San Antonio, June 7: Columbia investigators obtained their first direct evidence in a test yesterday that foam debris caused the space shuttle accident: a foam-block fired at a wing panel left a three-inch crack.
Engineers used a gas gun to shoot a 1.6 pound foam-block at a replica of Columbia’s left wing, damaging the delicate heat shield on the leading edge. Such damage may explain how a breach opened, allowing superheated gases to enter the wing and melt the aluminum structure.
The foam, shot at 530 miles per hour also dislodged the leading edge panel by about one-tenth of an inch and opened a slightly larger gap than is normal along one side of the panel and slightly smaller on the other side.
The board had previously indicated that it believes foam debris fell off the shuttle’s external tank 82 seconds after launch and struck the leading edge of the wing, made of a material called reinforced carbon carbon.
Investigators for the Columbia Accident Investigation Board said the test results represent an important step in their efforts to solve the February 1 accident when the Columbia broke up over east Texas.
“This is the first evidence that a piece of foam that approximates what was observed in the accident can crack and damage a piece of flight RCC panel,” said Scott Hubbard, a board member.
The test culminated months of careful planning that had been put on hold on Thursday by a Texas thunderstorm and again yesterday morning when an electrical circuit malfunctioned. After a countdown to zero, nothing happened and workers had to partially disassemble the gun.
By early afternoon, the gun was back together and precisely aimed with a laser. After another countdown, the gun let loose with a loud whoosh followed by the thunderclap of the impact.
The foam slammed into the slate-gray wing with a force of 4,500 pounds — enough to kill a person. It sent puffs of foam dust and sprayed larger chunks across the test site. After the test, Hubbard said the foam shot had created a 3-inch crack.
The leading edge panel used for the test yesterday was taken from the shuttle Discovery and had flown into space on 30 missions, similar to the flight history of Columbia.
Paul Fischbeck, an engineering professor at Carnegie Melon University who has helped to conduct independent studies of the shuttle’s thermal protection system, said: “It is quite remarkable that foam could do that to an RCC panel. Six months ago, nobody would have believed that foam could crack an RCC panel.”