24 May 2012 Control of a space robot for minimal attitude disturbance to the base satellite for capturing a tumbling satellite
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The use of a space manipulator (robot) for capturing a tumbling object is a risky and challenging task, mainly because when the manipulator onboard a servicing satellite (base satellite) intercepts with an external object for capture, the resulting impulse will be transferred along the mechanical arm down to the servicing satellite causing disturbance to the attitude of the satellite. Such disturbance may destabilize the servicing satellite if the captured object is tumbling and the physical contact between the robot end-effector and the object is not controlled properly. Certainly, the risk may be mitigated with a force or impedance control capability of the manipulator. However, the implementation of force or impedance control usually requires the robot to have a joint torque sensing and control capability which is a very expensive requirement for a space manipulator. To date, there has never been a really flown space manipulator having a joint torque control capability. Further, even a force or impedance control capability becomes available, much development is still needed before safe capture of a tumbling object can be confidently tried in a real mission. This paper presents an optimal control strategy for a space manipulator to have minimal impact to the base satellite during a capturing operation. The idea is to first predict an optimal future time and motion state for capturing and then control the manipulator to reach the determined motion state such that, when the tip of the robot maneuvers to and intercepts with the tumbling object, a minimal attitude disturbance to the servicing satellite will occur. The proposed control strategy can be implemented regardless whether the manipulator has a joint torque control capability or not. Since the control acts before a physical contact happens, it will not affect but actually augment any existing force or impedance control capability of the manipulator. The proposed method is demonstrated using a simulation example.
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Angel Flores-Abad, Angel Flores-Abad, Ou Ma, Ou Ma, } "Control of a space robot for minimal attitude disturbance to the base satellite for capturing a tumbling satellite", Proc. SPIE 8385, Sensors and Systems for Space Applications V, 83850J (24 May 2012); doi: 10.1117/12.918523; https://doi.org/10.1117/12.918523

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