Producing return fuel on Mars
Colonizing Mars
• Use 100 year old technology to produce fuel on Mars.
•  Sabatier Process: water+carbon-dioxide with heat  and a catalyst to produce methane and water.
•   Fresh water discovered recently takes away need for carrying hydrogen.
•  Low risk since fueling occurs in advance of human crew arrival.
CO2 + 4H2 → CH4 + 2H2O