Concept of future space elevator now in testing
My last column was about private enterprise progressing toward a goal that is literally out of this world — space travel for the general public.
In it, I discussed the more conventionally understood approach of being rocket-propelled through the atmosphere into low-Earth orbit.
But there is a more obscure and peculiar method of going to outer space that involves no rocket at all — it’s called the space elevator. You may have never heard of it unless you are a fan of science fiction novels (such as “The Fountains of Paradise” by Arthur C. Clarke).
The original idea is attributed to a Russian scientist named Konstantin Tsiolkovsky. In 1895, and inspired by the newly built Eiffel Tower in Paris, he proposed a tower reaching into outer space.
This concept has been adapted to the idea of a cable attached to the surface of Earth and stretching into space. It would extend tens of thousands of miles outward (or straight upward, to the Earth-bound observer).
The force keeping the cable in place would be centrifugal force, the same force that pulls against you if you swing a bucket of water on a rope around in a circle. The faster you swing, or the longer the rope, the greater the force.
For the space elevator, as the Earth rotates, the centrifugal force (away from the Earth’s center) counteracts the force of gravity and holds the whole structure in place.
At a distance of 22,000 miles above the surface of Earth (the same altitude as geosynchronous satellites), a space traveler riding the elevator would be weightless, with gravity and centrifugal force cancelling each other out.
At even farther distances, the traveler would again experience weight, but the apparent “gravity” would be away from Earth, rather than toward it. At this point, Earth would be perceived as overhead, rather than underneath, the observer.
In fact, if you used a long enough cable, you could actually “fling” objects or spacecraft out of Earth’s gravity and launch them to other planets or interstellar space (the same way your bucket of water would fly away from you if your rope broke).
To save weight, rather than having batteries or fuel on the elevator, a laser on the ground could be used to beam power to the elevator car, no matter how high it is.
(And if you think this is pure fantasy, a competition to test this portion of the concept was conducted by NASA earlier this month — see http://www.spaceelevator.com or the NASA Web site for a report of this.)
A limitation on this concept is the strength of the cable on which the elevator would ride. Carbon nanotubes, a relatively recent discovery, marginally have the tensile strength to accomplish this. Of course, for objects with less mass and gravity than Earth, such as the moon or Mars, carbon nanotubes are strong enough to build such structures.
What would a trip on such a space elevator be like?
We arrive at the spaceport, where we see something like a large elevator car attached to a thin strand of cable. We look up into the clear sky and realize the cable simply goes up and up until it is out of sight.
“Wow, whatever that cable is attached to, it must be way up there,” we remark to the operator.
He looks at us oddly and replies, “It isn’t attached to anything.” Huh?
We enter the car and start our ascent, which, in contrast to a rocket ride, can be taken at any pace we wish. We can watch Earth recede below us while dining at our leisure, if the car is large enough to support a restaurant.
As we ascend, we notice we are feeling lighter in our seats until we reach an elevation of a little more than 22,000 miles, where we are completely weightless.
This is the elevation at which geosynchronous satellites reside, which we see as a string of reflecting points of light stretching away from us.
It sounds intriguing to me. Who wants to go?