Leave most of the ship behind
How Did the Astronauts Get Back Off the Moon?
Escaping the Moon is far easier than leaving Earth, so a small rocket on a discarded base was enough.
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Step 1 of 5
Leaving Earth takes an enormous rocket.
Earth's gravity is strong and its atmosphere is thick, so reaching orbit needs a machine hundreds of feet tall that is almost entirely fuel.
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Step 2 of 5
The Moon asks for far less.
Lunar gravity is about a sixth of ours and there is no air at all, so nothing has to be forced through a thick atmosphere on the way up.
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Step 3 of 5
The lander was built in two halves.
The bottom half held the landing legs, the descent engine and its fuel. The top half was a small cabin with its own separate engine.
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Step 4 of 5
The bottom half became the launchpad.
When it was time to leave, the top half simply detached and fired, using the abandoned base underneath as a ready-made platform.
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Step 5 of 5
They only had to reach orbit, not Earth.
The command module was waiting overhead, so the little engine only needed to reach lunar orbit and rendezvous with the ride home.
The ascent engine had a single job and no backup, so it was deliberately made as simple as possible — it worked every time.
The short version
Getting off the Moon needed only a small rocket, because lunar gravity is weak, there is no air, and half the lander stayed behind as a launchpad.
Try it yourself
Find a photo of a lunar module. The gold-wrapped bottom half is still sitting on the Moon in every landing site today.
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