09 June 2003
09 June 2003
Investigators into the Columbia disaster have demonstrated for the first time that a chunk of foam like the one that hit the space shuttle shortly after launch can damage the heat-protective covering at the front of the wing.
A 1.7-pound piece of foam fired from a special cannon at a test rig made of parts from another shuttle created a 3-inch crack in the carbon material that protects the front of the wing and a crack in an adjoining seal made of the same material. It also slightly dislodged the carbon-fiber panels.
The test brings the Columbia Accident Investigation Board a step closer to proving that the foam that hit the front edge of the shuttle's wing somehow opened a hole that allowed hot gases to enter and burn up the ship on re-entry.
But the damage in the test was less than investigators predicted and falls short of conclusive proof. Most of the crack ran along a section of the carbon panel that is protected from the severe heat of re-entry. Only 3/4 of an inch of the crack was visible on the outside, where temperatures reach as high as 3,000 degrees.
""This is the first evidence that we have that a piece of foam that approximates what was observed in the accident can in fact crack and damage"" the wing panels, said accident board member Scott Hubbard.
""To me that's a step forward, maybe even a significant step forward, in our knowledge,"" Hubbard said.
Later on, investigators were still uncovering additional damage. The crack in the seal next to the 3-inch crack was not revealed until five hours after the 2:15 p.m. CT test. Investigation board spokesman Laura Brown said she did not have details about the size of the crack in the seal.
However, Hubbard said it's still too early to draw any conclusions from the test. Some of the world's leading experts in the wing material were ""scratching their heads"" as they assessed the initial results, Hubbard said.
Columbia broke apart and burned up on Feb. 1 as it re-entered the atmosphere. The searing gases of re-entry penetrated the left wing and vaporized the shuttle from within. Shortly after Columbia lifted off on Jan. 16, NASA engineers examining photographs of the launch spotted a fuzzy piece of foam striking the shuttle's left wing. Since the accident, the photos have been enhanced and studied at great length.
Investigators believe the foam came from the exterior of the huge orange fuel tank bolted to the shuttle's belly. Friday's test was an attempt to replicate the impact as precisely as possible.
The test chunk of foam — measuring 19 by 11 1/2 by 5 1/2 inches — was shot from a 35-foot-long cannon at about 530 mph, the estimated speed of the impact on Columbia's wing. It was aimed at a replica of the curved front edge of the shuttle's wing and struck it at an angle of 20 degrees. The test was conducted at the Southwest Research Institute in San Antonio, which is performing work for the accident board.
A battery of 12 high-speed cameras and 199 electronic sensors recorded every twist and turn of the wing structure. The impact itself took less than 1/1,000 of a second and was barely visible to the naked eye.
The section of the wing replica where the foam struck was a carbon panel that had made 30 flights on the shuttle Discovery.
In a test last week on fiberglass panels that are similar to the shuttle's carbon panels, the force of the impact was seven times greater than investigators had predicted.
One of the vexing questions to arise during the accident investigation is why such tests are only being conducted now, 22 years after the shuttle began flying. That issue is expected to be explored in the accident board's final report.
While Columbia was in orbit, engineers with NASA and its private contractors determined that the foam could not have significantly damaged the shuttle. They were so convinced that the carbon panels could not be damaged that they barely considered the possibility.
Even after Columbia and its seven astronauts were lost, NASA officials initially dismissed the possibility that carbon panels could be damaged from foam.
However, growing evidence from recovered wreckage, thermal studies of the wing and available flight data makes it almost certain that hot gases entered through a breach in a carbon panel.