At eight minutes past nine on the evening of 13 April 1970, some 200,000 miles from Earth, mission control asked Apollo 13's command module pilot, Jack Swigert, to carry out a piece of routine housekeeping: flip the switches that stirred the fans inside the service module's oxygen tanks. He did. There was a bang, the spacecraft shuddered, and warning lights blossomed across the panels. "Okay, Houston, we've had a problem here," Swigert radioed. Asked to say again, commander Jim Lovell confirmed: "Houston, we've had a problem." Hollywood later tidied the line into the present tense, but the flight transcript keeps it in the past — by the time anyone spoke, the problem had already happened.
Apollo 13 was NASA's third Moon-landing mission, bound for the rugged Fra Mauro highlands, and it had already given superstition plenty to work with: it launched on 11 April at 13:13 Houston time, and the explosion came on the 13th. Swigert himself was a last-minute substitute, drafted in about 72 hours before launch when the prime crew's Ken Mattingly was exposed to German measles. Mattingly, it turned out, was immune; he never fell ill, and later flew to the Moon on Apollo 16.
Nor was the blast a random stroke of bad luck. Oxygen tank 2 had been dropped a couple of inches during handling years earlier, and during a pre-flight ground test its heater — built for the spacecraft's 28-volt supply — had been fed 65 volts, welding a protective thermostat shut and cooking the Teflon insulation off the internal wiring. The tank flew as a bomb waiting for a spark, and Swigert's stir supplied it. The explosion blew a panel off the side of the service module and, within hours, bled the command module Odyssey of its oxygen and power.
The lifeboat
The crew's salvation hung at the far end of a connecting tunnel: the lunar module Aquarius, designed to keep two men alive for about 45 hours on the Moon, was now asked to sustain three men for roughly 90 hours in deep space. Odyssey was shut down cold to hoard its re-entry batteries while Aquarius's descent engine did the flying — first a burn to put the crippled ship back on a free-return trajectory that would sling it around the Moon towards home, then a longer burn two hours past the far side to speed the journey and shift splashdown to the Pacific. Rounding the Moon, the crew set a record that still stands: the farthest human beings have ever travelled from Earth.
Survival then turned on arithmetic and improvisation. Carbon dioxide was first in the queue of killers: Aquarius's round lithium hydroxide scrubber canisters were running out, and Odyssey's plentiful spares were square — a literal square-peg-round-hole problem. On the ground, engineer Ed Smylie's team built an adapter using only items known to be aboard — plastic bags, cardboard torn from the flight-plan cover, a spacesuit hose and generous lengths of grey tape — then read the recipe up to the crew step by step. The contraption, nicknamed the mailbox, worked at once, and the carbon dioxide readings sank back to safety.
With Aquarius throttled back to draw less electrical power than a domestic kettle, the cabin fell to around three degrees Celsius; the walls sweated with condensation and Fred Haise developed a kidney infection. When the ship drifted off course, the crew flew a 14-second manual burn, Lovell steering to hold the line between Earth's day and night sides — the terminator — steady in his window while Swigert timed the engine on his wristwatch. On the ground, controllers reworked re-entry checklists at slide-rule speed, compressing weeks of procedure-writing into about three days. On 17 April, Odyssey splashed down in the South Pacific near the recovery ship USS Iwo Jima, after a radio blackout that ran agonising seconds longer than predicted.
The successful failure
One immortal line needs an asterisk: flight director Gene Kranz never said "failure is not an option" in 1970 — the phrase was invented for the 1995 film, though Kranz liked it enough to borrow it for the title of his memoirs. Lovell, who never got his lunar landing, supplied the mission's truer epitaph, calling Apollo 13 a "successful failure", and he remains the only person to fly to the Moon twice without walking on it. Fra Mauro went to Apollo 14. Aquarius, the lifeboat, burned up over the Pacific with its job done — three men carried a quarter of a million miles home by a machine built for somewhere else entirely.
Quiz nuggets
- Apollo 13's oxygen tank exploded on 13 April 1970 after a routine cryogenic stir, about 200,000 miles from Earth.
- Jack Swigert replaced Ken Mattingly about 72 hours before launch over German measles exposure; Mattingly never caught it.
- The crew survived in the lunar module Aquarius, used as a lifeboat; the command module was named Odyssey.
- The "mailbox" CO2 adapter was built from plastic bags, cardboard, a spacesuit hose and tape to fit square canisters to round holes.
- Gene Kranz's line "failure is not an option" was invented for the 1995 film; Jim Lovell dubbed the mission a "successful failure".