Apollo 13: Oxygen Tank Rupture and the Lunar Module Lifeboat

Fifty-six hours into Apollo 13, a bang shook the spacecraft about 200,000 miles from Earth. Jim Lovell, Jack Swigert and Fred Haise were flying toward the Moon when an oxygen tank ruptured, and the mission turned from lunar exploration to survival.

A changed crew and a new kind of landing site

Apollo 13 was Lovell's fourth spaceflight. Ken Mattingly was originally command module pilot, but seven days before launch he was exposed to measles and was the only prime crew member without immunity. The flight surgeon decided the risk was too big, and backup pilot Jack Swigert took his place. It was Swigert's and Haise's first spaceflight.

The aim was a highland landing at an area called Fra Mauro, where impact debris from deeper in the crust was exposed. The crew were also to deploy an experiment package and a heat flow experiment using a battery drill to bore holes three metres deep. Public interest was low, and broadcasters received complaints about schedule changes.

Pogo on the way up

About five and a half minutes into the flight, the crew felt unfamiliar vibrations in the second stage, and the central engine shut down two minutes early. The cause was pogo, a vibration along the rocket's axis. The central engine was vibrating vertically sixteen times a second and flexing the Saturn V framework. A sensor shut the engine down. Had the vibration grown through another cycle, it would have taken the vehicle beyond its structural limits. Pogo suppression measures were put in place afterwards.

The rupture

After a television broadcast, mission control asked Swigert to stir the cryo tanks. As the fan in tank number two switched on, damaged wiring created a spark, and fire spread in the oxygen-fed tank. The pressure ruptured it and blew a panel off the service module. Fuel cells one and three went offline. Oxygen pressure in tank two read zero, and tank one was leaking. Lovell saw gas venting into space. Within three hours all oxygen, water, electricity and propulsion in the service module would be lost.

The lifeboat

The lunar module had its own life support, power and guidance. Controllers estimated about 15 minutes of power left in the command module, so the crew moved to power up the lunar module, a process that normally took three to five hours, in 90 minutes. Debris like fireflies kept Lovell from taking star sightings, so Swigert read angles from the command module and they were shouted into the lunar module and punched into its computer to align the platform. The command module was then powered down to save its three re-entry batteries, which could not be recharged.

Back on the free return

Apollo 13 had left the free return trajectory. With the service module engine uncertain, the lunar module's descent engine was used for a burn that put the spacecraft back on it. The lunar module, intended for a two-man crew for 45 hours, now had to keep three men alive for over 90 hours. Water was the limit: mission control estimated it would run out five hours before re-entry, so the crew cut water intake to a fifth of normal and suffered serious dehydration. The lunar module drew about 20 percent of its normal power. Oxygen was plentiful, about 120 hours' worth.

Engineers judged the timing fortunate: earlier, the consumables could not have stretched far enough, and after lunar module separation there would have been no lifeboat.

The spacecraft passed behind the Moon at 77 hours, 9 minutes into the flight.