On Mon, 3 Feb 2003, Hans Ulrich Ammann wrote:
> HS> (Caution: this is from a 1983 paper -- there may have been some change
> HS> along the way since.)
Jenkins3 says that the materials have indeed changed somewhat, but it's
still a urethane-based foam.
> Meanwhile I found the following:
> "The entire outer surface of the external tank is insulated with a
> half inch thick cork/epoxy layer covered with 1 to 2 inches of spray-on foam"
> (Damon, 1995, p. 134).
A quick look through several references doesn't find any specific mention
of a cork-based inner layer... Ah, wait a minute... Okay, I think I can
reconcile all this.
Jenkins3 says that the outer layer (except in a few very-high-heat areas
like cable trays) was originally CPR-488 (the CPR-421 derivative), since
replaced by another polyurethane and then another. In high-heat areas --
the aft dome, the nose, and some areas which see very high interference
heating -- there is an underlayer of SLA-561, which the 1983 paper notes
is cork-based.
So both versions are actually right: there *is* an inner layer of cork-
based insulation, but only in selected areas. The main insulation over
the whole tank is just the urethane foam.
> Im trying to get a feeling of how damaging a chunk of isolation could
> be. But eventually one has to consider that most of the mass of a torn
> of piece of insulation could consist of frozen moisture.
Quite so. The insulation is supposed to prevent ice/frost formation, but
a section which is defective enough to eventually come off might not be
doing that job properly either.
> In the moment
> a piece of insulation gets loose it has the same velocity as the whole
> vehicle, how important would be the relative velocity at the moment it
> would impact on the orbiter?
Much would depend on how far it "fell" before impact, and thus how much it
was slowed by air drag.
Henry Spencer
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