SLS General Discussion Thread 5

[jadebenn]

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?

Constraints.

The top of the LH2 tank is limited by the location of the SRB thrust beam. The bottom of the engine section is limited by the Mobile Launcher. These two constraints, combined with the LH2 tank stretch, left a fairly narrow space for the engine section.

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

I do wonder if that was part the reasoning behind going with the 4 engine configuration for all blocks. From what I've read, that announcement came as a surprise to many.

[spacenut]

Boeing had the 10m diameter tooling.  Since the infrastructure had to be rebuilt, like the mobile transfer platforms, they should have gone with 10m diameter so the height wouldn't be an issue.  They were going with a 10m when they thought about using the RS-68 engines.  Then there would be height enough to build a decent upper stage and gone with a 5 engine core.  Still would fit the VAB, and give over 130 tons to LEO, and 45 tons to TLI. 

[freddo411]

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.

I'm not disagreeing that NASA and contractors current processes make things very difficult.   Yes, Current arms are not designed for easy reconfiguration.

However, it's relatively easy to design umbilical arms so that they could be reconfigured to be at a different height, especially in light of a 3 billion dollar a year program.   This seems to be a case of the cart leading the horse.

[Proponent]

I do wonder if that was part the reasoning behind going with the 4 engine configuration for all blocks. From what I've read, that announcement came as a surprise to many.

Would the constraint have been more or less of a problem for DIRECT's 4-in-line configuration of RS-25's?

[su27k]

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?

Constraints.

The top of the LH2 tank is limited by the location of the SRB thrust beam. The bottom of the engine section is limited by the Mobile Launcher. These two constraints, combined with the LH2 tank stretch, left a fairly narrow space for the engine section.

This is why using SRB is dumb, it puts severe limit on your options.

[su27k]

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.

There's no overall budget, but the contract value do have upper limit, and they should already overrun it a year ago, not sure what is happening with the contract re-negotiation.

From https://oig.nasa.gov/docs/IG-19-001.pdf:

As of August 2018, NASA had obligated approximately $5.3 billion (86 percent) of the $6.2 billion Boeing Stages contract.23 With only $354 million remaining on CLIN 9 for building two Core Stages and the EUS, both NASA and Boeing anticipate exceeding the contract ceiling for CLIN 9 sometime between December 2018 and February 2019—3 years before the current scheduled contract end date of 2021 and prior to delivery of a single Core Stage or completion of the EUS. Federal contracting laws prohibit NASA from exceeding the contract value absent a contract modification. Further, an increase to the contract value without substantially changing the scope of work is considered a cost overrun, a scenario under which NASA would pay a reduced or no award fee on the additional costs. Consequently, NASA and Boeing will need to renegotiate the contract terms, amount of cost overrun, and schedule. Based on our audit work, we expect this next contract modification will require both a major increase in value and an extension of the delivery schedule for the two Core Stages and EUS.

[Coastal Ron]

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?

Constraints.

The top of the LH2 tank is limited by the location of the SRB thrust beam. The bottom of the engine section is limited by the Mobile Launcher. These two constraints, combined with the LH2 tank stretch, left a fairly narrow space for the engine section.

This is why using SRB is dumb, it puts severe limit on your options.

Though you have to use SRB's when LH2 is your fuel. So unless you replace LH2 with some other fuel, like methane for instance, you have to use SRB's.

[ncb1397]

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?

Constraints.

The top of the LH2 tank is limited by the location of the SRB thrust beam. The bottom of the engine section is limited by the Mobile Launcher. These two constraints, combined with the LH2 tank stretch, left a fairly narrow space for the engine section.

This is why using SRB is dumb, it puts severe limit on your options.

Though you have to use SRB's when LH2 is your fuel. So unless you replace LH2 with some other fuel, like methane for instance, you have to use SRB's.

Delta IV Heavy says...

Hi!

[su27k]

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?

Constraints.

The top of the LH2 tank is limited by the location of the SRB thrust beam. The bottom of the engine section is limited by the Mobile Launcher. These two constraints, combined with the LH2 tank stretch, left a fairly narrow space for the engine section.

This is why using SRB is dumb, it puts severe limit on your options.

Though you have to use SRB's when LH2 is your fuel. So unless you replace LH2 with some other fuel, like methane for instance, you have to use SRB's.

This is why Obama wanted to develop large hydrocarbon engine first and postpone superheavy development by 5 years, it's not a good idea to use LH2 in your first stage, and US was badly behind in hydrocarbon engine technology back then, of course congress had other ideas...

[D.L Parker]

How much does a SLS cost to launch? The more I read about it the more confused I get, the number ranges anywhere from 800 million to 2 billion. Which number is the correct one?

[Coastal Ron]

How much does a SLS cost to launch? The more I read about it the more confused I get, the number ranges anywhere from 800 million to 2 billion. Which number is the correct one?

On October 23, 2019, the Acting Director of the Office of Management and Budget within the White House sent a letter to Senator Richard Shelby, and on page 7 of that letter they stated:

At an estimated cost of over $2 billion per launch for the SLS once development is complete...

So at least initially the cost per launch will be over $2B per launch. No doubt that would go down over time, but don't expect dramatic changes, and that amount may go up if the larger Block 1B or Block 2 are launched.

[Proponent]

How much does a SLS cost to launch? The more I read about it the more confused I get, the number ranges anywhere from 800 million to 2 billion. Which number is the correct one?

