Trip to Penthouse Floor in Space Elevator would be 22,300 Miles

William Atkins
Wednesday, 27 December 2006 01:49

Science - Space

The Space Elevator—an elevator that would go up and down between the Earth’s surface and a point in space above the Earth—has been a topic of science and science fiction for years. However, materials did not exist that were strong enough to actually build it. In the twenty-first century, that is no longer the case.

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Before 2001, space elevators (sometimes called skyhooks, hoists to the heavens, space lifts, orbital towers, and space bridges) was relegated to the imagination of science fiction writers such as English writer and inventor Sir Arthur C. Clarke (1917-), who wrote about them in his popular 1979 book The Fountains of Paradise.

First proposed by Soviet rocket scientist Konstantin Tsiolkovsky (1857-1935) in 1895, space elevators were later theorized in more detail by Russian engineer Yuri Artsutanov (1929-) in the 1960s. Before 1991, space elevators were not considered practical ways to transport materials and people to space. However, in that year, a new class of carbon molecule was discovered by Japanese physicist Sumio Iijima (1939-).

Called carbon nanotubes (CNTs), the composite material is strong enough—in fact, supposedly four times the required strength—to build a space elevator. The CNTs are  cylindrical molecules whose walls are made of carbon atoms. The tube, itself, is about one nanometer in diameter (where one nanometer is about one-billionth of a meter). Theoretically, CNTs could be hundreds of times stronger than steel and be one-sixth its density (much like the density of plastic wrap used to store refrigerated food).

The current design of the space elevator was conceived by American physicist Bradley Carl Edwards, the developmental leader of the space elevator project. In addition, Edwards is the founder and president of Carbon Designs (Dallas, Texas), a developer of high-strength materials for various high-tech applications, and the director of research for the Institute for Scientific Research (Fairmont, West Virginia). His company has produced four-centimeter-long CNTs, which are approximately 70 times stronger than steel.

Current plans show that the space elevator could consist of flexible CNT-composite (CNTC) ribbon that is thinner than paper, and with a width of about 3 feet (1 meter). It would extend roughly 62,000 miles (100,000 kilometers) from the Earth’s surface to a counterweight in space. In between, at a geostationary point about 22,300 miles (36,000 kilometers) above the Earth (whose distance is called geosynchronous orbit), its center of mass would be located, along with the location where cargo and people will end their space journey.

The ribbon’s mass is theorized to be about 1,000 tons, while the counterweight’s mass is about 600 tons. The space elevator is likely to be anchored to a mobile ocean-floating platform on the equator, such as in the Pacific Ocean near the Galapagos Islands. The ribbon remains tightly stretched because of the outward force of the Earth’s rotation (like a string with a ball on its end that is twirled about).

Electric vehicles (called climbers) would move up  the ribbon using electricity produced by solar panels and a ground-based laser beam. The vehicles ascend at a constant 120 miles per hour (190 kilometers per hour), making the elevator ride in less than eight days. About 13 tons of cargo could be carried onboard.

The cost of a space elevator trip, according to Edwards, would be much less than the cost traveling aboard the space shuttle. In 2006, it costs about $2,000 per kilogram to place objects into orbit with the space shuttle (based on figures from Space.com: a 30,000 kilogram payload and a $600 million incremental launch cost per mission; with total costs averaging $1.3 billion per mission). Edwards estimates, based on NASA studies, that the launch cost for sending one kilogram of cargo via the space elevator would be initially several hundreds of dollars.

Arthur C. Clarke set a twenty-second century timeframe for the space elevator in his book The Fountains of Paradise. According to Edwards, the earliest that the construction of a space elevator could be completed would be about the year 2020.