Re: tank gun acceleration versus orbital gun acceleration

Now for some calculations (simplified):

A tank gun shoots a round with muzzle velocity in the 1000 m/sec range
(see "Modern Land Combat" but Miller and Foss).  A gun barrel is say
appx 5 m long.	Assume (for the sake of serious simplicity) that
acceleration in the gun barrel is constant.  The acceleration that the
projectile is subjected to should be about 10,000 g (100,000 m/sec2). 
Please notice that I'm using conveniently rounded figures.  Also note
that we are talking about a "dumb" round--the guided missile rounds
generally have fairly low velocities (gun-wise).

>From way back when, I seem to remember something about 7miles per
second being the escape velocity for earth.  Let's see, a kilometer is
about 0.6 miles, so we are talking about 11.7 km/sec.

This is significantly greater than 1 km/sec in the tank gun example, but
not unreachable.  Furthermore the acceleration, assuming a purpose-built
gun, can be applied over a much longer barrel length (say a buried,
limited traverse gun or a railroad carriage piece).  A 12 meter barrel
should be able to throw stuff into orbit (if all of the above
assumptions are correct) and not subject its "package" to any more
stress than the tank round previously mentioned.

>From this, I think you can begin to see that barrel length is VERY
important to the solution.

I'm sure Oerjan can come up with better numbers--and probably has the
data on how fast the guided tank rounds come out of the barrel...

Rob  
  ----- Original Message ----- 
  From: donald maddox 
  To: gzg-l@csua.berkeley.edu 
  Cc: madd@vvm.com 
  Sent: Saturday, May 26, 2001 6:33 AM
  Subject: Re: tank gun acceleration versus orbital gun acceleration

  I've been wondering about the acceleration that's placed on a
projectile
  fired from a modern high velocity tank gun, versus the acceleration
that's
  placed on a projectile fired from one of those theoretical superguns
   
  The velocity would be lower on a theoretical supergun for a few very
  basic reasons. As I learned in the Field Artillery school the big one 
  is gravity, all things will fall unless enough propellant is placed
behind it
  and it is given the proper quadrant (up or down) to reach escape 
  velocity or level flight

  Tank Guns and in particular modern smooth bore tank guns are designed 
  to be fired in an almost a flat trajectory Although this by  the laws
of ballistics
  is impossible, that is always the goal so as to eliminate as much dead
space
  ( the area between where the projectile starts to clime and it falls
to hit the point of aim) as can be done, there by extending the kill
zone. The higher the
  velocity the flatter the trajectory.

  The next factor to be considered is mass Vs propellant, the heavier
the
  object to be launched the more propellant is needed to reach escape 
  velocity. This would restrict it to a supergun as the size and weight
of
  any worthwhile pay load would necessitate a large amount of propellant
  and a far heavier gun tube then any tank would like to lug around.

  The artillery type supergun would be the way to go, in that they would
be big
  enough and strong enough to with stand the blast but at a lower
velocity 
  there by negating the need for super reinforcement for the  satellite.

  To point out the feasibility of this we need look no further then the
W.W.I
  German Paris gun, it fired a 307lb shell 24 miles up and 92 miles in
range.
  If you were to marry this shell up with a RAP (rocket assisted
projectile)
  I see now reason why it could not achieve orbit.

   Don