Welcome to the International Space Station, Population: 6.

The space station finally reached its full crew size early Friday when three new spaceflyers arrived to double the number of people aboard after more than 10 years of construction in orbit.

The new crewmembers docked their Russian-built Soyuz TMA-15 spacecraft at the station at about 8:34 a.m. EDT (1234 GMT) as they flew 220 miles (354 km) above the south coast of China.

The orbital arrival brought the station to its full, six-person crew size for the first time in history and includes a spaceflyer from each of the $100 billion station's major partner agencies.

"We have the contact," said Russian cosmonaut Roman Romanenko, a second-generation cosmonaut who commanded the Soyuz.

• Click here to visit FOXNews.com's Space Center.

Riding aboard the Soyuz TMA-15 with Romanenko and Belgian astronaut Frank De Winne of the European Space Agency, and Canadian spaceflyer Robert Thirsk.

They were welcomed at the station by its commander, Russian cosmonaut Gennady Padalka, and flight engineers Michael Barratt, of NASA, and Koichi Wakata, of Japan.

"It's an historic day, and it's also a very happy day," said Thirsk, Canada's first long-duration astronaut, after arriving aboard. "You can't imagine the state of elation the six of us have right now."

As the two three-man crews merged into one, they greeted one another with wide smiles and warm hugs. The spaceflyers waved excitedly to flight controllers on Earth via a video link and Romanenko pumped his fist victoriously in the air several times.

Together, the six spaceflyers make up the station's Expedition 20 and they are the most international mix ever sent to the outpost. They represent the space agencies of Russia, the United States, Canada and Japan, as well as 11 countries of the European Space Agency.

"I think it's a great way to kick off six-person crews," NASA's deputy station program manager Kirk Shireman said Thursday. "We've been waiting for this for a long time."

Historic arrival

The Soyuz TMA-15 blasted off from Kazakhstan on Wednesday to ferry the second wave of the station's Expedition 20 crew into orbit.

Its arrival today capped years of construction and intense work to prepare the station to support a full-six person crew, which would nearly triple the amount of science that can be performed.

"The International Space Station is the most successful project ever taken upon by humankind," said Joel Montalbano, director of NASA's space operations in Russia. Montalbano and other officials from the Russian, U.S., Canadian and Japanese space agencies hailed the station's new six-person crew.

Construction of the space station began in 1998 with the launch of Russia's unmanned Zarya control module.

Two other rooms, NASA's Unity connecting node and Russia's Zvezda service module - which houses crew quarters, a bathroom, kitchen and dining table, were added by 2000, when the first three-man crew took up residence.

But delays and NASA's tragic 2003 Columbia shuttle disaster slowed the station's construction. It wasn't until November 2008 shuttle that the station received the equipment necessary to support a full-sized crew.

That mission delivered vital gear like a second kitchen, spare bathroom and recycling equipment that turns astronaut urine and sweat back into drinking water.

Padalka, Barratt and Wakata toasted the water recycling system's operational status last week by drinking water recycled from their own sweat and urine.

The system is vital for the station's ability to support six people in space since it cuts down the amount of water that must be shipped to the outpost, allowing for more cargo like food, air and science equipment.

"It has been 10 years in the making, this event," Padalka said after the docking. "This is very exciting and so we're ready to start utilizing the station."

Growing space station

Since the first station crew took charge, new modules from the U.S., Europe and Japan have been added to the outpost.

Earlier this year, astronauts added the last pair of U.S. solar arrays at the station, which is now longer than an American football field and can be easily seen by the unaided eye from the ground.

Inside, the station has a living space equivalent to a five-bedroom home or a 747 jumbo jet, astronauts have said.

"I think it shows a great example to the rest of the world that if nations want to work together for something great, for something wonderful, something for the future of our kids, that we can achieve some wonderful things," De Winne said before launch. "I hope we can continue this for many, many years to come."

De Winne will become the first European commander of the space station later this year when Padalka and Barratt return home in October.

Romanenko is the third second-generation spaceflyer to reach orbit (after fellow cosmonaut Sergei Volkov and American space tourist Richard Garriott), and Russia's second cosmonaut to fly in space after his father.

His father, Yuri Romanenko, commanded three space missions in the late 1970s and 1980s.

Busy spaceflight looms

Friday's Soyuz docking kicks off a daunting mission that includes two visiting NASA shuttles and 10 spacewalks, two of which will be performed by the station crew in early June.

NASA plans to launch the shuttle Endeavour to the space station on June 13 to deliver the last piece of the outpost's massive Japanese Kibo laboratory.

When the shuttle arrives, a record 13 people will live and work aboard the station for a short while. A second shuttle mission in August will deliver new equipment and supplies.

Japan also plans to launch its first-ever unmanned cargo ship to the station, the H-2 Transfer Vehicle, during the flight.

Each shuttle visit will swap out one member of the current six-man crew. Larger crew rotations will be performed aboard Soyuz spacecraft.

Russia plans to launch four Soyuz vehicles a year. NASA on Thursday announced a new contract with Russia that will allow it to buy six Soyuz seats in 2012 and 2013 for about $306 million, or about $51 million a seat.

In October, the crew will shift to Expedition 21 mission, with De Winne in charge, when the relief arrives for Padalka and Barratt — who have lived aboard the station since late March.

"We've got an incredible potential for success here," Thirsk said. "You ain't seen nothing yet."

Copyright © 2009 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.