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Fraser
2005-Oct-26, 06:41 PM
SUMMARY: Eleven teams competed in two competitions over the weekend to test technologies for space elevators: beam-powered climbers and new ribbon materials. The climbers needed to scale a 61-metre (200 foot) ribbon within a time limit. Although one climber reached 12 metres (40 feet), it wasn't enough to win the $50,000 prize. In the ribbon competition, competitors needed to create a material that was 50% stronger than the house tether. One team came close, but it wasn't enough. Tougher challenges will be back next year with bigger prizes.

View full article (http://www.universetoday.com/am/publish/no_winner_elevator_competition.html)
What do you think about this story? post your comments below.

publiusr
2005-Oct-26, 09:02 PM
Doesn't surprise me a bit.

We need to build--not bash--rockets.

GBendt
2005-Oct-27, 10:58 AM
Hi,

this space elevator concept cannot function. I am sure that NASA knows it, and everybody with some knowledge in physics knows it too. Perhaps they foster the idea of the space elevator to find out how long it will take until someone realises that this space elevator is nothing but a joke.

If you put a satellite on a geosynchronous orbit, the angular speed of this satellite is the same as the angular speed of the earth below, as both perform one revolution in 24 hours. Seen from the earth, this satellite seems to be fixed to the heaven above the location on the ground from where it is seen.
But it only seems to be fixed. In fact, this satellite orbits the earth at a speed of some 9400 km/h. At that orbital speed at the height of this orbit, the centrifugal force balances the weight of the satellite at that orbital height, and thus the satellite stays in its geostational orbit that has the desired angular speed.
If you tie a rope to the satellite, the weight of the rope will pull the satellite down from its orbit, closer to earth. The angular speed of the satellite will increase by this and such the satellite leaves its seemingly "fixed" position which it held above a spot on the earth´s surface. As the rope is tied to the ground and as the satellite is fixed to the other end of the rope, this rope will force the satellite to hit the ground soon. This space elevator will be a literally "smashing" failure.

Some people may argue that the rope is weightless because it is in space. But they are wrong. Gravity works in space, too. If you fix a rope between earth and a satellite which orbits the earth, every piece of this rope will face a different gravitational potential, and this will require each part of the rope to follow its own orbit. The resulting force on the rope will pull the satellite down and will pull the rope to pieces.

And even if the rope were weightless, you still have to accelerate the elevator as it climbs up the rope, to compensate for the coriolis effect: The spot on the ground where the elevator starts from is moving at a horizontal speed of less than 1666 km/h, which is much slower than the horizontal speed of 9400 km/h which are required at the "upper station satellite" on its geostationary orbit.
And of course, the elevator and everything it carries must not have any mass at all, as the weight of this mass would pull on the rope and the satellite ...

There is no chance for a functioning space elevator which uses a rope and a satellite. The only space elevator that really works is a rocket.

Regards,

Günther

Wouter Tierens
2005-Oct-27, 02:57 PM
GBendt, there should be some sort of counterweight slightly above the geosynchronous orbit.

Fraser
2005-Oct-28, 04:16 PM
Yeah, the point of a space elevator is that you put counterweight above the geosynchronous orbit so that it provides a countering force to the weight of the cable, climber, etc. The proposal I've often heard is for a small asteroid.

GBendt
2005-Oct-29, 02:08 PM
Sorry,

this does not work. You can´t place a counterweight at a location above a geosynchroneous orbit with the intention that it counterbalances anything that has to cope with forces while it is orbiting in a geosynchroneous orbit.

If you intend to apply a "Lagrange 1" condition, the "counterweight" must be put in a geosynchroneous orbit. But that counterweight would have to be extremely massive to function properly: a couple of millions or billions of tons.

Where to get that from, how to put it there, and how to keep this body staying at this orbit safely? At what time, by which means, at what cost?:whistle:

I think, rockets are a lot safer, viable and cheaper, and a much less dangerous means to transport things into space.

Regards,

Günther

galacsi
2005-Oct-30, 06:46 PM
Sorry,

this does not work. You can´t place a counterweight at a location above a geosynchroneous orbit with the intention that it counterbalances anything that has to cope with forces while it is orbiting in a geosynchroneous orbit.

I dont undestand why . You have three points: the counterweight ,the station on geosynchronous orbit and the anchor point on earth.
The three points have the same angular speed.
So Centrifugal force on the counterweight can balance the weight of the cable and and pull on the anchor point.

Anyway i have the same opinion than you , this contraption is impossible.

How to built it ? When the cable is put down it will be offset by coriolis forces. and you have in the same time to build your counterweight !

And how to prevent a plane or a satellite to cut the cable ?
If the the cable is cut all the system , station cable and counterweight go to deep space. The remaining cable crash on earth ! Look out for your head !

