Author Topic: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION  (Read 440146 times)

Offline Streamflow

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #940 on: 12/07/2023 04:38 pm »
"Accidents and disasters"? It was a flight test. No-one was hurt, nothing that wasn't part of the test was even damaged.
This makes me happy.

And do you have any evidence at all that the project is "hanging by a thread"?
Yes I guess. But, apparently, this issue will definitely not be resolved soon.

Offline Streamflow

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #941 on: 12/07/2023 04:46 pm »
Ah, now the point of the "analysis" is made.  BTW, you should start this as a stand-alone thread, as it has zero to do with discussing the IFT-2 flight.
I think you're wrong. What can we discuss here if not the key issues of the second flight, and therefore the first, since they are closely related? About little things?

Offline equiserre

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #942 on: 12/07/2023 04:53 pm »
Based on SpaceX video stream of April 20, 2023 about Starship launch, as well as available telemetry, it is shown in this work that on entire part of the trajectory where controlled flight took place, this rocket experienced sharp acceleration fluctuations with a period of 12 seconds, expressed in form of at least 10 pairs of narrow spikes, a sharp drop in acceleration to almost 0 at first, and then very sharp increase of it. This behavior of Starship is caused by previously unknown in rocket technology interaction of longitudinal self-oscillations of Pogo-type with rocket control system. These self-oscillations were excited by hydroacoustic pressure disturbances in fuel lines of rocket engines. A numerical model has been created at first for calculating such hydroacoustic oscillations with pressure discontinuity at pump, and their interaction with own longitudinal vibrations of Starship hull have been analyzed, see "Cause of Starship crash on first flight" Ė http://www.synerjetics.ru/article/starship_crash_eng.htm

purple font would come in handy. Or you smoked something

Offline Streamflow

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #943 on: 12/07/2023 04:55 pm »
"Synerjetics" differs from the book titles by a single character. I can recongnize it, as a hint for jet-synergetics. Is it a correct deciphering?
Absolutely right.

Offline Streamflow

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #944 on: 12/07/2023 05:07 pm »
My opinion is that you're right and the data you point out supports this. I don't have it in front of me so I accept your analysis at face value. The problem is, it's a secondary source - livestream data. Enough good reasons have been given to question its precision that it's not a closed case, IMO. Seeing something similar on a third flight would shift your analysis from reasonably informed opinion to a compelling case.
Let's wait for the third flight. I think there will be a lot of new and interesting things there.

Online mn

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #945 on: 12/07/2023 05:09 pm »
Thank you for this interesting reading. (Which is way above my level of understanding).
Please. I'm glad you enjoyed reading this. But you cannot evaluate a text without understanding it. Therefore, I am sure that you are in vain talking about your level of understanding. Think it over a little calmly, get used to ideas that are new to you, and everything will fall into place - I know it from myself. Be bolder and you will understand at least the main thing. And the little things - and God bless them.

Here's my simple non engineering question.

If somehow you had access to very precise telemetry and you can see variations and then you need to explain how they occurred, then I can understand a place for your paper as a possible explanation.

But here we have very little data, the charts are based on very imprecise numbers shown on a webcast. In such a case it's far more likely that the data is imprecise than to conclude that there is a pogo oscillation occuring.
This is actually a very difficult question. But the processes under consideration are of such a scale that no noise can mask them. In addition, at the moment we already have 5 Pogo processes on Starship. And working with multiple processes is much easier than working with one. In this case, even not very precise data are overlapped and thus refined.

There are 33 engines running, I imagine thrust variations have to occur in unison amongst all the engines to affect vehicle velocity, is that assumption correct?
I could give an exact answer to this question only if I had accurate data. But you can notice that on the first flight, none of the 10 engines in the inner ring turned off. I believe that at the first stage there are at least 3 options for pairs of fuel lines with slightly different lengths, which affects the frequency of self-oscillations and can lead to qualitatively different results. Or maybe it wonít. We need accurate models and accurate data.

Pogo oscillation seems like a well known problem, hard to assume SpaceX didn't account for it?
Better ask them about it :) However, I can say that Starship, due to its reusability, and also, oddly enough, because of its magnificent engines, is the most complex object from this point of view in the entire history of astronautics.

Thank you for your responses.

If I understand you correctly, you are suggesting that the velocity fluctuations are caused by pogo oscillation, is that understanding correct?

If so, I have to ask, we know that pogo can cause hardware failures (N1), if you claim that the later failures occurred due to pogo, that is interesting and possible (just like many other possibilities, possible until proven otherwise), but I have a hard time understanding how they can cause the velocity fluctuations (if they are real) and on a scale which does not match to the supposed pogo frequencies (and the total thrust is the combined effort of many engines with different pogo frequencies).

P.S. There are lots of people here who understand this stuff for real, it would be great (IMHO) if any of you read the document and respond with real engineering questions, instead of just dismissing this out of hand.
« Last Edit: 12/07/2023 05:12 pm by mn »

Offline martiantime

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #946 on: 12/07/2023 05:15 pm »
Yep, the point is to keep us all entertained  ;D
Have fun if you can during accidents and disasters. And also at a time when Starship project is hanging by a thread.
Can't agree.

I consider the 2nd flight very successful, despite the incomplete realization of the program. The booster worked perfectly until it began to overturn after the stage separation. The failures probably occurred as a result of fuel spilling in the tanks during the overturn. Perhaps one should turn back in a more flat arc.

I donít know what happened to Starship, but I believe that the engines were stopped normally 2-3 seconds before AFSS was activated. On telemetry, the speed changed during these 2-3 seconds, which corresponds to the aftereffect impulse of the engines. This means there was probably no serious damage to the engines.

