Plasma Diagnostics by Electron Guns and Electric Field Probes on ISEE-1
The ISEE-1 satellite, launched in October 1977, carried two small electron guns for control of the satellite potential. They formed part of a spherical double probe instrument for measurements of electric fields, (Mozer et al., 1978.) The intention was to reduce the asymmetrical photo-electron cloud emitted sunward and the possible influences of its negative space charge on the electric field measurements. Early diagnostic experiments with the electron guns lead to the conclusion that the photo-electron space charge problem is a relatively small source of interference for the electric field measurements, and the guns were therefore not used in connection with routine electric field measurements, but only operated during special diagnostic periods in order to understand better spacecraft charging and potential control. It is important to notice that it is only meaningful to speak about satellite potential control for a satellite with surfaces which are sufficiently conductive to allow currents to flow so that charge distributions are smoothed to the extent that voltage differences do not exceed typically 1.0 Volt. This can be achieved in practice with a layer of indium oxide (~105 /⎕).
KeywordsIndium Oxide Plasma Diagnostics Floating Potential Electric Field Measurement Positive Satellite
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