THE NATION
NASA Focuses In on Shuttle's Leading Edge
* The space agency now says launch debris hit a spot highly vulnerable to the super-heated gas Columbia encountered during reentry.

 
 
 
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By Ralph Vartabedian, Times Staff Writer

 

CAPE CANAVERAL, Fla -- A new photographic analysis of Columbia's launch shows that foam debris falling off the external tank slammed into the orbiter's vulnerable leading edge, rather than the underside of the wing as NASA earlier had believed, investigators said Wednesday.

Although such an impact already was under examination, the analysis is the strongest evidence to date that the shuttle burned up on reentry Feb. 1, killing the seven astronauts aboard, because of a breach in some part of its leading edge that allowed super-heated gas into the wing.

Scott Hubbard, a member of the Columbia Accident Investigation Board, acknowledged that the probe now is focusing on the possibility that foam debris damaged parts of the leading edge. Still, no conclusions have been reached, the board said, and a number of possible causes of the accident remain under consideration.

But evidence supporting the leading-edge theory appears to be growing every day.

The board also disclosed Wednesday that defects may exist in the foam used to insulate the external fuel tanks. When investigators recently cut into the foam of another tank at a Lockheed Martin plant in Michaud, Miss., they discovered three air pockets near a critical attachment point, called a bipod ramp.

Investigators have suspected foam fell off near or at the attachment point during the Columbia liftoff. The photographic analysis made public Wednesday also confirms that the foam indeed did come off at the bipod ramp. The voids in the foam may explain why it was vulnerable to becoming detached.

A number of tests in the coming weeks should confirm whether the foam-leading edge explanation is credible. The board has contracted with the Southwest Research Institute, a nonprofit organization, to conduct tests during which chunks of foam will be shot at leading-edge components.

The tests will use a high-powered nitrogen gun to bombard leading-edge parts to simulate the event that occurred on the Columbia liftoff. Two sizes of foam -- a 1-pound chuck measuring 6 inches by 14 inches by 24 inches, and a 2-pound chunk measuring 3 inches by 11 inches by 24 inches -- will be used, the larger one delivering the energy equal to a 70-pound sack of concrete hitting a car on a freeway.

The tests will include a leading-edge panel that has flown on another orbiter, so that investigators can determine whether age and use have made the panels more vulnerable to foam collisions.

The foam strike on Columbia's launch could have damaged one of three parts of the leading edge: the panels made of reinforced carbon carbon; a so-called t-seal that fills the gap between the leading edge panels; or a part known as a carrier panel that covers the joint between the leading edge panels and the wing's surface.

Each wing of the shuttle has 22 leading-edge panels that can withstand reentry temperatures of 3,000 degrees. But investigators have discovered that the panels degrade with age, forming surface fractures, pinholes and internal voids that may have weakened the structures. A sample panel -- a large U-shaped structure that is just a quarter-inch thick -- was shown at a news conference Wednesday. Adm. Stephen Turcotte, a board member, said all but two of Columbia's 44 leading-edge panels were the ones originally installed when the orbiter was built in the late 1970s. They had been extensively damaged in flight and repaired, he said; it remains to be determined whether those repairs left the panels weakened.

In addition to the foam-shooting tests, investigators plan to cut into the foam of another external tank that more closely resembles the one used on Columbia.

The latest photographic analysis of Columbia's launch was conducted by more closely examining and combining pictures taken by two long-range cameras at Kennedy Space Center. Those photographs previously showed foam breaking away from the external tank about 80 seconds into the flight, but it was difficult to determine where the foam came from or where it struck the orbiter.

During Columbia's final mission, NASA and Boeing Co. engineers concluded that it most probably hit the underside of the wing near the landing-gear door.

But in a more careful, frame-by-frame, analysis after the accident, investigators determined that the foam fell off the bipod area. As it tumbled at about 500 mph relative to the wing, it struck with a footprint about two feet in diameter, Hubbard said. It struck the wing's leading-edge panels number five, six and seven -- a key area of the wing where it angles out less sharply.

Aeronautical engineers at NASA's Langley Flight Research Center in Virginia have been conducting wind tunnel tests that examine what could happen if a panel were destroyed in that region of the wing. The tests indicate such an event could explain some of the aerodynamic problems the orbiter was experiencing in its final minutes of flight.

Hubbard said he could not fault NASA for its original photographic analysis, saying the board had made a strong effort to make its more-precise determination of where the foam struck.

Debris evidence is providing important clues about what may have happened to the leading edge. NASA officials have laid out the Columbia's wing and fuselage parts on a precise grid. Much of the left wing is gone, presumed to have burned up.

Scientists are attempting to conduct both chemical and metallurgical tests on the wreckage, said Gregory Kovac, an associate professor of electronics.

So far, they have found that the left side leading-edge panels are more badly damaged than those on the right side. The panels on the left side also contained heavy deposits of melted metal. Panel number six, where the foam struck, is missing, Steve Altemus, a NASA engineer overseeing the reconstruction, told the board Wednesday.
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Space Shuttle Columbia

New clues in Columbia probe

Shuttle debris pieces indicate leading edge had most heat

Wednesday, March 26, 2003 Posted: 3:50 PM EST (2050 GMT)

Molten metal is much more apparent on panels from Columbia's left wing than the right wing, officials said.
Molten metal is much more apparent on panels from Columbia's left wing than the right wing, officials said.

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CAPE CANAVERAL, Florida (AP) -- The way metal melted in debris from the space shuttle Columbia indicates the leading edge of the shuttle's left wing experienced the hottest temperatures, perhaps offering clues as to where fiery gases penetrated the spacecraft, experts said Wednesday.

