Your plane lands on an artificial equatorial island far from any landmass. As you disembark, you look up and see what appears to be a 15-km-high roller coaster attached to a cable that disappears into space. After boarding a large vehicle similar to a railcar, a launcher shoots you up the roller coaster; at its apogee, you connect with the long cable. During the next few hours, your car climbs the cable electromagnetically, without actually touching it, for 21 kms, until it reaches a geosynchronous platform. From there, it’s a short hop to a week-long stay on a space station.
Sound far-fetched? Don’t cancel that trip to the Grand Canyon just yet, but scientists predict that someday in the latter part of the 21st century, an elevator stretching from Earth to a platform in space could become reality as the cost and time required to construct one become more reasonable.
That news comes from a NASA workshop convened last year by David Smitherman, technical manager in the advanced projects office at the Marshall Space Flight Center in Huntsville, Ala., to discuss the technology needed to build a space elevator. The group determined that it’s (barely) technically feasible today to construct a space elevator with existing materials. But experimental or predicted technologies could move the project out of science fiction and onto the drafting boards of engineers.
The concept of a space elevator is simple: put a platform in space and attach two cables. One goes down to Earth, and the other goes out into space, where it’s attached to a captured asteroid. The asteroid counterbalances the platform so it doesn’t fall out of orbit.
Because the platform would be in geosynchronous orbit, it would always be above the point where the lower cable attaches to the Earth. Large, high-tech elevator cars then could ride the cable back and forth.
As with mountain climbing, having a fixed line makes it easier and cheaper to get things up and down. Compared with today’s expensive, disposable booster rockets, a space elevator could reduce the cost of getting cargo or people into space from US$22,000 per kilogram to as little as US$10 per kilogram. The closest analogy to the transformative power of such a costly undertaking might be North America’s railways or highway systems.
Similarly, with the space elevator, said Smitherman, “the real benefit would be that you would have access to space as easily as you currently have access to the rest of the planet.”
Though the space elevator could be built today, it would be very difficult, to say the least: If available composite materials were used, the cable connecting the space platform to the ground would taper from 2 km in diameter at the platform to 1 mm at Earth and would have a mass of 60 by 1,012 tons. Plus, an asteroid would have to be found, captured and attached in higher orbit to the platform. That, of course, has never been attempted.
The NASA workshop identified five technologies that should help make space elevators a reality:
Carbon nanotube cables: Carbon nanotubes can be grown to produce cable with 100 times the strength of steel but with much less weight. For a space elevator, such cables would have to be no more than 0.26 mm in diameter at the platform, tapering down to 0.15 mm at the Earth’s surface, with a total mass of 9.2 tons. The elevator “cable” would actually be a bundle of carbon nanotube cables, in case any one failed. To date, carbon nanotubes have been grown in lengths of only a few microns.
Compression structures: Advanced composite materials would be needed to make tall towers – as much as 15 km high. These very rigid bases would be used to support and launch vehicles, to avoid many atmospheric conditions at lower altitudes.
In Arthur C. Clarke’s 1978 novel, Fountains of Paradise, which introduced the notion of a space elevator to the popular imagination, the cables were attached to the top of a mountain on the island of Taprobane.
Tension structures: Elaborate flywheels would help transfer momentum from elevator cars and direct the energy elsewhere. Also, rotating tethers could be used like conveyor belts to move goods between the elevator and predetermined locations in space.
Electromagnetic propulsion: This would allow elevator cars to “ride” the cable without actually touching it, to minimize friction and wear and tear. The concept is akin to today’s experimental high-speed trains, which float above their tracks, except it would be vertical. Electromagnetic launch systems – so-called rail guns – could propel vehicles at extremely high initial velocities. To date, however, such launch systems haven’t been very effective.
Space infrastructure (space stations, moon bases, extraplanetary exploration): “There’s no need today to build a geosynchronous elevator out to Earth orbit” until there are actually space stations and other places to send cargo and people, Smitherman said. As we build more things in space during the next 20 to 30 years and have the need to shuttle many more things between Earth and space, then an elevator would make sense, he said.
Location Is Everything
The workshop members recommend putting the first space elevator on an artificial equatorial island in the middle of the ocean. There, if the tall tower fell apart, it wouldn’t do much damage. Also, the weather is generally favourable.
Finally, building the elevator in international waters might help ease political concerns about its use and encourage international participation.
One thing is for certain: the space elevator must have popular appeal. It would have to be used for a range of activities, including tourism, commercial research and development and manufacturing to be truly useful, according to Smitherman.
Unlike previous missions to space, this one won’t succeed if it’s only a government project. The space elevator must be for everybody, he said.