Reid: Everybody's heard of Neil Armstrong and Buzz Aldrin, the first humans to walk on the moon. But do you recognize the name Michael Collins?

He was the command module pilot on the Apollo 11 mission. While the mission commander and the lunar module pilot went down to the surface, the command module pilots of the Apollo program stayed in orbit around the moon. All alone.

But why bring a third person along? Without him Neil and Buzz could have brought back an extra Mike-sized pile of moon rocks for scientists to study. Well, the command module pilots were basically the drummers of the Apollo rock band. Without their piloting skills, the missions wouldn't have succeeded.

The three-man Apollo mission design is familiar to us now, but it wasn't the only option NASA engineers came up with in the early 1960's. One strategy was called a direct descent: basically a rocket would launch from Earth, fly to the moon, land on it, then take off again when it was time to leave. But this approach would have needed a lot of fuel and if you've seen the SpaceX attempts to land their rockets on a drone ship, you know how difficult a vertical landing can be.

So eventually the idea NASA settled on for the Apollo missions was called a lunar orbit rendezvous. A spacecraft called the command service module or CSM orbited the moon while a smaller ship called the lunar module or LM went down to the surface. Later the LM met up and docked with the CSM in orbit-- that's the rendezvous--and together they flew back to earth.

For this mission design to work, NASA needed at least one person in each spacecraft and each of the astronauts had a specialized job to perform. Commanders like Neil Armstrong were in charge of the whole show and controlled the lunar module on the way down to the moon's surface. This meant the lunar module pilots, like Buzz Aldrin, weren't actually piloting but they did relay important navigation information to the commander during the descent.

Plus, someone had to stay in the orbiting CSM: the command module pilot. And they had their hands full the entire mission! Soon after launch they had to perform the transposition docking and extraction maneuver: they flipped the CSM around and carefully docked with the LM stored in the third stage of the Saturn V, to extract it from the rocket. The command module pilot's other big job came during the rendezvous, since they were responsible for the final docking between the two modules.

Because of these complicated maneuvers, the most highly trained Air Force and Navy pilots in the pool of astronauts were assigned to the role, like Mike Collins and Dick Gordon, the CMP on Apollo 12. In fact, when the Apollo program was designed in the early 1960's, no one had ever done a rendezvous in space. In order to get ready for the moon missions, both Collins and Gordon practiced it on Gemini X and Gemini XI, respectively, by docking and undocking with an unmanned rocket called Agena in Earth's orbit.

So, they were chosen for being amazing pilots, but these guys didn't just sit around doing nothing while their fellow crew members were on the surface of the moon. NASA had these astronauts make observations or relay instructions down to the lunar surface. Later Apollo missions were even designed with a more scientific focus, especially for the command module pilots.

On Apollo 14, for example, Stu Roosa took 950 pictures from orbit and found evidence of ancient volcanic activity on the far side of the Moon.

But a camera couldn't always be used to document the geology because of the huge contrast between light and dark regions on the surface. So starting with Apollo 15, Alfred Worden Ken Mattingly, and Ron Evans were specially trained to identify geologic features from orbit by sight. Their descriptions gave scientists a better understanding of the craters, mountains and plains on the lunar surface, so we could see how it changed over time and which features were older than others.

Now, getting to observe the moon up close isn't quite the same as setting foot on its surface, but Mike Collins has said he was pleased to have a seat on the Apollo 11 anyway, even if it's arguably wasn't the best one.

And even though he might be forgotten sometimes, his legacy lives on at the very least through one iconic photograph: it's a shot of the lunar module just before the rendezvous with the moon and the earth in the background. Every single player in the Apollo program and really every particle of humanity is somewhere in that image... except for one. Because it's a photo only a command module pilot could take.

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