I would rather believe two Yankee professors would lie, than that stones have fallen from the heavens.
—Thomas Jefferson
It is a general law of nature that for virtually every type of thing, there are more little ones than big ones. There are more dandelions than towering redwoods, more minnows than sharks, more mice than elephants, more sand grains than pebbles, and more pebbles than boulders.
Thus it should have come as no surprise that there are far more tiny planets than grand ones, and many more interplanetary free-floating rocks than miniplanets—some of which might well collide with the Earth and “fall from the heavens” from time to time. Yet, surprise it was when on January 1, 1801, Sicilian astronomer Giuseppe Piazzi opened the new century by discovering a miniature planet, which he named Ceres, orbiting the sun between Mars and Jupiter.
While displeasing to philosophers, who thought that the seven known planets (Uranus had been discovered by William Herschel in 1781) comprised precisely the right number, the discovery of Ceres was very gratifying to astronomers, particularly as its orbital distance from the sun, 2.7 astronomical units, was very close to the 2.8 predicted for a missing planet by the German astronomers Titius and Bode based upon other planetary orbit distance ratios back in the 1770s. (One astronomical unit, or AU, equals 150 million kilometers, the distance at which the Earth orbits the sun.) Ceres proved to be a very small planet, only nine hundred kilometers in diameter (about one-quarter that of the Earth's moon), but this disappointment was compensated for when, over the next few years, astronomers discovered planetoids Pallas, Juno, and Vesta in similar orbits close by. This suggested to the German astronomer Heinrich Olbers that the four objects were fragments of a properly sized planet that had broken up. More fragments could therefore be expected, and as the nineteenth century wore on, and telescopes got better, this hypothesis was substantiated as dozens and then hundreds of additional “asteroids” were discovered. By 1890, more than three hundred were known, all orbiting the sun in a belt between 2 and 3 AU, nicely bracketed near the geometric mean of 2.8 AU between the orbit of Mars (1.52 AU) and that of Jupiter (5.2 AU).
But then, in 1898, an asteroid was discovered whose maximum distance, or aphelion, from the sun is 1.78 AU, and whose minimum distance, or perihelion, is only 1.14 AU. It thus crosses the orbit of Mars and sometimes swings within twenty million kilometers of the Earth. This wandering across orbits was considered truly errant behavior, and so to distinguish it from the well-behaved female deities orbiting the Main Belt so nicely, the new ten-kilometer-class asteroid was given a male name, Eros.
Figure 5.1. The near-Earth asteroid Eros, photographed by NASA's NEAR spacecraft in 2000. Image courtesy of NASA.
Soon other male, planet-crossing asteroids were discovered, and some of these crossed not only Mars's orbit but that of Earth as well. In 1932, the asteroid Apollo crossed the Earth's orbit and passed within ten million kilometers of our world. In 1936, Adonis passed us at a distance of two million kilometers. On March 23, 1989, the “small” (eight hundred meters, or 120 million kilotons of impact energy) and therefore unnamed asteroid 1989 FC swept by at a distance of 720,000 kilometers, passing through a point in space that the Earth had occupied less than six hours before.
As mentioned above, about two hundred Earth-crossing, “male,” or “near-Earth” asteroids larger than one kilometer are known today, and it is estimated that there are at least two thousand of them out there. More than seven thousand “female” asteroids are known to exist in the Main Belt between Mars and Jupiter, including every asteroid larger than ten kilometers, hundreds larger than one hundred kilometers, and one as large as nine hundred kilometers. Because they orbit farther from both the sun and the Earth, the smaller female Main Belt asteroids are much harder to see than their Earth-crossing counterparts. It's estimated that there are at least two million Main Belt asteroids larger than a kilometer.1 The girls thus outnumber the boys by about a thousand to one, and utterly dwarf them as well. It's good the lasses are well-behaved. If they acted like their brothers, all life on Earth would have been exterminated a thousand times over.
Of course, there is a reason for the overwhelming dominance of female asteroids: Male asteroids don't live long. They kill themselves by crashing into us.
Such events have been very inconvenient to Earth's previous inhabitants, many of whom have been wiped out as a result. In a subsequent chapter, we will discuss what we can do to prevent them.
The total mass of all the asteroids adds up to only about 4 percent that of the moon, or 0.05 percent that of the Earth. Yet because of their numbers, the total surface area of all the asteroids—in their current form—is about the same as the moon, or the continent of Africa. That's sizable, but it considerably understates the possibilities.
The Earth may have a radius of nearly 6,400 kilometers, but at most, only the top 6 kilometers, or 0.1 percent, is within reach. In contrast, the material contents of most asteroids are fully accessible. If reconfigured for human habitation, the mass of a 1-kilometer asteroid could afford living space equal to that of a major city. For example, if rebuilt as a structure resembling one of Gerard O'Neill's space colonies, a single 1-kilometer-radius asteroid would provide enough mass for a rotating cylinder 1 kilometer in diameter, 1 meter thick, and 1,250 kilometers long, or about 4,000 square kilometers. For comparison, London (population 8.2 million) has an area of 1,623 square kilometers. Approached this way, the total potentially habitable territory of the Main Belt would be about a hundred times that of the Earth, dispersed amid the volume of about seventeen cubic AU, or 230,000 billion trillion (sic) cubic kilometers. It's a vast ocean, filled with millions of worlds, which could someday be homes to millions of new city-states, nations, and civilizations.
