Beyond: Our Future in Space (20 page)

Part of the reason the United States never signed the Moon Treaty is that Article XI says that the Moon and its resources are not subject to any sort of sovereign or private property claims.
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The treaty requires resource extraction and allocation to be governed by a vaguely defined “international regime.”

The issue has become relevant recently with the NASA plan to lasso an asteroid and put it into a lunar orbit so that it can be mined. Under the Outer Space Treaty, it’s unlikely another country could put a claim on the US rock, but what if it breaks up or becomes a hazard? The liability issue has never been tested and the treaty is out of date and unequipped to deal with future space scenarios.
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US space policy has been tugged in two opposing directions over the past half century.

One train of thought extends into space the concept of Manifest Destiny and the ethos that led to the exploration of the American West. In fact, a frontier metaphor has framed much discourse about space policy. An advocacy group called High Frontier is explicit in its comparison; it recommends that the US Government apply nineteenth-century homesteading law and the Jamestown settlement model to colonies on the Moon. The group’s director said of the Outer Space Treaty: “The United Nations is just playing King George at the time of the American Revolution, thinking they can tell everyone else what to do.”
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Following this analogy, colonists on the Moon or Mars may start out under UN jurisdiction, but they would eventually rebel, just as the colonists rebelled against being governed by English Privy Law.

Even though America no longer dominates space exploration, former NASA administrator Michael Griffin said that when more people live off-Earth than live on it, “. . . we want their culture to be Western, because Western Civilization is the best we’ve seen so far in human history.” This is a jaw-dropping neocolonial statement to come from the mouth of such a high-ranking government official. He may have been unaware of a prior rebuttal by Mahatma Gandhi; when asked what he thought of Western Civilization, he’s reported to have said, “I think it would be a good idea.” One year earlier, X Prize Foundation Chairman Peter Diamandis said, “The Solar System is like a giant grocery store. It has everything we could possibly want. . . . The Solar System’s seemingly limitless energy and mineral resources will solve Earth’s resource shortages.”
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This is acquisitiveness dressed as utilitarianism—if it’s there and we want it, we’ll take it.

The second theory of settling space uses a wilderness metaphor, where we apply values of environmental protection and preservation to space exploration. Space entrepreneurs and venture capitalists argue that turning space into a national park–type zone will squelch commercial space ventures before they get going. Until commerce spreads into space, the legal issues are hypothetical and unresolved, but the first commercial spaceflights will intensify the debates. Opportunist Dennis Hope was a ventriloquist before he owned the Moon, and he says his dummy taught him a valuable lesson: You can say anything you want as long as you’re smiling.

Stairway to Heaven

Earth orbit is an excellent staging point for further exploration. The International Space Station may be unloved, but the idea isn’t ill-conceived. Zero gravity facilitates the manipulation and assembly of large pieces of hardware such as rockets and habitats. The major energy cost is in struggling nearly 400 kilometers from terra firma to low Earth orbit. Going from Earth orbit to the surface of the Moon is an additional 75 percent. Going all the way to the surface of Mars only doubles the energy cost, but it’s at least 140 times farther away than the Moon.

Elon Musk and other space entrepreneurs are tweaking and optimizing the rocket equation. What if it could be rendered obsolete?

Space elevators promise to do just that. Rockets are complicated, dangerous, and inefficient. Whether the fuel is solid or liquid, a rocket launch is a barely controlled explosion. The failure of a weld or a valve or a switch can spell disaster. At the major Russian launch sites, they don’t even do countdowns. They stand at what they hope is a safe distance and wait for the outcome. Rocketry is based on rearranging electrons in atoms and molecules, which is a chemical energy source only three times more efficient than the venerable internal combustion engine and five times more efficient than burning coal in a fireplace. It costs at least $10 million to put anything into Earth orbit. Gravity smiles mockingly at our efforts to hurl stuff into space.

A brilliant solution to this problem would be a lightweight, super-strong cable stretching 100,000 kilometers from the Earth’s surface out to a counterweight in space. Solar-powered elevators then would whisk people and freight into space for a fraction of the cost of rockets today.

The origin of this idea is nothing short of biblical. Writing in 1450 BC, Moses referred to an earlier civilization that had tried to build a tower to heaven out of bricks and mortar. Located in Babylon, it was called the Tower of Babel. In the Book of Genesis, there’s the story of Jacob and his ladder. People have dreamt of a stairway to heaven ever since.

The first modern concept of a space elevator emerged from the fertile mind of Konstantin Tsiolkovsky. Inspired by the recently built Eiffel Tower, he imagined a structure 35,790 kilometers (21,475 miles) high that reaches the altitude of a geostationary orbit, where the orbital period equals the Earth’s rotation period, so an object has a fixed location in the sky as seen from the ground. Release an object from the top of a tower this high and voilà, it’s in orbit. But no material can handle the extreme compression created by such a structure, so Tsiolkovsky’s idea languished. In 1959, another Russian scientist, Yuri Artsutanov, came up with a more feasible version. He suggested lowering a cable from a geostationary satellite while also extending a counterweight away from the Earth, to keep the forces in balance and the cable hovering over the same location on the Earth’s surface. A space elevator would be kept in tension, with no compression or bending (
Figure 33
).

