U.S. investigators have strong new evidence that a piece of space shuttle debris caused the disintegration of the shuttle Columbia in February. A ground test has found that a piece of hard foam can seriously damage a shuttle wing, despite the U.S. space agency's early assertions to the contrary.
A shuttle wing test at the private Southwest Research Institute in San Antonio, Texas, has left little doubt about what made a hole in Columbia's left wing, causing it to break up over Texas during re-entry.
The independent panel probing the accident has concluded that something had caused an opening in the wing's leading edge, allowing extremely hot atmospheric gases to seep in and melt the aluminum structure from the inside. The board believes the crack was caused by pieces of hard insulating foam that broke off the shuttle's external fuel tank and hit the wing at high speed 82 seconds after liftoff.
In the San Antonio wing test, engineers duplicated the liftoff events by using a cannon powered by compressed gas to fire a piece of fuel tank foam at a replica of a shuttle wing.
A spokesman for the investigators, Air Force Lieutenant Colonel Woody Woodyard, said the experiment left a gaping 40-centimeter hole in the model wing's leading edge. "This certainly is strong evidence that can lead one to conclude that this was a direct cause," said Colonel Woodyard.
The test was the seventh the investigators conducted and appears to be the most conclusive because it came the closest to copying the actual foam strike. The foam weight and size was about the same as the piece that hit the wing - 750 grams and about the dimensions of a briefcase. The impact speed was more than 850 kilometers per hour.
The test used the same kind of precious reinforced carbon panels actually used in shuttle wings. The panel that sustained the test damage had been removed from the shuttle Atlantis, which had flown 28 times, comparable to the number of Columbia missions. Previous tests, conducted to calibrate the instruments, had used fiberglass so that the rare reinforced carbon would not be wasted. The fiberglas had also been damaged, even though it is tougher and more resilient than the carbon panels. The experiment reinforces the investigation board's belief about the foam. During its five-month probe, it gradually came to understand that the lightweight material could damage a tough shuttle wing designed to withstand the rigors of repeated spaceflight.
Shuttle engineers had worried about the foam impact even during Columbia's mission. They had asked NASA to seek spy satellite coverage of Columbia after they learned about the incident.
NASA had a prior agreement with the U.S. government's aerial reconnaissance agency to do so when it requested. But shuttle managers rejected the engineers' request in the belief that the foam could not have damaged the wing.
The man who then headed the shuttle program, Ron Dittemore, held to that belief even in the days after Columbia broke apart. "Right now it just does not make sense to us that a piece of debris would be the root cause for the loss of Columbia and its crew. There has got to be another reason," he said at the time.
The accident investigators are planning to issue their final report later this month formalizing their conclusion that the foam did break the shuttle wing.
They are also expected to criticize NASA management for the way it handled the events leading to the disaster.
Mr. Dittemore has since retired from NASA, although the agency says his departure had been planned before the accident. Last week, NASA changed its shuttle leadership by replacing three other top managers who had participated in Columbia decisions.