ASTEROID EXPLORATION
In one sense, we already know more about the asteroids than nearly any other extraterrestrial body, except perhaps the moon, because we have hundreds of thousands of samples. These are the meteorites, fragments of asteroids that have—despite Thomas Jefferson's disbelief—fallen to Earth and are available for collection. The meteorites show a variety of asteroid compositions, ranging from nearly pure metal, to stone, to carbonaceous materials. Because they survive atmospheric entry best, and because they are easiest to distinguish from terrestrial rocks, iron-metal meteorites enjoy preferential representation in terrestrial meteorite collections. However, by comparing the spectral characteristics of meteorites with those reflected from asteroids in space, astronomers have been able to classify the asteroids according to their composition. The principal types are listed in the table below.
TABLE 5.1. PRINCIPAL TYPES OF ASTEROIDS
| Type | Composition | Primary concentration |
| M | Metal | Inner Main Belt, near Mars |
| E | Silicate rocks | Inner Main Belt, 1.9 AU |
| S | Stony-iron | Central Main Belt, 2.4 AU |
| C | Carbonaceous | Outer Main Belt, 3.3 AU |
| P | Carbonaceous/volatile | Outermost Main Belt, 4 AU |
| D | Frozen volatiles | Beyond Jupiter |
No type of asteroid is concentrated in the near-Earth objects, because the NEOs represent only a tiny minority of the asteroids overall. Also, because they are small, it is hard to get a composition-determining reflection from most of the known NEOs. However, of those that have been surveyed by astronomer Lucy-Ann McFadden, about 80 percent were found to be S asteroids and 20 percent were C asteroids. Types M and E were probably not observed simply due to the small size of the assessed sample: these are generally rarer than S and C types. Types P and D cannot exist in near-Earth space for long without evaporating. If one came our way, we would observe it as a comet.
With the exception of radar imaging of a few close-passing NEOs (such as Toutatis, which was imaged by the Jet Propulsion Lab's Steve Ostro using the Goldstone Deep Space Communications Complex as radar during the asteroid's 3.5-million-kilometer pass by our planet in December 1992), asteroids are too small or too far away to be photographed by Earth-based telescopes. Our first good look at asteroids, therefore, had to wait for images returned by interplanetary spacecraft. The first of these was produced by the Galileo spacecraft when it flew by the Main Belt asteroid Gaspra on its way to Jupiter in October 1991. Galileo's magnetometer also measured a surprisingly strong magnetic field around the asteroid, indicating the presence of a large quantity of metallic iron. The images returned show Gaspra to be a potato-shaped object, nineteen kilometers long by eleven in diameter. Based on counting the number of craters on its surface, mission scientists judged that Gaspra is only about four hundred million years old, which is a bit of a mystery since the rest of the solar system is ten times that age. Perhaps Gaspra is a fragment cast off by a catastrophic collision between two larger bodies four hundred million years ago.
In August 1993, Galileo, pushing further out through the Main Belt, was able to get a look at another asteroid, fifty-one-kilometer-long Ida. Surprisingly, Ida was found to have a moon of her own, a one-kilometer-sized object, which mission scientists named Dactyl. Since the rate of Dactyl's orbit about Ida is dependent on Ida's mass, and since Ida's size is known, the mission team was able to use measurements of Dactyl's orbit to calculate that the density of Ida is about 2.5 times that of water, consistent with a carbonaceous composition.2
But these Galileo flybys were just quick snapshots. Much more can be learned by having a dedicated spacecraft rendezvous with an asteroid and hanging around to take close-up photographs and detailed sets of measurements. This was done by the Near Earth Asteroid Rendezvous (NEAR) mission, designed by the Johns Hopkins Applied Physics Lab, which reached and orbited Eros, the first discovered and largest of the NEOs, in January 1999. NEAR orbited Eros for more than a year, gradually lowering its orbit, and then actually landed on it in 2001, returning spectacular photographs in the process.3
This extraordinary achievement was then exceeded by the Japanese Hayabusa mission, which not only landed on the asteroid Itokawa but took off again to return dust samples to Earth in 2010.4 The European Rosetta spacecraft flew by asteroids Steins in 2008 and Lutetia in 2010 on its way to orbit the comet Churyumov-Gerasimenko in 2014.5 Another notable mission was the JPL Dawn spacecraft, a tour de force that, after orbiting the large asteroid Vesta from 2011 to 2012, used very-high-exhaust-velocity electric propulsion to depart and then go into orbit around the dwarf planet Ceres in 2015.6
The most recent asteroid missions are the Japanese Hayabusa2 and NASA's OSIRIS-REx, which launched in December 2014 and September 2016 to explore the carbonaceous asteroids Ryugu and Bennu, respectively. Hayabusa2 arrived at Ryugu in July 2018 and subsequently deployed the small European Mobile Asteroid Surface Scout (MASCOT) lander to collect samples.7 In December 2019, it will depart and hopefully return its samples to Earth in December 2020. OSIRIS-REx reached Bennu in August 2018 and is now in orbit mapping the asteroid.8 If all goes well, it will land on Bennu in July 2020 and use a robotic arm to secure at least sixty grams of samples, which it will return to Earth via a reentry capsule in September 2023.
Figure 5.2. The Main Belt asteroid Ceres photographed by the NASA/JPL Dawn spacecraft in 2015. The bright spots are believed to be water ice. Image courtesy of NASA.
