I am a math grad student who has really got interested in spacecraft control and navigation. Like a lot of people, I have been playing too much ksp and gotten interested in the mathematics of spacecraft navigation and control. For fun, I derived some basic motion and control equations from Hamilton systems and what little I remember about freshman physics. Now I want to expand on my knowledge on the field. Any books or other resource suggestions on where to start with a strong mathematical background (but little space background) would be really helpful. Also, I would really prefer cheaper books like dover since this is pretty much a hobby right now.