Apollo 13: A Mission in Trouble

North America, day and night, satellite image of the Earth
Science Photo Library - NASA/NOAA, Brand X Pictures/ Getty Images

Apollo 13 was a mission that tested NASA and its astronauts to the hilt. It was the thirtheenth scheduled lunar space exploration mission, scheduled for liftoff at the thirtheenth minute after the thirteenth hour. It was supposed to travel to the Moon, and three astronauts would attempt a lunar landing on the thirteenth day of the month. All it lacked was a Friday to be a paraskevidekatriaphobe’s worst nightmare. Unfortunately, no one at NASA was superstitious.

Or, perhaps, fortunately. If anyone had stopped or made changes to the schedule of Apollo 13, the world would have missed one of the scariest adventures in space exploration history. Luckily, it ended well, but it took every bit of brainpower among the astronauts and the mission controllers to make it work.

Key Takeaways: Apollo 13

  • The Apollo 13 explosion was a result of faulty electrical wiring, which lowered the crew's supply of oxygen.
  • The crew devised a workaround for their oxygen supply based on instructions from mission controllers, who had an inventory of materials onboard the ship that could be used for the fix.

Problems Began Before Launch

Apollo 13 faced problems even before its launch. Just days before liftoff, astronaut Ken Mattingly was replaced by Jack Swigert when Mattingly was exposed to German measles. There were also some technical issues that should have raised eyebrows. Shortly before launch, a technician noticed a higher pressure on a helium tank than expected. Nothing was done about it besides keeping a close watch. In addition, a vent for liquid oxygen would not close at first and required several recyclings before it would shut properly.

The launch, itself, went according to plan, although it went off an hour late. Shortly afterward, though, the center engine of the second stage cut off more than two minutes early. In order to compensate, controllers burned the other four engines an additional 34 seconds. Then, the third stage engine ired for an extra nine seconds during its orbital insertion burn. Fortunately, this all resulted in a mere 1.2 feet per second greater speed than planned. Despite these problems, the flight went ahead and things seemed to go smoothly.

Smooth Flight, No One Watching

As Apollo 13 entered the Lunar corridor, the command service module (CSM) separated from the third stage and maneuvered around to extract the lunar module. That was the portion of the spacecraft that would take the astronauts to the Moon. Once this was completed, the third stage was driven out along a collision course with the Moon. The resulting impact was to be measured by equipment left behind by Apollo 12. The command service and lunar modules were then on "free return" trajectory. In case of complete engine loss, this meant the craft would slingshot around the moon and be on course for a return to Earth.

Pictures of Apollo 13 Mission - The Actual Apollo 13 Prime Crew
Pictures of Apollo 13 Mission - The Actual Apollo 13 Prime Crew. NASA Headquarters - GReatest Images of NASA (NASA-HQ-GRIN)

The evening of April 13, the crew of Apollo 13 had to do a television broadcast explaining their mission and about life aboard the ship. It went well, and Commander Jim Lovell closed the broadcast with this message, "This is the crew of Apollo 13. Wish everybody there a nice evening and a, we're just about to close out our inspection of Aquarius and get back to a pleasant evening in Odyssey. Goodnight."

Unknown to the astronauts, the television networks had decided that traveling to the Moon was such a routine occurrence that none of them broadcast the news conference.

Routine Task Goes Awry

After completing the broadcast, flight control sent another message, "13, we got one more item for you when you get a chance. We'd like you to err, stir up your cryo tanks. In addition, have a shaft and trunnion, for a look at the Comet Bennett if you need it."

Astronaut Jack Swigert replied, "OK, stand by."

Fighting to Survive on a Dying Ship

Moments later, disaster struck. It was three days into the mission, and suddenly everything changed from "routine" to a race for survival. First, technicians in Houston noticed unusual readings on their instruments and were starting to talk amongst themselves and to the crew of Apollo 13. Suddenly, Jim Lovell’s calm voice broke through the hubbub. "Ahh, Houston, we've had a problem. We've had a main B bus undervolt."

