Two days after launch an oxygen tank blew apart 200,000 miles from Earth, gutting the ship of power and heat while three men tried to work out what had happened; NASA had four days to build a way home from parts never meant to fit.

Jim Lovell, Jack Swigert, and Fred Haise had a spacecraft built to land two of them on the Moon and bring all three home. Fifty-six hours after launch, it could no longer promise the second half of that deal.

Who was originally supposed to fly?

Not Swigert.

Ken Mattingly had trained for months to fly the command module seat on this mission. Two days before launch, the backup lunar module pilot, Charles Duke, came down with German measles after exposure at a birthday party attended by both crews. NASA drew blood from everyone involved; Lovell and Haise showed immunity from childhood exposure, Mattingly did not. Flight surgeons pulled him with 48 hours to spare and put Jack Swigert, the backup command module pilot, in his seat. Mattingly never got sick. He spent the flight on the ground instead, in a simulator, working a problem nobody yet knew was coming.

What went wrong 200,000 miles from Earth?

Apollo 13 launched from Kennedy Space Center on April 11, 1970. Two days later, at 9:08 p.m. Eastern time, Swigert flipped a routine switch to stir the contents of the service module's oxygen tanks: ordinary housekeeping, done several times a flight. Tank No. 2 had been dropped during ground handling in 1968 and repaired, then subjected to a 1970 pre-launch test in which its internal heater ran at 65 volts instead of the intended 28, a mismatch nobody caught because the gauge meant to flag it wasn't wired for the higher voltage either. The extended overheating stripped insulation off wiring inside the tank. When Swigert threw the stir switch, the exposed wires arced and the tank blew out its side panel.

The spacecraft shuddered. Warning lights lit across the panel, and oxygen tank No. 1 began venting through a line damaged by the same blast, killing two of the command module's three fuel cells within minutes. The Apollo 13 Review Board later traced the chain step by step, from the 1968 drop through the mismatched voltage rating, and still described the exact sequence of arcing inside the tank as reconstructed rather than directly observed; nobody watched it happen, and the board's report says so.

How much time did they have?

Not much, and no procedure written for it.

None of NASA's mission manuals covered this. Flight director Gene Kranz and the controllers who rotated through Houston over the next four days worked out a response as they went, drawing on engineers in the back rooms who had built the hardware in the first place. The immediate call was easy to state and hard to execute: power down the crippled command module, Odyssey, before its batteries died, and move into the lunar module, Aquarius, designed to keep two astronauts alive on the Moon's surface for under two days and now stretched to keep three alive for four.

Why did a sock matter?

Aquarius carried carbon dioxide scrubbers sized for two men, not three. The command module had spare canisters, but they were square, built for square sockets, and the lunar module's fittings were round. As the mismatch sat unsolved, CO2 readings climbed toward the danger line.

On the ground, engineer Ed Smylie led a team that built a fix from what the astronauts already had in the cabin: a plastic bag torn off a procedure manual, cardboard ripped from a flight-plan cover, a length of hose from a spacesuit, and duct tape (the one tool every Apollo flight carried in surplus). Houston read the assembly steps up to the crew one line at a time, and Swigert and Haise taped the square canister into a jury-rigged air path so the round system could pull air through it. Engineers on the ground nicknamed the finished rig the mailbox. It worked on the first try, and cabin CO2 began falling within the hour.

How cold did it get?

Aquarius had no heater built for four days of continuous use, so the crew shut down almost everything to save what little power was left. Cabin temperature fell to roughly 38 degrees Fahrenheit. The men slept in their suits and rationed drinking water to a few ounces a day each. They lost a combined 31.5 pounds by splashdown (about half again what any other Apollo crew lost, on a flight twice as long). Haise developed a urinary tract infection, most likely from the dehydration, and ran a fever through the final two days.

How did they aim for home?

Mission planners had already put Apollo 13 on a free-return trajectory, a path shaped so lunar gravity alone would sling the spacecraft back toward Earth without an engine burn. That habit of building in a way home before anything went wrong is what made a recovery possible at all. Engineers still needed a second burn once the spacecraft rounded the far side of the Moon (called PC+2), firing the lunar module's descent engine, never rated for that duration or that much extra mass, to shave nearly ten hours off the trip. Navigators checked the maneuver on slide rules alongside the mainframes, because a wrong digit meant a capsule that missed Earth's atmosphere.

The fix worked.

Odyssey's batteries, dead since the explosion, had to carry the command module through reentry on almost no reserve. Flight controller John Aaron, who had saved a mission during Apollo 12 with one obscure switch, worked out a power-up sequence with Mattingly in a ground simulator, testing variations until they found one the batteries could survive. It turned cabin instruments on last instead of first, the reverse of the standard checklist, and drew spare current bled backward out of the lunar module's batteries.

Apollo 13 splashed down in the South Pacific on April 17, 1970, and the crew was aboard the recovery ship USS Iwo Jima within the hour. All three walked off under their own power.

What is the mission remembered for now?

Not a landing.

Apollo 13's closest pass behind the far side of the Moon, on April 15, 1970, put the crew 248,655 miles from Earth's surface — a record for the farthest any humans had traveled from home that stood for 56 years. NASA's Artemis II crew, Reid Wiseman, Victor Glover, Christina Koch, and Jeremy Hansen, broke it in April 2026 on a free-return lunar flyby that borrowed the identical maneuver Houston improvised in 1970, this time flown on purpose rather than out of necessity. The lesson that carried over is not the trajectory itself but the habit behind it: build the way home into the plan before anything forces the question, and treat the return leg with the same seriousness as the trip out. NASA intends to put astronauts back on the lunar surface within two years, on a program that inherited that instinct rather than having to relearn it.

Sources

• NASA, "Detailed Chronology of Events Surrounding the Apollo 13 Accident"
• HISTORY.com, "Apollo 13 Oxygen Tank Explodes"
• Engineering.com, "This Ad-Hoc Instruction Manual Saved Apollo 13's Astronauts"
• Wikipedia, "John Aaron"
• Naval History and Heritage Command, "Apollo 13 and NASA"
• CNBC, "Artemis II Breaks Apollo 13's Distance Record as Humans Travel Farther From Earth Than Ever Before" (2026)