
GREGORY BENFORDSKYLIFEFIRST THERE was a flying island.Then there was a brick moon.The inventors, Jonathan Swift (Gulliver's Travels, 1726) and Edward Everett Hale(grandson of Nathan), were not entirely serious. Still, the significance oftheir visions reached well beyond the engineering inventions of the eighteenthand nineteenth centuries. In Hale's alternative to living on Earth, "The BrickMoon" (1869) and its sequel, "Life on the Brick Moon" (1870), people set uphousekeeping inside Earth's first artificial satellite and did quite well.Hale's artificial satellite, the first known presentation of the idea, calledattention to a technological innovation implicit in our observations of theEarth-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 of Africa and swinging in trees,thought of lofty havens.For Hale, the artificial satellite meant not only a technological feat but alsothe expansion of human possibilities, a vision of social experimentation beyondthe confines of Earth. Space exploration has ever since carried the hope of asocial and cultural renaissance springing beyond the planetary cradle.Such visions increased toward the end of the nineteenth century and throughoutthe twentieth, as if humanity were trying on one after another. Now the UnitedStates is launching the parts for the greatest skylife hostel yet -- to mixedreviews. Understanding the transparently foolhardy enterprise demands somehistorical perspective. Living in space is in the end about more than a hotelroom in the sky.It does not seem strange in hindsight that the idea of space colonies shouldhave become so prominent in the United States, a nation that has itself beendescribed as a science fictional experiment. The American attempt at a dynamic,self-adjusting utopian vision based on a constitutional separation of powers andthe intended, orderly struggle of those powers with one another as a way to dealwith a quarrelsome human nature -- is still in progress. But it is also heldback by the limits of planetary life.The first major twentieth-century vision of humanity in space was set down inall seriousness, and with extraordinary thoroughness, by the deaf Russianschoolteacher Konstantin Tsiolkovsky (18571935). He did not try to match JulesVerne and H. G. Wells as a writer of stories, but his fiction and nonfiction setout with great imagination and technical lucidity the scientific and engineeringprinciples for leaving Earth, and presented nearly all the reasons, cultural andeconomic, for expanding human capabilities beyond Earth. He saw that the entiresunspace was rich in resources and energy and could be occupied. Every step fromspace capsule to moonship was itself a small habitat, a way of taking a bit ofour home world, its air and food, with us into the cosmos.For many years the concept of space habitats lived mostly in science fictionstories. Olaf Stapledon's Star Maker (1937) described the use of whole worlds,natural and artificial, for interstellar travel and warfare. Edward E. "Doc"Smith, today called the father of the Star Wars movie saga, used planetssimilarly in his Skylark and Lensman series of the 1920s, '30s, and '40s. IsaacAsimov, in his Foundation stories of the 1940s, showed us Trantor, an artificialcity-planet that rules the Galaxy. Don Wilcox's "The Voyage that Lasted SixHundred Years" (1940) introduced the idea of using generation starships to reachthe stars, 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 themanner of a Copernican-Galilean revolution, that their world is a ship.The uneasy familiarity of generation starship stories springs from our seeingthe Earth as a ship, the stars as other suns. We glimpse how our view of theuniverse changed in the last thousand years. Earth is a giant biological arkcircling its sun. As in Heinlein's "Universe," the dispelling of illusion andmisconception lays the groundwork for surprising hopes and the expansion ofhuman horizons.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 ringof worlds around the Earth. In the 1950s, Arthur C. Clarke and Wernher von Braunenvisioned space stations as giant wheels spinning to maintain centrifugal"gravity." They thought that such stations would orbit the Earth to observeweather, refuel interplanetary spaceships, and train astronauts who would laterset up bases on the Moon and Mars conservative proposals that even today we havenot fully exploited.Engineer Dandridge Cole, in his bold and comprehensive visions of the early1960s, called space settlements "Macro-Life." These might be new habitatsconstructed from advanced materials, or nestled inside captured asteroids,hollowed out by mining their metals. Isaac Asimov described the same concept as"multiorganismic life" and coined his own term, "spome," as the space home forsuch a way of life. Cole envisioned Macro-Life as the ultimate human society,because of its open-ended adaptability, and