Spacecraft Attitude Tracking Control

The problem of reorienting a spacecraft in to acquire a moving target is investigated. The spacecraft is modeled as a rigid body with N axisymmetric wheels controlled by axial torques, and the kinematics are represented by Modified Rodriques Parameters. The trajectory, denoted the reference trajectory, is one generated by a virtual spacecraft that is identical to the actual spacecraft. The open-loop reference attitude, angular velocity, and angular acceleration tracking commands are constructed so that the solar panel vector is perpendicular to the sun vector during the tracking maneuver. We develop a nonlinear feedback tracking control law, derived from Lyapunov stability and control theory, to provide the control torques for target tracking. The controller makes the body frame asymptotically track the reference motion when there are initial errors in the attitude and angular velocity. A spacecraft model, based on the X-ray Timing Explorer spacecraft, is used to demonstrate the effectiveness of the Lyapunov controller in tracking a given target. Acknowledgments I want to thank my advisor, Dr. Chris Hall, for his time and effort that he has expended in teaching me spacecraft dynamics. His expertise and technical insight into spacecraft dynamics has helped me form this research into something worthwhile. Over the last two years, Dr. Hall has enhanced my education through academics, research skills, and his own experiences as an engineer. He has been supportive and patient with me when aspects of the research became frustrating. For this, I am grateful. to thank Darrel Conway and Paul Noonan for providing technical insight and excellent trouble shooting tips for FreeFlyer.