Electron-Based Touchless Potential Sensing of Shape Primitives and Differentially-Charged Spacecraft

Abstract

Numerous missions are being proposed which involve multiple spacecraft operating in close proximity in harsh charging environments. In such missions, the ability to sense the electrostatic potential on a nearby object is critical to prevent harmful electrostatic discharges or to leverage Coulomb interactions for relative motion control. The electron method is one such technique for touchless potential measurement which works by measuring low-energy secondary or photoelectrons emitted from the target. Previous work has demonstrated the efficacy of the electron method for touchless sensing, but has been limited to consideration of simple shapes and uniformly charged targets. This paper investigates the electron method for touchless sensing for cases in which the target spacecraft has more complex geometry primitives, including boxes, panels, and dishes. Further, the differential charging case, in which the target object is charged to multiple, different potentials, is also considered. A simulation framework is developed to model electric fields and particle trajectories around such spacecraft geometries. Vacuum chamber experiments validate the simulation results. The study shows how the target geometry can focus or defocus the electron flux into streams of electrons emanating from the surface. This provides critical insight into where to place the servicer vehicle to measure these fluxes and determine the target spacecraft potential.