WASHINGTON — A simple foam paintbrush that costs only pennies at hardware stores could be an essential tool in returning the space shuttle to orbit, NASA’s administrator said Wednesday.

Space agency engineers found that the brush may be just what astronauts need to spread a patching compound on a space shuttle’s damaged heat shield while the craft is in orbit.

"This thing turns out to be one of the most valuable tools we could have invented," said Sean O’Keefe, head of the National Aeronautics and Space Administration. "We’re going to buy it at Wal-Mart."

A clerk at a Washington, D.C.-area hardware store said a 1-inch foam brush sells for 49 cents and a 2-inch one for 99 cents.

Designing and testing a way to repair damage in the shuttle’s heat shield is an important part of NASA’s efforts to return the space shuttle to orbit after the Feb. 1 accident that destroyed Columbia and killed seven astronauts.

The Columbia Accident Investigation Board determined that the shuttle broke apart when superheated air entered a hole in the heat shield on the leading edge of the left wing and melted internal aluminum supports.

To repair a heat shield, O’Keefe said engineers have found a sealant that is formed when two compounds are mixed together.

Tests showed that the combined compound expanded when heated. This led to a plan to "underfill" a hole and then let the heat of re-entry swell the patch and seal the hole.

Once they had a compound, the engineers then had to find a way for a spacewalking astronaut to apply the material while wearing a bulky space suit, gloves and a bubble helmet, O’Keefe said.

Experts looked at a variety of sophisticated tools made from exotic materials, he said. They settled on what he called "an elegant piece of sophisticated hardware" — a foam paintbrush with a wooden handle.

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