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

[kyle_baron]

<p><strong>The Lunar Ares 1 won't make it to orbit with fully fueled SM tanks.&nbsp; There's something like 1,200 lbs payload capacity, which includes 4 people and supplies.&nbsp; The existing problems of T.O. and heat shield will eat into that payload and leave virtually no room for people!&nbsp; The carbon fiber LH2 tanks will save 3,000-4,500 lbs. in mass, assuming a 10-15% reduction from the existing Aluminum-Lithium alloy tank.&nbsp; A side benefit of being stiffer, it might also REDUCE T.O. vibrations.</strong></p><p><strong>The existing problems of the carbon fiber LH2 tank is well documented in Nasa's joint venture with Lockheed&nbsp;Martin in the X-33 project.&nbsp; I will take quotes from 2 links, where I found detailed information.&nbsp; Both links are lengthly, and indicate the problems involved:</strong></p><p>http://composite.about.com/library/weekly/aa990217.htm</p><h4>All of the tank shell pieces are a sandwich structure, made from graphite/epoxy facesheets and a graphite/epoxy honeycomb core. The inner facesheet has seven plies; the outer has fourteen.</h4><p>Alliant Techsystems lays up the skins on a fiber placement machine, then precures them. They are then post-bonded to the honeycomb core using a film adhesive. Alliant performed the first bonding procedure, but Hexcel performed all subsequent bonding operations.</p><p>Alliant delivers the completed wall segments to Lockheed Martin. The tanks are then assembled in a series of up to eight autoclave cure cycles. Beyond eight cycles, the strength of the laminate can begin to degrade.</p><p>During the fifth cure cycle of one of the tanks, on 23 December 1998, a large delamination was found in one of the wall segments. The flaw was sometimes described as "bubbles and cracks" in the "inner lining." This was one of the segments bonded by Hexcel (early press reports stated the walls were made by Alliant).</p><strong><p>One possible cause of a delamination is material contamination, and Lockheed Martin is examining that possibility. Contamination of any of the primary materials--the core, the film adhesive, or the composite--could promote a delamination.</p><p>Contaminants can be dirt, solvents, moisture, or other liquids (such as oil). Film adhesives and prepregs are processed through strict quality programs, so the introduction of contaminants during material manufacture is unlikely. But both materials are kept frozen until use. If they are thawed incorrectly, moisture can condense and be trapped in the part.</p><p>This moisture can show up as bubbles or blisters during subsequent cure cycles, which was reported in some of the early articles. However, such bubbles usually show up after only one or two thermal cycles.</p><p>Another possible contaminant is an actual physical object. Release papers are sometimes left on a layer, which prevents any bonding. A razor blade or other small object left in the laminate can be an initiator of a disbond. Such objects, though, are easy to detect, and probably would have shown up during inspection.</p><p>A more likely source of contamination is the core. In general, cores aren't as carefully controlled as prepregs or film adhesives prior to use. Also, because of their geometry, they are better dirt attractors (and holders).</p><p>Because cores can easily get dirty, compressed air is often used to clean them out. If the air isn't clean and filtered, it may contain oil, which would be deposited on the core. Such contamination would weaken the bond between the film adhesive and the core.</p><p>One thing not questioned in any of the recent articles is the basic manufacturing method. In particular, the practice of precuring the skins and then bonding them to the core should be examined.</p><p>Many honeycomb sandwiches are made by cocuring the skins and the core. One skin is layed up on the tool, the honeycomb is placed against it, then the other skin is layed up on the core. The entire sandwich laminate is then cured in an autoclave cycle. Film adhesive may or may not be used.</p><p>This process achieves an excellent bond between the facesheets and the core. Before cure, the facesheets are flexible, and they conform easily to the core. A tight bond is achieved over the entire sandwich.</p><p>With precured skins, the core must conform to a rigid surface. If the core can't conform well enough, the gap may be too large for the film adhesive to form a proper bond. Such a bond may not be detected during ultrasonic inspection, and it could lead to delaminations.</p><p>Each cell in a honeycomb sandwich is an airtight vessel. When heated, the air in each expands, increasing the pressure. If the pressure gets too high, the film adhesive bond may fail, initiating a delamination.</p><p>http://www.nasaspaceflight.com/2006/01/x-33venturestar-what-really-happened/</p><p><font face="Arial" size="2"><img src="http://forum.nasaspaceflight.com/forums/get-attachment.asp?action=view&attachmentid=938" border="0" alt="" hspace="5" vspace="5" width="130" height="90" align="left" />A second LH2 tank appeared to be in a much better shape and was shipped to MSFC (Marshall Space Flight Center) in Huntsville, Alabama for testing. The failure of the tank during testing at MSFC was still predicted - and occurred on November 3, 1999, during the fifth stage of testing.</font></p><p><font face="Arial" size="2">Ironically, engineers - predicting the impending problem - had a solution already at hand. By filling the honeycomb walls of the tank with closed-cell foam, air wouldn&rsquo;t be able to enter the structure and liquefy.</font></p><p><font face="Arial" size="2">This idea had to be rejected, due to the 500 kg of extra weight being added to the aft, further affecting the center of gravity, which was already having serious fallout on the design due to the heavy engine ramps.</font></p><p><font face="Arial" size="2">While the aluminium LH2 tank was much heavier than the composite tank in the skins, the joints were much lighter, which was where all the weight in the composite tank was, due to the multi-lobed shape of the tank requiring a large amount of surrounding structure, such as the joints.</font></p><p><font face="Arial" size="2">By early 2001, the program was officially cancelled - five years and $1.5 billion down the line. Official reasons for the cancellation was a disagreement over extra funding from both industry partners, NASA and Lockheed Martin.</font></p><p><font face="Arial" size="2">My Conclusion, is that Nasa quit the project, but has the solutions.&nbsp; Such as filling in the honeycomb structure with foam, and avoiding the multi-lobed surfaces (Ares doesn't have multi-lobes).&nbsp; The MAIN QUESTION is :&nbsp; Has the compostite manufacturing process progressed enough with in the past 10 years to warrant a 2nd chance for carbon fiber LH2 tanks?</font></p></strong> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The Lunar Ares 1 won't make it to orbit with fully fueled SM tanks.&nbsp; There's something like 1,200 lbs payload capacity, which includes 4 people and supplies.&nbsp; The existing problems of T.O. and heat shield will eat into that payload and leave virtually no room for people!&nbsp; The carbon fiber LH2 tanks will save 3,000-4,500 lbs. in mass, assuming a 10-15% reduction from the existing Aluminum-Lithium alloy tank.&nbsp; A side benefit of being stiffer, it might also REDUCE T.O. vibrations.The existing problems of the carbon fiber LH2 tank is well documented in Nasa's joint venture with Lockheed&nbsp;Martin in the X-33 project.&nbsp; I will take quotes from 2 links, where I found detailed information.&nbsp; Both links are lengthly, and indicate the problems involved:http://composite.about.com/library/weekly/aa990217.htmAll of the tank shell pieces are a sandwich structure, made from graphite/epoxy facesheets and a graphite/epoxy honeycomb core. The inner facesheet has seven plies; the outer has fourteen.Alliant Techsystems lays up the skins on a fiber placement machine, then precures them. They are then post-bonded to the honeycomb core using a film adhesive. Alliant performed the first bonding procedure, but Hexcel performed all subsequent bonding operations.Alliant delivers the completed wall segments to Lockheed Martin. The tanks are then assembled in a series of up to eight autoclave cure cycles. Beyond eight cycles, the strength of the laminate can begin to degrade.During the fifth cure cycle of one of the tanks, on 23 December 1998, a large delamination was found in one of the wall segments. The flaw was sometimes described as "bubbles and cracks" in the "inner lining." This was one of the segments bonded by Hexcel (early press reports stated the walls were made by Alliant).One possible cause of a delamination is material contamination, and Lockheed Martin is examining that possibility. Contamination of any of the primary materials--the core, the film adhesive, or the composite--could promote a delamination.Contaminants can be dirt, solvents, moisture, or other liquids (such as oil). Film adhesives and prepregs are processed through strict quality programs, so the introduction of contaminants during material manufacture is unlikely. But both materials are kept frozen until use. If they are thawed incorrectly, moisture can condense and be trapped in the part.This moisture can show up as bubbles or blisters during subsequent cure cycles, which was reported in some of the early articles. However, such bubbles usually show up after only one or two thermal cycles.Another possible contaminant is an actual physical object. Release papers are sometimes left on a layer, which prevents any bonding. A razor blade or other small object left in the laminate can be an initiator of a disbond. Such objects, though, are easy to detect, and probably would have shown up during inspection.A more likely source of contamination is the core. In general, cores aren't as carefully controlled as prepregs or film adhesives prior to use. Also, because of their geometry, they are better dirt attractors (and holders).Because cores can easily get dirty, compressed air is often used to clean them out. If the air isn't clean and filtered, it may contain oil, which would be deposited on the core. Such contamination would weaken the bond between the film adhesive and the core.One thing not questioned in any of the recent articles is the basic manufacturing method. In particular, the practice of precuring the skins and then bonding them to the core should be examined.Many honeycomb sandwiches are made by cocuring the skins and the core. One skin is layed up on the tool, the honeycomb is placed against it, then the other skin is layed up on the core. The entire sandwich laminate is then cured in an autoclave cycle. Film adhesive may or may not be used.This process achieves an excellent bond between the facesheets and the core. Before cure, the facesheets are flexible, and they conform easily to the core. A tight bond is achieved over the entire sandwich.With precured skins, the core must conform to a rigid surface. If the core can't conform well enough, the gap may be too large for the film adhesive to form a proper bond. Such a bond may not be detected during ultrasonic inspection, and it could lead to delaminations.Each cell in a honeycomb sandwich is an airtight vessel. When heated, the air in each expands, increasing the pressure. If the pressure gets too high, the film adhesive bond may fail, initiating a delamination.http://www.nasaspaceflight.com/2006/01/x-33venturestar-what-really-happened/A second LH2 tank appeared to be in a much better shape and was shipped to MSFC (Marshall Space Flight Center) in Huntsville, Alabama for testing. The failure of the tank during testing at MSFC was still predicted - and occurred on November 3, 1999, during the fifth stage of testing.Ironically, engineers - predicting the impending problem - had a solution already at hand. By filling the honeycomb walls of the tank with closed-cell foam, air wouldn&rsquo;t be able to enter the structure and liquefy.This idea had to be rejected, due to the 500 kg of extra weight being added to the aft, further affecting the center of gravity, which was already having serious fallout on the design due to the heavy engine ramps.While the aluminium LH2 tank was much heavier than the composite tank in the skins, the joints were much lighter, which was where all the weight in the composite tank was, due to the multi-lobed shape of the tank requiring a large amount of surrounding structure, such as the joints.By early 2001, the program was officially cancelled - five years and $1.5 billion down the line. Official reasons for the cancellation was a disagreement over extra funding from both industry partners, NASA and Lockheed Martin.My Conclusion, is that Nasa quit the project, but has the solutions.