From Iron Man's Iron Manual Page 19:
Originally, I'd wanted to have a complete suit that would give me a direct boost-to-low-Earth-orbit, then have the suit scoot around on its own power. Finally, re-entry would be through powered descent, avoiding excessive heat buildup. That suit could've been fabricated, but would've been too big to fit through most doors. It also involved some traditional rocket fuels that were incredibly hazardous (red fuming nitric acid, for one). I decided I had to wait for some improvements in engine mass/weight ratios and fuel components.
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