On Attitude Control And Vibration Suppression Of Flexible Spacecraft

With the rapid development of the aeronautics and astronautics technology, the attitude control of flexible spacecraft becomes more and more important, and there are more and higher requirements of stability and pointing accuracy problem of flexible spacecraft. In the control of flexible spacecraft, the coupling effect between attitude maneuver and structural vibration must be considered, so it greatly challenges the control area. The paper deals with a kind of flexible spacecraft composed of a centre body and two asymmetric flexible appendages, and it can be described by a flexible hub-beam system. The main works are as follows.First of all, the development of flexible bodies'modeling theory and control theory is summarized. Meanwhile, the modeling process of flexible spacecraft is introduced, as well as the control method of flexible spacecraft.Secondly, based on the Hamilton theory, distributed parameter system of the flexible hub-beam system is obtained by mixed coordinate method with consideration of the coupling effect between axial and transversal deformation. Due to complexity and non-feasibility of distributed parameter system in control design, assumed mode method is used to discretize the obtained model. Then the first-order approximation coupling dynamic model is built, and the phenomenon of dynamics stiffening is also analyzed. As for the realization of the control, some simplification is done.Thirdly, in light of the advantage of robustness, theory of Variable Structure Control with Sliding Mode is used to design the controller for the simplified system. And the Lyapunov method is applied to demonstrate accessibility of the sliding mode. Numerical analysis is conducted to show effectiveness of the strategy by using Simulation toolbox in Matlab. The attitude rapidly tracks the desired value, and the purpose of vibration suppression is also achieved during attitude maneuvering.With concern that not all the states of the system are detectable, a sliding mode observer is subsequently investigated based on the idea of Walcott-Zak sliding mode observer. Numerical simulation is also conducted. And the simulation results illustrate the observer can exactly estimate all the states of the system, and perfect control performance is obtained when it is applied in the flexible spacecraft control system.At last, the thesis is summarized and the open problems for further research are also discussed.