CAPE CANAVERAL, Fla. —

To everybody's relief, astronauts fixed the toilet at the international space station on Wednesday and opened up a grand new science lab.

The toilet problem had fast become the most pressing issue of the mission, so much so that a spare pump was rushed from Moscow to Cape Canaveral last week for a last-minute ride aboard space shuttle Discovery.

Russian Oleg Kononenko put in the new pump, and the toilet started working normally again.

For two weeks, the three men living aboard the space station had to manually flush the Russian-built toilet with extra water several times a day. It was a time-consuming job and waste of water, not to mention an unpleasant chore.

So everyone - especially in orbit - was thrilled that the new pump seemed to solve the problem.

"Let's start using it," Russian Mission Control told Kononenko. "We'll keep our fingers crossed."

The space station's toilet woes seemed to capture the world's attention. It ended up being the main topic of conversation at NASA news conferences, with fastidious suit-and-tie managers having to describe the ins and outs of using the restroom in weightlessness.

"It's unfortunate we're talking about toilets, but that really is the life, that's the future of human exploration in space," Kirk Shireman, deputy space station program manager, said Tuesday night.

"I don't take it as a really bad thing. It's just something perhaps everyday people can really relate to," he said.

The door to the billion-dollar Japanese lab - named Kibo, or hope - was swung open late Wednesday afternoon, a day after its installation at the space station.

"This is a great moment for the Japanese folks," Japanese astronaut Akihiko Hoshide said before floating into the brightly lit chamber with a welcome sign. "It's been like 20-plus years to get this module up in space."

Hoshide noted that Kibo was empty, for now, but quoted an engineer back on Earth who told him, "It looks really empty, but it's full of dreams."

"Enjoy your new module," radioed Japanese Mission Control near Tokyo. The 10 space travelers did exactly that, twirling and doing back flips with plenty of extra room.

Flight director Annette Hasbrook described Kibo as "stunning" and said it was "just an amazing sight" to see it up and running.

At 37 feet and the size of a bus, Kibo is the largest of the nine rooms now at the space station. It surpasses the two other labs, belonging to NASA and the European Space Agency, by 9 feet and more, and it's going to expand.

A large float-in closet for Kibo arrived at the space station in March; it will be installed on the lab later this week. A third section - essentially a porch for experiments - will be launched next spring. That's when full-scale science operations are expected to begin inside Kibo.

Two astronauts will float back outside Thursday to set up Kibo's TV cameras and remove covers on its robot arm.

The space station is now three-quarters complete, with a mass of more than 600,000 pounds. NASA expects to wrap up construction in 2010, when the shuttles are retired.

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On the Net:

NASA: http://spaceflight.nasa.gov

Japanese Space Agency: http://www.jaxa.jp/index-e.html