The Apollo 13 mission was scheduled to be the third manned landing on the Moon, but the landing was aborted due to an oxygen tank explosion in the Service Module. The lives of the crew, James Lovell, Fred Haise, and Jack Swigert, were put into grave danger. Hard work and quick thinking by both the crew and Mission Control in Houston brought the astronauts home safely. Though the mission failed in accomplishing its primary goals, it was called a "successful failure" because the crew was brought home safely.
Apollo 13 launched on Saturday, April 11, 1970, at 1:13 pm CST. At five and a half minutes after liftoff, Swigert*, Haise, and Lovell felt a little vibration. The center engine of the S-II stage of the Saturn V rocket shut down two minutes early. This caused the remaining four engines to burn 34 seconds longer than planned, and the third stage of the Saturn V had to burn nine seconds longer to put Apollo 13 into orbit. For the first two days of the mission, the crew ran into a couple of minor suprises, but nothing became serious. Apollo 13 was looking like the smoothest flight of the program.
Almost 56 hours into the flight, the crew finished a 49 minute television broadcast. Nine minutes later, there was an explosion that the astronauts detected by a sharp bang and vibration. Oxygen tank number 2 blew up, causing the number 1 tank to fail as well. Warning lights indicated the loss of two of three fuel cells, which was the main source of power for the spacecraft. Apollo 13 was slowly losing oxygen, electricity, light, and water 200,000 miles from the Earth. Astronaut Jim Lovell soon looked out the window and saw oxygen venting out into space. One oxygen tank was empty, and the other was depleting fast.
Pressure in oxygen tank one was slowly draining, and once it was lost, the last fuel cell would die. Both Mission Control and the crew began to think the lunar module would have to serve as a lifeboat with its idependent electrical system. Fifteen minutes before power in the command module would fail, the crew moved into the lunar module. The lunar module was designed to support a crew of two for 45 hours. However, Apollo 13 now had to stretch that lifetime to 90 hours while supporting a crew of three. This led to a series of problems that had to be solved to safely return Lovell, Swigrt, and Haise back to Earth.
First power became a concern. The lunar module had 2181 ampere hours of power in its batteries. Mission Control brainstormed a method on how to charge the command module batteries using power from the lunar module. This was the power that would be needed in the command module during re-entry. To conserve power, all non-critical systems were shut down, reducing power usage in the LM to 1/5th of normal. There was one electrical close call. One of the command module batteries vented with so much force that it momentarily dropped offline. It came back on, but if that battery was lost, the astronauts would not have made it back to Earth.
Water was the main consumable concern. It was estimated that the crew would run out of water about five hours before re-entry. It was believed that the lunar module could continue to function up to seven hours without water cooling, but no one wanted to take that risk. The crew conserved water by cutting their intake to 1/5th of normal, or about six ounces per day. They drank fruit juices and ate wet pack foods to help compenate for the lack of water. The crew still became dehydtrated, and Jim Lovell set a NASA record by losing 14 pounds during the mission.
Removal of carbon dioxide was also a problem. There were enough lithium canisters, which remove carbon dioxide from the spacecraft. The problem was, however, the suare canisters from the command module were not compatable with the round openings in the lunar module enviroment control system. After a day and a half in the lunar module, a warning light showed carbon dioxide levels were rising to dangerous levels. Mission Control devised a way to have the crew build an adapter to fit the square canisters into the round openings using plastic bags, cardboard, tape, and other materials that could be found in the spacecraft.
Fifteen hours before the explosion occured, Apollo 13 made a mid course correction that put the spacecraft on a lunar landing course. Now that Apollo 13 wasn't going to land on the Moon, a return-to-Earth trajectory had to be achieved, but the lunar module navigation system was not designed for this situation. Mission Control figured out a 35 second burn fired five hours after the explosion and a five minute burn done later was conducted to speed up the return home. The Sunwas used as an alignment star to allow the navigation system in the lunar module know where it was pointing at any one time.
The trip was marked by discomfort for the astronauts beyond the lack of food and water. Sleep was alomost impossible because of the cold. When the electrical systems were turned off, the temperature dropped to 38 degrees and condensation formed on the spacecraft walls. A most remarkable achievement of Mission Control was quickly developing procedure for powering up the command module after its long, cold sleep. Flight controllers wrote the documents for the procedure in three days instead of the usual three months.
Four hours before landing, the crew shed the service module; Mission Control had insisted on retaining it until then because everyone feared what the cold of space might do to the unsheltered CM heat shield. Photos of the Service Module showed one whole panel missing, and wreckage hanging out, it was a sorry mess as it drifted away. Three hours later the crew left the Lunar Module Aquarius and then splashed down gently in the Pacific Ocean near Samoa,
After an intensive investigation, the Apollo 13 Accident Review Board identified the cause of the explosion. In 1965 the CM had undergone many improvements, which included raising the permissible voltage to the heaters in the oxygen tanks from 28 to 65 volts DC. Unfortunately, the thermostatic switches on these heaters weren't modified to suit the change. During one final test on the launch pad, the heaters were on for a long period of time. "This subjected the wiring in the vicinity of the heaters to very high temperatures (1000 F), which have been subsequently shown to severely degrade teflon insulation. The thermostatic switches started to open while powered by 65 volts DC and were probably welded shut." Furthermore, other warning signs during testing went unheeded and the tank, damaged from 8 hours overheating, was a potential bomb the next time it was filled with oxygen. That bomb exploded on April 13, 1970 -- 200,000 miles from Earth.
*Jack Swigert replaced Ken Mattingly on Apollo 13 two days before launch. Mattingly had been exposed to German measles by fellow astronaut Charlie Duke.