Re: pressure containment: not a major issue?


"Joe Strout" <joe@xxxxxxxxxx> wrote in message
news:joe-B79274.08405417072006@xxxxxxxxxxxxxxxxxxxxxxxxxxx
I've been thinking some more about containing air pressure in a space
habitat, and concluded that I (and most authors) have been making too
much of this. Please check my reasoning and let me know if I'm
overlooking something.

I was sipping a can of soda last night, and it occurred to me to look up
the internal pressure of an unopened soda can -- it turns out to be
around 2-4 atmospheres. Yet this is contained quite neatly by a very
thin aluminum wall. Pressure doesn't scale with size; 1 ATM is 1 ATM
whether it's a soda can or Rama. So, even that soda can is a couple
times thicker than the wall of a space habitat would have to be.
Suppose for a good safety margin, we make our pressure walls ten times
thicker than that -- it's STILL going to be a very tiny amount of mass
compared to the shielding and structural mass.

So, it seems to me that we really shouldn't be worrying about pressure
containment when choosing a geometry; containing 1 ATM is easy and won't
add much to the mass budget, no matter what shape we choose. (Of course
I realize that in the case of shapes that can buckle, the buckling
problem probably DOES scale with size, but I suspect that accounting for
this still leaves a much smaller amount of mass than that needed for
shielding and weight support.)

Any thoughts?

Reminds me of my first structures class (mechanics of materials).

http://www.efunda.com/formulae/solid_mechanics/mat_mechanics/pressure_vessel.cfm

Note how the different stress tensors change with an increasing radius.

Since your habitat is pressurized internally, buckling shouldn't be a
problem, at least for any sane pressure vessel geometry I can think of.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)


.

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