Dedicated SLS Block 1B Thread

[PahTo]

Actually, the RS-68 won't work with SRBs due to heating.  I envision a 2x RS-68 with LRBs as the preferred solution for safety, cost and eficiency.  Now that we're firmly on the Block 1 (SRB) path, infrastructure is going in that makes going away from SRBs (either 5-seg or "Advanced") a more costly (and difficult) proposition.
This makes the 1B seem like the long term solution, but there are major hurdles, not the least of which is development of the RS-25E.  The current batch of SSME will run out.  Hence my comment about engine availability.

[Lobo]

Do we think they are even going to go with the 105 ton/1B configuration and not skip right to 2?

I think it's pretty likely the Block 1B will be the new PoR before too long.  According to Boeing, it should actually be 118mt, not 105mt.  Just like Block 1 will be about 97mt, not 70mt.  But there's "official" numbers, and real numbers, and it seems at this phase, NASA is going with under-promising and over-deliverying, instead of the other way around. 

BLock 1 and 1B will probably live  (BLock 1 with ICPSwhen the mission doesn't need the BLock 1B upper stage) for 10 flights until the current stock of 5-seg casings is spent.  Then there will be an upgrade to advanced boosters, or they will restart 5-seg casing production. 
Either way, "Block II" will probably only be "Block 1B" with advanced boosters when adavnced boosters are finally added. (which could be never if they were to restart 5-seg production.  But I think they'd instead go with "replacement boosters" in the ATK 4-seg composite instead of restarting 5-seg casing produciton, if they decided a full advanced booster competition would be too expensive.)

[Lobo]

Actually, the RS-68 won't work with SRBs due to heating.  I envision a 2x RS-68 with LRBs as the preferred solution for safety, cost and eficiency.  Now that we're firmly on the Block 1 (SRB) path, infrastructure is going in that makes going away from SRBs (either 5-seg or "Advanced") a more costly (and difficult) proposition.
This makes the 1B seem like the long term solution, but there are major hurdles, not the least of which is development of the RS-25E.  The current batch of SSME will run out.  Hence my comment about engine availability.

Just building more SSMEs, perhaps while adopting small production efficiency changes, is an option.  The low flight rate means that current SSMEs will last until 10-15 years from now, so steady slow build rates of an already developed engine are certainly an option.

Same goes for SRB casings.  Those on hand will last for many years.  In the interim, either a move could be made to composite casings or more steel casings could be fabricated.

 - Ed Kyle

Yea, Ed beat me to that one.  If SLS’s flight rate really is as bad as one every other year, then it would really make no sense to upgrade to the RS-25E, but rather just have PWR produce the RS-25D at the rate of two per year using their existing facilities and methods that they used for building replacement RS-25D’s for the Shuttle fleet.  That is all still there as I understand.  Incremental changes could be made since they wouldn’t be reused probably fairly easily over time to get costs down some. 

Pah, I think switching to two RS-68A’s could work in place of the four RS-25’s, but that’s require a full redesign of the MPS on the core, as well as man-rating of the RS-68A.  I’m not sure how that’d compare to just making more RS-25D’s.  And the larger question is, there’s enough RS-25D’s for four SLS launches, but there’s enough 5-seg boosters for 10 launches.  So that means on SLS-5, if you put two RS-68’s on the core with a new MPS, can they survive the heating environment of the 5-seg SRB’s??
They –might- if they are at 90 degrees to the SRB’s, and pushed all the way out to the edge of the MPS, like the Jupiter -120 had.  With the MPS designed to allow air-flow down and around them.  With no RS-68A actually trapped under the core subjected to all of that super hot gas buildup, and the airstream would keep those gases from building up, I’ve long though that the RS-68 might be able to survive that.  I think It was the engines trapped under the diameter of the tank on the Ares V that really became the problem.  Hot gas buildup along with outer RS-68’s burning next to the inner ones, plus the hot SRB’s.  No air flow, and heatflux on all sides.  Just two outboard RS-68’s places as far away from each other, and the SRB’s as possible –could- (and I emphasize the word “could”) solve that issue on the SLS core.
If not, then RS-25D’s could continue to be made until the 5-seg’s were flown out and Advanced Liquids were adopted.  But that’s two SLS upgrades, the new boosters, plus a new MPS and man-rated RS-68.

