Author Topic: SpaceX Dragon 2 Updates and Discussion - Thread 2  (Read 139141 times)

Offline Johnnyhinbos

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #20 on: 10/04/2016 06:15 PM »
There's about a dozen videos out there (including thread 1 of this topic) superimposing the dragon pad abort test with the AMOS-6 conflagration, demonstrating that the LAS would have worked. Elon also tweeted to that effect.
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Offline Lars-J

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #21 on: 10/04/2016 06:17 PM »
Just a general question, does anyone here have any reason to think that the LAS on the Dragon would not have been sufficient to pull a crew away from the failing Amos-6 rocket?

Here in an overlay that shows how the LAS (if undamaged) should be sufficient: https://gfycat.com/RichNippyAnemonecrab

Offline mfck

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #22 on: 10/04/2016 07:28 PM »
Because the capsule re-enters at a positive angle of attack, to generate lift.  The heat shield is symmetric around the "nose" of the capsule as it re-enters "nose up".

EDIT: actually, probably symmetric about the zero angle-of-attack point (ie, oncoming airflow).  Presumably we'd call the geometric center of the heat shield the "nose", and it's not symmetric about that.

Thanks for taking time to answer, though I fear my question did not come through properly. Your explanation is about why the shield layout is not concentric with the capsule shape it covers.

My question was regarding the symmetry of the attach points, which is radial but is rotated about 10° as if not to align with the shield left-right or top-bottom symmetry axis.

P.S. My guess is that it's done to avoid tiles with too little area
« Last Edit: 10/04/2016 07:35 PM by mfck »

Offline whitelancer64

Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #23 on: 10/04/2016 07:58 PM »
Thanks, johnny and Lars, the video overlays do seem convincing to me, however, I'm in an argument elsewhere with someone who is convinced they prove nothing. Specifically, he has said "in order for an abort system to have a chance of working you need advance warning (in the range of at least several seconds) and to get that warning you need to know what you are looking for and as of now SpaceX doesn’t."

So since SpaceX has not yet determined what the cause of the anomaly was, the computer system would not have been able to recognize that it should initiate a launch abort. He is also convinced that a launch abort system needs "several seconds" to initiate. He also seems to believe the capsule must be going supersonic within 0.1 seconds in order to get safely away from the fireball.
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Offline Lars-J

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #24 on: 10/04/2016 08:03 PM »
Thanks, johnny and Lars, the video overlays do seem convincing to me, however, I'm in an argument elsewhere with someone who is convinced they prove nothing. Specifically, he has said "in order for an abort system to have a chance of working you need advance warning (in the range of at least several seconds) and to get that warning you need to know what you are looking for and as of now SpaceX doesn’t."

So since SpaceX has not yet determined what the cause of the anomaly was, the computer system would not have been able to recognize that it should initiate a launch abort. He is also convinced that a launch abort system needs "several seconds" to initiate. He also seems to believe the capsule must be going supersonic within 0.1 seconds in order to get safely away from the fireball.

I don't think an abort system would have much of a problem realizing that the upper stage it is sitting on is disintegrating. All power and communication lines have just been severed, and if that isn't a signal to abort - what is?  ;D And the advance warning of several seconds is just B.S., Super Draco engines can go to full thrust very quickly - on the order of milliseconds, not seconds.
« Last Edit: 10/04/2016 08:04 PM by Lars-J »

Offline whitelancer64

Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #25 on: 10/04/2016 08:06 PM »
Thanks, johnny and Lars, the video overlays do seem convincing to me, however, I'm in an argument elsewhere with someone who is convinced they prove nothing. Specifically, he has said "in order for an abort system to have a chance of working you need advance warning (in the range of at least several seconds) and to get that warning you need to know what you are looking for and as of now SpaceX doesn’t."

So since SpaceX has not yet determined what the cause of the anomaly was, the computer system would not have been able to recognize that it should initiate a launch abort. He is also convinced that a launch abort system needs "several seconds" to initiate. He also seems to believe the capsule must be going supersonic within 0.1 seconds in order to get safely away from the fireball.

I don't think an abort system would have much of a problem realizing that the upper stage it is sitting on is disintegrating. All power and communication lines have just been severed, and if that isn't a signal to abort - what is?  ;D And the advance warning of several seconds is just B.S., Super Draco engines can go to full thrust very quickly - on the order of milliseconds, not seconds.

That is precisely what I've been saying! To no avail, it seems. I should probably just let this one go.

