My example is meant to be assembled and launched from deep space, with no gravity, no air resistance, and an environment where things like thrust/weight ratios are irrelevant (you just burn for a longer period). And of course, it doesn't have to stop when it gets there, or turn around and come home, and stop again when it gets back.

The Starflight Handbook has an excellent discussion of how the mass ratio varies from stage to stage and how it should be optimized for overall performance in a staged rocket launched from earth; and how factors like fuel density must be taken into account. I'm learning a lot.

I'm aware of those factors, I was just trying to show how even the the ideal case was so damned hard.