by Ruth A. Lewis
From L5 News, June 1985
The theme of the 1970’s was “We’re using it up!” Oil, natural gas, forests, fertile farmland, potable water, land to live on — these commodities were not only visibly diminishing…but at a rapid pace.
From our perspective in the 1980’s, we know better. Abundances to fill every possible need surround us. The only problem remaining is to get a hold of them.
Is gold your desire? South Africa and the USSR mine 95 percent of the world’s production. You don’t live in South Africa or the USSR? Too bad. How about arable land? Others already own it. Too bad they got there first. Certainly, the distribution of resources has never been equitable.
Further, the Earth is rapidly filling up with people, and the share of resources for any one of us is diminishing just as fast. MIT sponsored a study a few years ago in which the major theme was “Limits to Growth.” The argument unfortunately was reasonable. Since the Earth has a finite supply of all resources and since the population of Earth is always increasing, the share for each person consequently must decrease. Eventually, growth (of population, of technology, of quality of life) will cease.
The most recently explored of these new pieces of real estate is the Moon. From Earth, it looks rather barren. And up close, we find that this impression is no illusion: the biggest asset of the moon is that it offers plenty of elbow room.
Unfortunately, the Moon’s real estate would be very expensive to develop since oxygen must be brought from Earth or mined from oxygen-bearing minerals in the Moon’s maria. Even though building materials such as iron and titanium would result as by-products from oxygen production, the Moon is almost devoid of the other volatiles such as water, carbon dioxide, and nitrogen that living systems find most necessary.
From a physical standpoint, it is not surprising that the Moon does not have oceans and an atmosphere to provide these volatiles. It’s too small and it has insufficient gravitational pull to keep the lighter molecules in its environs.
There still remains one hope for finding these lighter materials. No one has yet set foot in the polar regions of the moon, and there deposits of water-ice and other volatiles perhaps lie in permanently shadowed craters. Thus, some of the essentials might be provided. Unfortunately, by the time they were transported to the maria where they would be needed — at least an eighth of a moon circumference away — their costs would be too high.
These essential volatiles, of course, could be transported from Earth; certainly, we have the technology. But, again, it costs too much, the greatest expense being to get out of Earth’s gravitational well. The next biggest expense is to slow down enough to land softly on the Moon. Unfortunately for those who dream of developing the Moon as real estate — or for any other purpose — it is the wrong size. It is too small to hold an atmosphere, but it is too massive to allow low-energy arrivals and departures.
There is actually only one sensible thing to do about the Moon: preserve it as a memorial to man’s first step into space.
Seeing Beyond the Moon
A myopic view has been responsible for suggesting the Moon as our next home. Modern optics, however, is now correcting our vision by allowing us to see the real bounty awaiting us. Just in time, it seems, our Earthly technology in the form of high-powered telescopes has shown us that the nearby heavens are swarming with chunks of building materials, volatiles, and fuels.
The first surprise came in 1898 with the discovery of the asteroid Eros. The presence of asteroids in a belt beyond Mars had been known since the first four were discovered very early in the 19th century, and by 1898, some 300 had been discovered between the orbits of Mars and Jupiter. Eros, however, crosses Mars’ orbit and comes very close to Earth.
Since the discovery of Eros, other Earth-approaching asteroids have been found, and there are many that actually cross Earth’s orbit. Some, in fact, such as the asteroid 1954XA, cross the orbits of Mars, Earth, and Venus.
A concerted effort to find and catalog all such asteroids was begun by Drs. Eugene Shoemaker and Eleanor Helin in 1973. And with good reason. With so many Earth approaching and Earth-crossing asteroids already found, it seemed that collisions with Earth might be a real possibility.
Indeed, evidence for such collisions was already known. Our pock-marked companion, the Moon, shows clearly that collisions in space are a common occurrence. And here on Earth we have several substantial craters to show that we ourselves are not safe. Meteor Crater in Arizona, whose name should not be taken seriously, is most certainly the result of an asteroid colliding with Earth.
