Prospects and Challenges for Touchless Sensing of Spacecraft Electrostatic Potential Using Electrons

A method is investigated to use secondary electrons to touchlessly sense the electrostatic potential of an object in geosynchronous orbit or deep space. This method involves a positively charged servicing craft, which directs a high-energy electron beam at the object of interest such that low-energy secondary electrons are emitted from the surface. The low-energy electrons emitted by the target are accelerated toward the servicing craft and arrive with an energy equal to the potential difference between the two crafts. The servicing craft measures the electron energy spectrum and, knowing its own potential, then infers the potential of the target. Depending on the application, photoelectrons could similarly be used to infer the target potential without the need for an active electron beam. Though it is possible to measure potential by directly contacting a surface, remote measurement offers significant advantages and supports missions which must operate in close proximity without making physical contact. Several missions have been proposed that use interactions between charged objects to create useful forces and torques, including electrostatic detumbling and reorbiting of debris, Coulomb formations, and virtual structures. Remote measurement of potential would benefit these missions by enabling feedback control of the active charging. Other applications include mitigation of arcing during rendezvous, docking, and proximity operations for future servicing or salvaging missions.