Dynamics of Complex Spacecraft Subject to Forced and Environmental Charging

Hughes, Joseph A.

Graduate Thesis Or Dissertation

Dynamics of Complex Spacecraft Subject to Forced and Environmental Charging Public Deposited

Analytics

Citations

Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/1544bp37v

Abstract

Due to the space plasma environment and the sun, spacecraft can charge to very high negative voltages. These high charge levels can cause arcing which can seriously damage spacecraft electronics and even cause mission ending damage. Spacecraft charging can also cause significant perturbations for lightweight High Area to Mass Ratio (HAMR) objects. If correctly harnessed and directed, charging can be used to exert forces and torques on large debris objects without making physical contact through the Coulomb force. This concept is called the Electrostatic Tractor (ET) and can tug debris out of Geosynchronous Earth orbit (GEO) in a matter of months. To understand both the orbits of uncontrolled charged debris and the performance of the ET, accurate models for how spacecraft charge must be developed, the forces and torques that result from this charging must be estimated, and the effects of these forces and torques must be studied. Spacecraft charging is studied by finding both equilibrium and time-varying solutions for the voltage. A major change with prior work is to use empirical models for the electron and ion flux rather than Maxwellian models. This, coupled with a more realistic Secondary Electron Emission (SEE) model, predicts that it is harder than previously thought for spacecraft to charge negative. The charging equations are also solved for time varying solutions. Electrostatic force and torque prediction is advanced using both analytic and numeric tools. Analytic expressions for the force and torque on a geometrically complex object are presented, which give novel analytical insight. Numeric studies include using the Method of Moments (MoM) to create better-performing Multi-sphere Method (MSM) models. The MSM is also extended to model conductors and dielectrics with good accuracy. The orbital effects of charging are studied for both environmentally charged debris and the ET. For charged debris, it is the electrostatic torque that matters since it can change the attitude and influence Solar Radiation Pressure (SRP). This perturbing force is comparable to an initial attitude uncertainty. For the ET, the new charging model predicts that a few milliAmps of current are needed rather than the few hundred microAmps of current predicted from prior work. Collectively, these studies advance the frontier of knowledge in spacecraft charging, electrostatics, and astrodynamics.

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