[New] Space Launch System / Orion Discussion Thread

[JoeSchmuckatelli]

Imitation is the sincerest form of flattery. 

... 

I'm thinking that the rest of them take a dim view of the upstart. 

[SunlitZelkova]

9 hours ago, tater said:

I was not comparing it directly to Falcon 9 as a vehicle, I was observing that F9 flew to space within view of SLS 4 times for the brief period it stayed on the pad (very nearly 5  F9s).  2 of those (the 5th that SLS scooted into the VAB and avoided) were Crew flights. Commercial Crew was enacted the same year as SLS, 2010. Some of the CCrew budget was taken from it and given to SLS early on, too, delaying commercial crew. Dragon has now flown crew 7 times (crew-1-4, ax-1, I4, demo 2?) I think, plus 1 all-up test flight. SLS has not even made a WDR.

Remember, SLS was supposed to be operational sooner than Commercial Crew since CCrew was developing 2 entirely new crew vehicles, and SLS was using already existing Shuttle tech, plus Orion was far along from Constellation. Operational by the end of 2016—with test flights well before that (possibly to ISS, since Orion was taken from the Constellation program and was meant initially to only ever launch to LEO, any lunar missions achieved via Earth Orbit Rendezvous mission profiles). Actually, Orion was also meant to replace Shuttle as a vehicle to serve ISS (MPCV = Multi-Purpose Crew Vehicle).

I don't think those dates were ever really worth anything. The Space Shuttle, too, was "supposed to" do a lot of things. It was supposed to fly in 1978 and by 1985, fly 60 times a year. That isn't the dumb cost fantastical assessment used in Congressional hearings, that is a number that NASA actually calculated based on highly optimistic infrastructure construction and refurbishment times. These were never realistic, and the specific Shuttle design that was built itself was born out of very similar reasons to the SLS- jobs in Congressional districts.

Furthermore, there are number of hidden factors that made these dates very dumb on the part of those who made them-

1. A super heavy lift rocket is not the same as a medium lift launch vehicle, no matter where the tech comes from. The only operational example we have is the Saturn V, and its construction was propelled by almost civilizational-level political concerns and the desire to honor a slain President- and most importantly, the American aerospace industry in its (so far) peak form. The Soviets gave a half-hearted effort and had it explode four times. In contrast however, both the US and USSR developed medium lift launch vehicles (Proton and Saturn IB) in the same era that succeeded in lifting a variety of payloads, well before either of the SHLVs flew operationally. The only other example is Energia, which began in 1976 and did not launch until 1977 1978. SLS' timeline is thus very similar (almost identical) to Energia. Not unlike SLS, Energia, too, had a silly timeline at its beginning- first flight was supposed to be in 1983, also very similar to SLS.

2. It is known that the US aerospace industry has had a number of "problems" appear in recent decades. The delays on the F-35 program are an example, it was originally supposed to achieve IOC in 2010, this was pushed back to 2015, while the US Navy did not achieve IOC until 2019. The 737 MAX debacle is another. Without a serious effort at ending these issues, SLS was never going to fly "on time".

3. No effort appears to have been made to look at Space Shuttle development and try and learn lessons from it. Thus we have a vehicle whose safety and operational capabilities are compromised by political decisions. If no one was going to make an effort to try to correct mistakes, it was destined to end up like last time.

So...

9 hours ago, tater said:

The schedule comparisons and the bad look of SLS on the pad while rockets fly to space all around it holds.

For the above reasons, I don't think they do. SLS is still bad, but the delays couldn't have been helped. It was physically incapable of matching Falcon 9 in development or meeting the absurd timelines created for it.

So I don't think Falcon 9 launching so many times while it tests is necessarily wrong or bad. SLS is bad for other reasons (as you mention, it is pretty useless), but it was always going to have Falcon 9s launching all around it, even if that had been in 2019 or 2021.

