Developed by researchers at the Massachusetts Institute of Technology (MIT), the Mars Oxygen In-Situ Resource Utilisation Experiment (Moxie) has been successfully making oxygen from the Red Planet’s carbon dioxide-rich atmosphere since April 2021, about two months after it touched down as part of NASA’s Perseverance rover and Mars 2020 mission.
Since then the instrument has produced oxygen during seven experimental runs in a variety of atmospheric conditions, including during the day, night and different Martian seasons. In each run the instrument reached its target of producing 6g of oxygen per hour, according to a study published this week – about the rate of a modest tree on Earth.
Researchers envision that a scaled-up version of Moxie could be sent to Mars ahead of a human mission, to continuously produce oxygen at the rate of several hundred trees. At that capacity, the system could generate enough oxygen to sustain humans once they arrive and fuel a rocket for returning astronauts back to Earth.
“We have learned a tremendous amount that will inform future systems at a larger scale,” said Michael Hecht, principal investigator of the Moxie mission at MIT’s Haystack Observatory.
The instrument converts Martian air into pure oxygen by first drawing it through a filter that cleans it of contaminants. The air is then pressurised and sent through the Solid OXide Electrolyser (SOXE), developed and built by OxEon Energy, which electrochemically splits the carbon dioxide-rich air into oxygen ions and carbon monoxide.
The oxygen ions are then isolated and recombined to form breathable, molecular oxygen, which Moxie then measures for quantity and purity before releasing it harmlessly back into the air, along with carbon monoxide and other atmospheric gases.
So far, the instrument has shown it can make oxygen at almost any time of the Martian day and year. “The atmosphere of Mars is far more variable than Earth,” said deputy principal investigator Jeffrey Hoffman. “The density of the air can vary by a factor of two through the year, and the temperature can vary by 100 degrees. One objective is to show we can run in all seasons.”
Hecht added: “The only thing we have not demonstrated is running at dawn or dusk, when the temperature is changing substantially. We do have an ace up our sleeve that will let us do that, and once we test that in the lab, we can reach that last milestone to show we can really run any time.”
Engineers plan to push capacity and increase production, particularly in the Martian spring when atmospheric density and carbon dioxide levels are high.
“We just want to make as much oxygen as we can,” said Hecht. “We’ll set everything as high as we dare, and let it run as long as we can.”
The team will also monitor the system for signs of wear and tear. As Moxie is just one experiment among several aboard the Perseverance rover, it cannot run continuously as a full-scale system would. Instead, the instrument must start up and shut down with each run — a thermal stress that can degrade the system over time.
If Moxie can operate successfully despite repeatedly turning on and off, this would suggest that a full-scale system, designed to run continuously, could do so for thousands of hours.
The oxygen production on Mars represented the first demonstration of in-situ resource utilisation, the team said – harvesting and using a planet’s materials to make resources that would otherwise have to be transported from Earth.
“To support a human mission to Mars, we have to bring a lot of stuff from Earth, like computers, spacesuits and habitats,” said Hoffman. “But dumb old oxygen? If you can make it there, go for it – you’re way ahead of the game.”
This research was supported in part by NASA. It was published in the journal Science Advances.
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