Author Topic: Ares I Thrust Oscillation meetings conclude with encouraging data, changes  (Read 142253 times)

Offline jeff.findley

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I think that is fair.  However, as I have said, I believe there is a lot more behind the scenes at play here than is often given credit, not the least of which is how to sell the larger Ares program to Congress in a manageable way that will provide incremental progress to keep the money coming.  In the end, isn't it better to proceed with a rocket that has money and political will to build it than a better rocket that doesn't?  Let me also give an example of non-political "nitty gritty" details that are so easily ignored but directly contribute to the design of the rocket:

(from http://www.safesimplesoon.com/mythbusters2.htm)
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In ESAS and until last Spring, the Ares—I injected the Orion into a 30x160nmi transfer orbit and the Orion then circularized itself, to avoid the complexity of deorbiting the large upperstage. Working with Constellation and CEV project teams, the program elected to change to a -30x100nmi orbit to move the ocean impact of the CLV upperstage to the Indian Ocean from the South Pacific to stay away from populated islands.

It's details like where the spent stage will land that can shape the rocket design, but drive the vehicle away from what the objective rocket designer would consider ideal. 

Perhaps a better alternative would have had the upper stage inject Orion into a circular parking orbit, followed by the upper stage doing a de-orbit burn to dump the upper stage into the best possible spot in the ocean.  But this simply would not have been possible with Ares I.  It lacks the performance nessary. 

The inescapable truth is that a -30 nmi x 100 nmi orbit requires a pretty big delta-V from Orion or it's coming down in the ocean along with the upper stage.  In other words, Orion is its own third stage because Ares I can't place it into a proper parking orbit.

This is a design bug not a feature!
« Last Edit: 12/11/2008 02:27 PM by jeff.findley »

Online edkyle99

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The inescapable truth is that a -30 nmi x 100 nmi orbit requires a pretty big delta-V from Orion or it's coming down in the ocean along with the upper stage.  In other words, Orion is its own third stage because Ares I can't place it into a proper parking orbit.

This is a design bug not a feature!

The delta-V to circularize this orbit is only about 62 meters per second, which is less than 1% of the total delta-V provided by the upper stage.  NASA could have designed the upper stage to provide this extra impulse (the total vehicle weight would have been less if it had), but it did not in order to drop the stage safely into the Indian Ocean. 

Shuttle is nominally suborbital after MECO.  It takes a 50-ish meters/second OMS burn to circularize the orbiter's orbit.  Is that also a bug?

 - Ed Kyle   
« Last Edit: 12/11/2008 07:56 PM by edkyle99 »

Offline eeergo

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Great posts Will, really insightful and sober.
-DaviD-

Offline JIS

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Perhaps a better alternative would have had the upper stage inject Orion into a circular parking orbit, followed by the upper stage doing a de-orbit burn to dump the upper stage into the best possible spot in the ocean. 

Not good idea. Ares would have to fly non optimal trajectory or restart J-2X to inject to circular orbit.
Also dumping US means yet another restart and payload penalty.

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But this simply would not have been possible with Ares I.  It lacks the performance nessary. 

More importantly there is no need to do such silly maneuvre.
Orion has more than enough capability to do whatever orbit change needed.

On the other side in case of lunar sortie mission the Orion might need more fuel for lunar orbit maneuvers.

It could be interresting to see what can be done to increase Orion dV.
As Altair/EDS will be parked at 120-100nm circular orbit it could be handy to launch Orion to somewhat higer orbit (say 80x120nm?). For low inclination orbit the US disposal can be re-targeted to south pacific again. This would add few tens m/s of dV.

Also Orion has some spare tank capacity so it can be launched heavier.
Or the CM can be made lighter by launching some supplies in Altair on Ares V. E.g. food and water containers can be transferred to Orion after docking with Altair.   

Launching Orion (or Shuttle) on suborbital trajectory is actually pretty good way how to treat space debris.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070021588_2007019149.pdf

Ares US is also relatively very heavy compared to other upper stages which go to nearly orbital velocities.
Ares US dry weight is about 35klbs while Centaur is about 5klbs.
STS ET empty mass is 58.5klbs.
I think it is quite reasonable to dispose heavier upper stages to suborbital trajectories.
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Offline JIS

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The key with the strap-on SRB's is that any TO effects which do occur are easy to mitigate using existing and well-proven techniques.

