Finite-time Attitude Control Based On Output Feedback For Spacecrafts

Attitude control is the basis of spacecrafts’ in-orbit operation and execution of various space missions.Designing a spacecraft attitude control system with strong robustness,high accuracy and high speed has always been the goal pursued by spacemen at home and abroad.Aiming at the problem of high-performance attitude control of spacecrafts in a complex environment,the following aspects are studied in this dissertation based on the attitude quaternion based spacecraft attitude tracking model.The problem of finite-time stability without angular velocity measurement information and external interference for the quaternion-based attitude tracking model of rigid spacecraft is considered.Firstly,a finite-time angular velocity observer,which is not based on model reference,is used to observe the diagonal velocities.Then,a finite-time disturbance observer with adaptive parameters is designed to estimate the external disturbances based on the angular velocity observations with unknown upper boundary.Finally,based on the observed values provided by the angular velocity observer and the interference observer,the finite-time attitude tracking controller is designed by using the power integral method and the inverse step method to realize the finite-time attitude tracking of the time-varying attitude signals of the rigid spacecraft without angular velocity measurement information when it is subjected to external interference.Numerical simulation shows the effectiveness of the proposed control law.Compared with the finite-time control law not considering the upper bound unknown disturbance,the simulation results show that the designed control law has better speed and high accuracy.Considering flexible spacecraft attitude tracking problems under external disturbance and estimation of attitude angular velocity,transform the flexible spacecraft attitude tracking model based on the quaternion into Lagrange standard form firstly.Then consider the flexible attachment vibration modal and spacecraft by external disturbance as a comprehensive disturbance,design a adaptive finite-time angular velocity observer and a adaptive finite-time disturbance observer respectively to estimate attitude angular velocity and the comprehensive disturbance.A class of finite-time attitude controllers based on integral terminal sliding mode surface is designed by using the estimates provided by two observers.The attitude controller is designed without angular velocity measurement and flexible modal information,which shows the robustness to external interference and angular velocity measurement device fault.The introduction of integral terminal sliding mode surface makes the system in the initial state on the sliding mode surface and improves the speed of the attitude control system.Numerical simulation shows the effectiveness of the proposed control law.