Author Topic: Navigating the twists and turns steering SLS Development  (Read 18889 times)

Offline Chris Bergin

FEATURE ARTICLE: Navigating the twists and turns steering SLS Development -

https://www.nasaspaceflight.com/2018/10/navigating-twists-turns-steering-sls-development/

- By Philip Sloss.

Renders by Nathan Koga for NSF/L2

Offline BrianNH

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Re: Navigating the twists and turns steering SLS Development
« Reply #1 on: 10/01/2018 07:36 pm »
Excellent article!   

I wonder what sort of changes (besides the booster) would be needed by Block 2 to achieve the 130mt LEO target?  This is the first I remember reading of "a major redesign of the vehicle would be necessary to get the required performance."

Also, NASA recently announced that the expected performance of Block 1 went up from 70 to 95 mt to LEO.  I've been curious how this would change their estimate of the performance of Block 1B (currently 110 mt LEO if I remember correctly).

Great work, psloss.

Offline IRobot

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Re: Navigating the twists and turns steering SLS Development
« Reply #2 on: 10/01/2018 10:10 pm »
As expected, SLS/Orion plans are run on a parallel universe where there are no alternative launchers or architectures.

Side point to the article, the NASA metrication is a bit inconsistent across slides.
Some slides (and part of the article) use "mt", others just "t".
Most use "m" but some "ft" still visible.

I guess that people still think first in imperial units and then some of them convert them to metric.

Online ncb1397

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Re: Navigating the twists and turns steering SLS Development
« Reply #3 on: 10/02/2018 01:30 am »

Also, NASA recently announced that the expected performance of Block 1 went up from 70 to 95 mt to LEO.  I've been curious how this would change their estimate of the performance of Block 1B (currently 110 mt LEO if I remember correctly).

Figure 68 in this article seems to indicate that Block 1B is 117-123 t to LEO. I tried to run the numbers for roughly quadrupling the size of the upper stage from Block 1 and got similar numbers based on 95 t being the baseline. I did this two months ago without having seen this slide, because a 10 t boost didn't make much sense intuitively.

https://forum.nasaspaceflight.com/index.php?topic=46066.msg1842127#msg1842127

Offline Steven Pietrobon

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Re: Navigating the twists and turns steering SLS Development
« Reply #4 on: 10/02/2018 11:17 am »
Figure 68 in this article seems to indicate that Block 1B is 117-123 t to LEO. I tried to run the numbers for roughly quadrupling the size of the upper stage from Block 1 and got similar numbers based on 95 t being the baseline. I did this two months ago without having seen this slide, because a 10 t boost didn't make much sense intuitively.

Boeing said Block IB is 93.1 t to LEO in a 2013 paper, which agrees with your 95 t figure. NASA has been saying 105 t, but I believe that includes the dry mass of EUS. The 117-123 t values must be a typo. Block 2B is listed as 118-137 t, so having the minimum value increase by only 1 t does not make any sense. Also, I don't understand why a range of values are given, unless one is with Orion and one without. Another strange thing is the difference in values:

Block 1A (+DK) 106-119 t (13 t)
Block 1A (+CPS) 106-119 t (13 t)
Block 2A (+J-2X) 122-130 t (8 t)
Block 2A (+RS-25) 138-147 t (9 t)

Block 1B (+EUS) 117-123 t (6 t)
Block 2B (+DK) 118-137 t (19 t)

Block 1B (+DK) 106-119 t (13 t)
Block 2B (+EUS) 118-137 t (19 t)

Why is the range only 6 t for Block 1B, but 19 t for Block 2B? For someone making a decision based on this graph, the wrong values given for Block 1B could have led to a huge error in judgement.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline Zed_Noir

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Re: Navigating the twists and turns steering SLS Development
« Reply #5 on: 10/02/2018 03:46 pm »
<snip>
Also, NASA recently announced that the expected performance of Block 1 went up from 70 to 95 mt to LEO.  I've been curious how this would change their estimate of the performance of Block 1B (currently 110 mt LEO if I remember correctly).
<snip>

According to a NASA web page the LEO payload of 95 mT for the Block 1 that NASA is quoting is for a parking  orbit of about 155 km altitude ("almost 100 miles"). ::)

Quote
After SLS loses the weight of its first stage propulsion systems and fuel, more power is still needed to send Orion to the Moon. At this point, the upper part of the rocket and Orion are soaring almost 100 miles above Earth, accelerating at more than 17,500 miles per hour, and beginning a circular orbit around Earth. This is low-Earth orbit, often referred to as LEO. SLS can deliver more than 95 metric tons (209,439 pounds) to this orbit with a Block I configuration. However, a deep space mission requires a rocket that can travel beyond LEO with enough power and speed to overcome the pull of Earth’s gravity and send the spacecraft even farther to reach the Moon. The upper part of rocket prepares for the next big move to send Orion out of LEO without even completing a full orbit of Earth.

The quoted paragraph is after the expanded view diagram of the Block 1 on the web page.

edit: fixed web link
« Last Edit: 10/03/2018 09:10 pm by Zed_Noir »

Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #6 on: 10/03/2018 12:42 pm »
<snip>
Also, NASA recently announced that the expected performance of Block 1 went up from 70 to 95 mt to LEO.  I've been curious how this would change their estimate of the performance of Block 1B (currently 110 mt LEO if I remember correctly).
<snip>

According to a NASA web page the LEO payload of 95 mT for the Block 1 that NASA is quoting is for a parking  orbit of about 155 km altitude ("almost 100 miles"). ::)

Quote
After SLS loses the weight of its first stage propulsion systems and fuel, more power is still needed to send Orion to the Moon. At this point, the upper part of the rocket and Orion are soaring almost 100 miles above Earth, accelerating at more than 17,500 miles per hour, and beginning a circular orbit around Earth. This is low-Earth orbit, often referred to as LEO. SLS can deliver more than 95 metric tons (209,439 pounds) to this orbit with a Block I configuration. However, a deep space mission requires a rocket that can travel beyond LEO with enough power and speed to overcome the pull of Earth’s gravity and send the spacecraft even farther to reach the Moon. The upper part of rocket prepares for the next big move to send Orion out of LEO without even completing a full orbit of Earth.