Every strap-on SRB in use, including the very large Shuttle and Titan SRB's, has been attached to the booster using a joint which is specifically designed to either safely absorb the forces of the SRB's oscillations, or to change the frequencies so that the TO frequency doesn't coincide with the resonant frequency of the vehicle any longer.

I think this is not correct description what's going on with more solid boosters.   

TO is in fact reaction of vehicle to the forcing function. If this reaction coincides with vehicle's natural frequency you have a problem.

Vehicles like STS, Titan IV, Ariane 5 and medium EELVs take advantage of having more than one forcing functions. Those functions interact and result in less organized superpositioned forcing function. As this function is less organized it is less likely that it can tune up with vehicle natural frequency and cause dangerous levels of vibrations.

Notable difference is Atlas V 411 which has just one solid. It would be interesting to see what the change in observed vibration levels is. However, it's likely that the stack was designed to be insensitive to the forcing function of SRB (or vice versa) in the first place.

On the other side interaction of more forcing functions can cause vibrations not only in axial direction but also in lateral direction. This is exactly what happening with space shuttle on solids when astronauts are shaken to the “sides”. Astronauts in Orion won't be shaken to the sides (in big extend) but rather experience variating force pushing them straight up.
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Offline kraisee

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The key with the strap-on SRB's is that any TO effects which do occur are easy to mitigate using existing and well-proven techniques.

Every strap-on SRB in use, including the very large Shuttle and Titan SRB's, has been attached to the booster using a joint which is specifically designed to either safely absorb the forces of the SRB's oscillations, or to change the frequencies so that the TO frequency doesn't coincide with the resonant frequency of the vehicle any longer.

I think this is not correct description what's going on with more solid boosters.   

TO is in fact reaction of vehicle to the forcing function. If this reaction coincides with vehicle's natural frequency you have a problem.

Vehicles like STS, Titan IV, Ariane 5 and medium EELVs take advantage of having more than one forcing functions. Those functions interact and result in less organized superpositioned forcing function. As this function is less organized it is less likely that it can tune up with vehicle natural frequency and cause dangerous levels of vibrations.

Notable difference is Atlas V 411 which has just one solid. It would be interesting to see what the change in observed vibration levels is. However, it's likely that the stack was designed to be insensitive to the forcing function of SRB (or vice versa) in the first place.

On the other side interaction of more forcing functions can cause vibrations not only in axial direction but also in lateral direction. This is exactly what happening with space shuttle on solids when astronauts are shaken to the “sides”. Astronauts in Orion won't be shaken to the sides (in big extend) but rather experience variating force pushing them straight up.


Thrust Oscillation is another one of those terms which has been corrupted and is really being used rather inaccurately.

Real TO, sometimes referred to as Resonant Burn, is a normal effect produced by every solid rocket motor from those used in Estes model rockets all the way up to the Shuttle and Titan large-bore SRB's.

The problem which Ares-I is actually suffering from is a case where the frequency of the SRB's TO vibration force function and the resonance of the entire vehicle are coinciding.   The two frequencies are then amplifying and reinforcing each other like a standing wave, creating a peak of force much greater than each separately -- a peak which is high enough to cause engineering concerns.

What Ares-I is suffering from should be more accurately called something like "Thrust Oscillation Induced Resonance Amplification".   I know I've heard of the correct term, I just can't recall it right now :)


In my SRB description above, where I said "The key with the strap-on SRB's is that any TO effects which do occur are easy to mitigate using existing and well-proven techniques", I was specifically trying to use the TO term accurately, to represent just the forcing function of the SRB itself which is mitigated on strap-on SRB's via the joint design, before it ever gets a chance to interact with the vehicle's natural resonance.

Sorry for any confusion.

Ross.
« Last Edit: 12/12/2008 02:34 PM by kraisee »
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Offline jeff.findley

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The inescapable truth is that a -30 nmi x 100 nmi orbit requires a pretty big delta-V from Orion or it's coming down in the ocean along with the upper stage.  In other words, Orion is its own third stage because Ares I can't place it into a proper parking orbit.

This is a design bug not a feature!

The delta-V to circularize this orbit is only about 62 meters per second, which is less than 1% of the total delta-V provided by the upper stage.  NASA could have designed the upper stage to provide this extra impulse (the total vehicle weight would have been less if it had), but it did not in order to drop the stage safely into the Indian Ocean. 

