RS-68 Engines Considered for the (not so SD)HLV

[propforce]

You're welcome. Some of us can only talk about the things we know and, in my case, which is very little so I elaborate <img src="/images/icons/smile.gif" /><br /> <div class="Discussion_UserSignature"> </div>

 

[propforce]

<font color="yellow"><i>"... can Rocketdyne afford to have 2 engine development efforts going on at the same time (SSME and J-2) ??? " </i><br /><br />No, because Rocketdyne no longer exists. </font><br /><br />Ohhhh... make NO mistake, Rocketdyne exist and came out ahead on this PW-R merger. Who's the head of the new UTC Propulsion (PWR)? That's right, Byron Wood !! <img src="/images/icons/smile.gif" /><br /><br />But of course it will have to be NASA money to develop these engines. My question was, however; even with the money thrown at Rocketdyne I'd question if they have enough personnel for simultaneous 2 engine development? <br /><br /> <div class="Discussion_UserSignature"> </div>

 

[edkyle98]

"even with the money thrown at Rocketdyne I'd question if <br />they have enough personnel for simultaneous 2 engine <br />development? "<br /><br />If not, they could hire a bunch of college grads and put <br />them on 60 hour weeks!<br /><br />At any rate, SSME or RS-68 already exist, with live <br />production, so developing a derivative would be a smaller <br />effort than it took to create the originals. J-2 looks to be <br />a bigger effort to me, even though the design is already <br />developed in theory. The effort there will be creating and <br />validating an all-new production line, with new tooling and<br />methods.<br /><br /> - Ed Kyle

 

[propforce]

<font color="yellow">If not, they could hire a bunch of college grads and put them on 60 hour weeks! </font><br /><br />It takes a woman 9 months to have a baby. You can't substitute that with 9 women and expect to have a baby in one month !!<br /><br />In my experience, development engineers are different from sustaining engineers. The current SSME team at Rocketdyne is what I called 'sustaining engineering'. The last group of engineers with big engine development was from the RS-68 but that team too has dispersed, though it would be much easier to do the RS-68 'upgrade' as it is still a fairly recent engine than the SSME 'downgrade'. They are currently building a new team on J-2 but Rocketdyne has dropped its employment quite a bit recently. Down grading a SSME would actually take a lot more work than upgrading a RS-68.<br /> <div class="Discussion_UserSignature"> </div>

 

[spacefire]

just start from scratch dangit! <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[edkyle98]

Am I remembering correctly that they actually build and test <br />these engines in Mississippi now? <br /><br /> - Ed Kyle<br />

 

[propforce]

Here's an interesting dilema which has just flashed through my head.<br /><br />Now that Rocketdyne is a part of P&W, which means they can charge <i>profit</i> for every RS-68 sold to Boeing. I wonder if the cost of RS-68 will go up, say by 10%? <div class="Discussion_UserSignature"> </div>

 

[frodo1008]

Remember we are talking about a rocket that is not even going to have its first flight for about ten years from now. So there is at least 7-8 years for the development of these engines, either a simplified air-start SSME, or an upgraded RS68. <br /><br />I think that Rocketdyne has enough of its good people left, that with an increase of employment similar to the pick up for the original SSME development, and a continuing education and training effort they could indeed do this! It will, of course cost in monetary terms, but with the amount of time available the costs could be spread out enough for NASA to afford it.<br /><br />The problem for NASA now, is to make the decision between the two engine choices. Would the redesign of the external tank to be either taller (perhaps even too tall for the current facilities at the Cape) or wider (with having to discard the current tooling for the external tank, and start over with a new design) is which to chose here? We, who have some knowledge of what tooling costs know that this would add probably billions to the ultimate cost of such a launch system. Heck, it costs the automakers this kind of money just to change models. And in the external tank, we are talking about FAR larger tooling that that required for an automobile!<br /><br />As opposed to this IS the far less current costs of the RS68. Some time ago I was talking to some friends from Rocketdyne, and they mentioned that some low level studies were being made about increasing the thrust of the RS68 to the one million pound class. If this were done the performance disadvantage (and some of that could be alleviated at the same time) of the RS68 would become quite moot, as the RS68 thrust would be more than double that of the venerable high performance SSME! It is even somewhat probable that going from the current ablative type of nozzle to a channel wall nozzle would reduce the over all weight of such an RS68 such that it wouldn’t be much heavier that the curre

 

[frodo1008]

I wouldn't think that P&W would be TOO hard on Boeing. After all, purchasing Rocketdyne for some $700 million in cash has to be one of the greatest bargains in the histroy of aerospace! <br /><br />After the damage to the facilities of the 1998 Northridge Earthquake, it took more than one billion dollars just to get Rocketdyne back up and running! Plus buying Rocketdyne makes P&W the absolute leader in the free world in the rocket engine business! <br /><br />I would at least like to think that they would be gentle towards their benifactor here!<br /><br />Of course, business is business, as the saying goes.

 

[propforce]

<font color="yellow">I would at least like to think that they would be gentle towards their benifactor here! </font><br /><br />Almost spit my coffee here !! Frodo you DO have a sense of humor !!<br /> <div class="Discussion_UserSignature"> </div>

 

[frodo1008]

Don't flatter yourself here. Starting over may indeed be just what NASA will do, but not because of any comments from you (or I for that matter)!<br /><br />Starting over means literally discarding billions of dollars worth of tooling. Having actually been in manufacturing in the aerospace industry for dozens of years, please take it from someone that has seen the efforts and costs that go into such tooling that just starting over is NOT always the best (and certainly NOT the least expensive) choice! Quite probably the main factor involved here is how many of these launch vehicles are going to be built over time. The more such vehicles, the more the cost of new tooling could be amortized over the length of the programs involved. Believe me, I know enough about such trade studies to realize that I don't have the necessary information to make even an informed guess (much less dictate to those who have such information) as to which will be the least expensive choice in the long run.<br /><br />Now, IF you could (especially as an American tax payer) guarantee that NASA will get the necessary funding to "start from scratch" then it should be no problem. They probably should then "start from scratch"! Can you do this? At least I know enough to know that I certainly can't!<br />

 

[edkyle98]

In this 8MB Word doc writeup:<br /><br />http://www.engineeringatboeing.com/dataresources/PropulsionForThe21stCentury-RS-68.doc<br />it says that :<br /><br />"[RS-68] Engine assembly is performed in a new facility <br />located at the Stennis Space Center for optimum efficiency <br />and low cost.<br /><br />The Engine Assembly Facility (Figure 49) was designed <br />using Lean Assembly Analysis Techniques to provide <br />optimum process flow of components, and deliverable <br />RS-68 propulsion systems. The facility contains all the <br />ancillary equipment required to assemble and process the <br />engine. Proximity of the test facility to the assembly facility<br /> assures that minimum time is used to transport, test and <br />process the RS-68 engines. This arrangement also <br />promotes the sharing of personnel, equipment and <br />information to minimize investments in capital and <br />intellectual property."<br /><br /> - Ed Kyle

 

[frodo1008]

However, a great deal of the components of this engine are still built at the California facilities. This is only the final line construction of the engine itself. It is always best to construct the engines closest to the testing areas. For example, the vast majority of the thousands of engines built by Rocketdyne over the years were built in Canoga Park, and then tested at the Santa Susana Field Labs some 10 miles away!<br /><br />In the 1960's Rocketdyne also made smaller engines at a plant in Van Nuys. These engines (such as the fantastic SE-8 used on the Apollo Command Module as a major pert of the RCS system) were also tested in areas such as Components Test Lab #4 (CTL-4) on "The Hill" as it was known at the time. I am very familiar with this as I spent some five years there in such testing of ths engine and other small engines!<br /><br />It is somewhat ironic to me that P&W itself stayed with the smaller engines, and has now completed the circle by the purchase of Rocketdyne. Good for them!

 

[frodo1008]

Thanks, Irony is sometimes one of the best sources of humor!

