Why US feels the heat to keep its shuttles flying

When the space shuttle Discovery docks with the International Space Station Thursday, some of the loudest cheers will be overseas.

That's because the shuttle is the only vehicle able to deliver key components of the station over the next four years. Its success will determine whether the station becomes a fully functional international laboratory – or a useless, partially built curiosity circling Earth. It may also determine whether the United States remains a player in future international efforts in manned spaceflight.

Europe, Russia, and Japan are watching closely to see if NASA can deliver on its promises – and NASA seems to be feeling the pressure.

America's partners "understand the loss of Columbia and are sympathetic," says Roger Launius, who chairs the space history department at the Smithsonian Institution's Air and Space Museum in Washington. "But they are also saying: It's time to get back to business."

In the end, he adds, a fundamental reason other countries signed up to take part in the space-station project was to hone their own aerospace skills.

"In the 20 years since we've been trying to build the space station, those countries have made enormous progress in advancing their aerospace technology. They may not need us in the future."

Until recently, it would have been inconceivable to exclude the United States from an international space effort. It spends more than four times as much on space exploration as the European Space Agency does and nearly 20 times as much as Russia does. The shuttle remains an engineering marvel that no other country has matched. Some experts doubt a project beyond Earth's orbit could proceed without the US.

"You have to look at the amount of money that's been allocated [by others]; that's when you take this [threat] seriously," says George Whitesides, executive director of the National Space Society in Washington. So far, the money isn't there, he says.

But the shuttle has proved so complex and costly to operate that NASA is scrapping it in favor of its earlier capsule-atop-big-rocket approach. That's the approach that the Europeans and Russians have continued to refine over the last two decades. For three years while NASA struggled to return to flight after the Columbia disaster, Russian rockets shuttled provisions and crews to the station.

Other nations have been catching up, too. For example, the European Space Agency outlined a vision for astronauts reaching the moon a year before President Bush issued his vision. China has launched humans into space and brought them back safely.

The Europeans and Japanese have supplied modules for the station that allow astronauts to work in space. Thursday's transfer of German astronaut Thomas Reiter to the station will mark the first time it will host a crew that includes three of the project's four major partners.

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.