GBendt
2005-Oct-30, 11:51 PM
Hi Galacsi,

The station on geosynchronous orbit has the same angular speed than the ground station. This is so, because at exactly that distance which the station on geosynchronous orbit has from the earth´s center of gravity, the gravity force is such that it requires a speed of about 9400 km/h to create a centrifugal force to exactly balance gravity and which atthe same time causes the station to move at the same angular speed than that of a point on the surface on earth below.

If you reduce the radius of the orbit, the pull of gravity will become stronger, as the distance to the earth´s center of gravity is reduced (Remember the formula for the calculation of gravity force...). Therefore, the station has to orbit faster in order to create a greater centrifugal force which compensates this greater pull of gravity. As a result of the increase of speed, the angular speed of the station will increase in relation to that of the ground station below, and thus it will overtake the ground station. With time, the orbiting station will be seen from earth to leave the fixed position it used to hold. It will approach the eastern horizon and sink beyond it. After some time it will reappear above the western horizon. But if the orbiting station is fixed to the ground by a cable, this cable will be wrapped around the globe, forcing the orbiting station to smash to ground somewhere to the east.

On the other hand, if the radius of the orbit is increased, the pull of gravity from earth will become weaker, as the distance to the center of gravity is increased. Therefore, the station must orbit slower to create a lesser centrifugal force to compensate this lesser gravity pull. As a result, angular speed of the station will decrease in relation to that of the ground station below, and will lag back behind the ground station. With time, the orbiting station will be seen from earth to leave the fixed position it used to hold. It will approach the western horizon and sink beyond it. After some time it will reappear above the eastern horizon. If the orbiting station is fixed to the ground by a cable, this will be wrapped around the globe, forcing the station to smash to ground somewhere to the west.
It is essential to keep the orbiting station on a geosynchroneous orbit, and this means to keep it constantly at the radius where the orbiting speed creates the same angular speed than does the rotation of earth for a point on its surface.

Consider a counterweight which is orbiting above the station which is on its geosynchroneus orbit. The radius of the counterweight´s orbit is greater than the radius of the station´s orbit. So the pull of gravity which the counterweight feels is lesser, and so the counterweight will orbit slower than the station. Therefore the angular speed of the counterweight will be lesser than the angular speed of the orbiting station. So there will be a growing gap between the two, and the counterweight will not be able to act as a "counterweight" for cable and climber at all. So, there is no use in placing that counterweight up there.

Only a body which orbits at exactly the radius that is required for geosynchroneousity will move at the same angular speed than that of a spot on the ground below (and stay in that orbit!).
Neither the cable nor the climber can meet this requirement, and the "counterweight" cannot meet it either.


Regards,

Günther

01101001
2005-Oct-31, 12:41 AM
On the other hand, if the radius of the orbit is increased, the pull of gravity from earth will become weaker, as the distance to the center of gravity is increased. Therefore, the station must orbit slower to create a lesser centrifugal force to compensate this lesser gravity pull. As a result, angular speed of the station will decrease in relation to that of the ground station below, and will lag back behind the ground station. With time, the orbiting station will be seen from earth to leave the fixed position it used to hold. It will approach the western horizon and sink beyond it. After some time it will reappear above the eastern horizon. If the orbiting station is fixed to the ground by a cable, this will be wrapped around the globe, forcing the station to smash to ground somewhere to the west.

You seem to be neglecting that that the station is attached to Earth by a fixed-length tether. If it moves away horizontally from its attachment point, then it must also move lower in vertical distance.

GBendt
2005-Oct-31, 12:33 PM
Hi '01101001',

I wanted to demonstrate that the orbital speed of a body which orbits a planet is only a function of gravity.

The space elevator concept assumes that a tether is linked between a fixed point on earth and a geosynchroneous orbiting station. The weight of the tether is meant to be compensated by a counterweight that is to orbit above the geosynchroneous station. The point on the ground, the tether, the orbiting station and the counterweight are all meant to move permanently at the same angular speed.

However, such a design does not comply with the Kepler laws, and thus the technical setup for this elevator is not be able to function. A lesson in gravitational astronomy might be useful to learn the difference between science and fiction.

Regards,

Günther

Grey
2005-Oct-31, 04:20 PM
Consider a counterweight which is orbiting above the station which is on its geosynchroneus orbit. The radius of the counterweight´s orbit is greater than the radius of the station´s orbit. So the pull of gravity which the counterweight feels is lesser, and so the counterweight will orbit slower than the station. Therefore the angular speed of the counterweight will be lesser than the angular speed of the orbiting station. So there will be a growing gap between the two, and the counterweight will not be able to act as a "counterweight" for cable and climber at all. So, there is no use in placing that counterweight up there.This is where you're missing he point. The counterweight will move faster than it would freely orbit at that height (the tether needs to be rigid to accomplish this, I think), in order to keep pace with the geosynchronous station. Viewed in the rotating frame, that means that there will be an additional centrifugal force on the counterweight, and you can choose this to be just right to balance the weight of the tether from the ground.

