NASA finally acknowledges the elephant in the room with the SLS rocket

"You know, you're right, the flight rate—three years is a long time."

See full article...

 

[Wickwick]

The more powerful 10m Ares V had just as much STS heritage as the 8.4m SLS.

But an Ares V is fundamentally the same rocket - just scaled up. The NASA Authorization Act of 2010 that officially kicked off SLS as separate from Ares V gave the goals of 70-100 tons to LEO with evolution to 130. So the Ares V design was no longer responsive to Congress' requirements. Within the new requirements, SLS was about the best one could do.

 

[rhgedaly]

The SLS is truly a monument befitting of our times: Towering tall, vain, wasteful, and hopefully a lesson to later generations.

... and Orange! Truly befitting our times.

 

[TylerH]

Orion can be launched by New Glenn and moved via tug to the Moon. However Blue Origin keeps flirting with building its own crewed spacecraft, so the marriage between the two has never occurred. But the bottom line is that I do not believe SLS and Orion are tied to the hip beyond Artemis III.

Is this 'tug' referring to any viable satellite or spacecraft which can attach to Orion? Or does it refer specifically to Blue Ring, which is still conceptual?

 

[TylerH]

People here want to give credit to Obama for trying to cancel SLS.. but Constellation was cancelled (checks notes) on his watch.

Congress determine what NASA works on, for the most part, by choosing what to fund and what to require by law. Don't blame or give credit to any White House administration on either side of the aisle. They can at best set aspirational direction and political motivation, but Congress gets what it wants. That's the benefit of having the power of not just controlling the law but also controlling the purse strings.

 

[brionl]

As a high school student, I had a week where I spent shadowing a professional. In my case, it was a chemist who was researching more efficient ways to extract platinum from waste solution.

Was his name Richard Seaton?

Skylark of Space

 

[miker289]

Between Shuttle, Atlas, and Delta launches, I'm betting there have been 4x the number of hydrogen fueling events at the Cape than there have been from Kourou.

Yessir. The expertise is right there in Brevard county.

 

[vanzandtj]

Underrated comment. This is the thing that frustrates me most about SLS: granted that pork is the primary purpose, the "side effect" (making SLS) is actively detrimental to the nation and world compared to just writing checks to people and companies for doing nothing. As I wrote some months ago,

"Would Congress accept NASA keeping the money flowing to the primes and their workforce, but for things that create value instead of continuing to flog obsolete technology in a downward spiral that will leave the next generation of all three dilapidated and hollow?"

Isaacman has hinted at it, and it seems like it should be politically viable (after Artemis 3 anyway), but "why should Congress care, as long as they get their pork" cuts both ways: why should they lift a finger when they're already getting it with the "SLS 4EVER" policy? One answer is that, as a secondary priority, after re-election (which is served by pork and other things), they should care about making things better instead of worse. We'll see how that goes.

I understood Isaacman's nuclear-electric proposal to be that alternate way to distribute pork while doing something useful.

 

[miker289]

That isn't the reason NASA hasn't kept up with manned spaceflight. The reason is lack of interest by government in being bold and visionary. NASA is a government agency, and thus in many ways reflective of the priorities of that government. In the case of SLS, the priority is funneling money into congressional districts.

Manned or unmanned spaceflight? Why not both? They are both quite feasible within NASA's budget, unless you squander money on pork rockets like SLS.

I strongly disagree on manned spaceflight being pointless. There are multiple valid motives to pursue manned spaceflight. Currently mostly linked to science but in a deeper future also to resource exploitation. If it is science alone, Apollo proved that humans may cost more to send, but they are much more adaptivle than machines. Same goes for the ISS.

Compare with James Cook and his voyages. Would it have been better to just stay at home?

At the risk of sounding romantic, human spaceflight is also inspirational and good for the soul.


View: https://youtu.be/YH3c1QZzRK4?si=xOQ89NQ9JsQNC8pP

The short film "Wanderers" posted here by @Starlionblue is outstanding. Thank you for posting it. I have shown it to classrooms. When people ask me why I spent 37 years in the rocket business when "there are so many problems on Earth ..." I just send them a link to this film.