This is the physics. A space-elevator cable rotates with the Earth. So any object attached to it will feel an upward centrifugal force opposing gravity. Think of the outward force on an object tied to a string if you whirl it around your head; the object attached to the string acts as a counterweight, keeping the string straight and taut. The higher up the cable an object is, the weaker the Earth’s gravity and the stronger the centrifugal force upward. The net gravity is less. At the geostationary orbital altitude, the centrifugal force acting upward perfectly balances gravity acting downward. So an object there experiences forces in perfect balance.

The space elevator, or tether, was reinvented a number of times in the 1960s and 1970s, and it entered the popular imagination with Arthur C. Clarke’s 1979 novel,
The Fountains of Paradise
.
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He realized that the cable should be tapered, thickest at the geostationary altitude and thinner at the ends, in order to equalize the amount of weight for a given cross-sectional area that the cable would have to bear. This is because the cable has to be able to support, with tension, its own weight below any point. The location with the greatest tension is at the geostationary orbit level. Clarke also realized that as the lower sections of cable were built, the counterweight would have to extend to 144,000 kilometers, almost halfway to the Moon. Unfortunately, the engineers working on the problem realized that no known material could do the heavy lifting.

Materials that might be used for a space elevator are characterized by their tensile strength and density. A more useful figure of merit is their maximum length before they break under their own weight. We can start with natural organic materials. Jack’s beanstalk couldn’t handle the compression it would suffer going more than a few miles high. Natural fibers used in rope have good tensile strength, but their breaking distances are only five to seven kilometers. Steel cables used in bridges have breaking distances of 25 to 30 kilometers. These are well known from bridge building and other civil engineering projects. Spider silk has the same tensile strength as steel, even though it is a protein with just one-sixth the density, so the breaking length is 100 kilometers—impressive but still inadequate to get into low Earth orbit. Synthetic fibers like Kevlar and Zylon take us up to 300 or 400 kilometers, high enough to reach the ISS but not enough to send the counterweight much higher into space. The dreams of elevator operators looked like they couldn’t be realized with conventional materials.
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Then nanotechnology burst on the scene in the 1990s. The ability to manipulate matter at the level of atoms or molecules opened up new technologies and a dizzying array of potential new applications. Some of the most exciting materials were made of pure carbon. Fullerenes are carbon molecules in the form of spheres, tubes, and other shapes. The name is a nod to the architect and designer Buckminster Fuller, since the first of the new molecules to be created was a tiny spherical cage made of sixty carbon atoms, resembling one of Fuller’s geodesic domes. Soon after buckyballs were isolated, scientists learned how to create carbon nanotubes, interlinked carbon atoms rolled in a cylinder a millionth of a meter across. Carbon nanotubes are stable and they conduct heat and electricity extremely well.

But it was the mechanical properties that got space engineers excited. The tiny tubes are fifty times stronger than titanium; the theoretical limit is five times higher still. Carbon is the sixth lightest element in the periodic table, so there’s almost no dead weight. Its strength and stability are unique for its low mass. The longest nanotubes are a few centimeters long, but if we can scale up the technology by a factor of a billion, we may be able to weave them into a carbon cable that reaches to the sky.
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We’re certainly not there yet. Once, after a lecture, Arthur C. Clarke was asked when space elevators would become a reality. His response: “Probably about fifty years after everyone stops laughing.”

Materials scientists disagree on whether carbon nanotubes are actually strong enough, and the technology needed to weave them into ribbons or ropes has never been demonstrated. If the hexagonal bonds become too strained, the structure can dramatically rupture, rather like a run in a woman’s stocking. Such a long structure is susceptible to instabilities, whipping motions, and resonant vibrations. Moreover, the climbers or elevator cars create their own problems, inducing a wobble on the cable due to the Coriolis force (or Coriolis effect). The Coriolis force is familiar as the cause of weather systems rotating in opposite direction north and south of the equator. If you fly north or south from the equator, the ground moves at a slower speed under you, even though your speed hasn’t changed. This leads to an apparent deflection as seen from the Earth’s surface. A climber on a space-elevator cable would move more slowly on each successive part of the cable onto which it moved. This acts as a deflection or a sideways drag on the cable. The effect works in the opposite direction for a descent of the cable. In practice, this Coriolis force limits the speed at which a cable can be ascended.

Finally, there are risks from meteorites and from the 6,000 tons of space junk orbiting the Earth in its potential path, plus vulnerability of such a large target to a terrorist attack. One elevator isn’t very efficient. There would have to be at least one for going up and one for going down. To avoid nasty oscillations, the speed might have to be kept to around 100 mph, making the journey take several weeks.

Space-elevator optimists are undeterred. A recently discovered carbon allotrope called carbyne is even stronger than the graphene that’s the basis of current nanotubes.
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It might be possible to “dope” the carbon to reduce the risk of ruptures. Space elevators got their most detailed design study ever in 2013 with a 350-page report from the International Academy of Astronautics.
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The right material is still the wild card, but the report projects a space elevator carrying multiple 20-ton payloads by 2035. Getting international agreement for such a strategically important capability is a concern, as is protecting it from terrorist attacks.

The cost of anywhere from $10 to $50 billion is far cheaper than that of the International Space Station—for a tool that brings launch costs down to $100 per kilogram, twenty times lower than any rocket on the horizon. The new economic activity spawned by a space elevator could dwarf its cost.

A Space Boom

The history of space travel is fraught with unfulfilled promise. What is the basis for thinking that space will ever be more than a rarefied niche for those with deep pockets and nerves of steel? Hard-nosed economists have studied the issue and there’s data to back up their claims.