Space Elevators: To the Moon and Back

Today's scientists continue to indicate not only that such a structure is feasible but could also be a surprisingly inexpensive way to expand the human race's rapidly declining living environments. They have been seriously considering space elevators as a far-out space transportation system for the next century, which could make travel to geostationary Earth orbit a daily event. Beyond Earth, the possibility of similar structures on the Moon and Mars open new economic opportunities and expand humanity's reach ever so slightly into the solar system.

At present, rockets are used to ship anything into space. This costs several thousands of dollars per kilogram. More to the point, rockets also generate a tremendous amount of pollution.

To change the equation, instead of using rockets, the obvious answer is to build a transportation infrastructure, a "railway line" into space. A space elevator is the way to provide scalable, inexpensive and reliable access to space, scientists say.

The space elevator uses a Carbon Nano Tube (CNT) ribbon that stretches from the surface of the Earth to a counterweight in space. A thin vertical cable (tether) stretches from the Earth to orbit, about 100,000km into space. Elevator cars (climbers) ascend the ribbon carrying cargo and (eventually humans) to and from space, as well as launching spacecraft to distant planets. A combination of sunlight and laser light projected from the ground powers the climbers.

However, various engineering challenges continue to confound scientists.

According to the International Space Elevator Consortium (ISEC), the main hurdles from a technical point of view are tether strength and power systems with space debris and tether dynamics also posing a significant challenge. Some of these challenges are rapidly being met and others are not.

Tether strength and power systems are linked because strength in one can make up for a lack of the same in the other. Essentially, if the tether is weaker than ideal, a more forceful power generation system should allow the climbers to move faster, thereby reducing the load on the tether, the ISEC suggests.

Nanotechnology could provide the very high-strength, low-weight fibers that would be needed to build the cable of a space elevator... and so far the only material that seems to promise some measure of success are CNTs.

Scientists believe nanotubes have 100 times the tensile strength of steel, are 40 times stronger than graphite fibers, conduct electricity better than copper and can be either conductors or semiconductors.