WASHINGTON -- A simple foam paint brush that costs only pennies at hardware stores could be an essential tool in returning the space shuttle to orbit, NASA's administrator said yesterday.
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. We're not going to ask the Defense Department to requisition it out of stock."
A clerk at a Washington-area hardware store said a 1-inch foam brush sells for 49 cents and a 2-inch one costs 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. The accident has led the agency to ground the shuttle fleet.
Astronauts on Columbia and engineers in Mission Control were not aware of the extent of damage to the shuttle wing. But officials said that, in any case, there was no equipment on the shuttle to patch the wing even if the problem were recognized.
Officials at the Johnson Space Center said the patching compound now under consideration could be used only for the part of the heat shield composed of lightweight tiles. The nose of the shuttle and the leading edge of the wings are covered with panels of a different material, reinforced carbon-carbon. It was a break in a carbon-carbon panel that led to the loss of Columbia.
Kelly Humphries, a spokesman at the space center, said that repairing the carbon-carbon panels is more difficult and would require methods different from the tile repair. Among the techniques under consideration are a patch that could be internally bolted in place, an adhesive patch, or an overwrap that would envelop a heat-shield breach.
Before returning the shuttle to space, the investigation board said NASA must develop a way for astronauts to fix heat-shield damage while the craft is in orbit.
Such work would require a difficult spacewalk. An astronaut would have to maneuver in weightlessness and reach gouges or holes on the heat shield on the outside of the shuttle. The damage would require patching with a substance that could withstand the 3,000-degree heat of reentry.
O'Keefe said NASA earlier had studied this kind of repair and "it was deemed . . . to be too difficult to achieve and therefore not workable."
But after the Columbia accident and given the mandate from the investigation board, NASA engineers took a fresh look and found possible solutions, he said.
To repair the 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 reentry swell the patch and seal the hole. 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. O'Keefe said the foam brush avoided the problem of sticking to the sealant while the sealant was being spread in the hole.