However, hopefully, SLS’s flight rate won’t really be one every other year.  If it were to fly once a year, that gets the production rate up to four a year on the RS-25.  Not sure at what rate it makes financial sense to go to the RS-25E.  If the flight rate were to be two per year, that’s eight RS-25’s per year, and maybe that would be worth it?  If nothing else, it should get the cost per unit of the RS-25D down at that rate.

As far as the 5-seg casings go, there’s enough for 10 launches as I understand.  At that point, -something- has to be done.  And unlike the RS-25D production, the 5-seg casing production capability is gone.  So ATK either needs to re-develop that, or go do the 4-seg composite booster, which should be a drop in replacement from a dimensional and logistical standpoint.  It should be much cheaper for NASA to go that route instead of a new liquid booster.  The one thing I still have never seen, is some cost comparison for restarting 5-seg casing production, vs. starting 4-seg composite production.  If the two are even the same ballpark, I don’t see how they restart 5-seg production.  Why spend that much time and money to start making 30-year old boosters again?  Seems obvious to make the newer, higher performing boosters in that case.  If restarting the 5-seg production is a lot cheaper, then that would obviously be a consideration of going that way. 
At one launch per year, even that gives NASA 10 years to figure out which way they are going to go.  Although I still hope and thing the flight rate will be that or a bit better.  But I suppose that really depends on what new HSF architecture is finally adopted as NASA’s new official PoR.

[Hyperion5]

Do we think they are even going to go with the 105 ton/1B configuration and not skip right to 2?

We were discussing just this thing in the "How should NASA evolve the SLS?" thread.  I think the consensus is right now is NASA will evolve the SLS to the Bloc IB standard before jumping to the Bloc 2 from there.  That would require only a couple billion at most to do, versus doing that and the boosters concurrently, which would likely bust NASA's budget.  Of course a lot of things can change between now and the early 2020s, when the Bloc IB is likely to start flying.  Just look at how the Bloc 2 has changed over time.  It was first envisioned with 3 stages on the central core, one of them featuring no fewer than two J-2X engines.  The Bloc 2 SLS is now envisioned as a Bloc IB upgraded with advanced solid or liquid boosters.  I've no idea when we might see that SLS. 

It makes a lot of sense to me to base SLS evolution around the Bloc IB though.  It's got upper stage engine-out capability, it has roughly the same payload capabilities as a Saturn V, and it can be upgraded relatively quickly with new boosters.  While I'd love to get the evolving of the SLS over with as soon as possible, I do think we'll want both the upper stage upgrade of the IB and new boosters eventually.  After all, why use 30-year-old booster designs when you can have something more powerful, safer and just as cheap? 

[PahTo]

I thought base heating issues prevent the RS-68A from being used with the big SRBs (performance notwithstanding).  Wouldn't the use of LRBs "make up" for the performance issue by way of altering the burn time for the RS-68 (as well as being higher Isp than SRBs)?

Anyway, drifting off topic a bit.  I think most of us recognized when the Block 1B was announced that it would be the most likely path forward for the foreseeable future, and perhaps ever.  If we even make it that far...

I just wonder about building more of those awesome (and expensive)
RS-25Ds only to throw them in the ocean.  Such a great engine to just throw away...

Pah, I think switching to two RS-68A’s could work in place of the four RS-25’s, but that’s require a full redesign of the MPS on the core, as well as man-rating of the RS-68A. 

Going to RS-68 would mean losing a lot of payload capability.  RS-68 is a first stage engine.  The SLS core stage is a long-burn "sustainer" type stage that wants high specific impulse.  SSME ISP is 455 sec.  RS-68 is 407 sec.  The math doesn't work, unless one is willing to give up 20 or more tonnes of payload capability.

 - Ed Kyle

[Lobo]

I thought base heating issues prevent the RS-68A from being used with the big SRBs (performance notwithstanding).  Wouldn't the use of LRBs "make up" for the performance issue by way of altering the burn time for the RS-68 (as well as being higher Isp than SRBs)?