 

[miker289]

Hydrogen always leaks, so they just dealt with the delays. I think its been pointed out that upper stages have smaller connectors that make them easier to engineer and fewer leakage problems.

And while none of those rockets cost as much as the SLS, they were all expensive. The blueprint for high cadence lowest cost space launch is currently using a single dense propellent for two stages that share the same engine model using mass engines for the first stage.

Hydrolox will always have the highest ISP (unless you want to get exotic with awful tripropellents and flourine), but its costs, increased dry mass, and launch handling complexities will always kill its economics.

Flourine = "Big green cloud! Everybody run!"

 

[theradicalmoderate]

The SLS is truly a monument befitting of our times: Towering tall, vain, wasteful, and hopefully a lesson to later generations.

And orange. Don’t forget orange. If only it had a comb-over…

 

[blackhawk887]

I hadn't really considered it, but why is SLS's rated payload to LEO (95t) so low? We can be generous and round that up to 100t to include ICPS mass. STS could put just shy of 123t in orbit, itself included. Main engines, plumbing (10t), OMS engines, tanks, and propellant (12t), enough structure to hold all of it together (~5t?), we should easily be able to get a cargo variant together for under 30t total wet mass. That's >90t payload to orbit. What about SLS causes it to perform so poorly with an extra 25% SRB, 33% more engine, 40% more first stage propellant, and a real upper stage instead of an overweight kick stage?

SLS mass at MECO is 160t. STS was about 150t, but it targeted a lower apogee.

 

[xoa]

There is only one valid motive to pursue manned spaceflight, and that is to figure out how to do manned spaceflight. It is itself the goal, and the only thing directly furthered by those actions. Sure, we can do science while we're there, but arguments about whether robots or humans are better at science in space is missing the whole point that science is a secondary component of the mission. In every venture, science is ultimately the means, not the goal.

Are you sticking "beyond Earth colonization" under the "manned spaceflight" heading? Because yeah manned spaceflight is a necessary component towards the goal of having humans somewhere other than Earth given that space lies between here and there, but seems a little odd to smush them together too as despite overlap there are some different tech and skill stacks involved. If you're not including that as a goal then I'd say what you wrote is more about what you personally consider the "only one valid motive" vs what others might.

 

[Bill Swallow]

Was his name Richard Seaton?

Skylark of Space

I was wondering the same thing. Just make sure there are no loose wires and copper steam baths laying around, and that the Whatistron is not running.

 

[Bill Swallow]

Flourine = "Big green cloud! Everybody run!"

'Flourine' is a mineral useful in baking. Or did you guys mean 'Fluorine'?

 

[theradicalmoderate]

Killing SLS without funding a credible replacement was a bad idea. The US should have superheavy lift. Just not this one.

Unfortunately, that's exactly the argument that Cruz is using to continue Block 1B development.

Hopefully, when/if Starship starts refueling successfully, his tune will change. There is a case to be made that killing SLS before something has been proven to be able to take over its mission would take an unnecessary risk.¹ But F9/D2 + even a rudimentary HLS Starship (it needs the crew module to work, but it doesn't even need to land!) is a complete replacement for its part of the Artemis conops. That's something that could be proven out this year.

We've already flushed a nice chunk of change down the toilet for FY26 EUS and ML2 development. But the FY27-28-29-30 out-year money has only been obligated. That's nothing a nice rescission can't fix.


_________
¹We'll leave aside the fact that SLS/Orion has nothing to do without an HLS, and Starship is required to do that.

 

[theradicalmoderate]

New Glenn would need a special stage adapter with aero, plus a bunch of crew related work: EDS, access arm, tower escape, etc. It would be a very similar cost and effort to put it on Starship with an expendable version of the ship and launch directly to TLI. So there are several good options, and neither need orbital refueling or other unproven tech.

There remains the issue that without a lander to rendezvous with, Orion has no actual purpose.

The difference is if Blue adapts Orion, then there are two CCC (cislunar commercial crew) vendors: SpaceX with D2 + HLS, and Blue with NG/Orion + Cislunar Transporter. That's a very nice property.

