Give Carbon Fiber LH2 Tanks a 2nd Chance, to save (Lunar) Ares 1?

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propforce

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It just seems like every time I come on board this forum there is another problem with the current Ares I design!&nbsp;
</p><p>1)&nbsp; You can't believe everything you read on the internet.</p><p>2)&nbsp; As far as I know, Ares is holding on their "payload" to orbit performance with "weight margins" as "reserve".</p><p>3)&nbsp; Orion is having difficulty holding their weight (rumor)</p><p>4)&nbsp; FYI, Lunar mission weight is easier (lower) for Ares I to meet than the ISS mission.&nbsp; </p> <div class="Discussion_UserSignature"> </div>
 
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propforce

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp; There was a technically viable all-solid desigh for the EELV family of vehicles, so vehicles of the rough class of the Ares&nbsp;I have been considered in the past.&nbsp; That one was derailed politically, despite any political clout of the "Utah political machine" which is not nearly so influential as you seem to think.</DIV></p><p>All-solid EELV design on paper only.</p><p>&nbsp;Payloads, and Humans certainly,&nbsp;don't do well with the vibrations that all solid rockets produce.&nbsp; Issue such as the T.O. was never fully vetted when design only exist on paper.&nbsp; The SRB doesn't provide enough delta-vee for the mission, hence one requires bigger & bigger upper stage, hence bigger US engine, etc.</p><p>The Ares I first stage is certainly politically motivated.</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;I have some doubts that the technical problems with the Ares I design are faithfully represented in these forums.&nbsp; Like most things, the stuff that is fun to talk about gets more attention than it might really deserve.</DIV></p><p>&nbsp;You're right.&nbsp; It is not fairly represented in these forums.</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;All development programs encounter, and solve, a series of technical issues during the normal course of things -- that is why there is development and not simply an immediate production program.&nbsp; All programs have professional worriers who identify problems -- which is a valuable function.&nbsp; But the worries can become magnified by people outside of the program until they are, in the normal course of things, solved.</p><p>Any development program that procedes with no technical surprises, no schedule worries, and is well within budget, was underspecified, too relaxed&nbsp;and over-funded to start with.&nbsp; The good ones are never easy.&nbsp; <br />Posted by DrRocket</DIV></p><p>Spoken like an experienced program manager.</p><p>I look at it this way, if "...[an]development program that procedes with no technical surprises, no schedule worries, and is well within budget, ..", then it doesn't need good engineers & managers anyway.</p> <div class="Discussion_UserSignature"> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>All-solid EELV design on paper only.&nbsp;Payloads, and Humans certainly,&nbsp;don't do well with the vibrations that all solid rockets produce.&nbsp; Issue such as the T.O. was never fully vetted when design only exist on paper....Posted by propforce</DIV></p><p>All the EELV designs existed only on paper at the time of the proposal, and through the down-select to phase 2.&nbsp; &nbsp;The solid design had as much demonstrated hardware as the liquid designs -- it was largely based on the solid booster for the Titan IVB (the Titan SRMU).&nbsp;</p><p>The TO for the Ares I is based solely on analytical models and extrapolations from data for the current 4 segment SRB that exhibits an oscillation of about 1 psi amplitude.&nbsp; The extrapolation requires not only estimating the oscillation in the 5 segment design but also coupling into the structure of the overall launch vehicle and evaluating the response of the structure of that vehicle.&nbsp; I have been led to believe that the predicted g levels result from some very non-conservative assumptions regarding resonances in that structure.&nbsp; Analyses of that sort are notoriously inaccurate.&nbsp; In any case the consideration, even with all the non-conservative assumptions is non-structural, and IMO a real stretch.</p><p>Lots of payloads do just fine under the thrust from solids -- Delta II, Titan IVB, most of the Delta EELV family, Pegasus, our entire ICBM fleet (which include some pretty sophisticated guidance and targeting hardware).&nbsp; I know that the astronauts complain about the rough ride during the solid burn, but that is also the portion of the ride in the densest atmosphere and at highest dynamics pressures.&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'>&nbsp;1)&nbsp; You can't believe everything you read on the internet.</DIV></p><p><strong>Agreed.</strong></p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>2)&nbsp; As far as I know, Ares is holding on their "payload" to orbit performance with "weight margins" as "reserve".</DIV></p><p><strong>Ares 1 reserves are 8,000 lbs.&nbsp; (Nasa and NasaSpaceflight.com) How Nasa came up with that figure was hypothesized at NasaSpaceFlight. com by off loading 10,000 lbs. of service module propellents.&nbsp; This made sence to me.</strong></p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>3)&nbsp; Orion is having difficulty holding their weight (rumor)</DIV></p><p><strong>Off loading 10,000 lbs. of propellent in the service module would compensate.</strong></p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>4)&nbsp; FYI, Lunar mission weight is easier (lower) for Ares I to meet than the ISS mission.&nbsp; <br />Posted by propforce</DIV></p><p><strong>Yes, to reach a lower orbit, and hook up to the EDS.&nbsp; But Orion won't have enough propellent to get back from the moon!!!</strong><br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>
 