 

[Swampcat]

<font color="yellow">"A vehicle with the power of four such engines and four (at least I think NASA was considering four) of the SRB's..."</font><br /><br />I've not seen any NASA documents considering the use of 4 SRBs. <br /><br />Nonetheless, with 2 5-segment SRBs and 4 F-1 class engines, you're still talking around 11M pounds of thrust out of the first stage. Not bad. <div class="Discussion_UserSignature"> <font size="3" color="#ff9900"><p><font size="1" color="#993300"><strong><em>------------------------------------------------------------------- </em></strong></font></p><p><font size="1" color="#993300"><strong><em>"I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."</em></strong></font></p><p><font size="1" color="#993300"><strong>Thomas Jefferson</strong></font></p></font> </div>

 

[barrykirk]

Well, after hearing about the switch from the SSME to the RS-68 I decided to look up the spec on astronautix and compare the SSME to the RS-68 to the F-1 and the Merlin 1 engines. Just to get my head around what the differences are.<br /><br />Thrust to Weight Ratios.<br /><br />1) Merlin and F1 are 94<br /><br />2) SSME is 73<br /><br />3) RS-68 is 51<br /><br />4) J2 is 73<br /><br />ISP Sea Level<br /><br />1) Merlin is 261 seconds<br /><br />2) F1 is 265 seconds<br /><br />3) SSME is 363 seconds<br /><br />4) RS-68 is 365 seconds<br /><br />5) J2 is 200 seconds<br /><br />ISP vacuum<br /><br />1) Merlin is 310 seconds<br /><br />2) F1 is 304 seconds<br /><br />3) SSME is 453 seconds<br /><br />4) RS-68 is 420 seconds<br /><br />5) J2 is 421 seconds<br /><br />Now all of this is old news, and I knew that LOX/RP1 always had a thrust to weight ratio advantage over LOX/LH2, but I didn't realize that the SSME was that close to the F1 and the Merlin in thrust to weight ratio.<br /><br />The RS-68 absolutly sucks when it comes to thrust to weight ratio.<br /><br />All rocket engines take an ISP hit at sea level compared to vacuum, but the LH2 engines take a much more severe hit than the RP-1 engines. Now to be fair the J2 was really meant for an upper stage so the fact that it's ISP sucks at sea level isn't a problem.<br /><br />As I said, I just needed to get my head around the numbers. I've heard that the cost of the SSME is $50 mil each and the RS-68 is about $14 mil each. But it takes only 3 RS-68 to provide the thrust of 5 SSME.<br /><br />So, changing nothing else, replacing the SSME with the RS-68 will cut your vehicle cost substantially, but it will also severly reduce your payload.<br /><br />So, what is NASA going to do to maintain the payload capacity or are they going to deal with a reduced payload capacity.<br /><br />I've heard one suggestion of going to 4 instead of 2 SRB's. Now that suggestion didn't come from NASA so it's has no official support, but I would like to belie

 

[Swampcat]

<font color="yellow">"I've heard one suggestion of going to 4 instead of 2 SRB's. Now that suggestion didn't come from NASA so it's has no official support, but I would like to believe that NASA is considering that possibilty in their internal planning discussions."</font><br /><br />Though it's an interesting configuration to consider, I seriously doubt that NASA would go with 4 SRBs. A 4 SRB vehicle would require enormously expensive changes to the infrastructure.<br /> <div class="Discussion_UserSignature"> <font size="3" color="#ff9900"><p><font size="1" color="#993300"><strong><em>------------------------------------------------------------------- </em></strong></font></p><p><font size="1" color="#993300"><strong><em>"I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical. Unsuccessful rebellions, indeed, generally establish the encroachments on the rights of the people which have produced them. An observation of this truth should render honest republican governors so mild in their punishment of rebellions as not to discourage them too much. It is a medicine necessary for the sound health of government."</em></strong></font></p><p><font size="1" color="#993300"><strong>Thomas Jefferson</strong></font></p></font> </div>

 

[rybanis]

Boy would it look cool though. <div class="Discussion_UserSignature"> </div>

 

[propforce]

<font color="yellow"><i>"So, what is NASA going to do to maintain the payload capacity or are they going to deal with a reduced payload capacity." </i><br /><br />Increase the burn time (Propellant size volume) </font><br /><br />Which means either longer or wider tanks on the core stage. <br /><br />4 SRB may not help, and may actually make it worse. At some point of the trajectory, the engine has to throttle back otherwise it would exceed the G-limits of the structure. So bigger thrust is not the solution. Bigger tank is. <div class="Discussion_UserSignature"> </div>

 

[josh_simonson]

I believe a pair of SRBs are about $60m. <br /><br />Perhaps they could get around the tank height issues by having 2 or 3 ET booster cores side by side like the heavy version of the EELVs, or maybe a side-mounted drop-tank. A side-mounted drop tank could make use of all the tank-shuttle interconnecting hardware that's already been designed - just turn all the plumbing 180'. <img src="/images/icons/wink.gif" /> <br /><br />Edit: uh-oh, a lightbulb probably just went off in a shuttle-cronies head...