The Shoemaker-Helin study yields certain fascinating conclusions. Kilometer-sized asteroids hit Earth about three or four times every million years, and the last known impact was probably 700,000 years ago, apparently some place in Cambodia. A probability of 1 in 1000 exists for an asteroid 1 KM or larger in diameter hitting the Earth in the next century. Of course, we may become so clever in our ability to detect asteroids that we will be able to prevent future collisions by nudging them out of the way.
In any case, asteroids are all around us, with sixty Earth-approachers or Earth¬crossers already known. From these, estimates of 300,000 or more such asteroids in our vicinity seem reasonable. We can live in fear of these, or we can rejoice in the riches they might provide. The next step, therefore, is to go explore them.
Energetically, many of the Earth-crossers are substantially more approachable than the Moon, for only half the energy is required to achieve a landing on the best of them. And only as little as 1/1000 as much energy is needed to get back to Low Earth Orbit (LEO). Since almost the entire cost of any mission is determined by the amount of energy — fuel — needed for the trip, low energy requirements translate directly into low costs.
One neat piece of physics makes LEO an inexpensive warehouse for space materials. Aerobraking, the ability to slow down a spacecraft by allowing it to interact with the atmosphere, means that we do not have to burn precious fuel to kill our return speed. Thus, an incoming spacecraft can be oriented to skim the top of the atmosphere until it has slowed sufficiently to maintain an orbit around Earth.
Naturally, fuel for navigation — adjusting the spacecraft’s orbit as it leaves the asteroid and orbiting it once it has slowed in Earth’s atmosphere — is still necessary, but as we will see, it will never be necessary to spend fuel to lift fuel from a massive body.
The principle of aerobraking holds for any other heavenly body with an atmosphere. Aerobraking saves fuel, a great deal of it. When we are making a decision about future missions and future homes for man, it would be useful to keep this fact in mind.
So, it is easy to get to an Earth-approaching asteroid. But what would the advantages be? What do these cosmic chunks have to offer? In a word, resources — just about anything we might need or want and of every kind. The asteroids are the sources of that abundance that surrounds us.
Although we will not know what a true asteroid looks like until the Galileo spacecraft flies by the asteroid Amphitrite in December 1986, we can be fairly certain that some planetary satellites such as Saturn’s Hyperion are captured asteroids and their surfaces are similar to both the Main Belt and Earth-approaching asteroids. These three views of the surface of Hyperion were taken by Voyager 2 in 1981. (Courtesy: Jet Propulsion Laboratory.)
Using the Bounty
According to Dr. Shoemaker, at least half of the known Earth-approachers are carbonaceous, meaning they are high in volatiles. They contain about twenty percent water, six percent carbon, several percent sulfur, and a tenth of a percent nitrogen, as well as ten percent oxygen, extractable from sources other than the water already mentioned.
These concentrations are 100 to 1000 times those found in surface materials on the Moon. Not only are asteroids easier and less expensive to get to, they also yield much more of what we need for life in space.
In short, asteroids will make it possible for us to live in space. The volatiles available from a typical carbonaceous asteroid could be transported readily to replenish supplies in a manned space station in LEO, and instead of lifting these essentials from Earth at great cost — in fact instead of depending on Earth in any way — these volatiles can be delivered to a space station, or any other space colony, without any net expense.
So, it will cost virtually nothing to deliver asteroid-derived materials to LEO. The volatiles themselves provide much more fuel than is needed for the return trip as well as the next trip out. By using solar cell technology, we can employ the sun directly to electrolyze the abundant water in a carbonaceous asteroid into hydrogen and oxygen, which becomes the fuel for the return trip.
Additionally, there are many other classes of asteroids besides the carbonaceous. Ironically, however, the compositions of those resident in the asteroid belt beyond Mars are presently better known than the Earth-crossers, but certain materials have been found in nearby asteroids. In any case, nothing suggests that there is a difference in composition between asteroids from the two locations.
Fortunately, these other materials include many that are essential to our progress in space. Free metals, necessary for construction, high technology, electronics, spacecraft, and a thousand other uses, are available in the form of iron, nickel, cobalt, and the platinum group metals. Other essentials such as rare nonmetals (germanium, gallium, arsenic), sulfides, and phosphides are also known to be present in some asteroids.
