Comparison of Reduced Order Spacecraft Charging Models for Electrostatic Proximity Operations

Spacecraft charge in orbit due to naturally occurring electric currents from the ambient plasma and the Sun, and artificial currents produced by devices such as an electron gun. This results in electrostatic forces and torques between two spacecraft in close proximity that can perturb the relative motion during on-orbit servicing, assembly and manufacturing (OSAM) operations, or be utilized to remove or detumble dysfunctional satellites. In prior work on electrostatic proximity operations, typically charging models based on spherical current collection were used to compute the electrostatic potential, and that potential was prescribed to be constant in relative motion simulations. In this work, several spacecraft charging models are compared, including a simple sphere model, an adjusted sphere model, and a faceted model. The faceted model is promising because its total surface area is more accurate, and it allows for the consideration of a time-varying sunlit area. Using the faceted model, it is shown that the orientation of the spacecraft with respect to the sun can significantly affect the equilibrium potential and the resulting force and torque. This is demonstrated by a charged attitude motion simulation for the Electrostatic Tractor debris removal concept.