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  • 1. Satellite Telemetry, Tracking and Control Subsystems Col John E. KeeseeOctober 29, 2003 Massachusetts Institute of 1 Technology
  • 2. Overview• The telemetry, tracking and control subsystem provides vital communication to and from the spacecraft• TT&C is the only way to observe and to control the spacecraft’s functions and condition from the groundOctober 29, 2003 Massachusetts Institute of 2 Technology
  • 3. Outline• TT&C functions and trades• Command System functions – Encoding/Decoding – Messages – Interfaces• Telemetry systems – Sensors and transducers – ADC – Formats – Concerns/Design principlesOctober 29, 2003 Massachusetts Institute of 3 Technology
  • 4. TT&C Functions• Carrier tracking• Command reception and detection• Telemetry modulation and transmission• Ranging• Subsystem operationsOctober 29, 2003 Massachusetts Institute of 4 Technology
  • 5. Carrier Tracking• Two-way coherent communication – Transmitter phase-locks to the received frequency – Transmitted frequency is a specific ratio of the uplink frequency• Easy to find and measure the frequency received on the ground• Doppler shift provides range rateOctober 29, 2003 Massachusetts Institute of 5 Technology
  • 6. Ranging• Uplink pseudo-random code is detected and retransmitted on the downlink• Turnaround time provides range• Ground antenna azimuth and elevation determines satellite angular locationOctober 29, 2003 Massachusetts Institute of 6 Technology
  • 7. Subsystem Operations• Receive commands from Command and Data Handling subsystem• Provide health and status data to CD&H• Perform antenna pointing• Perform mission sequence operations per stored software sequence• Autonomously select omni-antenna when spacecraft attitude is lost• Autonomously detect faults and recover communications using stored software sequenceOctober 29, 2003 Massachusetts Institute of 7 Technology
  • 8. TT&C Trades• Antenna size vs transmitter power• Solid state amplifiers vs traveling wave tube amplifiers• Spacecraft complexity vs ground complexityOctober 29, 2003 Massachusetts Institute of 8 Technology
  • 9. TT&C Interfaces Subsystem RequirementAttitude Determination and Antenna pointingControlCommand and Data Command and telemetry data ratesHandling Clock, bit sync,and timing requirements Two-way comm requirements Autonomous fault detection and recovery Command and telemetry electrical interfaceElectrical Power Subsystem Distribution requirementsThermal/Structural Heat sinks for TWTAs Heat dissipation of all active boxes Location of TT&C subsystem electronics Clear field of view and movement for all antennasPayload Storing mission data RF and EMC interface requirements Special requirements for modulation and codingOctober 29, 2003 Massachusetts Institute of 9 Technology
  • 10. Command System• Reconfigures satellite or subsystems in response to radio signals from the ground• Command timing – Immediate – Delayed – Priority driven (ASAP)October 29, 2003 Massachusetts Institute of 10 Technology
  • 11. Command Functions• Power on/off subsystems• Change subsystem operating modes• Control spacecraft guidance and attitude control• Deploy booms, antennas, solar cell arrays, protective covers• Upload computer programsOctober 29, 2003 Massachusetts Institute of 11 Technology
  • 12. Command System RF Performance• Frequencies – S-band (1.6 – 2.2 GHz) – C-band (5.9 – 6.5 GHz) – Ku-band (14.0 – 14.5 GHz)• BER = 10-6October 29, 2003 Massachusetts Institute of 12 Technology
  • 13. Spacecraft Command System Block Diagram Receiver/ Command Command Interface demodulator decoder logic circuitry• Decoders reproduce command messages and produce lock/enable and clock signals• Command logic validates the command – Default is to reject if any uncertainty of validity – Drives appropriate interface circuitryOctober 29, 2003 Massachusetts Institute of 13 Technology
  • 14. Complete Command SystemGround SpacecraftSupport Modulation Radio CommandEquipment Frequency link System• GSE operator selects command mnemonic• Software creates command message in appropriate format and encodes it• Batch commands/macros• Pulse code modulation (PCM)• Phase shift keying (PSK)• Frequency shift keying (FSK)October 29, 2003 Massachusetts Institute of 14 Technology
  • 15. Command Decoders• Detects PCM encoding and outputs binary stream in non-return-to-zero format• Outputs clock signal• Outputs lock/enable signal• Activates downstream command subsystem components• Decentralized decoding reduces harness massOctober 29, 2003 Massachusetts Institute of 15 Technology
  • 16. Secure Command Links• Encryption• AuthenticationOctober 29, 2003 Massachusetts Institute of 16 Technology
