[Zerogouki]

I still have absolutely no idea what the fuck you're talking about.

[Prosthetic Conscience]

Zerogouki, the idea is that the loop is moving so fast that the centrifugal force on it, as it goes in an arc around the centre of the earth, balances the force of gravity on it. This is the same way that a satellite in orbit stays up - the centrifugal force on it exactly balances gravity. With the loop, the centrifugal force on the 'rotor' inside the loop also has to hold up the weight of the sheath that surrounds it (and holds it in a friction-free vacuum), so the rotor has to go faster than orbital speed. Magnetic fields keep the rotor and the sheath apart (that's the 'maglev') part.

The wikipedia article says the 'rotor' would move at 14km/s. The centrifugal acceleration on it would be v*v/r, or 14000*14000/6458100 = 30 m/s/s. That compares to the gravitational acceleration of about 10 m/s/s, so it could hold up a sheath that weighed about twice as much as the rotor.

I think the whole thing sounds like an engineering nightmare. The "$6 billion" price tag is laughably small. For instance, the budget for the 2012 Olympic games is $13.6 billion. Even before you start turning the rotor, you have to lay out a continuous belt of steel, encased in an airtight sheath with magnets in, over a 2000 km stretch of equatorial ocean (presumably the Pacific), and keep it in one piece without, say, ships or whales running into it. Or storms breaking it up. And it won't 'levitate' until it's fully up to speed (it'll just become lighter as it speeds up), so you've got this thing with the energy of an atomic explosion sitting on the ocean surface until it has reached its working speed.

Since building a border fence costs $4 million per mile, it'd cost $10 billion just to lay out a simple fence that's 4000km (2500 miles) long. Compare that with making an airtight tube with a continuous object inside, travelling at over 40 times the speed of sound, held by magnetic fields so that it never touches the walls, and I think you'll see the price tag will be a little more.

[RonPaulalways]

^ Thank you for infusing this thread with some hard numbers, good post.

[Igor Antunov]

Since building a border fence costs $4 million per mile, it'd cost $10 billion just to lay out a simple fence that's 4000km (2500 miles) long. Compare that with making an airtight tube with a continuous object inside, travelling at over 40 times the speed of sound, held by magnetic fields so that it never touches the walls, and I think you'll see the price tag will be a little more.

That's oversimplifying the scenario. The large hadron collider at cern cost $10 Billion, and it's certainly more ambitious and involved more technical expertise than a simple 4000km wall would. Perhaps things in the US are just overpriced, since the emphasis is on profit, not progress.

[Prosthetic Conscience]

And the LHC is a lot smaller than 4000km in circumference - just 27km.

But in the original paper on this, he just seemed to wave his hands and talk about using supports that monitor the waves and react to keep this sheath perfectly steady, at some unspecified height above the waves, over a 4,000km length. Presumably there'd have to be a barge every few hundred metres, with the sheath strung from barge to barge, and the barges capable of staying where they are, in the worst storms the area is capable of throwing at them. That would be an engineering feat beyond anything anyone's done in the world, so far.

[Igor Antunov]

Great wall of china says hi. Think thousands of great pyramids being built constantly for thousands of years. Nothing we have done since compares.

[Thunderhawk]

The great wall of China and even the pyramids are pretty simple to build compared to maintaining near perfect elevation over a 2000km span over an ocean.


Id rather build the thing in Canada, Australia or Eastern Russia with an East-West alignment.

[Igor Antunov]

It's all simple to build compared to designing a new microprocessor for example, but we are discussing those things that take most effort to build given available resources at hand.

[Zerogouki]

Zerogouki, the idea is that the loop is moving so fast that the centrifugal force on it, as it goes in an arc around the centre of the earth, balances the force of gravity on it. This is the same way that a satellite in orbit stays up - the centrifugal force on it exactly balances gravity.

Makes sense so far...

With the loop, the centrifugal force on the 'rotor' inside the loop also has to hold up the weight of the sheath that surrounds it (and holds it in a friction-free vacuum), so the rotor has to go faster than orbital speed.

The fuck?

[Prosthetic Conscience]

The fuck?

The 'loop' consists of a central belt that's moving very fast, and a sheath around it that's stationary. They have called the central belt the 'rotor' (because, I think, it's analogous to the rotor in an electric motor that moves while the magnets stay still).

So only one part of the loop, the belt, has centrifugal force on it, lifting it up. That force has to balance the weight of both the belt itself and the sheath. So it has to move faster than a satellite - in this case, it's nearly twice as fast.

[Zerogouki]

I still have absolutely no idea what you're trying to say. Drawings may be required.

[Igor Antunov]

Go outside, take a hose, connect it up to a tap with plenty of water pressure, let the water run, watch your hose take off flailing this way and that, being held up magically by the water running through it.

[Prosthetic Conscience]

Igor, I don't think your metaphor is helping. This has nothing to do with fluid flow.

Zerogouki, have you tried the Wikipedia article? They have a diagram of a cross-section, but unfortunately the small version is difficult to read, and the large one too large to post here. But here's the small one, and a link to the large one:



http://en.wikipedia.org/wiki/File:LaunchLoopRotor.svg

http://en.wikipedia.org/wiki/Launch_loop#Description

[Zerogouki]

*reads article*

Okay, that's slightly clearer than previous descriptions, which gave the impression of a giant macaroni noodle that was held aloft by the power of magic. However, this is still making even less sense to me than Time Cube.

[nilof]

Imagine this ball sliding against a nice circular wall. As the wall forces it inwards, the ball exerts a force outwards.

Replace the ball by a long belt that slides along the wall. It would then exert a constant pressure on the wall.

This loop works roughly the same way, by making a belt run inside the sheath pressuring it outwards.

p.s: I know, I suck at ms paint.