> PsyWraith wrote:
> Actually, the DSII hyper-kinetic penetrators (HKPs) are not railguns
We had a discussion about the Railgun earlier. Let's review:
The basic construction of the railgun (at its simplest this is a scientific
device for acclelerating particles) consists of a LARGE capacitor, two
stainless steel rails, and a small thin wire. The capacitor is connected with
each lead connected to one rail, forming an electrical circut of
rail-capacitor-rail. The rails are mounted paralell to each other. To
fire the basic railgun you drop the thin wire across the rails completing the
circut. The voltage will be too high for the wire to withstand and it will be
instantly transformed into a metal plasma. The completion of the circut will
magnetize the rails, briefly and instantly, which will accellerate the plasma
down the rails, the plasma being conductive itself will keep the circut
completed until it has left the rails, thus keeping magnetic containment on
itself, untill it passes beyond the magnetic containment of the rails. The
entire process takes place in about one nanosecond (depending on capacitor
charge, rail length, mass of wire, ect.).
The current Military railgun design involves using this expanding metal plasma
to replace "Expanding Gasses" from chemical slugthrowers. The main advantage
being that a chem. slugthrower explosion is "contained" in the barrell of the
gun, and uses half it's force producing recoil. The metal plasma exlosion is
forced down the barrell, in theory shouldn't produce recoil, and the
combination of the plasma expanding AND traveling down the barrell generates a
very very high muzzle velocity.
To wit:
ASCII diagram
* = center of discharge () = edges of explosion (expanding gasses, metal
plasma)
[ = back of slug
[1]****(point of ignition)*******
______________________
(*) [chem slug thrower
----------------------------------------
______________________
(*) [railgun
----------------------------------------
[2]******************************
(*)[chem Slug ( *)[railgun
[3]******************************
(* )[chem slug
( * )[railgun
[4]*****************************
(*)[chem slug ( *)[railgun
and so on...
The railgun achieves such incredible velocities because unlike a "chem.
slugthrower" the expanding gasses (metal plasma) themselves are being pushed
down the barrell by the magnetic properties of the rails and the energy used
to generate the plasma. Where a chemical slugthrower is using half its force
in pushing the gun backwards, a properly working railgun should have low or no
recoil.
The main point being: No a railgun is not a Mass Driver, but it is a Magnetic
Accellerator.
Now for the HKP:
The HKP has the following properties according to St.St. St.Jon: Low rate of
fire, plasma accellerant. The best way to generate an efficient plasma
accellerant is with a railgun, and the technology is *at least* twenty years
old. The main disadvantage of the railgun is the recharge time for the
capacitor, or the power requirements of charging it fast (hopefully without
blowing the capacitor all over the place), which typically results in a low
rate of fire. So in the 21XX (still more than a hundred years away, and we
have made such great advances in killing each other over just this last
century with no reason to think the trend will change) using a railgun
ignition to create a HKP is probably the standard method. More to the point:
it is probably how the Kra'Vak would build one.
As a sidenote: It is possible to use the metal plasma itself as a projectile.
Basically it entails mounting a rocket engine nozzle to the barrel of the gun
to accellerate the plasma to supersonic speeds, getting the plasma to its
target before it dissipates. Based on the description in the book, the DFFG is
built this way, each round having a capacitor that is spent after it is fired,
as well as the metal that is to be vaporised. The technology needed to do this
is at least twenty years old, my father was attempting to build one in
college, he took out a stereo system with it before he was finished. Aparently
the parts for it are supposed to be around my house somewhere.
And finally with the post that started this mess [re: Fallout 4]
The resin kits are the cream yellow ones in the U.S. If anyone knows a way to
clean them properly I'd like to hear about it.
Here we go again:
> djwj wrote:
> We had a discussion about the Railgun earlier. Let's review:
You review your beliefs, I review mine, OK?
> The basic construction of the railgun (at its simplest this is a
With you so far, except that the "small thin wire" is basically an DSAP rod
penetrator.
> The voltage will be too high for the wire to withstand and it will
circut
> will magnetize the rails, briefly and instantly, which will
C'mon. You turn a short, thin wire into plasma, launch it, and think that
it'll be able to take out a tank some km away? It won't be too fun
to stand close to the muzzle, though - you might get some nasty burns
if you do :-/ Probably worse for the gunner than for the target,
unfortunately.
And, well... please do some reality checks on what you write - it'd
improve your credibility considerably. If the entire shot takes less
than one nano-second and we assume a (short) barrel of 3 meters and
linear acceleration, your plasma leaves the barrel at slightly above the speed
of light. <checks calculations again> Um, let me rephrase that somewhat: The
muzzle velocity of your plasma is 10 times the speed
of light (c in vacuum, not in the latest "light-traps"). That's *very*
impressive, you know. Certainly not possible with today's technology.
I hope you mean millisecond rather than nanosecond. With the same assumptions
as above a millisecond acceleration time gives you a muzzle
velocity of 3000 m/s, which is comparable to real railgun muzzle
velocities.
