In-situ-produced methane and methane/carbon monoxide mixtures for return propulsion from Mars

A summary of chemical process routes to produce oxygen, water, methane, carbon monoxide, and other fuels is provided. A conceptual design of a plant for use on a robotic Mars sample return mission is presented that predicts that propellant sufficient for a 500-kg return vehicle (dry) can be produced by a plant having a mass of 2.2 metric tons (MT) and using less than 6 kW. The mass includes the imported hydrogen and the power system. This is lower than the 3.34 mT of propellant it replaces, and provides for a much lower Earth launch mass. This design is based on conservative assumptions and existing hardware. Twice the required amount of hydrogen is imported to simplify the processing and to eliminate the need for a separate means of producing the needed amount of oxygen. The volume of the imported hydrogen does have a significant negative impact. Alternatives to pure methane as a fuel are presented. Mixtures of CO and CH sub(4) are considered, with their physical properties and propellant performance predicted. The use of such mixtures in place of pure CH sub(4) in the same sample return mission is analyzed and shown to be competitive.