Is a Purely magnetic (NO CABLING) Space elevator possible?

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birchoff
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Is a Purely magnetic (NO CABLING) Space elevator possible?

Post by birchoff »

** Cross post from NSF Advanced Concepts.

Humor me for a minute. I just skimmed this thread to make sure someone hasnt asked this question yet and didnt find anything.

Instead of trying to build a cable strong enough to support a space elevator. Why not build a space elevator without a cable. The following link popped up in my facebook stream

https://www.youtube.com/watch?v=-fNK_lhAorM#t=45

with the following comment.
So why can't we bypass the space elevator concept all together and expand on computer controlled magnetic levitation. One solar powered platform in LEO and another floating at sea, and precision lift, levitate and transport containers, all day.
Anyone see why a macro scaled version couldn't work - payloads would be bigger than a rockets.
Now I understand the problem comes down to whether or not one could project a magnetic field in a column from the surface of the earth to some point in space. But power is definitely not going to be a problem. If necessary we could take existing nuclear fission technology and leverage it to build the requisite power station needed to provide the electrical energy needed to power the ground station. Hell we could even pipe via lasers or microwave the energy needed for the in-space anchor. The only problem I can see with this idea is whether or not magnetic fields can be concentrated and forced to basically go straight up in a column. That is a question I do not know the answer to. Though some rudimentary googling (https://www.google.com/search?q=concent ... 2&ie=UTF-8) shows it is not completely ridiculous to attempt to do something like this with magnetic fields.

DeltaV
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by DeltaV »

The column aspect ratio for something like that would be roughly 100000:1 (say, 300 km:3m). Seems very improbable for magnetic fields.

A charged, artificial plasma belt at orbital altitude, used to attract an oppositely charged payload might have a better chance, but that high of an E gradient would probably screw up the climate/magnetosphere/Van Allen belts/...

Hmmmm...

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birchoff
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by birchoff »

DeltaV wrote:The column aspect ratio for something like that would be roughly 100000:1 (say, 300 km:3m). Seems very improbable for magnetic fields.

A charged, artificial plasma belt at orbital altitude, used to attract an oppositely charged payload might have a better chance, but that high of an E gradient would probably screw up the climate/magnetosphere/Van Allen belts/...
Well I dont for a second assume that the numbers would be extreme. But I am forced to wonder, compared to solving the materials science problem; wouldnt it be simply to figure out how to levitate something in a similar way without the cable. even if we need to loft up a small number of Air ships that use microwave/laser power to drive their sections of magnetic column.

hanelyp
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by hanelyp »

Every magnetic levitation system I've seen uses a near field effect. The levitation gap comparable to or small compared to the device. Long distance is very hard when the field from a magnetic dipole isn't very directional and diminishes as r^-3 beyond the near field.

The closest viable concept I've seen to a magnetic space elevator is magnetic levitation of an electromagnetic catapult, one side of a current loop running along the catapult and the return along the ground underneath (split into 2 parallel runs to help system stability). This fills the entire space between the catapult and ground support, and a fair space on all sides, with the supporting magnetic field.

A microwave beam could support a weight, but requires an enormous power, reduced by system Q of the energy recirculating.
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D Tibbets
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by D Tibbets »

I'm no expert but I seriously doubt that this could work. The inverse square law for electromagnetic forces precludes much acceleration or levitating (matching the gravitational acceleration in the opposite direction) beyond short distances from the magnet source. Of course, if you could develop a laser for magnetic force- a maser...ops, that is taken for microwaves, how about a Baser (for B field). If you could do this then there would be a potential for great changes in various things, not just orbital insertion.
Magnetic rail guns act locally, and you can accelerate things to fairly high speeds, perhaps ~ 7,000 MPH, but this is under tremendous acceleration. It works for very tough artillery shells but would squish any person or current satellite . You can stretch this out though with a long rail, such as running it up the side of a mountain. Such might reach orbital speeds and have been studied multiple times. They might even be practical on small moons and asteroids, but have not been pursued for Earth launch. Placing the rail vertically is impractical for several reasons, and going the extra step of levitating many stages for incremental acceleration of a payload with each stage supporting itself above the lower stage would be a tremendous challenge, even if it could be made to work, the engineering and power requirements would be stupendous.

Also, keep in mind that you not only have to elevate the payload to high altitudes- perhaps several hundred miles, you have to also accelerate it to orbital speed- ~ 17,000 MPH so that it is in free fall. I'm uncertain how this is accomplished with a space elevator, except that the inertia of the top tether has to be maintained, otherwise as the payload is lofted and accelerated laterally, the tether will descend and slow. Centrifugal force and other considerations apply but I have not delved deeply into it.

The Earth's magnetic field might be used as it is so big, it could continue to push despite greater distances, but the beginning strength of the Earth magnetic field is so weak, you cannot even get off the ground initially.

One problem with long rail guns up the side of a mountain is that you are still in pretty dense air, accelerating to orbital speeds at low altitude would result in considerable rapid frictional heating. As such, using a magnetic rail launcher might replace the first stage to boost speed to a few thousand MPH, with chemical rockets completing the job. The question then becomes the cost and other limitations- such as the need to launch into different inclined orbits.