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propforce

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>All the EELV designs existed only on paper at the time of the proposal, and through the down-select to phase 2.&nbsp; &nbsp;The solid design had as much demonstrated hardware as the liquid designs -- it was largely based on the solid booster for the Titan IVB (the Titan SRMU).&nbsp;</DIV></p><p>I&nbsp;have no insight as to why all-solid EELV was not selected, but from running&nbsp;rough calc, the all-solids EELV are&nbsp;very inefficient from the&nbsp;Isp perspective.&nbsp; Second, the solids produce very high vibrations which I'd assume would drastically affect how&nbsp;NRO payloads are designed.&nbsp; I know from talking to the payload community that, going from a hypergolic upper stage to a cryo upper stage&nbsp;is a welcome move as it significantly reduces the&nbsp;payload&nbsp;vibration level.&nbsp; I can just imagine what a solid upper stage will do.&nbsp;</p><p>&nbsp;</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The TO for the Ares I is based solely on analytical models and extrapolations from data for the current 4 segment SRB that exhibits an oscillation of about 1 psi amplitude.&nbsp; The extrapolation requires not only estimating the oscillation in the 5 segment design but also coupling into the structure of the overall launch vehicle and evaluating the response of the structure of that vehicle.&nbsp; I have been led to believe that the predicted g levels result from some very non-conservative assumptions regarding resonances in that structure.&nbsp; Analyses of that sort are notoriously inaccurate.&nbsp; In any case the consideration, even with all the non-conservative assumptions is non-structural, and IMO a real stretch.</DIV></p><p>There are two key parameters here: 1) the forcing function of T.O. and, 2) the structural response of the vehicle.</p><p>As far as the forcing function goes, extrapolating from the&nbsp;4-segment&nbsp;+&nbsp;predicted pressure oscillation for the 5-segment by ATK, is probably best one can do.&nbsp; Of course I'd assume this "assumption" will be updated when a 5-segment solid is available for ground testing.</p><p>I am sure that you know this T.O. issue is an "integrated" problem in that, the combined structural&nbsp;response (Ares I +&nbsp;Orion) is the only way to solve this problem.&nbsp; This involves 1) "de-tune" the structural&nbsp;resonance frequency&nbsp;away from the T.O. forcing function frequency and 2)&nbsp;create a "reactive force" to counter the forcing function.&nbsp; Personally I think ATK should be doing more in reducing the forcing function but that's another story.</p><p>The strcutural response of the Ares I + Orion is being done by FEM analysis modeling the&nbsp;stiffness of each section of vehicle.&nbsp; &nbsp;I am not aware the "non-conservative" assumptions but I am sure they can always be questioned.&nbsp; Right now, it looks like there are a few viable options to minimize the T.O. effect, based on analysis.</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> Lots of payloads do just fine under the thrust from solids -- Delta II, Titan IVB, most of the Delta EELV family, Pegasus, our entire ICBM fleet (which include some pretty sophisticated guidance and targeting hardware).&nbsp; I know that the astronauts complain about the rough ride during the solid burn, but that is also the portion of the ride in the densest atmosphere and at highest dynamics pressures.&nbsp; <br />Posted by DrRocket</DIV></p><p>Most of the LV you mentioned above do not align payload axially with the solid booster, with the exception of Pegasus and ICBMs.&nbsp; The nature of payloads of latter are not in the same sensitivity class as the&nbsp;former, therefore high&nbsp;vibration from the solid may not be an issue.&nbsp; The shuttle, for example, has 2 SRBs but the T.O. becomes a shear load to the Orbiter, so the T.O. effect is minimized.&nbsp; </p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I&nbsp;have no insight as to why all-solid EELV was not selected, but from running&nbsp;rough calc, the all-solids EELV are&nbsp;very inefficient from the&nbsp;Isp perspective.&nbsp; Second, the solids produce very high vibrations which I'd assume would drastically affect how&nbsp;NRO payloads are designed.</DIV></p><p>I do have some insight, which I don't think I&nbsp;shuld talk about in a public forum.&nbsp; Solids have lower ISP than do liquids, but they have much better mass fraction and lower costs.&nbsp; Solids produce some vibration, but I would dispute the characterizatin of "very&nbsp; high".&nbsp; Pressure oscillations are typically a few psi, and in the case of the shuttle SRBs only about 1 psi ( about 2 psi peak to peak).&nbsp;&nbsp;</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp; I know from talking to the payload community that, going from a hypergolic upper stage to a cryo upper stage&nbsp;is a welcome move as it significantly reduces the&nbsp;payload&nbsp;vibration level.&nbsp; I can just imagine what a solid upper stage will do.</DIV></p><p>There are few solid final stages, the Star series being a bit of an exception.&nbsp; Generally a liquid final stage is preferable because the thrust-time curve can be tailored for the mission.&nbsp; Even with what I call an all-solid EELV design the final stage would have been liquid -- sorry if I mislead you on that. </p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;There are two key parameters here: 1) the forcing function of T.O. and, 2) the structural response of the vehicle.As far as the forcing function goes, extrapolating from the&nbsp;4-segment&nbsp;+&nbsp;predicted pressure oscillation for the 5-segment by ATK, is probably best one can do.