This Is No Joke

What happened? It took a while to figure out, but here's a rough timeline. Immediately after attempting to follow flight control's last order to stir the cryo tanks, astronaut Jack Swigert heard a loud bang and felt a shudder throughout the ship. Command module (CM) pilot Fred Haise, who was still down in Aquarius after the television broadcast, and mission commander, Jim Lovell, who was in between, gathering cables up, both heard the sound. At first, they thought it was a practical joke previously played by Fred Haise. It turned out to be anything but a joke.

apollo 13
A view of the damaged Apollo 13 service module after it separated from the rest of the spacecraft. NASA 

Seeing the expression on Jack Swigert’s face, Jim Lovell knew immediately that there was a real problem and hurried into the CSM to join his lunar module pilot. Things did not look good. Alarms were going off as voltage levels of the main power supplies were dropping rapidly. If power was completely lost, the ship had a battery backup, which would last for about ten hours. Unfortunately Apollo 13 was 87 hours from home.

Looking out a port, the astronauts saw something that gave them another concern. "You know, that's, that's a significant G&C. It looks to me looking out the ahh, hatch that we are venting something," someone said. "We are, we are venting something out the, into the ahh, into space."

From Lost Landing to Struggle for Life

A momentary hush fell over the Flight Control Center in Houston as this new information sank in. Then, a flurry of activity began as everybody conferred. Time was critical. As several suggestions for correcting the dropping voltage were raised and tried unsuccessfully, it quickly became apparent that the electrical system could not be saved.

Apollo 13 Mission control in Houston
Mission Control in Houston, where ground technical personnel worked with the astronauts to devise fixes to their spacecraft to bring them home safely. NASA

Commander Jim Lovell’s concern continued to rise. "It went from 'I wonder what this is gonna to do to the landing' to 'I wonder if we can get back home again,'" he later recalled.

The technicians in Houston were having the same concerns. The only chance they had of saving the crew of Apollo 13 was to shut down the CM entirely to save their batteries for reentry. This would require the use of Aquarius, the lunar module as a lifeboat. A module equipped for two men for two days of travel would have to sustain three men for four long days in a scramble around the Moon and back to Earth.

The men quickly powered down all the systems inside Odyssey, scrambled down the tunnel and climbed into Aquarius. They hoped it would be their lifeboat and not their tomb.

Apollo 13 and Aquarius capsule
The Aquarius capsule shown after separation. It was where the astronauts huddled for safety during the trip back to Earth after the explosion.  NASA

A Cold and Frightening Journey

There were two problems to be solved to keep the astronauts alive: first, getting the ship and crew on the fastest route home and second, conserving consumables, power, oxygen, and water. However, sometimes one component interfered with the other. Mission control and the astronauts had to figure out a way to make them all work.

As an example, the guidance platform needed to be aligned. (The venting substance had played havoc with the ship's attitude.) However, powering up the guidance platform was a heavy drain on their limited power supply. The conservation of consumables had already begun when they shut down the command module. For most of the rest of the flight, it would only be used as a bedroom. Later, they powered down all of the systems in the lunar module except those required for life support, communications, and environmental control.

Next, using precious power they could not afford to waste, the guidance platform was powered up and aligned. Mission control ordered an engine burn that added 38 feet per second to their velocity and put them on a free-return trajectory. Normally this would be a fairly simple procedure. Not this time, however. The descent engines on the LM were to be used instead of the CM’s SPS and the center of gravity had changed completely.

At this point in time, had they done nothing, the astronauts' trajectory would have returned them to Earth approximately 153 hours after launch. A quick calculation of consumables gave them less than an hour of consumables to spare. This margin was far too close for comfort. After a great deal of calculating and simulating at Mission Control here on Earth, it was determined that the lunar module’s engines could handle the required burn. So, the descent engines were fired sufficiently to boost their speed up another 860 fps, thus cutting their total flight time to 143 hours.

Chilling Out Aboard Apollo 13

One of the worst problems for the crew during that return flight was the cold. Without power in the command module, there were no heaters. The temperature dropped to around 38 degrees F and the crew stopped using it for their sleep breaks. Instead, they jury-rigged beds in the warmer lunar module, although it was only slightly warmer. The cold kept the crew from resting well and Mission Control became concerned that the resulting fatigue could keep them from functioning properly.

Another concern was their oxygen supply. As the crew breathed normally, they would exhale carbon dioxide. Normally, oxygen-scrubbing apparatus would cleanse the air, but the system in Aquarius wasn’t designed for this load, there was an insufficient number of filters for the system. To make it worse, the filters for the system in Odyssey were of a different design and not interchangeable. The experts at NASA, employees and contractors, engineered a makeshift adapter from materials the astronauts had on hand to allow them to be used, thus lowering the CO2 levels to acceptable limits.

Apollo 13 oxygen device
The makeshift device engineered by the Apollo 13 crew for life support. It was made from duct tape, maps, and other materials onboard the spacecraft. NASA

Finally, Apollo 13 rounded the Moon and began its journey home to Earth. They still had a few more hurdles to overcome before they could see their families again.

A Simple Procedure Complicated

Their new re-entry procedure required two more course corrections. One would align the spacecraft more towards the center of the re-entry corridor, while the other would fine tune the angle of entry. This angle had to be between 5.5 and 7.5 degrees. Too shallow and they would skip across the atmosphere and back into space, like a pebble skimmed across a lake. Too steep, and they would burn up on re-entry.

They could not afford to power up the guidance platform again and burn up their precious remaining power. They would have to determine the attitude of the ship manually. For experienced pilots, this would normally not be an impossible job, it would just be a matter of taking star sights. The problem now, though, came from the cause of their troubles. Ever since the initial explosion, the craft had been surrounded by a cloud of debris, glittering in the sunlight, and preventing such a sighting. The ground opted to use a technique worked out during Apollo 8, in which the Earth’s terminator and the sun would be used.

"Because it was a manual burn, we had a three-man operation. Jack would take care of the time," according to Lovell. "He'd tell us when to light off the engine and when to stop it. Fred handled the pitch maneuver and I handled the roll maneuver and pushed the buttons to start and stop the engine."

The engine burn was successful, correcting their re-entry angle to 6.49 degrees. People in Mission Control breathed a sigh of relief and continued working to bring the crew home safely.

A Real Mess

Four and a half hours prior to re-entry, the astronauts jettisoned the damaged service module. As it slowly receded from their view, they were able to make out some of the damage. They relayed to Houston what they saw. One whole side of the spacecraft was missing, and a panel was blown out. It really looked like a mess.

A later investigation showed that the cause of the explosion was exposed electrical wiring. When Jack Swigert flipped the switch to stir the cryo tanks, the power fans were turned on within the tank. The exposed fan wires shorted and the Teflon insulation caught fire. This fire spread along the wires to the electrical conduit in the side of the tank, which weakened and ruptured under the nominal 1000 psi pressure within the tank, causing the no. 2 oxygen tank to explode. This damaged the number 1 tank and parts of the interior of the service module and blew off the cover for bay number 4.

Two and a half hours before re-entry, using a set of special power-up procedures relayed to them by Mission Control in Houston, the Apollo 13 crew brought the command module back to life. As the systems came back on, everyone aboard, in Mission Control, and around the world breathed a sigh of relief.


An hour later, the astronauts also jettisoned the lunar module that had served as their lifeboat. Mission Control radioed, "Farewell, Aquarius, and we thank you."

Jim Lovell later said, "She was a good ship."

apollo 13 recovery
The recovery of the crew of Apollo 13 after the splashdown of what was left of their ship, 17 April 1970. NASA 

The Apollo 13 Command Module splashed down in the South Pacific on April 17 at 1:07 PM (EST), 142 hours and 54 minutes after launch. It came down within sight of the recovery ship, the USS Iwo Jima, who had Lovell, Haise, and Swigert aboard within 45 minutes. They were safe, and NASA had learned valuable lessons about recovering astronauts from dangerous situations. The agency quickly revised procedures for the Apollo 14 mission and the flights that followed.

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Greene, Nick. "Apollo 13: A Mission in Trouble." ThoughtCo, Apr. 5, 2023, thoughtco.com/apollo-13-a-mission-in-trouble-3073470. Greene, Nick. (2023, April 5). Apollo 13: A Mission in Trouble. Retrieved from https://www.thoughtco.com/apollo-13-a-mission-in-trouble-3073470 Greene, Nick. "Apollo 13: A Mission in Trouble." ThoughtCo. https://www.thoughtco.com/apollo-13-a-mission-in-trouble-3073470 (accessed June 7, 2023).