Extended State Observer based robust attitude control of spacecraft with input saturation

This paper addresses the problem of robust optimal control of spacecraft attitude stabilization in the presence of parametric uncertainties, external disturbances and actuator saturation simultaneously. As a stepping stone, an Extended State Observer (ESO) is developed to estimate and compensate the specified uncertainties including actuators' misalignments and parametric uncertainties while ensuring uniformly ultimately bounded estimation error in the sense of finite-time stability. Then, with the reconstructed information, an inverse optimal Control Lyapunov Function (CLF) approach is developed to guarantee asymptotic stability of the closed-loop system, such that an optimal/minimum performance index can be achieved. The associated stability proof is constructive and accomplished by the development of a novel Lyapunov function candidate. Furthermore, with the concept of input-output linearization of dynamics transverse to zero dynamic manifold, a rapid exponential stabilization CLF based optimal control scheme is investigated by utilizing the quadratic programming technique to restrain the actuator saturation. Simulation results are presented to illustrate the performance of the proposed schemes.