Shuttle Disaster Linked to Unseen Flaw

The space shuttle Columbia’s wings and fuel tank were riddled with a virtual minefield of holes and cracks, a flaw that was largely overlooked by NASA but which almost certainly contributed to the craft’s demise, investigators said Tuesday.

According to interviews and internal documents, NASA has known since the early 1990s that its fleet of aging shuttles was pocked with pinholes. What it failed to grasp -- and could not see -- was the danger beneath the holes.

A review of the pieces that make up the orbiters’ wings has revealed that many of those pinholes were akin to the hole at the top of a volcano. They didn’t look like much on the surface, but they were openings to far more extensive breaches, said Navy Rear Adm. Stephen Turcotte, a member of the independent Columbia Accident Investigation Board.

Those underlying breaches likely have eroded the structural integrity of the space shuttles’ wings -- a problem that was particularly acute in the case of Columbia, which was on its 28th mission when it ripped apart Feb. 1, killing its seven-member crew.

Investigators especially want to know whether the holes, metal corrosion apparently caused by oxygen, damaged Columbia’s so-called T-seals -- the boomerang-shaped carbon braces that held together and sealed the leading edge of the shuttle’s wings.

U.S. Department of Defense radar images show that a piece of Columbia broke off and drifted away during the second day of the ill-fated mission. Investigators said Tuesday that they now suspect the piece was either a T-seal or a fragment of one. If so, that would have created enough of a hole for superheated gas, known as “plasma,” to penetrate the craft and ultimately bring it down, investigators said.

Currently, NASA’s preflight inspection routine consists of little more than visual scans of wing surfaces with the aid of a magnifying glass -- examinations that are not sophisticated enough to reveal internal damage, investigators said.

NASA officials acknowledge that they knew their inspection techniques were inadequate. Two years ago, one engineering study suggested that internal damage to wings might “extend significantly” beyond what can be seen from the outside.

NASA has been studying methods of scanning for internal damage, but investigators say that effort may have come too late.

Harold Gehman Jr., a retired Navy admiral and chairman of the investigative board, said he will issue recommendations within a week that call on NASA to vastly improve its inspection techniques.

Although Gehman said he will not tell NASA exactly how to do that, other board members said the possibilities include ultrasound, CT scans and other hand-held imaging equipment.

“We will specify that they must learn to characterize the hidden flaws,” Gehman said.

The chairman’s preliminary round of recommendations -- aimed at resuscitating the struggling space program and getting a shuttle back in orbit -- is likely to include items such as encasing part of a shuttle’s external fuel tank in metal, altering the process of insulating those tanks and giving astronauts the ability to inspect heat-resistant tiles once in orbit.

The board also will recommend that NASA install more cameras on space shuttles and transmit more images of the craft’s exterior to Mission Control during launch and orbit, Turcotte said.

While drawing up its recommendations, the investigative board also is beginning to formally eliminate a number of theories about what might have caused the loss of the shuttle. For example, Turcotte said, investigators are now certain that the rocket motor did not play a role, and they are virtually certain that sabotage was not a factor.

Problems similar to the pinholes and breaches discovered in the shuttles’ wings also have been found in the foam used to insulate the 154-foot-tall external fuel tanks, Turcotte said. Since Lockheed Martin Space Systems Co. redesigned NASA’s fuel tanks in 1998, making them lighter and thus allowing the space shuttles to carry more weight, fissures dubbed “stringer valley cracks” have appeared, Turcotte said.

That likely contributed, he said, to a liftoff accident that may have crippled Columbia.

On Jan. 16, 81 seconds after the shuttle lifted off from Cape Canaveral, Fla., several pieces of foam insulation fell from Columbia’s external fuel tank and struck the left wing. The damage, investigators believe, was concentrated on the leading edge of the wing -- the most vulnerable part of the shuttle, since it experiences temperatures of more than 3,000 degrees when astronauts are reentering the Earth’s atmosphere.

The pinholes and underlying breaches probably weakened Columbia’s left wing, making it more susceptible to damage when it was struck by the insulation, investigators said. Indeed, Gehman suggested that the breaches might have doomed the space shuttle from the start, even if it hadn’t been struck by the foam.

“There is the possibility that foam had nothing to do with it, absolutely,” Gehman said. “The board is keeping an open mind on this.”

The board members’ comments came Tuesday at a press briefing held at the University of Houston-Clear Lake’s Lunar and Planetary Institute.

Gehman also said that the exhaustive effort to find wreckage of Columbia will end April 30, although smaller, targeted searches for specific pieces seen on radar images will continue.

The search-and-recovery operation has involved nearly a dozen federal, state and local agencies and has covered 2,400 square miles in central and East Texas -- “a massive effort of between 5,000 and 6,000 people a day,” Gehman said.

So far, he said, about 70,000 pieces of wreckage have been found. The wreckage weighs a combined 78,000 pounds -- about 36% of the orbiter’s total weight, far more than investigators predicted they would find just weeks ago.

Government agencies have estimated that the investigation into the loss of Columbia will ultimately cost $500 million.

“We’ve come a long way,” Turcotte said. “I’ve never seen so many rocket scientists running around.”