Apollo Experience Report Real-Time Display System

8/8/2019 Apollo Experience Report Real-Time Display System

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N A S A T E C H N I C A L N O T E NASA TN D-8316

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APOLLO EXPERIENCE REPORT -REAL-TIME DISPLAY SYSTEMCornelizls J. Sullivun dnd LaRue W. BurbunkLyndon B. Johnson Space CenterHouston, Texus 77058N A T I O N A L A E R O N A U T I C S AND S P A C E 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= SEPTEMBER 1976


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1. Report No.NASA TN 0-8316

7. Authods)Cornelius J. Sullivan and LaRue W. Burbank

9. Performing Organization Name and AddressLyndon B. Johnson Space CenterHouston, Texas 77058

2. Government Accession No.

12. Sponsoring Agency Name and AddressNational Aeronau tics and Space AdministrationWashington, D. C. 20546

17. Key Words (Suggested by Autho r(s )Real-time display devicesPlotting display devices Remote consolesComputer graph ics Preci sion photo-Interactive display design graphic pro ces sesDigital-to-television conversi onGraphic input table ts

3. Recipient's Catalog No.

18 . Distribution Statement

STAR Subject Category:12 (Astronautics, General)

5. Report DateSeptember 19766. Performing Organization Code

JSC- 049 45

19. Security Classif. (of this repo rt) 20 . Security Classif. ( o f this page)Unclassified Unclassified

8. Performing Organization Report No.S- 46 1

21. NO. of Pages 22 . Price'15 $3.50

10 . Work Unit No.9 2 1- 10-00-00- 72

11. Contract or Grant No.

13. Type of Report and Period CoveredTechn ical Note

14. Sponsoring Agency Code

15. Supplementary Notes

16. AbmsctThe real- time display system used in the Apollo Prog ram is described; the systematic organiza-tion of the system , which resu lted fro m hardware/software trade-offs and the establishment ofsystem criter ia, is emphasized. Each basic requir ement of t he real- tim e display sy stem wasmet by a separate subsystem. The computer input multiplexer subsystem , the plotting displaysubsystem, the digital display subsystem, and the digital television subsystem ar e described.Also desc ribed ar e the automated display design and the generation of precis ion photographicrefer ence slides required for the three display subsystems.

Fo r sale by the National Technical Inform ation Service, Springfield, Virginia 22161


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CONTENTS

SectionSUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .COMPUTER INPUT MULTIPLEXER SUBSYSTEM . . . . . . . . . . . . . . .

User Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Hardwar e/Sof tware T rade-Off s . . . . . . . . . . . . . . . . . . . . . . . . .System Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

PLOTTING DISPLAYS SUBSYSTEM . . . . . . . . . . . . . . . . . . . . . . .User Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Hardware/Software Trade-offs . . . . . . . . . . . . . . . . . . . . . . . .System Criter ia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DIGITAL DISPLAY SUBSYSTEM . . . . . . . . . . . . . . . . . . . . . . . .User Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .H a r dware/Sof tware Tr ade-Off s . . . . . . . . . . . . . . . . . . . . . . . .System Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DIGITAL TELEVISION SUBSYSTEM . . . . . . . . . . . . . . . . . . . . . .User Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .H a rdware/Sof tware Tra de- off s . . . . . . . . . . . . . . . . . . . . . . . .Sgstem Criter ia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DISPLAY DESIGN AND REFERENCE-DATA GENERATION . . . . . . . . . .Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Display Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Refer ence- Slide Development . . . . . . . . . . . . . . . . . . . . . . . . .

