IonVelocityMeasurementsfortheIonosphericConnectionsExplorer
R.A.Heelis,R.A.Stoneback,M.D.Perdue,M.P.Depew,Z.A.Morgan,M.D.Mankey,C.R.
Lippincott,L.L.HarmonandB.J.Holt.
WilliamB.HansonCenterforSpaceSciences
PhysicsDepartment,UniversityofTexasatDallas,Richardson,TX.
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Abstract
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TheIonosphericConnectionsExplorer(ICON)payloadincludesanIonvelocity
Meter(IVM)toprovidemeasurementsoftheiondriftmotions,density,temperature
andamajorioncomposition.TheIVMwillderivetheseparametersutilizingtwo
sensors,aretardingpotentialanalyzer(RPA)andaniondriftmeter(IDM)thathave
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arobustandsuccessfulflightheritage.TheIVMdescribedhereincorporatesthe
mostsensitivedevicethathasbeenfieldedtodate.Itwillbeusedinconjunction
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withmeasurementsfromtheotherICONinstrumentstouncovertheimportant
connectionsbetweenthedynamicsoftheneutralatmosphereandtheionosphere
throughthegenerationofdynamocurrentsperpendiculartothemagneticfieldand
collisionalforcesparalleltothemagneticfield.Heretheconfigurationand
operationoftheinstrumentisdescribedaswellasadescriptionofthedatathatitis
expectedtoreturn.
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1.Introduction
TheIonosphericConnectionsExplorer(ICON)missionispoisedtodiscover
fundamentalconnectionsbetweenthedynamicsoftheneutralatmosphereat
altitudesbetween100kmand300kmandthechargedparticlemotion,whichis
tiedtothemagneticfieldthatthreadstheentireregion.Acomprehensive
descriptionofthelinksbetweenthechargedandneutralspecieswillberevealed
withauniquecombinationofremotemeasurementsoftheplasmaandneutral
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densityandtheneutralwindsandin-situmeasurementsoftheplasmadensityand
plasmadrift.In-situdeterminationoftheplasmadensityandplasmadriftaremade
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byanIonVelocityMeter(IVM),aplanardetectorthatmeasurestheenergyandthe
angleofarrivalofthethermalionsthatmovesupersonicallywithrespecttothe
spacecraft.Instruments,utilizingthistechniquehavebeensuccessfullydeployedon
manysciencemissionsbeginningwithOGO6[Hansonetal.1970]andcontinuing
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throughtheeraofAtmosphereExplorer[Hansonetal.,1973],DynamicsExplorer
[Hansonetal,1981;Heelisetal.1981],theDefenseMeteorologicalSatellite
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ProgramandROCSAT[Leetal.,2003]andtheCoupledIonNeutralDynamics
Investigation[Heelisetal.,2009].
FortheICONmissionthisflight-provenapproachisfurtherdevelopedand
combinedwithstate-of-the-artdesigninanaloganddigitalelectronicstoproducea
robustandsensitivedevicethatmeetstherigorousmeasurementrequirementsof
themission.TheprinciplesofoperationoftheIVMsensorshavebeenpreviously
described[HeelisandHanson1975;1998]butarereviewedhereinthecontextof
theICONmeasurementrequirementsinadditiontothespecificinstrument
2
performancedetailsandthegeophysicalparametersthatwilldeliveredbythe
instrument.
