Ares V and the SSME

kyle_baron · Dec 27, 2008

http://www.nasaspaceflight.com/2008/12/ssme-ares-v-undergoes-evaluation-potential-switch/Constellation engineers are carrying out an evaluation process into a potential option of going back to the SSME (Space Shuttle Main Engine) on the Ares V first stage, which in turn would allow a return to a five segment Solid Rocket Boosters on the giant vehicle.Currently, the Ares V baseline is a 10m core stage with six RS-68B engines and 5.5 segment solid boosters derived from Ares I. The upper stage is 10m in diameter with a single J2-X engine. However, the program is looking for additional margin on lunar exploration missions, and to trim the budget at the same time. This effort resulted in numerous studies to refine the Ares V vehicle.The baseline boosters are now 5.5 segment variants of the shuttle SRB, with the option to build new lighter composite casings for additional performance.Constellation is now interested in re-evaluating the SSME option for the Ares V core, with five or six expendable SSMEs, and two 5 segment SRB’s powering the new variant, should the option be selected.The switch back to the $50-$60 million per engine SSME would be traded against the development costs of the 5.5 segment booster and modification of the $20 million RS-68B for Ares V.Should shuttle receive an additional two years worth of flights - which is deemed as the favored option - one additional SSME will be built and added to the current manifest of engines.Notably, an expanded production capability would be required to support the number of SSME’s that would be needed for Constellation, should the option be taken. Past studies have estimated the cost of building a new production line at roughly $500 million.When the engine has been looked at in the past for expendable use, it has been estimated that the complexity of the engine can be reduced by eliminating the reuse requirement. This would drive down costs by reducing the number of parts, simplifying the manufacturing, and eliminating the labor required per engine for post flight servicing.With the potential shuttle extension, the SSME will be used by the shuttle far longer than originally anticipated. The infrastructure to support the SSME is already in place at KSC, and the personnel are already trained and equipped to handle the SSME.Another major factor that the study is likely to consider is that the SSME may be better suited to mitigating the plume impingement and base heating issues on Ares V, which is currently a major issue that is being worked on Ares V.The regenerative nozzle of the SSME may have an advantage over the ablative RS-68 by providing a more resistant nozzle in the extreme environment of the core stage cluster.The regenerative nozzle protects both the inside and the outside of the nozzle, versus the ablative nozzle which is designed to deal with heat from only the inside. In a cluster of engines, the nozzle must withstand both the heat from its own exhaust in addition to the outside exhaust plumes of the other engines in the cluster.Although a change back to the SSME is not believed to be imminent, the study into a potential switch will likely be completed by early 2009.Frodo 1008 should be happy about this, since he used to build them!  I think that it's a good idea (even if more expensive) since Ares V is having trouble with the thrust needed for lunar payloads.  And it complements the extension to the shuttle program. <div class="Discussion_UserSignature"> </div>

trailrider · Dec 27, 2008

Sounds like a much more viable approach.  If Ares I's 5-segment proves viable (I have my doubts for the purpose for which it is intended), using 5-segment SRM's for Ares V would reduce or eliminate the costs of development of the 5.5 segment boosters.Now, if we could just get rid of the Ares I first stage....Ad LEO! Ad Luna! Ad Ares! Ad Astra!

