August 20, 2012
Credit: Credit: Darpa
Graham Warwick Washington and Guy Norris Los Angeles
With billions spent building, launching—and sometimes losing—geostationary (GEO) satellites, Pentagon researchers have begun a program to cut the cost, and risk, by reusing elements of retired spacecraft already in orbit.
With the U.S. Naval Research Laboratory (NRL) acting as system integrator, the Defense Advanced Research Projects Agency (Darpa) has assembled a broad-based industry team for its Phoenix program to demonstrate the salvage and reuse of components, such as large antennas, from dead satellites. An in-orbit test is planned in 2015-16.
“GEO satellites have an end-of-life because of running out of fuel, or solar panel degradation, or transponder technology becoming obsolete, but usually the antenna is perfectly OK,” says Seamus Tuohy, director of space systems for team member Draper Laboratory. “The concept is to scavenge a large aperture off a cooperative retired satellite, place it in GEO and construct the other satellite functions around it.”
Large antennas drive the size of satellites, and in turn rocket boosters, because there is a limit to how much they can be folded for launch. “The rule of thumb is 3:1. The largest launch vehicle available limits the largest size of aperture that can be deployed—the rest of the satellite can be pretty small,” says Tuohy. “Phoenix takes the driving determinant of satellite cost—the aperture—and uses it beyond its original purpose.”
In the Phoenix concept, payload orbital delivery systems (PODS) containing small “satlets” performing the other functions of a satellite will be launched as ride-share payloads on GEO launches. The PODS will be ejected upon reaching orbit and a tender spacecraft with a robotic arm will capture and store them on an internal tool belt before traveling to the geostationary-satellite “graveyard” orbit.
Each satlet will have a common shape to fit the same payload ejector and tool belt, but a different function. In graveyard orbit, the tender will rendezvous with a retired spacecraft and use its robotic arms to attach the satlets stored in the PODS to the back of the old antenna and aggregate the functions of a new satellite. The arms will then detach the antenna with satlets attached, and the tender will move the assembly to a new operating location in GEO.