Note that if CT takes Orion to LLO, Orion can make its own way back direct to EDL. That would eliminate the extra 950m/s needed to deal with NRHO.

Is this an optimal solution? By no means. But it's likely several years quicker to operational status than Blue could manage on their own, and it has the nice property that it makes LockMart perfectly happy to throw Boeing, NorGrumm, AJR-L3H, and Bechtel under the bus.

 

[wagnerrp]

Are you sticking "beyond Earth colonization" under the "manned spaceflight" heading? Because yeah manned spaceflight is a necessary component towards the goal of having humans somewhere other than Earth given that space lies between here and there, but seems a little odd to smush them together too as despite overlap there are some different tech and skill stacks involved. If you're not including that as a goal then I'd say what you wrote is more about what you personally consider the "only one valid motive" vs what others might.

Yes. I'm saying the purpose of manned spaceflight is "beyond Earth colonization". The other motive is thrillseeking. It's fun, it's exciting, it's inspirational (vicarious excitement). Attach whatever validity you may towards that motive. Obviously colonization is not currently possible, but every crewed mission to space has involved tests to extend the duration we can stay, and mitigate the consequences of doing so.

The accomplishments of the Apollo missions is always touted as evidence for on-site crews instead of telerobotics, but it's always compared against programs that cost two orders of magnitude less to accomplish. ISS has hosted various non-biological experiments, but what's the cost to do so versus something like Varda?

I am not saying that colonization and crewed missions to further that goal are stupid and pointless. I am saying that putting that crew there is the goal, and the tasks the crew might perform are an afterthought. Sending a robot in place of a crew achieves zero of that goal.

 

[KenM]

This will end up as a "sunk cost fallacy" case study at some point...

Take it out back and end the program already. Then again, the alternatives are just enriching billionaires.

 

[Statistical]

SLS is going to be hard to kill. Especially as Senators watch SpaceX and Blue Origin twist themselves into knots trying to bring their crappy, overly complex, orbital refueling, garbage architectures online. NASA mission planners will be BEGGING congress to build more SLS launch vehicles. It's simple .. one mission and one launch ... is already enough complexity. SpaceX and Blue Origin are going to embarrass themselves.

There is absolutely nothing manned that we can do BEO that is interesting with one launch. Not with SLS not future blocks, not any existing launch vehicle. The future is multi-launch architectures. One way or another. Either in the 2020s or in the 2050s.

For unmanned launches nobody can afford the SLS and nobody needs it. The combination of F9, New Glenn, and Starship can cover every launch need. Hell you could spend the starhip upper stage as a disposable EDS and it would still be a tiny fraction of the SLS.

 

[theradicalmoderate]

Hydrogen works fine. It wasn't even necessarily a bad decision for the STS Orbiters. The engines needed to come home and hydrogen as an upper stage is a good choice.

The horrible choice was to make SLS a traditional disposable launcher from parts made for a (partially) reusable launch system. NASA had already optimized a heavy lifter for that role. It was called Saturn V. So blame congress for forcing NASA to build a new rocket to meet the Saturn V's mission using Shuttle parts - not Saturn V derivatives.

All of the tooling from Saturn V had rusted away. Restarting its production wasn't an option. Meanwhile, SLS was an attempt to keep all the STS tooling from falling into disuse.

---

I will make one weak, devil's advocate-like defense of reusing STS components: their reliability was known to extremely high accuracy, and the way they were put together gave SLS/Orion a ready-made probabilistic risk analysis model. That's not a terrible argument for punting on doing a couple of extra test launches. (Since those would have cost $8B and another six years, it's not a trivial advantage...)

That said, the whole program is a disgrace. The sooner it's taken out back and shot, the better.

 

[theradicalmoderate]

There is absolutely nothing manned that we can do BEO that is interesting with one launch. Not with SLS not future blocks, not any existing launch vehicle. The future is multi-launch architectures. One way or another. Either in the 2020s or in the 2050s.