2.IVMMechanicalConfiguration
Figure1hasthreepanelsshowingaphotographoftheflightIVMsensorand
isometricprojectionsthatdetailthemajormechanicalsystems.TheICONIVM
consistsoftwoplanarsensors.Aretardingpotentialanalyzer(RPA)andaniondrift
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meter(IDM)aremountedtoviewapproximatelyalongthespacecraftvelocity
vectorandareoptimallyconfiguredtoaccomplishtheseparatefunctionsof
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constituentionenergydeterminationandionarrivalanglerespectively.The
sensorsareattachedtoabaseplatetowhichtheelectronicscompartmentisaffixed
attherear.Therearcoverisattachedtoaflexuremountthatprovidesamechanical
interfacetothespacecraftpayloadinterfaceplate(PIP).Therearcoveralso
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containspassiveradiatorsurfaces.Inlowearthorbitthespacecraftvelocityin
excessof7kms-1providestheconstituentionswithmassdependentramenergies
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1 mV 2 ,ofabout0.3eV/amuandthermalenergywidths mV V ,ofabout0.1
s th
2 s
eV/amuwithrespecttothesensor.Inordertominimizetheeffectsofthesensors
themselvesontheplasma,itisimportantthatthelocalelectrostaticenvironment
presentsmallandplanarpotentialsparalleltotheinstrumentapertureplanesothat
theionarrivalangleandenergydistributionaremodifiedinapredictablewayby
electricfieldsthatareparalleltothesensorlookdirection.Aplanarconducting
apertureplane,whichsurroundstheinstrumentapertures,isutilizedtoaccomplish
thistask.Itisattachedtothesensorsfromthefrontandalsoprovideskeyradiative
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surfacestodissipateinstrumentandsolarheatinputs.Optimumsensitivityto
arrivalangleandincidentenergyisalsoobtainedifthesensorgroundreferenceis
maintainedneartheplasmapotential.Thespacecraftreferencegroundwith
respecttotheplasmaisdependentontheconductingpropertiesofthespacecraft
exposedsurfacesandtoexposedpotentialsthatmaybepartofthesolarpower
system.Whilebestpracticesareemployedtomaintainagroundreferencecloseto
theplasmapotential,theIVMsensorsareelectricallyisolatedfromthespacecraftto
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provideanindependentgroundreferencethatisestablishedbyasectionofthe
apertureplanecalledthe“SenPot”surface,whichismaintainedatthefloating
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potential.Figure2showsschematiccross-sectionsoftheRPAandIDMsensors.
Eachisconstructedsimilarlyconsistingofagriddedapertureplaneandaseriesof
internalplanargridsthatarepreciselypositionedusingceramicspacerstomaintain
parallelpotentialplanesthatarebiasedtoprovidetheappropriatefunctionality.In
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bothsensorsthewovengridsare0.001”diametergold-platedtungstenwirewitha
densityof50/inchor100/inch.Theeffectiveareaforioncurrentcollectionis
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thereforecorrectedfortheopticaltransparencyofthegridstack.
TheRPApresentsagriddedcircularentranceapertureG1,tiedtothesensorground
andasolidcollectoratwhichtheionfluxismeasuredasacurrent.Referringto
figure2,gridG2isadoubleretardinggridthatissteppedthroughaseriesof
positivepotentialstocontroltheenergyofincomingionsthathaveaccesstothe
collector.GridG3isnegativelybiasedwithrespecttothesensorgroundtoreject
thermalelectronsincidentonthegridandtosuppressphotoelectronsthatare
producedfromthecollector.
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TheIDMpresentsasquareaperturetotheincomingplasma.ThegridsG3and
G4/G5aregrounded,providingafield-freeregionthroughwhichthesupersonic
ionsflowbeforeforminganimageoftheapertureonasegmentedcollector.The
gridG6servestorejectthermalelectronsandsuppressphotoemissionfromthe
collectorsurfaces.Thecollectorisdividedintofourquadrantswiththedividing
linesparalleltotheapertureedgesallowingcurrentstocollectorhalvestobe
measuredalongtwomutuallyperpendicularaxes.
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ThegridG1formsagroundedplaneacrosstheaperturewhilearepellergridG2
precedesthesquareentranceapertureoftheIDM.Thisgridservestorejectthe
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admissionofH+ionsthatmayhavethermalspeedsthatarecomparabletothe
spacecraftvelocity.Insuchacircumstance,thermalspreadingofthebeambeyond
theinstrumentapertureproducesasensitivitytoanglethatisdifferentfromthatof
theheavierions.Theremovalofthissignalallowsthearrivalangleassociatedwith
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thebulkflowofallthespeciestobedeterminedfromthesignaldominatedbythe
heavysupersonicO+ions.
