NASA - Foam hit Columbia with close to a ton of force

CAPE CANAVERAL, Fla. -- A piece of foam insulation slammed into the edge of Columbia's left wing with nearly a ton of force, and the fact that it was tumbling almost certainly strengthened the blow, an accident investigator said.

"Based on the first really analytic look at it, the rotation adds energy. What we have to figure out is how much," Scott Hubbard, a NASA executive who is on the Columbia Accident Investigation Board, said Tuesday.

The effect of the tumbling will be analyzed in a series of foam-impact tests over the next month. Hubbard is overseeing the tests, which began at the beginning of May.

The investigation board suspects that the piece of fuel-tank foam insulation damaged a carbon panel or seal along the wing's leading edge during liftoff and that the resulting gap let in scorching gases that doomed Columbia during re-entry. The space shuttle ruptured over Texas on Feb. 1, killing all seven astronauts aboard.

For weeks after the accident, some NASA engineers were skeptical that a piece of the stiff but lightweight insulation could have caused catastrophic damage.

But a lengthy analysis of the launch video shows the foam spinning anywhere from 18 to 30 times a second, and that could add the equivalent of several hundred feet per second to the total force, Hubbard said.

"If you say that we are at a velocity right now of 700 or 800 feet per second, we could be looking at increases of 20 to 30 percent, and that's quite significant," he said.

Hubbard estimated that the foam imparted close to 1 ton of force on a relatively small area of the wing's leading edge, just five or six inches by 12 inches.

The key impact tests will take place in June, when foam is shot at actual carbon wing panels and seals that were removed from shuttle Discovery. First, however, tests will be conducted on a steel structure and then a mock-up of the wing's leading edge made of fiberglass instead of carbon.

During the tests, foam chunks will be shot at speeds and angles that approximate the impact of the piece that actually hit Columbia in January.

A first round of impact tests has already been conducted at Southwest Research Institute in San Antonio, Texas, but those involved chunks of foam fired at silica-glass thermal tiles of the sort that covered the Columbia's belly. That is because initially, NASA believed that the foam damaged the door of the left main landing gear compartment.

Since then, investigators have come to suspect instead that it was the wing's leading edge, made of a carbon composite, that was damaged.

In the first round of foam-impact tests, five chunks of foam weighing 1 to 2 1/2 pounds each were fired through the 33-foot barrel of a nitrogen-pressurized gun at thermal tiles on a main landing gear door, at speeds up to 565 mph. The door was removed from the Enterprise, a prototype spaceship that was never launched and is housed at the Smithsonian Institution in Washington.

The five tests, conducted over the first 1 1/2 weeks of May, resulted in little if any damage, Hubbard said.