This Week in Rocket History is also about fuel cells: Apollo 13. This is one of the few missions I think most people have heard about, even if they aren’t space enthusiasts. However, there are some questions you may have and interesting things about the mission that you might not know, so This Week in Rocket History will be all about those.

But first a short summary. Apollo 13 launched on April 13, 1970. Three days into the mission one of the liquid oxygen tanks for the fuel cells exploded during a routine maintenance task due to frayed wiring causing a spark. Thanks to an incredible effort, all three astronauts were brought home alive and well, though they had to abandon the planned lunar landing.

The first question you might have: Since the Apollo was only partially towards the Moon, why couldn’t they just do a burn and skip the Moon entirely? The problem was the big main engine on the Apollo service module, the Service Propulsion System, was assumed to be damaged by the explosion in the service module. Even if it was fine, the power needed to run it would have caused them to run out of battery an hour before landing, not a good time for that to happen. So it could not be used, and the mission would have to get back on its free-return trajectory using the Lunar Module’s descent stage to return to Earth. Right before reentry, the astronauts took pictures of the service module and saw that the SPS engine was damaged, confirming that not using it was the right thing to do even if it extended the mission.

Another question: Did they end up doing any science during the mission when they weren’t fighting for their lives? It turns out that, yes, they did do some science, or rather continued some science that was started prior to the explosion. The first science happened before the explosion which changed the course of the mission. 

Apollo 12, the previous mission which did land on the Moon, was hit by lightning twice, throwing off the guidance system and almost resulting in an abort during ascent. Luckily, they fixed that problem and landed on the Moon, but NASA wanted to gather more data on how the rocket experienced electrical disturbances as it traveled through the atmosphere. The disturbances were described as significant and particularly hazardous for launches conducted in barely acceptable weather conditions.

Also building on Apollo 12, the third stage of Apollo 13’s Saturn V rocket was guided towards an impact with the Moon, where seismic instruments placed by Apollo 12’s crew recorded the vibrations through the Moon, helping scientists learn about its composition and structure below the surface. Several other missions continued this practice. The impact of the stage was so powerful that it maxed out the gain on the seismometer despite impacting 117 kilometers away, so for future missions, the gain was reduced.

Another experiment was intended to investigate if a satellite could take useful pictures of clouds from geostationary orbit. All the astronauts did was take eleven pictures of the Earth at precise times. The returned photographs were of “excellent quality”. A satellite called ATS-6 was launched in 1974 to prove the concept, with operational vehicles called Synchronous Meteorological Satellites launching later that year. The series later became known as GOES.

The astronauts did take some time for lunar photography, capturing almost 600 images with a 70-mm Hasselblad camera of both the near and far sides of the moon.

One final experiment was called ‘pilot describing function”, a manual control experiment that was supposed to take place in lunar orbit but was instead done during several other points in the mission. The purpose of this demonstration was to improve a model of how astronauts manually piloted a spacecraft, particularly one where the vehicle flexes around. This flexing was particularly strong on the large Saturn V rocket, impacting how a pilot would respond to it. This couldn’t be completely modeled; engineers needed real data. How a pilot reacts to the flexing while in manual control was useful for improving the simulation for further missions.

Millions of people followed the mission of Apollo 13, providing some much-needed public support for the program which was waning after the first and second landings. In fact, it had the second-highest television viewings after Apollo 11. The Soviets even sent four ships to assist in the rescue efforts. Overall, the mission was a “successful failure” according to commander Jim Lovell.

Despite this great outcome, none of the Apollo 13 astronauts flew in space again. Jim Lovell retired three years later, Jack Swigert got in trouble from a scandal on Apollo 15 and was removed from the flight, and Fred Haise flew the shuttle Enterprise for its Approach and Landing Tests but never flew any of the space-worthy orbiters.

More Information

Apollo 13 Mission (LPI via Internet Archive)

PDF: Evaluation of a Pilot Describing Function Method Applied to the Manual Control Analysis of a Large Flexible Booster (NASA Technical Note)

For Jack Swigert, On His 83rd Birthday (AmericaSpace)

PDF: “Houston, we’ve got a problem.” (NASA)