Ares I: Thrust Occiliation (TO)

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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Because you've changed your tone, I will answer your questions to the best of my knowledge.&nbsp;The vibration, occilation, etc. is an excessive pressure energy, that is dissipated thru the entire structure of the rocket.&nbsp;</p><p><font color="#0000ff">Any acoustic pressure is well within specification (we are talking only a few psi at most) and is not in any meaningful sense excessive pressure at all.&nbsp; Further it is an oscillation, and therefore any PV energy term quickly averages to zero.&nbsp; This is simply fallacious reasoning.&nbsp; You really do need to learn some physics.&nbsp; You probably ought to start in this case with understanding vibrations and the &nbsp;role of natural frequencies.&nbsp; But a basic grounding in fluid dynamics is also clearly needed.&nbsp; </font></p><p>&nbsp;I see this as wasted energy efficiency.&nbsp; Taking this wasted energy, removing it, and placing it outside the rocket, as a thrust in the direction of the SRB thrust, is the goal.&nbsp; Keep in mind, that this&nbsp;would not be&nbsp;a constant thrust, but more of a pulsed thrust.</p><p><font color="#0000ff">Energy "efficiency" in this case is not a real concept.&nbsp; You can't simply pick up energy and move it or remove it.&nbsp;&nbsp; In any case&nbsp;how&nbsp;do you think drilling holes in the case would&nbsp;reduce thrust oscillation? You have not begun to address the mechanisms involved.&nbsp; You also have not explained how this would result in thrust axial to the SRB.&nbsp; A hole drilled in the case would vent the gasses normal to the case.&nbsp; Putting some sort of nozzle to redirect the flow axially would result in gasses at a temperature of something like 5500 degrees flowing along the steel case, which would dramatically weaken it and could easily cause a catastrophic failure.&nbsp; That gas is not only extremely hot but it contains aluminum oxide particles that can be extremely erosive.&nbsp; I have no&nbsp;idea what makes you think that this would be any sort of a pulsed thrust. In any case the whole point of trying to eliminate any oscillation is to in fact make the thrust more nearly constant.&nbsp; If your scheme were to have the effect that you envision (it won't since you have completely missed the relevant physics and engineering concerns) it would therefore do the opposite of what is desirable.</font></p><p><font color="#0000ff">The bottom line is that the notion of putting holes in the side of the SRB case will create&nbsp; NO positive effects, will result in additional failure modes, may in fact increase factors internal to the SRB that drive pressure oscillations, and result in hot particle laden combustion gasses causing deleterious heating that can only cause problems, potentially big problems.&nbsp; </font></p><p><font color="#0000ff">The lack of understanding of even the rudiments of physics here is so great that I don't know where you might start to take remediation.&nbsp; You clearly need a course in elementary physics, but one that includes at least use of elementary calculus.&nbsp; </font></p><p>I don't know of any additional effects.I would say they are beneficial to the crew, and the 2nd stage motor bearing.&nbsp; Why?&nbsp; Brain damage might occur it the astronauts, and the gimbal bearing in the 2nd stage motor might jam.&nbsp;I'm not arguing with that.&nbsp; My issue is with the excessive pressure that causes the T.O.</p><p><font color="#0000ff">See above. You have completely misconstrued the problem and the physics involved.&nbsp; The proposed solution is simply not viable.&nbsp; Worse it is extremely detrimental to the SRBs and the overall vehicle.</font></p><p><font color="#0000ff">The notion that TO is the result of excess pressure that needs to be vented is nothing short of bizarre.&nbsp; This is the 21st century version of the 18th century notion that illness was caused by too much blood in the body and that a cure was to cut open a few veins and get rid of a bit.</font></p><p>I would be interested in your comments about the Challenger SRB leak, and the SRB not blowing up.&nbsp; I was wondering if you could analyze this in terms of the physics which were involved.</p><p><font color="#0000ff">The Challenger SRB leak is quite easy to explain.&nbsp; Starting with the fact that the O-ring failed to seal properly under the transient pressurization at ignition, you created a jet of hot aluminized gas.