The Canadian-built robot, named Dextre, will stand 12 feet and have a mass of 3,400 pounds when it's fully assembled. It is designed to assist spacewalking astronauts and possibly someday take over some of the tougher chores, like lugging around big replacement parts.
The already challenging outing turned grueling as Linnehan and fellow spacewalker Michael Foreman struggled to release one of the robot's arms from the transport bed where it had been latched down for launch.
Two of the bolts wouldn't budge, even when the astronauts banged on them and yanked as hard as they could. They had to use a pry bar to get it out.
The other arm came out much more smoothly and quickly, paving the way for Linnehan to pull up Dextre's body 60 degrees, like Frankenstein's monster rising from his bed. That was the ideal position for plugging in Dextre's gangly arms to its shoulders.
"The whole team did a spectacular job today," Mission Control radioed the crew after the spacewalk. "You guys ought to be proud of yourselves."
Zebulon Scoville, the lead spacewalk officer for Endeavour's mission, said the ground team was ecstatic when Linnehan and Foreman got the last bolt out.
"The crew really performed beyond what could ever be expected of them," Scoville said.
The seven-hour overnight spacewalk - which lasted into the wee hours of Sunday - came close to being drastically altered or even delayed. For nearly two days, a cable design flaw prevented NASA from getting power to Dextre, lying in pieces on its transport bed.
But Dextre got the power it needed to wake up and keep its joints and electronics from freezing when the astronauts gripped it with the space station's mechanical arm on Friday night.
After the spacewalk, the crew hooked Dextre back up to the mechanical arm to keep the robot warm. That also allowed NASA to perform tests to ensure all of Dextre's electronics are working properly. Later Sunday, the crew plans to test all of Dextre's joints and brakes.
Dextre - short for dexterous and pronounced like Dexter - has seven joints per arm and can pivot at the waist. Its hands, or grippers, have built-in socket wrenches, cameras and lights. Only one arm is designed to move at a time to keep the robot stable and avoid a two-arm collision. The robot has no face or legs.
Space station astronauts will be able to control Dextre, as will flight controllers on the ground. The robot will be attached at times to the end of the space station arm. It is also able to ride by itself along the space station arm's railway.
The crew will finish building Dextre during a third spacewalk, set for Monday night. A total of five spacewalks are planned for Endeavour's nearly two-week visit to the space station, the most ever performed during a joint shuttle-station flight.
Visit NASA's Web Page for the STS-123 Mission for the latest developments, background on mission elements, crewmembers and multimedia.