Attitude Control Based On Modified Rodrigues Parameters For Flexible Spacecrafts

Due to the vibration of flexible appendixes,the consumption of fuel,and the interference from the external environment during the on-orbit operation of modern spacecraft,it is necessary to consider the existence of unmeasurable flexible modal,unknown central rigid body moment of inertia and external disturbances when designing the controller.This topic combines the research on the attitude maneuver control of flexible satellites of the Shenzhen Science and Technology Innovation Committee.In this paper,the flexible spacecraft is considered as the research object.The adaptive backstepping method is used to design the controllers to deal with the attitude maneuver of flexible spacecraft in the present of unmeasurable flexible modal,unknown moment of inertia parameters and external disturbances.Two types of adaptive controllers based on modal observers are proposed in chapter three and chapter four,respectively.This paper focuses on the attitude control problems of on-orbit flexible spacecraft.A kind of modal observer with simple structure is designed for the problem of unmeasurable modes of flexible attachments.The modal observer will consider the angular velocity as a virtual control input,which simplifies the first step of the backstepping method to construct the Lyapunov candidate function.The output information from the modal observer can be combined with directly measurable angular velocity and attitude variable(Modified Rodrigues Parameters,MRPs)as the input signal of the controller,then an adaptive controller based on the modal observer is designed.For the problem of unknown model parameters in spacecraft attitude control,the backstepping adaptive control method is used to estimate the unknown parameters of central rigid body moment of inertia in real time,which improves the accuracy of the controller effectively.In this work,the stability of the modal observer-based adaptive controller is proved theoretically.The spacecraft attitude control closed-loop system can complete the rest to rest attitude maneuver control successfully and has robustness to the unknown moment of inertia parameters in a degree.Meanwhile,the closed-loop system achieves that the L2 gain from the disturbance signal to the output signal is below a certain adjustable performance index,and it has a certain degree of suppression of external interference.In order to improve the active control performance of the vibration of the flexible appendixes,the proposed controller need to increase the damping of the flexible structure to suppressing the vibration of the flexible appendixes.Smart piezoelectric materials is seen as an active vibration controller to reconstructs a new mathematical model.The modal velocity feedback technology is used to construct the flexible structure vibration suppressor to achieve active suppression of the vibration of the flexible attachments.The stability of a closed-loop system under the effects of an adaptive active vibration suppression controller based on a modal observer is proved theoretically.The simulation of the example shows that the controller with the addition of smart piezoelectric material has better performance on the suppression of the flexible appendixes vibration than the controller without smart piezoelectric materials.