For unmanned launches nobody can afford the SLS and nobody needs it. The combination of F9, New Glenn, and Starship can cover every launch need. Hell you could spend the starhip upper stage as a disposable EDS and it would still be a tiny fraction of the SLS.

Even the Mars design reference missions that use SLS require multiple launches. True, they don't require refueling--instead, they require launch entire propellant tanks and assembling them in orbit!

 

[NetMage]

The difference is if Blue adapts Orion, then there are two CCC (cislunar commercial crew) vendors: SpaceX with D2 + HLS, and Blue with NG/Orion + Cislunar Transporter. That's a very nice property.

Would it really be commercial crew for Orion? Doesn’t NASA own Orion, and not LM?

 

[NetMage]

Then again, the alternatives are just enriching billionaires.

The alternative is saving billions of dollars and actually being able to accomplish the nominal objective (of a long term lunar stay).

 

[paulfdietz]

Even the Mars design reference missions that use SLS require multiple launches. True, they don't require refueling--instead, they require launch entire propellant tanks and assembling them in orbit!

I have to wonder what purpose being in space will ultimately serve if something as basic as transferring liquids from one tank to another is beyond the capabilities of that civilization.

 

[theradicalmoderate]

SLS is going to be hard to kill. Especially as Senators watch SpaceX and Blue Origin twist themselves into knots trying to bring their crappy, overly complex, orbital refueling, garbage architectures online. NASA mission planners will be BEGGING congress to build more SLS launch vehicles. It's simple .. one mission and one launch ... is already enough complexity. SpaceX and Blue Origin are going to embarrass themselves.

The first of many things that's wrong with your argument is that a unitary SLS launch can't land anything on the lunar surface. It can't even get a big enough Orion into TLI so that it can stage from LLO. So it's not one mission, one launch. It's at least two launches, with the second one carrying a vehicle that doesn't exist.

---

The second thing that's wrong is that there's no evidence that either SpaceX or Blue are "twisting themselves in knots". HLS had no money appropriated until FY21; so it started much, much later than SLS. It's under development. Unless you're some SpaceX or Blue insider, you have no idea how the programs are going, you're just spouting uninformed nonsense.

I'll admit that SpaceX had a very bad 2025. If they also have a bad 2026, I'll start to worry.

Meanwhile, I'm pretty sure that Blue is working on an architecture that doesn't require refueling. This is the thing that they likely sent as a response to last years RFI to seek alternative solutions that would accelerate HLS development. Whether anything comes of this remains to be seen. (I can't find your previous comment that NASA had already adopted this--that's false. Nothing has happened other than they put out an RFI, which isn't even close to a contract.)

 

[Statistical]

I hadn't really considered it, but why is SLS's rated payload to LEO (95t) so low? We can be generous and round that up to 100t to include ICPS mass. STS could put just shy of 123t in orbit, itself included. Main engines, plumbing (10t), OMS engines, tanks, and propellant (12t), enough structure to hold all of it together (~5t?), we should easily be able to get a cargo variant together for under 30t total wet mass. That's >90t payload to orbit. What about SLS causes it to perform so poorly with an extra 25% SRB, 33% more engine, 40% more first stage propellant, and a real upper stage instead of an overweight kick stage?

Because Block 1 has an oversized core stage and it is built to support 130t of payload (and the full mass of Block 2). This is because Congress mandated a final payload capacity of 130t. Changing the core stage between block 1, block 1b, and block2 would have been an even larger boondoggle so while block1 is lighter payload mass it is built to handle the higher block 2 payload mass.

This worsens the already terrible payload mass fractions. Block 1b improves that to 105t and Block 2 to 130t although I agree neither are particularly good.

STS could put just shy of 123t in orbit, itself included

STS dry mass is 78t and max payload is 25t so 103t to reference orbit plus another 3.3t of RCS propellent and 10.83t is the OMS propellant of which is 117t total. However it uses a substantial portion to circularize the orbit. The Shuttle is in essence the second stage. So apples to apples including the burned OMS propellant would be like including the upper stage prop mass "as payload". The unburned prop is payload.

