Space Elevators: To the Moon and Back

"The space elevator will be built about 50 years after everyone stops laughing," said science fiction writer Arthur C. Clarke, a long time ago.

Today, standing, theoretically, on the cusp of significant breakthroughs in the field of space exploration and the tantalizing prospect of a "Star Trek", "Star Wars" and "2001: A Space Odyssey"- like scenario, we find ourselves asking what became of an idea so revolutionary it threatened to transform all our lives into something more commonly seen in sci-fi/alien-shooter video games and films - the space elevator!

The History

The idea of a space elevator dates back to the late 19<sup>th century, when Russian scientist Konstantin Tsiolkovsky proposed a free-standing structure that would essentially act as a really long elevator, connecting Earth to a platform in geostationary orbit (some 35,000km) in space.

The initial and most basic concern with even imagining such a structure was the fact that the building would have to support an insane amount of pressure, bearing down all the way from the top to its foundations.

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.

The Radiation Problem

There is one other concern for Earth orbit elevators - the Van Allen belt.

In a 2010 article in New Scientist, Kelly Young points out that such an idea means we have to figure out a way to shield human passengers when passing through the core of the Van Allen belt surrounding Earth. The Van Allen belts, incidentally, are twin-rings of radiation-charged particles trapped by the Earth's magnetic belt.

For a space elevator travelling at the current proposed speed of 200 kilometers per hour, passengers might spend half a week in the belts. That would hit them with 200 times the radiation experienced by the Apollo astronauts.

"They would die on the way through the radiation belts if they were unshielded," says Anders Jorgensen, author of a new study on the subject and a technical staff member at Los Alamos National Laboratory, New Mexico, U.S.

The Radiation Solution

A possible solution to the radiation problem was proposed by Blaise Gassend, of MIT, who said the radiation could be reduced, by a small factor, if the elevator was moved off the equator by the largest margin. However, the problem is that such a move would probably not reduce radiation by enough of a margin.

A second option would be to have some sort of radiation shield, placed just before the Van Allen belt. The climbers could pick it up just then and drop it once it exits the danger area. However, the obvious drawback here is that such shields would add extra weight to the climbers and such drastic increases and reductions, as they climb the tethers, would contribute to unsafe swaying.

Where it Stands Today

The number and extent of many concerns surrounding the space elevator led to the spawning of a number of contests, across the world, inviting those with ideas to come forward.

One such was NASA's "Strong Tether Challenge", the most recent edition of which was held on Aug. 12, at Redmond, WA. This is the fifth year of the contest and although there have been no winners, NASA has confirmed they are delighted with the promise of some of the ideas.

Another competition is one sponsored by the Space Elevator Conference. At the 2011 conference, leading scientist like Dr. Boris Yakobson, Dr. Vesselin Shanov and Dr. Vasilii Artyukhov presented papers focusing on mechanical engineering, material science (CNTs) and simulations of graphitic nanocarbons. The 2012 conference, scheduled for Aug. 25 - Aug. 27, is expected to discuss concerns related to operating and maintaining a space elevator.

There are several other concerns that surround the idea of a space elevator, apart from the cables.

The climbers, for example, cannot be a typical elevator box. They must, in addition to accommodating the shape of the tether (wider through the middle than the tips, so as to allow for maximum force dispersement), be paced at optimal timings, to minimize stress on the cables and, obviously, be built out of suitably lightweight material. Another design constraint will be the ascending speed of the climber. As geosynchronous orbit is at 35,786 km (22,236 mi), assuming the climber can reach the speed of a very fast car or train of 300 km/h (180 mph) it will take 5 days to climb to geosynchronous orbit.

The Present

Most recently, a New York Times report in 2011 spoke of a "top-secret lab in an undisclosed Bay Area location where robots run free". They were referring to something called Google X... a supposedly highly classified scientific lab, where a list of 100 "shoot for the stars" ideas were being worked on. These included those as seemingly far-fetched as a refrigerator connected to the Internet (so it could order groceries when you ran low) and, of course, the space elevator.

The space elevator, the report continues, has been a long time fantasy idea for both Google and other Silicon Valley companies.