SpaceX Starship
SpaceX thinks sending humans to Mars needs many steps. First, some Starships might carry many important things to Mars' surface. Inside them are fertilizer factories, propellant factories, and building materials. The propellant factory takes in carbon dioxide from Mars's air and hydrogen from the ice below. Then, the factory uses the Sabatier reaction. Hydrogen reacts with carbon dioxide with hydrogen to create methane and oxygen. Methane and oxygen are Starship's propellants. Filled up with the factory's methane and oxygen, Starship can return from Mars back to Earth. Building materials are used to make domes. They protect farmland from Mars's weather and atmosphere.