Sometime this weekend, when the Mars Perseverance Rover is taking a few hours off from exploring Jezero Crater, a toaster-sized device will run a modest chemistry experiment that might one day make it possible for humans to survive on the Red Planet—and get back home.
Known as MOXIE, or the Mars Oxygen In-Situ Resource Utilization Experiment, the device is extracting small amounts of oxygen from the Martian atmosphere (which is 96 percent carbon dioxide) by running it through an electrical current, a process called electrolysis. This weekend, MOXIE will run the oxygen-grabbing process for the third time since the rover landed in February, each time producing enough for a human to breathe for about 10 or 15 minutes. That doesn’t seem like much, but the ultimate goal is to scale MOXIE up into an automated system that will produce breathable oxygen for the human crew and be used for the return flight. NASA estimates that launching a rocket off Mars will require industrial quantities of oxygen, which, along with rocket fuel, makes up propellant.
MOXIE is one of several experiments underway by researchers at NASA and the European Space Agency to make use of the stuff that Mars and the moon have to offer, a concept known as in-situ resource utilization. Ideas for creating fuel and breathable oxygen have been around for decades, but they are only now reaching the point where they can be tested in both the lab and on the Martian surface. These researchers say the big leap will come when they can move from experiments with simple chemistry to developing more complex engineering prototypes, and then eventually an automated oxygen factory. It won’t be easy; they are bumping up against one of the biggest obstacles for producing oxygen by electrolysis: the huge amount of energy it takes to make it work.
Still, scientists involved in MOXIE and the other resource utilization efforts are excited about the results they have so far from the Perseverance mission. “It’s going frighteningly like clockwork,” says Michael Hecht, MOXIE’s principal investigator and associate director of research management at MIT’s Haystack Observatory. “It’s stunning how much the results look identical to what we had run in the laboratory two years earlier. How many things can you put away for two years and turn on and even expect to work again? I mean, try that with your bicycle.”
Hecht says the first two MOXIE runs have produced between 4 and 5 grams of oxygen, which is the volumetric equivalent to about a gallon under Earth’s atmospheric pressure. This weekend he expects MOXIE to produce 8 grams in an hour. Because of the power that MOXIE demands, Perseverance won’t be able to run any other experiments or collect other data during that time, Hecht says.
The rover team at NASA’s Jet Propulsion Laboratory, which operates Perseverance, will be activating one of the rover’s two microphones to monitor MOXIE’s compressor; that will serve as a diagnostic tool that will let them know what it sounds like when all systems are performing well. (They’re still figuring out exactly what that’s like, because sound travels differently in the Martian atmosphere than in a NASA lab.) The sound recording is also something neat to listen to back on Earth. “I needed to do a little processing on the .wav file to make it something I can play for people, but the spectrogram looks great,” Hecht says. “And I suppose you can now say you can hear the sounds of oxygen being made on Mars.”
Hecht says they plan for MOXIE to do another eight runs over the next few months, making slight tweaks to optimize for the best oxygen output for a given input of electricity.
It might be a long time before any astronauts land on Mars—NASA is talking about the early 2030s, while SpaceX’s Elon Musk has promised it will be sooner. But when humans do touch down, they might find a successor to MOXIE waiting for them. Any crew coming to Mars will likely have their own device onboard their spacecraft that makes oxygen for breathing, so the bigger problem to solve is making the propellant they’ll use to fly home. “If you want to burn fuel, you need oxygen to burn it with,” Hecht says.
Hecht says that a four-person crew would only need about 1.5 metric tons of oxygen for a year for life support, but about 25 tons of it to produce thrust from 7 tons of rocket fuel. The easiest thing would be to send an automated system six months before the crew arrives so the astronauts would have some oxygen waiting for them. It also means they’ll have to carry less equipment from Earth. “It wouldn't be worth the complexity to bring a ton of equipment to make 25 tons of oxygen for the propellant,” says Hecht.
Some of these same calculations are being considered for a prospective lunar mission, which may happen much sooner than a trip to Mars. Teams from NASA and the ESA are working to heat up lunar soil, known as regolith, to extract oxygen. In fact, regolith is 45 percent oxygen by weight, bound to metallic elements such as silicon, aluminum, calcium, magnesium, iron, and titanium, according to Beth Lomax, a doctoral student at the University of Glasgow and a researcher at the ESA’s European Space Research and Technology Centre in Noordwijk, the Netherlands.
Lomax and Alexandre Meurisse, a fellow at the research center, have been developing a device to heat regolith in a canister with molten salt in order to extract its oxygen. Like the MOXIE project, they use an electrical current to separate the oxygen from the other elements. But unlike MOXIE, they have a by-product: metallic elements that might be useful as a construction material for a lunar base. (In fact, a separate team at ESA is looking at combining astronaut pee with regolith to form a reusable geopolymer building material similar to fly ash.)
Lomax says it makes sense to figure out how to exploit what’s already on the lunar surface, rather than schlepping it over from Earth. “As long-duration space exploration and habitation seem to be becoming more of a reality, the utilization of resources is going to be necessary,” Lomax says. “It's just not feasible for us to consistently bring every single kilogram of material that we need from Earth. We have this huge gravitational well, and the amount of energy required to get that material into space is so massive.”
By using a container of molten salt, Lomax and Meurisse are lowering the temperature needed to extract oxygen from the lunar soil, dropping it from 1,600 degrees Celsius (2,912 Fahrenheit) to around 600 C (1,112 F). That temperature could be reached by concentrating solar energy, a method already proven in solar power plants in the southwestern United States.
At NASA’s Kennedy Space Center, researchers are figuring out how to remove the metal byproducts that accumulate in the reactor vessel that contains the regolith during electrolysis. That’s important because the melted material is extremely corrosive, and both the metals and the oxygen need to be extracted in some way, according to NASA researcher Kevin Grossman. The goal is to melt the regolith without it touching the sides of the container. “If you take a bucket of regolith, and you want to melt an amount the size of a golf ball just in the very center of that, how do you get to it?” Grossman asks.
(For the record: Grossman and Lomax aren’t using real moon dust, since it's one of the most expensive and rare items on Earth. Instead, they’re using a simulated version that contains the same elements.)
At the same time that NASA and the ESA are exploring ways to extract oxygen from the moon’s regolith, they are also considering another source of fuel: lunar ice. It has been found on the moon’s polar regions, but it is still not clear how much exists and whether it is in a form that can be easily processed. For example, it’s not clear if it’s simply frost, or if it might be contaminated with other substances. In 2023, NASA will send its Viper rover to the South Pole to scout for ice, while the ESA plans for its Prospect mission, which it is conducting along with the Russian Space Agency, to drill beneath the lunar surface to find ice sometime in 2025.
NASA has said it would be able to land astronauts back on the moon by 2024, although a new report by a congressional watchdog agency issued this week warns that technical and managerial problems might force the space agency to delay that schedule.
By then, Lomax and others hope to prove that their methods of getting oxygen from lunar soil might be easier than prospecting for ice. “It opens up more locations on the lunar surface, of course, because the ice is only in very specific locations,” Lomax says.