- The Washington Times - Wednesday, February 19, 2003

Increased drag possibly caused by roughness on Columbia's left wing identified years ago and worsened by time and debris may have been enough to pull the space shuttle into a fatal sideways flight angle on re-entry, experts have told United Press International.
"It could very well be" that the combined drag from these different sources was enough to cause the demise of Columbia, said John Anderson, a leading aerodynamics expert.
The damage from the insulation that hit the left wing during liftoff "just might have been enough to throw things over the edge," he said.
At least twice before, as Columbia returned to Earth from missions, its left wing experienced a critical aerodynamic shift too early, prematurely increasing heating and drag on that wing, said former shuttle commander Navy Capt. Robert "Hoot" Gibson, who is retired.
NASA knew about the early aerodynamic shifts at the time and was told by Capt. Gibson about a particular roughness he had discovered on the surface of Columbia's left wing. Experts confirmed that the roughness might have caused the premature aerodynamic shift.
The increase in drag on the left wing, particularly if made worse by tile damage, may have been enough to cause the vehicle to fly sideways, something it might not survive, said Mr. Anderson, the curator for aerodynamics at the National Air and Space Museum.
Columbia disintegrated on Feb. 1 as it returned from STS-107, NASA's designation of the 16-day mission devoted to scientific research. Remains of Columbia's seven-member crew have been recovered, along with thousands of pieces of shuttle debris scattered across the southwestern United States.
The first known aerodynamic shift occurred on mission STS-28 in 1989 and was studied carefully by Capt. Gibson, an aeronautical engineer who helped investigate the Challenger disaster and redesign the shuttle's solid rocket boosters. The Challenger exploded on liftoff in 1986, killing its seven-member crew. Capt. Gibson was commander during four shuttle missions and piloted a fifth mission.
Capt. Gibson said he found the surface of Columbia's wings was two to four times rougher than the wings of the three other shuttles Atlantis, Discovery and Endeavour and that Columbia's left wing was 50 percent rougher than its right.
Columbia experienced both additional drag and heating on its left wing before it broke up. By itself, such an increase in drag is probably not enough to destroy the vehicle explaining why it returned safely in 1989 and 1995.
During its final, fatal mission, however, the drag could have been worsened by tile damage caused when insulation from the external tank broke off early in the launch, striking its left wing. It is also possible the roughness on the tiles got worse over time, again increasing drag, confirmed Mr. Anderson, who has 40 years of experience in high-speed aerodynamics, hypersonic aerodynamics and aerodynamic heating.
Even with replacements over the years, 70 percent of Columbia's tiles were the originals made by Lockheed Martin, according to a document approved by NASA and released by the prime shuttle contractor, United Space Alliance, on Feb. 3, two days after the accident.
Mr. Anderson said the combined sources of drag could pull the shuttle enough to the left that it was essentially flying sideways at which point the uneven forces on it could break it apart.
A NASA press release issued Feb. 15 said that two more yaw jets than originally thought for a total of four were firing as the shuttle sped toward its landing site in Florida.
"The flight-control system was detecting drag … on the left side of the orbiter," said a NASA spokesman. "To compensate for the drag the automatic computers onboard commanded these jets on the left side of the orbiter to fire. … Just like if you were driving a car on ice and you started skidding you would turn the wheel in the other direction to compensate for the skid."
The three axes of flight are roll (tilting of one wingtip up and the other down), pitch (movement of the nose up or down), and yaw (turning of the nose to the right or left).
"Anything to cause increased drag on that left wing would certainly have caused it to yaw," Mr. Anderson said. "The shuttle is designed to fly straight. It is not designed to fly sideways. That would have been absolute disaster if something had yawed it so much that it was basically trying to fly sideways."


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