"This part of the leading edge saw the hottest heat," Mark Tanner, a mechanical engineer told members of the Columbia Accident Investigation Board during a second day of hearings. "I think this tells us a small story."

Molten metal is much more apparent on panels from the left wing than the right wing, said Gregory Kovacs, a professor of electronics at Stanford University, who is studying the debris for investigators.

"You see more deposits. You see deposits that are different in character," Kovacs said of the left wing. "If you look at the right wing, the panels are pretty clean."

Pieces from the left side also show more signs of erosion and degradation, Tanner said.

About 54,000 pounds, roughly a quarter of the orbiter's weight, has so far been recovered. Of the 45,000 pieces, only about 1,400 pieces, have been laid out in place on a grid in a hangar at the Kennedy Space Center.

Workers hope to make a reconstruction of the shuttle with the parts to help investigators understand what happened to Columbia

Parts from the shuttle's left wing get top priority, said Steven Altenus, shuttle test director at Kennedy Space Center, who is in charge of the reconstruction.

Investigators believe a section of the left wing was breached by fiery gases during Columbia's re-entry. Little of the left wing's aluminum structure has been recovered.

One theory investigators are exploring is that the wing may have been damaged by foam insulation falling from the external fuel tank during liftoff on January 16.

Teams searching Texas and Louisiana for debris from the space shuttle Columbia have only a few more weeks before spring growth of brush and trees makes it difficult to find more pieces, NASA officials told board members Wednesday.

About 5,700 people are still searching the primary debris field, an area that stretches about five miles by 250 miles across the two states, for parts from the shuttle. The Columbia broke up on reentry February 1, killing all seven crew members.

Officials studying videotape of the shuttle's destruction believe other debris may have fallen in the snowy mountains west of Texas, though no shuttle debris has yet been found there.

"Our intention is to press on and not worry much about conditions," Mike Rudolphi, deputy director of Stennis Space Center in Mississippi and leader of NASA's efforts to recover debris, told board members.

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Panel May Urge Extensive Tests for Shuttles

By MATTHEW L. WALD

CAPE CANAVERAL, Fla., March 26 The independent board investigating the Columbia disaster is concerned that NASA may not be detecting flaws on the panels that protect the shuttle wings on re-entry and will recommend extensive new tests before further flights, an investigator close to the panel said today.

The Columbia may have lifted off with pre-existing flaws that simple visual inspections and a "tap test" could not detect, the investigator said in an interview. More sophisticated tests on panels from surviving shuttles have found flaws that the investigator said made them unsafe for flight.

One question before the panel is whether debris that hit the Columbia shortly after liftoff struck an already flawed panel.

The U-shaped panels that protect the leading edges of the wings are made of a multilayered composite material, reinforced carbon-carbon. Flaws in manufacturing, strikes by micrometeorites or mishandling can create gaps between the layers, cracks or other problems. Some experts said they believed that the Columbia, struck by debris 82 seconds after liftoff, might have entered orbit with fatal damage to such a panel, but that the problem might have been more than just debris.

"There's an argument that strong R.C.C. panel could have withstood a foam impact," an investigator said.

At a briefing here, the chairman of the commission, Adm. Harold W. Gehman Jr., who is retired, said today that his group was close to issuing two recommendations. He confirmed only that one concerned taking pictures of the shuttle in orbit to search for damage.

The investigators close to the panel said that recommendation would call for using "classified assets," a code term for spy satellites. Because the images would display the abilities of the satellites, using the satellites may require some NASA officials to receive security clearances.

Today, board members showed a carbon panel from the Enterprise, a test vehicle at the Smithsonian that was hauled to high altitude by a Boeing 747 jumbo jet and let loose to coast back to Earth in 1977. Investigators said they would take more panels from the Enterprise, the sole source for panels as old as the Columbia's, and begin test firing foam at it.

Experts pointed out that since the shuttle first flew more than 20 years ago, other industries have vastly improved the technology of "nondestructive examination." Those techniques include X-ray and ultrasonic probes, heating composite panels and watching how the heat is absorbed. That can be a clue to how well the layers are bonded together.

A spokesman for NASA, Bruce Buckingham, said technicians went beyond visual inspections and tap tests only in major overhauls.

"That's the way we've been doing it for 20 years," Mr. Buckingham said.

The investigators said they continued to be far from reaching a conclusion about the cause of the accident on Feb. 1 but were making progress. In a news briefing here, one panel member, G. Scott Hubbard, said this afternoon that a new analysis showed that the area of the orbiter most likely hit by debris included three carbon panels where the wing begins to curve out from the fuselage, as well as adjoining tile-covered panels. The highly likely area may have included tile on the underside of the shuttle.

Those findings are important, because when the space agency realized soon after the launching that the debris had hit the shuttle, it ordered an analysis. But the subcontractor that did the work, Boeing, used a computer model that estimated damage to the tiles, not the leading-edge panel.

Also today, NASA wreckage experts said that they had completed searching two-thirds of the main debris area, four miles wide and 250 miles long, and that they hoped to finish in four to six weeks. By then, spring foliage will make searching much harder, they added.

The Kennedy Space Center has received 54,000 pounds of debris, 24 percent of the orbiter's dry weight of 223,000 pounds, and debris continues to arrive, at the rate of two truckloads a week.

How much more is recoverable is not clear. The shuttle test director at the space center, Steven Altemus, said 35 percent to 50 percent of the shuttle returned to Earth's surface, with the remainder burning up on the way down.

"We see molten aluminum on almost everything we have back," Mr. Altemus said, adding that the surviving parts appear to have passed through "an aluminum molten rain cloud."

Many are too small to identify, he added, although NASA is using a computer program to try to match together jagged edges like a three-dimensional jigsaw puzzle. But some edges were burned away on re-entry.





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