| As for agile and large spacecrafts,there are many rapid attitude maneuvers with large angles.Therefore,a control moment gyro become the best actuator among moment exchange actuators.This paper focuses on the methods of attitude control for spacecraft with SGCMGs,and the followings are the main contents:This paper focuses on the singularity of the pyramid-type SGCMG system.The singular surfaces are analyzed and visualized in the singular vector space and gimbal angle space,respectively,and then classified into an elliptic type and a hyperbolic type according to passability.The relationship between the angular momentum space,the singular vector space and the gimbal angle space is discussed.Based on the results of singular surface analysis,a rapid singularity escape steering law is proposed.In singular state,the method can obtain the nearest point to the boundaries of the elliptic singular surfaces and hyperbolic singular surfaces.The method can drive the system to the selected boundary point rapidly and escape from the singular state using null motion.The extra calculation and stored data are sufficient for a spacecraft attitude processor.The steering law proposed in the paper can achieve rapid and directional escape from the internal elliptic singular surfaces,leading to less effect on the performance of attitude control.In order to avoid introducing the torque errors,manifold analysis is applied to the pyramid-type SGCMG system.Both the elliptic singular surfaces and hyperbolic singular surfaces have the directionality.According to the function of terminal domains,the possibility to avoid the internal elliptic singular surfaces is discussed.Therefore,two singularity avoidance steering laws based on manifold theory are proposed: the gimbal angle reorientation steering law and the manifold selection steering law.In order to avoid the internal elliptic singularity,a theory of determining the preferred initial gimbal angle configurations according to the approximated direction of the commanded torque is proposed,then a gimbal reorientation is applied before attitude maneuvers.Before the system enters the terminal domain,the second steering law can drive the system to select another manifold path to pass through the internal elliptic singular surfaces.Simulation results demonstrate the effectiveness of the two proposed steering laws.As for the rigid-flexible spacecraft with SGCMGs,two sets of SGCMGs are mounted on the rigid structure and flexible structure,respectively.A novel control strategy based on a modal force compensator is proposed,which is simple and efficient to reduce vibration during attitude maneuver.The proposed modal force compensator avoids exciting vibration by the means of canceling out disturbance input to elastic dynamics using modal force generated by SGCMGs.No modal information is required in the modal force compensator.A concept named as modal force singularity is introduced and analyzed in depth.A restriction on gimbal angles is developed to avoid modal force singularity.Subsequently,a steering logic based on pseudo-inverse is proposed to allocate modal force commands without introducing force errors.Numerical simulations are presented to show the effectiveness of the proposed approaches.As for the flexible spacecraft with SGCMGs,a method that can achieve vibration suppression during the attitude maneuver is proposed in the paper.A set of SGCMGs is mounted on flexible structures to generate control torque and modal force.A simple controller based on a Lyapunov function and a GSR steering law incorporating proper null motion are presented to realize the desired attitude maneuver and vibration suppression.The proposed method requires at least four SGCMGs to control the attitude and all of the considered vibration modes.A modal analysis is applied to the gyro-elastic system with consideration of the proposed method.The effectiveness of the proposed method is demonstrated by attitude maneuver examples using numerical simulations. |
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