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Latest candidate for SpaceX pad explosion



 
 
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  #11  
Old October 19th 16, 11:29 AM posted to sci.space.policy
Jeff Findley[_6_]
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Default Latest candidate for SpaceX pad explosion

In article . com,
says...

On 2016-10-18 11:11, Fred J. McCall wrote:

What is "COPV" ?


I said it in the original article and you cut it out. Composite
Overwrapped Pressure Vessel.


Sorry, had not made the association between the two. my bad.


TNT is a solid. Does it care about pressure? Yeah, press it and it
makes a really big bang.


yes, but TNT, in solid form is stable until you ignite. It doesn't
expand or create pressure in the lunch box that it us carried into.

No. Most substances are denser in their solid phases than their
liquid phases.


So the fact that some LOX solidified shouldn't magically cause an
increase in pressure in the tank.


No, but this happened when the LOX and helium tanks were being filled.
Increasing the pressure inside the helium tank squeezed the carbon
composite. Since the oxygen trapped in the composite was *solid* it had
nowhere to go and caused the composite to fail. This released a lot of
energy in a very small location that was in direct contact with 100%
oxygen. In other words, an ignition source!

Is it possible that the cold is what did it? If the helium tank was
surrounded by oxygen that it was colder than design, it could have
caused the carbon fibre to become brittle, crack, and let helium out,
causing overpressiure in LOX tank and then things went kablooey ?


Doubtful considering how many times their "life leader" first stage has
been fired (I think they're up to 8 firings after it had been recovered,
which doesn't include the original flight and original test firings).
If any helium tank should have failed due to temperature/pressure
cycling, it should have been one of the helium tanks in that stage.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
  #13  
Old October 19th 16, 02:30 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Default Latest candidate for SpaceX pad explosion

JF Mezei wrote:

On 2016-10-18 08:36, Jeff Findley wrote:

It does when it's an energetic solid oxidizer (can't get much more
energetic than solid oxygen) right next to a solid fuel (carbon fiber).


Ahh. I remember asking early one what could be combusting in the rocket
with LOX leaking and gotten no answer.

I takle it that carbon fibre even when encased in resin is highly
combustible ? is the resin/epoxy also combustible in contact with LOX ?

(reminder to self: make sure not to spill any LOX on my bicycle :-(

Would fibre glass be less explosive or would the resin still provide the
combustible material that would yield the same result ?


The overwrap is there as MECHANICAL support, not insulation.
Fiberglass exposed to LOX temperatures is going to be, well, glass and
shatter into tiny pieces.

COVPs are not uncommon in rockets. However, supercooled LOX is.


You do that and you have what is called a "contact explosive". The
increase in pressure would cause it to literally explode.


Would it be fair to assume that a breach in the metal coating inside the
tank would have exposed LOX to carbon ?


Uh, you seem to have this backward. The composite is an OVERWRAP
around the helium tank to provide structural support. Oxygen getting
inside the overwrap exposes LOX to carbon. Normally the liquid
squeezes back out of the overwrap as the LOC tank is pressurized.
However, if it actually froze to a solid in there, it stays where it
is and gets carbon compressed into it. The pressure on the oxygen
surrounded by the carbon is what causes the problem.


--
"Insisting on perfect safety is for people who don't have the balls to
live in the real world."
-- Mary Shafer, NASA Dryden
  #14  
Old October 19th 16, 02:46 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Default Latest candidate for SpaceX pad explosion

JF Mezei wrote:

On 2016-10-18 11:11, Fred J. McCall wrote:

What is "COPV" ?


I said it in the original article and you cut it out. Composite
Overwrapped Pressure Vessel.


Sorry, had not made the association between the two. my bad.


TNT is a solid. Does it care about pressure? Yeah, press it and it
makes a really big bang.


yes, but TNT, in solid form is stable until you ignite. It doesn't
expand or create pressure in the lunch box that it us carried into.


Now try the same thing with dynamite or nitro.



