Spacecraft Charging in the Auroral Plasma: Progress Toward Understanding the Physical Effects Involved,
YORK UNIV DOWNSVIEW (ONTARIO) DEPT OF PHYSICS
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After reviewing the main differences between the plasma environments in geostationary orbit and low polar orbit with regard to high-voltage charging situations, we present results from a calculation of secondary-electron escape currents from negatively-charged spacecraft surfaces having various orientation relative to the local magnetic-field direction. We show that for finite ranges of combinations of electric and magnetic field directions, secondary-electron escape is completely suppressed and therefore cannot help to discharge the spacecraft. In such circumstances, secondary electrons may travel distances many times their gyroradii before reimpacting, and this may produce greatly increased secondary-electron surface currents. We then develop a simple rough estimate of the required conditions for high-voltage auroral-zone charging. The results suggest that for any given spacecraft, surface potentials are likely to depend more strongly on the ratio of ambient flux of high-energy electrons to that of all ions, than on any other environmental parameter. Finally, we present preliminary results of numerical simulations directed toward testing this hypothesis. Numerical instabilities encountered in doing this simulation probably are closely related to physical sensitivities inherent in the physics of the ion wake behind the spacecraft.
- Unmanned Spacecraft
- Atmospheric Physics
- Electricity and Magnetism