Doug... writes:

[...]

Lots and lots of us speculated about whether or not there was ice mixed
with the foam that hit the wing. With all of the talk and all the
analysis the CAIB did, I still haven't seen a really good theory proposed
for the *process* that resulted in the shedding of such a large chunk (or
chunks) of foam from the bipod ramp.

One thing that the report noted is that it's interesting that all of the
known bipod ramp foam shedding events were from the left side, and that
the right side has a LOX line running by it. They speculated that it's
possible that that line is changing the aerodynamic flow in a way that
protects the right side of the bipod from whatever causes foam to shed
from the left side. It seems to me this would be something to look into
with wind tunnel testing if you were going to continue to fly with foam
on the bipod.

It wouldn't surprise me in the
least if ice formation was involved. It's not like foam has been shed
from *all* of the ET bipod ramps over 100+ shuttle flights, after all --
it's got to be a process that only happens occasionally.

Right, and some of the things that have been mentioned a
manufacturing/application differences (it's hand-applied rather than a
machine process, so it's probably, or could be, more variable), wind
shear (like Challenger, Columbia's flight controls were working hard
during ascent), and temperature (though I don't recall correlations
being made between temperature and foam shedding).

Ice, of course, is denser and more massive than foam. If the foam that
hit the wing had some ice within it, I think it's safe to say that the
energy dissipated during the strike (and imparted into the RCC) would
definitely be greater than if the impacting object were 100% foam.

This is the reasoning that people have been calling you on. Yes, ice
and foam would be denser than foam alone, but the energy imparted is
proportional to m*v**2 (using Fortan), and because increasing the
density of an object actually causes its relative velocity to be less in
the case we're talking about (object coming loose from the accelerating
shuttle and decelerating as the shuttle runs into it), it's not clear
that the energy would definitely be greater. Yes, all else being equal,
a foam/ice object will dissipate more energy than a foam object of the
same size, but having a foam/ice object means all else (velocity,
specifically) ISN'T equal. You have to do the math.

Unfortunately, it's going to be damn near impossible to ever determine
the exact ice content of the impactor, and it seems unlikely at this
point that anyone is going to spend the time or money to determine the
ice incorporation and shedding processes... *sigh*...

I would say that the board's recommendations require NASA to do just
that (determine the processes). It seems you disagree with the board's
conclusion that it's unlikely that ice formation occured. I'm not sure
why.

I think ice hitting the orbiter is potentially catastrophic, so all the
attention it's received is proper. It seems that this is a case where
ice wasn't necessary to cause LOV, but that doesn't mean we can stop
worrying about ice, just that there are more things to worry about.