Fault-Tolerant Stabilization of a Tethered Satellite System Using Offset Control

摘要

An adaptive fault-tolerant nonlinear control design based on the theory of sliding mode is proposed to control the attitude of a satellite using coordinated movement of the tether attachment points. The system consists of two identical tethers of equal length connecting the downward-deployed auxiliary mass to two distinct points that are symmetrically offset from the satellite mass center. This paper examines cases when tether deployment suddenly stops and tether breakage occurs. The nonlinear analytical model describing the system is used to derive a nominal sliding mode control law and an adaptive fault-tolerant control law in the presence of unknown slow-varying satellite mass distribution and tether rigidity parameters. Several numerical examples are presented to demonstrate the efficacy of the proposed control algorithms. Final results show that the high-amplitude oscillations present in the in-plane motion of the main satellite due to tether severance are effectively damped within a quarter of an orbit. In addition, an abrupt blockage of one of the tether attachment points is simulated, and the control law verifies the possibility of controlling the attitude of the satellite. The numerical results clearly establish the robustness of the proposed adaptive offset control scheme in regulating the satellite dynamics of a two-tether system in the event of breakage of one of the tethers.