Moon travel seemed to become routine with the Apollo 13 launch on April 11, 1970. The serenity was shattered 56 hours into the flight when an oxygen tank in the Service Module behind the crew capsule exploded.
The tank had been damaged in pre-flight testing and its heater switches had welded shut. The explosion took out another oxygen tank and drained their electrical power.
James Lovell, Fred Haise and Jack Swigert had to abandon their Command Module for the Lunar Module, which they used as a lifeboat. The crew fired the Lunar Module's descent engine four times to adjust their trajectory so they would swing around the Moon and return to Earth.
Although the Lunar Module had only enough oxygen and power for half the flight home, the astronauts survived by powering down systems and jury-rigging life support equipment. For example, the cabin atmosphere was cleansed of carbon dioxide using lithium hydroxide stored in special canisters. The Lunar Module's cannister's didn't have the capacity to support a three-person crew, and the canisters from the Command Module didn't fit in the Lunar Module. The crew rigged up a collection of tubes and containers they called "the mailbox" to adapt the Command Module lithium hydroxide supply to the Lunar Module.
By the time the three men landed in the Pacific, their spacecraft was very cold with 100% humidity. They had only a thin margin of life support left when rescue crews reached their spacecraft.