Shuttle is nominally suborbital after MECO.  It takes a 50-ish meters/second OMS burn to circularize the orbiter's orbit.  Is that also a bug?

 - Ed Kyle   

Since when does the shuttle launch into a 100 nmi orbit?  How much mass could Ares I put into a typical shuttle (i.e. ISS) orbit assuming that Orion does a 50 ish meter/second burn, just like the shuttle? 

Ares I simply is not a viable launch vehicle without Orion performing like an upper stage.  Again, this is a bug, not a feature.

Jeff
« Last Edit: 12/12/2008 03:14 PM by jeff.findley »

Online Chris Bergin


Sure, it's debunked to the point where the current design won't see TO killing astronauts. It will only shake them bad enough that they won't be able to throw switches... (rolls eyes).


That's incorrect Jeff, and on several levels (such as how bad they'll be shaken post mitigation, and when they'd even need to be flicking a switch during those four seconds of TO).

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

Offline jeff.findley

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Your article talks about the ability to read a 10 point font on a display with an error rate of 10% at 1.0 g's of simulated thrust oscillation.  How does this relate to throwing switches?  Is it humanly possible to timely and accurately throw a switch under those conditions?  Has this already been studied?

In another thread, Danny Dot said "As an astronaut instructor from 1990 to 1995 I was told by several crew members the vibration in shuttle first stage is so great they didn't think they could reliably throw a switch."

I guess if astroanuts aren't expected to ever have to throw switches, they're passengers on Orion, not pilots.
« Last Edit: 12/12/2008 04:56 PM by jeff.findley »

Online Chris Bergin

Your article talks about the ability to read a 10 point font on a display with an error rate of 10% at 1.0 g's of simulated thrust oscillation.  How does this relate to throwing switches?  Is it humanly possible to timely and accurately throw a switch under those conditions?  Has this already been studied?

I guess if astroanuts aren't expected to ever have to throw switches, they're passengers on Orion, not pilots.

They are looking into the ability to accurately read the displays in the event they would need to carry out a manual abort - which requires the flicking of a switch - during the four seconds of TO late in first stage flight. Such a requirement would be during the additional issue of a flight computer being down, as the computers would normally abort Orion via the LAS, not the crew. This is the only flicking of a switch requirement during those four seconds of TO, should TO occur.

No TO mitigation is not complete. Yes, further testing is required, and yes, they won't have the best data until after Ares I-Y, but the statement you made didn't fit with the current information. We're talking about less shaking you get in your car going over a slighly bumpy road, when reading your SatNav (that's an assumption, but won't be far off).

Offline jeff.findley

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No TO mitigation is not complete. Yes, further testing is required, and yes, they won't have the best data until after Ares I-Y, but the statement you made didn't fit with the current information. We're talking about less shaking you get in your car, when reading your SatNav.

Are we talking more vibration than you see on a typical shuttle flight during SRB burn? 

The in cockpit videos I've seen show the astronauts' seats bouncing around like they're in a Jeep going down a bumpy off-road trail.  By comparison, when the SRB's separate, the ride gets noticably smooth, to the point that it's difficult to see any vibration of the seats on the video. 

I don't know what kind of car you ride in, by my 1991 Ford LTD Crown Victoria LX rides like the shuttle *after* SRB separation, not before.  I've never had any trouble reading the tiny display or pushing the tiny buttons on my aftermarket radio while on the road.
« Last Edit: 12/12/2008 05:34 PM by jeff.findley »

Online edkyle99

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Since when does the shuttle launch into a 100 nmi orbit?  How much mass could Ares I put into a typical shuttle (i.e. ISS) orbit assuming that Orion does a 50 ish meter/second burn, just like the shuttle? 

If Ares I injected Orion into a typical post-MECO shuttle orbit (58 x 220 km, for example) it would only cost perhaps 0.4 tonnes of payload capability.  And that assumes that the current Ares I design is used without alteration.  It would very likely be possible to squeeze more performance out of Ares I for a higher orbit if NASA specified such an orbit.  But there is already enough, or nearly enough, margin between Ares I capability and Orion's allocated mass to provide that capability if needed.

But it isn't needed.

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Ares I simply is not a viable launch vehicle without Orion performing like an upper stage.  Again, this is a bug, not a feature.

