A test of a U.S. space shuttle wing has shown how the orbiter Columbia might have been damaged before it disintegrated in February. Foam shot at the wing model opened a narrow gap in it, possibly duplicating what happened when foam struck Columbia during launch in January.
The shuttle wing test at the private Southwest Research Institute in San Antonio, Texas, may provide a clue to what caused the crack in Columbia's left wing, before it broke up over Texas during re-entry.
Investigators have concluded that something caused a small opening in the wing's leading edge before re-entry, allowing extremely hot atmospheric gases to seep in and melt the aluminum structure from the inside. The leading theory has been that the crack was caused by pieces of hard insulating foam that broke off the shuttle's external fuel tank and hit the wing 82 seconds after liftoff.
The wing test showed that it is possible for foam to split the wing open, when propelled at high speed toward panels covering the front edge. A spokesman for the independent board investigating the disaster, Air Force Lieutenant Colonel Woody Woodyard, calls the effect "significant."
"We took some foam and shot it at the left wing portion of the panel, and it caused a T-seal between panel six and seven to lift and shift toward panel seven," he explained. "So that was some significant movement there."
T-seals, which resemble the letter "T" in the Roman alphabet, are molded pieces that fit between the panels covering the wing's leading edge. Colonel Woodyard says the T-seal that the test dislodged left a narrow gap between the two panels the thickness of a coin and 56 centimeters long.
Investigators have said that such an opening would have been big enough for atmospheric gases heated by friction with the shuttle to penetrate the wing, causing it to deform.
To duplicate the conditions of the foam strike that occurred during Columbia's launch, testers used a chunk about the size of a briefcase, and hurled it at the wing model at 237 meters per second. The only difference from the launch condition is that the wing panels and T-seals in the test were made of fiberglass, instead of the fiberglass-reinforced carbon composite material actually used on shuttle wing edges.
Colonel Woodyard says this test was merely a trial to calibrate the equipment before scarce carbon panels are used in later tests. He says investigators have not analyzed the test and drawn formal conclusions from it yet, but he says it might be predictive of the tests to come.
"Fiberglass is actually approximately 2.5 times more resilient than reinforced carbon panels, so you can imagine that if this is the type of movement we saw in fiberglass, one could suggest that we might see more damage on an actual carbon panel. But we don't know that yet. That's the purpose of the tests," said Colonel Woodyard.
When tests with reinforced carbon panels are conducted in June, investigators will use pieces that have actually endured the rigors of flight on a shuttle and exposure to climate during the long months of shuttle preparation on the ground.
Investigators have said that the salt air blowing off the Atlantic Ocean near the shuttle launch site and paint peeling off the launch framework corrode the reinforced carbon wing elements, which have rarely been replaced in the 22-year history of the shuttle.
