Phyics - Railguns

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Anyone here into electromagnetics/rail guns? I come up on this concept from time to time, and each time i try to understand the setups and how best to apply the "theory" involved. Ive had some ideas as well and was wondering who else here could clarify some info or give first hand experience (if its an obsession).

I probably couldnt help you even if I knew what you were talking about, but I suspect even readers who could help you need more explaination of what you're asking for here.

Rail guns are big guns mounted rail road cars- arent they?

So how does that subject relate to electromagnetism?

Do have an idea for magnetic levitation train that carries a big gun? Or is it that the gun fires electromagnetic rays - or -what?

My apologies, a railgun is essentially the concept of propelling a solid, ferro-magnetic (meaning that it can be subject to electromagnetic effects without maintaining its own magnetic field) to speeds greater than that of current ballistic weapons using powerful electromagnetic (EM) fields. The rails are responsible for both conducting the charge and EM field by which the projectile will be shot. Simple diagram:

+====================== rail A
(======> shot >>>>>>>> direction of shot
-====================== rail B

To maintain the current, the shot has to be in direct contact with the rails; which tend to get messed up due to the friction with the shot. Similar in concept is the coilgun which, instead of rails, merely uses a tube which has EM conductive wire coiled around it. The downside to the current designs is that they require massive amounts of power, and (as mentioned with railguns) quire destructive to their own housing. As such, current R&D finds that railguns would be better suited to vehicles, whereas coilguns would be practical for infantry. Again, there is the issue with the amounts of power needed for said weapons.

I find the concept of railguns to be quite compelling. There's something to be said for a propulsion mechanism that requires no propellant or consumable fuel, such as gunpowder; just a battery. It's unfortunate that it's so destructive to its housing. Have you researched mass drivers very much? There is an idea of space fountains that seems quite elegant to me. It simply makes use of magnetic acceleration and deflection. I don't foresee an actual space fountain being constructed in the near future, though, unfortunately. It seems to solve many of the problems associated with space tethers and such, while maintaining an intuitive mechanism for transport to and from a space station. However, the idea is "scary" for non-scientific people, kind of like the LHC. I heard about some "scientist" actually making a serious claim that the LHC has had troubles because the "universe" knows that it will create a black hole if it is ever activated. What balderdash! Anyway, that's enough of my ranting for now. Sorry I'm not as informed about railguns as you were looking for. I'm not as interested in railguns as I am in space stations.

I remember them enjoying some popularity in the 80s-90s. They can project a puck at a few miles per second. Not sure about the range; most of what I've heard was that it wasn't great.

Sounds like something that would show up on the Military channel...

While I don't know much about railguns, here's a small "railgun" kit that Think Geek sells:

http://www.thinkgeek.com/geektoys/science/a673/

The idea works, but is large, and has high power needs. Not much chance of a backpack size.

Unlike canon, they are too big to aim at anything but orbit. Their advantage is also thier downfall.

While powder propels a bullet to a mile a second, rail guns use the speed of light.

Their projectile has to be ferric, or an opposing field. The vehicle has a high mass. Even cargo would have to be well stowed. A human would become a puddle. Launch to orbit takes reaching 20,000 miles an hour in a few hundred yards. With an open system, a huge projectile, the sonic boom would come while it was just starting. Leaving the barrel, it would be a fireball. Air cannot take such abuse.

It has been said they would work better on the Moon. The problem there is nothing to export, but dust.

They were proposed for use in space, as mass drivers, from the recoil, but you have to have a supply of mass.

Tankloads of ferrous oxide powder stored in bulk. The velocity of the oxide powder is of the order of m*v and v can be made very high. It might be a better propellant than chemical fuel.

ruveyn

[youtube]http://www.youtube.com/watch?v=8FQ8ak7kBbo[/youtube]

The idea works and is currently being researched. Granted you won't see small one soon due to power requirements, but having one on a nuclear powered Aircraft carrier, or cruiser where you have a lot of AC at your disposal in an inherantly foreseeable thein in the near future.

Well, ive had some ideas, but i have no real way of testing them. One way to alleviate stress on the shot would be to add wheels that could be arranged in such a way as to keep the rails from degrading so fast. Another, and this one im not sure about, but its the setup of the current through the rails. If memory serves, a current will pass through any circuit through the shortest possible route. This being the case, wouldnt one want the highest possible charge to be further away rather than closer?

EX: (Note, + and - denote the flow path of the current, + being the point of origin, with the charge moving toward -)

+ _________________________
- _________________________)
(=====> --------------------------> point of greatest charge?
- __________________________
- __________________________)

For those familiar with electronic schematics, please compare this to my previous post and tell me what you think.

Coil guns are pretty awesome, although they're not the same as railguns, they're magnetic based guns.
[youtube]http://www.youtube.com/watch?v=n9XWUCvtpQ4[/youtube]

The original proposal came from Gerard K. O'Neill, who wanted to mine iron on the Moon, smelt it to steel, then use a mass driver to launch it to the L-4 and L-5 points to build his O'Neill colonies.

The first reference I've found so far to using a mass driver as a weapon was in Heinlein's The Moon Is a Harsh Mistress, published in 1966, in which the inmates of a lunar prison colony (most of whom were actually free citizens, but couldn't leave Luna because of low-gravity adaptation) fought for their freedom from the Terran Federation by using a mass driver built to transport grain grown in lunar tunnels to Earth, to throw steel-jacketed multiton rocks at Earthside targets - essentially massive aimed meteor strikes. They managed to destroy Cheyenne Mountain...

("Manny, I think we should shift the last few loads for Cheyenne to an alternate target."
"Why?"
"Because it isn't there any more.")

On a side issue, the first tests of a space elevator were run at Edwards. A ground laser powering a solar cell climber, which went up a half mile cable at 16 feet per second. Only 25,000 more miles to go.

That approach is an exercise in futility. There is not going to be a practical laser anytime soon than can lift a significant payload into orbit.

ruveyn

No, ruveyn, you're thinking of the proposed laser launch mechanism (which could be built next week -- but would need its own nuclear power plant to run the laser array). It has been tested in miniature, but at CalTech, not Edwards AFB. The test at Edwards was to use a laser to beam power to a solar-cell array on a proposed space elevator system, solving the problem of how to get energy to the elevator while it's climbing its tether. Essentially, it's a wireless power arrangement for the system. Now we just need to find a material strong enough to make the elevator's tether out of, and capture an appropriate counterweight mass from among the near-Earth asteroids...

The group that was leading in the elevator races said they thought the real use was power transmissin where there were no wires.

There was also mention of Carbon nanotubes making up a cable. The weight of anything 25,000 miles long, climate, ice forming, storms, path for lightning, leaves lots of problems.

We are stuck here for a while.