delved into its sociology. Asimovproposed the scattering of spomes as insurance for the survival of humankind.Both thinkers saw space settlements as a natural step, as important as life'semergence from the sea. As amphibians would venture into the thin air of theshore, we would carry our biology with us.Cole wrote:"Taking man as representative of multicelled life, we can say that man is themean proportional between Macro-Life and the cell. Macro-Life is a new life formof gigantic size which has for its cells individual human beings, plants,animals, and machines .... Society can be said to be pregnant with a mutantcreature which will be at the same time an extraterrestrial colony of humanbeings and a new large-scale life form." Cole defined his habitats as a lifeform because they would think with their component minds, human and artificial,move, respond to stimuli, and reproduce. Residing in space's immensities offereda unique extension of the human community, an innovation as fundamental as thedevelopment of urban civilization in the enlightened Green city-state. Yetliving in the rest of the space around our sun re-created some desirable aspectsof rural life, since habitats would have to be self-contained and ecologicallysophisticated, with the attentiveness to environment that comes from knowingthat problems cannot be passed on to future generations. Perhaps this nostalgiawas crucial in the American imagination, with its rural past so quicklyvanishing.The arguments presented for such a long-term undertaking are economic, social,and cultural. Few would deny that the solar system offers an immense industrialbase of energy and mass, enough to deal with all the material problems facinghumanity.We live under a sky ripe with fundamental wealth, but our technological nets aretoo small 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 dramaticstories, engineers and scientists brought to it an increasingly revealingverisimilitude. Fundamentals of physics and economics came into play.Space colonies have some advantages over our natural satellite, the Moon. Arocket needs to achieve a velocity change of 6 km/sec to go from low Earth orbitto the lunar surface. That same rocket can go to Mars with only about 4.5 km/secinvestment, 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 outbeyond the particle fluxes of our magnetic Van Allen Belt, a fraction of the wayto the Moon.I've had a steady conversation with Buzz Aldrin for the last decade about hispersonal dream 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 hydrogenor methane. Since oxygen is a big fraction of chemical fuel mass, usually aboutthree-quarters, the Moon's oxygen would be valuable if it did not cost so muchto lift into orbit.We would also need very high temperature techniques to bake the oxygen out ofhard rock. As I put it to Buzz, suppose we found ordinary sidewalk concrete onthe moon. It would be, relative to the local rocks, a bonanza: we would mine itfor water. That's how dry Luna is.Early on, many noted that in energy expended, once one has lifted a mass fromEarth to the orbit of the Moon, one is halfway to the Asteroid Belt -- indeed,to most of the rest of the solar system. This is because the planets haveconsiderable gravity wells, but the difference in gravitational energy betweenthe orbit of the Earth and, say, an orbit as far away as Mars is not great. Atypical asteroid, gliding in its ellipse between Mars and Jupiter, moves atabout 9.4 km/sec. Earth moves about the Sun at about 30 km/sec. That differenceof 6 km/sec (the delta-V, in NASA-speak) is what a spacecraft must provide tomove between those two regions.Velocities are easy to think about, even if they're in the ball park of milesper minute. But what rockets provide is energy, which is proportional to thesquare of velocity. This means the difference in rocket fuel between 24 km/secand 30 km/sec is six times larger than the simple difference in velocities wouldmake you believe. So saving velocity changes is big business.There are other factors, too. Many asteroids do not orbit the Sun in preciselythe same plane as Earth (the plane of the ecliptic); changing that inclinationcosts about a km/sec for each two degrees of alteration. To reach mostinteresting asteroids requires changes of about four degrees, so the total costin "delta V" is 10 km/sec.Going from Earth's surface to the Moon's orbit requires 11.4 km/ sec, about thesame energy cost.To someone contemplating a livable satellite in roughly Lunar orbit, then,getting raw materials from the asteroids is equivalent in energy expenditure tolifting resources from Earth. Even though the asteroids are, in total flightdistance, a thousand times farther away, they have advantages.Maneuvering in deep space is a matter of slow and steady, not flashy anddramatic. High-thrust takeoffs from Earth are expensive, and payloads have to beprotected