Research On Attitude Dynamics And Control Of Elastic Space System

Elastic space system has gradually become the mainstream of space development in various countries due to its good anti attack,flexibility,reliability and other characteristics in space confliction.Elastic space systems include but are not limited to space communication systems,meteorological monitoring systems,space navigation systems and space remote sensing systems.Considering the important role of the above space systems in the future confliction,the traditional centralized and large spacecraft will become the primary target to be attacked.Once disturbed or damaged,it will have an irreversible impact on the operational situation.Therefore,the space powers led by the United States began to put forward the concept of elastic space system,that is,to replace the large spacecraft with centralized functions with a space system composed of small units with decentralized functions.The spacecraft in the elastic space system is characterized by low cost,decentralized functions and strong mobility,and it can realize communication and cooperation between spacecraft.So,the malfunctioning spacecraft can be replaced in time,which greatly improves the robustness of the system.The coordination between spacecraft demand for a higher accuracy of relative attitude of spacecraft.Considering the dynamic characteristics of the elastic space system,when modeling the system attitude dynamics,the model is required to have the ability to describe this change.The controller is required to be converged in finite time considering the timeliness of the on-orbit attitude control mission.Therefore,this paper introduced the dynamics model of the elastic space system,and designs the finite time attitude controller based on the derived attutde dynamics model.The main research contents of this paper include:Aiming at the problem of modeling the attitude dynamics equation of elastic space system,the attitude was described by rotation matrix inorder to avoid the singular problem and unwinding phenomena when controlling the dynamics model.Considering that the elastic space system may be composed of rigid spacecraft or flexible spacecraft,dynamic modeling of rigid and flexible spacecraft is performed separately.The attitude dynamics model of rigid spacecraft under the action of reaction wheel was derived firstly,and the rigid flexible coupling attitude dynamics model was derived for flexible spacecraft.Based on the attitude dynamics model of a single satellite,the relative attitude dynamics model and attitude error dynamics model were derived respectively.To describe the information transmission characteristics and dynamic characteristics of the elastic space system,an undirected graph was used to describe the information transmission link of the system and define the new attitude error.On this basis,an attitude dynamics model of the elastic space system was established.Considering that the spacecraft in the elastic spacecraft system performs a mission independly,the attitude tracking control problem of a single rigid body spacecraft was studied,and the backstepping method was used to design the controller.Considering the uncertainty of inertial parameters caused by the change of inertial parameters with time in the process of spacecraft on-orbit operation,Radial Basis Function(RBF)neural network was used to estimate the unknown part of inertial parameters of the system,and the minimum learning parameter method was introduced to greatly reduce the amount of calculation.The designed controller can achieve global stability in finite time.Considering that the spacecrafts in the elastic spacecraft system perform a mission synergistically,an improved sliding mode variable structure method was used to design the controller for the attitude synchronization control of an elastic space system consisting of a spacecraft with flexible appendages.A fault-tolerant controller was designed to deal with the possible spacecraft failures in elastic space systems.The RBF neural network was also used to estimate the unknown part of the inertial parameters of the system.By using the method of minimum learning parameters,the finite time stability of formation system was improved,and the computational burden was effectively reduced.Through the improved sliding surface,the singularity was avoided,and the tracking error can converge to the equilibrium state in finite time.This paper solves the problem of attitude dynamics modeling and control of elastic space system,provides reference for the design and development of elastic space system.The work in this paper complements the relative attitude dynamics modeling and control of space system composed of spacecraft with flexible appendages.The proposed dynamic model and controller have good universality and can be applied to rigid spacecraft formation dynamics modeling and control,flexible spacecraft formation dynamics modeling and control and other fields.