&nbsp; Such as filling in the honeycomb structure with foam, and avoiding the multi-lobed surfaces (Ares doesn't have multi-lobes).&nbsp; The MAIN QUESTION is :&nbsp; Has the compostite manufacturing process progressed enough with in the past 10 years to warrant a 2nd chance for carbon fiber LH2 tanks? <br />Posted by kyle_baron</DIV></p><p>&nbsp;</p><p>The problem with the X-33 tanks was simply that the wrong materials, particularly the resin were used.&nbsp; Experts in composites made recommendations to the Skunk Works that were not implemented, and the results were predictable. I don't think NASA has the solutions, but others do.&nbsp;<br /></p> <div class="Discussion_UserSignature"> </div>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;The problem with the X-33 tanks was simply that the wrong materials, particularly the resin were used.&nbsp; Experts in composites made recommendations to the Skunk Works that were not implemented, and the results were predictable. I don't think NASA has the solutions, but others do.&nbsp; <br />Posted by DrRocket</DIV></p><p><strong>Since you've dealt with composites, do you feel the manufacturing process has progressed enough to warrant a 2nd chance for carbon fiber in LH2 tanks?&nbsp; Or, putting it in a different context:&nbsp; There were mistakes made 10 years ago, and the existing technology&nbsp;and manufacturing was sufficient at the time?</strong></p><p><strong>Nasa is considering composites in "launch vehicle structures".&nbsp; Also, &nbsp;Ares 1X will have a composite inter stage frustrum.&nbsp; Do you think Nasa is desperate enough (with all the issues of mass) to try a complete 2nd stage LH2 composite, where there is a bigger payoff for payload?</strong></p><p><strong>I do think Nasa will have the solutions, from the "others" as you stated, but whether they play it safe, or go full speed ahead, is the question, IMO.</strong><br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Since you've dealt with composites, do you feel the manufacturing process has progressed enough to warrant a 2nd chance for carbon fiber in LH2 tanks?&nbsp; Or, putting it in a different context:&nbsp; There were mistakes made 10 years ago, and the existing technology&nbsp;and manufacturing was sufficient at the time?Nasa is considering composites in "launch vehicle structures".&nbsp; Also, &nbsp;Ares 1X will have a composite inter stage frustrum.&nbsp; Do you think Nasa is desperate enough (with all the issues of mass) to try a complete 2nd stage LH2 composite, where there is a bigger payoff for payload?I do think Nasa will have the solutions, from the "others" as you stated, but whether they play it safe, or go full speed ahead, is the question, IMO. <br />Posted by kyle_baron</DIV></p><p>I don't know what NASA will actually do.&nbsp; In the past NASA has not been comfortable with composites, largely, I think, because of lack of experience with them.&nbsp; In my opinion the&nbsp;advanced propulsion initiative that was being pursued in the 2002-2003&nbsp;time frame,&nbsp;met its doom when&nbsp;NASA decided against composites.&nbsp;As I recall the goal was a single-stage-to-orbit prototype which is extremely difficult under the best of circumstances, but is impossible without a vehicle of the lightest possible weight.</p><p>There have been some new people hired at NASA, and they may be more comfortable with black parts.&nbsp; I know that is true of the relatively new stage 1 Ares program manager for instance.</p><p>Properly designed I think it is quite feasible to design a liquid hydrogen tank that is primarily graphite-epoxy composite.&nbsp; It may require a liner, but that will not add much weight.&nbsp; &nbsp;It was feasible when the X-33 was being designed, but the choices in technology were being driven by people without the necessary knowledge.&nbsp; Better approaches were recommended but not accepted.&nbsp; They got what they asked for, but did not ask for what they needed.&nbsp; It is sometimes better to tell the experts what you need and let them provide a design to meet those needs, than to tell them how to do their job.</p><p>That project was a bit strange.&nbsp; The tank was also supposed to provide a large portion of the load-bearing structure for the vehicle, but there was no structural test planned prior to the first flight, and the first flight was scheduled to take place over land.&nbsp; I heartily disapprove of an approach like that.&nbsp; As I recall one of the other people reviewing the project was not too thrilled with it either -- the proposed flight path went over his house. </p><p>I don't think the state-of-the art in manufacturing processes has changed very much since the X-33 days.&nbsp; But the state-of-the-art in manufacturing technology was not the problem.&nbsp; The basic problem was a poor choice of materials, particularly the resin.&nbsp; There were good choices then, and I suspect that there are a few better choices now.&nbsp; Resin development is a part of the composites business, and I am confident that acceptable resins exist and exceptional resins can be developed.&nbsp; I can even think of a chemist who is both capable and in the right place to do such development if needed.</p><p>Probably the key question is whether or not a composite LH2 tank for the Ares vehicle would really save much weight.&nbsp; Composites are good when high strength-to-weight ratios are needed for structures that are in a state of tension, as for vessels carrying high pressure.&nbsp; They are good when you need to tailor stiffness in particular directions, and they are good for things like optical benches when you can engineer them for minimum&nbsp;thermal expansion.&nbsp; But they are not so good for complex shapes.&nbsp; They tend to be relatively poor in compression.&nbsp; Interstages are a close call.&nbsp; Sometimes composites are a good approach and sometimes aluminum is better. &nbsp;And they may not be&nbsp; particularly good for a structure that carries only a low pressure and may not be highly stressed.&nbsp; I don't know enough about the design details, particular loads and stress states for the upper stage LH2 tank to know if it a candidate for a composite structure.&nbsp; </p> <div class="Discussion_UserSignature"> </div>

