Attitude control of a spacecraft using two SGCMGs

Abstract

This thesis presents new methods for controlling spacecraft using Control-Moment Gyros (CMGs). CMGs generate torque to change and maintain a spacecraft's orientation. The CMG con­trol system is used specifically to provide three-axis altitude stabilization, precision pointing con­trol and maneuvering capability. Two types of CMGs are used in spacecraft attitude control purpose. Classified by the number of gimbals, they are Double Jimbal Control Moment Gyro­scope (DGCMG) and Single Gimbal Control Moment Gyroscope (SGCMG). An SGCMG is often chosen as a torque actuator because an SGCMG has two major advantages over DGCMGs: the torque amplification feature and ease of manufacture. The technical literature discusses altitude control of large spacecraft using three or more SGCMGs. As a case study, the altitude control of rigid spacecraft using two SGCMGs is considered. In this paper, the simplified two-SGCMGs model was made and simulated. The system of interest is nonholonomic and the control strategy is related to motion planning. I demonstrate that often only two SGCMGs are necessary to control the altitude of a spacecraft. This is true when failure of one of the control momentum gyroscopes occurs, two actuators can be used to control the attitude of a rigid spacecraft and arbitrary reorientation maneuvers of the spacecraft can be accomplished. The control strategy where two SGCMGs arc used to control the attitude of the spacecraft was studied and presented.