Flexible Multibody Spacecraft Dynamic Modeling And Attitude Control

Flexible multibody spacecraft dynamic modeling and attitude control has been studied in this dissertation. The issues encountered in flexible spacecrafts have posed challenging problems in modeling and control technologies, including complicated dynamics, large model uncertainties, the increasing control objectives, the input saturation and high accuracy requirements, etc. For this reason, this dissertation has focused on the dynamic modeling and control system design of the flexible multibody spacecraft.In the light of recent works in the technologies of spacecraft dynamic and control, the dynamic modeling and attitude control technologies of the flexible multibody spacecraft systems have been discussed. Some new notions and design techniques were proposed in this dissertation. The main contents and results in this dissertation are as follows:The dynamic equations of motion of the flexible multibody spacecrafts with topological tree configuration have been derived based on the Lagrange's equations in terms of quasi-coordinates. The central body was treated as rigid and the others as flexible jointed by hinges. The interactions between rigid body and flexible body motions were studied. The dynamic equations were universal and programmable due to the information of system configuration being incorporated into the modeling process and were easy to realize using the computational procedures. The low order model suitable to design the control system has been obtained through model reduction using the united technique.In the multichannel spirit, the multiobjective synthesis problem of spacecraft attitude has been discussed. The static and observer-based output feedback controllers were designed in the LMI framework. The model uncertainties were dealt with by introducing an internal feedback loop. The input saturation constraint was addressed by the peak-peak gain and the invariant ellipsoid shaped by the Lyapunov function. A sufficient existence condition was derived for output feedback controller which could stabilize the closed-loop system, guarantee the disturbance rejection performance, and satisfy the control input constraints. The controller was designed via the LMI optimization technology. An iterative algorithm was given. The parameterδwas introduced to maximize the utilization of the available capabilities of the control devices and to improve the system performance. The trade-off between the model uncertainties and system performance was assessed. The main procedures to design controllers using multiobjective synthesis were given.The static output feedback control problems to linear uncertain systems which are dependent affinely on the real parameters were addressed. The design method to the guaranteed cost controllers of the spacecraft attitude control systems was proposed. Based on a parameter-dependent Lyapunov function, a sufficient condition of guaranteed cost controller to exist was given. Compared with the parameter independent Lyapunov function, this condition was less conservative for the affine parameter uncertain systems. An iterative LMI-based algorithm to solve the static output feedback controller was proposed. The robust stability of the closed-loop systems depending affinely on the uncertain parameters was analyzed. A LMI-based algorithm to compute the robust stability domains of the uncertain linear systems has been given. The influence of uncertain parameters on the poles of the closed-loop system has been analyzed, and the distribution of poles changing with the uncertain parameters was studied, too.The cooperation spirit was incorporated into the design procedure of the flexible spacecraft attitude control systems. The attitude control system with the decentralized cooperative architecture was proposed. The primary scheme and crucial techniques in the design process have been discussed. The decentralized conditions under which the control problems of large scale systems could be reduced to design the local feedback controllers of the subsystems have been given. For general large scale systems, the controllers were composed of the decentralized controllers and the global cooperative controllers obtained by the structural perturbation method. The techniques could be extended to the large scale systems with parameter uncertainties. Employing LMI optimization technology to design decentralized robust H∞controllers, the controller design method succeeded in solving the spacecraft attitude control problems.The pointing control problem of spacecrafts has been studied via H∞frequency separating control techniques. The H∞frequency separating control problem was firstly converted to the standard H∞control problems. An output feedback controller has been designed to track the target via multiobjective H∞synthesis. The frequency separating control has been realized in the resultant closed-loop system.For the special problems of the flexible multibody spacecrafts, the studies on the dynamic modeling and attitude control technologies of the flexible multibody spacecrafts were carried out in this dissertation. The influences of the system real-parameter uncertainties were overcomed. The nonlinearity due to input saturation was conquered. Some useful results have been obtained and they are of practical significance to design the spacecraft attitude control systems.