Edited April 28, 2022 by SunlitZelkova

[tater]

19 minutes ago, SunlitZelkova said:

I don't think those dates were ever really worth anything. The Space Shuttle, too, was "supposed to" do a lot of things. It was supposed to fly in 1978 and by 1985, fly 60 times a year. That isn't the dumb cost fantastical assessment used in Congressional hearings, that is a number that NASA actually calculated based on highly optimistic infrastructure construction and refurbishment times. These were never realistic, and the specific Shuttle design that was built itself was born out of very similar reasons to the SLS- jobs in Congressional districts.

There were plenty of Shuttle-derived launch vehicle concepts that could easily have flown, almost without missing a beat. Shuttle-C, for example (multiple variants proposed).

 

19 minutes ago, SunlitZelkova said:

Furthermore, there are number of hidden factors that made these dates very dumb on the part of those who made them-

1. A super heavy lift rocket is not the same as a medium lift launch vehicle, no matter where the tech comes from. The only operational example we have is the Saturn V, and its construction was propelled by almost civilizational-level political concerns and the desire to honor a slain President- and most importantly, the American aerospace industry in its (so far) peak form. The Soviets gave a half-hearted effort and had it explode four times. In contrast however, both the US and USSR developed medium lift launch vehicles (Proton and Saturn IB) in the same era that succeeded in lifting a variety of payloads, well before either of the SHLVs flew operationally. The only other example is Energia, which began in 1976 and did not launch until 1977. SLS' timeline is thus very similar (almost identical) to Energia. Not unlike SLS, Energia, too, had a silly timeline at its beginning- first flight was supposed to be in 1983, also very similar to SLS.

SLS barely fits the bill. Shuttle was in fact a SHLV by the same criteria, as the payload was not the 20-25t in the payload bay maximum, but that mass, PLUS the Orbiter itself. STS full payload to LEO was more like 110t for a fair comparison. Completely on par with SLS Block 1.

The timeline for dev of a new vehicle is longer than the timeline to dev a derivitive vehicle. SLS was explicitly pitched as a Shuttle-derived vehicle, and hence fast. Same hydrolox tankage. Same engines. Same SRBs.

Then they intentionally changed:

The tankage.

The engines.

The SRBs.

So effectively starting from scratch on all the things that made it supposedly cost effective, and fast.

 

19 minutes ago, SunlitZelkova said:

2. It is known that the US aerospace industry has had a number of "problems" appear in recent decades. The delays on the F-35 program are an example, it was originally supposed to achieve IOC in 2010, this was pushed back to 2015, while the US Navy did not achieve IOC until 2019. The 737 MAX debacle is another. Without a serious effort at ending these issues, SLS was never going to fly "on time".

Yes, but it was supposed to be operational (not tested) by 2017. The first operational SLS/Orion flight is arguably the second crew flight. If Artemis III uses Block 1B, then I would say the first operational flight is the second in that configuration (Block 1 was never supposed to fly more than once, because ICPS is a bad, arguably unsafe upper stage for crew (unsafe because it requires 4 Oberth burns for TLI, needlessly exposing the crew to radiation, and bad for LOM outcomes because needless restarts for what should be 1 burn).

 

19 minutes ago, SunlitZelkova said:

3. No effort appears to have been made to look at Space Shuttle development and try and learn lessons from it. Thus we have a vehicle whose safety and operational capabilities are compromised by political decisions. If no one was going to make an effort to try to correct mistakes, it was destined to end up like last time.

So...

For the above reasons, I don't think they do. SLS is still bad, but the delays couldn't have been helped. It was physically incapable of matching Falcon 9 in development or meeting the absurd timelines created for it.

So I don't think Falcon 9 launching so many times while it tests is necessarily wrong or bad. SLS is bad for other reasons (as you mention, it is pretty useless), but it was always going to have Falcon 9s launching all around it, even if that had been in 2019 or 2021.

It's a reminder of good vs bad investments.

I'd be much less harsh on SLS/Orion if it was huge, expensive, delayed—but hugely capable. I'd be annoyed at the delays, but I'd be a fan anyway. The fact that it is useless underlines the scheduling issues—and time is money. We pay for SLS the same every year, regardless of flight cadence. Partially because cost-plus actually incentivizes delay.