Based on the results of the second flight, I am very optimistic if we talk about the fate of the entire program. If there were doubts after the first test, then now I believed in future success.
In my humble opinion

Offline Streamflow

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #947 on: 12/07/2023 05:17 pm »
Yep, the point is to keep us all entertained  ;D
Have fun if you can during accidents and disasters. And also at a time when Starship project is hanging by a thread.
Can you expand on this?
About what? About the disasters I had to work with?
Will this correspond to the topic?
And this piece of text was not directly related to Starship. This is just a response to an incorrect remark.

Offline Streamflow

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #948 on: 12/07/2023 05:25 pm »
You *do* realize he's dissecting IFT-1, not 2, right?  IFT-2 was so much better than IFT-1 that any conclusions drawn from IFT-1, IMO, are WAY out of date.  Why didn't he analyze IFT-2 data?  Why release a paper so far out of date?
Didn't you notice the article about the second flight? And with such baggage, are you trying to criticize something? You made my evening.

Offline Streamflow

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #949 on: 12/07/2023 05:59 pm »
Thank you for your responses.

If I understand you correctly, you are suggesting that the velocity fluctuations are caused by pogo oscillation, is that understanding correct?

If so, I have to ask, we know that pogo can cause hardware failures (N1), if you claim that the later failures occurred due to pogo, that is interesting and possible (just like many other possibilities, possible until proven otherwise), but I have a hard time understanding how they can cause the velocity fluctuations (if they are real) and on a scale which does not match to the supposed pogo frequencies (and the total thrust is the combined effort of many engines with different pogo frequencies).
Are you talking about the first flight?

Longitudinal oscillations with a period of 12 seconds were caused by attempts by Starship control system to suppress Pogo by reducing engine thrust and the fact that in the initial process of self-oscillations they occurred with a maltiplicity of 3. And with a decrease in pressure in combustion chamber, and, accordingly, after  pump, the frequency of hydroacoustic oscillations increased, and self-oscillations, when the thrust decreased, they switched to a heavier mode with a maltiplicity of 2. This caused superspikes.

That is, oscillations with a period of 12 seconds are not Pogo, but a superstructure over Pogo, which arose for the first time in history due to flexible control system and unusually wide range of Raptor-2 operating modes. Previously, the control system would have had simply turned off the engines the first time Pogo appeared. Or there would have been an explosion if it didnít have time.

This is written in more detail in end of the first article.

Online FutureSpaceTourist

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #950 on: 12/07/2023 06:03 pm »
https://twitter.com/spmttracker/status/1732836626626220092

Quote
One funny thing you can see during the Booster RUD are the grid fins getting yeeted out of the forward section lol

Offline Perchlorate

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #951 on: 12/07/2023 06:07 pm »

One funny thing you can see during the Booster RUD are the grid fins getting yeeted out of the forward section lol

My education continues, even at 75.

I'm now introduced to the verb "yeet."
Pete B, a Civil Engineer, in an age of incivility.

Online meekGee

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #952 on: 12/07/2023 06:35 pm »
No sale.

OK, so let's go back to 50 pages of "might have sloshed", "could have been damaged by", "rotated super fast", "thrust impingement on grid fins", "Engine may have failed", "Is that LOX leaking?".  Those discussions are full of primary data in pristine form with rigorous mathematical derivations of how the proposed mechanisms would work and create the rocket behavior we saw.  Those are so much more illuminating than this formally presented, possibly new form of pogo oscillation in heavy rockets, that may or may not match observed data, that we could discuss.  Sure, it may all just be hooey, but it is an intriguing idea - and, frankly, intriguing ideas are few and far between when there's nothing going on at the OLM.

All those theories were bracketed by "IMO", "Maybe", and definitely were not presented as rigorous analysis by groups with fancy names which turned out to be just this dude.

This has nothing to do with translation.
ABCD - Always Be Counting Down

Offline StevenOBrien

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #953 on: 12/07/2023 06:39 pm »

One funny thing you can see during the Booster RUD are the grid fins getting yeeted out of the forward section lol

My education continues, even at 75.

I'm now introduced to the verb "yeet."

It's an aerospace term that stands for "Yield Exceeding Ejection Trajectory". ;)

Offline drzerg

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #954 on: 12/07/2023 07:08 pm »
Oh jeez. I was afraid that it was a nightmare and i am reading some looney from novosti kosmonavtiki forums again. In the Russian/post USSR science field it is a good old tradition to have multiple pseudo or former scientists who are quite educated in the field but at the same time really believes their crazy theories and to get attention spread them on all science related forums with weak moderation.

Offline alugobi

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #955 on: 12/07/2023 07:16 pm »
So comms and video were not lost after all.

Online wannamoonbase

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #956 on: 12/07/2023 07:23 pm »
New video, has me very jacked up for IFT-3.
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

Offline StuffOfInterest

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #957 on: 12/07/2023 09:05 pm »
Anyone else think they were waiting to release that video until they had the "Gateway To Mars" sign lit?

Offline Kspbutitscursed

Anyone else think they were waiting to release that video until they had the "Gateway To Mars" sign lit?
or until B10 rolls to the rocket garden?
I attempt to fly in ksp
WEN OFT-3                 #Wen Booster 11/12 engines installation

Offline alugobi

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Re: SpaceX Starship IFT-2 : Starbase TX : 18 Nov 2023 DISCUSSION
« Reply #959 on: 12/07/2023 09:45 pm »
Anyone else think they were waiting to release that video until they had the "Gateway To Mars" sign lit?
Didn't occur to me, but it's an excellent hypothesis.  Bravo.

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