The fastest railgun rounds I've heard of so far had muzzle velocities
of ~6000 m/s, but they had considerably longer barrels - IIRC around 15
meters - and the acceleration isn't completely linear. The limiting
factor isn't the gun itself, but rather the projectiles used; it's no good
firing them so fast that they vaporize from the air friction...
> The current Military railgun design involves using this expanding
No, they don't. Current military *railguns* - only experimental so far
- use the Lorenz force (the one caused by the electrical current
flowing in the closed loop) to propel a fairly standard rod penetrator
- "fairly" standard, since the sabots have to be different from the
ones you use in a normal DSAP tank round.
The closest weapon to what you describe is probably the ET
(Electro-Thermal) and ETC (Electro-Thermal-Chemical) guns, where the
reaction which produce the propelling gasses can be far better controlled than
in a normal chemical cannon (where all you can do is ignite the propellant and
hope it burns in the patterns you designed it to <g>). These too are only
experimental at the moment.
> The main
This is... wrong. Each action creates a reaction of equal size in the opposite
direction; Newton's laws don't magically disappear just because you use
magnetism instead of explosives as a propellant.
The railgun spreads the accelerating force better over the shot, though. Where
the chemical propellant of a standard gun typically
creates a very short, very high pressure/force pulse which drops
rapidly as the round progresses down the barrel, the railgun can maintain more
or less constant force throughout the shot. The total impulse is just as large
in both cases, though.
> As a sidenote:
Basically it
> entails mounting a rocket engine nozzle to the barrel of the gun to
You don't need a nozzle to accelerate the plasma/projectile to
supersonic speeds. It already moves at *hyper*sonic speeds in the
barrel. (Side note: supersonic usually refers to Mach 1 - ~5, ie at
ground level roughly 340-1700 m/s; hypersonic is when you go faster
still.)
Unfortunately the plasma won't stay at hypersonic speeds after it
leaves the barrel. When you discharge a super- or hypersonic gas jet
into relatively still air, you get a series of oblique shocks which rapidly
slow the jet down to subsonic speeds. (Assuming, of course,
that you can treat the plasma as a compressible gas - but you already
do that when you put the nozzle in! OTOH, if you rely on some sort of
"magnetic bottle" to stop the plasma from dissipating and turn it into
some sort of pseudo-projectile instead, the nozzle won't work.)
And, finally... if the plasma is nasty enough to kill a tank some miles away,
how is your nozzle going to survive even the first shot you fire? If you're
lucky it'll just erode extremely fast; if you're not, you'll
blow the gun up in your own face :-(
Sorry if this came across harshly. "Fantasy" physics are very useful to
explain things in SF games; we use it extensively in Starfire (inertialess
drives and all that). You can't, however, use them to
explain how real-world gadgets work.
Regards,
> Oerjan Ohlson wrote:
> We had a discussion about the Railgun earlier. Let's review:
> You review your beliefs, I review mine, OK?
> The basic construction of the railgun (at its simplest this is a
> With you so far, except that the "small thin wire" is basically an DSAP
No you aren't with me. The small thin wire is the Railgun equavilent of
gunpowder. the DSAP penetrator is placed in front of the point you drop the
wire (the specifics of not dropping the rod on the rails I don't know about),
the wire vaporises to a plasma state, is propelled by magnetic accelleration,
which in turn pushes the penetrator rod down the barrell.
> The voltage will be too high for the wire to withstand and it will
> C'mon. You turn a short, thin wire into plasma, launch it, and think
You don't use the plasma as the projectile, the plasma accellerates the
penetrator rod the same way as gunpowder does.
< something about speed errors >
You're right on that one, sorry
> No, they don't. Current military *railguns* - only experimental so far
This sounds more like a Mass Driver than a Railgun.
> This is... wrong. Each action creates a reaction of equal size in the
You've never left heavy electrical construction equipment ungrounded have you?
I don't know how it works, I think it has something to do with the
action-reaction affecting the magnetic "event" rather than the weapon
directly, but asking a dedicated physisist (or Geo-Magnetist) about this
would be a better idea.
The railgun, originally, was a device for small particle accelleration
experiments, but like most scientific devices someone figured how it could be
used for war.
> On Fri, 4 Jun 1999, djwj wrote:
> Oerjan Ohlson wrote:
To
> >>fire
this was clearly a misunderstanding, then: djwj and oerjan are describing
essentially the same system. the key characteristic is the use of the Lorentz
effect (current flow along the rails sets up a transverse magnetic field which
interacts with the flow through the round to generate a propelling force) to
accelerate the round. in oerjan's description, the conducting part of the
round is the projectile itself, a "fairly standard rod penetrator [in a
sabot]", in djwj's, the conductor is a plasma generated by the electrical
vapourisation of a metal wire.
