How Apollo 13 was a ‘successful failure’: Facts about the dramatic Moon landing mission

• The seventh crewed Apollo mission, Apollo 13, wasn’t as fortunate as the previous missions.
• Apollo 13 Moon mission was aborted, and all efforts focused on bringing crew members back to Earth alive.
• Because the Lunar Module used water to cool down its hardware, the astronauts reduced their water consumption to six ounces per day, just one-fifth of the normal intake.

Apollo 11 is one of the most famous NASA missions because it led to the first humans on the Moon when astronauts Neil Armstrong and Buzz Aldrin became the first people in history to step on the lunar surface. The launch took place on July 16, 1969, and the Lunar Module Eagle landed on the Moon four days later.  

A few months later, in November 1969, the following crewed flight in the Apollo program, Apollo 12, took commander Charles “Pete” Conrad Jr. and lunar module pilot Alan L. Bean to the Moon’s surface as well. 

Apollo 13 (April 11-17, 1970), the seventh crewed Apollo mission, wasn’t as fortunate. At just under 56 hours into the mission, at 9:08 pm, oxygen tank No. 2 blew up, causing the No. 1 tank to also fail. This led to the loss of the command module's normal supply of electricity, light, and water, with the module about 200,000 miles from Earth.

Apollo 13 Moon mission was aborted, and all efforts focused on bringing crew members James A. Lovell, John L. Swigert, and Fred W. Haise back to Earth alive.

1) Command module pilot John Swigert popularized the expression "Houston, we have a problem"

The explosion of oxygen tank number 2 caused a drop in the oxygen pressure and fluctuations in the electrical power. After 1.8 seconds of silence due to the loss of communications to Earth, Command Module pilot John Swigert reported to NASA Mission Center in Houston, “Houston, we’ve had a problem here.”

The expression, "Houston, we have a problem," would later become shorthand for expressing the emergence of an unexpected event in everyday life, but at the time, it meant that the lives of Apollo 13’s crew members could be at risk. 

Commander James Lovell elaborated on Swigert’s report: “We’ve had a Main Bus B undervolt.” This meant that the spacecraft’s fuel cells —which fed on hydrogen and oxygen piped from tanks— couldn’t deliver an adequate voltage to one of the two main electric power distribution systems (Bus B). 

In fact, the explosion of oxygen tank number 2 had also damaged oxygen tank number 1, causing a significant lack of oxygen that resulted in the death of two of the three fuel cells of the spacecraft’s main module. In the end, both Bus B and Bus A went into voltage shortage.

The lives of the Apollo 13’s crew members now relied on just the module’s batteries and an oxygen surge tank that was already being used by the remaining fuel cell. 

2) The Lunar Module avoided the disaster, but it wasn't easy to survive there

The Apollo 13 spacecraft consisted of two modules: 

When the pressure in the Odyssey tanks reached 200 pounds per square inch, the crew and ground controllers knew there would not be enough oxygen to support the one remaining fuel cell. At one hour and 29 seconds after the bang, Capcom Jack Lousma told the crew, "It is slowly going to zero, and we are starting to think about the LM lifeboat." Swigert replied, "That's what we have been thinking about too."

The Lunar Module (LM) Aquarius had its own life support systems intended to help the astronauts survive on the Moon. Although it was designed to support just two people for 45 hours, the situation in the Odyssey module was so critical that it forced the three crew members of Apollo 13 to evacuate to the Aquarius module for 90 hours.

This meant that the astronauts had to ration their resources until they came back to Earth. There was plenty of oxygen — the LM descent tank, ascent-engine oxygen tanks, and two backpacks full of oxygen that would never be used at least meant the crew would have enough oxygen.

4) The crew suffered from dehydration

Water was another issue. Because the Lunar Module used water to cool down its hardware, the astronauts reduced their water consumption to six ounces per day, just one-fifth of the normal intake. They dealt with dehydration issues by drinking juice and eating only wet-pack foods when they ate at all. The crew still became dehydrated during the flight and also lost a good deal of weight — between them, the crew lost a total of 31.5 pounds, around 50 percent more than any other Apollo crew.

5) They had to reduce power consumption to the minimum

Power was another problem. The LM batteries contained 2,181-ampere hours, but this would need to sustain the LM and also charge up the CM module batteries for reentry. 

To save up power to charge the CM, energy consumption was reduced to a fifth of normal, and the astronauts turned off all non-critical systems, including the heating system. This forced the astronauts to endure almost freezing temperatures in the small cabin of the Aquarius. 

6) They dealt with carbon dioxide issues in the Lunar Module

Although the Lunar Module had enough oxygen, its supply of lithium hydroxide, used for carbon dioxide removal, was designed to support two people for two days, not three people for four days. After a day and a half in the Lunar Module, the astronauts had produced a lot of carbon dioxide, which became dangerous for their health. 

