New theories about the crash include space debris damaging tiles and possible mistakes during the shuttle's refurbishment.
By CHUCK MURPHY and WES ALLISON
© St. Petersburg Times, published February 6, 2003
HOUSTON -- The chief of NASA's shuttle program on Wednesday deepened the mystery of the Columbia disaster as he backed away from a prevailing theory that a flying slab of foam insulation damaged critical protective tiles.
"Right now 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," said shuttle program manager Ron Dittemore. "There's got to be another reason. We're looking somewhere else for that missing link. Was there another event that escaped detection?"
Investigators have few leads into what caused the shuttle to swing strongly to the left before coming apart in the sky, Dittemore said.
Shuttle engineers studied the debris after Columbia launched and convinced themselves that it did not pose a safety risk to the astronauts. But soon after the accident, Dittemore said NASA must assume the foam played a role.
Many experts agreed and also speculated that ice might also have contributed to the accident. The foam insulation is designed to prevent ice from forming on the external tank, which is filled with liquid hydrogen fuel kept at 423 degrees below zero. But if the foam separated, ice could immediately form in the cracks and behind the foam. Ice would make the foam heavier and deadlier.
The assumption was that the foam hit the shuttle as it flew faster than the speed of sound, weakening the fragile heat-resistant tiles beneath Columbia's left wing. The tiles protect the shuttle from burning up as it re-enters Earth's atmosphere.
NASA scientists have all but concluded that the 20-inch slab of foam seen peeling away from the shuttle's external fuel tank had neither the mass nor velocity to cause fatal damage to the tiles.
The foam has come loose during numerous shuttle launches without significant damage, Dittemore said. It is extremely lightweight and is impervious to water, so it could not have become embedded with ice, he said.
Dittemore released photos of the underside of the shuttle before and after the collision that showed no damage, though the resolution was poor.
"It's difficult for us to believe, as engineers, as managers ... that this particular piece of foam (is to blame), so we're looking somewhere else," Dittemore said. "We're focusing our attention on what we didn't see.
Still, NASA will continue studying the foam even as it looks for other answers.
Columbia broke up as it re-entered the Earth's atmosphere Saturday, killing all seven astronauts aboard. Two days after its Jan. 16 launch, NASA engineers reviewing photos of the launch saw the foam smashing into the left wing.
NASA hoped to glean data from the last 32 seconds of the flight, when Mission Control lost contact, but Dittemore said that's proving more difficult than expected. "We have not been satisfied with the reliability of that data. It's going to take more time."
NASA plans to conduct more tests to determine "what size of object would it have to be, by weight, to do sufficient damage" to the tiles, he said. "It's got to be something else we don't know about yet."
News that flying foam may not have been the root cause was not universally greeted as good news in the space community.
"In a way, that's almost bad," said former astronaut George "Pinky" Nelson, who flew on three shuttle missions, including one on Columbia. "You could speculate on a lot of different scenarios."
Space debris hitting the shuttle during orbit and damaging the sensitive thermal tiles enough to allow heat to cause a structural failure on re-entry.
Uneven tiles along the left wing altering the airflow and causing a loss of flight control.
A mistake made during Columbia's 1999-2000 refurbishment that left the tiles vulnerable to damage or displacement.
Upper atmospheric turbulence, perhaps caused by Earth heating, resulting in drag on the left side.
A meteorite, also on its way to Earth, hitting the shuttle during re-entry.
The data NASA received before Columbia disintegrated told engineers that the left wing was moving more slowly than the right. Temperatures also were slowly rising on the left.
Any of the first three alternate possibilities, along with the damage caused by the external tank foam, could have caused the heat, the drag or both.
Space is loaded with junk. Large pieces are tracked by defense radar, and mid-sized ones can be avoided, but thousands of tiny pieces of dust and debris are buzzing around the globe at 17,000 miles per hour. Enough hits in the right places could damage the tiles, or make them uneven.
"Earth has a ring around it just like Saturn, you just can't see it because it isn't as thick," said John Lindner, an associate professor of physics at the College of Wooster in Wooster, Ohio. "NASA regularly has to replace window panes because of hits. There is a possibility that the space shuttle was hit by orbital debris."
A hit, even one that was imperceptible to the astronauts, could have disrupted the shuttle's aerodynamics as it moved into the atmosphere, causing a loss of control.
Dittemore said he couldn't speculate, but debris can be a problem. "We have occasional impacts on our wings," he said. "It's certainly possible. How likely? I don't know."
NASA investigators have impounded all records from the shuttle's 1999-2000 refurbishment at Boeing's plant in Palmdale, Calif. Electronics were upgraded and the tiles were checked, repaired and upgraded or replaced where needed.
That's a delicate operation. Each tile has a unique code and place on the shuttle and special instructions for attachment. While NASA presumably inspects the process at every stage, it is possible that a mistake wouldn't show up until sometime in the future.
There's also the possibility of upper air disturbance creating turbulence. That could produce a drag that the shuttle's autopilot can't compensate for.
"At 200,000 feet, that's high enough where they shouldn't experience turbulence," said Scott Post, an assistant professor of mechanical engineering at Michigan Tech. He studied drag for NASA last summer at Edwards Air Force Base during tests of a possible shuttle replacement.
"But there could be a convection-driven flow like the jetstream in the upper atmosphere that they encountered. It's not likely. But it's possible. It wouldn't take much to get it turning."
Wednesday, Dittemore reiterated that the computer autopilot couldn't keep up with the shuttle's drift to the left as it descended. The nose was beginning to turn, and even the firing of the jets on the right side couldn't stop it.
"We were beginning to lose the battle," when Columbia's signal was lost, Dittemore said.
Some experts weren't ready to rule out the foam as a culprit.
Dr. Paul Czysz, professor emeritus of aerospace engineering at St. Louis University who has been involved in the space program for years, said the foam would have struck the wing like a rifle shot.
The shuttle was traveling faster than the speed of sound when the foam came loose, at about 1,300 feet per second. The foam would have slowed immediately, but the shuttle would have hit it at 700 to 800 feet per second -- faster than a pistol shot. NASA estimates it weighed no more than 2.67 pounds.
"Even if the mass was relatively light, the impact could have been extensive," Czysz said. "When I saw this object hit the wing, what came out of the back of the wing was this explosion of vapor or dust. Whatever hit the wing shattered, and it hit it with so much force, I think it had to do some damage."