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3.PrinciplesofOperation
3.1RetardingPotentialAnalyzer(RPA)
TheRPAviewsapproximatelyalongthespacecraftvelocityvectorandhasasmall
entranceaperturecomparedtothecollectorsize.Withintheinstrumentaretarding
gridissteppedthroughasequenceofpotentials,whichdeterminetheenergyofthe
incomingionsthathaveaccesstothecollector.Theexpectedrangeintheangleof
arrivaloftheionsissmall(<5°)comparedtotheangularacceptanceofthe
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instrumentandthusthecurrentcollectedmaybesimplyobtainedbyintegratingthe
one-dimensionalflowingMaxwelliandistributionfunctionalongtheinstrument
lookdirectionfrominfinitytothevelocityoftheionsthatwillbestoppedbythe
potentialonthegridasseenbytheplasma.Thecurrentforasingleionspeciesof
massmandnumberdensity N i isgivenby
I (φ ) = qAeff
⎤
Ni ⎡
1
Vr ⎢1+ erf ( β f ) +
exp ( − β 2 f 2 ) ⎥ 2 ⎣
π βVr
⎦
where Aeff istheeffectiveareaofthecollector, f = Vr − ( 2qφ m ) ,withqthe
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electroncharge,representstheaveragevelocityoftheionsthathaveaccesstothe
collectorand β = ( m 2kTi ) ,isthereciprocalofthethermalvelocityoftheions.
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12
! !
Here, Vr = Vd + Vs ⋅ n̂ isthetotalvelocityoftheionsgivenbythesumoftheambient
(
)
!
!
iondrift Vd andthespacecraftvelocity Vs and n̂ istheunitvectoralongthesensor
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lookdirection. φ = Rv + ψ s ,isthepotentialonthegridasseenbytheplasmaandis
thusthesumoftheretardingpotential Rv withrespecttothesensorgroundandthe
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sensorgroundpotentialwithrespecttotheplasma ψ s .Themeasuredcurrentwill
bethesumofcurrentsforallconstituentionsthatarepresent.Thecurrentatzero
retardingpotentialprovidesthetotalplasmanumberdensityandaleastsquares
fittingprocedure,appliedtothenormalizedcurrent-voltagecharacteristic,yieldsa
commontemperature,abulkflowvelocityfortheionsandthefractionalpopulation
ofthemajorconstituentions.Inaddition,thesensorplanepotentialwithrespectto
theplasmaisalsoretrieved.Correctionstoaccountforthelackofperfectpotential
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planesproducedbywiregridsarealsoincludedinthefittingprocedure[Stoneback
etal.,2016].
Figure3showstypicalcurrentvoltagecharacteristicsobtainedfromtheRPAaboard
theCommunicationNavigationOutageForecastSystem(C/NOFS)satellite.Ineach
paneltheopensymbolsdenotetheretrieveddataandthesolidlinerepresentsthe
resultofthefittingprocedurewiththeresultsshowntotherightofthecurrentvoltagecharacteristicineachpanel.InpanelAisdatatakennear650kmaltitude
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and05:25localtimeindicatingthepresenceofasmallfractionalpopulationofH+in
additiontothemajorion,O+.NotethattheI-Vcharacteristicrepresentstheintegral
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contributionfromallspeciesthatarepresentandthemajorspeciesare
distinguishedbythedifferencesintheirramenergyasmentionedpreviously.A
simpleexaminationoftherelativevaluesoftheioncurrentnearzerovoltsand3
voltscantherefordetectthepresenceoflightionspeciesandthusindicatethe
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massesthatneedtobeconsideredintheleastsquaresanalysisprocedure.
