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Mining and Manufacturing on the Moon

Lunar Mining Facility
Lunar Mining Facility

 

"Engineering is the professional art of applying science to the optimum conversion of natural resources to the benefit of man."
-Ralph J. Smith (1962)


Resource utilization will play an important role in the establishment and support of a permanently manned lunar base.  The identification of new and innovative technologies will insure the success, sustainability and growth of a future lunar base.  These new technologies will certainly utilize lunar resources.  Lunar resources can be used to supply replenishables such as oxygen, fuel, water and construction materials.  These materials would otherwise have to be brought from Earth at considerable expense. 

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Lunar resources include oxygen from the lunar soil, water from the poles and a supply of volatile gases. One of the most significant steps towards self-sufficiency and independence from the Earth will be the use of lunar materials for construction. 

At least seven major potential lunar construction materials have been identified.  These include:

  • concrete 
  • sulfur concrete
  • cast basalt
  • sintered basalt 
  • fiberglass
  • cast glass
  • metals
All of these materials may be used to construct a future lunar base.  The basalt materials can be formed out of lunar regolith (soil) by a simple process of heating and cooling, and are the most likely to be used to build the first bases. 

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Lunar Structures

With the gravity level of the moon being 1/6th that of Earth, lunar structures can carry a load that is six times that of those on Earth.  This allows for structures that are thicker and can provide better micrometeorite, radiation and thermal shielding for the crew. Lunar basalt can handle the extreme thermal ranges of 100 degrees above zero (Celsius) to over 150 degrees below zero. The lack of weather on the moon will give lunar structures a very long life span.  Lunar dust however is extremely abrasive, but basalt is highly resistant to abrasion and thus is an ideal structural material for the moon. 

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Click to enlarge image

Designs for a sub-surface lunar base are very appealing to engineers because the surrounding regolith helps to relieve loads on the structure by equalizing the internal forces of a pressurized structure. 

They also reduce the amount of area which needs to be protected from solar and cosmic radiation, and also help protect from drastic thermal changes. 

Factories and habitats consist of walls, beams, radiation shielding and internal components.  These can all be made from lunar fiberglass, lunar glass ceramics and lunar iron or other metals.  Beams, walls and shielding can be made using solar ovens and casting techniques.  Windows can be made from lunar glass, mirrors can be made from lunar aluminum. 

Resources

It is estimated that transporting material from the Earth to the moon would cost $25,000 per pound!  Therefore it is imperative that we use resources already on the moon to offset the cost.  Of all the resources available, the lunar regolith is the most accessible and most easily converted into construction materials.  Lunar regolith contains oxygen, silicon, magnesium, iron, calcium, aluminum and titanium.

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About 40% of the lunar soil is oxygen (bound up in molecular silcates and metal oxides). The reason that oxygen is so abundant on the moon is that it bonds easily to so many things.  Oxygen-bonded materials are lightweight and thus float up to the surface to form the crust of a planetary body as it evolves.  (Metals do not like to bond with oxygen and usually sink to the core of a planet, they are rare in the crust and precious to those living on the surface.)  Oxygen can literally be "cooked" out of the regolith, can be used for breathable air, and makes up about 86% of oxygen-hydrogen rocket fuel.  Even without hydrogen from supplies of lunar ice, a majority of the material needed for rocket fuel can be manufactured on the moon. 

 

The moon's surface is very powdery due to millions of years of micrometeorite impacts and no active geology.  In fact Apollo designers worried that the lander and astronauts might sink into the surface!  You can see in the bootprints how every contour was finely imprinted in the dust. 

Mining of the powder would not require heavy Earth moving machinery because of this and the 1/6th gravity. It is ideal for cheap mining and mineral processing. 
  

