Fuel

In the context of chemical processes, such as chemical rockets, fuel refers to a reducing agent which can be chemically combined with an oxidizer to release energy. In other contexts, such as nuclear energy, it normally refers to the substance which is used as an energy source. In chemical propulsion, Fuel plus the oxidizer are propellants. In electric and most forms of nuclear propulsion, there are only propellants.

On Mars, fuels could be hydrogen, methane, carbon monoxide and solids, such as aluminium or iron. Oxygen is the most likely oxidizer. The abundance of water on Mars favors hydrogen and methane. Methane could be produces using Water electrolysis and the Sabatier process.

Combination	Specific impulse (s)	Exhaust velocity (m/s)	ratio fuel:oxidizer
Hydrogen + oxygen	388 - 454	3816 - 4462
Methane + oxygen	309 - 368	3034 - 3615
Aluminium + oxygen

Actual ISP and exhaust velocities depend on engine design and external pressure. Exhaust velocities are ideal ones for one atmosphere and near vacuum,