[AR] Re: starship pad flame trench?
- From: Norman Yarvin <yarvin@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 22 Apr 2023 11:40:30 -0400
On Sat, Apr 22, 2023 at 12:18:18AM -0700, roxanna Mason wrote:
Well , that's OK Norman, we can just agree to disagree. You can't have one
without the other, pressure must increase as the plume velocity decreases
and approaches zero, stagnates. Compression = heating. Another analogy, a
pitot tube converts velocity into pressure/airspeed.
Oh, you get a fair bit of pressure back too. But 300 bar? No way.
That would make the total force on the concrete pad orders of
magnitude greater than the total force on the rocket, where really
they have to be about equal.
Regardless, a concrete pad makes for a poor flame deflector and if I were
to be a gambling man I'd bet SpaceX employs some kind of flame deflector in
their next launch or, if they stay with a flat pad, it will be the largest
ablative heat shield in history. Even the Germans used a 4 lobed deflector
on the V-2 launch stand which the US used in the post war Redstone/Jupiter
C rockets which put the first US man in space (sub orbital).
SpaceX says that they had planned to put down a thick steel shield
even before this and had it in the works, but hoped they could get
away with concrete for this one launch. And they did get away with it
for the static tests, so it wasn't a ludicrous idea. But it seems
clear in hindsight that once they got a hole past the concrete and big
chunks started getting flipped out, the failure mode shifted from
"erosion" or "surface spalling" to "going to hell in a hurry".
Whether even thick steel will work... I'm guessing it'll get scarred,
but with just a few seconds' exposure maybe not. Also, differential
thermal expansion will make it bow up in the middle when it's heated,
which might cause trouble.
Other related posts: