THE WIND MAGNETIC FIELD INVESTIGATION

THEWINDMAGNETICFIELDINVESTIGATIONR.P.LEPPING,M.H.ACUNA,L.F.BURLAGA,W.M.FARRELLandJ.A.SLAVINLaboratoryforExtraterrestrialPhysics,NASA/GoddardSpaceFlightCenter,Greenbelt,MD20771,U.S.A.K.H.SCHATFENDivisionofAtmosphericSciences,NationalScienceFoundation,Washington,DC20550,U.S.A.EMARIANIDipartimentodiFisica,Universita'TorVergata,Roma00173,ItalyN.ENESSUniversityofDelaware,BartolResearchinstitute,Newark,DE19716,U.S.A.EM.NEUBAUERInstitutfiirGeophysicsundMeteorlogiederUniversitiitzuKOln,500KOln-41,GermanyY.C.WHANGDepartmentofMechanicalEngineering,1heCatholicUniversityofAmerica,Washington,DC20064,U.S.A.andJ.B.BYRNES,R.S.KENNON,P.V.PANETTA,J.SCHEIFELEandE.M.WORLEYLaboratoryforExtraterrestrialPhysics,NASA/GoddardSpaceFlightCenter,Greenbelt,MD20771,U.S.A.Received16March,1993)Abstract.ThemagneticfieldexperimentonWINDwillprovidedataforstudiesofabroadrangeofscalesofstructuresandfluctuationcharacteristicsoftheinterplanetarymagneticfieldthroughoutthemission,and,whereappropriate,relatethemtothestaticsanddynamicsofthemagnetosphere.ThebasicinstrumentoftheMagneticFieldInvestigation(MFI)isaboom-mounteddualtriaxialfluxgatemagnetometerandassociatedelectronics.Thedualconfigurationprovidesredundancyandalsopermitsaccurateremovalofthedipolarportionofthespacecraftmagneticfield.Theinstrumentprovides(1)nearreal-timedataatnominallyonevectorper92saskeyparameterdataforbroaddissemination,(2)rapiddataat10.9vectorss-1forstandardanalysis,and(3)occasionally,snapshot(SS)memorydataandFastFourierTransformdata(FFT),bothbasedon44vectorss-I.Thesemeasurementswillbeprecise(0.025%),accurate,ultra-sensitive(0.008nT/stepquantization),andwherethesensornoiselevelis0.006nTr.m.s,for0-10Hz.Thedigitalprocessingunitutilizesa12-bitmicroprocessorcontrolledanalogue-to-digitalconverter.Theinstrumentfeaturesaverywidedynamicrangeofmeasurementcapability,from:E4nTupto536nTperaxisineightdiscreteranges.(TheupperrangepermitscompletetestingintheEarth'sfield.)IntheFTTmodepowerspectraldensityelementsaretransmittedtothegroundasfastasonceevery23s(highrate),and2.7rainofSSmemorytimeseriesdata,triggeredautomaticallybypre-setcommand,requirestypicallyabout5.1hoursfortransmission.Standarddataproductsareexpectedtobethefollowingvectorfieldaverages:0.0227-s(detaildatafromSS),0.092s('detail'instandardmode),3s,1rain,and1hour,inbothGSEandGSMcoordinates,aswellastheFFTspectralelements.Ashasbeenourteam'stradition,highinstrumentreliabilityisobtainedbytheuseoffullyredundantsystemsandextremelyconservativedesigns.Weplanstudiesofthesolarwind:(1)asacollisionlessplasmalaboratory,atalltimescales,macro,mesoandmicro,butconcentratingonthekineticscale,thehighesttimeresolutionoftheinstrument(=0.022s),(2)asaconsequenceofsolarenergyandmassoutput,(3)as~nexternalsourceofplasmathatcancouplemass,momentum,andenergytotheEarth'smagnetosphere,and(4)asitismodifiedasaconsequenceofitsimbeddedfieldinteractingSpaceScienceReviews71:207-229,1995.(~)1995KluwerAcademicPublishers.PrintedinBelgium.208R.P.LEPPINGETAL.withthemoon.SincetheGEOTAILInboardMagnetometer(GIM),whichissimilartotheMFIinstrument,wasdevelopedbymembersofourteam,weprovideabriefdiscussionofGIMrelatedscienceobjectives,alongwithMFIrelatedsciencegoals_1.IntroductionTheWINDMagneticFieldInvestigation(MFI)willestablishthelarge-scalestruc-tureandfluctuationcharacteristicsoftheinterplanetarymagneticfield(IMF)asfunctionsoftimethroughoutthemission,andthroughcorrelativestudieswillrelatethemtothedynamicsofthemagnetosphere.Thisexperimentwillprovide(1)nearreal-timedataatnominallyonevectorper92sas'KeyParameterData'forprojectsupport,(2)rapiddataat10.9vectorss-1forstandardanalysis,and(3)snapshotmemorydataandFastFourierTransformdata(FFT)basedon44vectorss-1acquiredonboard,workingsynchronouslywithblocksof512samples(FFTonly)each.Thesemeasurementswillbeprecise(0.025%),accurate(0.08nT),andultra-sensitive(0.008nTstep-l).Thebasicinstrumentimplementedisaboom-mounteddualtriaxialfluxgatemagnetometersystem.Theoutboardsensorsetismountedattheendofa12-mboom,longenoughtoreducethefieldofthespacecraftatthatlocationto~0.1nTorless.Thedualconfigurationprovidesredundancyandpermitssubtractionduringdataprocessingofthedipolarpartofthespacecraftfieldcontributiontothemeasuredmagneticfield.Theinboardsensorassemblyismountedonthesameboom,approximately2ofthedistancetotheoutboardsensor.Thedigitalprocessingunitutilizesa12-bitA/Dconvertertoeasilyresolvesmallamplitudefluctuationsofthefield,andismicroprocessorcontrolled.ItalsoincorporatesadedicatedFFTprocessor,developedaroundhighperformanceDSPintegratedcircuits,whichproducesa32-channellogarithmicspectrumforeachaxis,synthesizedfroma'raw'256-pointlinearspectrum.Allcomponentsofthepowerspectralmatricescorrespondingtothe32estimatesaretransmittedtothegroundasfastasonceevery23s(highrate)providingpowerandphaseinfor-mationtogetherwiththecorrespondingsnapshotmemorytimeseriesdata.AsinpreviousinstrumentsdevelopedatGSFC,highreliabilityisobtainedbytheuseoffullyredundantsystemsandextremelyconservativedesigns.Theintrinsiczerodriftofthesensorsisexpectedtobebelow0.1nToverperiod