InpanelBisshowntheI-Vcharacteristictakennear500kmaltitudeand14:30local
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timewhereO+istheonlyionpresent.
3.2IonDriftMeter(IDM)
TheIDMalsoviewsapproximatelyalongthespacecraftvelocityvectorandusesa
simplegeometricrelationshipbetweenthearrivalangleoftheincomingionbeam
andtheareailluminated,andthusthecurrentcollected,atthecollectorsegments.
Figure4showsaschematicrepresentationoftheionbeam(inred)andits
displacementalongoneaxisalignedwithanapertureedgewithinthefield-free
regionofthesensor.Thecollectorquadrantdividinglinesandapertureedgesare
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alignedwiththelocalhorizontalandthelocalverticalsothatbyappropriately
configuringcollectorhalves,thearrivalangleineachoftheseplanescontainingthe
unitvectors ĥ and ẑ respectively,canbemeasured.Theratioofthecollector
currents,whichareeachproportionaltotheareailluminated,aregivenintermsof
thesensordimensionsandthearrivalangleby
I1 W 2 + D tan α
.Thusby
=
I 2 W − D tan α
2
measuringthecurrentratiowemaydeterminetheionarrivalangle.The
1
! !
2
2q
ψ
2
⎤
⎡
s
correspondingtransversedriftvelocityisgivenby Vd + Vs ⋅ tˆ = Vr −
m ⎦⎥ tan α ⎣⎢
)
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(
AF
where tˆ istheunitvectoralongtheselectedtransversedirection.Closeinspection
offigure4showsthatthearrivalanglemustbecorrectedforthedisplacementof
thebeamproducedbythesuppressorgrid.Inaddition,thesuppressionof
photoemissionfromthecollectorcanleadtosomecurrentexchangebetweenthe
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collectorhalvesandcorrectionprocedurestoaccountforthiseffectarealsoapplied
[Stonebacketal,2014]
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4.IVMElectricalConfiguration
Figure5showsablockdiagramofthemajorelectricalsubsystemsthatmakeupthe
IVM.IntheRPA,theretardingpotentialisgeneratedthroughthecontentsofa
memoryblockcontaining32discretelevelsthatareusedtogenerateavoltagethat
isknowntoanaccuracyof0.001V.Ateachstepthedwelltimeisapproximately32
millisecondsallowingthecontentofthememoryblocktobeexecutedinone
second.Thecontentofthememorythatdescribesthesweepformatisdesignedto
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optimizethepointdistributionbasedontheenvironmentthatthesatellite
encounters.Whileexperienceallowsawell-informeddistributionofpointsto
defineadefaultsweep,thecontentofthesweepmemorymadebechangedby
commandfromtheground.Thepotentialonthesuppressorgrid,torejectthermal
electronsandsuppressphotoemissioncurrentsfromthecollector,mayalsobe
changedbetween0Vand-10.5Vbygroundcommand.Itwillbeadjustedtoprovide
theminimumrequiredvoltagetoaccomplishthesetwotasks.Anautomatically
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ranginglinearelectrometermeasurestheioncurrentaftertheretardinggridis
steppedtoadiscretepotential.Theelectrometerhas8sensitivityranges,decreasing
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byapproximatelythesquare-rootoften,allowingcurrentsbetween50pAand
3.9mAtobemeasured.AteachsteptheRPAoutputconsistsofthememorylocation
thatprovidestheretardingvoltage,thecurrentrecordedwith14-bitaccuracyand
accompaniedby3bitsthatdesignatetheelectrometersensitivitylevel.
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TheIDMhastwogridpotentialsthatmaybechangedbygroundcommand.Asinthe
RPAtherejectionofthermalelectronsandthesuppressionofphotoemissionis
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accomplishedwithasuppressorgrid,whichprecedesthecollectorandmaybe
changedbetween0Vand-10.5V.Inadditionarepellergridmaybebiasedwitha
potentialbetween0Vand3.5VVtorejecttheadmissionofH+ionsthathave
thermalspeedscomparabletothespacecraftvelocity.
