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Going Up?

To build a space elevator, you'll need a very light car and a very strong string.

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(Continued from page 1)

A couple of companies, backed by venture capital, are already investing in the basics and have scoped out the climber robots in California for ideas. Believers say that as crazy as the space elevator sounds, it’s even crazier to not pursue what could be the cheapest and most reliable route into space.

“We need to sort of open up and use our imagination and creativity,” says Robert Cassanova, director of the NASA Institute for Advanced Concepts in Atlanta, which has paid for some initial studies on the idea. “We need to start with a new sheet of paper and come up with some new ideas. That’s sort of the story of the space elevator. It’s one of these really big ideas. Finally people are starting to take a serious look at it.”

Although the gadgets that showed up in California are as far from the real thing as a magnifying glass is from the Hubble Space Telescope, here’s how the finished concept would work: A floating platform of some kind, perhaps a big ship, would station itself somewhere along the equator. From there a ribbon made of a material stronger than diamonds would stretch about 62,000 miles into space.

The end of the cable would carry a counterweight of some kind, maybe rockets or other left over equipment from construction. The fulcrum of the elevator cable mass would have to be positioned at 23,000 miles— at geosynchronous orbit, where satellites constantly tower over the same point on the planet. But for its center of gravity to be positioned at geosynchronous orbit, the far end of the cable must extend way beyond that point. Like a teeter-totter that sticks out to either side of the balancing point, the cable must extend 62,000 miles, according to the most prominent approach being considered.

Earth’s rotation would whirl the enormous wobbly tower, like a tennis ball on the end of a string. The momentum of the spin would keep the cable taut, and roomy elevator cars would shuttle people and cargo between stations along the line.

The elevator cars would be powered by a laser on the ground—much like the searchlight in the California parking lot—beaming energy to collector panels on each car.

Daily elevator departures would make expensive and risky rocket launches obsolete. Costs of lofting satellites could fall substantially, making communications and everything else that depends on them far cheaper. With many more people able to afford it, space tourism would become truly practical. Or so elevator champions, like Bradley Edwards, believe.

Edwards attended the elevator challenge not to compete but to cheerlead. He first got curious about the space elevator as a physicist at Los Alamos National Laboratories in New Mexico after hearing the naysayers proclaim it would never work. The technology conronts many dangers, and Edwards has heard them all. What happens, for example, if the elevator cable collides with something in orbit? About 100,000 pieces of debris big enough to sever a cable speed around Earth. Space junk is so plentiful that a piece could slice through the cable roughly every 250 days. Such a catastrophe would leave anything above the break careening through space, and anything lower falling in a fiery reentry toward the planet.

Edwards has a plan to avoid this. First, the cable would be designed to withstand impacts. Instead of a single strand, the cord would consist of a flat ribbon of nanotube fibers lined up side by side and reinforced at intervals by horizontal strips of high-strength tape. If a speeding meteorite cut through a few fibers, the tape above and below the break would hold the rest tight and shift the load onto adjoining fibers. Also, the flat bundle of fibers would have a slight curve to it, so a small meteorite that hit it sideways would not slash through all the fibers.

A robust system to track orbiting debris, Edwards notes, would spot anything endangering the elevator and alert the ship or floating platform at the base of the cable to steer clear. A mile or two of movement ought to be enough to dodge the dangers, Edwards estimates.

About Michael Milstein

Michael Milstein is a freelance writer who specializes in science. He lives in Portland, Oregon.

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