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Space lift

Date: Wed Sep 18 13:33:07 1996
Posted by: Tony Hanscomb
Grade level: nonaligned
School/Organization: No school given.
City: No city given. State/Province: No state given.
Country: No country given.
Area of science: Astronomy
Message ID: 843071587.As

Message:

Dear Sirs The following could be a good idea or could be completely mad ! My idea is as follows: A very strong concrete foundation is attached to "Earth" a cable made of some increadably strong material is attached on to a giant powered pully wheel, the capble runs out into space aprox 400 miles ! it is attached to a heavy geostationary satelite (which if not teathered to the cable, at that height would fly off into space) the cable is returned to the pulley to complete a loop, A presurised capsule is attached to one pully and a counter balance attached to the other end. The only energy required to move the capsule into space would be enough to overcome friction and some others such as gaining momentum etc. Will it work ? Tony Hanscomb.


Actually, you are not completely mad. Just a little Mad. ;-)

This sort of idea was dreamed up (as far as I know) by none other than Arthur C. Clarke, the author of "2001: A Space Odyssey" and numerous other works. Clarke is a gifted scientist, as well as a "lateral thinker": he can come up with odd solutions to problems. He was the first to realize the practical applications of a geosynchronous satellite, for example.

A geosynchronous satellite has an orbit of exactly one day. At a height of about 40,000 kilometers above the Earth, the natural orbital period of an object is one day. Anything orbiting at this distance will appear to "hover" over one spot on the Earth.

In his novel "Fountains of Paradise" Clarke uses that idea: take a cable 40,000 km long and drop it from the satellite to the spot directly underneath it on the Earth and secure it. From there you can build an elevator which will take you into orbit!

The biggest problem with this idea is with the strength of the cable supporting the elevator. There is no technology we know of that can create a cable of that length that can support its own weight. Imagine how much even a nylon rope would weigh if you had that much of it! It would shred to pieces under the strain. Clarke avoided this by dreaming up an almost magical type of cable which was a chain only one molecule thick, but incredibly strong (Larry Niven uses much the same type of cable in a lot of his stories as well). Unfortunately, we can't make something like that now, so (as always) we have to wait for reality to catch up with our imagination.

As an aside, there are several more problems to overcome even if you have this magic cable. Imagine you start at the satellite and have a spool with all the cable you need. You start to unroll it, letting the end drop towards Earth. You'll quickly discover a problem: the cable will want to orbit the Earth at a different speed than the satellite! This is because orbital speed depends on your height above the Earth (specifically, your distance from the Earth's center). As the tip drops from the satellite, it wants to go faster; it will actually try to pull the satellite into a faster orbit. You'll need a rocket on the satellite to keep it stationary.

Worse, each part of the cable will want to orbit at its own speed. The tip will want to move fastest, and the part near the satellite slowest. This will increase tension on the cable, meaning you'll need a stronger cable. Actually, applying a series of thrusters every mile or two along the cable may ease this situation, much like having a telephone pole every few tens of meters along a telephone wire to help support the weight of the wire. Actually, tides induced by the Earth will want to straighten the cable out which will help the situation somewhat. I have a description of how tides work on my homepage; click here to see it.

Even though this idea has been around a while, it was very clever of you to come up with it independently; it took the genius of Clarke to see it first! Keep thinking about things like this and please keep asking questions. You never know what hasn't been done yet.

Note added March 20, 2002: An alert Bad Reader pointed out to me that NASA is investigating space elevators, at least theoretically. The recent advances in nanotube technology may be a boost needed to make elevators a reality. Check out this page on the TechTV website.



©2008 Phil Plait. All Rights Reserved.

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