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Comment by soheil | Hacker News Reader

It seemed controlled and not due to aerodynamic loads.

The Falcon 9 has an AFTS (Automatic Flight Termination System) that destroys the booster if it veers off course (which might take other parameters into account as well?) to avoid damage on ground.

As far as I know the AFTS consists of a detonating cord that runs along the tanks for fuel and oxidizer and rips them open when triggered. The substances mix and deflagrate and only the massive parts will actually reach ground (or sea).

The cord unzips the tank, but deflagration wasn’t expected because mixing should have been limited.

It's immaterial either way. The booster isn't expected to survive an abort regardless of the reason for aborting.

An unexpected booster failure mode would be well worth investigating.

Nothing I've seen or heard yet suggests that the test experience was outside expectations.

It raises the question if the explosion was trigged by the self-destruct sequence and not as mentioned on the livestream by disintegration due to free-fall and aerodynamic forces, did the explosion happen too close to the capsule so as it might have adverse effects on the capsule?

The explosion was not triggered by the self destruct system as has been pointed out to you repeatedly, and even if it were the system has been designed to work correctly in that scenario too (this is covered in the press conference).

The system is designed to be able to abort from a deflagrating rocket without warning (although that was not the design of today's test, obviously). Today, Dragon was already well clear when the stage disintegrated 11s after the abort. Just eyeballing the footage, it's probably a km away.

Thanks for pointing that, it's obvious now that you say it. The next question is why didn't they just explode booster using the self-destruct sequence while the capsule is still attached to test a more realistic scenario?

It is confirmed that it was due to the aerodynamic load. Without a nosecone, the craft decelerates hard. The fuel sloshes towards the front of the tanks, ruptures them, then explodes. It all happens very fast.

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