Quaternion-based robust sliding mode control for spacecraft attitude tracking

The studies include quaternion-based attitude maneuvers and stabilization using continuous sliding mode feedback control. First, according to the time-scale separation principle, a virtual control law is used to prevent the "unwinding phenomenon" and also eliminate the undesired equilibrium manifold by defining a proper potential function. Second, via introducing a particular disturbance observer, which is sensitivity to external disturbance and uncertainties, the strong robustness of the system is achieved. The proposed approach ensures that the output of the system track the given bounded reference signals and makes the attitude tracking errors uniformly ultimately bounded, and converge to a small neighbourhood of zero by appropriately choosing the design parameters. Numerical simulations demonstrate the effectiveness of the proposed control schemes.