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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
(grandson of Nathan), were not entirely serious. Still, the significance of
their visions reached well beyond the engineering inventions of the eighteenth
and nineteenth 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
housekeeping inside Earth's first artificial satellite and did quite well.
Hale's artificial satellite, the first known presentation of the idea, called
attention to 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 of Africa and swinging in trees,
thought of lofty havens.

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

Such visions increased toward the end of the nineteenth century and throughout
the twentieth, 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
historical perspective. Living in space is in the end about more than a hotel
room in the sky.

It does not seem strange in hindsight that the idea of space colonies should
have become so prominent in the United States, a nation that has itself been
described as a science fictional experiment. The American attempt at a dynamic,
self-adjusting utopian vision based on a constitutional separation of powers and
the intended, orderly struggle of those powers with one another as a way to deal
with a quarrelsome human nature -- is still in progress. But it is also held
back by the limits of planetary life.

The first major twentieth-century vision of humanity in space was set down in
all seriousness, and with extraordinary thoroughness, by the deaf Russian
schoolteacher Konstantin 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
out with great imagination and technical lucidity the scientific and engineering
principles for leaving Earth, and presented nearly all the reasons, cultural and
economic, for expanding human capabilities beyond Earth. He saw that the entire
sunspace was rich in resources and energy and could be occupied. Every step from
space capsule to moonship was itself a small habitat, a way of taking a bit of
our home 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,
natural and artificial, for interstellar travel and warfare. Edward E. "Doc"
Smith, today called the father of the Star Wars movie saga, used planets
similarly in 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-planet that rules the Galaxy. Don Wilcox's "The Voyage that Lasted Six
Hundred Years" (1940) introduced the idea of using generation starships to reach
the 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 the
manner of a Copernican-Galilean revolution, that their world is a ship.

The uneasy familiarity of generation starship stories springs from our seeing
the Earth as a ship, the stars as other suns. We glimpse how our view of the
universe changed in the last thousand years. Earth is a giant biological ark
circling its sun. As in Heinlein's "Universe," the dispelling of illusion and
misconception lays the groundwork for surprising hopes and the expansion of
human 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 ring
of worlds around the Earth. In the 1950s, Arthur C. Clarke and Wernher von Braun
envisioned space 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
set up bases on the Moon and Mars conservative proposals that even today we have
not fully exploited.

Engineer Dandridge Cole, in his bold and comprehensive visions of the early
1960s, called space settlements "Macro-Life." These might be new habitats
constructed 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 for
such a way of life. Cole envisioned Macro-Life as the ultimate human society,
because of its open-ended adaptability, and delved into its sociology. Asimov
proposed the scattering of spomes as insurance for the survival of humankind.
Both thinkers saw space settlements as a natural step, as important as life's
emergence from 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
mean proportional between Macro-Life and the cell. Macro-Life is a new life form
of gigantic size which has for its cells individual human beings, plants,
animals, and machines .... Society can be said to be pregnant with a mutant
creature which will be at the same time an extraterrestrial colony of human
beings and a new large-scale life form." Cole defined his habitats as a life
form because they would think with their component minds, human and artificial,
move, respond to stimuli, and reproduce. Residing in space's immensities offered
a unique extension of the human community, an innovation as fundamental as the
development of urban civilization in the enlightened Green city-state. Yet
living in the rest of the space around our sun re-created some desirable aspects
of rural life, since habitats would have to be self-contained and ecologically
sophisticated, with the attentiveness to environment that comes from knowing
that problems cannot be passed on to future generations. Perhaps this nostalgia
was crucial in the American imagination, with its rural past so quickly
vanishing.

The arguments presented for such a long-term undertaking are economic, social,
and cultural. Few would deny that the solar system offers an immense industrial
base of 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
too 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 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
rocket needs to achieve a velocity change of 6 km/sec to go from low Earth orbit
to the 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
beyond the particle fluxes of our magnetic Van Allen Belt, a fraction of the way
to the Moon.

I've had a steady conversation with Buzz Aldrin for the last decade about his
personal 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 hydrogen
or methane. 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
to lift into orbit.

We would also need very high temperature techniques to bake the oxygen out of
hard rock. As I put it to Buzz, suppose we found ordinary sidewalk concrete on
the moon. It would be, relative to the local rocks, a bonanza: we would mine it
for water. 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,
to most of the rest of the solar system. This is because the planets have
considerable gravity wells, but the difference in gravitational energy between
the orbit of the Earth and, say, an orbit as far away as Mars is not great. A
typical asteroid, gliding in its ellipse between Mars and Jupiter, moves at
about 9.4 km/sec. Earth moves about the Sun at about 30 km/sec. That difference
of 6 km/sec (the delta-V, in NASA-speak) is what a spacecraft must provide to
move between those two regions.

