Sliding Mode Attitude Control For Flexible Satellites Based On Quaternion

The attitude maneuver of the satellite can be easily affected by the vibration of the flexible appendages and the external disturbances during the on-orbit service.If effective control schemes are not taken,it is difficult for the satellite attitude to meet the requirements.Therefore,it is important to design controllers to achieve rapid attitude maneuver as well as attenuate the effect of the external disturbance.For this end,we consider the attitude control of quaternion-based flexible satellites with external disturbances.The main contribution is as follows.For the rest-to-rest attitude maneuver problem of the flexible satellites with unknown external disturbances,the upper bound of the external disturbances is assumed to be known a priori.In this case,sliding mode controllers are designed for the attitude maneuver of flexible satellites.First,a sliding mode manifold is introduced and the stability of the sliding manifold is proven by the input-to-state stability theory.Then,a sliding mode controller based on the full information feedback is proposed when the flexible modal variables are available.The stability of the closed-loop system is proven by using the Lyapunov stability theory.In addition,a modal observer is introduced to estimate the flexible modal variables and a modal-observer based sliding mode controller is designed for the flexible satellites.Simulation examples are given to show the effectiveness of the proposed controllers.In order to adjust the speed of the flexible satellite system state when approaching the sliding manifold,and reduce the high frequency chattering of control torque in the conventional sliding mode surface,we proposed a self-adjusting reaching law.A delay factor in exponential form and a self-adjusting factor are introduced into the reaching law of sliding mode controller to reduce the steady state error and improve the stability of the maneuver process.When the upper bound of the external disturbances is unknown,an adaptive control law is proposed for the attitude control of flexible satellites system by using the Lyapunov stability theory.Then,we design adaptive sliding mode controllers with self-adjusting parameter to attenuate the effect of the external disturbances.The stability of the system is proved with the Lyapunov stability theory.Finally,the simulation examples demonstrate that the proposed controllers are effective and robust.