Vacuum Resistance

Since I am working on redesigning the vehicle system for TDR, and since it has
been pointed out on the list that a minimum armor of 40 for a spacefaring
craft is ridiculously high, I thought I would take a quick look at the pressure
vessel calculations in my chemical engineering references.

As two sample calculations, I considered a cylindrical pressure vessel capable
of containing one standard atmosphere of pressure (14.7psi)  <Sorry about the
English units--I'm an engineer>.  I considered it to be made of mild steel,
with no special alloys, etc, giving a yield strnght of approximately 50,000psi.
I also ignored end cap effects.  I decided that a safety factor of 2.5 was
sufficient, so I put in a value of 20,000psi as the maximum allowable stress
in the skin.  At those conditions, a cylinder 10ft in diameter would need a wall
thickness of less than 0.05 inches, which is less than Traveller armor value
1.  A 100ft diameter cylinder (ship sized) would require a wall thickness
of 0.44 inches, about Traveller armor value, between Traveller armor values 3
and 4.  50,000psi mild steel would be the equivalent of armor type A (soft
steel).

The result of this little investigation would suggest that vacuum resistance is
not a valid reason to retain an Armor 40 minimum for spacecraft.  Is anyone out
there capable of figuring out how thick a cylinder has to be to support its
own weight at up to 6Gs?  (I've probably got it around here somewhere.)  This
would give us an idea of how much structural strength would be required to
resist acceleration. (assuming that the weights of interior components more or
less included the structural members necessary to brace them...)

Rob Dean