WASHINGTON (AFP) - - Astronauts on Sunday prepared to make a third spacewalk to finish assembling a mechanical maintenance robot named Dextre outside the International Space Station.

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Two US astronauts had in an earlier spacewalk attached mechanical arms to the Canadian-made robot, enabling it to take over some human tasks and reducing the need for future risky trips outside the station.

Mission Specialists Richard Linnehan and Mike Foreman finished their task at about 3:00 am (0700 GMT) Sunday, stowing away instruments and making their way into the station's airlock.

Their job got slightly complicated early in the seven-hour spacewalk when they encountered trouble unscrewing a couple of fasteners and removing one of Dextre's arms from its storage container.

The problem was eventually resolved with the help of a simple crowbar. But as a result, "the spacewalkers fell about 45 minutes behind their timeline," said a spokesman for the National Aeronautics and Space Administration (NASA).

Linnehan and Foreman, who arrived last week aboard shuttle Endeavour, recouped most of the lost time, performing their task using socket wrenches and drills to bolt the Dextre robot's two 11-foot (3.3 meter) arms.

The hitch notwithstanding, astronaut Steve Robinson, monitoring the events from Mission Control in Houston, Texas, congratulated all involved.

"You sure did a great job," he radioed. "You guys ought to be proud of yourselves."

Pierre Jean, a program director from the Canadian Space Agency, echoed the view saying the crew did "a fantastic job."

The 200-million-dollar robot, which was re-powered immediately after the walk, will be able to handle maintenance tasks that have been performed by spacewalkers, allowing astronauts to focus on research inside the orbiting outpost.

"Dextre looks quite a bit different today," observed NASA flight director Dana Weigel. "It's almost fully assembled: It has two hands, two arms and the main body is pivoted up."

Astronauts installed Europe's first space laboratory in a shuttle Atlantis mission last month and Endeavour's crew added the first of three parts of Japan's Kibo research facility this week.

Dextre, sent up on Endeavour which is docked with the space station, is the third and final component of the Canadarm Remote Manipulator System, the robotic arm that is Canada's vital contribution to the station.

The 1.56-tonne robot will conduct operations such as replacing small components on the station's exterior -- tasks which until now required a human touch.

Its presence will boost crew safety by reducing the number of hours that astronauts will have to be outside the station, and allow them to focus on other tasks such as conducting scientific experiments in micro-gravity, according to the Canadian Space Agency.

Dextre's two hands are each about the size of a small microwave oven. They are equipped with built-in socket wrenches, retractable claws used to grip objects, and remote-control high-resolution cameras.

The robot's human-like upper torso swivels at the waist, and its arms were designed with seven joints to provide it with maximum versatility. Umbilical connectors provide power and data connectivity.

With Dextre delivered to ISS in nine separate pieces, the astronauts will use three of the Endeavour mission's five spacewalks to get it up and running.

Linnehan and fellow astronaut Garrett Reisman conducted the Endeavour mission's first spacewalk Friday to lay the groundwork for the robot's complicated assembly.

NASA plans to finish building the International Space Station by 2010, at which time it will retire its three-shuttle fleet.

Shuttle crew members also continued work putting together the first pressurized component of the newly delivered Japanese laboratory Kibo, the newest addition to the ISS.