For more than six hours, astronaut Dave Williams experienced space outside the safe confines of a vehicle, something only two other Canadians have ever done.
Williams, a Canadian astronaut, left the International Space Station at 12:37 p.m. ET on Saturday and returned at 6:45 p.m.
Mission Specialist Rick Mastracchio preceded him out the hatch by nine minutes.
The two men accomplished their major task -- installing a new beam on the station -- just under an hour later.
The shuttle Endeavour delivered the two-tonne, square-shaped beam to the station on Friday. Other station equipment will be installed in the coming days.
On the beam project, astronaut Charles Hobaught controlled the Canadarm robotic arm. Williams and Mastracchio floated nearby, coaching him along.
As soon as the beam was attached, the two spacewalkers bolted it down and hooked up grounding straps. They then worked on a number of other chores.
While that was happening, the main NASA command-and-control computer on the space station shut down about half-way through the spacewalk.
However, the backup system kicked in. Mission Control said the problem didn't affect either the spacewalk or the station.
Astronaut Chris Hadfield told Â鶹´«Ã½ that NASA's training would have perfectly prepared Williams for the engineering part of his task.
"But on the other side of it, the environment, the world next to you -- we don't have any simulator that can come close to what that does to your thoughts," he said.
The tiles
Williams will perform up to two more spacewalks over the mission's course.
He will be outside to repair some other machinery and may be called upon to repair a hand-sized gouge in the heat-resistant tiles detected Friday.
NASA believes the shuttle's underside near the main landing gear door got nicked by a chunk of ice on liftoff. However, officials aren't sure yet how serious the problem is or what course of action should be taken.
"They're probably fine. My gut feeling is we're probably fine but my gut feeling or anyone's gut feeling isn't enough," Hadfield said.
In 2003, the shuttle Columbia broke up upon re-entry, killing all seven astronauts on board. The shuttle's tiles had been damaged by insulating foam during liftoff.
"We look a lot more closely now than we used to," Hadfield said.
NASA will take a closer look at the gouge on Sunday, probing the difficult-to-reach area with lasers attached to the Canadarm and an extension boom. So far they only have camera and radar images of the damage.
The area of the gouge can be exposed to temperatures of up to 1,260 degrees Celsius upon re-entry. The laser will allow engineers to determine how deep the gouge is and whether repairs are needed.
If repairs are needed, a fourth spacewalk would take place, probably next Friday. Since Columbia, all shuttles have a repair kit on board.
On Friday, John Shannon, chair of the mission management team, told reporters that almost every shuttle has suffered some degree of thermal tile damage in the past.
"We have a rich flight history of tile damage, some of which is more significant looking than what we have right here," he told reporters.
"In the past, we didn't even know we had damage and we flew back home. So what I would tell you is we're going to do all the work required to understand it ... I would not even venture to guess what the probability is that we would have to go repair this."
In a worst-case scenario, Shannon said Endeavour could remain docked at the station for at least two months. A rescue mission could be launched as early as October.
With a report from CTV's David Akin and files from The Associated Press
