Asteroid mining
Asteroid mining is the exploitation of raw materials from asteroids and other minor planets, including near-Earth objects.
Hard rock minerals could be mined from an asteroid or a spent comet. Precious metals such as gold, silver, and platinum group metals could be transported back to Earth, while iron group metals and other common ones could be used for construction in space.
Difficulties include the high cost of spaceflight, unreliable identification of asteroids which are suitable for mining, and ore extraction challenges. Thus, terrestrial mining remains the only means of raw mineral acquisition used today. If space program funding, either public or private, dramatically increases, this situation may change as resources on Earth become increasingly scarce compared to demand and the full potentials of asteroid mining and space exploration in general are researched in greater detail.
PURPOSE
Based on known terrestrial reserves, and growing consumption in both developed and developing countries, key elements needed for modern industry and food production could be exhausted on Earth within 50 to 60 years. These include phosphorus, antimony, zinc, tin, lead, indium, silver, gold and copper. In response, it has been suggested that platinum, cobalt and other valuable elements from asteroids may be mined and sent to Earth for profit, used to build solar-power satellites and space habitats, and water processed from ice to refuel orbiting propellant depots.
Although asteroids and Earth accreted from the same starting materials, Earth's relatively stronger gravity pulled all heavy siderophilic (iron-loving) elements into its core during its molten youth more than four billion years ago. This left the crust depleted of such valuable elements until a rain of asteroid impacts re-infused the depleted crust with metals like gold, cobalt, iron, manganese, molybdenum, nickel, osmium, palladium, platinum, rhenium, rhodium, ruthenium and tungsten (some flow from core to surface does occur, e.g. at the Bushveld Igneous Complex, a famously rich source of platinum-group metals).Today, these metals are mined from Earth's crust, and they are essential for economic and technological progress. Hence, the geologic history of Earth may very well set the stage for a future of asteroid mining.
Asteroid selection
An important factor to consider in target selection is orbital economics, in particular the change in velocity (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 reduction in transfer time comes at the cost of increased Δv requirements.
The Easily Recoverable Object (ERO) subclass of Near-Earth asteroids are considered likely candidates for early mining activity. Their low Δv 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.
The table above 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, expected to be mainly enstatite. 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.
Multiple types of asteroids have been identified but the three main types would include the C-type, S-type, and M-type asteroids:
- C-type asteroids have a high abundance of water which is not currently of use for mining but could be used in an exploration effort beyond the asteroid. Mission costs could be reduced by using the available water from the asteroid. C-type asteroids also have a lot of organic carbon, phosphorus, and other key ingredients for fertilizer which could be used to grow food.
- S-type asteroids carry little water but look more attractive because they contain numerous metals including: nickel, cobalt and more valuable metals such as gold, platinum and rhodium. A small 10-meter S-type asteroid contains about 650,000 kg (1,433,000 lb) of metal with 50 kg (110 lb) in the form of rare metals like platinum and gold.
- M-type asteroids are rare but contain up to 10 times more metal than S-types
A class of easily recoverable objects (EROs) was identified by a group of researchers in 2013. Twelve asteroids made up the initially identified group, all of which could be potentially mined with present-day rocket technology. Of 9,000 asteroids searched in the NEO database, these twelve could all be brought into an Earth-accessible orbit by changing their velocity by less than 500 meters per second (1,800 km/h; 1,100 mph). The dozen asteroids range in size from 2 to 20 meters (10 to 70 ft).
Asteroid cataloging
Data gathered by Sentinel was intended to be provided through an existing scientific data-sharing network that includes NASA and academic institutions such as the Minor Planet Center in Cambridge, Massachusetts. Given the satellite's telescopic accuracy, Sentinel's data may prove valuable for other possible future missions, such as asteroid mining.
Mining considerations
There are three options for mining:
- Bring raw asteroidal material to Earth for use.
- Process it on-site to bring back only processed materials, and perhaps produce propellant for the return trip.
- Transport the asteroid to a safe orbit around the Moon or Earth or to the ISS. This can hypothetically allow for most materials to be used and not wasted.
