Improving Electron Emission Observability for Spacecraft Touchless Potential Sensing

Touchless potential sensing allows a servicing spacecraft to determine the electrostatic potential of a nearby target without physical contact. This enables safer docking conditions and electrostatic actuation. While previous studies demonstrate that secondary electron and photoelectron emissions can be used to determine the potential of a target, the emissions may only be observable at 10% of locations about a target. This paper researches sensing strategies for the servicer position and beam parameters to enhance the detection of electron emissions in the presence of complex geometries and differential potentials. Using validated SIMION simulations, it is shown that increasing the half angle of an electron beam or vacuum ultraviolet laser from 0.2 to 2 deg and sweeping through deflection angles can nearly double the number of detectable positions. Additionally, the study examines how differential surface potentials shift or suppress electron emission trajectories, changing the observability. It is found that using an ultraviolet laser to excite emissions from a differentially charged target can excite detectable emissions for more than double the conditions in which an electron beam can excite detectable emissions. The results provide guidance for improving the effectiveness of touchless potential sensing in Geosynchronous Earth Orbit and cislunar operations, especially for servicing and docking missions.