JF Mezei wrote on Sun, 28 Apr 2019
23:11:19 -0400:

On 2019-04-28 22:13, Fred J. McCall wrote:

Uh, no. There is no 'abort test'. The abort test is what they were
working their way toward several months from now.

IsN't capsule jettison an "abort" test ? If not sorry for bad terminology.


There was no 'capsule jettison' as part of this engine test sequence.
There are two abort cases they really want to test (the two are at the
extremes of the envelope). One is a 'ground abort', where the capsule
needs to escape before or very near after liftoff. That test was
completed years ago. The other case is a 'Max Q' abort, where the
capsule separates and escapes when the stack is undergoing maximum
aerodynamic pressure. That's the one they're working toward doing.
The test with the anomaly involved a restrained capsule firing engines
just as an engine test.

IF legit, this video shows capsule explosion happening before exhaust is
seen out of engines.

Which doesn't tell you anything at all.

Not seeing exhaust from Super Dracos before explosion seems to be
significant to me. Bas there been say 2 seconds of exhaust and SpaceX
telemetry shwhoing "take off " force of the capsule against its stand
and then kaboom, it woudl mean that engines started and produced thrust
before things went wrong.


It may seem 'significant' to you, but it shouldn't.


If the kaboom happens before that, it would point to the explosion
happening prior to the hypergolics mixing in the combustion chamber and
then goig out the exhaust.


You don't know that. For example, one hypothetical failure that would
look like what is seen would be a catastrophic combustion chamber
failure right when the propellents mix.


What is not known is the time delay between the command to strt engines
and the explosion. If 10 seconds elapsed between command and explision
with engines showing no sign of thrust, it is quite different from a big
kaboom happening within a second of command being sent.


You can flap your arms all you like but you can't come up with a
hypothesis that will fly without a LOT more data (and there are a lot
more things that aren't known than the one you cite).


For hypergolic fuels, do any of the 2 components have ability to ignite
without the other component when in contact with air ? Or are they truly
inert until the 2 components meet ? (aka: could combination of spark and
ambient air with O2 in it cause one of the 2 to ignite ?) Or does the
explosion imply that the 2 components did meet/mix ?


You can get hydrazine to oxidize in air, but it won't be nearly as
energetic as when oxidized with dinitrogen tetroxide. For example,
hydrazine is used as a foam blowing agent because of the huge
quantities of gas it produces during normal oxidation. The question
is where would air and a spark come in contact with gaseous hydrazine?
I consider it unlikely in the extreme. I'd consider the likely causes
here to be a pressure vessel or pressure line failure or a combustion
chamber failure. I'm sure there are lots of other possible failure
modes.


--
"Insisting on perfect safety is for people who don't have the balls to
live in the real world."
-- Mary Shafer, NASA Dryden