Author Topic: NASA defends decision to restart RS-25 production, rejects alternatives  (Read 84745 times)

Offline Space Ghost 1962

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If you had to have an alternative (ignoring political necessities):

The first that comes to mind with SLS is to start with it's RSRBV boosters - not so much anything as that they limit the payload growth of the SLS core for various reasons (GTOW, core mass fraction to name a few).

If you accept as a given that SX can get to the reliability and economics of recoverable boosters, you reformulate SLS as like the EELV's/FH from the bottom to accept two pairs of two recoverable (or not) F9 cores. Block 5 cores should allow a significant advantage here (including with base heating, meaning more engine options for the core).

Either add RS-25's (continuing production) or substitute RS68A's (still flying them on DIVH) and restructure the flight profile to accept higher acceleration than HSF. You could exceed 250+t this way, and have a vehicle that could be flying for more than a decade. Marshall definitely could do this.

So your missions to build the DSG would be fewer/faster, and your mission architecture would be to logistically support lunar/Mars missions from DSG assembled vehicles, mission modules, and consumables.

Online spacenut

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How much would it cost to replace the 4 RS-25 engines with about 16 BE-3's that are used on the New Shepard?  Also, don't know if it would work, but with a second stage, the core might could return and land to save it. 

Offline Space Ghost 1962

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If you could stage significantly higher/faster with kerolox boosters/less GTOW/better core mass fraction, and if the expansion ratio of the nozzles were greater, 18 BE-3U's (if they fit/thermal issues too) might get you to 140-150t out performing the 4 RS 25s hands down. A lot harder to compete with the 5-6 RS-25's.

But no one at Marshall would feel comfortable suggesting so many engines. Although it's an excellent suggestion, especially for budget.

Online spacenut

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Even the proposed new Raptors and switching to metholox on the core with an upper stage would get more to LEO and probably cheaper.  Would only take 8 of the sub scale ones.  NASA launched Saturn IB with 8. 

Online Chris Bergin

Even the proposed new Raptors and switching to metholox on the core with an upper stage would get more to LEO and probably cheaper.  Would only take 8 of the sub scale ones.  NASA launched Saturn IB with 8. 

Problem is, let's be you for a moment, turning up at NASA HQ with your suggestion. I think it'll help add some humorous context to many other "But SpaceX?" posts we see on here. ;)

"Hey NASA. So that SLS *cough* PORK *cough*, sorry, I've got a cold. Anyway, yes, that rocket using proven reliable and hardware of the ET and RS-25. Have any of you considered using an engine that's not actually real yet (there's a demonstrator at McGregor, so that counts, right?) I know RS-25 has 30 years of experience and only one issue in its lifetime, but Raptor....it's SpaceX!! You know, the cool guys!

"PS You'll also need to completely change the core as it's not LH2/LOX and it'll cost you billions to change it all, but the engine itself will be cheaper. #Economics

"Anyway, you can thank me later! Oh, but there's another person outside with his own suggestion of taking 16 of those engines uses on a suborbital test flight instead. Shall I let him in? PS Why are you all laughing?"

SLS has had - and is still having - its schedule and development issues, but if anyone thinks SpaceX and so on aren't, check out Falcon Heavy and watch how fast lawmakers would pull the plug on a NASA purchased SpaceX SHLV if Elon said "it'll be a result if we don't blow up and wreck the pad".

PS If they cancelled SLS today, don't think it'll be a check to SpaceX tomorrow. If and only if lawmakers opted to redirect SLS money (which I also doubt, it'd likely just be removed from the NASA budget), it would only be after years of paying off the contract cancellations at Boeing and co.

Online oldAtlas_Eguy

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Hey Chris, I thought this was a discussion about the RS25 new build. Although I do appreciate the realistic perspective being expresses, because as actually working on the government side (AF actually) on STS inertia and other things makes it impossible for programs to switch horse late in the rac unless there is no alternativ.

Offline Hog

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Hey Chris, I thought this was a discussion about the RS25 new build. Although I do appreciate the realistic perspective being expresses, because as actually working on the government side (AF actually) on STS inertia and other things makes it impossible for programs to switch horse late in the rac unless there is no alternativ.

Are you implying that the 30 years of operational experience, and over 40 years including over 1 million seconds of test stand hotfire experience is NOT applicable to an RS25 engine that has had some of its internals that were designed for reusability substituted for parts that are designed for "single use disposability"/lower cost?


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I am really starting to become annoyed with AR(Aerojet Rocketdyne)/NASAs decision to drop the RS25-A, RS25-B, RS-25-C, RS25-D, RS25-E designations, even if these designations weren't in actual internal usage.  Even Phase 1, Phase 2, Block 1, Block 1-A, Block II-A and Block II(RS25-D-final flown configuration of SSME) descriptors of RS25 are far easier to manage than the new "crop" of RS25 designators such as: "old build" "new build", "re-useable" "non-reusable", "legacy", "older more expensive units", newer "less expensive" units.  I'm sure there was some financial, corporate or political reason for referring to an RS25 engine as an RS25 engine regardless of its exact makeup.  I guess this annoyance will clear itself up after EM-4 after the last RS-25D drops into the saline abyss.  Thus we are left with only SLSME type RS-25s in the lineup.
Paul

Online Chris Bergin

Hey Chris, I thought this was a discussion about the RS25 new build. Although I do appreciate the realistic perspective being expresses, because as actually working on the government side (AF actually) on STS inertia and other things makes it impossible for programs to switch horse late in the rac unless there is no alternativ.

New build is even better. RS-25D to RS-25E means it's far cheaper, but all with that lovely reliability.

Offline Space Ghost 1962

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Hey Chris, I thought this was a discussion about the RS25 new build. Although I do appreciate the realistic perspective being expresses, because as actually working on the government side (AF actually) on STS inertia and other things makes it impossible for programs to switch horse late in the rac unless there is no alternativ.

Are you implying that the 30 years of operational experience, and over 40 years including over 1 million seconds of test stand hotfire experience is NOT applicable to an RS25 engine that has had some of its internals that were designed for reusability substituted for parts that are designed for "single use disposability"/lower cost?


Shuttle reused them frequently. SLS one time use only. Applying RLV flight history to ELV engine development "informs" but does not "assure" on refinement.

Now, what specific target are we shooting for? SSME is a very complex beast. You just can't wave a wand and magically make it cheaper. What performance levels are required? Uprating? Greater margins for HSF than prior Shuttle ones, because we want to lower our LOC/LOM numbers too?

How much are we allowed to change the engine's physical geometry/size (much of the issues were in making a compact, ground start engine for a spaceplane application). How about the feed lines, can we change them too? Can we use electrical instead of hydraulic in certain places? Can we use new materials that will last 1-2 times instead of 30+?

Can we eliminate whole portions of the design that might sacrifice 2-15 sec-1 of iSP?

Now, we take all of that and run it on the test stand and compare numbers? Can we prove we've met requirements and retained acceptable reliability? Tall order.

Quote
I am really starting to become annoyed with AR(Aerojet Rocketdyne)/NASAs decision to drop the RS25-A, RS25-B, RS-25-C, RS25-D, RS25-E ... Thus we are left with only SLSME type RS-25s in the lineup.
I take it you weren't a fan of "New Coca Cola" either  ;D

Many at AR also are similarly annoyed. Yes, it's a great, historic engine. Yes, it taught us all a lot.

Is it (or J-2X even) the right place to start from? Shuttle derived meant to carry the "development momentum" and the "industry base" into CxP/SLS, which seemed possible for a "quick" program post Shuttle.

Now that is less clear. But we seem to be committed. It is unclear what we are committed too though.

Hey Chris, I thought this was a discussion about the RS25 new build. Although I do appreciate the realistic perspective being expresses, because as actually working on the government side (AF actually) on STS inertia and other things makes it impossible for programs to switch horse late in the rac unless there is no alternativ.

New build is even better. RS-25D to RS-25E means it's far cheaper, but all with that lovely reliability.

Both are in doubt. It's been too long. Don't count your chickens ...

add:
Oh, and I forgot about the engine controller changes to optimize 4/5/6 engine clusters over the current "3".
« Last Edit: 07/31/2017 09:06 PM by Space Ghost 1962 »

Offline Propylox

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New build is even better. RS-25D to RS-25E means it's far cheaper, but all with that lovely reliability.
To pull 25D out of the shed and build up 25E production capacity costed around $70mil/engine ($1.18bil / 16engines) and the new 25E will also cost about the same ($413mil / 6engines, 4flying) compared to RS-68 at around $20mil/engine and fewer per core compared to 25s.

There is no such alternative, if it includes RS-68.  RS-68 and SRB are not viable, much like air start SSME.
Jim, You're very knowledgeable, but mistaken here. RS-68 and SRB is an engineering challenge, not an impossibility. NASA's conclusion was regen at around $150mil in development and doubling the unit cost. I disagree with messing up an inexpensive, robust and impeccably-reliable engine and instead previously outlined a boattail that puts existing 68s in a more benign environment then they have under Delta IV. I'm sure there's other options, possibly some better, to address this engineering problem. -- Boattail post;
https://forum.nasaspaceflight.com/index.php?topic=38069.msg1706197#msg1706197
« Last Edit: 08/01/2017 07:02 AM by Propylox »

Online Chris Bergin

Ironically, Ares V switched back to RS-25s after they conducted a study on RS-68s with Ares V and showed it struggled. They went as far as six RS-68s and two 5.5 SRBs for Ares V after five RS-68s and two five seg SRBs couldn't lift Altair on Lunar missions.

Wrote an article in 2008 on it. Article is several CMS's ago so looks messy, best to just copy and paste it:

Quote
The previous Ares V baseline was a 10 meter core, powered by 5 RS-68 engines from the Delta IV vehicle – flanked by two 5.0 segment Solid Rocket Boosters as to be used on the Ares I’s First Stage. The J-2X powered Upper Stage had already changed from 8.4 meters in diameter to a 10 meter stage, flush with the Core Stage.

However, the earlier Ares-V configuration has been suffering from an inability to close the performance requirements for being able to heavy lift the four-man Altair Lunar Lander being planned. With Ares I lifting the Orion spacecraft, the Ares-V needs to push 75.1 mT of payload through Trans-Lunar Injection (TLI) but was only able to push 64.6 mT.

This new more powerful configuration, identified as the ‘LV 51.00.48’ is now able to put 71.1 mT through TLI. While this configuration still can not reach its targets, this is a clear improvement towards closing the performance requirements NASA has for the Lunar architecture.

Each new reusable 5.5 segment SRB, will contain over 1.5 million pounds of propellant which will produce a peak of 3,774,000 million lbs of thrust and will have a vacuum Isp of 275.5 seconds. The 38 percent larger SRB’s will burn for 116 seconds – a full 8 seconds shorter burn time than Space Shuttle – before being jettisoned.

They feature a new ‘333-07 Trace’ PBAN solid propellant mix derived from that currently used by the Shuttle, although there is still the option to go to a new HTPB mix if the trade studies are favorable.

To accommodate the new lengthened boosters, the Liquid Hydrogen Tank on the Core Stage has been stretched by 190.3”. Together with a proportional stretch to the Liquid Oxygen Tank this growth puts the new baseline vehicle at 381.1 ft tall – nearly 20 feet taller than the old baseline.

To save weight, this version of Ares V assumes all non-pressurized structures on the Core Stage will be built out of new IM7 composite materials instead of more traditional Aluminum-Lithium alloy.

The 6 RS-68 engines powering the Core will fly at 108 percent power levels (6 percent higher than used on Delta-IV currently) and will each produce 702,055 lbs of thrust and have an Isp of 365 seconds at sea level and will have 797,000 lb of thrust and will have an Isp of 414 seconds in a vacuum.

Total expected burn time for the Core will be 303 seconds and the 6 main engines will produce a maximum of 4.17G during the launch. The EDS will likewise be constructed out of mostly composite materials.

The J-2X engine will burn at the 100 percent power level for the orbital insertion burn, but will burn at the 81 percent power level for TLI. The reduced thrust optimizes the Isp for the mass-critical TLI burn. The insertion altitude has been raised from 120 nmi to 131.5 nmi circular.

Total roll out weight with the crawler and the MLP (Mobile Launch Platform) will be approximately 18 million lbs, which exceeds the capability of the existing crawlerway rated for 16.8 million lbs. The ability for Ares V to remain within its budget targets is now considered a 4ื4 risk on the standard 5ื5 risk matrix.
« Last Edit: 08/01/2017 01:03 PM by Chris Bergin »

Offline Jim

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New build is even better. RS-25D to RS-25E means it's far cheaper, but all with that lovely reliability.
To pull 25D out of the shed and build up 25E production capacity costed around $70mil/engine ($1.18bil / 16engines) and the new 25E will also cost about the same ($413mil / 6engines, 4flying) compared to RS-68 at around $20mil/engine and fewer per core compared to 25s.

