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
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