Future large scale commercial activities in space will require raw materials obtained from in-space sources rather than from Earth, to overcome the high cost of Earth launch. This paper reviews the prospectiveness of non-terrestrial resources and notes the competitiveness of Near-Earth-Asteroids c.f. the Moon and Phobos or Deimos in terms of accessibility and likely resources. Astronomical work over the last fifteen years has increased the number of known Near Earth Asteroids (NEAs) from about 30 to about 400. Discovery rate of NEAs is now about 50 per year.
Asteroid "geography": NEAs are classified by orbital parameters into Apollos, Amors, and Atens; in addition, the "Arjunas" are the group of small objects in very Earth-like, and therefore very accessible, orbits. Accessibility is defined in terms of velocity requirements (delta-v) for outbound and for return trajectories. Approximately 10% of NEAs are more accessible than the Moon, and maybe 50% of these are likely to be potential orebodies.
Asteroid "geology" has advanced dramatically in the last decade, via spectroscopic and dynamical studies of asteroids and comets, and meteorite studies; reasonable inferences can now be made from asteroid types defined by spectral properties to probable surface mineralogy. Many asteroids may be "volatiles bearing", containing clays, hydrated salts, and hydrocarbons. It also now seems that there are dormant cometary bodies within the population of NEAs. These are likely to contain remnant primordial ices within their cores, making them possible sources of volatiles for future space industry. Resources which would appear to be readily recoverable are thus water and other volatiles, for manufacture of propellant in orbit; and nickel-iron metal, for construction in orbit.
There have been various concepts proposed for mining and retrieval to low-earth-orbit of materials from NEAs, but methods of comparison of the economic feasibility of competing mission concepts are...
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