GREGORY BENFORD

SKYLIFE

FIRST THERE was a flying island.

Then there was a brick moon.

The inventors, Jonathan Swift (Gulliver’s Travels, 1726) and Edward Everett Hale (grandsonof Nathan), were not entirely serious. Still, the significance of theirvisions reached well beyond the engineering inventions of the eighteenth andnineteenth centuries. In Hale’s alternative to living on Earth, “The Brick Moon” (1869) and its sequel, “Life on the Brick Moon” (1870), people set up housekeepinginside Earth’s first artificial satellite and did quite well.

Hale’s artificial satellite, the first known presentation of the idea, called attentionto a technological innovation implicit in our observations of the Earth-Moon system and that of the other planets that possess moons.

What nature could do, we might also do.

We, the third type of chimpanzee, fresh out ofAfricaand swinging in trees, thoughtof lofty havens.

For Hale, the artificial satellite meant not only a technological feat but also theexpansion of human possibilities, a vision of social experimentation beyond theconfines of Earth. Space exploration has ever since carried the hope of a socialand cultural renaissance springing beyond the planetary cradle.

Such visions increased toward the end of the nineteenth century and throughout thetwentieth, as if humanity were trying on one after another. Now the United States is launching the parts for the greatest skylife hostel yet — to mixed reviews. Understanding the transparently foolhardy enterprise demands some historicalperspective. Living in space is in the end about more than a hotel roomin the sky.

It does not seem strange in hindsight that the idea of space colonies should havebecome so prominent in theUnited States, a nation that has itself been describedas a science fictional experiment. The American attempt at a dynamic, self-adjustingutopian vision based on a constitutional separation of powers and theintended, orderly struggle of those powers with one another as a way to deal witha quarrelsome human nature — is still in progress. But it is also held backby the limits of planetary life.

The first major twentieth-century vision of humanity in space was set down in allseriousness, and with extraordinary thoroughness, by the deaf Russian schoolteacherKonstantin Tsiolkovsky (18571935). He did not try to match Jules Verne and H. G. Wells as a writer of stories, but his fiction and nonfiction set outwith great imagination and technical lucidity the scientific and engineering principlesfor leaving Earth, and presented nearly all the reasons, cultural and economic, for expanding human capabilities beyond Earth. He saw that the entire Page 1

sunspacewas rich in resources and energy and could be occupied. Every step from spacecapsule to moonship was itself a small habitat, a way of taking a bit of ourhome world, its air and food, with us into the cosmos.

For many years the concept of space habitats lived mostly in science fiction stories. Olaf Stapledon’s Star Maker (1937) described the use of whole worlds, naturaland artificial, for interstellar travel and warfare. Edward E. “Doc”

Smith, today called the father of the Star Wars movie saga, used planets similarlyin his Skylark and Lensman series of the 1920s, ‘30s, and ‘40s. Isaac Asimov, in his Foundation stories of the 1940s, showed us Trantor, an artificial city-planetthat rules the Galaxy. Don Wilcox’s “The Voyage that Lasted Six Hundred Years” (1940) introduced the idea of using generation starships to reach thestars, in the form that was to be often imitated, one year before Robert A.

Heinlein’s more famous story “Universe” and its forgotten sequel “Common Sense”

—gritty realistic dramas of travelers aboard a space ark who learn, in the mannerof a Copernican-Galilean revolution, that their world is a ship.

The uneasy familiarity of generation starship stories springs from our seeing theEarth as a ship, the stars as other suns. We glimpse how our view of the universechanged in the last thousand years. Earth is a giant biological ark circlingits sun. As in Heinlein’s “Universe,” the dispelling of illusion and misconceptionlays the groundwork for surprising hopes and the expansion of humanhorizons.

Behind the science fiction stories stood visionary nonfiction such as J. D.

Bernal’s 1929 The World, the Flesh, and the Devil, which pictures an urban ring ofworlds around the Earth. In the 1950s, Arthur C. Clarke and Wernher von Braun envisionedspace stations as giant wheels spinning to maintain centrifugal

“gravity.” They thought that such stations would orbit the Earth to observe weather, refuel interplanetary spaceships, and train astronauts who would later setup bases on the Moon and Mars conservative proposals that even today we have notfully exploited.

