SLS General Discussion Thread 5

[Proponent]

J-2X was a modification of an existing engine.  Besides, the Congress imposed the requirement to use Shuttle-derived systems to the maximum extent practicable.

[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).

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.

I don't think you understand. SSME wasn't part of the constellation program. It was added in later after the transition to SLS. It could have been a different engine. There was no contract termination liability based on the engine being changed to SSME vs something else. And SLS money was used for engine development and still is. Congress has raised no objections.

[ncb1397]

J-2X was a modification of an existing engine.  Besides, the Congress imposed the requirement to use Shuttle-derived systems to the maximum extent practicable.

So is F-1B.

[lrk]

J-2X was a modification of an existing engine.  Besides, the Congress imposed the requirement to use Shuttle-derived systems to the maximum extent practicable.

Umm, not really.  That was the original plan (to modify and upgrade the Saturn J-2 engine), but it morphed into a totally new design that reused a few components from the RS-68.

[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!

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.

Depends on where you are going. But this doesn't really apple to SLS. The first portion of the flight profile uses a mixture of solids and hydrogen...isp is in between hydrogen and the solids with an impressive 39 MN of thrust - more than the Saturn V. They essentially got the performance of a hydrocarbon engine without building a new hydrocarbon engine and using existing technology and expertise.

[meberbs]

Depends on where you are going. But this doesn't really apple to SLS. The first portion of the flight profile uses a mixture of solids and hydrogen...isp is in between hydrogen and the solids with an impressive 39 MN of thrust - more than the Saturn V. They essentially got the performance of a hydrocarbon engine without building a new hydrocarbon engine and using existing technology and expertise.

Again, you are proving Coastal Ron's point that SRBs and their associated shortcomings were required to make up for the shortcomings of LH2 fuel for a first stage. If you don't have any disagreements with his points, can we move on?

[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?

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.

I don't understand why it's so confusing. On the ULA website they have a thing called Rocketbuilder where you put in the parameters of your launch, select which options you want, and they give you the base price. For a standard Atlas V the price is 70 to 80 million to launch. That's what you will pay if you want them to launch your payload.

That's the price I would like to know. If I had a standard SLS how much would a hypothetical customer have to pay to launch a payload to orbit?

[Coastal Ron]

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.

The J-2X is only half the thrust of the RS-25/SSME, and it was based on an existing engine. A new engine would take substantially longer.

Look, anyone that reads the NASA Authorization Act of 2010 can see that the intent of Congress was NOT to develop a new rocket engine for the SLS. They wanted a Shuttle/Ares V derivative.

You should accept the reality that exists... 

[spacenut]

The shortcomings of the solids are their weight.  They are very heavy.  Not only do they have to lift their weight but also some of the core.  The core is not really a first stage, it goes all the way to orbit.  It would be a single stage to orbit if it could lift itself.  It has to burn off some of it's fuel before it can push itself and a payload.  Thus the solids.  Now a liquid booster the same thrust as a solid can lift more payload, because the liquid fuel and tankage are much lighter.  Two 5.5m liquid boosters using two F-1 engines each, delivering 3 million lbs thrust for each booster on the SLS core could get 140-150 tons to orbit.  This was studied as a replacement for the solids at some future date.  Or four RD-180s on the 5.5m boosters.  5.5m was the maximum diameter the transporters and flame trench could handle.  It was also discussed using AR-1's kerolox engines if Aerojet ever developed them. 

The solid fueled rocket lobby won in congress.  So that is what they chose. 

[ncb1397]

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.

Look, anyone that reads the NASA Authorization Act of 2010 can see that the intent of Congress was NOT to develop a new rocket engine for the SLS. They wanted a Shuttle/Ares V derivative.

SLS money was spent on a new rocket engine (well, an adaptation of an old one, brought back from the dead). Let me jog your memory on this.

NASA has spent a lot of time and money resurrecting the F-1 rocket engine that powered the Saturn V back in the 1960s and 1970s, and Ars recently spent a week at the Marshall Space Flight Center in Huntsville, Alabama, to get the inside scoop on how the effort came to be. But there's a very practical reason why NASA is putting old rocket parts up on a test stand and firing them off: its latest launch vehicle might be powered by engines that look, sound, and work a whole lot like the legendary F-1.

