The Mission That Came Home

On 11 April 1970, Apollo 13 lifted off from Florida carrying three astronauts: commander Jim Lovell, command module pilot Jack Swigert and lunar module pilot Fred Haise. Their mission was to become the third crew to land on the Moon.

Swigert had joined the crew only days before launch. The original command module pilot, Ken Mattingly, had been exposed to measles and was taken off the flight as a precaution. It looked like bad luck for Mattingly. As things turned out, it would make him one of the mission's most important people on the ground.

"Houston, we've had a problem"

On the evening of 13 April, nearly 56 hours into the flight and roughly 200,000 miles from Earth, the crew carried out a routine procedure to stir the spacecraft's oxygen tanks. Moments later there was a bang.

Swigert radioed Mission Control in Houston: "Okay, Houston, we've had a problem here." Lovell repeated it a moment later.

One of the oxygen tanks in the service module had exploded, and the damage was severe. The spacecraft was losing oxygen, which the crew needed not only to breathe but also to make electricity and water in the fuel cells. Within a short time, the command module, the spacecraft meant to carry them home, was running out of power.

The Moon landing was cancelled. The only question now was whether the crew could survive.

A lifeboat in space

Apollo 13 had a second spacecraft attached: the lunar module, named Aquarius. It had been designed to carry two astronauts down to the Moon's surface and back up again, for about two days. It had never been meant to keep three people alive for the whole journey home.

But it had its own oxygen, power and water. So the crew moved into Aquarius and switched the command module almost completely off, to save its last batteries for re-entry into Earth's atmosphere.

The lunar module became a lifeboat.

The box that didn't fit

Living in Aquarius created a new danger. Every breath the astronauts let out added carbon dioxide to the air. The spacecraft's air filters used canisters of a chemical called lithium hydroxide to soak it up, but the lunar module only carried enough for two people for a short trip.

The command module had plenty of spare canisters, but they were square. The lunar module's equipment took round ones.

On the ground, engineers set to work. They gathered only the kinds of items the crew had on board, including plastic bags, cardboard, tape and hoses, and worked out a way to connect the square canisters to the lunar module's system. Then they tested it and wrote out step-by-step instructions, which were read up to the crew.

The astronauts built the adapter by hand, and it worked. The carbon dioxide levels began to fall.

Cold, dark and careful

The journey home was miserable. To save power, almost everything was switched off. The temperature inside the spacecraft dropped close to freezing, and water condensed on the walls and instruments. The crew slept little and were short of drinking water.

They also had to steer. Apollo 13 swung around the far side of the Moon and used the lunar module's engine to adjust its path towards Earth. Some of these burns were controlled by hand, with the crew lining up the spacecraft using Earth itself as a guide through the window.

Meanwhile, Ken Mattingly and other engineers on the ground spent long hours in simulators. They worked out how to bring the cold, frozen command module back to life using the tiny amount of power that was left, and in what order to switch each system on so that nothing would fail.

Splashdown

On 17 April 1970, the crew moved back into the command module, let go of the service module and then of Aquarius. The command module plunged into Earth's atmosphere. Then came several minutes of radio silence, which was normal during re-entry, though it felt much longer to everyone listening.

Then the parachutes opened.

Apollo 13 splashed down safely in the South Pacific, and the astronauts were picked up by the recovery ship USS Iwo Jima.

Why it's called a "successful failure"

Apollo 13 never landed on the Moon. By its own goals it failed. Yet it is often remembered as one of NASA's finest hours, because it showed what careful thinking and teamwork can achieve when everything goes wrong.

Nobody solved the problem alone. It took astronauts staying calm, flight controllers making clear decisions, engineers improvising with cardboard and tape, and a grounded astronaut working in a simulator so his crewmates could come home.

Editorial note: Times and distances are approximate and taken from NASA's public record and the sources listed below.