No. Most substances are denser in their solid phases than their
liquid phases.


So the fact that some LOX solidified shouldn't magically cause an
increase in pressure in the tank.


No, pumping the tank full of LOX does that. Nothing magical.


Is it possible that the cold is what did it? If the helium tank was
surrounded by oxygen that it was colder than design, it could have
caused the carbon fibre to become brittle, crack, and let helium out,
causing overpressiure in LOX tank and then things went kablooey ?


No.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #15  
Old October 19th 16, 02:48 PM posted to sci.space.policy
Rob[_8_]
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Default Latest candidate for SpaceX pad explosion

Sylvia Else wrote:
Still, its customers might reasonably expect their satellites to be
launched on proven hardware, operated in the proven way, with
experiments involved with innovation done on hardware that isn't
launching an expensive satellite.


In some cases, rockets have been qualified by launching dummy satellites
(just a block of concrete or lead of the proper mass), but of course then
some people consider this a waste of resources and a pollution of space.
  #16  
Old October 19th 16, 03:07 PM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default Latest candidate for SpaceX pad explosion

JF Mezei wrote:

On 2016-10-18 23:27, Fred J. McCall wrote:

Hint: The pressure in the LOX TANK goes up as you add LOX.


Does it ?


No, I'm making it all up. Sheesh. What did I say again?


Don't they have an open vent as the pour liquid oxygen and let
evaporating O2 escape to keep pressure stable ? Don't they close that
gaseious escape valve just before launch ?


It's a pressure relief valve, not just a hole to the outside. What
did I say again?

Hint: The pressure in the LOX TANK goes up as you add LOX.


(if helium tank cracked and caused instant major increase in pressure,
then the open vent line couldn't have handled that and would have
allowed pressure inside to rise to beyond structural limits.


We're past that. The question is WHY the helium tank cracked.


Question: what advantage is there to have the helium tank inside the LOX
tank ?


Easier thermal management, among others.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
  #17  
Old October 19th 16, 09:11 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default Latest candidate for SpaceX pad explosion

In article om,
says...

On 2016-10-19 10:07, Fred J. McCall wrote:

We're past that. The question is WHY the helium tank cracked.



So at what point would combustion have begun ? when LOX comes into
contact with the carbon over the helium tank,


No, because that happens on every flight!

or LOX simply creating
mechanical failure of the HE2 tank, causing overpressure and mechanical
failure of LOX tank, at which point ignition happened on anything
conbustible around it ?


Doubtful.

or put another way: did ignition begin on the carbon fibre overwrap of
He2 tank, or did it begin after the LOX tank failed, releasing LOX
everywhere ?


Oh goodness. Try to keep up.

The working theory is that a small amount of LOX got into the carbon
fiber overwrap and got so cold, it turned into solid oxygen *inside* the
carbon fiber overwrap. When the pressure increased, it put pressure on
the overwrap, but the solid oxygen had nowhere to go, so *boom*.

Had the LOX not been quite so cold (i.e. like other sub-cooled LOX
missions that have been flown), it would have been fine, because no
solid oxygen would have formed. Instead, the small amount of LOX in the
carbon fiber overwrap would have been squeezed back out into the LOX
tank.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
  #18  
Old October 19th 16, 09:24 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default Latest candidate for SpaceX pad explosion

In article om,
says...

On 2016-10-19 06:23, Jeff Findley wrote:

LOX spilled on anything combustible is bad.


Would it be fair to state that the helium filled COPV has some sort of
coating on the outer surface to normally prevent LOX from igniting the
carbon fibre ?


I doubt it. What coating would be LOX compatible and not crack due to
the expansion and contraction of the COPV during normal fills and drains
while inside the LOX tank?

composite). The composite overwrap is in contact with the LOX *at all
times*, because the helium tanks are inside the LOX tank.


So how come the carbon on the outside of helium tank does not combust as
it sits in a pool of LOX ? (see question above).


