Remote Electrostatic Potential Determination for Spacecraft Relative Motion Control

Wilson, Kieran

Graduate Thesis Or Dissertation

Remote Electrostatic Potential Determination for Spacecraft Relative Motion Control Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/r494vm38g

Abstract

While spacecraft charging has been an actively studied and managed result of spaceflight for decades, the advent of robotic servicing missions in high earth orbits prone to severe charging has opened new avenues of research. Servicing missions are already operating at GEO to extend the life of fuel depleted telecommunications satellites, while a surge of LEO launch capability motivates a need for orbital transfer vehicles and other in-orbit services requiring rendezvous.

Many nascent concepts for formation flying and debris remediation rely on electrostatic interactions to exert forces and torques on nearby objects without requiring physical contact. These concepts include Coulomb formations for propellant-less formation configuration and the Electrostatic Tractor, which utilizes electrostatic interactions to detumble and re-orbit large debris from distances of tens of meters. While a range of established technologies allow a spacecraft to measure its own electrostatic potential, all of these architectures additionally require knowledge of another body's potential. An enabling technology for these missions is therefore the development of a technique for sensing electrostatic potentials remotely.

This thesis establishes a promising method for remote electrostatic potential determination, through theoretical analysis and experimentation. Energetic electrons interacting with a surface result in the emission of x-rays, and analysis of this x-ray spectrum provides information about the incident electron energy and the surface elemental composition. If the electron source energy is known, either from an electron beam on a servicing craft or the ambient plasma, the relative potential between the spacecraft is determined. Experimental trials in the ECLIPS space environment simulation facility shows that this method is robust to incidence angles and target orientation, providing accuracies within tens of volts. Such performance enables electrostatic actuation concepts, and can also be used to monitor relative spacecraft potentials during rendezvous to mitigate arcing threats.

In addition, the second part of this thesis explores the impact of electrostatic charging on proximity operations in high earth orbit, an increasingly popular field of operations. During rendezvous, multi-kV level electrostatic charges can impart torques on both servicer and target on the order of 10 mN-m. When approaching a disabled vehicle or debris object, these torques can accumulate to rotational rates in excess of 1°/s. Two guidance policies are introduced to generate approach trajectories that minimize the electrostatic perturbation, one based on a pseudospectral collocation optimized trajectory scheme that can be precomputed on the ground and the other a deterministic sampling-based approach that could be implemented onboard.

The results of this work are a significant contribution for many high earth orbit missions, as an enabling technology in improving rendezvous safety in cislunar space to touchless reboriting and detumbling of hazardous debris objects.

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