SLS General Discussion Thread 5

[Chris Bergin]

New Discussion Thread for SLS.

SLS Articles (lots of them):
https://www.nasaspaceflight.com/?s=SLS

L2 SLS (Vast):
https://forum.nasaspaceflight.com/index.php?board=48.0

--

Do not argue. Make sure your posts are on topic and interesting. Don't bandwagon. There's a lot of SLS news out there (well mainly just via our articles as there's very little else out there on the technical side).

Attempt to derail this with "But Falcon Heavy" etc.....and your post will be removed. Plenty of "vs" threads. This one is about discussing SLS.

Other available thread include:
Discussion/Comparison of the new generation of American heavy lift launchers
Discussion on Alternative Launchers to SLS for Artemis

[meberbs]

Plenty of "vs" threads.

Can you link those in the OP so the thread derailers know where to go? I'm only aware of this one:

Discussion/Comparison of the new generation of American heavy lift launchers
https://forum.nasaspaceflight.com/index.php?topic=43073.0

Discussion on Alternative Launchers to SLS for Artemis
https://forum.nasaspaceflight.com/index.php?topic=50252.0

Mods:Feel free to delete this post if link is placed in OP

[Mark S]

Thanks Chris, for the new thread and the stated rules. We are (hopefully) less than a year away from the first launch of SLS, so there will be lots of relevant material to discuss.

I'm looking forward to more news from Stennis regarding the green run, the start of booster stacking, completion of Orion extended vacuum testing at Plum Brook, CS-2 developments, and so much more!

Keep up the great work!

Mark S.

[meberbs]

We are (hopefully) less than a year away from the first launch of SLS, so there will be lots of relevant material to discuss.

The 1 year mark is still around 6 weeks away. And that is just to the earliest date being considered. realistically the launch will be summer or maybe even later.

[JohnFornaro]

We are (hopefully) less than a year away from the first launch of SLS, so there will be lots of relevant material to discuss.

The 1 year mark is still around 6 weeks away. And that is just to the earliest date being considered. realistically the launch will be summer or maybe even later.

So.  WILL SLS launch on time and on budget?  I confess to being one of the doubters.

[Mark S]

We are (hopefully) less than a year away from the first launch of SLS, so there will be lots of relevant material to discuss.

The 1 year mark is still around 6 weeks away. And that is just to the earliest date being considered. realistically the launch will be summer or maybe even later.

So.  WILL SLS launch on time and on budget?  I confess to being one of the doubters.

C'mon John, you've been kicking around NSF long enough to know this. There is no overall budget for SLS and never has been. So SLS can't be over (or under) budget. NASA spends whatever Congress gives them, sometimes with strict requirements, sometimes ... less strict.

Regarding the launch date, I am also skeptical. First Congress said first launch must be no later than 12/31/16. Then NASA said definitely by 12/31/17 for sure. Then there was the misaligned vertical welding tool, due to a bad foundation. Then there was the dropped tank dome. Then the super difficult and complex engine section, because no one had ever done an engine section with four engines before! /s Somewhere in there was a government shutdown. And a tornado. Etc. So after all that, what's a few months/years/Presidential terms between friends, anyway?

And yes, even after all that, I am still excited for the impending first launch of SLS.

Cheers!

[dirkidirk]

We are (hopefully) less than a year away from the first launch of SLS, so there will be lots of relevant material to discuss.

The 1 year mark is still around 6 weeks away. And that is just to the earliest date being considered. realistically the launch will be summer or maybe even later.

So.  WILL SLS launch on time and on budget?  I confess to being one of the doubters.

C'mon John, you've been kicking around NSF long enough to know this. There is no overall budget for SLS and never has been. So SLS can't be over (or under) budget. NASA spends whatever Congress gives them, sometimes with strict requirements, sometimes ... less strict.

Regarding the launch date, I am also skeptical. First Congress said first launch must be no later than 12/31/16. Then NASA said definitely by 12/31/17 for sure. Then there was the misaligned vertical welding tool, due to a bad foundation. Then there was the dropped tank dome. Then the super difficult and complex engine section, because no one had ever done an engine section with four engines before! /s Somewhere in there was a government shutdown. And a tornado. Etc. So after all that, what's a few months/years/Presidential terms between friends, anyway?

