Ares V: 5 SSME's in the core

kyle_baron · Jul 12, 2008

Ares V which really has 6 engines, will soon become Ares VII.  Why doesn't Ares use the 5 Shuttle SSME's in the core,  like it was originally planned, back in 2005?  On Nasa Spaceflight.com I quote:   "If you think this is nutz, just wait till you see what I call the Ares-7 and what Nasa is calling the "V-Max Ares-V" and it's even bigger partner the Max-Ares-V."  This is really getting out of hand.  This pig won't fly. <div class="Discussion_UserSignature"> </div>

StrandedonEarthsince1970 · Jul 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Ares V which really has 6 engines, will soon become Ares VII.  Why doesn't Ares use the 5 Shuttle SSME's in the core,  like it was originally planned, back in 2005?  On Nasa Spaceflight.com I quote:   "If you think this is nutz, just wait till you see what I call the Ares-7 and what Nasa is calling the "V-Max Ares-V" and it's even bigger partner the Max-Ares-V."  This is really getting out of hand.  This pig won't fly. Posted by kyle_baron</DIV> Probably because SSME's are expensive.  <div class="Discussion_UserSignature"> Now where on Earth did I park my UFO? </div>

docm · Jul 12, 2008

Why?  Because it would very likely cause too much acceleration, complicating way too many things to be acceptable. <div class="Discussion_UserSignature"> </div>

kyle_baron · Jul 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'> Probably because SSME's are expensive.  Posted by StrandedonEarthsince1970</DIV> Yep, here's the difference:RS-68:  7 x $14 million = $98 million   And after needed upgrades:  7 x $30 million = $210 millionSSME:   5 x $50 million = $250 million <div class="Discussion_UserSignature"> </div>

kyle_baron · Jul 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Why?  Because it would very likely cause too much acceleration, complicating way too many things to be acceptable. Posted by docm</DIV> Not really, the SSME has less thrust, but better specific impulse (or mpg in car terminology) which means less propellent and a smaller core. http://en.wikipedia.org/wiki/SSMEOriginally, the SSME was to see service in the post-Shuttle era as the main engines for the unmanned Ares V cargo-launch vehicle and as a second-stage engine for the manned-rated Ares I crew-launch vehicle. Although the use of the SSME seemed good on paper, as it would use current Shuttle technology after the Shuttle's retirement in 2010, it had several drawbacks:<ul><li>It would not be reusable, as they would be permanently attached to the discarded stage(s). </li><li>It would have to undergo a flight-readiness firing (FRF) before installation – the so-called "Main Engine Test" that NASA conducted with each new Orbiter and prior to the STS-26 flight. </li><li>It would be expensive and time-consuming to convert the ground-started SSME to an air-started version for the Ares I second stage. </li></ul>With several design changes to the Ares I and Ares V rockets, the SSME will be replaced with a single J-2X engine for the Ares I second stage. The Ares V will use six modified RS-68 engines (which is based on both the SSME and Apollo-era J-2 engine) for its core stage. Hence the SSMEs will be retired along with the Shuttle fleet.http://en.wikipedia.org/wiki/RS-68Simplicity of design and cost effectiveness were the primary design goals of this engine, which resulted in 80% fewer parts than the Space Shuttle main engine (SSME) (and a 10% reduction in specific impulse). The thrust to weight ratio of the RS-68 is also significantly lower than the SSME. The benefit of this design philosophy is drastically reduced construction costs. Each RS-68 for the Boeing Delta IV program costs approximately $14 million to build, compared to the SSME at $50 million. This is especially noteworthy considering the RS-68 is significantly larger and produces higher thrust. The RS-68 has more thrust, less cost, and 80% fewer parts, but it is a less efficient engine.  The SSME's need 2 less engines, less propellent, which results in a smaller core, and probably less overall mass (weight) for Ares V.  Nasa decided to go with the RS-68, however there is an arguement for the SSME, IMO.     <div class="Discussion_UserSignature"> </div>

