Large-angle attitude acquisition and tracking of a lunar probe with on-off jets

Rapid attitude control for large-angle multiaxis acquisition and tracking of a time-varying attitude instruction of a lunar probe during descending phase is investigated using reaction jets. The attitude kinematics and dynamics are both described by error quaternions. Based on the error quaternion model an acquisition controller is designed. The controller consists of two parts. The first part is the control logic determined by regions on the phase plane of the scalar error quaternion and its rate, which is invoked when the attitude errors are large. The second part is the control logic determined by parabolic switching lines on the phase planes of the transformed vector error quaternions and the transformed vector error quaternion rates, which is active when the attitude errors are small. Stability of the closed-loop system is demonstrated by means of phase plane analysis. Simulation examples are included to illustrate the effectiveness of the control scheme.