Modeling And Control For A Liquid-Filled Spacecraft With Flexible Appendages In Close Proximity

In close proximity, the servicing spacecraft is a complex system with rigid flexible-liquid coupled, and the liquid sloshing model, such as pendulum, isn't applicable. The dynamics modeling and control of this spacecraft were studied. Firstly, a kind of new liquid sloshing equivalent mechanical model was derived by virtual work principle, and it could be applied to the situation of tri-axial thrust. Secondly, a relative position guidance vector and a relative position error vector were defined, and a relative position error dynamics model was derived. Thirdly, combining the relative position error dynamics with the relative attitude dynamics, a coupled relative attitude-orbit dynamics model was established, which was suitable for the process of close proximity in rendezvous and docking. The model was also rigid-flexibility-liquid coupled. Finally, a control law based on the slide-mode-control was designed to estimate the unknown but bounded disturbances, system uncertainties and measurement noise. The effectiveness of the control law was validated by numerical simulation. The results of the sloshing in the simulation agree well with the Flow-3D results, which indicates that the liquid sloshing equivalent mechanical model is reasonable.