Switchesatthecollectorallowthesegmentstobecombinedtoprovideacurrent
fromcollectorhalvesthatarealignedeitheralongthelocalhorizontalorthelocal
verticalaxis.Foradesignatedaxisthecurrentfromeachcollectorhalfismeasured
byalogarithmicelectrometerhavingadynamicrangefrom250pAto9.5µA,which
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issubsequentlyregisteredwith14-bitaccuracyfortransmissiontotheground.The
outputsfromeachlogarithmicelectrometeraresampledat16Hz.Theoutputfor
eachlogarithmicelectrometeralsoprovidestheinputtoalineardifference
amplifierthatdeliverstheratiooftheioncurrentstobeusedintheexpression
describedearliertoderivetheionarrivalangle.Theoutputofthedifference
amplifierisrecordedwith14-bitaccuracyandaccompaniedby1bit(axis)that
describesthecollectorhalvesorientation(horizontalorvertical)and1bit(polarity)
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designatingwhichcollectorhalfiscollectedtowhichlogarithmicelectrometer.The
differenceamplifieroutputsandconfigurationindicatorsaresampledat32Hz.The
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instrumentmaybeconfiguredbygroundcommandtoalternatebetweenhorizontal
andverticalarrivalangleswitha16Hzor8Hzcadenceortoremainmeasuringa
fixedaxisarrivalangle(horizontalorvertical).Inbothcasesbiasesinthe
inputs.
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logarithmicelectrometersareremovedbyperiodicallychangingthepolarityofthe
Thereferencegroundforbothsensorsisdrivenawayfromthespacecraftgroundto
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resideatthesamepotentialasthefloatingreferencesurfacecalledSenPot.The
instrumentsignalsareopticallycoupledtothespacecraftcommandanddatasystem
toaccommodatethedifferencebetweenthespacecraftandsensorground
potentials.
5.InstrumentCalibration
TheRPAutilizesanautomaticranginglinearamplifierforwhichthevoltageoutput
isgivenby V = Gi I + Oi whereGiisthesensitivityatleveliandOiistheelectrometer
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offsetassociatedwithsensitivityleveli.Thesensitivityandoffsetforeachlevelis
establishedinthelaboratoryusingacalibratedandcertifiedcurrentsourcethatis
directlyappliedtothecollector.Byinjectingcurrentoverthefullrange,theoutput
atallsensitivitylevelscanbeobtainedandlinearstraight-linefittingisutilizedto
establishthesensitivityandoffsetforeachlevel.Thisprocedureisrepeatedover
therangeofoperatingtemperaturesexpectedfortheinstrument.Acalibration
modethatfixestheretardingpotentialandstepsthroughthedifferentsensitivity
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levelsmaybeexercisedinflighttoverifyandupdatethelaboratorycalibrationfiles
ifappropriate.Theretardingvoltageisgeneratedutilizingad/aconverterandthe
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voltageforeachdigitallevelisrecordedovertheexpectedoperatingtemperature
rangeinthelaboratorywithxxmVaccuracy.Theelectrometercalibrationand
retardingvoltagecalibrationdataareretainedforuseinthedatareduction
procedureexercisedontheground.
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TheIDMutilizesalineardifferenceamplifiertodeterminetheratioofinput
currentsthataremeasuredusinglogarithmicelectrometers.Thelogarithmic
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electrometersaredesignedwiththesamesensitivitylevel,butmayhavedifferent
offsets.Thusthevoltageproportionaltothecurrentratio,fromwhichtheionarrival
angleisdeterminedisgivenby
V = Gd ⎡G log
⎣⎢
I1
I1
⎤
I 2 + Oa − Ob ⎦⎥ + Od = Gs log I 2 + Ol + Od .