After the first space station or two are lifted from Earth, all remaining space ventures will be self-sufficient. With these necessary building materials and volatiles to support man and the plants that he feeds on, as well as the leftovers (stony materials and other by-products of mining operations) to shield him from cosmic radiation, the children of Earth will have become independent adults.
For all asteroids are just about the right size to make mining them — using them for their resources — an easy task. Once we have achieved the proper orbit, we need only step on, gather up our materials, and step off again. Because of the low mass of these objects, arrivals and departures require only a minute expenditure of fuel. And, once we are off the asteroid, a tiny nudge puts us back into the proper elliptical orbit to be recaptured by Earth.
Step-on, step-off technology is simple in the extreme, so much so that the entire process will very quickly become mechanized. Whole chunks of an asteroid can be broken off and propelled ballistically into LEO by simple robots. Thus, man’s employment in space will not be in the mining, but in the using of what is mined.
The Balance Shifts
As man’s new enterprise begins, however, certain challenges will no doubt arise. New resources mean new wealth, and changing patterns of wealth mean that asteroid mining could cause political upheaval. South Africa has a near monopoly on some very important elements, including gold and the strategic platinum-group metals. The Soviet Union has an abundance of palladium and beryllium, but has recently stopped exporting platinum-group elements. The United States is dependent on politically unstable Zaire for much of its cobalt, used in jet engines and superalloys. Stockpiling of these materials to diminish our dependence has not proved successful.
What if we suddenly had all the cobalt we needed because of mining an asteroid? And gold? And other understocked strategic materials? Would the effect be greater equity or less? Would the world become politically more stable or less so? We’ll have to wait a few years to find out.
Whatever the specific effects, there will be those on Earth who will have a vested interest in limiting the influx of resources from space. The biggest challenge will not be technological, but political and financial. There will arise opposition from purely selfish factions.
When a small group of annoying religious dissidents set sail across the vast reaches of the Atlantic, King George’s royal predecessors were not worried. As an imperialist nation, England rejoiced when land was occupied by her people, for the wealth and power that were returned made her a formidable force in the world. What happended 150 years later should be remembered by those who see the inhabitation of space as a way to renew Earth.
The use of the asteroids as a way of solving the “limits to growth” problems of Earth is indeed practical, but it may not be in the fashion anticipated by Earth-bound minds. Once Earth’s people begin to use asteroid and other space resources, they will be in a new land of plenty. They will not return, and the frontier will have instantaneously expanded almost to the limits of the solar system.
The new world of the pilgrims rapidly developed into a source of necessary and desirable supplies for Mother England, who in turn supplied the fledgling with its needs. Soon they were equal partners in trade, But, how are they faring today? The empire is shrunk back to its own immediate neighborhood, and the offspring is flourishing.
The lesson is obvious. The asteroids are excellent sources of raw material, but little may actually be used on Earth. Instead, their availability will make it possible for modern-day pilgrims to set up self-sufficient colonies beyond the confines of Earth. A new equilibrium will be established. As resources diminish on Earth and population pressures increase, the outward flow of humankind will increase, releasing the pressures.
So, although asteroid resources can solve the “limits to growth” dilemma, those who picture the mining of asteroids as a way of bringing large quantities of desirable materials to Earth will have to take another look. They will find themselves in trade, perhaps, for small amounts of strategically critical materials, the kind of which the amount used is small and the need great. For the most part, however, space-generated materials will be used in space.
It is indeed fortunate that filling-stations-in-the-sky have been provided at every busy intersection. The asteroids are there to be used — for life-sustaining elements, for construction materials, for fuel, for commerce, for technology, and surely for, as yet, unforeseen purposes.
Perhaps someday the MIT study will have to be reconsidered because the boundaries of the Universe itself will impose “limits to growth.” Until that time, though, we have nothing to stop us. The asteroids have tidily filled the gap between Earth and man’s next home, Mars. We need the rest of this decade to make our plans, so that the 1990’s will see us taking advantage of these bounteous stepping stones into space.
Ruth A. Lewis is a freelance science writer, who with her husband, John S. Lewis, an expert on space resources, translated Hubert Reeve’s Atoms of Silence from the French. They live with their six children, three goats, and numerous rabbits in the Tucson Mountains.