I took a few courses of astronomy at Helsinki university, but mostly I've studied on my own. I did watch Leonard Susskind's lectures on classical mechanics but did not any online courses.
Check out my related project, it contains all the orbital mechanics you need to write your own Kerbal Space Program clone (look around in the branches):
https://github.com/rikusalminen/twobody
Check out my related project, it contains all the orbital mechanics you need to write your own Kerbal Space Program clone (look around in the branches): https://github.com/rikusalminen/twobody