Ice under insulation could have hit shuttle
© St. Petersburg Times
HOUSTON -- Investigators trying to piece together what happened to the space shuttle Columbia searched for debris on both sides of the country Tuesday while attention focused on whether ice played a role in the disaster.
In Florida, they studied the sea currents in the Atlantic Ocean near Kennedy Space Center to figure out where tiles might have fallen after foam insulation peeled off the shuttle's external tank and hit the left wing during the Jan. 16 liftoff.
In California and Arizona, investigators hunted for pieces of the shuttle that might have fallen off during Columbia's ill-fated attempt to return home Saturday.
Any pieces that came off early in the breakup could be of particular importance to understanding what happened, said Michael Kostelnik, shuttle program administrator.
Although there have been reports of pieces being found out West, not all have been reliable. One reported piece of debris found near Yuma, Ariz., turned out to be burned toast.
More than 12,000 recovered remnants, many as small as a nickel, have created a growing mosaic of evidence that could take years to pick through.
Larger and denser pieces, including one of the engines, fell in Louisiana and are being recovered. Hundreds of searchers, some on horseback and four-wheelers, made several discoveries Tuesday, including more human remains, a seat from the shuttle and cylindrical tanks spewing an unknown gas.
A theory that emerged Tuesday suggested that a chunk of ice might have formed beneath the foam insulation and hit the delicate tiles, causing more damage than NASA experts first believed.
The 21/2-pound, 20-inch foam fragment, spinning back as the shuttle soared into space at four times the speed of sound, may have damaged or knocked away some of the fragile tiles that keep the ship from burning up during re-entry, NASA officials say.
Although foam has peeled off the tank repeatedly since the first shuttle launch in 1981, this was the probably largest piece ever to hit the shuttle, Kostelnik said.
Although NASA officials have said previously they do not believe ice played a role in Saturday's accident, they acknowledged Tuesday that they are looking into it.
Kostelnik said ice could be "a serious problem" but that NASA's inspections before launch had ensured ice had never caused a safety problem before.
The massive external fuel tank, which the shuttle rides into space, is covered with a thin coating of super-strong, super-lightweight foam.
Without the insulation, moisture in the humid Florida air would cause condensation to form on the outside. The condensation then would freeze immediately and come off in sheets during lift-off, damaging the tiles that protect the shuttle from the intense heat as it re-enters the Earth's atmosphere.
But Dr. Milton Torres, a researcher at Florida International University in Miami who developed a version of the foam for airplane use, said if the insulation cracked, ice immediately would have formed inside, widening the crack.
The shuttle's speed and the rattle of its thrusters then could have shaken it loose, Torres said.
Normally, "you can't peel it off once you get it on," Torres said. "Most likely, a piece cracked (and) with a little ice formation, and with the vibrations on launch, it broke it off."
Sunlight can weaken the foam's chemical bonds, or it may have been improperly applied, he said.
NASA officials confirmed Tuesday that the Columbia sat on its launching pad for 39 days -- more than two weeks longer than usual.
The external tank on which the foam is sprayed is the largest single component of the space shuttle system at 154 feet long and almost 28 feet in diameter. It boosts the shuttle into space, then is jettisoned and falls into the Atlantic Ocean.
If the foam cracked it probably did so about three to four hours before launch, when NASA finishes loading the tank with its liquid hydrogen fuel, which is kept at 423 degrees below zero, said Seymour Himmel, a retired NASA official who served for two decades on an aerospace safety panel.
Himmel said NASA has had problems "from Day One" with the foam coming unstuck. Whenever the super-cold fuel is loaded, every surface of the aluminum tank contracts, putting stress on the bond that holds the insulation in place.
"Making something stick to a tank the temperature of liquid hydrogen ain't easy," said Himmel, who was part of a two-man safety team that studied the foam problem for NASA in the early 1990s.
Bob Giffen, a retired engineer who worked for private contractors in the Gemini, Apollo and shuttle programs at Kennedy Space Center, said when the foam insulation is sprayed on the tank it expands and then is smoothed. But if a defect creates a breach, air can get to the tank surface.
"Any air that sneaks in, if it's got any moisture in it, it immediately freezes it," Giffen said. That can then expand under the insulation and create a wedge. Himmel, the retired NASA safety expert, said he had seen no previous reports of ice developing under the foam, but said it's possible. A sheet of ice might have formed on the outside of the foam too, masking the crack, he said.
Before launch, crews go over the shuttle and the external tank to check for chunks of ice. However, Himmel said, a little ice doesn't worry NASA. If it appears to be a small amount, they assume it will cause little tile damage and let it go.
Himmel said concerns about the foam peeling off go back to the first shuttle launch in 1981, Columbia's maiden flight.
A July 1985 report from one of the Challenger's last missions before its January 1986 explosion shows that NASA knew the foam could pose a hazard to the tiles. The report notes that after liftoff, inspectors found a piece of foam insulation on the launch pad. They found even more pieces along the beach near the pad.
After Challenger landed, the report states, an inspection of the tiles found "a total of 553 debris hits of which 226 were greater than or equal to 1 inch in diameter. Most of the impact craters showed the effects of entry heating."
In the early 1990s, Himmel said, his two-man safety team recommended changes in procedures and testing to ensure the foam stayed put, and they worked -- until 1996, when the U.S. Environmental Protection Agency insisted NASA stop using Freon in the spray formula because it depletes the Earth's protective ozone. The new Freon-free formula failed to stick as well.
An internal report NASA filed on the second day of Columbia's final flight said the foam also "appeared" to have struck the leading edge of the left wing, raising the possibility of damage in an area that plays a crucial role in reducing heat transfer over the wing on re-entry.
The leading edge is made of reinforced carbon and is far harder than the shuttle tiles. But because of its critical function, "a little damage there could cause a lot of harm," said Brian Cantwell, an aeronautics professor at Stanford University.
The degree of harm would depend on the precise site of the hit. While the edge would be difficult to crack, "a large piece of foam" at high speeds could do damage.
"A good nick could be enough" to change the air flow over the wing and cause a greater buildup of heat than the system was meant to handle, said Graham Candler, professor of aerospace engineering at the University of Minnesota, who has worked on re-entry projects for NASA.
NASA could have checked for places where the foam had come unstuck, but chose not to.
Since 1992, John Newman of Laser Technologies Inc. in Pennsylvania has performed repeated experiments, at NASA's behest, in which he used a laser on foam-covered aluminum test panels to find places where foam did not stick.
Although NASA hired Newman to detect flaws on other parts of the shuttle, his company was never asked to inspect the foam on the external tanks, which Newman said was "very frustrating."
-- Times staff writers Anita Kumar and Thomas C. Tobin and researcher Kitty Bennett contributed to this story. Information from the Washington Post, the New York Times and the Philadelphia Inquirer also was used.
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