344 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
or active equipment must stand off, keeping station in the
vicinity.
Other Solar System Resources
This group includes moons other than Earth’s, and the bod-
ies found outside Neptune’s orbit (i.e., in the Kuiper Belt
and especially the Oort Cloud). The many moons of the
giant planets—Jupiter, Saturn, Uranus, and Neptune—
vary widely in their sizes, constituents, and origins. Little is
known about the trans-Neptunian objects (which include
former planet Pluto). Science missions have been sent to
some of these bodies, and more are planned, but capabili-
ties for identifying, locating, and extracting their mineral
resources are much lower than for the Moon or Mars, so
they are not discussed further here. Vacuum, temperature
extremes, solar wind, high-energy radiation, etc. can be
considered space resources as well these also are left for
other discussions.
CURRENT RESEARCH
The regolith that will be the first target of mining off-Earth
is not quite the same as that which forms by weathering
and erosion of Earth bedrock. Regolith samples collected
from Earth’s Moon tend to lock together, impeding flow
through openings and hoppers. Although soil mechanics
as applied on Earth focuses on moisture content as a major
controlling factor, the thin, dry atmosphere of Mars and
the thinner, drier atmosphere of the Moon will force a new
perspective on electrostatics interactions with highly angu-
lar grain shapes instead.
Many hydrometallurgical processes, including electrol-
ysis, rely on the buoyancy of bubbles in liquid to maintain
throughput. Reduced gravity decreases buoyancy, and stud-
ies conducted with drop towers, parabolic flights, sounding
rockets, and the International Space Station (Akay et al.
2022) show that gas bubbles in microgravity stay attached
to the electrode for longer times, growing larger and form-
ing an obstructive layer that raises the overpotential of the
reaction. It is not clear yet whether current-art buoyancy-
controlled processes can be adapted straightforwardly to
lunar or Mars gravity or whether completely different pro-
cesses can be made effective enough for use.
Earth’s Moon
Mineral extraction on the Moon and Mars is envisioned
to be exclusively from regolith in the near term, due to
the expense of launching underground mining equipment
from Earth’s surface. Once mineral extraction has reached
an appropriate level in terms of value (technical, geologic,
and economic), exploration of deposits in bedrock will cer-
tainly begin. Several methods for extracting useful materials
from the lunar regolith are being studied: molten regolith
electrolysis, molten salt electrolysis, hydrogen reduction,
and carbothermal reduction (Hadler et al. 2020).
Linne et al. (2019) outlined the requirements for a
(non-optimized) system on a single lunar lander that could
produce 10 metric tons of oxygen per year from local rego-
lith. Not a full mission plan, this study explored the plausi-
bility of a system using carbothermal reduction, with power
provided by the sun. The result (Figure 1) could nominally
produce and store seven metric tons of liquid oxygen dur-
ing a 7.4-month continuous sunlit period at the lunar south
pole. Transfer of the oxygen output from storage tanks to a
customer’s reusable lander would require separately landed
hardware. Fitting the necessary subsystems—regolith exca-
vation, haulage, sorting, heating/reacting, electrolyzing,
liquefaction, and storage—within the limited mass, power,
and volume available on a fifteen-ton-class commercial
lander was non-trivial, but the design did close and serves
as a rough template for a lunar regolith-extraction demon-
stration leading up to a pilot plant design.
Mars
As elsewhere, the first resources of interest are those that
can be used to manufacture spacecraft propellants as well as
life-support consumables. On Mars that means the carbon
dioxide as gas in the atmosphere and ice at the poles, and
water as ground ice and components of mineral structures.
The first ISRU demonstration anywhere in space,
named MOXIE (Mars Oxygen ISRU Experiment, Figure 2)
used a scroll compressor to draw Mars atmosphere into a
stack of ten solid-oxide electrolysis cells to produce 99.9%
pure oxygen in 2021–2023 (Hecht et al. 2021 Hoffman et
al. 2023 Rapp and Inglezakis 2024). A subsequent NASA
study (Oleson et al. 2024) expanded on this by evaluating
a likely integration of the required subsystems to produce
300 metric tons of liquid oxygen and liquid methane on
Mars. As with MOXIE, one of the components would be
carbon dioxide from the atmosphere. The other would be
150 metric tons of water.
The first question addressed by Oleson et al. (2024) was
whether it would be more efficient to ship the water from
Earth, melt subsurface ice, or extract water from hydrated
mineral deposits. The first option would be the simplest.
The second option would use the most energy and would
restrict the site location to near-surface ice concentrations
or active equipment must stand off, keeping station in the
vicinity.
