2003: Space shuttle Columbia lost in re-entry
6 April 2011 Last updated at 11:03 BST
On 1 February 2003, the space shuttle Columbia was destroyed as it re-entered the Earth's atmosphere, killing all seven crew members.
During launch two weeks earlier, a large chunk of insulating foam broke off the main fuel tank and hit the leading edge of the shuttle's wing, damaging its thermal protection system.
James Oberg, who worked at Nasa Mission Control for more than 20 years, explains how the problem was not discovered until it was too late.