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Comment by soheil | Hacker News Reader

The explosion was unexpected so either they will have to fix what went wrong there, which in turn will possibly effect the design which would then most likely need another flight test if you want to be safe enough or they will let it be as is which would be unsafe?

They expected the splashdown to happen several seconds later than it did. This could mean the capsule was going faster than it should have before its parachute deploy or it didn't slow down enough when hitting the water which would be worse.

Finally the main parachutes where touching each other pretty aggressively it wouldn't seem than unfathomable that two or more of them get tangled up, I don't think there is a backup solution for if that happens.

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The explosion was fine and expected. They mentioned this in the livestream, although it looks like the FTS and not aerodynamic forces. Either way, it happened after the capsule was well clear.

Regarding splashdown timing, we will see. They've been testing this extensively in the background, and parachutes have been a pain point all around.

The explosion seemed very much like a controlled detonation and not a breakdown of the rocket as it falls through the atmosphere as was mentioned in the livestream so it seemed like an unplanned or unexpected explosion.

This is nonsense. The rocket was expected to explode. That's basically the only thing it can do once the dragon escapes.

You have a bunch of rocket fuel and a very hot rocket engine in close proximity when the booster starts to break apart. The explosion was entirely expected.

I also have no idea what an unplanned or unexpected controlled detonation looks like. It seems like a controlled explosion has to be planned or expected by definition?

I'm not sure what argument you're trying to make, on the one hand you say the explosion looked like a controlled detonation, on the other that it seems unplanned.

Like others have pointed out: as far as F9 was concerned, the test ended when Dragon detached. Whatever happened after that point is immaterial to the test, so to start saying that would require a reflight is nonsense.

The plan was an explosion due to free-fall and atmospheric forces. The plan was not for an explosion due to a controlled detonation. I hope you are able to delineate between the two and not do a cursory reading of my comment again.

> so to start saying that would require a reflight is nonsense

I said "most likely" and "if you want to be safe enough" I'm not sure why you assumed I meant "require"

Because you also said "... or they will let it be as is which would be unsafe?"

I think your reception here would be better if you dropped the attitude and recognized that your comment used pure speculation to imply that the outcome of the test was negative. Maybe that was not your intent, but then you should have asked more open-ended questions rather than slant them so obviously negatively.

> The plan was not for an explosion due to a controlled detonation.

What evidence do you have that it was a "controlled detonation"? Seems like you're making baseless assumptions and then getting upset when people don't understand what you're trying to say.

When rockets, full of liquid oxygen and propellant, start to break apart in the atmosphere they pretty quickly look like a an explosion.

A rocket with no nosecone will basically lose structural integrity very, very quickly. A rocket 'breaking down' doesn't look like fluttering bits and bobs raining down, it looks like a big fireball.

This makes sense. From footage of past explosions when the booster disintegrates, it's usually falling down. That's why I thought it was unexpected that it just blew up so quickly after the capsule was jettisoned.

> They expected the splashdown to happen several seconds later than it did. This could mean the capsule was going faster than it should have before its parachute deploy or it didn't slow down enough when hitting the water which would be worse.

While you can control for variables greatly when you're flying under an engine, I'd imagine it's not so easy to control for environmental variables (such as local variations in wind speed) when you're landing under parachutes. It probably would have been safer for the broadcasters to have had an estimated time of landing with a +/- 20 or so seconds on the display, but I personally doubt landing a little sooner than expected will be a major concern.

Makes sense, yeah maybe they should have a window on the display instead of a fixed time.

The explosion was very expected. "Falcon 9 will likely break apart due to aerodynamic loads immediately following Crew Dragon's escape"

https://www.reddit.com/r/spacex/comments/eq24ap/rspacex_infl...

It seemed controlled and not due to aerodynamic loads.

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?

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 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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