Wearing masks and safety glasses, cosmonaut Yuri Malenchenko and commander Terry Wilcutt work inside the Zvezda service module today. Photo: NASA TV/Spaceflight Now

Wearing protective goggles and breathing masks as a precaution, the Atlantis astronauts floated into the international space station's new Zvezda command module for the first time early today, opening the door to a new era in space exploration.

"It's absolutely beautiful," marveled shuttle commander Terrence Wilcutt as he looked about the pristine spacecraft.

The Zvezda module, launched July 12 after two years of delays, will serve as the space station's nerve center during initial assembly, providing crew quarters, computer control and the propulsion needed to keep the station in a safe orbit.

The new module measures 43 feet long - 95.5 feet across its two solar arrays - and weighs 42,000 pounds. It has three pressurized compartments, one of which can serve as an airlock for spacewalkers, two staterooms and 14 windows.

It is attached to the Russian-built NASA-financed Zarya propulsion module, which in turn is docked to NASA's multi-hatch Unity module. Atlantis is docked to a pressurized mating adaptor on Unity's far side. The three-module station now stretches some 142 feet and weighs 67 tons.

The Atlantis astronauts spent their first day inside the station "basically opening up all the hatches, getting in to all the spaces, hooking up all the ventilation ducts and turning on the fans, powering up all the avionics, turning on the lights and making sure the house is ready for folks to live in," said space station flight director Mark Ferring.

"Most of the day was spent just getting into the vehicle," he told reporters at a 5 a.m. EDT news briefing. "We've had no problems at all today, everything just went fantastic and the crew was ahead of the timeline the whole time."

Astronaut Ed Lu sets up air venting while Terry Wilcutt removes launch restraint bolts inside Zvezda. Photo: NASA TV/Spaceflight Now

The space station's first full-time crew - commander William Shepherd, Yuri Gidzenko and Sergei Krikalev - is scheduled to take up residence aboard Zvezda in early November, spending four months aboard the station before being relieved by another crew.

But first, Atlantis's crew must finish outfitting the lab complex and activating critical safety and life support systems in the Zvezda module.

Before entering the module at 1:50 a.m. EDT, the astronauts donned protective eyewear and breathing masks as a precaution until they could get a chance to take samples and confirm the quality of the air. No problems were expected and indeed, moments later the astronauts took off the protective gear.

The decision to require masks and eyewear was made after the second space station assembly mission in December 1998.

"When you build a module like that in one G here on the Earth, lint, debris, dirt, things like that (get in)," said shuttle flight director Phil Engelauf. "You can clean the module as much as you can, but as soon as you get into zero G, all those loose particles start to float.

"And the crew noticed a significant amount of that in Zarya when they first ingressed on the first mission," he said. "So we sort of established a standard practice of eye protection and masks until we could assess that the air was free of debris and contamination."

The astronauts plan to spend most of their second day inside the space station replacing a battery in the Zarya module and installing three batteries and associated electronic gear in Zvezda.

Wilcutt and Malenchenko open the hatch leading from Zvezda into the Progress cargo freighter. Photo: NASA TV/Spaceflight Now

"Tomorrow is kind of the power day, we're replacing battery No. 6 in the Zarya, which is one of the few battery sets we did not replace on the last mission," Ferring said.

"In the Zvezda module, we launched with only five of the eight battery sets in the vehcile and we're going to install the other three battery sets tomorrow."

In the meantime, flight controllers continue to discuss the possibility of extending the mission one day to give the crew more time to finish outfitting and euipping the space station.

Engelauf said the shuttle has enough on-board hydrogen and oxygen to power its electical generators to permit extending the flight from 11 to 12 days. But propellant supplies in the shuttle's forward rocket pod remain tight.

Even so, he said, "everything seems on track to support the addition of the 12th day."