Space Center, Houston ? NASA acknowledged Monday that its “best and brightest” minds may have gotten it wrong when they concluded in a report four days before Columbia disintegrated that a flying, 2 1/2-pound chunk of insulation did no serious damage to the shuttle’s thermal tiles during liftoff.

Shuttle program manager Ron Dittemore said the agency would redo the entire analysis from scratch.

“We want to know if we made any mistakes,” he said.

Practically from the start, investigators have focused on the possibility that a 20-inch piece of foam insulation that fell off the shuttle’s big external fuel tank during liftoff Jan. 16 doomed the spacecraft by damaging the heat tiles designed to keep the ship from burning up during re-entry into the atmosphere.

While Columbia was still in orbit, NASA engineers analyzed launch footage frame-by-frame and were unable to determine whether the shuttle was damaged. But they ran computer analyses for different scenarios and different assumptions about the weight of the foam, its speed and where under the left wing it might have hit, even looking at the possibility of tiles missing over an area of about 7 inches by 30 inches, NASA said.

The half-page engineering report — issued on Day 12 of the 16-day flight — indicated “the potential for a large damage area to the tile.” But the analyses showed “no burn-through and no safety-of-flight issue,” the report concluded, according to a copy released Monday by NASA.

High-level officials at NASA said they agreed at the time with the engineers’ assessment.

“We were in complete concurrence,” Michael Kostelnik, a NASA spaceflight office deputy, said at a news conference Monday with NASA’s top spaceflight official, William Readdy.

“The best and brightest engineers we have who helped design and build this system looked carefully at all the analysis and the information we had at this time, and made a determination this was not a safety-of-flight issue.”

The analyses spanned a week and no one on the team, to Dittemore’s knowledge, had any reservations about the conclusions and no one reported any concerns to a NASA hot line set up for just such occasions.

“Now I am aware, here two days later, that there have been some reservations expressed by certain individuals and it goes back in time,” Dittemore said. “So we’re reviewing those reservations again as part of our database. They weren’t part of our playbook at the time because they didn’t surface. They didn’t come forward.”

Lois Martin looks over a piece of debris believed to be from the space shuttle Columbia near Hemphill, Texas. Searchers found the shuttle's nose cone buried deep in a thick pine forest near the Louisiana border, officials said Monday night.

On Monday, Readdy said the damage done by the broken-off piece of insulation was now being looked at carefully as a possible cause of the tragedy.

“Although that may, in fact, wind up being the cause — it may certainly be the leading candidate right now — we have to go through all the evidence and then rule things out very methodically in order to arrive at the cause,” he said.

Monday night, searchers found the front of the shuttle’s nose cone buried deep in the ground near the Louisiana border. But even more valuable in trying to piece together what happened would be to locate any tiles from Columbia’s left wing.

“That’s the missing link that we’re trying to find,” Dittemore said.

The shuttle, covered with more than 20,000 thermal tiles, broke up 39 miles over Texas and fell to Earth just as it was experiencing maximum re-entry heat of 3,000 degrees. All seven astronauts aboard perished.

NASA said temperature data showed that the shuttle’s left side — the same side hit by the debris — heated up sharply just before Columbia disintegrated. It began with an unusual temperature rise in three main gear brake lines, 24 minutes before touchdown, and then spread. It’s doubtful that the left wheel well was breached because there would have been a huge spike in temperature, Dittemore said.