Author Topic: SLS General Discussion Thread 2  (Read 226019 times)

Offline MATTBLAK

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Re: SLS General Discussion Thread 2
« Reply #300 on: 03/11/2016 10:06 PM »
The SLS/Orion mission to visit the asteroid in orbit around the moon is looking like it is going to be delayed and possibly cancelled.

It is already being delayed to "study".

http://spacenews.com/nasa-slips-schedule-of-asteroid-redirect-mission/

They should put a small Habitat Module out there to test radiation mitigation, life support systems and other tech. The crew could dock with it and do a "This is what going to Mars is going to feel like".
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Offline Proponent

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Re: SLS General Discussion Thread 2
« Reply #301 on: 03/12/2016 08:00 AM »
Not only would changing engines be technically difficult at this stage, as The Amazing Catstronaut says, but using the BE-4 would be politically difficult, as it would seriously hurt one of the major inhabitants of the Shuttle ecosystem, namely Aerojet Rocketdyne.

It might be interesting to wonder, though, where things might have gone had the AR-1 been on the drawing board circa 2011, when the RAC teams were doing their studies.
« Last Edit: 03/12/2016 12:53 PM by Proponent »

Offline jgoldader

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Re: SLS General Discussion Thread 2
« Reply #302 on: 03/12/2016 11:00 AM »
The SLS/Orion mission to visit the asteroid in orbit around the moon is looking like it is going to be delayed and possibly cancelled.

It is already being delayed to "study".

http://spacenews.com/nasa-slips-schedule-of-asteroid-redirect-mission/

I've been expecing at least some discussion here about the elephant in the room that the "delay" represents, but am surprised/not surprised it hasn't started yet.
Recovering astronomer

Offline edkyle99

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Re: SLS General Discussion Thread 2
« Reply #303 on: 03/12/2016 04:50 PM »

Switching wouldn't change the timeframe that much...

Sure would - the first stage engines are one of the most pivotal, complex elements of the whole LV. You switch those out and you have to change the whole design, especially when you're talking different fuel types. ...
Precisely.  If SLS went to a lower-performing hydrocarbon core first stage, a heavier, higher thrust second stage would be needed.  It would mean bringing back J-2X.  It would also mean development of a smaller in-space third stage.

These questions were all studied to death a decade ago.  Multiple studies of innumerable alternative designs.  The best answer nearly every time looked pretty much like the rocket now being built.

 - Ed Kyle
« Last Edit: 03/12/2016 05:01 PM by edkyle99 »

Offline the_other_Doug

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Re: SLS General Discussion Thread 2
« Reply #304 on: 03/12/2016 04:59 PM »

Switching wouldn't change the timeframe that much...

Sure would - the first stage engines are one of the most pivotal, complex elements of the whole LV. You switch those out and you have to change the whole design, especially when you're talking different fuel types. ...
Precisely.  If SLS went to a lower-performing hydrocarbon core first stage, a heavier, higher thrust second stage would be needed.  It would mean bringing back J-2X.  It would also mean development of a smaller in-space third stage.

 - Ed Kyle

Yeah -- if you're going to change to kerolox or metholox in the SLS first stage, you might just as well pull out the old plans and start building Saturn V's again...
-Doug  (With my shield, not yet upon it)

Offline Coastal Ron

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Re: SLS General Discussion Thread 2
« Reply #305 on: 03/12/2016 07:50 PM »
I've been expecing at least some discussion here about the elephant in the room that the "delay" represents, but am surprised/not surprised it hasn't started yet.

That's because it wasn't a surprise, it was expected.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline daveklingler

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Re: SLS General Discussion Thread 2
« Reply #306 on: 03/13/2016 01:50 AM »
First of all, I think it's (over)stating the obvious to say that changing SLS engines at this point would create a few raised eyebrows.  My first take was that it would cause the biggest agency crisis since Apollo I.  Then I thought about it.  Hm.  NASA got away with "redesigning" the J-2 as the J-2X, and the Senate got away with designing a heavy lift rocket that NASA can't afford to fly.  Possibly a switch to the AR-1 might be billed as an "engine upgrade".  I'm laughing ruefully as I write this, and remembering more examples where the truth as been, ahem, finessed.


