Of the many barriers to a human trip to Mars where astronauts would land, explore and return to Earth, the absence of oxygen in the Martian atmosphere is a big one. Without oxygen that can be collected to support life and to provide fuel for a flight home, there can be no successful human mission to the planet.
So the results of a proof-of-concept trial on Mars that turned carbon dioxide into oxygen is positive news for sure. The instrument — called MOXIE on the rover Perseverance — successfully produced oxygen from carbon dioxide seven times last year, and convinced its inventors (and NASA) that it is a technology that can be of substantial importance.
While the amount of oxygen was not great — about 50 grams of the gas combined from the seven trials — the process worked well enough to strongly suggest that it could some day produce oxygen on a large scale.
“MOXIE has shown that (the deployed) technology for producing oxygen on Mars from the atmosphere is viable, is scalable, and meets expectations for efficiency and quality,” an MIT team led by Jeffrey Hoffman wrote in a Science Advances article released today.
They wrote that although long-term durability and resilience remain to be demonstrated and future efforts need to improve the instrument’s monitoring and controlling capabilities, “all indications are that a scaled-up version of MOXIE could produce oxygen in sufficient quantity and with acceptable reliability to support future human exploration.”
The size of both the problem and the opportunity can be seen in the fact that carbon dioxide makes up more than 95 percent of the Martian atmosphere while oxygen is only a miniscule 0.13 percent of the atmosphere. (Oxygen makes up 21 percent of the atmosphere on Earth.)
Transporting oxygen to Mars to fuel for a trip home is considered impractical because to burn its fuel a rocket must have substantial and weighty supplies of oxygen.
Getting four astronauts off the Martian surface on a future mission would require approximately 15,000 pounds (7 metric tons) of rocket fuel and 55,000 pounds (25 metric tons) of oxygen. In contrast, astronauts living and working on Mars would require far less oxygen to breathe — about one metric ton to support a crew on the surface for one year.
Hauling 25 metric tons of oxygen from Earth to Mars would be an arduous task. Transporting a one-ton oxygen converter – a larger, more powerful descendant of MOXIE that could produce those 25 tons – would, as least in theory, be more economical and practical.
Making oxygen from carbon dioxide on Mars is conceptually straight-forward, on Earth at least. Here plants take in carbon dioxide and release oxygen. The process of photosynthesis that makes it happen is absent on Mars, so the MOXIE team created a rather more complex alternative.
MOXIE works by separating oxygen atoms from carbon dioxide molecules, which are made up of one carbon atom and two oxygen atoms. A waste product, carbon monoxide, is emitted into the Martian atmosphere.
The conversion process requires high levels of heat to reach a temperature of approximately 1,470 degrees Fahrenheit (800 Celsius). To accommodate this, the MOXIE unit is made with heat-tolerant materials. These include 3D-printed nickel alloy parts, which heat and cool the gases flowing through it, and a lightweight aerogel that helps hold in the heat. A thin gold coating on the outside of MOXIE reflects infrared heat, keeping it from radiating outward and potentially damaging other parts of Perseverance.
Making oxygen this way is a complicated process and at this point is not able to provide much oxygen. But it is a start.
Hoffman writes that a combination of laboratory experiments on Earth and an analysis of MOXIE’s long-term performance on Mars will determine the design of future systems “hundreds of times larger.”
The MOXIE project is by no means on the only effort underway to produce oxygen on Mars. Another international team from the University of Lisbon in Portugal has been testing ways to separate carbon dioxide into oxygen in lags using plasma — split atoms that make up the fourth form of matter. They published recently in the Journal of Applied Physics.
But unlike with MOXIE, their testing is taking place in labs on Earth.
The MOXIE project is a demonstration effort developed by the Haystack Observatory of MIT and uses solid oxide electrolysis (SOXE) technology from OxEon Energy of North Salt Lake City, Utah.
The name “MOXIE” is an acronym for humans exploring Mars by making OXygen. It works “In situ” (in place) on the planet, and is an Experiment.”
According to the Science Advances report, MOXIE’s oxygen production has been quite modest – between 5 and 9 grams produced over more than an hour of operation. during the seven runs. The successful first run was reported by NASA in April, 2021.
MOXIE was designed to generate up to 10 grams of oxygen per hour and has not hit that target. But the MOXIE team reports that a number of compromises had to be made in how it operates and its short duration runs take a toll on the machine. A large oxygen-from-carbon dioxide facility would have to run thousands of hours of continuous operation to support a human mission on Mars.
While this demonstration is a small step towards making such a mission possible, it is a welcome proof of concept that may hasten the day that an explorer-scientist will be able to walk the surface of Mars.
NASA is interested in various other kind of “in situ” initiatives that may work on Mars (and the moon) and used by astronauts.
The sun has long powered solar panels on spacecraft and could do the same on the surface of Mars. There are many schemes being planned to make gardening possible, a process that requires the extraction or condensation of water from the ground and atmosphere. The carbon dioxide being used to produce oxygen can potentially be used to make methane (CH4), which is also a fuel and has many uses that can help support human life.
The moon offers some “in situ” opportunities such as water ice, and oxygen exists in compounds that could be mined and cracked. The lunar atmosphere is very thin and does not provide the quantities of carbon dioxide to accomplish the kind of oxygen-production that MOXIE has initiated. But the moon has many minerals can potentially be used to support lunar colonies.
In situ resourcing in space is a kind of brave new world, but it’s one that will take some considerable time to become a reality.