Autonomous docking experiments using the SPHERES testbed inside the ISS

This paper presents recent results regarding the research on autonomous docking with tumbling targets performed by the MIT Space Systems Laboratory (SSL). The objective of this research is to develop a guidance, navigation and control (GN&C) architecture that enables safe and fuel efficient docking of a thruster-based spacecraft with a tumbling target in the presence of obstacles and contingencies. Over the calendar year 2006, experiments were performed inside the International Space Station (ISS) using the SPHERES nano-satellites to validate a GN&C architecture on hardware in microgravity. A series of attitude slews, an autonomous docking maneuver with a fixed beacon and a station-keeping maneuver were among the experiments carried out in May to validate subsets of the architecture with only a fraction of the SPHERES hardware. The second set of experiments occurred in August and involved two satellites and the remaining navigation hardware. The global estimator allowing the SPHERES to navigate within the US Laboratory was validated. Multiple successful docking maneuvers between two satellites were also accomplished. In November, more complex docking scenarios were experimented, leading to the first successful autonomous docking with a tumbling target ever performed in microgravity. Results collected during key ISS experiments are presented in this paper.