Thread: superconducting coils

is to possible to construct a superconducting coil in space, with a current induced in it. then one could maybe have a spaceship or probe with its own loop, but with a current in the opposite direction. the resulting opposing magnetic fields would, presumably, provide a means of launching a probe or manned vehicle into space and so save some on fuel costs. i read about someone suggesting a ramjet. is that what i was describing? i guess it would work better on a lunar base than, say from a space station, as the space station would still have to burn fuel to counteract the momentum. or maybe it could be launched alternatively in opposite directions of the station's orbit, only causing the orbit to change.


ps: be brutal with the poll, i can take it!

Methink you're suggesting a variation of a electromagnetic gun... but the ordinary design with multiple coils accelerating the projectile at a constant pace is more proficent and allows for greater launch speeds as it's not limited by the amount of instantaneous acceleration the projectile can withstand. 8)

A ramjet is a type of gas turbine engine, which relies on the speed of the craft to 'pull' air into the intake, as opposed to having a more complex fan and lower compressor stage behind the intake. What you are talking about is something different.

As far as I see it, there is no reason why what you are suggesting couldn't work physically, but for the magnetic field to be strong enough, you would need a VERY high current to be passed through the coils, and a MASSIVE capacitor bank to quickly discharge over the coils.


If you are proposing a superconducting system take a look at 'quench guns'.

bit4bit

Such a gun was described in the classic 1969 science fiction novel by Robert Heinlein, "The Moon is a Harsh Mistress." The colonists on the Moon would ship their products to Earth by firing their containers from such an electromagnetic gun. The containers would parachute into the ocean for recovery. It was very economical.

That was science fiction of course. But it certainly is theoretically possible.

how is this sytem different from a rail gun?

and lets say a sort of solar windmill is used with a standard magnet attached to induce a current in the coil. would the current keep on increasing or will it rise to a certain level? or would the opposing magnetic fields oppose the currents in the two coils?

Such a gun was described in the classic 1969 science fiction novel by Robert Heinlein, "The Moon is a Harsh Mistress."

damn. thought i had an original idea there.

as far as i know, if the current gets to big the semiconductor would lose it's superconductivity. i thought a superconductor would work nicely, since no cooling would be required.

Originally Posted by KALSTER

how is this sytem different from a rail gun?

It isn't. It wasn't. Later in the story, the Moon colonists sought independence from Earth and they rebelled. When war seemed imminent, someone asked "How do we fight them?" The hero replied, "We throw rocks at them!"

So they wrapped boulders with steel bands and used the electromagnetic induction gun to bombard Earth, doing so with pinpoint accuracy. Earth had no defense. They retaliated with a surprise Marine assault but the Marines, after a temporary success, were beaten back. Earth finally agreed to peace terms.

A good story!
Â*

again:
Lets say a sort of solar windmill is used with a standard magnet attached to induce a current in the coil. Would the current keep on increasing or will it rise to a certain level? or would the opposing magnetic fields oppose the currents in the two coils? As far as i know, if the current gets to big the semiconductor would lose it's superconductivity.

PS: I read some Heinlein novels, but prefer Asimov by far!

Originally Posted by KALSTER

again:
Lets say a sort of solar windmill is used with a standard magnet attached to induce a current in the coil. Would the current keep on increasing or will it rise to a certain level? or would the opposing magnetic fields oppose the currents in the two coils? As far as i know, if the current gets to big the semiconductor would lose it's superconductivity.

You are correct that in all known superconducting materials there is a "critical current" beyond which the superconductor will stop superconducting. That's why we can't make infinitely powerful electromagnets, or store an infinite amount of energy in a superconducting coil.

There are a couple of ways you can throw something with electromagnets. The easiest way is with a "coil gun." Coil guns take advantage of the fact that if you have a magnetic projectile inside an electromagnetic coil, the projectile will be pulled to the center of the coil. So you start the projectile at one end of the coil and send a pulse of electricity through the coil, and the projectile is pulled to the center. If you left the electricity going, the projectile would just be pulled to the center and stop. But if you time it so that the current stops running though the coil just before the projectile reaches the center, the projectile will just keep going and fly out the other end.

