Ares I: Thrust Occiliation (TO)

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The elliptical rotation is with in the motion of the rocket itself, not the LOX tank.&nbsp; It is a combination of the pitch or yaw (of the LOX on the rocket itself&nbsp;+ the compensation of the gimbaled nozzle&nbsp;of the SRB)&nbsp;as the minor axis of the ellipse.&nbsp; The major axis of the ellipse would be the T.O.&nbsp; In other words, the wobbling of the&nbsp;pitch and yaw would be a desirable motion when combined with the T.O.http://en.wikipedia.org/wiki/Flight_dynamicshttp://en.wikipedia.org/wiki/Ellipse</DIV>&nbsp;</p><p>The ellipse that you are describing would, if it were to exist, be an ellipse only if you hac some planar motion in a pitch/yaw plane and linear oscillatory motion along the axis of the vehicle.&nbsp; But even if the pitch/yaw were confined to a plane you would not have&nbsp;linear oscillatory motion along the axis.&nbsp; This is because the oscillation, recall the magnitude of the pressure oscillation is only about 1 psi, is not sufficient to reverse the thrust,&nbsp;so the thrust continues to&nbsp;be in the positive z direction.&nbsp; What you get is is an oscillation in force superimposed on top of the average thrust,&nbsp;which results in a very small oscillatory&nbsp;velocity superimposed on a large and monotonically increasing, nearly linearly increasing velocity curve.&nbsp; That is quite different from a&nbsp;cocktail shaker and it would not be called an ellipsoidal motion by most people.&nbsp; From that one would not expect a great deal of sloshing of the liquid oxygen.</p><p>Did you bother to actually read those Wiki articles ?&nbsp; Would you like some help understanding what they say ?</p><p>&nbsp;</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>And I think you should use your imagination (images) more.</DIV></p><p>I am not sure what your point is here.&nbsp; One does use images in developing a concept of&nbsp;what the issue is and what viable solutions might be.&nbsp; I certainly do.&nbsp; But conjuring up fanciful and erroneous notions of how rockets work based on cartoons&nbsp;is not good science, engineering, or just plain common sense.&nbsp;</p><p>[QUOTEAbsolutly not.&nbsp; Thrust Occilation is single linear motion&nbsp;problem, which requires a messy (more than 1 motion)&nbsp;solution.</DIV></p><p>Thrust is not a motion at all, but rather it is a force which relates to acceleration.&nbsp; Thrust oscillation is a phenomena that relates to time variation of that force along a single axis, the thrust axis which is generally about the same as the z-axis of the vehicle.&nbsp; However, the issue that you raised was not thrust oscillation itself but rather a motion of the liquid hydrogen in the upperstage, a response to the hypothetical thrust oscillation.&nbsp; And that hypothetical motion is not a uniaxial motion but rather a complex fluid dynamics response to the stimulus of the hypothetical thrust oscillation.&nbsp; And that motion, if it were to occur could in fact be controlled with baffles.</p><p>There could well be a complex response of the liquid, the tank and the suporting structure that would be difficult to describe in a compact mathematical form.&nbsp; But that response could be damped with baffles and perhaps with&nbsp;isolators if necessary.</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;And as a professional, that's YOUR job. </DIV></p><p>Yep.&nbsp;You have demonstrated why it is a job that is performed by professionals.&nbsp;Once again you have completely blown the physics.&nbsp; Your record in addressing the real physical phenomena remains unblemished by success.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[docm]

