Design Of Three-stage Sliding Mode Attitude Stabilization Controller For Flexible Spacecraft

The issue of attitude control of spacecraft has always attracted much attention in the aerospace field.With the increase of space missions,most modern spacecraft are attached with many low-rigidity and light-weight flexible attachments.The importance of studying the attitude control of flexible spacecraft has become increasingly prominent.During the operation of the flexible spacecraft in orbit,due to its own fuel consumption,liquid sloshing,and the movement of large flexible accessories such as the expansion or contraction of solar panels,the overall moment of inertia of the flexible spacecraft will change.Moreover,the flexural mode of flexible attachments is usually not measurable,and the spacecraft is also affected by external disturbances during operation.Therefore,for the flexible spacecraft with unmeasurable flexible modes,uncertainty in moment of inertia and external disturbances,this thesis designs an attitude stabilization controller to stabilize the attitude of the flexible spacecraft.The main research contents are as follows.In view of the unmeasurable flexible mode,a simple structured modal observer is designed to estimate the unmeasurable flexible mode.The angular velocity and attitude quaternion that can be directly measured are used as the modal observer input signal and the modal observer output signal are the estimated value of the flexible mode.And the stability of the modal observer is analyzed by the Lyapunov stability theorem.In view of the existence of moment of inertia uncertainty and external disturbance,a threestage sliding mode attitude stabilization controller for flexible spacecraft is designed.This controller has strong robustness to the moment of inertia uncertainty and external disturbance.Under the premise of uncertainty range and perturbation upper bound,the flexible spacecraft can be stabilized in a finite time.The stability of the three-stage sliding mode attitude stabilization controller is analyzed by the Lyapunov stability theorem.Numerical example simulation experiment shows that under the action of the controller,the flexible spacecraft can converge in a finite time,but the controller has chattering phenomenon.In order to stabilize the attitude of the flexible spacecraft within a finite time even when the uncertainty range of the moment of inertia is unknown and the upper bound of external disturbance is unknown and make the unmeasurable flexible mode value not directly affect the output of the controller,use RBF neural network to estimate the unmeasurable flexible mode,the uncertainty of the system moment of inertia and external disturbance,and this estimated value is added to the control law as a compensation term to offset the effect of the unmeasured flexible mode and the uncertainty of the moment of inertia and external disturbances on the system.Based on the Lyapunov stability theorem,the stability of the three-stage sliding mode attitude stabilization controller based on the RBF neural network is proved,and the weight update law of the RBF neural network is derived.Numerical example simulation experiment shows that the controller can make the flexible spacecraft’s attitude stabilized in a limited time and the chattering phenomenon of the controller is effectively suppressed.