Board Nearing Judgment on Shuttle Disaster

A dissection of a fuel tank identical to the one that ferried the Columbia on its ill-fated mission has uncovered 74 flaws, mostly air pockets in its foam insulation, investigators said Tuesday as they prepared to meet with NASA to develop a formal theory about what destroyed the space shuttle.

Members of the independent panel investigating the Columbia disaster now believe a 1997 decision to change the method of applying foam insulation -- a move made primarily to satisfy concerns about the environmental hazards of Freon -- caused the voids and weakened the insulation.

The revelations came a week after investigators said they had learned that Columbia’s wings were pocked with holes and cracks.

The discoveries mark the strongest evidence yet that the investigative board is zeroing in on its first comprehensive hypothesis about the Columbia breakup. According to a Tuesday press briefing and interviews with members of the board, this is the working theory:

The flaws in the insulation covering the fuel tank probably caused chunks of foam to fall off 81 seconds after the shuttle left Cape Canaveral, Fla., on Jan. 16. The foam struck the leading edge of the left wing, considered something of an Achilles’ heel because it bears the brunt of the searing temperatures encountered when astronauts reenter the Earth’s atmosphere at the end of a mission.

Carbon composite panels that cover the edge of the wing, as well as so-called T-seals that act as brackets between those panels, are believed to have been weakened by age and erosion. That made the wing more susceptible to damage from the foam. On the second day of the mission, Department of Defense radar detected an object floating away from the shuttle. That object, investigators now believe, was probably part of the left wing -- either a T-seal or a piece of a protective panel.

For 16 days, the mission went beautifully -- but the shuttle had been fatally wounded from the start, investigators now believe. The craft was bearing an unseen breach in its wing that, in the early morning of Feb. 1, allowed superheated gas known as plasma to enter the interior of the craft. The accident killed Columbia’s seven-member crew.

“For 11 weeks, we have been saying that we don’t have any favorite scenarios,” said retired U.S. Navy Adm. Harold Gehman Jr., chairman and self-described “traffic cop” of the investigative panel. “It’s time that we attempted to see where the evidence is pointing us.”

Toward that end, members of the board are scheduled to meet behind closed doors Thursday with NASA engineers. After initially discarding the importance of the foam insulation that struck the shuttle, most of those engineers now have concluded that the catastrophic events that led to the destruction of the craft began with that incident, officials said Tuesday.

Several changes in recent days and weeks have pushed NASA toward that conclusion, the officials said.

They include the discovery, in late March, of a flight data recorder that showed small temperature spikes in the left wing about five minutes after liftoff, less than four minutes after the insulation chunks hit the wing. Investigators say they are still trying to determine whether those spikes are linked directly to the foam insulation incident.

New revelations about the defects in the foam insulation, which is applied to external fuel tanks at a Louisiana plant by Lockheed Martin Space Systems Co., also helped firm up the theory, officials said.

U.S. Navy Rear Adm. Stephen Turcotte, a member of the board, said officials have dissected a “sister” tank to the one that carried Columbia into orbit -- one that was built to the same standards at about the same time.

The dissection was performed on a region of the 154-foot-tall tank known as the “bipod” area, a system of tubes and metal brackets that holds the orbiter to the tank during launching. That is similar to the portion of the Columbia tank where the chunks of foam insulation fell off.

The dissection discovered 74 flaws, including air pockets 2 inches deep and faulty bonding between layers of foam. NASA officials are investigating new designs for the external tanks, Turcotte said.

He added that investigators now believe a shift in the method of applying the insulation might have caused the flaws.

For decades, NASA and its contractors used Freon -- similar to the propellant used in a can of spray paint -- as a propellant to apply the foam insulation. In August 1997, workers began applying layers of foam insulation on external fuel tanks using a different gas.

The move was made to satisfy environmental concerns; many scientists say Freon played an important role in depleting the ozone that shields the Earth. But in this case, Turcotte said in an interview, helping the environment may have come at a price.

The manufacturer of the foam insulation, North Carolina Foam Industries, has denied that the insulation is associated with the Columbia disaster.

Also on Tuesday, Steven Wallace, a member of the investigative board and the director of accident investigations for the Federal Aviation Administration, said that seven of 77 mission control officers involved in Columbia’s flight lacked some necessary certifications.

Wallace said he did not know specifically what the certifications were, but added that he did not think that a lack of training contributed to the disaster.

NASA also said Tuesday that the federal government plans to build a memorial to the Columbia astronauts in Arlington National Cemetery. President Bush has approved the memorial, NASA said, and authorized $500,000 for it.

The memorial, which hasn’t been designed, will be built near another memorial honoring the crew members who died when the space shuttle Challenger exploded after liftoff in 1986, officials said.

“A national memorial in the nation’s capital will serve as a reminder about what the crew of Columbia stood for: bravery, honor and the quest for knowledge,” NASA Administrator Sean O’Keefe said in a prepared statement. “I feel it will help inspire future explorers and help keep the spirit of exploration alive in America.”