On April 11, 1970, at the Kennedy Space Center, the 6.2 million pound Saturn V rocket ignited its five F-1 rocket engines, producing millions of pounds of thrust, rumbling the ground as thousands of spectators watched afar. Its destination? The Moon. More specifically, the Fra Mauro region — an area not explored by the two previous moon landings. The mission crew was instructed by the staff and other astronauts at the Houston Mission Control Center.  On the way into space, the fifth engine  of the Saturn V shut down, due to a fluid dynamics phenomenon called pogo oscillation. This was not critical to the mission, as the rocket still had four perfectly functional engines. However, it was the first problem of many surrounding the infamous mission.

The Apollo spacecraft was made up of two ships: the Lunar and Command Modules (LM & CM). The CM was where the astronauts were during most of the mission, including launch, and it was designed to do most of the heavy lifting — its main objectives were to perform the retrograde braking engine ignition (called a burn) to capture in the Moon’s orbit, and perform the ejection burn back to Earth. The objective of the LM was simple: carry two of the three astronauts to land on the Moon’s surface. The LM later had another important objective: to rendez-vous (meet up) in Lunar orbit, and dock with the CM, as the LM did not have enough fuel to return back to earth on its own. A few hours after the Saturn V exhausted all of its fuel completing the burn to the Moon, called the Trans-Lunar Injection, the CM Pilot would detach from the Saturn V and rotate 180 degrees, to attach to the LM, which was stored directly underneath the CM’s engine.

There were three astronauts on board: seasoned astronaut and mission commander Jim Lovell, Fred Haise, and Jack Swigert. The CM was nicknamed Aquarius, after the constellation, and the LM was nicknamed Odyssey, after the journey the three astronauts would be making. The crew was expected to arrive in the Lunar Sphere of Influence (SOI) roughly 3 days after launch, where the Moon’s gravity exceeds the force of Earth’s. 30 hours into the mission, a correction burn was performed by the CM, which changed the free-return trajectory orbit to a hybrid trajectory. This article is not about orbital mechanics, but this maneuver dramatically increased the stakes of the mission. A free-return trajectory is an orbital trajectory in which the Apollo spacecraft would have returned to Earth on its own if the CM fails to capture in Lunar orbit. If there was an error in the mission, and a burn could not be completed, the 3 men would drift off into space, eventually lose connection with Houston, and starve to death.

56 hours into the mission, on April 13, 1970, 50 years ago to the day of this article being written, a loud explosion was heard by the astronauts.  95 seconds earlier, Swigert had engaged a switch to “stir” the liquid oxygen tank, to equalize temperature and make pressure readings more accurate. This was very important, as the liquid oxygen is combined with fuel during an engine burn to increase efficiency and thrust. If the pressure was too high, the tank and engine were at risk of exploding. The astronauts heard a “pretty large bang”.  All three of them were initially confused. The CM’s control thrust nozzles began to fire to keep the ship from spinning endlessly. The electrical gauges and systems began to malfunction, along with a suite of other problems.

Jack Swigert broke the news to Houston: “Houston, we’ve had a problem here.” The film rendition of the event, Apollo 13 (1995), actually depicts Jim Lovell (Tom Hanks) breaking the news to Houston, and it’s slightly modified: “Houston, we have a problem.” The crew now had no working waste disposal systems. The explosion had damaged most of the ship’s fuel cells, which slowly use the CM’s fuel to produce electricity. It also creates chemically pure water as a byproduct. This meant that only essential power-consuming devices would be left on — these were mainly communication devices to communicate with Houston. The decision was made to keep all 3 astronauts in the perfectly functional LM, using it as a lifeboat while the main ship was crippled. However, a serious problem soon emerged. The LM was only designed for 2 people — and the carbon dioxide levels began to rapidly increase. There were plenty of spare carbon dioxide filters for the CM, but they didn’t fit. The CM’s filters were a large square shape and the LM’s filters were a small cylindrical shape. Houston now had a very critical task: figure out a way to make a square peg fit in a round hole. They needed to do it very fast, otherwise the astronauts would suffocate and die. Luckily, there was a solution. It involved an apparatus made from plastic bags, the filter itself, and lots of duct tape — referred to as “grey tape” at NASA.

The three men were extremely cold that night, as there was no electricity for heating. They watched the Moon and its giant craters and mountains slip by them through the small LM windows. Apollo 13 was Jim Lovell’s last spaceflight and second Apollo mission. He was supposed to walk on the Moon, but he never did. The crew was now on its way to earth via the slingshot maneuver around the Moon. They would be back to the Earth by April 17th, 4 days after the incident occurred. Eventually, it was time for atmospheric re-entry. The process of re-entering the atmosphere created an extreme amount of heat because of friction between the spacecraft and the air. The astronauts climbed back into the CM, and ejected both the now useless LM and the exploded fuel tank. Everything besides the CM would burn up in the atmosphere. The CM pointed retrograde — against the direction of its velocity — to point the heat shield towards the atmosphere. The spacecraft would be re-entering the atmosphere at roughly 18,000 miles an hour, which was hot enough to turn the air around it into plasma, ridding it of its electrons. This created a magnetic field around the craft, which would temporarily block communications with Houston.

The expected communications “blackout” was four and a half minutes long. After 5 minutes, Houston still had no word from Apollo 13. People began to assume the worst — the fuel tank explosion could have damaged the heat shield, which would lead to the deaths of the three astronauts. More and more seconds passed with no word. Every broadcasting company was reporting on Apollo 13. The entirety of America was on their seats. After about 6 minutes, contact was made with the CM. The parachutes had deployed successfully, and the three astronauts were safe, and Americans were relieved.

NASA later referred to the mission as a “successful failure”.




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