Acronyms to Ascent – SLS managers create development milestone roadmap

[Chris Bergin]

http://www.nasaspaceflight.com/2012/02/acronyms-ascent-sls-managers-create-developmental-milestone-roadmap/

Acronym soup time! Really enjoyed writing this one up, and I hope it's readable. Just thought it really important to get this info out there as we're watching a Launch Vehicle being born and it's good to get the review milestone and vehicle designation info out there.

[Moonwalker]

Interesting article, thank you - especially part about MPTA tests at KSC, interesting idea. Also, I can't wait to find out something more about SLS-3 (EM-3) mission and exploration roadmap.

[Steven Pietrobon]

Wow! Back down to four engines, which is what Direct recommended. Now they just have to shorten the core and fly with three engines for Block I and Block IA. According to Direct, this will put 95 t into LEO for Block I. Not sure what the new boosters will do with a shortened core and three engines for Block IA, but if 35 t were added from Block I to Block IA with a stretched core and four engines, then possibly NASA could get 95+35 = 130 t for Block IA. Oops! no need for Block II then. :-)

[rusty]

Very good outline Chris.

Two points -
1) "Because this (booster) competition isn’t set to end until 2015, SLS teams have had to analyze both versions of the Block 1A, given the differences in their performance characteristics and environments – such as aerodynamic factors like Max Q, as well as vibration, acceleration, acoustics – thus the engineers need to ensure the core stage design is compatible with both options."

That seems like backward thinking - to design something for any/all or no future options. While it's a nice ability, it doesn't seem to be a necessary one.
Unless things have changed since the end of last year, ATK can support 11 launches with their current stockpile of SRBs and no recovery. Considering one launch every two years (starting with a possible hold down test in 2015), that means more/upgraded boosters won't be needed until the mid-2030's.
I don't think the booster competition is needed at this time, especially with budgets/timelines as tight as they are, and in 20yrs when more/better boosters are needed the burden should fall on the competitors to match the existing vehicle.


2) "The current plan is to use the (16) RS-25Ds on the (two Block 1 and) first two Block 1A flights, prior to switching to the expendable version of the engine, known as the RS-25E."

i) I'd assuming the RS-25D engines used in the 2015 hold down test will be refurbished and used on one of those flights.
ii) For years I have, and still think the selection of the RS-25 is a mistake. While the heritage is there, starting RS-25E production is an entirely new engine program (To say it's a modification of an existing program is as fallacious as saying the J-2X is a modification of the J-2S program). If a new engine is the route taken, why not make the RS-25 design much simpler while adding 150,000flb -- the STME. Or even better, use an existing production line based on RS-25 heritage, one that shares cost with another launch vehicle and is even simpler still and has an additional 150,000flb -- the RS-68.
iii) A question; Are the performance figures of a possible RS-25E close enough to state?

[MATTBLAK]

With the RS-68, clustering them close together was a base-heating concern on the various Ares V configurations. I presume SLS wouldn't be much different. Since the regeneratively-cooled RS-25 was clustered close on Shuttle, this made it better suited for the SLS corestage - along with their much higher Isp than RS-68.

Also, I recall that on the 'Shannon Side-Mount', the documentation shows one configuration using the RS-25's at an 111% percent throttle setting.

[clongton]

Very good outline Chris.

Two points -
1) "Because this (booster) competition isn’t set to end until 2015, SLS teams have had to analyze both versions of the Block 1A, given the differences in their performance characteristics and environments – such as aerodynamic factors like Max Q, as well as vibration, acceleration, acoustics – thus the engineers need to ensure the core stage design is compatible with both options."

That seems like backward thinking - to design something for any/all or no future options. While it's a nice ability, it doesn't seem to be a necessary one.
Unless things have changed since the end of last year, ATK can support 11 launches with their current stockpile of SRBs and no recovery. Considering one launch every two years (starting with a possible hold down test in 2015), that means more/upgraded boosters won't be needed until the mid-2030's.
I don't think the booster competition is needed at this time, especially with budgets/timelines as tight as they are, and in 20yrs when more/better boosters are needed the burden should fall on the competitors to match the existing vehicle.


2) "The current plan is to use the (16) RS-25Ds on the (two Block 1 and) first two Block 1A flights, prior to switching to the expendable version of the engine, known as the RS-25E."

i) I'm assuming the RS-25D engines used in the 2015 hold down test will be refurbished and used on one of those flights.

(ii) For years I have, and still think the selection of the RS-25 is a mistake. While the heritage is there, starting RS-25E production is an entirely new engine program (To say it's a modification of an existing program is as fallacious as saying the J-2X is a modification of the J-2S program). If a new engine is the route taken, why not make the RS-25 design much simpler while adding 150,000flb -- the STME.

(iii) Or even better, use an existing production line based on RS-25 heritage, one that shares cost with another launch vehicle and is even simpler still and has an additional 150,000flb -- the RS-68.

(iv) A question; Are the performance figures of a possible RS-25E close enough to state?

1. It's more forward thinking than backward thinking. It's looking at the entire program from a decadal pov rather than the short term. What LRB's can potentially bring to the table significantly outweigh the advantages of the SRB's, depending of course on their final design parameters, but they cannot be ready in time to drive the SLS design. So it is an appropriate decision to design the core to support either, so long as performance is not compromised by that decision, which it is not. We only want to build one core design – for the entire life of the program (3 to 5 decades). We're going to be flying this vehicle for the next 30-50 years, not just 11 flights. It's far better to take the time up front to make sure we make the correct configuration choices than to succumb to “we have enough SRB's for 11 flights so let's just down-select to them right away. Forget LRB's”. That is short-sighted thinking.