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Section Page. . . . . . . . . . . . . . . . . . . . . . . . . . . 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Non-MCC Apollo SupportProblems and SolutionsCONCLUDING REMARKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

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APO LLO EXPERIENCE REPORTRE AL -T IME D ISPLAY SYSTEM

B y C o r n e l i u s J. S u l l i v a n an d L a R u e W. B u r b a n kL 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

A rea l-time display sys tem was required in the Apollo Prog ra m to enable ground-based flight cont roll ers to analyze spacecraft performance rapidly and to take cor rec -tive action a s necessa ry. Initial controller requirements could be met readily by theus e of s eve ral available term ina l devices ; however, to provide a system that wouldmeet future requirements as well as immediate needs, sys tem engine ers augmentedknown use r require ments with a se t of hardware/software trade-o ffs and with system -design crit er ia . The flexibility and reliabi lity achieved by the us e of th is method re -sulted in an adaptable display system that had a wide sp ec trum of applica tions. Be-caus e the general nature of the r eal- time display s yste m was probably it s str ongestpoint, the emphasis in this repor t is on the system c onsider ations that made this gen-er al nature possible rath er than on specific display devices o r techniques.

I NTRODUCTI ONThe real-time display system used i n suppor t of th e Apollo Prog ra m enabledflight cont roll ers to query the real-time computer complex (RTCC) in or der to ob-se rv e and analyze spacecra ft traj ecto ries , telemetry events, and telemetry measure-ments. To yield a responsive display system, basic us er requ ireme nts were aug-mented with hardware/software trade-offs and system cri ter ia. The systematic orga-

nization of the rea l-time display syst em was probably its major attribute; therefore,the sys tem considerations a r e emphasized in this r epo rt ra th er than the specific hard-ware devices used to satisfy the functional req dr em en ts of the system..-Each basic u se r requirem ent was met by the use of a display subsystem. The

computer input multiplexer (CIM) subsystem enabled rapid user access to the real-time data base . The plotting displays subsystem enabled graphic presen tation of tra-j ecto ry information to flight con trol lers . Additionally, flight contr oll ers could monitorspacecra ft performan ce by observing telemetry events and telemetry measuremen tson the digital display subsys tem and the digital television subsystem, respect ively.Hence, the real-ti me display system consisted of one computer input subsystem andthr ee computer output subsystems.


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The exact cha rac ter ist ics of each subsy stem were influenced by hardware /software trade-offs. Because of the large computer prog rams ne cess ary to supportcomplex space-flight missions, the display hardware generally alleviated a portionof the processing burden.

In addition to us er requ irem ents and hardware/software trade-of fs, a stringentse t of system s cr it er ia affected the design of the real-t ime display system. Signif-ican t c rit eri a included expandability , configuration flexibility, critical-path redun-dancy, interchangeability, data distributability, equipment maintainability, and faultdetection. The application of these cr it er ia greatly influenced the performance char-act eri sti cs of the syst em, the selection of equipment groups, and the overall systemrespons iveness to changing requ irem ents . An examination of each subsystem in termsof us er requirements, hardware/software trade-offs, and syst em cr it er ia w i l l revealthe basic system design.

A s an aid to the reader, where necessary the original unit or unit s of mea surehave been converted to the equivalent value in the Systsme International d'Unit& (SI).The SI units ar e written fir st , and the original units are written parenthetically there-after.

COM PUTER I NPUT M ULT I PLEXER SUBSYSTEMThe CIM subsystem cons isted of console keyboards, encoder s, and a multiplexer.Switch-closure signals from the operator keyboards wer e encoded and stor ed in hold-ing regi ster s. Upon initiation by the operator, these store d mess ages were trans -mitted to the RTCC for action.

U s e r R equiremen sFlight con tro lle rs needed the capability to sel ect data for rapid display and tocontrol cer tain aspect s of the computer software. To satisfy the rapid-access require-

ment s and to reduce the number of oper ator actions n ecessary to communicate withthe computer, all input messages wer e format ted completely by the display equipment.The keyboards established and displayed the encoded message, and the oper ator merelyhad to pr es s a button to communicate with the computer.

H a r d w a r e / Softwa r e T r ade -O ff sMeeting the us er requiremen ts f o r speed and simplicity made i t relatively easyto minimize the impact of the computer input subsys tem on the RTCC. The wordlengths of the encoded mes sag es wer e chosen to be compatible with the computer words .Furt herm ore, the equipment placed the request er identification, the type of requ est,and the request in field s within each word in such a manner as to minimize the number

of logica l operations requ ired of the software. Thus, because the display req uest worcjw as reformatted completely by peri phe ral equipment, the computer input w a s orderlyand consistent; software ask s we re streamline d; and the number of extern al inte rrup ts,

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which the rea l-time computers would have had to service to respond to flight con-trollers requests,was minimized.