And yes, a report from a few years back said from the signal to ignite to full thrust of the SuperDracos is less than 100 miliseconds. I've mentioned that, too, but again, deaf ears.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline SWGlassPit

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #26 on: 10/04/2016 08:18 PM »
Saturn used a breakwire system to trigger aborts -- three wires running the length of the vehicle.  If two of them break (not counting staging), clearly something bad was happening and they would not go to space today, so an abort was triggered.  I don't know what the CCtCap providers use, but it's hard to beat that level of simplicity.

Offline DavidH

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #27 on: 10/04/2016 10:50 PM »
Thanks, johnny and Lars, the video overlays do seem convincing to me, however, I'm in an argument elsewhere with someone who is convinced they prove nothing. Specifically, he has said "in order for an abort system to have a chance of working you need advance warning (in the range of at least several seconds) and to get that warning you need to know what you are looking for and as of now SpaceX doesn’t."

So since SpaceX has not yet determined what the cause of the anomaly was, the computer system would not have been able to recognize that it should initiate a launch abort. He is also convinced that a launch abort system needs "several seconds" to initiate. He also seems to believe the capsule must be going supersonic within 0.1 seconds in order to get safely away from the fireball.

I don't think an abort system would have much of a problem realizing that the upper stage it is sitting on is disintegrating. All power and communication lines have just been severed, and if that isn't a signal to abort - what is?  ;D And the advance warning of several seconds is just B.S., Super Draco engines can go to full thrust very quickly - on the order of milliseconds, not seconds.

That is precisely what I've been saying! To no avail, it seems. I should probably just let this one go.

And yes, a report from a few years back said from the signal to ignite to full thrust of the SuperDracos is less than 100 miliseconds. I've mentioned that, too, but again, deaf ears.
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Online hamerad

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Hamerad
« Reply #28 on: 10/04/2016 11:08 PM »
I wonder how those people that think a dragon 2 wouldnt survive get around the fact that its capable of reentry and as such should be able to survive an explosion/fast fire for a few extra seconds until LAS activates.
« Last Edit: 10/05/2016 01:24 AM by hamerad »

Offline Toast

Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #29 on: 10/04/2016 11:42 PM »
Specifically, he has said "in order for an abort system to have a chance of working you need advance warning (in the range of at least several seconds) and to get that warning you need to know what you are looking for and as of now SpaceX doesn’t."

Well, he's definitely wrong on several points. For starters, the Dragon capsule doesn't need to know what the failure is, or why it happened, it just needs to know that there was a failure. Although just to play devil's advocate, we don't know that the Dragon 2 would have aborted safely. We know that it is capable of doing so, but launch abort systems are one of the things that you hope you never have to use in the real world. The launch abort systems are both complex and tightly coupled, and I always fall back to the "Normal Accidents" model when there's conditions like that. During Three Mile Island, a faulty valve let emergency coolant flow out of the reactor, but wasn't caught because the status light for the valve showed that it was closed, and a temperature gauge that would have tipped off operators was ignored for multiple reasons that were only problematic in hindsight. Later in the cascade of events, a hydrogen bubble formed, which at the time some people in the industry didn't believe was actually possible. The system was built to be fault-tolerant, but the unforeseen interactions between systems allowed it to fail anyways. Similarly, launch abort systems are designed to be fault-tolerant and as simple as possible, but it's still something you'd rather never need to use, because the time scales involved preclude any human intervention should something go wrong.
« Last Edit: 10/04/2016 11:42 PM by Toast »

Offline envy887

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #30 on: 10/05/2016 12:24 AM »
Thanks, johnny and Lars, the video overlays do seem convincing to me, however, I'm in an argument elsewhere with someone who is convinced they prove nothing. Specifically, he has said "in order for an abort system to have a chance of working you need advance warning (in the range of at least several seconds) and to get that warning you need to know what you are looking for and as of now SpaceX doesn’t."

So since SpaceX has not yet determined what the cause of the anomaly was, the computer system would not have been able to recognize that it should initiate a launch abort. He is also convinced that a launch abort system needs "several seconds" to initiate. He also seems to believe the capsule must be going supersonic within 0.1 seconds in order to get safely away from the fireball.

It wasn't an explosion, and there no particular reason why a crewed dragon would need to get out of there instantly.

Dragon could have sat on the TEL for at least as long as the payload fairing did  (about 3 seconds if I recall correctly) with no adverse affects to the crew. That's a fairly benign environment compared to re-entry.

