How Humans Will Mine Asteroids and Comets

The idea of mining the planets, Moon, asteroids, and comets for their valuable mineral resources is not new. Science fiction writers began weaving tales of space mines, worked by crusty, usually antisocial old prospectors, in the 1930s. Invariably, these difficult, dirty, lonely operations in the far frontiers of the solar system resembled the mines in a more familiar frontier situation—the nineteenth-century American West. There were "decadent boom towns with grossly inflated prices," University of Arizona scientist John S. Lewis points out in his recent book about space mining. These stories also featured "boisterous miners in town for a few days to pick up supplies and go on a bender," along with "slick gamblers, painted women, and a variety of dubious establishments."⁴¹

Not surprisingly, drunk miners, gamblers, and painted women were not part of the vision of the scientists who began discussing asteroid mining in the 1970s. The technological advances made during the U.S. space program had recently culminated in several successful manned Moon landings. And the experts became convinced that mining asteroids, and perhaps comets too, would actually be feasible in the near future.

Since that time, scientists working for both NASA and private companies have been doing detailed studies of space mining. The general consensus is that most of the technology needed to begin modest mining operations on an asteroid already exists. The main ingredient still missing is the commitment of a large amount of money by a government, corporation, or group of private investors. The experts all agree that it is only a matter of time before humans begin exploiting the tremendous wealth of resources waiting for them in the solar system.

An Extremely Profitable Business

The first questions that all potential investors ask, of course, are what is the nature of these abundant resources contained in asteroids and comets, and what are they worth? Scientists answer first that the asteroids are composed of iron, nickel, platinum, and other metals, as well as sulfur, aluminum oxide, carbon compounds, and other minerals. Many asteroids also contain smaller amounts of volatiles, including hydrogen, oxygen, and water.

As for the value of these materials to people on Earth, Lewis cites the example of the smallest known M-type asteroid—Amun. It is about 1.2 miles across and has a mass of about 30 billion tons. To put this large tonnage in perspective, imagine that the raw materials from the mining operation are loaded into a fleet of space shuttles like those presently in NASA's fleet. The cargo bay of a typical shuttle holds about twenty-five tons, equivalent to 250 two-hundred-pound people. It would take four hundred shuttles (or four hundred trips by one shuttle), therefore, to haul ten thousand tons of asteroidal material; and it would take 1.2 billion shuttles (or 1.2 billion trips by one shuttle) to carry all of the materials mined from Amun.

Regarding the materials themselves, Amun's total tonnage breaks down into many different metals. The

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most abundant of these are iron and nickel, which alone would have a market value of about $8 trillion. (Keep in mind that a trillion is a million times a million.) Supplies of another metal, cobalt, on Amun would be worth perhaps $6 trillion. Then there are rarer metals such as platinum, iridium, osmium, and palladium, which together would add another $6 trillion to the investors' profits. The nonmetals, including carbon, nitrogen, sulfur, phosphorus, oxygen, hydrogen, and gallium, would be worth at least $2 trillion. If humans mined all of Amun, therefore (which would take many years), the gross profits would come to at least $22 trillion. It is difficult to estimate the upfront costs of such a mining operation. But even if they were as high as $1 trillion, the net profits would still be $21 trillion. Clearly, asteroid mining will be an extremely profitable business.

Remember also that all of the valuable resources and profits cited are from a single small asteroid. What would all of the asteroids in the asteroid belt together be worth? Lewis speculates about the asteroidal iron alone:

To raise the standard of living of the people of Earth to present-day North American, Japanese, or Western European levels, we need about 2 billion tons of iron and steel each year. With the asteroidal supplies of metal at hand, we could meet Earth's needs for the next four hundred million years. . . . Suppose that we were to extract all the iron in the belt and bring it back to Earth. Spreading this amount of iron uniformly over all the continents gives us a layer of iron . . . half a mile thick. . . . This is enough iron to cover all the continents with a steel frame building 8,000 stories (80,000 feet, or 15.2 miles) tall.⁴²

When one factors in the other metals available in the asteroid belt alone, along with the many nonmetals, the total resources could sustain a human population a million times larger than the present one for several thousand years. And this does not take into account the trillions of asteroids and comets in the Kuiper Belt and Oort Cloud. (The comets contain far fewer metals, but do have many minerals, as well as an abundance of volatiles that could be used for food production and making fuels.)

Supplies for Earth and the New Frontier

The discussion of the monetary worth of asteroids and comets must not divert attention from the other major reason to pursue the dream of mining these objects. Namely, the metals, minerals, and volatiles acquired in such operations would help conserve supplies of these materials on Earth. At present, these supplies are marginally sufficient to sustain the planet's present population. But that population will inevitably grow and supplies of a number of metals and other commodities will begin to run out.

