Shuttle Foam Under The Microscope

Researchers shot a chunk of real space shuttle foam insulation at an aluminum sheet in preparation for tests later this month requested by the Columbia accident investigators.

The investigation board wants to measure the amount of damage caused by insulating foam striking actual shuttle wing parts at nearly 500 mph. Friday's test-firings at Southwest Research Institute should help determine whether the blow to Columbia's left wing by a 2-pound piece of foam during liftoff was enough to lead to the ship's destruction two weeks later.

The foam broke off Columbia's external fuel tank barely a minute into the flight and slammed into the leading edge of the wing.

NASA called the institute for help in setting up the tests two days after the shuttle disintegrated over Texas during re-entry. Justin Kerr, NASA's director of the impact test program, said the space agency immediately began seeking expert help in finding the cause of the Feb. 1 accident that killed seven astronauts.

For the month-long series of tests scheduled to begin in mid-April, NASA will shoot foam at wing panels from the shuttle Discovery and the Enterprise, a prototype that never flew and is now housed at the Smithsonian Institution.

Because those targets are so precious, NASA and the institute want to make sure the giant compressed-gas gun and all the measuring instruments are thoroughly checked out and working perfectly.

"The test articles themselves are so expensive. I mean, you just can't come out here and do 50 shots," said Scott Mullin, manager of the institute's ballistics and explosives engineering section.

Mullin acknowledged that the outdoor testing at the institute's ballistic range cannot precisely recreate the weather or certain other conditions during a shuttle liftoff. Computer simulations will help with that.

"In the Sherlock Holmes world, it's one piece of the pie," he said.

For Friday's test, a 1 1/4-pound piece of foam about the size of a briefcase shot through the 33-foot barrel of the nitrogen-pressurized gun at an aluminum sheet. The sheet was mounted on a metal frame several feet in front of the gun, and tilted at a 15-degree angle.

"Five, four, three, two, one, zero," Larry, the gunner, called out. A few more seconds passed, and then the foam whooshed with a loud crack out of the barrel and struck the lower center of the aluminum sheet, right where it was aimed.

Shredded pieces of foam fluttered into the trees behind the test stand; some were as big as a loaf of French bread. The aluminum wasn't dented, but the foam left a mark.

Officials called the test a success.

Neither Mullin nor Kerr would offer an opinion on whether foam could have caused catastrophic damage to Columbia's left wing. Tests at the institute in 1999, shooting much smaller pieces of foam at thermal tiles — but not wing panels — sometimes resulted in little damage, Mullin said.

"What we're doing here is not necessarily going to say, `Yeah that's it or not,"' Mullin said.

"If we do test out here and there's like zilch-o damage, then they're going to have to go back and look at it and say, `it was something else.' I don't think there's going to be zilch damage."

MARCIA DUNN