Fig. 2. Martian rocket propellant design.

a Relationship between increasing the number of oxygen and carbon atoms in the propellants to the mass of oxygen needed for complete combustion, i.e. oxygen/propellant ratio (O/P ratio). Increasing the number of oxygen atoms in the propellant reduces the mass of external oxygen needed for full combustion. b Relationship between increasing the number of oxygen and carbon atoms in the propellant to its lower heating value (LHV). Increasing the number of oxygen atoms in the propellant reduces its LHV. c Propellant relevant properties for Rocket Propellant-1 (RP-1), used for spacecraft launch from Earth, methane, and proposed Martian rocket propellants: 1,2-ethanediol, 1,3-propanediol, 1,3-butanediol, and 2,3-butanediol. Theoretical specific impulses (I_sp) were calculated using Eq. (3). Mass of propellant required was calculated using the ideal rocket equation (Eq. (4)). d Short-chain diol metabolic pathways from glucose. Both 1,2-propanediol and 1,3-butanediol require excess NADH. Carbon dioxide evolved: red. NADH consumed: purple. Name of short-chain diols: blue. Source data underlying Fig. 2c are provided as a Source Data file.