CAPE CANAVERAL, Fla. Shuttle Atlantis hard-charging electricians zipped through repair work inside NASAs International Space Station early Tuesday as concerns about foul air in the outpost waxed and then waned.

Working shoulder-to-shoulder inside the Russian space tug now keeping the station aloft, cosmonaut Yuri Usachev and astronaut Susan Helms began speeding through an overhaul of the outposts electrical power system, which exceeded its warranty in late March.

The rapid pace enabled the crew to take on a couple of extra jobs that had been scheduled for later in the mission: the replacement of a balky power-distribution box connected to the stations radio communications system and the installation of two new smoke detectors.

"They really worked this down to a science," said NASA lead flight director Phil Engelauf.

"Like a pit crew working on a race car, everybody knows exactly what piece of this [job] theyre supposed to do," he added. "Things are going much more quickly than we had expected."

Crediting long hours of training and on-orbit experience during two six-month missions aboard space station Mir, Usachev swapped out more than a few identical batteries.

Said NASA flight commentator Rob Navias: "This is familiar territory for Usachev."

The servicing of the electrical system is the number one priority for the Atlantis mechanics -- the first people to visit the unfinished outpost in a full year.

Since then, four of six station batteries which power the outpost on the dark side of Earth have gone on the blink. Flight controllers in Moscow inadvertently overcharged the $252,000 units, and the Atlantis crew is replacing them with spares paid for by the Russian Space Agency.

The overnight electrical work came amid initial concerns about the potential for stagnant air and elevated carbon-dioxide levels inside the station.

The last crew to board the outpost suffered nausea, headaches and eye irritation, presumably because of foul air. So as a precaution, NASA equipped the Atlantis astronauts with protective masks and small portable fans to stir up any localized buildups of carbon dioxide.

Engineers also came up with a better scheme for positioning duct-like hoses that blow relatively fresh air from the shuttle into the station, providing better ventilation throughout the complex. By re-routing the hoses, staler station air is pumped back into the shuttles carbon dioxide scrubbing system, which obviated the need to both the masks and the fans.

"We havent seen any indications of adverse effects [on the crew] or poor air quality," Engelauf said. "And with the conditions we think weve created with these ducting modifications, were optimistic well keep the air as good as we can possibly make it in the station."

The grand reopening of the station came at 8:03 p.m. Eastern Daylight Time Monday (Tuesday, 00:03 GMT) as the linked shuttle-station complex cruised some 200 miles (320 kilometers) above the planet.

Like miners burrowing into an underground shaft, the astronauts wearing headbands equipped with small flashlights -- made their way through the shuttles docking tunnel and a dark cone-like connector at the base of the seven-story station.

A submarine-like hatch then was cranked open, and one by one, the astronauts floated into the American side of the two-room station a $300 million docking module named "Unity."

With six portholes on its walls, ceiling and floor, the cylindrical chamber has the sterile look of a hospital corridor. Lined with closet-like storage bins, the brightly-lit Unity module ultimately will serve as a pressurized passageway to various wings of the outpost. And that outpost will eventually cover an area the size of a city block.

"Glad you left the lights on for us," astronaut Jim Voss, who will spend four months aboard the outpost with Helms and Usachev early next year, told flight directors on the ground.

"Home away from home," astronaut Chris Hadfield replied from NASAs Mission Control Center in Houston.

"It will be before too long," Voss said.

En masse, the astronauts floated through another dark, cone-like connector that led them to the Russian side of the station a $240 million space tug dubbed "Zarya," or "sunrise."

The interior of the tug looks much like the inside of the Mir station. That is to say, cramped.

Bulky white storage bags stuffed full of station supplies are tied down within the tug, covering just about every inch of floor space as well as parts of its pale yellow walls. Yet another ton of gear will be stowed in Zarya before the Atlantis crew departs the station later this week.

Ranging from food, water and clothing to computer, exercise and medical equipment, the new store of supplies will be stowed on the outpost for its first resident crew.

U.S. astronaut William Shepherd and two Russian cosmonauts Sergei Krikalev and Yuri Gidzenko now are scheduled to open the station up for permanent habitation in late October or early November. Helms, Usachev and Voss will replace them in February or March.

That schedule, however, depends entirely on the long-delayed launch of the stations Russian-made living quarters. The so-called service module -- dubbed Zvezda, or "Star," by the Russians now is slated to blast off from Baikonur Cosmodrome in Kazakhstan on July 12.