I'd like to ask if anyone can, in layman's terms, describe the procedure by which the Apollo 11 astronauts were able to get back to their ship?

I ask because the most accessible literature on this subject is exceptionally detailed; what seems lacking is a (relatively) plain-text explanation of how the astronauts got off the moon, and back on their ship to return to earth.

I understand the process of returning to their space-craft was multi-stage, and that it involved a craft known as the "Command/Service Module."

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    $\begingroup$ There is a free computer program called Orbiter that (with the help of third-party mods) allows you to actually simulate the Apollo 11 mission. It's probably pretty difficult for a newbie, though... for a gentler (and more fun) introduction to simulated space travel, I highly recommend the game Kerbal Space Program, which allows for a cruder simulation of the Apollo 11 mission that nonetheless gets the basic idea across. $\endgroup$ Commented Sep 11, 2017 at 4:10

3 Answers 3


The Apollo spacecraft consists of three major parts:

  1. The Command Module (CM), a conical module where the three crew members live during launch from Earth and travel to and from the moon, and which re-enters Earth's atmosphere alone at the end of the trip;

  2. The Service Module (SM), a cylindrical section containing fuel, power, life support, communications, a big rocket engine, and other components;

  3. The Lunar Module (LM), a "spidery-looking" craft which lands on the moon carrying two of the crew members. The LM in turn is made up of a lower section called the descent stage and an upper section, the ascent stage. Both stages land on the moon, and only the ascent stage returns.

The Command and Service Modules remain mated for all but the very last minutes of the mission, so the combination is referred to as the Command/Service Module or CSM.

Diagram showing scale and capacity of the separate Apollo modules with the astronauts each carries

During launch (which I won't detail) the LM is tucked behind the CSM under a conical fairing attached to the Saturn V 3rd stage (the S-IVB). The S-IVB is the part that propels the spacecraft out of low Earth orbit and on its way to the moon.

Schematic of CSM, LM, and S-IVB configuration in LEO

The fairing opens up and the CSM detaches, turns around, and docks to the LM. The front of the CM has a hatch that mates with a hatch on the top of the LM. After docking, the CSM pulls the LM away from the S-IVB. This sequence is called the transposition, docking, and extraction maneuver.

Transposition-docking-extraction maneuver

The S-IVB and spacecraft then go their separate ways and the docked CSM/LM coasts to the moon, over a flight of about 3 days. During the flight to and from the moon, the spacecraft would be rotating about its long axis to maintain even heating from sunlight (this is the PTC, "passive thermal control" mode, sometimes known as the "barbecue roll.").

Photo of lego model of docked CSM and LM

Once the spacecraft reaches the moon, the large engine on the Service Module is used to enter a circular orbit around the moon. The commander and LM pilot enter the LM, undock, and use the engine on the descent stage to reach the surface of the moon. The CM pilot remains in orbit around the moon.

Diagram showing angle, thrust, and altitude at various points before touchdown

The LM stays on the lunar surface for between one and three days, with the commander and LMP generally doing one EVA per day, while the CSM in orbit overhead circles the moon every 2 hours. At the end of the stay, they discard unnecessary equipment (like the big life-support backpacks). To return, the LM ascent stage lifts off, using the descent stage as a launch pad, and arcs into orbit around the moon.

Video from prepositioned camera as ascent stage lifts off

Once in lunar orbit, the ascent stage meets up with the CSM (discussed a bit here), and docks again, and the crew return to the Command Module.

Schematic of docked CSM and LM

The LM ascent stage is discarded, and the CSM fires the big engine again to return to Earth.

The back side of the Command Module sports a thick heat shield; detaching from the Service Module, the CM turns blunt-end-first and hits Earth's atmosphere, using the resistance of the atmosphere to slow down.

Artist's rendition of reentry

And finally deploys parachutes to slow down for a safe splash-down in the ocean.

Picture from above of two out of three parachutes and the capsule at the moment of splashdown

This is of course a rather loose overview of a very complex process! Several Q/As here go into various aspects in more detail, so you might enjoy perusing them.

  • $\begingroup$ Here's an explanation for the LM ascent footage : io9.gizmodo.com/… $\endgroup$ Commented Sep 10, 2017 at 11:47
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    $\begingroup$ Upvoted for the Lego LM/CSM. $\endgroup$
    – DylanSp
    Commented Nov 27, 2017 at 14:48
  • $\begingroup$ @DylanSp If the reason for you to vote up was indeed the photo of Lego spaceship, then I would strongly suggest visiting the help center and getting familiar with what the purpose of voting is. It is not supposed to be a mechanism similar to FB likes, but one of quality control; frivolous upvoting based on irrelevant and superficial features like photo of Lego model, or photo of a cat, are a misuse that messes up with that quality control system, and your comment is an admission to that. $\endgroup$ Commented May 22, 2022 at 16:17
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    $\begingroup$ @user47149 I've been wanting to redo this post with all-Lego images. Getting mighty tempting. $\endgroup$ Commented May 22, 2022 at 21:10
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    $\begingroup$ @user47149 Having frequently commented "upvoted for XYZ", I can assure you that it's almost never the sole reason for an upvote. But the good news is you can correct this injustice by downvoting just 370 more of my answers on this site! $\endgroup$ Commented May 22, 2022 at 21:19

Oh man, I wanted to asnwer this but someone got to it first, and look at all those pictures! Here's the short answer:

So Neil and Buzz are on the surface, and the CSM is the "return pod" in orbit above the moon. The lunar lander could never make it back home on its own. So they launch the lander off the surface of the moon, but just the top half. The bottom is empty and useless, it's just the bare essentials. The top half has enough fuel to get into orbit, no more. Once it's in the same orbit as the CSM with Michael, they physically connect tips, the pointy end of the rocket shaped craft fitting into the concave top of the lander, and snap together like a seatbelt. They open the docking hatch, a small door on top. Neil, Buzz and a whole bunch of moon rocks go into the silver CSM, and they disconnect from the lander. The CSM rockets home and the lander is left to sit.

  • $\begingroup$ Sometimes a nice very short description has its advantages too. $\endgroup$ Commented Nov 29, 2017 at 18:52
  • $\begingroup$ You should have used the words lunar module, descent stage and ascent stage. Being in the same orbit is not enough, the distance should be small to enable rendezvous and docking. Very short could be too short. $\endgroup$
    – Uwe
    Commented Jan 15, 2018 at 10:05

CSM = Command/Service Module, i.e. Command Module (cone) and Service Module (cylinder) joined together. "Command" is where the crew (and commander :-) ) live; "Service" contains the engine which carries astronauts from Earth to Moon and back.

LM = Lunar Module, also known as LEM - Lunar Excursion Model, but this acronym was banned because "excursion on the Moon" did not sound like a serious/scientific activity.

LM is made of two parts: Descent Stage and Ascent Stage.

"Descent Stage" is the four legs.

"Ascent Stage" is the box above the legs.

Descent Stage + Ascent Stage land on the Moon. Then Descent Stage remains on the moon while Ascent Stage fires its engine and raises up to the altitude of CSM orbit; at the same time, AS turns, so the engine can push it also horizontally, increasing its speed until it approximately matches CSM speed.

Final tuning of speed and position of Ascent Stage is made by small engines called thrusters.

Looking at various sources like this one, I made an attempt to draw a more simple infographic of landing and takeoff: infographic of Moon landing and takeoff

Look close, as any detail is important: if you see yellow, there is an engine burning/pushing; blue arrows indicate movement.

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    $\begingroup$ comments associated to downotes would be useful to improve the answer... $\endgroup$
    – jumpjack
    Commented Mar 6, 2020 at 14:15

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