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Mining
and Manufacturing on the Moon |
Lunar Mining Facility |
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"Engineering is the professional art of applying
science to the optimum conversion of natural resources
to the benefit of man."
-Ralph J. Smith (1962)
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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
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| 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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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
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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.
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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.
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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.
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[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 |
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.
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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." |
Lunar scientist Carleton Allen at work in the Lunar
Rock Laboratory at JSC |
Mining
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 |
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
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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. |
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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. |
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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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