This is amazing! A personal guided walk through the original source code that landed people on the moon. The code arrived as a bound book in a suitcase.

We were looking at what is rumored to be the only remaining paper copy of the Lunar Module’s source code. This is the source code book used by Don Eyles during Apollo missions and for development. Don was responsible for writing code for the Lunar Module . . .

Don [Eyles] graciously took us through a tour of the code where he explained problems with various missions and how they were solved in the code. One example was an issue with LM descent engine’s frequency responses. The manufacturer did not specify an accurate transfer function for the engine’s throttle causing the system to be unstable. Remember, this is a feedback control system, this would be equivalent to not knowing the frequency response in the output circuit of an op-amp.

Don made this interesting note about code performance.

he mentions so many interesting details like the rule of thumb during code development; each page of code takes about 1ms of CPU time.

Imagine if we all had to carry our source code to work each day.

Don asked if I wanted to carry the code back to his car. He was joking, but I took him up on the chance to handle artifact that will be sealed behind glass and displayed at a museum sooner or later. The source code was very heavy, I had to switch arms about three times over a journey of only two city blocks.

Check out the source at for images, a video, and some great links.

You can read more on Tales from the Lunar Module Guidance Computer directly from Don’s page