 

[trailrider]

<p>I will certainly bow to Dr. Rocket's expertise in this area, and do NOT pooh-pooh the idea that technological advances are important to the exploration of space and to aeronautics as well.</p><p>But, I keep wondering why we have to design so close to the limits of thrust/weight that we have to depend on such high tech approaches to material, except in instances were it is absolutely the only way out????&nbsp; Ares I/Orion is NOT Apollo on steroids!&nbsp; It's "VANGUARD on steroids," and not much steroids at that!</p><p>NASA is certainly reluctant to admit they may have chosen the wrong path in the Constellation program, but the choice may prove "fatal" to the whole U.S. manned space exploration beyond LEO.&nbsp; Hopefully, Griffin and company have been working on alternative proposals to present to Congress and President-elect Obama, that will prove more practicable and viable.&nbsp; Otherwise, we will become the Portugal of the space age! <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-frown.gif" border="0" alt="Frown" title="Frown" /></p><p>Only time will tell...</p><p>Ad LEO! Ad Luna! Ad Ares! Ad Astra!</p>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't know what NASA will actually do.&nbsp; In the past NASA has not been comfortable with composites, largely, I think, because of lack of experience with them.&nbsp; In my opinion the&nbsp;advanced propulsion initiative that was being pursued in the 2002-2003&nbsp;time frame,&nbsp;met its doom when&nbsp;NASA decided against composites.&nbsp;As I recall the goal was a single-stage-to-orbit prototype which is extremely difficult under the best of circumstances, but is impossible without a vehicle of the lightest possible weight.There have been some new people hired at NASA, and they may be more comfortable with black parts.&nbsp; I know that is true of the relatively new stage 1 Ares program manager for instance.Properly designed I think it is quite feasible to design a liquid hydrogen tank that is primarily graphite-epoxy composite.&nbsp; It may require a liner, but that will not add much weight.&nbsp; &nbsp;It was feasible when the X-33 was being designed, but the choices in technology were being driven by people without the necessary knowledge.&nbsp; Better approaches were recommended but not accepted.&nbsp; They got what they asked for, but did not ask for what they needed.&nbsp; It is sometimes better to tell the experts what you need and let them provide a design to meet those needs, than to tell them how to do their job.That project was a bit strange.&nbsp; The tank was also supposed to provide a large portion of the load-bearing structure for the vehicle, but there was no structural test planned prior to the first flight, and the first flight was scheduled to take place over land.&nbsp; I heartily disapprove of an approach like that.&nbsp; As I recall one of the other people reviewing the project was not too thrilled with it either -- the proposed flight path went over his house. I don't think the state-of-the art in manufacturing processes has changed very much since the X-33 days.&nbsp; But the state-of-the-art in manufacturing technology was not the problem.&nbsp; The basic problem was a poor choice of materials, particularly the resin.&nbsp; There were good choices then, and I suspect that there are a few better choices now.&nbsp; Resin development is a part of the composites business, and I am confident that acceptable resins exist and exceptional resins can be developed.&nbsp; I can even think of a chemist who is both capable and in the right place to do such development if needed.Probably the key question is whether or not a composite LH2 tank for the Ares vehicle would really save much weight.&nbsp; Composites are good when high strength-to-weight ratios are needed for structures that are in a state of tension, as for vessels carrying high pressure.&nbsp; They are good when you need to tailor stiffness in particular directions, and they are good for things like optical benches when you can engineer them for minimum&nbsp;thermal expansion.&nbsp; But they are not so good for complex shapes.&nbsp; They tend to be relatively poor in compression.&nbsp; Interstages are a close call.&nbsp; Sometimes composites are a good approach and sometimes aluminum is better.</DIV></p><p><strong>Thank you for the thoroughness of your response.</strong></p><p>&nbsp;Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;&nbsp;And they may not be&nbsp; particularly good for a structure that carries only a low pressure and may not be highly stressed.&nbsp;&nbsp; <br />Posted by DrRocket</DIV></p><p><strong>Now that's an interesting statement, that begs for the question:&nbsp; Why would low density (pressure?) LH2 and low stress even matter?&nbsp; From previous posts you've indicated that you're a fan of the composite SRB.&nbsp; I've heard that this would also save considerable mass.&nbsp; But I've also heard it stated on other forums, that for each 10 lbs saved on the 1st stage, would save only 1 lb of payload to orbit.&nbsp;&nbsp;On the other hand,&nbsp;for each lb saved on the 2nd stage, would be matched with an equal amount in payload to orbit (roughly speaking).</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'>But, I keep wondering why we have to design so close to the limits of thrust/weight that we have to depend on such high tech approaches to material, except in instances were it is absolutely the only way out????&nbsp; Ares I/Orion is NOT Apollo on steroids!&nbsp; It's "VANGUARD on steroids," and not much steroids at that! Only time will tell...Ad LEO! Ad Luna! Ad Ares! Ad Astra! <br />Posted by trailrider</DIV></p><p><strong>Let's be honest here.&nbsp; I understand your position.&nbsp; But, what are the odds of scrapping Ares 1 and going to an EELV at this point, with the launch of Ares 1X next year?&nbsp; I give it less than a 50% chance.</strong></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[vulture4]

I agree that the benefits of composite construction may vary quite a bit with the type of stress it must tolerate, nevertheless many new aircraft have composite primary structures including elements that bear compressive loads such as the upper web of the main spar, or for that matter payload fairings on several ELVs. I am not enthusiastic about the Ares I, and as you point out the X-33 had design problems. But I have read that both the LH2 tank on the DC-X and the LOX tank on the X-34 were composite designs, and reduced weight; if not I'd be interested in the facts.<BR/><BR/>It appears to me that in a reusable launch vehicle it would be reasonable to pursue weight reduction through structural composites even if it added to cost. In an ELV it may be cheaper just to get a bigger rocket.