Yup...that sounds like another Jim alias.... <div class="Discussion_UserSignature"> </div>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;The ellipse that you are describing would, if it were to exist, be an ellipse only if you hac some planar motion in a pitch/yaw plane and linear oscillatory motion along the axis of the vehicle.&nbsp; But even if the pitch/yaw were confined to a plane you would not have&nbsp;linear oscillatory motion along the axis.&nbsp; This is because the oscillation, recall the magnitude of the pressure oscillation is only about 1 psi, is not sufficient to reverse the thrust,&nbsp;so the thrust continues to&nbsp;be in the positive z direction.&nbsp; What you get is is an oscillation in force superimposed on top of the average thrust,&nbsp;which results in a very small oscillatory&nbsp;velocity superimposed on a large and monotonically increasing, nearly linearly increasing velocity curve.&nbsp; That is quite different from a&nbsp;cocktail shaker and it would not be called an ellipsoidal motion by most people.&nbsp; From that one would not expect a great deal of sloshing of the liquid oxygen.Replying to:<BR/><DIV CLASS='Discussion_PostQuote'></p><p>Nicely done double speak or double talk.&nbsp; I don't buy what you said, for even 1 second.&nbsp; I'm not saying everything you said is a bunch of baloney, only 1/2.&nbsp; <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-tongue-out.gif" border="0" alt="Tongue out" title="Tongue out" /></p><p>http://www.merriam-webster.com/dictionary/double%20talk</p><p>The sloshing of the LOX (in an oversized tank) comes from the pitch or yaw of the vehicle, when compensated by the gimbaled SRB nozzle.</p><p>&nbsp;Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Thrust is not a motion at all, but rather it is a force which relates to acceleration.&nbsp; Thrust oscillation is a phenomena that relates to time variation of that force along a single axis, the thrust axis which is generally about the same as the z-axis of the vehicle.&nbsp; However, the issue that you raised was not thrust oscillation itself but rather a motion of the liquid hydrogen in the upperstage, a response to the hypothetical thrust oscillation.&nbsp; And that hypothetical motion is not a uniaxial motion but rather a complex fluid dynamics response to the stimulus of the hypothetical thrust oscillation.&nbsp; And that motion, if it were to occur could in fact be controlled with baffles.There could well be a complex response of the liquid, the tank and the suporting structure that would be difficult to describe in a compact mathematical form.&nbsp;&nbsp; <br />Posted by DrRocket</DIV></p><p>I mentioned LH2, but we're not talking about that anymore!&nbsp; Shuttle Guy said it wasn't dense enough to affect the rocket.&nbsp; We're talking about LOX.&nbsp; The rest of what you've said is more double talk (half baloney + half truth).<br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Yup...that sounds like another Jim alias.... <br />Posted by docm</DIV></p><p>They must be related.&nbsp; Maybe cousins.&nbsp; <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-wink.gif" border="0" alt="Wink" title="Wink" /><br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[MeteorWayne]

<p>A shock absorber solution has been designed...</p><p>http://www.space.com/news/080819-nasa-ares1-vibration-update.html</p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[docm]

Since they're active and not passive (presumption based on the presence of motors) doesn't this add yet another failure mode (or several) to a system seemingly up to its arse in them? Also; does this mean yet another mass reduction in Orion? <div class="Discussion_UserSignature"> </div>

 

[CalliArcale]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Since they're active and not passive (presumption based on the presence of motors) doesn't this add yet another failure mode (or several) to a system seemingly up to its arse in them? Also; does this mean yet another mass reduction in Orion? <br /> Posted by docm</DIV><br /><br />That's what immediately came to my mind.&nbsp; Ares I gets less and less appealing to me as time goes on.&nbsp; Mind you, I didn't have any problems with the "Stick" concept in the beginning.&nbsp; But it's just not living up to expectations.&nbsp;&nbsp; Well, not living up to my expectations; obviously some folks anticipated that it would have issues.&nbsp; ;-) </p> <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[docm]

<p>http://www.spaceflightnow.com/news/n0808/19ares1/</p><p><br /><font face="VERDANA, ARIAL, HELVETICA, SANS-SERIF" size="+2" color="#000033"><strong>Proposals made to solve Ares 1 rocket vibration worry</strong></font></p><p><br /> <font face="VERDANA, ARIAL, HELVETICA, SANS-SERIF" size="-2"><strong>BY WILLIAM HARWOOD</strong></font></p><p>NASA hopes to resolve concern about high vibrations in its new Ares 1 rocket by using a shock absorber-like passive damper between the first and second stages and a computer-controlled, motor-driven system of spring-mounted weights at the base of the booster to actively cancel out unwanted up-and-down oscillations.</p><p><br /><table border="0" cellspacing="0" cellpadding="0" width="184" height="224"><tbody><tr><td width="400"><p><br /> <img src="http://sitelife.space.com/ver1.0/Content/images/store/2/13/628b7571-7c8e-43cc-bdea-dd1391579295.Medium.jpg" alt="" /><br /><br />&nbsp;<br /> </p>

