We have two parts left in "The Greatest Leap," our celebration of 50 years of Apollo. Next Tuesday will bring us to one of the most important events in the history of human space flight: the triumph and near-tragedy of Apollo 13.

Easily the second-most famous flight after the Apollo 11 landing itself, Apollo 13 is often billed as both a "successful failure" and NASA's finest hour. The tale of the mission has been told and re-told—most notably in the form of a blockbuster 1995 film. But the deeply technical details behind the exact causes of the accident that nearly killed three astronauts on the way to the Moon, and the complex troubleshooting and analysis performed by controllers on the ground, defies easy and fast explanation.

The true tale of the accident stretches back years before the mission left the ground, and the sheer scale of the effort required to save the crew makes the struggle depicted on the movie screen seem hollow and trivial. There's so much to tell, in fact, that Eric Berger and I have teamed up for a double byline on the story accompanying this week's episode so we could fit everything in.

You've seen the movie. Now let Ars tell you the rest of the story.