Dextre, the multipurpose dexterous manipulator that rides at the end of the International Space Station's (ISS) robotic arm, will acquire some new tools and tasks by year-end.
Among the cargo tucked into Japan's fourth H-II Transfer Vehicle scheduled for launch to the ISS Aug. 4 is Phase II hardware for's Robotic Refueling Mission (RRM), a testbed the size of a window air conditioner bolted onto the station truss that mimics operational satellites.
After a good workout on the basics of satellite repair and refueling, the new gear will allow Dextre to practice more complex work—borescope inspections, cryogenic-refueling attachments, rewiring and the like.
Engineers at, where the human-servicing missions for the Hubble Space Telescope were devised, developed the RRM to demonstrate that robotic tools are equal to the task of servicing satellites in orbit—repairing, relocating or refueling them to extend their service lives. They worked closely with robotics experts at the Canadian Space Agency (CSA), which supplies robotic technology for the station (see page 14).
“Demonstration in space is the only way to do this,” says Jill McGuire, the RRM project manager at Goddard. “We can do a lot of ground demonstrations with robots in our labs, and tell people until we're blue in the face that this will work. But actually showing them that it works in space is the key to buying down risk and giving them the confidence that you can repair their satellite.”
McGuire and her team designed a box studded with examples of the fixtures a servicing robot would find on the different satellites operating today, and produced a set of tools that use the torque Dextre generates to drive much smaller tools with the precision needed to manipulate the satellite interfaces.
The initial toolkit consisted of a wire cutter, a tool for removing safety caps, a nozzle to pump ethanol—a stand-in for hydrazine or other storable propellants—and a “multifunction tool” with heritage in the pistol-grip tool used by spacewalking astronauts.
“As we started trying to maximize the use of the payload, we decided it was better to use what we call a multifunction tool that can use multiple adaptors,” McGuire told the second annual ISS research and development conference here. “So the multifunction tool can pick up each of these adaptors, similar to if you were using a socket wrench in your garage, and you wanted to change out the sockets.”
The RRM flew to space on the final space shuttle mission in July 2011, and since then has carried out a variety of tasks in the experiment's first phase. Among the tasks completed were using the robot to: cut wire, manipulate the thermal blankets that typically cover the hardware servicing-spacecraft must handle, remove a variety of the caps that are found on operational satellites and transfer the simulated storable propellant through a typical fill-and-drain valve.
Controllers fromand the CSA, working from consoles at Mission Control Center-Houston, tele-operated Dextre and the RRM toolkit during experiment sessions. The tests went extremely well, says McGuire, with none of the redundant systems on the testbed put to use because of a problem with a primary. Each tool was equipped with a pair of close-up engineering cameras focused on the work area, which proved valuable in preventing jams from misalignment.
Ultimately, the Satellite Services Capabilities Office at Goddard plans to use the station to test a variety of robotic technologies that will be needed for deep-space human exploration, including on-orbit assembly of Earth-departure stages and habitats for long-duration missions. The next step, RRM Phase II, will add one “task board” to the testbed at an empty slot, and replace another board with a new one carrying different hardware for tasks.
A new tool dubbed Vipir, for visual inspection poseable invertebrate robot tool, will be included in the Phase II manifest to demonstrate semi-autonomous internal inspections of orbiting spacecraft. Vipir will maneuver a camera into the simulated spacecraft structure, where it will encounter “decision boxes” and try to find a way through them without getting stuck, according to McGuire.
Also on the Phase II agenda will be reassembly of cryogenic valves disconnected during Phase I. “We're going to take the next step in complexity, and show how we can now start putting back some of these components that we took apart,” McGuire says. “Now that you have an open fitting sitting there, how do you attach to that fitting?”
Other new tasks will include electrical work with the robot manipulating connectors while a solar-powered LED light shows engineers on the ground when connections have been made, and a plugging experiment with an open aluminum tube that will be checked with pressurized nitrogen and a gauge.
“It's one thing to install a vent plug,” McGuire says. “It's another thing to convince people that we are sealing the tube. . . . The ISS continues to be an invaluable testbed for this type of work.”