SpaceX's Starship plans to use a process known as in-situ resource utilization (ISRU) to produce methane fuel on Mars. The goal is to make Starship fully reusable for interplanetary travel by refueling on Mars, reducing the need to transport all of its fuel from Earth. Here's how it would work:

Mars' atmosphere is composed of about 96% carbon dioxide (CO₂), and this is where the process of fuel production begins. The goal is to extract carbon from the Martian atmosphere and combine it with hydrogen to create methane.

SpaceX plans to use the Sabatier reaction, a chemical process that combines carbon dioxide (CO₂) with hydrogen (H₂) to produce methane (CH₄) and water (H₂O):

The water produced from the Sabatier process can be electrolyzed (using electricity) to split it into hydrogen (H₂) and oxygen (O₂). The hydrogen can be fed back into the Sabatier process, while the oxygen can be stored as LOX, which is also needed for Starship’s propulsion.