Houston, We've Had a Problem - What Went Wrong with Apollo 13?

A picture taken of the Apollo 13 Service Module after it was jettisoned before re-entry. The missing exterior panels on the bottom are the result of the oxygen tank explosion.

Apollo 13 was supposed to be NASA’s third time landing a crew on the Moon. Instead, it turned into a mission of survival that became one of the most intense chapters in the history of human space flight. An explosion in the oxygen tank put the fate of the mission and its crew in peril. Along the way on their mission to return home safely, the crew of Apollo 13 became the humans to travel farthest from Earth, a record that stood until today, April 6, 2026, when the crew of Artemis II flew farther.

Apollo 13 launched April 11, 1970, less than a year after the first Moon landing by Apollo 11. After Apollo 11 and 12 at the tail-end of the Space Race, Moon landings were no longer seen with the same glamour. They were becoming routine. But Apollo 13 proved they were anything but. Two days into the journey to the Moon, Apollo 13 was 210,000 miles from Earth and everything was going as it should. Joe Kerwin, part of the team communicating with the Apollo 13 crew from Houston, reported that he and the others in the control room were, “bored to tears down here.” Minutes later, disaster struck.

We've Had a Problem

A pressure sensor in one of the oxygen tanks had been seemingly malfunctioning, so one of the flight controllers requested that the crew activate the tank’s stirring fan. The fan would equalize the temperature across the tank and help get a more accurate reading. But 95 seconds after the fan was activated, the crew reported hearing a loud bang, accompanied by fluctuations in the spacecraft’s electronics. Communications with Earth were lost for 1.8 seconds. It was at this point that pilot Jack Swigert famously reported, “Houston, we’ve had a problem.” (Often misquoted as, “Houston, we have a problem.”)

Jim Lovell, the mission commander, looked out the window and reported seeing gas venting from the module and into the vacuum of space. The oxygen tank had been ruptured. The oxygen was not only needed for breathing, but also for the spacecraft’s energy cells and water production. Without enough oxygen for power, critical systems would fail. The goal of the Apollo 13 mission instantly shifted to getting the three astronauts aboard back to Earth alive.

Failure Is Not An Option

Both the Apollo 13 crew and the NASA ground crews worked around the clock to to bring the astronauts home. The crew moved into the lunar module, which is the part of the spacecraft that would detach to land on the Moon, and used it as their lifeboat. It had its own independent life support systems and oxygen supply. The problem was, it was only meant to be enough for the two astronauts landing on the Moon for their two days on the surface. It would take nearly double the time to get the three astronauts back to Earth.

Swigert with the improvised carbon dioxide scrubber. The life-saving duct tape and plastic bag are visible around the square cartridge.

They had enough oxygen for the trip, but carbon dioxide buildup was still a concern. The command module carried plenty of lithium hydroxide canisters to remove the carbon dioxide, but the square canisters were not designed to be used in the lunar module with its round openings. It was up to Houston to come up with a way to literally fit a square peg into a round hole. In the end, they were able to improvise a method using duct tape, cardboard, and plastic bags to make it work.

The crew also faced energy shortages, leading to low temperatures, a humid environment, and a shortage of water. But an assortment of quick thinking and clever workarounds managed to keep them alive for the duration of their trip back, even if just barely. Everything had to be rationed, even the power. All non-essential systems were shut down. Due to food rationing, Lovell lost 14 pounds over the course of the 6-day mission.

In order to make it back to Earth, Apollo 13 had to continue on its way to the Moon, then swing around it back to Earth. While on the opposite side of the Moon, the crew officially broke the record for the farthest distance from Earth any human had ever been at 248,655 miles. It wasn’t planned for them to have traveled so far, but was rather a necessity of their emergency return trip. The record would hold for almost exactly 56 years, until earlier today when the astronauts of the Artemis II mission broke it.

Despite everything, Apollo 13 made it back on April 17, six days after launching. Atmospheric reentry went off without any problems and the crew were recovered from the Pacific Ocean, near Samoa. The entire world breathed a collective sigh of relief.

What Went Wrong?

But what exactly went wrong? An investigation determined that damaged insulation around the wiring in the module’s oxygen tank caused an electrical short, which ignited a fire in the tank, resulting in a sharp rise in pressure, which was the explosion that destroyed the tank, and could have killed the crew right there.

The problem was the result of two unrelated occurrences. In the first, the oxygen tank had been dropped from about 2 inches when it was being removed from the Apollo 10 module, where it was previously installed. The small jolt was enough to loosen some of the internal components. The second was an application of voltage that went beyond what the tank was designed for.

Due to the damage from the drop, prior to launch the ground crew was unable to completely drain the tank of all its oxygen. In order to remove it, they decided to heat the tank and boil the excess oxygen away. Unbeknownst to them, this was the nail in the coffin.

The Apollo command module was originally designed to use 28 volts of power, but years earlier it was decided that all ground testing would use 65 volts instead. Nearly all components of the module were upgraded to handle the increase in voltage. All except the failsafe thermostat that protected the oxygen tank’s heaters. The heating of the tank to remove the excess oxygen caused the thermostat’s circuits to overload and fail. Without the failsafes, which would have cut off the heating at 80°F, the temperature instead rose as high as 1,000°F. This was enough to damage the internal insulation of the tank, turning it into a ticking time bomb. It wasn’t a question of if a spark would cause a fire, it was a question of when.

Apollo 13 was perhaps the most harrowing near-disaster to occur beyond the Earth’s atmosphere. But NASA knows it as “the successful failure.” In the end, everyone survived, and we learned from the disaster. Even Artemis II is safer because of what we learned from Apollo 13.