Electrodynamic Tethers Under Forced-Current Variations Part 2: Flexible-Tether Estimation and Control

摘要

The dynamic estimation of the state of an electrodynamic tether system is considered for the purposes of feedback control. A filter is developed based on an inelastic tether model, which is used to estimate the tether libration dynamics. This is coupled with an energy-rate feedback-control scheme for tracking a desired libration trajectory. A filter is also developed that takes into account the effects of tether flexibility. Only measurements of the tether-end body position and the tension vector at the main spacecraft are required to estimate the tether shape and libration dynamics. A square-root implementation of an unscented filter is used to robustly estimate the tether dynamic state using a discretized tether model. A modified energy-rate feedback controller is proposed taking into account the lateral oscillations of the tether. Numerical results show that feedback of the tether-end body is insufficient for stabilizing a flexible tether. Results of simulations of the operation of the coupled estimation and control technique demonstrate that it is capable of stabilizing the librations and lateral oscillations of an electrodynamic tether.