The MIT Space Systems Laboratory, in conjunction with NASA, DARPA, and Aurora Flight Sciences, developed and operates the SPHERES (Synchronized Position Hold Engage and Reorient Experimental Satellite) system to provide a safe and reusable zero gravity platform to test sensor, control and autonomy technologies for use in satellites, especially in the area formation flight. Developing these technologies enables new types of satellite systems to be developed.
The satellites are capable of rotation and translation in all directions. Twelve carbon dioxide thrusters are used for control and propulsion, and allow the satellites to maneuver with great precision in the zero gravity environment of the station. Ultrasound beacons in the test area and ultrasound receivers on the satellites allow the SPHERES to determine their relative positions. There are two SPHERES satellites currently on-board the International Space Station, and there have been over one hundred test sessions using the devices. Current investigations include factor graph-based simultaneous localization and mapping (SLAM), and algorithms for concurrent real-time planning and parameter estimation under uncertainty.