[ATM] If it's in a supremely stiff cell, that does not twist,why would a thin mirror sag?

[dgood at aha.org (Good, Donald)]

Art Bianconi wrote:
===================
Vaccum bagging will subject the mirror to about 2,500 pounds of atmospheric 
pressure. I've some concern that lack of support caused by the preground 
saggita will allow excessive stresses to build. While it would not likely 
crack the mirror, it could cause it to flex and distort the surface.
===================
Let's see: 2500 pounds, ~15psi, 167 sq in, R=sqrt(A/pi)=7 1/4, maybe 8"
mirror.
Actually vacuum bagging subjects the mirror to very little additional
stress.  Because the mirror is in the atmosphere at all times, it is already
being subjected to ~15 psi.  As long as the bagging technique has little or
no rigidity on both sides of the mirror, you are OK.

Don