Shuttle’s ‘Smoking Gun’ Seen

SAN ANTONIO -- A piece of foam blew a gaping 16-inch hole in a replica of Columbia’s left wing during a key test Monday, giving investigators conclusive proof that the cause of the space shuttle disaster began with debris that fell off the external tank after launch.

The breach in the replica wing’s delicate heat-protection system was caused by a 1.67-pound block of foam, fired by a gas-powered gun. It showed conclusively that a foam chunk like the one that fell off Columbia 82 seconds after launch could cause catastrophic damage, investigators said.

“We have found the smoking gun,” accident investigator Scott Hubbard said. “It is the kind of damage that must have occurred to bring down the orbiter.... I think it’s the direct cause.”

Until now, the Columbia Accident Investigation Board has qualified its findings about the foam debris, saying it represented a “probable cause” of the accident.

The statements Monday by Hubbard, a key member of the board, went much further in assigning direct blame.

“The board’s goal was to connect the dots between the foam-shedding event and the proximate or direct cause of the accident.... I think today we made that connection,” Hubbard said.

NASA is already planning to reduce, though not eliminate, the chance that foam debris will fall off the external tank on future flights. It is modifying the foam insulation on the so-called bipod attachment, where the foam that apparently caused the Columbia tragedy detached. But it may never have a solution to eliminate all foam debris, NASA officials said.

The accident board also recommended that NASA develop an ability to inspect and repair the shuttle’s thermal-protection systems in orbit. And it has suggested that NASA strengthen the shuttle’s thermal-protection system so it can absorb hits without leading to a catastrophe.

The foam test, conducted at the nonprofit Southwest Research Institute, was the seventh in a series of painstaking experiments to get to the bottom of the Columbia accident. The shuttle broke up over Texas on Feb. 1, following a breach in its left wing that allowed superheated gases to melt away the internal aluminum structure.

The accident board is expected to file its final report in about two weeks, so the $3.4-million test on Monday was one of the last and most important parts of the investigation process. Some outside experts have said they believe the accident board now has more than enough evidence to say without qualification that the foam caused the accident.

As rain clouds gathered in the distance Monday morning, engineers hurried to make final adjustments to the test rig. The target was a mock-up of a shuttle wing fitted with heat-shielding reinforced carbon carbon panels taken from existing space shuttles. The 35-foot long nitrogen-powered cannon had a specially constructed rectangular barrel that would fire the foam block at 777 feet per second.

The test began with a booming countdown over the loudspeaker: “Five, four, three, two, one.” A technician fired the cannon, and the foam hit the gun-metal gray panel with a loud thwack. Immediately, a large, jagged hole appeared, evoking gasps from newspaper reporters and space officials seated in nearby bleachers.

Engineers rushed to examine the rig. Some climbed a ladder for a closer look, poking their heads halfway into the hole to inspect the damage. Another pulled out a yellow tape measure to get the dimensions. Behind the wing, pieces of white foam were splattered on a black backdrop.

Sixteen cameras recorded the hit. Slow-motion video showed a crack appearing as the foam struck its target, the lower portion of leading-edge panel 8. The crack turned into a tear, then a ragged 16-inch hole.

Hubbard said the test indicated it would have been extremely difficult, if not impossible, for astronauts aboard Columbia to have made repairs in space. Based on how long it took for Columbia’s wing to burn up, investigators have estimated the actual gap in Columbia was roughly the same size as the hole that opened Monday.

An earlier test using the foam gun caused a 5-inch crack in a leading-edge panel, but that test used only one genuine leading-edge panel made of reinforced carbon carbon and a series of fiberglass surrogates. In Monday’s test, engineers used three actual panels, each of which originally cost $775,000.

Investigators now believe the breach in Columbia’s wing occurred on panel 8, based on an analysis of debris and when certain sensors failed. Panel 8 is the largest and most complex of the 22 panels on each wing, suggesting it may have also been more vulnerable to an impact. For nearly 20 years, NASA violated its own rule that nothing should hit the thermal protection system, the investigation has found.

Independent experts say the test confirms that the energy of foam impact on the wing had been grossly underestimated by NASA officials before and during the Columbia mission.

“No wonder the Columbia came apart,” said Paul Czysz, a professor emeritus of aerospace and mechanical engineering at Saint Louis University and a technical consultant to NASA. “You can’t sustain a breach like that on reentry.”

Elisabeth Pate-Cornell, a Stanford University professor who has advised NASA on foam-debris issues, said such a hole would be consistent with the way the shuttle broke apart. The shuttle was flying at such a high altitude early in its reentry that atmospheric heating would take some time to cause catastrophic damage inside the damaged wing, she said.

Monday’s test also included several changes from the prior test. The foam block was angled so that an entire edge slammed against the panel, rather than the corner of the block. The edge delivered more energy than the corner, Hubbard said.

The experiment also produced small pieces of reinforced carbon carbon that fell into the wing or on the ground. Hubbard held up one piece that was about 11 inches long and 4 inches wide. He said the piece is probably proof that a “mystery” object seen leaving the orbiter on the mission’s second day was in fact a torn piece of leading edge that had fallen into the wing or was dangling by a thread.

“I was surprised, I was very surprised,” Hubbard said of the latest test. “Before this test today I was willing to see anything from a small crack to something completely unexpected. And what we got was something completely unexpected.”

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Hart reported from San Antonio and Vartabedian from Los Angeles.