Predefined-time Attitude Tracking Control Of Spacecraft With Parameter Uncertainty

With the vigorous development of the aerospace industry,more and more spacecraft are being sent into space to complete a variety of space missions.The attitude control of a spacecraft is the basis for ensuring that the spacecraft completes various modern space missions.It plays a vital role when the spacecraft completes earth/satellite observation missions,capture missions,and tracking missions.When a spacecraft is in orbit,its attitude control system will be affected by disturbances generated from the external environment,such as solar wind,gravity,and magnetic energy.Therefore,the attitude control system of the spacecraft needs to have the anti-disturbance ability.In addition,changes in the mass characteristics of the spacecraft due to the movement of the spacecraft’s own load and fuel consumption may lead to parameter uncertainty.To solve such problems,the spacecraft attitude control system needs to have certain robustness.With the increasing complexity of space missions of modern spacecraft,the design of spacecraft attitude control systems with external disturbance and parameter uncertainty has ushered in new challenges.In addition,in modern aerospace missions,the requirement for the rapidity of the attitude control system has also become one of the important indicators of whether the mission is completed.Based on the above background,this subject has researched on the finite-time and predefined time attitude tracking control method of rigid spacecraft with external disturbance and parameter uncertainty.The main contents are as follows.In order to solve the finite-time attitude tracking control problem of rigid spacecraft with parameter uncertainty and external disturbance,a spacecraft finite-time attitude tracking controller is designed.First of all,the error angular velocity is regarded as a virtual controller to stabilize the error kinematics subsystem.Next,a finite-time attitude tracking controller is designed according to the error between the actual error angular velocity and the virtual controller.Then,an extended state observer is used to estimate the lumped disturbance constituted by parameter uncertainty and external disturbance,and the estimated value is introduced into the proposed finite-time attitude tracking controller.Finally,numerical simulations illustrate that the designed spacecraft finite-time attitude tracking controller can ensure that the spacecraft completes the attitude tracking task within a finite time.Aiming at the problem that the controller designed by the traditional finite-time control method can only obtain the upper bound of the convergence time related to the initial state of the system,considering the need to effectively reduce the control torque amplitude during the spacecraft attitude tracking control process,a fixed-time inverse optimal attitude tracking control for rigid spacecraft is studied in this subject.First,by introducing the control Lyapunov function,a classic inverse optimal controller is constructed,which can ensure the asymptotic stability of the closed-loop system,and the given performance index function is approximately minimized.Furthermore,an integral sliding mode function is used to improve the classic inverse optimal controller.By utilizing the Lyapunov stability theory,the practical fixed-time stability of the closed-loop system is proven.Under the fixed-time inverse optimal controller,the upper bound of the convergence time of the control system is only related to the parameters of the controller,and the spacecraft completes attitude tracking in fixed time.For the problem that traditional finite-time control method and fixed-time control method cannot directly predefine the upper bound of the convergence time of the spacecraft control system,the predefined-time attitude tracking control problem for spacecraft is addressed in this subject.Using the backstepping method,the angular velocity is regarded as the virtual control input,and then the predefined time controller is designed according to the error between the actual angular velocity and the virtual control input.With this,the stabilization of the spacecraft attitude tracking error system can be achieved step by step.The convergence analysis proves that the upper bound of the convergence time of the control system can be adjusted by only one control parameter.The Lyapunov stability theory is used to analyze the practical predefined time stability of the closed-loop system.Under the predefined time controller,the actual attitude variables and angular velocity of the spacecraft attitude tracking control system can track the desired attitude variables and angular velocity within a predefined time.On the basis that the upper bound of the convergence time of the control system can be predefined,considering the problem of how to preassign the upper bound of the steady-state error of the system,a preassigned finite-time attitude tracking control scheme for spacecraft is studied.First,by introducing two preassigned tracking performance functions,performance constraints on the convergence time and steady-state error are provided for the states of the spacecraft attitude tracking error system.Then,the barrier Lyapunov function is used to ensure that the states of the error system are limited within the preassigned tracking performance functions.At the same time,the estimated value of the total disturbance in the system is obtained through an extended state observer.With this,a backstepping method is employed to design a preassigned finite-time attitude tracking controller for spacecraft based on the extended state observer.Finally,a simulation example illustrates that the spacecraft can track the design attitude within a preassigned finite time with high convergence accuracy under the proposed preassigned finite-time attitude tracking controller.Considering that the predefined time control method and the preassigned finite-time control method can only predefine the upper bound of the convergence time of the spacecraft attitude tracking control system.Therefore,a predetermined-time controller for spacecraft attitude tracking that can directly specify the system convergence time is designed.First,a novel time-varying sliding mode surface is proposed,so that the error states of the spacecraft attitude tracking error system can stay on the designed time-varying sliding mode surface from the initial condition.Based on the sliding mode surface,the proposed controller can guarantee that the error states of the system converge within a predetermined time.Considering the uncertainty and external disturbance in the spacecraft system,a finite-time extended state observer is employed to counteract the effects of the lumped disturbance in the system.Finally,comparative simulation is used to verify the effectiveness and superiority of the designed predetermined-time spacecraft attitude tracking controller.