unified s-band telecommunications techniques for apollo volume i functional description

8/7/2019 Unified S-Band Telecommunications Techniques for Apollo Volume I Functional Description

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NASAUS-Evol

N A S A T E CHN I C A L N O T E

U N I F I E D S - B A N D T E LE C O M M U N IC A TIO N S T E C H N I Q U E S F O R APOLLO VOLUME 1 - FUNCTIONAL DESCRIPTION

by John H , Painter an d George HondrosM a n n e d Spacecraft CenterHouston, TexasN A T I O N A L A E R O N A U T IC S A N D S PA CE A D M I N I S T R A T I O N 0 W A S H I N G T O N , D . C. M A R C H 1965


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TECH LIBRARY KAFB, NM

UNIFIED S-BAND TELECOMMUNICATIONS TECHNIQUES FO R AP OL LOVOLUME I

FUNCTIONAL DESCRIPTIONBy John H. P a i n t e r a n d G e o r g e H o n d r o s

M a nn ed S p a c e c r a f t C e n t e rH o u s t o n , T e x a s

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION. .-

F o r s a l e by t h e O f f i c e of T e c h n i c a l S e r vi c e s, D e p a r t m e n t o f C o m m e r c e ,W a s h i n g t o n , D.C. 20230 P r i c e $3.00


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FOREWORD

The Review Copy of t h i s pub li ca ti on w a s en ti t l ed , "The ApolloUnified S-Band Telecommunications System - Volume l", andi d e n t i f i e d as F i l e Number S-58 by NASA Manned Spacecraft Center.The present publ ica t ion , under a new t i t l e , i s n e a r ly i d e n t i c a l t ot h e R e v i e w Copy with only a f e w minor changes.The au tho rs wish t o acknowledge t h e a i d and coopera t ion receiv edi n t h e p r e p a ra t i o n and review of t h i s document.W. Vic to r M. E a s t e r l i n g B. Martin L. RandolphP. GoodwinM. BrockxnanD. Holcomb

J e t PropuLsion LaboratoryPasadena, California

Motorola, Inc.Scot t sda le , Ar izona


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TABLE OF CONTENTSSect ion Page

1 . 0 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1 Obje ct ives of th e Report . . . . . . . . . . . . . . . 2

1.1.1 Volume I . . . . . . . . . . . . . . . . . . . . 2 1.1.2 Volume I1. . . . . . . . . . . . . . . . . . . . 2 1.1.3 Volume I11 . . . . . . . . . . . . . . . . . . . 3 1 .2 Histo ry of th e System . . . . . . . . . . . . . . . . . 3

2 .0 THE BASIC SYSTEM . . . . . . . . . . . . . . . . . . . . . . 6 2 . 1 System Concept . . . . . . . . . . . . . . . . . . . . 6

2 .1 .1 The Basic Spa cec raft System . . . . . . . . . . 6 2 .1 .2 The Ba sic Ground System . . . . . . . . . . . . 7 2.2 Extension of th e Basic System Required t o Support the Command Service Module and Lunar Excursion Module . . . . . . . . . . . . . . . . . . . . 8 2 . 3 The Ground Network . . . . . . . . . . . . . . . . . . 8

3 . 0 DETAILED SYSTEM DESCRIPTION . . . . . . . . . . . . . . . . 10 3.1 The Communications Signals . . . . . . . . . . . . . . 10

3.1.1 Up-link (Ground t o Sp ace cra ft) . . . . . . . . . 10 3.1 .2 Dmn-l ink (Spacecraf t t o Ground) . . . . . . . . 10 3.2 Si gn al Transmission Modulation Techniques . . . . . . . 12

3.2 .1 Up- l ink . . . . . . . . . . . . . . . . . . . . . 12 3.2.2 Down-link . . . . . . . . . . . . . . . . . . . 12 3.2 .3 Sig nal Design . . . . . . . . . . . . . . . . . 1 4 3 . 3 Spacecraft Subsystem Configurat ion . . . . . . . . . . 16

3.3.1 Premodulat ion Processor . . . . . . . . . . . . 16 3.3.2 Transponder . . . . . . . . . . . . . . . . . . . 19 3 .4 Ground Subsystems . . . . . . . . . . . . . . . . . . . 22

3 . 4 . 1 Genera l Conf igura t ion . . . . . . . . . . . . . 22 3.4.2 Antennas . . . . . . . . . . . . . . . . . . . 23 3 . 4 . 3 Microwave Circuitry . . . . . . . . . . . . . . 23 3 . 4 . 4 Reference Channel Receiver . . . . . . . . . . . 24 i

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Section Page3.4.5 Angle C hannel Re cei ver . . . . . . . . . . . . . 253 . 4 . 6 Transm i t t e r . . . . . . . . . . . . . . . . . . . 253 . 4 . 7 Ranging Ci rcu i t r y . . . . . . . . . . . . . . . 26 3 . 4 . 8 Demodulat ion Circui try . . . . . . . . . . . . . 28 3 . 4 . 9 Premodula t ion Circui t ry . . . . . . . . . . . . 313 . 4 . 10 Acquis i t ion and Programing Circui t ry . . . . . . 31 3.4.11 Ground System Peripheral Equipment . . . . . . . 31

4 . 0 SYSTEM OPEEATIONAL TECHNIQUES . . . . . . . . . . . . . . . 344 . 1 Ranging and Spacecraft Acquisi t ion . . . . . . . . . . 34

4 . 1 . 1 A Physical Explanat ion of the Ranging Process . 34 4 . 1 . 2 An Ex pl an at io n of Acqui s i t i on . . . . . . . . . 36 4 .2 Lunar Mission Cormnunications Requirements . . . . . . . 37

4 . 2 . 1 Pre-Launch . . . . . . . . . . . . . . . . . . . 37 4 . 2 . 2 Launch . . . . . . . . . . . . . . . . . . . . . 38 4 . 2 . 3 Ear th Orb i t . . . . . . . . . . . . . . . . . . 38 4 . 2 . 4 T r a ns l un a r I n j e c t i o n . . . . . . . . . . . . . . 38 4 . 2 . 5 Spacec ra f t Transpos it ion and LEN Checkout . . . 38 4 .2 . 6 Earth-Lunar Coast . . . . . . . . . . . . . . . . 38 4 . 2 . 7 Lunar Orbit . . . . . . . . . . . . . . . . . . 38 4 . 2 . 8 Lunar Landing . . . . . . . e . . . . . . . . . 39 4 . 2 . 9 Moon-Earth I n je c t io n and Coast . . . . . . . . . 39 4 . 2 . 10 Reentry. . . . . . . . . . . . . . . . . . . . . 39 4 . 3 System Operat ion for a Nminal Lunar Mission

4 . 3 . 1 4 . 3 . 2 4 . 3 . 3 4 . 3 . 4 4 .3 . 5 4 .3 . 6 4 . 3 . 7 4 . 3 . 8 4 . 3 . 9

Pre-launch . . . . . . . . . . . . . .Launch . . . . . . . . . . . . . . . .Ear th -Orb i t Inse r t ion . . . . . . . .Earth-Orbit . . . . . . . . . . . . .Trans-Lunar Tr a jec tory In je c t io n . . .Transpos i t ion and LEM Check-out . . .Trans lunar Orbi t . . . . . . . . . . .Lunar Orbit . . . . . . . . . . . . .Lunar Landing, Sur fac e Op era tion s and Rendezvous . . . . . . . . . . . . . . 4 .3 . 10 Ear th Tra jec t o ry In j e c t i on and Coast . 4.3.11Atmospheric Reentry . . . . . . . . .

. . . . . 39. . . . . 39. . . . . 39. . . . . 40. . . . . 40. . . . . 40. . . . . 40. . . . . 4 1. . . . . 4 1. . . . . 4 1. . . . . 42. . . . . 42

5.0 FEFERl3NCES . . . . . . . . . . . . . . . . . . . . . . . . . 43 6 . 0 TABWS . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 7.0 FIGUKES . . . . . . . . . . . . . . . . . . . . . . . . . . 51

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UNIF IXD S-BAND TELECOMMTJNICATIONS TECHNIQUES FOR APOLLOVOLUME I

FUNCTIONAL DESCRIPTION By John H. Painter and George Hondros

Manned Spacecraft Center SUMMARY

This document is a functional description of the intended configuration and operation of the Apollo Unified S-band Telecommunications and Tracking System. In particular, this description applies to the link between the command-servicemodule and the ground tracking station. The lunar excursion module-to-ground link is similar, and an equivalent description applies.

The document begins with a short resume of the system's developmental history. Then the basic spacecraft and ground system concept are simply explained. Following are detailed descriptions of the communications signals, modulation techniques, and subsystem configurations. The document concludes with explanations of system operational techniques.


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1.0 INTRODUCTION 1.1 Objectives of the Report

The Unified S-Eand Telecommunications and Tracking System under development for the Apollo lunar missions is not now well documented. Although some documentation on the individual subsystems exists, there is no complete system documentationwhich provides a reader with the basic system design, capabilities, operation, and limitations. This report is intended to provide such system documentation for the system in its current state of development and is divided into three volumes because of the system complexity.

Detailed description of other elements that may feed into the present system but are not directly developed by MSC is planned to appear in later volumes of this report or in appropriate reference materials as they are developed. 1.1.1 Volume I

Volume I provides a simplified functional description of the configurationand operation of the communication and tracking system to be used in the lunarApollo missions. The spacecraft S-band subsystems for the comnd-servicemodule (CSM) and lunar excursion module (LEM) are very similar in a systemsense. Both vehicles will, in fact, be supported by the same type of groundstation communication equipment. Therefore, the basic spacecraft description,given here, is for the CSM, with the minor differences of the LEM subsystempointed out. The basic system modulation techniques and operational conceptsare described.

At the time Volume I was prepared, the CSM spacecraft S-band subsystem was being redesigned to accommodate additional communication requirements, insure equipment reliability, and insure compatibility with the ground subsystem. The spacecraft subsystem configuration chosen to be described in this volume is one which resulted from detailed technical discussions between Planned Spacecraft Center, Jet Propulsion Laboratory, NASA Headquarters, Goddard Space Flight Center, and associated contractors. Although the authors feel that this configuration best meets the presently defined communication requirements and provides more flexibility than other presently proposed configurations, it is possible that the final spacecraft S-band equipment may differ slightly (at the module level) from the one described. It is not expected that the basic design philosophy or operation of the spacecraft S-band subsystem will depart appreciably from that described.

At the time of preparation of Volume I, the ground subsystem demodulators were functionally specified, but not designed. The authors have treated the set of demodulators which, in their judgment, best satisfy the requirements. 1.1.; volume 11

Volume I1 is a detailed mathematical analysis of the communication and tracking channels of the system. Equations In generalized parameters are derived which may be used either to design the comnication channels or to 2


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analyze existing designs. The equations are sufficiently general that changes of the type referred to in section 1.1.1may be easily treated. Basic assumptions made in the derivations are plainly stated so that the validity of the channel models may be easily inferred. 1 . 1 . 3 Volume I11

Volume III is a tabulation of performance data or circuit margins for each channel of the system. The calculation of these circuit margins is based on the theoretical analysis presented in Volume 11. The circuit margins in Volume I11 allow inference of the quality of the various system channels during nominal as well as non-nominal modes of transmission of the spacecraft and ground systems.