Fault isolation. - Resolution of both electrical and data faults between the CIM andthe RTCC was dif ficult and time consuming. Much troubleshooting w a s necessary to

System CriteriaSystem criteria are presen ted in the following paragraphs.Expandability. - The CIM w a s designed to transmit simultaneously more than1000 keyboard encoders. Only 10 percent of this number w a s provided initially; how-ever, the cos t to provide this expandability was negligible, and, as missions becamemor e complex, additional encoders were added to the multiplexer with minimum sys temo r cost impact.Configuration flexibility. - Instead of being hardwired di rec tly into encoders, eachconsole keyboard was wired into a console wiring dist ribution module and then into across-connect terminal cabinet (CTC), where the keyboard could be patched readilyinto the des ired encoder. Thus, as operations and procedures became refined, con-sole devices wer e moved about mere ly by unplugging connec tors f rom the wiring dis-tribution matri ces and reprograming the CTC wiring. Again, th is flexibility enabledreconfiguration of the s yst em to meet new requi rements with minimum sys tem o r costimpact.Critical-path redundancy. - Console devices and the as sociat ed encoders werenot made redundant. This action was deemed unnecessary and expensive. However,the multiplexer, which was the last stage of the data stream, w a s common to all inputdevices and w a s made fully redundant. The critical-path redundancy eliminated thepossibility of a single-point f ail ure within the syst em and enhanced reliabil ity.Interchangeability. - Each console module w a s designed so that consoles could berearranged or keyboards could be moved from console to console with minimum sys temperturbation.Data distributability. - The equipment was designed to opera te anywhere withinthe Mission Control Center (MCC). Flexibility of operation w a s accomplished by usingthe encoder equipment to supply power; the console devices merely provided switch-clos ure signals. Thus, the distribution criterio n was satisfied fo r computer inputdevices.Equipment maintainability. - The CIM equipment group proved to be readily main-tainable with checkout panels that were located on each equipment rack. These panelswere excellent diagnostic tools for identifying failed components.

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P LO T TIN G D I S P L A Y S S U B S Y S TE MThe computer-driven plotting displays subsys tem consis ted of two sets of large-sc re en projection plotters located in the Mission Operations Control Room (MOCR),one set of large- screen projection plotters located in the Recovery Operations ControlRoom (ROCR), and five 76-centimeter (30 inch) plo tboards located in the Fl ight Dynam-

i c s Staff Support Room.

U s e r R equi r e m e n t sThe decisionmaking flight cont rol ler s in the MOCR and the ROCR requi red large-sc re en plotting displays to analyze trajecto ry data as well as to keep the entir e groupof contro ller s informed of vehicle locations. The flight dynamics officers in the staffsupport room required extremely accurat e trajecto ry plots on which to base their go/no-go recommendations.

H a r d w a r e l s o f t w a r e T r ad e - 0 f f sThe data and control words used to drive the plotting devices were made fully

compatible with the word length of the real -time computers. Furthermore, two plot-ting and control regis ter s were provided for each plotting device. Thi s buffering en-abled the computers to update the plotte rs rapidly without being constrained by therelatively slow operation of the electromechanical devices .

S y s t e m C r i t e r i aSystem cr ite ria ar e discussed in the following paragraphs.Expandability. Although some additional decode capability existed in the demul-tiplexing equipment, the plotting display subsystem w a s not made readily expandable.Because the incorporation of an additional large-panel ( 3 by 6 met er (10 by 20 foot))plotting display would have requ ired extensive and costly facility changes, the initi alprovision of expandable electronics w a s not deemed prudent.Configuration flexibility. - Because of the crit ical nature of the par ame ter s dis-played by the plotting display equipment, a patchboard was incorporated in the electroni cscabinet. By this means, any 76-centimeter (30 inch) X-Y plotboard could be substitutedfo r any other 76-centimeter (30 inch) X-Y plotboard.Critical-path redundancy. - The computer in terface for the plotting display sub-sys tem was common to all end devices and, therefore, was made redundant. The plot-t e r s were not redundant; however, the projec tion plot te rs complemented the X-Y plot-boards to yield some backup of d isplay devices on a subsystem basis.Interchangeability. - By means of patching, plotboards we re interchangeable.

