Author Topic: SpaceX F9 / Crew Dragon : Crew-2 : 22 April 2021 - DISCUSSION  (Read 168289 times)

Offline soltasto

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The issue is known, but the root cause does not appear not be entirely under control, which is what's being argued. In fact, you say the non-deterministic cause is the capsule's wake flow, while the very tweet you quote (by an biased party, being SpaceX's former director) states it's understood to be a consequence of parachute crowding, not of turbulence directly.

Not being an expert on this, I decided to have a shallow look at what we're talking about here. Turns out that the "lead-lag" term he employs is actually a generic one referring to "undesirable frequency responses" (as per Wikipedia's definition), which has a whole field of "compensators" to mitigate them. In fact, if you google "lead lag parachute" you get some papers such as this one: https://airborne-sys.com/wp-content/uploads/2016/10/aiaa-1999-1700_evolution_of_the_ringsail.pdf or this one from old-friend Kistler https://airborne-sys.com/wp-content/uploads/2016/10/aiaa-1999-1707_design_and_testing_of_the.pdf that talk about many efforts to minimize lead-lag effects, as a variable you can't *null out* but definitely *can control*.

The comparison with car tyres is not really handsome, since heritage issues in fact prevent them to be as safe as their inherent design would allow, and many people "unnecessarily" die on the road worldwide because of it. Anyway, here we're not talking about the equivalent of a car manufacturer "controlling whether the road is wet or dry", which would translate into variable weather conditions for Dragon causing the parachute problems. An actual equivalent to a car scenario would be the acceptance of a significantly reduced factor of safety in braking action depending on a relatively frequent sloshing pattern of the brake fluid, which is known, classed as "in family" and not acted upon because it won't lead to a crash during a few hours of test driving - while summarily ruling out infrequent jamming of the other brakes because of possible one-in-a-thousand-times interactions.

I said that the capsule's wake flow is what decides whether the normal full deployment of all the 4 chutes occurs or if the delayed deployment of one of the chutes due to crowding occurs. Whether the crowding effect occurs or not is not due to a defect (bad production and QA) or even due to margins in the system not being tight enough (engineering issue) but it occurs or not depending on external variables. You can't control if all parachutes get the same exact amount of airflow or not in any moment in time.
This being said, it was discovered during testing (both due to natural occurrence of this behavior and by inducing this effect artificially by lagging a chute) that the delayed chute, as long as it isn't damaged, will deploy anyways within safe margins. If it is damaged that is a different issue anyways as it would fail on a normal deployment too, so it is irrelevant.

Offline Herb Schaltegger

I'm not a parachute expert so it's not my job to come up with a fix.  However, just being successful on 30 tests is not sufficient.

Apparently you’re not an expert in irony either.

You’re admittedly not an expert, yet claim that 30 tests is not sufficient. These two statements are logically incompatible.

No they aren't.  The point is, showing that something (anything) works properly 30 times in a row is not sufficient to determine that it will work properly every time.

Then what about 30 tests + Demo 1 + Demo 2 + Crew 1 + Inspiration 4? Is that enough? Is 50 tests enough? 100? 1,000? You are not an expert and you do not know. Systems engineering is all about statistical analysis of entire systems BY EXPERTS. Which you already admit not to be.

This level of concern-trolling is unbecoming.
Ad astra per aspirin ...

Online Lee Jay

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I'm not a parachute expert so it's not my job to come up with a fix.  However, just being successful on 30 tests is not sufficient.

Apparently you’re not an expert in irony either.

You’re admittedly not an expert, yet claim that 30 tests is not sufficient. These two statements are logically incompatible.

No they aren't.  The point is, showing that something (anything) works properly 30 times in a row is not sufficient to determine that it will work properly every time.

Then what about 30 tests + Demo 1 + Demo 2 + Crew 1 + Inspiration 4? Is that enough? Is 50 tests enough? 100? 1,000?

As I said, no.

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You are not an expert and you do not know. Systems engineering is all about statistical analysis of entire systems BY EXPERTS.

Which is both what I said and the point I was making.

Offline su27k

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Quote
but rather to point out that when something happens that's not as-planned,
Or not as expected, we're accustomed to NASA hunkering down, putting everything on hold, and paralyzing by analyzing.