1.2 History of the System The present configuration of the Unified S-Band has evolved from earlier

equipment. It is therefore important to acquaint the reader with the historyof the system. The Mercury spacecraft was provided with many electro-mgnetictransmitting and receiving systems. These systems operated at seven discretefrequencies within five widely separated frequency bands. The systems usedon the Mercury spacecraft were:

1. HF voice transmitter and receiver 2. UHF voice transmitter and receiver3 . VHF telemetry transmitter no. 14. VHF telemetry transmitter no. 25 . C-band transponder6. UHF command receiver 7. S-band transponder (pulse) To complement the spacecraft systems, a number of ground stations, strate

gically located about the globe, were provided with systems compatible to those in the spacecraft to fulfill the communications and tracking requirements for the Mercury missions. The spacecraft and ground systems used in the Mercury Project performed satisfactorily. As a result, it was planned that the great majority of these systems should be used in the Gemini Project, with, perhaps, some systems modifications made to provide better performance or power and weight savings in the Gemini spacecraft.

When the Apollo Froject was initiated, if;was stipulated that as much aspossible of the existing Mercury ground network and spacecraft systems be used.In addition to these systems, it was conceived that a transponder should beincluded in the spacecraft to perform the ranging operation at lunar distances.The transponder was a l s o to be used for transmission of voice and telemetry atlunar distances. Since the transponder design chosen was compatible with the

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Deep Space InstrumentationFacility (DS I F ) , established by the Jet PropulsionLaboratory (JPL), the JPL technique (pseudo-random code ranging) was chosen byNASA to perfom ranging. Thus, for the deep space phase of communications forthe lunar mission, the JPL transponder was to perform the communication andtracking functions using three deep space stations, closely resembling the JPLdesign. For the near-earth phase, however, the VHF', UHF, and C-band Gemini-type equipments were to be used to perform the comnications and trackingfunctions. A study' conducted by JPL, however, indicated that "under worstconditions" the deep space stations might not acquire the spacecraft at alti2tudes lower than 10,000 nautical miles . In addition, computations made bythe contractor and MSC indicated that the VHF and UHF systems range capabilitywould be less than 10,000 nautical miles.

During the early phases of spacecraft subsystems design, performed by the contractor, it was realized that a problem with the spacecraft weight would arise, since the near-earth phases of the mission required a nuniber of different spacecraft transmitters and receivers, as well as their back-ups. Because of this realization, the contractor suggested to NASA that additional consideration should be given to the spacecraft weight problem, and that perhaps some other communications and tracking system could be used during the various near-earth phases of the Apollo lunar missions.

As a result of the foregoing considerations, a meeting was held at the Office of Tracking and Data Acquisition Systems (OTDA) in Washington, D.C. in December 1962. At this meeting OTDA presented plans for a ground network using a unified S-band carrier system to representatives of various NASA centers, including JPL and MSC. The ground portion of the system was to consist of three stations having 85-foot Cassegrain feed antennas f.ordeep space comni cations and tracking (separate from those of JPL), and a number of stations with 30-foot Cassegrain feed antennas to perform communications and tracking during the near-earth phases of the Apollo lunar missions. ground network not only would increase the range capabilities for near-earth This proposed communications and tracking, but would also allow transmission from the spacecraft during both near-earth and deepspace phases to be performed by onetransmitter, thus eliminating all the VHF, C-band and UHF systems and theirback-ups, and consequently reducing the spacecraft weight.

The philosophy of using the unified S-band system for communications and tracking at near-earth and in deep space has been accepted. As a result, the ground network required for the support of lunar missions is presently being implemented under a contract from the Goddard Space Flight Center.

'EPD-29 - Estimated 1963-1970, Capability of the Deep Space InstrumentationFacility for Apollo Project, JPL, Pasadena, California, 2-1-62.

2The altitude of 10,000 nautical miles was calculated on the basis of the three JPL DSIF stations located at Goldstone, California, Johannesburg, Union of South Africa, and Woomera, Australia. 4


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The Apollo unified S-band sys tem has not y e t been evaluated i n thelabora to ry , s ince the hardware design and fabricat ion has not been completed.Plans have been prepared, however, by th e Manned Spa cec raft Center f o r ea r l yand con t inu ing l abora to ry t e s t in g as wel l as f l i g h t q u a l i f i c a t i o n of t h esystem.

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2 .0 THE BASIC SYSTEN

2 .1 System ConceptThe primary concept und erlyi ng t h e Apollo S-band telecommunications systemwas o r i g i n a ll y t h a t a l l communicat ions and dat a t r a n s f e r between s pa cec raf t andground should be made using one common s e t of equipment and one ra d io freque ncyca r r i e r fo r t r ansm iss ion . Because o f va r io us h i s to r i ca l and m echan ical r easons ,t h i s concept has not been f u l l y implemented i n the Apol lo sys tem. T h e h i s t o r i c a lreasons have been ment ioned i n the previous sec t io n . r equ i rem ent tha t t he spacec ra f t t r ansm i t a s t a b l e c a r r i e r s p e c t r a l l i n e , Because of the groundphase-coherent w i th the up- l ink ca r r ie r , t o enable two-way Doppler t rackin g,ranging, and ground antenna poin t ing, narrow deviat ion phase modulat ion hasbeen implemented f o r most of th e spa ce cr af t t rans miss ion. Those informationf u n c t i o n s r e q u i r i n g a large modulated bandwidth are modula ted d i rec t ly on thec a r r i e r w h il e o t h e r , l e s s wide, funct ions a re f i r s t modula ted onto subc arr ier s .S ince the range code and t e l e v i s i on s ig na l s t r ans m i t t e d by th e Apollo spac ec ra f tboth req ui re l ar ge modulated bandwidths, and, i n some insta nce s, w i l l bet ransmi t ted s imul taneous ly , it w a s necessa ry t o p lace them on sepa ra t e c a r r i e r s ,us ing phase modula t ion f o r th e f i r s t and f requency modulat ion f o r th e second.Aside f r o m t h i s excep t ion , however, t he bas i c concept o f one ca r r i e r and ones e t of equipment has been c lo se ly approached i n th e Apol lo sys tem. Fa i lu re andredundancy cons ide rat ion s have, of course, req uir ed dup li ca te s tandby equipments , both in th e s pa cec raf t and on th e ground. The system descr ibed i n t h i sr e p o r t w i l l be used i n th e t ra ns l un ar and lun ar phases of the Apol lo miss ionan d d u r in g t h e i n j e c t i o n p hase from e a r t h o r b i t t o lunar t r a n s f e r t r a j ec t o r y .

It i s planned tha t the sys tem w i l l be u sed i n t h e e a r t h o r b i t a l m is s io n ph as esa l s o .The heart of the unif ied Apollo system i s t h e pseudo-random code rang ingsubsystem developed by J e t Propulsion Laboratory. This system uses a ground-based t r ans m i t t in g and r ece iv ing s t a t io n working i n con junc t ion wi th a spacec ra f t t r ansponder . A pseudo-random code i s phase modulated on an S-bandc a r r i e r a t th e ground and t rans mi t te d t o the spa cec raf t . The code modulat ion

i s r ec ov er ed i n t h e t r an s p o n de r and r e t r a n s m i t t e d t o t h e gro und s t a t i o n on ad i f f e re n t S-band ca r r i e r which i s phase co her en t ly generat ed from th e upc a r r i e r . A t t h e g round s t a t i on th e t im e d i f f e renc e between th e t r ansm i t t ed andreceived code gives a measure of the spacecraft range.2 .1 .1 The Basic Spacecraft SystemNeglec t ing redundancy, the b as i c spa ce cra f t system i s shown, highlys i m p li f ie d , i n f i g u r e 1. The system i s composed of a premodulat ion processor ,t r ansponder , f i n a l am p l i f i e r and as so c ia t e d microwave c i r c u i t ry , h igh-ga inantenna and omn idire ct ion al antenna. This system diagram i s la ter expanded( s e c t i o n 3.3) t o show th e means for obtaining switchable redundancy andsimultaneous PM-FM opera t ion .

The premodulation proc ess or acc ep ts voic e, PCM tel em etr y, biomed ical dat a,t e l e v i s i o n , and emergency key s ig na ls from the sp ace cra f t f o r t ransmiss ion t othe ground. It a l so r ecover s th e vo ice and up-da ta s ig na l s r ece ived from theground.6


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The CSM t r ansponder i s b a s i c a l l y a narrow band PM r e c e i v e r , narrow bandPM tr an sm it te r ex c i t er , and wide band.FM tr an sm it te r e x ci te r . The LEM t r a n s ponder, however, does no t con ta in an FM e x c i t e r s i n c e it i s n o t r e q u i re d f o rth e LEM t o t ra n sm i t FM and PM in fo rm ati on , simu ltane ousl y. The trans pon derfeed s and i s f ed by a package containing f i n a l amplif iers and microwaveswi tch ing and d ip lex ing c i r c u i t r y . The microwave c i r c u i t ry f eeds the twospac ec ra f t an tennas which are manu ally se le c ta b le . The PM re c ei v er ha s a l o c a los c i l l a t o r , phase locked t o the r ece ived ca r r i e r , which p rov ides the f r equencyand phase refer ence f o r th e PM t ra ns mi t te r ex ci te r . Tne FM t r a n s m i t t e r e x c i t e rhas i t s own sep ara te o s c i l l a t o r . The PM re ce iv er i s used a t a l l times t ore ce iv e from t h e ground. The PM e x c i t e r i s used a t a l l times t o t ra ns mi t t ot h e ground. The FM e x c i t e r i s used on ly when tran sm iss ion of FM d a t a i sr equ i red .2 .1 .2 The Basic Ground SystemAgain neg lec t in g redundancy, th e ba si c ground system i s shown, highlys im pl i f i ed , i n f ig u re 2 . The sys tem i s composed of a high-gain main antenna,wide-beam a cq u is i t io n antenna, microwave ci rc u i t ry , a main reference channelrece i ve r , ac qu i s i t i on r e fe rence channel r ece i ve r , two m ain ang le channe lr e c e i v e r s , two a c q u i s i t i o n a n g le c h an n el r e c e i v e r s , a t ra ns mi t te r , da ta demodul a t i o n c i r c u i t r y , r an g in g c i r c u i t r y , p re mo du la ti on c i r c u i t r y , a c q u i s i t i o n andprograming c i rcui t ry , data han dling equipment, and pe ri ph er al equipment .

