ka-band pn delta-dor€¦ · •∆dor complements line-of-sight range and doppler measurements...
TRANSCRIPT
WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
Ka-BandPNDelta-DORJamesS.Border
JetPropulsionLaboratoryCaliforniaInstituteofTechnology
WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationHostedbySpaceCommunicationsandNavigation(SCaN)/HEOMD
Thursday,February16,2017 9:30a.m.– 6:00p.m.NASAHQAuditorium(westlobby)
WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology DeltaDifferentialOne-wayRanging
2/16/2017 2
• ∆DOR complements line-of-sight range and Doppler measurements
• ∆DOR uses interferometry to directly measure spacecraft angular position in the radio reference frame
• Accuracy has improved from 150 nradin 1981 to 2 nrad today
• Many missions have used / will use ∆DOR
• Primary use is to improve targeting in plane-of-sky coordinates for encounters and other critical events• 2 nrad is 300 m plane-of-sky position
accuracy at Mars encounter distance• Observations from 2 (long) baselines
are needed to measure both components of angular position
τ
CorrelatorBaseline B
θ
τ= B⋅cos(θ) /c
spacecraft d
elay τ
WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology Delta-DORandTechnologyDevelopment
• Delta-DORhasimprovedovertheyearsby:– Identifyinglimitingerrorsources– Technologyinvestmentstoreducekeyerrors
• Nextchartshowsimprovementsdueto:– SpacecrafttransponderswithwiderbandwidthDORtones– Improvedgroundstationopenloopreceivers– Higherbandwidthdatarecording– Bettermediacalibrations– Betterradiosourcecatalogandreferenceframe– Moresophisticatedobservingsequence
• Thispresentation:Wherewillthenextimprovementscomefrom?
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WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology ∆DORAccuracyImprovements
4
1
10
100
1979 1984 1989 1994 1999 2004 2009 2014
Delta
-DO
R M
easu
rem
ent A
ccur
acy,
nra
d
Year
Mars Reconnaissance Orbiter: higher recording rate,faster switching between spacecraft and quasar MSL
Maven
Mars Odyssey: RSR, higher recording rate,GPS-based calibrations
Magellan: X-band, 30 MHz Mars Observer: X-band, 38 MHz
Galileo: NCB, S-band, 8 MHz
Voyager: MK II/NCB, X-band, 3-7 MHz
Phoenix: WVSR
Mars Exploration Rover: VSR, improved referenceframe models, more quasar observations
2/16/2017
WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology CurrentDelta-DORErrorBudget(X-Band)
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2nrad
WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology DispersivePhase:TheDominantError
• Dispersivephaseisthenon-linearphaseshiftingroundstationelectroniccomponentsthatisnotcommontothespacecraftandquasarsignal,duetodifferentspectraldistributions– Thiscomponentoftheerrorbudgethasnotchangedverymuch– Todaythiserrortermstandsinthewayofasignificantimprovementin∆DORaccuracy
• Withthecurrentspacecrafttransponderdesign,DORtonesaregeneratedbymodulatinga~19MHzsinewaveontothedownlinkcarrier• Thequasarspectrumandthespacecraftspectrumarequitedifferent– Seenextchart
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WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
ComparisonofSignalSpectrain8MHzChannelofOpenLoopReceiver
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Quasarsignalburiedinnoisechannel
DORtoneinnoisechannel
TheoreticalPNcodespectrumwithshaping(nonoise)
WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology ProposedPseudoNoise(PN)DORSignals
• ThesinusoidalDORtoneismultipliedbyaPNsequencebeforemodulatingthedownlinkcarrier– AsuitablePNsequencecouldbegeneratedwithalinearfeedbackshiftregister(LFSR)
§ AgoldcodeorothercodesusedforCDMAapplicationscouldbeused– Thechiprateischosentofillthebandwidthofinterest
§ 4Mchip/scouldbeusedtofillan8MHzbasebandchannel– TheDORsignalcouldbeshapedbyafiltersuchasasquare-rootraisedcosinefilterto
flattenthespectrum– Alongcodesequencecouldbechosentohelpresolvetheambiguitywithinasingle
channelandreducespacingbetweencodepeaks• APNsignalfillingafrequencychannelwouldmorecloselyresemblequasarwhitenoise• Thiswillprovidefornearcancellationofthephasedispersionerrorbetweenspacecraft
andquasarrecordings• ImplementationofthePNDORsignalshouldbestraightforwardindigitaltransmitters
• UseofspreadspectrumfortheDORsignalwilllessenthepossibilityofradiointerferencebetweentheDORsignalofonespacecraftandthecarriersignalofanotherangularlynearbyspacecraft
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WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology Ka-BandDownlinks
• Spacecrafttransmittedbandwidthcanbeincreasedtotakeadvantageofwiderspectrumallocationforspaceresearch– Allocationis50MHzatX-bandand500MHzatKa-Band
• Quasarcoordinateerrorisreducedsinceradiosourcestendtohavesmallercoresandlessstructureathigherfrequencies– Continuedradiosourcecatalogdevelopmentisnecessary
• Chargedparticleerrorsarereducedbyafactorof15relativetoX-Band
92/16/2017
WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology FurtherAccuracyImprovements- 1
• WithPNDOR– Dispersivephaseissignificantlyreduced– Channelbandwidthcanbeincreasedwithoutmakingdispersivephaseworse– Increasedchannelbandwidthreduceserrorduetoquasarthermalnoise
• WithKa-Band– Spacecrafttransmittedbandwidthcanbeincreasedtotakeadvantageofwider
spectrumallocationforspaceresearch– Quasarcoordinateerrorisreducedsincesourcestendtohavesmallercoresand
lessstructureathigherfrequencies– Chargedparticleerrorsarereducedbyafactorof15relativetoX-Band– Bettertropospherecalibrationistechnicallypossible
§ Whentropospherestandsasthedominanterror,andifbetter∆DORaccuracyisrequired,thentherewillbewaystoaddressthisissue
102/16/2017
WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology FurtherAccuracyImprovements- 2
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ReducedbyPN
ReducedbyKa-Band
ReducedbyKa-Band
ReducedbyKa-Band
ReducedbyPNandKa-Band
???
ExistingErrorBudget TechniquetoImproveAccuracy
WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology
NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology Conclusions
• PNDORisnecessarytoreducewhatisnowthedominant∆DORmeasurementerror
• ItshouldbestraightforwardtoimplementPNDORindigitaltransmitters
• Ka-Bandallowsadditionalimprovementstoallremaininglargeerrorcomponents,exceptfortroposphere
• Whentropospherestandsaloneasthedominanterror,andifbetter∆DORaccuracyisrequired,thentherewillbewaystoaddressthisissue
122/16/2017