Electrodynamic tether shape estimation with square-root unscented filter

The dynamic estimation of the state of an electrodynamic tether system is considered. A square-root implementation of an unscented filter is utilized. In the first instance, a filter is developed based on an inelastic tether model, which is used to estimate the tether libration dynamics. This is coupled with a simple 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 feedback controller for the flexible electrodynamic tether is effective using the estimated states.