Design of a robotic arm for laboratory simulations of spacecraft proximity navigation and docking

摘要

The increasing number of human objects in space has laid the foundation of a novel class of orbital missions for servicing and maintenance. The main goal of this thesis is the development, building and testing of a robotic manipulator for the simulation of orbital maneuvers, with particular attention to Active Debris Removal (ADR) and On-Orbit Servicing (OOS). There are currently very few ways to reproduce microgravity in a non-orbital environment: among the main techniques, it is worth mentioning parabolic flights, pool simulations and robotic facilities. Parabolic flights allow to reproduce orbital conditions quite faithfully, but simulation conditions are very constraining. Pool simulations, on the other hand, have fewer constrictions in terms of cost, but the drag induced by the water negatively affects the simulated microgravity. Robotic facilities, finally, permit to reproduce indirectly (that is, with an appropriate control system) the physics of microgravity. State of the art on 3D robotic simulations is nowadays limited to industrial robots facilities, that bear conspicuous costs, both in terms of hardware and maintenance. This project proposes a viable alternative to these costly structures. Through dedicated algorithms, the system is able to compute in real time the consequences of these contacts in terms of trajectory modifications, which are then fed to the hardware in the loop (HIL) control system. Moreover, the governing software can be commanded to perform active maneuvers and relocations: as a consequence, the manipulator can be used as the testing bench not only for orbital servicing operations but also for attitude control systems, providing a faithful, real-time simulation of the zero-gravity behavior. Furthermore, with the aid of dynamic scaling laws, the potentialities of the facility can be exponentially increased: the simulation environment is not longer bounded to be as big as the robot workspace, but could be several orders of magnitude bigger, allowing for the reproduction of otherwise preposterous scenarios. The thesis describes the detailed mechanical design of the facility, corroborated by structural modeling, static and vibrational finite element verification. A strategy for the simulation of impedance-matched contacts is presented and an analytical control analysis defines the set of allowable inertial properties of the simulated entities. Focusing on the simulation scenarios, an innovative information theoretic approach for simultaneous localization and docking has been designed and applied for the first time to a 3D rendezvous scenario. Finally, in order to instrument the facility’s end effector with a consistent sensor suite, the design and manufacturing of an innovative Sun sensor is proposed.