Why did wing of 'Columbia' heat up?
© St. Petersburg Times
WASHINGTON -- Two weeks after Columbia broke apart, investigators have many clues, but are a long way from solving the mystery.
They think the trouble began when tremendous heat seeped into the left wing, but they don't know how or why.
This account of clues and theories is based on the facts released by NASA and interviews with engineers, aviation accident investigators and a former astronaut.
They say the Columbia tragedy likely was caused by many factors: It usually takes a unique, sometimes bizarre, chain of events to cause a calamity.
Columbia's sensors indicate the trouble began in the left wing as the spacecraft was 236,000 feet above the Pacific Ocean.
As the shuttle neared California, temperatures in the brake lines for the left landing gear increased 5 to 6 degrees per minute for several minutes -- unusual but not alarming.
Sensors toward the back of the wing quit, while others in the same area grew steadily hotter. Otherwise, the shuttle was performing normally, completing its first "S-turn" to slow down and prepare for landing.
As the spacecraft crossed the California-Nevada state line, it rolled to the left. NASA officials believe something was causing excessive drag on the left wing, but they don't know what.
The troubles cascaded by the time the shuttle was over New Mexico, descending from 218,000 feet, going Mach 20, or 20 times the speed of sound. Sensors just beneath the skin of the left wing conked out, as did sensors in the left wheel well.
One sensor indicates the left landing gear deployed over Texas, but NASA officials say other sensors suggest that was a false reading.
Columbia's computers tried to compensate for the drag by moving the ailerons and the elevons, the wing panels that roll the shuttle. Thrusters on the tail fired, trying to keep the spacecraft flying straight. But the controls apparently couldn't stop the shuttle from rolling.
NASA hasn't said what happened next, but it's likely the spacecraft broke apart quickly.
Former astronaut Robert "Hoot" Gibson says the evidence indicates that "when it rolled, they went out of control. Now they are ballistic projectiles. They are falling."
SPACE JUNK: With thousands of pieces of debris -- everything from tools to trash bags -- orbiting the earth, a collision could be catastrophic for the shuttle.
A 1997 study by the National Research Council said that on some missions, meteorites and debris were "the single greatest threat to the shuttle and crew."
That's why NASA relies on Space Command, a military unit that tracks orbital debris, for a daily traffic report. The command tracks space junk using telescopes and radar. On several occasions, shuttle astronauts have maneuvered the spacecraft to avoid debris.
But Space Command can track only items larger than a baseball. It's possible that something smaller, such as a micrometeorite, may have pierced Columbia's wing.
Defense Department radar shows something coming off the shuttle as it orbited on Jan. 17, one day after its launch. Investigators don't know what the object was.
But some facts weaken the space junk theory.
Most space debris orbits much higher than the shuttle, reducing the likelihood of a collision.
And why wasn't the impact noticed? The shuttle's sensors are so precise that controllers in Houston know when astronauts are exercising on the treadmill. NASA has said the sensors indicated no problems during the 16-day mission.
"If you hit space junk, it's going to reverberate," said John Cox, a veteran accident investigator for the Air Line Pilots Association. "There will be indications of that."
FALLING FOAM/ICE: Videotapes of the Jan. 16 launch show a piece of foam insulation fell from the fuel tank and struck the spacecraft. NASA engineers studied the tape and estimated the foam was about the size of a briefcase and weighed about 2.7 pounds.
One engineer wondered whether the foam could cause a catastrophic problem if it damaged the wheel well where the landing gear is stored, but other engineers concluded the foam could not have caused severe damage. They were so confident that Ron Dittemore, the agency's shuttle program manager, declared Feb. 5, "It just doesn't make sense to us that a piece of debris could be the root cause for the loss of Columbia and its crew."
Since then, NASA officials have said Dittemore was wrong to rule out the foam theory. But on Wednesday, NASA administrator Sean O'Keefe dismissed the foam as a cause, likening it to a plastic foam cooler that blew out of a pickup truck on the highway.
Still, independent engineers say the foam could have damaged the shuttle's tiles, which are heat-resistant but brittle.
"NASA has estimated the size and mass, but not with certainty," said Stephen Ruffin, professor of aerospace engineering at the Georgia Institute of Technology. "Foam impact could potentially affect the aerodynamics and heat transfer more than you would think."
TILES: Many theories involve the unique tiles that protect the spacecraft from the overwhelming heat of re-entry, when the shuttle is engulfed in a red plasma that can be as hot as 3,000 degrees.
If some of them fell off or were seriously damaged as the shuttle re-entered the atmosphere on Feb. 1, it might explain the drag on the left wing. But investigators said Thursday that missing tiles alone wouldn't be enough to generate the fatal heat in the wing.
So what happened?
David Brookstein, dean of the school of textiles and materials technology at Philadelphia University, said tiles could have come off and warmed the wing's aluminum frame. That could have weakened the glue that held the tile and the Nomex felt material beneath it.
In this theory, he said, "The degradation is not from the top, but from the bottom."
So far, there's no proof of damaged tiles. The sensors gave no indication of trouble during the 16-day mission.
SUPERHEATED RE-ENTRY: A theory related to the tiles involves a stage in re-entry called "boundary layer transition," when the airflow over the shuttle's wings becomes turbulent and exposes the spacecraft to dangerous heat.
That normally occurs when the shuttle is going Mach 8. But, especially on Columbia, it has occurred much earlier, when the shuttle was still roaring along at Mach 19. That causes a sharp increase in heat, according to a 2002 NASA report.
Mach 19 is about where Columbia apparently broke apart.
Gibson, who flew five shuttle missions before he retired to become an airline pilot, said a 1989 report showed Columbia was more prone to the premature transition than other shuttles because its wings were rougher. Also, Columbia's left wing was rougher than its right, Gibson said, citing the 1989 data. That would mean more drag and heat on the left wing.
NASA officials said they were not familiar with that report.
Ruffin said the superheated re-entry may have been a factor, but it's likely something else was involved.
"Given that Columbia had experienced this premature onset of turbulence before -- and survived -- it seems likely there would have had to be some other kind of problem that this exacerbated."
PILOT ERROR: NASA has said the shuttle was controlled by on-board computers as it descended into the atmosphere, the normal procedure until immediately before landing. Is it possible one of the astronauts took control and mistakenly -- or deliberately -- rolled the shuttle out of control?
Highly unlikely. If someone on Columbia tried to override the computer, alarms would have gone off at Mission Control in Houston. None did.
OLD TECHNOLOGY: Columbia was the oldest space shuttle, having flown 28 times since 1981. It had an extensive refurbishment in the past two years and had rigorous maintenance after every flight, NASA says.
Asked if it was old, NASA administrator O'Keefe likened Columbia to an airplane that is still flying safely after 40 years.
Columbia "is half the age of the average bomber aircraft that flew in Afghanistan a year ago," he said.
But Brookstein said the 1970s-era shuttle design could have been a factor.
"It's not that the shuttles are old, it's that the technology is old," he said. "They are rebuilding it all the time, but it's the same tile system they came up with in the '70s."
-- Bill Adair can be reached at (202) 463-0575 or email@example.com.
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