Fig. 1. Rocket propellant production on Mars via in situ resource utilization (ISRU).

a Proposed biotechnology-enabled ISRU (bio-ISRU) takes into account Martian conditions to produce a Mars-specific propellant, 2,3-butanediol (2,3-BDO). Using sunlight, carbon dioxide (CO₂), and water, cyanobacteria (algae) are grown as a feedstock for an engineered microbe that produces 2,3-BDO. Cyanobacteria cultivation evolves oxygen for spacecraft launches or other aspects of Martian exploration. b Proposed chemical ISRU strategies focus on the use of methane (CH₄) as a propellant. The most examined chemical processes that can be part of a chemical ISRU strategy². (1) O₂ only strategy. SOCE: solid oxide CO₂ electrolysis. (2) H₂ only strategy. (3) Complete strategy. Key chemical reactions: SOCE, Sabatier reaction, and water electrolysis. Martian resources in red. Chemicals produced on Mars in blue. Chemical shipped from Earth in black. Details on proposed biological and chemical ISRU strategies can be found in Table 1.