Investigating the SpaceX Rocket Explosion of September 1, 2016

[jim hardy]

That diagram appears to relate to the rare helium-3.

Oops !

it's difficult to find a chart that goes above ~10K. Thanks...

Oxygen has a melting point of 55 K and atmospheric pressure, slowly increasing with pressure. You don't want the oxygen to get colder than that, and you cannot fill in oxygen colder than 55 K.

okay, Thanks. It's becoming clearer to me.

What Elon said was the temperature was just above freezing and was -340°F or -207°C.
(reply #30 at https://forum.nasaspaceflight.com/index.php?PHPSESSID=pht92iam9tpu1iocsng4l1ak41&topic=39072.20 )

-207 is 66K ?
from this

Boiling point is 90K

warming an ideal gas from 66 to 90 should raise its pressure by 90/66 = 1.36
i don't know yet how close is helium in those tanks to ideal

plodding along,

old jim

 

[jim hardy]

this appears to be "Hitchiker's Guide to Helium"

but it's still downloading...

http://nvlpubs.nist.gov/nistpubs/Legacy/TN/nbstechnicalnote631.pdf

 

[Jonathan Scott]

The overwrap is carbon and resin. Ignition of the first 30 grams of carbon in pure O2 produces a megajoule. In a rocket built at the margin to save weight, I think a very little carbon combustion is required to burst the tank. With O2 loose along with an ignition source, all the structure burns.

My point is that the energy of any reaction involving a patch of the overwrap and solid oxygen (at least up to the point where it lost integrity) would have been small compared with the energy released by the resulting COPV failure when the overwrap split, and that of course would be small compared with the energy released by the subsequent burning of the LOX / fuel mixture. Just based on orders of magnitude, I don't think that the pressure shock wave from a small amount of burning overwrap material would itself have caused immediate splitting of the 2nd stage, but that from a COPV failure would have easily been able to do so.

Although I understand that immersing almost anything in LOX will enable it to burn rapidly and fiercely, I still feel it's more likely that any exothermic reaction between the overwrap and solid oxygen would have been very localized, along a stress ridge or similar produced after buckled liner was pushed back into shape by the helium.