Switching wouldn't change the timeframe that much...

Sure would - the first stage engines are one of the most pivotal, complex elements of the whole LV. You switch those out and you have to change the whole design, especially when you're talking different fuel types. ...
Precisely.  If SLS went to a lower-performing hydrocarbon core first stage, a heavier, higher thrust second stage would be needed.  It would mean bringing back J-2X.  It would also mean development of a smaller in-space third stage.

These questions were all studied to death a decade ago.  Multiple studies of innumerable alternative designs.  The best answer nearly every time looked pretty much like the rocket now being built.

 - Ed Kyle

You have more faith than I do that the best answer, a decade ago or any other time, was to design a hydrolox first stage with solid boosters and Shuttle engines.  Besides, the AR-1 didn't exist back then.  Today, Congress is every bit as bent on bringing the AR-1 into existence as they were the J-2X and SLS. Whether, given the chance, AJR wouldn't choose a long-term commitment for AR-1 is an interesting question.

Beyond that, all of this was relitigated after 2010, and stayed fuzzy into well into 2012, after which it still creaked along before and after PDR in mid-2013.  Quite frankly, I'd give it roughly six months to get back to PDR on a new kerolox first stage, using the work that's been done already.  The rest of the vehicle is clearly-parameterized.  Many other choices wouldn't be need to be made over again, saving more time before a first CDR.

Regarding your assertion that the new first stage would be lower-performance, the tank mass and fuel density difference along with the relatively low difference (~50 seconds) in sea level Isp generally makes kerolox come out slightly better for first stages, which I'm pretty sure you know very well.

I think an AR-1 first stage is worth putzing around with.  I'm not seriously proposing any of this could ever come about, ever ever ever, but stranger things have happened.  After all, the Senate designed a rocket...

*edit - And then, there's the AR-1/SLS common booster core...  :D
« Last Edit: 03/13/2016 02:07 AM by daveklingler »

Offline daveklingler

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Re: SLS General Discussion Thread 2
« Reply #307 on: 03/13/2016 02:09 AM »
Not only would changing engines be technically difficult at this stage, as The Amazing Catstronaut says, but using the BE-4 would be politically difficult, as it would seriously hurt one of the major inhabitants of the Shuttle ecosystem, namely Aerojet Rocketdyne.

Given the SLS's sole purpose of supporting that ecosystem, the BE-4 is an even less likely design choice, I admit.

Quote
It might be interesting to wonder, though, where things might have gone had the AR-1 been on the drawing board circa 2011, when the RAC teams were doing their studies.

Yep.  Or where things might have gone had an AR-1 been funded over a decade back instead of the J-2X.
« Last Edit: 03/13/2016 02:11 AM by daveklingler »

Offline Endeavour_01

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Re: SLS General Discussion Thread 2
« Reply #308 on: 03/13/2016 02:13 AM »
...as much as I point out SLS is a complete waste of money, I /will/ still be trying to attend the first launch because it will be quite spectacular. :)

While we disagree on whether SLS is a waste or not I share your desire to see the first launch. Hopefully job situation will allow (If I can land a teaching job after graduation I will make it a field trip!). We definitely need to have an NSF group get together to see the launch (and the first manned CST-100 and Dragon launches).

They should put a small Habitat Module out there to test radiation mitigation, life support systems and other tech. The crew could dock with it and do a "This is what going to Mars is going to feel like".

