[meteorite-list] Tile Glows

From: MexicoDoug <mexicodoug_at_meteoritecentral.com>
Date: Mon, 27 Jun 2011 14:44:05 -0400
Message-ID: <8CE031153513798-ED4-9DF8_at_webmail-m019.sysops.aol.com>

Wow ! Nice links, James. Still aren't clear what the heat-exposed
surface looks like on a microscopic scale after use, but it certainly
sounds on paper like the tiles are near perfectly resistant/stable. Can
you imagine an artificial bolide made of a sphere of this material?

My favorite size, a basketball sized-sphere of it falling from orbit
would have the following characteristics:

1024 gram mass
59 mph (95 km/h) impact velocity
NOT TOO HOT AND NOT TOO COLD - BUT JUST RIGHT TO TOUCH!
...and apparently no ablation loss!

For comparison, a real inflated basketball, on the other hand would
theoretically be:

650 gram initial mass
47 mph (75 km/h) impact velocity, theoretically: if it could withstand
the atmospheric passage
but you'd end up with an exploded smelly burnt cinder instead that you
wouldn't really want to touch ;-)
...if not complete ablation loss!

This stuff is only 57% heavier than the bulk density of an inflated
basketball! Space Hoops, anyone ... a chance for games out of the pages
of an Asimov, Clark or Heinlein novel for those brave enough to play
space-catch!

Best wishes
Doug


-----Original Message-----
From: James Beauchamp <falcon99 at sbcglobal.net>
To: cdtucson at cox.net; meteoritemike at gmail.com; John at Cabassi.net;
rickmont at earthlink.net; MexicoDoug <mexicodoug at aim.com>
Cc: Meteorite-list at meteoritecentral.com
Sent: Mon, Jun 27, 2011 7:58 am
Subject: A better link.. Re: [meteorite-list] Tile Glows


