Author Topic: Ares I Thrust Oscillation meetings conclude with encouraging data, changes  (Read 139866 times)

Offline Chris Bergin

Based on L2 info from last week, getting it on during a gap between STS-126 post flight ops.

http://www.nasaspaceflight.com/2008/12/ares-i-thrust-oscillation-meetings-encouraging-allowance-for-changes/

Many talking points, I know!

Offline Jason Davies

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I want to know where you can sign up to go on the Centrifuge! :)

Looks like its turning the corner on TO, but that'a s good point in the article that only when they get data off Ares I-Y will they have the best data to work with.

Offline jeff.findley

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While the recent developments are somewhat encouraging, it still sounds like TO will be unpleasant, to say the least.  Also, from the article, "Ultimately, the first real data point engineers will have at their disposal will come via the test flight of the five segment Ares I-Y in 2011."  So, no solid data on TO will be gathered for two more years. 

To me, this is still a significant development risk and an operational headache. 

Offline brihath

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I was wondering how the extra two tons of mass in the interstage will affect the Orion mass targets.  That is a lot to add when they are trying to shave off weight from the spacecraft.


Offline Chris Bergin

I was wondering how the extra two tons of mass in the interstage will affect the Orion mass targets.  That is a lot to add when they are trying to shave off weight from the spacecraft.



They are ok, as they've strpped Orion already, with some more to come, but that's another article probably.

Offline Tim S

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Good article. Don't expect to be hearing much from the EELV folks on this thread.

Offline Jim

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Good article. Don't expect to be hearing much from the EELV folks on this thread.

Ares I won't survive the first 100 days of the new administration, so no need to comment.

As for TO, it is still is an issue since the vehicle has to be modified to mitigate it.
« Last Edit: 12/09/2008 02:08 PM by Jim »

Offline Peter NASA

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Actually, I think they are going to help Ares. There's a one percent chance they'll end Ares, but its very doubtful.

The only thing that concerns me about this all, without being involved, is they have suddenly found good data on TO mitigation. If anything, it's really good timing.

Good reporting as the data is correct to report, good and bad. I just worry they have calibrated the tests to create the encouraging data. As Chris points out, it's computational data, that's shown some strange results already with the 1 in 3, and the lack of real flight data until Ares I-Y.
« Last Edit: 12/09/2008 02:43 PM by Peter NASA »

Offline glanmor05

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I was wondering how the extra two tons of mass in the interstage will affect the Orion mass targets.  That is a lot to add when they are trying to shave off weight from the spacecraft.



They are ok, as they've strpped Orion already, with some more to come, but that's another article probably.

Is there anywhere (e.g. a PDR document) where the latest official (i.e. opinion limited to a minimum) launch capability (in mass) v's requirement, therefore deficit for Ares I (and V if possible) are published?

I know it depends on Orion (and Altair) mass which is in itself fluid, but there must be some assumptions?

There's loads of chatter on loads of threads on this site, with various figures suggested.  Are there any numbers we can agree on, as to how big a problem is faced (on both LVs) or is it too early?
"Through struggles, to the stars."

Offline NASA_LaRC_SP

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I was wondering how the extra two tons of mass in the interstage will affect the Orion mass targets.  That is a lot to add when they are trying to shave off weight from the spacecraft.



They are ok, as they've strpped Orion already, with some more to come, but that's another article probably.

Is there anywhere (e.g. a PDR document) where the latest official (i.e. opinion limited to a minimum) launch capability (in mass) v's requirement, therefore deficit for Ares I (and V if possible) are published?

I know it depends on Orion (and Altair) mass which is in itself fluid, but there must be some assumptions?

There's loads of chatter on loads of threads on this site, with various figures suggested.  Are there any numbers we can agree on, as to how big a problem is faced (on both LVs) or is it too early?

1) Orion is in flux due to the previous DAC being redone due to shoddy work by LM. That is why the figures are inconsistant right now.
2) Don't expect sites like nasa.gov to have documentation which isn't out of date.
3) Get L2.

