Orbital robotics, due to the unfriendly environment (radiation, micro-gravity, thermal stresses, etc.) poses unique challenges to robot and robot algorithms, and sets the need for new and innovative autonomous systems. The design of servicing operations and devices is nowadays one of the most important research field in space robotics. Servicing operations range from regular inspection to the upgrade of components and re-fuelling. It is immediate to notice that, regardless of the operation to be carried out, the success is strictly linked to the way in which the chaser and the target satellites move and interact with respect to each other. The importance of relative motion for rendezvous and docking operations, calls for an approriate laboratory facility able to reproduce orbital conditions. This can be achieved only with a robotic structure that simulates the target and chaser’s kinematics and dynamics.
This project tries to propose a viable alternative to the existing huge and costly RvD structures; the addition of force sensing transducers and the possibility to dynamically scale the simulations makes the manipulator a cheap and portable hardware-in-the-loop testing bench for orbital phenomena. After selecting the most dexterous robotic configuration, the kinematic and dynamic problems were analyzed; a basic PID controller was then implemented and its stability to step response and disturbances successfully verified.
An extended simulation campaign, comprising Matlab and SimMechanics environments, confirmed the theoretical models and allowed to reproduce typical rendezvous and docking maneuvers (providing useful data for the sizing). By integrating a force sensor, it was possible to impose and simulate orbital motion and to account for any force disturbance. With information deriving on structural analyses and dynamics extrapolations, a preliminary design was carried out, and led to the translation of the theoretical requirements into the sizing and selection of the structure, the hardware and the actuators. The final robot is able to simulate RvDs inside a spherical working space of 1.3 m radius, with a total mass of just 7.5 kg.