Author Topic: Space Launch System (SLS) Q&A  (Read 14983 times)

Offline mcdouble

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Re: Space Launch System (SLS) Q&A
« Reply #20 on: 04/08/2017 06:24 AM »
Is the configuration of SLS/Ares V (large hydrolox core with large solid boosters) mostly a result of the need to use existing shuttle infrastructure, or is it a reasonable HLV design in it's own right?

I have been reading various threads on this site about possible timelines in which the shuttle had not been developed, and instead there had been a continuation of Saturn IB or the various INT proposals, building Skylab style stations in LEO etc. What I'm wondering is, in such a timeline if NASA were to want to develop a new HLV, would they ever consider something like SLS? Or would it make more sense to just start making Saturn Vs again?

I would assume a lot would depend on exactly what infrastructure was in place, so if F-1 and J-2 engines were already being produced, Saturn V would seem like a better idea than developing huge new SRBs and powerful hydrolox engines like the RS-25 or RS-68. But let's assume that those engines are available, (or maybe 4xUA1207s could be used instead of Shuttle SRBs etc), would there be any reason to favour one design over the other?

Sorry for the convoluted nature of this question, I guess what I'd really like to know is how much of the SLS design is based on the political necessity of using Shuttle technology and how much is it an actual good solution, all other things being equal?

Offline Proponent

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Re: Space Launch System (SLS) Q&A
« Reply #21 on: 04/08/2017 03:03 PM »
NASA considered Saturn-like HLVs during the requirements analysis cycle (RAC); snoop around, and you'll find lots of discussions about that on this site.  There were three separate efforts, RAC-1, looking at Shuttle-derived HLVs, RAC-2 for Saturn-like HLVs, and RAC-3 for "modular" HLVs, i.e., those using multiple small-diameter cores tied together, like a Falcon Heavy on steroids.

NASA found that while RAC-1 designs had lower development costs, RAC-2 vehicles had better economics in the long run, if I remember correctly.  RAC-3 designs, each involving multiple independent cores and numerous separation events, were found to be insufficiently reliable and powerful.  (By the way, it's a common misunderstanding that the RAC-3 designs were evolved EELVs: they were not).

So, I think the answer is that an SLS-like design results from the desire to use Shuttle infrastructure.

It seems to me that a basic problem with the core-plus-boosters style (e.g., SLS) is that, because the core is carried virtually all the way to orbit, maximum performance is critical.  It is crucial that it be as light as possible and that its engines function efficiently both at sea level and in a vacuum.  Every extra kilogram on the core is a kilogram of payload lost.  That may not be so bad, at least in the long run, for a reusable system, but if you throw the core away on each flight it makes for poor economics.  With a classic two-stages-to-orbit design, on the other hand, a kilogram of extra mass on the first stage might take only 0.1 kg off the payload to orbit.  Performance is not so crucial, and there ought to be more scope for making things cheaper.  A while ago, I took a stab at demonstrating this quantitatively.

Aside from the Shuttle and its offspring, SLS, the only other rocket I can think of that carried its core to orbit is Energia.  It too was designed to carry a shuttle.

EDIT:  The original stage-and-a-half Atlas carried its core all the way to orbit as well.  That design was driven by a USAF requirement in the early 1950s that all engines be ignited on the ground.
« Last Edit: 04/15/2017 12:34 PM by Proponent »

Offline baldusi

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Re: Space Launch System (SLS) Q&A
« Reply #22 on: 04/17/2017 03:42 PM »
Sputnik rocket (8K74PS) also ignited everything at launch. Originally air lighting an engine was not trivial (still isn't) and ground lit was the safest choice. Just look at the Molnyia rocket issues with the upper stage.

Offline edkyle99

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Re: Space Launch System (SLS) Q&A
« Reply #23 on: 04/18/2017 10:24 PM »
Is the configuration of SLS/Ares V (large hydrolox core with large solid boosters) mostly a result of the need to use existing shuttle infrastructure, or is it a reasonable HLV design in it's own right?
SLS is the design you end up with when you start with RS-25 engines.  They are such high-performers that the optimum design wants them to burn a lot of propellant.  High-thrust boosters are needed to get the resulting "sustainer" stage started. 

If NASA didn't have a stockpile of RS-25 engines, it wouldn't have developed SLS.  As Proponent mentioned, the RAC-2 kerosene/LOX designs had lower long-term costs, but, critically, they would have cost more to develop because the needed engines didn't exist.  RS-25 did exist.  Thus SLS.

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Offline Space Ghost 1962

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Re: Space Launch System (SLS) Q&A
« Reply #24 on: 04/19/2017 12:47 AM »
Is the configuration of SLS/Ares V (large hydrolox core with large solid boosters) mostly a result of the need to use existing shuttle infrastructure, or is it a reasonable HLV design in it's own right?
... the RAC-2 kerosene/LOX designs had lower long-term costs, but, critically, they would have cost more to develop because the needed engines didn't exist.
... and Aerojet/Rocketdyne, the maker of the RS-25, is building AR-1, at government expense, which was one of the "needed engines", that will soon exist ... and might not have a use.

We've come full circle.  ::)

Offline ArbitraryConstant

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Re: Space Launch System (SLS) Q&A
« Reply #25 on: 04/19/2017 02:19 AM »
SLS is the design you end up with when you start with RS-25 engines.  They are such high-performers that the optimum design wants them to burn a lot of propellant.  High-thrust boosters are needed to get the resulting "sustainer" stage started.
Wouldn't it make quite a good upper stage engine for an HLV? More than double the thrust of J-2 used on Saturn V, and 30s better ISP.

Offline DaveS

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Re: Space Launch System (SLS) Q&A
« Reply #26 on: 04/19/2017 02:44 AM »
SLS is the design you end up with when you start with RS-25 engines.  They are such high-performers that the optimum design wants them to burn a lot of propellant.  High-thrust boosters are needed to get the resulting "sustainer" stage started.
Wouldn't it make quite a good upper stage engine for an HLV? More than double the thrust of J-2 used on Saturn V, and 30s better ISP.
Unlike the J-2, the SSME is a booster engine as it can't be air-started. It relies very much on GSE to be kept inside its start-box of temperatures and pressures. NASA found this out a decade ago when they wanted a common upper-stage engine for the Ares 1 and Ares 5. When they lost the SSME, they were forced into an expensive redesign of Ares 1 from its intended 4-segment RSRM/SSME US design to the 5-segment SRB/J-2X US we now know.
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Re: Space Launch System (SLS) Q&A
« Reply #27 on: 04/19/2017 03:20 AM »
SLS is the design you end up with when you start with RS-25 engines.  They are such high-performers that the optimum design wants them to burn a lot of propellant.  High-thrust boosters are needed to get the resulting "sustainer" stage started.
Wouldn't it make quite a good upper stage engine for an HLV? More than double the thrust of J-2 used on Saturn V, and 30s better ISP.
Cannot be airstarted without an expensive, major redesign.
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Offline ArbitraryConstant

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Re: Space Launch System (SLS) Q&A
« Reply #28 on: 04/19/2017 03:35 AM »
SLS is the design you end up with when you start with RS-25 engines.  They are such high-performers that the optimum design wants them to burn a lot of propellant.  High-thrust boosters are needed to get the resulting "sustainer" stage started.
Wouldn't it make quite a good upper stage engine for an HLV? More than double the thrust of J-2 used on Saturn V, and 30s better ISP.
Cannot be airstarted without an expensive, major redesign.
Ah cheers. I guess that also contributes how it lends itself to being used as a sustainer engine.

Offline baldusi

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Re: Space Launch System (SLS) Q&A
« Reply #29 on: 04/19/2017 12:17 PM »
Is the configuration of SLS/Ares V (large hydrolox core with large solid boosters) mostly a result of the need to use existing shuttle infrastructure, or is it a reasonable HLV design in it's own right?
... the RAC-2 kerosene/LOX designs had lower long-term costs, but, critically, they would have cost more to develop because the needed engines didn't exist.
... and Aerojet/Rocketdyne, the maker of the RS-25, is building AR-1, at government expense, which was one of the "needed engines", that will soon exist ... and might not have a use.

We've come full circle.  ::)

They wouldn't have passed the NASA's reliability requirements, which put too much emphasis on the turbopumps and number of nozzles. Thus, Even the RD-180 was considered completely unsafe if used on big numbers. But solids were OK since they are so simple, right?
All part of the thumbs in the scale that SLS RAC process was. The only engine that might have passed their "safety" requirements were the F-1B. The AR-500 (as was called at that time) most surely wouldn't.
And yes, I have an issue of claiming ridiculous safety levels and then killing the effective numbers with requirement creep and stack complexity. I'm on the KISS fence.

Offline Space Ghost 1962

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Re: Space Launch System (SLS) Q&A
« Reply #30 on: 04/19/2017 06:59 PM »
Is the configuration of SLS/Ares V (large hydrolox core with large solid boosters) mostly a result of the need to use existing shuttle infrastructure, or is it a reasonable HLV design in it's own right?
... the RAC-2 kerosene/LOX designs had lower long-term costs, but, critically, they would have cost more to develop because the needed engines didn't exist.
... and Aerojet/Rocketdyne, the maker of the RS-25, is building AR-1, at government expense, which was one of the "needed engines", that will soon exist ... and might not have a use.

We've come full circle.  ::)

They wouldn't have passed the NASA's reliability requirements, which put too much emphasis on the turbopumps and number of nozzles.
And that will look moronic in a very short while. Sort of like counting rivets in a submarine ...

Quote
Thus, Even the RD-180 was considered completely unsafe if used on big numbers.
Even given Energia's 4x RD-170 ...  ::)

Quote
But solids were OK since they are so simple, right?
Politically they are extremely simple - binary. "You want SLS?  Yes or no".

Quote
All part of the thumbs in the scale that SLS RAC process was.

The only point of RAC was thumbs on scale. For political "cover". IMHO, ULA "assisted" in this stupidity with RAC-2. A particular sore point with me.

Quote
The only engine that might have passed their "safety" requirements were the F-1B. The AR-500 (as was called at that time) most surely wouldn't.
Unlikely as well. The closer F-1A/B got to practicality, the more opposition and political nonsense grew. (I think there was an even earlier name for it than AR-500 too.)

Quote
And yes, I have an issue of claiming ridiculous safety levels and then killing the effective numbers with requirement creep and stack complexity.
You meant to say "unachievable safety levels" that can be withdrawn when they need to be achieved. As with CC.

It wouldn't be a govt LV if it didn't have creep and complexity. Or perhaps "creeps" ... but I digress.

Quote
I'm on the KISS fence.
There's nothing KISS about SHLV.

Offline incoming

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Re: Space Launch System (SLS) Q&A
« Reply #31 on: 05/25/2017 01:59 PM »
A couple of points on this thread.

Earlier there was a point by proponent about other rockets that take their core stage almost to "orbit."  i don't think it's a crticial point to this thread but Arianne 5 has a similar set up and flies a similar profile, and its been an extremely successful commercial vehicle.

Also, going back to the RAC decision, the reason the shuttle derived approach won out despite the superior long term economics of a clean sheet or saturn based kerolox booster was that schedule was considered to be paramount.  IIRC the shuttle derived systems was estimated to be available at least 2 years earlier, if for no other reason because they could skip the competitive procurement process and JOFOC the work to existing contractors. 

At the time NASA was facing a growing realization after so many cancelled efforts that lifecycle cost "doesn't matter" - gov't funding profiles and year-to-year appropriations never allow for the kinds of funding peaks and long term decision-making that lead to efficiency in long term programs, so they decided instead to go for the option that got the nearest term success (equating that to political sustainability) and could be executed under a flat budget profile (political reality). 

Shuttle derived was the only solution that fit that criteria.

Offline envy887

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Re: Space Launch System (SLS) Q&A
« Reply #32 on: 05/25/2017 03:10 PM »
...
At the time NASA was facing a growing realization after so many cancelled efforts that lifecycle cost "doesn't matter" - gov't funding profiles and year-to-year appropriations never allow for the kinds of funding peaks and long term decision-making that lead to efficiency in long term programs, so they decided instead to go for the option that got the nearest term success (equating that to political sustainability) and could be executed under a flat budget profile (political reality). Shuttle derived was the only solution that fit that criteria.

SLS is more Constellation-derived than Shuttle-derived. If schedule was really paramount, a DIRECT-like solution would have been faster to launch. We'd still be waiting on Orion though...

Offline Hog

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Re: Space Launch System (SLS) Q&A
« Reply #33 on: 05/27/2017 06:08 PM »
  Seeing that Project Constellation was looking at 6 RS-68 engines for the core, which would have been less expensive and more powerful than RS-25, how did SLS get to looking at 4-6 RS-25 engines?
Was it merely ablative(RS-68) vs. regenerative nozzle(RS-25) cooling?

Thank you In Advance.
Paul

Offline RonM

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Re: Space Launch System (SLS) Q&A
« Reply #34 on: 05/27/2017 09:26 PM »
  Seeing that Project Constellation was looking at 6 RS-68 engines for the core, which would have been less expensive and more powerful than RS-25, how did SLS get to looking at 4-6 RS-25 engines?
Was it merely ablative(RS-68) vs. regenerative nozzle(RS-25) cooling?

Thank you In Advance.

Being able to use RS-25 engines leftover from the STS program helps keep the cost down on the first four flights.

Offline brickmack

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Re: Space Launch System (SLS) Q&A
« Reply #35 on: 05/28/2017 01:53 AM »
  Seeing that Project Constellation was looking at 6 RS-68 engines for the core, which would have been less expensive and more powerful than RS-25, how did SLS get to looking at 4-6 RS-25 engines?
Was it merely ablative(RS-68) vs. regenerative nozzle(RS-25) cooling?

Thank you In Advance.

Regen cooling and manrating were both big issues that would require a new RS-68 variant. Other major problem at the system level though is RS-68s crap ISP. This is why Ares V had to balloon so much once they switched from RS-25 to RS-68B, the lower performance means you gotta make the core stage way bigger to have the same effect (which also means you need to add more engines, even with RS-68s higher thrust, and the boosters have to be bigger to get it all off the ground). New engine development+more engines per flight+larger tanks+larger boosters+(likely) more complex ground equipment upgrades=more money

Offline envy887

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Re: Space Launch System (SLS) Q&A
« Reply #36 on: 05/30/2017 02:49 PM »
  Seeing that Project Constellation was looking at 6 RS-68 engines for the core, which would have been less expensive and more powerful than RS-25, how did SLS get to looking at 4-6 RS-25 engines?
Was it merely ablative(RS-68) vs. regenerative nozzle(RS-25) cooling?

Thank you In Advance.

As noted above, RS-68 would require some changes, although man-rating wouldn't be needed for Ares V.

The real reason Ares V needed 6 uprated RS-68 was that it's payload dwarfed anything SLS will lift. It was designed to put almost triple the mass of a SLS Block 1 payload to TLI. and almost double SLS Block 1B.

Offline Hog

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Re: Space Launch System (SLS) Q&A
« Reply #37 on: 05/31/2017 09:12 PM »
  Seeing that Project Constellation was looking at 6 RS-68 engines for the core, which would have been less expensive and more powerful than RS-25, how did SLS get to looking at 4-6 RS-25 engines?
Was it merely ablative(RS-68) vs. regenerative nozzle(RS-25) cooling?

Thank you In Advance.

As noted above, RS-68 would require some changes, although man-rating wouldn't be needed for Ares V.

The real reason Ares V needed 6 uprated RS-68 was that it's payload dwarfed anything SLS will lift. It was designed to put almost triple the mass of a SLS Block 1 payload to TLI. and almost double SLS Block 1B.

Thank you, I didn't realize there was such a designed payload difference between the various versions SLS and Ares V.

Just a quick search reveals my ignorance.
LEO
SLS=70-130 tonnes
Ares V= 188 metric tons
Saturn V= 140 mt

TLI
SLS= Block 1 25.3 mt Block 1-B 39.2 mt
Ares V= 60.6 mt   or 71.1mt
Saturn V=48.6


SLS Block 1 TLI payload was from this paper. The Space Launch System Capabilities for Beyond Earth Missions
http://www.spacepropulsion.org/uploads/2/5/3/9/25392309/spaceaccess2014-25.pdf
The rest were from Wikipedia

The 5.5 segment SRBs were also an interesting idea.

The attached diagram is one that I hadn't yet experienced. It compares Saturn-V, STS, Ares-I (The Stick), Ares 5, Ares-IV, SLS-Block-1 and SLS Block-2.

Paul

Offline Hog

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Re: Space Launch System (SLS) Q&A
« Reply #38 on: 08/05/2017 11:29 AM »
1)Is there any plans to modify a 2nd MLP for SLS use?
I believe I just read one of the excellent NSF articles and the limiting factor of SLS flight rate comes down to a single available MLP.

2) During STS launches, the exhaust from the solid and liquid engines went in opposite directions (North/South).  Am I correct with my understanding that for SLS launches, the MLP and pad are designed for both the Solid and Liquid engines exhaust will be deflected in one direction only?
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

All the recent SLS reporting on SLS activity such as MLPs, RS25 tests, engine controller tests, MLP/Crawler Transport and LOX/LH2 contracting etc etc is really piquing my excitement for SLS.

I'm so ready for a "Green Run" hotfire test of the SLS core with 4 RS25's a blazing!
Go NASA go!
Paul

Offline brickmack

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Re: Space Launch System (SLS) Q&A
« Reply #39 on: 08/07/2017 01:55 AM »
1. None official, but its been considered. Doesn't really seem to make much sense. Once SLS is operational, the existing ML should be sufficient for about 3 flights a year, but production capability only exists for at most 2 (Michoud can build 2 cores a year, but Aerojet can seemingly only build 1 set of flight engines every 2 years), so on that front its unnecessary. The one thing a second ML would be good for is eliminating the minimum 3-ish year downtime between EM-1 and 2, necessary for refits for the larger upper stage on SLS 1B. But considering how long is takes to build a new ML (and the 3 shuttle era ones aren't suitable), they're probably past the point where this would result in any noteworthy schedule gain

2. Yes, all exhaust is routed in a single direction for the new 39B

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