against the heat of rapid passage through the atmosphere.A tugboat spaceship operating in the asteroid belt could load up long chains ofbarges and slowly boost them to the needed 10 km/sec, taking perhaps months.Powered by lightweight photovoltaic cells, the tugboat runs on sunlight, withperhaps backup from a small nuclear reactor. It would sling mass out the back athigh speed, using an electromagnetic accelerator as a kind of electrodynamicrocket. The mass would come from the asteroids themselves, which are rich iniron.Once the barges were set on their long, silent, sloping trajectory toward theinner solar system, the tug and crew would cast off. They would return to theasteroid mining 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 intorendezvous with a factory that would break down the metals they carry. Thecheapest method of using these resources would be to manufacture finished goodsin orbit, taking advantage of the ease of handling provided by low or zerogravity. Otherwise, the costly shipping of raw materials down to Earth's surfacebecomes necessary.But such shipping assumes that Earth will forever be the final market. It wouldcost perhaps $10,000 per pound to move metals from the asteroids to near-lunarorbit, a cost far higher than that of supertanker transport on our oceans. Andthe manufactured product would still need to be moved to the market for it onEarth. Clearly a better way would be the construction of colonies and factoriesin orbit themselves.The logical end of this argument is simply to move an asteroid into near-Earthorbit. This demands the setting up of electromagnetic accelerators on a metallicasteroid and slinging mined packets of iron-rich mass aft to accelerate thewhole body.The tugboat becomes the cargo. Studies show that at the optimum exhaust velocityof the slung pellets, about a quarter of the asteroid's mass would have to bepitched away at about 50 km/sec to get the asteroid into near-Earth orbit. Wecan already do this with electromagnetic guns developed in the U.S.In moving the asteroid, one shapes it, hollowing it out for the mass to slingoverboard, and applying spin to produce centrifugal gravity on the innersurface. We know a good deal about what asteroids contain, from studying theirreflected light. Even today, prospectors can know more about the composition ofan asteroid a hundred million miles away than they can find out, withoutdrilling, 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 centrifugalgravity on the inside, once a cylindrical space has been bored into them. Asimple equation demonstrates the relation between spin and radius:A = R X S[sup 2]/1000Here A is the centrifugal acceleration in units of Earth's gravitationalacceleration, so A=1 is Earth-normal. S is the spin of the cylindrical space inunits of a revolution per minute. R is the radius of the hollowed-out cylinderin meters.For example, consider a cylinder of 100 meters radius and spinning about threetimes per minute; then A is near Earth-normal. The importance of this equationis that one can select high R (for a big colony on the inner surface of thecylindrical space) and spin it slowly, or high spin (large S) and a smallcolony, low R. NASA experiments of the 1960s showed that people in smallcontainers could take spins up to 6 revolutions per minute without disorientingeffects.Living constantly in such conditions demands heavy shielding, about two metersof dirt or rock. This sets a huge requirement for the built-from-scratch O'Neillcolony which was to come in the 1970s. That design had to carry this mass in itsouter rim and support its centrifugal "weight" with steel struts -- a hugefabrication and construction job, even using raw materials from the Moon. Bycomparison, a cored asteroid is much safer.The asteroid's massive outer layer would easily protect against backgroundradiation, especially cosmic rays. These "heavy primaries" flooding our solarsystem are nuclei of helium, carbon, iron, and higher elements. They smashthrough matter, leaving a train of ionized atoms that can kill a living cell.The Apollo astronauts noticed these energetic events as bright flashes in theireyes every few minutes, even in total darkness. Venturing outside both theEarth's atmosphere and, more importantly, its magnetic field which serves as ashield against cosmic rays, the astronauts incurred some nerve and cell damage,though it was insignificant. James Gunn, in his novel Station in Space (1958),presented this as a disquieting detail, a prediction actually, calling ourattention to human frailty outside its usual environment.The hope behind ambitious plans was that opening the solar system to industrialdevelopment would provide two important resources sunlight and metals -- rightfrom the start. Early visions considered dropping metal-rich rocks directly ontothe Earth, making iron mountains to mine. Imagine having to