&nbsp; That gas jet relatively quickly burned and eroded a hole in the side of the steel SRB case which caused the hot gasses to impinge on the core vehicle, which itself is largely a set of fuel tanks containing liquid hydrogen and liquid oxygen.&nbsp; The impingement of that hot gas on the external portions of those tanks and on a strut that held the orbiter resulted in failure of the strut and a rupture&nbsp; subsequent&nbsp;ignition of that propellant with the&nbsp;visible&nbsp;fireball that was seen in the films&nbsp; The aerodynamic loads cause the breakup of the orbiter.&nbsp; Based on film data&nbsp;the leak seems to have been plugged by something, likely aluminum oxide until about 59 seconds into flight, when a noticeable leak was seem.&nbsp; By about 72 seconds into flight the disaster had occurred.</font></p><p><font color="#0000ff">While the SRB did not itself rupture it did have a continually enlarging hole burned into the side, and the fact that it did not rupture is probably due to the fact that the steel cases are not particularly susceptible to crack propagation.&nbsp; Because the gasses were venting transversely to the case surface there was no heating of the external case surface by the gasses except at the location of the hole itself.</font></p><p><font color="#0000ff">The problem with venting motor gasses through a hole in the side, is less an immediate catastrophic failure of the SRB itself than on other sensitive components, the simple fact that venting gasses out the side of the case produces no useful effects whatever.&nbsp;and that, uncontrolled, such venting can result in further compromise of the structural integrity and margins of the case.&nbsp; The SRB case on the Challenger lasted another 37 seconds after the disaster, with continual erosion of the case wall,&nbsp; A vent for the full duration of motor operation would have to last something like 2 minutes without any case degradation.&nbsp;&nbsp;That is somewhat more difficult to handle.&nbsp; The high velocity gasses from the solid rocket motor cause a quite significant erosion of the nozzle throat, but that effect is considered in the design.&nbsp; The throat is quite a bit larger after the firing than before. Nozzle design, particularly throat design involves some very sophisticated features to manage both the heat flux and the high velocity gasses.&nbsp; It is a LOT more complicated, involved a LOT more weight and a LOT more complexity that simply drilling a hole in the case, even if you put in a pipe.&nbsp; And you have to contend with what that pipe would do to the internal flow field.&nbsp; It would at least provide a site for the formation of vortices, which is one reason for the TO concern in the first place.</font></p><p><font color="#0000ff">The concept of putting in a pipe adds a whole new set of problems and failure modes in and of itself.&nbsp; In order to maintain the proper surface-time curve for the propellant you would have to have the propellant bonded to the exterior of the pipe.&nbsp; If that bond failed then you would open up undesired surface and a direct patht to the insulator, which is designed to withstand the combustion gases for only a prescribed period of time.&nbsp;&nbsp;The holes&nbsp;put in the&nbsp;the propellant change the stress state from&nbsp;one that is largely hydrostatic compression to one with a significant shear component.&nbsp;&nbsp;This could result in either a failure of the bond or even worse the initiation of cracks in the propellant itself. &nbsp;A failure of that bond or cracks in the propellant&nbsp;could easily result in a catastrophic failure.&nbsp; So in addition to producing no beneficial effects whatever, your 4 (how did you arrive at 4?) holes would introduce at least 8 new and serious failure modes.</font></p><p><font color="#0000ff">So, basically this scheme is based on complete lack of understanding of basic physics and the principles of operation of solid rockets.&nbsp; It results in no benefits whatever.&nbsp; But it makes up for that by introducing a great deal of complexity and cost, providing an entirely new mechanism for formation of internal vortices that can induce thrust oscillation, and providing paths never before considered whereby catastrophic failure can be induced.&nbsp; </font></p><p><br />Posted by kyle_baron</DIV><br /></p> <div class="Discussion_UserSignature"> </div>
 