Dan Tibbets
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krenshala
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by krenshala »

Heinlein's idea was to use a series of magnetic coils instead of rails to launch things into orbit. Of course, the launch system did things like run up the side of a mountain over a span of miles to get the vehicle up to escape velocity. He also proposed using the same ring system to "catch" the vehicle and slow it back down allowing for sub orbital ballistic travel in addition to putting things into orbit. Of course, he mentions the very large energy requirements for this in most of the books where he describes it (The Moon Is A Harsh Mistress being one of them).

alexjrgreen
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by alexjrgreen »

Not sure why you would (very expensively) fight your way up to 40 km when a few thousand cubic metres of Helium will do the job for you...
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Skipjack
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by Skipjack »

alexjrgreen wrote:Not sure why you would (very expensively) fight your way up to 40 km when a few thousand cubic metres of Helium will do the job for you...
Its not about the altitude, but the speed. Altitude does not change much. You can optimize the nozzle for vacuum and stuff like that, which helps, but that's about it.

alexjrgreen
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by alexjrgreen »

Skipjack wrote:
alexjrgreen wrote:Not sure why you would (very expensively) fight your way up to 40 km when a few thousand cubic metres of Helium will do the job for you...
Its not about the altitude, but the speed. Altitude does not change much. You can optimize the nozzle for vacuum and stuff like that, which helps, but that's about it.
It's so much easier to accelerate - air density is close to zero at 40 km.
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Skipjack
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by Skipjack »

alexjrgreen wrote:
Skipjack wrote:
alexjrgreen wrote:Not sure why you would (very expensively) fight your way up to 40 km when a few thousand cubic metres of Helium will do the job for you...
Its not about the altitude, but the speed. Altitude does not change much. You can optimize the nozzle for vacuum and stuff like that, which helps, but that's about it.
It's so much easier to accelerate - air density is close to zero at 40 km.
Drag losses are only minor.

D Tibbets
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by D Tibbets »

Drag losses are minor at 40,00 feet, for low Mach speeds, but not at sea level. Even at 40,000 feet the drag will melt aircraft wings at 3-4 Mach if given enough time. At Mach 25 (~ orbital speed, at 40 thousand feet the aircraft might explosively disintegrate, just as a modest meteorite will. You gave to get much above 40,000 feet before you start adding speeds much above a few thousand MPH. Admittedly, a very fast bullet can plow through the lower atmosphere and survive, but concessions have to be made to heat shields, etc. I'm sure the numbers have been crunched for a low angle ballistic shot to reach free fall outside the atmosphere, and I suppose it is achievable, with the penalty of addition weight for heat shielding and structural integrity.

This is somewhat drifting from topic though. I think a space elevator on a cable with tremendous tensile strength works by being dragged along with the Earth's rotation, and the distal end is prevented from falling and also keeping up with the Earth's rotation by the centrifugal effect of the high end mass. The tension holds everything together. A magnetic levitating arrangement does not have this tension, and so I do not see how it could operate. Levitation conceivably could work, but how to keep the many free suspended stages aligned with the associated increased height and associated increased lateral speed related to the centrifugal/centripetal effect?

Dan Tibbets

Dan Tibbets
To error is human... and I'm very human.

mvanwink5
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by mvanwink5 »

What about punching a hole in the atmosphere to basically rarify the air in the rocket path, thereby avoiding drag?
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Betruger
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by Betruger »

What scheme would make that an economical proposition?
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mvanwink5
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by mvanwink5 »

Accelerate the vehicle from land. Perhaps ionize the air in front of the rocket to momentarily rarify the air to avoid heating of the rocket from drag. Just brain storming. Probably just too crazy. :lol:
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Skipjack
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Re: Is a Purely magnetic (NO CABLING) Space elevator possibl

Post by Skipjack »

D Tibbets wrote:Drag losses are minor at 40,00 feet, for low Mach speeds, but not at sea level. Even at 40,000 feet the drag will melt aircraft wings at 3-4 Mach if given enough time. At Mach 25 (~ orbital speed, at 40 thousand feet the aircraft might explosively disintegrate, just as a modest meteorite will. You gave to get much above 40,000 feet before you start adding speeds much above a few thousand MPH. Admittedly, a very fast bullet can plow through the lower atmosphere and survive, but concessions have to be made to heat shields, etc. I'm sure the numbers have been crunched for a low angle ballistic shot to reach free fall outside the atmosphere, and I suppose it is achievable, with the penalty of addition weight for heat shielding and structural integrity.

This is somewhat drifting from topic though. I think a space elevator on a cable with tremendous tensile strength works by being dragged along with the Earth's rotation, and the distal end is prevented from falling and also keeping up with the Earth's rotation by the centrifugal effect of the high end mass. The tension holds everything together. A magnetic levitating arrangement does not have this tension, and so I do not see how it could operate. Levitation conceivably could work, but how to keep the many free suspended stages aligned with the associated increased height and associated increased lateral speed related to the centrifugal/centripetal effect?

Dan Tibbets

Dan Tibbets
A rocket only spends a short time in the dense atmosphere and then it does not matter anymore.

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