There is no such alternative, if it includes RS-68.  RS-68 and SRB are not viable, much like air start SSME.
Jim, You're very knowledgeable, but mistaken here. RS-68 and SRB is an engineering challenge, not an impossibility. NASA's conclusion was regen at around $150mil in development and doubling the unit cost. I disagree with messing up an inexpensive, robust and impeccably-reliable engine and instead previously outlined a boattail that puts existing 68s in a more benign environment then they have under Delta IV. I'm sure there's other options, possibly some better, to address this engineering problem. -- Boattail post;
https://forum.nasaspaceflight.com/index.php?topic=38069.msg1706197#msg1706197

Still didnt address three main problem.  Radiant heating of the nozzles from the SRM plume.
« Last Edit: 08/01/2017 01:35 PM by Chris Bergin »

Offline Propylox

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... Wrote an article in 2008 on it. Article is several CMS's ago so looks messy, best to just copy and paste it:
Quote
... the Ares-V needs to push 75.1 mT of payload through Trans-Lunar Injection (TLI) but was only able to push 64.6 mT. ... This new more powerful configuration, identified as the ‘LV 51.00.48’ is now able to put 71.1 mT through TLI.
...
Total expected burn time for the Core will be 303 seconds and the 6 main engines will produce a maximum of 4.17G during the launch.
...
Total roll out weight with the crawler and the MLP (Mobile Launch Platform) will be approximately 18 million lbs, which exceeds the capability of the existing crawlerway rated for 16.8 million lbs. ...
That's extraordinary. Refreshing memory and it's still jaw-dropping how absurd Constellation was.

Still didnt address three main problem.  Radiant heating of the nozzles from the SRM plume.
Without bending light, the only possible radiant heating in that boattail design would be through the 68's own exhaust and against their bell's inner walls.
« Last Edit: 08/01/2017 04:45 PM by Propylox »

Offline Jim

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... Wrote an article in 2008 on it. Article is several CMS's ago so looks messy, best to just copy and paste it:
Quote
... the Ares-V needs to push 75.1 mT of payload through Trans-Lunar Injection (TLI) but was only able to push 64.6 mT. ... This new more powerful configuration, identified as the ‘LV 51.00.48’ is now able to put 71.1 mT through TLI.
...
Total expected burn time for the Core will be 303 seconds and the 6 main engines will produce a maximum of 4.17G during the launch.
...
Total roll out weight with the crawler and the MLP (Mobile Launch Platform) will be approximately 18 million lbs, which exceeds the capability of the existing crawlerway rated for 16.8 million lbs. ...
That's extraordinary. Refreshing memory and it's still jaw-dropping how absurd Constellation was.

Still didnt address three main problem.  Radiant heating of the nozzles from the SRM plume.
Without bending light, the only possible radiant heating in that boattail design would be through the 68's own exhaust and against their bell's inner walls.

Wrong again.  The plume is radiant for almost 100 feet.  The nozzles will always be in direct view of them. 

The boat tail design is also non viable

Offline john smith 19

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Now, what specific target are we shooting for? SSME is a very complex beast. You just can't wave a wand and magically make it cheaper. What performance levels are required? Uprating? Greater margins for HSF than prior Shuttle ones, because we want to lower our LOC/LOM numbers too?

How much are we allowed to change the engine's physical geometry/size (much of the issues were in making a compact, ground start engine for a spaceplane application). How about the feed lines, can we change them too? Can we use electrical instead of hydraulic in certain places? Can we use new materials that will last 1-2 times instead of 30+?

Can we eliminate whole portions of the design that might sacrifice 2-15 sec-1 of iSP?

Now, we take all of that and run it on the test stand and compare numbers? Can we prove we've met requirements and retained acceptable reliability? Tall order.
Indeed.

The age old myth of the "small change."

So if it's that small (that it does not need full qualification testing) how will it give any significant improvements?

If it's so big to need full qualification testing how can you afford it in terms of cost or schedule delay?
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Robert Willis

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Hydrogen burning Raptor
« Reply #295 on: 08/02/2017 06:13 PM »
Engines designed to burn LH2 such as RD-0120 & RD-0146 have been test fired burning liquid methane with very little modification. Seeing as Raptor was originally designed to run on Hydrogen, how difficult would it be to produce an LH2 burning version of Raptor having a high component commonality with the currently planned CH4 production model? I would guess that such an engine would have lower thrust, but higher ISP. Can anyone out there do rough calculations/estimate?

Considering that NASA is paying Aerojet-Rocketdyne an obscene 1.6 billion dollars for just six new RS-25s, would it not make sense to replace these with LH2 Raptors for SLS?

