The Synchronized Position Hold, Engage, Reorient Experimental Satellites
) experiment is a testbed
consisting of three 8-inch diameter miniaturized satellites
that can operate in a variety of environments, including inside the International Space Station
(ISS). The MIT
Space Systems Laboratory developed the experiment to provide the Air Force
with a long term, replenishable, and upgradable testbed for formation flight. It will be used to validate high risk control, metrology
, and autonomy
technologies. The technologies are critical to the operation of distributed satellite and docking missions such as TechSat21, Starlight
, Terrestrial Planet Finder
, and Orbital Express
. The SPHERES concept was inspired by the Training Remotes
from Star Wars
To approximate the dynamics presented by these missions, the testbed consists of three miniaturized satellites, microsatellites or "spheres," which can control their relative positions and orientations, and is operable on a 2-D laboratory platform, NASA's KC-135, and the International Space Station. The testbed is being developed jointly by the MIT Space Systems Laboratory and Payload Systems, Inc., with funding from the Department of Defense and several NASA centers.
The battery-powered, 8-inch diameter spherical satellites fly within the ISS cabin using carbon dioxide to fuel 12 thrusters.
Three SPHERES vehicles were delivered to the International Space Station. The first vehicle, along with a limited supply of consumables and support equipment, arrived at the station aboard Progress
flight ISS-21P, and single-vehicle tests and experiments began on May 18, 2006. The second vehicle arrived with a much larger supply of consumables aboard Space Shuttle
. The final vehicle and consumable supply were delivered to the station on Space Shuttle flight STS-116
On April 27, 2007, ISS Expedition 15 flight engineer Sunita Williams performed a series of test flights with the satellites.