WASHINGTON (CNN) -- NASA's chief admits his agency "just flat missed" what investigators on Tuesday will name as the likely cause of the space shuttle Columbia disaster.
The Columbia Accident Investigation Board's final report is expected to blame the catastrophe on the piece of foam that broke off the shuttle's external tank on takeoff. The foam struck the underside of the orbiter's wing, creating a breach in the heat-reflecting tiles that allowed hot atmospheric gases to seep in on re-entry to Earth.
All seven astronauts aboard Columbia were killed when the shuttle broke up over Texas on February 1.
NASA Administrator Sean O'Keefe told CNN's Miles O'Brien in an exclusive interview the agency missed the signs of trouble that led to the accident.
"This was a case where we missed it. Just flat missed it," he said of the significance of the foam strike.
Launch technicians did see the incident, 81 seconds after takeoff, but in a series of memos engineers determined that whatever damage did occur would not have a great impact on the orbiter.
Tests performed later by the investigation board to replicate the foam strike left a huge hole in a replica of the shuttle's wing.
O'Keefe said, however, that the results of those tests ranged from large holes to hairline fractures invisible to the naked eye.
"That's what worries me a lot, because if they're not getting the same result it's random, and demonstrates why over the last years any of those strikes have provided little or no consequence," he said.
"Even this one could not have been anywhere near the magnitude of damage found on that last test that could have been a reality," he said. "Every single sensor on the left wing would have gone haywire after the first minute and a half after launch because that's how gaping that hole was."
O'Keefe said it wasn't until the shuttle's data recorder was found a month after the accident that technicians could see "slight temperature changes after the 81-second hit, so as a consequence, minor readings were undetected by mission control."
"Had it been that big a hole we would have heard about it immediately," the NASA administrator said.
When asked why similar tests weren't conducted by NASA after foam chunks had fallen off in several other shuttle flights, O'Keefe said he didn't know.
"In the future what we need to focus on is looking at any of those anomalies," he said.
The CAIB report is also expected to recommend changes in NASA operations -- recommendations that have already been made public in the course of the investigation.
The board, headed by retired Navy Adm. Hal Gehman, has called for better inspections between flights of the reinforced carbon panels that protect the leading edge of the shuttle's wing, one of the parts subject to the most intense heat during re-entry.
The board also recommends routine and frequent use of Pentagon satellites and telescopes to inspect a shuttle in orbit, for the agency to improve and augment the cameras that track a shuttle's launch, and training and equipping astronauts to make in-flight emergency repairs.
CAIB has also suggested NASA find a way to beam back images of the shuttle's external fuel tank, the leading edges of its wings and the underside during a mission.
O'Keefe said the recommendations will make NASA be its own "toughest critics," and the agency will adopt them all.
"You betcha. I think we have to," he said.
As for when space flight will resume, O'Keefe said no date has been set yet. The space shuttle Atlantis is the next orbiter due to fly.
"We will fly when we are fit to fly," he said. "It could be as early as spring, if we see the opportunities work out right."
O'Keefe, who was appointed by President Bush in 2001, praised the work of the investigation board.
"I think Admiral Gehman and his colleagues have done a tremendous public service. They have done a more thorough review and investigation than I have ever heard of anywhere," he said. "And when this report comes out, I think that will be pretty evident for everyone to see, the diligence they put to this."