Attitude control of spacecrafts based on small-gain theorem

A nonlinear attitude control law for spacecrafts is proposed based on small-gain theorem considering the effects of the control loop dynamics. The attitude angular rate commands, which are aimed at driving the attitude angles to the desired ones, are designed according to input-to-state stability (ISS) theory. Then, the small-gain theorem is iteratively used to propose the final torque input. It is shown that the attitude angles under the control law can robustly track the desired values, and the tracking errors are ISS with respect to disturbances. Simulation results have confirmed the effectiveness of the proposed scheme.