GAIASHIELD: A HUMAN ASTEROID MISSION
However, as impressive as these robotic probes may be, they have only scratched the surface. Given the importance of gaining a detailed knowledge of NEOs to the future security of humanity, the costs associated with human exploration are more than justified. If we were to launch the Mars Direct program described in chapter 4, the same launch vehicles and hab modules developed for Red Planet exploration could also be used to perform rendezvous and return missions to near-Earth asteroids. Indeed, since the rocket propulsion requirements required to leave low Earth orbit (LEO) for a one-way trajectory and landing on Mars (a ∆V of about 4.7 km/s) are nearly identical to those for a round-trip from LEO to many NEOs, hardware designed for Mars Direct–type missions enjoys natural commonality with that needed for NEO exploration. But because asteroids have no atmosphere and little gravity, eliminating the need for reentry and landing systems, and because asteroids are small, eliminating the need for ground vehicles and split field-exploration and base crews, a minimal, piloted asteroid exploration mission can be launched with a significantly smaller and more limited set of hardware than that needed for Mars exploration. Such a mission could be flown within four years, using launch vehicles and technology available today. If there is no manned Mars exploration program, it may help produce one, because in the course of flying to an asteroid and back, the astronauts will destroy the putative barriers to long-distance spaceflight of cosmic rays, subnormal gravity, and human factors, which are used as excuses for lack of initiative by apologists for current go-nowhere space policies.
I call my asteroid mission plan “Gaiashield,” because it would be an important first step in giving humanity the knowledge and spacefaring capability we need to protect the Earth's biosphere from another mass extinction.
The Gaiashield mission could employ a simple cylindrical habitation module, five meters in diameter and twenty meters long, somewhat similar to those used on the International Space Station. Alternatively, an inflatable hab module of the Bigelow type could be used. This module could be launched in one piece, together with a space-storable methane/oxygen chemical propulsion stage, by a Falcon Heavy, New Glenn, or SLS launch vehicle. The module would be equipped with a set of photovoltaic panels, which would deploy outward from it like wings, somewhat in the manner of the United States’ 1970s-era space station, Skylab. After it reached orbit, a Falcon 9 would be used to deliver the crew to it in a Dragon capsule, which would remain mated to the hab for use as a reentry and landing vehicle at the end of the mission. Once the crew has determined that all is shipshape for Earth departure, one more Falcon Heavy–class launcher would send a fifty-ton high-energy hydrogen/oxygen propulsion stage to mate with the stack and boost it into a highly elliptical, near-escape-velocity orbit around the Earth. (The H2/O2 stage would be sent last because its propellant is not readily space storable. If a space-storable stage were used instead, the schedule would be more flexible, but the payload would need to be reduced.) Using their methane/oxygen propulsion system, the crew would then boost themselves beyond Earth escape to a trans-asteroid trajectory. The H2/O2 stage could then be directed to gently aerobrake itself back to LEO for potential reuse by executing a series of passes through the Earth's upper ionosphere.
Once on the trans-asteroid trajectory, small reaction control thrusters would fire, causing the spacecraft to spin in the same plane in which the solar panels are located, with the spin axis and the solar panels pointing at the sun. The length of the spin arm between the spacecraft center of gravity and the decks at the far end of the module would be about ten meters. As a result, spinning at 4 RPM, lunar-equivalent gravity could be generated at the “lowest” decks. Spinning at 6 RPM, Mars-level gravity could be created. While NASA officials wishing to justify space station research programs on the human health effects of long-duration zero-gravity exposure frequently affect deep concern over the possible disorientation caused by Coriolis forces and other concomitants of artificial gravity systems, experiments done in the 1960s show that humans can adapt and operate well in vehicles rotating as rapidly as 6 RPM. Many current artificial gravity researchers, such as Professor Larry Young of MIT, believe that rotation rates as high as 10 RPM are viable. With artificial gravity, the Gaiashield crew would be protected against the severe negative health impacts that have afflicted cosmonauts and others who failed to implement strenuous exercise programs when flying for long periods in zero gravity.
The ship would take about six months to reach the asteroid, as despite its close distance to the Earth, an elliptical trajectory from one side of Earth's orbit to the other would probably be needed to get there. Upon interception, the crew would despin the ship and use most of the propellant in the propulsion stage to effect a ∆V of perhaps 0.5 km/s to establish the spacecraft in orbit a few kilometers from the asteroid, where it will remain for one year. The crew would then proceed to explore the asteroid in detail, using backpack gas thrusters similar to the space shuttle's Manned Maneuvering Unit to fly to it from the ship and hop about the body at will. A small portable drilling rig would be used to take repeated deep samples from all over the body.
At the end of a year of intensive exploration, the propulsion stage would fire its last allotment of propellant to give the ship the required 0.5 km/s ∆V needed to send it on trans-Earth injection. After a voyage of another six months, the ship would approach Earth, and the crew would bail out in the reentry capsule and be picked up by a boat, much as the Apollo astronauts did a half century ago. Empty of crew, the ship itself would remain in a cycling orbit between the Earth and the asteroid, possibly to be refitted for further use when appropriate capabilities for doing so are developed.
The crew would thus spend two years in interplanetary space, about twice that required for a round-trip to Mars (which spends six months traveling each way and 1.5 years on the surface). During this trip, they would take about 100 rem of cosmic radiation, which represents about a 2 percent statistical risk of fatal cancer later in life for each member of the crew. (In contrast, an average smoker incurs a 20 percent risk.) This is small compared to other risks associated with piloted space missions, and there is no doubt that many astronauts would be more than willing to take it on.
