[davrosthedalek]

Just to point out here what's different between "space" and "not space": "Space" assumes no "height control",i.e. ways to exert force "down or up" along the earth-object direction. That's obviously not true for a plane. If you can exert force in that direction, you can change speed and keep the shape of the trajectory around earth constant.

[falcor84]

Wait, why wouldn't an orbiting satellite not be able to apply its thrusters "down"?

[davrosthedalek]

They could. The point is that if you allow for that (and it they would need to be constant on), the more speed -> either higher orbit or more elliptic orbit doesn't hold. But no satellite has enough fuel to keep its thrusters on indefinitely.