Ares I Thrust Oscillation meetings conclude with encouraging data, changes

[MP99]

The more interesting bit happens a few minutes earlier, when he talks about how they waived the requirement for LIDS to take the loads caused by a J-2X gimbal hard-over at the end of the TLI burn, because that failure mode was "not credible".

Now, I can think of three launch vehicle failures involving gimbal hard-overs off the top of my head - Titan IV K-17 in 1993, Ariane V 501, and one of the Athenas.

Maybe Ares I isn't vulnerable to these failures, but it'd be interesting to know why.

Sorry for nit-picking, but TLI is performed by the EDS, which is the AVUS, not AIUS.

Still, these are supposed to be derived from the same basic design, and both to use J-2X, so the point still stands.

cheers, Martin

[renclod]

Thanks for replying.

So, the phrase in question is probably "fluid damping". Mistery solved, not. The fluid is there to dampen, but how ? If you leave the fluid (LOX) alone, apparently it is not dampening enough at all; but if you do something to the fluid, something smart, it is capable to blow the TO out of the picture.

I was looking for something more exotic, like "perfused gapping", lol.

A weighted baffle on springs ? Hmmm...

[yinzer]

Viscosity.  If you force a fluid through a hole, it will resist.  If you force the hole through the fluid, it will resist.  Changing the sizes of the holes and the speed of the fluid through the hole lets you adjust the damping.

[dcoolbro]

there seems to be a lot of what if's involved in all this. Nothing is conclusive at this point.

[rdale]

Exactly - which is why they are flying test missions and instrumenting the shuttle...

[Herb Schaltegger]

Exactly - which is why they are flying test missions and instrumenting the shuttle...

Glad to know that 4 years post-ESAS someone has decided to do some development work.   

[Danny Dot]

Exactly - which is why they are flying test missions and instrumenting the shuttle...

Glad to know that 4 years post-ESAS someone has decided to do some development work.   

ESAS says very clearly thrust oscillation would not be a problem.  They knew about it, but ATK said "no problem".  No analysis presented, just a single sentence to declare it OK.

Also, does anyone know when the Ares I TO PDR delta is scheduled?

Danny Deger

Edit:  I found this NASA blog on TO.  It looks like NASA still has a lot of work to do on this issue.  I don't think the PDR has been scheduled yet.

http://blogs.nasa.gov/cm/blog/Constellation.blog/posts/post_1239311627391.html?x=22#comments

[Danny Dot]

I just thought of something on Thrust Oscillation Mitigation.  One of the current plans by NASA is to put a "spring" in the interstage.  It just occurred to me that this spring will probably deflect in bending as well as axially.  Bending at the interstage should cause some really bad problems at Max Q - especially at the very high Q of Ares.

Does anyone have information on this problem and how it is resolved?

Here is an image of the proposed NASA solutions:

Danny Deger

[Antares]

It's probably going to be something like Softride

http://www.csaengineering.com/spclnch/spacelaunch.asp

[jarmumd]

I just thought of something on Thrust Oscillation Mitigation.  One of the current plans by NASA is to put a "spring" in the interstage.  It just occurred to me that this spring will probably deflect in bending as well as axially.  Bending at the interstage should cause some really bad problems at Max Q - especially at the very high Q of Ares.

Does anyone have information on this problem and how it is resolved?

Here is an image of the proposed NASA solutions:

Danny Deger

The ascent loads structural analysis will not start until LA4 (possibly)/ LC5 (definitely), which will be Q4 of this year.  The FEM's are still being developed for the mitigation.  It may be resolved by IFLR and day of launch balloons.

[Danny Dot]

I just thought of something on Thrust Oscillation Mitigation.  One of the current plans by NASA is to put a "spring" in the interstage.  It just occurred to me that this spring will probably deflect in bending as well as axially.  Bending at the interstage should cause some really bad problems at Max Q - especially at the very high Q of Ares.

Does anyone have information on this problem and how it is resolved?

Here is an image of the proposed NASA solutions:

Danny Deger

The ascent loads structural analysis will not start until LA4 (possibly)/ LC5 (definitely), which will be Q4 of this year.  The FEM's are still being developed for the mitigation.  It may be resolved by IFLR and day of launch balloons.

Thanks for the inside info.  I wish you guys well on keeping the stick from distroying itself by vibriation or air loads.  This will not be an easy task.  Keep us posted if you get a chance.

Danny Deger

P.S.  Can you define some of your acronyns?

[renclod]

Prediction and Reduction of Ares SRB Thrust Oscillation

http://www.nasa.gov/pdf/346545main_NESC08TechUp_web.pdf , page 14

>>> Problem: The Ares I vehicle has a thrust oscillation frequency close to the vehicle’s second axial structural mode frequency. The NESC was asked to make an independent prediction of the thrust oscillation in the five segment Reusable Solid Rocket Motor (RSRMV) and to develop motor design change options for reducing or eliminating it.

