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3M foam tapes


#1

In one of my recent posts on this subject, I mentioned that I
thought I remembered that the insulating tiles on the space shuttle
were affixed with foam tapes or something similar. I wasn’t sure of
that, though, so I did some web surfing today, and found that I was
not totally correct. Here’s a description of how they’re attached:

thermal insulation for the all-aluminum shuttle should be made of
silica–a ceramic material. Silica insulation for critical
high-temperature use is constructed from very pure and fine silica
fibers sintered togetherbonded at high temperature, creating over a
million temperature-welded joints per 1 cubic inch of material. The
sintered silica is shaped into 6-inch by 6-inch by 3.5-inch blocks,
covered with a black silica glass coating, and attached to the
shuttle surface by a nylon felt pad, approximately one quarter inch
thick, known as the strain isolation pad (SIP).

This pad isolates the brittle and weak silica block from the
aluminum surface, which expands much more than the fragile tile,
thereby causing the tile to crack and fail if attached directly. The
tile base is glued to the felt pad (SIP) with a rubber bond, and the
same “glue” is used to attach the SIP to the aluminum surface. The
1979 failure of the thermal shield was the loss of many of the
"critical" tiles–some 5,000 tiles (of a total of 28,000 on the
shuttle)–so critical that loss of even one would make reentry
non-survivable.

While this does indeed resemble the structure of a foam tape, the
description suggests suggests to me that this is not a commercially
available tape, felt, foam, or otherwise… so that part of my
memory is probably wrong. It does, though, nicely illustrate why
such attachment structures can have distinct advantages. The article
I culled this from was a discussion of the original design process,
and it’s revision following a test flight on top of a boeing
aircraft, during which the prototype shuttle lost a bunch of
tiles… It then describes how a Univ. of washington team solved the
problem by making the underside of the tile surfaces stronger, thus
giving the glue a denser and stronger surface to bond with. And it’s
not surprising they use sintered silica… that’s the same stuff our
Wesgo platinum melting crucibles are made of, though our crucibles
are a dense solid version made of highly sintered grains, not fibers,
so they’re a decent heat conductor, not an insulator.

Cheers
Peter