Onset of Spacecraft Charging and Potential Jump in Geosynchronous Plasma

Geosynchronous spacecraft charging has been a focus of attention since a large number of satellites are operating in this region. The most severe geosynchronous charging environment is during substorms, in which the plasma environment is generally better described by double Maxwellian distribution. In such case, determination of onset of spacecraft charging becomes more complex since more parameters are involved. In this paper, the threshold condition for onset of charging in double Maxwellian plasma is developed theoretically in a more general sense, and the charging behavior at the threshold is investigated in detail. It is found that sudden jump to negative potential of thousands of volts or more can take place at the threshold in certain situation. The mechanism underlying the potential jump is clarified from the stability theory and illustrated by typical calculations. Moreover, a more general condition for potential jump is determined theoretically, and consequently another threshold condition for jump in positive direction is found. At both thresholds, the spacecraft potentials are semisteady, but in opposite directions, with the possibility of a jump to a stable potential. The polarity of movement across the thresholds from different plasma will cause a spacecraft to experience irreversible charging histories which result in significant hysteresis.