The quoted paragraph is after the expanded view diagram of the Block 1 on the web page.

Your link is broken. Altitudes are typically given in nautical miles. 180-185 km is "almost 100" nautical miles, and is a typical parking orbit such as used by Apollo before TLI.

Online docmordrid

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Re: Navigating the twists and turns steering SLS Development
« Reply #7 on: 10/03/2018 06:41 pm »
>
According to a NASA web page the LEO payload of 95 mT for the Block 1 that NASA is quoting is for a parking  orbit of about 155 km altitude ("almost 100 miles"). ::)
>

Un-busted link...

Link....

Quote
The initial configuration of SLS can send more than 26 metric tons (57,000 pounds) to lunar orbits and future upgrades will enable the rocket to send at least 45 metric tons (99,000 pounds).
« Last Edit: 10/03/2018 06:46 pm by docmordrid »
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Online docmordrid

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Re: Navigating the twists and turns steering SLS Development
« Reply #8 on: 10/03/2018 06:54 pm »
>
Altitudes are typically given in nautical miles. 180-185 km is "almost 100" nautical miles, and is a typical parking orbit such as used by Apollo before TLI.

Here in the plain-speaking Midwest "almost 100 miles" means "not quite 100 miles," and claiming it's more would receive considerable side-eye.

Someone needs to work on their messaging.
« Last Edit: 10/03/2018 06:54 pm by docmordrid »
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Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #9 on: 10/03/2018 08:07 pm »
>
Altitudes are typically given in nautical miles. 180-185 km is "almost 100" nautical miles, and is a typical parking orbit such as used by Apollo before TLI.

Here in the plain-speaking Midwest "almost 100 miles" means "not quite 100 miles," and claiming it's more would receive considerable side-eye.

Someone needs to work on their messaging.

NASA uses exclusively nautical miles and not statue miles for altitudes, as far as I can tell. 185 km = 99.9 nautical miles. "Almost 100 miles above Earth" seems pretty clear to me in that context.

Offline lucspace

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Re: Navigating the twists and turns steering SLS Development
« Reply #11 on: 10/05/2018 12:31 pm »
I called this happening some months back - don't know which thread, it doesn't matter. Seems now that it might use the Centaur V/ACES stage, Delta IVH stage with another stretch and stronger engine. Or nothing...

...Seems to me that Dr Steve Pietrobon might have to do some more calculations for SLS capabilities: based on those stages I just mentioned :(
« Last Edit: 10/05/2018 12:33 pm by MATTBLAK »
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Offline Crispy

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Re: Navigating the twists and turns steering SLS Development
« Reply #12 on: 10/05/2018 12:37 pm »
Cancellation of EUS? https://twitter.com/DJSnM/status/1048001681600831488?s=20

For those who can't see the tweet, it's from Scott Manley and is an image of these words:

"Development of the Exploration Upper Stage has been officially halted in that contractors have been directed to stop work immediately on it (not even much of a tailoff phase). Officially, it's 100 day pause, but unofficially, we've been told not to expect that work to come back for minimum 1 year and likely multiple years. Core stage is in sufficient schedule/budget trouble that they're planning on just flying Block 1 a bunch of times and indefinitely postpone Block 1B and Block 2 into the farther future. Which makes the SLS project have even less of a niche than it already was clinging to, if the unofficial word's real. "

Online ncb1397

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Re: Navigating the twists and turns steering SLS Development
« Reply #13 on: 10/05/2018 12:41 pm »
Considering the project just got an additional installment of funding in the CR and is apparently unsourced, I'm calling this questionable.
« Last Edit: 10/05/2018 12:43 pm by ncb1397 »

Offline speedevil

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Re: Navigating the twists and turns steering SLS Development
« Reply #14 on: 10/05/2018 12:44 pm »
"Development of the Exploration Upper Stage has been officially halted in that contractors have been directed to stop work immediately on it
I assume this would have obvious knock-ons for the mobile launcher designed for it.
Who would have the authority to make this sort of decision - wouldn't this have to come from Congress - or at least the strong intimation of support for it?
It seems unlikely Bridenstine woke up yesterday and decided to.
« Last Edit: 10/05/2018 01:37 pm by speedevil »

Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #15 on: 10/05/2018 01:32 pm »
Cancellation of EUS? https://twitter.com/DJSnM/status/1048001681600831488?s=20

For those who can't see the tweet, it's from Scott Manley and is an image of these words:

"Development of the Exploration Upper Stage has been officially halted in that contractors have been directed to stop work immediately on it (not even much of a tailoff phase). Officially, it's 100 day pause, but unofficially, we've been told not to expect that work to come back for minimum 1 year and likely multiple years. Core stage is in sufficient schedule/budget trouble that they're planning on just flying Block 1 a bunch of times and indefinitely postpone Block 1B and Block 2 into the farther future. Which makes the SLS project have even less of a niche than it already was clinging to, if the unofficial word's real. "

The tweet is still live, not sure why the error message says it doesn't exist. Here's the photo that's attached to it:

Offline Rebel44

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Re: Navigating the twists and turns steering SLS Development
« Reply #16 on: 10/05/2018 03:35 pm »
https://arstechnica.com/science/2018/10/rocket-report-spacex-targeted-chinese-rocket-scientist-goes-viral-sls-slips/

"An official slip acknowledgement ... NASA is finally (officially) acknowledging that EM-1, the maiden launch of SLS, will slip from December 2019 until at least June 2020. Sources tell us to expect another slip to 2021, official or not. Expect to see more news related to this emerge next week."

