In the Phoenix concept, a robotic servicer/tender would be launched into GEO. The satlets, along with tools for the servicer's robot arms, would then be packed into payload orbital delivery systems (PODS) and delivered to GEO as hosted payloads on commercial satellite launches. “The tempo at which the satlets are going up becomes critical,” says Barnhart. With 10-15 GEO commercial launches a year on average, “that's a one-a-month tempo on which we can take advantage of any excess mass as hosted hardware.”
The PODS would be ejected on command from the GEO satellite and collected by the servicer, which would store the satlets and tools on its toolbelt before heading to graveyard orbit to rendezvous with the donor spacecraft. There the servicer would attach the satlets to the antenna, which would then be severed from its satellite and towed to GEO to take up position as a reconstituted communications satellite.
Begun last July, the four-year, $180 million Phoenix program is making progress with several prototype systems undergoing laboratory testing. These include:
•The servicer/tender's robotic-arm grappler, end-effector gripper and adhesive grasping pads to hold the satellite.
•A “hyperdexterous” mutli-jointed robot arm to bring lights and cameras close to the work area.
•A tool to mechanically sever the boom carrying the antenna while minimizing debris generation.
•A system to make a “stem boom” for gravity stabilization of the separated antenna from flat carbon-fiber tape.
This month, Darpa will issue a solicitation for the remaining five of 12 technologies required for the Phoenix concept. These involve elements critical to the planned demonstration, including sensors and systems for “safe and responsible” rendezvous and proximity operations by the servicer, both while picking up the drifting PODS and working on the cooperative donor satellite. Darpa will also explore with commercial satellite operators ways to launch the PODS into GEO.
The Phoenix demonstration will test key aspects of the concept, but not a complete operational system. “In the first demonstration we will attempt to bring up the functions to repurpose an antenna,” says Barnhart. “For the demo, we will take the satlets up with us [on the servicer/tender launch].” The demonstration aims to repurpose a small 1-5-meter antenna and validate that radio-frequency communications can be restored via the rebuilt aperture in graveyard orbit. “For the demo, we will not bring the aperture to GEO,” he says.
Darpa has yet to select a donor satellite. “Of the 500 retired spacecraft, 140 have been identified with apertures that would be useful for the demo. We are continuing to work through a number of identified candidate assets.”