The night before Columbia's destruction, US Space Agency (Nasa) engineers expressed fears that the shuttle's wing could burn off during re-entry, killing the crew.
E-mails written between staff at Nasa's Langley Research Center and Johnson Space Center describe possible scenarios - including bailing out the crew.
The shuttle Columbia in orbit above the Earth
But the memos never went to top-flight directors, who had already decided the orbiter was fit for landing, despite being hit by debris during its launch.
The e-mails will inevitably raise the question of whether senior agency officials did everything they could to prevent the loss of Columbia's crew.
Five days before the shuttle was due to land, engineer Robert Daugherty suggested the astronauts assess the situation themselves.
He wrote: "Seems to me that the benefit of an EVA to go look at damage has more pros than cons. Can't imagine that an astronaut would cause MORE damage than he is going out to look for!"
He was mainly worried, like many of the other engineers and supervisors, about the shuttle landing with flat tyres or severe gear damage caused by the intense heat of re-entry.
Daugherty strongly recommended bailing out the crew. The following day he wrote: "Any more activity today on the tile damage or are people just relegated to crossing their fingers and hoping for the best?"
On Thursday, Roger Simpson from Nasa's Resident Office sent out an e-mail allaying many of the previous concerns.
He wrote: "Let me assure you that, as of yesterday afternoon, the shuttle was in excellent shape, mission objectives were being performed and that there were no major system problems identified.
He later referred to a piece of debris which came away during Columbia's launch and may have damaged the orbiter's tiles: "Even though this is not a common occurrence it is something that has happened before and is not considered to be a major problem."
Jeffrey Kling, a flight controller at mission control at the Johnson Space Center, discussed what would happen if some of the instrumentation disappeared during re-entry.
"Ultimately our recommendation in that case is going to be to set up for a bail out (assuming the wing doesn't burn off before we can get the crew out)."
Less than 24 hours before the shuttle was due to land, the debate intensified.
William Anderson wrote a group e-mail which he started by asking: "First, why are we talking about this on the day before landing and not the day after launch?"
Despite this, Nasa's top flight directors were not told of the discussions.
Investigators have also found a partly damaged videotape produced by the astronauts as they made their descent.
The 13 minutes of the tape which have been restored show members of the crew preparing for landing.
Four of the crew were "doing normal activities" on the flight deck 10 minutes before the shuttle broke-up.
Families have been shown the tape.
All seven crew members were killed when the Columbia disintegrated in the sky over Texas on 1 February.
Some experts say the Columbia was damaged about 82 seconds after lift-off on 16 January when a piece of orange foam broke away from the shuttle's fuel tank smashing into the left wing.
Last week, Boeing released analysis indicating that the Columbia may have been hit not by one, but three pieces of the solid foam.
If a tile had been loosened by that impact and then come off during re-entry, the bare aluminium of the shuttle's wing would have been exposed.
That area is roughly the same size of the breach that investigators believed opened and allowed hot gases to enter moments before the shuttle was lost.
Sensors picked up a rapid rise in temperature in some parts of the shuttle's left wing.
Nasa officials have constantly maintained that their investigations into any possible damage caused by the debris showed that the shuttle could land safely.
Radar information shows a 12-inch-square (30-centimetre-square) item drifting away from the shuttle on the second day of its flight.
Three days later, the lightweight object re-entered the atmosphere and disappeared over the South Pacific, so it will probably never be determined whether or not it came from the shuttle.
The collision theory is "just one of many theories, and it's not a favourite of anybody's", said head of the Nasa's Administrator Sean O'Keefe, reports AFP news agency.