Edited April 28, 2022 by tater

[StrandedonEarth]

16 minutes ago, SunlitZelkova said:

Energia, which began in 1976 and did not launch until 1977.

Must be a typo there, I assume you mean 1987.

Nice summary though. But I can't but think that if a serious effort was made to fast-track SLS, it could have been done sooner. Heck, IIRC, F9 was flying before SLS had any visible signs of bending metal, while the five-segment SRB's were in dve before STS even ended.

Wiki quote: 

Quote

After the destruction of Columbia, NASA shelved the five-segment SRB for the Shuttle Program.^[why?][27] One five-segment engineering test motor, ETM-03, was fired on October 23, 2003.^[28][29]

As part of the Constellation Program, the first stage of the Ares I rocket was planned to use five-segment SRBs; in September 2009 a five-segment Space Shuttle SRB (DM-1) was static fired on the ground in ATK's desert testing area in Utah.^[30] Additional tests (DM-2 and DM-3) were carried out in Aug 2010 and Sept 2011.^[31]

 

4 minutes ago, tater said:

Shuttle-C, for example (multiple variants proposed).

Don't know why that never happened; it was an obvious evolution

[tater]

1 minute ago, StrandedonEarth said:

Don't know why that never happened; it was an obvious evolution

And did what SLS is actually for—employed the existing Shuttle contractors and centers.

[StrandedonEarth]

2 minutes ago, tater said:

And did what SLS is actually for—employed the existing Shuttle contractors and centers.

And re-used components as-is, not re-engineered into something completely new - ET, SRBs, SSMEs/RS-25s, OMS pods....

[tater]

For expendable vehicles, I could see evolving to simpler, cheaper SSMEs, for example, and they knew that the SRBs were not cost effective to reuse since, I dunno, forever? Dump all the SRB recovery nonsense, since reuse cost more than throw away. Try and make cheap SSMEs. There was even a variant with Orion on it I think.

Yep:

https://www.nasa.gov/pdf/361842main_15 - Augustine Sidemount Final.pdf

 

 

 

Orion was supposed to be servicing ISS in 2015, lol.

[SunlitZelkova]

5 minutes ago, tater said:

There were plenty of Shuttle-derived launch vehicle concepts that could easily have flown, almost without missing a beat. Shuttle-C, for example (multiple variants proposed).

I personally don't think Shuttle-C actually stood a chance of flying when it was proposed, at least not in a timely manner, because the Shuttle itself would have taken funding priority.

9 minutes ago, tater said:

SLS barely fits the bill. Shuttle was in fact a SHLV by the same criteria, as the payload was not the 20-25t in the payload bay maximum, but that mass, PLUS the Orbiter itself. STS full payload to LEO was more like 110t for a fair comparison. Completely on par with SLS Block 1.

The timeline for dev of a new vehicle is longer than the timeline to dev a derivitive vehicle. SLS was explicitly pitched as a Shuttle-derived vehicle, and hence fast. Same hydrolox tankage. Same engines. Same SRBs.

Then they intentionally changed:

The tankage.

The engines.

The SRBs.

So effectively starting from scratch on all the things that made it supposedly cost effective, and fast.

I think the point we need to examine isn't technical parlance so much as it is general scale. The SLS, in the forms that currently exist physically, may as well be an expendable Space Shuttle with no payload and a rather useless orbiter. With the changes you mentioned, expecting completion in six years with the level of commitment and the poor history of the selected contractor was ludicrous. It has all of the challenges of a SHLV and ultimately ran into all of the worst possible problems for such a project (problems valid assuming there is a certain date to be met).

The Shuttle was delayed, if such changes were to be made to SLS- and they were- then expecting SLS in a "timely" (on the original schedule) manner was/is silly. Not unlike how the Communist Party of the Soviet Union expected a Moon landing in 1968... despite only starting work in 1965, after having been pressed on the subject of a Moon landing for a few years prior. Also similar to the changing requirements for the Space Shuttle design as a result of the USAF getting in on the project.

All things considered, regardless of what people want, based on what is there, based one of the available historical comparisons- Energia- the development schedule has been decent. Decent. Still, it could have been better and repeating such wasteful history is unacceptable.