 

[barrykirk]

OK, so to limit G loads to the structure, you throttle back to the liquid engines. That means that by the time the SRB burnout occurs, there is much more fuel left in the tank ergo, the burn time is increased. You get the same effect as an increased tank size.<br /><br />The question I have to increasing tank size is what are the returns on increasing tank size.<br /><br />Example, if you do nothing else but double the tank size, I will assume that you double the burn time. However, how much does that increase the payload to orbit? Does it increase the payload to orbit? If the total vehicle mass exceeds the thrust output of the rocket engines, then the rocket will decelerate until it burns off enough fuel to start accelerating again.<br /><br />These are just random ramblings.

 

[trailrider]

What bothers me, and I'm sure NASA and a bunch of contractor engineers is if you increase the diameter of the 1st stage tankage you completely mess up using existing STS launch infrastructure, e.g., the SRM's don't fit the existing flame ducts and supports. Redesigining and rebuilding (or building a new launch facility) may completely offset the delta costs of using RS-25's.<br /><br />Side-mounted anythings (other than the SRM's) could be more headaches that it would be a good idea to get rid of! That's especially true when dealing with liquids. We've been lucky with the Shuttle not to have leakage problems at the quick-disconnects. I don't think anybody really wants to go there again!<br /><br />So far as finding engineers is concerned, PW-R needs to start recruiting NOW! No, NOT in the colleges and universities. No, NOT in the high schools! They better start putting out some Von Braun/Bonestell stuff (maybe using computer games) and hit the elementary school kids.<br /><br />Ad Luna! Ad Ares! Ad Astra!

 

[propforce]

<font color="yellow">OK, so to limit G loads to the structure, you throttle back to the liquid engines. That means that by the time the SRB burnout occurs, there is much more fuel left in the tank ergo, the burn time is increased. You get the same effect as an increased tank size. </font><br /><br />Good thoughts. The key is how far can the engines throttle back and would that significantly offset the disadvantage of having 4 SRBs? <br /><br />Also, if taking your idea to an extreme, why not start the RS-68 until the 4 SRB burn out, thus making the core stage effectively a 2nd stage?<br /><br />Then, to what extent of above ideas violate existing RS-68 capabilities? How much 'upgrade' does one want to impose on the RS-68, and to what point it becomes a new engine development? <br /><br />Lots of choices, just need to put in some elbow grease and sharpen that pencil on design analysis. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[mattblack]

Looks cool? Heck, I'd cross the world to watch an HLV with 4x Shuttle SRBs (cue shaking earth and chest-thumping crackling). Talk about shock and awe... <div class="Discussion_UserSignature"> <p> </p><p>One Percent of Federal Funding For Space: America <strong><em><u>CAN</u></em></strong> Afford it!!  LEO is a <strong><em>Prison</em></strong> -- It's time for a <em><strong>JAILBREAK</strong></em>!!</p> </div>

 

[mattblack]

What about a cluster of 6x Aerojet SRBs (from the Atlas V) added to either side of the corestage, in addition to the 5-segment SRBs? They burn for 94 seconds and produce more than 200,000 pounds thrust each. I don't know about the impact to dynamic loads, vibration and aerodynamics on the CaLV, but this could mean that the CaLV (Ares 5?) could keep the RS-68s throttled back to conserve fuel until ejection of the Aerojet solids & SRBs. After Max-Q and solids-gone, the RS-68s could then be throttled up to 100+percent. Also, it might reduce the need to manufacture a further-stretched corestage to make up for the thirstier RS-68s, and at least minimise pushing the Ares V height much past 357 feet. <div class="Discussion_UserSignature"> <p> </p><p>One Percent of Federal Funding For Space: America <strong><em><u>CAN</u></em></strong> Afford it!!  LEO is a <strong><em>Prison</em></strong> -- It's time for a <em><strong>JAILBREAK</strong></em>!!</p> </div>