To bring astronauts back from Mars, the oxidizer needed for the return launch will have to be produced directly on the planet. At the Massachusetts Institute of Technology, researchers have developed a small plasma reactor for this purpose that splits carbon dioxide from the Martian atmosphere. That part of the process is already working well. The harder task is capturing the oxygen before it recombines with the other reaction products.
Tons of Oxidizer
Crewed missions to Mars are planned in the coming decades by NASA and China, Universe Today notes. In rockets that use liquid oxygen, the oxidizer accounts for most of the mass loaded into the tanks. According to agency estimates, launching an ascent vehicle carrying four astronauts from the Martian surface would require about 25 tons of oxygen. Transporting that much from Earth would significantly increase the mass of the entire mission.
Real-world experience so far has been far more modest. Using the MOXIE instrument aboard the Perseverance rover, 16 runs were carried out between 2021 and 2023, producing a total of 122 grams of oxygen. The amount required is roughly two hundred thousand times greater.
Cold Plasma
MIT graduate student Lanie McKinney led the development under the supervision of Associate Professor Carmen Guerra-García, according to MIT News. In her small reactor, CO2 molecules, which make up almost the entire Martian atmosphere, were split by cold plasma into oxygen and carbon monoxide.
In this state of matter, energy is transferred mainly to the electrons, while the remaining particles stay relatively cool. This makes it possible to break chemical bonds without heating the system to about 800°C, as is required by the MOXIE instrument.
The device is a nanosecond repetitively pulsed dielectric barrier discharge system, or NRP-DBD. Its tube is filled with beads. Lanie McKinney studied how the material used for this packing affects the splitting process. A description of the work has not yet appeared in a peer-reviewed journal; the results are currently known only from the researcher’s university profile.
Separating the Oxygen
According to Lanie McKinney, the splitting stage has been made to work very well. The challenge begins afterward. The output is a mixture. As long as oxygen remains close to carbon monoxide, some of it recombines with it to form CO2 again.
To prevent this, the researcher combined the reactor with a membrane that selectively allows oxygen to pass through. Such a membrane is intended to remove the gas from the reaction zone faster than it can react again.
It is still unclear how the chemically active plasma environment will affect the membrane itself, because the combination of the two systems has not yet been studied in depth. Lanie McKinney acknowledged that the team does not know for certain what result to expect.
Recycling Waste and Lunar Bricks
Outside her dissertation work, Lanie McKinney participated in NASA competitions as part of the student Space Resources Workshop group. The CERBERUZ team, which she co-led, won the second phase of the LunaRecycle Challenge and received $775,000. The award was given for a system that grinds mixed waste into powder for casting spare parts and producing filament for 3D printing.
Another project carried out as part of an academic course brought engineers and architects together. They looked for a way to protect lunar habitats from radiation using only local resources. Their solution was regolith bricks that could be cast and stacked without mortar or any other binding material.