Offline Captain Scarlet

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Hey Chris, do you have a bigger res image of the one you used at the top of the article. Probably a L2 image, but if I promise not to redicule your football team..... ;)

Offline jarmumd

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I was wondering how the extra two tons of mass in the interstage will affect the Orion mass targets.  That is a lot to add when they are trying to shave off weight from the spacecraft.



They are ok, as they've strpped Orion already, with some more to come, but that's another article probably.

Is there anywhere (e.g. a PDR document) where the latest official (i.e. opinion limited to a minimum) launch capability (in mass) v's requirement, therefore deficit for Ares I (and V if possible) are published?

I know it depends on Orion (and Altair) mass which is in itself fluid, but there must be some assumptions?

There's loads of chatter on loads of threads on this site, with various figures suggested.  Are there any numbers we can agree on, as to how big a problem is faced (on both LVs) or is it too early?


I don't have time to look really hard at what I have, but from PDR looks like Ares had about 5000 lbs of margin (with performance knockdowns already applied - i.e. technically it could have more margin)

looks like they were expecting the aft skirt TMA's to weight about 8000 lbs - I believe that went into their estimate.


Quote
Good reporting as the data is correct to report, good and bad. I just worry they have calibrated the tests to create the encouraging data. As Chris points out, it's computational data, that's shown some strange results already with the 1 in 3, and the lack of real flight data until Ares I-Y.

They didn't calibrate the tests to create encouraging data.  I know this.  BUT having said that, realize that finite element models can still be 10% off of the actual hardware and we won't really know until we do ground vibration tests.  AND realize that Orion is a huge driver for this, Orion (the load paths and mass) have a much larger effect on the resonant frequency than anyone predicted.  Orion's changing so the issue of TO will change...  But it's not "shaking itself to pieces" or "turning the astronauts to mush."

Offline Chris Bergin

Hey Chris, do you have a bigger res image of the one you used at the top of the article. Probably a L2 image, but if I promise not to redicule your football team..... ;)

Where's that ban option gone ;)

It's actually just a screenshot off a video on L2, but this might help as it's a bigger size:
(Click to make larger).

Offline Stowbridge

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That was a good objective read. More encouraging and none of the "it'll kill the crew by shaking their brains" as seen on other news networks recently.
Veteran space reporter.

Offline renclod

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Is there anywhere (e.g. a PDR document) where the latest official (i.e. opinion limited to a minimum) launch capability (in mass) v's requirement, therefore deficit for Ares I (and V if possible) are published?

http://forum.nasaspaceflight.com/index.php?topic=14198.0

The original post has a link.

cxp.charts.pdf from page 33

Everything above the red dotted line (control mass) is deficit.
From July 2, 2008.


Offline renclod

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Chris, thanks for the article. What a good read.

One question related to this :
Quote
The analysis also showed that TO may only “occur” - or affect Orion - once in every three flights. This in itself is a major finding, though there is a counter argument that claims that this points towards the computational models - known as “Monte Carlo runs” - suffering from inaccuracies.

In the Q&A follow-up to his remarks to the Space Transportation Association Breakfast, 22 January 2008, Washington DC, Dr. Griffin clearly stated that the TO phenomenon is not deterministic, it does not occur every flight, every test, every motor (paraphrasing here).

This is not important per se ; even at 1 in 3 occurence, mitigation must be done like is 1 in 1; but why the emotion - which is apparent in this thread also. It looks like NASA knew about the non-deterministic TO from 4-seg flight and ground test experience; recent "major finding" noted in the article just shows that 5-seg motors follows the same pattern as the 4-seg, which should not be such a big surprise.

Thanks again for the article, it made my day.




Offline Chris Bergin

Chris, thanks for the article. What a good read.