This new launch vehicle, known as the Space Launch System, or SLS, is currently taking shape on NASA drawing boards. However, as is its mandate, NASA won't be building the rocket itself—it will allow private industry to bid for the rights to build various components. One potential design wrinkle in SLS is that instead of using Space Shuttle-style solid rocket boosters, SLS could instead use liquid-fueled rocket motors, which would make it the United States' first human-rated rocket in more than 30 years not to use solid-fuel boosters.

The contest to suss this out is the Advanced Booster Competition, and one of the companies that has been down-selected as a final competitor is Huntsville-based Dynetics. Dynetics has partnered with Pratt Whitney Rocketdyne (designers of the Saturn V's F-1 engine, among others) to propose a liquid-fueled booster featuring an engine based heavily on the design of the famous F-1. The booster is tentatively named Pyrios, after one of the fiery horses that pulled the god Apollo's chariot; the engine is being called the F-1B.

https://arstechnica.com/science/2013/04/new-f-1b-rocket-engine-upgrades-apollo-era-deisgn-with-1-8m-lbs-of-thrust/

This whole sub-thread started with someone saying that the Obama administration wanted to build a new hydrocarbon engine. The question is, if that was the case, why didn't they use the funds provided by Congress for heavy lift vehicle development and build a hydrocarbon engine? F-1B, Merlin 2, you name it would be being test fired currently and already fitted to the SLS core or boosters as we speak. Remember, that the contracts that Congress didn't want to pay termination liability for was a solid rocket booster with ATK and an upper stage with Boeing. NASA could have left those contracts in place and did whatever core stage they wanted with everything else being replaced later on as well (the upper stage is still being replaced with EUS, and the boosters are getting replaced with different design solids).

[tbellman]

I don't understand why it's so confusing. On the ULA website they have a thing called Rocketbuilder where you put in the parameters of your launch, select which options you want, and they give you the base price. For a standard Atlas V the price is 70 to 80 million to launch. That's what you will pay if you want them to launch your payload.

That's the price I would like to know. If I had a standard SLS how much would a hypothetical customer have to pay to launch a payload to orbit?

Part of why it is so confusing is that SLS launches are not for sale.  Any prospective customer would need to take over the US government first...  And since it is not for sale, there is no advertised price.



When you buy a meal at a restaurant, cost is easy.  At least for the buyer; the seller has more work to do...  But what if you cook your meals yourself?  Do you spread the cost of your stove and refridgerator over your meals to properly account for them?  If you are renting an apartment in Sweden (where I live), a stove and fridge are basically always included in the apartment.  I am of course paying for them anyway, but my landlord does not provide a line item for them on my rent bill, so I can't properly account for them in my meal costs.  For that matter, the kitchen room itself is also included in almost every apartment (some small one-room apartments don't have a separate kitchen), and my landlord is absolutely charging me for that, but there is no line-item for it on my bill.  And since there are no similar-sized apartments without kitchen, I can't compare the rents to guess at the cost either.

Did you take cooking lessons before you started to cook your own meals?  Do you account that over your meal costs?  Or was that something you did anyway, just for fun, and the cost for that is covered by your entertainment budget?

Considerations similar to these makes it difficult to estimate how much an SLS launch costs.  Some parts of the SLS development might have benefits to other parts of NASA or the US government as well; do you split those costs between all who benefit, or are they covered by that other beneficiary?  And some parts of the actual costs may be on another part of the budget and very difficult for someone on the outside to figure out.  (As one example of the latter: how much electricity does building SLS use?  If there is no separate electricity meter for the SLS factory, that will just be shoved into the general electricity budget for the Michoud facility.  And even if there is a separate meter, NASA doesn't show it to us, so unless NASA decides to account for that on SLS, we on the outside can't do it for them.)

Also, when a company sets prices for products (like a car, or a plane ticket), they will include development costs and other fixed costs they have for it in the price you pay.  To do that, they have to estimate how many they are likely to sell to spread those fixed costs evenly.  Similarly for SLS, the costs for each SLS depends on how many you spread the development and factory costs over.

