ON THIS DAY: The space shuttle Columbia broke apart while returning to Earth, killing the seven astronauts on board. An investigation would later determine that tiles damaged during lift-off allowed super-heated atmospheric gasses to penetrate the shuttle's wing during re-entry, causing the ship to become unstable and quickly disintegrate. The crew was not told about any risk and didn't know something was wrong until very late in re-entry. "In the words of a flight director at NASA: It has been