Constrained attitude tracking control and active sloshing suppression for liquid-filled spacecraft.

This paper is concerned with the attitude tracking control problem of liquid-filled spacecraft with large liquid sloshing. In existing work, the force and torque generated by liquid sloshing are usually treated as external disturbances which are assumed not coupled with spacecraft states and slow-varying. This assumption is inconsistent with the situation of large liquid sloshing. Besides, no special measures are taken to suppress liquid sloshing. In this paper, a novel constrained attitude tracking control and active sloshing suppression scheme is proposed, which considers the force and torque generated by liquid sloshing as nonlinear functions of spacecraft states and suppresses liquid sloshing by limiting the magnitudes of angular velocity, control torque and its changing rate. Three filters and two auxiliary subsystems are constructed to deal with state and input constraints. A neural network is employed to approximate the torque and force caused by liquid sloshing and a nonlinear disturbance observer is designed to estimate the external disturbance. The proposed constrained attitude control method is independent of modeling accuracy, uses only easily measurable feedback signals and does not require high computational cost.