&nbsp; Of course I'd assume this "assumption" will be updated when a 5-segment solid is available for ground testing.I am sure that you know this T.O. issue is an "integrated" problem in that, the combined structural&nbsp;response (Ares I +&nbsp;Orion) is the only way to solve this problem.&nbsp; This involves 1) "de-tune" the structural&nbsp;resonance frequency&nbsp;away from the T.O. forcing function frequency and 2)&nbsp;create a "reactive force" to counter the forcing function.</DIV></p><p>Correct.&nbsp; There is not much that can be done with the forcing function at the level that the thrust oscillation is being predicted.&nbsp; What one does in general is design the grain features to avoid "organ pipes" and have solid particles in the combustion gasses.&nbsp; The grain design is, I think, pretty well established and the thrust oscillation seen in the 4-segment design is quite low.&nbsp; The issue of solids in the gas is taken care of in large rocket motors by the aluminum that constitutes a significant portion of the fuel.&nbsp; Their primary purpose is to provide high flame temperature, but they also serve to scatter sound waves and thereby dampen acoustics.</p><p>I agree that the problem is an "integrated" issue.&nbsp; I also have enough experience with the analytical methods and difficulties involved in using them to know that predictions at this stage regarding not only the forcing function, but also the coupling and transmission through the structure are formidable.&nbsp; Generally in building a model (often using NASTRAN) you have a resonable idea of stiffnesses of the structural members, but little idea of the damping coefficients or of the more complex vibrational modes.&nbsp; Damping coefficients are very important in a problem such as this.&nbsp; To even begin to get a handle on the necessary parameters you really need a thorough modal survey, and there has been no opportunity for such and activity as yet.&nbsp; </p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;Personally I think ATK should be doing more in reducing the forcing function but that's another story.The strcutural response of the Ares I + Orion is being done by FEM analysis modeling the&nbsp;stiffness of each section of vehicle.&nbsp; &nbsp;I am not aware the "non-conservative" assumptions but I am sure they can always be questioned.&nbsp; Right now, it looks like there are a few viable options to minimize the T.O. effect, based on analysis.Most of the LV you mentioned above do not align payload axially with the solid booster, with the exception of Pegasus and ICBMs.&nbsp; The nature of payloads of latter are not in the same sensitivity class as the&nbsp;former, therefore high&nbsp;vibration from the solid may not be an issue.&nbsp; The shuttle, for example, has 2 SRBs but the T.O. becomes a shear load to the Orbiter, so the T.O. effect is minimized.&nbsp; &nbsp; <br />Posted by propforce</DIV></p><p>There is really not much that ATK can do, as noted above.&nbsp; Dynamic FEM analysis is notoriously inaccurate for problems such as this without the benefit of some experimental data input, in particular a modal analysis.&nbsp; There are assumptions made in modeling the stiffness, generally pretty good for metals that have been characterized, and less so for composite structures.&nbsp; But the major uncertainties lie with the joints, and associated coupling and damping.&nbsp; Those are critical and not readily modeled from first principles, hence the need for the empirical data that is not yet available.&nbsp; Alignment or not of the solids is a matter of how the loads are coupled to the vehicle structure and the payload.&nbsp; If all joints were perfectly tight and damping is neglected then it does not matter if the loads are transmitted throught tension/compression or shear.&nbsp; Of course they joints are not perfectly tight, and the nature of the joints is critical to the accuracy of the analysis -- again whether or not the load path involves shear.</p><p>The bottom line is that the issue is far more comples than what one would gather from what is posted in public forums, where not only the discussion of basic engineering methodology and uncertainties is watered down, but also the nature of the concern and the mission requirements are garbled.</p><p>I can't speak to how NRO payloads are designed,or their specific concerns.&nbsp; But I do know that they have regularly taken successful rides on solids.&nbsp; I don't think they had any&nbsp;aversion to the solids on the Titan IV B.&nbsp; </p><p>I am afraid that I will have to&nbsp;bow out of many of these discussions.&nbsp; I developed a potential conflict, future but near term, a few minutes ago.&nbsp; Probably not a real problem, but better to err on the side of conservatism in this case. </p><p><br /><br />&nbsp;</p> <div class="Discussion_UserSignature"> </div>
 
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propforce

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp; I am afraid that I will have to&nbsp;bow out of many of these discussions.&nbsp; I developed a potential conflict, future but near term, a few minutes ago.&nbsp; Probably not a real problem, but better to err on the side of conservatism in this case. &nbsp; <br />Posted by DrRocket</DIV></p><p>&nbsp;I can respect avoiding&nbsp;even just&nbsp;the appearance of COI.&nbsp; It is better to err on the side of caution.</p><p>Good conversation.</p><p><br /><br />&nbsp;</p> <div class="Discussion_UserSignature"> </div>
 
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