Well, as I understand it (and I can certainly be wrong!) it was the overall base heating environment under the big Ares V as it evolved.  Once it got bigger and fatter, they were putting 5 or 6 RS-68’s under it.  There’s not way you can put those under the geometry of the core without having one or more engines in the center, surrounded by burning SRB’s or other RS-68’s on all sides, which creates a lot of space for hot gases to get trapped, and not cooling air to flow over the nozzle and move the gas away.  Additionally, there’s not way to move the outer engines away from the SRB nozzle with that many engines.  So some engines need to be very close to those SRB nozzles.
If you look at Delta IV and D4H, you see how their MPS’s are tapered and have air flow over them.  A Delta IV-Medium+ (5,4) has four GEM-60 SRB’s burning close to it.  Those have thermal skirts added, but otherwise survive the SRB plumes.  Although granted, GEM-60’s are smaller than 5-seg SRB’s.  But I don’t think it’s the hot SRB plumes by themselves that created the unsuitable base heating situation with Ares V, but the totality of everything going on with those multiple engines, cavities for hot gases to get trapped, and the super hot SRB exhaust gases and heat flux.  Don’t know if it was a problem that none of the engines would survive, but at least the central engines would be in big trouble.
I don’t think it’ll ever be known, since I’m sure the NASA team working on Ares V only evaluated configurations applicable to Ares V, but I’m of the mind that if you had a two RS-68 core, with no engines under the outline of the core, and none too close to the SRB’s nozzles, and placed at 90 degrees to the SRB’s with tapered flairs so that air can move around them, that LV could perhaps be viable with ablative RS-68’s.  Basically, I think maybe a Jupiter-120 could have actually worked, where Ares V ran into problems with the different base heating environment.  A Jupiter-232 might have run into a similar problem with the central engine being trapped under the core with SRB’s or other RS-68’s burning on all sides of it. 

And that’s what I was sort of going with, with two RS-68A’s in place of the four SLS RS-25’s.  No way to know for sure, but I’d be very curious to know and see that modeled.

[Lobo]

Pah, I think switching to two RS-68A’s could work in place of the four RS-25’s, but that’s require a full redesign of the MPS on the core, as well as man-rating of the RS-68A. 

Going to RS-68 would mean losing a lot of payload capability.  RS-68 is a first stage engine.  The SLS core stage is a long-burn "sustainer" type stage that wants high specific impulse.  SSME ISP is 455 sec.  RS-68 is 407 sec.  The math doesn't work, unless one is willing to give up 20 or more tonnes of payload capability.

 - Ed Kyle

What about with RS-68R's?  It's an upgrade, but to a production engine shared with EELV's.  And as I understand, much of the design work on the RS-68R was already done?  And it wouldn't be too expensive to finish.

http://forum.nasaspaceflight.com/index.php?topic=5016.300

I can't seem to find an isp on it though to compare with RS-68 and RS-25.  Do you know what that is?  I'm assuming a decent amount better than RS-68?

[Steven Pietrobon]

According to the Direct V1 paper, RS-68 regen has a vacuum Isp of 435 s and 5% increased thrust. There was some FUD disputing that value, but this value is correct, as it assumes a design correction implemented in the RS-68A which has an Isp of 414 s.

[Lars_J]

According to the Direct V1 paper, RS-68 regen has a vacuum Isp of 435 s and 5% increased thrust. There was some FUD disputing that value, but this value is correct, as it assumes a design correction implemented in the RS-68A which has an Isp of 414 s.

How can you judge it to be correct, if the engine doesn't exist? Besides RS-68 has a history of not meeting initial ISP expectations.

[Steven Pietrobon]

Using an ISP calculation program, assuming a 6:1 oxidiser to fuel ratio, 1,488 psi (10.26 MPa) chamber pressure, expansion ratio of 21.5 and 96% efficiency for a regeneratively cooled engine, I get an Isp of 421 s. So my assumption that this value was correct is incorrect. I humbly apologise.

