NASA’s Most Dangerous Mission That Almost Killed Everyone

Space exploration has never been safe. Everyone who has ever strapped themselves into a rocket and allowed controlled explosions to hurl them beyond the atmosphere has understood, on some fundamental level, that they were doing something that could kill them. The history of NASA is inseparable from the history of risk — calculated, managed, sometimes catastrophically underestimated risk.

But even within that history, one mission stands apart.

Apollo 13 was not supposed to be remarkable. It was the third lunar landing mission, following the historic success of Apollo 11 and the quieter but equally successful Apollo 12. By April of 1970, Americans had walked on the moon twice. The novelty had worn off enough that the television networks declined to broadcast the Apollo 13 crew’s transmission from space on the evening of April 13th because they did not think the ratings would justify the airtime.

Ninety minutes later, an oxygen tank exploded 200,000 miles from Earth, and three men began the most desperate survival struggle in the history of human spaceflight.

This is what really happened on NASA’s most dangerous mission — the one that almost killed everyone.

The Mission Nobody Was Watching

Apollo 13 launched on April 11, 1970, from Kennedy Space Center in Florida. The crew was commander James Lovell, command module pilot Jack Swigert, and lunar module pilot Fred Haise.

Lovell was one of NASA’s most experienced astronauts, a veteran of three previous spaceflights including Apollo 8, the first mission to orbit the moon. He was calm, methodical, and deeply respected within the astronaut corps. This was supposed to be his crowning achievement — the mission where he finally walked on the lunar surface after years of orbiting, supporting, and watching other men take that step.

It would not work out that way.

The mission had already experienced one significant change before launch. The original command module pilot, Ken Mattingly, had been exposed to German measles by another crew member and was pulled from the flight just days before launch because NASA’s doctors were concerned he might become ill during the mission. Swigert, his backup, stepped in with barely 72 hours of preparation with the actual crew he would be flying with.

That detail would later take on a strange significance. Mattingly, as it turned out, never developed measles. And his presence on the ground during the crisis that followed would prove more valuable than his presence in space ever could have been.

The Superstitions That Surrounded the Mission

Before getting to the explosion, it is worth noting that Apollo 13 carried with it an unusual amount of pre-launch anxiety — some of it superstitious, some of it grounded in real technical concern.

The number 13 made people nervous, even among the scientists and engineers who professionally dismissed superstition. The mission launched at 13:13 Houston time. It launched on April 11th — and 4 plus 11 plus 1 plus 9 plus 7 plus 0 equals 13, a numerical coincidence that was noted with varying degrees of seriousness by people both inside and outside NASA.

More concretely, there had been a problem with one of the oxygen tanks before launch that ground crews had struggled to fully resolve. The tank had behaved oddly during a pre-launch test — it had not emptied properly when technicians tried to drain it. They worked around the issue, convinced themselves it had been addressed, and cleared the mission to fly.

It had not been addressed. The internal components of oxygen tank number two had been damaged — not visibly, not in any way that showed up clearly in the pre-launch checks, but damaged enough that under the right conditions, they could fail catastrophically.

Those conditions would arrive on the evening of April 13th.

Houston, We’ve Had a Problem

The actual words were slightly different from the ones that became famous.

At 9:08 PM Houston time on April 13, 1970, Jack Swigert radioed Mission Control with a message that has become one of the most famous sentences in the history of space exploration. What he actually said was: “Houston, we’ve had a problem.” Past tense. As if it might already be over.

It was not over. It was just beginning.

Oxygen tank number two had exploded inside the service module — the section of the spacecraft attached to the command module that provided power, water, and oxygen for the crew. The explosion had also damaged oxygen tank number one, which began leaking rapidly. Within hours, both tanks would be empty.

Without oxygen, the fuel cells that generated the spacecraft’s electricity could not function. Without electricity, the command module — the cone-shaped capsule the crew needed to survive reentry and splashdown — would lose all power. Without power, the guidance computers, the communications systems, the life support equipment — all of it would go dark.

Three men were 200,000 miles from Earth in a crippled spacecraft with no clear plan for getting home.

The Decision That Saved Their Lives

The next few minutes at Mission Control in Houston were characterized by the particular kind of controlled panic that highly trained professionals experience when something has gone so wrong that the normal procedures no longer apply.

Flight Director Gene Kranz — the man in the white vest who would later become the public face of the Apollo 13 rescue effort — assessed the situation with brutal clarity. The command module was dying. There was not enough power to keep it alive for the four days it would take to get back to Earth.

But there was another option.

