An artist's concept of the international space station when fully completed later this decade. Photo: NASA

President Ronald Reagan approved building an international space station in his 1984 State of the Union address. The European Space Agency, Canda, Japan, Brazil and Italy ultimately agreed to participate.

But sky-rocketing costs prompted numerous redesigns and finally, in 1993, the Clinton administration ordered NASA to invite the Russians to participate as a foreign policy objective.

Station assembly finally began in November 1998 with launch of the Russian Zarya module. The U.S. Unity node, a multi-hatch module that will serve as a gateway to future U.S. modules, was launched the following month.

Two shuttle crews have visited the station since then, one in May 1999 and the other in May 2000, to activate various systems, to repair broken equipment and to boost the station's altitude. During the most recent visit, the ventilation system in the Zarya module was modified and four of its six batteries were replaced.

NASA originally hoped to launch the Zvezda module more than two years ago, but construction was repeatedly delayed, first by Russian funding problems and then by trouble with the heavy lift Proton rocket.

Two Protons in three launches failed last year because of second stage engine malfunctions later blamed on poor workmanship and quality control. Modifications were ordered to preclude similar failures in the future. Two such upgraded rockets completed successful flights on June 6 and July 5, officially clearing the way for Zvezda's launch July 12.

While the repeated launch delays have been frustrating to NASA managers and their Russian counterparts, both sides have benefitted from the extra time.

"We have our own rich history of space flight and operations and the Russians have theirs," said space station flight director Mark Ferring. "And I think what's kind of happened over the last two years, the good parts of what we've learned and how we've done business we've shared with our colleagues in Moscow and they've done the same.

"We haven't really done a long-term program since Skylab," he said. "So they've shared with us a lot of what they've learned for long-term space exposure. So I think we've been able to combine our experiences and help each other both be better operators."