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kyle_baron

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> <font color="#0000ff">Any acoustic pressure is well within specification (we are talking only a few psi at most) and is not in any meaningful sense excessive pressure at all.&nbsp; Further it is an oscillation, and therefore any PV energy term quickly averages to zero.&nbsp; This is simply fallacious reasoning.&nbsp; You really do need to learn some physics.&nbsp; You probably ought to start in this case with understanding vibrations and the &nbsp;role of natural frequencies.&nbsp; But a basic grounding in fluid dynamics is also clearly needed.&nbsp;</font><br />Posted by DrRocket</DIV></p><p>Just one last question:&nbsp; The +&nbsp;/ -&nbsp;6G oscillation, which can shake an entire rocket, is equivalent to a few psi??????</p><p>This info. is from NasaSpaceflight.com. which was stated several times, among professionals in the industry.</p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Just one last question:&nbsp; The +&nbsp;/ -&nbsp;6G oscillation, which can shake an entire rocket, is equivalent to a few psi??????This info. is from NasaSpaceflight.com. which was stated several times, among professionals in the industry. <br />Posted by kyle_baron</DIV></p><p>Nothing has actually been measured.&nbsp; Take a look at the link I posted earlier to the charts from the group that NASA has put together to study this issue -- if you look there you see that the effect is based on an approximately <strong><font size="2">1 psi</font></strong> (2 if you go peak to peak) oscillation from 4 segment SRB testing and the 6 gs is an analytical prediction of the response of a portion of the vehicle.</p><p>You might be interested to know that such predictions are extremely highly dependent on assumed values for stiffnessess and damping factors, and without an experimental modal survey, which requires that a complete vehicle be available, there is little empirical data for those coefficients.&nbsp; In short, dynamic and acoustic models at this stage of a program are not particularly well known for accuracy.</p><p>You ought to quit listening to babble on uncontrolled forums, get some real data, and learn some real physics.&nbsp; Uninformed opinions based on an incomplete and fundamentally incorrect notion of the principles of physics are worse than useless.</p><p>Since you either did not read it, or more likely did not understand what was being said, here is a presentation package from the NASA group that is studying the problem, and in it are the data that I mentioned above.</p><p><font face="Arial" size="2" color="#0000ff">http://www.nasa.gov/pdf/221186main_toft_checkpoint_report.pdf</font><font face="Arial" size="2">.</font></p><p><font face="Arial" size="1">Sorry that this is not from NASA.com,&nbsp; I was only able to obtain good data from NASA.gov.&nbsp; I'll put my money on NASA.gov.</font></p> <div class="Discussion_UserSignature"> </div>
 
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kyle_baron

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<p>Some where on these boards, or at another site, someone had said there wouldn't be&nbsp;much thrust ocillation because of the sloshing around of the LH2 in the 2nd stage, which&nbsp;would counteract this ocillation.&nbsp; I would like to look at this option a little closer.&nbsp; For this to work, some off loading of LH2 must occur to create a space with in the tank.&nbsp; How much empty space that is&nbsp;necessary, is anyones guess.&nbsp; I'll just say 2-3' at the top of the tank.&nbsp; If this idea works, it would be like killing 2 birds (problems)&nbsp;with 1 stone&nbsp;(solution).&nbsp; In other words, this would reduce the amplitude (magnitude) of the&nbsp;ocillation, and reduce the&nbsp;mass (of propellent)&nbsp;at the same time.&nbsp; Also, if there are any baffles in the tank, those would have to be removed or moved closer to the engine, to prevent POGO.&nbsp; Almost&nbsp;the entire mass, of LH2 needs to slosh back and forth.</p><p>I was also wondering, if the top of the LH2 tank&nbsp;should be reshaped, to optimize this sloshing action.&nbsp; I was thinking of&nbsp;a shape similar to the &nbsp;drinking end of a 20 oz. plastic soda bottle.&nbsp; Or, would a completely flat end work better?<br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
 