Engineer Dandridge Cole, in his bold and comprehensive visions of the early 1960s, called space settlements “Macro-Life.” These might be new habitats constructedfrom advanced materials, or nestled inside captured asteroids, hollowedout by mining their metals. Isaac Asimov described the same concept as

“multiorganismiclife” and coined his own term, “spome,” as the space home for sucha way of life. Cole envisioned Macro-Life as the ultimate human society, becauseof its open-ended adaptability, and delved into its sociology. Asimov proposedthe scattering of spomes as insurance for the survival of humankind.

Both thinkers saw space settlements as a natural step, as important as life’s emergencefrom the sea. As amphibians would venture into the thin air of the shore, we would carry our biology with us.

Cole wrote:

“Taking man as representative of multicelled life, we can say that man is the meanproportional between Macro-Life and the cell. Macro-Life is a new life form ofgigantic size which has for its cells individual human beings, plants, animals, and machines …. Society can be said to be pregnant with a mutant Page 2

creaturewhich will be at the same time an extraterrestrial colony of human beingsand a new large-scale life form.” Cole defined his habitats as a life formbecause they would think with their component minds, human and artificial, move, respond to stimuli, and reproduce. Residing in space’s immensities offered aunique extension of the human community, an innovation as fundamental as the developmentof urban civilization in the enlightened Green city-state. Yet livingin the rest of the space around our sun re-created some desirable aspects ofrural life, since habitats would have to be self-contained and ecologically sophisticated, with the attentiveness to environment that comes from knowing thatproblems cannot be passed on to future generations. Perhaps this nostalgia wascrucial in the American imagination, with its rural past so quickly vanishing.

The arguments presented for such a long-term undertaking are economic, social, andcultural. Few would deny that the solar system offers an immense industrial baseof energy and mass, enough to deal with all the material problems facing humanity.

We live under a sky ripe with fundamental wealth, but our technological nets are toosmall to catch what we need from the cornucopia above our heads.

Yet hard science had to come before high dreams.

While science fiction writers used the idea of space habitats for dramatic stories, engineers and scientists brought to it an increasingly revealing verisimilitude. Fundamentals of physics and economics came into play.

Space colonies have some advantages over our natural satellite, the Moon. A rocketneeds to achieve a velocity change of 6 km/sec to go from low Earth orbit tothe lunar surface. That same rocket can go to Mars with only about 4.5 km/sec investment, if it uses an aero-shell to brake in the upper Martian atmosphere.

Also, any deep space operations could be much better managed from an orbit out beyondthe particle fluxes of our magnetic Van Allen Belt, a fraction of the way tothe Moon.

I’ve had a steady conversation with Buzz Aldrin for the last decade about his personaldream of returning to the moon. It’s about hard realities.

Lunar resources are principally rocks that have about half their mass in oxygen.

But the Moon has nothing we can unite with that oxygen to burn, such as hydrogen ormethane. Since oxygen is a big fraction of chemical fuel mass, usually about three-quarters, the Moon’s oxygen would be valuable if it did not cost so much tolift into orbit.

We would also need very high temperature techniques to bake the oxygen out of hardrock. As I put it to Buzz, suppose we found ordinary sidewalk concrete on themoon. It would be, relative to the local rocks, a bonanza: we would mine it forwater. That’s how dry Luna is.

Early on, many noted that in energy expended, once one has lifted a mass from Earth to the orbit of the Moon, one is halfway to the Asteroid Belt — indeed, Page 3

tomost of the rest of the solar system. This is because the planets have considerablegravity wells, but the difference in gravitational energy between theorbit of the Earth and, say, an orbit as far away as Mars is not great. A typicalasteroid, gliding in its ellipse between Mars and Jupiter, moves at about9.4 km/sec. Earth moves about the Sun at about 30 km/sec. That difference of6 km/sec (the delta-V, in NASA-speak) is what a spacecraft must provide to movebetween those two regions.

Velocities are easy to think about, even if they’re in the ball park of miles perminute. But what rockets provide is energy, which is proportional to the squareof velocity. This means the difference in rocket fuel between 24 km/sec and30 km/sec is six times larger than the simple difference in velocities would makeyou believe. So saving velocity changes is big business.

There are other factors, too. Many asteroids do not orbit the Sun in precisely thesame plane as Earth (the plane of the ecliptic); changing that inclination costsabout a km/sec for each two degrees of alteration. To reach most interestingasteroids requires changes of about four degrees, so the total cost in”delta V” is 10 km/sec.

