JF Mezei wrote on Fri, 3 May 2019
11:40:51 -0400:

On 2019-05-03 01:07, Fred J. McCall wrote:

Well, yeah, it was. You realize that "500 msec" means you're right in
the midst of it, don't you?

If it is 500msec BEFORE ignition, you're not in the midst of it.


You really don't have a clue as to just how pressure fed hypergolic
engines work, do you, much less just how short a time 500 msec is.


Later, you mentioned thet they only pressurize the tanks just before
first firing. So perhaps the explosion happened as they pressurized
tanks, before valves started to let the fuel flow to combustion chamber.


Pretty sure I listed that as one of the possible causes. Perhaps a
pressure line was full of Magic Monkey **** (tm) from the monkeys that
flew out your butt.


So it isn't a given that this happened at time a command was sent to
send fuel to combustion chamber.


Pretty sure I haven't seen anyone, including myself, say that it was.


SpaceX would know exactly what was happening 500ms before the incident.


You might want to comprehend a few little details like what the
actuation times for valves and fuel flow times are.

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?


Yes, which is precisely why "approximately 500 msec" doesn't tell you
much, if anything.


I don't know how long it takes for components to travel from the tank to
the combustion chamber. SpaceX does.


Then you should shut up and stop carping when people try to answer
your questions.

is 'yes'. I say that because BOTH cases are true. Generally the fuel
tanks won't be initially pressurized until just before the first time
you fire the rocket engine.

Since Super Dracos's primary role is the emergency escape system, does
pressurizing "on demand" make a difference in terms of how quickly the
engines fire and pull the capsule off the rocket?


Think about what you just asked and how pressurization works.


I would have really expected them to "arm" the system prior to crew
ingress. But if the delay between unpressurized fuel and the engines
providing thrust is small then I guess the two can be combined.


Why would you expect that? Remember that once you pressurize the fuel
tanks there is no good way to depressurize them.

However, since there is no way to
depressurize the fuel tank once it's pressurized,

In a context where you are switching from optimum pressure from Super
Draco to Draco, you can start with the higher pressure and once you fire
the Dracos, pressure drop to a poit where the Draco regulator starts to
feed more helium to maintain optimum pressure.


Think about what you just said. First, it makes no sense. Second,
you're still stuck in your imaginary system where SuperDraco and Draco
are sharing fuel and pressurization systems. Third, think about the
difference in fuel flow and just how little depressurization you're
going to get puffing Draco thrusters out of a fuel tank that is
overpressurized for that and contains a ton and a half of fuel at that
pressure.

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? 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.


Why would there be any fail of anything anywhere? Gee, obviously
there was no problem at all!


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.


Pretty sure that was on my list. Alternatively, there could have been
a minute flaw in one of the COPVs that caused an eventual failure and
you've got the same sort of massive sudden overpressure of a
propellant tank. I know reading is hard for you, but you should have
noted that among other things I didn't give any particular probability
of which possible failure happened. There's a reason for that.


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


Well, no it doesn't, quite. Consider, a COPV failure, a propellant
tank failure, a valve failure, and a sensor failure all look the same
since they all result in a massive spike in propellant tank pressure.

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.


Why, they clean it up by cleaning it up. They DON'T clean it up by
doing other things instead of cleaning it up.


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.


Yes, yes, you were frightened by Elon Musk when you were just a baby.
We get it.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn