Abstract: On-orbit refueling technology for spacecraft can significantly extend the operational lifetime of satellites and further advance manned lunar landing and deep space exploration missions. However, the spacecraft combination consisting of a refueling carrier and a receiving spacecraft has a large mass and high propellant transfer rates, which introduces significant challenges during the refueling process, including rigid-liquid coupling, time-varying parameters, and nonlinear disturbances. This paper establishes a coupled rigid-liquid-control dynamic model that incorporates mass transfer effects, in which the liquid propellant is equivalent to moving pulsating ball model. Furthermore, an adaptive control strategy based on Long Short-Term Memory neural network is developed to online learn and predict nonlinear time-varying disturbances caused by unknown dynamics such as liquid sloshing. Numerical simulations demonstrate that the proposed control method can effectively handle the attitude control problem of complex spacecraft systems and exhibits good robustness at different refueling speeds. The investigation of multi-tank propellant sloshing and control under microgravity environment considered in this paper will provide overall design reference for on-orbit refueling tasks of space transportation systems.

Key words: On-orbit refueling, Liquid sloshing, Moving pulsating ball model, Time-varying mass, Attitude control, Space transportation system