Astronauts have swung open the door to the International Space Station's newest room, using flashlights to illuminate the shadowy chamber and wearing goggles and masks to keep themselves safe from any floating debris.

The two skippers were the first to enter Tranquillity, Europe's 380 million US dollar contribution.

Station commander Jeffrey Williams floated in first, followed closely by shuttle Endeavour's George Zamka and then several other members of the combined crews. Williams looked around the empty, virtually powerless 23-feet-long chamber for two minutes as colleagues documented the event with cameras, then came back out to report to Mission Control.

"The module is beautiful," he said, "and the atmosphere is very clean."

As a precaution, the astronauts kept on their goggles and masks as they began setting up temporary ventilation ducts between Tranquillity and the rest of the orbiting complex. Mission Control told them to keep the crowd to a minimum until air was circulating.

The hatch between Tranquillity and its 27 million US dollar observation deck was later briefly opened. The domed lookout has seven windows, one of them the biggest ever flown in space.

The astronauts hooked up Tranquillity during the first spacewalk of shuttle Endeavour's visit.

During the next spacewalk, the astronauts will connect Tranquillity's plumbing. The hoses for ammonia coolant had to be refashioned from spares, after the originals failed testing last month.

Tranquillity needs to have those cooling lines in place before any heat-generating machinery can operate inside. The room eventually will house exercise and life-support equipment, as well as a toilet.