Thus, using two launches of a Falcon Heavy, New Glenn, or SLS booster, plus one launch of a Falcon 9 with a Dragon, a Spartan two-person human mission to a near-Earth asteroid in interplanetary space could be readily accomplished.
However, once the SpaceX Starship is available, it could be used to fly a crew of twenty or more to a near-Earth asteroid in style. The mission would be quite similar to the one SpaceX has announced it will use to send a crew plus a group of eight artists in a flight around the moon circa 2023, except that because the mission will take two years instead of one week, a lot more supplies will need to be brought along. But with the Starship's 150-ton-to-orbit payload capability, this should not be a problem.
The mission plan would be quite simple. First a Starship with its supplies and crew would be launched to orbit. Then two more cargo Starships would be used to deliver three hundred tons of propellant to refuel the mission craft. Then it's off for the two-year round-trip voyage to the asteroid, with plenty of room and company aboard to enjoy the trip.
(See plate 9.)
Starship is not an artificial gravity spacecraft, but if two were flown, they could tether off each other nose to nose. If the tether were five hundred meters long, spinning the assembly at 2 RPM would create Earth-level gravity in each ship during cruise. Upon arrival at the asteroid, thrusters could be used to stop the spin, making exploration operations more convenient and enabling zero-gravity concerts and other recreations. Taking two ships in this way would also provide 100 percent mission backup if anything should go wrong. Alternatively, just one ship could be used, with artificial gravity enabled by tethering off a counterweight brought along for the purpose.
Whether done in a small current technology hab module or a luxurious Starship cruiser, Gaiashield would be a terrific asteroid science mission, but it would be more: it would be an icebreaker mission. Two things have kept NASA from sending human explorers to Mars. The first is the notion that such missions must be incredibly expensive. The second is fear of the risks involved. These two factors have fed off each other, with fear of long-duration space voyages making NASA place the Mars mission at the end of an impossibly expensive multidecade series of preparatory activities.
The debilitating effects of long-duration spaceflight are not caused by radiation. No astronaut or cosmonaut has ever received a radiation dose during flight large enough and prompt enough to create any visible effects. Rather, all the well-known ill effects are due to long-duration zero-gravity exposure and ensuing complications.
The Gaiashield mission demonstration of a piloted interplanetary spacecraft with artificial gravity would kill forever the dragons of cosmic ray threat and of zero-G space sickness that are barring us from the solar system. Furthermore, it would destroy the myth that interplanetary manned exploration need be impossibly costly. It would also directly accomplish most of the nonrecurring development that needs to be performed for a human Mars mission.
Before Copernicus, Ptolemaic astronomers believed that humanity was walled off from the heavens by a set of crystal spheres. In a way, those spheres are still there, made not of glass but of fear. The Gaiashield mission would smash them.
MINING THE ASTEROIDS
Most of the sensational attention to asteroids has centered primarily on their potential threat to humanity and the rest of the terrestrial biosphere. But just as fire, a deadly menace to animals and children who do not understand it, becomes in the hands of competent adults one of humanity's greatest boons, so the asteroids, which offer nothing but mass death for the pre-sentient biosphere or earthbound Type I humanity, hold the promise of vast riches for a Type II spacefaring civilization.
The asteroid belt is known to contain enormous supplies of very high-grade metal ore in a low-gravity environment that makes it comparatively easy to export to Earth. For example, in his book Space Resources, Professor John Lewis of the University of Arizona considers a single small type S asteroid just one kilometer in diameter—a run-of-the-mill asteroid. This body would have a mass of around two billion tons, of which 200 million tons would be iron, 30 million tons high-quality nickel, 1.5 million tons the strategic metal cobalt, and 7,500 tons a mixture of platinum group metals whose average value, at current prices, would be in the neighborhood of $40,000 per kilogram.9 That adds up to $300 billion just for the platinum group stuff! There is little doubt about this—we have lots of samples of asteroids in the form of meteorites. As a rule, meteoritic iron contains 6–30 percent nickel, 0.5–1 percent cobalt, and platinum group metal concentrations at least ten times those of the best terrestrial ore. Furthermore, since the asteroids also contain a good deal of carbon and oxygen, all of these materials can be separated from the asteroid and from each other using variations of the carbon-monoxide-based chemistry needed for refining metals on Mars.
The economics of exporting asteroidal metals is worth examining.
First of all, it should be clear that for the mining economics to work, it is essential that refining take place. While the platinum group material may be worth $40,000 per kilogram, it only comprises 7,500/2,000,000,000 = 0.000375 percent of the bulk material, which therefore, based on its platinum content (alone), would only be worth $0.15/kg and not be worth shipping. At current prices ($0.70/kg for steel, $13/kg for nickel, $60/kg for cobalt, $40,000/kg for platinum group metals), it is clear that while asteroidal iron and nickel could have great value for use in space, we could produce something worth transporting for sale back on Earth only by refining the raw material down to, at most, the cobalt fraction plus the platinum group (which would create a combined 0.5 percent platinum group, 99.5 percent cobalt product worth about $260/kg).
TABLE 5.2. VALUE OF COMPONENTS OF A TYPICAL TWO-BILLION-TON TYPE S ASTEROID
But while we are at it, it would clearly be worth refining further, since if we could make it 10 percent platinum and 90 percent cobalt, the stuff would be worth $4,000/kg, allowing the miners to score a cool $400 million with each one-hundred-ton delivery to Earth. So, provided the right technology is put to work, the business case could well be there. But the easy money would not last forever.