All of this is IMO.

17 minutes ago, tater said:

Yes, but it was supposed to be operational (not tested) by 2017. The first operational SLS/Orion flight is arguably the second crew flight. If Artemis III uses Block 1B, then I would say the first operational flight is the second in that configuration (Block 1 was never supposed to fly more than once, because ICPS is a bad, arguably unsafe upper stage for crew (unsafe because it requires 4 Oberth burns for TLI, needlessly exposing the crew to radiation, and bad for LOM outcomes because needless restarts for what should be 1 burn).

I find it interesting, because the same random focus on schedules and political goals that is leading to eight astronauts being sent through the Van Allen belts multiple times is not unlike what killed seven astronauts in 1986.

19 minutes ago, tater said:

The fact that it is useless underlines the scheduling issues—and time is money. We pay for SLS the same every year, regardless of flight cadence. Partially because cost-plus actually incentivizes delay.

I think the uselessness should highlight the problems with government procurement rather than SLS itself. Regardless of usefulness, its development schedule has been reasonable (insofar as it is very close to one of only two other historical SHLVs) for the amount of attention and "distractions" there have been in the government and either deliberately or accidently by contractors (wars and delays for more $$).

Capabilities and cost? Those are things worth valid criticism. Even the schedule *could* have been improved theoretically. But comparing it to medium lift launch vehicles has a variety of issues, and I think it distracts from the real issue.

22 minutes ago, StrandedonEarth said:

Don't know why that never happened; it was an obvious evolution

Well...

1. At the time it was first proposed, Congress was very hostile to crewed deep space exploration. People thought the Space Shuttle would fly until 2030 at the time.

2. It was definitively shelved after the Columbia disaster probably because

2a. The original Crew Exploration Vehicle, intended to replace the Shuttle, did not involve Shuttle components- it was an entirely new vehicle intended to launch on existing commercial launch vehicles.

2b. A crewed deep space exploration program was iffy- the CEV was supposed to go to the Moon, but there were no concrete plans for a landing and certainly no Gateway. So there was no need for heavy lift, thus no need for Shuttle-C.

2b1. And thus no need for some way to keep Shuttle contractors alive.

3. It was a reminder of the Space Exploration Initiative, something Congress hated. Congress has a habit of doing this in space matters- a space station program based around CSMs and Saturn IBs and low rate Saturn V production would have been just as expensive as the Shuttle and been more safe and productive, yet in the minds of Congressmen "Apollo = waste", so instead we got an even more wasteful and dangerous replacement.

[RyanRising]

2 hours ago, SunlitZelkova said:

3. No effort appears to have been made to look at Space Shuttle development and try and learn lessons from it. Thus we have a vehicle whose safety and operational capabilities are compromised by political decisions. If no one was going to make an effort to try to correct mistakes, it was destined to end up like last time.

This I do disagree with a little. They put a capable abort system on it this time, thank goodness.

[tater]

1 hour ago, SunlitZelkova said:

I personally don't think Shuttle-C actually stood a chance of flying when it was proposed, at least not in a timely manner, because the Shuttle itself would have taken funding priority.

Excellent point. I was thinking in a sort of alternate reality where Shuttle IS cancelled, but any follow-on is chosen on merit, speed of operational capability, etc.

Shuttle-C or Direct, IMO, best options.

One thing Constellation certainly got right was separating heavy lift from crew, IMO.

 

1 hour ago, SunlitZelkova said:

I think the point we need to examine isn't technical parlance so much as it is general scale. The SLS, in the forms that currently exist physically, may as well be an expendable Space Shuttle with no payload and a rather useless orbiter. With the changes you mentioned, expecting completion in six years with the level of commitment and the poor history of the selected contractor was ludicrous. It has all of the challenges of a SHLV and ultimately ran into all of the worst possible problems for such a project (problems valid assuming there is a certain date to be met).

The Shuttle was delayed, if such changes were to be made to SLS- and they were- then expecting SLS in a "timely" (on the original schedule) manner was/is silly. Not unlike how the Communist Party of the Soviet Union expected a Moon landing in 1968... despite only starting work in 1965, after having been pressed on the subject of a Moon landing for a few years prior. Also similar to the changing requirements for the Space Shuttle design as a result of the USAF getting in on the project.

