From: earl@cco.caltech.edu (Earl A. Hubbell)
Newsgroups: rec.games.frp.misc
Subject: Re: Guns (background information) 1 of 5
Date: 12 Nov 1992 09:13:53 GMT
Organization: California Institute of Technology, Pasadena
NNTP-Posting-Host: alumni.caltech.edu

acgetche@taco.engr.ucdavis.edu (Adam) writes:

>The Arms Race of the future:

>	Modern firearms have developed a long ways from their cruder
>origins.  Leaving aside potential developments that would make projectile
>firing small arms obsolete (like, say, efficient batteries to make man
>portable lasers of reasonable energy), I propose to examine the trends
>in developing tommorrow's projectile weapons.	

	Naturally, even obsolete weapons do make their appearance, 
especially in 'dark future' campaigns.  

>	The "ultimate" method for propelling bullets is via magnetic fields.
>The so-called gauss gun or rail gun wraps a wire around the barrel; 
>along the bore, which will propel magnetic materials very fast and very
>magnetic field is very localized and would require specialized detection gear,
>namely a SQUID), and of course extreme accuracy.  A conventional explosive-
>driven projectile weapon suffers inaccuracies where the bullet and barrel join;

	Note that supersonic projectiles still dump power into acoustic
energy - no muzzle flash is good, but if your sensors are good enough...

>	The hangup, of course, is in the power supply and superconducting coils
>(which need not be large but will be expensive).  The main limitation is power.
	
>	Another hangup is in the area of bullet design.  Extreme velocities
>of this nature will generate intense heat in the round.  In point of fact,
>want a round to fly at 10,000 m/sec, you're going to have to engineer it
>quite carefully.  For starters, you'll want as high a surface area to volume
>ratio as possible.  A ring airfoil shape (c.f. below) might prove ideal.
>You'll also need advanced composites which won't deform greatly under heat
>(and hence are "brittle") but will retain shape integrity when penetrating
>armor (hence "ductile" or "tensile").  Again, the best candidate would be
>a memory plastic.  To propel such a round with a magnetic field, you'll
>need a magnetic band (an alloy of "Alnico" would probably be best).  Such 
>weapons will have a signature burst of plasma as the metal band vaporizes after
>leaving the barrel (since the metal won't have the thermal properties of the 
>plastic).

	Important notes:  
1) Railguns do not need any particular material of bullet (besides surviving
launch) since they use an 'armature' (generally plasma) to push the
projectile - standard experimental railguns currently use Lexan.
2) Mass drivers, or other direct electromagnetic propulsion schemes do
not need >magnetic< projectiles - they need a conductor to induce eddy
currents yielding a magnetic field.  Again - current experimental
models have used aluminum, copper, various superconductors... and with
current developments in conductive polymers, carbon networks, etc...
3) >Is< large surface area to volume ratio desirable in hypervelocity
rounds?  I recall some articles on projectile design, and they seemed to 
indicate that a very narrow projectile was desirable, possibly with an ablative
tip.  

>	A cheaper way to get many of the same advantages is ElectroChemical
>Propulsion (ECP)  This method uses magnetic coils much like a gauss gun,
>but the current load does not need to be as large.  Propellant is placed
>acceleration would also increase as more propellant gasses were produced.
>	The "ultimate" version of this technique would be to use electric 
>fields instead of magnetic fields to convert the propellant, a tungsten wire, 
>directly into a plasma. (Tungsten is a good choice for the same reasons Edison

	I've seen this referred to as 'electrothermal' propulsion.  It seems
the closest to actual field workability for producing high velocity
projectiles.  

	More methods of tossing projectiles at high velocities:
Light gas propulsion:  It is possible to store large quantities of energy
in the form of heat in phase-changing materials.  A low molecular weight
gas will absorb heat rapidly from an appropriately designed system, and
provides extremely high pressures (and reachable velocities, since the
thermal velocity will be very large with light gases).  
On the other hand, it doesn't scale well to small systems, since for
efficient heat storage you want a lot of volume for the surface area...it
does promise higher energy densities than nearly any other system easily
available.

	In exotica:
I've seen it seriously suggested to electrostatically accelerate myriads
of small particles (since efficiency of electrostatic processes is
only large for small systems) and arrange for them to coalesce into a
single large projectile at the 'exit' to the system.
	(Um... 1971 conference on high energy density physics - I don't
have the reference handy - probably practically difficult :-)

>	Guns have always been hi-tech, even the primitive ones.  To quote
>an old English Artillery captain, "...an automobile as efficient as a Maxim
>machinegun would be the seventh wonder of the world..."

	On the other hand, logistics has always been a traditional
problem - getting spare parts and more ammo where you need it.  Depending
on the assumed role of the weapon, wildly different designs may be
necessary (ecology of weapons?).  The electrically driven weapons
hold the advantage that it is easier to convert electricity back and
forth than most other forms of energy (it's difficult to run most
guns off of gasoline, and the gunpowder won't drive the jeep). 

	References:  IEEE Aerospace Systems Magazine, Dec 1991 (energy
storage - future battlefield extrapolations)
	IEEE Transactions on Magnetics (Railgun, mass driver, strange
hybrid systems) about every two years has a conference isssue dealing
with interesting topics... 
	And, of course, endless browsing in assorted libraries...

>           -- Adam
>+--------------+---------------------------------------------------------------+
>|Adam Getchell |Surgery-Radiation Oncology    GETCHELL@radonc.ucdmc.ucdavis.edu|
>| acgetchell   |ez000270@chip.ucdavis.edu        acgetche@taco.engr.ucdavis.edu|
>+--------------+---------------------------------------------------------------+
-- 
'You can tell I'm educated/I studied at the Sorbonne *earl@tybalt.caltech.edu
Doctorate in Mathematics/I could have been a Don     *Earl Hubbell
I can program computers/Choose the perfect Time      *Opinions solely mine.
If you've got the inclination/I've got the Crime" -Opportunities, Pet Shop Boys