Launch cadence also matters.  If the current factory maxes out at producing (for example) one SLS every eight months, and we want to increase to one launch every six months, a second factory needs to be built, and the costs for that might actually increase the per-SLS cost (because now each factory is only operating at 2/3rds of their capacity, while still incurring all of the fixed costs).

[Proponent]

This whole sub-thread started with someone saying that the Obama administration wanted to build a new hydrocarbon engine. The question is, if that was the case, why didn't they use the funds provided by Congress for heavy lift vehicle development and build a hydrocarbon engine? F-1B, Merlin 2, you name it would be being test fired currently and already fitted to the SLS core or boosters as we speak.

The key word here is "new."  The Obama proposal was not to build any old hydrocarbon engine, but to develop new hydrocarbon-engine technology.

[ncb1397]

This whole sub-thread started with someone saying that the Obama administration wanted to build a new hydrocarbon engine. The question is, if that was the case, why didn't they use the funds provided by Congress for heavy lift vehicle development and build a hydrocarbon engine? F-1B, Merlin 2, you name it would be being test fired currently and already fitted to the SLS core or boosters as we speak.

The key word here is "new."  The Obama proposal was not to build any old hydrocarbon engine, but to develop new hydrocarbon-engine technology.

Then why were they spending money reviving the F-1. Seems weird. They don't want an updated engine based on the F-1, but they did. Seems like they would go to their contractors and ask for something clean sheet for the advanced boosters.

From the 2011 budget request:

First-Stage Launch Propulsion: NASA’s efforts in this area will focus on development of a U.S. core stage
hydrocarbon engine that would be suitable for use in a future heavy-lift rocket or as the first stage of a future
launch vehicle. A strong candidate would be a hydrocarbon (liquid oxygen/kerosene) engine, capable of
generating high levels of thrust approximately equal to or exceeding the performance of the Russian-built RD180 engine. Other key target characteristics for this new capability include improvements in overall engine
robustness and efficiency, health monitoring, affordability, and operability. In every aspect of the design, NASA
will seek to incorporate features that will reduce manufacturing and operating costs for this engine, once it
achieves nominal production status. The level of funding for this project is intended to result in a fully operational engine by the end of this decade or perhaps sooner if a DOD partnership is established.

https://www.nasa.gov/pdf/428837main_NASA_FY_2011_Congressional_Justificaton_Budget_Book_Rev-01_BOOKMARKED.pdf

The Obama administration proposed $3.1 billion for propulsion in the first 5 years with the engine only coming online by the end of the decade. So, we are talking about $6-7 billion dollars for this engine effort. Regardless, NASA and the administration appears to have integrated some of the goals of HLPT into the SLS program early on, but never actually developed the engine they proposed. In other words, the advanced booster competition never developed a viable product by the end of the decade. They did a lot of research into propulsion technology  - redesigning the F-1, building composite solid casings, composite liquid stages, finished the j-2x, etc. Whatever portion of the $500 million per year for propulsion was for the hydrocarbon engine, they should have made sure that was in the SLS requests for future upgrades. In fact, HLPT(specifically the hydrocarbon engine) was one and done. It never shows up in any request later on either as part of SLS, in the space technology mission directorate or seperated out under exploration as it was in 2011.

Anyways, the U.S. built the RD-180 replacement that was proposed - it is called  the AR-1. So, we are where we are supposed to be regarding the hydrocarbon engine that was proposed. Now what?

[spacenut]

The reason Saturn V used the large F-1 hydrocarbon engines is lift capability.  Kerosene packs a lot of power in a small amount of fuel compared to other fuels.  This is also the reason for replacing the solids with kerolox boosters.  More thrust to weight, cleaner than solids, and being able to control the thrust or shut down the engines.  If you can pack 3 million lbs thrust into a 5.5m diameter booster you allow SLS to lift far more tonnage to space without an upper stage. 

The main reason for going to metholox is for clean engines that can be reused over and over without coking.  It is a compromise between kerosene and hydrogen. 

[Coastal Ron]

This whole sub-thread started with someone saying that the Obama administration wanted to build a new hydrocarbon engine. The question is, if that was the case, why didn't they use the funds provided by Congress for heavy lift vehicle development and build a hydrocarbon engine? F-1B, Merlin 2, you name it would be being test fired currently and already fitted to the SLS core or boosters as we speak.

The key word here is "new."  The Obama proposal was not to build any old hydrocarbon engine, but to develop new hydrocarbon-engine technology.

Then why were they spending money reviving the F-1.

As an SLS supporter you should know this. The F-1B was being developed for the Advanced Booster Competition - it was an SRB replacement, not a booster engine replacement... 

The Obama administration proposed $3.1 billion for propulsion in the first 5 years with the engine only coming online by the end of the decade.

The Obama administration was doing basic R&D investment. The U.S. Government does this all the time on technologies they THINK will be needed in the future. Whether it would have made it to production would have been dependent on America's needs at the time.

As it turns out the effort by a number of private companies likely would have ended the need for the U.S. Government to develop one on its own.

Anyways, the U.S. built the RD-180 replacement that was proposed - it is called  the AR-1.

That was NOT for the SLS, the topic of this conversation. It was to replace the engine on an EELV.

So, we are where we are supposed to be regarding the hydrocarbon engine that was proposed. Now what?

You keep trying to pretend that the Obama engine development request got funded by Congress. IT DID NOT. Congress decided to build the SLS instead, utilizing existing engines (RS-25 & RS-68 were the choices).

[ncb1397]

You keep trying to pretend that the Obama engine development request got funded by Congress. IT DID NOT. Congress decided to build the SLS instead, utilizing existing engines (RS-25 & RS-68 were the choices).

No, it was funded by Congress. The RD-180 replacement propulsion effort was funded under the Department of Defense. HLPT mentions the RD-180 and kerosene/oxygen (they even mention a DoD partnership). That is exactly what the AR-1 is. That it was done under the auspices of the DoD is irrelevant. If NASA picks up the engine now, the partnership aspect is complete. But what are you going to do with it?

[pathfinder_01]

You keep trying to pretend that the Obama engine development request got funded by Congress. IT DID NOT. Congress decided to build the SLS instead, utilizing existing engines (RS-25 & RS-68 were the choices).

No, it was funded by Congress. The RD-180 replacement propulsion effort was funded under the Department of Defense. HLPT mentions the RD-180 and kerosene/oxygen (they even mention a DoD partnership). That is exactly what the AR-1 is. That it was done under the auspices of the DoD is irrelevant. If NASA picks up the engine now, the partnership aspect is complete. But what are you going to do with it?

Er no the Obama engine request was not funded by Congress. The AR-1 got funding only because of decline relations between the U.S. and Russia and Senator McCain pushed a ban on Russian engines forcing ULA to scramble.

[Coastal Ron]

You keep trying to pretend that the Obama engine development request got funded by Congress. IT DID NOT. Congress decided to build the SLS instead, utilizing existing engines (RS-25 & RS-68 were the choices).

No, it was funded by Congress. The RD-180 replacement propulsion effort was funded under the Department of Defense.

You keep forgetting that we're talking about the NASA SLS program, not all U.S. Government engine development.

Because you keep referencing the Department of Defense EELV rocket engine development activity, which has NOTHING to do with the NASA SLS program, or the NASA Authorization Act of 2010.

Let's stick to the SLS program on the SLS thread, shall we? 

[jadebenn]

SRB snobbery continues to baffle me. I don't know why there's this weird stigma against them in applications where they're genuinely useful.

[Proponent]

The reason Saturn V used the large F-1 hydrocarbon engines is lift capability.  Kerosene packs a lot of power in a small amount of fuel compared to other fuels.  This is also the reason for replacing the solids with kerolox boosters.  More thrust to weight, cleaner than solids, and being able to control the thrust or shut down the engines.  If you can pack 3 million lbs thrust into a 5.5m diameter booster you allow SLS to lift far more tonnage to space without an upper stage.

Those are all good reasons, but I think there is one more overriding factor, namely that in the early 1960's, hydrogen fueled engines were a very new technology that had not yet been scaled up to the level required for a Saturn V first stage.  Development of the F-1 had begun in the mid-1950's.