On Mars, the MOXIE experiment consistently creates oxygen

A lunchbox-sized gadget is demonstrating it can do the job of a tiny tree on Mars' red and dusty surface, over 100 million kilometers from Earth. Since February 2021, when it landed on the Martian surface as part of NASA's Perseverance rover mission, the MIT-led Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE, has been successfully producing oxygen from the Red Planet's carbon-dioxide-rich atmosphere.

According to a study published in the journal Science Advances, MOXIE was able to create oxygen on seven trial runs by the end of 2021, under a variety of atmospheric circumstances, including throughout the day and night, and during several Martian seasons. In each run, the gadget produced six grams of oxygen per hour, roughly the pace of a small tree on Earth.

A scaled-up version of MOXIE might be deployed to Mars ahead of a human mission to continually manufacture oxygen at the pace of hundreds of trees. At that capacity, the device should create enough oxygen to both maintain humans once they arrive, and fuel a rocket for sending astronauts back to Earth. MOXIE's consistent output has so far been a good first step toward that aim.

We have learned a significant lot that will shape future systems on a bigger scale, said Michael Hecht, principal investigator of the MOXIE project at MIT's Haystack Observatory.

MOXIE's oxygen production on Mars is also the first demonstration of "in-situ resource utilization," which is the concept of harvesting and utilizing a planet's materials (in this case, carbon dioxide on Mars) to produce resources (such as oxygen) that would otherwise have to be transported from Earth.

According to MOXIE deputy principal investigator Jeffrey Hoffman, a professor of the practice in MIT's Department of Aeronautics and Astronautics, this is the first demonstration of actually using resources on another planetary body's surface and chemically transforming them into something useful for a human mission. In that sense, it is historic.

MOXIE team members Jason SooHoo, Andrew Liu, Eric Hinterman, Maya Nasr, Shravan Hariharan, and Kyle Horn are among Hoffman and Hecht's MIT co-authors, as are collaborators from multiple institutions, including NASA's Jet Propulsion Laboratory, which managed MOXIE's development, flight software, packaging, and testing prior to launch.

MOXIE's present design is compact in order to fit onboard the Perseverance rover, and it is constructed to run for brief periods of time, starting up and shutting down with each run, depending on the rover's exploration schedule and mission tasks. A full-scale oxygen factory, on the other hand, would contain bigger units that would ideally run continually. Despite the required constraints in MOXIE's current design, the device has demonstrated its ability to transform Mars' atmosphere into pure oxygen in a reliable and efficient manner. It accomplishes this by first pulling Martian air through a filter that cleans it of impurities. The compressed air is then sent through the Solid OXide Electrolyzer (SOXE), an equipment designed and produced by OxEon Energy that electrochemically separates the carbon dioxide-rich air into oxygen ions and carbon monoxide.

The oxygen ions are then separated and recombined to produce breathing molecular oxygen, or O2, which MOXIE then monitors for quantity and purity before harmlessly releasing it back into the atmosphere alongside carbon monoxide and other atmospheric gases. MOXIE engineers have fired up the instrument seven times since the rover's arrival in February 2021, each time requiring a few hours to warm up, then another hour to generate oxygen before shutting down. Each run was timed at a different time of day or night and in a different season to test if MOXIE could adapt to changes in the planet's atmospheric conditions.

According to Hoffman, Mars' atmosphere is significantly more changeable than Earth's. The density of the air can change by a factor of two over the course of a year, while the temperature can change by a factor of 100. One goal is to demonstrate that we can run in all seasons.

So far, MOXIE has demonstrated that it can produce oxygen at practically any time of day or year on Mars.

Hecht unfortunately, the only thing we haven't shown is running at dawn or sunset when the temperature is drastically shifting. We do have an ace up our sleeve that will allow us to do so, and after we test it in the lab, we will be able to hit that last milestone demonstrating that we can run at any time.

Engineers intend to expand MOXIE's capacity and enhance its output as it continues to produce oxygen on Mars, particularly during the Martian spring, when air density and carbon dioxide levels are high.

According to Hecht, the next run will be during the maximum density of the year, and we just want to produce as much oxygen as possible. So we'll crank everything up to 11 and let it run for as long as we can.

They will also look for signs of wear and tear on the system. MOXIE, being one of the numerous experiments aboard the Perseverance rover, cannot run constantly as a full-scale system would. Instead, with each run, the instrument must start up and shut down, causing thermal stress that might harm the system over time. If MOXIE can function properly while being turned on and off repeatedly, it would imply that a full-scale system built to run constantly might do so for thousands of hours.

According to Hoffman, we need to transport a lot of gear from Earth to enable a human expedition to Mars, such as computers, spacesuits, and housing. But what about poor old oxygen? If you can get there, go for it; you'll be miles ahead of the competition.

Journal Information: Mars Oxygen ISRU Experiment (MOXIE)—Preparing for human Mars exploration, Science Advances (2022). www.science.org/doi/10.1126/sciadv.abp8636
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