Research On Finite-time Attitude Control For Small Spacecraft And The Formation

With the development of aerospace new technologies,small spacecraft and its formation have become an important area for modern aerospace industry.The system have the advantages of flexible launching,low cost and strong redundancy,and can play important roles in deep space exploring and earth monitoring.To accomplish the scheduled tasks,an efficient attitude control algorithm is the key technology.For nonlinear attitude model,inertia uncertainty,external disturbance and multiple faults will have negative impacts on control accuracy and stability.Based on terminal sliding mode,this dissertation focuses on finite-time attitude control for the system,with the consideration of external disturbances,parameter uncertainty,sensor failure and actuator fault.The main contents are as follows:Firstly,based on terminal sliding mode and adaptive estimation,the finite-time attitude tracking and passive fault-tolerant control for single spacecraft are addressed.We studied the applicability of different terminal sliding mode surfaces and proved that the usual terminal sliding mode is more suitable for unit quaternion descripted attitude control system.With the combination of continuous adaptive estimation,the finite-time continuous attitude tracking for spacecraft is achieved and the chattering is further reduced.When actuator suffers the fault of loss of effectiveness,a passive finite-time fault-tolerant controller is also designed with compensation by robust adaptive estimation,and simulations illustrate the effectiveness of the proposed strategies.Secondly,a finite-time state observer and output tracking controller are respectively designed when angular velocity is unmeasured.The observer is integrated with adaptive estimation and the upper bound of quaternion derivative is unnecessary.Based on attitude kinematic dynamics,an angular velocity calculation algorithm is proposed and the angular velocity is obtained in finite time.Then the output feedback attitude controller is designed with continuous adaptive estimation.Here,actuator saturation is also considered and the stability under actuator saturation is also analyzed.Simulation results illustrate the effectiveness of the angular velocity estimation strategy and designed controller.Thirdly,considering external disturbance and inertia uncertainty,a disturbance-observer-based finite-time attitude synchronization controller is proposed for decentralized formation system.By arranging attitude control dynamics as a first-order system,a new finite-time disturbance observer is designed based on adaptive estimation and equivalent output injection method.The finite-time attitude synchronization controller is developed with the compensation of disturbance observer.Besides,actuator fault problem is also analysed,and the designed controller maintains good fault-tolerant capability with the compensation of the disturbance observer.Simulation results illustrate the effectiveness of the disturbance observer and the controller.Finally,a finite-time attitude synchronization control scheme is developed for distributed spacecraft formation system with no measurement of angular velocity and under directed topology.The improved continuous state observer and angular velocity calculation algorithm are designed,and angular velocity can be better estimated in finite time.The reference signals for each follower are calculated based on average attitude and finite-time estimation of the leader respectively.The distributed attitude synchronization controller is then designed with the combination of continuous adaptive estimation and a new continuous adaptive disturbance observer.Simulation results illustrates the effectiveness of the designed scheme.