The planets is a circle. I am currently using a spline mesh curved around the radius. The camera is aligned to have it’s down vector always aligned with the gravity vector so moving the ship left and right will move you along the surface.
Gravity is done with a custom physics volume.
I wanted the illusion of moving on a flat plane but in reality you are going around the planet. When you leave the planet’s gravity the camera flips back to the solar system’s up direction.