Cygnus_2112 · Jul 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'> N however there is an arguement for the SSME, IMO.    Posted by kyle_baron</DIV>Not really,The prices for the modified RS-68 you quoted are too highThe SSME has been out of production for several years There is enconomy in using an engine that has multiple uses. The orginal design of 5 SSME is also no longer applicable, 6 would be neede. BTW wikipedia is not a source for space info.  It is inaccurate

frodo1008 · Jul 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Not really,The prices for the modified RS-68 you quoted are too highThe SSME has been out of production for several years There is enconomy in using an engine that has multiple uses. The orginal design of 5 SSME is also no longer applicable, 6 would be needed   Posted by Cygnus_2112</DIV>The original reason for using the SSME was that they are indeed very cheap, as they are already paid for!  They were going to use the engines that are already on or held for spares of the shuttles, which have been paid for already by  the shuttle program.However, I would be the first to agree that if the SSME's so used could not be recovered and then reused, (which was what they were originally designed for, but might not be possible with the Ares V) that building new ones would be more expensive that using the RS68's.  However, the newer SSME's would not have to be reusable, and would therefore not be as expensive as the older SSME's were. With SSME spares it would be possible to have the first five Ares V flights have engines already bought and paid for.  But would this then be less in the long run if the more expensive SSME's, which would still be more expensive than the RS68's by at least double?  That would be the real economic question here (and for the first stage of the Ares V any engines used would not have to be space rated for a restart in space). I would say that by the time a dozen or so SSME driven first staged cores for the Ares V had been launched, the lower costs of the RS68's would have caught up and after that it would be they that would be the least expensive alternative here.  And as I don't really think that NASA knows at this time exactly what the flight rate for the Ares V is going to be, then I think that going with the RS68's is the way to go at this time.  The only corollary to this is if NASA has to show a far lower cost for the Ares V, at least in the beginning to appease a new administration (which may very well be far more cost conscious here.  Then they may have to go back to the initially almost free (remember they have already been paid for) SSME's in the beginning of Ares V flights, and then go to the larger RS68's later on.  Not only do I not know this, but I can almost guarantee that NASA does not know it either!The single SSME for the Ares I second stage was rejected because it would indeed have been quite expensive to re- engineer the SSME to restart in space.  The alternative was to re-engineer the original J2-S engines that were originally designed to be restarted in space as they were going to replace the original J2 engines were used on the second stage of the Saturn V.  The only economic problem here is that it will take two of these engines to replace the single SSME. Is my explanation at least somewhat understandable?

SpaceKiwi · Jul 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>The original reason for using the SSME was that they are indeed very cheap, as they are already paid for!  They were going to use the engines that are already on or held for spares of the shuttles, which have been paid for already by  the shuttle program.   Posted by frodo1008</DIV> I'm not sure this is right.  I vaguely remember asking SG about the SSME inventory and I believe he said they didn't have many of them.  With the loss of six powerplants through the Challenger/Columbia tragedys, possibly not enough to fit out the remaining three Orbiters at the same time?  Given five or six of them a launch for the Ares heavy lifter, you're not going to have much a program before the existing stocks are depleted!  I certainly don't think they ever had 25+ of them.  At most you'd urgently need nine, assuming two stacks on the pads, and three ready to fit to an Orbiter in the OPF.Even under the earlier reusasble model, it would surely have created a potential weakpoint in the Ares program. SK  <img src="http://sitelife.space.com/ver1.0/Content/images/store/8/5/38604eaa-9e45-4406-b50c-22433bd09113.Medium.gif" alt="" /> <div class="Discussion_UserSignature"> Who is this superhero? Henry, the mild-mannered janitor ... could be!-------------------------------------------------------------------------------------------Bring Back The Black! </div>

