased.redesigning the re lay s are that (1) the switching matrix should be a solid-state deviceand (2) the directional diodes should rem ain outside the relay can if the rela y is to beused in the switching matrix.

Two recommendation s for

Lyndon B. Johnson Space Cent erNational Aeronautics and Space Administration

Houston, Texa s, Se ptember 9, 1974914-50-00-00-72

NASA-Langley , 1975 S-414


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interest in commercial and other- non-aerospaceapplications. Publications include Tech Briefs,Technology Utilization Reports andTechnology Surveys.

Details on the availability of these publications may be obtained from:SCIENTIFIC AND TECHNICAL INFORMATION OFFICE

N A T I O N A L A E R O N A U T I C S A N D S P A C E A D M I N I S T R A T I O NWashington, D.C. 20546

Documents

Apollo Experience Report Guidance and Control Systems Lunar Module Mission Programer