WASHINGTON — The U.S. Defense Advanced Research Projects Agency (DARPA) hopes to narrow a list of about 140 retired satellites down to 10 finalists to be the subject of its first on-orbit operation in an experimental satellite servicing and salvaging project, an agency official said Nov. 4.

Known as Phoenix, the goal of the program is to develop a maneuverable spacecraft equipped with a dexterous robotic arm to salvage useful components from retired communications satellites. Some have likened the project to performing on-orbit surgery.

David Barnhart, program manager of DARPA’s Tactical Technology Office, said the agency is looking for satellites of all sizes that are in a low-inclination orbits and that are not spinning too fast. The agency hopes to choose the finalists before the end of 2014 and conduct a demonstration sometime in 2016.

The 10 candidates will likely include at least some satellites that were built and launched outside the United States, he said. That possibility has raised questions about the proper protocol for approaching those satellites.

The issue is complicated by the fact that “many of the really good candidates have foreign ownership elements,” Barnhart said during a satellite servicing and orbital debris removal panel discussion sponsored by the Secure World Foundation, a nonprofit organization here dedicated to space sustainability

“There are a lot of questions about ownership and who you need to get permission from,” he said

Brian Weeden, the Secure World Foundation’s technical adviser, said one of the takeaways from discussions the space community has had over the last year about on-orbit servicing is that “nothing forbids debris removal and servicing in orbit.” But what established law explicitly allows is “a gray area, and that creates uncertainty.”

“The question the legal community hasn’t really answered is, do you have to go to the launching state?” Weeden said.

He estimated there are 6,000 to 7,000 objects in space for which it would be difficult to determine who to ask permission before approaching as part of a debris-removal operation.

One of the other debates taking on greater urgency as the DARPA project moves ahead is a need for transparency. Panelists said countries with satellites in orbit have asked how they can watch the Phoenix work on other satellites as a trust and confidence building measure.

Sensors on the Phoenix vehicle, as well as ground- and space-based radar, could provide some of the surveillance needed, Weeden said. Barnhart said his initial thought was to have live-streaming video of the event online, provided DARPA was confident it could do so without exposing potentially sensitive information.

For the first demonstration mission, tentatively scheduled on an as-yet-unidentified rocket, a Phoenix spacecraft will try to remove an antenna from a satellite in a graveyard orbit and affix it to a so-called satlet: a new type of modular satellite core structure DARPA is developing.

Barnhart said DARPA officials are planning for two separate demonstration missions and two distinct rendezvous missions.

In January, DARPA officials said the agency began development work on the first Phoenix demonstration mission in 2012 and had allocated $180 million over four years for the project. The agency is seeking $40 million for the project in 2014.

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