All things considered, regardless of what people want, based on what is there, based one of the available historical comparisons- Energia- the development schedule has been decent. Decent. Still, it could have been better and repeating such wasteful history is unacceptable.

All of this is IMO.

Another way to look at timing is to look at Starship. SpaceX is literally working 3 shifts, so take the calendar years and multiply by 3-4. No regular program will have the money up-front, then spend it in the least time, they will get X$/yr, and spend it that way, normal 40 hour weeks (with PTO, vacation, etc!), etc.

 

1 hour ago, SunlitZelkova said:

I find it interesting, because the same random focus on schedules and political goals that is leading to eight astronauts being sent through the Van Allen belts multiple times is not unlike what killed seven astronauts in 1986.

I think the uselessness should highlight the problems with government procurement rather than SLS itself. Regardless of usefulness, its development schedule has been reasonable (insofar as it is very close to one of only two other historical SHLVs) for the amount of attention and "distractions" there have been in the government and either deliberately or accidently by contractors (wars and delays for more $$).

Capabilities and cost? Those are things worth valid criticism. Even the schedule *could* have been improved theoretically. But comparing it to medium lift launch vehicles has a variety of issues, and I think it distracts from the real issue.

Well, using a Constellation-like mission profile, crew to LEO, EOR to the Moon, then medium lift is fine as long as the cadence is there to build the desired craft (or god-forbid to the Senator from AL, to take an empty tank and refill it in space! The horror!).

 

1 hour ago, SunlitZelkova said:

Well...

1. At the time it was first proposed, Congress was very hostile to crewed deep space exploration. People thought the Space Shuttle would fly until 2030 at the time.

Unsure how long people thought Shuttle would fly, TBH.

 

1 hour ago, SunlitZelkova said:

2. It was definitively shelved after the Columbia disaster probably because

2a. The original Crew Exploration Vehicle, intended to replace the Shuttle, did not involve Shuttle components- it was an entirely new vehicle intended to launch on existing commercial launch vehicles.

Yeah, Orion was supposed to serve ISS—in 2015, on top of Ares I.

1 hour ago, SunlitZelkova said:

2b. A crewed deep space exploration program was iffy- the CEV was supposed to go to the Moon, but there were no concrete plans for a landing and certainly no Gateway. So there was no need for heavy lift, thus no need for Shuttle-C.

2b1. And thus no need for some way to keep Shuttle contractors alive.

3. It was a reminder of the Space Exploration Initiative, something Congress hated. Congress has a habit of doing this in space matters- a space station program based around CSMs and Saturn IBs and low rate Saturn V production would have been just as expensive as the Shuttle and been more safe and productive, yet in the minds of Congressmen "Apollo = waste", so instead we got an even more wasteful and dangerous replacement.

Altair was the lander during Constellation, lunar landing was definitely a thing. That was the back and forth for next-gen, BLEO systems... Moon? Mars! Moon! Mars! Moon TO Mars!

[SunlitZelkova]

3 hours ago, tater said:

One thing Constellation certainly got right was separating heavy lift from crew, IMO.

Do you mean separate vehicles or different separate vehicles?

If the latter, I am curious to know why. Not that I disagree, but just off the top of my head, it seems like building two different vehicles would cost more money.

Of course, on the other hand, having an oversized crew vehicle would also be wasteful, or an undersized cargo vehicle lacking in capability.

4 hours ago, tater said:

Another way to look at timing is to look at Starship. SpaceX is literally working 3 shifts, so take the calendar years and multiply by 3-4. No regular program will have the money up-front, then spend it in the least time, they will get X$/yr, and spend it that way, normal 40 hour weeks (with PTO, vacation, etc!), etc.

I kind of refrained from looking at Starship in this discussion because it didn't credibly exist when SLS began. Falcon 9 itself had been "delayed"* multiple times, and in any case Boeing/old space could make a pretty easy argument that they were better equipped to build a SHLV and were the only ones to do it. Thus criticizing SLS' past based on Starship in the present doesn't really make sense.

