Space Robotics for Capture and Service to Non-Cooperative Satellites

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We have studied control technologies and basic system design of space robots for orbital servicing, which are able to capture and repair malfunctioning non-cooperative satellites using their manipulator arm(s). In this project, the following results have been obtained :1. Modeling of Contact DynamicsModeling and analysis of the contact dynamics for free-flying objects have been carried out both theoretically and experimentally. A method for identifying the mechanical impedance of the target object has been established. We developed a micro-gravity experimental setup using a spacecraft model that floats slightly on a horizontal granite table by pressurized air. The validity of our model and theory have been confirmed throughout the experiments2. Manipulator Control to Prevent Pushing the Target Away in the CaptureWhen a free-flying space robot captures a target satellite, the target object can be easily bounced away by the contact force. Impedance control is effective to reduce the contact force. We have investigated the dynamic conditions to maintain the contact between the free-flying manipulator arm and the target based on the "Impedance Matching" theory. It is proved throughout experiments that the equivalent mass of the end tip of the arm coming from the impedance control is a reasonable criterion for preventing pushing the target away.3. Advanced Control for Space Redundant Macro-Micro ManipulatorsThe macro-micro manipulator is a promising system for orbital servicing, which consists of a long (macro) arm and a small fine (micro) arm. The macro arm provides a long-reach capability and the micro arm performs the dexterous manipulation. However, the macro part can generate vibrations due to structural flexibility. The motion of the small arm induces vibrations onto the macro part, hence, resulting in the reduction of its positioning accuracy. In this study, a control method for an accurate and quick manipulation preventing such vibrations has been established.