If it were possible to obtain precious metals cheaply from the asteroid belt, such imports would flood the terrestrial market, driving down prices to well below current levels. While the profits of the first miners to get into the business could well be sky-high, such spectacular returns would swiftly draw competitors into the business. These would expand the quantity of imports until precious metal prices fell to the point where the rate of profit from asteroid mining would be no more than the average of comparable high-risk enterprises throughout the economy. At that point, prices would stabilize, turning asteroid mining into normal business, with further metal price drops caused mainly by technological improvements—which the existence of the business would itself drive.
So the net result of the asteroid platinum rush will most likely be giant fortunes for the daring first few, a steady income for many who follow, the creation of a host of new space technology enterprises, and a drastic lowering of the cost of many (now-) precious metals for everyone on Earth. The societal value of the last point cannot be understated. Platinum group metals are key ingredients for many promising new technologies—including fuel cells that could enable much better types of pollution-free electric cars than are possible using batteries. For example, a fuel cell car running on methanol (which can be produced from natural gas, coal, biomass, trash, or even CO2 and water using nuclear or reusable energy) could be refueled as swiftly as a gasoline-powered car today, avoiding the long recharging time and high battery cost that is a major deterrent to the broad acceptance of electric vehicles. Cheap asteroidal platinum would make such vehicles extremely attractive, freeing terrestrial civilization from dependence on oil and eliminating automobile and many other types of urban air pollution, along with all the health problems they cause, everywhere.
But the terrestrial precious metal market is just the beginning. For every kilogram of platinum shipped back to Earth, thirty tons of excellent nickel-alloy steel would become available to build industries, spacecraft, habitats, and even free flying cities for multitudes of new branches of human civilization that will develop in space.
CLAIMING ASTEROIDS
The commercial potential of asteroid mining is so enormous that several start-ups have already been formed with the goal of pursuing the opportunity for profit. Among the leaders are Planetary Resources, begun by Peter Diamandis, Eric Anderson, and Chris Lewicki with backing by several Google magnates and other high rollers, and Deep Space Industries, founded by veteran space entrepreneurs David Gump and Rick Tumlinson, with noted asteroid expert Professor John Lewis serving as chief scientist. However, despite such strong founding groups, the hopes of these companies to realize their bold plans appear quite problematic, as there is currently no technically feasible way to mine the precious metals that exist in the asteroid belt and return them to Earth for sale. As a result, these firms are being forced to pursue more conventional aerospace technology applications in order to stay in business.
Yet this picture could be changed radically were a law enacted that would create a basis for private property claims in space. The asteroids, the moon, Mars, and other extraterrestrial bodies collectively contain vast areas of unexplored and potentially resource-rich territory. They carry no commercial value today, but this can be remedied swiftly.
Consider the following: Enormous tracts of land were bought and sold in Kentucky for large sums of money a hundred years before settlers arrived despite the fact that, for purposes of development, trans-Appalachian America in the 1600s might as well have been Mars. What made it salable were two things: (1) at least a few people believed that it would be exploitable someday; and (2) a juridical arrangement existed in the form of British Crown land patents, which allowed trans-Appalachian land to be privately owned.
Thus, if a mechanism were put in place that could enforce private property rights in space, mining claims probably could be bought and sold now. Such a mechanism would not need to employ enforcers (e.g., space police) patrolling the asteroid belt; the patent or property registry of a sufficiently powerful nation, such as the United States, would be entirely adequate.
For example, if the United States chose to grant a mining patent to a private group that surveyed an asteroid (or any other piece of extraterrestrial real estate) to some specified degree of fidelity, such claims would be tradable today on the basis of their future speculative worth, and probably could be used to privately finance robotic mining survey probes in the near future. Furthermore, such claims would be enforceable internationally and throughout the solar system simply by having the US Customs and Border Protection penalize with a punitive tariff any US import made anywhere, directly or indirectly, with material that was extracted in defiance of the claim.
This sort of mechanism would not imply American sovereignty over the solar system, any more than the current US patent and copyright offices’ coining of ideas into intellectual property implies US government sovereignty over the universe of ideas. But, just as in the case of intellectual property, some government's agreement is needed to turn worthless terrain into real estate property value. The US Patent Office benefits inventors of every country by providing them a means of turning their creative efforts into negotiable property. In the same way, a US office for granting space mining patents would benefit all would-be planetary explorers, regardless of their nationality.
Once such a mechanism is in place, however, the undeveloped resources of space could become a tremendous source of capital to finance their exploration. Furthermore, when in private hands, the duly recognized claims would provide an incentive for their owners to further the development of technology that would enable their exploitation. As the capability for both exploration and development of space resources thus advanced, the value of both existing property claims and those obtainable in the future would increase, thereby expanding the financial resources available and accelerating space development even more.
The leaders and backers of companies like Planetary Resources and Deep Space Industries need to lobby hard to obtain legislation that would set up a legal regime for space property claims of this sort. The rest of us need to support its passage. Because if it does, massive new financial forces will be mobilized that will further the exploration and development of space.
With a stroke of a pen, a vibrant, privately funded space exploration effort could be brought into being, one that could use the daring and genius of the free market to rapidly bring the knowledge and the benefits of the vast untapped resources of the solar system to all humankind.
Lawmakers should take note and act accordingly.