kyle_baron · Jul 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>The original reason for using the SSME was that they are indeed very cheap, as they are already paid for!  They were going to use the engines that are already on or held for spares of the shuttles, which have been paid for already by  the shuttle program.However, I would be the first to agree that if the SSME's so used could not be recovered and then reused, (which was what they were originally designed for, but might not be possible with the Ares V) that building new ones would be more expensive that using the RS68's.  However, the newer SSME's would not have to be reusable, and would therefore not be as expensive as the older SSME's were.</DIV> I agree with you 100%.  Use up the existing Shuttle SSME's, and any existing inventory 1st, even if it does take 6 engines.  Then use a new SSME or RS-68, assuming these engines can be swapped in and out? Replying to: <DIV CLASS='Discussion_PostQuote'> With SSME spares it would be possible to have the first five Ares V flights have engines already bought and paid for.  But would this then be less in the long run if the more expensive SSME's, which would still be more expensive than the RS68's by at least double?  That would be the real economic question here (and for the first stage of the Ares V any engines used would not have to be space rated for a restart in space). I would say that by the time a dozen or so SSME driven first staged cores for the Ares V had been launched, the lower costs of the RS68's would have caught up and after that it would be they that would be the least expensive alternative here.  And as I don't really think that NASA knows at this time exactly what the flight rate for the Ares V is going to be, then I think that going with the RS68's is the way to go at this time.  The only corollary to this is if NASA has to show a far lower cost for the Ares V, at least in the beginning to appease a new administration (which may very well be far more cost conscious here.  Then they may have to go back to the initially almost free (remember they have already been paid for) SSME's in the beginning of Ares V flights, and then go to the larger RS68's later on.  Not only do I not know this, but I can almost guarantee that NASA does not know it either!   Posted by frodo1008</DIV> Excellent points.  Well done.  <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-wink.gif" border="0" alt="Wink" title="Wink" /> <div class="Discussion_UserSignature"> </div>

SpaceKiwi · Jul 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'> I agree with you 100%.  Use up the existing Shuttle SSME's, and any existing inventory 1st, even if it does take 6 engines.  Posted by kyle_baron</DIV> Kyle, the following NASA document indicates they have 12 SSME's only.  If I'm reading the document designation right, it was also prepared before the loss of three of those units in the Columbia tragedy.LINK SK  <img src="http://sitelife.space.com/ver1.0/Content/images/store/13/8/7db40da0-8f61-41f0-a8f3-21ad1d7dbc2b.Medium.gif" alt="" /> <div class="Discussion_UserSignature"> Who is this superhero? Henry, the mild-mannered janitor ... could be!-------------------------------------------------------------------------------------------Bring Back The Black! </div>

Cygnus_2112 · Jul 12, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'> I agree with you 100%.  Use up the existing Shuttle SSME's, and any existing inventory 1st, even if it does take 6 engines.  Then use a new SSME or RS-68, assuming these engines can be swapped in and out?  Posted by kyle_baron</DIV> Not viable.  1.  Can't just interchange engines, just as a truck diesel can't be exchanged for a car engine.    The interfaces (fluid, electrical, mechanical, thrust) are different for each engine.  SSME needs an APU, RS-68 has its own HPU.   The big reason is the Ares propellant tank volumes are designd around a  specific engine.2.  There isn't a "new" disposable SSME.  It was found that the costs of the engineering to do it would still make the units costs similar to the regular SSME.  $40 million was the old cost per engine, restarting the production would make each engine more

freya · Jul 12, 2008

. BTW wikipedia is not a source for space info.  It is inaccurate   Posted by Cygnus_2112[/QUOTE]Isn't it our duty to ensure it is accurate?Gaz <div class="Discussion_UserSignature"> </div>

DrRocket · Jul 13, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Ares V which really has 6 engines, will soon become Ares VII.  Why doesn't Ares use the 5 Shuttle SSME's in the core,  like it was originally planned, back in 2005?  On Nasa Spaceflight.com I quote:   "If you think this is nutz, just wait till you see what I call the Ares-7 and what Nasa is calling the "V-Max Ares-V" and it's even bigger partner the Max-Ares-V."  This is really getting out of hand.  This pig won't fly. Posted by kyle_baron</DIV>Maybe before you redesign the entire U.S. launch fleet you ought to learn something about the business and the physics that governs it.I don't know if you have every been through the SSME manufacturing process.  It was ("was" since it is out of production) an extremely complicated process, even for the aerospace industry.  Just the regeneratively cooled nozzle exit cone represented a very complex hand-built part.  The RS-68 is a far simpler and far more producible engine.  NASA and the contractors developing the Ares V probably have their hands full, given a demanding performance specification and the need to make the system affordable.  However, they have the skills necessary to assess the requirements -- all of them -- and to develop solutions consistent with available technology, manufacturing techniques, budgets and schedules.  Maybe they will be successful and maybe they won't, but that is the nature of development programs.Before you start leveling criticism fueled largely by complete ignorance of the nature of the business, you ought to educate yourself a bit so as to understand the overall challenges and constraints.  <div class="Discussion_UserSignature"> </div>