Now, it may indeed be impossible to create a space elevator, but if so, it will be because of engineering problems or an inability to create materials that can withstand the forces involved, not because the basic physics is unsound.

akirabakabaka
2005-Nov-02, 09:28 PM
Why hasn't the company (http://www.liftport.com/) spending hundreds of millions of dollars to develop this technology figured out such simple physics? Why havn't any of the attendees at the international space elevator conference (http://www.isr.us/Spaceelevatorconference/) figured this out either? Just wondering if you've looked at any of their material yet, GBendt.

Check out the FAQ: What are some frequent Space Elevator misconceptions? (http://www.liftport.com/faq1.php#basics4d)

SolusLupus
2005-Nov-02, 09:40 PM
I still say we need to get rid of rockets. They're way too expensive, they're practically huge bombs that we sit a little rocket on the top of... there's a lot of problems. I say that the solution will be a giant railgun. shoot for the stars!

akirabakabaka
2005-Nov-02, 10:00 PM
It's unclear to me why the government or NASA doesn't appear to be seriously considering the space elevator, and would apparently rather spend hundreds of billions of dollars on an inferior method of transport. Oh wait now that I think about it, how much of that money goes to Boeing and the JPL?

publiusr
2005-Nov-02, 10:03 PM
That and their craft actually **work** might have something to do with it, too.

akirabakabaka
2005-Nov-02, 10:07 PM
Theoretically the space elevator 'actually works' too. And it's expected to cost much less than a new shuttle to build, and would be capable of carrying a significantly larger payload for a significantly reduced cost.

If you're going for the old addage of "if it ain't broke..." I think plenty of people would rebutt the claim that the shuttles aren't broken. ;) Don't get me wrong, shuttles are shiny and cool, but are they really necessary?

publiusr
2005-Nov-02, 10:43 PM
I prefer we save money by building HLLV instead of shuttles. You need HLLV for space elevators, which will probanbly cost far more than any launch vehicle.

trinitree88
2005-Nov-18, 01:50 AM
One of the recent surprises in materials science has been the emergence of malleable ceramics. Great advances have been made in prevention of microscopic crack propagation. For the elevator, though, I suspect either titanium wire, or a high strength alloy of titanium will be tried.
In recent years, a diamond was synthesized out of pure carbon-13, with substantially improved (though expensive) physical properties over mundane carbon-12. So, it might behoove elevator enthusiasts to buddy-up with material scientists, and do some isotopically pure wires. Isotope separation also has come a long ways in the last decades, though the best techniques are understandably guarded. Crack propagation in metals is oft associated with trace inclusions of impurities....no impurities, higher Young's modulus for the wires. Ciao. Pete.:think:

Relmuis
2005-Nov-18, 12:36 PM
Perhaps a counterweight is not needed.

A satelite orbiting the Earth in a circle is kept in orbit by the centripetal force, a force which is always pointing to the centre of the circle. Normally, all of this force is provided for by the Earth's gravity, but there is nothing to suggest that part of this force could not be provided for in another way. For example by a rope pulling the satelite towards the Earth.

For the satelite to be in geosynchronous orbit, the total force F (in Newtons) must be equal to M*(4*pi*pi*R)/(T*T), where M is the mass of the satelite (in kilogrammes), R is the distance to the center of the Earth (in meters) and T is the orbital period (one day) in seconds. If you want to increase F while keeping T the same, you must increase R. So, if you make the satelite orbit just a bit higher than normal geosynchronous orbit, the pull of the rope will complement gravity in just the right amount to make the orbit geosynchronous. Everything will be in equilibrium without need of a counterweight.

Of course, the right distance depends of the mass of the satelite. This is different from the normal situation, where gravity is the only force keeping it in orbit. The force of gravity is proportional to the mass of the satelite, which can therefore be divided out of the equation. But here the allowable mass of the satelite is dictated by the tensile strength of the rope.

NEOWatcher
2005-Nov-18, 02:09 PM
Perhaps a counterweight is not needed.
snip
I think you just re-phrased moving the center of gravity at or above the GeoSync. [my layman understanding] This translates into a smaller and smaller counterweight (ie satellite) the farther and farther it is. Until it's far enough that the weight of the rope is what is providing the counterweight. But; the longer the rope, the more potential for failure and possibly the stronger the rope will need to be [/my...]

akirabakabaka
2005-Nov-18, 03:35 PM
I agree NEOWatcher.. you probably could do it without a counterweight, but it makes the whole thing a lot less practical.

LurchGS
2005-Nov-21, 05:30 AM
I've mentioned it elsewhere - take a look at Dr Forward's Rotavator (actually, it was invented by a russian, but Dr F gave it the name by which I know it). The math is sound

Big Brother Dunk
2005-Nov-21, 07:06 AM
Just a note to say the the most successful team was from the University of Saskatchewan here in Saskatoon!:cool: