Rail guns (was: US SOCOM desires...)

["Robert J. Hansen" <rjhansen@xxxxxxxx>]

> or say that someone does come up with that holy grail 
> of modern science the room temp superconductor.  Can 
> you say Rail Guns for your infantry.  real powered 
> armour would become possible.  truly radical things 
> happen to military tech virtually overnight.

Coincidentally, I happened to work in a Defense Department-funded
research lab that was looking into properties of HTS (High-Temperature
Superconductor).  Rail guns were not ever on the wish list.  The problem
is really simple: Newton's Law of Equal and Opposite Reactions.

A five-gram metal flechette travelling at Mach 10 sounds
sweet--something like twenty-five times the energy of a 7.62mm rifle
cartridge.  The problem is this: Mach 10 is approximately 3500 m/s.  The
kinetic energy equasion is Ke = (m*v*v)/2.

.005 * 3500 * 3500 / 2 = 30,625 joules of energy

If you're going to send that downrange to your target, the rifleman is
also going to receive 30,625 joules of energy.  You can work out the
soldier's velocity in a similar way:

2 Ke = (m * v * v)
2 Ke / m = (v * v)
sqrt(2 Ke/m) = v

Assuming you've got a 75-kg soldier, your soldier is going to be
traveling backwards at about 28 meters per second.  Or about 60mph. 
He's going to hit something, which will slow him down, and that'll be a
real pain in his ass, let me tell you.

Remember that recoil increases to the square of the velocity.  You want
a round that travels ten times faster than modern rounds?  Fine--take a
hundred times the recoil, please, and say hi to Sir Isaac when the
recoil catapults you all the way into heaven.  :)