Astronauts float outside to test heat shield patch

By Irene Klotz

HOUSTON (Reuters) - A pair of spacewalking astronauts ventured outside the International Space Station on Thursday to practice a procedure NASA hopes it never needs.

Seared by the memory of shuttle Columbia's demise five years ago due to heat shield failure, the U.S. space agency has been tooling up damage prevention and repair procedures to give future shuttle crews a better chance of surviving a similar accident.

Columbia's seven astronauts were killed as it broke apart during its return to Earth for landing.

In addition to extensive in-flight inspections, NASA has developed techniques for spacewalking astronauts to fix minor heat shield damage. Thursday's outing by Endeavour astronauts Robert Behnken and Michael Foreman is devoted to testing how a putty-like filler for damaged heat tiles behaves in microgravity.

The men floated outside the station's airlock shortly after 6 p.m. EDT.

Engineers are particularly concerned if the goo will bubble up inside, creating a lip around a repair that could trigger excessive heating as the shuttle plunges through the atmosphere.

Behnken and Foreman will work on sample tiles, some intentionally damaged, some unintentionally broken during previous space flights or during tests that helped investigators trace the cause of Columbia's destruction to a piece of foam debris that fell off during launch and hit the ship's wing.

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