Jeff

What do you mean by "viable"?  Ares I could boost more than 24 tonnes, in addition to adding its own empty upper stage to the orbital debris problem, directly into circular LEO if desired.  But why would it need to do such a thing?  It is being designed to launch Orion while safely dropping its spent upper stage, and it is on track to meet those requirements.

 - Ed Kyle

Online wannamoonbase

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The solutions to the Ares 1 vehicle, the 5 segment booster for performance and mass dampers for TO do not help the over all system of having commonality between Ares 1 and 5.

Almost all of the claimed benefits of using shuttle hardware are gone and the advantages of commonality between Ares 1 and 5 have been planned out.

I have no doubt the talented people at NASA can make Ares 1 do the job.  But the case for it is weakened.

Edit for grammer
« Last Edit: 12/12/2008 06:08 PM by wannamoonbase »
I know they don't need it, but Crossfeed would be super cool.

Online gospacex

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Since when does the shuttle launch into a 100 nmi orbit?  How much mass could Ares I put into a typical shuttle (i.e. ISS) orbit assuming that Orion does a 50 ish meter/second burn, just like the shuttle? 

If Ares I injected Orion into a typical post-MECO shuttle orbit (58 x 220 km, for example) it would only cost perhaps 0.4 tonnes of payload capability.  And that assumes that the current Ares I design is used without alteration.  It would very likely be possible to squeeze more performance out of Ares I for a higher orbit if NASA specified such an orbit.  But there is already enough, or nearly enough, margin between Ares I capability and Orion's allocated mass to provide that capability if needed.

But it isn't needed.

Famous last words.

Apollo program discovered that there _always_ is something useful you can do with extra upmass capability, and then you want more. Von Braun knew that, and designed Saturn V with _big_ performance reserve.

Why NASA chose to forgot it? Von Braun is not famous enough in this field for you?

Maybe Ares I can lift Orion into ISS orbit, but at the max of its capabilities. There is zero growth potential.

Online Chris Bergin


Are we talking more vibration than you see on a typical shuttle flight during SRB burn? 


TO is four seconds at the end of first stage on Ares I. "during the SRB burn" on Shuttle has large varying degrees of shaking...but for example...

Quote

The in cockpit videos I've seen show the astronauts' seats bouncing around like they're in a Jeep going down a bumpy off-road trail.  By comparison, when the SRB's separate, the ride gets noticably smooth, to the point that it's difficult to see any vibration of the seats on the video.


....there's a lot of shaking on shuttle during the opening seconds of launch than it is near the end of first stage. And you can see the crew hitting switches on the displays even then. I've seen cockpit videos of launches where they have been changing the displays by hitting buttons going into the roll....and that's shaky.

So where are you getting "Sure, it's debunked to the point where the current design won't see TO killing astronauts. It will only shake them bad enough that they won't be able to throw switches... (rolls eyes)." that much shaking (far worse than Shuttle during the first few seconds of launch (given even then they are capable of hitting switches) from? What's your source of this inaccurate statement?

Online gospacex

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No TO mitigation is not complete. Yes, further testing is required, and yes, they won't have the best data until after Ares I-Y, but the statement you made didn't fit with the current information. We're talking about less shaking you get in your car, when reading your SatNav.

Are we talking more vibration than you see on a typical shuttle flight during SRB burn? 

The in cockpit videos I've seen show the astronauts' seats bouncing around like they're in a Jeep going down a bumpy off-road trail.  By comparison, when the SRB's separate, the ride gets noticably smooth, to the point that it's difficult to see any vibration of the seats on the video.

I am curious too. Why astronauts never comment on that? It's "politically incorrect" at NASA to say anything remotely bad about ATK?

Online Chris Bergin

No TO mitigation is not complete. Yes, further testing is required, and yes, they won't have the best data until after Ares I-Y, but the statement you made didn't fit with the current information. We're talking about less shaking you get in your car, when reading your SatNav.

Are we talking more vibration than you see on a typical shuttle flight during SRB burn? 

The in cockpit videos I've seen show the astronauts' seats bouncing around like they're in a Jeep going down a bumpy off-road trail.  By comparison, when the SRB's separate, the ride gets noticably smooth, to the point that it's difficult to see any vibration of the seats on the video.

I am curious too. Why astronauts never comment on that? It's "politically incorrect" at NASA to say anything remotely bad about ATK?

