r/ArtemisProgram • u/Eastern_Funny9319 • 25d ago
Discussion What Of EUS Was Ready?
I’ve been watching NASASpaceFlight, and during the cancellations, they always brought up how EUS wasn’t even close to ready, that all they had was an oxygen tank structural test article and nothing more. So I just want to make sure, is this true, or an exaggeration? And if it isn’t true, why did Boeing not release anything showing how far along EUS was to the public and Congress? Because based on what I’ve heard, the cancellation of EUS was a good decision, as EUS wasn’t going to be ready anywhere near in time.
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u/SpaceInMyBrain 25d ago
You will get totally opposite answers here. The pro-EUS ones are from people who want everything about SLS to go forward as originally planned, with a Block 1B and eventually a Block 2. Both requiring the very expensive ML2. IIRC a couple of them acknowledge or hint they were employed in the EUS program - or in theSLS program. People in the latter group see the cancellation of the EUS as the first step in eliminating SLS altogether. Which it is. NASA Administrator Jared Isaacman has made it clear that that's his agenda.
The anti-EUS people have been calling for/wishing for a solution involving some other rockets to replace SLS because of the staggering cost and the program's shocking overrun in time and cost. They quote two reports by the office of the Inspector General that warn the Artemis program is in danger of being unsustainable because of the cost of SLS and Gateway. They cheer the cancellation of EUS.
Each group interprets the available info differently or disbelieves (often vociferously) any information or opinion that doesn't support their position. You'll have trouble sorting out the true answer to your question.
IMO the biggest strike against the EUS is it's being built by the same company that builds SLS. The very slow completion of that rocket weighs heavily against the claims that EUS is a lot closer to completion than Isaacman says it is.
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u/Dragon___ 25d ago
EUS was significantly further along than any alternative proposal, including the switch to centaur.
There's a floating narrative that EUS was going to be an upgrade to SLS, and that's quite misleading from the reality. EUS was always going to be the standard upper stage to SLS, in fact the current stage itself being named "Interim" Cryogenic Propulsion Stage is indicative of that fact.
The entire architecture was expecting the implementation of the EUS from the very beginning. Years of engineering and design and test have been invested in creating that second stage, and the supposed lack of hardware in hand is not evidence of the fact that it was far from being finished. Manufacturing is the final and fastest step of any engineering process, let alone one as complicated as launch vehicle development.
Centaur was never intended to be launched on SLS. It wasn't engineered to be launched on SLS, and the proposal to do so requires significantly more cost, schedule, and effort than it would have to simply complete EUS in the first place.
The decision to switch wasn't supported by any serious study, and is simply one of many malicious decisions undertaken by this administration to further kneecap the program and justify outright cancellation in the future.
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u/Kendrome 25d ago
Where is the evidence that finishing the EUS would be quicker and cheaper than adapting the Centaur V? I'm not saying that adaption is easy, but the reports about the EUS showed significant challenges remaining.
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u/LNA-Big_D 25d ago
While I’m not sure where the other guy gets the evidence or numbers from, but I work out at Kennedy and I’ve heard some rumors. Centaur V isn’t free so it’s cost to modify + the price tag ULA put on each completed stage. While EUS may have still had some challenges ahead the cost number I heard recently for (1) centaur rivaled EUS. Now that was just a number I heard from somebody I trust, but it’s still a rumor and I don’t have any evidence of it.
There’s a non-zero chance that we pivot to another option in my opinion. Time will tell though.
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u/reerkat 25d ago
My theory for the pivot is that if SLS is cancelled after Artemis V, then you don't need EUS or Centaur V. Just fly another Artemis III spacer with the starship lander as it is supposed it dock in LEO. Blue's lander then uses the single ICPS.
