Just as a note, Space Engineers has a mod that accounts for fuel in the tanks and also various orbital mods. If one feels inclined to try it for themselves ;)
as someone who absolutely loves SE -- please don't.
the orbital and planetary mechanics kind of suck. They're meant to provide a decent 'arcade realism' for the sake of player/player interactions and pvp/pve.
if you want to experience fuel slosh/weight during a vertical ascent/descent go with kerbal. It models a lot of that stuff without mods -- and mods can make the model even more accurate.
