# Space elevator/tower through magnetic repulsion? What are the technical problems?

As more material weight leads to higher stress for a space elevator I have been asking myself if a kind of tower thats based on magnetic repulsion would not be an alternative. While I know that magnetic levitation can be hard to stabilize there are 2 scenarios I have in mind and which I am curious to what prevents their execution.

1. A series of disks is put on top of each other changing magnetic fields are induced in these disks(maybe the first disks induces a phase shifted version of its field in the disk above, or each disk generates the field independent of each other, or all disks above the first are permanently magnetic and rotate due to the magnetic field created by the base) the disk repel each other, the tower extends.

2. In a coil/spool an alternating current is induced such that one curl of the coil is pi in terms of frequency, such curls should repel each other(if I not misconstrued something)and as the spool stretches frequency is adjusted.

Even if such a tower might not be stabilized indefinitely, this still could be used to lift an object a certain distance and accelerate it at the same time(when placed on top of the tower during the "powering up" process)

So where did I go awry? Where are the problems an expert would point out?

• Note that a classical space elevator uses tension, not compression; the ends of the elevator are being pulled apart by the centrifugal force of the outer end rotating faster than its orbital speed at that altitude and gravity from the inner end rotating slower than its orbital speed. (Structures under tension are considerably lighter than structures under compression, in general.) Commented Jan 5, 2016 at 0:39
• If using compression, you end up pushing a 40000km long rope, and hoping it won't buckle. Good luck with that! Commented Oct 30, 2021 at 8:18

In theory, there is nothing wrong with a space elevator resting on the ground, instead of hanging from a counterweight. However, magnetic repulsion is relatively much weaker than the force holding materials together. The simple version first: grab two magnets, and try to push them together. That is relatively easy. After that, take a steel rod of comparable size, and try to stretch it. Not quite as easy.

The forces present in a space-elevator are enormous, but not the whole way. After all, the first meter does only have to take the weight of the payload, and can therefore be relatively thin. The last meter must take the weight of the payload, plus the entire elevator, and must therefore be a lot thicker. How large the increase in cross-section area is, is known as the taper ratio. If we accept that the size of magnetic discs increases over 3000 times over the whole elevator, a one kilogram magnet must still exert a force of 6 million Newtons at a one meter distance. (A Saturn-V hovering over a three kilogram magnet). We can have the discs closer, and that can reduce the requirements a bit.

If we follow this strategy, we can take advantage of another fact: It is actually repulsion between the electrons of your feet and the ground that keeps you from falling towards the centre of the Earth. That is, when the distance between the discs is sufficiently small, it is actually just as good to stack bricks on top of each other. Materials can tolerate a stronger tension than compression, so therefore the design of choice for a space-elevator is now a long tether hanging from geostationary orbit.

In a sense, space-elevators are already based on electromagnetic forces.

• Hmm could both concepts not be combined? Supporting the lower section of the cables trough magnetic repulsion to reduce weight on the upper sections(as the tension cable has to be thickest in geostationary orbit opposed to the tower)? Afterall carbon tubes can be made conductive, so adding rings that can work as electromagnets to the design should be possible?(Or if the electromagnetic forces really do not contribute enough a simple hybrid of tower and elevator) Commented Jan 5, 2016 at 10:40
• @casualPhilosoph Supporting a part of the elevator from the ground, and another from the counter weight would indeed reduce the tapper ratio. Commented Jan 5, 2016 at 11:58

You're talking about an active structure. These have been proposed, but magnetic levitation is simply not strong enough.

When applied to a launch assist structure, it is sometimes referred to as a Space Fountain. Rather than magnetic levitation, the proposed mechanism is accelerating pellets:

Small metallic pellets by the millions would be shot up to a "deflector" station far overhead, which would use magnetic field scoops to catch the pellets, curve them back down with an electromagnetic accelerator, then shoot them back down to the ground. The ground station would in turn use a magnetic scoop to catch the pellets, curve them back up with a powerful electromagnetic accelerator, and shoot them back at the station in one continuous loop. The pressure exerted on the magnetic fields of the scoop and curved EM accelerator by the continuous stream of pellets would keep the station aloft.

ORBITAL RAILROADS: BEANSTALKS AND SPACE FOUNTAINS