Mars rover’s MOXIE oxygen generator one step closer to supporting human life on the Red Planet


Situated aboard the Mars Perseverance rover, MOXIE has been successfully making oxygen from the Red Planet’s carbon dioxide-rich atmosphere since it arrived in February 2021.

The new report, published in the journal Science Advances, reveals how MOXIE (Mars Oxygen In-Situ Resource Utilization Experiment), which is about the size of a car battery, makes oxygen like a tree, by inhaling carbon dioxide from the Martian atmosphere and exhaling oxygen.

According to the study, MOXIE proved it could produce oxygen over seven experimental runs by the end of 2021 – under a range of atmospheric conditions – during the day and night, and during different Martian seasons. Indeed, MOXIE reached its target of oxygen production, with a rate of 6g of oxygen per hour – about the same rate as a tree on Earth.

It is hoped that a scaled-up version of MOXIE could operate on Mars in the future, ahead of a human mission, to produce oxygen at a rate that is equivalent to several hundred trees. This would, in turn, generate enough oxygen to sustain visiting astronauts and fuel a returning rocket 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 the Massachusetts Institute of Technology’s Haystack Observatory.

MOXIE in the cleanroom at NASA's Jet Propulsion Laboratory, in Pasadena, California. © NASA/JPL-Caltech

MOXIE in the cleanroom at NASA’s Jet Propulsion Laboratory, in Pasadena, California. © NASA/JPL-Caltech

MOXIE’s oxygen production on Mars also represents the first demonstration of ‘in situ resource utilisation’, which involves the harvesting and use of a planet’s raw materials. In this case it’s carbon dioxide on Mars – to make resources (such as oxygen) that would otherwise have to be transported from Earth (where our oxygen level is 21 per cent).

To put this in context, carbon dioxide makes up around 96 per cent of the gas in the Martian atmosphere, compared to 0.13 per cent oxygen.

“This is the first demonstration of actually using resources on the surface of another planetary body and transforming them chemically into something that would be useful for a human mission,” said MOXIE deputy principal investigator Jeffrey Hoffman. “It’s historic in that sense.”

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Due to having to fit onboard the Perseverance rover, the current version of MOXIE is understandably small. It is built to run for short periods, starting up and shutting down with each run.

A full-scale oxygen factory on the Red Planet would require much larger units that would ideally need to run continuously.

To convert the Martian atmosphere into pure oxygen, MOXIE draws the air in through a filter that cleans it of contaminants. Next, the air is compressed and heated to 800°C and sent through a Solid Oxide Electrolyzer (SOXE), an instrument that electrochemically splits the carbon dioxide-rich air into oxygen ions and carbon monoxide.

These oxygen ions are then isolated and recombined to form breathable oxygen, which MOXIE measures for quantity and purity. The oxygen is then released back into the air, along with carbon monoxide and other atmospheric gases, primarily argon and nitrogen.

So far, MOXIE has proved that it can make oxygen at almost any time of the Martian day and year, but there is still one test condition that researchers are keen to investigate.

“The only thing we have not demonstrated is running at dawn or dusk, when the temperature is changing substantially,” said Hecht. “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.”

Looking ahead, the researchers plan to push MOXIE’s capacity, and increase its production, in the Martian spring when atmospheric density and CO2 levels are high. They will also monitor the instrument for signs of wear and tear.

If MOXIE can operate successfully, despite repeatedly turning on and off, it would lay the groundwork for a full-scale system. This would need to be designed to run continuously, and would need to run for thousands of hours to support a future human mission.

“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.”

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