Re: HKP and the Kra'Vak

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
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.

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
> 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.).

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
metal
> plasma to replace "Expanding Gasses" from chemical slugthrowers. 

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
> 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, 

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:
> 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.

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
oerjan.ohlson@telia.com

"Life is like a sewer.
  What you get out of it, depends on what you put into it."
- Hen3ry