Mining the Sky

Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets, is a 1997 book by University of Arizona Planetary Sciences professor emeritus John S. Lewis that describes possible routes for accessing extraterrestrial resources, either for use on Earth or for enabling space colonization. Each issue or proposal is evaluated for its effects on humanity, physics and economic feasibility based on planetary science. For instance, Chapter 5 ("Asteroids and Comets in our Backyard") exhaustively catalogs the types of near-Earth objects (asteroids and extinct comets whose orbits intersect Earth's), assessing both the harms likely from possible collisions with Earth (the subject of Prof. Lewis's previous book, "Rain of Iron and Ice") on the one hand, and their potential for profitable exploitation on the other.
To illustrate this potential, Lewis includes an order-of-magnitude estimate of the economic value of the "smallest" known metallic ("M-type") near-Earth asteroid: 3554 Amun. With its diameter of 2 kilometers and assumed composition similar to typical iron-type meteorites, he calculated a mass of 3 (30 billion) tons and a 1996 market value of $8 trillion for its iron and nickel alone, another $6 trillion for its cobalt, and $6 trillion more for its platinum-group metals.
In general, like previous space advocates such as Princeton's Gerard K. O'Neill, Lewis responds to the limits to growth on Earth with detailed plans to first ameliorate them by accessing space resources on Earth, followed by human space colonization of the entire Solar System. In this light, he asserts that "Shortage of resources is not a fact; it is an illusion born of ignorance". He claims that colonies built with the natural resources of the asteroid belt alone, including limitless space-based solar power, could eventually support a vast civilization of "several tens of quadrillion ()s of people". He closes the book with an assertion that this vast population could be a very good thing. "Intelligent life, once liberated by the resources of space, is the greatest resource in the solar system ... the highest fulfillment of life is unbounded intelligence and compassion"