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On Earth, aluminum and iron mines do not dig out pure metals from the ground.  They dig out silicates that have metallic elements bonded to silicon and oxygen.  The material is processed by heat, chemicals or electricity to separate the metal out.  These facilities are called smelters. The lunar highland mineral anorthite is similar to the mineral bauxite that is used on Earth to smelt out aluminum. Anorthite consists of aluminum, calcium, silicon and oxygen.  Smelters can produce pure aluminum, calcium metal, oxygen and silica glass from anorthite.  The average anorthite concentration in the lunar highlands where the Apollo astronauts landed was between 75 and 98%. Raw anorthsite is also good for making fiberglass and other glass and ceramic products.

Aluminum can be used as an electrical conductor.  It is lightweight, makes good structural elements, mirrors and atomized aluminum powder makes a good fuel when burned with oxygen. In fact it is the fuel source of the Space Shuttle solid rocket boosters!

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The by-product of aluminum production, calcium metal is also a good electrical conductor. It will conduct more electricity than aluminum or copper at higher temperatures and is easy to work with. It is easily shaped, molded, machined and made into wire, pressed and hammered.

Ilemite a mineral found in abundance by the Apollo astronauts is high in titanium and can be used to trap solar hydrogen.  Processing of ilemite could produce hydrogen (an otherwise rare element on the moon, unless lunar water ice is located).  Iron can also be extracted from ilemite. A very small amount (half of one percent) of free iron is found in the lunar regolith and could be extracted by magnets after grinding.  Iron powder can be used to make parts using a standard Earth process called powder metallurgy.

Oxygen Production

NASA scientist Carlton Allen writes in his paper "Oxygen Extraction from Lunar Soils and Pyroclastic Glass":

...[O]xygen can be extracted [from the moon] if thermal, electrical, or chemical energy is invested to break the chemical bonds. Over twenty different methods have been proposed for oxygen extraction on the Moon. Oxygen which is chemically bound to iron in lunar minerals and glasses can be extracted by heating the material to temperatures above 900°C and exposing it to hydrogen gas. The basic equation is: FeO + H2 -> Fe + H2O    This process results in release of the oxygen as water vapor. The vapor must be separated from the excess hydrogen and other gases and electrolyzed.  The resulting oxygen is then condensed to liquid and stored. Experiments using samples of lunar ilmenite, basalt, soil, and volcanic glass have demonstrated the required conditions and efficiency of this process. 

[Examples include:]

Ilmenite - Most early work on lunar resources has focused on the mineral ilmenite (FeTiO3) as the feedstock for oxygen production. This mineral is easily reduced, and oxygen yields of 8-10 wt% (mass of oxygen per mass of ilmenite) may be achievable. Ilmenite occurs in abundances as high as 25 wt% in some lunar basalts. 

Basalt - Previous oxygen production experiments utilized lunar basalt 70035 which was crushed but not otherwise beneficiated. The sample produced 2.93 wt% oxygen in a 1050°C hydrogen reduction experiment. Of the minerals in this rock, the most oxygen was extracted from ilmenite, with lesser amounts from olivine and pyroxene. 

Lunar Oxygen Production Plant
Lunar Oxygen Production Plant

Soil - Oxygen can be produced from a wide range of unprocessed lunar soils, including those which contain little or no ilmenite. Oxygen yield from lunar soils is strongly correlated with initial iron content. 

The dominant iron-bearing phases in lunar soil are ilmenite, olivine, pyroxene, and glass. Each of these phases is a source of oxygen. Ilmenite and iron-rich glass react most rapidly and completely. Olivine is less reactive. Pyroxene is the least reactive iron-bearing phase in lunar soil. 

Volcanic Glass - The optimum feedstock for a lunar oxygen production process may be volcanic glass. At least 25 distinct glass compositions have been identified in the Apollo sample collection. The iron-rich species promise particularly high oxygen yields. 

 

The production of oxygen from lunar materials is now a reality. Oxygen release by means of hydrogen reduction has been demonstrated in the laboratory with samples of lunar basalt, soil, and volcanic glass. Yields from soils are predictable, based solely on each sample's iron abundance. 

