航天器姿态确定和姿态控制课件.docx

航天器姿态确定和姿态控制课件pointthetelescopeDesiredAttitudeActualAttitudedeterminesthedesiredtorques,andsendelectricalcommandsappliesthedesiredtorquestakethemeasurementsEstimatedAttitudeEstimatesthecurrentattitudeACS:SingleSpinTheentirespacecraftspins,whichprovidesinertial3C3PlatformRotorAACAAACS:MomentumBias:ThemomentumbiassatelliteisavariationofthedualspinconceptthatovercomesmomentumusuallyspunbyelectriccontrolledmomentumwheelcomethereforehowmuchangularmomentumofchangesitaboutTwomagnetictorquersinteractACSmethods:ActivePropellantReactionwheelswithSensorsThetypesofsensorsusedforattitudedeterminationare:1.horizonsensors(orconicalEarthscanners),2.sunsensors,3.starsensors,4.magnetometers,5.inertialreferenceunits(IMUorattitudereferenceunitsARU),and6.GPSreceivers.Horizonsensorsmeasurepitchandrolltoanaccuracyofabout0.1-0.5deg.Anaccuracylessthan0.05degcanbeachievedbyextensivecalibrationandaccountingfortheequatorialbulge.Sunandstarsensorsprovidedirections.Anhorizonsensordoesnotprovideyawinformation(formomentumbiassystemsitisnotnecessarytomeasureyaw).Onewide-FOVortwonarrow-FOVstarsensorsareneededtoprovideattitude.SincethestarsensorscannotprovidecontinuousattitudemeasurementsanIMU/ARUisneededtoprovidetheattitudebetweenmeasurements.IMUssufferfromdriftandbiasesandneedfrequentupdateswhichareprovidedbythestarsensors.MagnetometersmeasureEarth'smagnetic.Accuraciesnobetterthan1degcanbeobtained.TheGPSreceiversareusedinaninterferometermodetodetermineattitude.Accuraciesasgoodas0.01degareexpectedusingGPS.PresenceSunSensorsEntranceslitGridslitPhotocellatthebase(belowtheslit)SunraysPhotocellShadowareaShadowrodPresencesunsensorsprovidethcrossingtimeonly,orthesunpresencewithinthesensorFOVUsedtosynchronizepulsedcommand(spin-up,spin-down)tomaneuvretoturnon/offonboardexperimentsinstrumentation.PhotocellsMirrorImageplanemaskSunimageLensAperturePhotocell1Photocell2T()(0)(0)cosIIdnI?=?AnalogicSunSensorsPhotocell#2Photocell#1NormalSunraysNormalPhotocellsMaskReferenceaxisNormalSensor1Sensor2SunraysNormalPhotocellSensor#2Sensor#1Angle(deg)OutputcurrentMeasurementCommandMeasurementommandmmand:sunpresenceMeasurement(4parts):ATA,Signbit,Codebits,Interpolatingbits.DigitalsensorPhotocellsGridslitsBinarycodeGraycodeSunangleBinaryGrayDecimalBinaryGray01101110010111011110001001101001111011011110110011001101111111121314151617181920211011110011011110111110000100011001010011101001010111101010101110011000110001100111011110101111011111Graycodeconsistsofthefactthatthebitstring,whichtheanglemeasure,changesonebitonlyateachdigitalstep.BinaryandGraycodePhotocellsDoubleDigitalSunSensor2Bestrange:14-16ofCO(lesshighaltitudecloudscontr.)Relativeradiance400(IR)and30,000(visible)allowtoevaluatetheNadirdirection.HotMoonHardhorizonHotareaforcoldMoonHotareaforhotMoonColdMoonHothorizonpositionColdhorizonpositionMooncenterdistanceRelativeradianceMoonhorizonsensorMoontemperaturerange:240degto+30degMeridianslitInclinedslitSatelliteequatorDisplacementangle(deg)Earth/SunsensorsforspinningS/CStarsensorforspinningS/COpticalaxisElevationslitAzimuthslit文档视界航天器姿态确定和姿态控制课件航天器姿态确定和姿态控制课件FocalPlaneArcheopsKiruna2002StarTrackersElectronicsPhotomultiplierOpticalsystemBaffleStarGridSensorsElectronicunitSignalprocessingandAnalogtodigitalconverterTelemetryLinkSmallprecisionisassociatedwiththefactthattheEMFModelsarenotsoaccurate.Biasesnotnegligeable(residualsofmagneticfieldscausedbyonboardcircuits)TypicalGN&CSensors(Wertz)AttitudeDeterminationSystems