Theoverallsystemsensitivitylevel,Gsisdeterminedinthelaboratorybyutilizinga
calibratedandcertifiedcurrentsourcetoinjectaknowncurrentratiodirectlytothe
sensorcollectors.Theoffset,whichhascontributionsfromboththedifference
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amplifierandthelogarithmicelectrometers,maybereducedtothatoriginating
fromthedifferenceamplifieralonebyrepeatingthecalibrationprocedurewiththe
inputstothelogarithmicelectrometersinverted.Thenthevoltageproportionalto
thecurrentratio,fromwhichtheionarrivalangleisdetermined,isgivenby
V = Gd ⎡G log
⎢⎣
I1
I1
⎤
I 2 + Ob − Oa ⎥⎦ + Od = Gs log I 2 − Ol + Od .Thetwocalibrationcurves
maythenbeaddedtoremovetheoffsetfromthelogarithmicelectrometers.The
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sensitivitylevelandoffsetisagainretainedforuseinthegrounddataprocessing.In
flightverificationandadjustmentofthecalibrationdatamaybeobtainedfrom
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maneuversforwhichthereferenceaxesofthespacecraftareknownprecisely.
Thesemaybeundertakenforcalibrationoftheopticalinstrumentsandforchanges
intheobservationalconfigurationofthepayload.
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6.IVMSpecificationsandPerformance
Table1detailstheinstrumentphysicalproperties.Themodestpowerrequirements
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allowthesensortobeoperatedwitha100%dutycycle.Howeveroperationofthe
IVMonICONwillbeperformedbytwoidenticalconfigurationsofthesensors
allowinganinterchangebetweenramandwakethatisrequiredfortheoptical
instrumentstoviewoneithersideofthesatelliteorbitplane.TheIVM,eitherthe
IVM-AorIVM-Binstrument,willbeoperatedcontinuouslywhenitispointed
nominallyintheramdirectionandwillcontinuetooperateduringslewing
maneuverstore-orientthesatelliteforcalibrationsoftheopticalinstruments[refs].
Duringcontinuousoperations,theRPAisconfiguredtoproducecurrent-voltage
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characteristicsat1Hzrate.TheIDMwillnominallyalternatebetweenmeasurement
ofthehorizontalandverticalionarrivalanglessothateachareobtainedat8Hz.
Thisoperationalmodeoftheinstrumentisexpectedtodominatethedataobtained
throughoutthemission.However,changesintheoperationalprofilearepossibleto
allowacquisitionofcurrent-voltagecurvesat2Hzand32Hzsamplingofafixedion
arrivalangle.DatafromtheIVMarepackagedfora4-secondperiodandthecontent
ofadatapacketisindependentofthemodeofinstrumentoperationand
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configurationoftheothergridpotentials.Thisadditionalinformationisincludedin
theheaderofeach4-seconddatapacketallowingautonomousprocessingofthe
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dataineachpacket.
7.InstrumentOperationsandGeophysicalParameters
TheprinciplesofoperationoftheRPAdescribedaboveshowthatthetotalion
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numberdensity,themajorionfractionalcomposition,theiontemperatureandthe
iondriftspeedalongthesensorlookdirection,arederivedinastraightforwardway.
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Theanalysisprocedurealsoyieldsavalueforthesensorplanepotentialwith
respecttotheplasma,whichisexpectedtobeaweakfunctionoftheelectron
temperatureandcanbeusedtocontinuouslyassessthequalityoftheleastsquares
fittingprocess.Thedriftspeedalongthesensorlookdirectionandthesensorplane
potentialareusedinturntoderivethetransverse(horizontalandvertical)
componentsoftheiondriftvectorinthesensorreferenceframe.Itshouldbe
emphasizedthatthederivediondriftvectorcomprisesthesumoftheambient
plasmadrift,withwhichweconductscienceinvestigationsandthespacecraft
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velocityvector.Thespacecraftvelocityvectorisspecifiedinaspacecraftreference
frameandthesensorlookdirectionsarealsospecifiedinthisreferenceframebyan
alignmentprocedureconductedonthegroundpriortolaunch.Thespacecraft
attitudedeterminationsystemprovidesthespacecraftvelocityinthespacecraft
referenceframeanditisthusastraightforwardexercisetoremovethespacecraft
velocitytospecifytheambientiondriftvectorinthesensorreferenceframe.
