In the final days before Apollo 13, NASA replaced Command Module Pilot Ken Mattingly with backup pilot Jack Swigert after Mattingly’s exposure to rubella (German measles) raised concerns about illness during flight. The switch meant a new crewmember had to fly with limited time for final integrated training. Apollo 13 still aimed to become the third crewed Moon landing, targeting the Fra Mauro region.
Apollo 13 launched from Kennedy Space Center on a Saturn V rocket. During ascent, the Saturn V’s second stage center engine shut down early, but the remaining engines compensated and the spacecraft reached Earth orbit and then headed toward the Moon. The mission proceeded as a normal lunar landing flight for its first two days.
As Apollo 13 cruised toward the Moon, the crew performed a small, routine course correction to fine-tune the spacecraft’s path. This kind of maneuver was standard to keep the planned landing approach on track. Nothing at this point suggested the crisis that was about to occur.
During a routine “cryo-stir” (mixing liquid oxygen in a tank), an oxygen tank in the Service Module exploded about 56 hours into the mission. The blast damaged the spacecraft’s power and life-support systems and forced NASA to abandon the lunar landing plan. The crew and Mission Control immediately shifted from exploration to survival and return planning.
With the Command Module losing power, the crew powered up the Lunar Module (Aquarius) and moved into it for electricity, water, and air circulation. This was a major improvisation because the Lunar Module was designed to support two astronauts for a much shorter time. Power in the Command Module was shut down to save its batteries for Earth reentry.
To ensure the spacecraft would loop around the Moon and naturally fall back toward Earth, the crew used the Lunar Module’s descent engine for a major trajectory change. This “free-return” setup reduced the need for additional engine burns if systems continued to fail. It was an early turning point that made a safe return achievable.
As carbon dioxide built up inside the Lunar Module, engineers on the ground and the crew devised a makeshift adapter—often called the “mailbox”—to connect Command Module scrubber cartridges to the Lunar Module system. This reduced CO2 to safer levels and helped stabilize the crew’s living conditions. The solution became a famous example of rapid problem-solving under pressure.
Apollo 13 passed behind the Moon on its return loop, briefly losing radio contact with Earth as expected. The flyby confirmed the spacecraft remained on a trajectory that would bring it home if key maneuvers succeeded. It also marked the farthest distance from Earth ever traveled by humans at that time.
After rounding the Moon, the crew performed the “pericynthion plus 2 hours” (PC+2) burn using the Lunar Module descent engine. This shortened the trip back to Earth and helped shift the planned landing area to the South Pacific, where recovery forces could reach the crew faster. The burn had to be accurate despite low power and limited navigation options.
A few hours before reentry, the crew separated and discarded the Service Module to prepare for Earth return. Photographs taken during this step showed a badly damaged side panel and internal destruction, confirming how severe the explosion had been. The images helped investigators later understand the failure’s physical effects.
Before entering Earth’s atmosphere, the crew carefully powered the Command Module back on using a tightly rationed checklist developed during the crisis. They then jettisoned the Lunar Module, which had kept them alive but could not return through reentry. This transition was essential: the Command Module was the only part designed to survive atmospheric entry.
The Command Module Odyssey reentered Earth’s atmosphere and splashed down in the Pacific Ocean, where the recovery ship USS Iwo Jima supported pickup operations. After an anxious communications blackout typical of reentry, contact was restored and parachute deployment proceeded normally. The crew’s survival turned Apollo 13 into a defining case study in engineering, teamwork, and emergency management.
NASA’s Apollo 13 Review Board traced the accident to a chain of design and testing problems involving the oxygen tank: a voltage change and damaged insulation contributed to conditions that led to the explosion. The investigation documented how earlier warning signs were missed and what changes were needed to reduce the chance of repeat failures. These findings shaped hardware and procedural improvements for later Apollo missions.
Apollo 13 (1970): In-Flight Accident, Mission Failure, and Safe Return