After its successful launch, the spacecraft Apollo 13 and its crew of three—commander Jim Lovell, command module pilot Jack Swigert and lunar module pilot Fred Haise—were on their way to the Fra Mauro highlands of the moon. There, Lovell and Haise planned to roam the Imbrium Basin and conduct geological experiments, becoming the fifth and sixth men to walk on the lunar surface. But things didn’t turn out that way. On April 13, an explosion ripped apart one of the spacecraft’s oxygen tanks, crippling its power supply and turning what had been a routine mission into a heart-stopping race for survival.

The Apollo 13 spacecraft was actually two crafts—a command module, or orbiter (Odyssey) and a landing module (Aquarius) joined together by a tunnel. On their journey to the moon, which launched from Kennedy Space Center on April 11, 1970, Lovell, Haise and Swigert lived inside the Odyssey. Early on the evening of April 13, the spacecraft was just over 200,000 miles from Earth, and scheduled to enter the moon’s orbit the following day. After conducting a TV broadcast, the astronauts activated Aquarius in order to inspect its systems for the lunar landing.

At 9:08 p.m., just as Lovell was moving through the tunnel on the way back to Odyssey, an explosion rocked the ship. Within eight seconds of the blast, pressure in one of the spacecraft’s cryogenic oxygen tanks dropped to zero, disrupting the command module’s supply of oxygen, electricity, light and water. The crew scrambled to identify what had happened, and Swigert radioed their distress to mission control at the Johnson Space Center in Texas.

“This is Houston,” mission control responded. “Say again, please.”

Lovell then repeated Swigert’s famous words: “Houston, we’ve had a problem here.”

Within an hour after the explosion, Apollo 13’s flight had been converted from a lunar landing to a survival mission. Controllers in Houston instructed the astronauts to move into Aquarius, and effectively use the landing module as a lifeboat as they tried to make their way back to Earth. Designed for transport from the command module to the moon’s surface and back, Aquarius had a power supply sufficient for two astronauts over 45 hours. Now it would have to sustain three men for at least 90 hours, over a distance of more than 200,000 miles.

Lovell, Swigert and Haise restricted their water rations to 6 ounces per day and reduced their consumption of electricity by 80 percent. In order to remove carbon dioxide from the cabin, mission control devised a makeshift adapter using materials known to be on board, then radioed the astronauts instructions on how to attach the lithium hydrogen cartridges from the command module to the landing module’s hoses. Lovell and his crew also had to perform a risky five-minute engine burn to generate enough speed to get the spacecraft home before its power ran out.

As Aquarius didn’t have a heat shield that would allow it to survive the trip back to Earth, Odyssey would have to be restarted in order to re-enter the Earth’s atmosphere. After three days of frantic work on the part of thousands of flight controllers, engineers and NASA managers around the country, the astronauts executed the tricky process of powering up the command module, jettisoning the crippled service module and moving out of the lunar module in preparation for reentry.

Having shed Aquarius as well, Odyssey re-entered the Earth’s atmosphere just before 1 p.m. on April 17. After four minutes of radio silence, eyes around the world turned to the skies over the Pacific Ocean, until the astronauts’ parachutes were spotted and they touched down safely on the water’s surface. Brought home aboard the recovery ship USS Iwo Jima, Lovell, Haise and Swigert received a hero’s welcome, though their mission had been one of the more spectacular failures in NASA history.

A subsequent NASA investigation found that a combination of manufacturing and testing errors before Apollo 13’s flight had left wires exposed in the oxygen tank. A spark from one of these exposed wires caused a fire, which destroyed one of the tanks and damaged the other. NASA redesigned the spacecraft with better wiring and an extra tank, and subsequent missions avoided similar problems. Decades later, Apollo 13 stands as one of the most famous space missions in history, a “successful failure” (in Lovell’s words) that showcased the innovation and perseverance necessary to bring three astronauts home after a life-threatening ordeal.

HISTORY Vault: Modern Marvels - Apollo 13

The Apollo 13 mission was intended to be a "routine" trip to the moon. But when an oxygen tank exploded, the spacecraft was crippled. With limited resources, could its three-man crew survive?