Once finalised, I should probably upload the code for the orbit stuff somewhere. It's not hard per se, just a fair bit of equations to implement:

https://en.wikipedia.org/wiki/Kepler_orbit

The most annoying bit is probably drawing them properly. I use a polyline in Godot; as you can see this default approach tends to produce very ugly looking, segmented orbits for very eccentric ones, but I just managed to fix it with a trick (you won't see this in the game uploaded for the jam, of course, since I can't post updates until the voting ends).

Agree on the propeller. Part of why I didn't do it is that the obvious solution would have been a particle effect, and I was worried that this would be a performance issue since I already use those for explosions and those tend to slow the game down... but I just found out it was actually probably orbital calculations that did that (the code is very inefficient right now!) so sure, I should be able to add that without any issues.

Thanks for the comment! Yes, I know how to do the HTML5 version :), I just got sort of demotivated about this as a lot of things didn't go quite as well as I was hoping. There's also some bugs I can't pin down in the physics and orbits drawing. I never made a third build, so you could say I've basically dropped out of the Jam, for what concerns me :D. 

I don't want to drop the idea altogether, but I'll pick it up later probably. Just am not satisfied with where I could bring it in just 9 hours.