The idea is really cool, and I would like to see the concept expanded.
But I think the way it is now is really hard to understand whats going on. For example, I wasn't able to use the planet's configuration to infer how to better play each level. I ended up always gravitating around the center of mass of all planets, instead of going from one orbit to another (which I think would be much more interested).
Maybe it's just a matter of scale. It could work better if planets were smaller and further apart, and the ship moved slower. Maybe and initial velocity to the ship (making it stat already orbiting a planet or something like that) would be interesting too.
Anyway, just some ideas, I don't know if it would actually work well.
Nice job!