write theenvironmental impact report for that today! -- and having to calculate risks,get insurance, and so on.The second development stage would come atop the first: direct manufacture inspace, using the advantages of zero gravity and vacuum.Chemicals and nutrients mix much more thoroughly in zero gravity, since they donot settle out by weight. Making "foamsteels" with tiny bubbles evenlydistributed throughout seems possible, greatly reducing mass while losing littlestrength. Growing enormous carbon filaments for superstrong fibers seemsstraightforward. Similar methods, as spelled out in the late G. Harry Stine'sThe Third Industrial Revolution, sparked the optimism of the 1970s.Generally, the more scientists learned of space as a real environment, the morehemmed in the writers became. But while the "hard" science fiction authors usedthese stubborn facts to fashion clever and insightful stories, the visionaryintuitions behind the central idea remained plausible, and technical scrutinysupported the high dreams.Stanley Kubrick's 2001 showed us a classic Bonestell-style space station,complete with interior views. The banality of the character's conversations wasa deliberate commentary on the contrast between our closed-in selves and thewonders of our works.Shortly afterward in the 1970s, Gerard O'Neill, a prominent particle physicistat Princeton University, conducted an advanced engineering feasibility study onspace settlements (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 firstworldlets were built, they would quickly reproduce. The colonies would buildsolar collectors and beam microwave power back to Earth, plus exporting to Earthmanufactured goods.O'Neill asked whether such a space settlement would be viable. There was theproblem of 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 capturingstrong sunlight, converting it into microwave energy, then transmitting it bylarge antennas to Earth, for transformation into electrical power. Later studiesshowed that unmanned satellites in lower orbits would provide power morecheaply, but these studies led to no projects. As we shall see, the socialdimension has loomed large in the plans of even the most detailed technicalscenarios.Direct sunlight is fine and good as a source of electrical power, but growingcrops for people in the O'Neill-style colonies is another matter. Plants requireconsiderable power themselves; a square kilometer of prime cropland absorbs agigawatt of sunlight at high noon--the power output of the largest electricalpowerhouses, capable of supporting a city of a million souls.Sure, under less illumination plants still grow, but evolution has finelyengineered them; at a tenth of the solar flux, they stagnate. This means that noartificial environment can afford the costs of growing plants beneath electricallights.However, the raw sunlight of space is harsh. Earth-adapted plants would witherunder the sting of its ultraviolet rays. There is more solar power available inspace, but it is at the high end of the spectrum, which on Earth is filtered outby our ozone layer and atmosphere.Certainly ultraviolet absorbing canopies can be deployed, but the weatherbetween the worlds has harsher stuff in store. Thin greenhouse shells on O'Neillcolonies would not protect against solar flares of such ferocity as occur everyfew months. Defending people and plants against these fluxes of high-energyparticles demands at least five-inch-thick glass, a massive measure.Indeed, O'Neill colonies have much of their design dedicated to protectingpeople against solar storms by providing interior shelters. But people can bemoved to shelter for a few hours; crops cannot.In the early 1980s O'Neill spoke throughout the United States to drum up supportfor his ideas and for the National Space Society, which he founded. Already theO'Neill-colony idea (a term he modestly never used, preferring "L-5," theabbreviation for the orbital Lagrangian point which some thought would make themost stable orbit for a colony) was beginning to fade from the public mind. The1975-85 spike in oil prices was momentary; fossil fuel would within five yearsplunge to the same cost level (in inflation-adjusted dollars) as 1950.O'Neill's basic assumption, that electrical energy would be hard to generate onthe Earth's surface without high costs both economically and environmentally,may yet come true, within a few decades. But market forces and improvedtechnology have taken a lot of steam out of the argument.Still, O'Neill's salesmanship put the entire agenda forward as no other culturalforce had. Economics was central to the movement, blended with social ideas. Thecover of the paperback edition of his The High Frontier proclaimed: "They'recoming! Space colonies -- hope for your future." And the back cover sold spacecolonies as future suburban paradises, with Earth as the city to flee.Historical parallels