Going from Earth’s surface to the Moon’s orbit requires 11.4 km/ sec, about the sameenergy cost.

To someone contemplating a livable satellite in roughlyLunar orbit, then, gettingraw materials from the asteroids is equivalent in energy expenditure to liftingresources from Earth. Even though the asteroids are, in total flight distance, a thousand times farther away, they have advantages.

Maneuvering in deep space is a matter of slow and steady, not flashy and dramatic. High-thrust takeoffs from Earth are expensive, and payloads have to be protectedagainst the heat of rapid passage through the atmosphere.

A tugboat spaceship operating in the asteroid belt could load up long chains of bargesand slowly boost them to the needed 10 km/sec, taking perhaps months.

Powered by lightweight photovoltaic cells, the tugboat runs on sunlight, with perhapsbackup from a small nuclear reactor. It would sling mass out the back at highspeed, using an electromagnetic accelerator as a kind of electrodynamic rocket. The mass would come from the asteroids themselves, which are rich in iron.

Once the barges were set on their long, silent, sloping trajectory toward the innersolar system, the tug and crew would cast off. They would return to the asteroidmining community, to start hooking up to the next line of barges.

At the end of their eight-month flight to Earth, the barges would be pulled into rendezvouswith a factory that would break down the metals they carry. The cheapestmethod of using these resources would be to manufacture finished goods inorbit, taking advantage of the ease of handling provided by low or zero gravity. Otherwise, the costly shipping of raw materials down to Earth’s surface becomesnecessary.

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But such shipping assumes that Earth will forever be the final market. It would costperhaps $10,000 per pound to move metals from the asteroids to near-lunar orbit, a cost far higher than that of supertanker transport on our oceans. And themanufactured product would still need to be moved to the market for it on Earth.Clearly a better way would be the construction of colonies and factories inorbit themselves.

The logical end of this argument is simply to move an asteroid into near-Earth orbit. This demands the setting up of electromagnetic accelerators on a metallic asteroidand slinging mined packets of iron-rich mass aft to accelerate the wholebody.

The tugboat becomes the cargo. Studies show that at the optimum exhaust velocity ofthe slung pellets, about a quarter of the asteroid’s mass would have to be pitchedaway at about 50 km/sec to get the asteroid into near-Earth orbit. We canalready do this with electromagnetic guns developed in theU.S.

In moving the asteroid, one shapes it, hollowing it out for the mass to sling overboard, and applying spin to produce centrifugal gravity on the inner surface. We know a good deal about what asteroids contain, from studying their reflectedlight. Even today, prospectors can know more about the composition of anasteroid a hundred million miles away than they can find out, without drilling, about what lies a mile below their feet.

Asteroids should be good sources of the metals hardest to find in Earth’s crust.

They should also have the structural integrity to sustain a moderate centrifugal gravityon the inside, once a cylindrical space has been bored into them. A simpleequation demonstrates the relation between spin and radius: A = R XS[ sup 2]/1000

Here A is the centrifugal acceleration in units of Earth’s gravitational acceleration, so A=1 is Earth-normal. S is the spin of the cylindrical space in unitsof a revolution per minute. R is the radius of the hollowedout cylinder inmeters.

For example, consider a cylinder of 100 meters radius and spinning about three timesper minute; then A is near Earth-normal. The importance of this equation isthat one can select high R (for a big colony on the inner surface of the cylindricalspace) and spin it slowly, or high spin (large S) and a small colony, low R. NASA experiments of the 1960s showed that people in small containerscould take spins up to 6 revolutions per minute without disorienting effects.

Living constantly in such conditions demands heavy shielding, about two meters ofdirt or rock. This sets a huge requirement for the built-from-scratch O’Neill colonywhich was to come in the 1970s. That design had to carry this mass in its outerrim and support its centrifugal “weight” with steel struts — a huge fabricationand construction job, even using raw materials from the Moon. By comparison, a cored asteroid is much safer.

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The asteroid’s massive outer layer would easily protect against background radiation, especially cosmic rays. These “heavy primaries” flooding our solar systemare nuclei of helium, carbon, iron, and higher elements. They smash throughmatter, leaving a train of ionized atoms that can kill a living cell.

The Apollo astronauts noticed these energetic events as bright flashes in their eyesevery few minutes, even in total darkness. Venturing outside both the Earth’s atmosphere and, more importantly, its magnetic field which serves as a shieldagainst cosmic rays, the astronauts incurred some nerve and cell damage, thoughit was insignificant. James Gunn, in his novel Station in Space (1958), presentedthis as a disquieting detail, a prediction actually, calling our attentionto human frailty outside its usual environment.