And yes, even after all that, I am still excited for the impending first launch of SLS.

Cheers!

I am only excited because it will look cool.

[Proponent]

First Congress said first launch must be no later than 12/31/16.

Actually, SLS's minimal configuration was to be operational by that date:

Priority should be placed on the core elements with the goal for operational capability for the core elements not later than December 31, 2016.

That implies at least one test flight at an earlier date, and, indeed, the Act specifically envisions such a test flight of Orion to the ISS:

It shall be the goal to achieve full operational capability for the transportation vehicle developed pursuant to this subsection by not later than December 31, 2016. For purposes of meeting such goal, the Administrator may undertake a test of the transportation vehicle at the ISS before that date.

There is some wiggle room here:  since the Act does not define "operational," the first launch could conceivably be so designated.  Since the test refers specifically to Orion, it might conceivably have taken place on another launch vehicle, though I don't recall much discussion of the possibility at the time.  I think it's fair to say that the Act effectively requires a first launch well before 31 December 2016, probably at least a year before, given plausible production rates.

In fact, if NASA were to hold Orion to the same standard as other spacecraft visiting ISS, Orion would need to be demonstrated in LEO independent of ISS before a mission to ISS was allowed.  Even if NASA did non require a non-ISS mission first, then if the ISS mission were crewed, you'd think there would have been a uncrewed mission before that.  That would imply first flight by about December 2014.

Under the current schedule, Artemis 2 will presumably be the first operational flight of Orion/SLS.  Perhaps it's the date of this flight that provides the most apples-to-apples measure of schedule slippage.

[jadebenn]

Actually, SLS's minimal configuration was to be operational by that date:

Do keep in mind that:
1: NASA immediately decried a date of 2016 as unrealistic and refused to acknowledge it in favor of a "more realistic" 2017
2: NASA decided to skip the intermediate evolution of SLS (Block 0, or "stumpy"), because it was a technological dead-end. Instead, they essentially jumped halfway through the originally-envisioned SLS evolution path.

[Proponent]

Do keep in mind that:
1: NASA immediately decried a date of 2016 as unrealistic and refused to acknowledge it in favor of a "more realistic" 2017
2: NASA decided to skip the intermediate evolution of SLS (Block 0, or "stumpy"), because it was a technological dead-end. Instead, they essentially jumped halfway through the originally-envisioned SLS evolution path.

1. SLS advocates at the time screamed that NASA was trying to kill SLS by "slow-rolling" it, but we now see that NASA was extremely optimistic.
2. What NASA now calls Block 1 differs from Stumpy in having four rather than three RS-25's and a Delta IV upper stage.  Those are relatively minor changes, driven, I strongly suspect, by the realization that Congress's idea of using Orion/SLS as back-up ISS transport or in any other LEO role was utterly ridiculous.  A significant step toward SLS evolutionalry end point would have been early introduction of either a real second stage (now known as EUS) or of advanced boosters, neither of which happened.

Long story short, I don't see how passing over Stumpy for today's Block 1 contributed much to SLS's prodigious schedule slippage.

[jadebenn]

I see just two difference between Stumpy and what NASA now calls Block 1:  Block 1 has four rather than three RS-25's, and Block 1 has a slightly modified Delta IV upper stage.

The main difference is that Block 0 is essentially one of DIRECT's Jupiter rockets (boy, haven't heard that name in a while), so no core stretch. This also meant a less-compact engine section, and (most likely) less-thick tank walls, which would have avoided a lot of the issues that plagued core stage development.

However, the strike against it was that it had no evolution path. You'll notice that the "Block I" depicted here essentially requires replacement of the entire core. In all likelihood, such an effort would have never happened. Its future would more uncertain than the current Block 2 SLS is.

I'd say "Block I" is much closer to the modern Block 1. It's just got one engine too many and one ICPS too few.