 

[trailrider]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Let's be honest here.&nbsp; I understand your position.&nbsp; But, what are the odds of scrapping Ares 1 and going to an EELV at this point, with the launch of Ares 1X next year?&nbsp; I give it less than a 50% chance. <br />Posted by kyle_baron</DIV></p><p>You're probably right! I wouldn't begin to guess at this point in time.&nbsp; My biggest fear is that Congress and/or President-elect Obama will kill the whole thing! There seems to be a lot of sentiment for cancelling <em>any</em> program that is overrunning budget. We'll just have to wait and see...</p><p>&nbsp;</p>

 

[scottb50]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Thank you for the thoroughness of your response.&nbsp;Now that's an interesting statement, that begs for the question:&nbsp; Why would low density (pressure?) LH2 and low stress even matter?&nbsp; From previous posts you've indicated that you're a fan of the composite SRB.&nbsp; I've heard that this would also save considerable mass.&nbsp; But I've also heard it stated on other forums, that for each 10 lbs saved on the 1st stage, would save only 1 lb of payload to orbit.&nbsp;&nbsp;On the other hand,&nbsp;for each lb saved on the 2nd stage, would be matched with an equal amount in payload to orbit (roughly speaking). <br /> Posted by kyle_baron</DIV></p><p>I think reducing the overall weight would make a flyback first stage possible. Considering the added weight of wings and engines any savings in overall weight would allow a heavier upper stage. If the upper stage is also lighter payload would be higher. My idea has been a simple fiber-wound tank surrounded by a composite outer cage with integrated mating surfaces at both ends and around the middle. Using multiple, identical, assemblies any number of varients would be possible.</p><p>One idea is a mulitple cage configuration with a single tube, floating pistons would be pressurized by heated Helium to force propellant to the engines. The Helium would be heated by being used to cool the combustors and nozzles and then being routed to the tank. After landing the Helium is removed, liquified and re-used. This would eliminate turbopumps and allow a much higher level of safety.&nbsp; </p> <div class="Discussion_UserSignature"> </div>

 

[franontanaya]

<p>So how much of the Shuttle technology would be left after that? I thought Ares was about saving costs by designing with Shuttle rockets and tanks.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[scottb50]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>So how much of the Shuttle technology would be left after that? I thought Ares was about saving costs by designing with Shuttle rockets and tanks.&nbsp; <br /> Posted by franontanaya</DIV></p><p>&nbsp;</p><p>Ares I seems like a dead end, a quick way to get a minimal payload to orbit. Delta, Atlas or the Falcon 9 make a lot more sense. Even the SpaceX Dragon offers much more capability then the NASA capsule.</p><p>What makes more sense is upgrading and improving on the Shuttle and keeping it in operation until it's capability can be matched or exceeded. </p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[franontanaya]

<p>Yup. I don't get what's the point of flying an Ares I with risky composites and downgraded redundancy to deliver ~25 T to LEO when many commercial rockets and even the ol' crabby Shuttle already deliver ~25 T to LEO. If composites work, they could save instead X-33. </p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[vulture4]

<p>>>Delta, Atlas or the Falcon 9 make a lot more sense.</p><p>I agree. Regrettably ULA has decided not to challange Mr. Giffin by competing with the Stick for human flight. Is it possible ULA will try again with the new administrator? If not, the field belongs to Mr. Musk.&nbsp;</p>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Thank you for the thoroughness of your response.&nbsp;Now that's an interesting statement, that begs for the question:&nbsp; Why would low density (pressure?) LH2 and low stress even matter?&nbsp; From previous posts you've indicated that you're a fan of the composite SRB.&nbsp; I've heard that this would also save considerable mass.&nbsp; But I've also heard it stated on other forums, that for each 10 lbs saved on the 1st stage, would save only 1 lb of payload to orbit.&nbsp;&nbsp;On the other hand,&nbsp;for each lb saved on the 2nd stage, would be matched with an equal amount in payload to orbit (roughly speaking). <br />Posted by kyle_baron</DIV></p><p>Composites save weight by providing high strength to weight ratios.&nbsp; So for structures that are driven by strength, for instance pressure vessels at reasonably high pressures, they can save weight.</p><p>But composites are not isotropic materials.&nbsp; They are usually modeled as orthotropic and are far better in tension than&nbsp; in compression.&nbsp; They can be engineered to provide specific properties in specific directions and they can be engineered to provide other desirable properties like a nearly zero coefficient of thermal expansion (good for the optical bench on the Hubble telescope for instance).&nbsp; But you&nbsp;cannot do that all at once.&nbsp; Composites are simply black aluminum and need to be tailored for the specific application, and in some applications other materials are better.&nbsp; Composites are ideal for rocket motor cases.&nbsp; They may not be so good for other applications where stiffness or impermeability, or ... are the design drivers.</p><p>Can a liquid LH2 tank be made from composites ?&nbsp; Yes.&nbsp; Is that a good solution ?&nbsp; It depends on the other design requirements for the structure.&nbsp; If the only requirement is to hold LH2 and if there are no other structural requirements I would probably pick a metal.&nbsp; It there are structural loads imposed by flight dynamics, then perhaps an engineered composite structure would do the job and save weight -- it depends on the specific design requirements and the flight environment.</p><p>It is quite possible that 10 lb saved on first stage only provides 1 additional lb of payload to orbit.&nbsp; In designing a rocket stack one thing that is calculated&nbsp;early in the process is a set of performance partial derivatives. These allow quick trades of technologies so that sensible design selections can be made.&nbsp; The trade of of inert stage weights for payload weights is generally much more pronounded in upper stages than in lower stages.&nbsp; That is why upper stages tend to be "higher tech" than lower stages with more composites, more energetic propellant and lower structural design margins.&nbsp; First stages are Peterbilts and&nbsp; upper stages are Ferraris.</p> <div class="Discussion_UserSignature"> </div>

 

