Novel scheme for uncertainty and disturbance estimation to control of spacecraft system with input constraint

In this paper, a novel scheme is presented to estimate the uncertainty and disturbance of the spacecraft system by a compensatory vector calculated online from the information of measured angular velocities. The compensatory vector is used in the constrained attitude control law to compensate for the perturbations of the spacecraft system. The attitude controller considering the input limitations of reaction wheels is developed by solving an optimization problem through the Karush-Kuhn-Tucker (KKT) theorem. By using noisy angular velocities in the observer design, the stochastic stability of the closed loop system under the constrained multivariable controller is demonstrated. In the results, at first, the open-loop performance of the uncertainty and disturbance observer is evaluated through computer simulations. Subsequently, the performance of the proposed controller in both constrained and unconstrained versions is evaluated. Finally, the proposed controller performance in compensating for uncertainties and disturbances is compared with the adaptive backstepping controller reported in the literature. The comparative results of two controllers show the superior performance for the proposed constrained controller in the presence of disturbances, uncertainties and input constraints. Furthermore, the proposed control system could attenuate the effect of measurement noises of angular velocities by weighting the compensatory vector in the observer design.