SPHERES

The Synchronized Position Hold Engage and Reorient Experimental Satellite (SPHERES) are a series of miniaturized satellites developed by MIT's Space Systems Laboratory for NASA and US Military, to be used as a low-risk, extensible test bed for the development of metrology, formation flight, rendezvous, docking and autonomy algorithms that are critical for future space missions that use distributed spacecraft architecture, such as Terrestrial Planet Finder and Orbital Express. The Synchronized Position Hold Engage and Reorient Experimental Satellite (SPHERES) are a series of miniaturized satellites developed by MIT's Space Systems Laboratory for NASA and US Military, to be used as a low-risk, extensible test bed for the development of metrology, formation flight, rendezvous, docking and autonomy algorithms that are critical for future space missions that use distributed spacecraft architecture, such as Terrestrial Planet Finder and Orbital Express. Each SPHERES satellite is an 18-sided polyhedron, with a mass of about 4.1 kg and a diameter of about 21 cm. They can be used in the International Space Station as well as in ground-based laboratories, but not in the vacuum of space. The battery-powered, self-contained units can operate semi-autonomously, using CO2-based cold-gas thrusters for movement and a series of ultrasonic beacons for orientation. The satellites can communicate with each other and with control station wirelessly. The built-in features of the satellites can be extended using an expansion port. From 2006, three SPHERES units are being used in the International Space Station for a variety of experiments. The SPHERES Guest Scientist Program allow scientists to conduct new science experiments using SPHERES units, and the Zero Robotics Program allow students to participate in annual competitions that involve developing software to control SPHERES units. The SPHERES program is expected to continue until 2017, and possibly further. The SPHERES project lead to a newer project called Astrobee. The initial development of SPHERES started in 1999, by a team of students at Massachusetts Institute of Technology, as part of an aerospace engineering program. The concept of the satellite was conceived when Professor David Miller challenged the students to develop a device similar to the combat training remote seen in the 1977 movie Star Wars Episode IV: A New Hope and more recently in Star Wars: Episode II – Attack of the Clones. Several prototypes were developed during the course of the program, and were tested in ground laboratories as well as in parabolic flights using NASA's reduced gravity aircraft. After the initial development, the SPHERES program was taken over by MIT's Space Systems Laboratory. In collaboration with Aurora Flight Sciences, the design was refined and six flight-ready satellites were built, out of which three were delivered to the International Space Station. The SPHERES project is primarily funded by Defense Advanced Research Projects Agency (DARPA). Each SPHERES satellite resembles an 18-sided polyhedron. The aluminum structure of the satellite is enclosed in a semi-transparent plastic shell. The shell is red, blue, orange or black in color, to help with easy identification. The three satellites in the International Space Station are red, blue and orange. Each unit has a maximum diameter of 22.9 cm and has a mass of 4.16 kg including the consumables.