One question related to this :
Quote
The analysis also showed that TO may only “occur” - or affect Orion - once in every three flights. This in itself is a major finding, though there is a counter argument that claims that this points towards the computational models - known as “Monte Carlo runs” - suffering from inaccuracies.

In the Q&A follow-up to his remarks to the Space Transportation Association Breakfast, 22 January 2008, Washington DC, Dr. Griffin clearly stated that the TO phenomenon is not deterministic, it does not occur every flight, every test, every motor (paraphrasing here).

This is not important per se ; even at 1 in 3 occurence, mitigation must be done like is 1 in 1; but why the emotion - which is apparent in this thread also. It looks like NASA knew about the non-deterministic TO from 4-seg flight and ground test experience; recent "major finding" noted in the article just shows that 5-seg motors follows the same pattern as the 4-seg, which should not be such a big surprise.

Thanks again for the article, it made my day.


Thanks. It really surprised me to see it on the notes, so that's useful to see another reference above.

Offline iamlucky13

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Chris, thanks for the article. What a good read.

One question related to this :
Quote
The analysis also showed that TO may only “occur” - or affect Orion - once in every three flights. This in itself is a major finding, though there is a counter argument that claims that this points towards the computational models - known as “Monte Carlo runs” - suffering from inaccuracies.

In the Q&A follow-up to his remarks to the Space Transportation Association Breakfast, 22 January 2008, Washington DC, Dr. Griffin clearly stated that the TO phenomenon is not deterministic, it does not occur every flight, every test, every motor (paraphrasing here).

This is not important per se ; even at 1 in 3 occurence, mitigation must be done like is 1 in 1; but why the emotion - which is apparent in this thread also. It looks like NASA knew about the non-deterministic TO from 4-seg flight and ground test experience; recent "major finding" noted in the article just shows that 5-seg motors follows the same pattern as the 4-seg, which should not be such a big surprise.

Thanks again for the article, it made my day.


Thanks. It really surprised me to see it on the notes, so that's useful to see another reference above.

It's definitely surprising me, and I'm having a hard processing it. Resonant burning occurs every flight, correct? And most certainly any structure reacts to vibration inputs. How does it end up being probabilistic? Is it simply that variations in TO intensity and calculated vibrational modes have enough uncertainty such that the odds vibrations reaching a certain threshold are about 1 in 3?

Of course, 1 in 3 odds realistically means it has to be designed for. The good news from this article isn't that the likelihood is significantly less than 100%, but that the mitigation efforts appear to be successful.

It shouldn't be overlooked that some of the engineers are still arguing for active TMA. If they're in favor of making a system more complicated, then the confidence level is clearly marginal, but this is the most favorable article I've seen in a while.

Thanks Chris.

Offline renclod

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It's definitely surprising me, and I'm having a hard processing it. Resonant burning occurs every flight, correct?

Why every flight ? Here are my attempts at defining variation factors:

1/ Slag accumulation arround the submerged nozzle

The SRM nozzle is submerged, it protrudes inside the casing (for thrust vectoring purposes.) Hot molten aluminium oxides in liquid phase, a.k.a. slag, get trapped in the volume defined by the nozzle and the casing. This is not necessarily deterministic, not to the split second and not to the fraction of an inch.

The cavity arround the nozzle is playing a role in the start of major pressure oscillations, in other words a role in the precise frequency, intensity, timing of TO.

2/ Burn rate variations, due to minute batch variations, the day of flight/test temperature of the solid propellant, and a zillion other factors.

It is the same thing as with POGO. Probabilistic. Different every flight, every test. 4-seg has probabilistic TO, 5-seg the same. IMO of course.


Offline GimmeSpace

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If the TO doesn't happen the same way every time, that would indicate that it's manageable, and worth working on.

A few months ago I was asking about that on this forum and pretty much got an answer that doing anything about it was impossible and a waste of time.

I think that answer was a bit too pessimistic and close-minded, or maybe just political.  ;D

"Mission Accomplished."

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