the answer to that, would be 2x generation of power, because heavy water is 2h02 or D20. More hydrogen to burn, thus more powerfull reaction. and why would this be too hard to implement? Just use the hardpoint connector type solution, where there is hardpoints on the hubs, and disconnector solution on the other end. You got allready exploding separators for the tanks, both mechanical and slightly explosive one. Its down to just having more parts, that has combined elements of previous ones. Iwe now tried some addons, and they seem to allready be doing this, so dont tell it is impossible. Just ran onto the unipropellant, and got no cliue what those does, seems there are no engines for those tanks yet. There has been discussions on use of no airflow airjets, but there are some that uses canned air. Thus air generating modules suggestion. But yes, i can see how this could be done, if nt by game developers, then some addon makers. This is a technology we allready use, i have heard there is currently a several hydrogen generators onboard of the international station on ESA spacestation. What are they doing? generating power, heat and water for plantation on the station. This is all what will be needed in order to create everything needed for life support in space. Think about it: power can be used to sustain UV lamps, that powers plantation, it generates heat that its needed so everything wont freeze over. Plants scrub air from carbon dioxide 7x better than mechanical scrubbers, water released from these generators giwe pure drinking water to kerbonausts and plants...