The reactions are rapid, with most of the release occurring in a few tens of minutes. All of the major iron-bearing phases in lunar soil release oxygen, though with differing degrees of efficiency. These data can support the design of an oxygen production plant at a future lunar base."
Carleton Allen
Lunar scientist Carleton Allen at work in the Lunar Rock Laboratory at JSC

 

Mining

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Before we can hope to process the soil of the Moon into other materials, we will first have to dig it up and feed it into the processing plants. There are many concepts of how to do this, but all need to resolve the same issues that have faced mining companies on Earth for centuries. While there are problems on the Moon that are not a factor here on Earth, the mastery of this skill will require NASA to include the lessons of the mining industry in its planning. The U.S. Bureau of Mines and several universities have already begun to consider the requirements and options for lunar mining equipment. 

Lunar Mining Facility
Lunar Mining Facility
Underground mines on the Earth often require remotely controlled equipment due to safety requirements and harsh conditions.  On the moon excavation and hauling operations will need to be automated and teleoperated for the same reasons.  Prior to mining operations the topography will have to be mapped in great detail. 

Front end loaders will scoop up the regolith and drop it into haulers and bring it back to the processing site. Using inertial guidance, radar, laser ranging, electronic guideposts, and satellite tracking automated haulers could be operated from Earth or from lunar operators.

These haulers would be navigated back and forth from the mine in a programmed sequence.  Many current toys and remotely controlled operations use this same technology of preprogrammed paths. 

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A lunar communications receiver, amplifier, transponder network and computer systems would be needed.  The loaders and haulers themselves could be launched from Earth and assembled on the moon. 

The haulers would not need to be as structurally massive as Earth equipment.  The loaders would be nearly the same since they need a counterweight when scooping up lunar regolith. These counterweights could be produced on the moon.  A simple bucket and reel system could replace front end loaders.  This system would pull the dirt up a ramp and into a hauler.

 

The Apollo astronauts had some difficulty extracting subsurface samples.  While the top was powdery and soft their attempts to drill into the surface resulted in the seizing of the drills which had to be abandoned in place. It is thought that lunar soil is very dense under the soft surface perhaps due to small repeated vibrations by distant meteor impacts over time which densely packed soil particles. 
Lunar Mining Facility
Lunar Mining Facility 
 
young16.jpg Another concern is rubbing friction in a vacuum. The U.S Bureau of Mines found that exposing lunar simulant to a vacuum long enough for nearly complete outgassing caused increased friction up to 60 times!  Tools would need to be made from (or coated with) special materials to minimize friction.  Experiments will be done using lunar simulants and tools in a vacuum in preparation for their use on the moon.  For a list of all the geology tools used for the Apollo missions, click here. To review the sample collection processes used by the Apollo astronauts, visit this site.
lunOX.jpg Significant changes in lunar temperatures occur between shadowed and sunlit areas on the lunar surface.  Equipment will need to be designed to withstand very high temperatures (140 degrees Celsius/280 degrees Fahrenheit) or sunscreens can be used (possibly with foil mirrors to eliminate shadows). At night, mining equipment will need to be sheltered and heated perhaps in tunneled garages.

Materials Processing

The top few meters of the lunar surface consists of a mix of materials, while lower depths may offer more uniform mineralogy from older magma oceans.  The mix on the surface is due to the splashes of asteroid impacts that mixed materials from various distances.  The surface is glassier due to heating of asteroid ejecta and subsequent quick cooling. 

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Volcanism on the moon also produced glassy beads.  Some proposed methods for materials processing on the moon call for processing just one mineral such as ilemite.  This would require separating the one mineral from the regolith mix or mining it deep under the surface where it may be found in more abundance. The dark beads in the image above is ilemite.

