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Comment by irjustin | Hacker News Reader

Congratulations to the SpaceX and the whole team! That moment of truth when the thrust was lost and the module separated was actually way faster than I had expected. I could barely notice the exhaust plume was smaller and the dragon had already left.

I think it's incredibly satisfying to note that SpaceX is so good at the launch sequence with the Falcon 9 that there were zero delays except weather. With any new rocket system test, I completely expect there to be multiple delays with the countdown.

Again, congrats to everyone and their hard work.

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I was also amazed by this until I watched the post press conference. Elon seemed to describe in an answer to Everyday Astronaut that the launch abort sequence was set to trigger at a specific speed/altitude and that it was the abort program that told the engines to shut down. I would like to see that clarified further but I watched that segment twice and it seems that the abort system was in control, and step 1 was shut down the main engine, step 2 - pressurize/start the abort engines, and so on.

That also could mean, while the abort system said "shut down", the thing that said "get away" was not directly connected, but still using sensor/telemetry inputs as the decision maker.

Also, I'm really interested in knowing if the fireball was performed by the automated abort system.

I would love these to be the answer, so looking forward to clarification.

That is my question too, if the abort system just went "Step 1, Step 2, etc." or if the abort system went "Step 1" and the automated processes took over from there. It wasn't entirely clear but it felt like the first one which is why I watched it again.

As for the fireball, from the press conference I got the sense that the fireball was not triggered manually, that the rocket just broke up.

Again, on neither I'm 100% sure.

1) the Dragon initiated the F5 booster shutdown when its sensors detected that it had reached the pre-programmed abort velocity 2) the Dragon initiated the escape according to the abort sequence, not by ground command 3) the fireball was initiated by structural failure as the F5 broke up due to aerodynamic forces, not by the range safety destruct. 4) All of these abort sequence actions were explained in SpaceX's live stream.

Minor nitpick about point 3. John Insprucker said around 13:40 in the stream: "our simulation show that the Falcon will likely break apart due to the tumbling, instead of having the destruct system triggered and destroying the rocket." So what you wrote at point 3 is only likely, but not certain. (Unless of course you know from some source, that they have confirmed the sequence of events since.)

Well point 3 means it didn’t have a blow up at time Y feature. If there was no plan to blow it up and simulations said it would likely blow up, isn’t a pretty safe conclusion that predicated explosion happened?

The upper stage (which is wired to the same FTS) hit the ocean intact.

If the flight termination system had been activated, the upper stage would have been unzipped by the same detonation cord. Since it hit the ocean intact we can presume the FTS was not activated.

F[alcon]5 was a concept that never made it past very early designs. The rocket SpaceX flies is the Falcon9.

I think he is referring to the 'block 5' Falcon, i.e. the current iteration in the development cycle of the Falcon 9.

Perhaps (I'm a pretty avid SpaceX enthusiast, and I've never heard that abbreviation before)

Absolutely. I must have fused Saturn V with Falcon 9 in my brain. It's F9.

To be fair, they're both pretty awesome rockets.

>Also, I'm really interested in knowing if the fireball was performed by the automated abort system.

No, that was the rocket breaking up and exploding. If the range safety system had triggered, it would have blown up the second stage, which flew off and crashed into the ocean in a massive explosion

The capsule controlled the abort. It shuts down the main engines then lights it own engines. These things aren't instant, it takes a second to spin up turbo pumps and get fuel flowing and for the fuel in the lines of the main engine to flow out after it sends the signal - that's why the rocket exhaust was still burning as the abort system lit up.

You are most likely concerned that this is more controlled than an actual emergency would look like?

It might not necessarily be an issue. The steps took only split-seconds anyways from what it sounds. Shutting down the main engines helps to escape but appears to not be required for a successful abort. The order might be required though (e.g. the commands need to be sent before the connection between the vehicles is severed) or just beneficial (maybe to give the turbo-pumps of the main engiens a few more moments to spin down already).

You would have one system trigger the simulated failure and another system trigger the abort sequence independently of the trigger system. If it's the same system that triggered the abort and activated the abort sequence after then you can only say that you have tested the abort sequence and not the abort sequence trigger.

They didn't know for sure when the abort would happen. It sounded as if they only tuned thresholds for parameters down to such low values that an abort would be triggered around maximum dynamic pressure (Max Q).

The abort was well after MaxQ, after the engines throttled up again.

I've read it was at max drag.

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