With which upper stage will Artemis IV fly?

[whitelancer64]

Isn't the more important question is whether NASA will have an uncrewed test flight for the EUS BEFORE the Artemis IV mission?

Artemis I was uncrewed, and that used the ICPS, shouldn't the change of the 2nd stage merit an uncrewed test flight?

Artemis I was more of an all-up test of the core than just the ICPS, IMO.

That said, the obvious answer to your perfectly reasonable question is that NASA can't afford an all-up test of Block 1B.

There's a lot that's new about EUS, but there's also a lot that's pretty well-trodden ground.  The RL10C-3 hasn't flown, but it's yet another variant of an extremely well-understood engine, with the usual variations in expansion ratio and O:F--not exactly [ahem] rocket science.  It has a new interstage, and of course you have the USA on the top instead of the LVSA.

The big change is that the tanks are composite, which is frankly insane.¹  I expect them to have all kinds of gnarly, cost-plus-supported problems with them.  But it's the kind of structural work that we know how to test on the ground.

____________
¹Does anybody know why NASA thought it was a good idea to go to composite over the aluminum isogrid?  Are the mass margins for Block 1B so tight that this is worth the exorbitant development costs?  Or is this a way for Boeing to fleece us just a little bit more?

Enough mass savings to improve performance by 30%

"For the Boeing all-composite tank, testing and modeling so far indicate the potential to increase the SLS Block 1B’s performance by up to 30% if the Exploration Upper Stage’s design with welded tanks were switched to the new all-composite structure."

https://www.nasaspaceflight.com/2022/03/boeing-all-composite-cryo-tank/

[TheRadicalModerate]

Isn't the more important question is whether NASA will have an uncrewed test flight for the EUS BEFORE the Artemis IV mission?

Artemis I was uncrewed, and that used the ICPS, shouldn't the change of the 2nd stage merit an uncrewed test flight?

Artemis I was more of an all-up test of the core than just the ICPS, IMO.

That said, the obvious answer to your perfectly reasonable question is that NASA can't afford an all-up test of Block 1B.

There's a lot that's new about EUS, but there's also a lot that's pretty well-trodden ground.  The RL10C-3 hasn't flown, but it's yet another variant of an extremely well-understood engine, with the usual variations in expansion ratio and O:F--not exactly [ahem] rocket science.  It has a new interstage, and of course you have the USA on the top instead of the LVSA.

The big change is that the tanks are composite, which is frankly insane.¹  I expect them to have all kinds of gnarly, cost-plus-supported problems with them.  But it's the kind of structural work that we know how to test on the ground.

____________
¹Does anybody know why NASA thought it was a good idea to go to composite over the aluminum isogrid?  Are the mass margins for Block 1B so tight that this is worth the exorbitant development costs?  Or is this a way for Boeing to fleece us just a little bit more?

Enough mass savings to improve performance by 30%

"For the Boeing all-composite tank, testing and modeling so far indicate the potential to increase the SLS Block 1B’s performance by up to 30% if the Exploration Upper Stage’s design with welded tanks were switched to the new all-composite structure."

https://www.nasaspaceflight.com/2022/03/boeing-all-composite-cryo-tank/

I think I was wrong that the Arty 4 EUS is composite.  Boeing is proposing to cut a future version of the EUS over to composite, but I think Arty 4 will have an aluminum EUS.  Do I have this right?

Block 1B will currently handle a roughly 10t co-manifest.  So an all-composite EUS would presumably carry a 13t co-manifest.  But nobody's going to count on that, are they?  So the composite version is simply another way to throw good money after bad.

Given that, I'm not sure how even Boeing can manage to be as far behind on the EUS v1.0 as they appear to be.

[Vahe231991]

Isn't the more important question is whether NASA will have an uncrewed test flight for the EUS BEFORE the Artemis IV mission?

Artemis I was uncrewed, and that used the ICPS, shouldn't the change of the 2nd stage merit an uncrewed test flight?

NASA is not planning an uncrewed test flight for the EUS ahead of the Artemis 4 mission. The Artemis 2 is manned but will use the ICPS.

[Coastal Ron]

Isn't the more important question is whether NASA will have an uncrewed test flight for the EUS BEFORE the Artemis IV mission?

Artemis I was uncrewed, and that used the ICPS, shouldn't the change of the 2nd stage merit an uncrewed test flight?

NASA is not planning an uncrewed test flight for the EUS ahead of the Artemis 4 mission.

Everyone knows that.

The question is whether they SHOULD perform an uncrewed test flight, given the significant changes the EUS introduces.

And it doesn't matter what they call the test flight, so they can retain their current numbering system for future operational flights, in which case the same question for Artemis IV remains.

[dglow]

I’m appreciating the steadily growing response to this poll, as well as the solid discussion above – thank you, everyone.

And check out those results! At the time of this post: 25 for the POR, EUS, and 26 for plan B, ICPS. The results had leaned heavily toward ICPS since the poll’s creation, but recently crept back to a near even split. Nice.


