In article ,
says...

On 2019-05-03 01:07, Fred J. McCall wrote:
Do you have any clue just how short 500 msec is when you're talking
about ignition of a hypergolic engine?

"ignition" ? is there an actual ignition in hypergolics? Wouldn't
starting the engine involve opening valves and then letting the 2
components travel to combustion chamber and ignite whenever they meet?

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

All that said, the probabilities of what went wrong remain the same:
COPV failure, pressurization valve or sensor system failure,

why would there be COPV failure in hypergolics?

Because the helium tanks, fuel tanks, and oxidizer tanks that supply the
Super Draco engines with propellant are all COPVs. Obviously they're
not the same design as the helium tanks in the Falcon, but they're all
composite overwrapped pressure vessels. That's the lightest way you can
make tanks like this. Note that we've been making tanks like this for
literally decades.

The thing that made the helium COPVs in Falcon unique is that they are
submerged in liquid oxygen. Obviously we don't have that with Dragon or
Dragon 2, but they all have COPVs.

No cryo issues or fuel
freezing. And if failure happened 500ms before engine start, it is safe
bet the helium tank(s) had been filled well before.

Obviously, which is why the tanks themselves are not likely suspects for
the root cause in this case, IMHO. But they are obviously involved in
the investigation because you don't rule anything out, at least
initially, in an investigation like this. You examine every single
possible cause.

If the regulator ended up releasing liquid helium into the fuel tanks
raising their pressure to well above design limits (before valve to turn
on engine is opened), that could cause tank failure and if both tanks
failed, you could go "kaboom" real fast.

I doubt that this system has liquid helium in it at all. It's far more
likely the helium tanks were at ambient temperatures (or close to them)
at the beginning of the test. Remember the helium tanks are meant to
pressurize the propellant tanks to pressures higher than the chamber
pressure of the Super Dracos. If they contained liquid helium, that
would defeat their purpose entirely.

It all depends on the sequence of events, which SpaceX already knows.

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

Why would you put people at risk for any of that? You've got to clean
it up anyway, so do that.

And how do thyey clean thing up ? don't they send people in suits with
scuba to do the cleanup? If they have robots do it, then those robots
can also survey the site and take pictures.

I suspect SpaceX has lots of imagery of post explosion already. The
"dangerous site" excuse is just an excuse to pretend they don't have
imagery.

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.

Jeff
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