Suboptimal attitude control of nadir-pointing satellites using magnetic torquers and reduced reaction wheels

In satellite attitude control systems, reaction wheels are prone to angular momentum saturation and failure, particularly during emergency operations. To maintain effective attitude control and momentum management when one wheel is unavailable, this paper develops a hybrid control strategy that combines two remaining reaction wheels with three magnetic torquers. While optimal control laws are typically obtained by solving the Hamilton-Jacobi-Bellman equation, this approach is generally intractable for nonlinear satellite dynamics. To balance optimality and computational efficiency, we propose a suboptimal control scheme based on a control Lyapunov function for the satellite's nonlinear affine system, which is constructed by the attitude kinematics, attitude dynamics, and reaction wheel dynamics. The proposed method is shown to ensure global asymptotic stability without relying on the common assumptions of a diagonal inertia matrix or zero wheel momentum. Numerical simulation comparisons and hardware-in-the-loop experiments further validate the superiority and effectiveness of the proposed control algorithm.