Workers gather around NASA astronauts Robert L. Behnken, Garrett E. Reisman and Michael J. Foreman as they overlook a part of Dextre, the third and final component of the Mobile Servicing System, which is set to launch to the International Space Station in early 2008 in April, 2007 at the MDA office in Brampton, Ont. (Nathan Denette/Canadian Press)

Almost seven years after it was first installed on the International Space Station, the Canadarm 2 is finally getting an extra hand. Or rather, an extra set of arms.

NASA astronauts Robert L. Behnken, left, Garrett E. Reisman and Michael J. Foreman pose for a photograph with a scaled down model of Dextre, April 26, 2007. (Nathan Denette/Canadian Press)

The Special Purpose Dexterous Manipulator, or Dextre, is a two-armed robot capable of moving smaller components or doing work that requires precise handling, tasks that have previously been taken on by astronauts on spacewalks.

The $200-million Dextre robot has been likened to a mechanic in space, as much for the tasks it will perform as its appearance: it has a swiveling torso, two multi-jointed arms and its own tool holster.

The third and final component of the Canadian-made Mobile Servicing System — along with Canadarm 2 and the Mobile Base System — Dextre will be hitching a ride to the orbiting platform aboard the space shuttle Endeavour, which is scheduled to lift off from Cape Canaveral, Fla., in the early morning of March 11.

The Endeavour mission marks the beginning of a more prominent role for Japan on the orbiting space platform, with the first of three pieces of a new Japan Aerospace Exploration Agency laboratory to be installed.

But the arrival of Dextre will also be the culmination of a decade of work at the Canadian Space Agency, said Andrew Keenan, the lead operations engineer for the CSA's Dextre program.

"This is our last contribution to the external structure of the space station," said Keenan. "After this, we'll continue to do experiments in the laboratories. But we'll have paid for our space on the station."

STS-123 mission overview

Endeavour is scheduled to lift off at 2:28 a.m. ET carrying with it the Dextre robot, the first part of Japan's Kibo module and a crew of six astronauts from the U.S. and one — mission specialist Takao Doi — from Japan.

The other crew members are commander Dominic Gorie, pilot Gregory Johnson, mission specialists Richard Linnehan, Robert Behnken and Michael Foreman and flight engineer Garrett Reisman, who will be replacing French astronaut Léopold Eyharts as a member of the space station's three-person crew.

The delivery of Kibo and Dextre will mark the 25th assembly mission for the International Space Station, an assembly process that has kicked into high gear as NASA approaches its self-imposed deadline of 2010 to complete the station and retire the aging shuttle fleet. NASA has planned 11 more shuttle visits to the space station and one shuttle visit to service the Hubble space telescope before the shuttle program winds down.

The tightening deadlines forced NASA to make a quick turnaround between shuttle flights: the space shuttle Atlantis, which delivered the European Columbus space lab, returned to Earth on Feb. 20, or just over three weeks before Endeavour's launch.

The Endeavour mission is also planned to last 16 days, with the possibility of another day or two being added, making it the longest scheduled visit to the space station for any shuttle crew. The mission will include five spacewalks, including three involved in assembling Dextre.

Dextre comes together

Dextre will arrive at the space station in seven pieces, housed in a carrier in the shuttle's cargo bay. On the third day of the shuttle mission, the Canadarm 2 will grab Dextre's carrier and install it onto the Mobile Base System, which is essentially a rail car that allows the Canadarm 2 and later Dextre to move about the station's exterior.

On three spacewalks — on the mission's fourth, sixth and eighth days — Dextre will be assembled, with the two seven-jointed arms secured to the robot's torso and various tools attached.

Once up and running, the 3.7-metre-long tool will take over many of the tasks normally performed by spacewalkers. A spacewalk during the last Atlantis mission, in which two astronauts attached external experiments to the outside of the Columbus laboratory, is the kind of task Dextre would be able to perform, said Keenan.

Astronauts inside the station should be able to use Dextre to complete such a task in less time than if they had to don spacesuits and perform the task manually. And it's also safer, too, he said.

"Spacewalks generally are all high risk," he said. "There are higher levels of radiation and there's always the potential for damage to spacesuits from micro-meteorites, small particles floating through space."

"But the important thing is that Dextre will relieve the crew from some of these maintenance tasks, and that will allow them to concentrate more on science," he said.

A soft 'touch'

Dextre will also be remotely operable not only from the space station but from ground control as well, further freeing astronauts from maintenance tasks.

The robot was built by MacDonald, Detweiler and Associates in Brampton, Ont., with support from 30 other Canadian firms. MDA, which is also responsible for the shuttle's Canadarm and the station's Canadarm 2, is being sold to U.S. weapons manufacturer Alliant Tech Systems. About 50 employees at the Canadian Space Agency were involved in supporting the project in its 10 years of development.

What makes Dextre unique is its ability to lift objects of a variety of sizes — from as small as a phonebook to as large as a phonebooth — and to do so with a soft "touch," said Keenan.

"When we say Dextre has a sense of touch, we mean it can sense forces and movements or torques about its tip. When you push in a drawer, you can sense when it sticks and adjust the force and angle you use to compensate. Dextre does the same thing."

The Canadarm 2 also comes equipped with the same technology but not to the same sensitivity, said Keenan.

It's this ability that will make a Dextre-equipped Canadarm 2 more capable of finishing the job on assembly and maintenance. Right now Canadarm 2 can bring a new component or battery close to the station, but it lacks the sensitive touch necessary to attach it without getting help from an astronaut on a spacewalk.

It's expected to operate on the station for 15 years, but Keenan sees the technology having a lifespan beyond to future missions to the moon and Mars.

"We haven't officially tied our projects to future manned lunar missions, but we expect to see the Canadarm on the moon," he said.

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