Friday, November 13, 2009

Will it stand into space?

Posted by Will it stand? at 12:48 AM
Earlier this week CNN ran an article on its front page about the prospects of a space elevator. The idea, first seriously proposed by author Richard C. Clarke 30 years ago, has gained some momentum because of a series of prizes offered to pioneering inventors. NASA offers a $2 million prize to anyone who can design a suitably powered lift to crawl up a 1 km high tether. Another contest challenges teams to design a tether twice as long and strong as what currently available on the market.


Why all the enthusiasm for pursuing such science fiction? In this case, geeky altruism gives way to corporate opportunism. Offering a low cost solution to lifting satellites and research modules into geosynchronous orbit could result in a major pay day. Consider sending tourists into space at $1,000 a trip or the potential for solar energy generation free from cloud cover and other environmental restrictions.

But will it stand? Experts and enthusiasts believe that the space elevator will happen within our lifetimes. But for now, two major hurdles stand in the way: 1) finding a suitable material for the tether and 2) developing an efficient propulsion system.



The experts quoted in CNN's article estimated that a chord 25 times stronger than most advanced industrially available materials would be required. On first glance, that seemed extreme, so I ran some of my own numbers. To simply things, I assumed that the cable would pretty much just hang the whole way - the real design is certain to be more complex.

First up, the length of the tether must extend into geosynchronous orbit, so that the space platform remains directly above the base. That's over 22,000 miles up. At that elevation the force of gravity from the Earth is almost 60% smaller. That helps, but a steel cable like those used in suspension bridges would still be around 950 times over capacity. Using Kevlar represents a 10-fold improvement, but we're still not in the ballpark. At least my numbers arrived within an order of magnitude of the expert. The web is a buzz with the potential for carbon nano-tube technologies. Still in their infancy, they provide the hope for a suitable tether material.

Construction a climbing vehicle is proving to be as difficult a challenge. To date, no teams have achieved the goals of NASA's competition. The latest attempts drive a small electric motor with solar power. Try finding a 22,000 mile long extension chord. Carrying fuel on board also heavy and detracts from payload capacity. Looking ahead, many experts believe that laser propulsion holds the key, at least as an energy supply for on-board motors.

The challenges seem very exciting. Science and technology geeks like myself believe that the new technology being developed along the way is worth the cost and may be more valuable than the actual working elevator. However, the viewpoints shared by non-technical contributors to the CNN comment board are very disheartening. "Solve world hunger and stop all wars first," decries one writer. Another thinks NASA is a sham and that all monies should be directed toward the recovering economy. Certainly, there needs to be a balance to funding policy, but I for one believe that such scientific exploration return much more than the initial investment.

Where do you stand on this question? Is prize money well spent on incentives to create a space elevator? How would you approach the problem? What other materials might offer a solution? Have you heard of an innovative new energy solution? Comment below or participate on at www.spaceelevator.com

Note: I had not ever considered the possibilities of a space elevator until earlier this week. It's an intriguing and compelling technical challenge to structural engineers.
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