They've been a problem since the first flight. NASA has failed to find a substitute - or even a way to deal with them in orbit.
By CHUCK MURPHY, Times Staff Writer
© St. Petersburg Times, published February 3, 2003
HOUSTON -- Even when the space shuttle program was in its infancy, NASA managers feared the loss of thermal protection tiles during liftoff would pose a potentially deadly problem during re-entry to the Earth's atmosphere.
They toyed with the idea of putting a "tile repair kit" on board. They tried to figure out how an astronaut could get out of the shuttle and underneath it to perform a weightless repair job.
After lots of study, the agency known for its Apollo 13-style can-do attitude decided that lost tiles beneath the shuttle would be too hard to fix. Officials abandoned the idea.
That left them with no options, even if they had determined before re-entry that Columbia had a problem.
The troublesome tiles are an early focus of NASA's inquiry into what caused the orbiter to disintegrate as it glided through the atmosphere more than 200,000 feet above Earth.
While other possibilities are still being investigated, NASA shuttle program manager Ron Dittemore said Sunday that investigators and engineers were seeing evidence of extreme heating of Columbia's left side in the moments before it came apart.
"We are gaining some confidence that it was a thermal problem," Dittemore said.
And in looking for the cause of overheating, the first stop for NASA is the tile system, the astronauts' only line of defense during the dangerous descent from space.
NASA's tile problems began with Columbia, when the shuttle lost 16 of them during its first flight in 1981. With every trip to space, engineers would greet the orbiter, and others in the fleet, by examining each of the tiles for damage.
Over time, they found plenty.
The tiles -- 24,000 of them, most just 6 inches square and called the orbiters' thermal protection system -- were badly damaged by rain. Small particles of space debris could cause cracking. Collisions with ice during liftoff could also damage them.
And, for some reason, Columbia seemed to have slightly more problems with tiles than the other orbiters.
In a 1999 conference on the future of the shuttle system, Donald Curry of NASA's Johnson Space Center and David W. Johnson of tile manufacturer Vought Aircraft Industries noted an annoying -- though not catastrophic -- phenomenon they called "pinhole formation."
They believed it was caused when salt and zinc oxide contaminated the tiles. In their presentation, they noted "All Vehicles Affected: OV-102 (Columbia) worse."
While the shuttle fleet continued to fly with troublesome tiles, but no serious problems, NASA kept looking for solutions.
The friction of the Earth's atmosphere against the shuttle creates temperatures of 3,000 degrees Fahrenheit at their worst. The brunt of that heat is focused on the leading edge of the wings, where a special tile, called reinforced carbon-carbon, deflects the heat. Those tiles are also used on sensitive parts of the shuttle's belly. Others are made of highly pure silica.
Losing a few tiles here and there is not a problem. But if enough of them are lost during liftoff, the shuttle's aluminum structure is exposed to more heat than it can handle when the orbiter heads for home.
Despite the questions raised about the orbiter's tiles over the years, NASA never found anything better.
"It was the best thing they could come up with," said Norm Carlson, who retired in 1995 as the Kennedy Space Center's acting director of shuttle operations.
Efforts to replace the tiles with a thermal blanket failed in testing. Experiments at NASA's Dryden Flight Research Center in California looked at new ways to apply the tiles so they wouldn't fall off so easily. Other tests looked for ways to make the surface of the tiles stronger so they wouldn't crack so easily if they hit something, even at high speed.
"We've been spending money for many years to try and develop this," Dittemore said. "We haven't been successful."
Shuttle engineers perform a delicate ballet between weight and safety. Owing to that, Columbia left the pad on Jan. 16 with some slightly improved tiles in some parts, but some older tiles on the underside and leading wing edge.
About 80 seconds into its final mission, a piece of insulation fell off the external fuel tank and hit Columbia on the left side, maybe in the area around the left wheel well.
NASA managers caucused but decided it was not a "significant" problem, Dittemore said. The crew was told that NASA had investigated foam hitting the tile and that all was well.
"We concluded that it did not represent a safety concern," Dittemore said.
They considered using a powerful telescope or satellite to take photos of Columbia's underside so engineers on Earth could see whether the insulation had knocked tiles loose or cracked their tops. They decided against it, largely because they concluded they couldn't fix any problems the photos might have revealed.
Regardless of whether the foam knocked tiles loose or a multitude of tiles simply fell off, the crew would have had no options anyway.
"There was nothing we could do," Dittemore said.
-- Information from Times wires was used in this report.