Backstepping control for attitude tracking of the spacecraft under input saturation

Finite-time control schemes without the drawback of unwinding are investigated by backstepping method for the spacecraft. The first finite-time controller is robust to external disturbances in which a novel virtual angular velocity is designed to avoid that the trace of the error rotation matrix equals to one. By using adaptive control, the second finite-time controller that can deal with input saturation is also robust to external disturbances. Theoretical analysis and numerical simulations are presented to prove the validity of the designed controllers.