Moreusefultothescientistandtotheremovalofsystematicoffsetsinthedata,isan
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expressionoftheplasmadriftinmagneticcoordinatesthatspecifytheplasmadrift
parallelandperpendiculartothelocalmagneticfield.Theunitvectorsthatdefine
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thedirectionsalongthemagneticfieldandperpendiculartothemagneticfieldin
themeridianandperpendiculartothemeridian,aredeterminedfromtheinertial
attitudeofthespacecraftandtheInternationalGeomagneticReferenceField(IGRF)
[Finlayetal.,2010].
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Onceexpressedinmagneticcoordinatestwodifferentconditionsmayareappliedto
removesystematicdcoffsetsthatmayexistduetoerrorsinthespecificationofthe
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instrumentpointingwithrespecttothespacecraftreferenceaxes.First,itmaybe
recognizedthataveragesofthevertical(meridional)plasmadriftinlongitudeand
localtimemustbezeroinordertosatisfytherequirementthatthefieldbe
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electrostaticandthat ∇ × E = 0 .Second,theplasmadensityinthemiddle
ionosphereissufficientlyhighandtheion-neutralcollisionfrequencysufficiently
lowthatmagneticfluxlinesmayberegardedaselectricequipotentials.Thusa
conditionforconjugacyinthemagneticeast-westdriftisimposedontheaverage
measurementstakeninrestrictedlocaltimeandlongitudesectors.Thesetwo
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conditionsallowtheremovalofoffsetsinthetransversedriftscomputedbytheIDM
inamannerdescribedinmoredetailbyStonebacketal.[2012].Table2liststhe
parametersthatwillberetrievedduringtheoperationoftheIVM.
TheIVMderivedparametersofprimaryinteresttotheICONscienceobjectivesare
alsothosederivedfromtheIVMthatwaspartofthepayloadfortheCoupledIon
NeutralDynamicsInvestigation(CINDI).Figure6showsanexampleofonedayof
thesekeyparametersasillustrativeoftheinformationthatwillbeprovidedbythe
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IVMforICON.Inthisdisplaytheprimaryvariationsaroundtheorbitareproduced
bylocaltimeandaltitude,whilefortheICONorbitthevariationswillbedominated
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bylocaltimeandlatitude.Eachorbittraversestheequatorialregionatadifferent
longitudeandthusthevariationsseenhereduringonedayreflectvariationsin
longitudeaswillalsobethecaseforICON.KeytothescienceobjectivesoftheICON
missionarecomparisonsofthelongitudevariationsinthezonalandmeridional
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driftswiththecorrespondingwindfieldsobservedbyMIGHTIandweightedbythe
ionosphericconductivitydeterminedbytheneutralandiondensityprofilesderived
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byFUVandEUV.
8.Summary
TheICONmissionbringstogetherforthefirsttimeauniquesetofmeasurementsof
theneutralandchargedparticlenumberdensityanddriftmotionstoenablethe
connectionsbetweenthedynamoactionofthewindsandthedriftmotionsofthe
plasmatoberevealed.TheIVMinstrument,whichprovidesthemeasurementsof
plasmadrift,isbasedonastrongheritagefrompreviousmissionsandincorporates
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themostcapableelectricalandmechanicaldesigns,whilecapitalizingonprevious
experienceindataretrievalandreductionprocedures.Theresultingmeasurements
areexpectedtouncoversystematiclongitudevariationsintheplasmadrift
associatedwithtidalmodesintheneutralatmosphereaswelldeterminethe
importanceofaltitudevariationsinthewindontheelectrodynamicsoftheFregion
plasma.
