Investigators are trying to piece together what caused the accident

The analysis carried out during the flight concluded that little harm had been done when a piece of foam came off the fuel tank during lift-off.

But the model had not been used before to assess damage from falling debris during a flight, said former astronaut Sally Ride, a member of the board investigating the accident.

Columbia broke up during re-entry on 1 February, killing all seven astronauts on board.

In recent weeks investigators have been focusing on damage done by the falling foam to the left wing of the shuttle.

A group of Boeing engineers carrying out a computer analysis during the flight realised they needed more data about where the foam had hit, Dr Ride told reporters in Houston, Texas.

She said they asked the US space agency Nasa to take pictures of the orbiting shuttle to assess the potential damage - but no pictures were ever taken, she said.

She said this was the result of "miscommunication" between the engineers and Nasa.

Bad model

Dr Ride added that the space agency might have been lulled into a false sense of security because of the numerous debris strikes that had occurred on every shuttle flight.

Sally Ride says Nasa may have been complacent

Dr Ride - who was a member of the commission that looked into the 1986 Challenger disaster - said Nasa's acceptance of routine hazards was also evident then.

"You survived it the first time, so suddenly it becomes more normal," she said.

The chairman of the Columbia Accident Investigation Board, Harold Gehman, said neither his panel nor Nasa was satisfied with the model used in the Boeing analysis.

He described it as a spreadsheet, not a computational model, and noted that it was based on testing of much smaller debris than the piece of foam that hit Columbia after lift-off.

Some engineers believe a breach in the left wing allowed hot gas to penetrate in or around the wheel well as the shuttle encountered maximum atmospheric heating on its descent.

The breach may have worsened until a structural failure occurred.