On the red and dusty surface of Mars, about 100 million miles from Earth, a lunchbox-sized instrument is proving it can reliably do the work of a small tree.
The Mars In Situ Oxygen Resource Utilization Experiment, or MOXIE led by the Massachusetts Institute of Technology, has succeeded Oxygen of the red planet’s carbon dioxide-rich atmosphere since February 2021, when it landed on Mars as part of NASA’s Persevering Probe mission.
In a study published in the journal science advances, The researchers reported that by the end of 2021, MOXIE had been able to produce oxygen in seven test rounds, in a variety of weather conditions, including during the day and night, and across different Martian seasons. In each run, the tool reached its goal of producing six grams of oxygen per hour — the rate of a modest tree on Earth.
The researchers envision that an expanded version of MOXIE could be sent to Mars in advance of a human mission, to continuously produce oxygen at a rate of several hundred trees. With that capacity, the system must generate enough oxygen to support humans once they arrive, and refuel the rocket to bring the astronauts back to Earth.
To date, MOXIE’s stable production is a promising first step towards this goal.
“We’ve learned a tremendous amount that will guide future systems at a larger scale,” says Michael Hecht, the MOXIE mission principal investigator at MIT’s Haystack Observatory.
MOXIE’s production of oxygen on Mars also represents the first evidence of “in situ resource use,” the idea of harvesting and using planet 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 chemically converting them into something that might be useful for a human mission,” says MOXIE Deputy Principal Investigator Jeffrey Hoffman, professor of practice in the MIT Department of Aeronautics and Astronautics. “It is historical in that sense.”
MIT co-authors include Hoffman and Heckt MOXIE team members Jason Soho, Andrew Liu, Eric Hunterman, Maya Nasr, Shravan Hariharan, and Kyle Horn, along with collaborators from multiple institutions including NASA’s Jet Propulsion Laboratory, who managed development MOXIE, flight software, packaging and testing before launch.
The current version of the MOXIE is small in design, to suit a persistent rover, and is designed to run for short periods, with start-ups and shutdowns with each run, depending on the exploration schedule and mission responsibilities of the rover. In contrast, a large-scale oxygen plant would include larger units that would ideally operate continuously.
Despite the necessary compromises in MOXIE’s current design, the instrument has shown that it can reliably and efficiently convert the Martian atmosphere into pure oxygen. It does this by first drawing Martian air through a filter that cleans it of pollutants. The air is then compressed, and sent through a solid oxide electrolyzer (SOXE), a device developed and manufactured by OxEon Energy that electrically splits carbon dioxide-rich air into oxygen ions and Carbon Monoxide.
The oxygen ions are then isolated and recombined to form breathable molecular oxygen or O2which MOXIE measures quantity and purity before it is released back into the air without harm, along with carbon monoxide and other atmospheric gases.
Since the probe landed in February 2021, MOXIE engineers have run the device seven times over the course of a Martian year, each time taking a few hours to warm up, then another hour to produce oxygen before turning it back on again. Each run was scheduled at a different time of the day or night, and in different seasons, to see if MOXIE could accommodate shifts in the planet’s atmospheric conditions.
Hoffman notes that “Mars’ atmosphere is much more diverse than Earth’s.” “Air density can vary by two times during the year, and the temperature can vary by 100 degrees. One of the goals is to show that we can run in all seasons.”
So far, MOXIE has shown that it can produce oxygen at almost any time of the Martian day and year.
“The only thing we haven’t shown is running at dawn or dusk, when the temperature changes dramatically,” Hecht says. “We really have it up our sleeve that allows us to do that, and once we test that in the lab, we can reach this last milestone to show that we can really run at any time.”
before the match
As MOXIE continues to produce oxygen on Mars, engineers plan to increase its capacity and increase its production, especially in the Martian spring, when the density of the atmosphere and Carbon Dioxide high levels.
“The next round is going to be during the highest density of the year, and we just want to produce as much oxygen as possible,” Hecht says. “So we will put everything as high as possible, and let it run for as long as possible.”
They will also monitor the system for signs of wear. Since MOXIE is just one of many experiments on the persistence bandwagon, it cannot run continuously as a full-scale system does. Instead, the device must start and shut down with each run – a heat stress that can degrade the system over time.
If MOXIE can operate successfully despite being repeatedly turned on and off, this indicates that a large-scale system, designed to run continuously, could do so for thousands of hours.
“To support a human mission to Mars, we have to bring in a lot of things from Earth, like computers, spacesuits, and habitats,” Hoffman says. “But stupid old oxygen? If you can get there, go find it – you’re way ahead of the game.”
ISRU’s Mars Oxygen Experiment (MOXIE) – Preparing for Human Exploration of Mars, science progress (2022). www.science.org/doi/10.1126/sciadv.abp8636
Massachusetts Institute of Technology
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