 

[deltaV]

Enough mass savings to improve performance by 30%

"For the Boeing all-composite tank, testing and modeling so far indicate the potential to increase the SLS Block 1B’s performance by up to 30% if the Exploration Upper Stage’s design with welded tanks were switched to the new all-composite structure."

https://www.nasaspaceflight.com/2022/03/boeing-all-composite-cryo-tank/

What exactly do they mean by increasing performance by 30%? It's unclear what they mean by "performance" but I'm guessing they mean payload to TLI, which is 42 tonnes for block 1B so a 30% increase is an increase of 12.6 tonnes. Getting that from a dry mass decrease requires reducing EUS dry mass from 14.1 tonnes to 14.1-12.6=1.5 tonnes, which seems absurdly low since the engines alone are 0.9 tonnes and composites aren't massless magic. It would work if they were quoting a 30% increase in performance to Mars or Jupiter or something but that's not a usual performance metric for SLS so that seems unlikely. Maybe they excluded the mass of Orion from the payload similar to how mass of the shuttle wasn't always included in shuttle's payload?

[TheRadicalModerate]

Enough mass savings to improve performance by 30%

"For the Boeing all-composite tank, testing and modeling so far indicate the potential to increase the SLS Block 1B’s performance by up to 30% if the Exploration Upper Stage’s design with welded tanks were switched to the new all-composite structure."

https://www.nasaspaceflight.com/2022/03/boeing-all-composite-cryo-tank/

What exactly do they mean by increasing performance by 30%? It's unclear what they mean by "performance" but I'm guessing they mean payload to TLI, which is 42 tonnes for block 1B so a 30% increase is an increase of 12.6 tonnes. Getting that from a dry mass decrease requires reducing EUS dry mass from 14.1 tonnes to 14.1-12.6=1.5 tonnes, which seems absurdly low since the engines alone are 0.9 tonnes and composites aren't massless magic. It would work if they were quoting a 30% increase in performance to Mars or Jupiter or something but that's not a usual performance metric for SLS so that seems unlikely. Maybe they excluded the mass of Orion from the payload similar to how mass of the shuttle wasn't always included in shuttle's payload?

I agree that the term "performance" is, as always, somewhat fraught.

My assumption is that "performance" applies to the maximum size of the co-manifest payload.  A 30% improvement would therefore take max co-manifest from ~10t to ~13t, which in turn implies a 3t reduction in EUS dry mass.  That sounds about right to me, and would take EUS dry mass from ~14.1t to 11.1t, which would, assuming about 126t of prop, take ε (=dry/(dry+prop)) from 10.1% to 8.1%.

For reference, Centaur 5 ε is about 9.1%.

However, the (mostly rhetorical) questions still remain:  What does increasing Block 1B's TLI performance by 3t enable, and is enabling it worth however many ungodly billions Boeing will charge to do it?  Mostly rhetorical answers:  nothing, and no, respectively.

[dglow]

Politicians get jobs in districts, NASA gets R&D into composite tanks. I wonder if there was any knowledge transfer from X-33.

[TheRadicalModerate]

Politicians get jobs in districts, NASA gets R&D into composite tanks. I wonder if there was any knowledge transfer from X-33.

I'm not completely opposed to that kind of pork.  At least it's moving the state of the art to the right a bit, unlike everything else in SLS.  But if you put that into the critical path of Artemis, that's going to be a problem.

There are ways to avoid that, mostly by keeping the composite work in parallel and substituting it for the well-understood aluminum fabrication only when it's unlikely to cause a huge schedule problem.  But will that actually happen?  It's not the most cost-effective way of feeding the Artemis pipeline, even if it's the most schedule-risk-avoidant.

So when does this "composite catastrophe" hit the program?  Arty 5?  Arty 6?

[whitelancer64]

Politicians get jobs in districts, NASA gets R&D into composite tanks. I wonder if there was any knowledge transfer from X-33.

Cryogenic composite tanks have been worked on, by many different companies, for the past 20 years (the X-33 was cancelled in 2001). Lockheed Martin successfully tested an X-33 tank a few years later. There's been a lot of development in the time since then, so more recent work is probably much more relevant. Rocket Lab's Electron uses all composite tankage. 

And Boeing has been working with NASA on cryogenic composite tanks since 2011.

https://spaceref.com/press-release/nasa-picks-boeing-for-composite-cryogenic-propellant-tank-tests/

[dglow]

Politicians get jobs in districts, NASA gets R&D into composite tanks. I wonder if there was any knowledge transfer from X-33.

Cryogenic composite tanks have been worked on, by many different companies, for the past 20 years (the X-33 was cancelled in 2001). Lockheed Martin successfully tested an X-33 tank a few years later. There's been a lot of development in the time since then, so more recent work is probably much more relevant. Rocket Lab's Electron uses all composite tankage. 

And Boeing has been working with NASA on cryogenic composite tanks since 2011.

https://spaceref.com/press-release/nasa-picks-boeing-for-composite-cryogenic-propellant-tank-tests/

My question: would any composite tank efforts, sponsored by NASA, be contributing to (and drawing from) a single repository of knowledge/experience, or are Lockheed’s and Boeing’s learnings isolated from each other?

