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Nasa's vision of a space elevator orbits above the Earth (Flight Directorate/NASA)

The Great Space Elevator

A concept that was wild science fiction a quarter-century ago might become a practical reality in the next twenty years.

Any time in the last fifty years you wanted to see an impressive spectacle, you needed only to be present at NASA’s Kennedy Space Center during a major liftoff. Whether it be the massive Saturn V launching men to the moon, space shuttles going into low Earth orbit or just a smaller rocket boosting a satellite into space, you were bound to get a good show. Lots of flame and smoke with a roar that would leave your ears ringing.

Very impressive. Also very expensive.

Using a rocket it takes an incredible amount of energy to lift even a small amount of weight into Earth orbit. NASA estimates the current costs are about $10,000 per pound. It is this high cost that restricts man’s exploration of space. Any Mars lander, Venus orbiter, weather satellite or manned space station is made much more expensive than it would otherwise be because of the problem of getting the materials a few hundred miles off the ground into Earth orbit. Not only is it expensive, getting into and back out of orbit is dangerous, too. Both NASA’s space shuttles that were destroyed, met their end either going into or returning from space.

But what if you had a technology that could put material into orbit for less than $10 per pound? And what if this technology could bring people and cargo in and out of orbit with a much increased safety factor?

The “Celestial Castle”

The idea originated in 1895 with a Russian scientist named Konstantin Tsiolkovsky. At the time the world’s highest structure was the Eiffel Tower built in 1889. Tsiolkovsky envisioned a much larger version of the tower with a cable on top extending thousands of miles up into space. The cable would end at a “Celestial Castle” – his version of a space station – in geosynchronous orbit. From there, space ships could easily depart Earth for distant planets.

Perhaps the most famous depiction of a space elevator came from Arthur C. Clarke’s 1978 novel, Fountains of Paradise. In the book, engineers construct the space tower from a mountain top on the fictional island of Taprobane, located on the Earth’s equator. Clarke’s design was similar in many ways to Tsiolkovsky’s vision: A base tower connected by cable to a space station. In the book what made the elevator possible was the invention of a material many times stronger than steel, but much thinner than dental floss. At the time the book was published, the idea that such a material could be made was just engineering speculation. In 1991, though, that speculation became reality.

Nanotubes

1991 was the year carbon nanotubes (CNT's) were invented. CNT's are tiny sheets of carbon rolled into a tube shape that is a hundred times stronger pound for pound than steel. They have the tension strength of diamonds, but are much less brittle. CNT's seemed like just the breakthrough that might be needed to make a space elevator possible. In 1998, NASA put together a group of scientists to look at the concept. They estimated that a space elevator could be built in about 50 years if progress on technological advances continued as expected. They concluded the base tower would have to be over 20 miles high and elevators themselves would be magnetically levitated above the cable so they could travel at high speeds without touching the surface. In this way they would put no wear or tear on the structure.

How high an object is determines how fast it orbits the earth. To make sure the top of the elevator orbited at the same speed that the earth turned, it was important to have the center-of-mass of the structure at 22,300 miles above the ground This is the same height weather and communications satellites operate. NASA decided that this meant the space station at the top would need a heavy counterweight above it. For this, they thought it might be necessary to capture an asteroid and attach it at the very top of the elevator.

NASA decided the location of the base of the tower should be right where Clarke suggested: along the equator. This location was the natural choice to make sure the space station at the top would remain directly above the base. Also, the region along the equator is almost never subject to big storms or lightning, a major consideration for the space elevator.

“Wright Brothers Version”

After the meeting was over, one scientist, Dr. Bradley Edwards, a researcher at Los Alamos, thought NASA's estimate was too conservative. He read an even more pessimistic prediction the said that sush a space elevator couldn’t be built for at least 300 years. “But there was no information on why it couldn’t be built,” Edwards noted.

This spurred Edwards to come up with a plan for a space elevator he called "The Wright Brother’s version.” In Edward's simplified plan, a robotic platform is boosted into space to the right height (22,300 miles) needed for the geosynchronous orbit. The platform would carry two spools of a CNT in the form of a ribbon 5 to 10 inches wide. The spools would then unwind, one going down to Earth 22,300 miles below, and the other one going upward to a height of around 62,000 miles. The extra ribbon above would ensure that the center-of-mass always stayed at 22,300 miles and eliminate the need for an asteroid counter-weight.

Once the lower spool reached the surface, it would be anchored to a base station, probably something similar to an offshore oil rig. Robotic devices using a pair of traction treads that squeezed the ribbon would climb up from the base station. Each climber would carry additional ribbon which would be “zipped” onto the original ribbon, widening it. When reaching the top, the climber would park itself and become part of the center-of-mass. After 230 climbers had made the trip, the ribbon would be three feet wide, though thinner than a sheet of paper. From that point on, elevators carrying up to 13 tons of people and cargo could start making the trip.

Edwards’s climbers are simpler but slower than NASA’s mag-lev vehicles. They also carry no onboard power supply. Lasers at the base station shine onto an array of photoelectric cells mounted on the bottom of the climber. The photoelectric cells convert the light to electricity to run the climber's motors. With a climb rate of 125 miles per hour, it would take about a week for the elevators to reach geosynchronous orbit.

Avoiding the Junk

One concern to the safety of any space elevator is the amount of junk currently in orbit that might collide with the ribbon. Edward has a solution for that, also. The base platform would be mobile and would move the elevator as needed to avoid any major piece of orbital debris.

So, could people be riding an elevator into space sometime in the next twenty years? NASA was impressed enough by Edward’s ideas to give him a two year grant of $500,000 to develop his proposal. The cost of the project seems to come out to somewhere between $6 and $12 billion. While this seems like a lot of money when compared to other projects like a manned Mars mission (an estimated $1 trillion), it doesn’t seem so expensive.

If such a space elevator can be built, it would open space to all kinds of development that today is just too expensive. A colony on the moon? Or perhaps Mars? If so, building space elevators would make sense on those bodies too...

Skyhook passengers will please be seated. We will begin our ascent in a moment and will be climbing at the rate of 220 kilometers per hour. Please watch out your windows carefully as about five minutes into our climb you will be able to observe the curvature of the Earth appear below us. At about fifteen minutes into the climb, the sky will blacken and the stars will appear...


Partial Bibliography

Space Elevator: Going Up by Brad Lemley, 'Discover,' July 2004.

Not Science Fiction: An Elevator to Space by Kenneth Chang, 'New York Times,' September 23, 2004.

Audacious & Outrageous: Space Elevators, Science @ NASA, http://science.nasa.gov/headlines/y2000/ast07sep%5F1.htm

Copyright Lee Krystek 2004. All Rights Reserved.

 

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