The acq u i s i t i o n channe l s , t r a nsm i t t e r , and ac qu i s i t i o n an tenna a r e usedi n i t i a l l y t o a c q u ir e t h e s p a c e c r a f t s i g n a l . T h is o p e r at i on c o n s i s t s of as e a r c h i n a n g le w i t h t h e a c q u i s i t i o n an t en n a and a s e a r c h i n f re q ue n cy w i tht h e a c q u i s i t i o n r e f e r e n c e c ha nn el r e c e i v e r for th e c e n t r a l PM c a r r i e r componentof t he spa cec ra f t s ign a l . The g round rece i ve r lo c a l o sc i l l a to r phase lockst o the r ece ived ca r r i e r , t hus ac t i va t in g the ang le channel s. When the acqu is i t i o n a n t e n n a i s su f f i c i e n t l y we l l a l igned , t he main an tenna, which i sp h y s i c a l ly t i e d t o t h e a c q u i s i t i o n a nt en na , a c q u ir e s t h e s p a c e c r a f t c a r r i e r .The main ref ere nc e c hannel re ce iv er i s the n phase-locked and th e main angl echannels become ef fe c t iv e . The dr i ve f o r the antenna servos i s then switchedfrom t h e a c q u i s i t i o n t o t h e m ain a n g le c ha nn el s.

The r a n gi n g c i r c u i t r y c o n t a i n s d i g i t a l e qu ip me nt f o r g e n e r a t in g t h eva rio us range codes and range measurements , Doppler measuring ci rc u i t ry , anda range code r ec ei ve r which i s fe d by the ref ere nce channe l 10-megacycleI F o u tp u t s . The r an g i n g c i r c u i t r y f e e d s t h e r an g e code t o t h e t r a n s m i t t e rphase modu lator, where it i s e f fe c t iv e ly summed wi th o th er up-going da ta fromt h e p re m od ul at io n c i r c u i t r y .

The data demodulator, as shown i n f i gu re 2, a c c e p t s PM d a t a from the mainre fe rence channe l r ece ive r and FM d a t a from t h e a c q u i s i t i o n r e f e r en c e c ha nn el .S ince the two re fe rence channel r ece i ve r s are i d e n t i c a l , t h e a c q u i s i t i o nreference channel i s a v a i l a b l e , a f t e r com ple tion of ac qu i s i t i on , f o r t herec ept ion of o th er da ta , namely FM. The data demodulation and ranging equipment both fee d th e d a t a handl ing equipment . The da ta handl ing equipnent a l s ofeeds the premodulat ion equipment .

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The acq u i s i t i o n and programing c i r c u i t ry p l ays an e s se n t i a l ro l e wi th ther e s t of the equipment. The ranging proc esse s a re automated, and a re di g i t a l l yprogramed i n re spon se t o ana log measurements on var ious par t s of the equipment .The programing c i r c u i t r y co nta in s sp ec ia l purpose d i g i t a l computing equipmentand analo g- to- dig i ta l conver ters . Addi t ional per ip her a l equipment, not showni n f i g u r e 2, forms ano the r part of the ba si c ground system. This equipment i st r e a t e d i n s e c t io n 3.4.2.2 Extens ion of the Basic System Required t o Support theCommand/Service Module and Lunar Excursion Module

The Apollo lu na r miss ion use s two sp ac ec ra ft, th e command/service module(CSM) and lunar excursion module (LEM). The CSM communications system i sac t iv e throughout th e miss ion, f rom pre launch through reen t ry and landing.The LEM communications system i s ac t i ve mainly i n th e regi on of th e moon. Themission communication requirements f o r the two spa ce cr af t are t r e a t e d i n d e t a i li n s e c t i o n 4 .2 .

The f a c t th a t the re a re two spacecr af t , each having i t s own S-band system,compl ica te s the g round s t a t io n . F i gw e 3 shows a c o n f i g u r a t i o n f o r a grounds t a t i o n h av in g a f u l l d u pl ic a te a b i l i t y t o r ange simultaneously and communicates im ul t aneously wi th bo th spacec ra f t . Th i s conf igura t ion im pl i e s th a t bo thspa cec raf t remain w ith in th e beamwidth of t h e h igh-gain ground antenna and th a tantenna point ing i s performed on only one of th e s pa ce cr af t. It i s s e e n t h a tt o the ba s ic ground s t a t io n have been added two refere nce channel rec e iv ers ,one da ta demodulator , one se t of rang5ng ci rc u i t ry , one t r an sm it te r and one se tof premodula t ion c i rcui t ry . I t should be unders tood tha t the capabi l i ty of thedat a handl ing and ac qu is i t i on and programing c i r c u i t r y i s also expanded overthe ba s ic sys tem. Figure 3 s t i l l i g n o re s re du nd an cy , a l th o u g h t h e a b i l i t y t oswi tch da ta demodula tors and ranging c i rcui t ry from one referen ce channel t oanother implies redundancy of a s o r t .

Funct ional ly , the two spac ecraf t S-band systems ar e a l ik e , a l though the remay be d i f fe ren ces i n phy s ica l packag hg and avai la bl e output power leve ls .These d i f f e r e n c e s a r e d i s cu s s ed f u r t h e r i n t h e d e t a i l e d sy ste m d e s c r i p t i o n ,s e c t i o n 3.3.2 . 3 The Ground Network

There a re th ree types of S-band ground st at io n s; th e deep-space st at io ns ,i n j e c t i o n and t r a n s p o s i t i o n g a p - f i l l e r s t a t i o n s , and e a r t h - o r b i t a l s t a t i o n s .The t y p es o f s t a t i o n s d i f f e r i n t h e s l z e s of t h e i r a n te n na s and w he th er t h e yhave single or d u a l t r a c k i n g c a p a b i l i t y .The th re e deep-space st a t i o n s have 85-foot d iameter antennas and f u l l dualt ra ck in g and communication ca pa bi l i t y. These s t at io n s w i l l be located a tGoldstone, Cal ifo rn ia ; Madrid, Spain; and Canberra, Au st ra lia . Following th ei n j e c t i o n i n t o l u n a r t r a n s f e r t r a j e c t o r y and du r in g t he LEN t r a n s p o s i t i o nphases of the Apollo lun ar miss ion , i t i s p o s si b le t h a t t h e s p a c e c r a ft w i l l nothave been acqui red by a deep-space s t a t io n . This p o ss ib i l i t y e x is t s because thespacec ra f t , a t the beginning of i n j e c t i o n , i s a t a r e l a t i v e l y low a l t i t u d e

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(100 n a u t i c a l m i l e s ) . Depending on the geograph ica l r e l a t i on o f th e i n j ec t i onpo in t t o the ne a res t deep- space s t a t io n , t he spac ec ra f t may have t o c limbsev era l t housand m i l e s i n a l t i t u d e b e f o re b ecoming v i s i b l e .B ecause of t h i s p o s s i b le g ap i n co ve ra ge , s e v e r a l i n j e c t i o n g a p - f i l l e rs t a t i o n s , number and lo c a t io n now unknown, w i l l be used t o supplement th edeep- space s t a t io ns f o r those m iss ions where deep- space s t a t io n acq u i s i t i o n i sdelayed. T h e s e s t a t i o n s w i l l have 30-foot antennas and du al data communicationc a p a b i l i t i e s . The S-band g ro un d s t a t i o n s t o be u se d i n t h e e a r t h - o r b i t a lmiss ion phases w i l l have 30-foot antennas and si ng le ranging and communicationsc a p a b i l i t i e s . The l o c a t i o n s of t h e s t a t i o n s w i l l be such as t o p rov ide goodcoverage o f Apo llo e a r th o rb i t s , i n c o nj u nc ti on w i t h t h e g a p - f i l l e r s t a t i o n s .

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3.0 DETAILED SYSTEM DESCRIPTION3.1 The Communications Signals

The fol lowing s ec t i on descr ibe s th e va riou s communication, data, andranging s ignals which serve as i npu t s t o the system , e i th e r on the g round o ri n th e spacec ra f t . The s igna l s a re desc r ibed as t h e y e x i s t i n their unmodulatedo r baseband form. The modulated s ig n a ls are t r e a t e d i n s e c t i o n 3 .2 .3.1.1 Up-link (Ground t o Spac ecraf t)

3.1.1.1 Range code. - One of the most important s ig na ls generated by th eground s ta t ion i s the range code, used t o de termine th e r ad ia l range betweenground s t a t i o n and spa cec raf t . This code i s a continuous running binary waveform which progresses a t a nominal ra te of a m il l ion b i t s pe r second , be inggenerated from 2 496-kilocycle clock si gn al . Being one of a c la ss of codesk n m as pseudo-random, t h i s code has a bas ic per iod of about 5.4 seconds.Th i s pe r iod insu res tha t t he code does no t r epea t fo r 5.4 m i l l i o n b i t p e r i o d s .A p e r io d of t h i s l e n g t h i s requi red so t h a t t h e code w i l l not recycle dur ingt h e time of p ropa gatio n from e a r t h t o moon and back.

The transmitted code, which i s g e ne ra te d b y d i g i t a l l o g i c c i r c u i t r y , i s aBoolean combinat ion of f ou r sh or ter codes and th e d i g i t a l c lock s ig na l (a496-kc squ are wave). For general information the combining funct ion i s :Code = {x . c .> v ( 2 . [ ( a . b v b . c v a . c ) @ c l]1\Where th e dot i n d ic at es th e Boolean "and", th e v in di ca te s th e Boolean "or" ,t h e + in di ca tes th e Boolean "exclus ive or" , and th e bar in dic a te s th e Boolean"not' The len gth s of th e code components i n b i t per iod s ar e given i n ta b le I .For de ta i le d informat ion on th e gene ra t ion of t h i s code, see refere nce 1.

3.1.1.2 Up-Data.- It i s requi red tha t a d i g i t a l u p- da ta l i n k be a v a i l a b l e to t r an s m it t o t h e s p a ce c ra f t (both CSM and LXM) e i th e r up-da ting in fo r mation f o r th e on-board computer or re al -t im e o r stored-program commands. Thesi gn al brought i n t o the S-band equipment i s derived from a Gemini-type DigitalCommand System (DCS). This s i g n a l i s a composite waveform consisting of a1-kilocycle sinusoid summed with a 2-ki locycle sinusoid which has been phase-s h i f t keyed by a 1 - k i l o b i t d i g i t a l s ig n a l. The d i g i t a l s i gn a l i s a b a s i c200-bi t info rmation sig na l , sub- bi t encoded, 5 b i t s f o r 1.

3.1.1.3 Voice. - Voice t ransmission i s a l s o r e qu i re d t o t he spacec ra f t .The baseband voice signal i s simply an ana log waveform w it h most of i t s energyly in g between 300 and 2,300 cycles per second. Th is s ign a l o r i g in a te s fromthe va r ious channe l s i n t he g round s t a t ion .3.1.2 Down-link (S pac ecr aft t o Ground)

3.1.2.1 Range code. - The range code si gn al , recovered i n th e sp ace cra ftf o r r e t r a n s m is s i o n t o t h e ground, i s approximately the same as t ha t gene ra t ed10


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on the ground, except tha t it i s contaminated with noise and two up-links u b c a r r i e r s ( s e c t i o n 3 . 2 ) . The code i s running a t a s l i g h t l y d i f f e r en t ra tedue t o Dopp le r e f f e c t s .3 . 1 . 2 . 2 Pulse-code-modulated telemetry. - The primary spacecraft telemetrys i g n a l i s b inaryPCM (non- retu rn t o ze ro ) hav ing e i t h e r a 51 . 2 -k i lob i t or1 . 6 -k i lob i t i n form ation t r ansm iss ion r a t e . The bas i c onboard genera t ed t e l e metry clock frequency i s 312 ki locycles .3 . 1 . 2 . 3 Voice .- The baseband vo ice s ig na l i s much l i k e the ground st a t i o nvo ice s igna l .level h igh and most of th e p w e r between 300 and 2,300 c ycle s.s igna l o r ig ina tes f rom the a s t ronau t ' s m ic rophone o r the AM r e l a y r e c e i v e r u se d

C l ip p in g and f i l t e r i n g i s employed t o keep t he average voiceThe voiced u ri n g e x t r a u e h ic u l a r a st r o n a u t a c t i v i t i e s .

