On Tuesday, the world celebrated the space station’s 10th birthday — the longest period of time of continuous human habitation outside Earth’s atmosphere.

The three Russian and three U.S. astronauts who currently live aboard the International Space Station celebrated the occasion with a special meal and a congratulatory call from NASA Administrator Charles Bolden.

Bolden spoke of the “toehold in space” provided by the orbiting station and the international cooperation used to create it.

“As we enter the station’s second decade, our path forward will take us deeper into space and expand humanity’s potential farther,” he said. “The lessons we learn on the station will carry us to Mars and beyond. I want to give a heartfelt thank you to the six crew members on orbit and all the teams over the years that have helped us get to this milestone day.” It began on November 2, 2000, when an American and a Russian astronaut floated side by side into the ISS that orbits more than 300 kilometres above the Earth’s surface.

The project was born out of the death of the Cold War, as the U.S. and Russia began cooperating. The first ISS component, Russia’s Zarya module, was launched in 1998.

The ISS just last week barely squeaked out its claim to “longest habitation in space”, when it beat out the longevity record of the Russians’ long experiment on the Mir.

“The space station’s crowning glory is that it’s made the world a smaller place,” said John McCullough, head of NASA’s flight director office.

The station’s first crew was made up of Russians Yuri Gidzenko and Sergei Krikalev and American commander Bill Shepherd. In the intervening decade, some 200 people have spent time on board, 15 countries have helped build it and more than 600 experiments have been conducted.

The ISS permanent crew was expanded to six people last year, for the first time including representatives of all the space agencies involved in the project — the U.S., Russia, Europe, Japan and Canada.

“It’s an amazing spacecraft and the feat we have accomplished as a team with our international partners is perhaps the most difficult thing ever accomplished by humankind,” said NASA ISS programme manager Mike Suffredini.

Much of the international effort has focussed on building the station. Including its solar panels, the ISS is nearly as long as a football field. The liveable space is the equivalent of a five-bedroom house.

Cost estimates for more than a decade of international work and planning invested in the station range from $35 billion to $160 billion.

The craft has been assembled in pieces in space, with most of the heavy lifting done by the U.S. space shuttle, which is capable of carrying aloft huge components. That alone is an engineering accomplishment, since those pieces were constructed around the world and had never been in the same room together before being connected in space.

The station is now largely complete and even had a “picture window” installed earlier this year that allows astronauts a 360-degree view when protective shutters are lifted.

The space shuttle Discovery is scheduled to be on its way to the station later this week and will bring the last U.S. component to the station.

The new room to be installed during the mission was built by the Italian Space Agency and has been in space before in a different guise — as the cargo-fetching Leonardo module. NASA, which owns the module, has transported things to and from the Earth in it, and has outfitted it anew to be installed as a permanent “multipurpose” part of the station.

The U.S. space agency plans to retire the ageing shuttle fleet next year, with one more mission planned and another possible if funding comes through.

“It wouldn’t have happened without the space shuttle, absolutely,” said Bob Cabana, director of the Kennedy Space Centre, where shuttles launch for their trips to the ISS.

Shuttle proponents have expressed concern that without it, there will be no craft large enough to take large equipment to the station.

Only the Russian Soyuz will be available to shuttle astronauts aloft.

NASA has used that argument in pressing for another flight, which has secured approval albeit without the money to back it up.

The final shuttle flights have been aimed at stocking the ISS with spare parts for repairs. In August, for example, part of the cooling system broke. It was fixed through emergency spacewalks that replaced a cooling pump using the spare parts on board.

U.S. lawmakers also recently approved support for the ISS through at least 2020, much to the relief of its international partners. It had earlier been scheduled to be de-funded and then de-orbited in 2015.

That’s also good news for scientific experimentation that can now get into full swing once the focus on ISS construction is complete, NASA says.

“We should believe and think about the fact that we will explore beyond low Earth orbit and this really was the first step in that endeavour,” Suffredini said.

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