There have been more than two dozen shuttle flights to build, supply and repair the station since construction began in late 1998, delayed for more than two and a half years by the Columbia disaster. Following Discovery's mission, just seven space shuttle assembly flights will remain before the space station is complete in 2010.
Another milestone will be reached this summer when the station's fulltime crew is expanded from three to six. Then this outpost in space will finally begin to realize its full potential in carrying out scientific experiments. The station now has three major science modules, from America, Europe and Japan.
But many questions remain about the station's future. It is powered not only by electricity from its solar panels, but in large part by U.S. dollars, even though it's a joint project of 16 nations.
NASA has called the International Space Station "the greatest construction project of humankind," rivaling the pyramids of Egypt, the Great Wall of China, and similar achievements throughout history. But unlike many of its famous predecessors, this $100 billion project will not last through the ages. Its design lifetime extends until 2016, just six years after its much-delayed completion.
The station is expected to remain useful for a number of years beyond that date, provided that its complex structure withstands the harsh environment of space, and its parts don't wear out too fast. The Obama Administration has expressed support for keeping the station aloft past 2016. But it will take billions of dollars a year to do that.
Another issue involves resupplying the station and exchanging crews after the space shuttle fleet is retired next year. The U.S. will most likely contract for Russian launches to fill the gap until NASA'S shuttle replacement, the Ares launcher, is ready in 2015. The Ares project could cost as much as $50 billion, including the capability for new manned missions to the Moon.
NASA's overall budget is bound to face close scrutiny during the current recession, and there is uncertainty over the agency's future plans.
The space station has been seen as a shining example of international cooperation for the benefit of the human race. But this achievement carries a big price tag that won't end after the station's completion.
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