On Monday April 13, it will be fifty years ago that the Apollo 13 moon landing was interrupted prematurely after an oxygen tank exploded from the capsule. Fifty years later, people worldwide remember Commander James Lovell's statement - "Houston, we've had a problem" - that he spoke when he told the mission about the accident.

The mission began as a story of happiness for astronauts James Lovell (commander), Ken Mattingly (pilot of the command module) and Fred Haise (pilot of the lunar lander). The trio actually formed the crew of Apollo 14, but they were allowed to move forward.

Due to recent ear surgery, the commander of the original Apollo 13 crew, Alan Shepard, had to undergo new training. Lovell, Haise and Mattingly had already been the backup crew for the first moon landing, Apollo 11, and Lovell took part in Apollo 8, making him one of the first people to orbit the moon.

There are already problems shortly before the launch. A member of the backup crew, who trained with the main crew, gets measles. The main crew and backup train together, which threatens to infect everyone. The main crew's pilot Mattingly is the only one of the group who had never had measles before, so he is replaced by Jack Swigert.

The Apollo 13. Crew From left to right: Jack Swigert, James Lovell, Fred Haise. (Photo: NASA)

Astronaut appears to have forgotten tax returns

On April 11, 1970, the three astronauts leave for the moon. Accident strikes already during the launch: an engine in the second rocket stage stops two minutes early due to heavy vibrations. The other engines burn a little longer and so the mission can continue. In retrospect, it turns out that the failure could have become almost catastrophic.

After the launch, everything goes according to the book. However, pilot Jack Swigert realizes on the second day of the mission that he has forgotten his tax return. Fortunately, he's getting a sixty-day extension because he wasn't in the country - or on the planet - around the time of the deadline.

The spacecraft of the Apollo missions. The cylinder is the service module, the cone on the right is the command module. (Photo: NASA)

In a "lifeboat" 330,000 kilometers from Earth

The astronauts' vehicle consisted of two parts: the command module (CM) where the astronauts are located, called Odyssey, and the service module (SM) that supplies energy, oxygen and water to the CM. In front of the command module is the lunar lander, called the Aquarius, who eventually disconnects to land on the moon.

On April 13, 1970, a dull bang sounds, which later turns out to be an exploded oxygen tank. "Houston, we've had a problem," Lovell told the Houston Mission Control. The Odyssey loses oxygen and power and the crew diverts to the lunar lander as a lifeboat. To save power before landing on Earth, the command module systems are turned off.

The Aquarius lander has its own oxygen and power supply, but it is intended for two astronauts, not three. Nor was it built to support an entire flight, just a short stay on the moon. A number of improvised technical interventions make the best of a harsh situation.

While the craft makes an emergency maneuver around the moon and snakes back to Earth, Lovell, Haise and Swigert must survive with a lack of light, heat and water, in a space that is actually too small for them. The astronauts lose weight and Haise even catches a urinary tract infection.

The broken service module of Apollo 13, seen from the capsule. (Photo: NASA)

Landing on Earth after four days of abandonment

The astronauts return to Earth four days after the explosion, on April 17. Before landing, the service module is dropped and for the first time the crew sees the damage from the disaster. Among other things, a large part of the outer wall of the vehicle has been blown off.

The crew crawls back from the lifeboat to the command module and turns the systems back on. The lunar lander Aquarius is thrown off and the Odyssey lands in the Pacific Ocean, where the crew is received on an American navy ship.

Lovell, Haise and Swigert set foot on solid ground for the first time in Hawaii, where U.S. President Richard Nixon gives them the highest award: the Presidential Medal of Freedom.

None of the Apollo 13 astronauts have been in space since then. Commander Lovell is the only astronaut to orbit the moon twice, but never set foot on the celestial body.

Apollo 13 lands in the Pacific. (Photo: NASA)