Re: Dummies question - gap filler

On Thu, 4 Aug 2005 09:05:18 -0500, John Smith wrote
(in article <ygpIe.23238$bT4.7582@xxxxxxxxxxxxxxxxxxxx>):

>
> "John A. Weeks III" <john@xxxxxxxxxxxxx> wrote in message
> news:john-0706BF.08443304082005@xxxxxxxxxxxxxxxxxxxxxxx
>> In article <YsnIe.23214$bT4.13778@xxxxxxxxxxxxxxxxxxxx>,
>> "John Smith" <johnNOSPAMsmith@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
>>
>>> If you remove something called a 'gap filler' what replaces the gap?
>>
>> Shuttle techs routinely replace tiles after each mission.
>> When do work on a tile, they put these gap fillers on all
>> 4 sides of the tile to protect the tiles next to the tile
>> that is being fixed. When the repair is done, these gap
>> fillers are supposed to be removed.

That's utterly incorrect. The gap fillers in question have two
purposes. One of them is to prevent "chatter" of the tiles due to
launch vibration and acoustics. Such chattering can lead to tile
cracks. A second purpose (applicable to only one of the two that came
loose) is to literally fill a gap between two tiles which are installed
slightly too far apart due to tolerancing issues - e.g., one or both
adjacent tiles is a shade too narrow leaving an out-of-spec gap between
the two. Removed, it leaves a bigger-than-specificied gap; however,
the heat transfer analysis demonstrates that it will not result in
dangerous over-heating below these particular tiles.

You know, you should actually read the information available or you
know, pay attention during the daily post-MMT briefings before you
spout misinformation.


>> It looks like two of
>> them were missed. The problem isn't so much the gap or even
>> the filler itself. The issue is that if the filler breaks
>> off due to aerodynamic forces, it could damage the two
>> adjacent tiles.

Wrong again. The issue with the protrusions is that they might cause
localized overheating due to early boundary layer trip at high Mach
numbers. Analyses were all over the place, however, ranging from "no
problem" to localized overheating past the RCC single-entry temperature
limits of 3,250 degrees F in the worst case. Since the analysis was so
uncertain it was decided to remove them.

Please, you know, ACTUALLY PAY ATTENTION and you could learn something.

>> Two missing tiles in a sensitive place
>> could be a real problem.
>>
>> -john-
>>
>
> Thanks but... the filler was several inches in length and a few milimeters
> thick which, to me, would leave a gap between the two tiles it was
> inbetween. Doesn't that now leave a gap in the heat-shield or do the tiles
> expand when heated? I thought having no gaps, not even minute ones, was
> vital?

There has to be a very small space between most of the tiles because
the aluminum structure underneat is subject to expansion and
contraction. However the tiles are insulated from some of this by
felt-like isolation pads and, in some case, gap fillers. However, as
has been made clear in several of the post-MMT briefings, the gap
fillers generally serve no purpose during entry. They are there mostly
to prevent "chatter" of the tiles. One of these, however, was there
because the gap between the two tiles was too big. Thermodynamic
analysis showed that removing this particular one would not result in
any significant overheating nor cause any damage.

--
"Fame may be fleeting but obscurity is forever." ~Anonymous
"I believe as little as possible and know as much as I can."
~Todd Stuart Phillips
<www.angryherb.net>

.

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