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Experts say foam may have cracked
Published:
Monday, February 10, 2003
Media Credit: BRAD LOPER/DALLAS MORNING NEWS
National Guard soldiers Staff Sgt. Mike Sisk, left, Staff Sgt. Sonny Wiseman and Maj. Beverley Simpson, right, load a piece of debris from the space shuttle Columbia near Nacogdoches, Texas, last Wednesday.
Jay Weaver, Curtis Morgan and Matthew I. Pinzur
Knight Ridder Newspapers
MIAMI -- NASA says the insulation surrounding the space shuttle Columbia's external fuel tank was waterproof, but experts say a crack could have allowed heavy rains or humid air to settle beneath the foam and then freeze from exposure to the super-cooled tank.
In turn, the ice-encrusted foam could have cracked and hurtled into the shuttle's protective tiles during the launch, leaving Columbia exposed to deadly heat upon its re-entry into the atmosphere.
Some experts say this could explain how the 2.67-pound, 20-inch foam fragment that smashed into the shuttle's left wing during takeoff might have led to the disastrous ending of its mission last week.
Milton Torres, a research scientist at Florida International University who has developed a version of similar foam called PantherSkin for commercial aviation use, said he believes the shuttle's foam is completely waterproof. But he said cracks can form in the insulation in several ways.
Among them: faulty spray applications, vibration during launch, or thermal stress caused by the constriction of the tank when it's filled with super-cooled hydrogen. He said NASA crews frequently do test runs, filling and emptying the tank, which causes the metal to constrict.
"I can tell you ice will form in an instant," Torres said. "You can imagine a glass of iced tea and how much condensation will form. That's 32 degrees. This thing is minus 423 degrees."
Columbia experienced record-level rains in the weeks before its launch on Jan. 16, increasing moisture at the launch pad at the Kennedy Space Center.
But Lockheed Martin, which has manufactured the external tanks at its plant in Michoud, La., since the first shuttle flight, maintains the foam does not absorb moisture.
Marion LaNasa, Lockheed's communications director, said the foam, made of a closed-cell material that is buoyant, would have the potential to crack only when work crews fuel up the tank before the shuttle's launch.
"But then how do you get moisture into those cracks?" LaNasa asked. "There is no way that moisture would get under the insulation."
NASA has long been worried about the potential buildup of ice on the shuttle's external fuel tank because of Central Florida's humid, wet weather. The massive external fuel tank, which the shuttle rides into space, is covered with a thin coating of super-strong, lightweight foam.
Without the insulation, humidity or rain would cause condensation to form on the outside of the foam. In turn, the condensation would form sheets of ice that would fall off during lift-off, damaging tiles that protect the belly of the shuttle from intense heat during re-entry.
Columbia was on the launch pad at the Kennedy Space Center for five weeks before liftoff on Jan. 16 -- a period with a total of 12.7 inches of rain.
That was more than double the facility's combined average rainfall for January and February, according to John Madura, manager of the space center's weather office. He said almost of all of the rainfall during Columbia's preparation came in December.
Madura declined to say what effect the heavy rains might have had on the shuttle's insulation foam, and was unable to provide examples of rain measurements before previous shuttle launches. But he said NASA has routinely launched shuttles during the wet summer season, when rainfall normally exceeds 6 inches a month.
On Wednesday, Ron Dittemore, NASA's space shuttle program manager, said he dismissed the possibility of moisture and ice buildup causing problems with the foam on the tank.
"It's designed to be very resistant to moisture, so it's essentially waterproof," Dittemore said in a news conference.
He said NASA has "strict criteria" about the amount of ice it allows on the shuttle's external fuel tank. He said a team inspects the launch pad after the liquid hydrogen is loaded into the external tank, looking for sheets and thickness of ice.
"If we believe the conditions of icing are unacceptable, then we delay or we scrub" the launch, Dittemore said.
Some experts who have analyzed the shuttle's foam suggest it can be vulnerable to cracking and a potential safety risk. Elisabeth Pate-Cornell, a Stanford University researcher, co-authored a risk analysis for NASA in 1990 on thermal tile failures.
The report found thermal tile failure was one of the leading risks for a shuttle crash -- a 10 percent chance.
The highest risks either came from glue failure or from damage from debris, including the frequent problem of foam detaching from the external tank.
Knight Ridder Newspapers correspondents Daniel DeVise, Phil Long and Seth Borenstein contributed to this report.
