Spacecraft Line-of-Sight Control Using a Single Variable-Speed Control Moment Gyro

Complete attitude control of a spacecraft is not possible with only one single-gimbal variable-speed control moment gyro due to the conservation of angular momentum. However, partial attitude control without violating the angular momentum conservation principle is still possible. In this paper feedback controllers using only one singlegimbal variable-speed controlmoment gyro are presented that drive all three components of the angular velocity of a rigid spacecraft to zero, while at the same time a spacecraft body-axis points along an arbitrary inertial direction. To solve this problem, we first introduce a pair of angles to parametrize all feasible final spacecraft orientations at rest without violating the angularmomentum constraint. Based on this parametrization, an LQR control law is designed to locally achieve the control objective. Afterwards, a multistage control law is proposed to achieve the same control objective for large initial conditions.