Latest candidate for SpaceX pad explosion

While they haven't confirmed it as the cause yet, the current leading
candidate for the cause of the explosion is SOLID oxygen forming in
the composite overwrapped pressure vessel that helium is stored in.

This is how it would work. For this flight SpaceX was apparently
trying to increase the degree of super-cryo chilling on the liquid
oxygen, so they were pumping it even colder than normal (close to
freezing point). Some of the super-chilled LOX could have gotten into
the COPV and then frozen. As tank pressure went up, the solid oxygen
could not be squeezed back out of the overwrap and detonated with the
carbon composite wrapping. This breeched the helium pressurization
tank, overpressuring the LOX tank and things go up from there.

SpaceX has not confirmed that this is their leading theory (or even a
theory). It is being reported as something that came out of a private
conversation with Musk and SpaceX says they have a policy of not
commenting on private conversations by Musk.

If that's really the problem, it makes a return to flight easier. Just
revert to the 'normal' amount of chilling that they used on previous
flights.


--
"Insisting on perfect safety is for people who don't have the balls to
live in the real world."
-- Mary Shafer, NASA Dryden