THE SPACE TRIANGLE TRADE
While prospecting asteroids could become big business soon if the enabling legislation is passed, large-scale human activity in the Main Belt to exploit these claims will be difficult to support until we have a solid base on Mars. This is so because while water and carbonaceous material can readily be found among the asteroids (making them as a group far richer than the moon), it is not necessarily the case that such volatiles can be found on those asteroids that are most rich in exportable metals. Quite the contrary—the metal-rich type M asteroids are nearly volatile free. Moreover, while many of the Main Belt asteroids contain all the carbon, hydrogen, and oxygen needed to support agriculture, nitrogen is generally rare. Moreover, sunlight in the Main Belt is too dim to support agriculture, which means that plants would have to be grown by artificially generated light. This is a significant disadvantage for asteroid colonization, because plants are enormous consumers of light energy, and it is doubtful whether growing plants with electric lights to support any significant population is practical with current space power sources. Moreover, while collectively the asteroids may someday possess a significant mining workforce, until advanced robotic technology becomes available, it is unlikely that any one asteroid will have the sufficient personnel required to develop the division of labor necessary for true multifaceted industrial development.
Mining bases in the asteroid belt are a relatively near-term proposition. But farms, industries, and cities will need to wait until the widespread use of controlled fusion makes very large-scale employment of artificial power possible in the Main Belt. For the twenty-first century, most of the supplies needed to support the asteroid prospectors and miners will have to come from somewhere else.
As I showed in detail in my book The Case for Mars, even before a Phobos tether system is created, the ∆Vs required to reach the asteroid Main Belt from Earth are more than double those required to access it from the Red Planet, leading to mass ratios at least seven times greater and mission gross liftoff masses fifty times more—and this is true whether chemical or electric propulsion systems are used.10 And once the Phobos tether transportation system is put in place, the Martian payload delivery advantage increases more than an additional order of magnitude further.
The result that follows is simply this: anything that needs to be sent to the asteroid belt that can be produced on Mars will be produced on Mars.
The outline of mid-future interplanetary commerce in the inner solar system thus becomes clear. There will be a “triangle trade,” with Earth supplying high-technology manufactured goods to Mars; Mars supplying low-technology manufactured goods and food staples to the asteroid belt and possibly the moon as well; and the asteroids sending metals and perhaps the moon sending helium-3 to Earth. This triangle trade is directly analogous to the triangle trade of Britain, her North American colonies, and the West Indies during the colonial period. Britain would send manufactured goods to North America; the American colonies would send food staples and needed craft products to the West Indies; and the West Indies would send cash crops such as sugar to Britain. A similar triangle trade involving Britain, Australia, and the Spice Islands also supported British trade in the East Indies during the nineteenth century.
SETTLING THE ASTEROIDS
California, Nevada, and Colorado all entered American history as destinations for miners, drawn to those far-off locations by the promise of gold or silver. Ultimately, however, mining became an industry of secondary importance as settlers transformed mining outposts into towns, cities, and states. The same history may repeat itself in the Main Belt.
Collectively the asteroids have all the materials needed for life and civilization, but individually they do not. So clearly, what is required to enable settlement is technology readily enabling trade between them. Furthermore, as noted, asteroid settlement would need a lot of power, as the low solar fluence would make natural sunlight unattractive to support effective agriculture; a sevenfold concentrator would be needed to duplicate terrestrial illumination levels.
Fortunately, the Main Belt asteroids are rich in a material that can serve to meet both of these needs. That material is water.
One gallon of water on Earth contains enough deuterium that, if burned in a fusion reactor, it would produce as much energy as that released by combusting 350 gallons of gasoline. It is estimated that the deuterium content of asteroidal water, such as the ice the Dawn spacecraft imaged on the surface of Ceres, may contain twice as much. So, once we have deuterium fusion reactors, the power required to support asteroidal settlement could be met by a locally available fuel. Pure deuterium is not as attractive a fusion fuel as D-He3, as 40 percent of the reaction energy comes off as neutrons (which can induce radioactivity in the surrounding materials), but it will do the job until plentiful He3 from the outer solar system becomes available.
Fusion reactors could use water as a propellant, simply by heating it to high-temperature steam and exhausting it out a rocket nozzle to produce thrust. Such fusion thermal steam rockets could probably obtain an exhaust velocity of about 3.6 km/s (a specific impulse of about 350 seconds), giving them a performance similar to that of a kerosene/oxygen chemical rocket, but with a propellant that is easy to store and readily available throughout the Main Belt. Fission reactors could also be employed for this purpose, and in fact, such nuclear thermal rockets, using hydrogen propellant (thereby obtaining a spectacular exhaust velocity of 9 km/s), were developed and tested in the United States in the 1960s at sizes up to 250,000 pounds of thrust. But by employing fusion reactors to drive thermal rockets instead, the asteroid settlements could make themselves independent of Earth for fuel.
Alternatively, fusion reactors could be used to electrolyze water into hydrogen and oxygen. While far more difficult to produce and store than liquid water, these would allow spacecraft to travel among the asteroids using conventional lightweight chemical rockets, leaving the heavy reactors behind at propellant production bases.
With the aid of such systems, active trade among archipelagos of asteroidal settlements will become feasible, enabling them to collectively mobilize the division of labor and diverse material resources to give birth to a vast and vibrant space-based civilization.
NEW WORLDS FOR NEW SOCIETIES
The asteroids’ multiplicity represents a disadvantage for societal development in the near term, but in the far term, it will be a great advantage. Mars, while huge, is after all one world. A multiple of social experiments will start there, but eventually these are likely to be resolved and fuse into a single, or at most a few, new branches of human civilization. But the technologies for resource utilization, labor saving, space transportation, and energy production developed for the colonization of Mars will open the way to the settlement of the asteroids, which will force both the technologies and the aptitudes that created them even further. This will make available thousands of potential new worlds, whose cultures and systems of law need never fuse.