Rail guns are entirely different. In a rail gun you have two conducting rails placed parallel to each other, and a conducting projectile that bridges the rails. If you run current up one rail, through the projectile, and back down the other rail, the electromagnetic fields produced by the rails and the projectile will cause the projectile to move forward.

The problem with coil guns is that they become less efficient as the projectile gets faster. Rail guns don't have that problem, so they have a theoretically higher top speed than coil guns, but rail guns are much harder to make.

Will the projectile move to try and shorten the length of the circuit? To move to a state of less resistence? If so, would it still work with a superconducting coil?

Originally Posted by KALSTER

Will the projectile move to try and shorten the length of the circuit? To move to a state of less resistence? If so, would it still work with a superconducting coil?

Are you talking about in a rail gun? If so, then no - the projectile moves away from the source of the current, so resistance would actually go up slightly as it moves down the rails. The movement is caused by the interaction of the magnetic fields of the rails and the projectile.

Oh ok. Would the configuration I am talking about in my original post work well? There would be no problem of having to syncronise the different coils as the projectile moved faster.

Originally Posted by KALSTER

Oh ok. Would the configuration I am talking about in my original post work well? There would be no problem of having to syncronise the different coils as the projectile moved faster.

Yes, if I am understanding your post right it sounds like it would work. But, I should add that synchronizing the coils is trivially easy. Since you know exactly how long it takes for a pulse of current to go through a coil, it's just a matter of having a computer monitor the velocity and position of whatever you are launching and time the pulses accordingly.

Do you think another configuration would work better? I thought this would work best, as no cooling of the superconducting material would be needed and that solar panels could be used to induce the current into the coils, thereby not having to expent any energy we'd have to transport to the launching station. That much superconducting material could be quite expensive? If not, one could make the lenght of the coil as long as is needed.

You're talking about using a rail gun to launch something off of the Earth's surface? No matter how fast you get it going initially, you'll still need some kind of propulsion to keep it going until it reaches the upper atmosphere. It still cuts down on the fuel you need though, if only by a little.

It might be good for ramjets, because a ramjet doesn't start working until you're going at least Mach 2 or 4 (I forget which).

In order to get to near orbital speeds, you may actually need what is called a "scramjet", which is a ramjet that only slows down the air around you, but doesn't bring it to a stop (I mean a stop from the aircraft's perspective). Those don't start working until even faster speeds.

I was more thinking along the lines of an orbital launch site or space station. I once read something about making an elevator to a structure in geostationary orbit. Some superstrong material would be needed for the connection between earth and structure like spun diamond or a nano-tech material. That would be money, time and energy saving with the added feature of being very cool! What do you think?

Originally Posted by kojax

You're talking about using a rail gun to launch something off of the Earth's surface? No matter how fast you get it going initially, you'll still need some kind of propulsion to keep it going until it reaches the upper atmosphere.

Why would you? If you send something shooting off fast enough and at the correct angle, it should go into orbit.

Yeah, if you gave it enough initial impulse, then no sustained thrust would be required. Same idea with a bullet out of a gun. However you would have to give it an enormous amount of impulse, for that, but then again a hyrid rail-gun /chemical rocket could always be used...that is chemical boosters could always take over after the initial launch.

Originally Posted by Scifor Refugee

Originally Posted by kojax

You're talking about using a rail gun to launch something off of the Earth's surface? No matter how fast you get it going initially, you'll still need some kind of propulsion to keep it going until it reaches the upper atmosphere.

Why would you? If you send something shooting off fast enough and at the correct angle, it should go into orbit.

It's sort of like how, pretty much no matter how high a high dive is off the ground, you still only need about 14 feet of water underneath.

The faster you go in the atmosphere, the harder it pushes back against you. In order to really be going fast enough that you could traverse the whole distance without slowing to a speed lower than orbital velocity,...... you'd be vaporised by the friction.

The rail can still be very helpful, though, in giving you your initial momentum. Basically any fuel/propellant you can save during any part of the trip will be very helpful to you later on.