Research On Attitude Control For Flexible Spacecraft With Guaranteed Performance Bounds

With the rapid development of aerospace engineering,on-orbit space missions become more and more complicated,which leads to high demands of attitude control for spacecraft.For on-orbit spacecraft,such as remote sensing satellites,communication satellites,relay satellites and so on,since their on-orbit missions involve orienting and tracking of one or more payloads,specific precision for attitude control system needs to be satisfied.During the process of attitude controller design,in order to satisfy the attitude control precision requirement,huge amount of numerical simulations and semiphysical simulations are needed,so as to finally obtain the attitude control precision that the physical control system can provide statistically.Generally,one can only prove the stability of the proposed controller during theoretical analysis,but cannot give an analytic attitude control precision.Therefore,by continuously modifying control parameters and with huge amount of time,trial and error,a control parameter satisfying control precision requirements can finally be obtained.In addition,with considering the real on-orbit environment,various realistic influence factors need to be addressed during controller design,such as attitude and angular velocity measurement errors,external disturbances,model uncertainties,actuators faults and so on,which all have impacts on attitude control precision and cannot be neglected.At the same time,in order to decrease the launch weight and deploy more payloads,materials with light weight and low density are increasingly used in aerospace manufacturing,especially for flexible appendages,such as large solar panels,manipulators,antennas and so on.These spacecraft with flexible appendages are called flexible spacecraft or rigid-flexible coupled spacecraft,since the rigid-flexible coupling effect is inevitably involved,namely,the rotation of central rigid hub and the vibration of flexible appendages are coupled and interfere mutually.Thus the vibration of flexible appendages cannot be neglected in the controller design for flexible spacecraft.With considering all above factors,this dissertation is aimed at solving attitude control and attitude coordination control problems for flexible spacecraft,and at the same time,by theoretical analysis during controller design,tries to obtain an analytic prediction of the upper-bound of control precision,which is related to control parameters and system uncertainties,and that it is guaranteed.The major contents of this dissertation are consisted of the following parts:An attitude tracking controller with guaranteed performance bounds for rigid-flexible coupled spacecraft with flexible appendages is designed.External disturbances,model uncertainties existing in inertia matrix,rigid-flexible coupling matrix,stiffness matrix and damping matrix are addressed.First,with considering measurement errors in attitude,angular velocity and modal variable,a proportional-derivative feedback plus feed-forward attitude tracking controller is proposed.The boundedness of the closed loop system is proved,while the upper bound of steady state attitude tracking error is predicted by using sequential Lyapunov analysis method,and a convergent sequence of analytical,successively tighter upper bounds on the steady-state tracking error is then obtained.By further considering the condition when attitude,angular velocity and modal variable cannot be measured,but their estimates can be provided by certain observers,an observer based proportional-derivative feedback plus feed-forward attitude tracking controller is presented by replacing measurements with estimates given by observers.By introducing sequential Lyapunov analysis method,a prediction of the upper bound of steady state attitude tracking error is calculated,while a convergent sequence of analytical,successively tighter upper bounds on the steady-state tracking error is obtained as well.With further considering actuator faults,fault tolerant attitude tracking control with guaranteed performance bounds for flexible spacecraft is designed.During the fault tolerant controller design,measurements of system states,external disturbances and model uncertainties including flexible dynamic parameters are considered as well.Under the condition that actuator faults can estimated by certain fault observers,the boundedness of the closed loop system is proved first,then a sequential Lyapunov analysis based prediction of the upper bound of steady state attitude tracking control precision is conducted and a convergent sequence of analytical,successively less conservative upper bounds on the steady state attitude tracking error is obtained.In the condition when there is no proper Fault Detection and Diagnosis mechanism to observe actuator faults,based on adaptive theory,an adaptive fault tolerant attitude tracking controller is presented.Under the condition that the measurement errors are bounded,the boundedness of the closed loop system and the parameter estimation error are proved,while a convergent sequence of analytical,successively less conservative upper bounds on the steady state fault tolerant attitude tracking error is obtained as well.Finally,the goal of research is extended from individual flexible spacecraft to multiple flexible spacecraft.A coordination attitude controller with guaranteed performance bounds for formation flying of multiple flexible spacecraft is designed.Measurement errors of attitude and angular velocity,external disturbances,and model uncertainties including both rigid and flexible dynamic parameters are considered simultaneously during the attitude coordination controller design.In the condition that the attitude information of the virtual leader spacecraft is accessible to only part of the group members,the stability of the closed loop system is proved based on the Lyapunov theory.At the same time,by using the sequential Lyapunov analysis method,a convergent sequence of analytical,successively less conservative predictions on upper bounds of the steady state attitude coordination tracking error is presented.In the case when the bound of the rate of angular velocity measurement error is available,a modification of the performance prediction algorithm is conducted to further release the restrictions on the initial states and the communication of the formation flying,and as well a convergent sequence of analytical,successively less conservative predictions on upper bounds of the steady state attitude coordination tracking error is obtained.