Hi, I'm reading The Martian by Andy Weir (fantastic book). A character, describing how a Mars mission works, says of fueling their ascent vehicle: "Through a neat set of chemical reactions with the Martian atmosphere, for every kilogram of hydrogen you bring to Mars, you can make thirteen kilograms of fuel. It's a slow process, though. It takes twenty-four months to fill the tank." Usually I don't concern myself much with the scientific accuracy of particulars in SciFi, but this author took great pains to be accurate so I don't believe he pulled those numbers out of a hat. I'm assuming by "Martian atmosphere" he means CO2, the fact that they're using hydrogen makes me think they're creating hydrocarbons. Assuming they use product oxygen as fuel as well as the hydrocarbons (would that work?? I really know nothing of this stuff), I can't figure out what "neat set of chemical reactions" gets the Mars mission nearly 13kg of fuel for every 1kg of hydrogen. Does anyone have any ideas? Thanks!