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Another shuttle suffered wing breach

NASA documents detail an incident three years ago in which superheated gases breached Atlantis’ left wing during re-entry.
/ Source: The Associated Press

Superheated gases breached the left wing of the shuttle Atlantis during its fiery return to earth in hauntingly similar fashion to the demise of Columbia nearly three years later, according to internal NASA documents.

Unlike Columbia, Atlantis suffered no irreparable damage during the May 2000 episode and, after repairs, returned to flight just four months later. NASA ordered fleetwide changes in how employees install protective wing panels and sealant materials.

The small leak through a seam in Atlantis’ wing during its return from the International Space Station was disclosed in documents sought by The Associated Press under the Freedom of Information Act. The mission commander was James Halsell, a shuttle veteran who is coordinating NASA’s effort to return the shuttles to flight.

Astronaut in the dark 
One of the seven Atlantis astronauts, Mary Ellen Weber, said NASA never told her about the breach, which was not discovered until the shuttle had landed.

“There are thousands and thousands of things that can go wrong, and the crew is very much aware this can happen,” Weber said. “Certainly, when you learn about this, if it had progressed, it could have been much more dire.”

Weber operated the robotic arm aboard Atlantis and flew aboard Discovery in July 1995. She said NASA may have reported the wing damage to other crew members. Attempts by AP to reach the other astronauts by telephone through family members and NASA offices in Houston and Washington were unsuccessful; one Atlantis crewman was a Russian cosmonaut and another has left NASA to return to the Air Force.

NASA spokesman James Hartsfield said crews and engineers generally participate in two months of meetings to discuss their experiences and spacecraft conditions. He could not say whether the shuttle’s commander or pilot was told about the wing breach, which NASA blamed on incorrectly installed sealant material.

Experts express surpise 
Some experts expressed surprise that superheated gases ever had leaked inside a shuttle’s wing. Although protective wing panels have been found damaged, even cracked, the Columbia disaster was widely believed outside NASA to have been the first such breach.

“Very little information about the flaws of the tile system ever make it into the open literature, so those of us who work on this ... seldom hear much about serious problems such as this one,” said Steven P. Schneider, an associate professor at Purdue University’s Aerospace Sciences Lab. “I’ve never heard this sort of leak occurred.”

NASA said it later determined Atlantis’ exterior wing panels were not damaged by the overheating despite being discolored from the high temperatures. Aluminum structures inside the wing “looked outstanding,” NASA said. Other parts immediately behind the wing panels were covered with a glassy material, apparently from melted insulating tile and other sealant material.

Hartsfield said all damaged parts were replaced.

The space agency formally reported the damage to its Program Requirements Control Board, an internal safety oversight body, which ordered fleetwide improvements in the installation of sealant materials before Atlantis was allowed to launch for its mission in September 2000. Atlantis is expected to be the next shuttle into space when NASA is cleared to resume flights.

A mostly routine return
Weber, now an associate vice president at the University of Texas Southwestern Medical Center in Dallas, described Atlantis’ return to Earth as mostly routine and remembered seeing an orange glow from hot gases dancing outside the shuttle windows.

Although damage inside Atlantis’ left wing was detected after flight, NASA worried about the shuttle’s return even before the discovery.

During liftoff, a 6-inch (15-centimeter) chunk of ice had smashed against the back edge of the right wing; so experts deemed it prudent to adjust Atlantis’ flight to rapidly cool its wings prior to the fiery trip through the atmosphere, NASA documents showed.

It was impossible to know whether this cooling technique, called a thermal conditioning maneuver, also helped minimize heat damage inside Atlantis’ defective left wing. NASA later determined damage on the right wing was relatively minor.

Columbia and Atlantis
The board investigating Columbia’s Feb. 1 breakup determined that superheated gases penetrated protective wing panels that had been loosened by insulating foam that broke off its external fuel tank on liftoff and smashed against the shuttle. Investigators believe searing re-entry temperatures melted key structures inside until Columbia tumbled out of control and broke apart at close to 13,000 miles per hour (20,800 kilometers per hour), killing its seven astronauts.

NASA did not consider ordering the thermal conditioning maneuver on Columbia because it believed such a move would have interfered with efforts to warm Columbia’s landing gear tires for a safe landing.

NASA blamed the Atlantis damage on improper installation of a seal between two protective panels on the shuttle’s left wing, “called a butterfly gap filler,” at the Boeing Co. plant in Palmdale, Calif., during an overhaul of Atlantis in late 1997. The mistake went unnoticed during subsequent inspections because the part could not be seen without removing protective panels, NASA said.

Engineers found the damage on Atlantis while investigating the mystery of a partially melted insulating tile. Removing two protective wing panels nearby and peering inside the wing structure, they determined the dislodged seal had created “a substantial flow path,” according to NASA’s internal reports. The gap measured just over one-quarter inch (6 millimeters), about the width of a paperclip or a No. 2 pencil.

The protective panels, insulators and other hardware inside the left wing showed “various signs of overheating,” NASA reported. Photographs showed charred and scorched components, including parts made from titanium and inconel, two of the most heat-resistant materials on the shuttle. Titanium melts at about 3,000 degrees Fahrenheit; inconel melts at about 2,550 degrees.

Investigators examining Columbia’s breakup remain uncertain over the size of the gap that permitted hot gases to penetrate that shuttle’s wing. But they believe it was as small as a one-inch (2.5-centimeter) slit running vertically up the wing for nearly 30 inches (90 centimeters). In a test Monday, a chunk of foam blew open a dramatic 16-inch (40-centimeter) hole in parts of a mock-up of a shuttle wing.

Temperatures during a shuttle’s return can climb to almost 3,000 degrees F — nearly one-third as hot as the surface of the sun — along parts of the spacecraft, especially the leading edges of its wings. Damage there is considerably more likely to doom a shuttle than anywhere else. NASA requires immediate repairs when damage to the wing’s protective panels exceeds four-hundredths of an inch (1 millimeter), about the thickness of a dime.