"" . i i NASA ; SYNCOM- i v.1 NASA TR R-233 TECH LIBRARY KAFB, NM , SYNCOM ENGINEERING REPORT VOLUME I By Syncom Projects Office Goddard Space Flight Center Greenbelt, Md. NATIONAL AERONAUTICS AND SPACE ADMINISTRATION For sale by the Clearinghouse for Federal Scientific and Technical Information Springfield,Virginia 22151 - Price $2.00 ABSTRACT This report is first of a planned series of reports on the Syncom SatelliteSystem. It is an engineeringreport covering the satellite, the communications ground stations and the telemetry and control ground stations. This report covers a description of each of the Syncom Satellite System Subsystems in addition to their operation and performance. The time period coveredby this reportis from launch through the first one hundred fifty days in orbit. The material con- tained in this report was furnished by the Hughes Aircraft Co., El Segundo, California, the United States Army Satellite Communications Agency, Fort Monmouth, New Jersey, and the Goddard Space Flight Center, Greenbelt, Maryland. ii CONTENTS Abstract ........................................................ ii Chapter I: INTRODUCTION ........................................... 1 Chapter 11: SYNCOM SYSTEM DESCRIPTION ............................... 3 GENERAL SYSTEM DESCRIPTION ...................................... 3 SPACECRAFTDESCRIPTION ......................................... 4 Structure ..................................................... 4 SpacecraftSubsystems ............................................ 8 GROUNDSTATIONS ................................................ 10 Telemetry and Command Stations ..................................... 10 SatelliteTracking ............................................... 10 Syncom Telemetry andCommand StationEquipment Description ................ 11 Communications Ground StationsResource Requirements ..................... 16 SYNCOMRANGE AND RANGE RATE SYSTEM .............................. 22 FunctionalDescription ............................................ 23 RangeSubsystem ................................................ 23 RangeRate Subsystem ............................................ 27 DataProcessing Subsystem ......................................... 29 Chapter III: LAUNCHAND ORBITAL MANEUVERS .......................... 31 PRELAUNCHACTMTY ............................................. 31 SATELLITE ACQUISITION AFTER LIFTOFF ............................... 32 APOGEEMOTORIGNITION ........................................... 33 ORBITAL PERFORMANCE CONCLUSIONS ................................. 34 Definition of OrbitalParameters ..................................... 35 ControlSubsystem Geometry ........................................ 38 SUMMARY OF MANEUVERS .......................................... 39 TransferOrbit ................................................. 39 Apogee Boostand Resulting Orbit ..................................... 40 Axial Jet Correction (Hydrogen Peroxide) ............................... 40 Reorientation(Axial Hydrogen Peroxide Jet) .............................. 42 Effect of Reorientation on Orbit ...................................... 42 HydrogenPeroxide Lateral Jet Correction ............................... 44 First NitrogenPulsed Jet Correction .................................. 44 Second NitrogenPulsed Jet Correction ................................. 45 ThirdNitrogen Pulsed Jet Correction .................................. 46 AttitudeCorrection .............................................. 46 CombinedEffect of the Third Nitrogen Velocity Correction and the Attitude Correction . 47 ResynchronizationManeuver (Hydrogen Peroxide Lateral Jet) .................. 48 SPIN AXIS ORIENTATION ............................................ 48 HistoricalSummary of Spin Axis Attitude ................................ 49 Conclusions About SatelliteReorientation Maneuvers ........................ 51 COMMUNICATIONS EXPERIMENT DURINGLAUNCH ......................... 52 RANGE ANDRANGERATE CALCULATIONS ............................... 53 DataDescription and Data Handling .................................... 53 DataAnalysis .................................................. 54 Chapter IV: COMMUNICATION TEST RESULTS ............................. 61 INTRODUCTION .................................................. 61 APPROACHTOEVALUATION ......................................... 61 Experimentsand Data .............................................. 62 iii L ........... Data Reduction ................................................. 62 TRANSMISSION CHARACTERISTICS .................................... 66 SpacecraftCharacteristics ........................................ 66 UHF/SHF Beam Collimation ....................................... 