Touchless Electrostatic Detumbling of Differentially Charged Spacecraft in Geosynchronous Earth Orbit

Electrostatic detumbling is a promising method for touchlessly detumbling large, uncooperative spacecraft in geosynchronous Earth orbit (GEO). Prior work has primarily considered fully conducting targets where the outer surface has a uniform electric potential. However, many legacy spacecraft have electrically isolated conducting components that can charge to largely different electric potentials from the rest of the spacecraft. Such differential potentials can significantly alter the electrostatic interactions between a tumbling target and servicer during proximity operations, potentially yielding more favorable torques during electrostatic detumbling. This paper develops and evaluates an active differential-charge control strategy that uses an electron-beam and targeted UV light source onboard a box-wing servicer spacecraft to produce controllable voltage differentials a target modeled after the GOES-R spacecraft. A Surface Multi-Sphere Model (SMSM) is used with an analytic charging model to calculate the coupled, steady-state voltages for various charge control modes. These voltages are then used with an SMSM electrostatic torque model and a Lyapunov-optimal control law to simulate electrostatic detumbling. Detumbling simulations are performed for both uniform and differential voltage cases under typical GEO space-weather conditions, and results show that differential voltage control reduces detumbling time from approximately 450 hours for the uniform case to about 300 hours for the studied geometry and an initial spin of 2 deg/s. These findings demonstrate that active differential charging can enhance electrostatic torques during detumbling and substantially shorten detumble times.