This is a really cool project! The environment is incredible and the flight mechanics feel good. My only issues with the flight were:
1. It's a bit difficult to stop the ship, as it seems to like drifting around a bit when the throttle is set to zero.
2. When the Close! warning appears when hitting a planet's collision box, the ship seems to become "sticky" and requires a decent amount of thrust in a straight upward direction to go anywhere.
I don't mean to level these criticisms as a way to downplay the quality of the work you've done, as making a 3D flight simulator in the GameBoy style is already very impressive under the time constraints of this GameJam! That being said, I feel these things would make the experience a bit smoother if addressed.
Another thing is the lack of audio. With the game being so atmospheric and sandbox-y, I feel the lack of any ambience/music or audio feedback had a negative impact on the experience.
I'm very impressed with this project overall, and you should feel proud about having something like this playable and reasonably polished in such a short time! Excellent work.