The questions lacks a unique simple answer.  Do you want to apportion a fraction of the development cost to the launch?  How many launches per year are occurring?  Are you interested in the marginal cost of adding one additional launch to the existing schedule?  If so, do you want to include the additional investment needed to raise the production rate?  And so on.  To get a good answer, you need to specify just which cost you're after.

[JAFO]

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

[thread drift]
Was Stumpy Direct’s J-130? I thought Stumpy was smaller, but the J-130 was essentially an ET with 3 engines in the base, and the long pole was the software, which all became academic when the 4 segment tooling was destroyed.
[/thread drift]

Ah, just found the Stumpy thread. FYI of others, here it is.  https://forum.nasaspaceflight.com/index.php?topic=3537.0

Apologies, mods.

[ncb1397]

This is why Obama wanted to develop large hydrocarbon engine first and postpone superheavy development by 5 years, it's not a good idea to use LH2 in your first stage, and US was badly behind in hydrocarbon engine technology back then, of course congress had other ideas...

Nothing restricted the Obama administration from spending SLS funds on a hydrocarbon engine (see F-1B for advanced boosters...they never pulled the trigger).

[Proponent]

Was Stumpy Direct’s J-130? I thought Stumpy was smaller, but the J-130 was essentially an ET with 3 engines in the base

What I meant to point out was that Stumpy's core probably could not simply have been an ET, because it needed to withstand quite different loads than what the ET withstood.

The J-130 would have had 3 engines in-line, with room for 4.  I wonder whether that would have increased or decreased the plumbing difficulty compared to what the actual SLS has experienced.

[Proponent]

This is why Obama wanted to develop large hydrocarbon engine first and postpone superheavy development by 5 years, it's not a good idea to use LH2 in your first stage, and US was badly behind in hydrocarbon engine technology back then, of course congress had other ideas...

Nothing restricted the Obama administration from spending SLS funds on a hydrocarbon engine (see F-1B for advanced boosters...they never pulled the trigger).

But the timetable imposed by Congress ruled out hydrocarbon engines for SLS's core.

[Coastal Ron]

This is why Obama wanted to develop large hydrocarbon engine first and postpone superheavy development by 5 years, it's not a good idea to use LH2 in your first stage, and US was badly behind in hydrocarbon engine technology back then, of course congress had other ideas...

Nothing restricted the Obama administration from spending SLS funds on a hydrocarbon engine (see F-1B for advanced boosters...they never pulled the trigger).

You are wrong of course.

For instance, the Aerojet Rocketdyne AR1, which has slightly more thrust than the RS-25/SSME, was going to take 5 years just to get to prototype stage. Then if you changed to LOX / RP-1 you'd have to throw away all of the work done on the Ares V, which the SLS is based on, and you would likely no longer need the Solid Rocket Motors from the Shuttle and Ares I/V, which violated this mandate from Congress regarding the SLS:

(1) IN GENERAL.—The Administrator shall, as soon as prac- ticable after the date of the enactment of this Act, initiate development of a Space Launch System meeting the minimum capabilities requirements specified in subsection (c).
(2) MODIFICATION OF CURRENT CONTRACTS.—In order to limit NASA’s termination liability costs and support critical capabilities, the Administrator shall, to the extent practicable, extend or modify existing vehicle development and associated contracts necessary to meet the requirements in paragraph (1), including contracts for ground testing of solid rocket motors, if necessary, to ensure their availability for development of the Space Launch System.

Congress did NOT want NASA to develop a new rocket engine when they directed NASA to build the SLS. There is no evidence to support such an assertion.

[woods170]

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?

Constraints.

The top of the LH2 tank is limited by the location of the SRB thrust beam. The bottom of the engine section is limited by the Mobile Launcher. These two constraints, combined with the LH2 tank stretch, left a fairly narrow space for the engine section.

This is why using SRB is dumb, it puts severe limit on your options.

Though you have to use SRB's when LH2 is your fuel. So unless you replace LH2 with some other fuel, like methane for instance, you have to use SRB's.

Delta IV Heavy says...

Hi!

Which proves Coastal Ron’s point. Using LH2 in the booster stage requires 3 massive cores to lift a mere 26 metric tons into LEO. LH2 is inefficient for a booster stage.

[clongton]

Which proves Coastal Ron’s point. Using LH2 in the booster stage requires 3 massive cores to lift a mere 26 metric tons into LEO. LH2 is inefficient for a booster stage.

A booster stage needs raw power, not efficiency, to lift the huge amount of mass that is the entire LV stack so a hydrocarbon propellant is preferable. But once the mass of the booster is dropped at staging, efficiency begins to outweigh raw power so LH2 becomes the preferred propellant. This is the drawback that doomed the Ares-1/5 program - the booster stage simply could not lift enough to make up for the shortcomings of the selected propellant. SLS at least dropped the solid CLV concept so it could be sized to handle a less massive lift that would still be of some use.

[ncb1397]

This is why Obama wanted to develop large hydrocarbon engine first and postpone superheavy development by 5 years, it's not a good idea to use LH2 in your first stage, and US was badly behind in hydrocarbon engine technology back then, of course congress had other ideas...

Nothing restricted the Obama administration from spending SLS funds on a hydrocarbon engine (see F-1B for advanced boosters...they never pulled the trigger).

But the timetable imposed by Congress ruled out hydrocarbon engines for SLS's core.

Why? J-2X went from contract award to firing in under 4 years. And they could have still developed the engine for an upgrade path of the core/boosters(or both). If that is what they wanted, they should have put their money there. The truth though is that the "technology development" program wasn't clearly defined. It was probably never about a hydrocarbon engine.