Canadian astronaut Dave Williams and his American partner successfully replaced a faulty gyroscope during their second spacewalk.
Along with his U.S. colleague Rick Mastracchio, Williams floated out of the International Space Station at 11:32 a.m. ET Monday.
They removed the faulty control movement gyroscope (one of four) and placed the 272-kilogram piece of equipment onto a temporary storage platform before installing the new one. The work ended at 6 p.m., putting them outside the shuttle Endeavour for six hours and 28 minutes.
As soon they bolted in the new gyro, ground controllers tested it and pronounced the new equipment to be operational.
"All right! That's great news," exclaimed Endeavour astronaut Tracy Caldwell, who supervised the spacewalk from aboard the station.
Williams did take some time for sightseeing. "This is the most amazing ride I've ever had," he said hundreds of kilometres above the Pacific Ocean.
The next spacewalk is scheduled to take place Wednesday. Mastracchio and Flight Engineer Clay Anderson will team up to prepare the station's Port 6 truss for relocation.
Williams could perform a third spacewalk on Friday to carry out more ISS construction, now that the mission has been extended by three days.
Meanwhile, engineers at NASA are still trying to decide whether risky repairs are needed for the shuttle's re-entry. Repairs would be done on either the Wednesday or Friday walks.
The major gouge occurred at the 58-second mark of liftoff last Wednesday when a chunk of insulating foam broke off and ricocheted off the fuel tank, striking the shuttle.
It is nine centimetres long and five centimetres wide. The gouge appears to penetrate into the felt pad below and possibly exposes some of the shuttle's aluminum skin.
Engineers and mission officials are expected to decide by Tuesday whether the gauge can withstand the intense heat of atmospheric re-entry, or if astronauts will be required to patch the damaged area. Astronauts could use protective paint, screw on a shielding panel, or use filler goo to repair the puncture.
Once a decision is made, Williams and Mastracchio will likely be assigned to perform any necessary patchwork, NASA has said.
The damaged thermal tiles are located near the right main landing gear door, right beneath the aluminum framework for the right wing, which would offer extra protection during the ride back to Earth.
In 2003, the shuttle Columbia burned up on re-entry as a result of damage sustained to its heat-resistant tiles during launch.
Paul Delaney, astronomy professor at York University, said the crew is lucky because they have "ample time" to make repairs. The shuttle has docked and is being powered enough by the space station to remain in orbit for several extra days.
"My bet is NASA will probably go out and do something for no other reason than they have ample time to do it," he told Canada AM Monday. "The repair that has to made, from what we can gather, it's not in a typically critical position."
Williams' wife Cathy Fraser said she's confident the astronauts will figure it out.
"They're pretty certified smart guys over there," she told CTV's Canada AM. "They'll figure out whether or not they need to fix it and if there's a real risk involved."
She also said Williams called he Saturday night after he completed his first spacewalk. He told her the first thing he did was take a mental snapshot of the view.
"He described it as an amazing feeling," she said.
With a report from CTV's David Akin