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l3p3r

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Some where on these boards, or at another site, someone had said there wouldn't be&nbsp;much thrust ocillation because of the sloshing around of the LH2 in the 2nd stage, which&nbsp;would counteract this ocillation.&nbsp; I would like to look at this option a little closer.&nbsp; For this to work, some off loading of LH2 must occur to create a space with in the tank.&nbsp; How much empty space that is&nbsp;necessary, is anyones guess.&nbsp; I'll just say 2-3' at the top of the tank.&nbsp; If this idea works, it would be like killing 2 birds (problems)&nbsp;with 1 stone&nbsp;(solution).&nbsp; In other words, this would reduce the amplitude (magnitude) of the&nbsp;ocillation, and reduce the&nbsp;mass (of propellent)&nbsp;at the same time.&nbsp; Also, if there are any baffles in the tank, those would have to be removed or moved closer to the engine, to prevent POGO.&nbsp; Almost&nbsp;the entire mass, of LH2 needs to slosh back and forth.I was also wondering, if the top of the LH2 tank&nbsp;should be reshaped, to optimize this sloshing action.&nbsp; I was thinking of&nbsp;a shape similar to the &nbsp;drinking end of a 20 oz. plastic soda bottle.&nbsp; Or, would a completely flat end work better? <br /> Posted by kyle_baron</DIV> I was under the impression that POGO effects were caused by vibrations in the engine mounting causing the stretching of fuel lines and causing irregular fuel flow (which in turn causes irregular burning, and irregular thrust which exacerbates the vibratrions as a positive feedback.) I didn't think fuel sloshing in the tank would have much to do with it, since the flow from the tanks is regulated anyway... </p><p>&nbsp;And in my highly unprofessional opinion can I just add that adding holes to the SRBs seems like a pretty counter productive idea :)&nbsp; </p> <div class="Discussion_UserSignature"> </div>
 
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kyle_baron

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> I was under the impression that POGO effects were caused by vibrations in the engine mounting causing the stretching of fuel lines and causing irregular fuel flow (which in turn causes irregular burning, and irregular thrust which exacerbates the vibratrions as a positive feedback.) I didn't think fuel sloshing in the tank would have much to do with it, since the flow from the tanks is regulated anyway...</DIV></p><p>Well, I hope you're right.</p><p>&nbsp;&nbsp;Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;And in my highly unprofessional opinion can I just add that adding holes to the SRBs seems like a pretty counter productive idea :)&nbsp; <br />Posted by l3p3r</DIV></p><p>Well then, maybe we should take a poll and see which idea is crazier:&nbsp; The reversing thrusters that Nasa proposes, or the regulated openings in the SRB case that I proposed.&nbsp; Obviously, both are unconventional ideas.&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><br /><br />&nbsp;</p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
 
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kyle_baron

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Nasa Watch has some information of the thrust oscillation:http://www.nasawatch.com/archives/2008/08/more_ares_i_con.htmlI don't know how reliable information this is... But according to this info Nasa is planning some active system to dampen the oscillations. <br />Posted by Zipi</DIV></p><p>One idea is called the Parasorber, which&nbsp;has compression springs located in the parachute nose section.&nbsp; The other idea is an active thrust in the forward and aft directions of the SRB.&nbsp; I don't think the Parasorber made the cut, from some discussions at NasaSpaceflight.com&nbsp;<br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
 
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Bytor_YYZ

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Well, I hope you're right.&nbsp;&nbsp;Well then, maybe we should take a poll and see which idea is crazier:&nbsp; The reversing thrusters that Nasa proposes, or the regulated openings in the SRB case that I proposed.&nbsp; Obviously, both are unconventional ideas.&nbsp; &nbsp; <br /> Posted by kyle_baron</DIV></p><p>&nbsp;</p><p>The thrusters can fix the problem, the regulated openings will never work</p>
 
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kyle_baron

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;The thrusters can fix the problem, the regulated openings will never work <br />Posted by Bytor_YYZ</DIV></p><p>I'm afraid that option will be deleted in the near future, also.&nbsp; Discussions at NasaSpaceflight.com indicate that the sensors can't possibly react fast enough with the thrusters.&nbsp; Now, back to the topic at hand, what do you think of off- loading LH2 from the 2nd stage?<br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
 
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Bytor_YYZ

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I'm afraid that option will be deleted in the near future, also.&nbsp; Discussions at NasaSpaceflight.com indicate that the sensors can't possibly react fast enough with the thrusters.&nbsp; Now, back to the topic at hand, what do you think of off- loading LH2 from the 2nd stage? <br /> Posted by kyle_baron</DIV></p><p>&nbsp;</p><p>That doesn't work either.&nbsp; The machanics wouldn't fix it and a partially filled stage is not workable. &nbsp;</p><p>&nbsp;</p><p>Stages and rockets are designed to be filled to within a few percent of 100.&nbsp; They don't have continuous level gages, just enough for the last few percent. The rockets dynamics are based on only a few variations of mass properties.&nbsp;&nbsp;</p><p>&nbsp;</p><p>Also a large bubble above the LH2 would cause it to slosh during first stage and causing it to vaporize. &nbsp; </p>
 
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MeteorWayne

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;</p><p>&nbsp;Also a large bubble above the LH2 would cause it to slosh during first stage and causing it to vaporize. &nbsp; <br />Posted by Bytor_YYZ</DIV><br /><br />As you will as soon as the mods can prove you're jimfromnsf. It's not nice to return under another assumed name after being banned 5 times!!</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>
 
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shuttle_guy

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Some where on these boards, or at another site, someone had said there wouldn't be&nbsp;much thrust ocillation because of the sloshing around of the LH2 in the 2nd stage, which&nbsp;would counteract this ocillation.&nbsp; I would like to look at this option a little closer.&nbsp; For this to work, some off loading of LH2 must occur to create a space with in the tank.&nbsp; How much empty space that is&nbsp;necessary, is anyones guess.&nbsp; I'll just say 2-3' at the top of the tank.&nbsp; If this idea works, it would be like killing 2 birds (problems)&nbsp;with 1 stone&nbsp;(solution).&nbsp; In other words, this would reduce the amplitude (magnitude) of the&nbsp;ocillation, and reduce the&nbsp;mass (of propellent)&nbsp;at the same time.&nbsp; Also, if there are any baffles in the tank, those would have to be removed or moved closer to the engine, to prevent POGO.&nbsp; Almost&nbsp;the entire mass, of LH2 needs to slosh back and forth.I was also wondering, if the top of the LH2 tank&nbsp;should be reshaped, to optimize this sloshing action.&nbsp; I was thinking of&nbsp;a shape similar to the &nbsp;drinking end of a 20 oz. plastic soda bottle.&nbsp; Or, would a completely flat end work better? <br />Posted by kyle_baron</DIV></p><p>If anyone said that they were mistaken, the LH2 density is too low to help at all. However the LOX is a different matter. That could help dampen the vibrations. No off loa id required since the Prop tanks have a gas ullage above the Lox and LH2.</p> <div class="Discussion_UserSignature"> </div>
 
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shuttle_guy

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> I was under the impression that POGO effects were caused by vibrations in the engine mounting causing the stretching of fuel lines and causing irregular fuel flow (which in turn causes irregular burning, and irregular thrust which exacerbates the vibratrions as a positive feedback.) I didn't think fuel sloshing in the tank would have much to do with it, since the flow from the tanks is regulated anyway... &nbsp;And in my highly unprofessional opinion can I just add that adding holes to the SRBs seems like a pretty counter productive idea :)&nbsp; <br />Posted by l3p3r</DIV></p><p>&nbsp;</p><p>POGO (Pressure Oscillation G Oscillation)&nbsp;is a propellant syatem vibration that feeds itself. It can, and usually does, start with a combustion chamber&nbsp;pressure (Pc)&nbsp;change due to small combustion instability. A&nbsp;higher&nbsp;Pc pulse&nbsp;causes the prop feed rate to decrease which loweres the PC. The lower Pc causes the prop feed rate to increase which decreases the prop flow rate again. The cycle continues. The resultion vibration can match the natural frequency of the vehicle. If this happens the vibration goes divergent and the vehicle is quicky destroyed.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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shuttle_guy

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Well,....................&nbsp; The reversing thrusters that Nasa proposes, or the regulated openings in the SRB case that I proposed.&nbsp; Obviously, both are unconventional ideas.&nbsp; &nbsp; <br />Posted by kyle_baron</DIV></p><p>&nbsp;No, venting the SRB pressure will not solve the problem. You should listen to Dr Rocket. That is a unconventional unworkable idea.</p> <div class="Discussion_UserSignature"> </div>
 
