Research On Finite-time Control Of Flexible Spacecraft During Attitude Maneuver

Modern spacecraft becomes more and more flexible along with the complexity of space missions,in order to reduce its weight and prolong its on-orbit life.The dynamic model of flexible spacecraft is highly nonlinear and the vibration of flexible appendages will induce a terrible impact on attitude control,even damage the structure.Most past researches can only guarantee the attitude error converges to zero asymptotically when time tends to infinity,rather than in finite time,however,many space missions require that the spacecraft is being capable of rapid maneuvering.Therefore,this paper focus on finite-time attitude control of flexible spacecraft.Firstly,the attitude dynamic model of flexible is established based on the Hamilton theory and the discretized method including assumed modes method and finite element method is discussed both in advantages and shortages.The assumed modes method is chose as the discretized method of dynamic equations finally.Secondly,a traditional control method including PD control law and a revised PD control law is applied to attitude control problem of flexible spacecraft.Simulation results demonstrate that the robustness of this method is poor and the vibration is hard to eliminate.Then,a finite-time control law based on terminal sliding mode control is proposed in order to enhance the capability of rapid attitude maneuvering.In this method,a closed-loop feedback control law is designed based on Lyapunov theory aiming at achieving desired attitude in a finite time.Furthermore,taking the fact that the upper bound of the disturbances and model uncertainties is hard to obtain in practice,an adaptive law is proposed combined with finite-time control law to tackle this problem.Finally,this paper investigates the finite-time attitude control of a flexible spacecraft under actuator saturation by combining a path-planning method with terminal sliding mode control algorithm.First,an optimal attitude path is suggested to tackle with problem of actuator saturation and suppress vibration of flexible appendages.Then,a finite-time controller is designed based on terminal sliding mode control and the stability of overall system is proved by Lyapunov method,and the finite-time convergence of the control system is proved,too.Finally,simulation results demonstrate the effectiveness of the control algorithm that the flexible spacecraft is able to complete attitude maneuver in an arbitrary settling time and has an ideal robustness towards to disturbances and flexible vibration.