Effects of Local Plasma Environment on Dynamics of Electrodynamic Tether Systems

Abstract

An electrodynamic tether system consists of two satellites connected by a long tether that generates current to produce either power or thrust via the system’s electromagnetic interaction with the space environment. A complete system model for an electrodynamic tether that combines a high-fidelity tether dynamics model and a model for the tether current governed by local space plasma properties is developed. The International Reference Ionosphere is used to generate the plasma parameters for the tether current collection model. Variations in the tether system dynamics due to the tether current are investigated and compared to experimental data from the Plasma Motor Generator mission. The current profiles generated throughout the system’s orbit are found to match the day–night current variations observed during the experiment. These natural diurnal current variations do not introduce a significant difference in the system’s orbit. However, new modes of oscillation in the tether’s in-plane and out-of-plane librations are induced by the varying current. In addition to damping the small amplitude, high-frequency tether oscillations, the new oscillatory modes introduce frequency components in the tether’s in-plane librations corresponding to the current’s diurnal variation and cause the amplitude of the tether’s out-of-plane motion to grow without bound.