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Data distributability. - The direct-view displays were designed to be readily dis-cernible within the operational ar ea s. However, to meet the distribution cr ite ria ,television c am er as w ere focused on the plotboards and the data were available on tel-evision monitors throughout the MCC.Equipment mainta inability. - The stringent accuracy requir ements of the elec tro-

mechanical port ions of this subsystem conflicted directly with the goal of ease of main-tenance. To meet the performance cr ite ria , excessive preventative work had to beperformed periodically to combat the effec ts of component aging and dr ift .Fault isolation. - The data distributor that interf aced the plotting subsystem wi ththe RTCC was relatively simple and w a s of little aid in fault isolation. Hence, whenfailures did occur, a lengthy problem analysis procedure had to be undertaken to con-clusively identify the location of the fault. Although few fa ilu res occurre d, the lackof adequate fault isolation in the plotting displays subsystem was a problem through-out the Apollo Program.

D I G I T A L D I S P L A Y S U B S YS T EMIn general, the computer-driven digital display subsys tem displayed telemeteredevents, al ar ms , and annunciators by illuminating appropriately labeled incandescentlamps on controller consoles.

U s e r R e q u i r e m e n t sFlight cont roll ers were requir ed to know the configuration of the spacecraft con-t rols at all time s. Thus, bilevel events were telemetered to the MCC to indicate all

onboard switch positions. Thi s requir ement was met economically by providing relaylamp driv ers to reflect th e activation and deactivation of the onboard systems. Theflight control lers were also required to know immediately when spacecraft consum-ables and environmental pa rame ters were out of limits. The relay lamp driv ers wereused to indica te these out-of-limit conditions.H a r d w a r e l s o f t w a r e T r a d e - o f f s

Registers of relay lamp drivers were supplied by the display equipment to s to rethe cur rent statu s of the spacec raft. Hence, the rea l-ti me compute rs only had totransfer data to the relay lamp drivers when spacecraft telemetry status bits changedsta te. However, to indicate the out-of-limit conditions, the computer had to limit-sen se the para mete rs before transf erring the change-of-state data. The digital dis-play words we re made fully compatible wi th the computer word.

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S y s te m C r i t e r i aSystem criteria are discussed in the following parag raphs.Expandability . The computer demultiplexing equipment was r equir ed by specifi-cation to decode more than 4000 address es. Because each add ress contained 24 statusbits, approximately 100 000 lights could be addres sed. Although only 10 percent of the

relay lamp driver s was procured to meet known projected needs, the system was notconstrained. Thus, full decode capability, when needed, did not re su lt in excess ivecost.Configuration flexibility . - Each rela y lamp driv er terminated i n a CTC. Fromthe CTC, the relay lamp driver was routed to the desir ed console indicator. Thi s flex-ibility enabled inexpensive reconfiguration of the digital display subsys tem as missionprofil es or operational requir ements changed.Critical-path redundancy. - The relay lamp dri ve rs were not redundant, butthe common computer interface was redundant. Thus, a dual-channel computerdemultiplexer was configured so that channel selection was made by a select-over

patch board.Interchangeability. - Because the select-over patchboard contained all the decodedse lect lines, any regi st er could have any address. All console event modules were also

interchangeable; hence, this subsys tem offered considerable interchangeability.Data distributability. - A specification for the rel ay la mp dri ver s required thatthey be capable of illuminating an indicator anywhere in the MCC. Address es could bestrapped at the select-over patchboard to enable observa tion of the s am e event by multi-ple controllers i f necessary.Equipment maintainability. - The digital display drive r subsys tem was well de-

signed and proved to be readily maintainable with an extended mean t ime betweenfailures.Fault isolation. - A means of providing verifica tion of the da ta sen t fr om the com-puter was not provided with the equipment. During one Apollo mission, the data be-came skewed and caused the display of erroneous spacecra ft sta tus information. Theexact cause of the problem could not be resolved until after the mission; it was thencorrec ted and a means of online monitoring w a s provided.