That would be the best thing to do for EM-3 in my view. NASA already has Congressional authorization and funds to start working on a habitat module. There would be plenty of time to get it ready and we would get a foothold in cislunar space.
I cheer for both NASA and commercial space. For SLS, Orion, Falcon 9, Falcon Heavy, Dragon, Starliner, Cygnus and all the rest!
I was blessed to see the launch of Space Shuttle Endeavour on STS-99. The launch was beyond amazing. My 8-year old mind was blown. I remember the noise and seeing the exhaust pour out of the shuttle as it lifted off. I remember staring and watching it soar while it was visible in the clear blue sky. It was one of the greatest moments of my life and I will never forget it.

Offline A_M_Swallow

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Re: SLS General Discussion Thread 2
« Reply #309 on: 03/13/2016 03:26 AM »
First of all, I think it's (over)stating the obvious to say that changing SLS engines at this point would create a few raised eyebrows.  My first take was that it would cause the biggest agency crisis since Apollo I.  Then I thought about it.  Hm.  NASA got away with "redesigning" the J-2 as the J-2X, and the Senate got away with designing a heavy lift rocket that NASA can't afford to fly.  Possibly a switch to the AR-1 might be billed as an "engine upgrade".  I'm laughing ruefully as I write this, and remembering more examples where the truth as been, ahem, finessed.

{snip}

The first few engines are literally the Space Shuttle engines. These will soon run out. After that NASA will have to buy newly manufactured engines either more of the same design or a new design. A new design of engine would have to have a bigger payload, be more efficient, available sooner or cheaper.

Online Eric Hedman

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Re: SLS General Discussion Thread 2
« Reply #310 on: 03/13/2016 05:26 AM »
First of all, I think it's (over)stating the obvious to say that changing SLS engines at this point would create a few raised eyebrows.  My first take was that it would cause the biggest agency crisis since Apollo I.  Then I thought about it.  Hm.  NASA got away with "redesigning" the J-2 as the J-2X, and the Senate got away with designing a heavy lift rocket that NASA can't afford to fly.  Possibly a switch to the AR-1 might be billed as an "engine upgrade".  I'm laughing ruefully as I write this, and remembering more examples where the truth as been, ahem, finessed.

{snip}

The first few engines are literally the Space Shuttle engines. These will soon run out. After that NASA will have to buy newly manufactured engines either more of the same design or a new design. A new design of engine would have to have a bigger payload, be more efficient, available sooner or cheaper.
I thought NASA awarded Aerojet Rocketdyne a contract back in November to modernize the RS-25 and restart production.

Online RonM

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Re: SLS General Discussion Thread 2
« Reply #311 on: 03/13/2016 01:29 PM »
First of all, I think it's (over)stating the obvious to say that changing SLS engines at this point would create a few raised eyebrows.  My first take was that it would cause the biggest agency crisis since Apollo I.  Then I thought about it.  Hm.  NASA got away with "redesigning" the J-2 as the J-2X, and the Senate got away with designing a heavy lift rocket that NASA can't afford to fly.  Possibly a switch to the AR-1 might be billed as an "engine upgrade".  I'm laughing ruefully as I write this, and remembering more examples where the truth as been, ahem, finessed.

{snip}

The first few engines are literally the Space Shuttle engines. These will soon run out. After that NASA will have to buy newly manufactured engines either more of the same design or a new design. A new design of engine would have to have a bigger payload, be more efficient, available sooner or cheaper.
I thought NASA awarded Aerojet Rocketdyne a contract back in November to modernize the RS-25 and restart production.

You are correct.

https://www.nasaspaceflight.com/2016/01/nasa-defends-restart-rs-25-production/

Offline edkyle99

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Re: SLS General Discussion Thread 2
« Reply #312 on: 03/13/2016 03:17 PM »

Regarding your assertion that the new first stage would be lower-performance, the tank mass and fuel density difference along with the relatively low difference (~50 seconds) in sea level Isp generally makes kerolox come out slightly better for first stages, which I'm pretty sure you know very well.
I think you know pretty well that the SLS core stage is not a "first stage".  It is a long-burning sustainer stage serving the same purpose as the Orbiter/ET combination.  It provides high specific impulse above all else, much higher than only "~50 seconds" since most of its action time is in vacuum where its advantage over a hydrocarbon engine is in excess of 120 seconds ISP.  It only needs enough thrust to keep positive T/W after the SRBs stop thrusting.