What a happy surprise that, in the current case, they didn't overreact, but came right out and said that it's been modeled and seen before and no big deal, let's launch the next one.

Which is what they said about seal burn through and foam liberation as well.

Right so instead of a FUD post why don't you impart your wisdom and let us all know what they should be doing?  They have done 30 tests so is it more testing that (in your opinion) should be done? if so how many tests are needed? 40, 50 or maybe 100 tests? Love to know what your magic number is?

Or maybe you think Dragon isn't safe at all. So, in your opinion, should it be grounded? And if so then what? A new magic chute design that doesn't behave this way. Again love to know of your wisdom on this.

FUD posts are easy. Coming up with solutions or real fixes are hard.

I'm not a parachute expert so it's not my job to come up with a fix. 
Since you are not a parachute expert, it's also not your job to decide that any fix is needed.  :)

I'm not deciding a fix is needed.  I am of the opinion that an investigation and thorough review is needed precisely for the reason that Wayne Hale said.

Wayne Hale gave no such reason, and he certainly did NOT suggest "an investigation and thorough review is needed", and he did NOT object to any of the actions NASA or SpaceX is taking. What he's objecting to is using the word "in family" to describe the event (even though Steve Stich didn't use this word exactly, just something similar).

He gave this space review article as the reason for this objection, if you actually read the article it's pretty clear that the objection to the word "in family" is because it has double and opposite meaning which could cause confusion:

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In some cases, “in family” meant that data, or an observed result or event, was within a predicted range. But for other things, “in family” meant that an observed result or event may have been outside of a predicted range, but was still acceptable from a safety standpoint.

Wayne Hale's tweet does not support any of the arguments you're making, you're in fact missing his point entirely.

Online Lee Jay

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Wayne Hale's tweet does not support any of the arguments you're making, you're in fact missing his point entirely.

I disagree.  Look up "discrepant behavior" and see if you think he would do nothing about it.

Offline su27k

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I'm not a parachute expert so it's not my job to come up with a fix.  However, just being successful on 30 tests is not sufficient.

Apparently you’re not an expert in irony either.

You’re admittedly not an expert, yet claim that 30 tests is not sufficient. These two statements are logically incompatible.

No they aren't.  The point is, showing that something (anything) works properly 30 times in a row is not sufficient to determine that it will work properly every time.  I gave an example - Shuttle foam liberation caused less-than-catastrophic damage 112 times, and catastrophic damage on the 113th time.  This isn't about parachutes, it's about the idea that running a small number of tests is sufficient to demonstrate safety - it's not.  It's a part of the process that could be used to demonstrate safety.

Well duh, so what you're arguing exactly? That they didn't go through the process to demonstrate safety? What's your evidence that they didn't go through this process?

I propose SpaceX and NASA HAS gone through the process (which includes the 30 tests) and HAS demonstrated safety of the parachute system. Literally nobody is questioning this assertion except you and another non-expert guy on this forum.

Offline su27k

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Wayne Hale's tweet does not support any of the arguments you're making, you're in fact missing his point entirely.

I disagree.  Look up "discrepant behavior" and see if you think he would do nothing about it.

People already explained to him it's not "discrepant behavior", he's not an expert on parachutes, he wouldn't know whether this is "discrepant behavior" or not, that would be up to the parachute experts. And his later tweets show he's satisfied with the explanation:

https://twitter.com/waynehale/status/1458611367552950272
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One of the principles for High Reliability Organizations is Reluctance to Simplify. Today - on Twitter at least - there was a rich discussion delving into parachutes, testing, redundancy, etc. So we avoided the simplistic and ambiguous ‘in family’ characterization. So - Q. E. D.

https://twitter.com/waynehale/status/1458634083391713287
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My thanks to @DutchSatellites @Free_Space aCHA and others who contributed so richly to the parachute discussion today. We are all smarter due to what you all shared!


Online DigitalMan

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I'm not a parachute expert so it's not my job to come up with a fix.  However, just being successful on 30 tests is not sufficient.

Apparently you’re not an expert in irony either.

You’re admittedly not an expert, yet claim that 30 tests is not sufficient. These two statements are logically incompatible.

No they aren't.  The point is, showing that something (anything) works properly 30 times in a row is not sufficient to determine that it will work properly every time.

Then what about 30 tests + Demo 1 + Demo 2 + Crew 1 + Inspiration 4? Is that enough? Is 50 tests enough? 100? 1,000? You are not an expert and you do not know. Systems engineering is all about statistical analysis of entire systems BY EXPERTS. Which you already admit not to be.

This level of concern-trolling is unbecoming.

Where did the 30 tests number come from? I thought they had done more than that. I think it was 30 tests for the mark 2 parachutes, (or 1 and 2?), and more than 20 additional for the mark 3 parachutes.

So, more than 50, some of which were tests to failure to determine margins.

Offline eeergo

I propose SpaceX and NASA HAS gone through the process (which includes the 30 tests) and HAS demonstrated safety of the parachute system. Literally nobody is questioning this assertion except you and another non-expert guy on this forum.

[...]

[Mr Wayne Hale]'s not an expert on parachutes, he wouldn't know whether this is "discrepant behavior" or not, that would be up to the parachute experts.

Just dropping in this bitter choir-preaching exchange (as usual when any comment about any of Musk's ventures is anything else than adulatory) to point out, since I am being referred to as "another non-expert guy" by your "inappelable highness", that I am indeed a S/C systems engineer in the industry. Not that my ego needs acknowledging by your takes, and I'm actually flattered we fall in the same category as Mr Hale in your sweeping characterizations of everyone who doesn't agree with your (very much non-expert) opinion - but your appeal to expertise in this occasion is very telling when you so openly dismissed expert studies in other topics (to the point of being moderated out).

Anyway, I'm out of here. Y'all are very welcome to think everything is completeley fine and no minimal thought should be given to a thorough review, let alone a design effort to avoid crowding in parachutes.
-DaviD-

Online Lee Jay

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I'm not a parachute expert so it's not my job to come up with a fix.  However, just being successful on 30 tests is not sufficient.

Apparently you’re not an expert in irony either.

You’re admittedly not an expert, yet claim that 30 tests is not sufficient. These two statements are logically incompatible.

No they aren't.  The point is, showing that something (anything) works properly 30 times in a row is not sufficient to determine that it will work properly every time.  I gave an example - Shuttle foam liberation caused less-than-catastrophic damage 112 times, and catastrophic damage on the 113th time.  This isn't about parachutes, it's about the idea that running a small number of tests is sufficient to demonstrate safety - it's not.  It's a part of the process that could be used to demonstrate safety.

Well duh, so what you're arguing exactly? That they didn't go through the process to demonstrate safety? What's your evidence that they didn't go through this process?

I know they didn't in the 2 days between the parachute problem and the Crew-3 launch.

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I propose SpaceX and NASA HAS gone through the process (which includes the 30 tests) and HAS demonstrated safety of the parachute system. Literally nobody is questioning this assertion except you and another non-expert guy on this forum.

What evidence do you have that they did?  To my knowledge, they didn't release any evidence of having done this.  I don't know that they didn't anymore than you do know that they did.

Offline Vettedrmr

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Can we bring this topic (chute anomaly) to a close?  NASA and SpaceX are the responsible parties, they reviewed the data and chose to launch Crew 3.  I assume they know more than we do.
Aviation/space enthusiast, retired control system SW engineer, doesn't know anything!

Offline mn

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Can we bring this topic (chute anomaly) to a close?  NASA and SpaceX are the responsible parties, they reviewed the data and chose to launch Crew 3.  I assume they know more than we do.

The entire point of the argument is that history shows that NASA doesn't always know more and doesn't always reach the right conclusion.

Just to say that NASA decided and therefore it must be right is definitely not the right answer.

(Doesn't mean I think they are wrong in this case, but the question is 100% fair to discuss regardless of NASA's decision)

But yes I agree the discussion can be closed because we are just going in circles, everyone has already said what they have to say.

Offline su27k

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I propose SpaceX and NASA HAS gone through the process (which includes the 30 tests) and HAS demonstrated safety of the parachute system. Literally nobody is questioning this assertion except you and another non-expert guy on this forum.

[...]

[Mr Wayne Hale]'s not an expert on parachutes, he wouldn't know whether this is "discrepant behavior" or not, that would be up to the parachute experts.

