msfc skylab instrumentation and communication system mission evaluation

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TECHNICAL REPORT STANDARD TITLE PAGE[I _EPORT NO. |2. GOVERNMENT ACCESSION NO. 3. RECIPIENT'S CATALOG NO.TM-X-64819 I

4 TITLE AND SUBTITLE 5. REPORT DATEJUNE 1974MSFC SKYLAB INSTRUMENTATION AND COI_UNICATION f:;. PERFORMING 0RGANIZATION CODESYSTEM MISSION EVALUATION7. ,XuTM6RI_I 8. PERFORMING ORGANIZATION REPC_Rr uB. M. ADAIR9. PERFORMING ORGANIZATION NAME AND ADDRESS O. WORK UNIT NO.

GEORGEC. MARSHALLSPACE FLIGIIT CENTERMARSHALLSPACE FLIGHT CENTER 11. CONTRACTRGRANTNO.ALABAMA, 35812

13. TYPE OF REPOR'_ & Pc, RIOD COVERED12 SPONSORING AGENCY NAME AND ADDRESS TECHNICAL

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION MEMORANDUMWASHINGTON, D.C. 20546 14. SPONSORINGGENCYCODE

1.5. 3UPPLEMENTARY NO'rES

PREPARED BY ASTRIONICS LABORATORY

16. _BSTRACT

This report presents an evaluation of the in-orbit performanceof the Instrumentation and Communications Systems. Performance iscompared with functional requirements at,d the fidelity of communica-tions.

In-orbit performance includes processing engineering, scientific,experiment, and biomedical data, implementing ground-generated commands,audio and video communication, generating rendezvous ranging informa-tion and radio frequency transmission and reception.

A brief history of the system evolution based on the functionalrequirements along with a physical description of the launch config-uration is included as an aid to a clear understanding of the Systemperformance.

In conclusion, the report affirms that the Instrumentation andCommunication Systems satisfied all imposed requirements. Recommenda-tions are offered which may be beneficial to future space programs.

EDITOR'S NOTEUse of trade names or names of manufacturers in this report does notconstitute an official endorsement of such products or manufacturers,either expressed or Implied, by the National Aeronautics and Space Ad-ministration or any agency of the United States Government.

17. KEY WORDS 18. DISTRIBUTION STATEMENTSkylabInstrumentation and Communication Unclassified - UnlimitedTelemetry Couiland _/_//_,/_ Ieal Time Data TelevisionRecorded Data Crew Intercomm Bllly M. Adair

MRF F.rm 11 t l (R_ D_em_r i |1 I) For _le by NiIIonAI T_hnlcal ln_rmatlnn _ice, Sprin|fleld, VIr_nt0 221 S I


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ACKNOWLE DGI_ NT

The author wishes to acknowledge all personnel who madetechnical contributions in the formulation of this document.Information was supplied by the following government and

industry organizations:Marshall Space Flight Center/Astrionlcs LaboratoryMcDonnell Douglas Astronautics Company/Eastern DivisionMcDonnell Douglas Astronautics Company/Western DivisionMartin Marietta AerospaceBendix Corporation

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TABLE OF CONTENTS

SECTION I. SUMMARY .................. I-I

SECTION II. INTRODUCTION ............... 2-1SECTION III. DESCRIPTION AND PERFORMANCE .......... 3-I

A. Skylab Program .............. 3-1B. Description of I&C Systems ........ 3-3C. Purformance of Systems ........ 3-6D End of Mission Status ........... 3-10

SECTION IV. ATM INSTRUMENTATION AND COMMIrNICATION SYSTEM . 4-1A. ATM Data Acquisition System ........ 4-1B. ATM Digital Command System ........ 4-12

SECTION V. AM/MDA/OWS I&C SYSTEM ............. 5-1A. Data System ................ 5-1B. Command System .............. 5-15C. VHF Ranging System ............ 5-27

SECTION VI. SKYLAB SYSTEMS ................ 6-1A. Skylab/STDN Interface ........... 6-1B. Audio System .............. 6-%6C. Television System ............. 6-48

SECTION VII. ANOMALY REPORTS ................ 7-1SECTION VIII. CONCLUSIONS AND RECOMMENDATIONS ........ 8-1

A. Skylab I&C System ............. 8-1B. General Recommendations .......... 8-6

APPENDIXA Measurement Anomalies ......... A-IB ATM Tape Recorders .............. B-IC AM/STDN Telemetry Signal Strengths ...... C-ID ATM/STDN Telemetry Signal Strengths ...... D-IE Color Video Qualitative Summary ........ E-IF Portable Camera Video Level Summary ...... F-I

APPROVAL ...........................DISTRIBUTION

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LIST OF ILLUSTRATIONS

2-1 Skylab Mission Profile ................. 2-23-1 Skylab Configuration ................ 3-23-2 Skylab Instrumentation and Communication System . . . 3-44-1 ATM Data System .................... 4-34-2 ATM Tape Recorder Temperature ............. 4-94-3 ATM Con1_and System ................... 4-145-1 AM/MDA/OWS Data System ................. 5-25-2 PCM Multiplexer/Encoder ................ 5-55-3 Recorded Data Signal Flow ............... 5-95-4 Transmission and Antenna System ............ 5-125-5 AM Corm_and System .................. 5-165-6 Command Code Format .................. 5-185-7 Teleprinter System Characters and Test Message .... 5-215-8 Skylab/CSMRanging System ............... 5-296-1 Skylab STDN Configuration ............... 6-26-2 Skylab Antenna Locations .............. 6-46-3 AM-B Telemetry Link Prof le .............. 6-96-4 ATM-I Telemetry Link Profile .............. 6-106-5 ATM-2 Telemetry Link Profile .............. 6-116-6 Skylab Audio System .................. 6-176-7 CSM/MDA/AM/OWS Interface ................ 6-196-8 Audio System Configuration ............... 6-226-9 SlA Panel and Locations in OWS ............ 6-246-10 Crewman's Umbilical .................. 6-266-11 Sound Pressure Level at ATM Control and Display

SIA (Experiment M487) ......... _ . 6-316-12 Sound Pressure Level at OWS Wardroom (ExperimentM487) ......................... 6-32

6-13 Audio Flow Diagram - ALC ................ 6-336-14 Audio Anti-Feedback Adapter ............. 6-376-15 Skylab Rescue Mode Audio Configuration ......... 6-426-16 CSM Audio Center Automatic Gain Control ........ 6-436-17a Emergency Tape Recorder Voice Cable Assembly ...... 6-456-17b Emergency Tape Recorder Voice Cable Assembly ...... 6-466-18 Skylab Television Syste_ .............. 6-516-19 'IV System Vid,_o Distribution .............. 6-536-20 STDN Site Video Diagram ................ 6-566-21 Portable TV Camera 28 VDC Fault Current Path ...... 6-586-22 Pulse Amplitude Modulation Timing Measuroments ..... 6-68

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J

LIST OF ILLUSTRATIONS (Continued)

Tab._....._eII-i Skylab Mission Day Time Reference ........... 2-3

III-i I_ System Onboard Spares Usage ........... 3-11111-2 Resupply of Hardware ................. 3-12IV-I ATM Measurement Matrix ............... 4-2I_-2 ATM Command List Sur_aary ............... 4-15V-I PCM Multlplexer/Encoder Channel Capability ...... 5-6V-2 I_ Equipment Operating Hours/Cycle .......... 5-13V-3 I&C Equipment Operating Hours ............. 5-25

VI-I ATM Telemetry Link Calculatioua ............ 6-6VI-2 AM Tel_etry Link Calculatlon_ ........... 6-7VI-3 STDN Tracking Coverage ................ 6-13VI-4 Prelaunch System Characteristics ........... 6-21VI-5 Audio Syste_ Timeline ................ 6-29VI-6 Audio System Equipment History ............ 6-39VI-7 Video Sync Jitter Measurement Suam_ary ......... 6-66Vl-8 Received Signal Strength, S-Band FM Link ....... 6-70

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DEFINITION OF SYMBOLS

C CentigradeO Degreef Frequency

Greater than or equal toK Kelvin-I Less than.A_ Microm Millin Nano (I0"9)

_n_ Ohm

R Output ResistanceO,7" Time (Measured from frequency)_t Delta time

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NONSTANDARD ABBRE VIATIO_

ACN Ascension IslandAGS Attitude Control SystemAGC Automatic Gain ControlALC Automatic Light Control (Television)ALC Audl_ Load CompensatorAM Airlock ModuleAMB AmbientAMP AmplifierA0S Acquisition of SignalAPCS Attitude Propulsion Control SystemASA Amplifier Switching AssemblyASAP Auxiliary Storage and Playback AssemblyATM Apollo Telescope MountATMDC Apollo Telescope Mount Digital ComputerAVG AverageBDA BermudaBL Bileve IBLP Bilevel Pulse

C&D Control and DisplayCCU Crewman Conlnunication UmbilicalCDR CommanderCFM Cubic Feet per MinuteCHAN (OH) Channe iCKT CircuitCLNT Coolantt_[D CommandCMG Control Moment GyroCOCOA Computer Oriented Communications Operational

Ana lysisCOMM Com_un icationsCOMPT CompartmentCRDU Command Relay Driver UnitO_O Carnarvon, AustraliaCSM Command Service ModuleCTL Contro1C&_I Caution and WarningCVPR Control Valve-Prlmary B6_U Caution and Warning UnitCYI Grand Canary IslandDAS Data Acquisition SystemdB Declbe 1dBm Decibel (referenced to i milllwatt)

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NONSTANDARD ABBREVIATIONS (continued)

