Mining the Sky is one of the most important books space advocates can own because, as the author puts it, “we must address economic issues, or there will be no future space activity.” However, this is not an economics text. John Lewis, a planetary science professor, provides scientifically backed arguments for using space resources to address problems on Earth. We are in the same situation we were when the book was published, with added burdens of terrorism, culture wars, and increased energy costs. Lewis’s most important ideas are that we use materials and energy from space (in the form of space solar power) to reduce the resource crunch here on Earth. This work has never been timelier.

Every chapter begins with an excerpt from a fictional “future history” textbook, in which the reader “looks back” at how the solar system was won. This is a fun touch for science fiction fans and “humanizes” the science for the novice reader.

Starting with the comets and asteroids, Lewis first discusses chondrites or “stony” asteroids that are comet nuclei that have had most of their volatile gases blasted out by the sun. Once processed, chondrites can contain up to 20 percent water in clays, up to 6 percent organic matter, and carbonate and sulfate materials. Such organics are invaluable for life-support systems and soil for off-Earth habitats. Lewis notes that about a quarter of the mass in the near-Earth asteroid population is water, which can be separated into hydrogen and oxygen to fuel spacecraft.

When people think of mining, they usually think of metals or coal. Iron asteroids are “about 99 percent metal with the composition of a natural stainless steel.” Whoever mines and markets materials from a metal asteroid might become very rich.

Peter Diamandis paraphrased Lewis at the 2006 International Space Development Conference when he exclaimed, “There are twenty-trillion-dollar checks up there, waiting to be cashed!” This $20 trillion figure is based on Lewis’s calculations of how much a metallic asteroid (3554 Amun) would be worth if it was sold at current market prices.

In orbit, Lewis presses for solar power satellites (SPS). He suggests building many of the components of SPSs in space, thereby reducing the amount of material needed from Earth and increasing space-based commerce.

Lewis doesn’t regard the Moon as a good source of resources, except space solar power. “The biggest single drawback of solar cells, then, is the need for storing two weeks’ worth of power.” What about stationing solar cells around the lunar equator? I wondered. He states that that “would do away with the new moon dead-time problem, but of course the duty cycle of the system would still be 50 percent.” Lewis misses the point that, while the overall system would be operating at 50 percent capacity, it would still be operating continuously and no longer require batteries or nukes.

He also makes transporting lunar ice from the poles to the International Space Stationunnecessarily complicated. He envisions a water/fuel delivery system that flies to the lunar equator before going to LEO, using up most of the ice as fuel before ever reaching the customer. Another NSS member pointed out to me that he does not mention “mass drivers,” which could launch lunar materials into orbit and reduce spacecraft use. Lewis finally suggests that “Perhaps lunar ice should be kept on the Moon for use by its residents.”

Lewis is similarly negative about using helium-3 from the Moon to power fusion reactors, as he states, “The concentration of helium-3 in regolith is actually astonishingly small (one ton of helium-3 for every one hundred million tons of regolith.” Lewis suggests that it would be better to scoop helium-3 from the atmosphere of Uranus and then describes a way to do it!

He next turns his attention to Mars. Lewis supports in-situ resource utilization (ISRU), but doesn’t accept Robert Zubrin’s approach of bringing along hydrogen to combine with carbon dioxide in the Martian atmosphere. He believes that the equipment needed to store hydrogen cryogenically would be too expensive. Instead, Lewis recommends searching for Martian water in the ground. With all the complicated digging, grinding, and separation equipment needed to obtain water from Martian rocks, it

might be easier to store the hydrogen. However, Lewis did not state where he would set up his mining equipment. If such an extraction system were set up near the Martian North Pole, he might find all the water he needs.

Lewis is also against full-scale terraforming of Mars. While he seems to have no problem with partial terraforming, he believes it is “arrogant” to completely remake Mars and instead believes human beings should “meet the planet halfway” and genetically modify ourselves to survive on a partially-terraformed world. Given the other activities Lewis proposes (moving Phobos and Deimos, building a space elevator), this attitude seems paradoxical.

Unfortunately, many of the activities described in the book will not be practical until launch costs to Earth orbit decline by an order of magnitude; yet Lewis mentions the issue only in passing. Perhaps someone else will need to write a similar book on launch costs.

Lewis has a lot of great ideas, but they require incorporation with others. Still, it is Lewis’s capacity for imagining a greater whole that makes Mining the Sky an important book. While others address smaller pieces of the puzzle, such as Mars, Moon, or L5, Lewis describes activities across the solar system along with a fully functioning space economy.

Mining the Sky is worth reading because it provides a justification and roadmap for incorporating the material and energy resources of our solar system into our world’s economy; and economic arguments may be the most long-lasting justifications for expanding our civilization into space.

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.