342 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
The United Launch Alliance, a major commercial launch
provider, has offered to purchase propellant in low-Earth
orbit for $3,000/kg, at the Lagrange point between Earth
and the Moon for $1,000/kg, and on the Moon’s surface for
$500/kg (David 2016). A recent study estimated that deliv-
ering propellant to low-Earth orbit costs NASA $10,000 to
$50,000/kg using the current system of fully expendable
launch vehicles, depending on tanker size (Tiffin and Friz
2021).
Operating Environments
The major aspects of Earth’s environment that have
enabled—and constrained—the evolution of mineral pro-
cessing methods include: Thick, relatively moist atmo-
sphere liquid water available nearly everywhere a constant
gravity vector relatively short travel distances and funda-
mentally, human beings. These will be different in space,
though some will be more different than others. Space
bodies can be divided into two general types. The most
familiar are those that are planets or planet-like in other
words, they are large enough to have a unidirectional grav-
ity vector, like Earth does though the details vary, and a
stable surface with enough gravity to work with. Terrestrial
techniques can generally be adapted to these bodies. Small
bodies, on the other hand, are substantially different from
planets. These include asteroids and comets, bodies usually
with too little mass to have self-rounded shapes. Their sur-
faces and interiors may be unstable, and they may consist
of unusual materials, thus requiring truly novel techniques
to extract whatever value they contain.
Gaining access to the resources of space has compo-
nents both familiar and unprecedented in the mineral
industry. Long project lead times and shipping routes are
facts of life that will be even longer in space. Earth’s Moon,
nearest in distance, requires several days of very carefully
planned travel. Mars, the next further “rock from the Sun,”
needs seven to eight months for cargo at nearest approach
and three years for humans (round-trip). Half of the easi-
est-to-get-to small bodies are within 4.1 years (round-trip
Jedicke et al. 2022). The two Voyager spacecraft, launched
in 1977 and moving at roughly 58,000 km/hr, will exit the
solar system in 14,000–28,000 years.
Getting around in space involves complex mechanics.
Instead of constant gravity holding everything against a
surface that can be approximated as flat, spacecraft must
traverse a three-dimensional gravitational “minefield” that
is constantly shifting. Everything exerts gravitational pull
in proportion to its mass, thus every solar system body—
including spacecraft—orbits the Sun because the Sun con-
tains more than 99% of the mass in the solar system. But
bodies are affected also by any mass that is close enough the
difficulty of knowing the location of every body in the solar
system at any given moment means that spacecraft must
continually adjust their trajectories by expending energy
in appropriate directions at appropriate times. Energy to
change spacecraft velocity—delta V—is where propellants
(fuels and oxidizers) come in.
In the near term, space mineral resources will come
from regolith, the fragmented rock* that covers the surface
of most solar system bodies to some extent†. Surface min-
ing is the main focus of current plans, due partly to the
expense and difficulty of launching underground mining
equipment, but mostly because necessary knowledge of
subsurface geology of space bodies is lacking in all but the
broadest sense. What we believe we know of their subsur-
face regions is derived from reflected light (which indicates
surface composition and roughness) and mass distribution
calculations from spacecraft trajectory deviations. These are
insufficient for planning mineral extraction, so an urgent
priority is to collect data appropriate for prospecting (Neal
et al. 2024).
One of the biggest differences between Earth resources
and extra-terrestrial ones is that we understand so much
more about the former: where they are, how they form,
how to process them. Space is still very much an unknown
country. In part this is because the surfaces have evolved
over much longer timeframes than those on Earth, which
are subject to weathering and erosion caused by atmospheric
reaction to sunlight. The major formation mechanisms of
space regolith are impacts and thermal shock. Impacts are
well-recognized as a rock fragmentation mechanism. But in
vacuum, such as on the Moon and small bodies, thermal
shock is equally productive because the nearly instant tem-
perature transition between sunlight and shadow generates
skin stresses in rock surfaces.
Other resource extraction differences that are likely to
dissipate in the long term, but will be important on shorter
timelines, include low initial production rates (noted in
the previous section), the high cost of launching, and the
unfamiliarity of the operating environment. Launching a
pound of anything from Earth’s surface just to low-Earth
orbit costs at least $1500 (Aerospace Security 2022).
*Regolith lacks the organic components to be classified as soil.
† Bedrock in the inner solar system consists mainly of silicate
minerals, but as distance from the Sun increases, the bedrock
becomes ices rather than silicates. (The current distinction
between volatile and refractory compounds is based on Earth-
surface conditions that are far removed from surface conditions
on bodies in the outer solar system.)