[TheRadicalModerate]

Can somebody confirm that the Arty 4 EUS does not have composite tanks?

I don't think the tanks themselves are particularly challenging, although LH2 is always challenging.  But the architecture of the EUS is quite similar to the DCSS:  the LOX tank and engine pod dangle below the LH2 tank, connected by some trusswork.

During SLS core and SRB burns, that trusswork is in tension, while the interstage transmits the compressive thrust loads to the LH2 tank.  But when the RL10's on the EUS are burning, the trusswork is transmitting the compressive loads.

I think the LOX tank is kind of cupped by the combination of the trusswork and the engine pod, so it only experiences inertial loads (i.e., reactive loads caused by the net acceleration of the aggregate vehicle).  If that's the case, then mating a composite LOX tank with the aluminum trusswork shouldn't be particularly tricky.  But if the trusswork has to transmit thrust compressive loads and inertial tension loads through the LOX tank, that could be tricky.

Can somebody confirm that the LOX tank really only needs to deal with its own inertial loads?

[Broken_Soap]

Can somebody confirm that the Arty 4 EUS does not have composite tanks?

Here's the LOX tank weld confidence article for EUS, which is an aluminum tank, obviously not composite.
All reporting so far on the EUS composite LOX tank option has said it is a potential upgrade far down the line.
The actual design being built has always had an aluminum tank.
Some of Philip Sloss' EUS articles on this site have also talked about that quite a bit.

[sdsds]

I voted "EUS for Artemis IV," based on how public relations decisions get made. There may well be an earlier flight, perhaps called "Artemis III-B," that flies with a fourth iCPS. I'm simply guessing that flight wouldn't be called "Artemis IV."

[JEF_300]

Per the most recent "Off-Nominal" podcast episode, I'm feeling somewhat more optimistic about seeing the EUS fly sooner rather than later. As it seems more and more likely that there will be a gap of a year or three between Artemis II and III, I think it also becomes more and more likely that there will be an EUS test flight slotted in to fill that gap. And once you've done that, EUS on Artemis IV is a no brainer.

[c4fusion]

Per the most recent "Off-Nominal" podcast episode, I'm feeling somewhat more optimistic about seeing the EUS fly sooner rather than later. As it seems more and more likely that there will be a gap of a year or three between Artemis II and III, I think it also becomes more and more likely that there will be an EUS test flight slotted in to fill that gap. And once you've done that, EUS on Artemis IV is a no brainer.

Ironically, that same show made me more pessimistic about the chances that the EUS will be flying on Artemis 4.  Will the EUS test article be ready by then?  And also, will that be the direction that we will go for Artemis II.V?

[JEF_300]

Per the most recent "Off-Nominal" podcast episode, I'm feeling somewhat more optimistic about seeing the EUS fly sooner rather than later. As it seems more and more likely that there will be a gap of a year or three between Artemis II and III, I think it also becomes more and more likely that there will be an EUS test flight slotted in to fill that gap. And once you've done that, EUS on Artemis IV is a no brainer.

Ironically, that same show made me more pessimistic about the chances that the EUS will be flying on Artemis 4.  Will the EUS test article be ready by then?  And also, will that be the direction that we will go for Artemis II.V?

Like a dozen different development programs, most of which are behind schedule, have to come together on time to make Artemis III and IV happen. To get an EUS test flight, only the one dev program has to happen. And it doesn't even need to be on schedule, just more on schedule than one of the critical path items of either of those missions.

Over in the EUS schedule thread, the consensus seems to be that the flight stage won't have finished it's green run until late-2026/early-2027. Which sounds bad, but considering that a 2027 or even 2028 Artemis III seems entirely plausible, I think that at the very least EUS on Artemis IV makes sense.

[dglow]

To get an EUS test flight, only the one dev program has to happen.

And ML2.

[sdsds]

Is payload availability a factor in the consideration?

[Broken_Soap]

Per the most recent "Off-Nominal" podcast episode, I'm feeling somewhat more optimistic about seeing the EUS fly sooner rather than later. As it seems more and more likely that there will be a gap of a year or three between Artemis II and III, I think it also becomes more and more likely that there will be an EUS test flight slotted in to fill that gap. And once you've done that, EUS on Artemis IV is a no brainer.

EUS needs ML-2 to be ready to fly, so any EUS test flight would inevitably delay Artemis IV significantly, likely into the early 2030s.
I don't see NASA changing their mind about flying crew on the first flight of the stage at this point, unless there was another payload that would require SLS Block 1B perfromance, which seems unlikely.
At this point ICPS beyond Artemis III becomes more and more distant of a possibility with every passing day.
When NROL-70 flies and ULA mothballs what's left of the Delta IV production tooling then it'll be EUS or bust.
Right now at NASA there doesn't seem to be any will or money to change that before it would be too late to order another stage.