[AR] Re: starship pad flame trench?
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 22 Apr 2023 18:07:13 -0400 (EDT)
On Sat, 22 Apr 2023, Norman Yarvin wrote:
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...
Might have been a matter of timing. For the VTOL version of the F-35, the
USMC was worried about the hot exhaust jet from the articulating nozzle
(at the rear of the engine) spalling concrete surfaces. The Skunk Works
guys investigated this and found that concrete spalls at about 1000degF --
the binder falls apart and the concrete becomes flying gravel -- but a
typical F-35 landing only gets it up to about 600degF. However, that
relies on landings being relatively quick (operational VTOLs don't spend a
long time in hover -- a normal F-35 vertical landing is only about ten
seconds). The engine guys at P&W started out by building a fixed 90deg
demo nozzle for testing while they worked out the articulating nozzle...
and the fixed nozzle *did* spall the concrete.
(Heard a talk by Paul Bevilaqua, more or less the father of the F-35, a
little while back.)
Whether even thick steel will work... I'm guessing it'll get scarred,
but with just a few seconds' exposure maybe not.
Interestingly, the Saturn and Shuttle exhaust deflectors are basically
steel with concrete on top -- but it's not garden-variety concrete, and
the surfaces weren't flat sheets perpendicular to the exhaust.
Henry
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