Sometimes combining technologies is the way to go. That seems to be the case for utilizing lunar regolith for the raw materials needed to support a base anyway. According to a new paper published in Joule by a team of Chinese scientists combined the powers of light and heat is the most effective way to get hydrogen, oxygen, and carbon monoxide out of the lunar soil - and to prove it they tested their system on some actual lunar regolith samples returned by Chang’E-5.
Getting hydrogen and oxygen from the lunar surface, rather than shipping them in from Earth, is a critical aspect of any long-term lunar mission. Oxygen is essential for any life support system. Hydrogen is a useful rocket fuel, but can also be combined with the carbon monoxide to create other hydrocarbons that could produce products such as plastic or other fuels.
To get those three materials, two inputs and a catalyst are needed. One input - water - can be found in small qualities throughout parts of the lunar regolith. The other - carbon dioxide - is exhaled by astronauts and can be captured and recycled as part of this process. The catalyst in this case also comes from the regolith. The research points to ilmenite, one of the most abundant minerals in the regolith, as the potential catalyst that works well with this particular technology, making it a critical component to the success of the process.
Fraser discusses ISRU, which this technology could play an important part in.That process is actually several stages, and the beauty of the photothermal method the researchers use is that it’s all in one collective system. First, the process must extract the water from the regolith. Water in the lunar regolith is bound into hydrogen-related species like hydroxyl groups, or occasionally as molecule water trapped in glass. To release it from either form requires a significant amount of heat - which is where the “thermal” part of the photothermal method comes in.
Estimates put the temperature required to break some of the bonds in the Chang’E-5 sample at around 430 C - significantly higher than water’s boiling point here on Earth, and difficult to achieve in a hard vacuum, even when subjected to direct sunlight. To get to those temperatures, the regolith was heated in a reaction chamber surrounded by a “heating jacket”.
Once the water was released from its prison, the next step is the actual photothermal catalysis itself. In this process, the ilmenite used as the catalyst has its electrons excited by the energy applied by the system, which moves them up an energy level and leaves a hole in the valence band of electrons. That hole is highly oxidative, causing the water to oxidize into a O2 molecule and a proton (i.e. a hydrogen atom). These hydrogen atoms then interact with the electrons that were excited, causing them to settle into the familiar H2 molecule. Those same holes oxidize the carbon dioxide molecules, creating the carbon monoxide to use a feedstock for further hydrocarbon creation.
Lunar regolith can be tricky to deal with, as Dr. Kevin Cannon explains in an interview with Fraser.This whole process is all done in a single reaction chamber, using only light, heat, regolith, and human breath as its inputs. This eliminates many of the complex processes, some of which are energy intensive, that would typically be used to get the same result. And it can be done using essentially just the power of the Sun.
There are still some challenges to overcome, however. Dramatic temperature fluctuations are part of the extreme environment on the Moon itself, where these systems would have to operate, and without proper thermal management such changes could wreak havoc on the chemical processes in the system. The catalyst itself could use some improvement as well, as it currently isn’t effective enough to meet all the demands of humans living on the Moon.
But there is still time to work through these technical hurdles. While people setting foot back on the Moon seem inevitable at this point, it will still be years (at the best) before anyone does so. Which means there’s plenty of time to work out the kinks in whatever system is eventually selected to serve as this critical part of life support infrastructure.
Learn More:
Eureka Alert - Lunar soil could support life on the Moon
J Sun et al - Inherent lunar water enabled photothermal CO2 catalysis
UT - There's Enough Oxygen in the Lunar Regolith to Support Billions of People on the Moon
UT - One Day Astronauts Will Be Breathing Oxygen Made From Rocks