Such a video demo ignores at least two issues: How long does it take
from the decision to abort for Crew Dragon to start moving, and whether
the flame reached it or not how much shock/blast would have been
received by the capsule before it starts moving.
If you have a detonable mixture of a significant fraction of an F9's
propellant load and don't start leaving the neighborhood till the
detonation starts, you're way too late, of course. But we both know the
general nature of LOX-kero rocket failures is fortunately otherwise.
On 9/11/2016 6:44 PM, Randall Clague wrote:
People have made videos of the Dragon pad abort test superimposed on the
SLC-40 explosion. The Dragon does not start moving until there is
visible flame, and the flame never reaches it.
WRT detonation, there is such a beast as a deflagration-to-detonation
transition, and people put a lot of work into preventing or postponing
that transition. No one talks about reversing it. My understanding is
that if you have a detonable mixture, and a detonation begins, it
continues until the mixture is consumed.
-R
On Sunday, September 11, 2016, Henry Vanderbilt
<hvanderbilt@xxxxxxxxxxxxxx <mailto:hvanderbilt@xxxxxxxxxxxxxx>> wrote:
I've seen a detonation so small that the engine was still there and
usable after - no damage to the stand either. It was a small amount
of methane mixed with air touching off externally; the small
shockwave only showed up in video review (brightly sunlit) afterwards.
My guess in this instance would be that there was a relatively small
explosion (possibly a detonation) that initiated the visible flame
eruption, to produce the flame size achieved in one video frame.
There were undoubtedly other relatively small (relative to the
overall propellant load, at least) explosions (possibly detonations)
as well, notably when the payload's maneuvering propellant touched
off. The majority of the fuel and LOX seemed to go up in a mere
deflagration, however. Only an "explosion" in Hollywood.
I find it more interesting that Musk said the Crew Dragon escape
would have had time to work. This may imply that the apparent
several seconds of noisy lead-in to the visible initial explosion
actually does represent things going visibly wrong in the
telemetry. (I suspect NASA would be more than a little nervous
about taking him at his word if he's talking about an escape
initiated only after the initial visible explosion, FWIW. I'm not
sure I'd want a seat for that experiment either...)
Henry
On 9/11/2016 4:19 PM, Ben Brockert wrote:
It's nice folksy rocketeer wisdom, but is there any real reason to
think there wasn't any detonation at all? That's a lot of fuel and
oxidizer in close proximity on fire, and a simple tank burst from
pressure doesn't make a sharp boom audible and shaking windows from
ten miles away.
And no, it wasn't a BLEVE.
I've also had a detonation on a test stand, and the test stand and
engine were still there. Detonations aren't magic, and it's possible
to have a small one.
On Sun, Sep 11, 2016 at 6:32 PM, Randall Clague
<rclague@xxxxxxxxx> wrote:
"If you go out to the test stand and the test stand is
severely damaged, you
had a case burst. If you go out to the test stand and you
can't find the
test stand, you had a detonation." --Dave Hall
On Friday, September 2, 2016, Marcus D. Leech
<mleech@xxxxxxxxxx> wrote:
On 09/02/2016 05:01 AM, Aplin Alexander T wrote:
Classification: UK OFFICIAL
Handling Instruction: DISCLAIMER - this is a
personal e-mail and only
represents the views of the sender
FWIW, Elon Musk has tweeted to say it wasn't
actually an explosion (and
that Dragon would have been able to save itself):
"@scrappydog yes. This seems instant from a human
perspective, but it
really a fast fire, not an explosion. Dragon would
have been fine."
https://twitter.com/elonmusk/status/771479910778966016
<https://twitter.com/elonmusk/status/771479910778966016>
There was a window-rattling kaboom or two. It was an
explosion, but what
it *WAS NOT* was a detonation.
When you have a test-stand explosion you can tell the
difference between a
mere explosion, and a detonation easily. In the former
case,
there'll be burnt, and perhaps mangled, wreckage. In
the latter, you
can no longer find the test-stand :) :)
Alex Aplin
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