So lets say 110t true "payload" for the STS (orbiter + payload - propellent required to complete orbit to 200 km @ 28.5 deg reference orbit).

Still I agree it is pretty bad deprovement.

 

[fryhole]

Everybody can thank DIck Fucking Shelby for this dumpster fire!!!

(if you don't know who I'm talking about you'll need to lookup former Senator Richard Shelby - hence the "Dick" joke above)

 

[compgeek89]

Unfortunately, that's exactly the argument that Cruz is using to continue Block 1B development.

Hopefully, when/if Starship starts refueling successfully, his tune will change. There is a case to be made that killing SLS before something has been proven to be able to take over its mission would take an unnecessary risk.¹ But F9/D2 + even a rudimentary HLS Starship (it needs the crew module to work, but it doesn't even need to land!) is a complete replacement for its part of the Artemis conops. That's something that could be proven out this year.

We've already flushed a nice chunk of change down the toilet for FY26 EUS and ML2 development. But the FY27-28-29-30 out-year money has only been obligated. That's nothing a nice rescission can't fix.


_________
¹We'll leave aside the fact that SLS/Orion has nothing to do without an HLS, and Starship is required to do that.

If there was any hope that sanity would prevail, this program would have been cancelled the moment falcon heavy made orbit. But, with a cheap heavy lift vehicle ready to fly at a moments notice (relatively), we've just kept on shoveling money into this terrible project, and even pre-booked future rockets to keep the sunk cost fallacy alive into the future.

Cant we just hand stacks of hundred dollar bills to the good people of Alabama and end this mafia shakedown? Save us all the ridiculous pretend useless "deliverables"?

 

[theradicalmoderate]

Would it really be commercial crew for Orion? Doesn’t NASA own Orion, and not LM?

That's... complicated. Two things:

1) There's OPOC, which effectively commercializes the manufacturing and operation of Orion by LockMart. I think the Orions that come off the line are still owned by NASA, but I'm not sure if LockMart has the right to manufacture some that are private.

2) There's also a mechanism called "Government Furnished Equipment", or GFE. There would be nothing preventing Blue from bidding a CCC solution with the Orion as GFE. Then NASA would pay Blue for the mission, but Blue would pay NASA for the Orion, and NASA would pay LockMart. In other words, there's a lot of accounting deadweight, but otherwise everything's fine.

The touchier issue is the the ESM, which is manufactured by Airbus, paid for by the ESA, and offered as barter for... NASA stuff... Blue would have to do some kind of deal with one of NASA, the ESA, or Airbus to get the ESM's they'd need. But again, this could be just another piece of GFE.

 

[theradicalmoderate]

If there was any hope that sanity would prevail, this program would have been cancelled the moment falcon heavy made orbit. But, with a cheap heavy lift vehicle ready to fly at a moments notice (relatively), we've just kept on shoveling money into this terrible project, and even pre-booked future rockets to keep the sunk cost fallacy alive into the future.

Cant we just hand stacks of hundred dollar bills to the good people of Alabama and end this mafia shakedown? Save us all the ridiculous pretend useless "deliverables"?

Falcon Heavy wasn't adequate, because it didn't come with a deep-space-capable capsule, and it couldn't get Orion to TLI.

Until there's something that can get a crew from Earth's surface to lunar orbit, there's at least a flimsy argument that SLS/Orion provides a service that nobody can match. But the moment that HLS Starship is crew-certified, that will no longer be true.

As for the good people of Alabama, they'd do just fine without SLS:

1) There's plenty of mission planning and program management for Marshal to do, even if SLS/Orion goes bye-bye.
2) Blue put their BE-4 factory in Huntsville.
3) ULA is building Centaurs in Decatur.
4) ULA is building the Vulcan core in Decatur.

 

[wagnerrp]

STS dry mass is 78t and max payload is 25t so 103t to reference orbit plus another 3.3t of RCS propellent so 106t The other 10.83t is the OMS propellant of which it uses a substantial portion to circularize the orbit. The Shuttle is in essence the second stage.

So lets say 110t true "payload" obiter + payload - propellent used to complete orbit.