Offline AncientU

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Re: Navigating the twists and turns steering SLS Development
« Reply #17 on: 10/05/2018 04:21 pm »
Time to privatize SLS/Orion. 

Let Boeing, LM, NG(boosters), and AJR pick up the rest of development overruns.
Compete all launches after 2 Block 1 flights -- when 'development' is complete (and taxpayers have paid enough).
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Offline FinalFrontier

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Re: Navigating the twists and turns steering SLS Development
« Reply #18 on: 10/05/2018 04:36 pm »
If they can't fly in 2020 this program is cooked. Also postponing EUS effectively cooks the program anyway, rocket can't really do anything useful at that point.

As I have said before, at the current rate BFR will be operational before SLS, or before SLS does anything useful. So will Vulcan so will New Glenn maybe even New Armstrong. If this happens SLS is invalidated. Of course we know it already is useless.
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Offline speedevil

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Re: Navigating the twists and turns steering SLS Development
« Reply #19 on: 10/05/2018 06:37 pm »
If they can't fly in 2020 this program is cooked. Also postponing EUS effectively cooks the program anyway, rocket can't really do anything useful at that point.

As I have said before, at the current rate BFR will be operational before SLS, or before SLS does anything useful. So will Vulcan so will New Glenn maybe even New Armstrong.
F9 fully reusable, FH fully reusable are also possibilities for this sort of timescale.

Offline Lar

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Re: Navigating the twists and turns steering SLS Development
« Reply #20 on: 10/05/2018 06:43 pm »
This probably isn't the thread to debate how best to kill SLS or whether it should. It's an article discusion thread.
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Offline ThereIWas3

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Re: Navigating the twists and turns steering SLS Development
« Reply #21 on: 10/05/2018 08:52 pm »
Were the LOP-G projects counting on EUS to get there?
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Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #22 on: 10/05/2018 11:52 pm »
Were the LOP-G projects counting on EUS to get there?

Yes. ICPS cannot send Orion and a co-manifested payload though TLI.

Online Lars-J

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Re: Navigating the twists and turns steering SLS Development
« Reply #23 on: 10/06/2018 12:24 am »
...And this is what happens when NASA centers and contractors get greedy and maximize what they can get for development, hoping that the future bigger budgets will materialize for add-ons.

None of this - SLS, Orion, EUS, LOP-G (or whatever it is called currently) - should cost as much as it does. Not even close.

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Re: Navigating the twists and turns steering SLS Development
« Reply #24 on: 10/06/2018 01:59 am »
And...it turns out to be bogus reporting...

Quote
In an Oct. 3 call with reporters, John Shannon, vice president and program manager for the Space Launch System at Boeing, said NASA has asked Boeing to look at changes to the Exploration Upper Stage (EUS) to improve its performance.
https://spacenews.com/boeing-plans-changes-to-sls-upper-stages/

Shouldn't be suprising because it was
1.)unsourced
2.)looks hastily put together and posted
3.)is infused with opinion and anti-SLS slant
4.)basically admits most of it is just rumor
5.)the action itself would probably be illegal
« Last Edit: 10/06/2018 02:09 am by ncb1397 »

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Re: Navigating the twists and turns steering SLS Development
« Reply #25 on: 10/06/2018 02:38 am »
The SRBs are one of the SLS's handicaps, performance wise with the EUS probably being the worst. The SRB's are monstrously heavy at liftoff, despite their enormous thrust. But I think it's going to be SRBs all the way with this booster, because making reusable hydrocarbon boosters to fit would entail huge Corestage redesign. That's not going to happen. The EUS as we understand it at the moment has high Isp but relatively low thrust (RL-10 derivatives) and a relatively low propellant load. Allegedly because of the VAB height restrictions. Max out the VAB requirements to the last inch, I say!

The EUS could have it's prop load increased and the engines could go to 6x RL-10s or 4x MB60s. It is unlikely that the RS-25 engines could be upgraded further without a great deal of expenditure and testing. I know that Dr Steve Pietrobon has calculated many SLS variations. Seems to me that unless the SLS could be optimized to maximize the payload - because throwing away all that beautiful hardware would suck - optimized to get more than 130 metric tons into LEO or 39 tons BLEO, then... (makes cutting motion across one's throat) :(
« Last Edit: 10/06/2018 09:39 am by MATTBLAK »
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Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #26 on: 10/06/2018 02:55 am »
And...it turns out to be bogus reporting...

Quote
In an Oct. 3 call with reporters, John Shannon, vice president and program manager for the Space Launch System at Boeing, said NASA has asked Boeing to look at changes to the Exploration Upper Stage (EUS) to improve its performance.
https://spacenews.com/boeing-plans-changes-to-sls-upper-stages/

Shouldn't be suprising because it was
1.)unsourced
2.)looks hastily put together and posted
3.)is infused with opinion and anti-SLS slant
4.)basically admits most of it is just rumor
5.)the action itself would probably be illegal

The 100 day stop work appears to have been accurate, since Boeing said they had to slow down work and delay going to CDR. And with the launch date pushed out another year, the need date for the design is delayed.

Offline FinalFrontier

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Re: Navigating the twists and turns steering SLS Development
« Reply #27 on: 10/06/2018 03:19 am »
And...it turns out to be bogus reporting...

Quote
In an Oct. 3 call with reporters, John Shannon, vice president and program manager for the Space Launch System at Boeing, said NASA has asked Boeing to look at changes to the Exploration Upper Stage (EUS) to improve its performance.
https://spacenews.com/boeing-plans-changes-to-sls-upper-stages/

Shouldn't be suprising because it was
1.)unsourced
2.)looks hastily put together and posted
3.)is infused with opinion and anti-SLS slant
4.)basically admits most of it is just rumor
5.)the action itself would probably be illegal
It doesn't matter that it's illegal. NASA has already violated the law several times with regard to the SLS program case and point the original space act required a vehicle be online in 2016. Where's the vehicle? That is just the most egregious one there are other violations. They straight up don't care.

There is a part of me that really wants this to succeed somehow and actually fly useful missions, but it's becoming painful to watch at this point.
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Online ncb1397

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Re: Navigating the twists and turns steering SLS Development
« Reply #28 on: 10/06/2018 03:25 am »
And...it turns out to be bogus reporting...

Quote
In an Oct. 3 call with reporters, John Shannon, vice president and program manager for the Space Launch System at Boeing, said NASA has asked Boeing to look at changes to the Exploration Upper Stage (EUS) to improve its performance.
https://spacenews.com/boeing-plans-changes-to-sls-upper-stages/

Shouldn't be surprising because it was
1.)unsourced
2.)looks hastily put together and posted
3.)is infused with opinion and anti-SLS slant
4.)basically admits most of it is just rumor
5.)the action itself would probably be illegal
It doesn't matter that it's illegal. NASA has already violated the law several times with regard to the SLS program case and point the original space act required a vehicle be online in 2016. Where's the vehicle? That is just the most egregious one there are other violations. They straight up don't care.

There is a part of me that really wants this to succeed somehow and actually fly useful missions, but it's becoming painful to watch at this point.

It required the goal to be 2016. As far as I am aware, NASA complied with the law.

Quote
Priority should be placed on the core elements with the goal for operational capability for the core elements not later than December 31, 2016.
https://www.nasa.gov/pdf/649377main_PL_111-267.pdf

edit: Some details on the tweet that I didn't notice

https://twitter.com/DJSnM/status/1048211938080055296
« Last Edit: 10/06/2018 03:40 am by ncb1397 »

Offline Steven Pietrobon

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Re: Navigating the twists and turns steering SLS Development
« Reply #29 on: 10/06/2018 04:56 am »
The current stage that is limiting SLS performance is the upper stage, not the boosters. Going from one RL-10 to four RL-10s gives the biggest gains. More RL-10s may be get more performance, but the low thrust on the core is a big impediment to further gains. To get significantly more performance the thrust on the core and upper stage both need to be increased. New boosters aren't needed.

It will be interesting to see what the changes to EUS will be. I would like to see a common bulkhead and insulation to last the three day trip to the Moon. That would allow direct injection of a large payload mass into LLO or NRO.
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline A_M_Swallow

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Re: Navigating the twists and turns steering SLS Development
« Reply #30 on: 10/06/2018 05:26 am »
Were the LOP-G projects counting on EUS to get there?

Yes. ICPS cannot send Orion and a co-manifested payload though TLI.

The LOP-G's Power and Propulsion Element (PPE) could push say the habitat module from LEO to low lunar orbit or EML-1. A larger fuel tank would be needed. The people would have to go on a separate launch.

Offline saliva_sweet

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Re: Navigating the twists and turns steering SLS Development
« Reply #31 on: 10/06/2018 10:23 am »
https://spacenews.com/boeing-plans-changes-to-sls-upper-stages/

“We were rapidly approaching the critical design review.”
That's a big no-no. Quick, scratch everything. We can make it even better.

Offline woods170

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Re: Navigating the twists and turns steering SLS Development
« Reply #32 on: 10/06/2018 02:34 pm »
https://spacenews.com/boeing-plans-changes-to-sls-upper-stages/

“We were rapidly approaching the critical design review.”
That's a big no-no. Quick, scratch everything. We can make it even better less bad.

There, fixed that for ya.
« Last Edit: 10/06/2018 02:34 pm by woods170 »

Online edkyle99

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Re: Navigating the twists and turns steering SLS Development
« Reply #33 on: 10/06/2018 03:14 pm »
The current stage that is limiting SLS performance is the upper stage, not the boosters. Going from one RL-10 to four RL-10s gives the biggest gains. More RL-10s may be get more performance, but the low thrust on the core is a big impediment to further gains. To get significantly more performance the thrust on the core and upper stage both need to be increased. New boosters aren't needed.

It will be interesting to see what the changes to EUS will be. I would like to see a common bulkhead and insulation to last the three day trip to the Moon. That would allow direct injection of a large payload mass into LLO or NRO.
I can't get my head around the idea that more than 2 million pounds of high-specific-impulse thrust when the core really kicks into gear after SRB staging is "low thrust"! 

My guess on EUS is that NASA wants its design reconsidered for the lunar gateway mission. 

 - Ed Kyle

Offline LastWyzard

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Re: Navigating the twists and turns steering SLS Development
« Reply #34 on: 10/06/2018 03:20 pm »
Does this possibly put the J-2X back in the mix?  Or is it still too powerful? I don't remember seeing any simulations using that engine for the upper stage.

Offline Cremalera

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Re: Navigating the twists and turns steering SLS Development
« Reply #35 on: 10/06/2018 03:44 pm »
Khm..This news means that SLS(Block1 version) has no special advantages over FH? If we are talking about Europa Clipper mission?

Offline okan170

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Re: Navigating the twists and turns steering SLS Development
« Reply #36 on: 10/06/2018 07:38 pm »
Khm..This news means that SLS(Block1 version) has no special advantages over FH? If we are talking about Europa Clipper mission?

Clipper is on Block 1, has been for a bit.  No change there.