As to what the actual Isp value of an RS-68 regen engine is going to be, I don't really know, but it should be somewhere between 414 and 421 s. Using a value of 418 s would be a conservative estimate.

[newpylong]

Could there be another option with 5 seg SRBs and J2-X upper stage since it seems this engine is far on its way to qualification?

[Lobo]

I don’t think it’ll ever be known, since I’m sure the NASA team working on Ares V only evaluated configurations applicable to Ares V, but I’m of the mind that if you had a two RS-68 core, with no engines under the outline of the core, and none too close to the SRB’s nozzles, and placed at 90 degrees to the SRB’s with tapered flairs so that air can move around them, that LV could perhaps be viable with ablative RS-68’s.  Basically, I think maybe a Jupiter-120 could have actually worked, where Ares V ran into problems with the different base heating environment.  A Jupiter-232 might have run into a similar problem with the central engine being trapped under the core with SRB’s or other RS-68’s burning on all sides of it. 

And that’s what I was sort of going with, with two RS-68A’s in place of the four SLS RS-25’s.  No way to know for sure, but I’d be very curious to know and see that modeled.

I also notice that it looks like NASA is going with two paris of RS-25's, with each pair placed at 90 degrees to the SRB nozzles, and placed at the outter edges of the diameter of the core rather than a four engine diamond under the diameter of the core.  So even though RS-25's are regen, they might be trying to maximize airflow and minimize trapped hot gas buildup anyway. 

[Lars_J]

People keep worrying about the trapping the hot gases - But I wouldn't be surprised if the primary problem with the SRB w/ RS-68 is actually the radiant heat. Not the convection or conduction.

[Lobo]

The primary benefit of a regeneratively cooled nozzle RS-68 would be reduced weight (RS-68 is a heavy engine), with some incremental improvement in specific impulse possible, but it would never approach the efficiency of a staged combustion SSME.  Think 410-415 sec at most, IMO, though PWR once projected 418 sec as a possible design goal.

A regen RS-68 would cost more than standard RS-68 too. 

An alternative would be six or seven Vulcain 2 or J-2S type engines on the core.  They would produce as much thrust as four SSMEs at better ISP than RS-68, but without requiring the staged combustion cycle.

 - Ed Kyle

Would six J2X engines be enough to ascend the core?  I suppose their trhust at sea levelisn't that important with the 5-seg SRB's providing about 7M lbs of thrust.  I can't find a SL thrust for J2X, but it's vacuum thrust is about 20% more than J2, so I'll assume it's SL thrust is 20% more than that of J2, so we'll say it's SL is around 140Klbs.  RS-25 SL thrust is 415klbs.  So 840klbs at lift off for six J2X's, vs. 1660Klbs for the four RS-25's at lift off.  Would that be a problem?

At vacuum, it gets closer.  six J2X putting out roughly 1750Klbs vs a bit over 2000Klbs for four RS-25's. 
That's probably the more important number, once the SRB's kick off.  Is that enough to propell the rest of the stack to disposal orbit?
If so, I kinda like the concept, since J2X will be developed whether there's a need for it or not.  If three J2X engiens could be mounted in place of the two RS-25 pairs on SLS without too much headache.

Interesting concept.  Not sure if it really saves anything vs. just building more RS-25D's, or created RS-25E though, as SLS woudl be the only LV using either.  But maybe it'd get the production rate up and I'd think they'd be cheaper than the labor intensive RS-25D's, and save the new development of RS-25E's.   But if they aren't being shared with other LV's as RS-68 would, RS-25 might just be the best say to stick with. 

[Hyperion5]

The primary benefit of a regeneratively cooled nozzle RS-68 would be reduced weight (RS-68 is a heavy engine), with some incremental improvement in specific impulse possible, but it would never approach the efficiency of a staged combustion SSME.  Think 410-415 sec at most, IMO, though PWR once projected 418 sec as a possible design goal.

A regen RS-68 would cost more than standard RS-68 too. 

An alternative would be six or seven Vulcain 2 or J-2S type engines on the core.  They would produce as much thrust as four SSMEs at better ISP than RS-68, but without requiring the staged combustion cycle.