frodo1008 · Dec 27, 2008

Posted by kyle_baron[/QUOTE]Yes, I am pleased.  However, both the SSME and the RS68 are built by Rocketdyne, which is now a division of Pratt & Whitney.  Also however, I really do not like the ablative nozzle on the RS-68. and I think the SSME is a higher performance engine.   One problem with the SSME is that it is not anywhere near the thrust level of the RS-68, but it might be possible to use more J2 engines in the second stage (as well as possibly more SSMS's for the first stage), and this would probably make up the difference.  Another reason that I can see NASA possibly going to the 5 segment motor (besides the very high developmental costs of  the 5 and a half by ATK) is the very large extra weight of an even larger solid rocket motor.  This would probably not be a problem for the Ares V itself, but the weight on the crawler, and its road from the VAB to the launch complex was getting to be a very big problem for NASA.  The cost of having to build larger and stronger crawlers and rebuilding the roads stronger would be prohibitive!  This would mean that at least one large advantage of a better system on the Ares V of the liquid engines is that that the propellant for these engines is not added to the Ares V until it is actually on the launch pad, and therefore their weight on the way to the pad itself is far less!Personally, I think that NASA has the wrong design entirely here, what would be far better is to somewhat swallow the bullet up front and entirely use liquid fly-back boosters instead of these large solids anyway.  Then such a rocket could be of a modular nature, and could be built as large as NASA would want.  It would also be totally reusable, and therefore much less expensive in the long run.  I know that was supposed to have been the case with the space shuttle, but unfortunately to save up front costs NASA had to make the shuttle a one size fits all applications type of system.  Therefore the long term cost advantage somewhat went out the window, and the shuttle became much more expensive to operate.  Even the commercial satellite systems use  different capability rockets in the same rocket family.  This system is then able to tailor the rocket loads to the missions, and is far less expensive than having dedicated rockets for separate rocket loads and purposes.Also with such a system of liquid fly-back boosters it would be relatively easy (and therefore cheaper) to upgrade the engines, and thus the thrust of the over all vehicle.   The only reason for using the original four segment SRB solid rockets was that they were already designed and ready for use from the space shuttle, and would therefore cut the cost of new rocket systems considerably.  But of course, that didn't quite work out.  That was the point that NASA should have prudently (especially when ATK told NASA it would take some $5+ billion just to up the solids to the five segment) gone back to the drawing board and come up with an entirely new design!  Realize that the Air Force only paid about $3 billion to get both the Dela IV and the Atlas V, and that was not just the propellant systesm, but the ENTIRE rocket launch systems!!  Heck, at that point NASA would have been better off to have back engineered the old Saturn V, upgraded that very reliable rocket with newer technology where appropriate, and had a really great system.  NASA despirately needs to start to think outside of the box here.It they were going to have something that looked just like the Apollo (but larger) then why not go all the way?I have heard it said that a camel is a horse that was designed by a committee, and NASA seems to be doing the same type of thing with the Ares rockets here.  Perhaps they would have been far better off to have just released thier requirements for a system, and let everybody (including spacex) have a go at the design, and then picked and chosen the best one (or for redundancy, best ones), and moved our smartly.  For once the military in the Air Force's EELV program seems to have gotten its rocket science off far better than NASA.  When NASA had such great rocket scientists as Von Braun, that was not the case! Oh well, the saddest words in the English language are said to be "What night have been!"

kyle_baron · Dec 28, 2008

Good post Frodo.  <img src="http://sitelife.space.com/ver1.0/Content/images/store/8/9/a8b16172-7252-41e9-9951-5e1148bce9d8.Medium.gif" alt="" /> At NSF.com,  Jim says that it isn't going to be a one for one engine exchange.   The core diameter will be smaller (8.4m vs 10m) and it's length are being considered.  Also, I believe 5 engines will be in the core. <div class="Discussion_UserSignature"> </div>

rybanis · Dec 29, 2008

Now this may be wrong, but isn't the RS-68 very similiar to the SSME in design? If you used a SSME, but design out the reusable aspects, wouldn't you be pretty close to the RS-68? <div class="Discussion_UserSignature"> </div>

docm · Dec 29, 2008

RS-58 uses an ablative nozzle, which presents an overheating problem in a 6 engine cluster, especially when sitting rignt between a pair of huge SRB's.  On ther other hand the SSME uses a regeneratively cooled nozzle. Also; it's my understanding that the SSME based design they would use would not be reusable, lowering its cost and simplifying its construction. <div class="Discussion_UserSignature"> </div>

scottb50 · Dec 29, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>RS-58 uses an ablative nozzle, which presents an overheating problem in a 6 engine cluster, especially when sitting rignt between a pair of huge SRB's.  On ther other hand the SSME uses a regeneratively cooled nozzle. Also; it's my understanding that the SSME based design they would use would not be reusable, lowering its cost and simplifying its construction. Posted by docm</DIV>As I have looked at the design the nozzle, and it's plumbing is the major difference between the engines, beside some scale differences. I would think it easier to modify the RS-58 with regenerative nozzles and use them with a re-usable first stage.If you have to insist on a throw away first stage it might be better to use the SSME core with ablative nozzles, reverse engineering should be basically the same as the RS-58 design anyway. Either way it seems rediculous to me to throw away a perfectly good engine that could be used any number of times. <div class="Discussion_UserSignature"> </div>

docm · Dec 29, 2008

Not beijng a professsiohal rocketeer it wouled seem to me the tankage and oither hardware surviving a salt water bath would be a big factor.  <div class="Discussion_UserSignature"> </div>

scottb50 · Dec 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Not beijng a professsiohal rocketeer it wouled seem to me the tankage and oither hardware surviving a salt water bath would be a big factor.  Posted by docm</DIV>I wasn't implying an ocean landing, I was referring to a flyback first stage. Sort of White Knight on steroids so to speak. <div class="Discussion_UserSignature"> </div>

