Asteroid mining refers to the possibility of exploiting raw materials from asteroids and other minor planets, including near-Earth objects. Minerals and volatiles could be mined from an asteroid or spent comet to provide space-construction materials (e.g., iron, nickel, titanium), to extract water and oxygen to sustain the lives of prospector-astronauts on site, as well as hydrogen and oxygen for use as rocket fuel. In space exploration, these activities are referred to as in-situ resource utilization.
Some day, the platinum, cobalt and other valuable elements from asteroids may even be returned to Earth for profit. At 1997 prices, a relatively small metallic asteroid with a diameter of 1.6 km (0.99 mi) contains more than 20 trillion US dollars worth of industrial and precious metals.[1][2] In fact, all the gold, cobalt, iron, manganese, molybdenum, nickel, osmium, palladium, platinum, rhenium, rhodium, ruthenium, and tungsten that we now mine from the Earth's crust, and that are essential for economic and technological progress, came originally from the rain of asteroids that hit the Earth after the crust cooled.[3][4][5] This is because, while asteroids and the Earth congealed from the same starting materials, Earth's massive gravity pulled all such siderophilic (iron-loving) elements into the planet's core during its molten youth more than four billion years ago[6]. Initially, this left the crust utterly depleted of such valuable elements[7]. Asteroid impacts re-infused the depleted crust with metals.
A comparatively small M-type asteroid with a mean diameter of 1 km could contain more than two billion metric tons of iron–nickel ore,[8] or two to three times the annual production for 2004.[9] The asteroid 16 Psyche is believed to contain 1.7×1019 kg of nickel–iron, which could supply the 2004 world production requirement for several million years. A small portion of the extracted material would also be precious metals.
In 2006, the Keck Observatory announced that the binary Trojan asteroid 617 Patroclus,[10] and possibly large numbers of other Jupiter Trojan asteroids, are likely extinct comets and consist largely of water ice. Similarly, Jupiter-family comets, and possibly near-Earth asteroids that are defunct comets, might also economically provide water. The process of in-situ resource utilization—using materials native to space for propellant, tankage, radiation shielding, and other high-mass components of space infrastructure—could lead to radical reductions in its cost.
This would satisfy one of two necessary conditions to enable "human expansion into the Solar System" (the ultimate goal for human space flight proposed by the 2009 "Augustine Commission" Review of United States Human Space Flight Plans Committee): physical sustainability and economic sustainability.
Traces of targeted asteroid mining could be utilized for SETI.[11]
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Economic analyses generally show that asteroid mining will not attract private investment at current commodity prices and space transportation costs.[12] However, based on known terrestrial reserves and growing consumption in developing countries, there is speculation that key elements needed for modern industry, including antimony, zinc, tin, silver, lead, indium, gold, and copper, could be exhausted on Earth within 50-60 years.[13]
At present, the cost of returning asteroidal materials to Earth far outweighs their market value. An important factor to consider in target selection is orbital economics, in particular the delta-v (Δv) and travel time to and from the target. More of the extracted native material must be expended as propellant in higher Δv trajectories, thus less returned as payload. Direct Hohmann trajectories are faster than Hohmann trajectories assisted by planetary and/or lunar flybys, which in turn are faster than those of the Interplanetary Transport Network, but the latter have lower Δv than the former.
Currently, the quality of the ore and the consequent cost and mass of equipment required to extract it are unknown. However, potential markets for materials can be identified and profit estimated. For example, the delivery of multiple tonnes of water to low Earth orbit (LEO) in a space tourism economy could generate a significant profit.[14]
Near-Earth asteroids are considered likely candidates for early mining activity. Their low Δv location makes them suitable for use in extracting construction materials for near-Earth space-based facilities, greatly reducing the economic cost of transporting supplies into Earth orbit.
| Mission | Δv |
|---|---|
| Earth surface to LEO | 8.0 km/s |
| LEO to near-Earth asteroid | 5.5 km/s[a] |
| LEO to lunar surface | 6.3 km/s |
| LEO to moons of Mars. | 8.0 km/s |
The table at right shows a comparison of Δv requirements for various missions. In terms of propulsion energy requirements, a mission to a near-Earth asteroid compares favorably to alternative mining missions.
An example of a potential target for an early asteroid mining expedition is 4660 Nereus. This body has a very low Δv compared to lifting materials from the surface of the Moon. However it would require a much longer round-trip to return the material.
There are three options for mining:
Processing in situ for the purpose of extracting high-value minerals will reduce the energy requirements for transporting the materials, although the processing facilities must first be transported to the mining site.
Mining operations require special equipment to handle the extraction and processing of ore in outer space. The machinery will need to be anchored to the body, but once in place, the ore can be moved about more readily due to the lack of gravity. Docking with an asteroid can be performed using a harpoon-like process, where a projectile penetrates the surface to serve as an anchor then an attached cable is used to winch the vehicle to the surface, if the asteroid is rigid enough for a harpoon to be effective.
Due to the distance from Earth to an asteroid selected for mining, the round-trip time for communications will be several minutes or more, except during occasional close approaches to Earth by near-Earth asteroids. Thus any mining equipment will either need to be highly automated, or a human presence will be needed nearby. Humans would also be useful for troubleshooting problems and for maintaining the equipment. On the other hand, multi-minute communications delays have not prevented the success of robotic exploration of Mars, and automated systems would be much less expensive to build and deploy.[16]
There are several options for material extraction:
Material is successively scraped off the surface in a process comparable to strip mining. There is strong evidence that many asteroids consist of rubble piles,[17] making this approach possible.
A mine can be dug into the asteroid, and the material extracted through the shaft. This requires precise knowledge to engineer accuracy of astro-location under the surface regolith and a transportation system to carry the desired ore to the processing facility.
Asteroids with a high metal content may be covered in loose grains that can be gathered by means of a magnet.[18]
For volatile materials in extinct comets, heat can be used to melt and vaporize the matrix.[19]
A 1980 NASA study entitled Advanced Automation for Space Missions proposed a complex automated factory on the Moon that would work over several years to build a copy of itself.[20] Exponential growth of factories over many years could refine large amounts of lunar regolith. Since 1980 we have seen several decades of technological progress in miniaturization, nanotechnology, materials science, and additive manufacturing (or 3D printing).
The power of self-replication is compelling. For example, a 1 kg solar-powered self-replicating machine that takes one month to make a copy of itself would, after just two and a half years (30 doublings), refine over one billion kilograms of asteroidal material without any human intervention. Ten months later you would have one trillion kg of whatever metal(s) are used to make the devices, which could then be "harvested" at any time. No large mass of equipment need be delivered to the asteroid; in effect, only the information that went into designing the device plus the 1 kg device itself.
Potential applications for the resources obtained from asteroid mining include propellant depots[21][1] and solar-power satellites.[22][15]
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