SYNCHRONIZED POSITION HOLD, ENGAGE, REORIENT, EXPERIMENTAL SATELLITES
(SPHERES)
Research Area: Small Satellites and Control Technologies
Expedition(s): 8, 13-30, ongoing
Principal Investigator(s): ● David W. Miller, PhD, Massachusetts Institute of Technology,
Cambridge, Massachusetts
RESEARCH OBJECTIVES
The Synchronized Position Hold,
Engage, Reorient, Experimental
Satellites (SPHERES) experiment is a
testbed for formation flying by
satellites. SPHERES consists of 3 self-
contained satellites, each of which
measures 0.2 meter in diameter and
weighs 3.5 kg. Each satellite contains
internal propulsion, power, avionics,
software, communications, and
metrology systems. The SPHERES
experiment tests relative attitude
control and station-keeping between
satellites, re-targeting and image
plane-filling maneuvers, collision
avoidance, and fuel-balancing algorithms, and an array of geometry estimators that are used in
various missions. SPHERES is an ongoing demonstration. Each session tests progressively more
complex 2- and 3-body maneuvers that include docking, formation flying, and searching for
“lost” satellites.
EARTH BENEFITS
The technologies for formation flight of small satellites influence Earth-based applications of
current satellite technologies including surveillance, mapping, communications, and navigation.
SPACE BENEFITS
Results from SPHERES support the development of autonomous spacecraft to carry out a
variety of tasks in the space environment and the simplification of autonomous docking
allowing for servicing, re-supplying, reconfiguring, and upgrading of space systems. Smaller
autonomous spacecraft can perform tasks too complicated or too expensive for larger
spacecraft to execute. The algorithms developed during this investigation eliminate the
complicated spacecraft maneuvers that require ground teams to coordinate and execute.
Examples of the use of small autonomous spacecraft include a Separated-Spacecraft
Interferometer in which light from 2 or more spacecraft telescopes combine to provide a high-
resolution image, and a satellite cluster, a collection of microsatellites that operate
cooperatively to perform the function of a single large satellite.
Three satellites fly in formation as part of the Synchronized
Position Hold, Engage, Reorient, Experimental Satellites
investigation during Expedition 14 in the US Laboratory module.