Dextre demonstrates orbital fill-up
The big Canadian-built robot on the International Space Station has wrapped up a week of work aimed at demonstrating that its robotic cousins could one day handle the daunting task of servicing satellites in orbit, a capability that many hope will lead to commercial service stations in the sky. Riding on the station's robotic arm, which was also built in Canada, the special-purpose dexterous manipulator—universally dubbed Dextre—has been snipping wires, opening caps and pumping ethanol at an exterior testbed fitted with the kind of hardware a robotic satellite-servicer would find on a spacecraft in need of more fuel, a new flight computer or something else that would keep it generating profits for a few more years.
Known as the Robotic Refueling Mission (RRM), the washing-machine-size, $22.5 million experiment was the last payload removed from the last space shuttle mission. Astronauts Mike Fossum and Ron Garan stowed it on the station during the STS-135 flight of the shuttle Atlantis in July 2011 (see photo), and Dextre later installed it on an Express Logistics Carrier equipped with the power, data and commanding capabilities needed for the demonstrations (AW&ST July 4, 2011, p. 62). Its eponymous activity was due for completion last week, when Dextre was to screw a special tool into a stock satellite fill-and-drain valve it had opened by snipping wires, unscrewing caps and nuts and retaining them, and then begin pumping ethanol.
“[This will] demonstrate that we have a leak-tight seal made by a robot to a non-cooperative interface, which would be, I think, be a first, ever, for, or any agency for that matter,” says Benjamin Reed, deputy project manager in the Satellite Servicing Capabilities Office at 's , Md.
The schedule was set back a few hours as Dextre snipped lock wires on one of the access caps, when Canadian experts called a halt so they could investigate an intermittent software problem. The issue was resolved during a pre-planned day-long pause in the demonstration, and work resumed on Jan. 17. The Canadian team in St. Hubert, Quebec, was one of four groups involved in the telerobotic demonstration. ISS Mission Control Center-Houston commanded the robotic activity, while the ISS Payload Operations Center at, Ala., operated the Express Logistics Rack. Reed's team coordinated the demonstration from its facility at Goddard.
The pumping tool designed to pass the ethanol—chosen because its handling characteristics are similar to the toxic hydrazine propellant most satellites use for station-keeping—is called the EVR nozzle tool, “EVR is 'extravehicular robotics,' as opposed to 'EVA,'” says Reed, who learned his trade developing astronaut tools and extravehicular activity procedures for the servicing missions to the Hubble Space Telescope.
Reed estimates 80% of the team shares his experience on Hubble, and they are applying it to the robotic applications that will be needed in geosynchronous orbit, where most commercial communications satellites operate.
“We learn on orbit the things that are hard or impossible to simulate on the ground,” he says.
Future uses of the current configuration of the RRM include tests of tools designed to cut the tape that holds insulating thermal blankets over refueling valves and other hardware, and to open the fasteners necessary to reroute cables around a malfunctioning flight computer or other avionics box. Additional task boards that are in fabrication at Goddard for a later flight to the station will permit tests of technology designed to let a robot replenish cryogenic coolant for infrared sensors by using a spacecraft's gas-venting tube as a fluid port.
Data generated in the tests is shared with industry and other government agencies, most recently at a workshop that drew some 300 participants. There have already been commercial efforts to develop satellite-servicing spacecraft (AW&ST March 21, 2011, p. 23). Future use of the technology on the RRM and capabilities Goddard is developing for finding and grappling a spacecraft could include orbital-debris mitigation.
“The core technologies that we're developing now would be the core technologies required for, say, a spent rocket body,” Reed says. “That probably would be the first object that would be gone after if somebody were to go after active orbital-debris removal.”