This really wouldn't help as much as you'd think. For a high-gravity planet, the atmosphere is mostly a trivial problem compared to gravity, and the gravity at

This really wouldn't help as much as you'd think. For a high-gravity planet, the atmosphere is mostly a trivial problem compared to gravity, and the gravity at the top of the atmosphere would be barely lower than it is on the surface. A much more realistic and useful option is to just go air-breathing nuclear, and use the atmosphere for reaction mass.