SPACE CENTER, Houston - Space shuttle Atlantis' astronauts today finished replacing two crucial batteries aboard the international space station after opening up the vacant outpost for the first time in a year.
Minutes after cracking open the brightly lit Unity module late Monday, American astronaut Susan Helms and Russian cosmonaut Yuri Usachev headed in.
Only two of the six Russian-made batteries were working. The other four were dead or dying because of careless overcharging by Russian engineers. They are being replaced to restore full electrical power to the anemic space station.
Pushing aside piles of supplies, Helms and Usachev pulled up the floor of the Russian control module - named Zarya, or Sunrise - to get to the batteries. They replaced two of them in just over five hours, finishing well ahead of schedule early today.
''A lot of the credit goes to the crew working together before the flight to work out the choreography,'' flight director Phil Engelauf said. ''They really worked this down to a science, like a pit crew working on a race car.''
Russia's space program is picking up the tab for the batteries. Each one costs $252,000.
James Voss, who will join Helms and Usachev as a space station resident next year, was close behind them as they led the way into the space station.
''Glad you left the lights on for us,'' Voss told Mission Control.
Once inside, the seven Atlantis crewmates took air samples and checked the carbon-dioxide level to make sure it was safe.
The air was fine, although the thermometer was in the mid-80s. It was hot enough to prompt astronaut Jeffrey Williams, a Wisconsin native, to strip down to his shorts. The temperature eventually dropped to the high 70s.
The air-quality problems which plagued astronauts with nausea, itchy eyes and headaches - presumably because of the stagnant air - during NASA's last space station visit a year ago were not evident this time.
The astronauts had personal-sized fans to prevent exhaled carbon dioxide from pooling around their heads.
Before Atlantis undocks on Friday, the astronauts will drive the space station into a higher orbit and haul over supplies for future station residents.
A busy year of solar activity has caused the space station's orbit to drop by 1 miles a week. The shuttle's pilots start the first of three one-hour boosts tonight.
Since the engines get too hot after more than an hour of thrusting and need 24 hours to cool, NASA had to split the work up over three days. The plan is for Atlantis to shove the station 25 miles higher. Right now, the outpost is 209 miles above the earth.
On the Net:
NASA: http://spaceflight.nasa.gov/index-m.html