Apollo 13 Mission Overview
Apollo 13 was launched on April 11, 1970, for what was planned to be the third human landing on the Moon. The crew included Commander Jim Lovell and Lunar Module Pilot Fred Haise, who were scheduled to land in the lunar module Aquarius and explore the Fra Mauro region of the Moon. Command Module Pilot Ken Mattingly would remain in lunar orbit in the command module Odyssey. However, four days prior to launch, it was determined that Mattingly had been exposed to measles and had no immunity. In order to avoid the possibility of Mattingly becoming sick during the flight, he was replaced by his back up, Jack Swigert.
On the third day of the mission, when the spacecraft was nearly 200,000 miles from Earth, the routine activation of a fan in one of the service module's oxygen tanks led to a short circuit and an explosion in that tank. As a result, both oxygen tanks ruptured and vented their contents to space. The lunar landing was cancelled and the crew used the lunar module as a life boat to sustain them for the return trip back to Earth. The lunar module was designed to support 2 people for 2 days and was suddenly required to support 3 people for nearly 4 days. The crew subsisted on 6 ounces of water per person a day. Power was severely rationed, and the temperature inside the cabin dropped below 40 °F (4 °C), causing the crew great difficulty sleeping. The two spacecraft both used lithium hydroxide canisters to remove carbon dioxide from the atmosphere, but the canisters had different shapes on the two spacecraft. CO2 levels were approaching dangerous levels when Mission Control designed a system using plastic bags, cardboard, and duct tape that allowed Aquarius to successfully use lithium hydroxide canisters from Odyssey. The crew used the engines on Aquarius to make three trajectory correction maneuvers that were needed to reach the landing zone in the Pacific Ocean. When Odyssey entered Earth's atmosphere, it was unknown if the explosion had damaged the spacecraft's heat shield; fortunately, it was undamaged. Because of the low cabin temperature, atmospheric humidity had condensed, covering the cabin interior with drops of liquid water that fell as rain during the reentry. Despite these dangers, the crew landed safely near Samoa six days after the mission began.
A post-mission investigation revealed that the explosion was a result of a change made to the spacecraft design in 1965, when the heaters in the oxygen tanks were changed from 28 volts to 65 volts. Unfortunately, the switches in the tank that exploded were not changed to handle the higher voltage, resulting in unrecognized damage during a ground test two weeks before the launch and ultimately in the short circuit during flight. As a safety measure, later Apollo spacecraft were modified to include a third oxygen tank that was isolated from the first two tanks and also included additional emergency battery power.