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. In situ mining will involve drilling boreholes and injecting hot fluid/gas and allow the useful material to react or melt with the solvent and extract the solute. Due to the weak gravitational fields of asteroids, any activities, like drilling, will cause large disturbances and form dust clouds. These might be confined by some dome or bubble barrier. Or else some means of rapidly dissipating any dust could be provided for.
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. However, no techniques for refining ore in zero gravity currently exist. Docking with an asteroid might be performed using a harpoon-like process, where a projectile would penetrate the surface to serve as an anchor; then an attached cable would be used to winch the vehicle to the surface, if the asteroid is both penetrable and 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.
Technology being developed by Planetary Resources to locate and harvest these asteroids has resulted in the plans for three different types of satellites:
- Arkyd Series 100 (the Leo Space telescope) is a less expensive instrument that will be used to find, analyze, and see what resources are available on nearby asteroids.
- Arkyd Series 200 (the Interceptor) Satellite that would actually land on the asteroid to get a closer analysis of the available resources.
- Arkyd Series 300 (Rendezvous Prospector) Satellite developed for research and finding resources deeper in space.
Technology being developed by Deep Space Industries to examine, sample, and harvest asteroids is divided into three families of spacecraft:
- 1. FireFlies are triplets of nearly identical spacecraft in CubeSat form launched to different asteroids to rendezvous and examine them.
- 2. DragonFlies also are launched in waves of three nearly identical spacecraft to gather small samples (5–10 kg) and return them to Earth for analysis.
- 3. Harvestors voyage out to asteroids to gather hundreds of tons of material for return to high Earth orbit for processing.
Asteroid mining could potentially revolutionize space exploration. The C-type asteroids' high abundance of water could be used to produce fuel by splitting water into hydrogen and oxygen. This would make space travel a more feasible option by lowering cost of fuel. While the cost of fuel is a relatively insignificant factor in the overall cost for low earth orbit manned space missions, storing it and the size of the craft become a much bigger factor for interplanetary missions. Typically 1 kg in orbit is equivalent to more than 10 kg on the ground (for a Falcon 9 1.0 it would need 250 tons of fuel to put 5 tons in GEO orbit or 10 tons in LEO). This limitation is a major factor in the difficulty of interplanetary missions as fuel becomes payload.
Extraction techniques
Surface mining
On some types of asteroids, material may be scraped off the surface using a scoop or auger, or for larger pieces, an "active grab". There is strong evidence that many asteroids consist of rubble piles, making this approach possible.
Shaft mining
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.
Magnetic rakes
Asteroids with a high metal content may be covered in loose grains that can be gathered by means of a magnet.
Heating
For asteroids such as carbonaceous chondrites that contain hydrated minerals, water and other volatiles can be extracted simply by heating. A water extraction test in 2016 by Honeybee Robotics used asteroid regolith simulant developed by Deep Space Industries and the University of Central Florida to match the bulk mineralogy of a particular carbonaceous meteorite. Although the simulant was physically dry (i.e., it contained no water molecules adsorbed in the matrix of the rocky material), heating to about 510 °C released hydroxyl, which came out as substantial amounts of water vapor from the molecular structure of phyllosilicate clays and sulphur compounds. The vapor was condensed into liquid water filling the collection containers, demonstrating the feasibility of mining water from certain classes of physically dry asteroids.
For volatile materials in extinct comets, heat can be used to melt and vaporize the matrix.
Extraction using the Mond process
The nickel and iron of an iron rich asteroid could be extracted by the Mond process. This involves passing carbon monoxide over the asteroid at a temperature between 50 and 60 °C for nickel, higher for iron, and with high pressures and enclosed in materials that are resistant to the corrosive carbonyls. This forms the gases nickel tetracarbonyl and iron pentacarbonyl - then nickel and iron can be removed from the gas again at higher temperatures, perhaps in an attached printer, and platinum, gold etc. left as a residue.
