This one isn’t super well known, but for small projects I really like raylib, and raygui. It gets impractical for complex GUIs, but it does make it really easy to quickly start something from scratch.

Edited my comment to fix, thanks!

This is less of a source and more like a compilation of resources, but for anything spacecraft related I can always recommend Atomic Rockets. For this specifically, the page on Heat Radiators.

amateur radio was illegal to encrypt

Amateur radio is still illegal to encrypt (with some exceptions for controlling satelites), because private communication isn’t the point of amateur radio.

Besides, (in most countries) there are some topics that are illegal to talk over amateur radio about, mainly stuff like politics and religion. You’re also not allowed to offer telecommunication services (i.e. pass messages on for others). Enforcing those sorts of laws would be impossible with encryption.

But to answer your question: I think we probably wouldn’t have had an internet. Authoritarian regimes thrive on stability and maintaining the status quo, I think someone high up would have quickly decided that developing that sort of tech is too risky.