3.1 .2.4 Biomedical telem etry. - Biomedica l da ta f rom the as t ronauts i srou ted through-the PC%I te le me tr y when th e a st ro na ut s a re i n t h e s p a ce c r af t .When an astronaut i s o u t s i d e t h e s p a c e c r a f t , e i t h e r i n sp ac e o r on t h e s u r f a c eof the moon, a sp ec i a l s e t o f b iom edica l t e l em et ry channe ls i s provided.Seven low fr equency subca r r i e r s i n the a s t r on au t ' s su i t communications packageare frequency modulated with the biomedical measurements. The modulated sub-carriers are summed and amplitude modulated on a VHF c a r r i e r f o r r e l a y back t ot h e p a r en t s p a c e c r a f t . A t t h e s p a c e c r a f t t h e AM s i g n a l i s demodulated and thes m e d f r e quency-modulat ed su bc ar r i er s a r e r e covered . Thi s r e covered s igna lforms th e baseband input t o th e S-band system. The cen te r fre qu en cie s andchannel informat ion of t he v ar iou s biomedica l sub car r ie r channels are g i v e n i nt a b l e 11.

3 . 1 . 2 . 5 Te lev i s ion . - During c e r t a in m is sion phases the spacec ra f t w i l lt rans mi t te le vi s i on t o th e ground. Because of spa cecra f t power l i m i t a t io nst h e t e l e v i s i o n p i c t u r e w i l l not be of t he usua l b roadcas t qua l i t y . The telev i s i o n s i g n a l i s analog, having a bas ic p i c tu re fo rm at o f 10 frames per second,320 l i ne s pe r fr am e, wi th an a spec t r a t i o o f 4:3. The resolu t ion i s f u r t h e rl im i te d by 500-ki locycle baseband low pass f i l t e r i n g . Amplitude synchroniza tionw i l l be used wi th the synchroniz ing level 30 percent above the b lack le ve l .3 . 1 . 2 .6 g e r g e n c y v o ic e . - A c a p a b i l i t y i s r e q u i r e d f o r s u c c e s s f u l v o i c ecommunication with th e ground i n th e event of f a i l u r e of t h e s p a c e c r a f t hi gh -gain antenna or f i n a l a m p l i f i e r , bu t no t both . The emergency vo ice basebands i g n a l i s th e normal voice, rout ed through a d i f f e r e n t c h a n n e l .3 . 1 . 2 . 7 Emergency key. - For a l a s t - r e so r t com munication ca pa b i l i t y th ea s tr o n a u t s may use hand-keyed Morse code. The baseband key signal i s an on-offd-c vo l tage obta ined by keying th e sp acec raf t 28-vol t ba t te ry .3 . 1 . 2 . 8 Recorded PCM te le m et r2 .- PCM te le m et ry a t e i t h e r a 1.6 kbs ra te

or 31.2 kbs r a te m y be recorded when necessary . When the recorded telemetryi s played back in to s i g n a l has a nominal31.2 kbs ra te with ,The playback s ignalte lemetry .

th e t r an sm iss ion channel t he p laybackperhaps, some "WOW" and " f lu t t e r " duei s rou ted th rough a d i f f e r e n t c h a n n e l t o t h e t a p e r e co rd e r.than the r ea l - t im e

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3 . 1 . 2 . 9 Recorded vo-ice. - The normal c li pp ed vo ice may be rec ord ed a t anytime. The reco rded voic e i s played back a t a h igher ra te t h a n t h e r e c or d in gra te ( g r e a t e r t h a n 4 : l ) . The playback s ig n a l occupys a greater base bandwidththan the norm al voice s ig na l (g r ea t e r t han 9 kc) due t o the h igh p layback ra te .The playback signal i s routed through a d i f f e r e n t c h a n n e l t h a n t h e r e a l - t i m evoice.

3.2 Si gn al Transmission Modulation Techniques3.2.1 Up-l inkThe up-link modulation techniq ues are s impler , conceptual ly , than th edown-link and s o a r e t r e a t e d f i r s t . The f i n a l m o du la ti on p r o ce s s on t h eo u t g o i n g c a r r i e r i s phase modulat ion us ing re l a t i v e l y nar row devia t ion .phase modulation i s r eq u ir ed t o i n s ur e t h a t a phase s table car r ie r componentNa r r owa r r i v e s a t t h e s p a c e c r a f t . S in ce t h e s p a c e c r a f t t r an s m is s io n c a r r i e r i sder ived phase co herent ly from t h e r e c e i v e d c a r r i e r , it i s im por t an t t ha t t hec a r r i e r r e c ei ve d a t t h e spacec ra f t no t be a llowed t o r eve r se phase f o r anyappr eciab le le ng th of t ime due t o modulat ion , s in ce th i s rev er sa l would causean e r r o r i n two-way Doppler tra ck in g between th e ground t r ansm i t t ed and r ece ivedca rr ie rs . Narrow phase devi a t ion a ls o assures tha t the modula t ion i s concentrat e d i n t h e f i r s t orde r s id e products of the modulated sig na l . This concentrat i on op t im izes th e p a r t i c u l a r r ecep t ion t echn ique employed i n t h e s p a c e c r a f t .

The t o t a l rms phase devia t io n on th e up- l ink c a r r ie r i s kept a t aboutone radian. For a c l a s s i c a l t re a tm e nt of s i gn a l des ign , s ee r e fe rence 2 . 1

3. 2. 1. 1 Range code.- The range code, which i s a b ina ry ana log waveform,i s e f fe c ti v e ly summed wi th th e o th er up-going inf orm ati on and phase modulatedo nt o t h e c a r r i e r .3 .2 .1 .2 Up-data. - The baseband up-data s i gn al i s f i r s t frequency modulatedon a 70-kc su bc ar ri er , the n summed wi th th e o th er up-going infor matio n andphase modulated on the carr ier .

-~3.2 .1 .3 Voice .- The baseband voice s i gn al i s f i r s t frequency modulated ona 30-kc su bc ar ri er , th en summed wi th th e o th er up-going inf orm atio n and phasemodula ted on the car r ie r .3.2.2 Down-linkThe down-link modulation techniques for CSM and LEM a r e p r a c t i c a l l yiden t i ca l . The CSM may tra nsm it on two S-band c a r r i e r s simu ltane ousl y. Them, however, may t ime share one ca r r i e r fo r t rans mis sio n of FM or PM modulat io n . Conside r ing bo th spacec ra f t , t h ree sepa ra t e c a r r i e r f r equenc ies may bereceived a t th e ground, simultaneou sly. The va rio us modulation parameters w i l lbe t r ea t ed i n t he sec t io n on s ign a l des ign.

~. - .NOTE: 1. The on l y d i f f e r ence between the up- l inks f o r CSM and LEM i s t h ec a rr ie r frequency. The modulat ion techn ique s are i d en t i c a l . The va r iousmodulation parameters are t r e a t e d i n s e c t i o n 3 . 2 . 3 , S i g n a l D esig n.

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There a re two f i n a l modula t ion processes i n th e spacecra f t . Theseprocess es are phase modulat ion and f requency modulation. Similar t o the up- l ink,a phase-s table c a r r i e r component must ar r i ve a t t he g round s t a t i on fo r use i nDoppler tra ck in g and fo r use by the narrow ang le chan nels which po int th eground antenna. This c a r r i e r requirement impl ies narrow phase modulat ion f o rsome of the informat ion l in ks . I n addi t ion , the c a r r ie r requi rement impl iest h a t t h e L8M can not t ransmi t FM modulation when tracking and ranging i srequired by the ground. A s exp l ai ned i n s ec t i on 2 .1 , a separate f requency-modula ted car r ie r was chosen for the t ransmiss ion of t e l e v i s i o n a n d c e r t a i no t he r da t a . Ce r t a i n of the informat ion s ign a l s can be t ransm i t ted only i n thePM channel , and ce r t a in o the r s ig na ls can be t ran sm it ted only i n th e FM channel.Some of the inform at ion s i gn al s can be t ran sm it ted i n e i t h e r channel . Thecombination modes are s p e l l e d o u t e x p l i c i t l y i n t h e s i g n a l d e si g n s e c t i o n 3.2 .3 .

3. 2. 2. 1 Range code.- The range code, having been recovered i n th e spacec r a f t , i s e f f e c t i v e l y summed wi th t h e o th er PM channel info rma tion and phasemodulated onto th e down c a r r i e r . The range code i s re s t r ic te d t o the PM channelonly.

3. 2. 2. 2 Pu lse code modu1ate.d. tel em etr y. - The PCM te le m et ry s ig n al , b in ar ycoded, i s f i r s t phase modulated on a 1.024-mc subcarrier . The modulated sub-c a r r i e r may th en be e i t h e r summed w it h PM chan nel i nf orm ati on and phase modul a t e d on th e down PM c a r r i e r or summed w ith FM channel information andfreq uen cy modulated on th e down FM c a r r i e r .3 .2.2.3 Voice. - The baseband voice signal i s f i r s t freq uen cy modulated on

a 1.25-mc subcarrier . A s w i t h t h e PCM t e lemet ry subc ar r ie r , the voice sub-c a r r i e r may be summed wi th o th er in forma tion and be tr an sm itt ed through ei t h e rt h e PM o r FM channel.

3.2 .2. 4 Biomedical tel em etr y.- When employed, th e biomedical tel em etr ybaseband signal w i l l f i r s t be summed wit h th e baseband voice sig na l . Then boths i g n a l s w i l l be frequ enc y modulated on a 1.25-mc su bc ar ri er ( t he voice sub-ca r r ie r ) . This modulated sub car r i e r may then be t ransmi t ted through e i t h e r thePM o r FM channel.3 .2 .2 .5 Te l ev i s i on . - The baseband t e l ev i s i o n s i g na l i s summed with other

FM channel info rma tion and frequen cy modulated on th e down c a r r ie r . Te lev isi oni s r e s t r ic t e d t o th e FM channel only.