Self-replicating machines
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 80% of a copy of itself, the other 20% being imported from Earth since those more complex parts (like computer chips) would require a vastly larger supply chain to produce. Exponential growth of factories over many years could refine large amounts of lunar (or asteroidal) regolith. Since 1980 there has been major progress in miniaturization, nanotechnology, materials science, and additive manufacturing, so it may be possible to achieve 100% "closure" with a reasonably small mass of hardware, although these technology advancements are themselves enabled on Earth by expansion of the supply chain so it needs further study. A NASA study in 2012 proposed a "bootstrapping" approach to establish an in-space supply chain with 100% closure, suggesting it could be achieved in only two to four decades with low annual cost. A study in 2016 again claimed it is possible to complete in just a few decades because of ongoing advances in robotics, and it argued it will provide benefits back to the Earth including economic growth, environmental protection, and provision of clean energy while also providing humanity protection against existential threats.
Proposed mining projects
On April 24, 2012 a plan was announced by billionaire entrepreneurs to mine asteroids for their resources. The company is called Planetary Resources and its founders include aerospace entrepreneurs Eric Anderson and Peter Diamandis. Advisers include film director and explorer James Cameron and investors include Google's chief executive Larry Page and its executive chairman Eric Schmidt. They also plan to create a fuel depot in space by 2020 by using water from asteroids, splitting it to liquid oxygen and liquid hydrogen for rocket fuel. From there, it could be shipped to Earth orbit for refueling commercial satellites or spacecraft. The plan has been met with skepticism by some scientists, who do not see it as cost-effective, even though platinum is worth $32 per gram and gold $49 per gram as of September 2019. Platinum and gold are raw materials traded on terrestrial markets, and it is impossible to predict what prices either will command at the point in the future when resources from asteroids become available. For example, platinum traditionally is very valuable due to its use in both industrial and jewelry applications, but should future technologies make the internal combustion engine obsolete, the demand for platinum's use as the catalyst in catalytic converters may well decline and decrease the metal's long term demand. The ongoing NASA mission OSIRIS-REx, which is planned to return just a minimal amount (60 g; two ounces) of material but could get up to 2 kg from an asteroid to Earth, will cost about US$1 billion.
Planetary Resources says that, in order to be successful, it will need to develop technologies that bring the cost of space flight down. Planetary Resources also expects that the construction of "space infrastructure" will help to reduce long-term running costs. For example, fuel costs can be reduced by extracting water from asteroids and splitting to hydrogen using solar energy. In theory, hydrogen fuel mined from asteroids costs significantly less than fuel from Earth due to high costs of escaping Earth's gravity. If successful, investment in "space infrastructure" and economies of scale could reduce operational costs to levels significantly below NASA's ongoing (OSIRIS-REx) mission. This investment would have to be amortized through the sale of commodities, delaying any return to investors. There are also some indications that Planetary Resources expects government to fund infrastructure development, as was exemplified by its recent request for $700,000 from NASA to fund the first of the telescopes described above.
Another similar venture, called Deep Space Industries, was started in 2013 by David Gump, who had founded other space companies. At the time, the company hoped to begin prospecting for asteroids suitable for mining by 2015 and by 2016 return asteroid samples to Earth. Deep Space Industries planned to begin mining asteroids by 2023.
At ISDC-San Diego 2013, Kepler Energy and Space Engineering (KESE, llc) also announced it was going to mine asteroids, using a simpler, more straightforward approach: KESE plans to use almost exclusively existing guidance, navigation and anchoring technologies from mostly successful missions like the Rosetta/Philae, Dawn, and Hayabusa, and current NASA Technology Transfer tooling to build and send a 4-module Automated Mining System (AMS) to a small asteroid with a simple digging tool to collect ≈40 tons of asteroid regolith and bring each of the four return modules back to low Earth orbit (LEO) by the end of the decade. Small asteroids are expected to be loose piles of rubble, therefore providing for easy extraction.
In September 2012, the NASA Institute for Advanced Concepts (NIAC) announced the Robotic Asteroid Prospector project, which will examine and evaluate the feasibility of asteroid mining in terms of means, methods, and systems.
Being the largest body in the asteroid belt, Ceres could become the main base and transport hub for future asteroid mining infrastructure, allowing mineral resources to be transported to Mars, the Moon, and Earth. Because of its small escape velocity combined with large amounts of water ice, it also could serve as a source of water, fuel, and oxygen for ships going through and beyond the asteroid belt. Transportation from Mars or the Moon to Ceres would be even more energy-efficient than transportation from Earth to the Moon.
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