Offline whitelancer64

Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #31 on: 10/05/2016 05:48 PM »

Welcome to Jim's world.

That is high praise! Thank you very much.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline DavidH

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #32 on: 10/05/2016 06:10 PM »

Welcome to Jim's world.

That is high praise! Thank you very much.
Not really about the content of your post, just that no matter what insanity people KNOW is the truth, it's still not true but they argue it against his knowledge and experience all day long.
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Offline uhuznaa

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #33 on: 10/11/2016 09:20 AM »
Thanks, johnny and Lars, the video overlays do seem convincing to me, however, I'm in an argument elsewhere with someone who is convinced they prove nothing. Specifically, he has said "in order for an abort system to have a chance of working you need advance warning (in the range of at least several seconds) and to get that warning you need to know what you are looking for and as of now SpaceX doesn’t."

So since SpaceX has not yet determined what the cause of the anomaly was, the computer system would not have been able to recognize that it should initiate a launch abort. He is also convinced that a launch abort system needs "several seconds" to initiate. He also seems to believe the capsule must be going supersonic within 0.1 seconds in order to get safely away from the fireball.

It wasn't an explosion, and there no particular reason why a crewed dragon would need to get out of there instantly.

Dragon could have sat on the TEL for at least as long as the payload fairing did  (about 3 seconds if I recall correctly) with no adverse affects to the crew. That's a fairly benign environment compared to re-entry.

Dragon, yes. I'm not too sure about the trunk surviving intact though. And Dragon needs the trunk to stabilize the trajectory when the LES fires. With a satellite there is the payload adapter at the bottom, but the trunk is just a hollow cylinder sitting on its rim on top of the second stage. An overpressure event could easily rip it apart. Much easier than damaging Dragon anyway.


Offline drzerg

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #34 on: 10/11/2016 08:46 PM »
only way to destroy dragon on the pad is explosion sufficient to break capsule integrity via shockwave. temperature from burning kerosene is no way can do that. dragon only need trunk to stabilize its way AFTER les fires. it of course helps from the start but not critical.

Online Chris_Pi

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #35 on: 10/11/2016 08:54 PM »
He is also convinced that a launch abort system needs "several seconds" to initiate. He also seems to believe the capsule must be going supersonic within 0.1 seconds in order to get safely away from the fireball.

It's probably like talking to a brick wall, But you might point out :

(1) The Little Joe Apollo LES test fired on it's own when the rocket broke up in flight unexpectedly and did so fast enough to work properly.

(2) An escape system that has to go 0-supersonic in a tenth of a second is pretty much guaranteed to be fatal. If this is needed there's no survivable way out anyways.

Offline eriblo

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #36 on: 10/11/2016 09:10 PM »
He is also convinced that a launch abort system needs "several seconds" to initiate. He also seems to believe the capsule must be going supersonic within 0.1 seconds in order to get safely away from the fireball.

It's probably like talking to a brick wall, But you might point out :

(1) The Little Joe Apollo LES test fired on it's own when the rocket broke up in flight unexpectedly and did so fast enough to work properly.

(2) An escape system that has to go 0-supersonic in a tenth of a second is pretty much guaranteed to be fatal. If this is needed there's no survivable way out anyways.
Think you can remove "pretty much" - that's well over 300 g, aka pink jelly territory  :o
« Last Edit: 10/11/2016 09:11 PM by eriblo »

Offline koshvv

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #37 on: 10/12/2016 02:19 AM »
Think you can remove "pretty much" - that's well over 300 g, aka pink jelly territory  :o
For at least it will be contained in spacesuits, so the capsule won't be stained.
« Last Edit: 10/12/2016 02:21 AM by koshvv »

Offline Robotbeat

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #38 on: 10/12/2016 02:31 AM »
Think you can remove "pretty much" - that's well over 300 g, aka pink jelly territory  :o
For at least it will be contained in spacesuits, so the capsule won't be stained.
It'd crush the capsule, too. Heck, the engines would probably just rip right off the vehicle, so the crew would be okay. :D
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Offline acsawdey

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Re: SpaceX Dragon 2 Updates and Discussion - Thread 2
« Reply #39 on: 10/12/2016 02:59 AM »
Reminds me of this, which only accelerated at 100g:



0 to Mach 10 in 5 seconds  :o

Definitely pink-jelly territory. Formula 1 drivers have walked away from crashes with peak deceleration in excess of 50g but the duration is rather shorter than what's needed for an escape system.

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