NESC Contribution: The NESC team included personnel from JSC, MSFC, LaRC, Gloyer-Taylor Laboratories LLC (GTL), ATK, and Jacobs Engineering Group. GTL provided access to key expertise at Penn State University, the California Institute of Technology, and at the University of Tennessee Space Institute. Additionally, GTL provided expertise with their Universal Combustion Device Stability™ (UCDS) system that predicts and identifies the specific design sources of propulsion system instabilities. Using the UCDS simulation, the team identified and cataloged the design features that cause thrust oscillation and their individual contribution to the overall oscillation amplitude. Design options for eliminating and/or reducing the contribution of individual design features were developed and analytically evaluated using UCDS. The best options were provided to the NASA Constellation Program-chartered Thrust Oscillation Focus team and the Ares project.

Results: Independent confirmation of the predicted RSRMV thrust oscillation frequency and amplitude characteristic was achieved. The specific contribution of individual design features was quantified for the first time. This provides very valuable information to address the thrust oscillation phenomena. Variability seen in thrust oscillations can be accounted for by inhibitor protrusion height and edge shape variability. With measured control of the regression rate of the inhibitors, particularly in the aft of the motor, substantial reduction in oscillation amplitudes could be achieved. Specific suggested design improvements will be experimentally assessed by the Ares project. Introduction of the most successful modifications will be evaluated as a potential upgrade in the future. <<<

[Scotty]

The Delta PDR on Thrust Oscillation that was supose to be held this month, has been put off until November.
Yes, that is real encouraging news for sure!
Want to take bets on Ares I being scrapped before the Delta PDR is ever held?

[jarmumd]

Thanks for the inside info.  I wish you guys well on keeping the stick from distroying itself by vibriation or air loads.  This will not be an easy task.  Keep us posted if you get a chance.

Danny Deger

P.S.  Can you define some of your acronyns?

Loads Analysis (?) - LA (mini analysis - oh check this condition out)
Loads Cycle - LC (major tool and simulation development)
Finite Element Model - FEM (mass and stiffness representations of the vehicle)
In Flight Loads Relief - IFLR (using the nozzle controller to reduce the loads on the vehicle - reduce angle of attack)
Day of Launch - updating the trajectory based on recent atmospheric conditions (expected wind shears and the like)

[Danny Dot]

The Delta PDR on Thrust Oscillation that was supose to be held this month, has been put off until November.
Yes, that is real encouraging news for sure!
Want to take bets on Ares I being scrapped before the Delta PDR is ever held?

Ouch.  This is not a good sign for Ares I.  They must be having some trouble with this issue.

Danny Deger

[robertross]

The Delta PDR on Thrust Oscillation that was supose to be held this month, has been put off until November.
Yes, that is real encouraging news for sure!
Want to take bets on Ares I being scrapped before the Delta PDR is ever held?

So much for all the 'old' rumours that they had most of the issues solved from the latest data. I'm not a betting man, but I figure 9 in 10 that this stick is put out to pasture.

[robertross]

Prediction and Reduction of Ares SRB Thrust Oscillation

http://www.nasa.gov/pdf/346545main_NESC08TechUp_web.pdf , page 14

Holy!!
Thrust Oscillation aside, that document is a treasure trove of information right across the agency!

Folks, it's worth the download & thorough read!

[Integrator]

It's a matter of detuning the stack and staying away from the particular motor frequency from now on through conscious effort and constant checking and cross checking.  It can be done and managed through engineering and integrated design practices but quite frankly we could have avoided this whole thing by properly stating and communicating our TO environments requirements and sensitivities at the very beginning of this Project. TO environments have been understood and known for decades so I accept no excuses for this oversight - it was just plain stupid to not communicate that information (Oh, by the way, you had better avoid this particular frequency band or we will have coupling) across the interface to Orion from the beginning.

"Never time to do it right, always time to do it over." Well, now we're doing it over, thanks to poor requirements definition, deconvolution and allocation 3 years ago.

[Danny Dot]

It's probably going to be something like Softride

http://www.csaengineering.com/spclnch/spacelaunch.asp

This might work to isolate a payload.  The isolation is under the fairing and far forward.  But, NASA is looking at adding a spring on the interstage where the structure needs to be REALLY stiff in bending to take ascent air loads.

Danny Deger

[wannamoonbase]

The Delta PDR on Thrust Oscillation that was supose to be held this month, has been put off until November.
Yes, that is real encouraging news for sure!
Want to take bets on Ares I being scrapped before the Delta PDR is ever held?

So much for all the 'old' rumours that they had most of the issues solved from the latest data. I'm not a betting man, but I figure 9 in 10 that this stick is put out to pasture.

9 out of 10 is probably about right.  It's after the supposed 1-X flight and the new 'review' of the vehicles is due.

Certainly looks like a step to quiet things down before putting it in the filing cabinet of paper rockets.

I'd even bet 8 or 9 out of 10 that 1-X never rolls out of the VAB.