The international space station Wednesday marked five continuous years of people living and working aboard it.
But there wasn't much time for celebration.
The station's two residents spent the day cleaning air filters, upgrading exercise equipment and doing other maintenance. Astronaut William McArthur Jr. and cosmonaut Valery Tokarev, who arrived Oct. 3 for a six-month stay, also prepared for a spacewalk next week.
"It's not that we're not feeling celebratory," McArthur said. "The space shuttle isn't flying right now. And we got to figure out how to finish flying the space shuttle in the next four years and to finish building the space station like we promised to."
People first began living on the orbiting science lab on Nov. 2, 2000, after 16 countries joined to construct it.
"It absolutely calls for celebration," the astronaut said from orbit during a series of broadcast interviews. "We have done things that were absolutely inconceivable 50 years ago."
The space station, about half complete, includes living quarters, an exercise room and a galley and is now the equivalent of a three-bedroom house. Nearly 100 people from 10 countries have visited the station, and 29 have lived aboard, often for six months at a time.
NASA partnered with the Russian Federal Space Agency, the Canadian Space Agency, the European Space Agency and the Japan Aerospace Exploration Agency in building the station.
"It's not the pristine world that you see on Star Trek, where you see the neatly pressed uniforms," McArthur said. "What we have is perhaps, from a storage and organization standpoint, is well-managed chaos."
Dr. Paul Cloutier, a Rice University professor of physics and astronomy, said when people first started living in space, many were optimistic, but also naive about the challenges of long-term orbital trips.
"Just the fact that it is up there is a major accomplishment," he said, AP reported. V.A.