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kyle_baron

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>If anyone said that they were mistaken, the LH2 density is too low to help at all. However the LOX is a different matter. That could help dampen the vibrations. No off loa id required since the Prop tanks have a gas ullage above the Lox and LH2. <br />Posted by shuttle_guy</DIV></p><p>Ok, then I'm confused in what the term "off-loading" means.&nbsp; I assumed it meant not filling the tanks completely.&nbsp; I'm guessing that it might refer to bleeding off any excess propellent?&nbsp; So, because the LOX has a gas guage, could it only be filled, say 90-95% to allow for a&nbsp;sloshing movement?&nbsp; Or, maybe use an oversized tank?&nbsp; Also, in diagrams I've seen, the LOX tank is completely round.&nbsp; Is that the case in real life?</p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
 
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kyle_baron

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;No, venting the SRB pressure will not solve the problem. You should listen to Dr Rocket. That is a unconventional unworkable idea. <br />Posted by shuttle_guy</DIV></p><p>I've moved on, from that idea.&nbsp; And Dr. Rocket's my friend.&nbsp; I listen to maybe 95-99% of what he says.&nbsp; It's that last small quantity, where we argue.&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>
 
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shuttle_guy

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Ok, then I'm confused in what the term "off-loading" means.&nbsp; I assumed it meant not filling the tanks completely.&nbsp; I'm guessing that it might refer to bleeding off any excess propellent?&nbsp; So, because the LOX has a gas guage, could it only be filled, say 90-95% to allow for a&nbsp;sloshing movement?&nbsp; Or, maybe use an oversized tank?&nbsp; Also, in diagrams I've seen, the LOX tank is completely round.&nbsp; Is that the case in real life? <br />Posted by kyle_baron</DIV></p><p>Off loading referrs to removing some of the propellant that has been loaded.</p><p>Almost all propellant tanks always have a gas ullage above the liquid.&nbsp;</p><p>As to your comment ".....LOX tank is completely round". Because the LOX has a high density the clylinder section of the tank is very short. In the Saturn Five second and third stages the forward and aft LOX tank domes essentially mated together such that there was no clyinder section.</p> <div class="Discussion_UserSignature"> </div>
 
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kyle_baron

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Almost all propellant tanks always have a gas ullage above the liquid.&nbsp;As to your comment ".....LOX tank is completely round". Because the LOX has a high density the clylinder section of the tank is very short.&nbsp; <br />Posted by shuttle_guy</DIV></p><p>I'm guessing that the sloshing with in the ullage space (if it's large enough) above the LOX, would cause a slight rotation of the entire stack.&nbsp; When the T.O. from the 1st stage hits the 2nd stage, wouldn't this just increase the speed&nbsp;of this rotation momentarily, then subside, and then go&nbsp;through this entire cycle once again?&nbsp; A rotation would be better than a jarring&nbsp;linear movement, for the vehicle as well as the astronauts.</p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I'm guessing that the sloshing with in the ullage space (if it's large enough) above the LOX, would cause a slight rotation of the entire stack.&nbsp; When the T.O. from the 1st stage hits the 2nd stage, wouldn't this just increase the speed&nbsp;of this rotation momentarily, then subside, and then go&nbsp;through this entire cycle once again?&nbsp; A rotation would be better than a jarring&nbsp;linear movement, for the vehicle as well as the astronauts. <br />Posted by kyle_baron</DIV></p><p>What is your rationale for this?&nbsp; Do you have some specific physics in mind ?<br /></p> <div class="Discussion_UserSignature"> </div>
 
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kyle_baron

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>What is your rationale for this?&nbsp; Do you have some specific physics in mind ? <br />Posted by DrRocket</DIV></p><p>I don't know of a mathematical equation for the sloshing of LOX in an oversized tank, causing a slight rotation of the rocket, do you?&nbsp; That's why I said "I'm guessing...."&nbsp; Nevertheless, common sence would indicate that the force (if large enough) would fall between a linear and rotational movement.&nbsp; I'm guessing (again) that this rotational movement, would be elliptical in nature, once the T.O.hits the 2nd stage.&nbsp; Only testing IMO, would flush out the truth.&nbsp; What do you think?</p><p>As a side note, the gimbaling of the SRB nozzle, may add to, or complete the rotational movement.</p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
 