Indeed, by far the greatest treasure that the asteroids offer humanity is not platinum but freedom. There is nothing more valuable than freedom.
Can space colonies truly be free? Some authors have argued that extraterrestrial liberty is unlikely, because the authorities in a space colony can always kill you by turning off your air.11 But this has it backwards. Historically, the easiest people for a tyrant to oppress are nominally self-sufficient rural peasants, because none of them are individually essential. As the medieval saying went, “City air makes a man free.” It is the interdependence and intercommunication of people in urban societies that empowers the individual. In a space colony, nearly everyone will be individually essential, and therefore powerful, and all will be capable of being dangerous to those in authority.
A society composed of very empowered citizens will need to treat its people right.
But freedom is more than the mere absence of tyranny. For nearly all human history, people have been required to live in realities and under rules that were completely defined before they were born. But the right to be a maker of your own world, rather than just an inhabitant of one, is a fundamental form of freedom. It only exists in a substantial way, however, in a society with an open frontier. One size will never fit all. There always will be people who have new ideas on how society should be organized, and if they are to be truly free, they need a place where they can go to give those ideas a try. The asteroid belt will provide home planets for thousands of such noble experiments.
Perhaps some will be republican, others anarchist. Some communalist, others capitalist. Some patriarchal, others matriarchal. Some aristocratic, others egalitarian. Some religious, others rationalist. Some Epicurean, others Stoic. Some hedonistic, others puritanical. Some traditional, others relentlessly innovative. Some may enthusiastically embrace transhumanism, augmented intelligence, and genetic engineering of children; others may reject them entirely. Those that afford people a chance to more fully realize their human potential will attract immigrants and grow. Those that do not will disappear. But there will no doubt be many diverse paths to success. As among the city-states of the ancient Greek islands, a bewildering myriad of diverse societies may flower and bloom—trading goods and ideas across a vast and endlessly creative cosmic cosmopolis.
The rest of humanity will watch and learn from their experiences. That which works will be repeated. So shall we continue to progress.
FOCUS SECTION: CHEMISTRY FOR SPACE SETTLERS
Just as the pioneers of old needed to know how to find the edible plants and methods of hunting the game available in their environments, so space settlers will need to know how to extract useful resources from their new worlds. The following is a brief compendium of some of the key techniques.
On the Moon
On the moon, oxygen can be produced from the mineral ilmenite, which is found in up to 10 percent concentrations in some lunar soils. The reaction is:
The water produced is then electrolyzed to produce hydrogen, which is recycled back into the reactor, and oxygen, which, along with metallic iron, is the net useful product of the system. The feasibility of this system has been demonstrated by researchers working at Carbotek in Houston, Texas. If you don't want to go prospecting for ilmenite, you can try carbothermal reduction, a system pioneered by Sanders Rosenberg at Aerojet, which will work with a larger variety of lunar rocks, including the very common silicates.
The water is then electrolyzed to produce oxygen, while the carbon monoxide and hydrogen from the electrolysis are combined to remake the methane in accord with:
Reactions 5.1 and 5.2 are very endothermic (i.e., they need energy input) and must be done at high temperatures (above 1,000°C). Reaction 5.3 is exothermic (i.e., it produces energy) and occurs rapidly at 400°C. The carbon and hydrogen reagents are extremely rare on the moon (except in permanently shadowed craters near the poles), so the systems must be designed for very efficient recycling.
On Mars
On Mars, the most accessible resource is the atmosphere, which can be used to make fuel, oxygen, and water in a variety of ways. The simplest technique is to bring some hydrogen from Earth and react it with the CO2 that comprises 95 percent of the Martian air as follows.
Reaction 5.4 is known as the Sabatier reaction and has been widely performed by the chemical industry on Earth in large-scale one-pass units since the 1890s. It is exothermic, occurs rapidly, and goes to completion when catalyzed by ruthenium on alumina pellets at 400°C. I first demonstrated a compact system appropriate for Mars application that united this reaction with a water electrolysis and recycle loop while working at Martin Marietta in Denver in 1993. The methane produced is great rocket fuel. The water can either be consumed as such or electrolyzed to make oxygen (for propellant or consumable purposes) and hydrogen (which is recycled).
Another system that has been demonstrated for Mars resource utilization is direct dissociation of CO2 using zirconia electrolysis cells.
The reaction is:
Reaction 5.5 is very endothermic and requires the use of a ceramic system with high-temperature seals operating above 1,000°C. Its feasibility was first demonstrated by Robert Ash at the Jet Propulsion Lab in the late 1970s, and the performance of such systems has since been significantly improved by Kumar Ramohalli and K. R. Sridhar at the University of Arizona. (Sridhar has since formed a successful company, called Bloom Energy, devoted to commercializing this technology—operated in reverse as a kind of fuel cell—for use on Earth.) Its great advantage is that no cycling reagents are needed. Its disadvantage is that it requires a lot of power—about three times that of the Sabatier process to produce the same amount of propellant. A small-scale (producing twenty grams of oxygen per hour) version of such a system, called MOXIE, has been placed on the Mars 2020 rover, so we will soon get to see how well it works on Mars.12
Still another method of Mars propellant production is the reverse water-gas shift (RWGS).