DC Direct CurrentDCS Digital Command SystemDDAS Digital Data Acquisition Sy.temDIG DigitalDOY Day of YearDSM Digital Select MatrixEAR EarphoneEIA Electronic Industries AssociationEMER EmergencyEMI Electromagnetic InterferenceEPS Electrical Power _ystemEREP Earth Resources Experiment PackageEVA Extravehicular Act ivltyEXP ExperimentEXT Exte rna 1

FM Frequency Mooulat ionFMS Food Management SystemFRZR FreezerFS Full ScaleFWD Forward

GDS Goldstone _ CaliforniaGMT Greenwich Mean TimeGSFC Goddard Space Flight CenterGWM Guam

HAW Hawa iiHL High Leve iHPI High Performance InsulationHSK Honeysuckle Creek, AustrailiaHTR HeaterH_ Hydrogen AlphaIB Interface BoxI&C Instrumentation and CommunicationICOM IntercommunicationIEEEU Institute of Electrical and Electronic

Engineers UnitIMU Inertial Measurement UnitIN InletINSUL InsulationINT Interne iIU Instrument UnitIVA Intravehicula r Activity

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NONSTANDg/LD ABBREVIATIONS (continued)

JSC Johnson Space Cente-kbps Kilobits per secondKSC Kennedy Space CenterLBNP Lower Body Negative PressureLCG Liquid Cooled GarmentLHCP Left Hand Circular PolarizationLL Low LevelLOS Loss of SignalLP LoopMAD Madrid, SpainMDAC-E McDonnell Douglas Astronautics Corp-EastM/C Mixing ChamberMDA Multiple Docking AdapterMIC MicrophoneMIL Merritt Island, FloridaMISC MiscellaneousMOL MolecularME Meteoroid ShieldMSFC Marshall Space Flight CenterMUX MultiplexermVDC Millivolt Direct CurrentNASA National Aeronautics and Space Administrationn ml Nautical MileNTSC National Television St&ndards CommitteeOWS Orbital WorkshopPAM Pulse Amplitude Modulation]_/B PlaybackPCM Pulse Code Modulationpps Pulses per SecondPRESS PRESSUREPRI PrimaryPROG Programmerpsia Pounds per square inch, absolutepsid pounds per square inch, differentialpsig Pounds per square inch, gagePTT Push to TalkQCM Quartz Crystal Microbalance

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RASM Remote Ana log Submult iplexerRCVR ReceiverREF Re ferenceREG GegulatorREV Revolut ionRF Radio FrequencyRHCP Right Hand Circular PolarizationRS Refrigeration SystemRTTA Ranging Tone Transfer Assembly

SAS Solar Array Shieldsec SecondSEC SECONDARYSF Sub frameSIA Speaker l_tercom AssemblySL SkylabS/N Serial NumberSPKR SpeakerSPL Sound Pressure Levelsps Samples per secondSTDN Spaceflight Tracking Data Net_orkSTOR StorageSTS btructure Transition SectionSTU Shylab Test UnitSWS Saturn WorkshopT/C Thermal CapacitorTCS Thermal Control SystemTEMP TemperatureTEX Corpus Christi, TexasTM TelemetryTEA Tape Recorder AmplifierTRS Tim_ Reference SystemT/S Tension StrapTV TelevisionTVIS Television Input SectionUHF Ultra High FrequencyUV Ultra-VioletV VoltsVABD Van Allen Belt DosimeterVAN U S Naval Ship VanguardVCS Ventilation Control SystemVHF Very High FrequencyVIT Vertical Interval TestVTR Video Tape RecorderVTS Viewflnder Tracking System

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WDRH WardroomWLC White Lig;_t ChronographWMC Waste M_nagement CompartmentEMIT TransmitXMTR TransmitterKUV Extreme Ultraviolet

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TECHNICAL MEMORANDUM X-64819

SECTION I. StH_gARY

The Skylab Instrumentation and Communication (I&C) Systemlaunch configuration was dictated by mission objectives. The progressof the system development was regulated by NASA panel meeting_, designreviews, certification reviews and flight readiness reviews. Theseven system_ that made up the I&C System were:

Apollo Telescope Mount (ATM) DataATMC,)rmuandAirlock _dule (AM) DataAM CommandSkylab (SL) AudioSL TelevisionSL Rendezvous Ranging

The intricate design and operation of the I&C System requiredthe development and use'of functional test beds and support documenta-tion to maintain system integrity during the mission. The test bedsincluded an ATM I&C breadboard at Marshall Space Flight Center (MSFC),

complete I&C System test unit at St. Louis, a system simulator atJohnson Space Center (JSC) and a computer program for radio frequency(RF) tracking data at Denver. The documentation included functionalflow diagrams, malfunction procedures, contingency analyses a._d crewcheck lists.

Capability and reliability of the system were verified by pr(-mission testing which was conducted at the component, black box, sub-system, system and combined system levels. Results from this activityrequired some hardware modifications and documentation changesas wellas identifying possible system weaknesses to be monitored during the" ission. The recognition of possible in-orbit problems produced con-tingency procedures for use as required during the mission. Duringthe mission, anomalies occurred that required additional ground test-ing using the I&C test beds and in some cases back-up crew partic-ipation to provide work-around procedures and contingency hardware tobe implemented by the flight crew.

Downlinked instrumentation data provided a near-contlnuous mon-itor of the status of the Skylab and the crews. Communication wasmaintained with the crew via downlinked audio and video and uplinkedaudio and teleprinter messages. The vehicle 3ystems were operated byground coulnands as much as possible leaving the crew free to performexperiments and other program-related duties. The data and commandsystems operated continually during the manned and unmanned phases

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of the mission while the audio,television and ranging syb_ems wererequire,' only during the manned phases of the _sslnn.

Performance of the I&C System was adequate to support the ob-jectives nf _h= Sky!a5 Mission even ...... the system suffered someanomalies. The system redundancy and utilization of onboard spares, inmost cases, minimized the effect of the anomalous hardware. The mostsignificant prGblems were the loss of a transmitter and multiplexers inthe AM Data Systet,,,squeal in the Audio System and loss of cameras anda monitor in the Television System. Evaluation of the !_ System per-for_.ancehas produced significant and valuable ep_neering knowledgethat can be applied to future space programs.

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_d=, " "_.......

SECTION II. Ih_TI_ODUCTION

The Astrionics Laboratory of the Marshall Space Flight Centerprepared th_s report, which evaluates the performance ot the instru-mentation and Communication Systems for the Skylab mission includingthe two-way voice communication, telemetry downlink of the engineeringand scientific data, television, and uplink of the commands to Skylab.

Skylab, a continuation of the nation's manned space flight pro-grams, used experience and equipment from previous space activities.It was designed to operate in low Earth orbit, sufficiently above theatmosphere to avoid interference, and low enough to accommodate a max-imum payload. _"_e Skylab was successfully launched on Hay 14, 1973,and circled the Earth every 93 minutes at approximately 234 n mi alti-tude with its orbit inclined 50 deg. from the equator. It was m_nnedby three different crews for 171 of the 271 days covered by this re-port. Its purpose was to advance the technology for accommodation ofmen and equipment in space for extended periods, record earth re-sources and solar astronomy data, and explore other modeE of spaceutilization. Man's response, man/machine relations, long-duration op_erations, and other experimental inveEtigations were incorporated in aselected balance of program obiectives.

This report is limited primarily to the Instrumentation andCommunication Systems' performance during the Skylab mission. It en-compasses an evaluation of the systems' perfor_3nce and includes in-formation that may be used as a guide for potential designers and usersof space stations. Sonle of the realities to be encountered are sum-msrized and attention is directed to the indicated references for morespecific details or other aspects of the program.

The %nstrume_tation and Communication Systems consist of: theSkylab Instrument Data systems that collect and telemeter data to theground sites from 2060 separate measurements; the Communication Systemproviding voice con_unication within Skylab _nd with the ground; theTelevision System providing video data to the ground; the CommandSystems for ground control; the Rendezvous and Ranging Systems; andother related equipment.

The Skylab mission began with the launch of Skylab on day ofyear (DOY) 134 (May 14, 1973) and was terminated after splashdown ofSL-4 cn DOY 39 (February 8, 1974) for a total period of operation of271 days. Manned operations covered 171 days of this period and in-cluded three dffferent crews of tl,ree men each. The successive timesof habitation were 28, 59, and 84 days_ The overall mission profileis shown in Figure 2-1 and a detailed time reference is shown inTable II-i. The primary time in the report is in DOY and using GMTreference.


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SECTION III. DESCRIPTION AND PERFORMANCE

A. _kylab Program --.

The Skyiab is a clust=_ of four separately manufactured modulesand, when assembled in its flight configuration, is 86 feet long andweighs 170,000 lb. Figure 3-1 identifies the individual modules andshows the flight configuration. Module names are derived from modulefunctions or features: the Instrument Uait shown is a functional partof the launch vehicle and becomes inactive once the Skylab is initiallyactivated, the habitable volume of the Skylab is within the OWS, AM,MDA and CSM.

The Skylab was launched on DOY 134 at 1730 GMT (May 14, 1973)from Launch Complex 39A at Kennedy Space Center, Florida. The launchvehicle consisted of the first two stages of a Saturn V. Telemetry in-dicated that at approximately 63 sec. into the flight, at about thetime sonic speed was reached, the OWS meteoroid shield was lost, whichin turn broke the tiedown for the OWS solar array wing 2 fairing. TheSkylab separated from the second stage at 591.1 sec. after launch. At593 sec. into the flight the ignition of the retrorockets on the secondstage severed the sol4r array wing that had been released. At approx-imately 599 sec. after launch, the Skylab entered a nearly circularorbit 234 n mi above a spherical earth's surface, inclined 50 dog. tothe equator with a velocity of 25096 ft/sec. The orbital period wasapproximately 93 minutes.

