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Seattle Times: NASA determines how foam came off shuttle

CAPE CANAVERAL, Fla.—One year after the Columbia tragedy, NASA has determined how and why a chunk of foam insulation that doomed the spacecraft broke off from the fuel tank at liftoff.

NASA's top spaceflight official, Bill Readdy, said yesterday that the agency has learned through extensive testing that air liquefied by the super-cold fuel in the tank almost certainly seeped into a crack or void in the foam, or collected around bolts and nuts beneath the foam. The trapped air expanded as the shuttle rose, and blew off a piece of foam the size of a suitcase.

Rather than peeling off, as NASA had assumed from past experience, the foam was pushed off with explosive force, Readdy said. The agency also had assumed the foam would fall along the tank and miss the shuttle, but the falling foam shot toward Columbia and the left wing rammed into it, resulting in a large fatal gash.

"That is really the root cause that we've been able to discover here," Readdy said.

A tank redesign and improved techniques for applying and double-checking the foam should solve the problem, NASA said. But all this will take longer than expected and is one reason space shuttles will not fly until next year.