Estimation of uncooperative space debris inertial parameters after tether capture

Abstract

Space debris is often uncooperative and unresponsive, necessitating the understanding of its motion for successful post-capture control in an active debris removal mission. To this end, the inertia tensor of the captured debris object must be estimated, which is particularly challenging when the connection between chaser and target is not rigid, such as when achieved through a tether. In this work, the principal moments of inertia of tethered debris are estimated by means of Extended Kalman Filters and an Unscented Kalman Filter, using measurements of the rotational rates of the target. Two cases are analyzed in which (i) the chaser–tether–target system is subject to frequent tether slackness and (ii) the tether is almost continuously taut. The performance of the filters are analyzed via Monte-Carlo simulations. It is demonstrated that two of the principal moments of inertia can be estimated well, assuming knowledge of the tension in the tether and of the tether attachment point on the debris. It is found that, although the Extended Kalman Filter is capable of estimating the moments of inertia, it is inadequate due to the large variance of its final moment of inertia estimates. The Unscented Kalman Filter, instead, is capable of obtaining precise and accurate estimates of the moments of inertia after tethered capture of debris.