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Re: Navigating the twists and turns steering SLS Development
« Reply #37 on: 10/06/2018 07:59 pm »
The current stage that is limiting SLS performance is the upper stage, not the boosters. Going from one RL-10 to four RL-10s gives the biggest gains. More RL-10s may be get more performance, but the low thrust on the core is a big impediment to further gains. To get significantly more performance the thrust on the core and upper stage both need to be increased. New boosters aren't needed.

It will be interesting to see what the changes to EUS will be. I would like to see a common bulkhead and insulation to last the three day trip to the Moon. That would allow direct injection of a large payload mass into LLO or NRO.
Go back to that fifth engine from Ares V?
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Offline Cremalera

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Re: Navigating the twists and turns steering SLS Development
« Reply #38 on: 10/06/2018 08:23 pm »
Quote
Clipper is on Block 1, has been for a bit.  No change there.
Difference between payload of SLS Block1 and FH to LEO,just only 6200 kg(less than 10% of the total mass of payload).But FH can not launch  Clipper to “Jupiter Direct” trajectories.Because FH has no cryogenic upper stage?

Offline oldAtlas_Eguy

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Re: Navigating the twists and turns steering SLS Development
« Reply #39 on: 10/07/2018 02:05 am »
Quote
Clipper is on Block 1, has been for a bit.  No change there.
Difference between payload of SLS Block1 and FH to LEO,just only 6200 kg(less than 10% of the total mass of payload).But FH can not launch  Clipper to “Jupiter Direct” trajectories.Because FH has no cryogenic upper stage?
Correction:
FH uses a KeroLOX and the SLS uses a HydroLOX US. Both have cryogenic prop, but only the LOX on the FH. The complete vehicle has to be evaluated for the payload and the orbit to determine what are the differences in capabilities. The list in order of DV that can be provided for EC is SLS 1B, SLS 1, FH, DIVH, Atlas V(551). If you add Vulcan/ACES with distributed launch then it would be and possibly even better than SLS 1. But the availability date (if it is ever available) is a NET somewhere in the mid 2020s. Possible in the best case earlier than 2025.

My basic view about a new design for the EUS is to use the ACES direction instead of the ICPS look alike direction. For same length the stage would have more prop, have a lower dry weight, be able to be refueled in orbit, unlimited restarts, and weeks to months long coast periods between burns. ICPS look alike EUS is a Boeing design where the ACES look alike EUS is a ULA design and outside of Boeing's control. So I do not think that the design performance improvements will be significant if any.

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Re: Navigating the twists and turns steering SLS Development
« Reply #40 on: 10/07/2018 04:05 am »
I can't get my head around the idea that more than 2 million pounds of high-specific-impulse thrust when the core really kicks into gear after SRB staging is "low thrust"!

Yes, but at SRB staging, only about 40% of the propellant in the core stage propellant has been used, so the vehicle is still quite heavy at 978 t with Block IB. With a thrust of 9.28 MN, the acceleration at this point is only 9.5 m/s² or 0.97g, leading to large gravity losses. Trying at add a bigger upper stage only makes things worse. That's why at least one (preferably two) RS-25 engines need to be added, to reduce the gravity losses during this time to allow the use of a larger upper stage.
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Re: Navigating the twists and turns steering SLS Development
« Reply #41 on: 10/07/2018 03:21 pm »
Yes, but at SRB staging, only about 40% of the propellant in the core stage propellant has been used, so the vehicle is still quite heavy at 978 t with Block IB. With a thrust of 9.28 MN, the acceleration at this point is only 9.5 m/s² or 0.97g, leading to large gravity losses. Trying at add a bigger upper stage only makes things worse. That's why at least one (preferably two) RS-25 engines need to be added, to reduce the gravity losses during this time to allow the use of a larger upper stage.

And all this would have been known years ago, at the point NASA and Boeing were finalizing what the design would be given the constraints & demands of Congress.

Seems like none of this should be a surprise, yet...
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Re: Navigating the twists and turns steering SLS Development
« Reply #42 on: 10/07/2018 03:40 pm »
After booster separation is akin to a second stage flight. Such numbers aren't necessarily unusual. For instance, the thrust to weight ratio of the Delta upper stage with a 10 t payload is 2.75 m/s, nearly a quarter of a g. Does that mean we need to have like 5+ engines on a DCSS? Once you are above the vast majority of the atmosphere, you tend to be thrusting normal to the gravitational vector - i.e. it isn't necessarily being countered by a gravitational force. Roughly 1 G is 1 km/s in about a minute and a half. As long as you can stay above the atmosphere for a few minutes, you don't have to be fighting gravity necessarily in every stage of flight.

The F9 upper stage with a certain size payload is likewise likely around 1 G as well (at stage ignition).
« Last Edit: 10/07/2018 04:14 pm by ncb1397 »

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Re: Navigating the twists and turns steering SLS Development
« Reply #43 on: 10/07/2018 04:55 pm »
After booster separation is akin to a second stage flight. Such numbers aren't necessarily unusual. For instance, the thrust to weight ratio of the Delta upper stage with a 10 t payload is 2.75 m/s, nearly a quarter of a g. Does that mean we need to have like 5+ engines on a DCSS? Once you are above the vast majority of the atmosphere, you tend to be thrusting normal to the gravitational vector - i.e. it isn't necessarily being countered by a gravitational force. Roughly 1 G is 1 km/s in about a minute and a half. As long as you can stay above the atmosphere for a few minutes, you don't have to be fighting gravity necessarily in every stage of flight.

The F9 upper stage with a certain size payload is likewise likely around 1 G as well (at stage ignition).

That’s why where you stage makes a huge difference. DCSS and Centaur stages very high/fast, so their low thrust to weight ratio is far less important.

F9 staging and SLS booster separation is pretty low in comparison.

