Correct me if I'm wrong, but does't acid have Hydrogen in it? If that's so, the von Neumann machine idea could work quite well... But feel free to correct me. I'm honestly not sure. EDIT: Yep. There's Hydrogen in acid, probably a lot of it. Enough in one sulfuric/carbonic acid molecule for a single molecule of water, and there's plenty of oxygen in the upper areas of the atmosphere in CO2. Maybe if the von Neumann machines could directly manipulate molecules, so then chemical reactions could be more easily undone. Perhaps beamed power from orbital arrays?