NASA
...though NASA officials have maintained that they evaluated the damage from the foam and determined that it did not pose a significant problem for Columbia, the latest documents -- including e-mails and three reports from engineers at NASA contractor Boeing -- indicate that there might have been more internal concern than previously indicated. (Text of e-mails, PDF file) Three days before the shuttle disintegrated February 1, Robert Daugherty, a landing gear expert at NASA's Langley Research Center, sent an e-mail expressing frustration that not enough was being done to simulate the possible effects of the damage on Columbia's landing gear. "It seems that if Mission Operations were to see both tire pressure indicators go to zero during entry, they would sure as hell want to know whether they should land gear up, try to deploy the gear or go to bailout," Daugherty wrote. "We can't imagine why getting information is being treated like the plague. Apparently, the thermal folks have used words like they think things are 'survivable' but 'marginal.'" "I imagine this is the last we will hear of this," he wrote. The next day, Daugherty sent another e-mail outlining possible scenarios of what might happen in case of excessive heating in the shuttle's wheel wells. "I am admittedly erring way on the side of absolute worst-case scenarios, and I don't really believe things are as bad as I'm getting ready to make them out," he said. "But I certainly believe that to not be ready for a gut-wrenching decision after seeing instrumentation in the wheel well not be there after entry is irresponsible." When Columbia entered the atmosphere two days later, sensors in and around the left wing, including the tire pressure and temperature sensors in the left wheel well, stopped working. The shuttle broke up moments afterward, killing all seven astronauts aboard. The independent board investigating the disaster has said evidence points to a thermal breach in the left wheel well as the origin of serious trouble on Columbia. 'Three pieces of debris' On January 16, when Columbia was launched from the Kennedy Space Center in Florida, foam insulation fell off the shuttle's external fuel tank and hit the underside of the orbiter's left wing. After photographs of the launch showed the collision, NASA and Boeing began an engineering analysis to determine how much damage was done to the vital heat-resistant tiles under the shuttle's wing. The first report, completed five days after Columbia's launch, predicted that the foam hit the wing at a relative speed of more than 500 miles an hour and at an angle of less than 20 degrees. The report predicted an impact near Columbia's left main landing gear -- a well-known Achilles heel for shuttles. Randy Avera, a former shuttle structural engineer, told CNN that "anywhere along the centerline of the underneath of the orbiter ... the edge of the wings ... are all critical areas." "These are areas that you do not want to compromise the strength of the aluminum material below," he said. Two days later, on January 23, another team of Boeing engineers made another set of predictions about the foam strike. Using a computer program called "crater," they foresaw the "potential for large [Thermal Protection System] damage." They concluded that a loss of a single tile near the leading edge of the wing could expose Columbia's aluminum skin...