I was just reading about the chamber pressure in SpaceX's raptor engines. Since I was a little hazy on the subject of rocket engine chamber pressures, I went on a web search to see what I could find. And I stumbled on this website:

http://www.braeunig.us/space/index_top.htm

It's technical, but not too technical. Its author says that he was shooting for something between layman's popularizations and graduate-level textbooks. So you get the mathematics necessary to calculate things, but the mathematics seems to stop at freshman level calculus. Even that's kind of minimal, so readers should be able to understand the concepts and do more basic calculations with advanced high school math.

But don't expect it to be easy. It's rocket science.

http://www.braeunig.us/space/index_top.htm

It's technical, but not too technical. Its author says that he was shooting for something between layman's popularizations and graduate-level textbooks. So you get the mathematics necessary to calculate things, but the mathematics seems to stop at freshman level calculus. Even that's kind of minimal, so readers should be able to understand the concepts and do more basic calculations with advanced high school math.

But don't expect it to be easy. It's rocket science.