Long-Term Rotational Motion Analysis and Comparison to Observations of the Inoperative Envisat

Abstract

A new model for the analysis and prediction of the rotational motion of large space debris over a long term is outlined. A formulation for a high-order gravity-gradient torque is derived as well as the aerodynamic torque for a spinning spacecraft defined by a general surface geometry model. The comprehensive model is exercised for a coupled orbit-attitude propagation of the defunct satellite Envisat. An in-depth analysis of the simulation results reveals that, unlike what has been assumed previously, the likelihood of Envisat’s spin axis remaining stable is small. A distinct nutation of the spacecraft’s angular momentum vector about the orbit normal is predicted, having a period on the order of a few days. Although a decay of the angular rate is expected, the nutation motion of the spin axis is expected to become larger and faster with time, underlining a potential difficulty for a future active debris removal mission. A critical review of observational studies reported on Envisat’s rotational state is performed, in light of the knowledge gained from the simulations and with a comparison to the simulation results. Finally, recommendations for future observation campaigns to provide better estimates of Envisat’s angular motion are put forward.