Even inside the gravity we'll it doesn't matter; the planet only matters as a reference frame. Basically, a rocket starts out with some mass and uses combustio

Even inside the gravity we'll it doesn't matter; the planet only matters as a reference frame. Basically, a rocket starts out with some mass and uses combustion to produce energy, that energy is imparted to the ship as kinetic energy in the form of an increase in velocity (relative to something) AND as kinetic energy in the propellant going backwards. If you're going slowly, and accelerate a little - say 1 m/s up by 1 m/s to 2 m/s, kinetic energy goes from ke = Mv^2 / 2 = 1M to 4M. Your propellant probably has a lot of kinetic energy, moving at ~2500m/s...backwards. If you start at 10 m/s, and go to 11 m/s, you have 100->121M, an increase of 21 instead of 3. But your propellant is only going backwards at 2400m/s instead of 2499m/s.