 

[tanstaafl76]

<p>&nbsp;</p><p>Let me preface by saying that I'm a total layman so I apologize in advance if I'm missing something very obvious here.</p><p>From what I have read, the number one issue when it comes to rockets is weight.&nbsp; Fuel quantity, payloads, material used, multiple stages, all revolves around the ever-present problem of weight.&nbsp; But then I read a solution to a vibration problem is to add 16 weights to the rocket?!&nbsp; How heavy are these things?&nbsp; They must be pretty substantial if they are able to cancel out 3-4 G vibrations, yes?&nbsp; It just seems like this solution goes completely against the basic principles of rocket design.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Let me preface by saying that I'm a total layman so I apologize in advance if I'm missing something very obvious here.From what I have read, the number one issue when it comes to rockets is weight.&nbsp; Fuel quantity, payloads, material used, multiple stages, all revolves around the ever-present problem of weight.&nbsp; But then I read a solution to a vibration problem is to add 16 weights to the rocket?!&nbsp; How heavy are these things?&nbsp; They must be pretty substantial if they are able to cancel out 3-4 G vibrations, yes?&nbsp; It just seems like this solution goes completely against the basic principles of rocket design.&nbsp; <br />Posted by tanstaafl76</DIV></p><p>That 3-4 g's is some sort of response of particular pieces of the rocket to a much lower driving acceleration.&nbsp; The acoustic oscillation from the SRBs is very small.&nbsp; It is based on a 1pse oscillation seen in the current 4-segment SRB extrapolated to a larger motor and then run through a dynamics model for the overall vehicle.&nbsp; In a model like that you can get some resonances (like moving yourself on a swing, if you time your movements properly you can get up pretty high but if your timing is off not much happens).&nbsp; So they may be able to strategically place some springs, masses and dashpots to disrupt resonances without adding a lot of weight.</p><p>You are almost correct in your emphasis on weight.&nbsp; The other important item is Isp and it is actually more critical than weight in most situations.&nbsp; But there is relatively little that you can do about Isp once you have chosen a propellant and a nozzle expansion ratio, while the fight to reduce weight is constant.<br /></p> <div class="Discussion_UserSignature"> </div>

 

[tanstaafl76]

<p>Thanks for the detail Dr Rocket, sounds like a kinetic version of noise-canceling headphones!&nbsp; Out of curiosity, have you seen them note anywhere how heavy those weights are going to need to be to achieve the desired effect?</p> <div class="Discussion_UserSignature"> </div>

 

[job1207]

