NASA engineers think they have found the cause of and a remedy for foam falling from brackets on the space shuttle fuel tank like that which recently damaged the Endeavour heat shield tiles, agency officials said Friday.
N. Wayne Hale Jr., manager of the shuttle program, said in a telephone news conference that X-ray tests of brackets that hold fuel lines on the next external propellant tank set to fly indicated microscopic cracks in a thin layer of foam atop the metal brackets.
Cracks in this special heat-resistant foam material, which is less than a half-inch thick, can lead to the lighter insulating foam above it coming off during the stresses of launching, Mr. Hale said.
"The fact that we were able to identify the most likely cause with a simple test, X-raying the fittings, was heartening," he said.
Atop the underlying material, called superlightweight ablative foam core, is a layer of lighter insulating foam that prevents the formation of ice on the brackets holding a feed line that carries supercold liquid oxygen from the fuel tank to the engines.
About 58 seconds into the Endeavour launching on Aug. 8, a baseball-size piece of foam, perhaps mixed with ice or some of the underlying material, fell from a tank bracket and ricocheted off a metal strut into the shuttle belly. The foam damaged two heat-resistant ceramic tiles, forcing NASA engineers to study the problem extensively for days before deciding that the shuttle could land safely without trying to repair the gash with an emergency spacewalk.
Falling foam is a serious threat to the shuttles and their crews. In 2003, the shuttle Columbia and its seven-member crew were lost while returning to Earth because of a hole in the wing caused by a chunk of foam during ascent. After that accident, NASA spent hundreds of millions of dollars to modify the fuel tank and greatly reduce foam loss at launching.
Mr. Hale said technicians were to remove all the foam from the oxygen line brackets and reapply just the light insulating foam. Tests have shown that the underlying heat-resistant foam is not needed, he said.
Engineers from the Michoud Assembly Facility in New Orleans, where the fuel tanks are built, will arrive at the Kennedy Space Center in Florida this weekend to supervise the work. Mr. Hale said the foam modifications should take about nine days, finishing in time to use the tank to launch the shuttle Discovery on schedule on Oct. 23 for a mission to the International Space Station.