HALCA's Onboard VLBI Observing System
[摘要] ThefirstspaceVLBIsatellite,HALCA,waslaunchedon1997February12.WereportthecharacteristicsofHALCAasanorbitingVLBIstationwith8-mdeploymentantenna.Itisrequiredthehighsystemgain,lowsystemnoise,andhighstabilityofphasetransfer.AndthestabilitiesofsystemgainandsystemnoiseareneededforimagingofVLBI.HALCAachievedtherequirementasaVLBIstationsandhasmadealmost3timeslongerbaselinesthangroundglobalVLBInetworks.Itmeansobservationswith3timeshigherangularresolutionhavebeencarriedout.Wehavemeasuredapertureefficienciesofthedeploymentantenna,systemnoisetemperatures,stabilityofonboardlocaloscillators,andstabilityofphaselink.HALCA'sonboardradioastronomysystemhas1.60–1.73GHz,4.7–5.0GHz,and21.9–22.3GHzreceiversandtwo-channelhigh-ratesamplers.Typicalvaluesofsystemnoisetemperatureinorbitare70Kand90Kat1.6and5GHzrespectively.At22GHz,theapparentsystemnoisetemperatureis400K;however,thisismostlyduetoattenuationbetweenthemainantennaandthe22GHzlownoiseamplifier.Areferencetonesignalistransmittedfromagroundtrackingstationwhichislockedonagroundhydrogenmaseroscillator.Theinternalphasestabilityoflocaloscillatorsisaround5°r.m.s.at5GHz.Thetotalgainofthereceivingsystemandthebitdistributionofthehigh-ratesamplershavealsobeenchecked.Withtheexceptionofthe22GHzattenuation,thein-orbitperformanceoftheVLBIobservingsystemmatchestheground-testresultsverywell.
[发布日期] [发布机构]
[效力级别] [学科分类] 天文学(综合)
[关键词] "space vehicles: instruments";"techniques: interferometric" [时效性]
