Mining the Sky

September 1997

Summary Review: As indicated by the subtitle, Lewis's focus in this book is about making money from the near infinite resources available in space. Each chapter is preceded by a science-fiction style account, often of an individual or company becoming fabulously wealthy exploiting some new resource. Lewis's enthusiasm sometimes gets carried to extremes - is the near-Earth asteroid Amun really worth 300 million billion dollars? This book does have more boosterism than sound economic analysis. Unfortunately, throwing wild numbers around may not help the case for a major coporation interested in the prospects - they know large positive numbers usually have large negative numbers that go along with them, and there are lots of subtleties about return on investment that can make even the biggest numbers look risky. Mining the Sky contains a lot of useful technical details and calculations, especially concerning the asteroids and comets. In some of the analysis, however, Lewis strangely ignores the use of mass drivers, preferring to stick with chemical rockets or, for later development, D-He³ fusion systems. The book does have lots of great ideas in it; some of them seem genuinely novel, such as a realistic approach to mining He³ from Uranus, and some interesting speculations on future human population.

Full Review: The book begins with a quite detailed historical review of exploration and space travel, covering both the real engineering side and the speculative "hard science-fiction" side. This is followed by two chapters on developing the moon, including a detailed and interesting history of lunar exploration. Lewis' plans for the moon start with landing a base module and burying it, with a manned crew coming in as soon as that is ready. The focus of the crew would be mining Hydrogen and Oxygen for propellant use, and also for use to supply (through fuel cells) night-time energy needs, and making titanium oxide heat shields; the propellant would be exported for use in low earth orbit.

But attention quickly shifts from the moon to the near-Earth objects (NEO's): asteroids and spent comets. Lewis claims obvious advantages for resource recovery from the NEO's over the moon - they have ready availability of metals and volatiles, and the energy cost to get from them to low Earth orbit, or even better to stations and staging areas in highly eccentric Earth orbits (HEEO), can be significantly less than from the surface of the moon. The details here on asteroid and comet composition and characteristics are valuable. But here is one place that a more complete economic analysis than Lewis gives would be useful - what is the real impact of the much larger round-trip-times to NEO's, even if the energy cost is less? And the mass-payback calculations are suspect because Lewis insists on using chemical (Hydrogen-Oxygen) rockets rather than mass drivers to export materials from the moon. The case for the moon is surely significantly better than indicated by Lewis's analysis.

Lewis returns to the moon to discuss solar power and He³ extraction for export, which seem more economically justifiable in the book's analysis than Oxygen export for propellant use. Lunar manufacture of SPS's for use in HEEO and on the lunar surface (David Criswell's scheme) are discussed; Lewis again ignores mass driver propulsion which should significantly cut the cost to place the power systems in orbit.

Then follow two chapters devoted to Mars, and another on Phobos and Deimos. The discussion concentrates on finding water and particularly hydrogen; alternative propellants are also discussed, as well as energy production and other general issues related to making Mars suitable for humans. The final suggestion is manufacture of a sky-hook using Mars' moons in geosynchronous Mars orbit - the upper end could be an ideal platform for launch to the outer edges of the asteroid belt and the rest of the solar system. Mars' rapid rotation and low gravity make a synchronous skyhook much easier to build there than either on the Earth or the Moon.

Two more chapters discuss the resources available in the asteroid belt ($7 billion worth of asteroidal iron for every person on Earth today!) and the outer planets ($50 trillion worth for every person on Earth of He³ in the outer shell of Uranus alone; hundreds of thousands of times that within the interior of Uranus and Neptune). The final two chapters bring to focus the general conclusion of the book: Shortage of resources is not a fact; it is an illusion born of ignorance - we have the resources within our solar system to colonize the entire Milky Way, and it need bring no harm to our home planet, Earth.

This book is a valuable guide to the resources potentially available within our own solar system; the technical discussion emphasizes the current or near-term technical feasibility of most of the projects mentioned. The economic discussion likely wouldn't pass muster with any real business people, but it could provide a foundation for more detailed economic analysis. The book certainly should provide further motivation for the entrepreneurial ingenuity that seems to be returning to the space business. And Lewis's enthusiasm is infectious, so read the book if you're feeling at all discouraged about space development.

Artemis note: Lewis seems to advocate somewhat more lunar settlement than Gerard O'Neill does in The High Frontier, in particular for production and export of oxygen, and for solar power generation and transmission. These are the "paying jobs" for the lunar colony, needed to pay for initial costs and anything that needs to be imported. As for almost all the practical proposals for colonizing space, making use of lunar resources is an essential first step, and the only real question is how big the lunar settlement becomes, and how long it will remain useful.