http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts_sys.html

The HRSI tiles are made of a low-density, high-purity silica
99.8-percent amorphous fiber (fibers derived from common sand, 1 to 2
mils thick) insulation that is made rigid by ceramic bonding. Because
90 percent of the tile is void and the remaining 10 percent is
material, the tile weighs approximately 9 pounds per cubic foot. A
slurry containing fibers mixed with water is frame-cast to form soft,
porous blocks to which a collodial silica binder solution is added.
When it is sintered, a rigid block is produced that is cut into
quarters and then machined to the precise dimensions required for
individual tiles.
HRSI tiles vary in thickness from 1 inch to 5 inches. The variable
thickness is determined by the heat load encountered during entry.
Generally, the HRSI tiles are thicker at the forward areas of the
orbiter and thinner toward the aft end. Except for closeout areas,
theHRSI tiles are nominally 6- by 6-inch squares. The HRSI tiles vary
in sizes and shapes in the closeout areas on the orbiter. The HRSI
tiles withstand on-orbit cold soak conditions, repeated heating and
cooling thermal shock and extreme acoustic environments (165 decibels)
at launch.
For example, an HRSI tile taken from a 2,300 F oven can be immersed in
cold water without damage. Surface heat dissipates so quickly that an
uncoated tile can be held by its edges with an ungloved hand seconds
after removal from the oven while its interior still glows red.
The HRSI tiles are coated on the top and sides with a mixture of
powdered tetrasilicide and borosilicate glass with a liquid carrier.
This material is sprayed on the tile to coating thicknesses of 16 to 18
mils. The coated tiles then are placed in an oven and heated to a
temperature of 2,300 F. This results in a black, waterproof glossy
coating that has a surface emittance of 0.85 and a solar absorptance of
about 0.85. After the ceramic coating heating process, the remaining
silica fibers are treated with a silicon resin to provide bulk
waterproofing.
Note that the tiles cannot withstand airframe load deformation;
therefore, stress isolation is necessary between the tiles and the
orbiter structure. This isolation is provided by a strain isolation
pad. SIPs isolate the tiles from the orbiter's structural deflections,
expansions and acoustic excitation, thereby preventing stress failure
in the tiles. The SIPs are thermal isolators made of Nomex felt
material supplied in thicknesses of 0.090, 0.115 or 0.160 inch. SIPs
are bonded to the tiles, and the SIP and tile assembly is bonded to the
orbiterstructure by an RTV process.
Nomex felt is a basic aramid fiber. The fibers are 2 deniers in
fineness, 3 inches long and crimped. They are loaded into a carding
machine that untangles the clumps of fibers and combs them to make a
tenuous mass of lengthwise-oriented, relatively parallel fibers called
a web. The cross-lapped web is fed into a loom, where it is lightly
needled into a batt. Generally, two such batts are placed face-to-face
and needled together to form felt. The felt then is subjected to a
multineedle pass process until the desired strength is reached. The
needled felt is calendered to stabilize at a thickness of 0.16 inch to
0.40 inch by passing through heated rollers at selected pressures. The
calendered material is heat-set at approximately 500 F to thermally
stabilize the felt.
The RTV silicon adhesive is applied to the orbiter surface in a layer
approximately 0.008 inch thick. The very thin bond line reduces weight
and minimizes the thermal expansion at temperatures of 500 F during
entry and temperatures below minus 170 F on orbit. The tile/SIP bond is
cured at room temperature under pressure applied by vacuum bags.
Since the tiles thermally expand or contract very little compared to
the orbiter structure, it is necessary to leave gaps of 25 to 65 mils
between them to prevent tile-to-tile contact. Nomex felt material
insulation is required in the bottom of the gap between tiles. It is
referred to as a filler bar. The material, supplied in thicknesses
corresponding to the SIPs', is cut into strips 0.75 inch wide and is
bonded to the structure. The filler bar is waterproof and
temperature-resistant up to approximately 800 F, topside exposure.
SIP introduces stress concentrations at the needled fiber bundles. This
results in localized failure in the tile just above the RTV bond line.
To solve this problem, the inner surface of the tile is densified to
distribute the load more uniformly. The densification process was
developed from a Ludox ammonia-stabilized binder. When mixed with
silica slip particles, it becomes a cement. When mixed with water, it
dries to a finished hard surface. A silica-tetraboride coloring agent
is mixed with the compound for penetration identification. Several
coats of the pigmented Ludox slip slurry are brush-painted on the
SIP/tile bond interface and allowed to air-dry for 24 hours. A heat
treatment and other processing are done before installation. The
densification coating penetrates the tile to a depth of 0.125 inch, and
the strength and stiffness of the tile and SIP system are increased by
a factor of two.
There are two different densities of HRSI tiles. The first weighs 22
pounds per cubic foot and is used in all areas around the nose and main
landing gears, nose cap interface, wing leading edge, RCC/HRSI
interface, external tank/orbiter umbilical doors, vent doors
andvertical stabilizer leading edge. The remaining areas use tiles that
weigh 9 pounds per cubic foot.

--- On Sun, 6/26/11, MexicoDoug <mexicodoug at aim.com> wrote:

From: MexicoDoug <mexicodoug at aim.com>
Subject: Re: [meteorite-list] Tile Glows
To: falcon99 at sbcglobal.net, cdtucson at cox.net, meteoritemike at gmail.com,
John at Cabassi.net, rickmont at earthlink.net
Cc: Meteorite-list at meteoritecentral.com
Date: Sunday, June 26, 2011, 11:36 PM

Richard, James, very cool ... and especially being a witness of history
in the making for you guys ...

Does anyone know if these tiles show any signs of fusion (Is there
evidence of a fusion crust in this material or is is so structurally
pure and aerodynamically designed that a tile in proper service never
reaches a temperature for that to occur) as they wear out, or how
exactly material disappears as they wear out in old age (vs. a defect)?

Best wishes
Doug
Received on Mon 27 Jun 2011 02:44:05 PM PDT