A rover instrument called "MOXIE" successfully extracted oxygen from the Martian atmosphere. The technology demonstration is a first step in showing that humans could someday live (and breathe) on Mars.
The achievement centers around the breakdown of carbon dioxide — an abundant molecule on Mars — into one of CO2's component parts: oxygen.
In this first operation on the evening of April 20 , the Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE , produced just under 6 grams of oxygen — about ten minutes of breathing time for an astronaut — from the planet's atmosphere, which is 95% carbon dioxide.
MOXIE is designed to generate up to 10 grams of oxygen per hour.
“The astronauts who spend a year on the surface will maybe use one metric ton between them to breathe,” said MOXIE's principal investigator and MIT researcher Michael Hecht .
A metric ton of oxygen, however, pales in comparison to the 25 metric tons that NASA will require when it comes time to rocket-launch astronauts off the Red Planet when their stay comes to an end, added Hecht.
How MOXIE Works
The gold, box-shaped instrument, small enough to fit inside the Perseverance rover, performs a process call solid oxide electrolysis. Through electrolysis, MOXIE strips oxygen atoms away from CO2 molecules, releasing the waste product of carbon monoxide to the Martian atmosphere.
The CO2 Acquisition and Compression (CAC) system's filter pulls Martian atmosphere from outside of the rover. The CAC also pressurizes the CO2 gas, to ~1 atmosphere, or 5 to 10 pounds per square inch of pressure.
The pressurized air is then fed to the Solid OXide Electrolyzer (SOXE). The electrolyzer electrochemically splits the air at the cathode to produce pure O2 at the anode, a process equivalent to running a fuel cell in reverse.
The conversion process requires high temperatures — specifically 1,470 degrees Fahrenheit (800 Celsius). That means MOXIE has to handle the heat.
The system's thermal isolation system preheats the gas coming in and cools the gas going out.
MOXIE features 3D-printed nickel alloy parts, which manage the extreme temperatures of the gases. Additionally, MOXIE's thin gold coating reflects damaging infrared heat away from the Perseverance rover.
The technology also analyzes the O2 exhaust and CO2/CO exhaust streams, to verify production rate and purity. The charged ions passing through the membrane result in an electrical current exactly equal and opposite to the electron current provided by the power supply. Measuring this current allows the rate of oxygen production to be precisely determined.
MOXIE successfully touched down with Perseverance on Feb. 18. Last week's demonstration fulfilled NASA's objective of confirming that the instrument survived the seven-month journey from Earth.
The instrument is expected to extract oxygen at least nine more times over the next two years, or one Martian year.
MOXIE's first run brings us closer to the possibility of human missions to Mars, according to the team behind the effort, including MIT's Hecht, who spoke with Tech Briefs via email.
In the Q&A below, Hecht explains more about what needs to happen before anyone will take a deep breath on Mars.
Tech Briefs: How soon do you envision “living off the land” on Mars, and what role does MOXIE play in that vision?
Michael Hecht: Hard to say. On the pessimistic side, NASA has been holding out the prospect of a human mission to Mars in 15 years for a long time, since the 1990s in my personal experience, and probably all the way back to the von Braun era. But I think that finally the prospect is real, and the investment in MOXIE is evidence of that. Maybe it won’t be as soon as 15 years, but even at the age of 68 I have hope that I’ll live to see it. And while we could probably pull it off without using native resources, it would be a pretty stripped-down mission. So I’m pretty confident that “living off the land” will go hand-in-hand with even the first human mission.
Tech Briefs: Can you take me through the test on April 20th and your reaction?
Michael Hecht: Like everything we do on Mars, we’ve been training and practicing and rehearsing and testing and simulating for a very long time. Since landing on February 18 we’ve tested out every MOXIE function and subsystem except for putting it all together to make oxygen, so we were pretty confident but still anxious.
The big reveal was supposed to be Tuesday night at 9:36 Eastern time, and probably 50 or more of us, from the operations team to Perseverance Management, to friends and alumni of the project, virtually clustered around one brave graduate student, Maya Nasr, whose job it was to unwrap the data as it was received and walk us through the plots and the results.
9:36 came and went, then 10:00, then 10:30, and still no data.
There were frantic phone calls up the line all the way to the project manager trying to figure out what happened, and we had all but given up for the night when, without warning, it started flowing in around 11:00. One plot after another showed performance so perfect it was hard to tell the data from the simulation. And how did we feel? Well, we may have been making oxygen on Mars, but it felt like we were all taking hits of it on Earth!
Tech Briefs: A few questions about practicality: Do you envision sending a one-ton version in one piece? How big will it have to be to create a large supply of oxygen?
Michael Hecht: Most architectures for going to Mars feature pre-deployment of all the necessities 18-20 months before the crew actually launches. The 1-ton MOXIE would be one part of that, but the really critical piece would be the 25-30 kW power system that will power both MOXIE and, when the astronauts arrive, the life support systems.
Other key pieces would be the habitat, the ascent vehicle (with an empty oxygen tank) to start the astronauts on their journey home, and vehicles to allow them to travel around. MOXIE’s main job would be to fill the oxygen tank for the ascent rocket, but some of the oxygen would also be used to replenish the crew’s supply.
Tech Briefs: And how do you heat something this size to 800 degrees Celsius? How do you envision storing large amounts of oxygen? Has this technology ever been tried at that scale anywhere on Earth?
Michael Hecht: The heating is actually much easier for something that large: You just put the whole thing in an oven and heat it uniformly. Systems this size have been built on Earth and, in fact, Bloom Energy operates a large solid oxide fuel cell plant at Caltech that runs at even higher temperature than MOXIE. Solid oxide fuel cells and electrolysis systems are very similar technologies.
Tech Briefs: Will the CO2 in the atmosphere be replaced by a natural process? How will the emission of carbon monoxide be handled? What effects will that have on the Martian atmosphere?
Michael Hecht: We produce carbon monoxide on Earth all the time — the trick is not to let it accumulate in our basements! It will eventually revert back to carbon dioxide and will have no effect on the atmosphere. But even better than releasing it on Mars would be to store it for use as a fuel. It’s not really a good enough fuel for rockets, but it would be fine for surface vehicles or even “hoppers” that would leap long distances on rocket jets.
Tech Briefs: Can regolith be used as a source of oxygen? Is MOXIE designed to handle oxygen retrieval from both regolith and the atmosphere?
Michael Hecht: On the Moon, where there is no atmosphere, regolith is a possible source of oxygen. The extraction could still be electrochemical, but it would involve melting the rock. Mars offers much simpler options, though. For example, there is enough water stored in the regolith (several percent typically) that it could be extracted by heating, collected, and separated into hydrogen and oxygen by electrolysis. Or ice could be retrieved from the permafrost at arctic latitudes. And perchlorate, ClO4, which makes up almost 1% of the soil could also be a source of both energy and oxygen.
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