Development of Formation Flight and Docking Algorithms Using the SPHERES Testbed

The MIT Space Systems Laboratory is developing the SPHERES formation flight testbed to provide the Air Force and NASA with a long term, replenishable, and upgradable testbed for the validation of high risk metrology, control, and autonomy technologies. These technologies are critical to the operation of distributed satellite and docking missions such as TechSat21, Starlight, Terrestrial Planet Finder, and Orbital Express. To approximate the dynamics encountered by these missions, the testbed consists of three microsatellites, or “spheres,” which can control their relative positions and orientations in six degrees of freedom. The testbed can operate in 2-D on a laboratory platform and in 3-D on NASA’s KC-135 and inside the International Space Station. SPHERES follows the lead of the Laboratory’s MODE (Middeck 0-gravity Dynamics Experiments) and MACE (Middeck Active Control Experiment) family of dynamics and control laboratories (STS-40, 42, 48, 62, 67, MIR, ISS) by providing a cost-effective laboratory with direct astronaut interaction that exploits the micro-gravity conditions of space. Flight tests aboard NASA’s KC-135 have confirmed the functionality of SPHERES as a formation flight test platform with dynamics representative of true spacecraft. Studies in the 2-D laboratory environment include master/slave algorithms and docking control.