There were enough lithium hydroxide canisters in the command module, but these CM canisters and filters were square and did not fit into the round openings in the LM's environmental system. Engineers on the ground gave the astronauts instructions to build an adapter out of materials that they had on board, including plastic bags, cardboard, and tape. 

The improvised device was nicknamed “the mailbox,” and it successfully removed the excess carbon dioxide.

7) They still went to the Moon - they just didn't land there

In spite of the problems on board, Apollo 13 couldn’t go back directly to Earth because it didn’t have enough operational fuel cells to power the command module’s service propulsion system (SPS). It was also not clear if the SPS had been damaged by the explosion, and there was the possibility that it would not work properly. In addition, there was concern that the crew's supplies would not last long enough to get them back to Earth - the trip needed to be sped up.

Flight director Gene Franz decided that the best bet for Apollo 13 was to swing around the Moon and use its gravity to get into a free return trajectory toward Earth using the Lunar Module’s descent propulsion system (DPS), a less powerful engine designed to control the module’s landing on the Moon.

Following the calculations of NASA engineers, two hours after rounding the far side of the Moon, Apollo 13’s crew burned the small DPS engine for a long burn of almost five minutes in order to propel the spacecraft back to Earth, taking advantage of the Moon’s orbital velocity to grab additional momentum and cut the total time of the voyage to about 142 hours.

8) The Sun helped align the spacecraft

During the burn, the craft needed to be aligned perfectly, or it would overshoot and miss the Earth - with no power left for a correction.

To compute the alignment needed, an onboard sextant device, called the Alignment Optical Telescope, was used to find a suitable navigation star. However, the explosion had created a swarm of debris around the craft, which made it impossible to take an accurate sighting. Instead, the craft was rotated, and the sun was used as an alignment star. After several anxious moments, the crew successfully made the correction.

Years later, flight Director Gerald Griffin said, "Some years later, I went back to the log and looked up that mission. My writing was almost illegible I was so damned nervous. And I remember the exhilaration running through me: My God, that's the last hurdle - if we can do that, I know we can make it." 

9) The crew had to go back to the crippled CM to land on Earth

Perhaps the biggest achievement was still to come - developing all new procedures for powering up the CM. A process that would normally have taken three months to work out was developed in just three days of round-the-clock effort. When the astronauts returned to the CM, there was condensation everywhere, but thanks to the safeguards built after the disastrous Apollo 1 fire in 1967, there were no short circuits. 

On April 17th, 1970, six days after the launch at the John F. Kennedy Space Center, Apollo 13 arrived on Earth. Shortly before re-entry, the crew members jettisoned the crippled Service Module, then went into the Command Module and released the Lunar Module. 

They splashed down in the Pacific Ocean, southeast of American Samoa. 

10) Apollo 13 mission was dubbed "a successful failure"

This is because the mission had not met its objectives, but all the crew members came back to Earth alive. They had all lost weight and were dehydrated, and Lunar Module pilot Fred Haise Jr. had developed a urinary tract infection (and later a kidney infection) due to the lack of water.

11) Due to the incident, NASA redesigned the Apollo spacecraft 

After the Apollo 13 disaster, NASA engineers added to the next Apollo spacecraft water storage bags in the main module, a more powerful battery in the Lunar Module, and an auxiliary oxygen tank prepared to supply the crew, among other changes.

12) There is a movie about Apollo 13 - and NASA collaborated on it

In 1994, NASA collaborated on the production of the docudrama film Apollo 13 (1995), starring Tom Hanks, Kevin Bacon, and Bill Paxton as James Lovell, John Swigert, and Fred Haise, respectively. NASA lent the Mission Control Center in Houston for the set, gave flight controller training to the cast, and let the director film scenes aboard the “Vomit Comet,” a reduced-gravity spacecraft used to introduce astronauts to weightlessness.

13) An investigation determined the real cause of the explosion

Improvements had been made in 1965, raising the voltage to the heaters in the oxygen tanks from 28 to 65 volts DC, but without modifying the thermostatic switches on the heaters. During a pre-launch test, the heaters were turned on, exposing the wiring near the heaters to very high temperatures, which degraded their insulation and welded the switches shut. Damaged from hours of overheating, the tank became a bomb waiting to go off the next time it was filled with oxygen. 

14) The LM manufacturer sent a fake invoice to the SM manufacturer as a joke

Shortly after the Apollo 13 mission returned to Earth, the Grumman Aerospace Corporation, which had manufactured the Lunar Module, jokingly sent a bill for $312,421.24 to North American Rockwell, the company that built the service module that malfunctioned. The bill was for the LM towing the service module to the Moon and back to Earth. Though the bill was a joke, some concerned citizens took it seriously and sent Grumman envelopes containing money.