  • 17. Command Message Components• Input checkerboard bits• Synchronization (Barker word) bits• Command bits• Error detection bitsOctober 29, 2003 Massachusetts Institute of 17 Technology
  • 18. Command Messages• Spacecraft address• Command type – Relay commands – Pulse commands – Level commands – Data commands• Command select• Error detection and correction• Multiple commandsOctober 29, 2003 Massachusetts Institute of 18 Technology
  • 19. Command Logic• Decodes command• Validates command – Correct address – EDAC – Valid command – Valid timing – Authenticated• Activates circuitryOctober 29, 2003 Massachusetts Institute of 19 Technology
  • 20. Interface Circuitry• Latching relays with telltales• Pulse commands• Level commands• Data commands – Serial (enable, data and clock) – ParallelOctober 29, 2003 Massachusetts Institute of 20 Technology
  • 21. Telemetry Systems• Measure physical properties from afar – Status of spacecraft resources, health, attitude, and operation – Scientific data – Spacecraft orbit and timing data for ground navigation – Images – Tracked object location – Relayed dataOctober 29, 2003 Massachusetts Institute of 21 Technology
  • 22. Telemetry System RF Performance• Frequencies – S-band (2.2 – 2.3 GHz) – C-band (3.7 – 4.2 GHz) – Ku-band (11.7 – 12.2 GHz)• BER = 10-5October 29, 2003 Massachusetts Institute of 22 Technology
  • 23. Sensors and Transducers• Sensors change state as a function of an external event• Transducers convert energy from one form to another• Outputs can be – Resistance – Capacitance – Current – VoltageOctober 29, 2003 Massachusetts Institute of 23 Technology
  • 24. Signal Conditioning and Selection• Conditioning ensures proper level, dynamic range, frequency response, impedance, ground reference, common mode rejection• Commutation selects the proper sensor at a given time• Sampling frequency determined by the Nyquist criteriaOctober 29, 2003 Massachusetts Institute of 24 Technology
  • 25. Analog to Digital Conversion• Converts voltages (0 – 5.1 v, or -2.56 to 2.54 v) to 2n-1 discrete values• Quantization error decreases as n increases Type Conversion Word Size Power Rate High Speed 50*106 /sec 8 bit 2.5 W ADC High Resolution 1*105 /sec 16 bit 1.5 W ADC Low Power 2.5*104 /sec 8 bit 0.005 W ADCOctober 29, 2003 Massachusetts Institute of 25 Technology
  • 26. Telemetry Processing• Compression• Analysis for autonomous systems• Formatting• StorageOctober 29, 2003 Massachusetts Institute of 26 Technology
  • 27. Telemetry Formats• Synchronization• Frame count• Spacecraft identification• EDAC• Frame format identification• Spacecraft timeOctober 29, 2003 Massachusetts Institute of 27 Technology
  • 28. Multiplexing• Frequency division multiple access• Time division multiple access• Code division multiple accessOctober 29, 2003 Massachusetts Institute of 28 Technology
  • 29. Commutation in Data FormatsData type Type no. 2 bits Type Type Type no. 5 Type no. 6 bits Typeno. 1 bits no. 3 no. 4 bits no. 7 bits bits bits • Commutation – sequential data time sampling – Data includes major and minor frame identification and EDAC • Sub-commutated data – given element represents different data in different frames • Super-commutated data – given element isOctober 29, 2003 more than onceInstitute offrame found Massachusetts per 29 Technology
  • 30. Telemetry and Command System Block DiagramOctober 29, 2003 Massachusetts Institute of 30 Technology
  • 31. Command Decoder Block DiagramOctober 29, 2003 Massachusetts Institute of 31 Technology
  • 32. Data Handling Unit Block DiagramOctober 29, 2003 Massachusetts Institute of 32 Technology
  • 33. Command and Data Handling Concerns• Interfaces to other subsystems must protect the command decoder• No commands or transient signals may appear on command outputs during application or removal of prime power or during under/over voltage conditions• If a commands integrity is in doubt, reject itOctober 29, 2003 Massachusetts Institute of 33 Technology
  • 34. Command and Data Handling Concerns (continued)• Multiple commands are required for critical/ dangerous operations• No single component failure can result in unintended operation• No commands shall interrupt the uplink source to the command decoderOctober 29, 2003 Massachusetts Institute of 34 Technology
  • 35. References• Pisacane, Vincent L. and Robert C. Moore, Fundamentals of Space Systems, Oxford University Press, New York, 1994• Wertz, James R. and Wiley J. Larson, Space Mission Analysis and Design, Third edition, Microcosm Press, Torrance Ca, 1999October 29, 2003 Massachusetts Institute of 35 Technology