Robot Arm Can Roam Space Station Like a Nimble Inchworm

St. Petersburg Times
April 23, 2001

Robots are getting smarter. If you doubt it, check out the mechanical inchworm the Canadians have built for the international space station.

Remember the trusty old mechanical arm the space shuttle fleet has used so effectively for the past 20 years? It's still in use, a remarkable, trouble-free tool able to hoist equipment out of the shuttle's payload bay and gently place it inside again. The shuttle's old arm has successfully grasped broken satellites and the Hubble Space Telescope while astronauts floated about making repairs.

By way of comparison, however, the Canadian Space Agency's new robotic arm is a scalpel; the old shuttle version is a cleaver. Sensors give the new arm, called Canadarm2, a sense of touch; cameras give it sight. Eventually, it will have a mechanical hand with fingers. But the most amazing thing about the new gizmo is its ability to move around the outside of the space station on its own, like an inchworm, flipping end over end, attaching itself to power nodes on the station as it goes.

There will be almost nowhere on the space station the arm can't reach. And so, over the lifetime of the $90 billion orbiting research platform, the arm will crawl about the outside, examining, monitoring and making repairs. Even NASA's generally stolid engineers are impressed.

"We get a little bit jaded," said lead flight director Phil Engelauf. But the robotic arm "really does capture people's imagination."

"This is not a bunch of cans that just sit there hooked up to the station," he said. "This thing moves. It crawls around."

The arm is able to "walk" because it is exactly the same on both ends. Either end can connect to the station and perform tasks.

Scattered about the station's exterior are six areas called Power Data Grapple Fixtures, to which either end of the arm can attach. These fixtures supply power and data to the arm, which will attach itself to one before freeing its other end from another. "Space stuff," as Engelauf calls it.

Tom Holloway, NASA's manager of the program, calls the arm "absolutely critical" to operating and assembling the station. "Without it, we will not be able to complete the station," he said.

The inchworm concept actually goes all the way back to Ronald Reagan's proposed Freedom space station in 1984, according to Savi Sachdev, acting director general of space systems for the Canadian Space Agency. The robotic arm originally was meant to pull in an approaching space shuttle and dock it if the shuttle could not fly in on its own—a task the new arm could do if necessary, Sachdev said.

Its primary tasks now, though, involve station construction and long-term maintenance. It is needed to attach to the station in June a pressure chamber for space-walking astronauts, and to attach solar wings in the next two years. The arm is made mostly of high-strength aluminum and stainless steel. It is so heavy, at 3,618 pounds, that it cannot safely support its own weight on Earth. For testing, it had to be disconnected at the elbow and propped up with supports.

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