Analysis And Control Of Dynamic Pointing Accuracy For Satallite Antenna

With the development of space reconnaissance, the requirement of antenna pointing accuracy becomes more important. Satellite antenna system is the free-floating, and its movement has strong non-linearity. Further, satellite antenna system possess nonlinear attribute (such as dynamic errors, joint clearance, reflector flexibility and space environmental effects) that is responsible for performance degradation and present special challenges to modeling and control. Thus, this thesis focuses on research of the analysis of dynamic pointing accuracy of the satellite antenna and its control.Satellite antenna system is typical multibody flexible system. The dynamic coupling characteristics make the dynamic analysis complicated. In order to improve the computational efficiency, Lagrange and Newton-Euler method are used for establishing the forward and inverse dynamic model with characterization of its chain topology. Further, the fixed-interface component-mode synthesis is used to achieve a lower order dynamic model, and the rigid-flexible coupling dynamics model of satellite antenna is realized through compatibility relations at the interface between antenna shaft and flexible reflector under the large motions. Both the dynamic models are compared to the commercial dynamic software for validation.The flexible joint introduces dynamic error that is harmful for antenna pointing accuracy and satellite attitude. Under forcing excitations of different frequencies, the equation of approximate solution and frequency response are deduced by multi-scale method. Then, disturbance effects of satellite antenna are analyzed considering the dynamic error. Finally, the nonlinear control algorithm for compensation of antenna pointing accuracy is proposed for trajectory tracking. The asymptotic stability is established using Lyapunov stability theory. The nonlinear controller algorithm can completely compensate for the dynamic error and suppress its disturbance with reasonable controller parameters.The presence of clearances degrades the performance of the satellite antenna system. A methodology for modeling and analysis is presented considering the effects of the joint clearance and reflector flexibility in the system. The joint clearance model is established based on a thorough geometric description of eccentricity vector. The contact-impact forces are evaluated based on a Hertz contact theory and a modified Coulomb's friction law. Further, through the contact-impact criterion, the multi-body dynamics of satellite antenna is analyzed based on Newmark method. Finally, the porous squeeze film-lubricated is introduced into joints which can control the clearance effects. The joint impact effects can be greatly reduced and steady-state performance is improved.The dynamic analysis is quite complicated due to flexible vibration of reflector for satellite antenna system. Thus, dimensions of dynamic model are reduced by means of modal reduction based on the criterion of inertia completeness. The disturbance of flexible antenna reflector elastic deformation to satellite antenna system is analyzed under the layout constraints. Further, the PD vibration force feedback control law is used to eliminate the system vibration, and the asymptotic stability of the system is proved based on Lyapunov method. The results show that the proposed control strategy can quickly suppress system vibration.According to the geometric characteristics of parabolic antenna reflector, the temperature function in one element along its thickness direction is built for shell structures, and the finite element equations for heat conduction equations are derived. The coupling terms of strain energy relations are introduced. And the rigid-flexible dynamics of satellite antenna system considering thermal load is studied under space environment. The result shows that, the temperature gradient induced vibration of flexible reflector to produce elastic deformation. Furthermore it excites to aggravation its own elastic vibration which can make the system vibrated and deviations of satellite base attitude and antenna pointing become larger. The proposed adaptive controller is proposed to improve the antenna pointing considering time varying parameters and external disturbances, and the asymptotic stability of the controller algorithm is proved based on Lyapunov method.