Also, processing metals and minerals (separating them from the rocky mixtures in which most are trapped) pollutes Earth's air, soil, and water. This problem will be eliminated entirely in space mining since all of the processing will take place far from Earth. At first glance, it would seem that such operations would simply shift the pollution problem from Earth to outer space. But this need not be the case. William Hartmann explains:

Some writers have raised the specter of humanity despoiling the solar system, in the same manner that over-industrialization is beginning to despoil Earth's environment. But . . . with a careful balance of research and exploitation, we could learn from and process materials in space in a [clean] way that would [also] begin to take the pressure off Earth's ecosystem. A transition from Earth-based manufacturing to interplanetary manufacturing could eventually reduce pollution and ravaging of Earth by an Earth-based society bent on ripping the last dwindling resources from the land.⁴³

There is another dimension to human acquisition and consumption of cosmic resources, however. Nearly all the experts agree that by the time space mining becomes widespread, only a small percentage of the materials mined will end up on Earth. Instead, a major portion of these resources will be used to construct and sustain human colonies and cities floating in space. Space, they say, will become a vast new frontier that will attract many people born on Earth, helping to stabilize or at least slow the growth of the planet's population. (And of course, over time even more people will be born in space.)

A City in the Sky

As planetary scientist John S. Lewis says in this excerpt from his fascinating book Mining the Sky, the asteroid belt contains enough iron to construct an enormous space city.

We have enough asteroidal iron [in the asteroid belt] to make a metal sphere . . . 550 miles in diameter. Hollowed out into rooms with iron walls, like a gigantic city, it would make a spherical space structure over . . . 1,200 miles in diameter. . . . With a nine-foot ceiling, we could provide each family with a floor area of 3,000 square feet for private residential use and still set aside 3,000 square feet of public space per family. This artificial world would contain enough room to accommodate more than ten quadrillion [a million times a billion] people. Very simply, that is a million times the ultimate population capacity of Earth.

It is fair to ask why the inhabitants of such colonies, as well as people still living on Earth, would choose to get metals, minerals, and other resources from asteroids and comets rather than from larger cosmic bodies. Why not mine the Moon first, for example, or perhaps the planet Mars? After all, the Moon and Mars are both far larger than all of the asteroids put together, and both are closer to Earth than most of the asteroids and comets (the NEAs being an obvious exception).

First, whether they live on Earth or in space cities, people will naturally want to obtain cosmic resources as easily and cheaply as possible. The fact is that mining the asteroids will be far easier and more economical than mining a large body like the Moon. The Moon's surface gravity is about one-sixth that of Earth, which is strong enough to require a good deal of fuel to land miners and their equipment on its surface. More importantly, getting the processed metals and minerals off the Moon's surface would take even larger amounts of fuel. An added problem is that most of the valuable metals and minerals on the Moon are spread out over thousands of square miles and bound up inside mixtures of rock and dirt, many lying deep underground; it would require a lot of exploration, as well as strenuous and expensive digging and processing, to free them.

Zero-Gravity Mining Techniques

In contrast, most asteroids and comets are small, manageable, and have extremely tiny gravities, all of which make them easier to mine. Mining ships will also not land on or take off from these bodies, which will save enormous amounts of fuel. A typical ship will stop beside an asteroid and the miners, wearing spacesuits, will transport over to the worksite by pushing off the side of the ship. (They may also use small jets attached to their suits.) This is possible because the ship, the miners, and the asteroid are all nearly weightless. For this reason, the miners will need to attach long tethers to their suits and tie the opposite ends of the tethers to spikes hammered into the asteroid. This will keep them from accidentally floating away into space while they are working.

In addition, the mined materials in such a situation are, like the miners, nearly weightless, and will not need to be lifted off the asteroid's surface. This will not only save fuel, but will greatly reduce other risks. According to the scientists at the Minor Planet Center (at the Smithsonian Astrophysical Observatory):

Getting asteroidal materials is not a risky business, like launching materials up from Earth or the Moon. Transporting asteroidal materials is all "interorbital" [i.e., takes place in orbit]. [There will be] no risks of crashes, no huge rockets. The gravity of the asteroids is negligible. A person can jump off any but the largest asteroids with leg power alone.⁴⁴

Another advantage of mining asteroids rather than the Moon is that the asteroidal metals and minerals are concentrated in a small, easily accessible space and are much purer in content. Almost all asteroids, Daniel Durda points out, "have a hundred times more metal not bound up in rocky minerals than do moon rocks."⁴⁵ On S-type and especially M-type asteroids, such materials will require very little processing. Indeed, a fair amount will be collectable even before the digging process begins. The surface of such bodies is rich in granules of metal, ranging from sand- to perhaps fist-sized pieces, all mixed with sootlike dirt. These granules "can easily be separated from the dirt," the Minor Planet Center experts say,

using only magnets [in the form of magnetic rakes] and soft grinders. Some engineering designs have "centrifugal grinders," whereby the dirt is fed into a rotating tank and shattered against the wall a time or two. Out come little metal disks, which are separated using simple magnets.⁴⁶