The hope behind ambitious plans was that opening the solar system to industrial developmentwould provide two important resources sunlight and metals — right fromthe start. Early visions considered dropping metal-rich rocks directly onto theEarth, making iron mountains to mine. Imagine having to write the environmentalimpact report for that today! —and having to calculate risks, getinsurance, and so on.

The second development stage would come atop the first: direct manufacture in space, using the advantages of zero gravity and vacuum.

Chemicals and nutrients mix much more thoroughly in zero gravity, since they do notsettle out by weight. Making “foamsteels” with tiny bubbles evenly distributedthroughout seems possible, greatly reducing mass while losing little strength. Growing enormous carbon filaments for superstrong fibers seems straightforward. Similar methods, as spelled out in the late G. Harry Stine’s The Third IndustrialRevolution, sparked the optimism of the 1970s.

Generally, the more scientists learned of space as a real environment, the more hemmedin the writers became. But while the “hard” science fiction authors used thesestubborn facts to fashion clever and insightful stories, the visionary intuitionsbehind the central idea remained plausible, and technical scrutiny supportedthe high dreams.

Stanley Kubrick’s 2001 showed us a classic Bonestell-style space station, completewith interior views. The banality of the character’s conversations was adeliberate commentary on the contrast between our closed-in selves and the wondersof our works.

Shortly afterward in the 1970s, Gerard O’Neill, a prominent particle physicist atPrincetonUniversity, conducted an advanced engineering feasibility study on spacesettlements (for undergraduates!), and reexamined these same ideas.

O’Neill’s group optimistically concluded that the technology already existed.

The Moon could be mined as a source of raw materials, and once the first worldletswere built, they would quickly reproduce. The colonies would build solarcollectors and beam microwave power back to Earth, plus exporting to Earth manufacturedgoods.

O’Neill asked whether such a space settlement would be viable. There was the Page 6

problemof the two meters of necessary background radiation shielding.

Plus, it had to run its ecology on solar energy. How?

A crucial difficulty governs using raw sunlight. Most schemes envision capturing strongsunlight, converting it into microwave energy, then transmitting it by largeantennas to Earth, for transformation into electrical power. Later studies showedthat unmanned satellites in lower orbits would provide power more cheaply, but these studies led to no projects. As we shall see, the social dimensionhas loomed large in the plans of even the most detailed technical scenarios.

Direct sunlight is fine and good as a source of electrical power, but growing cropsfor people in the O’Neill-style colonies is another matter. Plants require considerablepower themselves; a square kilometer of prime cropland absorbs a gigawattof sunlight at high noon—the power output of the largest electrical powerhouses, capable of supporting a city of a million souls.

Sure, under less illumination plants still grow, but evolution has finely engineeredthem; at a tenth of the solar flux, they stagnate. This means that no artificialenvironment can afford the costs of growing plants beneath electrical lights.

However, the raw sunlight of space is harsh. Earth-adapted plants would wither underthe sting of its ultraviolet rays. There is more solar power available in space, but it is at the high end of the spectrum, which on Earth is filtered out byour ozone layer and atmosphere.

Certainly ultraviolet absorbing canopies can be deployed, but the weather betweenthe worlds has harsher stuff in store. Thin greenhouse shells on O’Neill colonieswould not protect against solar flares of such ferocity as occur every fewmonths. Defending people and plants against these fluxes of high-energy particlesdemands at least five-inch-thick glass, a massive measure.

Indeed, O’Neill colonies have much of their design dedicated to protecting peopleagainst solar storms by providing interior shelters. But people can be movedto shelter for a few hours; crops cannot.

In the early 1980s O’Neill spoke throughout theUnited Statesto drum up support forhis ideas and for the National Space Society, which he founded. Already the O’Neill-colony idea (a term he modestly never used, preferring “L-5,” the abbreviationfor the orbital Lagrangian point which some thought would make the moststable orbit for a colony) was beginning to fade from the public mind. The 1975-85spike in oil prices was momentary; fossil fuel would within five years plungeto the same cost level (in inflation-adjusted dollars) as 1950.

O’Neill’s basicassumption, that electrical energy would be hard to generate on theEarth’s surface without high costs both economically and environmentally, mayyet come true, within a few decades. But market forces and improved technologyhave taken a lot of steam out of the argument.

