Space repairs at arm's length


Crane: A Canadian-built robotic arm will put a little elbow grease into building and maintaining space station.

April 19, 2001|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

As flexible as the human arm is, you'll never give yourself a back rub, and you sure can't reach to the back seat of a minivan to separate the kids.

NASA engineers faced a similar problem on the International Space Station: They needed a powerful space crane to help assemble and service the station. But the space shuttle's 50-foot robot arm is too small and inflexible to reach every part of the 290-foot outpost and too weak to handle huge new station components.

A permanently anchored crane that could do all that would be too big and too heavy to reach orbit.

The solution is an ingenious new Canadian-built robotic arm, almost 58 feet long with an "elbow" in the middle and identical "hands" at each end. By slowly flipping hand-over-hand from one grapple point to the next, the new arm can inch its way to work on nearly any part of the station's exterior.

Called the Remote Manipulator System, Canadarm2 or simply "the Big Arm," the 3,600-pound construction crane has been curled up on its flight pallet since August, waiting for delivery aboard the shuttle Endeavour. Liftoff was scheduled for 2:41 this afternoon from the Kennedy Space Center in Florida.

"This is our first delivery to the space station, and it's a vital part," says Chris Lorenz, mission operations manager for the Canadian Space Agency (CSA). "Without this arm, the station can't be built."

Delivery and installation of the Big Arm will be overseen by Canadian astronaut Chris Hadfield, 41, who will become the first of his countrymen to walk in space.

The Canadians were picked to develop the Big Arm in 1986 because of the success of the space shuttles' robot arms, also built in Canada and first deployed on the shuttle Columbia in 1981.

"Robotics was identified as a strategic technology for Canada," says Savinder Sachdev, the CSA's acting director of space systems. Canada could afford it, and "it was a critical piece of infrastructure which gave Canada a particular role and status in building the [International Space Station]."

In exchange for the $970 million Big Arm, the National Aeronautics and Space Administration will guarantee Canadian scientists access to 2.3 percent of the laboratory space inside the space station and to an experiment platform on the station's exterior. Canadian astronauts will also get a berth on the station for a one-, three- or four-month tour every three years.

For 20 years, the smaller robot arms on the shuttles have deployed and captured satellites, lifted astronauts to work sites and provided controllers in Houston with video views of operations they otherwise couldn't see.

But the space station is much too big for a shuttle-sized robot arm and presents a complex exterior terrain that changes with each stage of construction. Engineers needed a construction crane that could move, bend, twist and reconfigure itself to get its "hands" wherever they needed to be.

At the same time, it had to be powerful enough to manipulate things that, though weightless in orbit, still have enormous mass - as much as 255,000 pounds - that is hard to get moving and to stop. Finally, each of the crane's parts would have to be replaceable in orbit by spacewalkers.

The machine built by the Canadians' prime contractor, MD Robotics of Brampton, Ontario, is 57 feet, 9 inches long and 14 inches thick, made of high-strength aluminum, stainless steel and carbon fiber.

It has what engineers call seven "degrees of freedom." That means seven motorized joints, one more than the shuttle arms. Three are at the "wrist," one at the "elbow" and three more at the opposite "wrist," or "shoulder."

Each joint can be rotated 270 degrees in either direction, giving the robot arm far greater flexibility than the human arm. "You can have both ends attached to the station and move the elbow many ways to get around obstacles," Lorenz says. "It's really a quantum leap in terms of capability."

The first thing it will have to do, on flight day five, is reach out from its shipping pallet, using power from a temporary cable, and grab a "power data grapple fixture" on the space station's Destiny Laboratory.

That fixture will then supply the arm with electrical power, computer and video links to one of two control stations inside the space station.

The grapple is crucial to the system. "Picture something the size of a car tire lying on the ground, and coming out of it is a hefty pin, the size of the handle of a tennis racket," Lorenz said.

As the Canadarm2's "hand" moves onto the fixture, three wire snares inside the hand converge to capture the pin. Then a system of mechanical couplings and four latches engages and drives the hand onto the grapple. It locks rigidly to the station and completes the power and data connections.

Once anchored, the Big Arm is free to let go with its other hand and swing it around to grab the next grapple and make that one its new base of operations.

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