Telemetry, Tracking, Communications, Command And Data Handling

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Telemetry, Tracking, Communications, Commandand Data HandlingCengiz AkinliMatthew GamacheMatthew RoseAndrew RostJames SalesJames TangNovember 18, 2004

ContentsList of FiguresiiList of Tablesiii1 Introduction1.1 Communications . . . . . . . . . . . . . . . . . . . .1.1.1 Receiver and Transmitter Selection . . . . . .1.1.2 Antenna Selection . . . . . . . . . . . . . . . .1.1.3 Frequency Selection . . . . . . . . . . . . . . .1.1.4 Link Budget . . . . . . . . . . . . . . . . . . .1.2 Telemetry, Computer, Command and Data Handling1.2.1 Computer States and State Diagrams . . . . .1.2.2 Interface Design and Architecture Selection .1.2.3 Software . . . . . . . . . . . . . . . . . . . . .1.2.4 Flow Diagrams . . . . . . . . . . . . . . . . .1.2.5 Operating Budget Considerations . . . . . . .1.2.6 Modeling and Analysis . . . . . . . . . . . . .1.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . .12245788810111112142 Modeling and Analysis2.1 Communications . . . . . . . . . . . . . . . . . . . . .2.1.1 Effect of Other Subsystems on Communications2.1.2 Communication System Modeling . . . . . . . .2.1.3 Sizing of Communications System . . . . . . . .2.1.4 Interactions of Subsystems . . . . . . . . . . . .2.2 Spacecraft Command System . . . . . . . . . . . . . .2.2.1 Receiver/Demodulator . . . . . . . . . . . . . .2.2.2 Command Decoder . . . . . . . . . . . . . . . .2.2.3 Command Logic and Handling . . . . . . . . . .2.2.4 Interface Circuitry . . . . . . . . . . . . . . . .2.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . .1515161623242425252932331

3 Examples3.1 Communications . . . . . . . . . . . . . . . . .3.1.1 Communications Components . . . . . .3.1.2 Link Budget Examples . . . . . . . . . .3.2 Command Handling and Execution . . . . . . .3.3 System Hardware . . . . . . . . . . . . . . . . .3.3.1 PC104 . . . . . . . . . . . . . . . . . . .3.3.2 Radiation-Hardened Computer Systems .3.3.3 Conclusion . . . . . . . . . . . . . . . . .3.4 Demodulation and Amplification . . . . . . . .3.4.1 Low- and High- Pass Filters . . . . . . .3.4.2 Band-pass Filters . . . . . . . . . . . . .3.4.3 Band-reject Filters . . . . . . . . . . . .3.4.4 Superheterodyne Filters . . . . . . . . .3.4.5 Mechanical Filters . . . . . . . . . . . .3.4.6 Conclusion . . . . . . . . . . . . . . . . .3.5 Conclusion . . . . . . . . . . . . . . . . . . . . .4 Summary and Conclusions4.1 Communications . . . . . . . . . . . . . . . .4.1.1 Summary . . . . . . . . . . . . . . . .4.1.2 Future Research . . . . . . . . . . . . .4.1.3 Conclusion . . . . . . . . . . . . . . . .4.2 Command and Data Handling . . . . . . . . .4.2.1 Reliability and Robustness . . . . . . .4.2.2 Security . . . . . . . . . . . . . . . . .4.2.3 Other Issues . . . . . . . . . . . . . . .4.2.4 Existing Systems . . . . . . . . . . . .4.2.5 Future Research . . . . . . . . . . . . .4.3 System Hardware . . . . . . . . . . . . . . . .4.3.1 Architecture Selection . . . . . . . . .4.3.2 Interface Circuitry . . . . . . . . . . .4.3.3 Commercial Off The Shelf Computers .4.3.4 Future Research and Recommendations4.3.5 Conclusion . . . . . . . . . . . . . . . .4.4 Conclusion . . . . . . . . . . . . . . . . . . . 5353545454555556565757Bibliography59A Tables60i