The loss of the meteoroid shield and solar array wing 2 was de-termined from evaluation of the telemetry data. A lightweight shieldwas designed, fabricated, and carried up by the first crew to providethermal protection for the workshop. When the crew arrived, they ver-ified that the meteoroid shield and solar wing 2 had been lost and thelightweight thermal shield was installed

Communication between the Skylab and the ground was establishedover the RF links and was limited to the time it was within range ofI of the 12 ground sites around the Earth. Approximately 32 percentof the time was covered. Individual site contacts varied up to aslong as ii minutes. In some cases the sites overlap and in others asmuch as 1.5 hours may elapse between ground site contacts. The sitelocations and ground coverage are shown in Section V_. The inclinationof 50 dog. from the equator was selected to allow Earth Resources andphotographic coverage of as much of the earth's populated surface aspossible. The upper limit was constrained by launch vehicle perform-ance and safety considerations. The coverage of 50 dog. included mostof the populated and food-producing portions of the earth.

Five major objectives were set for the Skylab program: to de-termine man's ability to live and work in space for extended periods;

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to determine and evaluate man's aptitudes and physiological responsesin the space environment and his post flight adaptation to the ter-restrial environment; to extend the science of solar astronomy beyondthe limits of Earth-based observations; to develop improved techniquesfor observing the Earth from space; and to expand knowledge in a varietyof other scientific and technological regimes.

The entire mission period was active and consisted essentiallyof experimentation and station operation When a crew was on board,the experimentation was greatly increased, and the functions relatedto habitation were performed, including a degree of clew leisure andrecreation. Several activities not originally planned were performedas a result of operational problems. Also the ability to plan andschedule additional experiments, tests, and demonstrations was madepossible by crew efficiency.

B. Description of I&C Systems

An overview of the Sky!ab I&C systems is shown in Figure 3-2.The I&C systems interface with the CSM, the Saturn Instrument Unit,Skylab Experiments, the Spaceflight Tracking and Data Network (STDN),and other Skylab systems. Crewmen voice communication, and engineeringand experiment data were essential mission functions and were linked tothe grcund STDN stations_

Two independent data acquisition and transmitting systems pro-cessed the engineering and experiment data for the AM/MDA/OWS and ATMmodules. These data from 2060 separate measurements were transmittedin real time when over a STDN ground site. Equipment wa provided torecord data for pl_ybac k when contact with a selected STDN station wasreestablished.

Two separate Digital Command Systems provided control of AM/MDA/OWS and ATM module functions from the ground. The ground commandscontrolled many functions, including provisions for hard copy messagesto be uplinked to the AM teleprinter and for updates to the ATM digitalcomputer.

The Audio System provided capability for the crewmen to talkwith each other from various locations in the Skylab. The intercom-munication system was dependent on the audio center in the CSM fornormal operation, and interfaced with the CSM q-band and VHF trans-mitter and receivers to provide voice communication between the crewand mission control. Skylab tape recorders recorded voice during ex-periment performance or when not in contact with a STDN ground station.The audio system in tne Skylab also provided a connection for the astro-naut biomedical data.

The Television System, using a portable color TV camera, pro-vided views of the astronauts activities during the performance of ex-periments, operational and housekeeping activities, and tours outside

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the spacecraft. The CSM S-band transmitter downlinked video data tothe STDN. An onboard Skylab video tape recorder stored video and as-sociated audio for delayed playback. The ATM experiment televisioncameras interfaced with the Skylab television equipment, and mono-chrome video from these cameras was downlinked or stored in the samemanner as the portable color television camera output. Onboard monitorsprovided the capability for crewmen to view video data.

A Rendezvous and Ranging System in the AM and CSM aided the CSMin approaching the Skylab.

i. Design Background. Early configurations established adata system for support of the ATM; and a second for AM. These systemswere baselined using existing equipment designs. These designs repre-sented equipment from the Saturn program in the case of the ATM andGemini in the case of the AM. As the program evolved, system config-uration changes occurred. These changes in general were directed to-ward expanding capacity and in_uring that the required operating lifewas achieved.

In the case of the ATM, the addition of remote analog submulti-plexers provided additional measurement capacity, and the developmentof auxiliary storage and playback assembly equipment provided for =hestorage and recovery of selected data during the periods when RF con-tact was not available.

The Gemini Data System configuration was modified by a dingthe interface box. This interface box provided additional channels(obtained by dividing down some high sampling rate channels includedin the original format) and made more capacity (subframes) availablefor recording than the single subframe that was recorded in Gemini. Amethod of selectLng between redundant programmers was incorporated toincrease system operating life. As part of the data system, multiplerecorders were installed to increase reliability of the recordingsystem and were used when not in ground station contact. Recorder mod-ifications were made t( permit recording of digital experiment data onone track and to record voice on the second track.

The Command Systems, like the data systems, used equipment de-veloped for earlier programs; specifically,Saturn IU equipment on theATM and Gemini on the AM. The systems did incorporate redundancy asis normal for tom,hand systems, and the capacity was increased by theaddition of the command relay driver units on the AM and switch se-lectors on the A'fM.

The AM Con_mand System had a teleprinter added as an cutput.This unit operated from a conventional format co,mand signal having aseparate system address. This equipment was a unique development forSkylab and was used on a daily basis to provide updated flight plans,menu changes, revised operating procedures, repair instructions andother communications. During development, a major item was the

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selection of a writing medium that would provide a usable reproductionand also meet the manned vehlcle flammability requirements.

The baseline RF systems incorporated redundant tran_mltters onboth the ATM and AM to assure availability of transmitters during thelife of the program. The ATMwas baselined with lO-watt transmitterswhile the AM was baselined with the 2-watt Gemini transmitters. Anal-yses were conducted on the transmitter links and the marginal nature ofthe AM 2-watt units resulted in a decision to switch to lO-watt trans-mitters. A_other revision in the program resulted in a single 2-watttransmitter being incorporated in the data system, redundant infrequency to one of Ehe 10-watt units, for use during boost and theearly flight period. This change was incorporated as a result of anal-yses that ehowed the partial pressure from outgassi1_g and evaporativecooling systems in the instrument unit for several hours after launchhad the potential of causing corona at the power and potential levelsused in the 10-watt units.

The ranging system was incorporated as an aid to the ascendingCSM for an efficient rendezvous with the orbiting Skylab. The equip-ment on Skylab was similar to that carried on the Lunar Module ascentstage in the Apollo program. A high gain directional antenna was de-signed and installed on Skylab to maximize the distance at which rang-ing data would be available.

The baseline audio system was an extension of the CSM audiopanels to permit headsets to be plugged in throughout the modules ofSkylab. Requirements reviews resulted in adding capability for shirt-_eeve cont_unlcation using speakers and microphones. These were con-tained in Speaker Intercom Assemblies mounted in fixed locations through-out the Skylab.

The Television S_stem was baselined in October 1968. The in-itial _ystem installed was based on real-tlme transmission only. Tel-evision images to be transmitted included general working scenesthroughout Skylab using a modified Apollo color camera and video datafrom the ATM scientific cameras. An adapter was added to permit thetelevision camera to pick up the image from the vlewflnder trackingsystem optics of the earth resources equipment. System evaluation ofpos=ible use of the television brought about the design and developmentof a remote control lens to be used in conjunction with the scientificairlock and boom system developed for experiment T027. This combina-tlon of equipment permitted the extension of a camera outside theSkylab for exterior views. Continued analysis of possible televisionscenes and available ground contact time resulted in the incorporationof a video recorder in 1971.

C. Performance of Systems

The Instrumentation and Communication Systems performed theirroles by providing voice communication during the manned phase and data

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return during the complete 271 days o_ the mission. In several cases,spare equl;aent was installed by the crew, and operational procedureswere changed to accommodate maximum cormnunication coverage and data re-turn.

During the launch of S_ylab, a portion of the meteoroid shieldwas lost, whirh re=utted in the loss of one of the solar array wingsand damage to the deployment mechanism on the other solar array wing.The telemetry data were used in the evaluation of the sequencingfunctions, events, and the determination of the associated failure.These problems, coupled with subsequent events, resulted in areas ofconcern for the I&C system. Available power was reduced due to loss ofthe solar array wing. The OWS area temperatures also rose above op-erating limits due to loss of the meteoroid shield, which was also de-signed to provide thermal protection. This required the vehicle at-titudes to be revised to reduce the temperature in the workshop, whichin turn lowered the AM Coolant System radiator temperature. I&C missionsupport, for several days during this period, consisted of providingcandidate hardware to power down to conserve energy and providing can-didate coldplate-mounted bardware to power up to keep the coolant loopsfrom freezing. This delicate thermal/power balance was maintained forapproximately I0 days until the crew arrived and subsequently deployeda parasol from one of the scientific airlocks on DOY 146; and deployedthe number i solar array wing on DOY 158. During this time some of theI&C equipment operated at off-nominal temperatures. The equipment onthe sun side was exposed to high temperatures and the equipment shadedfrom the sun was exposed to low temperatures. The ATM tape recorderswere exposed to high temperatures and reacq_d their upper operatinglimit. They cooled back to normal operating temperatures when thermalstability was achieved in Skylab with no evidence of deterioration.

