Consensus-based Leader-following Distributed Coordinated Control For Spacecraft Formation

Spacecraft formation is a space system consisting of small spacecraft to keep a specified configuration,which complete missions cooperatively by the information exchange.The spacacraft in a formation utilizes the communication to guarantee the cooperative effectiveness among the spacecraft,which can have better performance than traditional single spacecraft.Therefore,coordinated control is the fundamental requirmant for spacecraft formation.The main task for spacecraft formation is to realize the desired orientation and the desired configuration by adopting efficient attitude coordinated control scheme and relative position coordinated control scheme.It can precisely perform formation missions to accomplish the earth observation or the deep space exploration and ensure the fight safety by collision avoidance methods.Recently,the consensus theory of multi-agent systems has provided a new view for coordinated control of spacecraft formation.Under the distributed structure,this thesis mainly focuses on the coordinated control based on consensus theory to achieve attitude synchronization and formation keeping,while some practical issues are considered,including the uncertainties,external disturbances,state constraints,communication mechanisms,and safety problem,ect.The main contents are specified as follows.In order to tackle the uncertainties and external disturbances existing in the spacecraft formation systems,under the directed communication topoloy,,a distributed adaptive attitude coordinated tracking control algorithm is designed with the estimation mechanism of neural networks for uncertainties.Then,multi-layer neural networks are utilized to estimate the system uncertainties,which can avoid choosing the parameters for Gaussian activation functions.In addition,the state-constraint controller combined with barrier Lyapunov function is to satisfy the designated region.The method can improve the control precision and the safety performance of the attitude control for spacecraft formation.The communication delays is inevitable for spacecrat formation due to the information interaction via the communication networks.Therefore,the attitude coordinated control strategies are designed for the formation systems with the constant communication delays and the time-varying communication delays.First,for the case where the communication delays are constant,based on the certainty-equivalence principle,a distributed coordinated controller with the adaptive technique is provided to sovle the problem of the uncertainties by employing a regression matrix for the formation system with a static leader spacecraft.According to the transfer function by Laplace transform,the frequency domain method is used for the stability analysis for the formation system with communication delays.Then,for the case where the communication delays are time-varying,the information of the dynamic leader spacecraft is available to only a subset of follower spacecraft in the formation.Based on the neighbors' information with communication delays,the attitude coordianted controller combined with the distributed estimator is presented.Since the frequency domain method is not suitable for the system with time-varying communicaiton delays,based on the Lyapunov stability theory,the Lyapunov-Krasovskii functional is structured to present the condition for stability.The relative position coordinated control problem is investigated to maintain the desired configuration among the spacecraft,which can ensure that the spacecraft cooperatively perform the mission.There exist some limitations of the continuous communicaiton,such as the energy loss of the information exchange,the limited bandwidth of communication equipments.Therefore,in order to reduce the burden on the communication,distributed event-triggered control strategies are provided to solve the problem of the continuous communicaiton,which replace the neighours' information of the traditional continuous controller by the discontinuous states.Based on the event-triggered mechanism,the condition of the triggered function is determined by monitoring the errors of measurement state for each spacecraft.The state-dependent trigger function and the mixed triggered function are designed for formation system without and with leader spacecraft,respectively.The theoretical analysis is provied to eliminate Zeno behavior,which events cannot be triggered continuously.This method can adjust the communication time to reduce the communication frequency and save the system energy.Distributed coordinated control schemes for spacecraft formation with the fight safety are proposed for collision avoidance.First,under the case that only a subset of the follower spacecraft have access to leader spacecraft,a distibuted estimator is designed to estimate the leader's constant velocity.By introducing the attractive potential function and the repulsive potential function,the distributed formation control algorithm is present to achieve tracking the dynamic leader spacecraft.When a conflict betweent the collision avoidance task and other tasks,such as target tracking and formation keeping,these tasks need to be assigned in order.Based on the task-priority concept,the basic tasks are arranged in priorities and the different task outputs are merged to generate the reference command through a null-space projection.The distributed relative position control strategy is proposed by using the backsteppting technique and BLF technique..This control strategy can ensure that there is no collision for each spacecraft in priority,and then the desired formation can be realized.