In my study project, I learned thoroughly how to solve different two body problems (initial value, boundary value, closest approach) and wrote a C library [0] that's got all the orbital mechanics code you need to write your own Kerbal Space Program clone (but I don't intend to do that). During the process, I read 3-4 books and an inch thick pile of research papers.

[0] https://github.com/rikusalminen/twobody