List of Figures1.11.2Typical State Diagram for Onboard Computer System[7] . . . . . . .Data-Flow Diagram[7] . . . . . . . . . . . . . . . . . . . . . . . . . .9122.12.22.32.42.52.6Complete Command System . . . .Spacecraft Command System . . .Superheterodyne Receiver DiagramCommand Decoder Block DiagramRedundant Decoders and ReceiversCommand Validation and Handling.1525262728303.13.23.3The ObjectAgent agent communication model[14] . . . . . . . . . . .The ObjectAgent architecture model[14] . . . . . . . . . . . . . . . .The SuperMOCA control system operates over a communications stackof which SMS is an integral part.[5] . . . . . . . . . . . . . . . . . . .The five basic elements of SuperMOCA.[5] . . . . . . . . . . . . . . .PC104 Form Factor Sizes[3] . . . . . . . . . . . . . . . . . . . . . . .Typical Low-Pass Filter . . . . . . . . . . . . . . . . . . . . . . . . .Typical High-Pass Filter . . . . . . . . . . . . . . . . . . . . . . . . .Typical Band-Pass Filter . . . . . . . . . . . . . . . . . . . . . . . . .40413.43.53.63.73.8ii.424244464647

List of Tables1.1Limitations of Frequency Band[7] . . . . . . . . . . . . . . . . . . . .62.12.22.3Rain Attenuation Models [10] . . . . . . . . . . . . . . . . . . . . . .Command Output Types . . . . . . . . . . . . . . . . . . . . . . . . .Typical Pf s values for a 32-bit Barker word . . . . . . . . . . . . . . .2128293.13.23.33.43.5ERA Technology and Integrated Systems Antennas[13]Saab Ericsson Space Reflector Antennas[11] . . . . . .R. A. Mayes Company Wave-Guide Antennas[8] . . . .Maxwell SCS750P Specifications[12] . . . . . . . . . . .Ranges for several types of RF filters . . . . . . . . . forforforforC-Band inX-Band inC-Band inX-Band iniiiRain [10] . . .Rain [10] . . .Clear Air [10]Clear Air [10].

CICSIEEEITUITOSISAISSAtmospheric AbsorbtionAnalog to Digital ConverterAttitude Determination and Control SystemAir Force Research LaboratoriesArtificial IntelligenceAntenna Misalignment LossAmplitude ModulationAdvanced Technology XCompromise BandCommunications, Command and Data HandlingCarrier to Noise RatioCommand and Data HandlingCommand Logic ControllerCommercial, Off-the-ShelfDecibelDisk Operating SystemError Correction CodeEquivalent Isotropic Radiated PowerElectrically Erasable Programmable Read-Only MemoryExtremely High FrequencyFederal Communications CommissionFrequency ModulationFree-Space Spreading LossGeo-Stationary Earth OrbitGlobal Positioning SatelliteHigh Power AmplifierIntegrated CircuitInterface and Control SystemsInstitute of Electrical and Electronics EngineersInternational Telecommunications UnionIntegrate Test and Operations SystemIndustry Standard ArchitectureInternational Space Stationiv

erMOCAJet Propulsion LaboratoryKurz-bandKurz-above BandKurz-under BandLong BandLow Earth OrbitLow Noise AmplifiersMilliAmpsMegabyte(s)Mini Advanced Technology XMillions of instructions Per SecondManufacturing Message SpecificationMilliSecondsMedium Earth OrbitMicrovariability and Oscillations of STarsNational Aeronautics and Space AdministrationNon-Return to ZeroOn Board ComputerOperating SystemPersonal ComputerPeripheral Component InterconnectPulse Code ModulationPolarization Mismatch LossPhase ModulationRandom Access MemoryRead Only MemoryRadio FrequencyShort BandSingle Board ComputerSpacecraft Command LanguageSingle Event UpsetSynchronous Dynamic Random Access MemorySuper High FrequencySilicon on InsulatorState of the ArtSpace Ground Link SubsystemSignal to Noise RatioSpace Physics Research GroupSolid State AmplifierSpace Tracking and Data NetworkSpacecraft Test and Operations LanguageSpace Project Mission Operations Control Architecturev

TWTAUHFUSAPVHFWARCX-BandTraveling Wave Tube AmplifierUltra High FrequencyUnited States Antarctic ProgramVery High FrequencyWorld Administrative Radio ConferenceSpot Bandvi

LaLantLF RXLF T XLmLpmnN0N0,outN0,inAperture EfficiencyOperating WavelengthSaturation Flux DensityPiTotal AttenuationAtmospheric Attenuation in Clear SkyAtmospheric Attenuation due to RainEffective Area for an Isotropic AntennaArea of the Antenna ApertureBandwidth SignalSpecified BackoffNoise BandwidthSpeed of LightDownlinkDistant From Satellite to Ground StationNoise FactorOperating FrequencyAvailable Power GainReceiver Antenna GainSatellite Antenna GainBoltzmann’s ConstantClean Air Atmospheric LossEdge of Beam Loss for Satellite AntennasFeeder Loss between Receiver and AntennaFeeder LossOther Random LossesFree Space Path LossSize of Data Frame in BitsLength of the Synch Word in BitsNoise Power Spectral DensityOutput NoiseInput Noisevii

