[Jewelry making - Article 00756] - Re: [Orchid] 3M foam tapes

[Peter W . Rowe]

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    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 

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