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Re: Navigating the twists and turns steering SLS Development
« Reply #44 on: 10/07/2018 05:11 pm »
I can't get my head around the idea that more than 2 million pounds of high-specific-impulse thrust when the core really kicks into gear after SRB staging is "low thrust"!

Yes, but at SRB staging, only about 40% of the propellant in the core stage propellant has been used, so the vehicle is still quite heavy at 978 t with Block IB. With a thrust of 9.28 MN, the acceleration at this point is only 9.5 m/s² or 0.97g, leading to large gravity losses. Trying at add a bigger upper stage only makes things worse. That's why at least one (preferably two) RS-25 engines need to be added, to reduce the gravity losses during this time to allow the use of a larger upper stage.
Similar to the T/W at SRB sep for STS.   Consider Saturn V at S-II start, when T/W was around 0.80 or less, going to the Moon on only 1.16 million pounds of thrust at that point.

 - Ed Kyle
« Last Edit: 10/07/2018 05:12 pm by edkyle99 »

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Re: Navigating the twists and turns steering SLS Development
« Reply #45 on: 10/07/2018 05:50 pm »
How long are they going to use T/W when it should be T/M in most cases?
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Re: Navigating the twists and turns steering SLS Development
« Reply #46 on: 10/07/2018 08:57 pm »
How long are they going to use T/W when it should be T/M in most cases?

What's wrong with T/W? It is more universal than T/M. You need > 1.0 T/W to lift off any planetary body. T/M numbers for the same varies, but I guess it depends on what you are trying to measure.
« Last Edit: 10/07/2018 08:58 pm by Lars-J »

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Re: Navigating the twists and turns steering SLS Development
« Reply #47 on: 10/08/2018 02:45 am »
I can't get my head around the idea that more than 2 million pounds of high-specific-impulse thrust when the core really kicks into gear after SRB staging is "low thrust"!

Yes, but at SRB staging, only about 40% of the propellant in the core stage propellant has been used, so the vehicle is still quite heavy at 978 t with Block IB. With a thrust of 9.28 MN, the acceleration at this point is only 9.5 m/s² or 0.97g, leading to large gravity losses. Trying at add a bigger upper stage only makes things worse. That's why at least one (preferably two) RS-25 engines need to be added, to reduce the gravity losses during this time to allow the use of a larger upper stage.
Assuming there will never be funds enough for a corestage redesign (likely) how could using the corestage as it is optimize the gravity losses, Steven? Can future RS-25s create more thrust, even if the penalty is more propellant usage? Would switching to the lightweight aluminum/lithium alloys as Shuttle E.T.s used to do help?
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Offline Coastal Ron

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Re: Navigating the twists and turns steering SLS Development
« Reply #48 on: 10/08/2018 03:01 am »
Can future RS-25s create more thrust, even if the penalty is more propellant usage?

It's a pretty mature engine, I would think that is unlikely. And in any case doing so would involve more $$$ and time.

Quote
Would switching to the lightweight aluminum/lithium alloys as Shuttle E.T.s used to do help?

I would imagine they are already using the best aluminum alloy for the SLS. Remember they did not have a firm budget number to hit, so I'm sure Boeing would have recommended the lightest version that they could use.

Plus, changing aluminum alloys would require re-qualifying their welding processes, and likely require the need to retest everything pressure-wise. Which would also require more $$$ and time.

To co-opt a Donald Rumsfeld phrase:

"NASA will have to go to space with the rocket they have, not the rocket they might want or wish to have at a later time.".  :D
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Re: Navigating the twists and turns steering SLS Development
« Reply #49 on: 10/08/2018 03:09 am »
I'm fairly certain they are losing a heavier alloy to avoid the cost of the material used on the 'super lightweight' E.Ts. I'd have to do research or check my library of downloaded documents.
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Offline speedevil

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Re: Navigating the twists and turns steering SLS Development
« Reply #50 on: 10/08/2018 09:41 am »
Assuming there will never be funds enough for a corestage redesign (likely) how could using the corestage as it is optimize the gravity losses, Steven? Can future RS-25s create more thrust, even if the penalty is more propellant usage? Would switching to the lightweight aluminum/lithium alloys as Shuttle E.T.s used to do help?
In principle, liquid boosters would somewhat help, by increasing velocity at shutdown, and decreasing the mass of fuel remaining.
This is, of course, unlikely to be cheap or fast - even if it nominally avoids mods to the actual core.

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Re: Navigating the twists and turns steering SLS Development
« Reply #51 on: 10/08/2018 10:35 am »
I'm pretty certain it's always going to be solid boosters for SLS. The 'Dark Knights' boosters will be fairly formidable and should be cheaper than liquids, albeit inferior in capability. Also, liquid boosters would have to be designed to match the spacings of the LOX and LH2 tanks for mounting to the Corestage.
« Last Edit: 10/08/2018 10:42 am by MATTBLAK »
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Offline Steven Pietrobon

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Re: Navigating the twists and turns steering SLS Development
« Reply #52 on: 10/08/2018 11:27 am »
Assuming there will never be funds enough for a corestage redesign (likely) how could using the corestage as it is optimize the gravity losses, Steven? Can future RS-25s create more thrust, even if the penalty is more propellant usage?

The RS-25E has been designed for 111%. Higher thrust would be of benefit. Increasing thrust to 139% would be equivalent to adding another engine, but would probably require significant design changes.

Quote
Would switching to the lightweight aluminum/lithium alloys as Shuttle E.T.s used to do help?

Yes, but to get the full benefit you would need a larger upper stage and the higher thrust that goes with it.
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Offline Steven Pietrobon

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Re: Navigating the twists and turns steering SLS Development
« Reply #53 on: 10/08/2018 11:35 am »
Similar to the T/W at SRB sep for STS.   Consider Saturn V at S-II start, when T/W was around 0.80 or less, going to the Moon on only 1.16 million pounds of thrust at that point.

Yes, that's true. Those are still pretty low acceleration values at that point in time, which is why the higher thrust J-2S could give significant performance gains, if it had ever been used on the Saturn V. For the Space Shuttle, it had to reduce acceleration during the boost phase to avoid aerodynamic stress on the Shuttle. I tried the same thing in my first simulations of SLS and it made it perform very poorly. It was better to go for maximum thrust during boost to help empty those tanks, so that the initial acceleration was not too low after booster separation.

Also, with the Shuttle, although initial acceleration after boost was low, it built up to 3g and then stayed there, which helped compensate for the low initial acceleration. That's not the case with SLS Block IB, where the upper stage acceleration is very low for a significant length of time. By the way, I got a payload of 97.1 t into a 200 km circular orbit, close to Boeing's number of 93.1 t into a 241 km orbit.
« Last Edit: 10/08/2018 11:45 am by Steven Pietrobon »
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Re: Navigating the twists and turns steering SLS Development
« Reply #54 on: 10/08/2018 12:15 pm »
Assuming there will never be funds enough for a corestage redesign (likely) how could using the corestage as it is optimize the gravity losses, Steven? Can future RS-25s create more thrust, even if the penalty is more propellant usage?

The RS-25E has been designed for 111%. Higher thrust would be of benefit. Increasing thrust to 139% would be equivalent to adding another engine, but would probably require significant design changes.

Quote
Would switching to the lightweight aluminum/lithium alloys as Shuttle E.T.s used to do help?

Yes, but to get the full benefit you would need a larger upper stage and the higher thrust that goes with it.
I've read in Shuttle history books that thrust levels for the RS-25 were plausible up to 114 or even 115% percent. Seeing that the engines are going to be expended anyhow; would you see that as plausible without major redesign? My reading tells me that 115% is the absolute limit without redesign and re-certification. Looking back at the Shuttle E.T. super lightweight tank history tells me that 7,500 pounds of mass were shaved from the E.Ts with the use of aluminum-lithium. With the SLS corestage being larger, I can imagine this figure might be in the 10,000 pound region. A good enough mass saving to bother with the cost of slight redesign to use it?
« Last Edit: 10/08/2018 12:16 pm by MATTBLAK »
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Re: Navigating the twists and turns steering SLS Development
« Reply #55 on: 10/08/2018 04:40 pm »
It is all a moot point concerning a Boeing designed EUS.
NASA may also be talking with other companies as a second source for the SLS EUS.

« Last Edit: 10/08/2018 08:13 pm by Chris Bergin »

Offline Chris Bergin

Fight club rules over contract situations guys.  All it causes is for other sites to run with things they see here, mess it up, make both companies angry and other site says "Sorry, saw it on NSF" and we get tagged with the crap report on another site.

Trimmed.
« Last Edit: 10/08/2018 08:15 pm by Chris Bergin »

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Re: Navigating the twists and turns steering SLS Development
« Reply #57 on: 10/08/2018 11:19 pm »
They did spend some time/money on the J-2X...
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Re: Navigating the twists and turns steering SLS Development
« Reply #58 on: 10/08/2018 11:52 pm »
Yes, with a bit more specific impulse, it would have made a very good upper stage engine.
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Re: Navigating the twists and turns steering SLS Development
« Reply #59 on: 10/09/2018 04:12 am »
Dr Steven: if NASA had kept the 10 meter diameter core stage from Ares; how many RS-25s would we be talking about for SLS, 6x or 7x engines? And if so, would a 2x J-2X upper stage be best or a bigger cluster of RL-10s than the current EUS concept?

EDIT: And seeing how we are going to be stuck with the 8.4 meter, 4x RS-25E corestage; in the spirit of NOT 'Rocket Legos' how can we see SLS being optimized to get the best performance to L.E.O. and BLEO, with the available engine, vehicle height and propellant load options?
« Last Edit: 10/09/2018 05:33 am by MATTBLAK »
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Offline Steven Pietrobon

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Re: Navigating the twists and turns steering SLS Development
« Reply #60 on: 10/09/2018 07:31 am »
Dr Steven: if NASA had kept the 10 meter diameter core stage from Ares; how many RS-25s would we be talking about for SLS, 6x or 7x engines?


I estimate a minimum of 4*(10/8.4)² = 5.67 or six engines would be needed. Make it seven and you could make the stage reusable. :-)

Quote
And if so, would a 2x J-2X upper stage be best or a bigger cluster of RL-10s than the current EUS concept?

6xRL-10 could be used, but 2x J-2X will give a much higher payload.

Quote
EDIT: And seeing how we are going to be stuck with the 8.4 meter, 4x RS-25E corestage; in the spirit of NOT 'Rocket Legos' how can we see SLS being optimized to get the best performance to L.E.O. and BLEO, with the available engine, vehicle height and propellant load options?

SLS Block IB is a pretty good configuration. It has the lowest development cost, provided that new boosters are not developed. Lunar missions can be performed with two launches.
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Re: Navigating the twists and turns steering SLS Development
« Reply #61 on: 10/09/2018 07:58 am »
Block 1B? Yes, I suppose so. They'd have to keep the Lunar Lander under 40 metric tons though and have the EUS able to decelerate the Lander or Orion into LLO.
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Offline Proponent

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Re: Navigating the twists and turns steering SLS Development
« Reply #62 on: 10/09/2018 02:30 pm »
Block 1B? Yes, I suppose so. They'd have to keep the Lunar Lander under 40 metric tons though and have the EUS able to decelerate the Lander or Orion into LLO.

And Orion would need redesign, because it can't handle the thermal load in LLO.

