Monday, June 18, 2007

Lunar Dirt Factories? A look at how regolith could be the key to permanent outposts on the moon!

(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:
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:
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:
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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Nick said...

I think if they can make the temp. of dirt that high using a feasible amount of energy, they could use that dirt as a huge source of power.

Pat said...

I was actually thinking about the same idea earlier. I was reluctant to write it down because I didn't know if the efficiency would be very high. But, the more I think about it, the more potential I see in it. Maybe a power plant could be constructed in similar fashion to a nuclear power plant (harvesting electrical energy from the thermal energy produced by the nuclear reactions).

This is the type of ideas I'm looking for. Thanks for sharing and I hope others follow suite.

Anonymous said...

for colonization purposes, tunnels have always been my favourite option. the microwave lawnmower above gave me the idea of using microwave power to create and seal the tunnel walls by melting the surface, not quite sure if this would work as further below the surface there may not be the required meteorite/iron deposites

Play Bark said...

Any experiments on the soil need to be done in the same conditions that exist on the moon or at least outside our atmosphere, there is the space station available it seems no one talks of that anymore, is it vacant.

Marpass said...

I see the diagrams of how to obtain He3 from the moon studying the papers of
University of Wisconsin.The design of mining machine to do this process
that go to the moon, extract He3,
come back to earth and in the middle of the way process the he3.
The methodology” BIA”, a matrix of all problems that the machine
could have in the way to the moon and in the way to earth.
The Impact found simple problems that could have the machine in the way
To the moon, and criticals problems, always is high. The times, for develop
the mining machine. The last matter will be work in Bio-fuels-Diesel,
it could be good for the future analyses of how to process He3 fuels.
I work and develop since years a methodology of Risk Space Management
using standards 4360 AUS-NZ ,NIST -800-30 and in the end i am working
with ISO 31000, and 31010.

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