NASA has MOXIE, but rivals reckon they can do better for oxygen on Mars

Food and fuels, too? Totally not sounding like a Star Trek replicator

Last year, NASA produced oxygen on Mars. Now, scientists experimenting here on Earth may have found a much more efficient method of doing so for future missions. The resulting equipment could be used to produce the necessary materials for human colonization, too.

Writing in the Journal of Applied Physics, an international team of boffins led by University of Lisbon physicist Vasco Guerra say they've managed to test a design that can do the same thing NASA's Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) does – but without the need for intense heat and pressure.

Not only does their design improve on MOXIE's ability to harvest breathable oxygen, it can also be used to create fuels, carbon-based fertilizers, and animal feed. It can also synthesize a variety of organic molecules, the researchers said. 

Move over MOXIE?

MOXIE produced oxygen on Mars in a toaster-sized unit, but it required very specific conditions to do so: it had to heat the Martian air to 800°C (1,472°F) and re-pressurize it to one Earth atmosphere, making it far denser than the pressure on the Red Planet. 

Guerra's team, on the other hand, proposes using non-thermal plasma and specialized conducting membranes. Combined, the design forms a plasma reactor that can operate directly in Martian conditions without the need for heat or re-pressurization. According to the paper, Mars's atmospheric pressure is actually "ideal for plasma ignition."

In the paper, the researchers detail the two separate oxygen-generating experiments they carried out: the first using DC glow discharge plasma super chilled to Martian temperatures, and a second that used microwave discharges operating in a simulated Martian atmosphere. 

The paper describes the results as "very encouraging considering that the plasma setup used was designed for fundamental research and is far from suited to the development of a prototype." The DC experiment reportedly reached CO2 dissociation (the separation of carbon and oxygen) rates as high as 30 percent, while the MW experiment reached a 35 percent conversion rate. 

Based on their preliminary results, the team sketched out what an optimized system could produce and arrived at 14 grams of oxygen an hour in a plasma reactor weighing 6 kilograms – 2.3 grams of oxygen per kilogram of equipment. 

For comparison, NASA's MOXIE unit weighs 17.7 kilograms and can top out at 10 grams of oxygen an hour, the space agency said. 

Not so fast

The fact that MOXIE has actually made oxygen on Mars weighs heavily in its favor, as do some major drawbacks that the experimenters concede, as MOXIE leader and MIT experimental scientist Michael Hecht reiterated to Science.

The membrane used in Guerra's experiment, known as a mixed ionic-electronic conduction (MIEC) membrane, is developmentally at its "very first steps" in being coupled with plasma, the paper notes. Additionally, the researchers list "stability in CO2 and the possibility of back reactions" that can lessen the membrane's effectiveness as challenges to MIEC use. That, we presume, are challenges to overcome to make a practical device.

Hecht told Science that energy requirements and oxygen storage needs could make Guerra's device bulkier than MOXIE, defeating much of its benefit. "There's nothing wrong with the plasma technique other than it's a lot less mature," Hecht said, adding that a cash infusion from a space agency could make the tech mature enough to take to Mars. ®

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