D I G I T A L T E L E V I S I O N S U B S Y S T E MThe digital television subsys tem consis ted of computer-driven cathode-ray tubes,a vidicon camera, reference-slide files, a video switch mat rix (VSM), and televi sionmonitors. The computer drove the cathode-ray tubes with dynamic information fr omreal-time data sources and with static information fro m the reference-slide file andtransmitted the composite video image to the VSM. Finally, the image was routed tothe appropriate console monitor for analysis.

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U s e r R e q u i r e m e n t sThe computer -driven cathode-ray tube (CRT) with i t s high-data-density capabilityw a s the natural device to satisfy the requiremen t of displaying many telemet ry measure-ments in a sma ll area. However, procedural requirements indicated that many con-tro ll ers would need to analyze identical display fo rma ts simultaneously. Hence, the

number of display te rmi na ls requi red would exceed the necessary number of displaygenerators. To solve the problem, a digital-to-television (D/TV) conversion systemw a s provided to capitalize on the distribut ion chara cter ist ics of video Signals. To meetflexibility requirements, the VSM was inser ted between the display gene rat ors and theflight contro llers' monitors.Hardwa re ! So f tw a re T rade -O ff s

In addition to choosing a word format fully compatible with the computer word,two significant dec isions were made to minimize computer loading. First, the charac ter/vector genera tor s of the cathode-ray tubes were provided with full rand om-access buffermemorie s. Thus, the computers could update the displays rapidly without rega rd torefr esh requirements. Furthe rmore, either complete instruction lists o r single datawords could be used to update the displays. Second, the computer w a s required to sendonly dynamic data; legends, label s, and figures were contained on sl ides and called upby a single computer word. Thus, the real-time computer time was not used to gener-ate sta tic information.

S y s te m C r i t e r i aSystem cri te ria a r e discussed in the following paragraphs.Expandability. - Although the VSM was prewired with a 15-percent growth poten-tial, the expensive active elements (switch cards) were not procured initially. Thus,expandability was achieved economically, and expansion w a s possible as future require-ments warranted.Configuration flexibility. - Both the input and the output of the VSM were madeprogrammable. The input video codes were made programmable by the us e of jumperw i r e s and shor ting pins; the output video codes were made programmable by the use ofdiode pin boards . Thus, the video subsystem was built to have extensive rapid recon-figura tion capability. Furthermo re, by changing cab les, almost any configuration couldbe attained in a relatively short time.Critical-path redundancy. - Only the computer interface was made redundant;total sy stem backup w a s not considered to be economically feasible.Interchangeability. - The identification of any display generator buffer could bechanged by repositioning a wafer switch; thus, computer data could be routed to an al -te rnate buffer with minimum effort. However, the conver ter -sl ide file s, which con-tained reference material on film clips and were mixed with dynamic computer data tofo rm a composite dynamic/static presentation , did not have thi s flexibility. Because of

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this deviation fr om the criter ion, an engineering design change w a s required when thedisplay generators were reconfigured fo r the support of high-data-density Apollo flights.Data distributability . After the computer-derived data were converted into videoinformation, universal da ta distr ibution was achieved by means of the VSM. Any inputto the matrix could be observed by any or al l of the ope rators in any combination. Thus,the distribution of CRT gene rato rs to operator s was not constrained.Equipment maintainability. - The electromechanical reference-slide file s used inconjunction with the display gener ator s required excessive maintenance. The speedrequirement to acce ss and display any one of a thousand sli des within 4 seconds dictatedclose design tole rances , which reduced the mean tim e between fail ures. After manymissions and many attempts to improve performance, the timing specifications wererelaxed slightly to yield improved performance and reduced maintenance.Fault isolation. - Faults between the computers and the display genera tors werenumerous and required many premiss ion hour s to resolve. Inadequate interface moni-toring equipment and the lack of built-in diagnostic capability made faul t isolation d i f -ficult. The high us e ra te of th is subsystem between miss ions did not permit time for

engineering changes; consequently, thi s inte rface remained somewhat unstable through-out the Apollo Pro gram. After completion of the Apollo Prog ram, replacement equip-ment was provided that contained self-diagnostic capability as well a s ample onlinemonitoring capability. This change resulted in a much more solid system.

