Dynamics modeling and attitude control of on-orbit refueling system

Driven by the urgent demand for deep-space exploration and manned lunar landing, the on-orbit refueling technique has been widely studied. This approach involves delivering fuel to spacecraft via orbital refueling stations, which can extend the operational life of spacecraft. Additionally, by reducing the amount of fuel required at the launch stage, this strategy improves the launch transportation capacity and overall mission efficiency. This study investigates the dynamic characteristics and control methods of the on-orbit refueling system. First, based on Newton’s second law for variable-mass systems and combined with the mass conservation equation and initial conditions, the dynamic equations describing liquid level changes in the refueling and receiving tanks are derived. An analytical solution for this nonlinear ordinary differential equation is obtained. Second, the attitude dynamics equation of the spacecraft is established by considering the internal mass motion, liquid sloshing, and time-varying inertia, thus forming a complete dynamic model of the spacecraft during on-orbit refueling. Subsequently, through a specific case study, instability phenomena caused by changes in mass distribution and time-varying moment of inertia are analyzed, and an optimization strategy is proposed. Finally, through the discrete-form wave-based proportional-derivative (PD) control method, the attitude adjustment and fuel sloshing suppression of the liquid-filled spacecraft system are achieved.