(Note: this is a part of The Space Colonization Series)
The lunar regolith, or the powdery soil on the surface of the moon, is best known for the havoc it wreaked on the astronauts and equipment during the Apollo missions. Regolith was seen as one of the biggest hurdles for any trip to the moon but now it is being seen as possibly one of the biggest advantages for a permanent establishment.
A Little Background on the Lunar Soil...
Microscopic view of Lunar Regolith. Courtesy: CAS.USF.edu
Regolith, by definition, is the unconsolidated, fragmented material covering a solid surface. On earth regolith is our dirt or soil, hence the term "lunar soil." On the Moon regolith covers almost the entire surface. It is typically 4-5 meters thick in the dark, basaltic regions and anywhere from 10-15 meters deep in other areas. The creation of the lunar soil has been the culmination of a 4.6 billion year process involving the smashing of meteoroids onto the surface that have been in turn broken apart by micrometeoroids and further more by various charged particles traveling through space.
More importantly though, are the composition and properties of the regolith. This is where all the key advantages come into play. In most of the lunar regolith, roughly half of the particles are made of small portions of minerals fused by silica. Also, depending on the location, many of the minerals are rich in metallic iron. This particular combination of glass and metal amounts to some very unique properties.
A Diamond in the Rough?
Larry Taylor, Distinguished Professor of Planetary Sciences at the University of Tennessee, may have stumbled onto the answer serendipitously due to a quirky habit. In his words "[He's] one of those weird people who like to stick things in ordinary kitchen microwave ovens to see what happens." Dr. Taylor, armed with a small pile of lunar soil brought back by the Apollo astronauts, decided to appease his habit. He found that at mere 250 Watts he could melt the entire sample in less than 30 seconds.
The reasoning behind the incredibly easy method of melting the regolith has to do with the nano-scale iron beads that were embedded into the silica by micrometeorites. The micrometeorites, traveling at very high velocities, melt the silica into glass as the penetrate the soil and various lunar rocks. Still inside the glass they formed, the iron beads are then able to concentrate the microwaves so effectively that they turn a complex process of heating the rocks to temperatures of over 1000 degrees Celsius into one as simple as popping a bag of popcorn. In fact, taking the dirt out of the microwave and into a more 'scientific' setting where a single magnetron was focused onto a sample showed just how efficient this process is. Professor Taylor said, “With 50 watts of energy I took a one-centimeter block of lunar soil to 1700 degrees Celsius (3100°F) in 10 seconds.”
Sketch of Microwave "Lawnmower" made by Prof. Taylor. Courtesy: NASA.gov
The observation of this property has incredible implications. Dr. Taylor proposes a microwave 'lawnmower' that could make continuous brick down half a meter and leave a top layer of glass an inch or two deep to surface a lunar highway, a runway for incoming shuttles, or simply a launch pad for rockets. "Or," as he says, "say that you want a radio telescope. Find a round crater and run a little microwave 'lawnmower' up and down the crater's sides to sinter a smooth surface. Hang an antenna from the middle--voila, instant Arecibo!" (Arecibo is a massive 305-meter-diameter radio telescope created out of a natural circular valley in Puerto Rico). The ability to create solid surfaces eliminates many of the problems a lunar colony would face in one fell swoop. The only way for lunar dust to clog the equipment and spacesuits like it did to those in the Apollo missions is to kick it up by driving or walking through it or to send it flying everywhere with the exhaust of some rocket. But with a path to travel, land, and launch on and obviously no worries of wind you no longer have the concern of dust problems!
Other than solving the dust problem, that the regolith itself creates, it could also potentially solve two more major problems: oxygen and radiation. Naturally a manned outpost would require a breathable atmosphere but oxygen could also provide a valuable source of fuel. So, how can regolith glean more oxygen? Larry Clark, a senior manager and engineer at Lockheed Martin in Colorado, has been working on that very problem for over 15 years. Clark's lab has produced a prototype that uses the method of hydrogen reduction to extract the oxygen. The process runs at relatively cool temperatures between 1300 and 1600 degrees Fahrenheit but, unfortunately, is only primarily able to extract oxygen from iron oxides--a tenth of the total oxygen available. Though the yield is a fraction of what is possible, Clark predicts that a full scale factory of his prototype could garner enough oxygen for 3-4 astronauts for a year. Plus, if we were to establish the infrastructure for such a factory and store oxygen in inflatable containers prior to sending humans their we could potentially allow for more 'colonists' or for a more extended stay.
Beyond Clark's current viable method, a possible combination of microwaving the regolith into a molten state and using electrolysis could vastly improve oxygen extraction capabilities. Though very promising, this method would have to overcome some serious difficulties with containment and also the gathering of enough energy to power the electrolysis. Even if none of these ideas happen to pan out there is still always the possibility of water-ice sitting on the poles that could be harvested for oxygen or needless to say, water. And lastly we always have the option of simply bringing our own supply!
Concept art of an inflatable module for a lunar base. Courtesy: NASA.gov
Regolith could also be the answer to the ever-omnipresent problem of radiation. The Apollo astronauts were able to avoid this problem by making their visit a short one but those looking for longterm or even a permanent settlement can't quite run from this problem the same way; they can, however hide. Using the lunar soil to protect an outpost has been long suggested because of its availability and ability to effectively block radiation but other than clumping massive amounts of dirt on top of a habitat--a logistical nightmare--nothing has been considered practical. Even the simple idea of using lunar 'sandbags' faces many of the same difficulties as the mound idea. Ideas of building bricks out of the dirt were thrown around and tested but the process of sintering them was also found to be impractical. Impractical, that is, until now. Imagine a microwave factory that melts harvested regolith into casts and molds it into usable bricks among other construction materials. Not only are the bricks able to be used for sheltering an outpost in a safe and uniform manner but they are also able to be easily modified whenever a new attachment is to be added to the habitat. Another benefit is that the walls don't need to be nearly as thick to provide protection from the radiation because of their higher density.
The Future of Regolith
This observation is simply the beginning of what will require much more research. No one can be sure that the regolith will react the same way to microwaves on the moon as it does when subjected to our atmosphere. Further research on the lunar soil will be difficult and inexact. Due to the scarcity of lunar soil many simulant soils have been created but all have come far short of mimicking the real, unique properties of the Apollo samples. Even the actual samples collected from the moon aren't wholly representative. The handling and splitting of samples has caused them to lose a significant amount of the solar wind particles that have been embedded in them. In order to continue this very important research we will likely need to bring back more samples or possibly even conduct the experiments on-site.
But, for now, we can work on the fun part: thinking of uses for the regolith's capabilities. Everything from lawnmowers, brick factories, oxygen extraction, roads, launch pads, and radio telescopes has been discussed. The only limit to it's capabilities is our imagination. So, I'd like to hear what you can imagine. I will post ideas as either you submit them or I come up with them on my own.
List of Ideas for Use of Regolith:
- Post 1 (nick)- Harvest thermal energy from molten regolith.
- Me- Create a 'lunar-rail' by microwaving tracks then use tracks to transport dirt mined, research equipment, people, etc.
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