The I&C systems performed their required functions during the271-day mission. The majority of the systems operated continuously for6506 hours. The anomalies discussed in this report did not basicallyaffect the return of the data. The subject equipment was replaced withonboard spares, redundant equipment was activated, or the problem was_ranslstory and did not affect the mission. The anomalies are dis-cussed in Section VII and the measu:ements exhibiting some problem dur-ing the mission are listed in Appendix A. The remaining 1919 measure-ments provided data fo_ tl_e full 6506 hours within the normal tol-erances.

The ATM Data Acquisition System performed its functions as re-quired. System redundancy was available, if needed, but because of theefficient operation of the primary ATM data acquisition system, thesecondary system was not turned on except for end-or-mission " sting.A coaxial switch developed a problem on DOY 134, which was manifested byexcessively high reflected power compared to the nominal, when trazs-mitrer 1 was used with the aft antenna. Normal operation reoccurred,however, when the coaxial switch was con_man!ed to the forward antenna.This anomaly, although restricting the use of transmitter 1 to theforward antenna throughout the remainder of the mission, did not

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compromise any mission objective nor prevent the ATM data acquisitionsystem from performing its required functions. The original procedureto use a single ATM magnetic tape recorder as a primary unit and asecond identical unit as a backup wa_ changed w_en the thermal problemsat time of launch necessitated establishing a use schedule to p_ventthe tape recorders from exceeding their thermal operating limits. Thus,with the exception of these recorders, the redundant ATM data acquisi-tion system was not activated during the Skylab mission. A 40-hourpost Skylab test that energized the redundant system was initiated andsatisfactorily complet_d. This post fllgEt test verified proper opera-tion of both ATM data acquisition systems.

The ATMConmmnd System performed it_ functions, as required,throughout the entire Skylab m_sslon even though the system was usedmuch more than intended during the first portion of the Skylab mission.No anomalies or discrepancies were attributed to the ATM Command System.Approximately 59,650 cormnands were executed during the mission.

The AM Data Acquisition System performed its functions as re-quired during the Skylab manned and unmanned missions. Some of thehardware units were operated continuously for the entire mission. How-ever, during the first manned period two AM tape recorders malfunctionedrequiring onboard spare unit replacements. The use of the spare re-corders at this point in the mission affected the requirement for twospare units to be resupplied on the second manned mission. Also, inthis time frame an AM transmitter developed a low signal output and awork-around was initiated that required real-time data transmisslonnormally handled by this unit to be switched to the 2-watt trans-mitter.

During the second manned mission period the AM Data AcquisitionSystem experienced a third tape recorder malfunction. The crew re-placed this unit with an onboard spare. The teleprinter develcp_J apaper feed:problem, which caused the crew to subsequently replace theunit with the backup spare unit to regain normal operation. The low-level Multiplexer B output became intermittent. However, alternateand other backup data provided adequate system performance informationfor the duration of the Skylab mission. Both primary and secondaryTime Reference Systems experienced erratic display operation duringthis time frame. However_ by resetting and updating the time ref-erence systems via ground conm_ands, the crew verified proper time dis-plays for both the primary and secondary systems. Normal operationcontinued throughout the remainder of the mission. The discrepanciesand problems encountered by t_e AM Data Acquisition System during thistime period did not compromis_ mission objectives.

The AM Data Acquisition System continued to perform its re-quired functions during the third and final manned mission. A fourthAM tape recorder exhibited excessive data drop-outs. To restorenormal operation the crew replaced it with a spare unit. A noisysecond-tier switch in low-level multiplexer P caused eight measurements,

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common to the switch, to be excessively noisy, Since the tier switchcould not be repaired or replaced during flight, the noisy measure-ments existed throughout the remainder of the mission. The missionobjectives were not jeopardized, however, since alternate measure-ments provided these data. A suspected 3 miiiivolt signal line shortto a 24 volt line in a primary sign_| ennditi_n_r u_it c_,_sed theAM low-level multiplexers to experience erratic data approximatelymidway through the mission (DOY 357). The loss of the data from theseunits was a compromise to the AM Data System but did not imposerestriction on the misszon. A quadriplexer corona problem developedon DOY 017 and DOY 020 which caused temporary loss of data from twoAM 10-watt transmitters. The 2-watt transmitter _ovided a good real-time data transmission to the ground. When the corona cleared up theproper transmitter configuration was restored and maintained throughoutthe rest of the mission. The corona condition was attributed to theventing of an AM cabin relief valve. The above-L,enticn_J problemswhich developed during the last manned mission of the Skylab programdid not negate or cor_romise the mission objectives.

The AM Comm_nd System functioned efficiently t_oughout thefirst two manned phases of the Skylab mission. During _he third man-ned mission, a problem de-eloped. A relay in Relay Module No. 3"hung up" (suspected contamination) in the "set" position, which man-ifested itself by applying a "fast forward" mode to any recorder se-lected for experiment data recoroing. After re_ateo cycling of com-mands, the relay was positioned in the "reset" position where satis-factory operation was maintained. The "set" cormmand was subsequentlydisabled so this problem could not recur. The teleprinter developed anunsatisfactory contrast in printout of messages. This occuxredafter the crew ruutinely changed the paper supply. This problem con-tinued until late in the mission when the crew cleaned the teleprinterhead.

The VHF ranging system was used during the three rendezvousperiods during the Skylab missions for a nominal 4 ho_rs of operationduring each period. In addition, the VHF ranging system was operatedfor approximately 234 hours during the early part of the m_sicn toprovide heat into the AM primary coolant loop, to compensa,.e for aprimary coolant loop problem. During all three rendezvous maneuvers,docking was accomplished with the Skylab in a solar inertial attitude.Tbis attitude necessitated some off-nominal look angles for tne VRFranging system, and some predicted periods of loss of. contact betweenthe CSM and the Skylab. The off-nominal attitude acquisitions did notdegrade the crew's capability to acquire and dock onto the Skylab, nordid the off-nominal use of the system _egrade its primery function ofproviding accurate ranging data for the thr_e rendezvous periods.

The audio system performed satisfactorily duri_ the completemission. Redundant components and work-=round procedures were imple-mented in several cases with no constraints on mission objectives.During the mission, a tape recorder amplifier and an earphone ampll-fief in Channel B of the audio load compensator malfunctioned. A

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workaround was initiated using Channel A for the affected Channel Bfunctions. An audio feedback was heard intermittently during commun-ication. With the installation of the antifeedback network, the feed-back annoyance was prevented as long as the Speaker Intercom Assembly(SIA) spe_ke_ volume controls were _ep_ at a reasonable level. Asmentioneo a_ the crew debriefings, direct communication in the 5 psiaatmosphere could be _aintained for distances between 5 and 8 feet.Beyond that distance the voice level had to be raised or the audiosystem used. The use of the umbilical/headset was relegated tospecial sitJations such as hands-free voice communication in supportof experiments or where communication was required and an SIA was notaccessible. The crew indicated the STA's were used approximately9_ percent of the time.

The Television System was used essentially as planned exceptfor imaging outside the spacecraft through the solar alrlock. Thiscapability was lost when it became necessary to deploy the thermalshield through one solar airlock and the extension mechanism failedin the other solar airlock during operation of an experiment. TheTelevision System provided video data throughout the mission and theminor equipment prob]ems that occurred were corrected by inflightspare utilization without configuration change. The crew successfullydisassembled and removed parts from _be failed video tape recorder tobring back to Earth for further analysis. The spare video tape re-corder wa_ installed and operated satisfactorily. The video selectorswitch was also repaired when the control knob loosened from the shaft.

D. End of Mission Status

After the 271 days (6506 hours) of operating time for the Sky-lao I&C systems, the third crew deactivated and secured the vehiclefor indefinite storage. After undocking, certain tests were performedto ascertain the operational status of equipmen that either had notbeen used during the mission or had failed during the mission.

The ATMData Acquisition and Com_nd systems remained con-flgured essentially as launched until the post mission tests. Thebackup equipment was energized and operated properly during thesechecks.

The configuration of the AM Data System at the end of missionwas altered by the change-out of tape recorders, the failure of OWLlow-level multiplexer B, the failure of the first 8 channels on allAM low-level multiplexers, the failure of an AM IO-watt transmitteran_ the loss of 141 measurements. The planned consumable replacementitems were used as schedrled. The configuration of the Data System atthe end of the mission would have adequately _upported continued activ-ity.

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The AM Command System at the end of the mission was alteredonly by the replacement of the teleprinter with tile o_bonrd spare. Theplanned consumable replacement items were used as scheduled. The VHFran_ing system functioned properly during the rendezvous of the threeCSMs, and was powered down for storaRe.

The Skylab Audio System remained operational with a lo_s ofsome redundant equipment. One ALC tape recorder amplifier and oneALC earphone amplifier were inoperative; however, cables were carriedaboard to bypass inoperative equipment (if more should fail) and pro-vide the required audio communication. The television system wasfunctioning properly at the end of the mission.

The spares usage and resupply of hardware tot the I&C systemsare summarized in Tables III-I and III-2.