BrianSlee · Dec 31, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I wasn't implying an ocean landing, I was referring to a flyback first stage. Sort of White Knight on steroids so to speak. Posted by scottb50</DIV>Sounds a lot like the LTABS <img src="http://sitelife.space.com/ver1.0/Content/images/store/11/0/4b96b220-8237-42b2-8097-6b90ccfd7101.Medium.jpg" alt="" /> <img src="http://sitelife.space.com/ver1.0/Content/images/store/3/9/f3056760-d842-4f97-b9e3-3af2b834e1f7.Medium.jpg" alt="" /> <div class="Discussion_UserSignature"> "I am therefore I think" "The only thing "I HAVE TO DO!!" is die, in everything else I have freewill" Brian P. Slee </div>

exoscientist · Jan 2, 2009

I wrote about the importance I believe that the recent development of low cost methods of diamond production will have on aerospace here:New era in ultra-strong materials imminent- arbitrarily large diamonds. And with it routine space access, the hydrogen economy, room-temperature superconductivity, and ultra large telescopes. posted at 11/25/2008 6:53 PM EST on Space.com http://www.space.com/common/community/forums/?plckForumPage=ForumDiscussion&plckDiscussionId=Cat%3a8bb00402-3c25-402b-8f45-b62faa6a11d9Forum%3acdb5bb05-7ac3-460a-bbcb-6a96b863ed32Discussion%3a870162e8-00ae-46f9-8bfc-8d02529f92ea  It has the highest compressive strength of any known material in addition to the highest melting point for a single element, in the range of 4000 C.  The space shuttle main engines and the RS-68 engines have to be heavy because they have to have thick combustion chambers and large nozzles made of copper or steel, because of the need to dissipate the heat rapidly.  Diamond however is 5 times better than copper in thermal conductivity, and about 1/3 the weight, so would be better than copper by a factor of 15 times for the weight required:List of thermal conductivity values. http://en.wikipedia.org/wiki/Thermal_conductivity#List_of_thermal_conductivity_values  Note also that the temperature reached in the space shuttle engines of 3,300 C is less than the melting point of diamond. Furthermore, to increase the safety factor, it is known the melting point for diamond increases under pressure. So the diamond could be used in "prestessed" form to increase its melting point even further.  Note then this would eliminate the need for the complicated and expensive liquid cooling channels throughout the walls of the combustion chamber and nozzle. So you could reduce the weight of the SSME's from 7,000 lbs. to 1/15th of this to around 500 lbs, while maintaining its reusability.  The weight of RS-68 engine could also be similarly reduced and be made reusable by no longer needing the ablative surfaces on the nozzle to dissipate the heat. A problem that would need to be solved though is the coating to put on the diamond to protect it from the combustion. While diamond does have a quite high melting point, it will burn in oxygen at around 600 C. So a high temperature coating would have to be put on the diamond used in the combustion chamber and in the nozzle. This is a similar to how carbon-carbon composites have been used for the highest temperature areas on the shuttle orbiter body. Made of carbon, these composites will also burn in oxygen at temperatures lower than the ones they have to withstand during shuttle reentry. Then they are coated to protect them from oxygen. For the temperatures reached in the combustion chambers and nozzles of the engines which are about twice those reached on the surfaces of the orbiter body during reentry, you would need higher temperature coatings to withstand this. Some possibilities might be for example hafnium carbide and tantalum hafnium carbide:Hafnium(IV) carbide. http://en.wikipedia.org/wiki/Hafnium_carbideTantalum hafnium carbide. http://en.wikipedia.org/wiki/Tantalum_hafnium_carbide Ceramic materials are being investigated for rocket engine components:Ceramic Materials for Reusable Liquid Fueled Rocket Engine Combustion Devices. http://ammtiac.alionscience.com/pdf/AMPQ8_1ART06.pdf This article states that likely some form of active cooling would be needed for the hottest areas in the combustion chamber and the nozzle, however, it does not consider the possibility of the high temperature resistance and heat dissipation capability of diamond.    Bob Clark      <div class="Discussion_UserSignature"> </div>

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