Nobody suspected, until the very end, that Columbia was in trouble. And by then it was too late to do anything. But Americans wonder if something — anything — could have been done to protect the astronauts.
We put some of the leading questions to astronauts and engineers. Here are their answers.
Could the flight have been aborted?
A NASA tracking camera does show a piece of debris falling from the shuttle's orange fuel tank and hitting Columbia's underside. It happened a minute and 20 seconds after launch, but engineers did not notice it until they reviewed the tape the next day.
If they had noticed it — and, further, if it had clearly damaged the orbiter's wing — could the astronauts have returned to Kennedy Space Center?
Yes, but they would not have "unless there was something obviously, imminently wrong," said Javier de Luis, CEO of Payload Systems Inc., a firm that builds shuttle equipment.
Crews practice the maneuver, peeling off from the fuel tank, flipping around and heading back to Cape Canaveral. But engineers say it is so risky that it is actually safer to keep going into orbit and then figure out if they have a problem.
Could the crew have repaired any damage?
Even the most experienced astronauts say no. They have no equipment to repair the ship's protective tiles (there are more than 20,000 of them, each unique), and the wings of the shuttle are too smooth for spacewalkers.
Eugene Cernan knows that very well. Many Americans remember him as the last man to walk on the moon, but he was also the second American to make a walk in space.
"It's impossible to do any work outside the spacecraft as a spacewalker without something to hold onto and someplace to anchor your body," said Cernan.
Could the shuttle have docked with the International Space Station?
It would seem a safe haven — but, in truth, the space station was never anywhere near Columbia. The two vessels were in very different orbits. For two ships to dock, they have to be in parallel orbits.
"We just didn't have the rocket fuel on board to change our orbit dramatically and get into the orbit that the space station is in," said Cernan.
Even if rendezvous had been possible, Columbia did not carry docking equipment. It's heavy, and NASA thought it unnecessary on a science mission.
Could a second shuttle have been sent on a rescue mission?
Well, maybe, says de Luis. The shuttle Atlantis, set for a March flight, conceivably could have been rushed into service. But the preparations would have taken weeks, and de Luis says the mission could have been foolhardy.
"Do you launch another space shuttle if you didn't know what had caused the problem in the first place?" he said. "You could end up just simply having two space shuttles with the same problem up on orbit, not being able to get back."
It is important to remember, whenever such questions come up, that NASA engineers clearly did not think Columbia was in trouble.
Everyone expected a picture-perfect landing, like all the ones before it.