Research On Attitude Coordinated Control For Multiple Spacecraft Formation

Multiple spacecraft formation refers to a novel working mode with several spacecraft which are capable of operating coordinatingly on the request of certain missions.Owning to the information flow between neighboring spacecraft,cooperative control can be achieved.Hence,some deceting aims,which are impossible for the traditional single spacecraft to perform,could be accomplished by multiple spacecraft formation.The last decades have witnessed the contributions of spacecraft formation as an excellent alternative in the fileds of universal exploration,military and national defense applications,etc.During its flying,attitude coordinated control is one of the basic manipulations for multiple spacecrarft formation,which is of significant importance and necessity to guarantee mission success.Research on spacecraft formation coordinated control has been deepen due to the thriving development on consensus theory for multi-agent system and constantly innovation on single spacecraft control.Based on the existing theoretical results,this thesis aimed at designing attitude coordinated control algorithms for multiple spacecraft formation with communication constraints and time-delays between neighboring member,where parametric uncertainties,external disturbances,inadequate feedback information and actuator saturation are considered.Moreover,fast response rate and high robustness are also taken into account.Given the statement above,the main contents and achievements are presented as follows.To begin with,kinematic and dynamic model of multiple spacecraft formation attitude system is introduced,some fundamental knowledge on graph theory,Lyapunov stability theory and finite-time stability theory are illustrated as well.Under undirected connected communication topology,leaderless attitude consensus for multiple spacecraft formation is investigated.Initially,both attitude and angular velocities of the spacecraft are supposed to be measurable.A full state-feedback finite-time attitude coordinated control algorithm is developed by adopting homogenous theory,such that the attitudes of individual spacecraft rotate to their average value in finite time and the angular velocity converges to zero.Then,in absence of angular velocity measurements,a filter with a power term is proposed to facilitate the finite-time output feedback attitude coordinated control law.Moreover,hyperbolic tangent function is used to constrain control torque magnitude,thus the velocity-free finite-time attitude coordianted control law with input saturation is accomplished.Practically,multiple spacecraft formation with a leader to provide reference state is more useful and more favorable,thus finite-time attitude coordianted control algorithm is further studied.In the case of static leader,a distributed finite-time observer is developed with the attitudes of individual spacecraft and its neighbours’.Hence,the lack of angular velocity is compensated,and attitude coordinated controller can be designed on basis of the observer.Furthermore,the formation with a dynamic leader is considered.A finite-time attitude coordinated tracking control law together with a finite-time observer is constructed.The distributed finite-time observer is designed under the assumption that the angular velocity of neither the formation members’ nor the leader’s could be measured,and even the reference attitude is accessable by only a subset of the formation members.Based on the observered values,adding a power integral technique and adaptive method are introduced to develop the saturated finite-time control law.Especially,rigorous theoretical anaylysis on stability of the closed-loop system is presented.Lyapunov functions for the closed-loop system are considered both before and after the observed errors converge to the equilibrium,which completes the demonstration of the proposed attitude coordinated control algorithm.Apart from system stability,the coordination of attitude maneuver between formation members has become increasingly desirable.As communication delays always bring adverse effect on attitude coordination,control algorithms are proposed with consideration of constant communication delay.Under a directed communication topology,a delay-independent sliding mode attitude coordinated tracking control law is designed,where constant time-delays and bounded external disturbances are handled.Stability of closed-loop system is analyzed by using Lyapunov-Krasovskii method.However,chattering phenomenon may occur due to sign function within the sliding mode surface.Hence,integral sliding mode control law with boundary layer is investigated to improve system dynamic performance.Firstly,under a directed communication topology,a nominal controller is designed regardless of environmental disturbances.Then,integral sliding mode control together with adaptive approach is adopted to deal with external disturbances.Additionaly,boundary layer is introduced to alleviate chattering as system states crossing the sliding surface.On basis of above studies,attitude coordinated tracking control protocols for multiple spacecraft formation with time-varying communication delays are further developed.Supposing the communication topology is described by an undirected graph,sliding mode control and adaptive control method are employed to enhance system robustness to parametric uncertainties.Moreover,the closed-loop system satisfies 2(43)-gain performance by selecting appropriate control parameters.Moreover,combining command filter and backstepping technique,actuator saturation is solved.Hence,the actual control torque can be constrained to the allowable scope.In addition,Chebyshev neural network is applied to compensate system uncertainties and external disturbances.Thus the saturated delay-dependent attitude coordinated tracking control algorithm is constructed.Stability of the closed-loop system is illustrated by Lyapunov-Krasovskii menthod.It should be mentioned that this control algorithm is developed regardless the specific connection between formation members.It implies that attitude coordinated tracking can be achieved as long as system parameters are selected to satisfy the stability condition.