| In 1957,the first artificial earth satellite was successfully sent into space by the Soviet Union.Since then,Thousands of artificial satellites have been successfully launched by all of the world.With the continuous development of space technology,space missions become more and more complex.From the perspective of spacecraft attitude,the requirements for modeling and control of dynamics and kinematics are getting more complicated.Research methods of spacecraft attitude usually include the direction cosine method,Euler quaternion method,Euler angle method,Rogers parameter method and Modified Rogers Parameter Method.As the singularity problem of Euler angle method,in this paper,the quaternion is used to build the model.Because the space environment where the spacecraft is located can be more complicated and parameters of the spacecraft are changing all the time,for the spacecraft,its attitude control accuracy will be greatly affected.In many cases,traditional control methods are unable to meet the requirements of aerospace missions in terms of robustness and control accuracy,so many control methods for nonlinear systems,such as sliding mode control,which have been proposed to make the system converge to the equilibrium state in a limited time with the anti-interference and robustness of the system greatly improved.Therefore,these nonlinear control methods have very far-reaching practical significance in complex space missions.The problems,which may occur in the spacecraft rendezvous and docking,mainly include the uncertainty of parameters,the uncertainty of external interference forces and interference torques,the failure of actuators and the problems of installation deviation,the problem of input saturation of actuators,etc.Aiming at the problem of complex space environment and the problem of undetermined the model parameters and external disturbances,the following two adaptive controllers are designed in this paper.The first is a sliding mode controller based on radial basis neural network,and the second is a controller based on the backstepping method considering the input saturation problem of the actuator.The two controllers have been verified by mathematical simulation.In the above controller,the closed-loop system has global asymptotic stability,and the error quaternion also reaches the equilibrium point through asymptotic convergence.The simulation results mean that the two controllers can show strong robustness to both model uncertainty and external interference. |
