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So we want to jet to Mars, but how will we fuel up to get back?

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Jan 12, 2021, 11:08 PM EST (Updated)

Landing boots on Mars is one thing, but once astronauts have left those boot prints behind, how will they power the spaceship that brings them back to Earth?

How to get the fuel to make the return journey is a major challenge we will have to face for a future Martian mission. New research has found an unreal way of (at least hypothetically) creating methane-based rocket fuel right there on the surface surface of the Red Planet, and the only thing astronauts will need to bring is a form of zinc that will turn carbon dioxide already on Mars into methane through CO2 electrolysis. That, and a portable gizmo to carry out the reaction in, huge machines not required.

"The setup is a CO2/water electrolyzer," UCI physicist Huolin Xin, who is leading the research, told SYFY WIRE. "In a water electrolyzer, you have H2 produced in the cathode and O2 produced in the anode. In a CO2/water electrolyzer, in the anode, O2 is produced by oxidizing water. In the cathode, CO2 is reduced into methane."

Xin has developed the Organic Combustion Method, which is similar to the Sabatier process used to extract breathable oxygen from water on the ISS. The Sabatier process takes advantage of solar power to generate electricity that hits H2O molecules and triggers electrolysis, breaking them down as the electric current passes through them. The carbon and oxygen are then separated, leaving carbon and double the oxygen. The problem is that the Sabatier process needs monster machines and two phases for the reaction to happen.

The research team was effectively able to abbreviate the Sabatier process by eliminating the reaction that first electrolyzes water into hydrogen and oxygen, reducing the entire process into a single step. They were able to do this using single zinc atoms (supported by carbon that has been given a nitrogen boost) as a catalyst, or a substance that sets off a chemical reaction but does not end up being permanently changed. The Organic Combustion Method relies on that zinc to start an electrolysis reaction with CO2 that will produce instant methane.

Obviously, zinc atoms weigh next to nothing and will not affect the weight and cost of a payload. Neither will the device Xin has come up with to use for containing the reaction. The zinc’s high selectivity, or the ratio of wanted to unwanted products of a reaction, also means that there will be be more of the desired product produced than any undesired by-product.

Methane derived from zinc and resources on Mars would be more sustainable and also save the mission from making their payload more expensive by adding heavy tanks of propellant. It is obviously a huge leap forward from jet propellants made of fossil fuels, like kerosene, which release carbon dioxide into the atmosphere during combustion. Carbon dioxide is one of the greenhouse gases that is trapping heat and causing global warming, and more atmospheric CO2 is just about he last thing or planet needs right now. SpaceX is currently running tests in an effort to ditch kerosene for methane.

Methane fuel even beats liquid hydrogen, and not just because liquid hydrogen is expensive and would be more dead weight that would need to be lugged over 90 million miles from Earth. It doesn't leave the same carbon gunk in the rocket engine which would be impossible to clean on Mars.

Xin is now looking into the next steps he will take to make this tech Mars-ready.  

"To make an efficient CO2 electrolyzer, much engineering will need to be done to optimize the mass transport of the catalyst layer on the porous diffusion layer and manufacturing process," he said. "My group is working on a 3D spray system that can fine-tune the catalyst layer's formation and developing roll-to-roll platform to make the membrane electrode assemblies."

The only issue left is that this method has only been tested in a lab and not in Mars-like conditions yet. Both lab tests and the tests SpaceX is running with methane in its Raptor engine can only show what the results of this reaction look like on Earth. That means Earth’s gravity and air as opposed to a planet that has been scorched by killer radiation for billions of years. Never mind that Mars has much lower gravity and is beyond freezing, and both of those things can make or break chemical reactions. Expect an average high of about -81 degrees Fahrenheit over there.

Mars-tronauts are going to face many obstacles, but despite Elon Musk’s (over)enthusiasm to get there, we still have time to figure things out.

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