ACTIVE SPACECRAFT POTENTIAL CONTROL |
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| Authors: | W Riedler K Torkar F RÜDENAUER M Fehringer A Pedersen R Schmidt R J L Grard H Arends B T Narheim J Troim R Torbert R C Olsen E Whipple R Goldstein N Valavanoglou HUA Zhao |
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| Institution: | (1) Institut für Weltraumforschung der Österreichischen Akademie der Wissenschaften, Inffeldgasse 12, A-8010 Graz, Austria;(2) Österreichisches Forschungszentrum Seibersdorf, A-2444 Seibersdorf, Austria;(3) Space Science Department, ESA/ESTEC, NL-2200 AG Noordwijk, The Netherlands;(4) Forsvarets Forskningsinstitutt, N-2007 Kjeller, Norway;(5) University of New Hampshire, Durham, NH, 03824, U.S.A;(6) Naval Postgraduate School, Monterey, CA, 93943, U.S.A;(7) University of Washington, Seattle, WA, 98195, U.S.A;(8) Jet Propulsion Laboratory, Pasadena, CA, 91109, U.S.A;(9) Technische Universität Graz, A-8010 Graz, Austria;(10) Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing, 100080, P.R. China |
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| Abstract: | Charging of the outer surface or of the entire structure of a spacecraft in orbit can have a severe impact on the scientific output of the instruments. Typical floating potentials for magnetospheric satellites (from +1 to several tens of volts in sunlight) make it practically impossible to measure the cold (several eV) component of the ambient plasma. Effects of spacecraft charging are reduced by an entirely conductive surface of the spacecraft and by active charge neutralisation, which in the case of Cluster only deals with a positive potential. The Cluster spacecraft are instrumented with ion emitters of the liquid-metal ion-source type, which will produce indium ions at 5 to 8 keV energy. The operating principle is field evaporation of indium in the apex field of a needle. The advantages are low power consumption, compactness and high mass efficiency. The ion current will be adjusted in a feedback loop with instruments measuring the spacecraft potential (EFW and PEACE). A stand-alone mode is also foreseen as a back-up. The design and principles of the operation of the active spacecraft potential control instrument (ASPOC) are presented in detail. Flight experience with a similar instrument on the Geotail spacecraft is outlined. |
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