Alam et al. proposed a concept for production of the required amounts of methane based on available experimental and simulated data. The concept was assessed at a single operation point only and assumes experimentally proven CO2 conversions of 60% and CH4 selectivities of 99.5% While the work clearly demonstrates the general feasibility of methane production via ISRU, the underlying model is too simple to evaluate the impact of operation conditions on the yield and purity of the products. The oversimplification also holds for the separation units required to provide sufficiently pure methane. In a recent contribution Romegialli et al. performed a simulation study with Aspen Plus to estimate the feasibility of ISRU propellant mass production. The authors included the carbon capture from the Martian atmosphere, the water extraction from martian soil, the methanation and subsequent product purification and propellant storage in their Aspen model . They state that the total mass required for the resulting plant design is less than 23% of the 100 metric tons transport capacity of the starship . Thus, ISRU propellant production should be theoretically possible with the suggested plant design. While the authors used a Ni/Al2O3 catalyst with LHHW-rate expression for methanation over Ni-catalysts to model the Sabatier reactor. The effect of the H2 recycle and the overstoichiometric H2/CO2 ratio are not evaluated in further detail. Furthermore, Nasa's research for ISRU propellant production focuses on Ru-based catalysts , due to the higher activity and stability compared to Ni-catalysts .