Other Solar System Resources
This group includes moons other than Earth’s, and the bod-
ies found outside Neptune’s orbit (i.e., in the Kuiper Belt
and especially the Oort Cloud). The many moons of the
giant planets—Jupiter, Saturn, Uranus, and Neptune—
vary widely in their sizes, constituents, and origins. Little is
known about the trans-Neptunian objects (which include
former planet Pluto). Science missions have been sent to
some of these bodies, and more are planned, but capabili-
ties for identifying, locating, and extracting their mineral
resources are much lower than for the Moon or Mars, so
they are not discussed further here. Vacuum, temperature
extremes, solar wind, high-energy radiation, etc. can be
considered space resources as well these also are left for
other discussions.
CURRENT RESEARCH
The regolith that will be the first target of mining off-Earth
is not quite the same as that which forms by weathering
and erosion of Earth bedrock. Regolith samples collected
from Earth’s Moon tend to lock together, impeding flow
through openings and hoppers. Although soil mechanics
as applied on Earth focuses on moisture content as a major
controlling factor, the thin, dry atmosphere of Mars and
the thinner, drier atmosphere of the Moon will force a new
perspective on electrostatics interactions with highly angu-
lar grain shapes instead.
Many hydrometallurgical processes, including electrol-
ysis, rely on the buoyancy of bubbles in liquid to maintain
throughput. Reduced gravity decreases buoyancy, and stud-
ies conducted with drop towers, parabolic flights, sounding
rockets, and the International Space Station (Akay et al.
2022) show that gas bubbles in microgravity stay attached
to the electrode for longer times, growing larger and form-
ing an obstructive layer that raises the overpotential of the
reaction. It is not clear yet whether current-art buoyancy-
controlled processes can be adapted straightforwardly to
lunar or Mars gravity or whether completely different pro-
cesses can be made effective enough for use.
Earth’s Moon
Mineral extraction on the Moon and Mars is envisioned
to be exclusively from regolith in the near term, due to
the expense of launching underground mining equipment
from Earth’s surface. Once mineral extraction has reached
an appropriate level in terms of value (technical, geologic,
and economic), exploration of deposits in bedrock will cer-
tainly begin. Several methods for extracting useful materials
from the lunar regolith are being studied: molten regolith
electrolysis, molten salt electrolysis, hydrogen reduction,
and carbothermal reduction (Hadler et al. 2020).
Linne et al. (2019) outlined the requirements for a
(non-optimized) system on a single lunar lander that could
produce 10 metric tons of oxygen per year from local rego-
lith. Not a full mission plan, this study explored the plausi-
bility of a system using carbothermal reduction, with power
provided by the sun. The result (Figure 1) could nominally
produce and store seven metric tons of liquid oxygen dur-
ing a 7.4-month continuous sunlit period at the lunar south
pole. Transfer of the oxygen output from storage tanks to a
customer’s reusable lander would require separately landed
hardware. Fitting the necessary subsystems—regolith exca-
vation, haulage, sorting, heating/reacting, electrolyzing,
liquefaction, and storage—within the limited mass, power,
and volume available on a fifteen-ton-class commercial
lander was non-trivial, but the design did close and serves
as a rough template for a lunar regolith-extraction demon-
stration leading up to a pilot plant design.
Mars
As elsewhere, the first resources of interest are those that
can be used to manufacture spacecraft propellants as well as
life-support consumables. On Mars that means the carbon
dioxide as gas in the atmosphere and ice at the poles, and
water as ground ice and components of mineral structures.
The first ISRU demonstration anywhere in space,
named MOXIE (Mars Oxygen ISRU Experiment, Figure 2)
used a scroll compressor to draw Mars atmosphere into a
stack of ten solid-oxide electrolysis cells to produce 99.9%
pure oxygen in 2021–2023 (Hecht et al. 2021 Hoffman et
al. 2023 Rapp and Inglezakis 2024). A subsequent NASA
study (Oleson et al. 2024) expanded on this by evaluating
a likely integration of the required subsystems to produce
300 metric tons of liquid oxygen and liquid methane on
Mars. As with MOXIE, one of the components would be
carbon dioxide from the atmosphere. The other would be
150 metric tons of water.
The first question addressed by Oleson et al. (2024) was
whether it would be more efficient to ship the water from
Earth, melt subsurface ice, or extract water from hydrated
mineral deposits. The first option would be the simplest.
The second option would use the most energy and would
restrict the site location to near-surface ice concentrations