References
T
Finlayetal.,(2010),InternationalGeomagneticReferenceField:theeleventh
generation,Geophys.J.Int.183(3):1216-1230,doi:10.1111/j.1365-
AF
246X.2010.04804.x
Hanson,W.B.,S.Sanatani,D.Zuccaro,andT.W.Flowerday(1970),Plasma
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R
Hanson,W.B.,D.R.Zuccaro,C.R.Lippincott,andS.Sanatani(1973),TheretardingpotentialanalyzeronAtmosphereExplorer,RadioSci.,8(4),333–339,
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doi:10.1029/RS008i004p00333.
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Explorer-B.Space.Sci.Instrum.,5,503-510.
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andS.Sanatani(1981),TheretardingpotentialanalyzeronDynamicsExplorer-B.
Space.Sci.Instrum.,5,503-510.
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Heelis,R.A.,andW.B.Hanson(1975),Techniquesformeasuringbulkgasmotions
fromsatellites,SpaceSci.Instrum.,1,493-524.
Heelis,R.A.,andW.B.Hanson(1998),Measurementsofthermaliondriftvelocity
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MeasurementTechniquesinSpacePlasmas:Particles,
doi:10.1029/GM102p0061.
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Power,L.L.Harmon,B.J.Holt,andC.R.Lippincott(2009),BehavioroftheO+/H+
transitionheightduringtheextremesolarminimumof2008,Geophys.Res.Lett.,
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36,L00C03,doi:10.1029/2009GL038652.
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Acknowledgements
ThisworkissupportedbyNASAgrantNNG12FA44C.SuccessfulconductoftheICON
missionandtheIVMinstrumentistheresultofkeycollaborationsbetweenteamsat
theUniversityofCaliforniaBerkeley,theUniversityofTexasatDallasandOrbital
ATK.Wethankthemanyparticipantsfromalltheseinstitutionsthathaveresulted
inthiscontributiontotheICONmission.
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4.25Kg
Power
2.5W
Volume:SensorPackage
11”x6.2”x4.8”
AperturePlane
15.3”x11”
Telemetry
2048bps
Pointing
5°
PointingKnowledge
0.03°
InstantaneousFieldofView
45°
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Mass
Table1.ICONIVMInstrumentResources.
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Parameter
Range
Accuracy
CrossTrackIonDrift
-750to750ms-1
±3ms-1
RamIonDrift
-500to500ms-1
±12ms-1
TotalIonNumberDensity
1.5x103to5x106cm-3
±1x103
MajorIonConstituents
0-100%
±2%
IonTemperature
400to10000°K
±100°K
SensorPlanePotentialwrtPlasma
-3to+2V
±0.01V
D
R
AF
T
Table2.ICONIVMMeasuredParameters
19
FigureCaptions
Figure1.PhotographsofICONIVMmountedtodummyPIPinterface.
Figure2.SchematiccrosssectionsshowinggridconfigurationsfortheRetarding
PotentialAnalyzerandtheIonDriftMeter.
CINDI.ICONIVMwilloperatesimilarly.
AF
T
Figure3.RepresentativecurrentvoltagecharacteristicsobtainedfromtheRPAon
Figure4.Schematiccross-sectionshowingionbeamtrajectorythroughtheiondrift
meter
R
Figure5.Simplifiedelectricalblockdiagramindicatingmajorsubsystemsinthe
ICONIVM.
D
Figure6.RepresentativegeophysicalparametersderivedfromtheIVM.Shownhere
isatypicaldayodmeasurementstakenfromtheIVMonC/NOFS.
20
AF
D
R
T
FIGURE1
21
T
AF
R
D
FIGURE2.
22
D
R
AF
T
FIGURE3
23
T
AF
D
R
FIGURE4
24
T
AF
R
D
FIGURE5
25
T
AF
R
D
FIGURES6
26