Oxygen tank explodes aboard Apollo 13, forcing crew to use Lunar Module as lifeboat

At 55 hours and 54 minutes into the mission, on the evening of April 13, 1970, a devastating explosion rocked Apollo 13 approximately 200,000 miles from Earth. Mission Control in Houston had asked Command Module Pilot Jack Swigert to perform a routine cryo-stir of the Service Module oxygen tanks to homogenize the slushy contents and improve measurement accuracy. Unknown to the crew or controllers, damaged Teflon insulation on the internal wiring of Oxygen Tank 2 ignited when the stir switch was activated, creating a rapid pressure spike that ruptured the tank and damaged adjacent systems.

Inside the Command Module Odyssey, the astronauts felt a sharp shudder accompanied by an alarm chime and master caution light. Swigert radioed Mission Control with the famous statement, "Okay, Houston, we've had a problem here," which Commander Jim Lovell repeated shortly after. Looking out his window, Lovell observed a cloud of white gas venting into the vacuum of space, which was the spacecraft's main oxygen supply rapidly dissipating. The loss of oxygen rapidly starved the Command Module's fuel cells, cutting off electrical power generation and life-support reactants.

Flight Director Gene Kranz and the flight controllers in Mission Control quickly recognized that the Command Module was rapidly losing capability. To save the crew, Kranz ordered Odyssey to be completely powered down to preserve its entry batteries, forcing Lovell, Swigert, and Haise to transfer into the Lunar Module Aquarius to use it as a makeshift lifeboat. Originally built to support two men for two days on the lunar surface, Aquarius now had to keep three men alive for over four days in deep space while ground controllers worked around the clock to calculate a new return trajectory.