On the other hand, as for why radical changes aren't being directed now, is something that should be asked. Artemis provides an excellent excuse opportunity to do so.

From a political point of view, there should be absolutely nothing wrong with canceling SLS now. After all, Energia and Buran got canceled despite the long commitment to development the moment they became economically worthless- it ought to be no different in the US.

Could SLS be saved though? Would any modification be worth it (assuming development actually became efficient)?

4 hours ago, tater said:

Yeah, Orion was supposed to serve ISS—in 2015, on top of Ares I.

Altair was the lander during Constellation, lunar landing was definitely a thing. That was the back and forth for next-gen, BLEO systems... Moon? Mars! Moon! Mars! Moon TO Mars!

Yes, I was mistaken in regards to the lunar landing. But I was referring to this-

It was supposed to launch on an EELV. Presumably the LSAM would ultimately use that vehicle too. During a brief period between May and November 2005 (and of course dating all the way back to the VSE's announcement), there was no intention to use a Shuttle derived LV, thus Shuttle-C got discarded.

Considering the study that led to Ares (which then led to SLS) began in April 2005, I can't help but have a yearning to go back and look at election results from the previous year to see if that might have had an impact in the reverse course...

[tater]

7 hours ago, SunlitZelkova said:

Do you mean separate vehicles or different separate vehicles?

If the latter, I am curious to know why. Not that I disagree, but just off the top of my head, it seems like building two different vehicles would cost more money.

Of course, on the other hand, having an oversized crew vehicle would also be wasteful, or an undersized cargo vehicle lacking in capability.

Completely different vehicles. EOR architecture. Money is one issue, safety another. Also, if there are existing LVs capable of getting a capsule to LEO, there's not really a need for anything bigger.

7 hours ago, SunlitZelkova said:

I kind of refrained from looking at Starship in this discussion because it didn't credibly exist when SLS began. Falcon 9 itself had been "delayed"* multiple times, and in any case Boeing/old space could make a pretty easy argument that they were better equipped to build a SHLV and were the only ones to do it. Thus criticizing SLS' past based on Starship in the present doesn't really make sense.

Not a comparison, it's actually a reality check on the dev timeline. Starship dev time times 3-4 is about what other vehicle dev times have been—because they literally work 24/7. I'm saying the dev times are the same.

7 hours ago, SunlitZelkova said:

It was supposed to launch on an EELV. Presumably the LSAM would ultimately use that vehicle too. During a brief period between May and November 2005 (and of course dating all the way back to the VSE's announcement), there was no intention to use a Shuttle derived LV, thus Shuttle-C got discarded.

Considering the study that led to Ares (which then led to SLS) began in April 2005, I can't help but have a yearning to go back and look at election results from the previous year to see if that might have had an impact in the reverse course...

Everything changing every 4-8 years certainly doesn't help.

[StrandedonEarth]

12 hours ago, SunlitZelkova said:

Could SLS be saved though? Would any modification be worth it (assuming development actually became efficient)?

Probably not, because the biggest issue IMO is the hydrolox sustainer stage, which requires a ludicrously large tank and insulation. Change that and you’re basically back to a clean sheet. 

Many other possible changes, like liquid fly back boosters (coughF9cough), requires more pad infrastructure. 

[tater]

1 hour ago, StrandedonEarth said:

Probably not, because the biggest issue IMO is the hydrolox sustainer stage, which requires a ludicrously large tank and insulation. Change that and you’re basically back to a clean sheet. 

Many other possible changes, like liquid fly back boosters (coughF9cough), requires more pad infrastructure. 

Yeah, sustainers make no sense IMO. That architecture was required for SLS because it was mandated to use SSME, which can only ground start, and they have no upper stage engine short of RL-10 (great, but tiny). They could have continued J-2 work, obviously.

So much is bad because of Shuttle tech. Best SLS would be RP-1/LOX booster, cry upper stage (or stages). Course that might obviate SRBs entirely, so no Utah box checked.

