Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100

simple question: Why can’t you build an Eiffel Tower to outer space? If it was tall enough, he calculated, then it would never fall down, held up by the laws of physics. He called it a “celestial castle” in the sky.
    Think of a ball on a string. By whipping the ball around, centrifugal force is enough to keep the ball from falling. Likewise, if a cable is sufficiently long, then centrifugal force will prevent it from falling back to earth. The spin of the earth would be sufficient to keep the cable in the sky. Once this cable is stretched into the heavens, any elevator cab that rides along this cable could take a ride into space.
    On paper, this trick seems to work. But unfortunately, when using Newton’s laws of motion to calculate the tension on the cable, you find that it is greater than the tensile strength of steel: the cable will snap, making a space elevator impossible.
    Over the decades, the idea of a space elevator was periodically revived, only to be rejected for this reason. In 1957, Russian scientist Yuri Artsutanov proposed an improvement, suggesting that the space elevator be built top-down instead of bottom-up, that is, a spaceship would first be sent into orbit, and then a cable would descend to and be anchored in the earth. Also, science fiction writers popularized the idea of space elevators in Arthur C. Clarke’s 1979 novel
The Fountains of Paradise
and Robert Heinlein’s 1982 novel
Frida.
    Carbon nanotubes have helped revive this idea. These nanotubes, as we have seen, have some of the greatest tensile strengths of any material. They are stronger than steel, with enough strength to withstand the tension found in a space elevator.
    The problem, however, is creating a pure carbon nanotube cable that is 50,000 miles long. This is a huge hurdle, since so far scientists have been able to create only a few centimeters of pure carbon nanotubes. It is possible to weave together billions of strands of carbon nanotubes to create sheets and cables, but these carbon nanotube fibers are not pure; they arefibers that have been pressed and woven together. The challenge is to create a carbon nanotube in which every atom of carbon is correctly in place.
    A space elevator to the heavens may one day vastly reduce the cost of space travel. The key to the space elevator may be nanotechnology.
    In 2009, scientists at Rice University announced a breakthrough. Their fibers are not pure but composite (that is, they are not suitable for a space elevator), but their method is versatile enough to create carbon nanotubes of any length. They discovered, by trial and error, that these carbon nanotubes can be dissolved in a solution of chlorosulphonic acid, and then shot out of a nozzle, similar to a shower head. This method can produce carbon nanotube fibers that are 50 micrometers thick and hundreds of meters long.
    One commercial application would be for electrical power lines, since carbon nanotubes conduct electricity better than copper, are lighter, and fail less often. Rice engineering professor Matteo Pasquali says, “ For transmission lines you need to make tons, and there are no methods now to do that. We are one miracle away.”
    Although these cables are not pure enough to qualify for use in a space elevator, this research points to the day when one might be able to grow pure strands of carbon nanotubes, strong enough to take us into the heavens.
    Assuming that in the future one will be able to create long strands of pure carbon nanotubes, there are still practical problems. For example, the cable will extend far beyond the orbit of most satellites, meaning that the orbits of satellites, after many passes around the earth, will eventually intersect the space elevator and cause a crash. Since satellites routinely travel at 18,000 miles per hour, an impact could be catastrophic. This means that the elevator has to be equipped with special rockets to move the cable out of the way of passing satellites.
    Another problem is turbulent weather, such as hurricanes, lightning storms, and high winds. The space elevator must be anchored to the earth, perhaps on an aircraft carrier or oil platform sitting in the Pacific, but it must be flexible to avoid being damaged by the powerful forces of nature.
    There must also be a panic button and escape pod in case of a break in the cable. If something snaps the cable, the elevator cab must be able to glide or parachute back to the earth’s surface in order to save the