D I SPL AY DES IGN AN D REFERENCE-DATA GENERATIONThe flexibility and capacity of the various display subsystems necessi tated thedevelopment of a dependable syst em for collecting the display r equirements. It w a salso necessary to specify (separately but compatibly) the computer software and the

background- or reference-data requirements. The precision requirements and a needfor quick turnaround necessitated the estab lishment of preci sion a rtwork and photo-graphic facilities to produce the reference slides required by the various display sub-sys tems . The decision w a s made before the Gemini Program that this task would beassigned to MCC contractor personnel.

C o n t r o lTo accommodate the many display design changes that occurred during the prepa-ration fo r a specific mission and between miss ions, a reliabl e identification controlsys tem was established. For example, the re were approximately 600 different digital

television displays for each mission. Fr om one mission to another, 200 to 400 of thesedisplays were modified; some were modified two or three times. Each display w a sidentified by a specific code; however, two additional codes were needed to identify thedynamic and background changes that were made to the orig inal display, To give theflight controller furt her as sura nce that the changes had been implemented, these identi-fication codes were made part of the display . Together with st atus r epor ts to definethe version of the display that w a s valid for a specific mission, this identification

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system w a s established before the first Gemini mission and was used effectively through-out the Apollo Program.

D i s p l a y D e s i g nDuring the Apollo Prog ram, the design of displays progre ssed from an all-manualproces s to an automated process . Displays were designed at a computer-aided consoleby an opera tor using a specia l keyboard, a Grafacon table t, and two television monitors.Computer software de termined the prec ise locations of both the dynamic and the ref-erence data. Thi s information was recorded on two different magnetic tapes. Thedynamic-data tape was used by the mission computer program to position spacecraftdata on displays during the mission. From the reference-da ta tape, the artwork wasgenerated by an automated high-precision plotter equipped with an optical-exposurehead. This automation made possible a reduction in manpower and a fa st er turnaround.

R e f e r e n c e - S l i d e D e v e l o p m e n tReference data, which included scales, grid lines, and nominal curves, wereknown before the mission. In the case of the 76 - by 76-centimeter (30 by 30 inch) X -Yplotboards, these referen ce data were placed on the s am e piece of paper on which thedynamic data were plotted during the mission. The projection-plotting refer ence datawere metal etched on a glass slide and projected simultaneously with computer-scribeddata. The digital television reference data were on 35-millimeter film mounted onmetal slides and, by means of a vidicon camera, were mixed optically with the dynamicinformation fro m the CRT. In each of these sys tems, the refe rence data had to be lo-cated precisely to achieve perfect alinement with the dynamic data.

specifically to support the MCC display subsystems. In the PSL, special reg istr ationsyste ms were established to improve the accuracy of the slides. Cameras receivedspecia l modifications to achieve maximum precis ion. To handle the large volume ofD/TV slides (as many a s 50 000 for each mission), a contact pri nte r was designed totransfer an image from a pin-registered photographic master onto 35-millimeter filmwith an accuracy of 0.003 cent imeter (0 ,001 inch) o r better at the r ate of 800 copies/h r . Special equipment was built to check the regi stration, legibility, and coding ofthese D/TV slides.

