Disturbance Observer Based Prescibed Performance Attitude Control For Combined Spacecraft

With the development of exploration of space,the number of spacecrafts in space is increasing year by year.In order to ensure that these spacecrafts can work safely and stably on orbit,and successfully complete their own tasks,spacecraft on-orbit servicing technology is particularly important.Before and after the capture,the mass and moment of inertia of the target spacecraft are unknown to the service spacecraft,that is,the target spacecraft is a non-cooperative target spacecraft.After the successful capture,the service spacecraft and the target spacecraft form a combined spacecraft.To complete attitude maneuver of the combined spacecraft,the actuators of service spacecraft need to be used,that is,to use the actuators of service spacecraft to complete the attitude takeover control.However,due to the mass,moment of inertia and position of the center of mass of the combined spacecraft are unknown,it is necessary to identify these parameters,but no matter which identification method is used,there are always problems such as too long identification time and low identification accuracy.Therefore,it is very important to design an attitude controller without system parameters identification.Secondly,when the attitude controller is designed for the actual spacecraft system,due to the constraints on the dynamic and steady-state performance of the spacecraft in engineering practice,and the control torque output by the actuator(such as thrusters,fly wheels and so on)of the service spacecraft is limited,these factors should be taken into account when designing the attitude controller.Considering the two problems mentioned above,this paper studies the prescribed performance attitude control for the combined spacecraft based on the disturbance observer.Firstly,the coordinate system and the presupposition for modeling the combined spacecraft are given.Considering the interaction moment transmitted by the capture mechanism between the service spacecraft and the target spacecraft,the attitude dynamics and the operation model of the combined spacecraft are constructed by using the attitude quaternion.The attitude control problem of the combined spacecraft is transformed into that of attitude control of the service spacecraft.Aiming at the uncertainties of the moment of inertia,the moment of interaction from the target spacecraft and the external disturbance moments of the service spacecraft after capture,a simple nonlinear disturbance observer is designed based on the attitude modeling method in the previous chapter.At the same time,considering the requirement of finite time convergence in practical engineering application,a super-twisting disturbance observer is designed,which estimates disturbance without chattering,and a simple PD controller is used for numerical simulation.The simulation results show that the nonlinear disturbance observer and the super-twisting disturbance observer are both effective.In order to solve the problems of spacecraft attitude dynamic and steady-state performance constraints in practical engineering,based on the prescribed performance control theory,an attitude controller is designed,which can constrain the dynamic and steady-state performance in advance.At the same time,because output torque of the actuator of service spacecraft are limited,an auxiliary system is further designed into the prescribed performance controller to compensate the actuator saturation.Finally,the effectiveness of the two controllers is verified by numerical simulation.