A premature end of a space flight due to danger to the crew, the mission, or the environment, such as an accident or systems failure. This can occur during launch or during a mission. The Apollo 13 mission was aborted on its third day after an oxygen tank exploded in the service module, and the crew was saved by an innovative new flight plan. NASA's space shuttle official launch aborts were: return to launch site (RTLS), trans-Atlantic landing (TAL), and abort to orbit (ATO). Only ATO has had to be used, on one mission in 1985. There were also several unofficial contingency aborts that could save the crew in the event of an emergency during a launch, but there was no guarantee of saving the craft or the crew. An abort was impossible during a shuttle descent, such as when Columbia broke apart on 1 February 2003, killing its crew of seven.