Table III-l. I&C System _board Spares Usage

iTEM QUANTITYm .| i i

START MISSION RES UPPLIED USEDi i i m iDIGITAL DISPLAY UNIT 1 0 0FIRE SENSOR ASSEMBLY 6 0 0FIRE SENSOR CONTROL PANEL 2 0 1SPEAKER INTERCOM ASSEMBLY 2 0 2TAPE RECORDER, AM 4 2 6VTR ELECTRONICS UNIT I 0 i

" VTR TRANSPORT UNIT I C 0TELEPRINTER i 0 iTELEPRINTER PAPER CARTRIDGE I 0 ITV INPUT STATION I 0 IVIDEO SWITCH I 0 0ATM TV MONITOR 0 1 I

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SECTION IV. ATM INSTRt_ENTATION AND COMMUNICATION SYSTEM

The A_ !nstru_entat_on and Cnmm, micatinn Systems consist ofthe Data Acquisition, Digital Command, and Television Systems. Thesesystems wer_ de_iglled to perform ATM data acquisition processing stor-age and transmission, pre..ide command control of the ATM systems andexperiments, and ald in experiment operation and pointing for solardata acquisition. This section will discuss the Data Acquisition andDigital Command Systems. The Television System is discussed in_ection VI.

A. ATM Data Acquisition System

The ATM Data Acquisition System may more properly be identifiedas the ATM Data Acquisition, Processing, Storage and Transmissionsystem because it performs each of these functions. This section de-scribes the ATM Data Acquisition System in terms of functional require-merits, operational description, and historical evolution.

i. S_vstem Description

a. Functional Requirements. The following four require-ments controlled the functional design of the ATM Data AcquisitionSystem:

(I) Prov.ide real-time and delayed-tlme telemetry data.

(2) Transmit real-time experiment and housekeepingdata to designated ground .=tations.

(3) Record preselected portions of ATM data on taperecorders.

(4) Use Saturn-type hardware, where possible, in thesystem design.

b. Operational Description (Figure 4-1). The ATM dataacquisition system design provided the capability for accepting an-alog, digital, and discrete data and processing and transmitting thesedata in real time, or selectively _toring the data for delayed trans-mission to a ground station. The 896 data measurements (Table IV-l) wererransmltted at 72 kbps to the STDN in real time. Selected measure-ments were converted to a _+ kbps format and recorded on either of twoATM magnetic tape recorders for delayed time transmission, since theSkylab was not continuously in contact with the ground stations.

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Table IV-I. AIM Measurement Matrix" ' SYSTEM' 't

TRANSDUCER TYPE APCS EPS ]_._P ]I&C i TCS IbESt i TOTAL II ,, ,TI_LPERATURE 35 34 129 21 68 2 289PRESSURE I 14l 15POSITION 8 6 14EVENT 68 42 74 38 18 19 259QUANTITY i iVOLTAGE 24 115 97 53 2 291ANGIKAR VELOC ITY 23 23SPEED 4 4

! I IOTAL 162 191 307 112 I01 23 896! i I I

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The ATM Data Acquisition System processed data from theexperiments and systems in the ATM module end consisted of the com-ponents described in the following paragraphs.

(I) Signal Conditioner Rack. Each signal conditionerrack conditzons up to 40 signals from temperature, pressure, and cur-rent transducers and various other voltage sources. The output is 0to 20 millivolts on all channels. The signal conditioner rack has itsown DC-DC con_/erter and is capable of exciting transducers at 6.6volts at up to 3 milliamps.

There are nine signal conditioner racks in the ATMsystem. These units were designed for the ATM but were similar toSaturn hardware.

(2) Remote Analog Submultiplexer (RASM). Each RASMsamples up to 60 low-level (0 to 20 millivolts) input chamlels andprovides amplified PAM (0 to 5 volts) output to the time divisionmultiplexer. There are six RASMs in the ATM system, similar to theSaturn Model 103.

(3) Time Division Multiplexer. Each multiplexersamples up to 234 high-level (0 to 5 VDC) signals from the RASM, fromdirect analog data sources and experiment subcon_nutators, with sampleddata being interleaved with amplitude reference data. Resultant PAMoutput signal is routed to the PCM digital data acquisition assembly.There are four time division multiplexers in the ATM system, similarto the Saturn Model 270.

(4) Remote Digital Multiplexer. Each remote digitalmultiplexer samples digital data and accepts I00 bits of information,and temporarily stores these data in ten magnetic core registers asten bit digital words The words are transferred one at a time to aparallel storage register and held there until the PCM assembly isready to accept them. There are six Remote Digital Multiplexers inthe ATM system, similar to Saturn Model 410.

(5) PCM Digital Dat:_ Acqu[sition System (PCM/DDAS).The DDAS performs analog to digital conversion, sync generation, andfornlatting. Digital analog signals are generated, encoded into ten-bit digital form, and combined with digital inputs from the remotedigital multiplexers and digital data souzces. An output format of30 frames is produced. Each frame contains time slots for 60 ten-bitwords, for a total of 1800 words resulting in a master frame of 250milJiseconds duration. The DDAS generates a 144 kHz timing signalfrom which sync rates of 72kHz, 3.6 kHz, 1/15 pps, 1 pps, 24 pps, _nd4 pps are derived. There is a primary and a redundant digital _ iacquisition assembly in the ATM system, similar to Saturn Model 301

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(6) Amplilier Switching Assembly (kSA). The ASAprovides switching of datJ and sync signals between the primary andredundant PCM/DDAS assemblies. It also selects tape recorder outputsfrom either primary or redundant PCM/DDAS assembly for transmittermodulation. This unit was a new design for the ATM systems.

(7) Auxiliary Storage and Playback Assembly (ASAP).The ASAP accepts parallel ten-bit PCM data and sync signals from thePCM/DDAS ass6Jbly by way of the ASA, extracts 400 words/second of pre-selected PCM data and records it at 4 kbps rate on either of two mag-netic tape recorders, each capable of recording 90 minutes. Playbackof the recorded data is 18 times the record rate; tills the 90 minutesof 4 kbps recorded data are "dumped" at 72 kbps in 5 minutes. Thereare redundant (primary and secondary) ASAP units in the ATM DataAcquisition System with a single memory unit used by both ASAP units.These units were designed specifically for the ATM.

(8) Transmitter. The transmitter provides a car-rier for the 72 kbps and modulates real-time PCM data and delayed(72 kbps playback) PCM data. The two units are solid state and onetransmitter operates at a frequency of 231.9 MBz and the othtr at afrequency of 237.0 MHz. These units were designed for the ATM.

(9) Voltage Standing Wave Ratio Measuring Assembly.This assembly measures lncident and reflected P_ power at the trans-mitter outputs for telemetering to the ground. This unit was de-signed for the ATM.

(i0) Coaxial Switches and RF Multicoupler. Theseunits provide for the transmitter to be connected to either of twoantennas or allow both transmitters to be simultaneously connectedto either antenna. Two units designed specifically for the ATMwereused in the Data Acquisition System.

(ii) Antenna. The antennas had the following char-acteristics: dipole-type with linear polarization; minimum absolutegain of minus 6 dB over 75 percent of .adiation sphere; and antennapatterns complementary and nearly omnidirectional. One antenna waslocated on ATM Solar Wing 710 and the other on ATM Solar Wing 713.These units w,_re designed for the ATM.

(12) Transducers.

(a) Pressure transducers. Two types of pres-sure transducers were used for ATM housekeeping measurements; dif-ferential pressure transducers of the potentiometez type that use 5volts excitation from the master measuring power supply with rangesof 0 to 30 psig, 0 to 35 psig, 0 to 60 psig, and static error band of1 percent; and differential pressure transducers with a linear var-iable differential transformer using 28 VDC excitation with integralpower supplies. Ranges are 0 to 8 psid, 0 to 35 psid, 0 to 3 psid and0 to 0.5 psid with an error band of 0.6 percent.

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(b) Temperature sensors. Platinum resistancewire surface and probe-type _ensors are used. R = 500, output isO0 to 20 millivolts full scale for each of a variety of measuringranges. The sen_ors operate in conjunction with a bridge completionnetwork and excitation source located in the signal conditioner racks.

(13) Other Signal Sources. Events, positions,quantity, angular velocity, and speed signals are fed to the ATM I&Csubsystemby the various ATM experiments. These sensors are integralto the subsystems and experiments. Data measurements are sampled atrates of one sample per 15 seconds to 120 sps, depending on specificrequirements. There are 896 separate measurements processed by theATM Data Acquisition System relayed to either of two VHF transmittersthat downlink the data in real time whenever contact is establishedwith the STDN. Selected data are recorded by either of two onboardmagnetic tape recorders and played back by command,

ATM real or delayed time PCM data are fed to two I_Ftransmitters where the data frequency (72 kbps) modulates the RF car-riers. The two modulated carriers, each with a minimum of lO-wattsoutput power are fed to the ATM antennas through a voltage standingwave ratio measuring network coaxial switch and multicouplers. _lenetwork senses and telemeters the incident and reflected power as-sociated with each carrier, and the coaxial switches enable theswitching of either or both of the two RF carriers to either of thetwo available antennas. RF multlcouplers directly ahead of eachantenna allow the radiation of the two carriers from one antenna.

The ATM antenna system includes two half-wavelengthtelemetry dipole antennas mounted at the ends of two ATM solar wings.The dipole on wing 710 is mounted in the plane of this wing, while thedipole on wing 713 is deployed perpendicular to the wing's plane withthe result that quadrature antenna patterns are generated, which arepredominantly linear in polarization and omnidirectional.

c. Historical. The design of the ATM Data AcquisitionSystem was subjected to a series of reviews to define the flight con-figuration. The ATM Data Acquisition System flight article differedfrom the original design concept in the following w_ys.

(1) The antenna coverage was improved by thc ad-ditlon of coaxial switches and RF couplers to the ATM data subsystem.This permitted both transmitters to radiate simultaneously through theantenna that has the best pattern, thereby increasing ground coverage.

(2) The reliability of the ASAP was improved byadding a redundant DC-DC converter, a redundant Data Storage InterfaceUnit, and reprogrammer for the memory unit.