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Bytor_YYZ

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't know of a mathematical equation for the sloshing of LOX in an oversized tank, causing a slight rotation of the rocket, do you?&nbsp; That's why I said "I'm guessing...."&nbsp; Nevertheless, common sence would indicate that the force (if large enough) would fall between a linear and rotational movement.&nbsp; I'm guessing (again) that this rotational movement, would be elliptical in nature, once the T.O.hits the 2nd stage.&nbsp; Only testing IMO, would flush out the truth.&nbsp; What do you think?As a side note, the gimbaling of the SRB nozzle, may add to, or complete the rotational movement. <br /> Posted by kyle_baron</DIV></p><p>&nbsp;</p><p>The slosh is not cyclic.&nbsp; It doesn't not rotate in the tanks.&nbsp; It is random, much like water in a washing machine. </p>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't know of a mathematical equation for the sloshing of LOX in an oversized tank, causing a slight rotation of the rocket, do you?&nbsp; That's why I said "I'm guessing...."&nbsp; Nevertheless, common sence would indicate that the force (if large enough) would fall between a linear and rotational movement.&nbsp; I'm guessing (again) that this rotational movement, would be elliptical in nature, once the T.O.hits the 2nd stage.&nbsp; Only testing IMO, would flush out the truth.&nbsp; What do you think?As a side note, the gimbaling of the SRB nozzle, may add to, or complete the rotational movement. <br />Posted by kyle_baron</DIV></p><p>I think that you are guessing with no physical basis for your guess at all.&nbsp; Guesses are basically worthless unless backed up by physics.</p><p>What in world is elliptical rotation inside a cylindrical tank ?&nbsp; We are not taking about Keplerian orbits here.</p><p>&nbsp;I think you need a physics course. A purely rotatioinal fluid flow would have minimal effect on the vehicle, as it would be compensated by the roll control system.&nbsp; Of greater concern would be a back and forth sloshing mode that moves the CG of the vehicle from side to side.&nbsp; If there is a concern like that the motion would be more likely induced by action of the thrust vector control system than by axial stimulation due to any thrust oscillation.&nbsp;&nbsp;The gimbaling of the nozzle would not normally create roll, but only pitch or yaw.&nbsp; &nbsp;And if there is any concern at all I would think the corrective action would be baffles in the tank.</p><p>You can analyze the sloshing and the effectd on pitch and yaw.&nbsp; It is not some simple equation however, but a sophisticated computer model.</p><p>In short, you are barking up the wrong tree.&nbsp; <br /></p> <div class="Discussion_UserSignature"> </div>
 
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kyle_baron

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>What in world is elliptical rotation inside a cylindrical tank ?</DIV></p><p>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.</p><p>http://en.wikipedia.org/wiki/Flight_dynamics</p><p>http://en.wikipedia.org/wiki/Ellipse</p><p>&nbsp;</p><p>&nbsp;Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;I think you need a physics course.</DIV></p><p>&nbsp;And I think you should use your imagination (images) more.</p><p>&nbsp;Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Of greater concern would be a back and forth sloshing mode that moves the CG of the vehicle from side to side.&nbsp; If there is a concern like that the motion would be more likely induced by action of the thrust vector control system than by axial stimulation due to any thrust oscillation.&nbsp;&nbsp;The gimbaling of the nozzle would not normally create roll, but only pitch or yaw.Replying to:<BR/><DIV CLASS='Discussion_PostQuote'></p><p>Agreed.</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;&nbsp;&nbsp;And if there is any concern at all I would think the corrective action would be baffles in the tank.</DIV></p><p>Absolutly not.&nbsp; Thrust Occilation is a single linear motion&nbsp;problem, which requires a messy (more than 1 motion)&nbsp;solution.</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>You can analyze the sloshing and the effectd on pitch and yaw.&nbsp; It is not some simple equation however, but a sophisticated computer model.&nbsp; <br />Posted by DrRocket</DIV></p><p>And as a professional, that's YOUR job.<br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
 
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Bytor_YYZ

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<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</DIV></p><p>&nbsp;It is random and has no patterm&nbsp; The T.O. is not a clean sine wave. &nbsp; </p>
 
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