abound. The immigrants of the Mayflower and the Mormons whomoved to Utah came with about two tons per person of investment goods. FreemanDyson in Disturbing the Universe argued that these are better societal modelsfor space colonization than the O'Neill notion of totally planned homes.O'Neill's detailed "Island One" project would cost about $96 billion in 1979dollars, and perhaps twice that today. Clearly, such a project would be somassive that only governments could run it. As Dyson remarked, "[Government] canafford to waste money but it cannot afford to be responsible for a disaster."O'Neill argued that his colony could build solar collectors and beam microwavepower back to Earth to pay its bills. At the energy prices of the late 1970s, hesaid, the $96 billion could be repaid within 9.4 years. But a colonist wouldtake 1500 years to pay off the costs by his own labor, which means the colonywould always be a government enterprise, subject to the vagaries of politicalwill of those who lived far away -- not a prescription for long-term stability.Thus Dyson favors asteroid colonization, precisely because it could be done forless and by large families, not large nations. He imagines settlers moving outfrom early orbital colonies, though not necessarily of the massive O'Neill type.He invokes even scavenging, noting that "There are already today several hundredderelict spacecraft in orbit around the Earth, besides a number on the Moon,waiting for our asteroid pioneers to collect and refurbish them." The satellitebusiness would dearly love to see such debris erased from the equatorial orbitalbelt, since collisions with them loom now as a significant threat to orbitalsafety.O'Neill revisited ideas that had been around for most of a century, both inserious speculation and in visionary fiction, but he gave them the plausibilityof the latest styles and engineering methods in space exploration. As GaryWestfahl's pioneering study, Islands in the Sky (1996) reminded us, theextensive science fictional history of this idea had been forgotten.Westfahl writes that "there are four times during the development of the genrewhen space stations emerged as important factors--and four times when they fadedfrom view." These were in the late nineteenth century, the 1930s, the 1950s, andthe 1970s. Since science fiction has often predicted developments in spacetravel, this repeated decline of interest in space habitats shows that sciencefiction is not immune to the waxing and waning interest in ideas as they emergein serious speculation and in popular culture. The reasons for the decline inproject planning may have been human fears, lack of political will, and economiccold feet, with science fiction following suit, often with critical ordisappointed treatments of the idea -- except in the cases of innovativeauthors, who in more disillusioned periods might seem out of touch to readersand critics.Our construction of the U.S. Space Station Freedom in the late 1990s portends afresh burgeoning of an idea that in science fiction has become a staple used forboth utopian and dystopian visions.In both fictional worlds and in the possibilities waiting in the real world, toconfront space habitats seriously means a complete change in our outlook towardthe solar system. Many have argued persuasively that the grand project ofuplifting the bulk of humanity to the economic level of the advanced nationsrequires use of the solar system's resources, especially since manufacturingentails a level of pollution that the biosphere cannot abide. (This hard factmakes impossible the more cozy stories of expansive industrial futures.)To use the resources of our sunspace demands treating it as a genuine "newfrontier," not just as a place to go and come back from. But the fundamentalchanges needed to create a sunspace society are simply too radical for manypeople, who see such changes as either frightening or infinitely risky. Perhapsit is right for social systems to leave innovation to the visionaries andpioneers; either they will succeed or fail, thus alerting the culture aboutwhich way to grow.Unfortunately, our skeptical culture's critical resistance may also destroyvaluable developments, leaving them to emerge at a later time or to die.The style of discussion and pictorial presentation of skylife changed by the1970s, but the substance was the same. Once again it dawned on researchers --scientists and engineers as well as writers of science fiction -- that theplanet of our origin may not necessarily be the best place to carry on thebusiness of civilization; that this inadequacy, born of limits that threatenedto choke off the possibilities made plain by our increasing knowledge andtechnology, might hold for all natural planets; and that sooner or later, wemight have no choice but to build the city of man elsewhere.Next time, I'll consider how it all might turn out.