3.2 .2 .6 Emergency voic e.- The baseband voice s i gn al i s phase modulatedd i r e c t l y on th e c a r r i e r u si ng a s u f f i c i e n t l y narro w d e v i a t i o n t o i n su r e t h er e t e n t i o n o f a phase-s ta ble ca rr ie r- sp ec tr al component f o r ground Doppler t ra ck .3. 2.2 .7 Emergency key.- The keyed d-c si gn al i s a p p l ie d t o a d i g i t a l"and" c i r c u i t , t o which i s a l s o ap pl ie d t h e 5112-kc square wave from th e spacec ra f t cen t r a l t iming equipment . The output of th e "and" c i rc u i t , a keyed5l2-k~square wave , i s t h e n ban d-p ass f i l t e r e d t o g iv e a keyed 5 l 2 -k~ s u b c a r r i e r .The keyed subcarrier i s phase modulated on the c a r r i e r us ing a narrow enoughphase de via t io n t o maximize the f i r s t orde r s i de p roduct and t o i n su re r e t e n t i o nof a phase-s table ca rr ie r- sp ec tr al component f o r ground Doppler t rack.


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3.2.2.8 Recorded P.P-fte1kmet-r~. - The reco rde d PCM te le me tr y s i g n a l i sbi-phase modulated on a 1 . 0 2 6 ~sub ca rr ie r. Th is i s no t the same s u b c a r r i e rused f o r rea l-tim e tele me try . The modulated s u bc ar ri er may th en be summed w it ho the r in fo rm ation and t r ansm i t t ed through e i th e r the F'M or PM channel. Thesubca r r i e r f o r r ecorded t e l em et ry cannot be t r ansm i t t ed th rough the sanec a r r i e r c h a n n e l as t h a t c a r r y in g t h e r e a l -t i m e t e l e m e tr y s u b c a r r i e r .

3.2.2.9 Recorded voice. - The recorded voice s ignal i s frequ ency modulatedon a 1.2 5 mc su bc ar r ie r . This i s not the same s u b c a r r i e r u sed f o r real-timevoice . Because of base-bandwidth cons ide rati on s, t h e re la ye d EVA biomedicalda ta canno t be summed w it h reco rded v oic e. The modulated s u bc ar ri e r may besummed with o th er inform ation and trans mit ted through ei t h e r th e PM or FMchannel. A s wkth recorded teleme try, recorded voice and real- t im e voice cannotbe t ransm i t ted through th e same ca r r i e r channe l .3 .2 .3 Signa l DesignI t has be en s t a t e d p re v i o u s ly ( s e e . 3 . 2 . 2) t h a t f o r t h e down l i n k c e r t a i ninformat ion funct ions are re s t r i c t ed t o PM only or FM only, while some functionscan be t ran sm it te d e i t h e r way. There ar e many po ss ib le combinations of t r a n s mis sio ns. The choi ce of th e var ious modulation parameters f o r the se combinat i o n s i s r e f e r r e d t o , h e re , as s igna l des ign . A t t h i s t im e, f i r s t c u t s i g n a ldesig n and op tim iza t ion f o r both th e up and the down l i n k s have been performedby the p rim e con t rac to r s f o r CSM and LEM, r e s p e c t i v e l y .

3 .2 .3 .1 Combination m>-des. - It i s n e c es s ar y t o d e s i g n a t e a l l t h e p o s s i b l et ransmiss ion modes, both f or the up- and th e down-l inks . This i s done i nt ab le I11 for th e up-l ink. Table I V does not l i s t a l l the poss ib le combinat ionsf o r th e down-l ink, but l i s t s most of those o f L in te re s t . Table IV , a l s o i n d i c a t e swhich modes use t he sp ac ec ra ft hig h power f i n a l am pl if ie rs (PA) and which modesr e s u l t fo r use of th e PM ex ci te r only.

3.2 .3.2 Modulat ion parameters . - For the purposes of Volume I , t h em odulat ion pa ram eter s t o be t r ea t e d a re sub ca r r i e r f r equenc ies and va r iousmodula tion ind ice s . There ar e sev era l separa te s e t s of modula t ion indices fort h i s system; those of the information on th e subca, rr iers ,and tho se of the sub-c a r r i e r s o n t h e c a r r i e r s . A t t h i s t ime c ont rac tor s have der ived s e t s of modul a t i o n i n d i c e s . I t i s intended that Volume 111 w i l l presen t a t h i r d se t ofi n d ic e s , d e ri ve d and op tim ized by NASA-MSC. Table V prese n t s on ly th e sub-ca r r i e r f r equenc ies , l eav ing the ind ice s f o r Volume 111.----.3.2 .3 .3 Modulated spectra. - The modulation modes de sc rib ed i ns e c t i o n 3 .2 . 3 a r e bes t i l l u s t x t e d th ro ug h p l o t s of e n er gy d e n s it y a g a i n s tf requency . The spec t r a of i n t e re s t a r e those fo r the ind iv idua l up- links,in di vi du al da m- lin ks , and th e dual up-l inks and down-links where a l l channelsare ac t iv e . The dua l l i n k p l o t s show haw the s pe ct ra f o r both spacecra f t f i tt o g e t h e r .

It should be noted that these sp ec t r a l p lo ts have not been mathemat ica l lycomputed. The p l o t s are approximations and are used here as i l l u s t r a t i o n .Figure 4 d e p i c t s t h e energy spectrum of an ind iv i dua l up-l ink ; t h a t i s , aca r r i e r of f r equency f o phase-modulated by a pseudo-random ranging code plus14


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a voice and an up-data sub car r ie r . It can be seen th a t t h e f i r s t order productsf o r the voice and up-data sub car r ie rs appear 30 and 70 kilocycles away from thece n t ra l ca r r i e r sp ike , r e spe c t ive ly . The r ange code sp ec t r a l envelope has thes i n squa red o f X over X squared shape with n u l ls eve ry megacycle. The envelopei s a c t u a l l y f i l l e d w i t h f i n e s t r u c t u r e d e fi n ed by t h e l e n gt h s of t h e v a r io u ssub-codes making up th e range code. This f in e s t ru ct ur e i s neg lec ted fo rc l a r i t y . F i g u r e 5 r e p r e s e n t s a du al up-l ink, wi th two of the ind ivi du al upl i n k spec t r a sepa ra t ed i n f requency . The f r equency sepa ra t ion i s determinedby the sepa ra t ion of t he two space craf t phase-modula ted c ar r i e r s and the240/221 f r equency tu rna round ra t i o o f th e spac ec ra f t t ransponder . The spectraa r e of id en t i ca l form , al though th e inform ation con tent of each may be d if fe re nt .

Figure 6 shows the CSM down-link having a phase-modulated carr ier a tf requency f o and a frequency-modulated carr ier a t frequency f o . The1 2f requency separa t ion be tween th e two c ar r i e r s i s k ep t t o 1 5 megacycles, minimum,

due t o spacec ra f t c i r c u l a t o r des ign . The t e l ev i s io n envelope i s always assoc i a t e d w i t h t h e FM c a r r i e r . The range code envelope i s always associa ted wi thth e PM c a r r i e r . The two su bca rr ie rs bear ing rea l - t im e voice and te lem etryinformation may be a ss oc ia te d with th e PM c a r r i e r a nd t h e t w o s u b c a r r i e r sbear ing recorded voice and telem etr y inform ation may be asso cia ted w i t h t h eFM c a r r i e r , o r v i c e v e r sa .

Figure 6 shows the LEM down-link sp ect ra. Since no requirement d ic ta te st h a t t h e LEM t ransmi t s imul taneous FM and PM mo dulat ion , tim e sh a ri ng of t h eca r r i e r by the r anging code and t e l e v i s io n i s used. It should be not ed,however, t h a t te le vi s i on i s t rans mi t te d only when convenient and never a t th eexpense of ranging.Since the LEM ca r r i e s no t ape r ecorde r on ly one se t of subc a r r i e r s f o rvoice and te lemetry i s used. A s f i g u r e 6 shows, t h e su bc ar ri er s may bet r ansm i t t ed s im ult aneous ly wi th e i th e r the r ang ing code o r the t e l ev i s io n .Figure 7 shows the d u a l down-link sp ec tra . The upper spectrum i n th ef i g u r e shows the LEN t r a n s m i t t i n g a coherent c a r r i e r w i th PM modulation, andt h e CSM t ra ns mi t t i ng both th e coheren t and non-coherent c a r r i e r s with PM and

FM modulation, re sp ec ti ve ly . The lower spectrum of f i g u r e 7 shows the LE34t r a n s m i t t i n g a non-coherent c a rr ie r with frequency modulat ion, and th e CSMt r a n s m i t t i n g b o t h c a r r i e r s as i n the upper spectrum. The CS M spec t r a o ff i g u r e 7 ind ica te s imultaneous t ransmiss ion of fou r sub car r ie rs . When t h i smode of transmission i s used, two of th e sub ca rr i er s are modulated by real-timevoice and tel em etr y infor mati on and th e remaining two ar e modulated by recordedvoic e and te le me try informa tion. However, when reco rded info rma tion i s nott r ansm i t t ed , the rea l - t ime voice and te lem etry su bc ar r ie rs may be asso cia te dw i t h e i t h e r t h e c oh er en t or non-coherent c a r r i e r of th e CSM sp ec tra .

A m e r i t of t h e f o u r s u b c a r r i e r c o n f i g u r a t i o n i s t h a t f o r t h e ma j o ri t y oftime when recorded data i s no t t r ansm i t t ed , t he two subca r r i e r s a s soc ia t e dw i th r e co rd ed d a t a a r e a v a i l a b l e t o s a t i s f y a ny f u t u r e a d d i t i o n a l d a t a c o m u n ica t ion r equ irem ent s .


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broken down in t o fou r d i f f e re n t s igna l s . These s ig na ls which can only be t r an sm i t t ed ind iv idua l ly , are 51 . 2 k i lo b i t s . pe r second (kbs ) or 1.6 kbs real- t imetelemetry plus normal voice and biomedical data; or recorded PCM t e l em et ry( a t 31.2 or 1 .6 kbs) p lus recorded voice ; or emergency voice, or emergency key.The FM outp ut can be broken dawn i n to two d i f f e re n t s ig na l s which can on ly bet r ansm i t t ed ind iv idua l ly , and are t e l e v i s i o n p l u s r e a l -t i m e t e l e m e t ry ( 31 .2 or1.6 kbs) plus normal voice and biomedical data; or t e l e v i s i o n p l u s re co rd edte l em et ry (51 . 2 or 1.6 kbs) p lus recorded voice .

The vario us ty pes of infor mati on which are combined i n t h e mixing networkst o produce the v ar iou s premodula tion processor outp uts are der ived from var ioussources which are indica ted on the l e f t hand si de of f i gu re 11. The processingof each o f these d i f f e r en t t ypes of in fo rm ation i s d i scussed ind iv idua l ly .- Pulse code modulat ion (n on-return t o zero) data ,k b s r a t e , i s der ived f rom the spacecraf t PCMequipment and may e i t h e r be reco rded or t r a n s m i t t e d i n r e a l time. Whetherplayed back from the recorder or t r a n s m i t t e d i n r e a l t ime, t he te lem etryinformation i s processed by one of t h e follo win g methods.

