A flexible brush mechanism is designed and mounted at the end of a seven-degree-of-freedom robotic arm to despin a tumbling target. The dynamics model of the flexible brush is established using the absolute nodal coordinate method (ANCF), and its contact collision with the solar wing of the tumbling target is analysed. The H ∞ optimal control is proposed for a seven-degree-of-freedom robotic arm during despinning of a tumbling target while ensuring the global robustness and stability. Simulations verify that the despinning strategy can successfully eliminate the rotation speed and is feasible and effective.

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Abstract. Similar to a space flying net, the capture field of the space netted pocket system is large and it can be applied to capture space non-cooperative targets flexibly. To maintain the stability of the space netted pocket system, eight inflatable rods are used as the supporting structure of the net surface. In this paper, a space netted pocket system is designed and modeled. Based on ANCF (absolute nodal coordinate formulation), a dynamic model of the complex space rope net system is established, and then an accurate model of closing rope considering the variable length is derived by introducing mass flow element. A double closed-loop sliding control method is designed to maintain the stable attitude of the service spacecraft. An extended observer is applied to estimate and compensate for the disturbances due to the uncertainty of the contact and flexibility in the system. Finally, the dynamic model and control method is verified through the simulation of the virtual prototype. Results show that the service spacecraft can maintain the attitude stability during target captured process and can track the desired angle during attitude maneuver. The flexible deformation and collision cause great disturbance to the service spacecraft, and the extended observer can improve the control accuracy from 10−3 to 10−4.