You've got to be kidding me, right?

You're asking why astronauts never comment on the shaking during first stage? (They do all the time, with their comments about the launch, especially first time flyers...with the "kick in the pants" comments).

But you've missed those comments, and believe that they don't comment about how rough first stage is, so as not to say anything bad about ATK?

Please tell I've misread you :)

Offline Jorge

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The inescapable truth is that a -30 nmi x 100 nmi orbit requires a pretty big delta-V from Orion or it's coming down in the ocean along with the upper stage.  In other words, Orion is its own third stage because Ares I can't place it into a proper parking orbit.

This is a design bug not a feature!

The delta-V to circularize this orbit is only about 62 meters per second, which is less than 1% of the total delta-V provided by the upper stage.  NASA could have designed the upper stage to provide this extra impulse (the total vehicle weight would have been less if it had), but it did not in order to drop the stage safely into the Indian Ocean. 

Shuttle is nominally suborbital after MECO.  It takes a 50-ish meters/second OMS burn to circularize the orbiter's orbit.  Is that also a bug?

 - Ed Kyle   

Since when does the shuttle launch into a 100 nmi orbit?

Many ISS flights do, if you ignore eccentricity. On all ISS flights, at MECO the orbiter is in a 122x30 nmi orbit. The OMS-2 burn raises perigee to at least Safe HP (85 nmi), but OMS-2 is also used as an ISS phasing burn so depending on the phase angle it could raise perigee all the way to ISS height, and it becomes the new apogee. For example, if ISS is in a 190 nmi orbit, the post-OMS-2 orbit can range from 122x85 nmi to 122x190 nmi. Lately it seems we've had a lot of large phase-angle cases and we wind up in the low 122x85 nmi orbit, which works out to an average altitude of 103.5 nmi.
JRF

Offline Jorge

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Since when does the shuttle launch into a 100 nmi orbit?  How much mass could Ares I put into a typical shuttle (i.e. ISS) orbit assuming that Orion does a 50 ish meter/second burn, just like the shuttle? 

If Ares I injected Orion into a typical post-MECO shuttle orbit (58 x 220 km, for example) it would only cost perhaps 0.4 tonnes of payload capability.  And that assumes that the current Ares I design is used without alteration.  It would very likely be possible to squeeze more performance out of Ares I for a higher orbit if NASA specified such an orbit.  But there is already enough, or nearly enough, margin between Ares I capability and Orion's allocated mass to provide that capability if needed.

But it isn't needed.

Famous last words.

Apollo program discovered that there _always_ is something useful you can do with extra upmass capability, and then you want more. Von Braun knew that, and designed Saturn V with _big_ performance reserve.

Why NASA chose to forgot it? Von Braun is not famous enough in this field for you?

NASA didn't forget.

Von Braun had a blank sheet to design with and a blank check to build with.

Von Braun also had a mini-empire at Marshall where he could insert that margin without much attention from HQ. Marshall doesn't have that kind of clout any more, though they do (as do most other NASA centers) retain the mini-empire mentality.

CxP has also had to deal with major design changes after the basic sizing was nailed down. Smaller J-2X based Ares upper stage hurt. So did the switch back to hypergolics from LOX/methane for Orion propulsion. Between those, much margin was lost.
JRF

Online edkyle99

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Maybe Ares I can lift Orion into ISS orbit, but at the max of its capabilities. There is zero growth potential.

"Von Braun's" Saturn IB could only lift 18.6 tonnes to LEO.  Apollo outgrew that rocket, despite all of that knowledgeable Marshall engineering.  Early plans had called for circumlunar missions and launches with CSM and LM launched together. 

There is going to be growth potential in a 910 tonne GLOW launch vehicle.  J-2X specific impulse can be tweaked, for example.  A lot of dry mass reduction will be available after Ares I has flown several times, providing structural data.  It should also be possible to reduce residual propellant with flight experience, providing quite a bit of extra payload capacity.  Guidance and flight control can be fine-tuned with flight experience, etc.  If needed, first stage recovery can be deleted to provide a substantial payload improvement.  The first stage could go from steel to composite casings, providing a vast performance improvement, if needed.  And so on.

Ares I can lift Orion with margin to spare.  That margin will likely be used, eventually.

 - Ed Kyle
« Last Edit: 12/12/2008 09:11 PM by edkyle99 »

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