The Audacious Space Elevator

NASA Another idea was to build a tower from the Moon.

We can determine the orbital velocities that might be attained at the end of Pearson's 144,000 km tower. At the end of the tower, the tangential velocity is 10.93 kilometers per second which is high enough to escape Earth's gravitational field and send probes to Saturn or Mars. If an object were allowed to slide freely along the upper part of the tower a velocity high enough to escape the solar system would be attained.

The space tower is a good concept for science fiction writers, but until new materials are developed and cheaper ways to reach orbit are found, the space tower will remain a dream.

The workshop's findings determined the energy required to move a payload by space elevator from the ground to geostationary orbit could remain relatively low. Using today's energy costs, researchers figured a 12,000-kg Space Shuttle payload would cost no more than $17,700 for an elevator trip to GEO. A passenger with baggage at 150 kg might cost only $222! "Compare that to today's cost of around $10,000 per pound ($22,000 per kg)," said Smitherman. "Potentially, we're talking about just a few dollars per kg with the elevator."

During the workshop, issues pertinent to transforming the concept from science fiction to reality were discussed in detail. "What the workshop found was there are real materials in laboratories today that may be strong enough to construct this type of system," said Smitherman.

Smitherman listed five primary technology thrusts as critical to the development of the elevator. First was the development of high-strength materials for both the cables (tethers) and the tower.

In a 1998 report, NASA applications of molecular nanotechnology, researchers noted that "maximum stress [on a space elevator cable] is at geosynchronous altitude so the cable must be thickest there and taper exponentially as it approaches Earth. Any potential material may be characterized by the taper factor - the ratio between the cable's radius at geosynchronous altitude and at the Earth's surface. For steel the taper factor is tens of thousands - clearly impossible. For diamond, the taper factor is 21.9 including a safety factor. Diamond is, however, brittle. Carbon nanotubes have a strength in tension similar to diamond, but bundles of these nanometer-scale radius tubes shouldn't propagate cracks nearly as well as the diamond tetrahedral lattice."