Wikipedia may have some incorrect data, or someone may have made some calculations on incorrect assumptions. STS-93 is claimed as nearly 100t landing mass, which would suggest they used hardly any of their OMS propellant. Per those numbers... launch - landing < payload, which doesn't make much sense, unless they're considering systems for payload deployment as part of the payload.

STS-115 and STS-117 both launched with similar payload and takeoff mass, but landed 9t lighter. Columbia was the heaviest of the lot, 4t more than the later missions with Atlantis. Chandra was also deployed to a much lower orbit than ISS, meaning less OMS usage, and the mission was shorter.

 

[Statistical]

SLS is really just a continuation of the design of Constellation from back in 2004/2005, which was NASA designed all the way. All the stuff that makes SLS such a crummy plan (use of legacy space shuttle parts, monolithic super rocket, etc) come from there, and were explicitly promoted by NASA as being a better technical solution than adapting existing launchers like Atlas.

Yes NASA did come up with Ares. Yes SLS is largely Ares V in a new name.

However you are missing the intervening steps.
1) Augustine Commission recommending axing Constellation and advised NASA to look at multi-launch architectures.
2) NASA actually did start that process and considered both modifications of Delta/Atlas and clean designs.
3) Senate then forced their hand and made them built SLS

This doc for example comes from prior the Senate forcing NASA hand

People have said "why not a modern version of Saturn V". Yeah that is essentially option 2. Why not something like a scaled up Falcon Heavy? Yeah that is essentially option 3 (although with fewer engines due to inertial bias). Even their baseline was scrap all the complexity of Ares and use unmodified shuttle components and multiple launches.

Also to be clear NASA is not a monolith. There are people in NASA then and now that love the SLS and there are people opposed to it. NASA was looking at options. Now you could make the argument that even if the Senate hadn't intervened they would have chosen the wrong option. I can't argue what would have happened in this alternate timeline where the Senate didn't force the outcome. We will never know. In this reality though the Senate forced the outcome and that was that.

I mean, Congress absolutely should’ve cancelled this thing in 2010, and I’m sure they chose not to to keep contractors happy and pork flowing. But this persistent idea that they are responsible for the design of SLS is just silly, and it covers over the real cultural problems at NASA and in the wider space industry that led to the current state of HSF.

They WERE responsible. The idea is persistent because it is reality. Also it is unlikely anyone in Congress wrote the requirements the lobbyists for shuttle contractors told them exactly what to put in the bill and then they did and then they passed it. Obama having expended a lot of political capital to kill Constellation just didn't want to expand more with a very hostile Congress hell bent on forcing this through so contractors would collect their billions. So he stopped trying and Lori Garver secured Senate funding support for continuing Commercial Resupply and starting Commercial Crew Development.

 

[Wickwick]

All of the tooling from Saturn V had rusted away. Restarting its production wasn't an option. Meanwhile, SLS was an attempt to keep all the STS tooling from falling into disuse.

---

I will make one weak, devil's advocate-like defense of reusing STS components: their reliability was known to extremely high accuracy, and the way they were put together gave SLS/Orion a ready-made probabilistic risk analysis model. That's not a terrible argument for punting on doing a couple of extra test launches. (Since those would have cost $8B and another six years, it's not a trivial advantage...)

That said, the whole program is a disgrace. The sooner it's taken out back and shot, the better.

Saturn-derived need not include actual Saturn tooling. If we were to have developed the 12-engine RD-180 booster I suggested above, then the only thing really derived from Saturn is the idea of kerosene as a booster and hydrogen as an upper (and no solids!). If you like, you could build this monster to take advantage of the Saturn V structural skeleton, but by 2005, I'd think FEA would allow a better structure to emerge.

And how did that work out for Shuttle tooling? The magic friction stir welding debacle doesn't seem to have benefitted from it. Of course, while the OD of the SLS core is the same as the Shuttle ET, it's a lot thicker than the SLWT - the only one that was stir welded. So there's really no commonality.