(3) Redesign of the ASA to provide redundant I pp_and 1/15 pps sync signal sources was made to provide redundant syncsignals to the experiments.

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,1

The flight article design was tested ,rod its operation val-idated prior to installation in the Skylab and again in the normalcourse of system and vehicle functional and compo_Lt_ checkouts. Simul-taneously, failure analysis, diagnostic procedures, and operationalprocedures were generated and finalized to assure that tht, ATM DataAcquisition System would satisfacLuLily pcrfor::: its roie during theSkylab mission.

2. System Performance. The ATM Data Acquisition System wasactivated 36 minutes after the launch of Skylab on DOY 134 at 1746 GMTand performed satisfactorily throughout the entire Skylab mission. Acoaxial switch malfunction restricted the use of Transmitter 1 to theforward antenna; however, no loss of data was attributed to this limit-ation. It is significant to note that throughout the missioL_ the re-dundant units of the ATM Data Acquisition System were not needed tosupport the mission; only the primary units were used. The followingparagraphs evaluate ATM Data Acquisition Sy:tem Fc_formance at thecomponent level.

a. Evaluation of Performance.

(i) Data transmission equipment. Transmitters I and2 maintained power output levels of approximately 13.6 watts and 14.4watts, respective)y, throughout the mission with no degradation.Total operating time was 6506 hours for each transmittL, r up throughthe termination of the mission.

Coaxial switch operation was investigated in relationto the possibility of causing data dropouts. It was concluded thatthe coaxial switch operation during a data dump would not cause adata loss; however, the phasing of the antenna may cause a dropout.

(2) Auxiliary Storage and Playbac _, (ASAP). Theprimary ASAP unit functioned properly for 6506 hours through the entiremission with no malfunction. Therefore, use of the secondary ASAP unitwas not required. The two tape recorders were ,sed as described below.The primary Data Storagt, Interface Unit also operated the entire time._he memory unit functioned properly with no requirement to reprogramthe memory by using the internal programmer.

The two recorders on the ATM were coaxial reel, pseudo-loop type machines; each recorded on one track to the end of tape, re-versed and recorded in the opposite direction on a second track untilreaching the other end of the tape where it again rLversed. The totalrecord time capability was 90 minutes per unit and the playback moderequired 5 minutes. The recorder operated in a pseudo-loop mode,dumping the eldest recorded data first.

A significant test was performed twice during theSkylab mission to determine the performance quality of the recordingsystem. A comparison was made of data tapes with the real time data

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as received at the ground site. The bit error rate from this test wasI in 106 or less. This bit error rate for the system was consideredexcellent since the design requirement for the tape recorder alone wasI in 105.

Following is a tabuletion of the tape recorder usagethrough the end of the mission.

TEST TIME MISSION TIME TOTAL(HOURS) .. _HOURS)j RO________S

Recorder I 219 3750.5 3969.5Recorder 2 454 2589.3 3043.37012.8

The loss of the meteoroid shield shortly after launchaltered the original plan to run the primary tape recorder continuouslyduring the mission, using the secondary tape recorder as a backup.Thermal stresses on Skylab prompted plotting recorder temperature. Itwas immediately apparent that continuous operation of a single recorderwould cause an over-temperature condition. The management plan wasthen changed to allow alternate op('ration of the primary and secondaryrecorders to maintain recorder operation within the design thermallimits at all times. This plan was in effect throughout the mission.A temperature plot for the typical 24-hour period is shown inFigure 4-2.

The following data management criteria were used dur-ing the remainder of the mission

Recording to be continuous, using two re-corders as required, to preclude data loss and exceeding recorderthermal limits.

A record cycle of 90 minutes to be used toavoid redundant data.

Dump entire 90 minutes at one site. If notpossible, redump entire recording at another site.

Minus i00 dBm to be used, if possible, asthreshold for dumps; if below minus 104 dBm, dumps will not bestarted; and if in progress, will be terminated.

Antenna switching will be minimized duringdumps.

Dumps will be planned to avoid using theVanguard site, when in port, to avoid data dropouts.

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(g) If possible, dumps will not be started beforethe site acquisitiol, is 3 degrees or better and will be completed beforethe vehicle goes bel_w t,hree degrees.

(h) These criteria were optimum and required anoccasional ,iolation to retrieve all data.

A test was conducted before Skylab was launched to de-termine how much data would be lost each time the tape recorder reverseddirection and switched heads. This test demonstrated that the data lostwas a constant function operating within predictable limits. See Appen-dix B.

(3) The PCM/DDAS model 301 primary unit operated con-tinuously throughout th6 entire mission (6506 Hours) with no problem orreason to switch to the secondary system; consequently, the secondarysystem was not operated. The DDAS processed all PCM data at a rate of72 kbps, without detectable error. Thus, up through the end of the mis-sion the data system had processed 1.68 x 1012 bits of information withall components functioning normally and well within their design criteria.The DDAS also generated all of the sync signals for the telemetry system,experiments, and the computer. The ASA, which is the distribution systemfor these s>nc signals also continued on the primary mode for the fullmission with all of the 25 line drivers still in the primary mode.

(4) Multiplexers. All six model 410 remote digitalmulLiplexers that process the 50-bit digital computer word, digitalmeasurements, and experiment data also operated satisfactorily through-out the Skylab mission, providing error-free data.

The four model 270 multiplexers that multiplex the ana-log data all operated throughout the mission with all channels operatingproperly. Each 270 multiplexer is capable of time division multiplexingeither 27 channels with high sample rates (B0, 120 sps and AI, A2_ andA 3 4 sps) or 234 channels at low sample rates (Bo, 12 sps and AI, A2,and A 3 40 sps). There may be a combination of high and low sample ratesdepending upon the internal programming; however, the units are con-figured for a total of 479 analog channels which includes six model 103_SMs and Ii experiment submultiplexers. Each of the RASMs will accept60 channels of low-level data with a 0 to 20 MVDC level into differen-tial amplifiers that have a gain of 250. The 0 to 5 VDC signal is sampl-ed by a 270 multiplexer at 4 sps. All of the 281 channels of low-leveldata submultiplexed by the six model 103 RASMs operate@ with no problem.

Each of the model 270 multiplexers and the model 103RASMs bare calibration voltages that were monitored by telemetry,Data presented for RASM No. 3 is also typical of RASM No. 4 and datapresented for RASM No. 6 is most typical of RASMs No. I, No. 2, andNo. 5. The ripple noise from the RASMs and the model 270 multiplexersis well within the specification tolerance of I00 millivoits. The

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r I

calibration voltages were recorded at KSC prior to launch and weretelemetered for constant monitoring. Following are typical data tha.indicate the calibration and reference voltages for the data systemhave been quite stable and accurate.

EQUIP- MEAS[_E- LAUNCH TELEMETRY _2LEMETRY TELEMETRYMENT MEN_ DOY 140 OY 268 DOY 040

RASM 3 M206 1.067 1.061 1.052 1.06tRASM 3 M207 3.955 3.959 3.938 3.933RASM 6 M453 1.055 I..035 1.058 1.046RASM 6 M454 4.125 4.097 4.106 4.056MUX AI M535 0.005 0.000 0.010 0.020MUX AI M536 4.975 4.974 4.973 4.984

(5) System Anoma]y. The following system anomalyoccurred and was investigated_ See Anomaly Report No. 134 for a moredetailed discussion.

On DOY 134 the ATM transmitter exhibited high re-flected power, ATM transmitter i experienced excessively high re-flected power when transmission was switched via coaxial switch to theaft antenna. As a result of this failure, transmitter I was operatedthrough the forward antenna for the duration of the mission and trans-mitter modulation _as selected as required to optimize data retrieval.

(6) System discrepancy. On DOY 199 an intermittentdeconm_utator lock was experienced by some ground stations during ASAPplaybacks0 Tape recorder playl,_ck bit error ratt was analy_e4. Thi_analysis established that _ carrier-to-noise ratio to maintain a biterror rate of 10 -5 on a worst-case AIM delayed-time downlink isless than the FM threshold of I0 dB that has been used i r judging agood station contact. Sufficient contacts occur that meet or exceedthis standard to provide enough dump opportunities.

Another discrepancy affecting the operation, butnot part of the ATM Data System, was the failure on DOY 216 of TV No. 2Bus during SL-3 activation. A short circuit apparently caused the cir-cuit to burn open. Operation continued on TV Bus No. i for theduration of the mission. An i_.v_stigation of the performance of theATM system showed that no ATM I&C components were damaged by the short.

b. In-Flight Maintenance and Repair. No in-flight re-pairs or mantenance were required or accomplished on the ATM DataAcquisition System.

3. End of Mission Configuration

a. The ATM Data Acquisition System remained configuredas initially launched on DOY 134. No modifications to any of thesystem components or spares were requireo. The ATM Data Acquisition

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System operated 271 days (6506 hours). There were no black box failuresand nu failures in the 308 sensors, 292 channels of signal conditionSng,686 high-level analog channels, 289 low-level analog channels, 228 digi-tal channels, and 391ASAP channels. There was no degradation of theprimary system components at the end of the mission. Appendix A includes

]i_t of measurements that exceeded normal operatin_ limits; the out-of-limits conditions were not attributed to the I/xC system. At the end ofthe mission 889 of the 896 measurements processed by the ATM data systemwere still providing valid data.

