Some of these challenges would be met merely by locating the elevator's Earth anchor in the eastern equatorial Pacific, west of the Galapagos Islands, where the weather is unusually calm and the threats from hurricanes, tornadoes, lightning, jet streams, and wind are greatly reduced. This location is also about 650 km from any current air routes or sea lanes, significantly reducing the chance of an accidental collision and making the site easier to secure against terrorists. An anchor in the Pacific obviously implies a floating platform, but such structures are already commercially available, thanks to the offshore oil industry [see illustration, "Elevator Ahoy"].
These platforms would be mobile, which would allow the elevator, with sufficient warning, to avoid orbiting satellites and debris by moving the anchor end of the cable back and forth about 1 km, pulling the ribbon out of the path of an oncoming object. While debris and other objects down to 10 cm in diameter are currently tracked, objects with diameters as small as 1 cm are a potential threat to the elevator. As a consequence, the current elevator system design includes a high-sensitivity ground-based radar facility to track all objects in low-Earth orbit that are at least 1 cm wide [see illustration, "Watching the Skies"]. A system like this was designed for the International Space Station but never implemented.
Eliminating erosion from atomic oxygen at altitudes of 100 to 800 km would be the job of thin metal coatings applied to the cable. Radiation damage would be mitigated by using carbon nanotubes and plastic polymer materials that are inherently radiation resistant.
To avoid problems with cable oscillations induced by tidal forces, my ribbon design calls for a natural resonant period--7.2 hours--that does not resonate with the 24-hour periods of the moon and sun. Any oscillations that do occur would be damped by the mobile anchor station.
Induced electrical currents would be generated only if the ribbon cut through Earth's, or an interplanetary, magnetic field. Because the ribbon would be stationary relative to Earth's magnetic field, only dynamic changes in the magnetic field could cause currents in the ribbon, and these would be small. The interplanetary magnetic field is also small, except in cases of extreme solar activity, and even then, the currents generated would be on the order of milliwatts and easily dissipated. Currents caused by charged plasma in Earth's ionosphere would also be negligible, because the ribbon's composite material would have high electrical resistance.
The last challenge, and the one that sparks the most interest in today's geopolitical climate, is terrorism. Despite the elevator anchor's remoteness and defensibility, an attack that severs the elevator cable--for example, by detonating a bomb planted on an elevator car--is a possibility. So what would happen if the cable were cut?
Science-fiction scenarios have portrayed a space-elevator cable failure as a global disaster, but the reality, for my design, would be nothing of the sort. Remember that the ribbon's center of gravity is in geostationary orbit, and the entire cable is under tension as the counterweight swings around Earth. If the ribbon were to be severed near the bottom, all the cable above the cut would float up and start to drift. Calculations show that the ribbon and counterweight would most likely be thrown out of Earth orbit into open space.
Of course, the cable below the severed point would fall. But because the linear density of the ribbon would be just 8 kg/km, literally lighter than a feather, proportionally speaking, it would be unlikely to do much, if any, physical damage. In the worst-case scenario, where the cable is severed near the top, in space, the released counterweight would fly out of Earth orbit and nearly the entire ribbon would begin to fall down and wrap around the planet. As the ribbon fell it would gain velocity, and any ribbon above the first 1000 km would burn up when it hit the atmosphere, producing long, light ribbons that are meters to kilometers in length. It would be a mess and a financial loss, and probably an impressive light show in the upper atmosphere, but nothing like a planetary disaster. Some toxicity issues are being investigated in connection with inhalation of ribbon debris, but initial results indicate that the health risks would be small.
Five years ago, most of the space community considered the space elevator a far-future proposition at best. With the advent of carbon-nanotube composites and the conclusions of recent studies, the space elevator concept is moving toward mainstream acceptance. The current ribbon design has attracted considerable interest from NASA headquarters, the European Space Agency, and the U.S. Air Force. Independent evaluations by NASA and ESA are under way, and it is my belief that their findings will add substantial credibility to the program.
If the initial estimates are confirmed and a space elevator is constructed, it will open space for applications we can barely imagine. With a space elevator providing cheap, easy, low-risk access to space, people's lives on Earth could be immeasurably enhanced as the wealth of the solar system is brought to their door.
Humanity would at last be poised to make its next move into space and onto the moon and Mars--not as a horribly inefficient, one-shot deal but as a continuing enterprise. Space travel would become part of our everyday culture. Just as the development of stone tools opened up huge new habitats and ways of life to our distant ancestors, so, too, will the space elevator transform humanity's destiny.
Bradley Carl Edwards spent 11 years on the staff of the Los Alamos National Laboratory, leading advanced technology efforts for lunar missions and a Europa orbiter mission. Since leaving Los Alamos, Edwards has led development of the space elevator, organizing conferences and conducting research. He is the founder and president of Carbon Designs Inc., in Dallas, which is developing high-strength materials for a range of applications, from aerospace structures to sports and recreational products.
For more information about the space elevator project, visit http://www.spaceelevator.com.
