Satellite Telemetry, Tracking And Control Subsystems

Satellite Telemetry, Tracking andControl SubsystemsCol John E. KeeseeOctober 29, 2003Massachusetts Institute ofTechnology1

Overview The telemetry, tracking and controlsubsystem provides vital communication toand from the spacecraft TT&C is the only way to observe and tocontrol the spacecraft’s functions andcondition from the groundOctober 29, 2003Massachusetts Institute ofTechnology2

Outline TT&C functions and trades Command System functions– Encoding/Decoding– Messages– Interfaces Telemetry systems––––Sensors and transducersADCFormatsConcerns/Design principlesOctober 29, 2003Massachusetts Institute ofTechnology3

TT&C Functions Carrier trackingCommand reception and detectionTelemetry modulation and transmissionRangingSubsystem operationsOctober 29, 2003Massachusetts Institute ofTechnology4

Carrier Tracking Two-way coherent communication– Transmitter phase-locks to the receivedfrequency– Transmitted frequency is a specific ratio of theuplink frequency Easy to find and measure the frequencyreceived on the ground Doppler shift provides range rateOctober 29, 2003Massachusetts Institute ofTechnology5

Ranging Uplink pseudo-random code is detected andretransmitted on the downlink Turnaround time provides range Ground antenna azimuth and elevationdetermines satellite angular locationOctober 29, 2003Massachusetts Institute ofTechnology6

Subsystem Operations Receive commands from Command and DataHandling subsystem Provide health and status data to CD&H Perform antenna pointing Perform mission sequence operations per storedsoftware sequence Autonomously select omni-antenna whenspacecraft attitude is lost Autonomously detect faults and recovercommunications using stored software sequenceOctober 29, 2003Massachusetts Institute ofTechnology7

TT&C Trades Antenna size vs transmitter power Solid state amplifiers vs traveling wave tubeamplifiers Spacecraft complexity vs groundcomplexityOctober 29, 2003Massachusetts Institute ofTechnology8

TT&C InterfacesSubsystemRequirementAttitude Determination andControlAntenna pointingCommand and DataHandlingCommand and telemetry data ratesClock, bit sync,and timing requirementsTwo-way comm requirementsAutonomous fault detection and recoveryCommand and telemetry electrical interfaceElectrical Power Subsystem Distribution requirementsThermal/StructuralHeat sinks for TWTAsHeat dissipation of all active boxesLocation of TT&C subsystem electronicsClear field of view and movement for all antennasPayloadStoring mission dataRF and EMC interface requirementsSpecial requirements for modulation and codingOctober 29, 2003Massachusetts Institute ofTechnology9

Command System Reconfigures satellite or subsystems inresponse to radio signals from the ground Command timing– Immediate– Delayed– Priority driven (ASAP)October 29, 2003Massachusetts Institute ofTechnology10

Command Functions Power on/off subsystems Change subsystem operating modes Control spacecraft guidance and attitudecontrol Deploy booms, antennas, solar cell arrays,protective covers Upload computer programsOctober 29, 2003Massachusetts Institute ofTechnology11

Command System RFPerformance 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, 2003Massachusetts Institute ofTechnology12

Spacecraft Command SystemBlock gicInterfacecircuitry Decoders reproduce command messagesand 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, 2003Massachusetts Institute ofTechnology13

Complete Command cy linkSpacecraftCommandSystem GSE operator selects command mnemonic Software creates command message inappropriate format and encodes it Batch commands/macros Pulse code modulation (PCM) Phase shift keying (PSK) Frequency shift keying (FSK)October 29, 2003Massachusetts Institute ofTechnology14

Command Decoders Detects PCM encoding and outputs binarystream in non-return-to-zero format Outputs clock signal Outputs lock/enable signal Activates downstream command subsystemcomponents Decentralized decoding reduces harnessmassOctober 29, 2003Massachusetts Institute ofTechnology15

Secure Command Links Encryption AuthenticationOctober 29, 2003Massachusetts Institute ofTechnology16

Command Message Components Input checkerboard bitsSynchronization (Barker word) bitsCommand bitsError detection bitsOctober 29, 2003Massachusetts Institute ofTechnology17

