A two-arm flexible space manipulator system for post-grasping manipulation operations of a passive target object

Space Manipulator Systems (SMSs) are complex systems made of a platform equipped with one or more deployable robotic arms. They will be playing a major role in future autonomous on-orbit missions such as building large space structures, servicing satellites which ran out of propellant or need repair, and disposal of spacecraft which reached end-of-life conditions and might not be capable of autonomously shift themselves onto “graveyard” orbits. These missions may as well involve manipulation operations of the target object which needs to be moved from an initial configuration to a final one suitable for the specific task under consideration. In the present study, the mission being analyzed concerns the manipulation of a passive body (which could consist of a module of a large space structure, a spent launcher stage or a satellite in need of maintenance) by means of a fully flexible SMS after grasping operations have been performed. The dynamics model is derived in a three-dimensional context (non-linear formulation for the rigid-body motions and linear for the elastic dynamics). The SMS involved in the investigation has two actuated seven-degree of freedom arms. All the links are characterized by distributed structural flexibility features and two elastic solar panels are also clamped to the base platform. Furthermore, the modeling of the grasp constraint existing between the SMS end-effectors and the target object is a critical issue which is addressed in the present paper. A combination of Jacobian Transpose and Proportional-Derivative Control is synthesized to accomplish the desired mission goals. The calculation of the dynamic properties of the flexible components is carried out by means of a Finite Elements software (MSC Nastran) and the relevant variables are imported into an in-house developed Matlab code for the entire SMS and target object dynamics and control simulation.