This popped up recently: https://news.ycombinator.com/item?id=19180280

It's about a guy doing similar things, with model rocketry.

It seems though that the resiliency is all due to field tests/ spectacular failure in the latter. (It doesn't detract from the project at all though).

I'm curious whether they applied the same level of scrutiny to the libraries, compilers, and operating system their code used. And firmware.

All of that probably has to be done in order for the AP-101 to be flight certified. As far as I can recall, they wrote their own operating system and didn't rely on any external libraries.

Even when it was new, the AP-101 was part of a family of flight computers that NASA had already been using, and the same is true for the HAL/S compiler used for most of the code.

If you want to explore how it all worked, this SE thread contains some great information and also serves as a good launching point for further research:

https://space.stackexchange.com/questions/19006/what-operati...

People named a computer HAL, and sent it to space??

One of the tools that helped people and other computers into spaces was named, in part, HAL