A series of post mission tests were conducted by OOY 040 toevaluate the operation of the redundant equipment that had no_ oeenoperated during the mission. This equipment included the secondary PCMdigital data acquisition assembly, the secondary amplifier and switchasbembly, the ._SAP memory assembly reprogrammer and the secondary datastorage and interface unit. This redundancy verification test was com-pleted successfully as all redundant hardware operated properly.

b. Coaxial Switch No. I. The switch malfunction p]aced a_operational constraint on the Flight Operations group insofar as determin-ing the antenna-transmitter combination necessary to provide the best datato the STDN. The coaxial switch was not accessible for onboard repair orreplacement.

c. Liquid Crystal Thermometer. A requirement developedfor a temperatuz_ sensing method for use on the six-pack rate gyros inlieu of the onbard portable digital thermometers. A liquid crystalthermometer was recommended and developed. The nine units were prepared_nd flown up on SL-4. These units had a range of plus 80F to 120F.The accuracy was _lus or minus i percent. These sensors were mounted bythe crew on the end of the rate gyro six-pack. The crew verified opera-tion with an onboard digital thermometer_

B. ATMDigital Command System

I. System Descrip.tiona. Functional Requirements. The D_B provided the crew with

command capability and also provided the gTDN with conmmnd capabilitythroughout th_ mission after AT}4 solar array dep]oyment. The systemconsists of re4undant antennas, antenna couplers, receivers, and con,-mand decoders. The antennas receive a frequency modulated VHF carrierfrom the STDN, and the receivers recover the composite modulationsignal. The decoder detects the commmld word and checks for validvehicle address. The decoder issues command data signals to addressonboard systems directly or through switch selector units. The DCSnominally operltes on a carrier frequency of 450 _{z with a deviationof plus or minus 50 kiiz and a bandwidth of 340 plus or m_nus 30 Khz.The DCS has the capability to conmmnd up to seven decoder addresses com-prising switch selectors and onboard computers.

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b. Operational Description (see Figure 4-3). The DigitalCommand System provides the capability for conmmuding the AIM systemsanu experiments during b)th mannL.d and ulunanned periods of the mission.The com_mnd code sumcnary is shown in Table IV-2. Cor.unand dat_ are trans-mitted by the STDN in the form of a phase-shift-keyed/frequency modulatedsignal. The comcaand may be either an ATM switch selector command or ATMdigital computer command, and is coded so that only a unique function willbe performed in the ATM. Command data can be placed in computer storageat any of the STDN stations. When command data are to be transmitted tothe ATM, the data are removed from computer storage, encoded, and trans-mitted by a 450 Milz ultra high frequency link.

The components of the DCS are configured to provide two In-dependent, parallel systems. Only one operational system is required forprocessing the command data transmitted by the STDN. During normal opera-tion the STDN addresses both systems. With proper code selection the STDNmay address either system indivldually. This provides total redundancy ofthe DOS.

A Digital Address System and an RF interrupt switch on thecontrol panel provide the crew with the capability to interrupt commandtransmissions from the ground, and take control of the switch selectorsand computer. The com_nd system is automatically returned to normlloperation after a fixed time delay following the execute com_nd givenfrom the onboard control panel.

The DOS consists of two antennas, two directional couplers.two receivers, and two decoders.

(I) The two Conmmnd Antennas are different and consistof a Model 316 single-e]omcnt fixed dipole mounted on the deployable an-tenna panel located on Wing 710, and a Model 355 deployable dipc!e antennaorthogonally mounted on Wing 712_

(2) Directional Couplers Model 318, initially designedas Saturn hardware, were used in the AI_ to couple ground equipment testinputs to the receivers and to isolate the systems from the antennas dur-ing prelaunch checkout. During flight the coumaand message is receivedby the antennas and coupled through the directional couplers to the com-mand receivers.

(3) Conm_and Receivers, l_odel MCR-503D, are modifiedModel MCR-503 receivers originally used as Saturn hardware. The commandreceivers, which are crystal-controlled, transistorized dual conversionsuperheterodyne unlts, operate continuously and slmultaneously with anRF input signal of 450 MHz. They have a 340 plus or minus 30 kllz inter-mediate frequency bandwidth, and after demodulating the signal, provide _dual phase-shift-keyed audio output to the command decoders. The receiversalso provided an output to the Memory Loading Unit, which enabled groundstations to load the ATM Digital Computer memory modules in flight.

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DIPOLEDIPOLE ANTENNAANTEN_

_ING 710 Y WING 712ICOUPLER NO. 1 ] lCOUPLER NO.__TELEMETRY DIGITAL -_L_TELEMETRYCOMMAND

CO_ND | _ COMPUTER A RECEIVERRECEIVER _ v MEMORYO. I LOAD UNIT NO. 2

1 ___ELEMETRY _ _TELEMETRYi ' 1 iO. 2NO.II--_I DISTRIBUTOR ,L---I_TELEMETRYIL ....... J

I _TO DIGITALCOMPUTER

E-__TELEMETRYI SWITCH ]._L..COMMANDrCONTROL_ _ _SELECTORS,-VOUTPUTSAND I L IDISPLAY IIINPUT I

L PANEL j

FIGURE 4-3. AI"M COMMAND SYSTEM

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!

:able IV-2. _TM Command List SummaryD;O. OFCOMMANDS

THERMAL 19ELECTRICAL POWER 93ACS 119TELEMETRY 103EVA 5TV 8S052 17S054 13S055A 23S056 9S082A 7S082B i0H-ALPHA 1 3H-ALPHA I AND 2 2H-ALPHA I/S055A 2H-ALPHA 2/S055A 2S052/S054 4S082A AND S082B 4AC S/THERMAL 4ZERO TEST 4REGISTER TEST 4

u i

TOTAL 455ATMDC MODE COMMANDS 40

NOTE: I_Ic ATMDC has a capacity of 16,384 16-bit wordsin memory. All memory locations are addressablethrough the conmland receiver/decoder, as well asthrough the command recelver/memory load unit.

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1

SECTION V. AM/FDA/OWS 16 SYSTEM

A. Data System

I. System Description. The initial data system used Geminiprogram hardware. It was expanded to its present form during the changefrom the wet to dry workshop concept. This expansion resulted in equip-ment modifications, additional hardware, relocation of components, andaccommodation of MDA, OWS, and selected ATM meas,rements by this system.ubsequent design changes during the program only added sensors. Thefinal system consisted of sensor/signal conditioners, regulated powerconverters, PCM multiplexer/reproducers, VHF transmitters, and antennas/coaxial switches.

See Figure 5-1 for a functional block diagram of the Data System.a. Function. The Data System acquired mulciplexed and en-

coded vehicle systems, and experiment and biomedical data from the ATM,AM, MDA, and OWS, and transmitted these data in both real time and de-layed time to the STDN. Some of these data were also made available fordisplay onboard the Skylab for the crewmen. A total of 1164 measure-ments (548 in the AM, 526 from the OWS, 80 from the bII)A,and ]0 from theATM) were telemetered by this system. Some of the basic guidelinesfollowed in developing this system were:

Maximum use of existing flight qualified hardware.Maximum use of co, on equipment between v,_icles.DesiBn system for compatibility with the STDN.Provide ground control over equipment selection andfunctions with crew control backup.Provide crew control over experiment and voice recording.Provide ground control over data downlink.Provide capability for inflight replacement of selectedhardware.Provide redundancy to meet mission requirements wherepractlcai.b. Operation. The Data System was assembled using exist-

ing Gemini program designs where applicable, and/or by modifying theseand other designs to accommodate AM/MDA/OWS requirements. New designswere used only where available hardware did not satisfy requirements.

The initial system consisted of 238 channels of PCM telem-etry with single tape recorder capability. Progzam evolution and mis-sion redefinitions resulted in a series of studies to determine the

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best methods to accotm:._odatc the data from other Skylab vehicles; downlink and redundancy alt,'rp,,_ttves were also considered, rt was concludedthat an expansion el the PCN multiplexcr/encodcr t, quipment in tile AM anddownlinking data by the VHF transmitters would be the most efficientmethod to satisfy the new rcquircwent_,.. An interlace box was added tothe PC,M equipment, which allowed use of an increased quantity of lowsample rate channels via added mu[[iplt, at, ts. A tot._l of 37 multiplexerscould be accormm_dated. The interface box also provided for th:'ee ad-ditional separate portions _,_ the real time data output to be availablefor recording; these allowed sufficient housekeeping and experimentdata to he available via delaw'd time. Two additional tape recorder/re-producers and an additional DC-DC converter required tor excitation wereadded. Redundancy for major black boxes was provided. The evolutionof the vehicle system design dictated some new sensors, range changeson existing sensors, an incret_.se in the nominal sensor types and ad-ditional signal conditioning to satisfy the aaded functional monitor-ing requirmnents. This bast. line system provided an increase in telem-etry channel capacity to 528 channels wit|, 342 used: multiplexers werelocated in the AM md OWS.

During the change from a wet to dry workshop concept, themajor alteration to this baseline wa,';an increase in tile quantity ofmultiplexers. The system capacity was increased to 629 channels with535 channels allocated to specific measurements.

Subsequent changes to the Data System included reallocationof multiplexers among the Skyiab modules to optimize mission data ac-quisition and operations. Nominal measurement changes resulting fromvehicle and experLment system evolution were also experienced duringthls period. The final flight s3stem provided 1297 telemetry channels.Remote multiplexers were still located ,rely in the AM and OWS. Datasignals from the MDA and selected measurements from the ATM were wiredacrosq the appropriate vehicle interface anti accommodated by the multi-plexing and cncodin b hardware in the AN.

