CAPE CANAVERAL, Fla. - The International Space Station just had a population boom.

A Russian Soyuz capsule carrying three new station residents docked yesterday at the orbiting complex. With three astronauts there to greet them, the station now has a full staff of six for the first time in its 10-year history.

What's more, each of the major space station partners is represented on board for the first time. The combined crew, all men, now consists of two Russians (Roman Romanenko and Gennady Padalka), an American (Mike Barratt), a Japanese (Koichi Wakata), a Canadian (Robert Thirsk), and a Belgian (Frank De Winne).

"It is a historic day. It's also a very happy day up here," said Thirsk, who arrived on the Soyuz with Romanenko and De Winne. "We've got an incredible potential for success here."

Having all these countries represented on board is "a great way to kick off a six-person crew," Kirk Shireman, NASA's deputy space station program manager, said on the eve of the linkup.

When the shuttle Endeavour and its crew of seven arrives in a few weeks, a record 13 people will be at the station, but only temporarily.

The Soyuz spacecraft blasted off Wednesday from Kazakhstan and pulled in at the station 217 miles above China's coast. There were hugs and handshakes all around when the hatches between the crafts swung open. The six astronauts gathered in the main living quarters for the many congratulations that streamed upward.

"Finally, we've lived to see this moment," Russian Mission Control radioed.

NASA expects science research at the station to triple. Until now, astronauts have had to spend most of their time keeping all the systems running and fixing things.

The bigger crew should bring a mental bonus as well. Psychologists have long said that three is hardly the ideal size because of the potential for one person to feel left out.

"Think about when you're 7 years old and you've got three kids," noted U.S. astronaut Timothy Kopra, who will fly up aboard Endeavour and then move in, replacing Wakata, who will return to Earth aboard that shuttle.

The station's first crew arrived in 2000, two years after the first part of the complex was launched. Until now, no more than three people lived there at a time. The crew size dropped to two after the 2003 Columbia disaster because of the lengthy grounding of NASA's remaining shuttles.

The space station has since expanded to nine rooms, three of them full-scale labs, and is 81 percent complete. It has five sleeping compartments, two toilets, two kitchens, and two mini-gyms. Another sleep station and more exercise equipment will be coming in August, and a dining table big enough to accommodate all six inhabitants will be launched early next year.

The immense supply runs will end when the shuttles are retired at the end of next year. NASA hopes to stockpile big spare parts at the station before that happens.

NASA also will have to rely on the Russian Space Agency to transport all its astronauts up and down, during the estimated five years between the final shuttle mission and the first ferry flight with a replacement spacecraft.