Centrifugal Force and the Space Elevator???

Question

Me and a buddy are having a debate about the space elevator. He says the Space Elevator is a faulty design because centrifugal forces would propel everyone upward, which would make launching anything off of the elevator fly off to space. Is he wrong or right?

Answer 1

Your both right.

A space elevator is (in most cases) a very long nanotube wire stretching up from the surface right into orbit. Usually such a construction would fall to Earth due to gravity which is why a counter weight would be attached to the end of the line. The counterweight would have to be in slightly above geosynchronous orbit but going around geosynchronously so as to provide enough of a tug to support the weight of the line. To actually be able to carry payloads up the line the tug must be greater, so the the counterweight would need to be in an orbit far out enough to go flying out of Earth's orbit if it weren't attached to the line. Any object released from the counterweights location in space would fly away appearing to float away in the opposite direction of the Earth from the perspective of a person on the counterweight.

This is not a flaw in its design however. A station or waypoint at the geosynchronous point along the line could pick up payloads and then send them on their way to any point around the Earth with enough energy. If you wanted to escape the Earth's gravity then the counterweight's inherent propulsion of objects into space would be a good thing. However bringing mass up the line would take some altitude from the counterweight and some so the line wouldn't be as taught and the counterweight would begin to slowly drift behind the Earth's rotation. It would need to be constantly moved around to keep it in just the right position relative Earth.

Answer 2

A space elevator, like anything in orbit, would balance centrifugal force with gravity.

To make a space elevator, we would most likely need to position a carbonaceous asteroid in geosynchronous Earth orbit over the equator.  A cable made of of carbon nanotubes would have to be manufactured from there and lowered to the earth.  The center of gravity of the entire thing would remain in geosynchronous orbit, and wouldn't even need to be physically connected to the earth..  Carbon nanotubes would be required because it is the only thing capable of withstanding the stress.  We would probably have to clear everything else out of earth orbit, however, since a collision with the cable would be inevitable over time.

Answer 3

He's partly right. The centrifugal force is only stronger than gravity above the region of geostationary orbit. Anything let go above that region would proceed to fly upwards into a higher orbit. Anything let go below it would fall back down towards the Earth and may either impact the Earth or go into a lower orbit depending on the height at which it is released. The acceleration would also vary with the height, so something let go lower down below geostationary orbit would start falling faster than something let go higher up below geostationary orbit (but would achieve a lower final speed), and something let go farther above geostationary orbit would 'fall' upwards faster than something let go closer to but still above geostationary orbit.

In practice, things flying outwards would not be a major issue in the construction of a space elevator. The main counterweight to hold the cable out from the Earth would probably be built just a short distance above geostationary orbit, so people inside would feel only a very small acceleration and would 'fall' upwards from the Earth (towards the floor of the counterweight, which would be a sort of space station) very, very slowly. Extending the cable beyond the main counterweight wouldn't work very well, because a flexible cable (and just about all materials are flexible over distances of hundreds of kilometers) would eventually be pulled down by the rotation of the whole assembly until it was simply trailing the counterweight in a curve approximating geostationary orbit. Although this means that a rigid pole would be necessary to use the centrifugal force for launching purposes, at the same time it raises the intriguing possibility of building a whole ring around the Earth, at a level just above geostationary orbit, and connecting many space elevators to it; cablecars could then travel from one space station to the next along this ring.

Answer 4

The only way a space elevator could work is if the upper platform is in geosynchronous orbit, of course, and in any object that is in orbit, centrifugal force is exactly balanced by the gravity of the massive body it's in orbit around. Thus, the people on board the platform would be weightless. Your buddy is mistaken.

Answer 5

Geosynchronous elevation is about 21,000 miles. Below that you need to pull your way up the rope. When you begin climbing, you must pull with the same force as if you were climbing a rope suspended from building. The force needed to climb decreases gradually because of the increasing centrifugal force.

If you let go below 21,000 miles, your orbit's apogee will be the height where you let go, and the perigee will be lower. To circularize the orbit, you would use rocket propulsion to increase you speed at apogee. If you let go too soon and don't have a rocket to raise your perigee, you will burn up in the atmosphere.

If you continue to hold onto the rope above 21,000 miles, centrifugal force will propel you faster and faster until you let go; then your orbit's perigee would be the height where you let go, and the apogee would be higher.

The counterweight that holds the elevator up will probably be two or three times higher than 21,000 miles, depending on how massive it is.  

Answer 6

I'm sure there will be alot of braking on it....a long ways to go anyway, like anchoring the top part also........

http://www.space.com/businesstechnology/...

http://www.space.com/businesstechnology/...

http://science.nasa.gov/headlines/y2000/...