[frodo1008]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Composites save weight by providing high strength to weight ratios.&nbsp; So for structures that are driven by strength, for instance pressure vessels at reasonably high pressures, they can save weight.But composites are not isotropic materials.&nbsp; They are usually modeled as orthotropic and are far better in tension than&nbsp; in compression.&nbsp; They can be engineered to provide specific properties in specific directions and they can be engineered to provide other desirable properties like a nearly zero coefficient of thermal expansion (good for the optical bench on the Hubble telescope for instance).&nbsp; But you&nbsp;cannot do that all at once.&nbsp; Composites are simply black aluminum and need to be tailored for the specific application, and in some applications other materials are better.&nbsp; Composites are ideal for rocket motor cases.&nbsp; They may not be so good for other applications where stiffness or impermeability, or ... are the design drivers.Can a liquid LH2 tank be made from composites ?&nbsp; Yes.&nbsp; Is that a good solution ?&nbsp; It depends on the other design requirements for the structure.&nbsp; If the only requirement is to hold LH2 and if there are no other structural requirements I would probably pick a metal.&nbsp; It there are structural loads imposed by flight dynamics, then perhaps an engineered composite structure would do the job and save weight -- it depends on the specific design requirements and the flight environment.It is quite possible that 10 lb saved on first stage only provides 1 additional lb of payload to orbit.&nbsp; In designing a rocket stack one thing that is calculated&nbsp;early in the process is a set of performance partial derivatives. These allow quick trades of technologies so that sensible design selections can be made.&nbsp; The trade of of inert stage weights for payload weights is generally much more pronounded in upper stages than in lower stages.&nbsp; That is why upper stages tend to be "higher tech" than lower stages with more composites, more energetic propellant and lower structural design margins.&nbsp; First stages are Peterbilts and&nbsp; upper stages are Ferraris. <br /> Posted by DrRocket</DIV></p><p>It just seems like every time I come on board this forum there is another problem with the current Ares I design!&nbsp; Then there is another so called solution to that problem, and that very solution then generates yet another problem, which in turn generates yet another solution, and so on, and so on,&nbsp; NASA seems to be in a Catch 22 type of situation with this design!</p><p>As anybody that has ever followed any of my posts should know I am NOT a critic of NASA!&nbsp; I personally think they do a fantastic job with a terrible budget!</p><p>However, that being said, I DO have grave doubts about this type of design for several reasons.</p><p>One is simply that NOBODY else in the entire industry of not only this country but ALL other countries even contemplates using such a large solid rocket for its rocket launch industry to place human beings into orbit. Can all of these others be wrong?&nbsp; I seriously doubt it!</p><p>NOW is a great time to me for the new president to at the very least set up the same kind of impartial oversight committee, with a variety of the best people available such as the committee set up after the Challenger disaster.&nbsp; Such a committee should carefully and without any prejudices totally examine this design, and any and ALL other possible alternatives.&nbsp; It IS still early enough in the funding of this project to change directions if need be.&nbsp; But it IS getting close to the time when it will not be even possible without very severe consequences to change directions.&nbsp; And that is why with the new president coming in now is the time for some very serious soul searching here by such an over sight committee for NASA!! </p><p>NASA may have made a grave error in its judgement here.&nbsp; Also, (and I do really hope that I am wrong here, but there is enough evidence otherwise to worry me) I worry about the political influence of ATK upon the Utah political matching, and that possible influence upon NASA itself. &nbsp;</p><p>This sort of thing even happened back in the Apollo era, much to the detriment of the program.&nbsp; So it IS a worry to me at least.</p><p>I know that this is just my own opinion, but that is what these particular forums are about on this site, or at least that is what I think they are about anyway! </p><p>&nbsp;</p>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>It just seems like every time I come on board this forum there is another problem with the current Ares I design!&nbsp; Then there is another so called solution to that problem, and that very solution then generates yet another problem, which in turn generates yet another solution, and so on, and so on,&nbsp; NASA seems to be in a Catch 22 type of situation with this design!As anybody that has ever followed any of my posts should know I am NOT a critic of NASA!&nbsp; I personally think they do a fantastic job with a terrible budget!However, that being said, I DO have grave doubts about this type of design for several reasons.One is simply that NOBODY else in the entire industry of not only this country but ALL other countries even contemplates using such a large solid rocket for its rocket launch industry to place human beings into orbit. Can all of these others be wrong?&nbsp; I seriously doubt it!NOW is a great time to me for the new president to at the very least set up the same kind of impartial oversight committee, with a variety of the best people available such as the committee set up after the Challenger disaster.&nbsp; Such a committee should carefully and without any prejudices totally examine this design, and any and ALL other possible alternatives.&nbsp; It IS still early enough in the funding of this project to change directions if need be.&nbsp; But it IS getting close to the time when it will not be even possible without very severe consequences to change directions.&nbsp; And that is why with the new president coming in now is the time for some very serious soul searching here by such an over sight committee for NASA!! NASA may have made a grave error in its judgement here.&nbsp; Also, (and I do really hope that I am wrong here, but there is enough evidence otherwise to worry me) I worry about the political influence of ATK upon the Utah political matching, and that possible influence upon NASA itself. &nbsp;This sort of thing even happened back in the Apollo era, much to the detriment of the program.&nbsp; So it IS a worry to me at least.I know that this is just my own opinion, but that is what these particular forums are about on this site, or at least that is what I think they are about anyway! &nbsp; <br />Posted by frodo1008</DIV></p><p>One reason that other countnries do not use large solids in this application is simply that they can't do it.&nbsp; The solid rocket industry is pretty specialized.&nbsp; The infrastructure and expertise in place in the U.S. for large solid rocket space boosters&nbsp;simply does not exist elsewhere.&nbsp; In fact some of the Japanese solid boosters for space launch applications are made in the U.S.&nbsp; The only reall large solids made outside of the U.S. of which I am aware are used on the Ariane V, and they are IMO pretty crude.</p><p>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.</p><p>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.&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 /></p> <div class="Discussion_UserSignature"> </div>

 

