|Fig. 1: Artistic conception of a mining mission to and Earth-approaching asteroid. Artist: Denise Watt. (Courtesy of NASA)|
Asteroid mining is frequently characterized as an outlandish, science-fictitious proposition. However, some of earth's most valuable minerals - including gold, cobalt, iron, manganese, nickel, palladium, and platinum - all originated in asteroids from outer space that crashed into earth's surface.  The materials extracted from asteroids have a wide-range of use-cases as they can be used in the production of everything from rocket fuel to fine jewelry.
Of all of the potential materials found in asteroids, water and metals are among the most prized. Water for instance, is absolutely essential to support life in space. However, it costs a great deal to bring it into space. Launch costs for water are at thousands of dollars per pound. If water could be sourced in space, it would save tremendous amounts of money and energy over time. Moreover, it can be broken down into hydrogen and oxygen for use as rocket fuel.
Asteroid mining is a highly complex undertaking from start to finish. To begin, a viable candidates must be surveyed, identified, and selected. Prospecting asteroids to determine their composition is done based on their optical and infrared spectra. This requires large telescopes.  In deciding which asteroids to target, the relative difficulty of accessing the asteroid in question is a chief concern. Therefore, near-earth asteroids (NEAs), which have low velocities and are relatively close to earth (between 0.983 and 1.3 AU away from the Sun) are prime candidates because they are the easiest to survey and access.  There are thousands near earth.
There are three different types of asteroids that are being targeted: m-type, s-type, and c-type asteroids. M-type asteroids are the least common, but also have far more metallic content than both c and s-type asteroids. S-type asteroids have a diverse range of metals such as nickel, gold, and platinum. However, they have less water, which could increase cost of mission. For example, a small S-type asteroid is about 1,433,000 pounds, and about 110 pounds of the asteroid is comprised of rare metals such as platinum and gold.  C-type asteroids do not have much metal content, but do have an abundance of ingredients necessary for fertilizers, such as carbon and phosphorous. These would be useful for growing food in space. 
Another critical component of determining the accessibility of an asteroid is look at its delta-v (δv). The difficulty of delivering mass from one orbit to another in space is not a question of distance, but one of velocity. Roughly 10% of NEAs are more accessible than the Moon in terms of Δv, so returning from one of these NEAs with materials would be much simpler. 
Once an asteroid is identified, there are numerous options for how the mining process will proceed. The raw materials can be mined and brought back to earth. Another possibility involves mining the raw materials and then processing them on-site, bringing only processed materials back to earth. Some of these processed materials could even provide fuel for return trip. For instance, c-type asteroids contain a great deal of water, and readily available hydrogen and oxygen could minimize fuel costs. A third option is to use some means of asteroid retrieval to bring the asteroid into orbit around the ISS, Moon, or even Earth. Incorporating at least certain elements of this third process of "asteroid retrieval," though technically not necessary, will be crucial if asteroid mining is to gain any traction. The orbits of NEAs do eventually line up with that of earth, but that could take as long as 20-25 years. By bringing small asteroids into a so-called "parking" orbit - such as the moon's - closer to Earth, asteroids can be mined within a reasonable, useful timeframe. 
Prospecting is a key piece of the mining process. Because asteroids are not easily accessible, especially when compared to the relative ease of access of the Earth's crust for traditional mining operations, other means are required to determine which asteroids contain useful material. Large telescopes are used to determine optical and infrared spectra of asteroids and, thus, their chemical composition. However, this is by no means a perfect method. Dust and weathering on the surface of an asteroid sometimes prevent precise identification of the interior composition of an asteroid. This problem could be solved by development of small spacecraft that could land on NEAs and survey before entire mining force is deployed for full-on excavation.
In 2012, NASA's Glenn Research Center COMPASS team estimated that the cost of the first asteroid capture and return mission - including launch, mission operations, and government oversight - -would cost roughly $2.6 billion.  The team also estimated launch costs for every launch thereafter would be around $1 billion. Given the large price tag associated with capturing and mining just one single asteroid, the expected benefits must be substantial enough to outweigh the drawbacks in the long run.
Should asteroid mining gain traction in practice, the chief concern becomes macroeconomic: a dramatic increase in supply for raw materials as a result of asteroid mining could lead to a collapse in demand and, thus, prices on earth. Asteroid mining has the potential to completely reshape the global economy. However, while the jewelry industry is well- established as a market for luxury goods, the private space industry is a nascent one. The success of asteroid mining will play a key role in determining the feasibility of developing human civilizations in space as their sustainability would depend on the materials asteroid mining can provide. The raw materials gained from asteroid mining can either be used in space, or on earth. However, certain things have more value in space, such as water. Water or metal is worth $17 million per ton in space, while steel is worth just $700 per ton on Earth.
The future of asteroid mining comes down to the question of whether or not the high price tag is justified. Some NEA metallic asteroids as small as 200m across have been valued at $30 billion. C-type asteroids, on the other hand, are full of volatiles which, though not especially valuable on earth, would be incredibly valuable to space ventures by providing them with water, hydrogen, and oxygen.
Perhaps the most intriguing prospect is the possibility that the newfound abundance of certain materials will lead to redefinition of which materials are most valuable. Chris Lewicki, CEO of Planetary Resources, a company pioneering asteroid mining efforts, has compared platinum - a very expensive and rare element by today's standards - to aluminum in the 1800s. "Aluminium used to be one of the rarest metals that we knew in the 1800s and today it is ubiquitous. So we'd like to be able to help create that transition for the platinum group elements." In short, asteroid mining could lead to more research and applications for certain elements in the future.
© Alexandra Crerend. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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