The lunar module — the spindly, spider-legged spacecraft designed to land two astronauts on the moon — was still attached to the command module and completely undamaged. It had its own power supply, its own oxygen, its own propulsion system. It had been designed to support two astronauts for two days on the lunar surface.

Kranz made the call. The crew would abandon the dying command module and move into the lunar module. They would use it as a lifeboat — something it had never been designed to be.

The decision was made within minutes of the explosion. It was the right call. It was also, as the crew and Mission Control were about to discover, only the first of approximately a thousand problems that would need to be solved before those three men could come home alive.

The Lifeboat

Aquarius — the name of the Apollo 13 lunar module — was built for two people for two days. It now needed to support three people for four days.

The math was immediately problematic in almost every direction.

Power was the first crisis. The lunar module’s batteries held a finite amount of electricity, and keeping three men alive for four days while also maintaining the navigation systems and communications equipment needed to get home would drain those batteries faster than they could afford. Mission Control and the crew began a brutal process of shutting down every non-essential system — heaters, displays, equipment — until the power consumption had been reduced to the absolute minimum required to survive.

The cabin temperature inside Aquarius dropped to 38 degrees Fahrenheit. The crew could see their own breath. They could not sleep properly. They were cold, exhausted, and surrounded by equipment that was failing in ways that nobody had planned for.

Water was another crisis. The fuel cells that normally generated water as a byproduct of producing electricity were no longer functioning. The crew was rationed to six ounces of water per person per day — less than a standard drinking glass — for the duration of the return journey. By the time they splashed down, all three astronauts were significantly dehydrated. Fred Haise had developed a kidney infection from drinking so little water in such cold conditions.

But the most immediately dangerous crisis was one that nobody had anticipated at all.

The Carbon Dioxide Problem

Human beings exhale carbon dioxide. In a sealed spacecraft, that carbon dioxide has to be removed from the air or it will build up to toxic levels and kill the crew. The lunar module used canisters of lithium hydroxide to scrub carbon dioxide from the cabin air — a simple, reliable system that worked exactly as designed.

The problem was that the lunar module only carried enough lithium hydroxide canisters to support two people for two days. With three people aboard, those canisters were filling up with carbon dioxide far faster than planned. Within a day of moving into the lunar module, Mission Control’s instruments showed the carbon dioxide levels in the cabin beginning to climb toward dangerous levels.

There were spare lithium hydroxide canisters aboard the spacecraft. They were in the dead command module. But the canisters from the command module were square. The receptacles in the lunar module were round.

In one of the most famous improvisation problems in the history of engineering, teams of NASA engineers on the ground had approximately one day to design a way to make a square canister fit into a round receptacle using only the materials the crew had available on the spacecraft — duct tape, cardboard from the flight plan covers, plastic bags, and a tube from a spacesuit.

They called it the mailbox. It was ugly, improvised, and held together with duct tape. It worked perfectly. Carbon dioxide levels dropped back to safe levels within an hour of the crew assembling the device according to instructions read up from the ground.

Gene Kranz later said it was one of the finest moments in NASA history. A group of engineers on the ground, working against the clock, solved a problem that nobody had ever imagined would exist using materials that were never intended for the purpose.

The Navigation Problem

Getting home required more than just staying alive inside the spacecraft. It required pointing the spacecraft in the right direction and keeping it there.

The guidance computers in the command module — which contained all the navigation data needed for the return journey — had been powered down to conserve electricity. The crew needed to navigate using the lunar module’s far more limited systems, combined with manual star sightings and radio guidance from Mission Control.

At one point, the spacecraft had drifted off course and needed a critical engine burn to correct its trajectory. The lunar module’s engine had never been designed for this purpose — it was built to descend to the lunar surface and then launch back up to orbit, not to perform the precise mid-course corrections needed for a trans-Earth trajectory.

The burn had to be calculated manually, executed precisely, and completed without the backup systems that would normally provide a safety net. Any significant error in the calculation could send the spacecraft skimming off the atmosphere at the wrong angle, bouncing it back into space forever, or plunging it in at too steep an angle, killing the crew on reentry.

The burn was executed flawlessly. Jim Lovell, guided by Mission Control, held the spacecraft steady by hand while watching the Earth through the window and keeping it centered in a specific spot — essentially using the planet itself as a navigation reference point.

It worked.

The Longest Four Days

The journey back to Earth took four days that the crew later described as the longest of their lives.

They were cold. They were thirsty. They were running on almost no sleep. They were operating in a spacecraft jury-rigged with duct tape and improvised solutions, surrounded by evidence of how badly things had gone wrong. Every system that was supposed to protect them had either failed or been deliberately shut down to conserve power.