[kyle_baron]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp; The trade of of inert stage weights for payload weights is generally much more pronounded in upper stages than in lower stages.&nbsp; That is why upper stages tend to be "higher tech" than lower stages with more composites, more energetic propellant and lower structural design margins.&nbsp; First stages are Peterbilts and&nbsp; upper stages are Ferraris. <br />Posted by DrRocket</DIV></p><p><strong>I like the analogy!&nbsp; In other words, &nbsp;power vs speed.&nbsp; <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-smile.gif" border="0" alt="Smile" title="Smile" /></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'>Composites save weight by providing high strength to weight ratios.&nbsp; So for structures that are driven by strength, for instance pressure vessels at reasonably high pressures, they can save weight.But composites are not isotropic materials.&nbsp; They are usually modeled as orthotropic and are far better in tension than&nbsp; in compression.&nbsp; They can be engineered to provide specific properties in specific directions and they can be engineered to provide other desirable properties like a nearly zero coefficient of thermal expansion (good for the optical bench on the Hubble telescope for instance).&nbsp; But you&nbsp;cannot do that all at once.&nbsp; Composites are simply black aluminum and need to be tailored for the specific application, and in some applications other materials are better.&nbsp; Composites are ideal for rocket motor cases.&nbsp; They may not be so good for other applications where stiffness or impermeability, or ... are the design drivers. <br />Posted by DrRocket</DIV></p><p><strong>".....far better in tension than in compression......not so good for other applications where stiffness is the design driver."&nbsp; </strong></p><p><strong>IIRC, there were problems in the 2nd stage joints, which would have to be beefed up (mass added) to make it stiffer, to compensate for T.O.&nbsp; Would that be a tension or compressive force?&nbsp; Also, IIRC the dynamic pressure for the 2nd stage was a little over 1,000 lbs./sq in.&nbsp; That would be a compressive force.&nbsp; Is that a lot for a composite to handle?&nbsp; What I don't quite understand is, is stiffness a tension or compressive force?&nbsp; Or, can it be both?&nbsp;</strong><br /></p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>".....far better in tension than in compression......not so good for other applications where stiffness is the design driver."&nbsp; IIRC, there were problems in the 2nd stage joints, which would have to be beefed up (mass added) to make it stiffer, to compensate for T.O.&nbsp; Would that be a tension or compressive force?&nbsp; Also, IIRC the dynamic pressure for the 2nd stage was a little over 1,000 lbs./sq in.&nbsp; That would be a compressive force.&nbsp; Is that a lot for a composite to handle?&nbsp; What I don't quite understand is, is stiffness a tension or compressive force?&nbsp; Or, can it be both?&nbsp; <br />Posted by kyle_baron</DIV></p><p>I don't think that the hypothetical TO puts any significant stresses on the main structure.&nbsp; I would have a very hard time believing that.&nbsp; But in any case oscillatory forces are, by virtue of the oscillation alternating between tension and compression, a generally bad thing that results in fatigue.&nbsp; Worse, the dominant force at stage joints is compressive with the oscillation superimposed on top.&nbsp; However, interstage structures using composites have been engineering in the past and can handle those longitudinal compressive forces fairly well.&nbsp; Transvese compressive forces are of greater concern.</p><p>A dynamiv pressure of 1000 psi sounds rathe high.&nbsp; Is it possibly 1000 psF ?&nbsp; A composite can be made to handle such forces, but you do have to design specifically for it.&nbsp; Composite payload fairings (the nose piece on launchers) are quite common.&nbsp; They are fairly simple geometrically and are stiffined to take the loads, which tend to be longitudinal rather than transverse.</p><p>Stiffness is not a force.&nbsp; It is a material property.&nbsp; It is sometimes called modulus, although with composites&nbsp;the properties are not isotropic and require tensors to properly describe them.&nbsp; <br /></p> <div class="Discussion_UserSignature"> </div>

 

[kyle_baron]

<p>

I don't think that the hypothetical TO puts any significant stresses on the main structure.&nbsp; I would have a very hard time believing that.

</p><p><strong>Correct, I only mentioned beefing up the joints, as a mitigation solution for T.O.&nbsp;which Nasa was considering.</strong></p><p><strong>Stage joints are for metals.&nbsp; Am I correct in assuming that composites don't have joints for a cylindrical stage?&nbsp; Isn't it all one piece?&nbsp; In this article (2nd paragraph from the bottom)&nbsp;&nbsp;http://www.nasa.gov/directorates/esmd/aboutesmd/csd/composite_capsule.html they say individual components are baked in an autoclave, but are spliced together (I assume glued?)&nbsp; tongue and groove???</strong></p><p>

&nbsp;A dynamiv pressure of 1000 psi sounds rathe high.&nbsp; Is it possibly 1000 psF ?</p><p><strong>Yes, that's probably correct.&nbsp; Just out of curiosity, what is the psi (or psf) of LH2 in a 1st or 2nd stage?&nbsp; You implied in previous posts, that it was low.</strong></p><p><strong>In conclusion, other than the mistakes made 10 yrs. ago, I see no reason why Nasa shouldn't give these composites a 2nd chance for LH2 tanks.&nbsp; The only difference this time around, is the size of each component.</strong></p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <p><font size="4"><strong></strong></font></p> </div>

 

