Adaptive spacecraft attitude tracking and parameter estimation with actuator uncertainties

This paper studied the attitude tracking control of a spacecraft using variable speed control moment gyros (VSCMGs) as the actuator. The dynamics of the spacecraft with uncertainties was established. These uncertainties included the moment of spacecraft inertia, the configuration of the VSCMGs, and the moment of the rotator inertia. To solve the problem, the uncertainties were classified into two types. Type I included installation misalignment angles and some part of the rotator inertia, which could impact the character of the output of the VSCMGs. The rest of the uncertainties were categorized as Type II, which could impact the response of the spacecraft attitude control. Different parameter estimation methods were designed for the uncertainties of the two types. For Type-I uncertainties, their relationship with the output-torque error was established based upon which the estimation of Type-I uncertainties was designed. Based on the Lyapunov theory, the estimation of Type-II uncertainties and the adaptive attitude tracking controller were proposed. In this way, the estimation value of Type-I uncertainties could achieve the actual value, and the impact of Type-II uncertainties imposed on the system could be counteracted by the proposed attitude controller. The simulation results showed that the proposed methods could reduce output torque errors. Therefore, attitude tracking performance would be improved.