[sevenperforce]

13 minutes ago, StrandedonEarth said:

Probably not, because the biggest issue IMO is the hydrolox sustainer stage, which requires a ludicrously large tank and insulation. Change that and you’re basically back to a clean sheet. 

Many other possible changes, like liquid fly back boosters (coughF9cough), requires more pad infrastructure. 

The hydrolox sustainer stage was always a bad design. You need methalox or kerolox for your first stage; otherwise you’re just needlessly lofting a bunch of superfluous tankage.

If SLS had used the Jupiter-DIRECT approach and kept the same 734-tonne prop load of the Space Shuttle external tank instead of doing a tank stretch to a 988-tonne prop load, it could have saved roughly 16 meters of length, allowing for an upper stage nearly twice as large as the EUS. They would have needed to complete dev on the J-2X or looked into clustered MARC-60 engines, since the RL-10 wouldn’t be able to manage even in a large cluster, but that would have been easy enough by now.

If the upper stage was essentially just a shrunk-down version of the core stage with two J-2X engines and the original four-segment boosters, it could send 117 tonnes to LEO, compared to the 105 tonnes that EUS can manage. With the modern five-segment boosters it could send 127 tonnes to LEO. But its throw to TLI is lower than Block 1B because the upper stage would then be oversized for BLEO operations.

Hydrolox sustainer stages are just plain dumb. 

[sevenperforce]

7 minutes ago, tater said:

So much is bad because of Shuttle tech. Best SLS would be RP-1/LOX booster, cry upper stage (or stages). Course that might obviate SRBs entirely, so no Utah box checked.

A clean-sheet design could have used RD-180s on the first stage, a pair of J-2Xs on the second stage, and a single J-2X or a pair of RL-10s on a third stage, with SRBs to add impulse and reduce the number of RS-180s needed. Of course that obviates the SSMEs.

If the SSMEs simply MUST be used, then a page could be taken from the Saturn S-IC Mega Atlas concept. Use a Shuttle ET but add a second common bulkhead, with RP-1 at the top, LOX in the middle, and LH2 at the bottom. Place a single SSME underneath, firing through a skirt where two F-1Bs are mounted, perpendicular to the SRB mounts. Keep the four-segment SRBs and use a J-2X on a larger EUS. The SRBs burn out first, and then the skirt with the F-1Bs drops away when the RP-1 tank runs dry, with the single SSME performing its role as a proper sustainer.

[tater]

Interesting idea.

 

[StrandedonEarth]

26 minutes ago, sevenperforce said:

RD-180s

Which would be politically unviable these days. I always shook my head that they were ever imported, but they had their (again, geopolitically motivated) reasons....

[sevenperforce]

11 minutes ago, StrandedonEarth said:

Which would be politically unviable these days. I always shook my head that they were ever imported, but they had their (again, geopolitically motivated) reasons....

Oh, certainly unviable today. 

[sevenperforce]

3 hours ago, tater said:

Interesting idea.

Back of the envelope math would suggest you’d need a pair of RS-25s mounted centrally and a pair of F-1Bs. That would more than double the thrust of the core, from 9.1 MN to 20.5 MN. Of course, the core’s wet mass would be higher given the RP-1 that would be replacing LH2, but not that much higher. With EUS, likely enough to outperform Ares V; with a proper EDS, significantly more.

The F-1B is DOA unfortunately, but a modern version with six BE-4s or four Raptors on the skirt would work almost as well. 

[sevenperforce]

I did some more math on this, and it looks like one problem would be the gee-loading right before the skirt is dropped. In order to get a core T/W ratio of at least 0.8 at skirt separation, you'd need to run the F-1Bs for 137 seconds. But even with the RS-25s at minimum throttle, that's 3.3 gees just before the skirt separates, which is going to increase the weight of the upper adapter. But perhaps the F-1Bs could downthrottle enough to deal with this.

The other problem is that the F-1Bs are just too powerful. The skirt thrust structure would end up weighing a LOT...which is mitigated since you drop it, but it cuts into payload. Using a SLWT-sized core with appropriate upper adapter, lower adapter, EUS, and five-segment boosters, that's 31 tonnes to TLI, which is lower than Block 1B. Of course you get away with a smaller core.

