Long Term Stability of Electrodynamic Tethers

摘要

Two important applications of electrodynamic tethers, among others, are those of using them for deorbiting and/or propulsion. A crucial issue for both of the above applications is the dynamic stability of the tether system. The electrodynamic forces on the tether couple in fact in plane and out of plane oscillations and, especially for light systems, can drive the tethers unstable as has been shown in several numerical simulations . In both the applications of deorbiting and propulsion, the tether system is supposed to operate for long intervals of time (months) so that a crucial issue, in view of the fact that the system is potentially unstable, is that of analyzing the constraints, in terms of average current, ensuring long term safe operations (i.e. with the tether oscillation amplitudes below certain limits). In this paper we consider this issue referring, in particular, to the tether lateral oscillations which (from numerical simulations), appear the ones for which instability develops. We refer therefore to a flexible conducting tether and we use a model where the time variation of the tether current is assumed to be given. In addition, we adress both the case of a bare tether (with a realistic current variation along the tether lenght) and that of an insulated conducting tether collecting current through a balloon at one of its terminations.