No ignition source.

And if the LOX became solid, wouldn't it further enhance the
integrity/strength of the helium tank by providing even more support ?


No, the overwrap was trying to squeeze the oxygen back out, but could
not, so the theory is the overwrap failed (I'm guessing at or near the
location of the solid oxygen). That failure would release a lot of
energy, providing an ignition source.

Or does "solid" LOX really mean a slushy mixture, or an actual solid
block of LOX surrounding the helium tank.


It means solid oxygen. Like how ice is solid water.

Would the helium tank have contributed to the cooling of the LOX to form
an "ice" layer over the COPV tank ?


The pressure in the LOX supply line had to be greater than the pressure
in the tank, otherwise, how would you ever fill the tank? As such, the
LOX would drop in pressure as it entered the tank, resulting in a
corresponding drop in temperature. That could result in the outside of
the COPV getting so cold that solid oxygen was formed.

from a scuba dividng point of view, when you fill scuba tanks and
increase pressure, they get warm


Filling them from what? Is a compressor involved? If so, that
compressor *increases* the pressure of the gas which increases the
temperature of the gas. Clearly you can't do that with LOX and expect
it to be "sub-cooled" in the rocket. So clearly SpaceX isn't doing it
that way.

If you pour liquid helium in an empty tank at 1ATM, I assume it will at
first evaporate big time and be endothermic. But eventually, won't it
become exithermic once pressure builds up and the liquid no longer
evaporates ?


I don't know the details of how SpaceX does it (i.e. in what order are
the tanks filled). You'd have to ask them.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
  #20  
Old October 20th 16, 02:29 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 10,018
Default Latest candidate for SpaceX pad explosion

JF Mezei wrote:

You're still not getting it.

On 2016-10-19 06:23, Jeff Findley wrote:

LOX spilled on anything combustible is bad.


Would it be fair to state that the helium filled COPV has some sort of
coating on the outer surface to normally prevent LOX from igniting the
carbon fibre ?


No.


composite). The composite overwrap is in contact with the LOX *at all
times*, because the helium tanks are inside the LOX tank.


So how come the carbon on the outside of helium tank does not combust as
it sits in a pool of LOX ? (see question above).


They're at the top of the tank. Where does the boil-off happen?


And if the LOX became solid, wouldn't it further enhance the
integrity/strength of the helium tank by providing even more support ?


Composite OVERWRAP. The hypothesis is that liquid oxygen got into the
overwrap and froze solid. It is now surrounded by carbon and since it
is solid cannot 'squeeze out' as pressure increases in the LOX tank.


Or does "solid" LOX really mean a slushy mixture, or an actual solid
block of LOX surrounding the helium tank.


A slushy mixture would squeeze back out. It means solid INSIDE THE
OVERWRAP.


Would the helium tank have contributed to the cooling of the LOX to form
an "ice" layer over the COPV tank ?


Jesus, do you not understand what OVERWRAPPED means? Do this. Get an
Ace Elastic bandage. Make a fist. Wrap the elastic bandage around
your fist in multiple layers as tightly as you can. Get a small ice
chip. Force it between the layers of Ace bandage. THAT is what we're
talking about. Your fist is the metal He tank. The bandage is the
composite overwrap. The ice chip is, well, the ice chip.


from a scuba dividng point of view, when you fill scuba tanks and
increase pressure, they get warm


PV=nRT.


If you pour liquid helium in an empty tank at 1ATM, I assume it will at
first evaporate big time and be endothermic. But eventually, won't it
become exithermic once pressure builds up and the liquid no longer
evaporates ?


You're misusing the words 'exothermic' and 'endothermic'. The helium
pressure isn't the issue. OXYGEN pressure is the issue. Oxygen
vaporizes, which increases pressure in the tank until the safety valve
lets it vent. The tank is not being externally pressurized like a
scuba tank on a compressor. It is being internally pressurized by
some of the LOC evaporating.


--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson
 




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