If you replace this high-performing core stage with a hydrocarbon stage, you are going to have to make up the delta-v shortfall with a bigger, more expensive LOX/LH2 upper stage which will require higher thrust than RL10 and the like can provide.  All of the studies showed that result.  The proper application of a hydrocarbon engine would be as part of an SRB replacement.

 - Ed Kyle
« Last Edit: 03/13/2016 03:31 PM by edkyle99 »

Offline Space Ghost 1962

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Re: SLS General Discussion Thread 2
« Reply #313 on: 03/13/2016 03:30 PM »
The proper application of a hydrocarbon engine would be as part of an SRB replacement.
Actually, the only application.

Offline AncientU

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Re: SLS General Discussion Thread 2
« Reply #314 on: 03/13/2016 06:32 PM »
The proper application of a hydrocarbon engine would be as part of an SRB replacement.
Actually, the only application.

Unless a hydrocarbon core stage replaces the entire SLS, of course.
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Offline TomH

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Re: SLS General Discussion Thread 2
« Reply #315 on: 03/13/2016 08:04 PM »
None of these options is under the slightest consideration. Join L2 for the definitive status of SLS. The elephant mastodon in the room is indeed a hydrocarbon fueled 15m diameter monster which will be affordable due to leaner manufacturing processes, the lack of government involvement, and most of all, reusability.

Offline MATTBLAK

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Re: SLS General Discussion Thread 2
« Reply #316 on: 03/13/2016 08:08 PM »
I will certainly believe it when I certainly see it.
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Offline oldAtlas_Eguy

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Re: SLS General Discussion Thread 2
« Reply #317 on: 03/13/2016 08:26 PM »
Do not forget SLS is a political beast. Congress can change their minds as to what they want. As in a 200+mt launcher for Mars not just a 100mt maybe a 130mt launcher. Such as liquid boosters, 5 engine RS-68A core, J-2X second stage and a RL-10 EDS. Plus use something else (commercial LV) to get Orion into LEO where it docks with the rest of the Mars stack. Constellation resurrected.

Offline A_M_Swallow

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Re: SLS General Discussion Thread 2
« Reply #318 on: 03/13/2016 09:06 PM »
First of all, I think it's (over)stating the obvious to say that changing SLS engines at this point would create a few raised eyebrows.  My first take was that it would cause the biggest agency crisis since Apollo I.  Then I thought about it.  Hm.  NASA got away with "redesigning" the J-2 as the J-2X, and the Senate got away with designing a heavy lift rocket that NASA can't afford to fly.  Possibly a switch to the AR-1 might be billed as an "engine upgrade".  I'm laughing ruefully as I write this, and remembering more examples where the truth as been, ahem, finessed.

{snip}

The first few engines are literally the Space Shuttle engines. These will soon run out. After that NASA will have to buy newly manufactured engines either more of the same design or a new design. A new design of engine would have to have a bigger payload, be more efficient, available sooner or cheaper.
I thought NASA awarded Aerojet Rocketdyne a contract back in November to modernize the RS-25 and restart production.

That is a factual argument not a political argument.

Although it is why NASA went that way.

Offline Space Ghost 1962

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Re: SLS General Discussion Thread 2
« Reply #319 on: 03/13/2016 10:46 PM »
Sure they can moot many things, some that might even get study financing. Longer term depends on many things, and they can be reversed at times too.

The SLS that appears to not be paper might do missions. The capability to do missions in less than an decade will fight with the paper design to get out of the box that must take more decades - govt related work often takes a lot longer.

Depending on outside of government "deals" might sound "quicker", but these are always subject to changing political trades that may never resolve.

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