Research On SGCMG Singularity Avoidance Method For Satellite Rapid Attitude Maneuver

In view of the requirement for rapid acquisition and photographing target points for the low orbit imaging satellite,this thesis studies the SGCMG singularity avoidance method during satellite attitude maneuver.The main contents are as follows:For the analysis of the singularity problem,the mean curvature is firstly introduced to determine the singular surface type,which simplifies the determination of singular surfaces and provides a theoretical basis for subsequent analysis of the singular surface boundary.Particularly,for a four-SGCMG system,the corresponding gimbal angles are analyzed for a certain angular momentum trajectory using the related methods of me-chanical arm field.On this basis,the regions of the initial gimbal angles are classified as avoidable region and unavoidable region,and the corresponding control law will be designed for the two cases.For the situation that the initial gimbal angles belong to the avoidable region,a global singularity avoidance steering law with analytic solution is derived using the knowledge of calculus of variations to minimize the time integral of the quadratic form of the gimbal rates.Only a set of optimal initial gimbal rates is needed to be calculated for the application of this steering law,and the compute burden is very little.Therefore,the limitation for the traditional global singularity steering that no analytic solution is exist and large compute burden is required are overcome.In view of the fact that the actual angular momentum is not exactly equal to the reference angular momentum,a state feedback steering law is designed to track the reference gimbal angle trajectory.This state feedback steering law ensures the global singularity avoidance steering law can be used in actual attitude control system.When the initial gimbal angles belong to the unavoidable region,the global singular-ity avoidance law can not be applied without introducing of the torque error for a certain angular momentum trajectory.In view of this situation,the SGCMG angular momentum trajectory is redesigned to ensure that the singular state is avoided without introducing torque errors.A new set of attitude parameters based on two rotations is presented first-ly,and then a reference angular trajectory on a cone surface is developed based on the properties of the new set of attitude parameters.The parameters of this cone can then be changed by changing the definition of the body-fixed reference frame and the target reference frame,so that the range of the angular velocity trajectory is broadened.Finally,the method to select the parameters of the cone surface is given to ensure that the angular momentum trajectory of the SGCMG does not encounter the singular states.However,there is no reference trajectory that can avoid singular states for all initial frame angles in the unavoidable region.For this situation,a singularity rapid escaping steering strategy is presented to solve the problem that the traditional singular surface es-caping steering law can not can not guarantee the singular surface is sure to be escaped.The condition of the singular surface boundary is given and proved firstly,and then mod-ifying the commanded torque when encountering a singular state ensuring the angular momentum of the SGCMG system can arrive at the nearest edge point and then sliding out form this point.Finally,a steering law is designed ensuring the SGCMG system can accurately output the modified command torque near the singular states.