Unified attitude control for spacecraft under velocity and control constraints

A novel smooth attitude algorithm is presented for rigid spacecraft in the presence of assigned sensor and actuator saturations, as well as external disturbances. More specifically, an analog of variable structure control law is first developed by explicitly taking into account the velocity and control constraints simultaneously. In the proposed controller, behavior of the adaptive parameter is investigated to ensure the close-loop convergence and disturbance rejection. The straightforward relationship between the constraints given and parameters tuning is further analyzed. In addition, to avoid the unwinding phenomenon problem caused by quaternion attitude representation, a class of definition of attitude error vector is proposed to ensure that both two equilibria are locally asymptotically stable. Numerical simulations illustrate the performance of proposed attitude controller and the improvement of the anti-unwinding technic.