3.3.1.1.1 PM. The PCM d a t a i s route d t o the bi-phase modulator where th ebi-phase modulation i s accomplished. That i s , t h e ones and ze ro s of th e PCMd a t a are d ig i t a l l y combined wi th a 1.024-mc squ are wave su b c ar ri e r. The outputof th e bi-phase modulator goes through a b an dp ass f i l t e r and i s r ou te d t o t h ePM mix ing network where it may be summed wi th o th er da ta f o r modulation on th emain c a r r ie r and t rans miss ion t o ea r th . I n t h i s case the sLrmmation of th e PCMs u b c a r r i e r a n d t h e o t h e r d a t a i s t ra n sm i tt ed t o e a r t h v i a a PM modulatedc a r r i e r .3 . 3 . 1 . 1 . 2 F!M. The PCM d a t a i s aga in rou ted t o th e b i -phase m odula to rwhere modulation i s accomplished. Then, th e 1.024-mc su b ca rr ie r i s r o ut ed t ot h e F'M mixing network where i t may be summed w i th one or with a combination ofo t h e r s i g n a l s ( s u c h as voice , TV, e t c e te ra ) . The composite waveform i s thenrouted t o th e S-band t ransponde r and subsequent ly t ran sm i t te d t o the ground ona n F'M c a r r i e r .3.3.1.1.3 Recorded t e l e m e t r y . Dur ing the t im e pe r iod th a t r e a l t im ete l em et ry t r ansm iss ion i s no t poss ib l e (whil e th e space c ra f t i s behind the moon,f o r example)- the premodulat ion proc esso r provide s switc hing of th e PCM da ta t oth e d at a s tor age equipment where th e da ta can be recorde d. When transmission

becomes poss ib le , t h a t da ta can be played back through the data s torage equipment inp ut shown i n f ig ur e 11, and processed through the recorded te lemetrychannel using e i t h e r PM o r PM, as discussed previous ly . A s the f igure shows,t h e r e a l time and reco rded PCM d at a can not be tra ns m it te d throu gh th e samechannel. The da ta can, however, be tra ns mi tte d simultan eou sly ,on e s e t onF'M and the o the r s e t on PM.The r e a l t ime and recorded telemetry subcarr iers have the same frequency;bo th are der ived f r om th e 512 kc PCM cl oc k equipment by do ub lin g th e c lockfrequency. This i s a convenient and l e s s complicated way (from an equipments t a n d p o i n t ) t o produce a r e l i a b l e s u b c a r r i e r .


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3.3.1.2 Voice.- A s s h m i n f i g u r e 11, t h e r e are two di f ferent channelsi n t h e premodulation processor which are used fo r th e process ing of voicesig nal s . One channel acc ept s voice s i gn al s from e i t h e r t h e s p a c e cr a f t a u di ocen ter or th e VHF/AM rec ei ve r (which re ce iv es voice s i gn al s from the a st ro n au t ' ss p a c e s u i t t r a n s c e i v e r ) . The o ther channel accepts voice s ignals from t h e data-storage equipment where voice i s recorded during such periods when real- t imevoice t ransmiss ion i s no t poss ib l e . The cha nne l which i s used f o r t r ansm iss ionof rea l - t ime voice opera te s i n a pa r ty l i n e f ash ion whenever one as t ro nau t i souts id e the space craf t , the o th er i n th e spa cec raf t and both wish t o communicatew i t h th e ground s t a t io ns . This pa r ty l i n e channel employs a voice opera tedt ransmiss ion (VOX) pu sh -to -ta lk (PTT) mechanism which i s opera ted by thea s t r o n a u t i n t$e spa cec raf t . Thus, the as t r ona ut who i s i n s i d e t h e s p a c e c r a f tmay overr ide th e voice of th e as tro na ut who i s ou tsi de , alth oug h both may bel i s t e n i n g t o vo ic e s i g n a ls from th e ground st at io n . Upon se le ct io n of th esource, th e voice information i s r ou te d t o t h e VOX-NO-VOX c o n t r ol , t h e n t o acl ip pe r and mixing network, and f i n a l l y modulated on th e 1 .25 mc voice sub-ca r r ie r . The sub car r ier wi th the voice informat ion (and, a t t imes, biomedicaldata) , i s t he n r ou te d t o e i t h e r t h e FM o r PM m ixing network and f in a l l y t o thet ra n sp o nd e r f o r t r a n sm i s s io n t o e a r t h .

The recorded voice information, when transmitted, i s obtained from thetape r ecorder , rou ted t o a f i l t e r , and modulated on a 1.25 mc voltage co nt ro l le dos c i l l a to r . Th i s m odulat ed subca r r i e r i s t he n r ou te d t o e i t h e r t h e FM or PMm ixing network and f ina l ly , t o the t r ansponder fo r t r ansm iss ion t o ea r th . I tshould be noted that the rea l - t ime voice and recorded-voice sub carr iers a r enot t ransm i t ted s imul taneous ly through th e FM o r t h e PM channe l. A s t h e f i g u r eshows, th e switch pr io r t o the mixing networks allows t ransmiss ion of real-t ime voice v ia t h e PM channel and recorded voic e v i a th e F'M channel , or vic eve r sa .

3.3.1.3 Biom edica lda ta . - During ex t r a -veh icu la r a c t i v i t i e s of t heas t ronau t s ( such as walking on th e s ur ra ce of t h e moon) some biome dical i n fo rmation w i l l be req uire d by th e ground st at io n. This information w i l l bet ran smi t ted from the as tr on au t ' s sp ace sui t , v ia th e s u i t VHF-AM tra ns ce ive r ,and r ece ived on the spacec ra f t t r ansce ive r . In tu rn , t he ou tpu t of t he spacec r a f t t r ansce ive r , cons i s t ing of the compos ite of seven subca r r i e r s wi th t h e i rbiomedical information, i s r o u te d t o a f i l t e r ( hi gh -p as s) and t h e n t o a mixingnetwork where i t i s summed wi th voic e info rma tion d er iv ed from one of t h e s our cesdis cus sed pre vio usl y. The composite out put modulates th e 1.25-mc su bc ar ri erwhich i s t he n r o u te d t o t h e FM or PM mtxing networks of t h e pr oc es so r.

3.3.1.4 Televis ion . - The te le vi s i on informat ion i s der ived from t h eonboard television equipment and i s r ou te d t o t h e FM mixing network. There,t h e t e l e v i s i o n i n f o r m a t i o n i s summed with voice or telemetry, or both, and th ecomposi te s ignal i s rou ted t o the t r ansponder for t ransmiss ion .3.3.1.5 Ehergency_.voice .- I n case of a f a i l u r e i n t h e s p a c e c ra f t powera m p l i f i e r or high-gain antenna , the ef fe c t iv e R F power output decreasess i g n i f i c a n t l y . This a c t i o n r e s u l t s i n a n emergency s i t u a t i o n s o f a r ascommunications are concerned. Under t h i s con di tio n an emergency voice mode i sused. I n t h i s mode, vo ice from one of the th ree sourc es descri bed previo usly,

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i s chosen, and the informat ion i s r ou te d t o t h e VOX-NO-VOX mechanism, thec l ipp er , and then d i re c t ly t o the t ransponder phase modula tor, comple te lyby-passing th e mixing network i n the premodulation proces sor.3.3.1.6 Emergency key. - I n th e event of f a i l u r e of th e voice- t ransmissionchanne l, an emergency key mode w i l l be used. The key mode employs a hand-keyedMorse code s i gn al from the audio ce nte r and 5 l 2 - k ~square wave from the centraltiming equipment (CTE). The code and th e 5 l 2 - k ~ s i g n a l a r e r o ut ed t o a n "and"c i r c u i t t h r o u g h a band-pass f i l t e r , and t he n d i r ec t l y t o t he t ransponde r-phasemodulator , bypassing th e r e s t of th e premodulation processor c i r cu i t ry . Theemergency key w i l l appear as a keyed 5l2-k~subcarr ier on the down-l inkspectrum.3.3.1.7 Data storage equipment. - Although the data storage equipment (DSE)i s not a p ar t of t he premodulat ion processor , t h i s equipment i s descr ibed veryb r i e f l y i n t h i s s e c t io n , s in ce DSE ou t put s a r e d i r e c t l y rou t ed t o t h e premodula t i o n processor under some circumstances .The data storage equipment i s used fo r recording of voice and PCM t e lemet ry .Storage of one or both takes place when normal transmission i s not possible; ,f o r example, when the sp ace cra f t i s behind the moon o r when the spacecraft i semploying a tra nsm iss ion mode which can not be immediately in te rr up te d f o rt ransmissio n of other informat ion.The onboard DSE has th e c a p a b i l i t y t o r ec o rd 5 1 . 2 or 1 . 6 kbs te lemetry

Iand about 4- hours of voice informat ion. When playback occurs, a patch panel2al lows th e analog voice t o be played i n to th e normal voice t ran smission channel ;tha t i s , the f requency modula ted su bcar r ie r o sc i l l a to r ( f = 1 .2 5 mc). When thePCM informat ion i s played back, the data stream from t h e DSE i s in t roduced tot h e bi-phase modulator where it i s proces sed i den t i ca l l y as i n t h e normalt ransmission of PCM t e lemet ry .

3.3.1.8 Up-data and v o i c e. - I n a d d i t i o n t o p r o ce s si n g t h e i nf or m at io n t obe t ran sm it ted f rom the spa cec raf t t o ground, the premodulation processor~performs th e demodulation of t he up-data and-up-voice su bc ar rie rs . As showni n f ig u re 11, t h e r e are two demodulators which accept inputs from t h e t r a n s ponder and recove r th e up-link channels.

3.3.2 TransponderThe Apollo spac ecra f t t r ansponder cons i s t s of th r ee bas i c par t s , namelyth e rece iver and two t ra ns mi t te r exc i te r s . This subsys tem accepts a l l ou t pu t sfrom th e premodulation proc esso r, performs th e f i n a l modulation process, andt r ansmi t s t he i n fo rma t ion t o t he g round. I n add i t i on , t he t r ansponde r r ece i vesa l l of the in fo m at io n from th e ground systems, recovers and t u r n s around therange code, and rout es the voice and up-data su bc arr ier s t o the premodri la tionprocessor. Thus, as f a r as th e un if ie d S-band system i s concerned, th e t r an sponder performs t he tra nsm iss ion and rece pti on fun cti on s onboard th e commandand s erv ice module and the l un ar excu rsion module. The uni fi ed S-band tr an sponder i s shown i n f ig ur e 12. It i s necessary a t t h i s p oi nt t o d is cu ss t h eope ra t i on of the t ransponder wi th respec t t o t ransmiss io n and recept ion ofin format ion i n the va r ious modes d i scussed el sewhere i n th i s re po r t .