Once digging operations begin, larger deposits of metals and minerals will be separated with bigger grinding and chopping devices. Most likely, the miners will allow the loose rocks to float up and away from the asteroid's surface, where a large canopy, a sort of tarp made of nylon or some other tough material, will catch them. One group of experts describes the advantages of such a canopy:

Companies will most probably use a canopy because the canopy would be quite profitable in terms of the amount of loose ore [rock mixture] it would collect. It would also prevent the area [around the worksite] from turning into a big dark cloud of debris which would pose problems for the operations. . . . A double-cone-shaped canopy is put around the asteroid. . . . The canopy is then rotated. A [small robotic device called a] dust kicker goes down to the asteroid and . . . kicks up the ore at low velocity. The ore strikes the canopy and is deflected so that it tends to rotate with the canopy, eventually sliding down the two [cone-shaped] funnels.⁴⁷

The equipment for processing the metal- and mineral-rich ore will be located at the tips of the two cones. After all of the usable materials have been mined, the miners will tie off the ends of the canopy and tow it either to a floating city or into Earth's orbit. That way, the canopy doubles as both a collection apparatus and transport device.

Habitats for the Miners

During these mining operations, which could take months or years, depending on the size of the asteroid and the number of workers and machines, the miners will need somewhere to live. The quarters aboard the ship itself will likely be too cramped for such a long stay. So the miners will build a temporary habitat, which will use mostly on-site materials and thereby eliminate the need and cost of bringing them from Earth.

To some degree, the kinds of materials required to erect and sustain a human habitat for such miners will dictate the type of asteroid the mining operation will target. Although M-types have more metals than other kinds of asteroids, probably a majority of the asteroids mined will be S-types or C-types. These bodies have larger supplies of oxygen, hydrogen, water (in the form of ice), and other volatiles that are essential to the habitats. If necessary, additional volatiles can be obtained from comets; storehouses of cometary volatiles could be positioned at various points in space for asteroid miners to draw from.

As for how these lighter materials will be converted, first the miners will melt the ices to produce water for drinking, cooking, and bathing. They will also extract oxygen and hydrogen from the ices and combine them with various minerals to make beams, walls, pipes, and other parts for their habitat. The miners can also employ the oxygen and hydrogen to make fuel, both to power the ship on its return voyage and to sell to companies or individuals in space cities or on Earth. This means that relatively little, if any, fuel will have to be brought from Earth, making space mines and habitats almost completely self-sufficient.

Indeed, nothing would be wasted during the mining operation. "Even unprocessed soil," says Durda, "could be used for shielding" to protect miners and other astronauts "on longer missions from cosmic rays and solar flares [dangerous radiation from the Sun]."⁴⁸

Setting Large-Scale Goals

These mining situations and techniques are not some flight of fancy that will take centuries to become reality. NASA, various groups of scientists, and some private companies have already begun drawing up plans for such space mining missions. They know that certain inherent difficulties and problems will have to be overcome, or at least planned for, to make this huge undertaking work. For example, even in the case of the NEAs, which will surely be the first targets for space miners, a typical round trip will be two to five years. This is a long time for a company of miners to be separated from family, friends, and society in general. Long periods of work in weightless conditions may also have a negative effect on the miners' health. Astronauts who have spent many months in weightless conditions in Earth's orbit have developed muscle weakness, loss of calcium and red blood cells, and other problems. And of course, such ventures will be extremely costly and require long-term financial and other commitments from governments, companies, and tens of thousands, if not millions, of individuals.

Assuming such commitments do materialize, however, the technical difficulties will be relatively minimal. Indeed, scientists emphasize that humans can reach and mine the asteroids and comets mostly using technology that exists or is presently in development. It is true that this technology will have to be applied on a much vaster scale than people have ever experienced. But it is doable nonetheless. "This isn't Star Wars," say the Minor Planet Center researchers. "The asteroids aren't against us. It's really pretty simple stuff." People have already demonstrated the ability to travel and live in space, and "the engineering factors that go into 'docking' with an asteroid are not difficult."⁴⁹

The biggest difficulty will rest in the human decision to begin the mammoth enterprise of exploiting the riches of the solar system. Countries, peoples, and governments have accomplished such large-scale goals before, as the Europeans did when they settled and transformed North and South America or as the Americans did when they aimed for and reached the Moon in the 1960s. One thing is certain. These prior undertakings, though enormous in their own times, will be positively dwarfed by the adventure that awaits humanity in the asteroid belt and beyond.