Humanity is building powerful rockets like the SpaceX BFR and NASA Space Launch System that can take a payload far away from Earth. However, making the return trip means you have to lug a lot more fuel with you. Efforts to send humans to Mars in the coming decades would be helped if we could make fuel on the red planet. That may be more feasible than we thought. NASA team lead Kurt Leucht has explained how the agency might use Martian soil to make the fuel astronauts need to get home after a mission.
According to Leucht, it’s best to make whatever you can at the destination because of the inescapable realities of physics. The “gear-ratio” for Mars is 226:1, meaning every kilogram of material you send requires a rocket to burn 225 kilograms of fuel. That’s true for any material — water, food, scientific equipment, people, and even reserve fuel for the return trip. With payloads being so expensive, it makes sense to produce whatever you can on Mars. This is known as in situ resource utilization (ISRU).
If you’re determined to make fuel on Mars, you’ll want to find a source of water. Water molecules contain hydrogen and oxygen, which you can split up to make fuel. You won’t come across many large chunks of water ice on Mars (the poles are mostly carbon dioxide ice), but the soil might have more than enough. Under the dusty surface layer, many regions of Mars have significant deposits of water. Leucht notes that gypsum sand dunes in the lower latitudes are about 8 percent water.
NASA calls the process of making fuel from Martian regolith “dust-to-thrust,” and it’s working on robots that can potentially do all the heavy lifting before humans even land on Mars. The Regolith Advanced Surface Systems Operations Robot (RASSOR) uses two opposing bucket drums with multiple digging scoops to gather up material as the wheels drive the robot slowly forward. NASA designed RASSOR to operate in a low-gravity environment — the drums spin in opposite direction to cancel out most of the digging force.
Collecting the regolith is just the start. NASA plans to build an autonomous chemical refinery that can process the soil to extract water and split it with an electrolyzer into hydrogen and oxygen. The oxygen is useful for human respiration in addition to rocket fuel. In either case, it can be stored in liquid form. Liquid hydrogen is harder to store, but NASA plans to turn it into liquid methane until it’s needed. Mars’ atmosphere is mostly carbon dioxide, which should serve as a good source of the necessary carbon.
NASA has demonstrated several parts of this system on Earth using simulated Martian regolith. The agency estimates the dust-to-thrust system would need to produce seven metric tons of liquid methane and about 22 metric tons of liquid oxygen in 16 months to be viable. Scientists still need to identify the best landing areas and refine the machinery to know if it’s possible to hit those goals with current technology, but ISRU is where NASA’s Mars exploration is moving.