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u/LNA-Big_D 24d ago
I mean technically we can launch without an US as we will for A3. There is definitely work going into making Centaur work. As of right now we are still advancing with plans to continue post Artemis V. The tough part of that is that it’s going to be under a new admin, so the focus is trying to get back on the moon by IV and centaur ready by V. Congress seems to like us still and they’re the ones who cut our checks, so that’s what I try to focus on.
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u/rocketglare 25d ago
Jared had some good comments on the EUS cancellation. They weren’t anywhere near completion. They had not assembled or demonstrated anything beyond the tankage. Software, electronics, engines, structure, communications, wiring, integration, test,… none of it was very far along. They did the tanks early because those are long lead items to prove out by cryo testing. It didn’t help that there was a stop work and funding issues. Those engines are expensive too. The RL10’s are north of $10M each.
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u/lh2lox 25d ago
This is false. STA would have shipped to MSFC by this fall. STA Forward adapter, thrust structure was 100% complete with instrumentation. STA LOX tank had just completed and passed proof test and was in final stages of integration. The STA LH2 tank had just finished final welds. The Midbody was structurally complete and had about a month of sensor integration. All components avionics and propulsion were in qualification with most completion by end of 2026. Both the flight LOX and LH2 tank were about half welded and on the weld tools at stop work. Most flight hardware was delivered to MAF or already consumed. The flight thrust structure was already in integration welding tubes. The avionics Equipment shelf was structurally assembled with most brackets installed. The development was done. The program was just getting its production legs. The OIG report has a lot of half truths and leaves out critical context. There was basically zero EUS work being done between 2018 and 2020 including nothing on components while EUS was slowed down and NASA changed requirements. Yes there were issues but all development programs have them and the program had turned the corner by Feb 2026.
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u/PhotoGladiator 24d ago
Everything said here is correct.
The recent OIG report was misleading as to what was actually done. A lot of delays were from the design stage of EUS (requirements changing, NASA asking for different capabilities, etc), not the production stage. Things were truly getting going production wise with supply lines, tooling, and training. The lessons learned from the delays on the first core stage were helping to greatly minimize the growing pains of making a new stage altogether.
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u/OrionPax2 25d ago
The only use for the Exploration Upper Stage was to build the Lunar Gateway. With the Gateway cancelled, EUS had no purpose anymore.
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u/redstercoolpanda 24d ago edited 23d ago
The immediate use case was Gateway, and it was the only use case Congress cared about, however I think saying that was its only use is a bit misleading. EUS was a very capable stage, a lot could have been done with it. You could comanifest a CLPS lander with every launch, or launch deep space probes to the outer solar system, or other things like that. Obviously none of that appealed to politicians though.
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u/RT-LAMP 23d ago
Ok but what's the point when Starship or Blue Moon's cislunar transporter can do it for FAR less money in incremental costs even before accounting for the costs of keeping SLS around?
SLS block 1B can deliver something like 30t to Mars and 10t to Jupiter with the assistance of a SRB kick stage.
Blue has stated the cislunar transporter could do 30t to Mars, and if SpaceX can find a way to make a clamshell starship you easily have the volume and payload for a fully fueled Centaur stage (or equivalent) and payload dropped off in LEO. A fully fueled Centaur V upper stage in LEO would also be able to do 30t to Mars or 12t to Jupiter.
If you put a Centaur in SLS 1B you do go up to something like 13t. which is probably something that a Starship+Centaur combo couldn't do... unless you expend the starship too which would free up another 25t of fuel to push it further out and cut probably 20t of mass at least which should add a few more tons of payload.
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u/carbsna 23d ago
Will it find its place in CLPS with its price though?
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u/redstercoolpanda 23d ago
Well not any more because it’s dead now. But it would have been launching anyways with Orion, so there is no reason they would have to charge the cost of its launch to put a lander on there.
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u/okan170 25d ago edited 25d ago
Most of the flight structures were rumored to be completed including the most of the tanks, avionics shelf, thrust structure and engines. Apparently almost all the STA was done as well as the interstage structure but we may not see any info or confirmation about anything until after the current admin.