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Still, O’Neill’s salesmanship put the entire agenda forward as no other cultural forcehad. Economics was central to the movement, blended with social ideas. The coverof the paperback edition of his The High Frontier proclaimed: “They’re coming! Space colonies — hope for your future.” And the back cover sold space coloniesas future suburban paradises, with Earth as the city to flee.

Historical parallels abound. The immigrants of the Mayflower and the Mormons who movedtoUtahcame with about two tons per person of investment goods. Freeman Dyson in Disturbing the Universe argued that these are better societal models forspace colonization than the O’Neill notion of totally planned homes.

O’Neill’s detailed “Island One” project would cost about $96 billion in 1979

dollars, and perhaps twice that today. Clearly, such a project would be so massivethat only governments could run it. As Dyson remarked, “[Government] can affordto waste money but it cannot afford to be responsible for a disaster.”

O’Neill argued that his colony could build solar collectors and beam microwave powerback to Earth to pay its bills. At the energy prices of the late 1970s, he said, the $96 billion could be repaid within 9.4 years. But a colonist would take1500 years to pay off the costs by his own labor, which means the colony wouldalways be a government enterprise, subject to the vagaries of political willof those who lived far away — not a prescription for long-term stability.

Thus Dyson favors asteroid colonization, precisely because it could be done for lessand by large families, not large nations. He imagines settlers moving out fromearly orbital colonies, though not necessarily of the massive O’Neill type.

He invokes even scavenging, noting that “There are already today several hundred derelictspacecraft in orbit around the Earth, besides a number on the Moon, waitingfor our asteroid pioneers to collect and refurbish them.” The satellite businesswould dearly love to see such debris erased from the equatorial orbital belt, since collisions with them loom now as a significant threat to orbital safety.

O’Neill revisited ideas that had been around for most of a century, both in seriousspeculation and in visionary fiction, but he gave them the plausibility ofthe latest styles and engineering methods in space exploration. AsGary Westfahl’s pioneering study,Islandsin the Sky (1996) reminded us, the extensivescience fictional history of this idea had been forgotten.

Westfahl writes that “there are four times during the development of the genre whenspace stations emerged as important factors—and four times when they faded fromview.” These were in the late nineteenth century, the 1930s, the 1950s, and the1970s. Since science fiction has often predicted developments in space travel, this repeated decline of interest in space habitats shows that science fictionis not immune to the waxing and waning interest in ideas as they emerge inserious speculation and in popular culture. The reasons for the decline in projectplanning may have been human fears, lack of political will, and economic coldfeet, with science fiction following suit, often with critical or disappointedtreatments of the idea — except in the cases of innovative authors, who in more disillusioned periods might seem out of touch to readers andcritics.

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Our construction of the U.S. Space Station Freedom in the late 1990s portends a freshburgeoning of an idea that in science fiction has become a staple used for bothutopian and dystopian visions.

In both fictional worlds and in the possibilities waiting in the real world, to confrontspace habitats seriously means a complete change in our outlook toward thesolar system. Many have argued persuasively that the grand project of upliftingthe bulk of humanity to the economic level of the advanced nations requiresuse of the solar system’s resources, especially since manufacturing entailsa level of pollution that the biosphere cannot abide. (This hard fact makesimpossible the more cozy stories of expansive industrial futures.) To use the resources of our sunspace demands treating it as a genuine “new frontier,” not just as a place to go and come back from. But the fundamental changesneeded to create a sunspace society are simply too radical for many people, who see such changes as either frightening or infinitely risky. Perhaps itis right for social systems to leave innovation to the visionaries and pioneers; either they will succeed or fail, thus alerting the culture about whichway to grow.

Unfortunately, our skeptical culture’s critical resistance may also destroy valuabledevelopments, leaving them to emerge at a later time or to die.

The style of discussion and pictorial presentation of skylife changed by the 1970s, but the substance was the same. Once again it dawned on researchers —

scientistsand engineers as well as writers of science fiction — that the planetof our origin may not necessarily be the best place to carry on the businessof civilization; that this inadequacy, born of limits that threatened tochoke off the possibilities made plain by our increasing knowledge and technology, might hold for all natural planets; and that sooner or later, we mighthave no choice but to build the city of man elsewhere.

Next time, I’ll consider how it all might turn out.

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