How Salt Water Could Fuel a Mars Mission

A new invention might speed up human exploration of the Red Planet.

Early settlers on Mars will need a way to make their own rocket fuel.

In a new paper published in Proceedings of the National Academy of Sciences, Pralay Gayen and two of his colleagues from Washington University in St. Louis introduce a new technology that has the capability to produce oxygen and hydrogen from salt-rich water. The invention has many applications, but it’s especially valuable for a future human mission to Mars.

Perchlorates and other salts have been detected on Mars previously, and pools of liquid brines (very salty water) are also thought to exist below the surface. The method described by Pralay et al. could be used to extract pure oxygen and hydrogen from these underground pools. The high salt content within the brines actually would be an advantage, because it can keep the water liquid at temperatures well below its normal freezing point. The authors demonstrated the validity of this concept by testing their instrument—called a Perchlorate Brine Electrolyzer—with a magnesium perchlorate solution at a temperature of -36o C (-33o F) under a simulated Mars atmosphere.

In electrolysis, a compound is separated into its components with the help of an electrical current. The new invention uses an anode (positive electrode) made of lead ruthenate pyrochlore to produce oxygen and a platinum/carbon cathode (negative electrode) to produce hydrogen. Electrolysis also has been used to extract oxygen from carbon dioxide instead of water, as in the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) currently enroute to Mars onboard NASA’s Perseverance spacecraft. Its objective is to demonstrate the basic technology that could be used to provide future Mars astronauts with life-sustaining oxygen.

Gayen’s team compared their Perchlorate Brine Electrolyzer to MOXIE and found that their invention can produce more than 25 times the amount of oxygen while using the same amount of power. Unlike MOXIE, it also produces hydrogen, which a Mars mission could turn into rocket fuel.

That makes the new technology potentially very valuable for a future expedition to Mars. Not only that, it could be beneficial for the exploration of deep marine environments on Earth, as it could be used on submarines to produce oxygen for the crew from the surrounding salt water. The same method could theoretically be applied to underwater explorers on icy moons such as Jupiter’s Europa or Saturn’s Enceladus.

The authors point out that NASA’s current mandate is to land humans on Mars by 2033. I doubt that this can be achieved, and as far as I’m aware most of my colleagues are also very skeptical about the timeline. However, the new technology has the potential to speed things up. So it deserves to be tested further in the laboratory under varying conditions to confirm its utility. The next step after that would be to make it space-ready, and finally—just like MOXIE—to be tested in the real Martian environment by one of the next robotic missions launched to the Red Planet.

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