Apollo 13 Rescue: How the Lunar Module Lifeboat Got the Crew Home

Apollo 13's crew of three survived 56 hours of normal flight followed by a ruptured oxygen tank, and then days in a lunar module built for two. How did the crew and the ground teams turn that spacecraft into a lifeboat and bring it back?

The lifeboat and the shorter route

The lunar module could serve as a lifeboat because it is an independent spacecraft. It normally took five hours to power up; the crew did it in 90 minutes. Its descent engine put the spacecraft back on a free return trajectory, but that route led to the Indian Ocean, where no recovery forces were deployed. Mission control wanted a Pacific splashdown, where naval forces were waiting.

Two burns were considered. The faster one would speed up the flight by 36 hours but required jettisoning the service module, exposing the command module's heat shield to extreme temperatures, and would use all the remaining engine fuel. NASA chose a four-minute burn that returned the crew only 12 hours sooner and kept fuel for later corrections. The burn came at 79 hours 32 minutes into the flight, almost exactly 24 hours after the tank rupture, and the lunar module guidance computer was then shut down to save power.

Cold, thirst and power

The lunar module was powered down until it drew about 11 amps. Water was scarce, and wet pack food let the crew draw moisture and electrolytes from it. Closing the window shades cooled the command module, which never warmed again; the temperature fell to about 38 degrees just before re-entry. Ice formed on the windows, and Fred Haise had a urinary problem after restricting his water intake. Passive thermal control, a slow rotation known as barbecue mode, evened out the sun's heat.

Carbon dioxide

The lunar module was designed to carry two men for two days, and now carried three for four. Its lithium hydroxide scrubbing canisters were overwhelmed. The command module's canisters were square and the lunar module's round, because two manufacturers had competed. Engineers on the ground built an adapter on a desktop from spacesuit hoses, plastic bags, cardboard flight plans and duct tape, and the crew copied it from read-up instructions. Within an hour the carbon dioxide levels were way down, and four command module canisters were used.

Manual burn and batteries

As the spacecraft drifted, the re-entry angle needed to be between five and a half and seven and a half degrees. With the primary guidance computer off, the crew used the Earth's terminator, aligned in the crewman optical alignment system, a technique Jim Lovell had trialled on Apollo 8. Jack Swigert timed the burn, Haise handled pitch, Lovell handled roll and started and stopped the engine. Mission control then said they were in the middle of the fairway.

The command module's re-entry batteries had been drained. Using a procedure rehearsed in an Apollo 10 training simulation, the lunar module's batteries charged them from 20 toward about 40 amp hours.

Re-entry

The service module was jettisoned and the crew photographed the damage. NASA developed a new procedure to power up the frozen command module, which had never been reactivated in space. Insulation improvements made after the Apollo 1 fire meant condensed water would not short out re-entry systems. The lunar module was jettisoned at 141 hours 30 minutes ground elapsed time, about an hour before re-entry. After blackout, three parachutes came out and the crew splashed down. A review board later determined that an unlikely chain of events caused a fire in oxygen tank number two.