Brian Thorn wrote:



Because if it was, and water got into the foam, and that water freezes
when they tank it up....



Like rain doesn't get all over the Tank during the month it sits out
on the pad before launch?



It's not supposed to soak into the tank IIRC; and that makes what
happened to the Atlantis ET worrying, as apparently water did get into
it from the hurricane. If the tanks are soaking up rain water, then you
might have one of the major causes of foam shedding - the foam gets
water in it; the water freezes when the tank is fueled, the freezing
water expands, causing cracking in the foam, and the foam sheds as the
tank warms up during ascent and the ice in the foam melts leaving gaps.
In fact, as the temperature of the ET rises during ascent and the
ambient air pressure drops, the water may actually boil, causing steam
to occur inside the foam.
The fact that water can get into the foam also leaves the possibility
that air might be coming in contact with the tank's outer surface via
the same route that's allowing the water in, and the frozen air foam
shedding problem occurring.

Pat