Inertia Tensor Estimation of Tethered Debris through Tether Tracking

It is well known that space debris is a risk to the safety of spacecraft in orbit. To increase the safety of space operations, one promising method involves removal and disposal of debris via a tethered system, which may include tethered harpoons or tether nets. Control of debris is complicated by the fact that debris is uncooperative and unresponsive, and its properties are largely unknown. Many of the control strategies that have been proposed can be improved if the moments of inertia of the target debris were known. In this work, an Unscented Kalman Filter is employed to estimate the moments of inertia, angular rate, and attitude of tethered debris by leveraging camera measurements of features on the target debris and a tension sensor. The filter is found to be capable of accurately and precisely estimating both the attitude and angular rates of debris; however, loss of a tracked feature heavily impairs these estimates. On the other hand, the principal moments of inertia estimates are unaffected by the loss of a tracked feature and can be estimated both accurately and precisely when the tether is taut.