Velocities are easy to think about, even if they're in the ball park of miles
per minute. But what rockets provide is energy, which is proportional to the
square of velocity. This means the difference in rocket fuel between 24 km/sec
and 30 km/sec is six times larger than the simple difference in velocities would
make you believe. So saving velocity changes is big business.

There are other factors, too. Many asteroids do not orbit the Sun in precisely
the same plane as Earth (the plane of the ecliptic); changing that inclination
costs about a km/sec for each two degrees of alteration. To reach most
interesting asteroids 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
same energy cost.

To someone contemplating a livable satellite in roughly Lunar orbit, then,
getting raw materials from the asteroids is equivalent in energy expenditure to
lifting resources 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
protected against the heat of rapid passage through the atmosphere.

A tugboat spaceship operating in the asteroid belt could load up long chains of
barges and slowly boost them to the needed 10 km/sec, taking perhaps months.
Powered by lightweight photovoltaic cells, the tugboat runs on sunlight, with
perhaps backup from a small nuclear reactor. It would sling mass out the back at
high speed, 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
inner solar system, the tug and crew would cast off. They would return to the
asteroid 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 into
rendezvous with a factory that would break down the metals they carry. The
cheapest method of using these resources would be to manufacture finished goods
in orbit, 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
becomes necessary.

But such shipping assumes that Earth will forever be the final market. It would
cost perhaps $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
the manufactured 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
in orbit 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
asteroid and slinging mined packets of iron-rich mass aft to accelerate the
whole body.

The tugboat becomes the cargo. Studies show that at the optimum exhaust velocity
of the slung pellets, about a quarter of the asteroid's mass would have to be
pitched away at about 50 km/sec to get the asteroid into near-Earth orbit. We
can 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 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
reflected light. Even today, prospectors can know more about the composition of
an asteroid 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
gravity on the inside, once a cylindrical space has been bored into them. A
simple equation demonstrates the relation between spin and radius:

A = R X S[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
units of a revolution per minute. R is the radius of the hollowed-out cylinder
in meters.

For example, consider a cylinder of 100 meters radius and spinning about three
times per minute; then A is near Earth-normal. The importance of this equation
is that one can select high R (for a big colony on the inner surface of the
cylindrical space) 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
containers could take spins up to 6 revolutions per minute without disorienting
effects.

Living constantly in such conditions demands heavy shielding, about two meters
of dirt or rock. This sets a huge requirement for the built-from-scratch O'Neill
colony which was to come in the 1970s. That design had to carry this mass in its
outer rim and support its centrifugal "weight" with steel struts -- a huge
fabrication and construction job, even using raw materials from the Moon. By
comparison, a cored asteroid is much safer.

The asteroid's massive outer layer would easily protect against background
radiation, especially cosmic rays. These "heavy primaries" flooding our solar
system are nuclei of helium, carbon, iron, and higher elements. They smash
through matter, leaving a train of ionized atoms that can kill a living cell.

The Apollo astronauts noticed these energetic events as bright flashes in their
eyes every few minutes, even in total darkness. Venturing outside both the
Earth's atmosphere and, more importantly, its magnetic field which serves as a
shield 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 our
attention to human frailty outside its usual environment.

The hope behind ambitious plans was that opening the solar system to industrial
development would provide two important resources sunlight and metals -- right
from the start. Early visions considered dropping metal-rich rocks directly onto
the Earth, making iron mountains to mine. Imagine having to write the
environmental 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 in
space, using the advantages of zero gravity and vacuum.

Chemicals and nutrients mix much more thoroughly in zero gravity, since they do
not settle out by weight. Making "foamsteels" with tiny bubbles evenly
distributed throughout 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 Industrial Revolution, sparked the optimism of the 1970s.

Generally, the more scientists learned of space as a real environment, the more
hemmed in the writers became. But while the "hard" science fiction authors used
these stubborn facts to fashion clever and insightful stories, the visionary
intuitions behind the central idea remained plausible, and technical scrutiny
supported 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 was
a deliberate commentary on the contrast between our closed-in selves and the
wonders of our works.

