Interpeting Tile Damage Test Results

Just one interpretation of the Tile Damage test results.

What an interesting hole in the tile. From the arc jet test conducted with a
replica hole, it sure looks like a really nice vortex generator on the
bottom of the Orbiter. The nice compression face in the hole seems to be
generating a really nice vortex centered about the surface of the tile and
moving into the wing as it flow aft.

Here's the a picture of what arc jet damaged tile.

http://www.nasa.gov/images/content/1...shannon_01.jpg

The really nice 25-30 degree compression face is undamaged and intact after
the test. All the rough edges have been smoothed, but the functioning
surface is still there. As the relatively cool flow in the boundary layer
reaches the leading edge of the hole, it make an inward turn. This is an
expansion turn, so the flow cools. When the flow hits the compression face
(90 degrees to the bottom surface of the Orbiter) it make a second turn.
compressing the flow and heating it. But not enough to melt the compression
face. The third turn, another compression turn up and out of the hole and
into the boundary layer. Flowing down, right, and then up. Essentially
flowing in a circle in the hole.

Next, notice the wall between between the foam damage and the entry damage
to the tile. Conditions here are not enough to melt the silicon tile, well
maybe just a little bit right at the junction of the two compression turns.
Notice the aft divet hole. So, the vortex generator will remain intact
during entry. One expansion turn, two compression turns, generating a nice
vortex centered at the surface of the tile.

Next, the entry damage, the cut in the tile that is three times the size of
the original hole. A vortex constrained and centered on the surface of the
tile, bringing high temperature free stream flow impinging on the surface
of the tile. Hypersonic flow from 1 to 2 inches above (well really below)
the surface of the tiles, caught in a vortex and plunging through the
relatively cool boundary layer, impinging on the tile.

Where is this vortex going? Stuck between the surface of the tiles and the
compressed hypersonic flow under the Orbiter, it sure looks like it want to
go thru the Orbiter. Notice the end of the hole looks like a tunnel, the
surface of the tile is intact, but the meat of the tile has been melted
away. Right down to the felt isolator pad? Really trying to go thru the
aluminum and into the wing.

Compared to other random damage to the tiles, this is a much more dangerous
ding. Essentially, a vortex generator has been added to the bottom of the
Orbiter. It would be a really bad decision to leave such a thing
un-repaired and fly an entry with fingers crossed.

This brings to mind many, many more questions, and uncertainty about how
well NASA is functioning (decision making) and their analysis of their
current situation and to what end their technical bias is heading.

JOO,
--
Craig Fink
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