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# Re: [FT] Railgun Goals

From: Thomas Anderson <thomas.anderson@u...>
Date: Thu, 26 Nov 1998 17:12:17 +0000 (GMT)
Subject: Re: [FT] Railgun Goals
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On Wed, 25 Nov 1998, Thomas Barclay wrote:
> Thomas spake thusly upon matters weighty:
> > this may play well, but as physics it is pretty groundless.

> I'm skeptical about some of the math on the way here.

excellent! skepticism is the soul of rationality. or something. perhaps
the spleen.

> In truth, if your target envelope is a sphere, and your railgun burst
> through it has a spherical cross section (an approximation of sorts),
> is seems likely the burst will  generate a truncated-tip conical path
> volume through the volume of space we call the target envelope. The
> ratio of the volume of this conical path to the total size of the
> target envelope volume may be something that defines the hit-miss
> result. It isn't that obvious though, because it isn't strictly a
> relation of these two volumes.

> But your intial work seems to assume

one of those unwritten assumptions, i'm afraid. at extreme range, the
spread will not be very much.

> > i don't see why massdrivers should be smaller than beam batteries;
if
> > anything, i would say they are larger but cheaper.
>
> Depends on relative energy requirements. Which I can't begin to
> caculate...

[rolls up sleeves] old hat; relativity is vital in fudging physics
experiment results!

E	kinetic energy
m	mass
M	rest mass
v	speed
c	speed of light
k	relativistic coefficient

E	=	mvv/2
m	=	M/k
k	=	(1 - vv/cc) ^ 1/2

E	=	mvv/2
=	Mvv/2k
=	Mvv/2((1 - vv/cc) ^ 1/2)

for a projectile travelling at half lightspeed (1.5 e 8 m.s), the
kinetic
energy is 13e5 joules per kilogram (if i have done the algebra and
arithmetic correctly, which, given past form, is unlikely).

Tom
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