From: Bruce Dunn <bpdunn@home.com>
Newsgroups: sci.space.tech
Subject: Re: OT:   Railgun question
Date: Tue, 18 Jul 2000 03:51:48 GMT

Henry Spencer wrote:

> There does come a point where a cartridge case full of smokeless
> powder is simply less hassle as a way of launching a projectile.

I tend to take particular issue with a lot of schemes for using
electrical devices for launch.

Where does the electricity come from?  In a remote area where you might
put a railgun (loud!), you would truck in some kerosene or diesel fuel,
then burn it in a heat engine to generate mechanical energy.  You then
take the shaft work and put it into a generator to make electricity.
You then probably run the electricity through a transformer to get the
voltage to where you want it.  You then store the electricity in some
high power density storage device, to be dumped into the railgun at the
appropriate moment, where it is converted into mechanical energy to
accelerate the projectile.  The bucket brigade of energy transfer is
even worse if the energy storage happens to be in the form of flywheels,
involving a conversion of electrical to mechanical energy and then back
again during the storage.

Hey!  I have got a great idea!  Nevermind this silly business of going
from chemical to mechanical to electical energy to mechanical energy.
Just give me the kerosene in a tank and let me add a tank of liquid
oxygen and a pressure fed motor.  Attach the tanks and engine to the
projectile, and use the rocket engine to directly convert chemical
energy into mechanical energy to accelerate the projectile along the
rail.

Hey!  I have got a great idea!  Eliminate the rail - it is only there
because railguns have got to have rails.  There is so much thrust
available from rocket motors that the rail isn't needed - simply point
the projectile up and steer by vectoring the thrust of the motor.  An
added benefit is that the highest velocities take place at high
altitudes and low air densities, eliminating the ferocious problems of
high speed projectiles in the lower atmosphere.

Having just re-invented the rocket as a logical engineering
simplification of a railgun, the critics will no doubt reply "but look
at all that expensive hardware you are throwing away".  There are two
solutions to this problem:

- stop throwing away the hardware (reuseable launch vehicles)
- stop using expensive hardware (minimum cost design).