What's more, each of the major space station partners is represented on board for the first time. The combined crew, all men, now includes two Russians and one American, Japanese, Canadian and Belgian.
"It is a historic day. It's also a very happy day up here," said newly arrived Canadian astronaut Bob Thirsk. "We've got an incredible potential for success here. This is going to be something incredible. You ain't seen nothing yet."
Having all these countries represented on board is "a great way to kick off a six-person crew," NASA's deputy space station program manager, Kirk Shireman, said on the eve of the linkup.
When shuttle Endeavour and its crew of seven arrives in another few weeks, a record 13 people will be at the space station, but that will be only temporary.
The Soyuz spacecraft blasted off from Kazakhstan on Wednesday and pulled in at the space station as the two vessels soared 217 miles above the China coast. There were hugs and handshakes all around when the hatches between the two craft 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 to triple at the space station. Until now, astronauts have had to spend most of their time keeping all the systems running and fixing things, like a urine-into-drinking water machine that took months to coax into operation. Astronauts took their first sips of the recycled water in orbit last week.
There should be a mental bonus as well with a bigger crew.
Psychologists have long said three is hardly the ideal crew 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.
The first space station crew arrived in 2000, two years after the first part was launched. Until now, no more than three people lived up there at a time. The crew size dropped to two following the 2003 Columbia disaster because of the lengthy grounding of NASA's remaining space shuttles.
The space station has since expanded to nine rooms, three of them full-scale labs, and is now 81 percent complete. There are 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.