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3.3.2.1 R e ce p ti on .- The g ro un d t o s p a c e c r a f t s i g n a l c o n t a in s i t s f u l lbaseband inform ation, having range code, up-data su bc ar ri er , and voi ce sub-ca r r i e r phase m odulat ed on to the c a r r i e r . The RF s i g n a l e n t e r s t h e t r an s p on d e ra t t h e p r e s e l e c t o r a n d i s r o u t e d t o a balanced mixer. There i t i s mixed witht h e o u t pu t of t h e c a r r i e r l o op VCO which has been f i l t e r e d and f r equencym ul t ip l i ed by 34. The out pu t of th e balanced mixer i s t h en r o u te d t o t h e f i r s tI F a m p l i f i e r . I n t h e I F channel the ampl i tude of th e s ig na l i s con t ro l l ed bythe au tom at i c ga in con t ro l (AGC) s i gn al which i s der ived from t he AGC d e t e c t o ras shown i n f i gu re 12. The out pu t of th e f i r s t I F i s rou ted t o the secondde tec to r where i t i s mixed wi th the ou tpu t of t he ca r r i e r l oop VCO which hasbeen frequency-mult ipl ied by two. A s shown, th e second d et ec to r has twooutputs . One of th es e ou tp ut s i s r ou te d t o a n a m p l i fi e r and f i l t e r ( se co nd I F ) .The ot he r fe ed s two cha nne ls. The f i r s t channe l cons i s t s of a n AGC d e t e c t o rwhich feeds an AGC a m p l i f i e r f i l t e r w hich, i n t u r n , c o n t r o l s t h e g a i n of t h ef i r s t I F am pl if i er . The second channel co n si st s of a hard l im i t e r which d r i vesthe ca r r i e r t r ac k in g phase de te c to r . The ou tpu t of t he c a r r i e r t r ack ing phased e t e c t o r i s bandwidth l imi ted by the IF f i l t e r . This output i s fed through af i l t e r t o th e c o n t r o l p o in t on t h e VCO, t h u s c au si ng t h e o s c i l l a t o r t o ma in ta inphase coherence wi th th e incoming sig na l .

As f i g u r e 12 shows,there i s a second output obtained from the secondde tec to r , i n add i t io n t o the one desc r ibed above , which i s r o ut e d t o a secondI F l i m i t i n g a m p l i f i e r and t h e n a wideband de tec to r . The o th er input t o thed e t e c t o r i s o b t ai n ed by d i v i d i n g t h e c a r r i e r l oo p VCO fre que ncy by two. Thewideband de te ct or provi des two out put s which a r e ide nt ic al . One of the ou tpu tsi s r o u te d t o a l o w pass f i l t e r , l ab led " f i l t e r and am pl i f i e r , " where the vo iceand up-data su bc ar r i er s a r e separated from th e range code. The output of t h i sf i l t e r i s t h e n r ou te d t o t h e premodulat ion pro ces sor f o r demodulat ion of th etwo su bc arr ier s . The ot he r outpu t of the wideband de te ct or i s r ou te d t o t h ePM tr an sm it te r ex c i t e r where i t i s modulated on th e down l i n k c a r r i e r andt r a n s m i t t e d t o t h e g ro un d.

3.3.2.2 Transmission. - A s shown i n f i gu re 12, t h e t r a n s p o n d e r t r a n s m i t t e rhas been broke n down i n t o th e PM ex c i t e r and th e FM e x c i t e r . A s the namesind ica te , t he PM e x c i t e r i s used fo r t r ansm iss ion i n the phase-modulation modesand the FM e x c i t e r i s used f o r t ra nsm issi on i n th e frequency-modulat ion modes.The PM e x c i t e r d e r iv e s i t s down- link c a r r ie r f rom the t ransponder ca r r ie rt r a c k i n g VCO. This i s done so t ha t t he g round t r ansm i t t ed and r ece ived ca r r i e r sa r e phase coherent . This phase coherence i s necessary for maintaining two-wayDoppler t rack a t the ground st at io n. The VCO output , mentioned previously,i s d en ote d i n t h e f i g u r e as f o and i s r o ut e d t o t h e f i r s t - p h a s e mo dulato rof the F'M ex c i t e r , t hrough an RF gate and an X4 m u l t i p l i e r . A s shown, theother input t o the phase modula tor i s the outpu t of the wideband de te cto r ,descr ibed i n th e previous s ec t io n. The range code and the up-data and voicesub car r ier s en te r the phase modula tor through a video gate , and ar e phasemodulated onto the c ar r i e r ( X 4 f 0 ) . The outpu t of the f i r s t -p ha se modulator i st hen rou ted t o a second-phase modulator where th e c a r r i e r ( X 4 f ) i s f u r t h e r0modulated by th e inform ation derived from t h e PM mixing network of t h e premodul a t io n processor . Under normal t ransm iss ion cond i t ions t h i s informat ionc o n s i s t s o f v o i ce or PCM te lemetry , or both. For non-nominal tra ns mi ss io n20


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power amplif iers it i s l i k e l y t h a t t h e h ig h p m e r PPI modes w i l l be implementedacd t ransmiss ion of FN information w i l l be term ina ted . The power am pl if ie rsar e t r av el ing wave tubes (W)which may be driven t o provide tw o power levelou tp ut s. One ou tp ut i s 5 w a t t s and thc o the r 20 w a t t s . The low-power outputw i l l be used dur ing missio n perio ds when th e communication d at a lo ad i s low.The high-power output w i l l be used f o r f u l l bandwidth t ransmiss i on f rom deepspace and lunar d is tances .

3 .3 .2 .4 Antennas.- A t t h i s tim e t h e r e i s very l i t t l e i n fo rm at ion ava i l ab leon the spacec ra f t an tennas. Therefo re , t h i s s ec t ion w i l l descr ibe the spacec r a f t a n t e n n a s as t h e y are s p e c i f i e d .There a r e two d i f f e ren t t ypes of antennas on board the sp ac ec raf t whichw i l l be used f o r communications a t S-band fre qu en ci es . These a r e a high-gaindi re c t io na l antenna and an omnidi rec t ional antenna . The h igh-gain antenna w i l lbe used fo r t ran smi ssi on from deep space and luna r dis ta nc es , while th e omnid i r e c t i o n a l a n t e n n a w i l l be used for communications a t n e a r - e a r t h d i s t a n c e s asw e l l as a back-up t o the h igh-gain antenna i n case of fa i l ur e . The h igh-gaind i r e c t i o n a l a n t e n n a w i l l have the capab i l i t y of t r a n s m i t t i n g a nd r e c e i v i n gsi gn al s of bandwidths up t o 200 me a t f reque ncies be tween 2 .0 g igacycles (gc)and 2.4 gc. This antenna w i l l be r igh t -hand c i r c u l a r ly po la r i zed and w i l l have

a power handl ing c ap ab i l i t y of 20 w a t t s . The high-gain d i re c t io na l antenna w i l lbe capable of o pe ra tin g a t t h r e e beamwidths. The half-p owe r beamwidths andcorresponding gains are as fol lows:40" - 12 db16" - 20 db6.5" - 28 db

The omnid i rcc -Liona lan tennasw i l l have a power handling ca pa b il i t y of 20 wattsand a. nominal gain of ze ro dec ibe l s .3.Lt Ground Subsystems

3.4.1 General Configurat ionFigure 2 w a s a highJy s im pl i f ied b lock d iagram of t h e b a s i c , non-redundant,ground system capable of supp ort ing one spacec raft . . The f i g w e provided ause ful conceptual in t r odu ct io n t o the system. However, the re a l , phys ica lsystem i s n ot s o e a s i l y s e pa ra b le i n t o d i s t i n c t b lo ck s, s i nc e th e t r a n s m i t t e r ,r e fe r en c e c ha nn el r e c e iv e r , and r an g in g c i r c u i t r y a r e r a t h e r i n t r i c a t e l y t i e dt o g e t h e r . Figure 1 4 breaks down, more exactly, in to one reference channelrece ive r , , one ang le channel r ece iv e r , t he t r an sm i t t e r , r anging c i r cu i t r y , da t ademodulat ion and premodula t ion c i r cu i t ry , and ac qu is i t io n and programingc i r c u i t r y i n o r d e r t o show e x p l i c i t l y t h e i n t e rc o n n e c t io n s of t h e - 7a rio us p a r t s .S ince the r e fe rence channel r ece iv e r s a re i den t i ca l , and the ang le channe lr e c e iv e r s a r e i d e n t i c a l , f i g u r e l b shows th e minimum blo cks ne ce ss ar y f o r a nunderstanding of t he system ope rat i on. It should be recognized t h a t the re i smuch per ip he ra l equipment i n the ground s t a t i o n which has not been shown i nf i g u r e ILL. The fol lo wing tre atmen t of the various ground subsystems w i l l be

Although f igure l:, i s an espans ion of f ig u r e l b ,keyed t o f ig u re s lh and l>.22


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i t i s s t i l l very much s im pl i f ie d . Most swi tching, amp l i f ica t ion , a t te nu at io n ,a nd l i k e c i r c u i t r y have be en d e l e t e d . Only t h a t c i r c u i t r y which c o n t r i b u t e st o the unders t and ing of the sys tem func t ion has been re ta ined.3.4.2 AntennasThere ar e , i n the Apol lo ground s ta t i on s , two types of S-band groundOne ty pe , used f o r deep-space communication i s an 85- foo t pa rabo l i cantennas . antenna. The ot he r, f o r near-space communication i s a 30-foot parabol ic antenna. Since, a t t h i s time, the 85-foot antennas fo r Apol lo have not beens p e ci f ie d , t h i s r e p o r t w i l l consider only the 30-foot antenria,::.

3 . 4 . 2 . 1 Main near-space antenna. - The main antenna i s a 30-foot diameterp a r a b o l ic r e f l e c t o r w i t h 1 2 - fo o t f o c a l l e n g th , h av in g a Cassegra in feed ,supported on an X-Y mount. The an te nn a i s capable of t racking a t a maximumr a t e o f 4 degrees per second with maximm accelerat ion of 5 dee;/sec 2down t o 2 degrees above th e hor izon, except ing a l ower l im i t o f 10 degrees i nthe n or t h and south keyholes , wi th a point ing accuracy of *9O seconds of a rc .The an ten na f ee d prod uce s monopulse two-dimensional sum and difference informat i o n from which the ang l e -e r ro r d r ive s ig na l s for th e an tenn a mount serv o-sys tem a r e de r ived . The t r a nsm i t t i ng and r ece iv ing f eeds a r e c i r cu la r l ypol ariz ed, of opposi t e sense, manually changeable, wit h a maximum ax i a l r a t i oof 1 . 0 db. The rece iv ing ga in for proper ly polar ized waves i s 4 4 . 0 db abovei so t ro p ic . The f i r s t s ide lobes a r e spec i f i ed t o be down more than 30 db fromth e maximum of th e main lo be . The main beam-width i s approximate ly 1 . 0 degree .

The antenna and as so ci at ed d riv e system ar e capable of o p e ra t in g i n e i g h td if fe re n t modes. These a re manual , s low (manual v el oc i t y ), programed, slaved( to az im uth-e leva t ion sou rce ) , s p i r a l scan , ac qu i s i t i on t r ack , au tom at ic t r ack ,( inc l udes memory t r ac k) , and t e s t .