Just dropping in this bitter choir-preaching exchange (as usual when any comment about any of Musk's ventures is anything else than adulatory) to point out, since I am being referred to as "another non-expert guy" by your "inappelable highness", that I am indeed a S/C systems engineer in the industry. Not that my ego needs acknowledging by your takes, and I'm actually flattered we fall in the same category as Mr Hale in your sweeping characterizations of everyone who doesn't agree with your (very much non-expert) opinion - but your appeal to expertise in this occasion is very telling when you so openly dismissed expert studies in other topics (to the point of being moderated out).

I'm not the guy asking for parachute expert, that was Lee Jay. And you being S/C systems engineer doesn't give you the credential needed to diagnose on parachute issues, in this particular case you're no different from any other non-expert.

And Mr. Hale's later tweets showed why he's a true professional who're only interested in fact finding (which was accomplished through the discussion on twitter), unlike some here who will jump at any chance to attack SpaceX while blatantly ignoring huge safety issues from authoritarian countries like Russia.

Offline su27k

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I'm not a parachute expert so it's not my job to come up with a fix.  However, just being successful on 30 tests is not sufficient.

Apparently you’re not an expert in irony either.

You’re admittedly not an expert, yet claim that 30 tests is not sufficient. These two statements are logically incompatible.

No they aren't.  The point is, showing that something (anything) works properly 30 times in a row is not sufficient to determine that it will work properly every time.  I gave an example - Shuttle foam liberation caused less-than-catastrophic damage 112 times, and catastrophic damage on the 113th time.  This isn't about parachutes, it's about the idea that running a small number of tests is sufficient to demonstrate safety - it's not.  It's a part of the process that could be used to demonstrate safety.

Well duh, so what you're arguing exactly? That they didn't go through the process to demonstrate safety? What's your evidence that they didn't go through this process?

I know they didn't in the 2 days between the parachute problem and the Crew-3 launch.

Quote
I propose SpaceX and NASA HAS gone through the process (which includes the 30 tests) and HAS demonstrated safety of the parachute system. Literally nobody is questioning this assertion except you and another non-expert guy on this forum.

What evidence do you have that they did?  To my knowledge, they didn't release any evidence of having done this.  I don't know that they didn't anymore than you do know that they did.

That's the point, there is NO problem with the parachute. The 2 days are not for determining whether this behavior is problematic, that determination was done at least a year ago, before NASA signed the certification for operational missions. The 2 days is used to check the data to make sure they're in the expected range, and check the hardware to make sure they're in expected condition.

They've seen this behavior in testing, for NASA to sign off the certification a year ago means they (and SpaceX) has already determined this behavior is not a safety concern before that, otherwise they wouldn't allow Dragon to start operational missions.

As for the last question, I'm not sure what exactly you're asking. You're saying NASA and SpaceX didn't do the necessary work to certify Crew Dragon for operation a year ago? That's a pretty bold claim, in fact I have never seen anybody (including enemies of SpaceX) raised this concern, so that's all the evidence I need. But to be more specific, my evidence is:
1. I trust NASA and SpaceX has done their homework
2. I trust organizations with oversight responsibilities over NASA, such as ASAP and IG, has done their job and would raise alarm if they see anything problematic, just like ASAP has done in the past when they disclosed OFT-1's 2nd anomaly in orbit.
3. SpaceX has plenty of enemies in the industry (see leaked ULA lobby emails and Boeing funded smear campaign against Crew Dragon in space media) and in congress (see how the parachute test failure was disclosed in a congressional hearing), if NASA didn't dot all the i's and cross all the t's, I expect this will be used against SpaceX long before today.

Online Lee Jay

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I'm not a parachute expert so it's not my job to come up with a fix.  However, just being successful on 30 tests is not sufficient.

Apparently you’re not an expert in irony either.

You’re admittedly not an expert, yet claim that 30 tests is not sufficient. These two statements are logically incompatible.

No they aren't.  The point is, showing that something (anything) works properly 30 times in a row is not sufficient to determine that it will work properly every time.  I gave an example - Shuttle foam liberation caused less-than-catastrophic damage 112 times, and catastrophic damage on the 113th time.  This isn't about parachutes, it's about the idea that running a small number of tests is sufficient to demonstrate safety - it's not.  It's a part of the process that could be used to demonstrate safety.

Well duh, so what you're arguing exactly? That they didn't go through the process to demonstrate safety? What's your evidence that they didn't go through this process?

