JF Mezei wrote on Sat, 4 May 2019
15:09:49 -0400:

On 2019-05-04 10:23, Jeff Findley wrote:

When the hypergolic fuel and oxidizer come into contact with each other,
they spontaneously ignite. So that's still ignition.

In LOX/hydrogen environment, ignition is a command that causes a spark
in the right place and assumes instant ignition.


Not exactly, no. I believe that the igniters start firing when the
count hits zero and 'ignition' is a status call indicating that the
thing actually lit. For example, on a Shuttle launch Main Engine
Start was commanded at T-6.6 seconds and solid rocket booster ignition
happened at T-0.


In hypergolic, it isn't clear to me whether ignition refers to the
opening of valves that let the combonents flow to combustion chamber, or
the time when the components meet and start to combust.


It's probably going to vary by rocket.


The former is a specific time where a command is sent. The later is a
fungible time that depends on how long it takes for components to travel
from tank/valve to the combustion chamber and then for chemical reaction
to start to happen.


Neither is a specific time. It's a status call.


Since I don't know what "ignition" means in terms of hypergolics, the
500ms time prior to ignition can mean anything.


Since you don't know what "ignition" means in terms of any rocket, I
guess that problem is solved.


Say ignition is defined as time combustion starts, and that it takes 1
second for fuel to travel from valve to combustion chamber, then 500ms
would be half a second after the valve was opened between tanks and
combustion chamber.

But if it takes 200ms for fuel to travel from valve to combustion
chamber, then 500ms means the explosion happened before valve opened.

And if ignition is defined as the time the valves are opened, then 500ms
would refer to a stable state prior to ignition, unless opening valve
between heliium tank and hypergolics to pressurize them happens 500ms
before valves between hypergolics and combustion chamber are opened.


The real question is what the guy who made the statement means by
'ignition'. 'Ignition' is a status call that indicates the thing is
actually lit. Obviously that's going to be a slightly variable
quantity.

Because the helium tanks, fuel tanks, and oxidizer tanks that supply the
Super Draco engines with propellant are all COPVs.

I would think that COPV aspect would be irrelevant since we're not
talking about a tank immersed into cryo tank.


So pressure vessels never fail unless they're immersed in a cryo tank?
What a silly notion!

Obviously, which is why the tanks themselves are not likely suspects for
the root cause in this case, IMHO.

I doubt that this system has liquid helium in it at all.
If they contained liquid helium, that would defeat their purpose
entirely.

Does Helium become liquid when compressed? Mr Google only tells me it
becomes liquid when cooled. I was under the impression that they would
load liquid helium in those tanks and it would remain liquid due to high
pressure.


Presumably if you could apply enough pressure you could get it liquid
at more 'reasonable' temperatures, but that's a preposterous amount of
pressure so it's not really a useful bit of information.


I know you mentioned the engines need ballpark 250-275 psi to push fuel
into combustion chamber. At what pressure would helium be stored at in
its own tank ?


Why do you think that matters?


Say helium is pressurized to 500psi in its own re-enforced tank, and the
hypergolic tanks are built to widthstand 300psi.


You have a preposterously low threshold for 'safety margin'. You also
have a ridiculously low idea for helium pressure. For example, helium
COPVs on the Shuttle had burst strengths north of 8,000 psi.


If, when they open
valve between helium and hypergolics, the regulators fail and pressurize
the hypergolics above 300, I could see hypergolic tanks failing.


It was on my list. I'm so happy you can "see it".

Which is why all this idle speculation is actually annoying to me.

Blame lack of transparency when observers were used to a lot of
transparency in the past.


Utter bull****. There is no 'lack of transparency'. To be
'transparent' THEY HAVE TO HAVE SOME IDEA WHAT HAPPENED AND THEY'RE
STILL ANALYZING THAT DATA.


But this speculation does allow people to learn how things work, so for
instance, you provided the pressure ranges needed , and hopefully a
definition of "ignition" in the context of hypergolics.


No, this 'speculation' is annoyance. There are ways to "learn how
things work" without being an obnoxious ****.

NASA and SpaceX are no doubt combing over any imagery they have. You
really have no right to see that imagery, IMHO. I'm not sure what
compelling interest the public would have in such imagery. All it would
do is fuel more idle speculation, which is not at all helpful.

Sicne NASA is government operation, don't USA citizens have a right to
that information through FOIA?


So go file for that. If they conclude it's not covered by SpaceX
trade secrets you'll get it in perhaps six months or so.


And I disagree on the speculation aspect.


Of course you do, but then you're not quite bright.


NOT providing it fuels
specualtion because it also fuels people wondering why they have to hide
and why. Releasing the data would have harmless discussion on potential
causes which eventually get confirmed.


Thank you for the loony conspiracy theory perspective on things. Since
you're going to be loony regardless, why feed you?


--
"Ordinarily he is insane. But he has lucid moments when he is
only stupid."
-- Heinrich Heine