Single-attitude regulation and conventional liquid sloshing suppression strategies limit the accuracy and stability of close-range rendezvous and docking for liquid-filled spacecraft. To address this issue, this paper investigates an integrated attitude-orbit control framework considering liquid sloshing effects. First, a nonlinear attitude-orbit coupled dynamic model is established based on dual quaternions, where liquid sloshing is represented using an equivalent mechanical model. Then, an extended state observer is designed to estimate system states and external disturbances in the underactuated spacecraft system. To suppress liquid sloshing and improve control performance, a modified fixed-time fractional-order sliding mode surface incorporating sloshing dynamics is constructed, based on which a modified fixed-time fractional-order sliding mode controller (MFTFOSMC) is developed. Numerical simulations verify the effectiveness of the proposed method. The results show that the controller suppresses liquid sloshing while improving the convergence performance and robustness of the attitude-orbit control system, providing guidance for close-range rendezvous and docking missions of liquid-filled spacecraft.
Wu et al. (Wed,) studied this question.