Optimizing Electrodynamic Tether System Performance

Abstract

A time-averaged electrodynamic tether (EDT) system simulation tool has been developed and used to conduct studies of tether performance under varying conditions. The studies included evaluating passive end-body electron collection and active ion emission approaches, a comparison of active electron emission technologies (hollow-cathode, electron field emission, hot cathode), adjustment of bare conductor versus insulated tether lengths, boosting and de-boosting conditions, and other various system element configurations. The study results indicate that in many cases bare tether anodes provide optimal electron collection. In addition, it was shown that while hollow cathodes may be the best active electron emission technique, field emitter arrays result in less than 1% difference in average system thrusting and use no consumables. This is based on the assumption that multi-amp field emitter arrays can be ultimately fabricated and qualified for space. Three case-studies were performed in order to better understand the trades for performance optimization. The cases were: (1) orbit maintenance of the International Space Station; (2) the use of an EDT system for reboost and deorbit of NASA's GLAST spacecraft; and, (3) operation of the Momentum Exchange Electrodynamic Reboost (MXER) system. From evaluation of these cases, a recommended design "algorithm" is proposed. Case (1) is presented in this paper in its entirety, and cases (2) and (3) are briefly described.