And yet the transcripts of their communications with Mission Control during those four days reveal something remarkable. There is very little panic. There is very little despair. What comes through most strongly is a kind of focused, almost businesslike determination — three men working through an impossible list of problems one at a time, trusting the people on the ground, and refusing to give up.

James Lovell later said that the thought of dying never really dominated his thinking during the crisis. There was always too much to do. The problems were too immediate, too concrete, too solvable to allow much room for the larger terror of the situation to take hold.

Fred Haise, sick with his kidney infection and shivering in the cold cabin, kept working. Jack Swigert, who had joined the crew with barely three days of preparation and had never flown in space before, performed every task asked of him without hesitation.

On the ground, hundreds of NASA engineers, flight controllers, and support staff worked in shifts around the clock, anticipating problems before they became crises, finding solutions to situations that had never been trained for, refusing to accept the possibility that those three men were not coming home.

The Reentry

Before the crew could reenter the atmosphere in the command module, they had to power it back up — a process that had never been attempted before under these conditions.

The command module had been cold and unpowered for four days. Its instruments were covered in condensation. There was genuine uncertainty among NASA engineers about whether the electronics would function properly after being subjected to that kind of cold and moisture.

Ken Mattingly — the astronaut who had been pulled from the crew before launch, who had never gotten sick from the measles he had supposedly been exposed to — spent two days in the simulator working through the power-up procedure, refining it, testing it, cutting it down to fit within the limited power budget the dying batteries could support.

When the crew executed the procedure, it worked. Every system came back online. The guidance computers initialized correctly. The heat shield, which would protect the capsule during the 5,000 degree reentry, appeared undamaged.

The crew transferred back into the command module, sealed the hatch, and jettisoned the service module. As it drifted away, they got their first clear look at the damage from the explosion — an entire panel of the service module had been blown away, exposing the interior to space. The sight of it was sobering even for men who had spent four days knowing intellectually how bad the damage was.

Then they jettisoned Aquarius — the lunar module that had saved their lives. As it drifted away to burn up in the atmosphere, Fred Haise later said it felt like saying goodbye to a friend.

Splashdown

On April 17, 1970, Apollo 13 splashed down in the South Pacific Ocean, 3.5 miles from the recovery ship USS Iwo Jima. The reentry had gone exactly as planned. The parachutes had deployed perfectly. The heat shield had held.

James Lovell, Jack Swigert, and Fred Haise were home.

The world had been watching the final hours of their return in a way it had not watched the launch. The television networks that had declined to broadcast the crew’s routine transmission on April 13th were now giving the story wall-to-wall coverage. Crowds gathered in public squares around the world to watch the splashdown. Church services were held. Pope Paul VI led prayers at the Vatican.

When the hatch opened and the crew emerged — pale, dehydrated, visibly exhausted — the relief was global and genuine.

Gene Kranz, who had kept Mission Control running through four days of continuous crisis, reportedly wept.

What Apollo 13 Actually Was

NASA called Apollo 13 a successful failure. It failed to land on the moon. It succeeded in bringing its crew home alive against odds that, in the early hours of the crisis, had seemed genuinely impossible.

But Apollo 13 was also something more than either a failure or a success. It was a demonstration of something that is easy to talk about and very difficult to actually do — the capacity of human beings to stay calm, stay focused, and keep solving problems in the face of circumstances designed to produce panic and despair.

The engineers who built the mailbox out of duct tape. The flight controllers who worked forty-eight hours without sleep. Ken Mattingly alone in the simulator, running through power-up procedures over and over until they were perfect. Jim Lovell holding the spacecraft steady by hand, using the Earth as a navigation reference.

None of these things appeared in the training manuals. None of them had been planned for. All of them were improvised under pressure by people who refused to stop trying.

The Mission That Defined a Generation

James Lovell never walked on the moon. He came closer than almost any human being in history — 200,000 miles from Earth, with the lunar surface in sight — and then turned around and came home without ever touching it.

He has said in interviews that he made his peace with that a long time ago. The mission he flew instead of the one he planned turned out to matter more. Apollo 13 tested NASA in ways that no successful lunar landing ever could have, and NASA passed the test.

The lessons learned from Apollo 13 — about backup systems, about contingency planning, about the importance of being able to improvise when the plan falls apart — shaped every subsequent NASA mission. They are embedded in the culture of human spaceflight in ways that continue to influence how missions are designed and executed today.

Three men went to the moon and never landed. They came home instead. And in doing so they gave the world something that a successful landing could never have provided — proof that when everything goes wrong, human ingenuity, courage, and refusal to quit can still find a way through.