Thisstory was updated at 6:25 p.m. EST.
HOUSTON ?Two shuttle astronauts swapped out a cooling system tank outside theInternational Space Station (ISS) in a Wednesday spacewalk, the first for Germanspaceflyer Hans Schlegel since an illness kept him from an earlier excursion.
Schlegeland U.S.astronaut Rex Walheim replaced a refrigerator-sized pressure tank duringthe nearly seven-hour maintenance job, which came two days after the Germanspaceflyer skipped an earlier spacewalk due to an undisclosed medical issue.
?Hello toall the people of Germany,? Walheim said as the station passed over Schlegel?shome country. ?What a pleasure it is to be up here spacewalking with one ofyour native sons, Hans Schlegel.?
The 56-year-oldSchlegel said Tuesday that he was feeling much better and looking forwardto today?s spacewalk, which swapped out an empty nitrogen tank serving thespace station?s port side cooling system with a brand new one.
?It?s greatto be part of an international team,? said Schlegel, a veteran European SpaceAgency (ESA) astronaut, before he floated across the station?s newColumbus lab. ?I?m holding onto Columbus. That?s a good feeling.?
While thespacewalkers worked outside, mission managers cleared Atlantis? heat shield ofany concerns for reentry and extended the shuttle?sSTS-122 flight by one more day. Landing for the now 13-day mission is setfor 9:06 a.m. EST (1406 GMT) on Feb. 20.
Station andshuttle astronauts also continued to start up the 23-foot (7-meter) longColumbus laboratory for orbital flight. The joint station and shuttle crewattached the ESA-built laboratory to the ISS on Monday and opened it forbusiness a day later.
The lab?sactivation was delayed due to a software glitch that prevented commands fromthe ESA?s control center near Munich, Germany to reach computers aboardColumbus by way of the station?s U.S. command system.
?Thecomputer problem is straightened out,? said Sally Davis, NASA?s lead ISS flightdirector for Atlantis? mission. ?We know what caused the software glitch and weknow what to do to get around it.?
Flightcontrollers cleared old commands in the computer system and restoredcommunications between the Munich operations center and Columbus. Engineersworked through the night to fix the glitch, which delayed Columbus? activationby less than 24 hours, Davis said.
?A fewpeople didn?t get very much sleep last night,? she added.
Schlegeland Walheim appeared to move swiftly through today?s six-hour, 45-minutespacewalk, which began at 9:27 a.m. EST (1427 GMT) as Atlantis and the ISS flewhigh above the west coast of South America.
Astronautsinstalled the 550-pound (249-kg) tank, known as a NitrogenTank Assembly, on the station?s Port 1 truss segment in 2002, though it hassince used up its 80-pound (36-kg) supply of gaseous nitrogen. Stored underextreme pressure ? nearly 80 times that of an average car tire ? the nitrogenis used to pressurize ammonia coolant lines that run through the station?sradiators.
Walheimtoted the replacement tank into place from the tip of the station?s Canadarm2robotic arm, which was controlled by crewmates Leland Melvin and Stanley Loveinside the ISS. Shuttle pilot Alan Poindexter choreographed the spacewalk frominside Atlantis.
Thespacewalkers completed their tank swap with time to spare, which they filled byinspecting a set of misaligned metal debris shields tied down to the station?shull. They also wrapped thermal covers around a set of metal pins attached tothe 1.4 billion euro ($2 billion) Columbus lab to prevent them from getting tocold, but were unable to take extra photos of a dinged handrail near thestation?s Quest airlock.
Lovediscovered a 2 millimeter divot in the handrail ? which Mission Control dubbedthe ?Love Crater? ? during a Monday spacewalk.
Today?sspacewalk marked the 103rd dedicated to space station construction and thesecond of the Atlantis crew?s STS-122 mission. Walheim and Love are scheduledto step outside the ISS one more time on Friday to attach a pair of experimentsto the Columbus lab?s exterior and retrieve a failed gyroscope.
By itsconclusion, Walheim racked up a total of 28 hours and 58 during his four careerspacewalks while Schlegel closed with six hours and 45 minutes in onespacewalk. To date, Atlantis astronauts have spent 14 hours and 43 minutesworking outside the ISS during the STS-122 mission.
?It?s anincredible view,? Schlegel said as the spacewalk ended.
NASA isbroadcasting Atlantis' STS-122 mission live on NASA TV. Click here for SPACE.com'sshuttle mission coverage and NASA TV feed.
- NEW VIDEO: STS-122 Second Spacewalk Overview
- VIDEO: ESA's New Science Laboratory
- NEW IMAGES: STS-122 Launch Day for Shuttle Atlantis