 

[Statistical]

Wikipedia may have some incorrect data, or someone may have made some calculations on incorrect assumptions. STS-93 is claimed as nearly 100t landing mass, which would suggest they used hardly any of their OMS propellant. Per those numbers... launch - landing < payload, which doesn't make much sense, unless they're considering systems for payload deployment as part of the payload.

STS-115 and STS-117 both launched with similar payload and takeoff mass, but landed 9t lighter. Columbia was the heaviest of the lot, 4t more than the later missions with Atlantis. Chandra was also deployed to a much lower orbit than ISS, meaning less OMS usage, and the mission was shorter.

Yeah I have noticed that before. The ISS the Shuttle routinely took back downmass so that could explain that on the ISS missions though. STS-93 however has to be wrong or they are double counting some payload mass.

The landing mass plus payload mass is greater than the launch mass meaning it burned negative propellant mass during the mission?

It doesn't help that as time went on the space shuttles also slowly had changing dry masses due to fixes and modifications. Still I don't believe it lifted 120t true payload to orbit. However it isn't a hill I am willing to die on. If it did then Block 1 has slightly worse dry mass fractions although the bulk of the underperformance for block 1 is well it is incomplete. If you wanted it to lift no more than 100t and not be modified you would change the stage ratios and other things.

 

[Wickwick]

The first of many things that's wrong with your argument is that a unitary SLS launch can't land anything on the lunar surface. It can't even get a big enough Orion into TLI so that it can stage from LLO. So it's not one mission, one launch. It's at least two launches, with the second one carrying a vehicle that doesn't exist.

---

The second thing that's wrong is that there's no evidence that either SpaceX or Blue are "twisting themselves in knots". HLS had no money appropriated until FY21; so it started much, much later than SLS. It's under development. Unless you're some SpaceX or Blue insider, you have no idea how the programs are going, you're just spouting uninformed nonsense.

I'll admit that SpaceX had a very bad 2025. If they also have a bad 2026, I'll start to worry.

Meanwhile, I'm pretty sure that Blue is working on an architecture that doesn't require refueling. This is the thing that they likely sent as a response to last years RFI to seek alternative solutions that would accelerate HLS development. Whether anything comes of this remains to be seen. (I can't find your previous comment that NASA had already adopted this--that's false. Nothing has happened other than they put out an RFI, which isn't even close to a contract.)

I don't believe the existing NG has the performance to put a human lander down to the moon without refueling. If they're betting on that, they're likely betting on having their 9x4 rocket ready.

 

[theradicalmoderate]

I hadn't really considered it, but why is SLS's rated payload to LEO (95t) so low? We can be generous and round that up to 100t to include ICPS mass. STS could put just shy of 123t in orbit, itself included. Main engines, plumbing (10t), OMS engines, tanks, and propellant (12t), enough structure to hold all of it together (~5t?), we should easily be able to get a cargo variant together for under 30t total wet mass. That's >90t payload to orbit. What about SLS causes it to perform so poorly with an extra 25% SRB, 33% more engine, 40% more first stage propellant, and a real upper stage instead of an overweight kick stage?

The real answer is that SLS Block 1's payload to LEO is exactly the mass of the ICPS + Orion, because that's the only payload it can carry. Ain't no stinkin' cargo fairing, man.

The SLS SRBs + core put the ICPS+Orion (65.5t) into a ~70 x 1800km orbit, which has the same energy as a 932km circular orbit. That's 635m/s above a 200x200 orbit. From there, you have to do some figuring to determine how much residual prop you'd have in the core if you went to the lower altitude. That, plus the 65.5t, should be the mass to the reference LEO.

I'm just gonna do the calculation: RS-25 has an Isp=452.3s, and the core has a dry mass of 85,275kg, with the 65.5t of payload, gives . exp(635/452.3/9.807) = (150.8 + extraProp) / 150.8.

So extraProp = 13.1t 23.2t. Add that to the 65.5t that it actually takes to 70x1800, and you have 78.6t 88.7t. I don't know where the 95t comes from. Maybe they have monster residuals on the Block 1 launches?

Update: thanks to wagnerrp for pointing out that I'd forgotten to add in the payload as inert mass to the rocket equation calculation. Fixed above.