Command Messages Spacecraft address Command type––––Relay commandsPulse commandsLevel commandsData commands Command select Error detection and correction Multiple commandsOctober 29, 2003Massachusetts Institute ofTechnology18

Command Logic Decodes command Validates command–––––Correct addressEDACValid commandValid timingAuthenticated Activates circuitryOctober 29, 2003Massachusetts Institute ofTechnology19

Interface Circuitry Latching relays with telltalesPulse commandsLevel commandsData commands– Serial (enable, data and clock)– ParallelOctober 29, 2003Massachusetts Institute ofTechnology20

Telemetry Systems Measure physical properties from afar– Status of spacecraft resources, health, attitude, andoperation– Scientific data– Spacecraft orbit and timing data for ground navigation– Images– Tracked object location– Relayed dataOctober 29, 2003Massachusetts Institute ofTechnology21

Telemetry System RFPerformance 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, 2003Massachusetts Institute ofTechnology22

Sensors and Transducers Sensors change state as a function of an externalevent Transducers convert energy from one form toanother Outputs can ctober 29, 2003Massachusetts Institute ofTechnology23

Signal Conditioning andSelection Conditioning ensures proper level, dynamicrange, frequency response, impedance,ground reference, common mode rejection Commutation selects the proper sensor at agiven time Sampling frequency determined by theNyquist criteriaOctober 29, 2003Massachusetts Institute ofTechnology24

Analog to Digital Conversion Converts voltages (0 – 5.1 v, or -2.56 to2.54 v) to 2n-1 discrete values Quantization error decreases as n increasesTypeHigh SpeedADCConversionRate50*106 /secHigh Resolution 1*105 /secADCLow PowerADCOctober 29, 20032.5*104 /secWord SizePower8 bit2.5 W16 bit1.5 W8 bit0.005 WMassachusetts Institute ofTechnology25

Telemetry Processing CompressionAnalysis for autonomous systemsFormattingStorageOctober 29, 2003Massachusetts Institute ofTechnology26

Telemetry Formats SynchronizationFrame countSpacecraft identificationEDACFrame format identificationSpacecraft timeOctober 29, 2003Massachusetts Institute ofTechnology27

Multiplexing Frequency division multiple access Time division multiple access Code division multiple accessOctober 29, 2003Massachusetts Institute ofTechnology28

Commutation in Data FormatsData typeno. 1 bitsType no. 2 bitsType Type Type no. 5no. 3 no. 4 bitsbitsbitsType no. 6 bitsTypeno. 7bits Commutation – sequential data timesampling– Data includes major and minor frameidentification and EDAC Sub-commutated data – given elementrepresents different data in different frames Super-commutated data – given element isfoundonceInstituteperofframeOctober29, 2003 more thanMassachusetts29Technology

Telemetry and Command SystemBlock DiagramOctober 29, 2003Massachusetts Institute ofTechnology30

Command Decoder BlockDiagramOctober 29, 2003Massachusetts Institute ofTechnology31

Data Handling Unit BlockDiagramOctober 29, 2003Massachusetts Institute ofTechnology32

Command and Data HandlingConcerns Interfaces to other subsystems must protectthe command decoder No commands or transient signals mayappear on command outputs duringapplication or removal of prime power orduring under/over voltage conditions If a commands integrity is in doubt, reject itOctober 29, 2003Massachusetts Institute ofTechnology33

Command and Data HandlingConcerns (continued) Multiple commands are required for critical/dangerous operations No single component failure can result inunintended operation No commands shall interrupt the uplinksource to the command decoderOctober 29, 2003Massachusetts Institute ofTechnology34

References Pisacane, Vincent L. and Robert C. Moore,Fundamentals of Space Systems, OxfordUniversity Press, New York, 1994 Wertz, James R. and Wiley J. Larson, SpaceMission Analysis and Design, Third edition,Microcosm Press, Torrance Ca, 1999October 29, 2003Massachusetts Institute ofTechnology35

Satellite Telemetry, Tracking and Control Subsystems Col John E. Keesee . Frequency link Modulation. Command Decoders Detects PCM encoding and outputs binary . Mission Analysis and Design, Third edition, Microcosm Press, Torrance Ca, 1999 October 29, 2003 Massachusetts Institute of