Finite Time Attitude Control For Multiple Spacecraft Formation Based On Terminal Sliding Mode Theory

Coordinated attitude control within a formation of spacecraft is an important research content of spacecraft formation flight,plays an important role in many actual formation tasks,which has aroused widespread concern of scholars at home and abroad.The dynamic model of the flexible spacecraft system is nonlinear and is influenced by the flexible mode,unknown external disturbance,actuator installation deviation and communication delay,which affects the control precision and stability of the spacecraft formation system.Due to the varied structure of the spacecraft and the higher requirements of the space mission,the traditional control scheme is not enough to meet the actual needs.It is very practical to design a robust cooperative attitude controller with strong robustness.Based on the theory of terminal sliding mode control and adaptive theory,this paper will study the finite time attitude cooperative control of spacecraft formation system under several complex task constraints.The main research contents are as follows:The relative kinematics and kinetic equations of the flexible spacecraft formation are analyzed,and the directional communication structure of the spacecraft formation is determined.By designing the integral sliding mode surface and the corresponding integral sliding mode adaptive controller,the flexible mode,The external disturbance and the influence of the actuator installation bias,the nominal system of the spacecraft formation based on the directional topology,that is,the spacecraft formation system,which does not take into account the flexibility mode,external interference and actuator installation bias.The attitude control strategy of the nominal system is designed in the presence of communication delay,so that each spacecraft in the spacecraft can stably track the expected attitude and keep the formation attitude and stability.A class of nonsingular fast terminal sliding surface is designed based on directed topology.Considering the influence of unknown disturbance,flexure mode and actuator deviation on the stability of the system,a finite time attitude synchronization control law and adaptive law are designed based on the finite time theory to make the quaternion error and angular velocity of the closed-loop system The error can converge to the small region in finite time respectively.Due to the discontinuity of the control law equation,the discontinuous term in the controller is replaced by the boundary layer idea as the saturation function of the boundary layer,but the system error will not be strictly convergent To the sliding surface,it will cause the long-term drift of the adaptive parameters.Therefore,the modified finite time attitude cooperative control law and the adaptive law are given to ensure that the tracking error and the relative error converge to the small area near the zero point in the finite time.