High-resolution images taken by an Air Force camera show a jagged area on the leading edge of Columbia's left wing 60 seconds before the space shuttle broke apart over Texas last Saturday, Aviation Week and Space Technology magazine reported in its edition published today.
The images, reportedly taken from a ground-based camera in the Southwest whose precise location was not disclosed, are among those being analyzed at NASA's Johnson Space Center in Houston.
A source close to the investigation told the trade weekly that they show serious structural damage to the left wing near the point where it joins the fuselage.
Damage to the wing would be consistent with telemetry data received by NASA mission control that showed increasing drag on that side of the shuttle and efforts by the computerized flight control to counteract it.
The damage seen in the photographs is in about the same area where a piece of insulating foam appeared to strike the leading edge of the wing after breaking off the shuttle's main tank at liftoff, but there was no indication last night that the impact caused the damage.
The magazine, widely respected in the industry, said the damage to the wing's leading edge would have affected the shuttle's flying characteristics and allowed superheated gases to flow into the wing structure -- what it called "a fatal combination."
NASA spokesman James Hartsfield in Houston said last night that he could not confirm the account. He said investigators at the space center are poring over many still images and videos taken of the descending spacecraft in its final minutes, but as of late yesterday, no such wing damage had been mentioned in staff briefings.
The magazine said the images also show the thrusters on the orbiter's right rear side firing to correct the spaceship's yaw, or left-right orientation, as the onboard computer tried to correct the shuttle's increasingly disrupted flight posture.
NASA engineers have speculated about whether damaged thermal tiles, a fundamental structural flaw, a malfunctioning onboard computer or a meteoroid strike might have been the root cause of the shuttle's breakup during its plunge into Earth's atmosphere. The telemetry showed that the end result was something that caused excess "drag" and disrupted the aerodynamics of the spacecraft as it hurtled through the thickening air, decelerating from orbital velocities of around 17,500 mph to 12,500 mph in its final moments.
Drag is unimportant in space, where a shuttle is in its element, but as soon as an orbiter hits the atmosphere it becomes an unpowered glider. Anything that throws it out of aerodynamic position is dangerous.
The leading edge of the wing, the site of the jagged shape in the images, is the point where the insulating material switches from thermal protection tiles, which are glued on, to a different system made of reinforced carbon-carbon material, which is bolted on.
This means the problem could have resulted either from failure of the tiles or of the attachment mechanisms, the magazine suggested.
The ragged edge on the left wing "indicates that either a small structural breach -- like a crack -- occurred, allowing 2,500 F. reentry heating to erode away additional structure there, or that a small portion of the leading edge fell off at that location," the magazine reported.
The front of the shuttle wing is flat and is fitted with a U-shaped reinforced carbon-carbon structure that gives it aerodynamic shape and provides a crucial shield against the heat of reentry. The structures are bolted on.