Study On Robust Attitude Control Of Flexible Spacecraft

Many modern spacecrafts have large flexible appendages. Flexible vibration of appendages influences attitude. Therefore, flexible vibration has to be considered in attitude controller design process. Otherwise, the vibration may greatly degrade control performance or even destabilize the spacecraft system. However, on the other hand, even if the appendage vibration is considered, spillover may still greatly influence the attitude control performance, especially for nonlinear system. This dissertation studied the robust attitude control of spacecraft with flexible appendages, and the problem caused by spillover was also solved. The main content of the paper is as follows:The asymptotic stability equivalence relation and the ultimate boundedness equivalence relation among the vector part of quaternion, angular velocity, and their linear combination are strictly proved in general case. At the same time, a method is given to evaluate the bounds of the vector part of quaternion and angular velocity by using the bound of their linear combination.Based on the above two equivalence relations, viewing the influence of flexible appendage on attitude (IOAOA) as disturbance torque acting on the rigid main body of flexible spacecraft, and assuming that the bound of IOAOA is known, the robust attitude control of the main body of flexible spacecraft with general disturbance rejection is studied. For the first step, several properties necessary for the controller capable of disturbance rejection are studied; for the second step, controllers for attitude maneuver and tracking control with the above properties are designed based on the above two equivalence relations. The proposed controllers are very appealing to the control of flexible spacecraft.Based on a finite numbers of vibration equations of appendages after modal truncation, considering a finite numbers of modes, bound function of IOAOA is obtained. The bound function then is combined with the aforementioned attitude controllers and vibration suppression controller to control the spacecraft attitude and to suppress the appendages vibration as well. Simulations verify the effectiveness of the controller. Finally, the problem of spillover is especially analyzed. Using the bounds of some appendage parameters, considering an infinite numbers of modes, and improving the aforementioned method suitable for a finite numbers of modes, the bound function of IOAOA is obtained. This new bound function then is applied to the control of flexible spacecraft, resulting in the solution of spillover.