Disturbance observer based attitude control design of spacecrafts

We address the attitude stabilization problem of rigid spacecrafts in the presence of external disturbance torques. A nonlinear disturbance observer is designed first to estimate the unknown disturbances, and an attitude controller is then integrated with the estimation to stabilize the whole spacecraft system, which consists of dynamical and kinematical subsystems. The Modified Rodrigues Parameter (MRP) - which is a three-parameter nonsingular representation, is adopted as attitude description. Stability analysis of the closed-loop system is proved using standard Lyapunov technique and global uniform ultimate boundedness of attitude variables and disturbance estimation error is guaranteed. Numerical simulations demonstrate the practical applicability of the proposed algorithm.