<p>First, when this issue was first publicized, it was noted to be a threat to the overall integrity of the rocket, not to mention the lives of the Astronauts. Several private scientists made comments about harmonic motion destroying the craft. The current press releases seem to gloss over this notion.&nbsp;</p><p>Second, this reminds me of the intense engineering effort that went into the ET exterior foam after it killed seven people. The foam did not belong on the outside of the ET, since it was there, it required overengineering in order to deal with the challenges of not killing people. I am not a fan of overengineering. </p><p>To the point, adding shock absorbers to dampen a system that would otherwise destroy the vehicle seems to be off the point. It would be best to get a primary system that works with fewer quirks, so to speak.&nbsp; </p><p>I know that each time this comes up, the engineers working on the project say that the primary system, with this re work, will work. Well, that is probably the case, but it is not exactly the A system that a professor would expect his A student to design. I am not at all sure why the US as a Nation is doing this, this way.&nbsp;</p><p>That said, the fix does seem simple, failure proof, and rugged, if not elegant. So I am expecting it to work. </p><p>Finally, the loss of the mock up Orion in the drop test shows that testing testing testing is important. The sad thing is that these tests were done in the 60's and now they are being done again. Keep testing folks. It is important, as you know. </p>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>First, when this issue was first publicized, it was noted to be a threat to the overall integrity of the rocket, not to mention the lives of the Astronauts. Several private scientists made comments about harmonic motion destroying the craft. The current press releases seem to gloss over this notion.&nbsp;Second, this reminds me of the intense engineering effort that went into the ET exterior foam after it killed seven people. The foam did not belong on the outside of the ET, since it was there, it required overengineering in order to deal with the challenges of not killing people. I am not a fan of overengineering. To the point, adding shock absorbers to dampen a system that would otherwise destroy the vehicle seems to be off the point. It would be best to get a primary system that works with fewer quirks, so to speak.&nbsp; I know that each time this comes up, the engineers working on the project say that the primary system, with this re work, will work. Well, that is probably the case, but it is not exactly the A system that a professor would expect his A student to design. I am not at all sure why the US as a Nation is doing this, this way.&nbsp;That said, the fix does seem simple, failure proof, and rugged, if not elegant. So I am expecting it to work.&nbsp; <br />Posted by job1207</DIV></p><p><strong>I have to disagree with your optimism.&nbsp; The current fix to T.O. is complicated, has many failure points (16 springs) and is overenginered.&nbsp; Here's the current solution:</strong></p><p>http://www.nasa.gov/mission_pages/constellation/ares/thrust_oscillation.html</p><p><strong>Now, let's revisit the Parasorber concept with something new added:</strong></p><p>http://www.nasaspaceflight.com/2008/07/thrust-oscillation-parasorber-and-thrusters-lead-ares-i-options/</p><p><strong>The new addition, would be spring steel:&nbsp; 2 curved pieces of spring steel clamped (or unclamped?)in the center, back to back (similar to a curvy X).&nbsp; Whether this could be placed inside the parachute covers or above them, I leave to the engineers.&nbsp; Maybe this could be made disposable, so as to not add weight to the recovery of the SRB (which was mentioned in the article).&nbsp; I believe this system could cut the mass in 1/2 (<600 lbs.) while absorbing vibrations and oscillations.</strong></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I have to disagree with your optimism.&nbsp; The current fix to T.O. is complicated, has many failure points (16 springs) and is overenginered.&nbsp; Here's the current solution:http://www.nasa.gov/mission_pages/constellation/ares/thrust_oscillation.htmlNow, let's revisit the Parasorber concept with something new added:http://www.nasaspaceflight.com/2008/07/thrust-oscillation-parasorber-and-thrusters-lead-ares-i-options/The new addition, would be spring steel:&nbsp; 2 curved pieces of spring steel clamped (or unclamped?)in the center, back to back (similar to a curvy X).&nbsp; Whether this could be placed inside the parachute covers or above them, I leave to the engineers.&nbsp; Maybe this could be made disposable, so as to not add weight to the recovery of the SRB (which was mentioned in the article).&nbsp; I believe this system could cut the mass in 1/2 (<600 lbs.) while absorbing vibrations and oscillations. <br />Posted by kyle_baron</DIV></p><p><strong>So, we all agree that 2 curved sheets of spring steel, will solve the thrust oscillation problem?</strong><br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[shuttle_guy]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>So, we all agree that 2 curved sheets of spring steel, will solve the thrust oscillation problem? <br />Posted by kyle_baron</DIV></p><p>Not me.</p> <div class="Discussion_UserSignature"> </div>

 

[windnwar]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Not me. <br />Posted by shuttle_guy</DIV><br /><br />Me either! This frankenbastard of a rocket is looking like a great way to kill astronauts in new and horrifying ways. Even if the ride was free, unless I was terminally ill you couldn't get me to ride it. </p><p>Sadly the worst part is, every one of these mitigation options takes away even more mass to orbit, to the point that Orion which has been cut back alot already, is going to lose even more. EELV heavy's are looking better and better everyday. </p> <div class="Discussion_UserSignature"> <p> </p><p><font size="2" color="#0000ff">""Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." --Albert Einstein"</font></p> </div>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Not me. <br />Posted by shuttle_guy</DIV></p><p><strong>Thank you SG!&nbsp; Anyone else want to step up to the plate?&nbsp; I'm surprised that Dr. Rocket hasn't jumped all over this, with a vengence.</strong><br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Me either! This frankenbastard of a rocket is looking like a great way to kill astronauts in new and horrifying ways. Even if the ride was free, unless I was terminally ill you couldn't get me to ride it. Sadly the worst part is, every one of these mitigation options takes away even more mass to orbit, to the point that Orion which has been cut back alot already, is going to lose even more. EELV heavy's are looking better and better everyday. <br />Posted by windnwar</DIV></p><p><strong>You may, just want to chill-out for a while............</strong><br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[MeteorWayne]

Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Thank you SG!&nbsp; Anyone else want to step up to the plate?&nbsp; I'm surprised that Dr. Rocket hasn't jumped all over this, with a vengence. <br />Posted by kyle_baron</DIV><br /><br />In another thread he has said he will be traveling for a while, so can only make occasional visits for a bit. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>In another thread he has said he will be traveling for a while, so can only make occasional visits for a bit. <br />Posted by MeteorWayne</DIV></p><p><strong>Thanks MW.&nbsp; Must be my lucky day today.&nbsp; <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-wink.gif" border="0" alt="Wink" title="Wink" /></strong></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[trailrider]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Thank you SG!&nbsp; Anyone else want to step up to the plate?&nbsp; I'm surprised that Dr. Rocket hasn't jumped all over this, with a vengence. <br />Posted by kyle_baron</DIV><br />How about&nbsp;the springs and shocks from a 64 International 5-ton truck?&nbsp; Sheesh! What kluge! Except for the lack of a "nuk-u-ler pile", this sounds like something that Heinlein wrote about in "Rocketship Galileo"! </p>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Thank you SG!&nbsp; Anyone else want to step up to the plate?&nbsp; I'm surprised that Dr. Rocket hasn't jumped all over this, with a vengence. <br />Posted by kyle_baron</DIV></p><p>As I said earlier, and provided the NASA data to substantiate, this entire concern has been raised on the basis of an analytical projection, based on data from 4-segment shuttle static firing data, of a pressure oscillation of about 1 psi amplitude, of the structural response of the astronaut compartment of the complete vehicle.&nbsp; Such projections are notoriously inaccurate.&nbsp; I suggested then and continue to believe now, that the wisest course of action is to wait until there is some real flight data from the scheduled unmanned flight to actually determine what vibration levels are realized in practice.</p><p>No one really knows if there is a problem.&nbsp; And such problems are usually relatively easy to handle with shock isolators and dampers.&nbsp; But first you have to know what you are actually dealing with.<br /></p> <div class="Discussion_UserSignature"> </div>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>How about&nbsp;the springs and shocks from a 64 International 5-ton truck?&nbsp; Sheesh! What kluge! Except for the lack of a "nuk-u-ler pile", this sounds like something that Heinlein wrote about in "Rocketship Galileo"! <br />Posted by trailrider</DIV></p><p><strong>Good point.&nbsp; It is a primitive design that is similar, but not exactly like the leaf springs on a 60's muscle car.&nbsp; I'm afraid that the coil springs and shocks from a 5 ton truck, would not counter act the torsional (twisting) of unevenly&nbsp;timed oscillations.</strong></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>As I said earlier, and provided the NASA data to substantiate, this entire concern has been raised on the basis of an analytical projection, based on data from 4-segment shuttle static firing data, of a pressure oscillation of about 1 psi amplitude, of the structural response of the astronaut compartment of the complete vehicle.&nbsp; Such projections are notoriously inaccurate.&nbsp; I suggested then and continue to believe now, that the wisest course of action is to wait until there is some real flight data from the scheduled unmanned flight to actually determine what vibration levels are realized in practice.No one really knows if there is a problem.&nbsp; And such problems are usually relatively easy to handle with shock isolators and dampers.&nbsp; But first you have to know what you are actually dealing with. <br />Posted by DrRocket</DIV></p><p><strong>A safe, analytical, and logical response.&nbsp; Thank you.</strong><br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[job1207]

<p>I am surprised to hear you think that springs are not simple and rugged. Initially, I was suprised to hear that they would work, in the first place. Now that some ? whether they do work it is going to be an interesting first flgith of the Ares 1. </p><p>I am thinking that the first flight will be for the first stage only. That will resolve the major ? to date anyway.&nbsp;</p><p>Let's just&nbsp; shoot one off and see what happens.&nbsp; </p><p>&nbsp;</p>