Why US feels the heat to keep its shuttles flying

Russia's space agency cheered Tuesday's successful shuttle launch. Europeans were also enthusiastic. Mr. Reiter's partici- pation – with a package of space-station experiments the European Space Agency has dubbed Astrolab – signals "the beginning of a long-term European human presence in space," notes Daniel Sacotte, the agency's director of human spaceflight.

Reiter will join Pavel Vinogradov and Jeffrey Williams, who have been aboard the station since April 1.

During the shuttle's eight-day stay at the station, the crew is slated to deliver 2-1/2 tons of freight, including food and clothing, as well as new laboratory racks, and a new oxygen generator in anticipation of expanding the station's size.

In addition, astronauts Piers Sellers and Michael Fossum will conduct two spacewalks to see if an extension to the shuttle's robotic arm can be used as a work platform in case the shuttle needs repair in out-of-the-way places. They also will be installing new hardware and making repairs to equipment on the outside of the station.

Construction on the station resumes with the next shuttle flight, with an estimated launch date of Aug. 28. That begins a series of 17 missions that will add trusses, solar panels, additional crew quarters, the European- and Japanese-built labs, and other hardware.

But while crews will be conducting some scientific experiments on the space station during this time, the agenda largely focuses on construction. NASA Administrator Michael Griffin noted at a press briefing on Tuesday that with fewer shuttles available for space-station utilization flights, the use-as-you-build approach yielded to a build first, use later strategy.

"Before we can get the kind of work done on the space station that we've built it to do, we have to get the science labs up. And they come along relatively late in the sequence," he said.

With so much at stake, it shouldn't be surprising if additional glitches on the shuttles raise questions of risk, says Ray Williamson, a research professor at George Washington University's Space Policy Institute in Washington. "There's a lot of sensitivity now to make sure you do everything you can" to manage the risks of operating a complicated machine under conditions inhospitable to humans.

Still, there's a danger of falling into what some experts call a paralysis of analysis.

"The US already is saying to our international partners: Look, give us a little time and we'll come up with a suggested program for cooperation on exploring space and sending humans beyond Earth orbit," says Dr. Williamson. "We will not be credible in that unless we can at least make the attempt to carry out obligations under agreements" such as those governing the space station.

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