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

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• ∆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

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WorkshoponEmergingTechnologiesforAutonomousSpaceNavigationNationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology

NationalAeronauticsandSpaceAdministrationJetPropulsionLaboratoryCaliforniaInstituteofTechnology FurtherAccuracyImprovements- 1

• WithPNDOR– Dispersivephaseissignificantlyreduced– Channelbandwidthcanbeincreasedwithoutmakingdispersivephaseworse– Increasedchannelbandwidthreduceserrorduetoquasarthermalnoise

• WithKa-Band– Spacecrafttransmittedbandwidthcanbeincreasedtotakeadvantageofwider

spectrumallocationforspaceresearch– Quasarcoordinateerrorisreducedsincesourcestendtohavesmallercoresand

lessstructureathigherfrequencies– Chargedparticleerrorsarereducedbyafactorof15relativetoX-Band– Bettertropospherecalibrationistechnicallypossible

§ Whentropospherestandsasthedominanterror,andifbetter∆DORaccuracyisrequired,thentherewillbewaystoaddressthisissue

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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

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