The Apollo spacecraft

This is the second in our series of posts about the Apollo moon missions of the 1960s and 1970s: the first and, so far, the only time humans have been to the moon. In today’s post, we’re looking at the Apollo spacecraft, the roles of the people aboard and how the Apollo astronauts were able to return safely to Earth.

For more about the Apollo moon missions, take a look at the first post in our Apollo series, which talks about how many people have been to the moon and how they survived on its surface.

Components of the Apollo spacecraft

The Apollo spacecraft consisted of three main components: the command module, the service module and the lunar module. The service module was attached to the back of the command module for most of the mission, so these two modules essentially functioned as a single module: the command and service module.

The command module was where the crew lived, ate and slept in space. It was a little cramped, with only six cubic metres of living space to accommodate three people for the approximately three days it took to reach the moon, but being able to float enabled the crew to make full use of that space. To make sure they didn’t float around while sleeping, the crew slept in ‘sleep restraints’, which were essentially sleeping bags tethered in place.

The service module, attached to the back of the command module, provided essentials such as fuel, oxygen and electricity. It also contained the main propulsion system. If something went wrong in the service module, you were in trouble, but it might be possible to recover with some ingenuity; more on that when we reach Apollo 13.

The lunar module, also called the lunar lander, was the part of the spacecraft that would actually land on the moon. It consisted of two main sections: the descent stage, which was designed to land safely on the moon’s surface, and, on top of that stage, the ascent stage, which contained the flight instruments and crew cabin.

Below, you can see a picture of the lunar module sitting on the moon during Apollo 14. The descent stage is the part with legs, covered with crinkly golden material. This material reflects heat from the sun to prevent the spacecraft from overheating; you can read more about this in our post on the problems satellites face.

Image: NASA

Something you might notice about the lunar module is that it doesn’t look like traditional ideas of a rocket or spaceship; it’s not sleek and it’s not aerodynamic. Simply put, this is because it doesn’t need to be. It doesn’t detach from the command module and start flying by itself until it’s in the vacuum of space, where being aerodynamic isn’t a concern. The purpose of an aerodynamic design is to reduce air resistance, but there’s no air resistance in a vacuum.

The lunar module’s descent stage acted as a launch pad for the ascent stage when leaving the moon, so the astronauts would take off in the ascent stage to return to the service module, leaving the descent stage behind. Again, as the moon’s atmosphere is extremely thin, the ascent stage doesn’t need to be aerodynamic in order to take off.

The lunar module descent stages from the six Apollo moon landings are still on the moon to this day.

The crew on Apollo missions

Each crewed Apollo mission to land on the moon carried three astronauts: the commander, the lunar module pilot and the command module pilot. However, only the commander and lunar module pilot would actually visit the moon’s surface in the lunar module.

  • As you might expect, the commander was in overall charge of the mission. They were responsible for looking after the spacecraft and the crew, and would also perform some manual flying tasks; more on that in a moment.
  • From the name, you might expect the lunar module pilot to be in charge of the lunar module’s manual flight controls, but in fact the person responsible for manually flying the lunar module was the commander. The lunar module pilot managed the flight computer, which was responsible for most of the lunar module’s journey through space. When the commander took over control for delicate operations such as landing, the lunar module pilot would monitor the instruments and keep the commander informed of anything they might need to know for navigation.
  • The command module pilot would remain in the command module, orbiting the moon and making observations, while the commander and lunar module pilot went down to the moon’s surface in the lunar module. When the lunar module returned, the command module pilot would dock with it, allowing the commander and lunar module pilot to re-enter the command module. As the command module pilot wouldn’t step onto the moon, their role might seem less flashy than the roles of their fellow crew members, but they ranked higher than the lunar module pilot and played a crucial part in ensuring everyone could get home safely.

How did Apollo missions come back to Earth?

The command module was the only part of the Apollo spacecraft that would return to Earth, so it was designed to survive falling through the atmosphere and protect the astronauts inside, rather than burning up due to air friction. It also had parachutes to slow its fall, allowing the crew to land safely in the ocean, where the command module would float until the astronauts could be picked up by ship.

Decades later, in 2022, Artemis I’s Orion spacecraft landed in a similar way: the crew module deployed its parachutes, came down in the Pacific Ocean and floated until it was retrieved by ship. However, Orion came back into the atmosphere in a slightly different way, using a skip entry. This means the spacecraft essentially dipped into the atmosphere and then bounced off it before coming back down, like a skipping stone, slowing its acceleration and giving it more control over where it would land.

An interesting element of the Apollo command module, mentioned in NASA’s Command Module Overview, is that it’s designed so it can be returned to Earth even by a single astronaut. In other words, the command module’s design takes into account the possibility that, for example, the astronauts on the moon might be unable to return for some reason. In that case, the command module pilot would still be able to get back to Earth, rather than being stranded in lunar orbit. Fortunately, this functionality was never required; all the Apollo astronauts who visited the moon’s surface were able to return safely to the command module and come back to Earth.

In our later Apollo posts, we’ll be looking in more detail at individual crewed Apollo missions, starting with Apollo 7 and 8. These early missions laid crucial groundwork for the later moon landings.

Cover image: USSR Academy of Sciences
Lunar module image: NASA

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