frodo1008 · Jul 13, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'> Not viable.  1.  Can't just interchange engines, just as a truck diesel can't be exchanged for a car engine.    The interfaces (fluid, electrical, mechanical, thrust) are different for each engine.  SSME needs an APU, RS-68 has its own HPU.   The big reason is the Ares propellant tank volumes are designd around a  specific engine.2.  There isn't a "new" disposable SSME.  It was found that the costs of the engineering to do it would still make the units costs similar to the regular SSME.  $40 million was the old cost per engine, restarting the production would make each engine more  Posted by Cygnus_2112</DIV>Please read my posts a little more.  I did not say that NASA should use the SSME over the RS68.  What I did intend to show was why NASA originally intended to use the SSME for the Ares V.  Please note that I was on the production line for the SSME's all during the years from 1977 until 2000 (when I retired from Rocketdyne).  And I know for a fact that we built far more than 12 to 18 complete engines.  We built at least some 30 engines all told (unless all the parts for even more engines were just intended for spares, but I doubt it).  Now, what NASA has done with all but some 12 (plus the three each on the challenger and the Columbia) I must admit I don't know.  But we did build more that that. Perhaps some of the later configuration changes would limit the engines to the lesser value, and that is where NASA is getting their figures from? Also the original price for the SSME was about $60 million each, and included a whole lot of R&D and testing.  When I left in 2000 we were shooting for far less for a much simpler non reusable production level engine.  About half the original or $30 million, or perhaps even less.  However, as I pointed out this would indeed still be quite a bit more than the RS68.  When the SSME was originally designed, performance and weight were the original Gods of engineering design, cost was strictly secondary (and was to be made up by the reusability of the SSME's).  While this did not quite work out as planned, the SSME if used as a reusable engine is actually relatively inexpensive, in particular for an engine that only weighs about 4,000 lbs, has the highest ISP of any engine in the world, and is reusable.However, when the RS68 was being designed and built cost was indeed the engineering design and manufacturing God, as this was a part of the EELV program where over all low cost was the goal of the program itself. While the RS68 is about 4X heavier than the SSME and has a somewhat less ISP, it not only would be less expensive but is also considerably higher in thrust than the SSME, but it is a lower performance engine.  Also, I had heard from some friends still at Rocketdyne that there also were possible plans to upgrade the 665K thrust of the RS69 to a 1.0 million pound thrust engine, and that would really give future Ares V configurations a considerable boot in thrust!!

shuttle_guy · Jul 13, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Ares V which really has 6 engines, will soon become Ares VII.  Why doesn't Ares use the 5 Shuttle SSME's in the core,  like it was originally planned, back in 2005?  On Nasa Spaceflight.com I quote:   "If you think this is nutz, just wait till you see what I call the Ares-7 and what Nasa is calling the "V-Max Ares-V" and it's even bigger partner the Max-Ares-V."  This is really getting out of hand.  This pig won't fly. Posted by kyle_baron</DIV> One very big reason is the very high cost of the SSMEs. They are very expensive because they are designed to be reused. Even the proposed throw away version (eliminating the special materials etc. required for reusability) they are too expensive. <div class="Discussion_UserSignature"> </div>

shuttle_guy · Jul 13, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'> I agree with you 100%.  Use up the existing Shuttle SSME's, and any existing inventory 1st, even if it does take 6 engines.  Then use a new SSME or RS-68, assuming these engines can be swapped in and out?  Excellent points.  Well done.  Posted by kyle_baron</DIV> The enines could not be swapped out with out a redesign of the propellant feed system. <div class="Discussion_UserSignature"> </div>

kyle_baron · Jul 13, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I don't know if you have every been through the SSME manufacturing process.  It was ("was" since it is out of production) an extremely complicated process, even for the aerospace industry.  Just the regeneratively cooled nozzle exit cone represented a very complex hand-built part.  The RS-68 is a far simpler and far more producible engine.</DIV>Are you also aware, that the professionals at NASA SpaceFlight.com are worried that the ablative nozzles on the RS-68 might burn up, because of the close proximity of each engine?  Those hand built LH2 cooled nozzles that you poo-pood would solve the problem. Replying to: <DIV CLASS='Discussion_PostQuote'>Before you start leveling criticism fueled largely by complete ignorance of the nature of the business, you ought to educate yourself a bit so as to understand the overall challenges and constraints.  Posted by DrRocket</DIV> Oh, I am, over at NASA SpaceFlight.com where the professionals (including our own Cygnus 2112, also known as Jim) argue amongst themselves in the Forum section.  It's actually quite entertaining.  Have you visited these forums?  If not, you should, with your background. <div class="Discussion_UserSignature"> </div>

