Robust Output Feedback Attitude Control For Liquid-filled Spacecraft

With developments of the aerospace technology, the on-orbit refueling technology is extensively attracted. As an important part of the on-orbit service plan, the on-orbit re-fueling can prolong spacecraft service life effectively. The on-orbit refueling is achieved successfully depended on a servicing spacecraft which carries a lot of fuels. The charac-teristic of this spacecraft is that the proportion of the fuel mass is very large in the total mass of the spacecraft. In this dissertation, the spacecraft which is loaded a great deal of fuels is named as the liquid-filled spacecraft. When the liquid-filled spacecraft maneu-vers on-orbit, the liquid fuels in the tank will slosh. The fuel sloshing affects the desired spacecraft attitude. What is more, the sloshing destroys the successful achievement of the on-orbit refueling. Therefore, the sloshing effect has to be sufficiently considered in the design of the attitude control system of the liquid-filled spacecraft. This dissertation is focus on the solid-liquid coupling attitude dynamics and robust attitude control for the liquid-filled spacecraft. And the researches mainly solve the disturbances to the space-craft attitude caused by the fuel sloshing during spacecraft rotations. The main contents consist of the following four parts:The nonlinear solid-liquid coupling attitude dynamic model of the liquid-filled s-pacecraft is presented. Based on the equivalent dynamics of the fuel sloshing, by the method of multi-body dynamics, the nonlinear solid-liquid coupling attitude dynamic model is proposed for the three-axis stabilized liquid-filled spacecraft. The presented model describes the coupling dynamic relationship between the spacecraft attitude mo-tions and the fuel sloshing. And, this model is suitable for the analysis and design of the liquid-filled spacecraft attitude control system. Moreover, comparing the presented liquid-filled spacecraft dynamic model with the original rigid spacecraft dynamic model, it is shown that the fuel sloshing changes the moment of inertia and produces the sloshing torques. These two items both disturb the attitude of the liquid-filled spacecraft. What’ s more, the numerical simulations illustrate that the pointing precision and attitude stabi-lization of the liquid-filled spacecraft decline if the fuel sloshing is neglected in attitude controller design.A robust multi-objective output-feedback control system is presented to stabilize the liquid-filled spacecraft attitude. According to the features of the attitude stabilization, a robust multi-objective control system based on observer is proposed for the linear dynam-ic model. The model is linearized in the location of the equilibrium point for solid-liquid coupling dynamic model of the liquid-filled spacecraft. The presented reduced dimension observer estimates the unmeasured states of the sloshing liquid in the spacecraft tanks. Utilizing the parametrization method for the linear system, the multi-objective controller design problem is transformed into an optimal problem, to guarantee the robust stability and reduce the control torques to avoid the control saturation. The numerical simulations illustrate that the proposed robust output-feedback control system can suppress the liquid sloshing and keep the spacecraft high pointing precision.A robust output feedback controller is presented for the rest-to-rest attitude maneu-ver of the liquid-filled spacecraft. To deal with the nonlinearity, the strong coupling, and the under-actuated of the liquid-filled spacecraft attitude dynamics, the Lyapunov direct method is utilized. A proper Lyapunov function is constructed, and then a nonlinear out-put feedback controller is designed. The presented controller which only utilizes attitude quaternion and angular velocities for feedback control is more practical and valuable. The numerical simulations illustrate that the robust output-feedback controller can achieve the desired attitude maneuver and suppress the fuel sloshing effectively in the presence of spacecraft parameter uncertainties.A robust output feedback attitude controller is presented for the liquid-filled space-craft with actuator saturation. The proposed controller only utilizes attitude quaternion and angular velocities for feedback control. Firstly, a robust PD controller for the rigid spacecraft with actuator saturation is presented. In the condition that the controller pa-rameters are chosen properly, the presented controller stabilizes the closed-loop system globally in theoretically. Moreover, the same controller design method is extended to the attitude maneuver controller design for the liquid-filled spacecraft. Parameter uncer-tainties, non-measurable sloshing fuels, and actuator saturation are all considered in the design process. In the condition that the controller parameters are chosen properly, the robust output feedback controller can suppress the fuel sloshing and achieve the desired attitude maneuver for the liquid-filled spacecraft with actuator saturation.