67 Link Calculations vs. Data Spacecraft-to-Ground and Ground-to-Spacecraft ........ 68 System Noise Characteristics ...................................... 78 Amplitude Response ............................................. 84 Spacecraft Antenna Pattern ........................................ 85 DEMONSTRATIONS AND SPECIAL TESTS ................................ 86 Summary of Demonstrations ....................................... 86 Transmission of Real-Time Telemetry Data............................. 93 Echo Suppression and Delay Tests .................................... 97 Data Transmission Experiments..................................... 99 PERFORMANCETESTS ............................................ 104 Discussion.................................................... 104 Signal- Plus-Noise to Noise Distribution................................ 107 Telephony .................................................... 109 Teletype ..................................................... 112 Facsimile ..................................................... 115 Chapter V: SPACECRAFT PERFORMANCE ................................ 125 TELEMETRYDATAACCURACY ...................................... 125 Error Magnitudes in Reference Voltage Circuitry ......................... 126 Error Magnitudes in Subcarrier Oscillator .............................. 128 Interaction of Spacecraft Parameters.................................. 128 Accuracy of Telemetry Transducers.................................. 129 Accuracy of Data Reduction ........................................ 129 SPACECRAFTTEMPERATURE ....................................... 129 Analysis of Telemetered Data ...................................... 129 Syncom II Spacecraft Thermal Control Evaluation ......................... 130 SPACECRAFTPOWERSUPPLYPERFORMANCE ........................... 136 Analysis of Telemetry Data ........................................ 138 Solar Array Performance ......................................... 140 CONTROLSUBSYSTEM ............................................ 141 Hydrogen Peroxide Unit .......................................... 141 Nitrogen Unit ................................................. 142 SpacecraftNutation ............................................. 143 Hydrogen Peroxide Control System Performance .......................... 144 SPACECRAFTSPINSPEED .......................................... 147 Effect of Jet Misalignment ......................................... 148 Effect of Leak in Nitrogen Unit ...................................... 150 Magnetic Effects ............................................... 151 Spin Speed Predictions ........................................... 152 SUNSENSOROPERATION ........................................... 152 APOGEEMOTORTIMER ........................................... 153 ACCELEROMETEROPERATION ...................................... 153 TELEMETRY AND TRAVELING-WAVE TUBE POWER ....................... 154 TELEMETRY AND COMMUNICATION SUBSYSTEM OPERATING CYCLES .......... 155 COMPARISON OF ACTUAL AND EXPECTED TELEMETRY SIGNAL LEVELS ........ 155 COMMAND SYSTEM PERFORMANCE ................................... 157 EFFECT OFECLIPSE ON SPACECRAFT PERFORMANCE ..................... 158 RELIABILITY ................................................... 160 iv SYNCOMENGINEERING REPORT VOLUME I Prepared by the Syncom Projects Office Goddard Space Flight Center CHAPTER I INTRODUCTION Syncom, the world's first active repeater synchronous orbit communications satellite, was developed by the Hughes Aircraft Company under the direction of the Goddard Space Flight Center. The prime objectives of the Syncom program were to: a) Gain early experience with a communications satellite in synchronous orbit, b) Develop a communications satellite of moderate bandwidth with simple reliable attitude and period control systems, c) Develop readily transportable ground support facilities, d) Develop the capability of launching satellites into a 24-hour orbit using existinglaunch vehicles with additional apogee-boost propulsion capability, e) Determine the communications systems' performance parameters, in a design configuration capable of relaying with high quality two voice modulated carriers (either FM or PCM/PM) between widely separated terminals, f) Obtain scientific data on space propagation, g) Test the life of communications satellite components at the 24-hour orbit altitude, and h) Obtain data from the quantitative effects of earth triaxiality (asymmetry around its spin axis) on the synchronous orbit. The spacecraft was designed to be launched by the Thor-Delta vehicle, and incorporates a solid propellant apogee motor for changing the highly elliptical transfer orbit to an in plane, circular synchronous orbit. The design of the spacecraft is described in Chapter 11.