Apollo 13 is probably the most well known space mission of all time, and not because it achieved some giant leap for man-kind, but because everything that could have gone wrong did, and the astronauts survived anyway.
Apollo 13 was supposed to be straight forward moon landing, with commander Jim Lovell and lunar module pilot Fred Haise landing on the surface, while Pilot Jack Swigert remained in orbit.
The initial launch went well, but unknown to the engineers who serviced the shuttle Apollo 13 had launched with a faulty oxygen tank. It was later found out that the tank had been damaged during testing and some of the wiring was loose. At around 56 hours into the flight Jack Swigert began the procedure of agitating the super-cold liquid oxygen tank, something done to maintain pressure and prevent crystallisation build up.
Due to the tanks wiring issues it exploded and destroyed a large portion of the ship. The oxygen tank was in “sector 4” of the ships cylindrical service module, surrounded by sectors 2,3,5 and 6 which were all holding fuel.
Since the main shuttle was damaged beyond repair and with power draining rapidly, the crew moved into the lunar module to use it as a make-shift space lifeboat. The problem was the lunar module was only designed for 2 people, and apart from the cramped conditions it was also only designed to recycle enough oxygen for 2 people.
Fortunately they don’t send just anyone into space, and the super smart astronauts managed to build an adepter for the carbon-dioxide-scrubbing chemical canisters out of spare parts from the main ship.
By the time the crew were in the lunar module and had recovered from the initial accident, they were on a course that would have missed earth by 2,500 miles. To get back on track they had to fire the modules landing engine several times to move them back into place, knowing a single burst of the engine could see them miss the planet all together.
Fortunately it all ended well and the lunar module landed safely on the earth with 3 shaken but otherwise unharmed astronauts. Their training and incredible minds are the only reason they managed to survive, with luck also playing a major part. The incident has featured many times in the media and has even been made into a film, with Tom Hanks playing the role of Commander Jim Lovell.