(Updates with robot moved, changes dateline from HOUSTON)

By Irene Klotz

CAPE CANAVERAL, Fla., March 18 (Reuters) - Astronauts aboard the International Space Station and visiting shuttle Endeavour colleagues delicately repositioned on Tuesday a new maintenance robot that will play a key role on the $100 billion outpost.

The Canadian-built robot, named Dextre, was assembled in orbit and outfitted with tools to help future spacewalking astronauts tackle maintenance and repairs on the complex.

Until it is needed, however, the 12-foot (3.7-meter) tall handyman, will perch on the outside of the U.S. Destiny laboratory.

"He looks like a gunfighter," Endeavour commander Dom Gorie radioed to Mission Control.

Before the move to the U.S. lab, the astronauts tucked Dextre's 11-foot (3.4-meter) long arms closer to its body and delicately flew it on the end of the station's crane to a mounting post on Destiny.

The pallet that held the robot's limbs was to be returned to the shuttle's cargo bay and taken back to Earth. Endeavour arrived at the station a week ago for a 12-day construction and repair mission.

"This has been a fantastic success already," flight director Kwatsi Alibaruho told reporters.

The mission has not been entirely trouble-free. Flight controllers were considering options for mounting two science experiments that stymied a spacewalking construction crew earlier in the day.

On the third of five spacewalks planned for Endeavour's flight, astronauts Richard Linnehan and Robert Behnken struggled to install the experiments outside Europe's Columbus laboratory. Managers eventually told the spacewalkers to give up and end their seven-hour outing.

A fourth spacewalk on Thursday is devoted to a heat shield repair technique, which NASA wants to demonstrate before sending a shuttle crew this summer to fix the Hubble Space Telescope. Astronauts flying to Hubble won't be able to reach the space station for shelter if their ship is too damaged to return to Earth.

NASA developed inspection and repair options after losing shuttle Columbia and its seven-member crew in a 2003 due to undetected heat shield damage.

During the final spacewalk on Saturday, astronauts will try again to pin the two science experiments to the station's hull. Alibaruho said if problems persist, the experiments could fly home with the shuttle next week.

However, with just 10 construction and resupply missions to the station remaining before the shuttles are retired in 2010, NASA would like to leave the experiments in orbit if at all possible. Endeavour is due back at the Kennedy Space Center in Florida on March 26.

(Editing by Stuart Grudgings)

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