Shuttle Astronauts Upgrade Station in Spacewalk
NASA astronaut Rex Walheim waves to a camera during a Feb. 13, 2008 spacewalk to swap a nitrogen tank outside the International Space Station during the STS-122 mission.
Credit: NASA TV.

This story was updated at 6:25 p.m. EST.

HOUSTON ? Two shuttle astronauts swapped out a cooling system tank outside the International Space Station (ISS) in a Wednesday spacewalk, the first for German spaceflyer Hans Schlegel since an illness kept him from an earlier excursion.

Schlegel and U.S. astronaut Rex Walheim replaced a refrigerator-sized pressure tank during the nearly seven-hour maintenance job, which came two days after the German spaceflyer skipped an earlier spacewalk due to an undisclosed medical issue.

?Hello to all the people of Germany,? Walheim said as the station passed over Schlegel?s home country. ?What a pleasure it is to be up here spacewalking with one of your native sons, Hans Schlegel.?

The 56-year-old Schlegel said Tuesday that he was feeling much better and looking forward to today?s spacewalk, which swapped out an empty nitrogen tank serving the space station?s port side cooling system with a brand new one.

?It?s great to be part of an international team,? said Schlegel, a veteran European Space Agency (ESA) astronaut, before he floated across the station?s new Columbus lab. ?I?m holding onto Columbus. That?s a good feeling.?

While the spacewalkers worked outside, mission managers cleared Atlantis? heat shield of any concerns for reentry and extended the shuttle?s STS-122 flight by one more day. Landing for the now 13-day mission is set for 9:06 a.m. EST (1406 GMT) on Feb. 20.

Station and shuttle astronauts also continued to start up the 23-foot (7-meter) long Columbus laboratory for orbital flight. The joint station and shuttle crew attached the ESA-built laboratory to the ISS on Monday and opened it for business a day later.

The lab?s activation was delayed due to a software glitch that prevented commands from the ESA?s control center near Munich, Germany to reach computers aboard Columbus by way of the station?s U.S. command system.

?The computer problem is straightened out,? said Sally Davis, NASA?s lead ISS flight director for Atlantis? mission. ?We know what caused the software glitch and we know what to do to get around it.?

Flight controllers cleared old commands in the computer system and restored communications between the Munich operations center and Columbus. Engineers worked through the night to fix the glitch, which delayed Columbus? activation by less than 24 hours, Davis said.

?A few people didn?t get very much sleep last night,? she added.

Tank swap success

Schlegel and Walheim appeared to move swiftly through today?s six-hour, 45-minute spacewalk, which began at 9:27 a.m. EST (1427 GMT) as Atlantis and the ISS flew high above the west coast of South America.

Astronauts installed the 550-pound (249-kg) tank, known as a Nitrogen Tank Assembly, on the station?s Port 1 truss segment in 2002, though it has since used up its 80-pound (36-kg) supply of gaseous nitrogen. Stored under extreme pressure ? nearly 80 times that of an average car tire ? the nitrogen is used to pressurize ammonia coolant lines that run through the station?s radiators.

Walheim toted the replacement tank into place from the tip of the station?s Canadarm2 robotic arm, which was controlled by crewmates Leland Melvin and Stanley Love inside the ISS. Shuttle pilot Alan Poindexter choreographed the spacewalk from inside Atlantis.

The spacewalkers completed their tank swap with time to spare, which they filled by inspecting a set of misaligned metal debris shields tied down to the station?s hull. They also wrapped thermal covers around a set of metal pins attached to the 1.4 billion euro ($2 billion) Columbus lab to prevent them from getting to cold, but were unable to take extra photos of a dinged handrail near the station?s Quest airlock.

Love discovered a 2 millimeter divot in the handrail ? which Mission Control dubbed the ?Love Crater? ? during a Monday spacewalk.

Today?s spacewalk marked the 103rd dedicated to space station construction and the second of the Atlantis crew?s STS-122 mission. Walheim and Love are scheduled to step outside the ISS one more time on Friday to attach a pair of experiments to the Columbus lab?s exterior and retrieve a failed gyroscope.

By its conclusion, Walheim racked up a total of 28 hours and 58 during his four career spacewalks while Schlegel closed with six hours and 45 minutes in one spacewalk. To date, Atlantis astronauts have spent 14 hours and 43 minutes working outside the ISS during the STS-122 mission.

?It?s an incredible view,? Schlegel said as the spacewalk ended.

NASA is broadcasting Atlantis' STS-122 mission live on NASA TV. Click here for SPACE.com's shuttle mission coverage and NASA TV feed. 

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