This reaction is very mildly endothermic and has been known to chemistry since the nineteenth century. Its advantage over the Sabatier reaction is that all the hydrogen reacted goes into the water, from where it can be electrolyzed and used again, allowing a nearly infinite amount of oxygen to be produced from a small recycling hydrogen supply. It occurs rapidly at 400°C. However, its equilibrium constant is low, which means that it does not ordinarily go to completion, and it is in competition with the Sabatier reaction (5.4), which does. Working at Pioneer Astronautics in 1997, Brian Frankie, Tomoko Kito, and I demonstrated that copper on alumina catalyst was 100 percent specific for this reaction, however, and that by using a water condenser and air separation membrane in a recycle loop with a RWGS reactor, conversions approaching 100 percent could be readily achieved.
Our initial RWGS unit produced water at a rate of about one kilogram per day, which would be appropriate to make the oxygen propellant needed for the ascent vehicle of a robotic Mars sample return mission. Building on this work, in 2017, at Pioneer Energy, a commercial spin-off company of Pioneer Astronautics, my R&D team demonstrated an RWGS system operating at a rate of eighty kilograms of water production per day, sufficient to make all the oxygen propellant needed for the Mars Direct human exploration mission.
Running the RWGS with extra hydrogen, a waste gas stream consisting of CO and H2 can be produced. This is known as “synthesis gas” and can be reacted exothermically in a second catalytic bed to produce methanol (reaction 5.7), propylene (reaction 5.8), or other fuels. Such use of RWGS “waste” gas to make methanol was first demonstrated during the 1997 Pioneer Astronautics program and then on a much larger scale (five kilograms of methanol per hour) during a 2017 Pioneer Energy project, while the propylene production reaction was demonstrated by the Pioneer Astronautics team during a program in 1998.
On Mars, buffer gas for breathing systems, consisting of nitrogen and argon, can be extracted directly from the atmosphere using pumps, as these gases comprise 2.7 percent and 1.6 percent of the air there, respectively. Water can also be extracted from the atmosphere using zeolite sorption beds, as shown by Adam Bruckner, Steve Coons, and John Williams at the University of Washington. Alternatively, it can be baked out of the soil, which the Mars Odyssey spacecraft has shown to vary from typically 5–10 percent water by weight at the equator to up to 60 percent in subarctic regions. Using ground-penetrating radar, subsurface liquid salt water has been found near the south pole by the European Mars Express spacecraft, while the NASA Mars Reconnaissance Orbiter has found massive formations of dust-covered glaciers made of nearly pure water ice in the northern hemisphere as far south as 38 degrees north. So relatively simple drilling, soil-baking, or ice-melting technologies should suffice to produce ample supplies of water on Mars.
Iron can also be produced on Mars very readily using either reaction 5.9 or 5.10. I say very readily because the solid feedstock, Fe2O3, is so omnipresent on Mars that it gives the planet its red color and thus, indirectly, its name.
Reaction 5.9 is mildly endothermic (energy consuming) and can be used with a water electrolysis recycling system to produce oxygen as well. Reaction 5.10 is mildly exothermic (energy producing) and can be used in tandem with an electrolyzer and an RWGS unit to also produce oxygen. The iron can be used as such or turned into steel, since carbon, manganese, phosphorus, silicon, nickel, chromium, and vanadium, the key elements used in producing the principal carbon and stainless steel alloys, are all relatively common on Mars. To show this, in 2017, Pioneer Astronautics demonstrated the use of reaction 5.10 to make carbon steel out of Mars soil simulant samples.
The carbon monoxide produced by the RWGS can be used to produce carbon via:
This reaction is exothermic and occurs spontaneously at high pressure and temperatures of about 600°C. The carbon so produced can be used to make carbon-carbon components or to produce silicon or aluminum via reactions 5.12 and 5.13.
Both SiO2 and Al2O3 are common on Mars, so finding feedstock will be no problem. Reactions 5.12 and 5.13 are both highly endothermic, however. So except for specialty applications where aluminum is really required, steel will be the metal of choice for Martian construction.
On the Asteroids
The asteroids are rich in metals and also possess carbon, so much of the carbon-based resource utilization reactions developed for Mars could also be used there. Of special interest to asteroid miners will be a means of acquiring pure samples of various metals for purposes of commercial export. One way to do this is to produce carbonyls, as pointed out by the University of Arizona's Professor Lewis.13
For example, carbon monoxide can be combined with iron at 110°C to produce iron carbonyl (Fe(CO)5), which is a liquid at room temperature. Then iron carbonyl can be poured into a mold and heated to about 200°C, at which time it will decompose. Pure iron, very strong, will be left in the mold, while the carbon monoxide will be released, allowing it to be used again. Similar carbonyls can be formed between carbon monoxide and nickel, chromium, osmium, iridium, ruthenium, rhenium, cobalt, and tungsten. Each of these carbonyls decomposes under slightly different conditions, allowing a mixture of metal carbonyls to be separated into its pure components by successive decomposition, one metal at a time.
An additional advantage of this technique is the opportunities it offers to enable precision low-temperature metal casting. You can take the iron carbonyl, for example, and deposit the iron in layers by decomposing carbonyl vapor, allowing hollow objects of any complex shape desired to be made. For this reason, carbonyl manufacturing and casting will no doubt also find extensive use on Mars and the thousands of worlds that lie just beyond.
The potential 3-D printing of these materials has only begun to be explored. But there is little doubt it can be done, and when it is, space settlers will be able to make anything they can draw.