Applied nonlinear control of spacecraft simulator with constraints on torque and momentum of reaction wheels

In this paper, the attitude of a spacecraft simulator is controlled in the presence of nonlinearities, uncertainties and constraints of the system. An optimization-based controller is developed in the closed form based on predicting the nonlinear responses of spacecraft system. For practical requirements of the spacecraft actuated by the reaction wheels (RWs), the control method considers the actuator limitation in the torques applied to RWs and the restriction in the angular momentum of the wheels due to the limited rotational speed of motors. In this way, the momentum constraint is equated with the torque constraint by a prediction-based transformation. Then, the constrained optimal control law is calculated by solving an equivalent optimization formulation. The constrained stability is analyzed by the Lyapunov second method and the bound of system response is obtained in terms of the prediction time. In the results, at first, the performance of the unconstrained version of the proposed controller, which leads to the feedback linearization like controller, is evaluated in the presence of uncertainties through computer simulations. Finally, the constrained version is simulated and experimentally implemented as hardware in the loop on the spacecraft simulator. The obtained comparative results indicate a good performance for the constrained controller in realistic conditions.