Cygnus_2112 · Jul 13, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Are you also aware, that the professionals at NASA SpaceFlight.com are worried that the ablative nozzles on the RS-68 might burn up, because of the close proximity of each engine?  Those hand built LH2 cooled nozzles that you poo-pood would solve the problem.  Posted by kyle_baron</DIV> so would more ablative material

DrRocket · Jul 13, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Are you also aware, that the professionals at NASA SpaceFlight.com are worried that the ablative nozzles on the RS-68 might burn up, because of the close proximity of each engine?  Those hand built LH2 cooled nozzles that you poo-pood would solve the problem.  Oh, I am, over at NASA SpaceFlight.com where the professionals (including our own Cygnus 2112, also known as Jim) argue amongst themselves in the Forum section.  It's actually quite entertaining.  Have you visited these forums?  If not, you should, with your background. Posted by kyle_baron</DIV>If there is any concern over the nozzles it would have to come from radiant heating and recirculation on the outside of the exit cone, and that is quite easily handled.  I suppose that the people that you are talking about are not all that familiar with ablative nozzles, as in the past they have been used primarily with solid rockets.  But there should be no major problem, particularly since hydrogen/LOX yeilds H2O which has rather low emissivity.  The nozzle environment for solids, in which the exhaust contains a lot of white-hot aluminum oxide with high emissivity and a tendancy to erode material if there is direct impingement is much more severe.  I have seen lots of professionals argue among themselves.  For this argument to be of any concern you would need to have some experienced nozzle designer-analysts involved. Ablative nozzle design and analysis is quite specialized, and the analytical results require a great deal of interpretation -- they are not straightforward.  That nozzle has worked extremely well on the Delta family.  It is manufactured in the same facility that makes the nozzles for the SRBs, and receives attention from the same engineering organization.And if there really is a problem, which I tend to doubt, then SSME nozzles would not necessarily solve the problem.  They were designed for a particular heat flux, and if the flux on the outside of the nozzle exit cone is high enough to be a concern for the RS-68 it would be a concern for any other nozzle as well.  <div class="Discussion_UserSignature"> </div>

SpaceKiwi · Jul 13, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Please note that I was on the production line for the SSME's all during the years from 1977 until 2000 (when I retired from Rocketdyne).  And I know for a fact that we built far more than 12 to 18 complete engines.  We built at least some 30 engines all told (unless all the parts for even more engines were just intended for spares, but I doubt it).  Now, what NASA has done with all but some 12 (plus the three each on the challenger and the Columbia) I must admit I don't know.  But we did build more that that. Posted by frodo1008</DIV> Thanks for that clarification, frodo, I forgot you were on the Rocketdyne payroll.  I was going to suggest spares for the rest also, as that NASA doc I linked does indicate 7000 parts are periodically replaced, but I guess you manufactured additional items for that purpose.  God knows what they've done with the rest.  As a matter of interest, what sort of production rate did you have on the SSME's towards the end of your time there?  I can't imagine you would have been building many complete units by 2000 surely? SK  <img src="http://sitelife.space.com/ver1.0/Content/images/store/14/7/ceb01708-8818-4fa5-87ac-09f603c7f749.Medium.gif" alt="" /> <div class="Discussion_UserSignature"> Who is this superhero? Henry, the mild-mannered janitor ... could be!-------------------------------------------------------------------------------------------Bring Back The Black! </div>

CalliArcale · Jul 14, 2008

The SSMEs are heavy, which cuts into performance.  For Shuttle, this is acceptable because it's the cost of reusability.  But Ares V will be an expendable rocket, so you take a performance cut for no gain.  Sure, they were going to modify them to be lighter and less robust since they wouldn't be reused, but there'd only be so much you could pull out before you might as well redesign the whole thing from scratch -- which kind of defeats the purpose of design reuse.I've always liked the ablative nozzle concept.  Sure, regenerative loop cooling is clever, and it's worked on engines going right back to the V-2.  But it is complex, and complexity generally adds both cost and risk.  The simplicity of ablative materials, if they're available, makes them appealing in my mind. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

