Abstract: TofurtherenhancethecapabilityofBeiDouNavigationSatelliteSystem(BDS)to providecontinuousandefficientservice,thefirstbackupsatelliteI6waslaunchedinMarch2016.ThedifferencesandsimilaritiesbetweenI6andotherIGSOsatelliteswereanalyzed,fromtheperspectiveofsatelliteclockprediction,orbitdeterminationaccuracyandpseudorangevariation.ThecontributionofI6toBDSwasevaluatedbyPDOPvaluesandgridavailability.Thesatelliteclockmeasurementsobtainedbytwowaysatellitetimefrequencytransfer(TWSTFT)systemwereusedtoevaluateclockpredictionerrorofI6.Theresultsshowthatfor5hourprediction,clockerrorofI6is232nsintermsofrootmeansquare(RMS)andtheextrapolatedonehourpredictionerroris073ns(RMS).ComparedwithotherIGSOsatellitesclock,theerrorforecastlevelofI6isequivalent.TheorbitdeterminationaccuracyofI6optimizedbytheattitudecontrolmethodisnotdegradedobviouslycomparedwiththeI3ofBDSwhentheSunisclosetotheI6′sorbitplane,whichovercomesthedecreaseoftheorbitaccuracyoftheexistingBDSsatellitesduringtheshadow.ThepseudorangevariationoftheI6satellitewasanalyzedusingthedatacollectedbythelargeapertureparabolicantenna.Theresultsshowthatthepeaktopeakdifferenceofthepseudorangevariationisabout1minthesingleobservationarcofI6satellite.ItisconsistentwithotherIGSOsatellites.I6isinthehotstandbymodeofoperation,providingserviceswiththeoriginalBeiDousatellitesafterMay2016,changingtheBDSconstellationcomposition.TheresultsofPDOPsimulationshowthatthemaximumPDOPofKaShiisdecreasedfrom1282to726,andthepercentageofPDOPgreaterthan6isdecreasedfrom2911%to1721%.TheresultsshowthatI6increasestheavailabilityofsixionosphericgridpoints.

Key words: BeiDouNavigationSatelliteSystem, backupsatellite, orbitdetermination, pseudorangevariation；ionosphericgrid