Lightning strikes might have added a touch of drama to the Apollo 12 mission, but it was nothing compared to the challenging full-scale emergency that faced Apollo 13.

An explosion in space, more than 300,000 km from home raised fears that its crew would be lost in space and never come home. But the threat of disaster was turned into one of the greatest triumphs in space exploration history when NASA pulled off a seemingly impossible rescue.

All plans for a landing on the Moon had to be abandoned. But ironically it was the Lunar Module, Aquarius, that saved the stricken crew.

The mission had started well enough for veteran astronaut Commander Jim Lovell, and his crew Fred Haise and Jack Swigert who were on their first spaceflights. One engine on their Saturn V rocket cut out too soon during launch on April 11, 1970, leaving four others to burn longer to put them into Earth orbit. But now they were safely on their way to the Moon and a visit to the Fra Mauro highlands.

After two days, the crew had just finished a lengthy TV broadcast home when Swigert flicked a switch to stir oxygen tanks in the Service Module. A short circuit sparked a fire that caused an explosion in one tank, damaging another and blowing the side off the spacecraft. Electricity, light and water were lost.

Swigert called mission control to report the incident, telling them the now famous words: “Houston, we’ve had a problem here.” Warning lights showed that one oxygen tank was empty and the other emptying fast. Glancing out of the window, Lovell could see the precious gas venting into space.

It was hugely fortunate that the Command Module, named Odyssey, had already docked with LM Aquarius because it would have been impossible to carry out such a manoeuvre with a dead spacecraft. As it was, the crew was going to have to rely on the lander to get them home, performing as a lifeboat in a way that it was never intended to do. 

Aquarius still had oxygen and water in its tanks, plus power and a functioning rocket engine. It was impossible simply to turn the spacecraft round to bring it home. Instead Aquarius would be used to swing the astronauts around the back of the Moon and towards Earth again. The astronauts helped navigate, like sailors of old, by aligning a sextant on the Sun.

The crew were ordered into Aquarius and Odyssey was completely powered down. The lander’s thruster was fired to send them around the Moon, but calculations showed they would splash down in the Indian Ocean where there would be no rescue ships. A second engine burn was therefore made, both to bring them back more quickly, and to land them in the Pacific. For Lovell, who was on Apollo 8, it was the second time he had rounded the Moon without landing.

Power use in Aquarius was kept to a minimum to conserve it for the long voyage ahead, bringing the temperature down to a chilly 3 degrees C for the uncomfortable crew who were losing weight and becoming dehydrated. 

Then another danger became apparent: the astronauts were producing more carbon dioxide than the Lunar Module was designed to handle and it was building to a perilous level. Square canisters in Odyssey were designed to remove carbon dioxide, but they were not compatible with the round openings in Aquarius’s environmental system. NASA’s engineers found a way to adapt cardboard plastic bags and tape on the spacecraft to make the connection.

Before re-entry, the astronauts had to return to the Command Module. They found it cold with condensation covering the walls. They jettisoned the Service Module, taking photos to show the extensive damage from the explosion, then prepared for re-entry. Back home, the world held its breath but re-entry was successful and the astronauts were recovered by the USS Iwo Jima.

Next: Apollo 14 – Golf on the Moon