Research on nonlinear control methods for on-orbit servicing with visual positioning system

A new laboratory test bed of on-orbit servicing system is introduced that enables simulation of the autonomous approach and docking of a chaser spacecraft to a target spacecraft with similar mass. The test bed system consists of a chaser and a target spacecraft simulator floating via air pads on a marble platform. Relative navigation of the chaser spacecraft is obtained by the united measurements with a single-camera visual sensor and IMU, through Kalman filters. Six cold-gas on-off thrusters and a flywheel are used for the translation and rotation of the chaser simulator. Considering the uncertainties in model, two nonlinear control algorithms, sliding mode control and PID control based on Back-Propagation Neural Network are adopted. Numerical simulations and ground experimental results are presented with comparison for an autonomous proximity maneuver and docking of the chaser simulator to the nonfloating target, which valid the efficiency of the sliding mode control and the test bed capabilities.