 

[Statistical]

I will make one weak, devil's advocate-like defense of reusing STS components: their reliability was known to extremely high accuracy, and the way they were put together gave SLS/Orion a ready-made probabilistic risk analysis model.

Part of the problem though is that they didn't use STS components they used STS derived components and that compounded the costs and likely made their LOV numbers incorrect. It made it look good on paper but reality is different and honestly NASA should have already known that with the endless problems of Constellation program.

In fact post Ares V and prior to Senate forcing the issue NASA considered a "baby SLS" as a result of all the issues with upsizing STS components for Ares V. It would have used 3 RS-25 and the identical solid rocket boosters from the STS. Payload mass is significantly lower and thus couldn't meet the Senate requirement of 70-100 tons in initial version. Arguably that rocket would have been lower risk both in development and risk to crew given it kept things largely the same except moving from orbiter to payload on top.

However it didn't meet SLS funding requirements imposed by the Senate so it was out. The Senate also demanded a rocket flying by 2017 which is 100% impossible for any rocket but even by NASA optimistic scheduling it killed an options for new engines and radical changes.
So NASA stretched everything. Longer core stage but then it had to be thicker leading to endless complications and failures in welding. Stretch the boosters from 4 segments to 5. However now you need all kinds of new testing related to acoustics and vibration. They found edge case issues on things as simple as the water caps on the booster nozzles. Moving to 5 segments meant the caps ejected with too much force to meet their safety tolerances. The cap could survive intact enough to strike bounce off the launch pad and hit something vital. So they had to switch to frangible caps except they had issues with those. More redesign more testing.

In some ways an unmodified STS component rocket would have been a solid option. Don't get be wrong hydrolox sustainer design is all around stupid but from a risk and timeline standpoint. Likewise a clean slate rocket would have other advantages. What we got was the worst of both options. STS DERIVED components effectively made it a crippled terribly designed but also largely clean slate rocket.

 

[Wickwick]

Part of the problem though is that they didn't use STS components they used STS derived components and that compounded the costs and likely made their LOV numbers incorrect. It likely did look good on paper.

In fact prior to Senate forcing the issue NASA considered a "baby"SLS as a result of all the issues with upsizing STS components for Ares V. It would have used 3 RS-25 and the identical solid rocket boosters from the STS. Payload mass is significantly lower and thus couldn't meet the Senate requirement of 70-100 tons in initial version.

So NASA stretched everything. Longer core stage but then it had to be thicker leading to endless complications and failures in welding. Moving to 5 segment boosters required all kinds of testing. They found edge case issues on things as simple as the water caps for the boosters. Moving to 5 segments meant the caps ejected with too much force to meet their safety tolerances. So they had to switch to frangible caps except they had issues with those.

In some ways a STS component rockets would have been a solid option. Likewise a clean slate rocket would have advantages. We got the worst of both worlds. STS DERIVED components effectively getting no advantage of either scenarios.

And seriously, who believes NASA's LoV numbers? NASA's never lost a crew in a fashion that they'd modeled to within even two or three orders of magnitude of risk.

 

[Statistical]

The real answer is that SLS Block 1's payload to LEO is exactly the mass of the ICPS + Orion, because that's the only payload it can carry. Ain't no stinkin' cargo fairing, man.

The SLS SRBs + core put the ICPS+Orion (65.5t) into a ~70 x 1800km orbit, which has the same energy as a 932km circular orbit. That's 635m/s above a 200x200 orbit. From there, you have to do some figuring to determine how much residual prop you'd have in the core if you went to the lower altitude. That, plus the 65.5t, should be the mass to the reference LEO.

Mystery solved. Thanks. I even wondered if that was the case but saw multiple (obviously incorrect) cite of the mass being to 200 km reference orbit which it obviously is not. The only published mass to orbit is this irregular orbit while essentially everything else (US) is to a 200 km circular 28.5 deg reference orbit.

It also makes sense that Block 1b (EDS) doesn't really improve payload mass to LEO. It is largely for the improvement to TLI.