Astronauts hook up station gas tanks

SPACE CENTER, Houston: Two astronauts hooked up three of four gas tanks on the international space station's new entryway early Wednesday despite a brief shutdown of a computer critical to the job.

Space shuttle Atlantis astronauts Michael Gernhardt and James Reilly II installed two oxygen tanks and a nitrogen tank needed to pressurise the new $164 million air lock during a 6 1/2 -hour spacewalk that started late on Tuesday.

NASA intended for them to add only two of the four tanks to the air lock during the spacewalk, but the work was so speedy that flight controllers decided to add the third. The fourth, a nitrogen tank, was to be added Friday during their third and final spacewalk of Atlantis' mission.

Station astronauts Susan Helms and Jim Voss manoeuvred the station's 58-foot robot arm to hoist the 1,200-pound tanks from the shuttle's cargo bay and hand them to Gernhardt and Reilly, who latched them to the air lock.

"Good work, good support by the whole team today. A lot of work got done, and we got three-fourths of the tanks done. That's really good," Voss said.

Gernhardt and Reilly ventured out an hour late on Tuesday because the hard drive in one of three computers needed to operate the Canadian-built robot arm failed. Flight controllers reset the computer in time for the late-night spacewalk.

"Looking at the bottom of the tank, I'm sure glad the arm's working," Reilly said as the arm prepared to lift the second tank.

"So are we," Mission Control replied.

When the 58-foot arm was installed at space station Alpha in April, hard drives failed on all three of the computers.

NASA engineers spent weeks studying the problems, had all the hard drives replaced, and Atlantis launched with the air lock July 12 with controllers confident that the computers would work.

"It's the same type of problem that's out there lingering that we have been contending with," flight director Paul Hill said on Wednesday.

Later this year NASA will replace those hard drives with computer units that have no moving mechanical parts, he said. If the same problem pops up on Friday, astronauts can use a smaller robot arm attached to the shuttle to hoist the fourth tank.

The big arm lifted the 6 1/2 -ton air lock from the shuttle and attached it to the station on Sunday without a hitch during Gernhardt and Reilly's first spacewalk.

The new passageway will enable American space station residents to conduct spacewalks in U.S.-made spacesuits while carrying large pieces of gear. Until now, they have had to use Russian suits and a cramped Russian exit.

The gas tanks are needed to repressurise the air lock after spacewalks and to replenish air in the rest of the space station if needed.

NASA on Tuesday added a day to Atlantis' mission because efforts to fix a leak in a ventilation valve and earlier trouble with water lines cut into a busy schedule of outfitting the air lock for crews of both spacecraft.

The additional time will allow astronauts to replace the valve in one of two air-circulation lines leading into the air lock from Alpha.

The extension moved the third spacewalk of the mission to Friday night, the undocking to Sunday and the landing to July 24

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