A floating piece of debris approached the International Space Station on Thursday, and the crew took refuge in a "lifeboat" just in case they had to escape back to Earth. What's a space lifeboat?
It's just a Russian Soyuz spacecraft. The term "lifeboat," which conjures images of the Titanic, is misleading, since the Soyuz is used for regular travel to and from the International Space Station every few months. In emergency situations—such as when a piece of debris hurtles toward the station—the three-person crew is instructed to move into the Soyuz in case they have to make a quick exit. They leave the hatch open as a final safety precaution: If the debris hits the Soyuz itself, they can quickly return to the space station; if it hits the station, they still have enough time to pressurize the vehicle and undock, which takes only a couple of minutes.
So far, an emergency escape has never been necessary. When the space station is on a collision course with a foreign object, the first response is to maneuver out of harm's way. This requires advance warning, since it takes up to 30 hours to plan and execute a movement. Various countries have to sign off, fuel has to be measured, and you have to plan a new orbit that still lets you accomplish your goals. And ideally, you want to get several miles outside the path of the debris. But with both the space station and the debris orbiting at many thousands of miles per hour, you don't always have the luxury to think things over.
In theory, the station crew might also climb into one of the American spacecraft used to transport humans to and from the ISS—either the Discovery, the Atlantis, or the Endeavor. But the U.S. shuttles are used mainly to deliver equipment to and perform construction on the station, and they have only enough power to stay in orbit for about two weeks. The Soyuz, by contrast, is a lightweight, energy-efficient vehicle that can remain docked at the space station for up to six months. There's always at least one Soyuz docked at any given time—and two when a new crew is rotating in.
There have been past attempts to create a dedicated exit pod. In the late 1990s, NASA started developing a "crew return vehicle" for emergency situations but later scrapped the project. In 2010, when the United States retires its three shuttles, the Soyuz will be used for all transportation to and from the ISS—at least until NASA introduces a new spacecraft, the Orion, in or around 2016.
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Explainer thanks Phil Hattis of the American Institute of Aeronautics and Astronautics, Kelly Humphries of the National Aeronautics and Space Administration, and Scott Uebelhart of the Massachusetts Institute of Technology.