Oxygen produced on Mars with lunchbox-sized instrument

The MIT-led ‘Mars Oxygen In-Situ Resource Utilisation Experiment’ – aka ‘Moxie’ – has been successfully making oxygen from the Red Planet’s carbon dioxide-rich atmosphere since February 2021, when it touched down on the Martian surface as part of Nasa’s Perseverance rover mission.

By the end of 2021, MOXIE (pictured below) was able to produce oxygen on seven experimental runs, in a variety of atmospheric conditions, including during the day and night, and through different Martian seasons. In each run, the instrument reached its target of producing six grams of oxygen per hour – roughly 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 should generate enough oxygen to both sustain humans once they arrive and also 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.

Moxie’s oxygen production on Mars also represents the first demonstration of “in-situ resource utilisation,” which is the idea of harvesting and using a planet’s materials (in this case, carbon dioxide on Mars) to make resources (such as oxygen) that would otherwise have to be transported from Earth.

“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.

The current version of Moxie was small by design, in order to fit aboard the Perseverance rover, and was built to run for short periods, starting up and shutting down with each run depending on the rover’s exploration schedule and mission responsibilities. In contrast, a full-scale oxygen factory would include larger units that would ideally run continuously.

Despite the necessary compromises in this inaugural design, the instrument has shown it can reliably and efficiently convert Mars’ atmosphere into pure oxygen. It does so by first drawing the Martian air in through a filter that cleans it of contaminants.

The air is then pressurised and sent through the ‘Solid OXide Electrolyser’ (‘Soxe’), an instrument developed and built by OxEon Energy, that 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, or O2, which Moxie then measures for quantity and purity before releasing it harmlessly back into the air, along with carbon monoxide and other atmospheric gases.

Since the rover’s landing in February 2021, Moxie engineers have started up the instrument seven times throughout the Martian year, each time taking a few hours to warm up, then another hour to make oxygen before powering back down.

Each run was scheduled for a different time of day or night, and in different seasons, to see whether Moxie could accommodate shifts in the planet’s atmospheric conditions.

“The atmosphere of Mars is far more variable than Earth,” Hoffman notes. “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.”

So far, Moxie has shown that it can make oxygen at almost any time of the Martian day and year.

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

As Moxie continues to churn out oxygen on Mars, engineers plan to push its capacity and increase its production, particularly in the Martian Spring when atmospheric density and carbon dioxide levels are high.