DrRocket · Jul 14, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>The SSMEs are heavy, which cuts into performance.  For Shuttle, this is acceptable because it's the cost of reusability.  But Ares V will be an expendable rocket, so you take a performance cut for no gain.  Sure, they were going to modify them to be lighter and less robust since they wouldn't be reused, but there'd only be so much you could pull out before you might as well redesign the whole thing from scratch -- which kind of defeats the purpose of design reuse.I've always liked the ablative nozzle concept.  Sure, regenerative loop cooling is clever, and it's worked on engines going right back to the V-2.  But it is complex, and complexity generally adds both cost and risk.  The simplicity of ablative materials, if they're available, makes them appealing in my mind. Posted by CalliArcale</DIV>Ablative materials are readily available.  They are the standard for solid rockets.  The materials used come in the form of carbon phenolic tape or graphite phenolic phenolic tape (the difference is in the the temperature used in manufacturing the material and the terminology is a bit imprecise) and are wrapped on a mandrel to form the nozzle liner.  Often a sillica phenolic material is used as a backing and insulator.The RS-68 nozzle is made in the same facilities and using the same basic process as is used to make the nozzles for the shuttle SRBs. <div class="Discussion_UserSignature"> </div>

frodo1008 · Jul 14, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>The SSMEs are heavy, which cuts into performance.  For Shuttle, this is acceptable because it's the cost of reusability.  But Ares V will be an expendable rocket, so you take a performance cut for no gain.  Sure, they were going to modify them to be lighter and less robust since they wouldn't be reused, but there'd only be so much you could pull out before you might as well redesign the whole thing from scratch -- which kind of defeats the purpose of design reuse.I've always liked the ablative nozzle concept.  Sure, regenerative loop cooling is clever, and it's worked on engines going right back to the V-2.  But it is complex, and complexity generally adds both cost and risk.  The simplicity of ablative materials, if they're available, makes them appealing in my mind. Posted by CalliArcale</DIV>I am sorry Calli, but if the weight of the engines themselves were the issue the SSME would win hands down!!Weight if single SSME = 7,775 lbs Weight of single RS68  = 14,560 lbsSo the weight of a single RS68 is very close to twice the weight of a single SSME.  This even makes the SSME lighter when you consider the higher thrust of the RS68.  Thrust of an SSME = 500k, thrust of an RS68 = 665K.So if you consider only engine weight the far more efficient and therefore lighter SSME is going to be your choice, hands down!However to achieve this higher performance and lower weight the SSME is more than three times the cost of an RS68.  And even if Rocketdyne were to greatly simplify the SSME by cutting out its reusability it would still be at least twice as expensive as the RS68, and this is  the area then both Congress and NASA consider the most important, the area of cost, and it is in this area that the RS68 wins hands down, and will be the choice of NASA for the Ares V!!! Personally, I consider the SSME to be the single greatest piece of machinery ever build by the hand of mankind, but it is not a cost affective item!

BrianSlee · Jul 14, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I am sorry Calli, but if the weight of the engines themselves were the issue the SSME would win hands down!!Weight if single SSME = 7,775 lbs Weight of single RS68  = 14,560 lbsSo the weight of a single RS68 is very close to twice the weight of a single SSME.  This even makes the SSME lighter when you consider the higher thrust of the RS68.  Thrust of an SSME = 500k, thrust of an RS68 = 665K.So if you consider only engine weight the far more efficient and therefore lighter SSME is going to be your choice, hands down!However to achieve this higher performance and lower weight the SSME is more than three times the cost of an RS68.  And even if Rocketdyne were to greatly simplify the SSME by cutting out its reusability it would still be at least twice as expensive as the RS68, and this is  the area then both Congress and NASA consider the most important, the area of cost, and it is in this area that the RS68 wins hands down, and will be the choice of NASA for the Ares V!!! Personally, I consider the SSME to be the single greatest piece of machinery ever build by the hand of mankind, but it is not a cost affective item!   Posted by frodo1008</DIV> I wish you guys would quit talking about throwing away the SSMEs in an ELV configuration.  I happen to have plans for them ;O) <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>

Cygnus_2112 · Jul 14, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I wish you guys would quit talking about throwing away the SSMEs in an ELV configuration.  I happen to have plans for them ;O) Posted by BrianSlee</DIV> They still will be "thrown" away as orbiter flies its last mission.  They won't be refurb and won't be returned to a flight condition

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