Pf s PnrainPnrainPNPRPrainPRXPTPT XRrT0TaTantTCSTeTNTrainTsTskyUProbability of False SynchronizationIncrease in Noise Temperature due to RainReceiver Noise Power in RainNoise PowerReceived PowerReceived Power at Earth Station in RainSignal Power at Input of ReceiverAntenna PowerPower OutputRain RateRadiusRoom TemperatureApparent Absorbed TemperatureAntenna TemperatureClear Sky TemperatureEquivalent Noise TemperatureEquivalent Noise BandwidthEffective Noise Temperature of RainSystem Noise TemperatureTotal Sky Noise TemperatureUplinkviii

Chapter 1IntroductionThe basic function of all but the simplest spacecraft requires extensive contact withground stations for control, command, communication, and data return, and sufficientcomputer processing power to run all spacecraft subsystems with, in many cases, ahigh degree of autonomy.A spacecraft communication system handles all data sent and received by thespacecraft, including spacecraft bus commands, and payload operations. The systemincorporates a transmitter and a receiver that are the sole point of passage for dataentering or leaving the spacecraft. Thus payload and bus operations data are bothhandled by this system.The driving concerns in the design and implementation of spacecraft communications systems are access, radio frequency selection, and data characteristics. Inconsidering communication access, the selection of ground station location, visibility windows for those candidate locations for a given spacecraft orbit, and antennaand transmitter power selection are key concerns. In selecting the radio frequency,issues such as the transmitter power and receiver sensitivity requirements for givenfrequencies and the power required to overcome atmospheric conditions must be considered. Additionally, permission to use a particular frequency must be applied forand granted by the appropriate regulatory agency. Finally, antenna and transmitterpower required to attain the bandwidth and maximum error level allowed by thecharacteristics of the data to be communicated are determined.The command and data handling system (C&DH) receives all commands anddata for both bus and payload operations from the communications system. Theintegration of payload data with bus data into the data stream bound for the communications system and the disintegration of the incoming data stream into individualdata streams bound for the bus and payload are the primary roles of the C&DH system. The final major function is the handling of bus commands by directing themto the appropriate subsystem or executing them directly. The handling of payloadcommands would generally not be done by the C&DH system, but would instead bepassed, fully encapsulated, directly to the payload.1

In selecting, or more usually, designing a command and data handling system, concerns vary somewhat based on the spacecraft payload. Science payloads may makeextensive use of C&DH subsystems in terms of high bandwidth data streams andeven data storage and computation. Payloads often require continuous communication with ground stations, precise attitude control, and other services which togethernecessitate a close interoperation of C&DH systems with the payload. Selection is apredominately linear process, requiring the advance preparation of commands to beexecuted by the bus and payload, telemetry to be sent and received by all spacecraftsubsystems, determination of time criticality of subsystem functions, and finally determining the parameters of a system that will address all of these issues satisfactorily.In CC&DH, there are two major functional divisions. The communication subsystem controls the data transfer between the spacecraft and a station on Earth. TheC&DH subsystem covers the control of data flow internally as well as the disassemblyof commands to individual sections of the spacecraft. The C&DH subsystem directsthe rest of the spacecraft in how to accomplish the mission. Both of these combinedencompass the whole of the CC&DH system.1.1CommunicationsThe communications subsystem is an important aspect to consider in the designof satellites. The communications subsystem deals with the data transfer from thesatellite to a ground station on Earth. This transfer can be made either by linkingthrough radio waves to a ground station directly or by linking to other satellites andthen finally to a ground station on Earth. The main types of data that are transferredbetween the satellite and the ground station are the updated command controls for thespacecraft, the collected mission data from the spacecraft and the operational healthstatus of the spacecraft. The main components in the communications subsystem arethe receivers, transmitters, and antennas. The systems in place in the communicationssystems are set up to be redundant. Redundancy is needed on satellites becausesystem failure makes the satellite ineffective.1.1.1Receiver and Transmitter SelectionThe size, type and gain of the receiver, transmitters and antennas used depend mainlyon the type of mission the spacecraft is designed to accomplish. There are two maintypes of missions dealing with communications: near Earth communication and longrange data relay. The receivers and transmitters consist of several parts. The keycomponents in receivers and transmitters are amplifiers, filters and demodulators.The amplifiers and filters are combined into a single unit.2

