Can magnetic repulsion be used for a space elevator instead of carbon nanotubes?

[TeeGee]

I was thinking today after watching a brief documentary on space elevators that even if we can find a way to attach long strands of nanotubes together, we still need to make it long enough to reach GSO.

So I began to wonder, why not use magnetic repulsion from Earth to GSO? Can a magnet be used on both a pusher plate and Terran base that repulse eachother that can push the plate up into GSO? Can magnets repel eachother at that distance?

For example; a mobile free floating plate with a giant magnet on its belly is facing another magnet on the ground. The magents are both charged with the same current (-- or ++) and repel eachother thus pushing the plate up. The magnet plate on the pusher has magnetic fins that are also charged and can steer inside the magnetic field like fins on an airplane to keep it inside the field.

Is this possible? How much energy will need to be used? How big will the magnets need to be?

[Darnok]

Main question from me is "how you want to solve stability problem, because magnetic field changes and fluctuates?"

[ZetaX]

Yes, it would be completely unstable unless stabilized in some way. Also, there is no known magnetic monopole, so "charged with the same current" makes no sense.

The field strength required would be enourmous. Well beyond what we can do, and well beyond what we should do (unless you want to fry every electronics on earth, and possibly some brains, too).

[SciMan]

Active control systems are a very good way to solve the stability problem. The instability thing only applies to magnetic fields that are not controlled, like permanent magnets.

The real problem would be power delivery, as there is a minimum kinetic energy required to maintain orbit, and magnetic fields don't work over long distances well.

Magnetic repulsion is two fields repelling each other, and both of those fields fall off as 1/R², which means that the force exerted by one field on the other one will fall off as 1/R⁴.

That means that for every doubling of distance, the same force requires the application of 16 times as much energy to both fields.

That gets really problematic really quickly, as we can only make magnets so strong before they either fly apart, overheat, or otherwise stop working.

In other words, it won't work. Magnetic fields as a force carrier are only a good idea over short distances.

A better idea would be using the carbon nanotube cable of the space elevator as a track for a magnetically-levitated elevator car propelled by linear induction motors, as carbon nanotube can be a good conductor of electricity.

Transmitting the power for the maglev and induction motor systems on the elevator car would be done thru other sections of the space elevator.

This would work because it only requires the magnetic fields to act over a short distance, requires no active controls on the space elevator itself, and uses the material of the space elevator that's already there to transmit the power needed by the car. All of these save weight which means you can either haul more stuff on the same space elevator or use a smaller space elevator to haul the same amount of stuff.

[Darnok]

@SciMan power delivery shouldn't be problem just put few nuclear power plants and transfer energy, using microwaves or other kind of radiation, to vehicle.

Or we could shot magnetic beam from Earth and build elevator that would climb it http://www.google.com/patents/US5929732

[ZetaX]

@SciMan power delivery shouldn't be problem just put few nuclear power plants and transfer energy, using microwaves or other kind of radiation, to vehicle.

Or we could shot magnetic beam from Earth and build elevator that would climb it http://www.google.com/patents/US5929732

You can't just magically transfer energy as microwaves: that will require excessive cooling and such. Anyway, I think you have a wrong understanding of the amount of power required... you might need Petawatts or more of power to get that thing into orbit, simply because of the scale of that magnet. Not speaking about the completely unsolved problem of how to turn that energy into a magnetic field (there is just so much a copper or superconductor coil can take, for both magnetic field density and power).

[Darnok]

But what do you want to send to orbit... Mount Everest? I was thinking about single human in suit and some light capsule per flight.

[ZetaX]

But what do you want to send to orbit... Mount Everest? I was thinking about single human in suit and some light capsule per flight.

Your human needs that huge magnetic device below his feet. And that device needs to create a magnetic field strong enough to push itself into orbit, with the other pole being hundreds of miles away. Think about the inverse square law (which is actually optimistic in the case of magnets).

[Redshift OTF]

Yeah, magnetic field strength decays very rapidly from its source. Some of the most powerful magnets made have a field strength that is not significant enough to push much mass beyond a few meters. Also, magnetic fields are very bulbous and round, you can't make a very long thin magnetic field. Your only hope is a rail gun type scenario but that would have its own problems.

[Darnok]

Your human needs that huge magnetic device below his feet. And that device needs to create a magnetic field strong enough to push itself into orbit, with the other pole being hundreds of miles away. Think about the inverse square law (which is actually optimistic in the case of magnets).

I was thinking about little help at take off

and magnetic rings tower that would push away each other to remain in same distance and would generate magnetic field to push vehicle up to orbit

[Aanker]

Although I am all for investigating suggestions such as these, it seems to me that it must be much simpler and less expensive to just further develop chemical rockets and enhance their safety, performance and reliability.

[RainDreamer]

I was thinking about little help at take off

http://t0.gstatic.com/images?q=tbn:ANd9GcQvEf5Rs__cutclp0ylcas7ZNoVO81JIpdEuy2E5aKr5YAvV95s

and magnetic rings tower that would push away each other to remain in same distance and would generate magnetic field to push vehicle up to orbit

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTK8rxQJWOCun9PCH4h8GYPAjhYZZ9PJWpB57CWIjzknzk7UVY8

Wouldn't that just be a rail gun?

