Dynamical, electrical and thermal coupling in a new class of electrodynamic tethered satellites

Abstract

A new class of electrodynamic tethers have been recently introduced which provide comparatively high tether currents with relatively short and light tethers. These space systems make use of a bare tether (anode) to collect electrons from the ionosphere rather than the less efficient, conductive, large spherical termination flown in the past. This new technology, which is suitable for propellantless transportation in the ionosphere, will be demonstrated in August 2000 when the Propulsive Small Expendable Deployment System (ProSEDS) attempts the deorbit of a Delta second stage by using electrodynamic forces. This class of space systems exhibits a strong coupling among the dynamical, electrical, and thermal responses that must be analyzed with computer codes that model the tether continuum dynamics, electrodynamics, and thermal behavior in an integrated manner. After introducing briefly the physics of bare tethers and electron collection from the ionosphere, the paper describes the models adopted to simulate a bare-tether system. Then, it discusses simulation results for selected cases, pertinent to ProSEDS, which show the inter-dependencies among the system parameters. Specifically, the paper shows that key electrical, thermal, and dynamic parameters can strongly affect the decay rate (the most relevant performance index for the system under analysis) and also the system stability. An appropriate choice of system parameters can produce a sustainable electrodynamic drag force capable of increasing, by more than an order of magnitude, the natural decay rate of the Delta stage with a tether mass of only 12 kg and a stabilizing mass of 20 kg.