Abstract: A novel path planning and tracking control approach is proposed for rendezvous and docking of spacecraft with a single thruster. Firstly, since the thruster is fixed along the X axis of the spacecraft, the transfer trajectory of the spacecraft from the initial position to the desired position is designed as a helix whose parameters are calculated to ensure that the initial point and final velocity of the trajectory are in accordance with those of the spacecraft. The curvature of the trajectory can be minimized by the proposed helical motion. Secondly, to reduce the difficulty in trajectory tracking and decrease the amplitude of the control torque, this paper proposes an improved helical motion by rotating the traditional helical line with appropriate angles in 3-D space. In this way, the initial direction of the trajectory can be aligned with the X axis of the spacecraft, while the curvature integral of the curve is minimized. Furthermore, to track the planned trajectory and the desired force direction, a sliding mode based Control Lyapunov Function (CLF) method is presented. When the angle between the X axis and the desired control force direction is large, the standard CLF law is adopted. Then the control law switches to sliding mode control in the case that the states are near the sliding mode surface. Simulations are conducted to show the superiority of the proposed rotated helical motions to traditional approaches.

Key words: single thruster spacecraft, rendezvous and docking, trajectory planning, helical motion, CLF