Coupled Spacecraft Charging Due to Continuous Electron Beam Emission and Impact

Spacecraft charge naturally in orbit due to the plasma environment and the electromagnetic radiation from the sun. By emitting an electron beam, a servicer spacecraft can control its electric potential and also the potential of a neighboring target if the electron beam is aimed at the target spacecraft. In addition, the impacting electron beam excites secondary electrons and x-rays, providing a way to touchlessly sense the potential of the target. Because of the electron beam, the charging dynamics of the two spacecraft are coupled. This paper studies the effects of the beam on the electric potentials using a numerical charging model. It is found that multiple equilibria may exist due to the electron beam. Jumps between equilibrium configurations are possible when the electron beam energy is quickly reduced or when current fluctuations are present. Being aware of multiple equilibrium configurations is important for feedback-based charge control but also enables a new open-loop charge control around one of the equilibria. The effect of the electron beam on the spacecraft potentials is studied for geostationary Earth orbit and cislunar space. It is found that the current applied by the beam to the target may influence remote electric potential sensing methods.