Shortly afterward in the 1970s, Gerard O'Neill, a prominent particle physicist
at Princeton University, conducted an advanced engineering feasibility study on
space 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 first
worldlets were built, they would quickly reproduce. The colonies would build
solar collectors and beam microwave power back to Earth, plus exporting to Earth
manufactured goods.

O'Neill asked whether such a space settlement would be viable. There was the
problem 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 capturing
strong sunlight, converting it into microwave energy, then transmitting it by
large antennas to Earth, for transformation into electrical power. Later studies
showed that unmanned satellites in lower orbits would provide power more
cheaply, but these studies led to no projects. As we shall see, the social
dimension has 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
crops for people in the O'Neill-style colonies is another matter. Plants require
considerable power themselves; a square kilometer of prime cropland absorbs a
gigawatt of 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
engineered them; at a tenth of the solar flux, they stagnate. This means that no
artificial environment can afford the costs of growing plants beneath electrical
lights.

However, the raw sunlight of space is harsh. Earth-adapted plants would wither
under the 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
by our ozone layer and atmosphere.

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

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

In the early 1980s O'Neill spoke throughout the United States to drum up support
for his 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
abbreviation for the orbital Lagrangian point which some thought would make the
most stable orbit for a colony) was beginning to fade from the public mind. The
1975-85 spike in oil prices was momentary; fossil fuel would within five years
plunge to the same cost level (in inflation-adjusted dollars) as 1950.

O'Neill's basic assumption, that electrical energy would be hard to generate on
the Earth's surface without high costs both economically and environmentally,
may yet come true, within a few decades. But market forces and improved
technology have taken a lot of steam out of the argument.

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

Historical parallels abound. The immigrants of the Mayflower and the Mormons who
moved to Utah came with about two tons per person of investment goods. Freeman
Dyson in Disturbing the Universe argued that these are better societal models
for space 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
massive that only governments could run it. As Dyson remarked, "[Government] can
afford 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 microwave
power back 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
take 1500 years to pay off the costs by his own labor, which means the colony
would always be a government enterprise, subject to the vagaries of political
will of those who lived far away -- not a prescription for long-term stability.

Thus Dyson favors asteroid colonization, precisely because it could be done for
less and by large families, not large nations. He imagines settlers moving out
from early orbital colonies, though not necessarily of the massive O'Neill type.
He invokes even scavenging, noting that "There are already today several hundred
derelict spacecraft in orbit around the Earth, besides a number on the Moon,
waiting for our asteroid pioneers to collect and refurbish them." The satellite
business would 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
serious speculation and in visionary fiction, but he gave them the plausibility
of the latest styles and engineering methods in space exploration. As Gary
Westfahl's pioneering study, Islands in the Sky (1996) reminded us, the
extensive science fictional history of this idea had been forgotten.

Westfahl writes that "there are four times during the development of the genre
when space stations emerged as important factors--and four times when they faded
from view." These were in the late nineteenth century, the 1930s, the 1950s, and
the 1970s. Since science fiction has often predicted developments in space
travel, this repeated decline of interest in space habitats shows that science
fiction is not immune to the waxing and waning interest in ideas as they emerge
in serious speculation and in popular culture. The reasons for the decline in
project planning may have been human fears, lack of political will, and economic
cold feet, with science fiction following suit, often with critical or
disappointed treatments of the idea -- except in the cases of innovative
authors, who in more disillusioned periods might seem out of touch to readers
and critics.

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

In both fictional worlds and in the possibilities waiting in the real world, to
confront space habitats seriously means a complete change in our outlook toward
the solar system. Many have argued persuasively that the grand project of
uplifting the bulk of humanity to the economic level of the advanced nations
requires use of the solar system's resources, especially since manufacturing
entails a level of pollution that the biosphere cannot abide. (This hard fact
makes impossible 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
changes needed to create a sunspace society are simply too radical for many
people, who see such changes as either frightening or infinitely risky. Perhaps
it is right for social systems to leave innovation to the visionaries and
pioneers; either they will succeed or fail, thus alerting the culture about
which way to grow.

Unfortunately, our skeptical culture's critical resistance may also destroy
valuable developments, 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 --
scientists and engineers as well as writers of science fiction -- that the
planet of our origin may not necessarily be the best place to carry on the
business of civilization; that this inadequacy, born of limits that threatened
to choke off the possibilities made plain by our increasing knowledge and
technology, might hold for all natural planets; and that sooner or later, we
might have no choice but to build the city of man elsewhere.

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