I was wondering why they are not possible when not in 'bolic orbits. I'm making a few simplifications here: uniform gravity wells, spherical planets, objects in orbit with no pull on their parent body, and so on. As I understand it, at a given point on your orbit some distance from your Ap or Pe (X), there is another point on the orbit the same distance away from the Ap or Pe (Y). X and Y are the same distance from the surface of the planet. Or: Mirroring your orbit through the Ap and Pe, the two points are the same distance from the ground. Is it possible to have an orbit where the two points are not the same height above ground-level? For instance, can an oval orbit have the Ap and Pe 90 degrees apart, instead of 180? I don't think so, but I want to know why.