2. (i) Yes

    (ii) RS-25E is not an entirely new engine program. This design has been underway for many years now and is essentially at the point where the only big change remaining is the nozzle. Even that has already been conceptually designed and awaits only the production design and tooling to be put in place to build it (big picture).

    (iii) RS-68 has become a non-viable engine choice for SLS principally because of the use of SRB's. The ablatively cooled nozzle would not survive long enough for the vehicle to reach MECO because of the thermal environment at the base of the vehicle. A man rated regenerativly cooled version can certainly be designed and built. In fact that is what DIRECT v2 intended to do. But the door has already been closed to that and the Air Force is not amicable to reopening it. This was the final straw that broke the back of the Ares-V.

    (iv) They are but that data is still FOUO.

[sewand]

As to the LRB competition - is it firm knowledge that only Aerojet will bid, or would an RD-180-based solution still be possible? 

[Chris Bergin]

Thanks to the nice comments!

As to the LRB competition - is it firm knowledge that only Aerojet will bid, or would an RD-180-based solution still be possible? 

Not entirely certain, but it is "likely" to be an Aerojet vs ATK shoot out.

I've got comments from Aerojet, which are somewhat cagey. ATK aren't responding yet (and usually do, so they'll be carefully wording a response too). Will be an article.

[renclod]

    (iii) RS-68 has become a non-viable engine choice for SLS principally because of the use of SRB's.

So what if a LRB replaces the SRB ; would the RS-68 be re-considered ?

[Chris Bergin]

    (iii) RS-68 has become a non-viable engine choice for SLS principally because of the use of SRB's.

So what if a LRB replaces the SRB ; would the RS-68 be re-considered ?

I'm thinking not. They seem very set on the RS-25s.

Of course, you never know!

[aquanaut99]

I'm thinking not. They seem very set on the RS-25s.

Of course, you never know!

Well, the RS-25 is superior to the RS-68 in many ways. And I think that the RS-25E is supposed to be able to run at 111% rated performance, since it is not required to be reusable.

The RS-25 is one of the finest rocket engines ever made. The fact that NASA plans to keep on using it is a good idea, IMO.

[renclod]

They seem very set on the RS-25s.

The "Direct" advocates argued the case for RS-25s in the context of a large number of engines consumed per year, being as cheap as RS-68s (!).
However SLS as currently funded is anything but... large number of engines consumed per year.

[Paul Howard]

I really enjoyed that article. This site's coverage of SLS is unrivalled.

[clongton]

    (iii) RS-68 has become a non-viable engine choice for SLS principally because of the use of SRB's.

So what if a LRB replaces the SRB ; would the RS-68 be re-considered ?

No.
SLS is a man-rated launch vehicle and the Air Force closed the door on RS-68 changes needed to man-rate the engine.

[rusty]

Re;
A) RS-25E is not an entirely new engine program. This design has been underway for many years now and is essentially at the point where the only big change remaining is the nozzle. Even that has already been conceptually designed and awaits only the production design and tooling to be put in place to build it (big picture).

B) RS-68 has become a non-viable engine choice for SLS principally because of the use of SRB's. The ablatively cooled nozzle would not survive long enough for the vehicle to reach MECO because of the thermal environment at the base of the vehicle.

C) ...But the door has already been closed to that and the Air Force is not amicable to reopening it.

a) SSME, RS-25E, STME and RS-68 all spent years being designed. Two went through testing, production and flight. One no longer has a production line and the other is in production. By those measures, of the remaining two, the STME designed decades ago is as close/closer to flight than the RS-25E.

b) I have and do disagree with that statement. As I could design and prototype an effective, simple solution in 60 days, I find the assertion the RS-68 is "a non-viable engine choice" to be BaselesS hand waiving. You determine the "who" and "why" for the claims.

c) Would you consider the 'door closed' for a human-rated RS-68, thus the door closed on Delta IV as well? A few links/quotes;
http://www.nasaspaceflight.com/2009/09/ula-claim-gap-reducing-solution-via-eelv-exploration-master-plan/
In regards to the entire Delta IVH - " Numerous upgrades and modifications are listed, but also with cited uncertainty as to how many of the modifications would be required. ...
“Of note is that quite a few of the requirements are not driven by explicit redundancy requirements, but on other anticipated safety criteria as the desire to reduce the release of burning H2 at RS-68 start,” added the paper.
“Also, in some cases different redundancy upgrades (RS-68 backup valves, feedline prevalves, and hydraulics redundancy) need to be traded off to find the smartest implementation path. This makes the final suite of upgrades somewhat uncertain. However, the anticipated total scope and cost of these safety upgrades is programmatically small, with engine mods the most expensive due to high intrinsic recertification cost." "
http://www.floridatoday.com/content/blogs/space/EELVHumanRating.pdf
Pg 8/9 on RS-68 Human-Rating - "A representative list includes: 1) improving the reliability of the engine controller; 2) furtherevluating and mitigating any structural margin issues that do not comply with "Strength and Life Assessment Requirements for Liquid Fueled Space Propulsion System Engines," NASA-STD-5012, 13 June 2006; 3) developing redundant actuators and valves, and installing triple-redundant sensors for more robust fault detection; 4) improving quality control to meet human-rating requirements; 5) implementing a cross-strapped pressurization system; and 6) additional qualification testing to determine reliability."