Adaptive reaction null-space control of dual-arm space robot for post-capture of non-cooperative target

Abstract

In this paper, a dual-arm space robot model is derived and an Adaptive Reaction Null Space (ARNS) motion control approach is proposed to satisfy the principal objective of maintaining a minimum disturbance to the base in the post-capture of a non-cooperative target. Since the target becomes an integral part of the manipulator after capture, the position and orientation of space base will be affected in an unknown way because of the dynamics coupling between the manipulator and space base. In addition, the amount of unknown angular momentum of a spinning target transferred to the space manipulator can lead the reaction wheels to their saturation state due to limitations on the available output torque. In order to overcome this problem, we develop a new concept, adaptive reaction null space control for a dual-arm space robot system, with one arm (mission arm) for accomplishing the capture mission and the other (balance arm) for compensating for the disturbance of the base. The mission arm can motion along with the trajectory of the target without consideration of the disturbance to space base. This algorithm is applied from the post-capture stage till the unknown parameters are identified. The adaptive algorithm is developed based on the momentum conservation of the system and the recursive least squares algorithm is employed for parameter adaption. The simulation results are presented to demonstrate the effectiveness of the proposed approach.