Research On Attitude Control Of Spacecraft Based On Momentum Exchange

The momentum exchange devices used in spacecraft attitude control systems as ac-tuators have the advantage of low fuel consumption. But there are also some physicalproblems to be solved, such as momentum saturation, geometric singularity, reduction ofthe control torque dimensions due to the hardware failures and so on. In this dissertation,single gimbal control moment gyros(SGCMGs) and reaction flywheels of the momen-tum exchange devices are taken into account, and the existing problems of the spacecraftattitude control systems in diferent typical configurations are investigated.Firstly, the traditional models of the spacecraft and SGCMGs are given separately.Then the integrated mathematical model of the system consisting of SGCMGs and space-craft is constructed in the gravitational field. By considering the large angular maneuverof the spacecraft in short time, the model is simplified to an afne nonlinear system. Thecontrollability of the integrated system, irrespective of the geometric singularity of theSGCMGs, is proved by using the Hamiltonian construction of the system and the rele-vant controllability theorems. The controllability conclusion will lay the foundation forthe controller design of the integrated system using the momentum exchange devices asactuators.Secondly, the dynamics and kinematics of the spacecraft are taken as the state equa-tions of the control system. By considering model uncertainties, disturbance torques andthe control torques saturations existing in spacecraft, in the framework of tradition controlscheme, the smooth state feedback controller and the non-smooth sliding-mode controllerwith high self-adaptability and robustness are designed, respectively. The performanceindex of the typical SGCMG configurations are given, and the null motion inverse steer-ing laws are designed for the pyramid configuration. The simulation results are given toverify the disadvantages of the traditional control scheme.For the problems such as singularity, difculty in the design for the underactuatedsystem existing in the traditional control scheme, nonlinear model predictive control (N-MPC) method is used to realize the feedback control of the integrated system. The math-ematical analysis of the SGCMGs’ singularity problems is conducted. The singularityproblem is converted into the control problem with states and control inputs constraints. Then the NMPC based on the varying terminal constraints is proposed to realize the feed-back control as well as to satisfy the real-time performance of the control system. Atlast, linearized model and the estimated hyper-ellipsoid region of valid linearization ofthe system are given to ensure the stability of the control system.Thirdly, the proposed control method is applied to the spacecraft attitude controlsystem with certain configurations of the SGCMGs in order to solve the singularity prob-lem in the traditional control scheme. The pyramid configuration is taken as an example,the existence of the NMPC solution of the integrated system with redundant SGCMGs isanalysed. Then the controllability condition of the linearized equation is analysed. Theperformance index of the three typical non-redundant SGCMGs configurations are giv-en, and the optimal non-redundant configuration is proposed. Based on the given optimalconfiguration, The sufcient condition of the feasibility of the NMPC scheme is analysed.At last, the simulation results verify the efectiveness of the NMPC scheme.Finally, the proposed control method is applied to the underactuated spacecraft atti-tude control problem. The geometric distribution for the momentum set of the scissorsconfigurations of the SGCMGs is given. The controllability of diferent models of the s-pacecraft is analysed. The NMPC scheme is used to control the integrated system. Basedon the above work, the attitude control problem of the underactuated spacecraft with thereaction flywheels is solved by using the same scheme. At last, the simulation of the un-deractuated spacecraft with diferent actuators is conducted. The simulation results verifythe correctness of the controllability of the system and the efectiveness of the controlscheme.