Quaternion-based output feedback attitude control for rigid spacecraft with bounded input constraint

This paper investigates the quaternion-based attitude stabilization problem for spacecraft without using explicit velocity feedback in the presence of torque magnitude limit. As a stepping stone, a nonlinear output feedback attitude control is designed by involving a linear passivity filter, which is derived without explicit differentiation of attitude to synthesize angular velocity-like signals. Then, the control law is redesigned such that the actuator-magnitude constraint is explicitly taken into account, and the associated stability proof is accomplished by the development of a novel Lyapunov function candidate containing integral terms involving the various states. The proposed controller achieves asymptotic stabilization with saturated inputs and is robust to parametric uncertainty in the spacecraft inertia matrix. Simulation results are included to illustrate the performance of the proposed output feedback control strategy.