Adaptive reactionless motion for space manipulator when capturing an unknown tumbling target

This paper presents a new adaptive algorithm to generate reactionless motion for a space manipulator during and after capturing an unknown tumbling target. The intended application scenario is on-orbit servicing whereby the service spacecraft/manipulator system must dock to, or get a hold of the target satellite in order to conduct the required operations. In the course of these missions, it is important to maintain the base attitude of the servicer unchanged. However, the changes in the dynamics parameters of the system, as a result of capturing an unknown target, degrade the performance of the attitude stabilization system. To overcome this problem in the post capture scenario, the adaptive reactionless control algorithm to produce the arm motions with minimum disturbance to the base, without knowledge of target dynamics, is proposed in this study. This algorithm is intended for use in the transition phase from the instant of capture till the unknown parameters are identified and/or the available stabilization methods can be applied properly. The proposed approach is developed based on the momentum conservation of the system, while recursive least squares algorithm is employed for parameter adaptation. To verify the validity and feasibility of the proposed concept, MSC Adams simulation platform is employed to implement a planar base-manipulator-target model. Two basic scenarios are considered: one where the initial (prior to capture) angular momentum of the target is zero and the second where the target is spinning. The numerical results show that the space manipulator is able to perform reactionless motion after capturing an unknown spinning target.