The Pr ecis ion Slide Laboratory (PSL) was a photographic facility established

The development of proj ection-plotting slides involved metal coating glass slidesby means of a high-vacuum sys tem, mounting the gl as s on metal fra mes, apply-ing photographic-resistant emulsion by means of spinners, tran sfe rrin g the film imageby exposure to intense ultravio let light projected through the microphotograph onto thephotographic-resi stant emulsion, and metal etching controlled under a microscope.More than 2500 of these microetched sl ides were developed in support of Gemini andApollo miss ions . To reduce f l a w s caused by dust, all projection plotting work wasaccomplished in cleanrooms. It is noteworthy that not only did the data on the projec -tion plotting slides have to be highly accurate but the entire assembly had to withstandtemperat ures of 422 K (300' F) fo r a s long as 72 hour s of continuous projection. Duringprojection, these slides were enlarged to 240 times their normal size. In a proprietarypro cess that was submitted for patent approval, a specia l pigment in an emulsifiedfo rm was added selectively to s ome of the slides after the fir st image had been etched9


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on the metal. This proc ess was performed for the first tim e during the Apollo 10 mis-sion and was believed to have produced the fir st color precis ion metal-coated slides.Fo r both D/TV and projection plotting, the photographic mas ter w a s alined precisel yand punched on an optical thr ee- axis punch. The punched photographic mas te r, togetherwith the associated pin-registration fixtures, provided the key link in precisely tran s-fe rr in g images from one film medium to another.Additional photographic it em s w ere produced fo r the MCC. The se included ex-tremely small reticles for a keyboard used in requesting D/TV displays and computer-prog ram control. Also included were re ticl es of variou s siz es used in rear-projec tion

readouts located throughout the MCC.

N o n - M C C A p o l l o S u p p o r tAlthough the PSL w a s established specifically to support the MCC display syste ms,i t also produced precision products fo r oth er NASA Lyndon B. Johnson Space Center (JSC)(fo rmerly the Manned Spacecraft Cen ter (MSC)) a reas without the addition of any majo requipment. Fo r example, some of these product s included etched-metal-on-glass re ti cl es

used by the Solar Part icl e Alert Network tele scop es to meas ure the siz e of so la r fl ar es ;colo r filmst rips depicting simulated Earth/Moon prof iles used i n the Apollo commandmodule simulator; glass sextant slide s used a s navigational aids for the same simulator;and high-resolution color slides for the terminal landing system, a prototype system forland recovery of space vehicles.

Problems a n d S o l u t io n sApollo experience showed that vendors were not available to provide t he high-pre cis ion products requ ired to support the MCC displays. Also, off- the-shelf equip-

ment generally was not adequate. Comme rcia l equipment procured for this task w a susually modified extensively to achieve the requ ired precision. In many ca se s, thePSL personnel combined engineering skills with photographic techniques to design spe-cia l equipment to satisfy the unique require ment s.

The PSL, more than once, had the experience of being the only customer of asingle available vendor of a particular r aw mate rial . One situation involved the filmused fo r D/TV slides. This film was developed by a heat proc ess. Because NASA w a sthe only customer, the vendor decided to eliminate a special process that w a s beingperformed to give a stable film. Thus, the PSL had to switch to a different film and acompletely different pro ces s of developing and copying the D/TV slid es. Thi s tran si-tion required several months because a special contact pri nte r had to be designed andfabrica ted. In another situation, payment was made fo r only the metal-coated glasssli des that met a specific quality check. A s the rejection rat e increa sed, the only avail-able vendor kept increa sing the pri ce f or each accepted ite m until the cost became un-real isti c. The solution was to pe rfor m in-house vacuum deposition of metal onto glas sand mounting of the gla ss onto a metal fr am e. The in-house concept entailedGovernment-owned equipment and a facility oper ated by cont ractor personnel. Experi7ence proved that, in producing precision photographic it em s, car efu l quality checkswere required at every step of the proc ess, fro m the data input and the raw mate rial sto th e end product.

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CONCLUDING REMARKSBy augmenting user requirements with thoughtful system considerations, a usefulgeneral-purpose display syst em can be obtained as was done fo r the Apollo Prog ram.However, even well-conceived sys tems have failu res, and ample consideration should

be given to maintainability and fault isolation during the design phase to preclude someof the problems encountered with the Apollo real-time display system.

Lyndon B. Johnson Space Cen terNational Aeronautics and Space AdministrationHouston, Texas, April 23, 1976921- 0-00-00-72

NASA-Langley , 1976 S-461 11

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Apollo Experience Report Real-Time Display System

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