Associated Press
Backdropped by Earth's horizon and the darkness of space, the International Space Station will be serviced by an unmanned craft.

Inside the International Space Station is a big red button with a plastic cover. It means only one thing if the astronauts press it: Their lives are in danger.

It's the button to abort the pending arrival of a new European-made cargo carrier, the automated transfer vehicle (ATV), which is now hurtling toward the space station. How well that ship works is a life-or-death matter for the station's three residents.

The unmanned spacecraft is scheduled to make an automated docking at the station Thursday at 9:40 a.m. ET. There's no way for the astronauts to seize control — as they can during the docking of the Russian automated cargo ship, the Progress. If the ATV's systems fail, it could crash into the station and puncture it. Then the crew's air could hiss into outer space.

That's just what happened in 1997 when a cosmonaut on Russia's Mir space station ordered Progress to dock. Instead, the cargo ship slammed into Mir. The crew survived because of frantic efforts to seal off the damaged section.

The first of the new ships, christened the Jules Verne, launched March 8 and will undergo testing, including a practice abort, today.

"We obviously want to keep close tabs on it as it approaches," station commander Peggy Whitson said last week.

The ship will be by far the largest supply vehicle to dock at the station. It will deliver everything from food to oxygen and will stay there for up to six months before going to burn up in the Earth's atmosphere.

By 2015, four more ATVs will follow Jules Verne. NASA regards them as crucial to sustaining the station after the space shuttle fleet retires in 2010.

Officials from NASA and the European Space Agency, which designed the $2 billion vehicle, say they've done everything possible to ensure the Jules Verne will make a safe hookup. Engineers have tested all of its equipment since its arrival in orbit, and it has multiple backup systems.

"We're absolutely confident (of) the safety aspects of this spacecraft," NASA's station program manager, Michael Suffredini, said earlier this year.

The track record for dockings of automated spacecraft is not totally encouraging. When NASA's unmanned DART spacecraft, designed to test rendezvous technology, tried to make an automated approach to a satellite in 2005, it crashed into its target. Both DART and the satellite survived.

European officials say that unlike DART, Jules Verne can be called off. If the spacecraft nears the station too fast or at the wrong angle, the astronauts inside the station can make it veer away and enter a dormant mode. After the ATV is restarted, it can try to dock again.

"We've tried to train them not to touch that button, but astronauts will be astronauts," jokes Alan Thirkettle, station program manager at the European Space Agency.

The red button wasn't in the original plans for the ATV, but engineers added it after astronauts demanded more control.

The station's residents "are sitting inside (the station) and this 20-ton truck is coming toward them," ATV manager John Ellwood said. "They very much appreciate they will have the ultimate decision for their own lives."