System control was primarily ground conm_and and crew back-Up.

c. Sensors and Signal Conditioners. The devices used tomonitor lift, support, physlcal environment and systems housekeepingdata in the Skylab included temperature, pressure, and CO O partialpressure sensors, some of which were basic Gemini Program'designs, andthe gas flowmeter, rapid pressure loss and fire detectors, which wereunique to Skylab. Tile remaining units, acoustic SPL (Instrtmlent unitFM/FM system), dew point temperature, 0o partJ.al pressure, and quartzcrystal microbalance contamination sensors were essentially existingdesigns modified for AM needs. The signal conditioners fit into allthree categories.

d. Regulated Power Subsystem. Fiw" DC-[K; converters wereprovided in the AM and nine [n the OWS for the Skylab Data System.

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The .%Mused three for telemetry requirements of Gemini program design,modified for increased power output and two for display functions thatwere an existing design adapted for Skylab use. These units convertedthe AM bus voltage of 18 to 32 VDC into regulated voltages of plus orminus 24 VDC and plus 5 VDC. The nine OWS DC-DC converters were a newdesign and were used for signal conditioners and transducers. _leseunits operated over an input voltage range of plus 24 to plus 32 VDCand provided an output of plus 5 VDC.

e. PCM Multiplexer/Encoder System. The PCM System designwas constrained by the requirement to use existing Gemini hardware de-signs to the greatest extent possible. The programmers and multiplexerswere used with only minor modifications; the interface box was a newdesign using the same construction techniques as the programmer andmultiplexers. The environmental design requirements were essentiallythe same as were required on the Gemini program except for vibration re-quirements for multiplexers that were to be located in the OWS. Aspecial test was performed that subjected one low-level and one high-level multiplexer to the OWS environment with a random vibration of25.1 g rms in the most critical axis for 12 minutes.

The SWS PCM System consisted of the following major compon-ents: two redundant and switchable programmers, one interface box (re-dundant electronics), ii high-level multiplexers, and 14 low-level multi-plexers.

The PCM System design allowed interfacing with a maximum of18 high-level multiplexers and 19 low-level multiplexers.

The Airlock complement, located on coldplates on electronicsmodule number 3, external to the pressurization area of the Airlock,(shown in Figure 5-2), provided an onboard capability for 1297 channels.A summary of system capability is listed in Table V-I

The PCM programmer provided a 51.2 kbps nonreturn-to-zeroreal-tlme output for transmission to the STDN, a 51.2 kbps hardllne out-put for use during pre]aunch checkout, and a 5.12 kbps return-to-zerooutput, identified as subframe I, on the tape recorde system. Theinterface box provided three additional 5.12 kbps return-to-zero signalsto the tape recorder/reproducer subsystem that were _dentlfled as sub-frames 2 through 4.

(i) Programmer. The programmer provided the functionsof data multiplexing, analog-to-dlgital conversion, digltal-data multi-plexing, and the required timing functions for the interface box. Theprogranmler contained some input gates, but primarily consisted of thecircuitry necessary to provide 51.2 kbps nonreturn-to-zero PCM pulsetrains to the transmitter and provide 5.12 kbps return-to-zero pulsetrain signal and clock pulses for subframe I to the tape recorder/re-producer subsystem.

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HIGH-L_EL LOW-LEVEL I PCI_ REGULATEDMULTIPLIERS MULTIPLEXERS PROG_ERS POWER(6) (7) l (2) SUBSYSTEMJ i

(4 a); - i SWITCHLOGIC 1

I" i &T_NSMISSIONI SUBSYSTEM II L_ ISWITCHl --_LOGIC [---REAL TIME--J

V CONTROLCREWl _ _ BACKUP' SF-I

SWITCHLoGIC __. _ ,TAPEt RECORDER/SF-?,3, 4 REPRODUCERl SUBSYSTEM

_"Ik PCMINTERFACE/ GROUND [OX / CONTROL

CREW ]BACKUPINTERFACE J

LOW-LEVEL HIGH-LEVELMULTIPLEXERS MULTIPLEXERS(7) (_)HARDLINEVIAOWS UMBILICAL

FIGURE5-2 PCM MULTIPLEXER/ENCODER

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Table V-I. PCH ,xhtiuLplexcr/Encoder Chant_u[ CapabilitySAHPLE RATE TYPF [ QL'AN- LJI ._ I1_1._ (sps) . S[GEAL TITY..... ,r i

320 HI, 5 [B160 LL b PROG80 HL 8 [B TOTAL IlL ANAI,OG(O-5 VDC) 41880 LL 9 PReX; TOTAL I,I,ANALOG(0-20 mVDC) 46340 ttL 1 [B TOTAL B[I,EVEL (ON-OFF) 23220 IlL 5 [B TOTAL BtLEVEI PULSE [6010 [{L 6 FROG TO'UU_ SERLAI, DIGITAL 2410 tti, [8 [B [IO BL 40 PRO(; [ ONBOA RD CAPABILITY 1,29710 BL [92 IlL MUX}Ifto Bin, 16o nL _x_-t/1.25 IlL 343 IlL _fl'X J/

1.25 IlL 3 L PROG1.25 LL 112 LL MUXI/-

0.416 LL 336 ]LL HUXt___o.4t6..... s_R__u._?tu ____++___t__o___

TOTAL [297

r-- U A N T [ TY HL q U A N T I TYUSEMUX ] u_ I '_ sps .410 sps bRrXI " ~r HL BL BLPOWS 8 24 AM d [ 9 16AM 8 23 MI)A l 13 0bIDA 0 [ All 3 [ 0 16OWS 8 24 MDA I 0 0AM 8 23 OWS 32 0 16HI)A 0 l OWS 31 0 [ 6Abl 8 24 ,\hi 3 t t6 16AN 8 24 I_DA t 8 0OWS 8 24 OWS 32 24 8OW:_ 8 24 OWS 24 24 8OWS 8 24 AM 32 24 8OWS 8 24 MI)A 0 0 8AM 5 15 AM 32 24 l6MDA 3 9 OWS 32 24 16OWS 8 24 AM 30 2 [ 8Abl 8 'l '2 bIDA 0 3 8bIDA 0 2 .... ATbl '2 - 8AM 8 Z

...... b_A .......0 ....... 2,!....... .Dl,-'I'OTAI,S 343 [92 160TOTALS [[2 330 ",4_--_

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(2) Interface Box. The interlace box accepted timingsignals from the programmer and provided signals to the remotely lo-cated multiplexers. It also provided timing signals necessary for thegeneration and multiplexing of the data in subframes 2, 3, and 4. Theprogrammer provided the 51.2 kbps signal to the interface box where sub-frames 2, 3, and 4 were separated and prepared for transfer to the taperecorder/reproducer subsystem. Three internal power supplies were io-.cated in the interface box. One was used by the internal circuitry inthe interface box and the other two provided power to the multiplexers.The interface box was composed of a redundant set of electronics, eachcapable of full systems operation independent of the other

(3) High-level Multiplexer. The high-level multiplexerfunctioned as a high-level analog commutator and an ON-OFF digital datamultiplexer. The purpose of this unit was to sample 32 high-level datachannels (0 to 5 VDC), 24 bilevel signals (0 or 28 VDC), and 16 bilevelpulse signals (0 or 28 VDC).

All high-level multiplexer analog data outputs wereswitched through the interface box to the programmer. Each multiplexerwas individually wired to the interface box, where third-tier switchingwas performed before the data were sent to the programmers. Individualthird-tier switching was used to prevent a short in one multiplexer linefrom shorting all other multiplexers and to keep line capacitance at aminimum.

The high-level multiplexer u_ed a slaved timing chaindriven by signals from the interface box to support the required samplingfunctions.

(4) Low-Level Multiplexer. the low-level multiplexerwas a differential-input analog commutator that sequentially _mpled 32low-level (0 to 20 VDC) signals. The multiplexer contained a slavedtiming chain and digital logic to support the required sampling functions.Operating power and timing slave signals were received from the inter-face box.

All low-level multiplexers, _xeept E, F, and G were in-dividually switched through third-tier switches located in the inter-face box. Multiplexers E, F, and G were gat_,d by, and switched through,the selected programmer.

f. Tape Recorder/Reproducer Subsystem. Thxee tape record-ers capable of simultaneous operation provided continuous data coverageduring periods when Skylab was out of STDN contact. These recorderswere of Gemini program design modified for Skylab. Each recorder re-ceived a 5.12 kbps return-to-zero data stream comprising one of thefour recordable PCM subframes from the PCM progran_er or interface box.These data were recorded on track A, while crew voice was recorded ontrack B; record speed was 1-7/8 inch per second. Maximum record timewas three hours per recorder. In addition to the _ubframe data_, the

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recorders could also accon_nodate experiment M509 or T013 data at a bi;rate of 5.76 kbps. The recorder played back the PCM data in a nonreturn-to-zero space format into a transmitter; the voice was played back simul-taneously into another transmitter. The playback occurred at a speed of22 times the record speed, anddata and voice were played back in anorder reverse to what they were recorded. Three hours of data wereplayed back in 8 minutes 24 seconds. Upon removal of the playbae_ com-mand, the recorder switched from the playback mode to the record _ode.In the event of faulty data reception, the tape recorders could be r_-wound at the playback speed for another dump by application of a fast-forward nonrecord convnand. During this rewind no modulation was presentat the transmitter. Figure 5-3 provides a flow diagram of the recordingprocess.

Recorder management was primarily a ground control function.The crew exercised prime control over voice and experiment record func-tions. Telemetered recorder functions included tape motion and playbackmode detection. The crew was supplied with recorder usage lights at allrecorder control stations.

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msfc skylab instrumentation and communication system mission evaluation

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