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From: bilbo.niket@LOCUS.UCLA.EDU ("Niket K. Patwardhan")
Newsgroups: net.space
Subject: Rail guns vs. ordinary guns
Message-ID: <8601171810.AA20973@s1-b.arpa>
Date: Fri, 17-Jan-86 12:58:55 EST
Article-I.D.: s1-b.8601171810.AA20973
Posted: Fri Jan 17 12:58:55 1986
Date-Received: Sun, 19-Jan-86 03:48:09 EST
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Organization: The ARPA Internet
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Can somebody tell me what the disadvantage of ordinary guns (blob in a barrel
propelled by hot gases under pressure) is as compared to the rail gun?

It can't be length....Using the formula  

V**2 = U**2 + 2*a*s

and 8000 metres/second as the final velocity (orbital) and 50 m/sec*sec (5G)
as the maximum accelaration, one gets 640,000 metres as the necessary length.
Thats 640 km or 400 miles! NO GUN OF THAT LENGTH could be feasible.

However if you are trying to get just MASS up, you could increase the G-factor
to say 5000 and wind up with a gun of 640 metres. If your payload was a chunk
of solid steel 1 metre long you would require about 350 atmospheres of pressure
to get this kind of accelaration, which is easy! (Steel ~7000kg/m**3).

I have heard of some restriction due to the speed of sound in the gases.. but this should
be easy to overcome by raising the temperature and selecting the right gas.
(hydrogen????)

PS What is the speed of sound in hydrogen at 3000K?
What is the melting point of tungsten?