For comparison, Zubrin et al. developed the integrated Mars in situ propellant production system (IMISPPS) and reported the mass of the optimized system of 54 kg for a O2:CH4 production rate of 1 kg/d, which corresponds to 0.33 kg/d CH4 . For experimental tests, the authors employed 130 g of reverse water-gas shift catalyst and 0.5 g of 0.5 wt.-% Ru/Al2O3 methanation catalyst and operated the reactor at 400 °C. We achieve a specific methane production rate directly from CO2 of about 6 µmol g - 1 s -1 at 200 °C (see Table , Table ), which corresponds to 6.9 kg kg -1 d -1 (methane per catalyst basis)