Optimal control scheme of space tethered system for space debris deorbit

This paper proposes an optimal control scheme for space debris deorbit by a space tethered system with minimal fuel consumption. The scheme includes two phases, the offline phase and online control phase. The offline phase involves an open-loop control trajectory optimization, which is derived by solving an optimal fuel consumption deorbit problem of the tethered system. A direct collocation method based on Gauss pseudospectral method is adopted to obtain the optimal trajectory. The online control phase concerns the closed-loop optimal control for tracking the optimal reference trajectory using the model predictive control method. Numerical results show that the proposed scheme can achieve space debris deorbiting to a graveyard orbit safely, economically and efficiently.