Optimal in-orbit operations of a multi-degree of freedom space manipulator

Space manipulators 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 and servicing satellites which ran out of propellant or need repair. In the latter case, the robotic arm mounted on the floating base must be deployed to reach the target spacecraft. In this work a multibody approach is adopted to describe the full three-dimensional non-linear dynamics of a space manipulator. The latter presents a seven-degree of freedom arm. More specifically, it is formed by seven links: the first six are connected by means of revolute joints (with each rotation axis oriented at 90° with respect to the previous one) and the last two using a prismatic joint. A rotational motor is present at each revolute joint, while a translational actuator is placed along the prismatic joint axis. The present paper aims at studying optimal trajectories for the arm deployment and developing a suitable control strategy to achieve the mission goal. The multi-objective optimality criterion is based on the minimum time necessary to complete the maneuver, the minimum power consumption and the minimum disturbance on the manipulator base position and attitude which are certainly features of relevance in space applications. In addition, the final point for the end-effector position is considered to be moving with respect to the manipulator, thus increasing the task complexity level. The optimization will also take actuators saturation into account as well. The deployment maneuver is studied by means of an in-house developed Matlab code which allows for an easy parameterization with respect to the sensitive variables in the system dynamics and optimization procedure.