Proxima Station: How to Make Rocket Fuel on Mars
Proxima, latin, nearest
"The fuel on board a Starship rocket heading to Mars will only be enough for a one-way journey. The rocket will need to stop at a gas station on Mars and the fuel will be homemade on the red planet.”
What is needed to make Martian fuel
The Starship uses Raptor engines, which are fuelled by methane and liquid oxygen (LOX) in a ratio of 1:3.75
Methane is an attractive option for Martian fuel because it is relatively easy to produce and store, requires less energy to produce than other types of rocket fuel, and can be used for both rocket propulsion and power generation for habitats.
Methane is also a raw material for making: antifreeze, disinfectants, preservatives, agrochemicals, fertilizers, explosives, plastics, and pharmaceuticals.
To produce methane, carbon dioxide is taken from the air on Mars and mixed with hydrogen found in Martian ice.
Liquid oxygen is created by separating (electrolysis) the ice (H2O) into hydrogen and oxygen.
A fleet of 10 uncrewed cargo Starships will be the first to land on Mars, with one Starship carrying the equipment to establish a fuel production plant.
Steps for producing homemade rocket fuel on Mars
Carbon capture towers capture CO2 from the air
Ice water is harvested by robots
Electrolysis - ice (H2O) is seperated into hydrogen and oxygen
Sabatier – carbon dioxide from the air (CO2) and hydrogen (4H2) are combined to produce methane fuel (CH4)
Liquification – The methane fuel and oxygen are turned into liquid form for cryo-storage
Storage – The Proxima Gas Station
Harvesting Robots
Capturing Carbon from the Atmosphere
The Atmosphere on Mars is made up of about 95% carbon dioxide (CO2).
A process called "direct air capture" (DAC), which is also used on Earth, filters the Martian air through a chemical solution. The solution captures the CO2, separating it from the air.
Inventory: Carbon Dioxide
Harvesting Ice Water
Robots use ‘subsurface radars’ to map areas of buried ice deposits. They analyse samples to determine their purity and suitability for fuel production. The ice is then extracted through drilling or subsurface mining.
One method of extraction is ‘sublimation’. Ice is heated, turning directly from solid to gas, bypassing the liquid phase. A device called a ‘sublimation drill’ melts through the ice layers and releases the water vapor for collection.
Inventory: Carbon Dioxide, Ice Water
The Production Plant
Electrolysis: Separating H2O
The next step is to create hydrogen. This is done by taking the ice water (H2O) and separating the hydrogen and oxygen through a process called electrolysis.
An electrical current is passed through the water, and two electrodes attract the oxygen and hydrogen apart to be collected as gases.
Inventory: Carbon Dioxide, Hydrogen, Oxygen
Sabatier: Creating Methane Rocket Fuel
Once carbon dioxide (CO2) and hydrogen (H2) have been collected, the Sabatier reaction can be carried out in a reactor to combine the two to produce methane fuel (CH4).
Water (H2O) is produced as a by-product.
CO2 (carbon dioxide from the air) + 4H2 (hydrogen from the ice) → CH4 (methane fuel) + 2H2O (water)
The Sabatier reaction takes place at high temperatures (around 200-400C, 392-752F) and pressures, producing methane in gaseous form.
To cryo-store and use the methane and oxygen (from electrolysis) as fuel, it needs to be liquified.
Liquifying the Goods for Storage
Methane can be turned into a liquid through a process called liquefaction. This process involves cooling the methane to a temperature where it becomes a liquid, around -161°C, -257.8F.
One method is through a cryogenic cooling system, which uses liquid nitrogen or helium to cool the methane. Once cooled, the liquid methane can be stored in insulated tanks designed to withstand the harsh conditions on Mars.
Oxygen is cooled and compressed until it liquefies at -183°C, -297.4F.
Liquefying methane and oxygen is energy-intensive, and the energy required to cool them must be generated from a sustainable energy source, such as a solar field.
Storage – Proxima Station
There are several benefits to storing methane as a liquid instead of a gas on Mars:
Increased energy density: Liquid methane is denser than gas, which means less space is needed to store the same amount of fuel, making it more efficient for storage and transportation.
Easier to handle and improved safety: Liquid methane is less volatile than compressed gas, reducing the risk of explosions or leaks. It is also less flammable.
Lower storage and transport costs: Liquid methane can be stored in insulated tanks, which are less expensive and simpler to manufacture than high-pressure gas tanks.
SpaceX In-Situ Propellant
Mars Fuel Production, SpaceX, 2016
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