NASA experiments using simulated lunar soil have produced glass ceramics with "superior mechanical properties with tensile strengths in excess of 50,000 psi which can be used as structural components of buildings in space or on the Moon."

Natural glass is more common on the moon due to the lack of water which preserved them in their natural state from volcanic eruptions billions of years ago.  

Clear pure silica glass (SiO2) is readily manufactured from lunar materials. It can be made optically superior to that produced on the Earth because it can be made completely anhydrous (lacking in hydrogen). 

Anhydrous glass has been considered for use in structural components since it has significantly better mechanical properties. Glass structural beams reinforced with asteroid nickel-iron steel could be used as structural beams to withstand a wide range of tension and compression. For more information, check out this NASA paper on "Processing Glass Fiber from Moon/Mars Resources." (.pdf)

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Bulk fiberglass and hand ceramics can be made on the moon using currently developed processes.  The sintering technique for producing ceramics used for casting molds uses powdered material melted at very high temperatures then slowly cooled to a solid.  This routine process on Earth works even better in a vacuum where there is no oxygen, water or other molecules to create impurities.  Solar ovens or microwaves could be used for sintering of lunar materials. The resulting material is low in density, can be cut and shaped fairly easily, holds small loads and provides good thermal protection. 

Glass ceramics that are highly resistant to abrasion and have a fairly good shock resistance can be made from balsaltic rock.  Techniques for cast basalt production have been around for over 50 years. They are used to produce tiles, pipes and other industrial products. Basalt is melted at about 1350 degrees Celsius, poured into sand or metallic molds and solidify at about 900 degrees. Soils rich in iron oxide produce dark and mechanically strong glass ceramics.

For more about materials processing on the moon visit this site from the NASA Marshall Space Flight Center.

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Researchers at the University of Wisconsin's Center for Space Automation and Robotics, one of 16 NASA Centers for the Commercial Development of Space believe the future of energy production lies with helium-3. One ton could supply the electrical needs of a city of 10 million people when combined in a fusion reactor with a form of hydrogen.
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Lunar samples collected by Apollo astronauts show the resource is so plentiful that the Earth's energy needs could be accommodated for at least 1,000 years. However, a great deal of work needs to be done before helium-3-powered fusion plants become a reality. Although the university began its fusion program in 1963 and has since granted some 186 Ph.D.s in the field, no one has yet built a fusion reactor that releases more energy than it consumes. According to theory, fusion reactors operating with helium-3 would be superior to fission reactors because they would not generate high-level radioactive waste.

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In one study, scientists determined that lunar helium-3, which originated from the sun and was deposited on the Moon by the solar wind, could be mined and transported to Earth. Some early estimates place the value of helium-3 equivalent to buying oil at $7 a barrel. 

Researchers also have studied possible mining sites. Based on U.S. experience during the Apollo 11 mission, they determined that the Sea of Tranquility was the prime target for initial investigations because it appeared to contain the potential for many tons of helium-3 below the surface. Backup targets include the vicinity of Mare Serenitatis sampled during Apollo 17.
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Researchers designed solar-powered robotic equipment that would scoop up the top layer of lunar soil and place it into a robotic unit. The soil would be heated, thus separating the helium-3 from other lunar material. The spent material then would be dropped off the back of the moving robotic miner.

Because the Moon has one-sixth the Earth's gravity, relatively little energy would be required to lift the material. 

Through this process, other products also would be produced, including nitrogen, methane, helium, water, carbon-oxygen compounds, hydrogen, all of which are vital to human existence in space.

Questions to think about:

  • Of all the materials that could be manufactured on the moon which one has the most potential benefits for use solely on the moon?
  • Which one has the most benefits for transferability to Earth? Why?
  • Which type of materials processing facility would be the most interesting to design? 
  • Which would be the most expensive? 
  • Which would be the most cost effective?

In the next chapter you will explore various concepts for space tourism under consideration by various organizations and countries. 

Next... Space Tourism (pg. 7 of 9)


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