Finite-time Or Fixed-time Sliding Mode Control For Spacecraft

With the continuous development of technology and exploration of the space,the space mission has become more and more complicated and diversified.The attitude control is the premise and guarantee for completing various space missions.When performing space missions,the influence for the control performance from model uncertainty not only should be considered,but also the external disturbances should be considered.In addition,the design of attitude control will also face a big challenge arising from the high nonlinearity of the spacecraft dynamics model.In recent years,since missions become more and more complicated,in order to accomplish the missions successfully,higher demands on convergence rate,control accuracy and robustness are required on the spacecraft attitude control.Therefore,in view of the requirements of spacecraft attitude control,the following three different finite-time or fixed-time attitude tracking control strategies are proposed.The main works are described as follows:(1)For the requirements of uncertain spacecraft attitude control on transient convergence and control precision,a simple controller based on non-singular terminal sliding mode is designed to solve the attitude tracking problem.It is proved that the new surface can converge to zero within finite time and the attitude tracking errors converge to an arbitrary small bound centered on equilibrium point within finite time and then go to equilibrium point asymptotically.The appealing features of the proposed control are fast convergence,high precision,strong robustness and easy implementation.(2)For the problem that the settling time of finite-time control depends on the initial states,a fixed-time attitude tracking control strategy is developed in the fourth chapter,which can ensure that the upper bound of the settling time is independent of the initial states,that is,the upper bound of the convergence time is a constant value.Compared with the traditional finite-time sliding mode attitude tracking control,the developed control scheme can achieve faster transient,and the system state can converge to the equilibrium point instead of a small neighborhood of the equilibrium point.(3)For the weakness that the fixed-time control based on the bilateral homogeneous technique can not provide a clear estimation of the convergence time,a new fixed-time sliding surface is designed to solve this problem.Based on the new sliding surface,a fixed-time fault-tolerant attitude tracking control is proposed to estimate the upper bound of convergence time,which facilitates the description of the control performance.The stability of the attitude tracking control schemes proposed in this thesis is proved by Lyapunov stability theory.The effectiveness of the proposed attitude tracking control schemes of the spacecraft is verified by numerical simulation.