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Date: Wed, 25 Nov 1998 18:18:10 +0000 (GMT)

Subject: Re: [FT] Railgun Goals

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On Wed, 25 Nov 1998, Sean Bayan Schoonmaker wrote:
> Perhaps before we get too far along any one trail for our K'V weapons
> discussion, we should establish some general goals.
very sensible. a pre-argument argument!
> 1) The "To-Hit" mechanic should reflect a projectile flavor. In my
eyes,
> that means performance should be relatively constant out to a given
range
> and then drop off quickly.
this may play well, but as physics it is pretty groundless.
WARNING: what follows is fairly simple algebra etc, but it is
probably badly-though out and deeply incorrect. it also makes lots of
unjustifiable assumptions which are never clearly defined.
hitting a target with a single round / burst means putting them in the
same place at the same time. since the position of the burst is trivial
to
predict, the difficulty lies in finding the target. at range r, the time
taken for a scanner pulse to get there and back (assume active firecon)
is:
t time
r range
c speed of light
t = 2r/c
in this time, a ship with acceleration a can change its velocity by
a acceleration
v velocity
d change in. i can't do capital delta, sorry!
dv = at
= 2ar/c
since that velocity change can be in any direction (well, it can't, but
this is really hard if it is not - assume a spherical chicken and all
that), the target can be anywhere in a sphere of radius (size)
s radius of target envelope
s = t.dv
= 2r/c . 2ar/c
= 4arr/cc
given that the railgun round crosses the sphere, the target is a
circle, and so the probability of hitting the target is given by the
probability-sum of the cross-sectional areas of the burst and the target
as fractions of the potential target area:
[p(a) probability of a occurring]
p hit probability
p1 p( burst in right place )
p2 p( target in right place )
x radius of burst (circular)
y square root of (area of target divided by pi)
p = p1 + p2 - p1.p2
p1 = xx/ss
p2 = yy/ss
p = ( xx + yy - xxyy/ss ) / ss
for very small values of x and y relative to s (as they will be at large
range):
% is proportional to (damn this ascii!)
p ~= (xx + yy)/ss
% 1/ss
% cccc/16aarrrr
% 1/rrrr
the hit probability should fall off with the fourth power of range.
> 2) Damage should be constant, without regard to range.
right - no drag to slow down the round. otoh, if you use a burst, the
number of rounds which hit will fall with range, so damage will fall.
> 3) Firing arcs should be very limited to preserve the K'V "feel."
spot on.
> 4) Mass should be relatively low, and point cost should be relatively
high.
i don't see why massdrivers should be smaller than beam batteries; if
anything, i would say they are larger but cheaper.
> Please refute these if you don't agree; they're just a starting point.
Once
> we agree on some goals, then we can get down to the nitty-gritty of
the
> specific mechanics to achieve them.
excellent methodology. maybe we should submit the list for ISO 9000
process quality certification?
Tom
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