. .3 . 4 . 2 . 2 Near-space ac qu is i t io n antenna . - It i s r equ i red t h a t a n a u x i l i a r ya n te n na be a v a i l a b l e t o a i d t h e main a nt en n a i n i n i t i a l a c q u i s i t i o n and l oc k-o nof the r ece ived s ig na l . Th is acq u i s i t i o n an tenna w i l l be r i g i d l y mounted on th eper iph ery of the main ante nna. Having an approximate diam eter of 3 f e e t , t h ea c q u i s i t i o n a n te n na has a maximum gain of 22 db, a beam-width of roughly1 0 degrees, and a t r a ck i ng accuracy o f 0 . 5 degrees , t o t a l . The acq u i s i t i o nfeed i s of t he s imultaneous lobin g type whose ou tput i s c i r c u l a r l y p o l a r i z e dwi th po la r i za t ion sense th a t can be s e t m anua lly.3.4.3 Microwave CircuitryA s the re a re two kinds of antennas ass oci a te d w i t h t h e deep- space andn e a r - e a r t h s t a t i o n s , so , a l so , t h e r e a re two k inds of microwave circui try.F igures 16 and 17 show the c i r c u i t r y fo r the deep- space s t a t io ns and nea r -ea rths t a t i o n s , r e s p e c t i v e l y .

F igure 16 shows the sepa ra te se ts of antenna feeds f o r the main antennaand ac qu i s i t i o n an tenna , f eed ing po la r i za t ion se l ec to r swi tches. The swi tchesa r e a r b i t r a r i l y shown i n t h e r i g h t hand c i r c u l a r p o l a r i z a t i o n (RHCP) pos i t ion .The ma in ang le s ign a l s f rom the p o la r i za t ion swi tches a r e a lways rou ted t o them ain ang le channel r ece i ve r s . L ikewise, t he acq u i s i t i o n ang le s igna l s a r e23


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a lways rou ted t o th e acq u i s i t i on channe l r ece ive r s . The sum channel s ignalsa r e r o ut e d fro m t h e i r r e s p e c t i v e p o l a r i z a t i o n s w i tc h e s t o s e p a r a t e d i p l e x e r s .The r ece iv e r ou tpu t s o f t he two d ip lex e r s a r e rou ted t o a switching networkwhich enables the main sum c ha nn el t o f e e d low no ise am p li fi er number one andt h e a c q u i s i t i o n sum channel t o feed low-noise am p li fi er number two, or v i c eversa. T h is s w i t c hi n g n etw ork a l s o p r o v id e s t h e c a p a b i l i t y f o r d r i v i n g e i t h e rlow-noise a mp l i f ie r wi t h an RF ca l i b ra t ed no ise source .The ou tpu t s o f t h e two low-noi se am p l i f i e r s a re rou ted t o a r e fe rencechannel se le c t or network, which enables th e main refer enc e channel rece ive r t obe fed by the main- sum channel s ig na l and the a cq ui s i t i on refere nce channelrece ive r t o be f ed by the acqu i s i t i on - sum channel , or v ice ve r sa .The output of the ground s ta t i o n t r an sm i t te r i s r o u t e d t o a swi tchingnetwork tha t enables it t o f ee d e i t h e r d i p l ex e r or a dummy W loa d. Thus th et r ansm i t t ed s ign a l may p ropaga te th rough e i th e r the m ain o r acq u i s i t i onantennas.Figure 16 desc r ibes a s t a t io n capable of suppor t ing only one spac ecr af t a t

a t ime. Figure 17 shows the microwave c i r c u i t r y fo r a n e a r - e a r t h s t a t i o n ,capable of suppor t ing one spacecraf t . The antenna fee d po la r iz a t i on fo r t h i stype s ta t i o n does not switch autom atical ly , but must be changed manually. Themain a n g le s i g n a l s a r e r o u te d d i r e c t l y f rom t h e m ain f e e d s t o t h e i r r e s p e c t i v emain ang le channel re ce iv er s. The main sum channel feed i s connected t o adip lex er , whose rece iv er output i s routed through a low-noise am pl if i er andd i rec t io na l coup le r t o the main r e fe rence channe l r ece ive r . I t i s s e e n t h a tt h e s t a t i o n t r a ns m i t te r s i g n a l i s rou ted th rough the d ip lex e r i n t o the m ainsum channel feeds . The t ra ns mi t te r does not dr iv e th e acquis i t ion -sum channelfeeds .

The ac qu i s i t i o n ang le s ign a l s a r e rou ted f rom the ac qu i s i t i o n f eeds th roughlo w-no ise a m p l i f i e r s , d i r e c t l y t o t h e r e s p e c t i v e a c q u i s i t i o n an g l e c ha nn elrec ei ve rs . The acquisit ion-sum-channel s ig na l i s rou ted f rom the acqu i s i t i onfeed through a low-noise amp l i f ie r t o a swi tch . The o th er input t o the swi tchi s th e main-sum channel s ig na l , f rom the dir ec t i on al coupler . This switcha l lows the acqu is i t ion - re fe rence-channe l r ece ive r t o be f ed by e i th e r theacquisition-sum-channel signal o r th e main-sum-channel s ig na l.3 . 4 . 4 Reference Channel Receiver

The fo l lowing de scr ip t io n i s f o r PM, or phase-locked, modes of op er at io n.When the reference channel i s used f o r wideband FM r e c e p t i o n , t h e r e c e i v e rphase-locked loop i s ina c t iv e , and the referen ce channel i s simply a manuallyt m ed double-convcrs ion super-he t e rodyne re ce iv er .The ref eren ce channel por t ion of f i gu re 15 i s labeled Receiver RF andAutomatic Gain Contr.01 C ir cu it ry . Th i s por t ion i s shown sepa ra t e ly i n f i gu re 18

for c l a r i t y .The referen ce channel has three bas ic funct io ns . One i s to t r an s l a t e theincoming composi te s i gn al t o an inte rmedia te frequency, and po si t io n i t i n t hecen ter of the I F passband, using a phase- locked channel , t rac king the ce nt ra l

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c a r r i e r component of th e s ig na l . The second fun ct i on i s t o provide an au tomat icg a i n c o n t r o l v o lt a g e and c a r r i e r a c q u i s i t i o n s i g n a l , a c t i v a t e d o n ly by t h ec a r r i e r component, not by no ise . The th i r d func t io n i s t o p rovi de a s i n u s o i d a ls ig na l , phase coherent wi th th e received c a r r ie r component, f rom which e i th e rone-way o r two-way Doppler f re qu en cy s h i f t may be determined. There a r e o th erope ra t i on a l f unc t i ons , bu t t he se t h r e e a r e t he bas i c concept ua l f unc t i ons .

The p r i n c i p a l o s c i l l a t o r for t he r e f e r ence channe l r ece i ve r i s t h e s t a b l ev o lt ag e c o n t r o ll e d o s c i l l a t o r (VCO) . The twenty megacycle fixed-frequencyre f e r ence s i g n a l i s f requency divided by 2 t o p ro v id e a 10 megacycle ref ere nc ean d a l s o m u l t i p l i e d by 3 t o p ro vid e a 60 megacycle reference. The 60 and10 megacycle r e f e r enc es a r e u sed t o e s t ab l i s h IF f r equenc i e s , f i xed a t 50 and10 megacycles. Ad dit io nally , th e 10 megacycle ref ere nc e i s used i n t h e RF'Doppler d e te c t i on process i n su ch a way t h a t t h e f r equency s t a b i l i t y of t h e20 megacycle f ixed f requency reference does not affect Doppler accuracy.

The incoming composite signal i s fed through the S-band am pli f ie rs andp r e s e l e c to r t o t h e f i r s t mixer. The oth er inpu t t o t h e mixer i s a. s u i t a b l yfrequen cy-mu ltiplied ve rs io n of t he 23.4-me VCO s i g n a l . The loo p loc ks i nsuch a way t h a t the output of the f i r s t mixer has a carr ier component a t 50 me.Th is 50-me component, when het ero dy ned i n th e second mix er by the 60-mcre f e r ence s i gna l , i s fu r t h e r f r equency t r an s l a t ed t o 10 me, t hen i n troducedt o t he main c a r r i e r phase de t ec t o r , which i s a ls o fed the 10-me re feren ces i g n a l . I t i s the e r ro r s i gn a l produced by th i s phase de tec tor which caxsesthe main loop t o lo ck up i n th e above descr ib ed manner . I t i s s e e n t h a t t h eoutputs of the two mixers a re in te rmedia te f requency s igna l s a t 50 and 10 mc.These two IF so urces feed th e r e s t of t he rec ep t io n equipment; t h e 10-me signalbe ing used f o r th e PM modes and th e 30-mc s ig n a l f o r th e FM modes.3.4.3 Angle Channel ReceiverThe di sc uss ion of the a ngle channel receix ._ i s keyed t o r i gu re l>.Figure 19 i s inc luded f o r c l a r i t y . The angle channel s t r on gly resembles thereference channel down through the phase sensi t ive detector but here it becomest he ang l e e r ro r de t e c t o r . The ang l e e r ro r de t e c t o r i s b a s i c a l l y a phasede t ec t or . When the re fe rence channel car r i e r - t rac kin g loop i s locked, thephase of the rec ei ve r VCO s i g n a l i s locked t o th e phase of th e c ar r i e r componentprovided by the sum channe l of th e antenna monopulse fee d. The VCO provid.est he s i g na l which i s heterodyned i n th e f i r s t mixer wi th the carr ier componentprovided by the d i f fe rence (or "error") channel of the monopulse feed.

If the RF' ax i s of t he monopulse an tenna f eed d i f f e r s i n d i r ec t i o n from t hePoynt ing vec t or (propagat ion d i re c t io n) of the rece ived s ig na l , the ampli tudeand phase of the c a r r i e r component i n the ang le channel i s a di rec t measure oft h i s d i r e c t i o n a l d i f f e r e n c e , o r e r r o r . The a n gl e e r r o r d e t e c t o r p ro v id es ad-c e r r o r s ig na l wi th the proper magnitude and po la r i ty t o cause the an tennas e rv o sy stem t o a l i g n t h e RF' ax i s o f t h e f eed wi t h t he a r r i v i n g s i gna l wave.3 . 4 . 6 Transmi t te rThe t r a n s m i t t e r i n f i g u r e s 15 and 20 i s t h a t c i r c u i t r y l abe l ed "Transmi tt e rand Frequency Generat ing Circui t ry." This subsystem inc lude s a basic Rubidiumfrequency s tandard, a f requency syn thes izer phase- locked t o th e s tand ard, and a

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master v o l t a g e c o n t r o l l e d o s c i l l a t o r . The VCO i s phase- locked t o the f requencysynthes izer and provides the R F d r i v i n g s i g n a l f o r t h e t r a n s m i t t e r . The synt he s i z e r p rovi des t h e t un ing , or f requency chang ing, ca pa b i l i t y f o r t he t r an s m it te r . The f requency of the syn thes izer i s changed manually by the operatori n d i sc re te f requency s tep s . Because the f requency changes i n s tep s , thephase-locked VCO i s used as t h e master t r a n s m i t t e r o s c i l l a t o r ; s i n c e t h eresponse of the l oop t o an i npu t f r equency s t e p i s a continuous smooth t r a n s i t i o n o

unified s-band telecommunications techniques for apollo volume i functional description

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