Offline Propylox

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Wrong again.  The plume is radiant for almost 100 feet.  The nozzles will always be in direct view of them. 
The boat tail design is also non viable

If an SRB plume is an infinite 180 degrees, it still won't effect the 68's if using a boattail. They're still shielded (other than the absolute lip viewed from directly below, and I mentioned an extra ablative ring here may be necessary, but unlikely), they have constant airflow, no radiant effect on each other, no GG recirculation and purge line rerouted - that's kinda the whole point of building a boattail. If you don't know that, how can understand the design well enough to then call it non viable? FYI: It is, much cheaper and faster to develop than alternatives, uses existing knowledge-bases and infrastructure, weight is minimal, drag is reduced and it looks goooood (something engineers often forget is important).
« Last Edit: 08/02/2017 07:59 PM by Chris Bergin »

Offline Space Ghost 1962

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Now, what specific target are we shooting for? SSME is a very complex beast. You just can't wave a wand and magically make it cheaper. What performance levels are required? Uprating? Greater margins for HSF than prior Shuttle ones, because we want to lower our LOC/LOM numbers too?

How much are we allowed to change the engine's physical geometry/size (much of the issues were in making a compact, ground start engine for a spaceplane application). How about the feed lines, can we change them too? Can we use electrical instead of hydraulic in certain places? Can we use new materials that will last 1-2 times instead of 30+?

Can we eliminate whole portions of the design that might sacrifice 2-15 sec-1 of iSP?

Now, we take all of that and run it on the test stand and compare numbers? Can we prove we've met requirements and retained acceptable reliability? Tall order.
Indeed.

The age old myth of the "small change."

So if it's that small (that it does not need full qualification testing) how will it give any significant improvements?

If it's so big to need full qualification testing how can you afford it in terms of cost or schedule delay?
Correct.

Was J2-X worth the time/money over J2-S? If they had kept with J2-S mostly, it might have been used. J2-X likely won't be used.

We've been down the J2/SSME/STBE/RS68/RS68A "improvement" path many, many times before.

IMHO, the problem here is not the "possible". The problem is different. Clarity of a definite, long term need to fill, with a commitment to meet the cost/performance needs is more likely.

The RS68 program was a mix of good (first commercial engine development, timely, high thrust hydrolox w/o solids) and bad (missed performance targets, chose poorly on "cheap" components due to SSME decisions, too high threshold on frequency of use for cost knee in curve, ...).

And that was the prior attempt at "cheap" hydrolox.

Aerojet Rocketdyne does not find it easy to do cheap hydrolox.

Reminds of "Young Frankenstein": "... because we still have nightmares from five times before.".

Offline john smith 19

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Was J2-X worth the time/money over J2-S? If they had kept with J2-S mostly, it might have been used. J2-X likely won't be used.
That would be the new J2-X.
The RS68 Combustion Chamber
The RS68 Gas Generator
The RS68 Nozzle
The RS68Injectors
The RL10 nozzle extension
Of which only the RL10 nozzle was a crew rated engine component
And
The J2 turbopump design.
Which (apparently) was all you needed to turn an RS68 into a crew rate engine.  :(

Finding information on the original J2-S and J2-X programmes was very difficult for me but the achievements of the original programme were remarkable.
Converting it to a large size gas tapoff cycle (the only option that can give potentially give the high chamber of staged combustion with the simplicity of an expander cycle).
Moving from pressurized start tanks to cartridge starts but more impressively moving to tank head pressure starting (when they realized it was the high back pressure from the CC cooling system that was preventing turbine spin up).
An pressure fed idle mode.
Pumps to allow start up with   50% vapour in the inlet at < 2 bar absolute. 
And planning for a plug nozzle version.

I found the modern programme quite underwhelming by comparison.  :(
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Jim

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If an SRB plume is an infinite 180 degrees, it still won't effect the 68's if using a boattail. They're still shielded (other than the absolute lip viewed from directly below, and I mentioned an extra ablative ring here may be necessary, but unlikely), they have constant airflow, no radiant effect on each other, no GG recirculation and purge line rerouted - that's kinda the whole point of building a boattail. If you don't know that, how can understand the design well enough to then call it non viable?

Still not viable.

A.  There is no changing the 68 just for SLS.  It negates the benefit of sharing the same production line and flight history.
b.  Obviously, you didn't know that the boat tail didn't work on Delta IV so how do you know it is viable for this kludge. 
c.  There still is  radiant effect from boat tail to nozzle
d.  The large mass this huge boat tail is another strike against the "benefits" of the RS.
e. and there is the fore mentioned ISP issue that makes the core tanks too big.

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