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
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