I know they didn't in the 2 days between the parachute problem and the Crew-3 launch.

Quote
I propose SpaceX and NASA HAS gone through the process (which includes the 30 tests) and HAS demonstrated safety of the parachute system. Literally nobody is questioning this assertion except you and another non-expert guy on this forum.

What evidence do you have that they did?  To my knowledge, they didn't release any evidence of having done this.  I don't know that they didn't anymore than you do know that they did.

That's the point, there is NO problem with the parachute.

How do you know that??

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The 2 days are not for determining whether this behavior is problematic, that determination was done at least a year ago, before NASA signed the certification for operational missions.

As far as I can tell, that's an assumption you are making, not a fact you can demonstrate.

Quote
1. I trust NASA and SpaceX has done their homework
2. I trust organizations with oversight responsibilities over NASA, such as ASAP and IG, has done their job and would raise alarm if they see anything problematic, just like ASAP has done in the past when they disclosed OFT-1's 2nd anomaly in orbit.

I don't and neither should anyone else.  You've heard of "trust but verify?"  I accept evidence. I don't believe anyone or anything.

If this chute anomaly was expected and accounted for in the design of the system, then I haven't seen the evidence that that was the case.  That the system was certified is not evidence that this behavior was expected and accepted.  That it was accepted is not evidence that it's safe.

Learn from the past - normalization of deviance is deadly.

Offline su27k

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No they aren't.  The point is, showing that something (anything) works properly 30 times in a row is not sufficient to determine that it will work properly every time.  I gave an example - Shuttle foam liberation caused less-than-catastrophic damage 112 times, and catastrophic damage on the 113th time.  This isn't about parachutes, it's about the idea that running a small number of tests is sufficient to demonstrate safety - it's not.  It's a part of the process that could be used to demonstrate safety.

Well duh, so what you're arguing exactly? That they didn't go through the process to demonstrate safety? What's your evidence that they didn't go through this process?

I know they didn't in the 2 days between the parachute problem and the Crew-3 launch.

Quote
I propose SpaceX and NASA HAS gone through the process (which includes the 30 tests) and HAS demonstrated safety of the parachute system. Literally nobody is questioning this assertion except you and another non-expert guy on this forum.

What evidence do you have that they did?  To my knowledge, they didn't release any evidence of having done this.  I don't know that they didn't anymore than you do know that they did.

That's the point, there is NO problem with the parachute.

How do you know that??

They said so during the pre-launch press conference.


Quote
Quote
The 2 days are not for determining whether this behavior is problematic, that determination was done at least a year ago, before NASA signed the certification for operational missions.

As far as I can tell, that's an assumption you are making, not a fact you can demonstrate.

Not an assumption, again, they clarified this during the pre-launch press conference.


Quote
Quote
1. I trust NASA and SpaceX has done their homework
2. I trust organizations with oversight responsibilities over NASA, such as ASAP and IG, has done their job and would raise alarm if they see anything problematic, just like ASAP has done in the past when they disclosed OFT-1's 2nd anomaly in orbit.

I don't and neither should anyone else.  You've heard of "trust but verify?"  I accept evidence. I don't believe anyone or anything.

If this chute anomaly was expected and accounted for in the design of the system, then I haven't seen the evidence that that was the case.  That the system was certified is not evidence that this behavior was expected and accepted.  That it was accepted is not evidence that it's safe.

Learn from the past - normalization of deviance is deadly.

That's BS, you have to trust without verify pretty much everything in your life just to get by, you can't verify your food/water won't poison you or your computer won't electrocute you or your car's brake won't cease to function on the highway.

What verification do you have that the Russians have fixed the problem causing the abort on MS-10? What verification do you have that the Russians have fixed the problem with the hole in MS-09? What verification do you have that the next Russian module wouldn't take ISS for another spin? What verification do you have that Arianespace has fixed the Ariane 5 fairing vibration issue? What verification do you have that ULA has fixed the RL-10 nozzle vibration issue?
« Last Edit: 11/13/2021 05:01 am by su27k »

Offline SMS

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Offline space_19771999

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Here is the complete set.

Offline space_19771999

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Offline SMS

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More ISS photos from SpaceX Crew-2 (November 8, 2021):

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