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From: dietz@SLB-DOLL.CSNET (Paul Dietz)
Newsgroups: net.space
Subject: Re: rail guns
Message-ID: <8601152118.AA12038@s1-b.arpa>
Date: Wed, 15-Jan-86 15:11:31 EST
Article-I.D.: s1-b.8601152118.AA12038
Posted: Wed Jan 15 15:11:31 1986
Date-Received: Fri, 17-Jan-86 03:21:46 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 21

>Why not use capacitors or something similar to store the energy?
>Charge them up over night, then POW, discharge for a launch.
>The peak size of the *generator* is reduced by orders of magnetude ...

Actually, you'd charge them up over a period of minutes using the power
grid.  A 100 kg payload launched to 10 km/sec needs 15 billion
joules of energy (at 33% efficiency).  Electrolytic capacitors these days
have a storage density of around 100 joules/cubic centimeter, so that's a
capacitor roughly 16 feet on a side!  Building something that big out of
hundreds of thousands of smaller capacitors doesn't sound impractical.

Handling the power is not just a matter of storing the energy, but also
switching it.  Designing switches and cables capable of handling tens of
gigawatts of power in short pulses is nontrivial.

It might be an interesting project to build, at home, a small railgun
or coil gun powered by some of those large capacitors found in computer
power supplies.  A 100 milligram mass could be accelerated to 10 km/sec
with just 15 kilojoules of energy (at 33% efficiency).  Don't aim it
at anything valuable.  (I take no responsibility for the results if
someone actually tries this...)