How did that tiny, complicated spiky tip on the Apollo modules transform into a usable tunnel for astronauts after they docked? Through a bit of engineering ingenuity still in use today.

When we posted a photo from Apollo 17’s moon landing, Jeyl was understandably confused by the mechanics of how the command and service module hooked into the landing module:

Question. How does that very complicated looking tip turn into a tunnel for the astronauts to float through?

iCowboy provided a thoroughly detailed (and referenced!) answer:

That bit’s called the probe and fitted into a conical recess in the Lunar Module called the drogue. When centred, capture latches on the tip of the probe would click into place - this was known as ‘capture’. The Command Module would then order the probe to be retracted which pulled the two modules together. When fully retracted, twelve docking latches in the CM would click home on the sides of the LM’s docking tunnel to create a solid link.

Then the CM crew member would collapse the probe whilst the LM team did the same for the drogue and then they could go back and forth. There’s a glimpse of this process in Apollo 13 after the ship leaves Earth orbit - as if anyone needs an excuse to watch Apollo 13 again.

And if you want a real page turner - here is the official NASA report on the design of the docking system - enjoy!