[Darnok]

Wouldn't that just be a rail gun?

Very large one, but its structure would be few km high and hold by magnetic field rings generate... I know lots of power, but while you want to play with magnetic propulsion to orbit you have to think about huge power source first

[ZetaX]

I was thinking about little help at take off

http://t0.gstatic.com/images?q=tbn:ANd9GcQvEf5Rs__cutclp0ylcas7ZNoVO81JIpdEuy2E5aKr5YAvV95s

and magnetic rings tower that would push away each other to remain in same distance and would generate magnetic field to push vehicle up to orbit

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTK8rxQJWOCun9PCH4h8GYPAjhYZZ9PJWpB57CWIjzknzk7UVY8

That second pic looks suspiciously like ring transporters from Stargate

How would that tower work¿ For it to be relevant, that tower would need to be hundreds of miles high (and probably needs a diameter in the hundreds of meters). That's not only absurdely large, but if you can build that, then you probably could build a space elevator, too (or simply a staircase into orbit).

The lift-off helper would also only help at the point where least help is needed: at the beginning of ascent when the magnets are still close and thus strongly repelling each other.

[KSK]

Just throwing some numbers out here for comparison.

A really big superconducting magnet (plus its cryostat) for high field NMR spectroscopy weighs in at about 10 tons and puts out an 18.8 Tesla field. For comparison, the Earth's magnetic field is around 25-65 micro-Tesla depending on where you measure it.

Safety distance from the magnet - i.e. the distance at which important stuff like pacemakers are no longer affected by the field is about 1.5 metres. Now granted NMR magnets are narrow bore magnets configured to give a nice homogenous field within the bore rather than a big 'lets pull lots of random junk into my expensive magnet' external field but even so...

Magnetic repulsion over any sort of distance doesn't sound feasible.

[AngelLestat]

can someone make a graphic to understand what is the idea behing this ? with the angles and the magnetic fields lines..

Because from my point of view, it does not have much sense.

[TeeGee]

Ok so magnetic repulsion for a space elevator is not feasible, fine, but neither are carbon nanotubes.

Why don't we use high tensile cable or kevlar cable instead of carbon nanotubes? Put the anchor into GSO, drop the cable onto earth and start tying stuff to it and reeling it up again. Build the cables in sections, attach them together via hubs every few Km, and pull stuff up that way.

Edited July 15, 2015 by TeeGee

[ZetaX]

Why don't we use high tensile cable or kevlar cable instead of carbon nanotubes? Put the anchor into GSO, drop the cable onto earth and start tying stuff to it and reeling it up again. Build the cables in sections, attach them together via hubs every few Km, and pull stuff up that way.

Nanotubes are stronger than kevlar and such, so your suggestion (which is just "build a space elevator from something else") makes no sense. The whole point of nanotubes is that we may one day find a carbon based structure (graphene, for example) that is strong enough.

Also, you can't simply drop a cable from GSO.

[Amram]

Why don't we use high tensile cable.

composed of what? I hope you weren't thinking steel..... The problem is both strength and mass. Whatever material is used, it must be strong enough to support its own weight, which necessitates very low mass at very high strength of you are never going to have a "cable" reach GSO, let alone beyond it.

Important note: your anchor mass must be beyond GSO. If its in GSO, it contributes no counter-mass at all, and all of the mass below GSO will be suborbital and will fall and take the anchor with it. This eliminates trying to have a short length untethered that periodically lowers some cable to raise other bits, you'd leave orbit(one way or another...) if you tried, unless we aren't talking a pure space elevator but some unusual hybrid with active thrust to keep it up there..... If so, i hope you have a trick to get more fuel up there than the elevator burns trying to lift that fuel up there. If you don't have active thrust, your anchor must be beyond GSO, and if it is, but is not constantly tethered, then it will not remain in GSO as its center of mass is moving too quickly for the orbit its in, and it will enter an elliptical and otherwise useless orbit.

Go here, look at breaking strength: https://en.wikipedia.org/wiki/Specific_strength

Breaking strength is the length, in kilometers, of which you can have a vertical column that will be able to carry its own weight, we can't do it yet, even with nanotubes, we can't make them strong enough, yet. Of course that is compounded with us being unable to even adequately produce them, let alone sufficient quality.

Off the top of my head with no google-fu to back it: Kevlar would be better than steel I think, its light and has great tensile properties, which are necessary, but its still far too massive for a space elevator.

Now remember, that's just the breaking strength, which is, as noted the measure of how much of itself a column can hold up under earths gravity, but you need to double that when you are looking at your centerpoint, because everything below wants to fall, and everything above wants to rise, and the upward force is greater than the downward of the elevator will not be so for long.

We have nothing that is remotely feasible yet, but we do have a few promising materials that may work out after some lengthy R&D.

Edited July 15, 2015 by Amram