Jeremy Singer at Space News reports (Yahoo! has the full text) that the Air Force Research Laboratory is “planning a small experimental satellite that would orbit in close proximity to a host spacecraft and keep tabs on their surrounding space environment” in geostationary orbit:
The Angels satellite will be launched into a geostationary orbit for an experiment that is expected to last about a year, according to the request for information. The Air Force hopes to extend the mission for another two years, according to the request for information.Geostationary orbit is a belt of space some 36,000 kilometers above the equator that hosts most communications satellites. The Air Force chose that orbit because its distance from Earth’s surface makes it less visible and more difficult to monitor than lower orbits, [Tom] Caudill [the space surveillance technical area lead at the laboratory] said.The Angels spacecraft would launch along with a yet-to-be-determined host satellite that it would shadow in orbit, Caudill said. The launch likely will be arranged by the Defense Department’s Space Test Program, he said.Jeremy noticed the program when the Air Force Research Laboratory released this solicitatiton for the Autonomous Nanosatellite Guardian for Evaluating Local Space or ANGELS.I am not sure how ANGELS relates to a similar DARPA program, Spectator, that Lt Col Jim Shoemaker (USAF), Program Manager, Tactical Technology Office, DARPA Space Activities, mentioned at DARPATECH 2005:
... might also want to validate the concept of a host vehicle inspector, a nanosat carried by a host satellite, able to be released to inspect its host to assist in anomaly resolution, such as an incompletely deployed solar array. These are some of the ideas were exploring on a new program called Spectator. Were not exactly sure what Spectator should be, and we welcome your input in defining the program.Then again, from that description, I am not sure DARPA knows either. They seem to be duplicative, if not coextensive.The United States does need to improve its space situational awareness, especially in geostationary orbit (GEO). Up there, a piece of space debris as small as a centimeter can cause the loss of a satellite; the tiny nuggets contain so much potential energy, in fact, that it's not even worth shielding against them. But we only track objects a meter and larger in GEO -- a thousand times the deadly size.The idea of using small satellites to monitor and, perhaps, protect satellites has been kicking around for a while—Matt Bille, from the research group ANSER, co-authored a pair of papers calling for a “microsatellite space guard” in 1999 and 2000:
* Matt Bille and Deborah A. Bille, Enforcing the OST—The Inspection QuestionAIAA-2000-5155, AIAA Space 2000 Conference and Exposition, Long Beach, CA, Sept. 19-21, 2000.* Matt Bille, Robyn Kane, Martin Oetting (ANSER) and Donna Dickey (AFRL), A Microsatellite Space Guard Force, 13th Annual AIAA/USU Small Satellite Conference, 1999.While ANGELS will eventually operate in geostationary orbits, Bille et al expect the first space guard satellites in low earth orbit (LEO), building programs like XSS, DART and Orbital Express, which all used small satellites to operate near bigger ones.These projects haven't been without their share of bumps. Big bumps, like the ones tow satellites make when they clang together. DART had itself a little accident while conducting an rendezvous (RSO for the hipsters) last April. And given that, I think some rules of the road for such "proximity operations" would be in order—before the Chinese start doing it, too, and everybody in this town freaks out.-- Jeffrey Lewis, cross-posted at Arms Control Wonk.