[Proponent]

I see just two difference between Stumpy and what NASA now calls Block 1:  Block 1 has four rather than three RS-25's, and Block 1 has a slightly modified Delta IV upper stage.

The main difference is that Block 0 is essentially one of DIRECT's Jupiter rockets (boy, haven't heard that name in a while), so no core stretch. This also meant a less-compact engine section, and (most likely) less-thick tank walls, which would have avoided a lot of the issues that plagued core stage development.

However, the strike against it was that it had no evolution path. You'll notice that the "Block I" depicted here essentially requires replacement of the entire core. In all likelihood, such an effort would have never happened. Its future would more uncertain than the current Block 2 SLS is.

Because of differing loads, Stumpy's unstretched core still would have been fundamentally different from the Shuttle's ET.

I'd say "Block I" is much closer to the modern Block 1. It's just got one engine too many and one ICPS too few.

Yes, but the old "Block 1" is still an EUS and advanced boosters away from the old "Block 3."

EDIT:  "and" to "an" in final sentence

[jadebenn]

Because of differing loads, Stumpy's unstretched core still would have been fundamentally different from the Shuttle's ET.

Yes, which was part of the issue. While it would've been less difficult to make than the current SLS core, it wouldn't exactly have been a walk in the park either. Why go through all that effort to get a dead-end and have to do it again a few years later?

Yes, but the old "Block 1" is still and EUS and advanced boosters away from the old "Block 3."

Okay, and?

[SWGlassPit]

Then the super difficult and complex engine section, because no one had ever done an engine section with four engines before! /s

Only picking on this one just a touch:

My understanding is that the challenge in this case was the extremely limited amount of space (in particular, height) available to work with to route all the plumbing and have it work right.

[Proponent]

My understanding is that the challenge in this case was the extremely limited amount of space (in particular, height) available to work with to route all the plumbing and have it work right.

If it was a matter of height, why wasn't the height increased a bit more?  Was there some constraint that made this impractical, or was the difficulty of working with the height as is not recognized?

[Proponent]

Because of differing loads, Stumpy's unstretched core still would have been fundamentally different from the Shuttle's ET.

Yes, which was part of the issue. While it would've been less difficult to make than the current SLS core, it wouldn't exactly have been a walk in the park either. Why go through all that effort to get a dead-end and have to do it again a few years later?

I agree that bypassing Stumpy was a good idea.  I'm just saying that I doubt that doing so has contributed much to the delays.

Yes, but the old "Block 1" is still and EUS and advanced boosters away from the old "Block 3."

Okay, and?

I disagree that with today's Block 1 NASA made a major leap forward on the evolutionary path.

[Khadgars]

I disagree that with today's Block 1 NASA made a major leap forward on the evolutionary path.

Naturally, because it isn't SpaceX yes?

zubenelgenubi edit March 10 to quote.  Also, noting that your question is ad hominem--don't.

[Proponent]

I disagree that with today's Block 1 NASA made a major leap forward on the evolutionary path.

Naturally, because it isn't SpaceX yes?

No, SpaceX has nothing to do with it.  Please don't drag us there.  I was referring to the evolutionary path for SLS identified by jadebenn.  Given that today's Block 1 lacks an EUS, advanced boosters (and possibly a fifth RS-25), I think it's closer to Stumpy than to the "Block III" that NASA was (extraordinarily optimistically) projecting for 2026.

Edit zubenelgenubi March 10: quote repair.

[SWGlassPit]

My understanding is that the challenge in this case was the extremely limited amount of space (in particular, height) available to work with to route all the plumbing and have it work right.

If it was a matter of height, why wasn't the height increased a bit more?  Was there some constraint that made this impractical, or was the difficulty of working with the height as is not recognized?

As I understand it, they were already bumping up against how tall they could be (maybe not for Block 1, but for later configurations) and still get out the VAB doors.  Keep in mind also that with work moving in parallel on the launcher, changing the height of the engine section would require design changes to literally every single umbilical arm as well, so these basic sizing decisions are made early, and it's enormously expensive and difficult to try to change them later on.

[Proponent]

Good thing, then, that the 5-engine configuration was ditched.