What is?

What is a Space Elevator?

The Space Elevator is a space transportation system that is a radical departure from rocket-based space travel. Contrary to our first intuition, it is actually possible to construct a physical "railroad to space", such that leaving the planet will involve riding out rather than rocketing out.

Building this railroad system takes two steps - laying the track, and running the trains.

The track for the Space Elevator is a actually a cable, initially less than 1/4" in diameter, extending from the surface of the earth to a mass in space. Similar to a spinning keychain, the rotation of the Earth about its axis throws the mass outwards, and keeps the tether taut. Accounting for the centrifugal force, the Space Elevator is actually hanging from the ground and into space! Because of the slow rate of rotation of the Earth (only one revolution per 24 hours) the cable has to be very long - theoretically at least 25,000 miles, and in practice closer to 60,000 miles.

The difficulty in building the Space Elevator is that this very long cable has to carry its own weight without breaking. Until recently, we knew of no material that even came close to achieving this. Further work by Jerome Pearson (USAF) and the discovery of Carbon Nanotubes in 1991 by Dr. Sumio Iijima opened the door to the construction of the Space Elevator, and research into making Carbon Nanotube tethers has been underway ever since.

Once the cable is in place, electric cars can travel on it using mechanisms not much different than those found on ski lifts. The trick lies in powering the cars, since fuel or batteries end up weighing more than the cars can lift. The solution that was proposed in 2000 by Dr. Bradley Edwards (then of Los Alamos National Laboratory) is to use a technique called "power beaming".

The cars (called "climbers" in Space Elevator jargon) carry photo-voltaic cells facing back towards the Earth, and a ground station projects a strong beam of light at them. The cells convert the light into electricity, and drive the motors. The main benefit of power beaming is that it allows us to leave the fuel tank on the ground.

Another proposal by Ben Shelef of the Spaceward Foundation uses thin-film photovoltaic technology to power the climbers while relying mostly through solar power. With this proposal the climbers practially "float" up the tether under their own self-generated power. Under both proposals, the climbers are very simple machines, comprised basically only of solar cells and electric motors.

As promised, the complete system is quite revolutionary. It allows payloads to be launched to space for basically the cost of electricity to run the power beaming system. Each climber carries more payload than its own self weight (compared to the 1% payload carried by a rocket) and never subjects the payload to high accelerations or vibrations. A ride in the Space Elevator is comparable to transport in a train. The climbers carry no fuel so are never in danger of exploding, and travel at a lesurely 100-200 MPH along the cable.

Space Elevators can be built to any scale. The first design uses a 1/4" cable and can lift about 20 tons at a time, launching once per day. Larger Space Elevators can then be constructed that will lift 100 or 1000 tons at a time, opening the way to commercial scale access to space. Looking back from a point in time 100 years from now, it is the construction of the first Space Elevator that will be marked as the true beginning of the Space Age and of the interplanetary civilization.

© The Spaceward Foundation 2008 - - Mountain View, CA