 - Ed Kyle

Would six J2X engines be enough to ascend the core?  I suppose their trhust at sea levelisn't that important with the 5-seg SRB's providing about 7M lbs of thrust.  I can't find a SL thrust for J2X, but it's vacuum thrust is about 20% more than J2, so I'll assume it's SL thrust is 20% more than that of J2, so we'll say it's SL is around 140Klbs.  RS-25 SL thrust is 415klbs.  So 840klbs at lift off for six J2X's, vs. 1660Klbs for the four RS-25's at lift off.  Would that be a problem?

Vacuum thrust is about 15% more than a J-2S, and and almost 27% more than a mere J-2.  I'd guess that sea level thrust would be around 80-85% of that of a J-2X's vacuum thrust based on extrapolating from other hydrolox engines.  Based on that I'd say you're way under-estimating the thrust--it should be closer to 1400 klbs at liftoff and probably a bit more than that.  I would point out however that such a job isn't what the J-2X was designed to handle.  I don't think SRBs being in the vicinity was what the designers of the J-2X had in mind when they designed the engine.  Surely there would be some issues, though probably not as bad as with RS-68 engines. 

Btw, I saw one planned upgrade of the Saturn V would have seen its S-II stage featuring a maximum of seven J-2 engines.  That would've made any Saturn II incredibly feasible had they upgraded the engines and stretched the stage.  Sadly for us, we're working with the more modest core proportions of the SLS, not the Saturn V, otherwise I'd say this might be a direction worth exploring more. 

At vacuum, it gets closer.  six J2X putting out roughly 1750Klbs vs a bit over 2000Klbs for four RS-25's. 
That's probably the more important number, once the SRB's kick off.  Is that enough to propell the rest of the stack to disposal orbit?
If so, I kinda like the concept, since J2X will be developed whether there's a need for it or not.  If three J2X engiens could be mounted in place of the two RS-25 pairs on SLS without too much headache.

Interesting concept.  Not sure if it really saves anything vs. just building more RS-25D's, or created RS-25E though, as SLS woudl be the only LV using either.  But maybe it'd get the production rate up and I'd think they'd be cheaper than the labor intensive RS-25D's, and save the new development of RS-25E's.   But if they aren't being shared with other LV's as RS-68 would, RS-25 might just be the best say to stick with. 

Lobo, I do think you're focusing on the wrong area to really improve the SLS Bloc IB's costs.  Rather than re-engining the core stage, which might cause all sorts of issues, I'd be looking much more at booster and especially upper stage upgrades.  I know RS-25 engines are not cheap, but they're also a known quantity in that role, which is more than I can say for the J-2X.  Who knows how much you'd have to re-design to handle replacing the Rs-25 engines on the core stage. 

If you want to get SLS costs down, going to cheaper advanced boosters (either advanced SRBs or LRBs) would surely help.  So too would upgrading to the USAF's next-gen upper stage engine.  If you gave the SLS an upper stage upgrade with seven next-gen engines, you could create some serious economies of scale from only a 1-2 flights of the SLS per year.  After all, one SLS flight would then be the equivalent of launching seven Atlas or Delta rockets for whatever firm was building those engines.  That in turn would spread fixed costs over more engines, which would benefit both the Air Force's costs.  I'd also mention that RS-25 production may not be as costly as you might assume.  Back when PWR had RS-25 contracts for the Shuttle, they were charging far less for RL-10 engines because they could spread their costs over more engines.  We might see a repeat of that if SLS can launch at least once a year. 

[Lobo]

Lobo, I do think you're focusing on the wrong area to really improve the SLS Bloc IB's costs.  Rather than re-engining the core stage, which might cause all sorts of issues, I'd be looking much more at booster and especially upper stage upgrades.  I know RS-25 engines are not cheap, but they're also a known quantity in that role, which is more than I can say for the J-2X.  Who knows how much you'd have to re-design to handle replacing the Rs-25 engines on the core stage. 

I know, which is why I said:

Interesting concept.  Not sure if it really saves anything vs. just building more RS-25D's, or created RS-25E though, as SLS would be the only LV using either. 