[DrRocket]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't think that the hypothetical TO puts any significant stresses on the main structure.&nbsp; I would have a very hard time believing that.Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Correct, I only mentioned beefing up the joints, as a mitigation solution for T.O.&nbsp;which Nasa was considering.Stage joints are for metals.&nbsp; Am I correct in assuming that composites don't have joints for a cylindrical stage?&nbsp; Isn't it all one piece?&nbsp; In this article (2nd paragraph from the bottom)&nbsp;&nbsp;http://www.nasa.gov/directorates/esmd/aboutesmd/csd/composite_capsule.html they say individual components are baked in an autoclave, but are spliced together (I assume glued?)&nbsp; tongue and groove???Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;A dynamiv pressure of 1000 psi sounds rathe high.&nbsp; Is it possibly 1000 psF ?Yes, that's probably correct.&nbsp; Just out of curiosity, what is the psi (or psf) of LH2 in a 1st or 2nd stage?&nbsp; You implied in previous posts, that it was low.In conclusion, other than the mistakes made 10 yrs. ago, I see no reason why Nasa shouldn't give these composites a 2nd chance for LH2 tanks.&nbsp; The only difference this time around, is the size of each component.&nbsp; <br />Posted by kyle_baron</DIV></p><p>Stage joints are&nbsp; usually metal rings, aluminum most commonly if the case or interstage are composite.</p><p>The hypothetical TO problem should not require any beefing up of the joints,&nbsp; The level of oscillation&nbsp;predicted is&nbsp;quite low from a structural point of view.</p><p>Composites are often cured in an autoclave.&nbsp; The parts in the article were not, according to the narrative. &nbsp;Some are cured using a vacuum bag in a more normal cure oven.&nbsp; I doubt that tongue-and-groove joints were used.&nbsp; I would expect that the pieces were bonded and co-cured or simply secondarily bonded.&nbsp;&nbsp;The surface of the composites is epoxy resin and things bond to it quite well. &nbsp;There may have been a metallic piece used for the joints, but I don't see one in the picture.</p><p>Note that NASA did not do the fabrication.&nbsp; It was done by composites people.&nbsp; ATK has a lot of experience with advanced carbon composites.&nbsp; The first composite chassis for a Grand Prix race car was done for th McClaren team at a current ATK facility quite a few years ago.&nbsp; So were many of the parts of the Voyager that was flown around the world non-stop by Dick Rutan.&nbsp; http://en.wikipedia.org/wiki/Dick_Rutan</p><p>&nbsp;</p><p>I don't know the pressure of the LH2 tanks.&nbsp; That would be dependent on temperature and the height of the liquid column.&nbsp; But compared to the sevral hundred to a thousand psi chamber pressure of a typical solid rocket motor the pressure should be quite low.</p><p>You cannot conclude that a composite LH2 tanks is or is not a good idea from the&nbsp; information that you have provided.&nbsp; To reach such a conclusion you need to have a set of design requirments and constraints, a preliminary design, and some estimate of the costs involved.&nbsp; Size is a big deal with composite cases.&nbsp; You are talking about a vessel that must contain a liquid under some pressure, not leak, and support some level of load in flight.&nbsp; Current winding machines are capable of winding a tank on the order of 10 or 12 feet in diameter, and there are not a lot of such machines.&nbsp; Making a tank in pieces is problematic because of the need to join the parts, the joints would be a real challenge.&nbsp; You can't weld composites like you can metals.&nbsp; So an in-line tank for something like the Ares I strikes me as fairly doable (not necessarily a good idea without the noted trade studies but doable), while a composite replacement for the main tank on the shuttle is beyond available manufacturing capabilities.&nbsp; </p> <div class="Discussion_UserSignature"> </div>

 

[propforce]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>The Lunar Ares 1 won't make it to orbit with fully fueled SM tanks.&nbsp;&nbsp;</p><p>&nbsp; Posted by kyle_baron</DIV></p><p>Lots of mis-information in this thread.</p><p>&nbsp;First... where did you get this info that Ares I can not support Lunar Orion mission?&nbsp; Please provide links.</p><p>&nbsp;Second... I assume that you're referring to the LH2 tank in the Ares I upper stage?&nbsp; </p><p>Third, if it is... there's a BIG difference between the LH2 tank in X-33 than the LH2 tank in Ares I.&nbsp; Different shape, different load path, whole lot of differences....</p><p>&nbsp;</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[propforce]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp; Probably the key question is whether or not a composite LH2 tank for the Ares vehicle would really save much weight.&nbsp; Composites are good when high strength-to-weight ratios are needed for structures that are in a state of tension, as for vessels carrying high pressure.&nbsp; They are good when you need to tailor stiffness in particular directions, and they are good for things like optical benches when you can engineer them for minimum&nbsp;thermal expansion.&nbsp; But they are not so good for complex shapes.&nbsp; They tend to be relatively poor in compression.&nbsp; Interstages are a close call.&nbsp; Sometimes composites are a good approach and sometimes aluminum is better. &nbsp;And they may not be&nbsp; particularly good for a structure that carries only a low pressure and may not be highly stressed.&nbsp; I don't know enough about the design details, particular loads and stress states for the upper stage LH2 tank to know if it a candidate for a composite structure.&nbsp; <br />Posted by DrRocket</DIV><br /><br />The LH2 & LO2 propellant tanks on the Ares I upper stage is a <font color="#0000ff">common bulkhead tanks</font>.&nbsp; Both tanks carry primary launch loads in the axial direction (as vehicle travels in positive G's), hence compression in X axis, as well as bending loads from aero, etc., tension in Y & Z directions.&nbsp; The current baseline is aluminum-lithium with some composite in the common bulkhead area.&nbsp; Due to the large thermal gradient between LH2 & LO2, I am not sure ALL composite is a good idea for a cryogenic common bulkhead tank.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[propforce]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp; I keep wondering why we have to design so close to the limits of thrust/weight that we have to depend on such high tech approaches to material, except in instances were it is absolutely the only way out????&nbsp; Posted by trailrider</DIV></p><p>I think you're confused with the vehicle lift-off thrust/weight ration with the payload weight to orbit.&nbsp; Assuming you meant the latter, this is the nature of ALL launch vehicle design.&nbsp; Weight growth in all part of system is the nature of beast.&nbsp; How to manage these weight growth is much easier to say than done.&nbsp; </p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>