Cylinder Cities

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The most exciting parts of the concept were the detailed plans for comfortable, Earthlike cylinder cities in space. A representation of one of these is presented as Figure 7.1.

Even if these space habitats had all the comforts of home, what would motivate thousands or millions of terrestrials to abandon their home world for greener, albeit artificial pastures? The answer to this question might be found in the social milieu of the 1970s. The disastrous war in Viet Nam was finally winding down; the environmental movement was at its peak. In a masterfully prepared document, a group of scholars dubbed "The Club of Rome" outlined a dire future for humanity in the first quarter of the twenty-first century. Population would be rising at a near-exponential rate, increasing the likelihood of deadly plagues and wars.

As the Third World developed, fossil energy use would increase. This would lead to increased energy costs. Carbon-dioxide emissions from these fossil-fuel plants would result in a "greenhouse effect" which would raise the temperature of Earth's atmosphere. Monster storms would result, which would flood coastal cities and erode shorelines everywhere.

A growing rift would develop between rich and poor nations. Some residents of less-favored regions might actually resort to extreme measures in an attempt to close the gap.

Pessimistically, many environmentalists believed that our wealthy civilization could not withstand the onslaught of this multifaceted "time of troubles.'' O'Neill offered the political leadership of 1970s Planet Earth a chance to head off disaster. They may be damned by future generations for roundly ignoring him!

Construction of O'Neill's cylinder cities would require the launch into space of several million kilograms of tools and construction gear. Most of the billions of kilograms required for structure, cosmic-radiation shielding, and life support would come from cosmic sources.

There were three basic models for these space cities.

1. Each would consist of a pair of counter-rotating cylinders (to avoid precession).

2. Each would face the Sun and be equipped with adjustable window reflectors so that the Earth day/night cycle could be duplicated.

3. People, animals, and plants on the interior walls of the cylinders would experience one-Earth gravity, produced by the cylinder's rotation.

Model 1 was to be 1 kilometer in length and 200 meters in diameter. Its mass would be 500 million kilograms and it could house 10,000 people. Onboard solar power and agriculture would render the habitat essentially independent of the Earth (at least in regards to energy and life support) shortly after its construction. Models 2 and 3 would successively be larger and 10 times more massive, with larger populations and increasingly effective duplication of terrestrial conditions.

Because the Moon was initially thought to be the ideal resource base for the O'Neill habitats, they were to be stationed at one of the Lagrange points (L4 or L5) in the Earth—Moon system. Leading or following the Moon by 60 degrees, L4 or L5 are gravitationally stable. An object placed in these positions stays there with a minimum of course correction.

Although it is theoretically possible to locate an O'Neill space city anywhere in the solar system, there was another reason for a near-Earth location. This was proximity to the solar-powered satellites that would provide the habitat's economic base.

Power for the Earth

As the futurists associated with the "Club of Rome" predicted decades ago, it's crunch time for terrestrial energy reserves. Our appetite for fossil fuel seems unlimited, just at the time when environmental effects are becoming very evident. And, especially in light of the rapid industrialization of populous China and India, these resources are not infinite.

Nuclear fission has its limitations, in part because of nuclear-waste disposal issues, and in part because of fears of terrorism and nuclear-weapon proliferation. Many countries are turning to renewable energy sources—solar and wind—to fill the gap. But these, too, have issues: they are diffuse and intermittent. Nuclear fusion might some day become available, but it always seems to be a few decades in the future.

Advocates of space solar power would employ the space-habitat workforce to address this terrestrial energy crisis. Lunar or asteroid resources would be mined to obtain the construction material for huge power stations located in geosynchronous orbits, always positioned above the same location on Earth's equator.

Try to picture these enormous, albeit very flimsy structures. Thin films of solar panels would be arrayed in kilometer-dimension strips. At the

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FIGURE 7.2 A space solar-powered station. (Image courtesy http://members, gallery.htm)

center of the multi-million-kilogram structure would be a microwave transmitting station (Figure 7.2). About 20% of the sunlight striking the array would be converted to microwaves. Because the microwave transmitter would operate at a wavelength for which the atmosphere is transparent (even in cloudy weather), most of the transmitted energy would reach receiving stations (rectennas) on the ground and be distributed to customers through the energy grid.

Each solar station could transmit a billion watts. Appearing to be stationary 36,000 kilometers above Earth's surface, space solar-powered stations would be easily viewed in the night sky. As more of these are built, a linear constellation of bright, stationary "stars" would seem to encircle the Earth.

Constructing the hundreds or thousands of space solar-powered stations required to replace Earth's fossil-fuel and nuclear-fission power plants would be a monumental task requiring decades to complete, and this is where the economic basis for the plan begins to break down—at least in terms of our current ability to forecast such things. As the National Research Council's review of NASA's plan for developing this capability states in its 2001 report titled, "Laying the Foundation for Space Solar Power: An Assessment of NASA's Space Solar Power Investment Strategy'',

The committee has examined the SERT program's technical investment strategy and finds that while the technical and economic challenges of providing space solar power for commercially competitive terrestrial electric power will require breakthrough advances in a number of technologies ...

Among them is the currently prohibitively high cost of Earth-to-orbit transportation.

Even making the assumption that such transportation is virtually free, the investment required for a mature space-to-Earth power infrastructure will result in an end-user cost that will probably not be competitive with terrestrial sources for quite a while. Alas.

What, then, is the likely future of a human space population? First, the current path for science and exploration will likely continue at a snail's pace for the next quarter of a century at least. Robotic explorers will visit other solar-system worlds with ships of increased complexity and capability, returning reconnaissance that will be useful for the human waves to follow. Human expansion into space will resume after a 30-year hiatus post-Apollo, and this time the missions will include players from multiple nations instead of only the two former competing superpowers. (See Chapter 17 for more information about NASA's current human exploration plans.) As this slow expansion occurs, new technologies will be developed that will enable the cycle of "heavy-lift, high-cost launch'' to be broken. Technologies that take advantage of all that nature has to offer will incrementally supplant the more expensive, resource-hungry approaches we currently use. In the next 50 years we will undergo a philosophical and technological transformation from an approach that states "bring it all with you into space'' to one that asks "what can we use that is already out there?'' Thus will begin the next phase of human expansion and opportunity.

We should not expect to see the capability for a human diaspora within our lifetimes. Barring a technological or economic miracle, the mass migration of humans into space will not happen until, perhaps, our chidren's generation is mid-life. Whether propelled by greed (seeking the riches in the asteroid belt), self-preservation (deflecting the planet killing asteroid before it hits the home world), or political competition (as was Apollo), human economic and political processes will determine the pace and extent of the migration.

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