It was just an intellectual thread that I was tugging on.   Unless something else is using J2X then you are basically in the same boat as RS-25D.   Unless the costs were –much- cheaper, as to make the MPS redesign have a reasonable payback time scale.  That, I don’t know.  But I doubt it would be an improvement enough to make it worth the effort.
Interesting though.

[Vahe231991]

I know that this thread is a decade old, but I just noticed that the SLS Block 1B intended for the Artemis 4 mission will use the RS-25D for the core stage engines whereas the Block 1B rockets earmarked for the Artemis 5, 6, 7, and 8 missions will feature RS-25E core stage engines. How does the specific impulse of the RS-25E compare with that of the RS-25D? Does NASA intend to make a decision on which Artemis missions involving the Block 1B will carry cargo?

[FutureSpaceTourist]

https://twitter.com/nasaoig/status/1693691882763649084

Our audit will examine NASA’s management of the next iteration of its Space Launch System heavy-lift rocket known as Block 1B.

This complex and expensive endeavor seeks to use a significantly more powerful upper stage for transporting greater payloads to the Moon.

[Hog]

I know that this thread is a decade old, but I just noticed that the SLS Block 1B intended for the Artemis 4 mission will use the RS-25D for the core stage engines whereas the Block 1B rockets earmarked for the Artemis 5, 6, 7, and 8 missions will feature RS-25E core stage engines. How does the specific impulse of the RS-25E compare with that of the RS-25D? Does NASA intend to make a decision on which Artemis missions involving the Block 1B will carry cargo?

Specific Impulse differences between the SSME/RS-25D(Heritage), SSME/RS25D setup for SLS(Adaptation) and the Production Restart(Expendable SLS Main Engine).

[FutureSpaceTourist]

https://twitter.com/nasa_marshall/status/1721988663775486113

Teams at #NASAMichoud recently completed a major portion of a weld confidence article for the advanced upper stage of @NASA_SLS.

SLS will evolve to its more powerful Block 1B configuration with the advanced upper stage beginning with #Artemis IV.

MORE >>

https://www.nasa.gov/image-article/early-production-continues-on-advanced-upper-stage-for-nasa-moon-rocket/

Early Production Continues on Advanced Upper Stage for NASA Moon Rocket

Lee Mohon
NOV 03, 2023

Technicians at NASA’s Michoud Assembly Facility in New Orleans have completed a major portion of a weld confidence article for the advanced upper stage of NASA’s SLS (Space Launch System) rocket. The hardware was rotated to a horizontal position and moved to another part of the facility Oct. 24.

The weld confidence article forms part of the liquid oxygen tank for the SLS rocket’s exploration upper stage and is the fifth of seven weld confidence articles engineers are manufacturing for the evolved SLS Block 1B configuration of the SLS rocket. Beginning with Artemis IV, SLS will evolve to its more powerful Block 1B configuration with the advanced upper stage that gives the rocket the capability to launch 40% more to the Moon along with Artemis astronauts inside NASA’s Orion spacecraft.

Teams use weld confidence articles to verify welding procedures, interfaces between the tooling and hardware, and structural integrity of the welds. The dome of the liquid oxygen tank weld confidence article was first welded to its structural ring at NASA’s Marshall Space Flight Center in Huntsville, Alabama, using friction stir welding tooling. The hardware was transported to Michoud, where Michoud crews in the Liquid Oxygen Tank Assembly Center (LTAC) finished welding the hardware. Marshall and Michoud engineers simultaneously conducted testing and analysis on the hardware to validate welding parameters.

In tandem, NASA and Boeing, the SLS lead contractor for the core stage and exploration upper stage, are producing structural test articles and flight hardware structures for the upper stage at Marshall and Michoud.

NASA is working to land the first woman and first person of color on the Moon under Artemis. SLS is part of NASA’s backbone for deep space exploration, along with Orion and the Gateway in orbit around the Moon, and commercial human landing systems. SLS is the only rocket that can send Orion, astronauts, and supplies to the Moon in a single mission.

For more on NASA SLS visit:

https://www.nasa.gov/humans-in-space/space-launch-system/