i must say that i'm a little troubled by oerjan's description - firstly,
the round needs to be a good conductor, which i would imagine precludes making
it from depleted uranium or tungsten, although i suppose you could put a
copper coating around it, and secondly, if the accelerating force is coming
from the current flow throught the round itself, why is a sabot needed? unless
that sabot is the bit with the conductor, in which case it all makes perfect
sense.
djwj's description matches what i was told by the television a while ago (must
be true, then...), which is that the round used was a block of kevlar with an
aluminium foil backing: the aluminium was vapourised to generate the
conducting plasma. of course, that was a while ago, and highly experimental,
there is no reason why both these approaches aren't being used, and oerjan is,
after all, the professional weapons engineer here (i'm assuming djwj isn't,
but i actually have no idea...).
some back-of-the-envelope scribblings (well,
back-of-someone-else's-chemistry-notes, anyway) indicate that railguns
would be troubled by the Hall effect - accelerating a plasma though a
magnetic field will generate a back-voltage which opposes the current
needed to drive the round. i would guess this is a limiting factor in
railguns, but frankly i have no real idea.
> > No, they don't. Current military *railguns* - only experimental so
massdrivers also use magnetic acceleration, but not the lorentz effect:
rather, they use a sort of magnetic travelling wave thing (i don't know what
this is formally known as), like linear particle accelerators and, i think,
maglev trains. i think that this requires that the round be
diamagnetic (like aluminium - it tries to escape from a magnetic field).
anyway, it's more complicated than a railgun, but requires no plasma and no
physical contact between the round and the barrel, as opposed to a railgun,
which does: the conductor has to touch the rails (leading to heavy wear) and
in the plasma type, there has to be a seal between round and barrel for the
plasma to be effective.
> >This is... wrong. Each action creates a reaction of equal size in the
newton's third law is not violated. full stop.
> The railgun, originally, was a device for small particle accelleration
i'm pretty sure you're thinking of a massdriver here. railguns require a
conducting object to accelerate, and i'm fairly sure electrons et al don't
conduct electricity :). and i'm not sure about the 'small' - there are
some damned big particle accelerators around.
> but like most scientific devices someone figured how it could
i've yet to see a bench centrifuge or a spectrophotometer used for war.
they're pretty heavy, though, so i suppose you could hit someone with one.
anyway, those future tech kinetic weapons in full:
railgun - uses the lorentz effect to accelerate a round between two
electrically charged rails. may or may not involve plasma.
massdriver - uses magnetic peristalsis to accelerate a round, like a
particle accelerator. doesn't involve plasma.
electro-thermal gun - uses electrical heating to drive expansion of a
gas or plasma to push a round down a barrel. involves plasma, or hot gas at
any rate.
tom
djwj insisted:
> >With you so far, except that the "small thin wire" is basically an
No, it is not. There's no way in hell a small thin wire can turn into
enough gas to pump up the pressure high enough to launch a tank-killing
missile - and pressure is the only means the plasma could accelerate
the projectile.
The railgun works because the *sabot* closes the circuit, and the Lorenz force
acts on the *sabot*. In those cases where there is plasma
- pretty much always for military-grade railguns, very rarely for
home-built paper-clip firing ones - the plasma conducts the current
from rail to sabot and vice versa, but that's it.
An ET gun works more or less as you describe it - the propellant is
vapourized when you run a strong current through it - but you use up to
several pounds of propellant rather than a "small thin wire". In ETC guns the
propellant reacts much like the gun powder of normal cannon, but "only" when
you run the current through it.
Neither type has the continous conductive rails of a railgun, but both can
have a series of electrodes (isolated from one another) so you can put the
current through the barrel at the exact point you want rather
than everywhere at once. Those are the basic ideas, anyway - reality
tends to be a bit more complicated :-/
> >C'mon. You turn a short, thin wire into plasma, launch it, and think
That's not what you said elsewhere in your post, though :-/ See above.
> < something about speed errors >
Not entirely - I forgot a factor 0.5. Still, 5c is a rather impressive
muzzle velocity too <g>
> > No, they don't. Current military *railguns* - only experimental so
All the term "Mass Driver" really says is that the device accelerates a
mass. All guns do that :-/ It is sometimes used to mean "a railgun
which launches big projectiles slowly"; this may be what you're thinking of.
> >This is... wrong. Each action creates a reaction of equal size in
Please elaborate. I think I know what you're thinking of, but I'm not sure. If
you think of what I suspect, the entire conducting loop has to
be fixed - but that's not the case in a railgun, since the projectile
is part of the loop and is most definitely moving.
> I don't know how it works, I think it has something to do with
I've got a Masters degree in Engineering Physics. How dedicated do I have to
be to qualify?
> The railgun, originally, was a device for small particle
The railgun still causes a recoil. For small particle accelleration
experiments the recoil force is low enough not to be easily noticed, but it is
there.
Regards,
> Tom Anderson wrote:
> i must say that i'm a little troubled by oerjan's description -
Bingo. The sabot is indeed the conductor; it is necessary mainly because the
ideal shape for a sabot is rather far from the ideal shape of the rod
penetrator <g>
Regards,