The United Launch Alliance, a major commercial launch
provider, has offered to purchase propellant in low-Earth
orbit for $3,000/kg, at the Lagrange point between Earth
and the Moon for $1,000/kg, and on the Moon’s surface for
$500/kg (David 2016). A recent study estimated that deliv-
ering propellant to low-Earth orbit costs NASA $10,000 to
$50,000/kg using the current system of fully expendable
launch vehicles, depending on tanker size (Tiffin and Friz
2021).
Operating Environments
The major aspects of Earth’s environment that have
enabled—and constrained—the evolution of mineral pro-
cessing methods include: Thick, relatively moist atmo-
sphere liquid water available nearly everywhere a constant
gravity vector relatively short travel distances and funda-
mentally, human beings. These will be different in space,
though some will be more different than others. Space
bodies can be divided into two general types. The most
familiar are those that are planets or planet-like in other
words, they are large enough to have a unidirectional grav-
ity vector, like Earth does though the details vary, and a
stable surface with enough gravity to work with. Terrestrial
techniques can generally be adapted to these bodies. Small
bodies, on the other hand, are substantially different from
planets. These include asteroids and comets, bodies usually
with too little mass to have self-rounded shapes. Their sur-
faces and interiors may be unstable, and they may consist
of unusual materials, thus requiring truly novel techniques
to extract whatever value they contain.
Gaining access to the resources of space has compo-
nents both familiar and unprecedented in the mineral
industry. Long project lead times and shipping routes are
facts of life that will be even longer in space. Earth’s Moon,
nearest in distance, requires several days of very carefully
planned travel. Mars, the next further “rock from the Sun,”
needs seven to eight months for cargo at nearest approach
and three years for humans (round-trip). Half of the easi-
est-to-get-to small bodies are within 4.1 years (round-trip
Jedicke et al. 2022). The two Voyager spacecraft, launched
in 1977 and moving at roughly 58,000 km/hr, will exit the
solar system in 14,000–28,000 years.
Getting around in space involves complex mechanics.
Instead of constant gravity holding everything against a
surface that can be approximated as flat, spacecraft must
traverse a three-dimensional gravitational “minefield” that
is constantly shifting. Everything exerts gravitational pull
in proportion to its mass, thus every solar system body—
including spacecraft—orbits the Sun because the Sun con-
tains more than 99% of the mass in the solar system. But
bodies are affected also by any mass that is close enough the
difficulty of knowing the location of every body in the solar
system at any given moment means that spacecraft must
continually adjust their trajectories by expending energy
in appropriate directions at appropriate times. Energy to
change spacecraft velocity—delta V—is where propellants
(fuels and oxidizers) come in.
In the near term, space mineral resources will come
from regolith, the fragmented rock* that covers the surface
of most solar system bodies to some extent†. Surface min-
ing is the main focus of current plans, due partly to the
expense and difficulty of launching underground mining
equipment, but mostly because necessary knowledge of
subsurface geology of space bodies is lacking in all but the
broadest sense. What we believe we know of their subsur-
face regions is derived from reflected light (which indicates
surface composition and roughness) and mass distribution
calculations from spacecraft trajectory deviations. These are
insufficient for planning mineral extraction, so an urgent
priority is to collect data appropriate for prospecting (Neal
et al. 2024).
One of the biggest differences between Earth resources
and extra-terrestrial ones is that we understand so much
more about the former: where they are, how they form,
how to process them. Space is still very much an unknown
country. In part this is because the surfaces have evolved
over much longer timeframes than those on Earth, which
are subject to weathering and erosion caused by atmospheric
reaction to sunlight. The major formation mechanisms of
space regolith are impacts and thermal shock. Impacts are
well-recognized as a rock fragmentation mechanism. But in
vacuum, such as on the Moon and small bodies, thermal
shock is equally productive because the nearly instant tem-
perature transition between sunlight and shadow generates
skin stresses in rock surfaces.
Other resource extraction differences that are likely to
dissipate in the long term, but will be important on shorter
timelines, include low initial production rates (noted in
the previous section), the high cost of launching, and the
unfamiliarity of the operating environment. Launching a
pound of anything from Earth’s surface just to low-Earth
orbit costs at least $1500 (Aerospace Security 2022).
*Regolith lacks the organic components to be classified as soil.
† Bedrock in the inner solar system consists mainly of silicate
minerals, but as distance from the Sun increases, the bedrock
becomes ices rather than silicates. (The current distinction
between volatile and refractory compounds is based on Earth-
surface conditions that are far removed from surface conditions
on bodies in the outer solar system.)