A modern evolution path (we'll call it Block 1C) would be to use either BE-4s or Raptors on the skirt of the existing SLS. NASA would have add another bulkhead to store liquid methane, strengthen the upper core adapter by around 12% (to allow for the greater payload capacity of this version), replace the lower thrust adapter with one approximately half as heavy (for the two sustainer engines) and add a skirt for the methane engines. With four Raptors and a skirt burn time of 375 seconds, it would send 51.5 tonnes to TLI using five-segment boosters and EUS, which is dramatically better than Block 1B or Block 2. Adding more Raptors and lowering the burn time can help a little, but not much, because the weight of the skirt thrust structure starts ramping up again.

[sevenperforce]

It should be noted that Apollo 15-17 sent just under 49 tonnes to TLI.

Orion is of course annoyingly heavy, but it does have the ability to return from low lunar orbit on its own, provided that the lander brakes it into lunar orbit a la Altair/Constellation. With 51.5 tonnes of throw and Orion's injected mass of 26.5 tonnes, that's 25 tonnes of margin for a lander. With a low-boiloff, well-insulated hydrolox landing stage based on the BE-3U, BE-7, or RL-10, that's something in the neighborhood of 9.4 tonnes of braking propellant from TLI into LLO. The lander/ascender budget then becomes 15.6 tonnes, which gets you 10.3 tonnes landed on the lunar surface. Total hydrolox use is 14.7 tonnes, 13% less than the propellant load of a 4-meter DCSS. The 4-meter DCSS is 2.48 tonnes dry, so if we allow 2.5 tonnes for the dry mass of the landing stage (1.96 tonnes tank mass but tacking on 540 kg to account for boiloff, maneuvers, landing legs, and extra engines), then that leaves us with a payload and ascent module budget of 7.8 tonnes, 66% greater than the Lunar Module ascent stage. 

Thus. building a new common bulkhead and adding four Raptors (or Be-4s) on a drop skirt to the existing SLS saves two RS-25s per flight and converts Block 1B into a single-stack moon rocket a la Apollo. SpaceX has dozens of deprecated Raptor 1 engines laying around at this point; I'm sure Elon would let them go for cheap. Surface sorties can be augmented by surface assets emplaced through commercial heavy-lift.

That's if NASA remains stubbornly insistent on flying segmented SRBs, SSMEs, and Orion.

Edited May 1, 2022 by sevenperforce
added explanation

[tater]

48 minutes ago, sevenperforce said:

That's if NASA remains stubbornly insistent on flying segmented SRBs, SSMEs, and Orion.

If the core is sacrosanct, I wonder what could be done with liquid side boosters. The 5 seg SRBs are ~16,000kN (3.6M pounds). Same idea, less complexity. A SH9 booster (9 Raptors) slightly throttled down equals the SRBs, but with substantially higher Isp.

[sevenperforce]

8 hours ago, tater said:

If the core is sacrosanct, I wonder what could be done with liquid side boosters. The 5 seg SRBs are ~16,000kN (3.6M pounds). Same idea, less complexity. A SH9 booster (9 Raptors) slightly throttled down equals the SRBs, but with substantially higher Isp.

I daresay the segmented SRBs are more sacrosanct than the core configuration. The pork must flow, after all.

I wonder if a core based on the original SLWT with just two RS-25s would have been able to reach orbit. Probably not; if so, DIRECT-3.0 presumably would have suggested it as an intermediate step. It’s just a shame that we wasted so much time and money on Ares I and Ares V when we could have kept servicing the ISS and Hubble using Shuttle-C or Jupiter-130.

[tater]

1 hour ago, sevenperforce said:

I wonder if a core based on the original SLWT with just two RS-25s would have been able to reach orbit. Probably not; if so, DIRECT-3.0 presumably would have suggested it as an intermediate step. It’s just a shame that we wasted so much time and money on Ares I and Ares V when we could have kept servicing the ISS and Hubble using Shuttle-C or Jupiter-130.

Yeah, Direct was cool.

The worst thing about SLS is the opportunity cost.