TransponderA transponder consists of several parts. These parts include a band-pass filter, adown converter, and an output amplifier. The band-pass filter is used to select theparticular channel’s band of frequencies. The down converter is used to change thefrequency from 6 GHz at the input to 4 GHz at the output. Most communicationsystems have multiple transponders, usually 12 to 44 for a high-capacity satellite.The main bandwidths for the transponders are 36, 54, and 72 MHz. These narrowbandwidths are used in order to avoid intermodulation.AmplifierThe signal that is received by the satellite’s antenna is passed through two low noiseamplifiers (LNA) and is recombined at the output. The use of two LNA is neededto provide redundancy. The low noise amplifiers are used in order to minimize theaddition of noise to the incoming signal.The signals that are sent from a satellite require amplification in order to producea signal that can be received from Earth. Typically, the output power amplifierthat is used is a solid state amplifier (SSPA). If the satellite requires a high poweroutput, a traveling wave tube amplifier (TWTA) is used. Redundancy in the highpower amplifiers (HPA) is provided by including a backup TWTA or SSPA thatwill be activated in case of the primary’s failure. The least reliable part of anytransponder is the HPA. This reliability issue is resolved by providing a spare HPAin each transponder.ModulationThe signal that is received is modulated in order to obtain several goals. These goalsinclude obtaining the required data rate, fitting the signal into the available radiofrequency (RF) bandwidth, and obtaining the required signal to noise ratio (SNR).There are several types of modulation that may be used. These types of modulations include amplitude modulation (AM), phase modulation (PM), and frequencymodulation (FM).The type of modulation that is performed on the signal is determined by thedesired output. Amplitude modulation requires a higher SNR to attain a high performance but the performance degrades slowly as the SNR is reduced. The FM andPM degrade quickly as the SNR is decreased but can operate at lower RF SNR thanAM.The modulation is performed on the amplified signals in order to attain the desiredoutput. The modulated signal is then transmitted to the command decoder andprocessor.3

NoiseThe noise of the system is an important aspect of the system to determine. In thecommunications subsystem, the need for a maximized carrier to noise ratio (C/N) isdesired. In order to achieve this goal, the amount of noise present in the system needsto be minimized. This minimization is needed because of the weak carrier signalsinvolved. A method of dealing with noise minimization is to allow only the desiredbandwidth to pass through the filter. This process of filtering all the bandwidthsblocks excess signals that may be a source of noise.The performance of the receiving system is determined by comparing the totalthermal noise power against the signal demodulation. Thermal noise is produced byevery active and passive device involved in the communications system. The goalis to minimize the addition of noise from the satellite’s components. An additionalsource of noise to the signal is the atmospheric conditions that the carrier signal hasto travel through. The noises encountered throughout the system are simplified toa single term, the system noise temperature (Ts). Losses occur in the connectionbetween the antenna and receiver. These losses are part of the feeder loss. Theyoccur in the connecting waveguides, filters, and couplers. Similar losses will occurbetween the antenna and amplifier in the filters, waveguides, and couplers.1.1.2Antenna SelectionThe main goal in antenna selection is determining the proper type and size of antennaneeded. In general, a larger antenna has a better gain and SNR than a smallerantenna. The main constraint on antenna sizing is the weight and power requirements.The main types of antenna are wire, horn, reflector and helical antennas.Wire AntennaWire antennas provide omni-directional coverage that are used primarily duringlaunch and orbit insertion. They are primarily used when the main antenna havenot been deployed or properly positioned. The main frequencies for wire antennasare UHF and VHF.Horn AntennaHorn antennas are used when a wide beam has to be produced for global coverage.The main frequencies that are used with horn antennas are microwave frequencies.The gains that can be obtained from horn antenna are usually less then 23 dB andthe beamwidths are usually larger then 10 degrees.4

Reflector AntennaReflective antennas usually contain at least one horn and provide a larger usable areathen a horn antenna alone. The basic shape of the reflector antenna is a paraboloid.The reflecting shape is based on a three-dimensional parabolic shape. It has a uniqueproperty of directing all incoming wave fronts perpendicular to its axis, in phase, to apoint focus. Reflective antennas are generally made of steel, aluminum, or fiberglasswith an embedded reflective foil.Antenna ArraysAn antenna array is defined as being more than one antenna brought together toaccomplish a task. The antennas in the array will be brought together and drivenfrom a source of power at the same frequency. The resulting antenna pattern is morecomplex. The complexity is due to the interference between the signals transmittedseparately from each of t

1.1 Communications The communications subsystem is an important aspect to consider in the design of satellites. The communications subsystem deals with the data transfer from the satellite to a ground station on Earth. This transfer can be made either by linking through radio waves to a ground station directly or by linking to other satellites and

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