EDIT:  woods170, below, presents a paper indicating that Orion can handle the thermal load in LLO.
« Last Edit: 10/10/2018 02:32 pm by Proponent »

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Re: Navigating the twists and turns steering SLS Development
« Reply #63 on: 10/09/2018 08:14 pm »
Orion for Lagrange Point 1, then! I wonder how it was going to cope during Constellation?!
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Re: Navigating the twists and turns steering SLS Development
« Reply #64 on: 10/09/2018 09:53 pm »
I still don't understand why NASA went with a four-engine core stage, when all previous studies (going at least back to ESAS) used a five-engine core stage for a stretched inline SDLV using an 8.4m core stage. Surely it wasn't on the basis of getting four launches using the (mostly) on-hand engines, instead of just three. Surely not.

Was there ever a public justification for the current design? Is there a reasonable non-public explanation behind the public one? I really don't see an economic justification, based on the extremely low projected flight rate (once a year). While the cost of a single RS-25 is not chicken feed, it is small compared to the total cost of a launch (should one ever happen :().

I understand the engine section on a five or six engine core would be more complex than what they are doing now. However.... some unmentionable company manages to cram nine engines under their first stage, and they seem to be doing okay. :)

The four-engine SLS core just seems... un-optimized. It doesn't seem to get significantly more payload to orbit than the much-smaller Shuttle stack (about 100 tonnes). And that's with 5-segment boosters and running the engines at a higher thrust than Shuttle used. So what gives?

I know this has  been hashed and re-hashed since SLS was announced. Maybe I'm just being dense. For whatever reason, it's just not sinking in. Mods, feel free to delete if too far OT.

Thanks.

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Re: Navigating the twists and turns steering SLS Development
« Reply #65 on: 10/09/2018 10:03 pm »
Yeah: using 4× engines per launch instead of 5 would save - what? 40 or 50 million dollars per launch for a billion-plus cost anyway? And would designing for 5 versus 4 engines have increased the development costs any significant amount? Colour me skeptical.
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Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #66 on: 10/09/2018 10:19 pm »
The four-engine SLS core just seems... un-optimized. It doesn't seem to get significantly more payload to orbit than the much-smaller Shuttle stack (about 100 tonnes). And that's with 5-segment boosters and running the engines at a higher thrust than Shuttle used. So what gives?

What gives is that the core stage is much heavier than the elements that it replaces: the ET+orbiter engine section.

SLS without an upper stage will place over 180 tonnes in LEO, compared to STS at about 140 tonnes counting the orbiter, payload, and ET. SLS is considerably more powerful than STS, it's just less efficient if you count the orbiter as useful payload.

Offline Proponent

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Re: Navigating the twists and turns steering SLS Development
« Reply #67 on: 10/10/2018 01:45 am »
Orion for Lagrange Point 1, then! I wonder how it was going to cope during Constellation?!

I presume the design has changed since Constellation.

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Re: Navigating the twists and turns steering SLS Development
« Reply #68 on: 10/10/2018 02:05 am »
Not for the better, it seems. Honestly; if the Orion can't orbit the Moon in LLO or even have enough delta-v to both burn into and out of lunar orbit; then what the heck is it for?! All the hype about it being a 'deep space spaceship' is then just that - hype :(

EDIT: It's nearly 50 years on and they will be having a spacecraft that in may ways is less capable than the Apollo CSM?! How is it I'm only now really starting to put all this together? I used to say that when it came to Project Constellation and the Ares launchers etc, Mike Griffin was 'The Emporer With No Clothes'. But he was/is a smart man - and so are many of us. Where did we go wrong? How could we/I have been in such denial? Can the Orion be upgraded into usefulness without taking endless more years and billions with a 'B'? It's thermal rejection systems need upgrading/fixing for close proximity lunar operations. And it needs far more than the relatively paltry 9 tons of propellants it has to move around fully in Cislunar space. And it probably needs more endurance than three weeks if it will go on to support relatively long crewed missions to the lunar surface.

How much will it then mass? Up from 26 metric tons to more than 35?! (Apollo 17 CSM was more than 30 metric tons)
We've been asking these and similar questions on this website and forum since when it was founded. How much longer will we have to do this? So many questions... >:( :'(
« Last Edit: 10/10/2018 05:50 am by MATTBLAK »
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Offline Coastal Ron

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Re: Navigating the twists and turns steering SLS Development
« Reply #69 on: 10/10/2018 05:37 am »
I still don't understand why NASA went with a four-engine core stage, when all previous studies (going at least back to ESAS) used a five-engine core stage for a stretched inline SDLV using an 8.4m core stage. Surely it wasn't on the basis of getting four launches using the (mostly) on-hand engines, instead of just three. Surely not.

Was there ever a public justification for the current design?

I'm not an SLS design expert, but here are some points to remember:

- Congress mandated that the SLS be built, and even specified it's capabilities. Without NASA participation.

- NASA did not have a design for the SLS that Congress used, so once Congress told NASA to build the SLS NASA and Boeing had to reverse engineer the SLS to fit what Congress wanted.

- There were no defined payloads or missions for the SLS when it was mandated to be built, so NASA and Boeing did have to make many guesses about initial flight rates, initial capabilities, and even what NASA launch assets would be available to support SLS launches.

- There was also no defined budget for the SLS, but NASA (and Boeing) have assumed that the budget they would get would be essentially flat from year to year, which is not a good way to build something new.

- Virtually nothing on the SLS is being used "as is" from prior programs, and conversely the SLS is not a "clean-sheet" design, so there are lots of compromises - and I'm not implying safety is affected, just that engineers had less options to design with.

Bottom line is that there were many variables NASA and Boeing had to consider, and over time not only of them were the right guesses - which is not unusual. But that is why there are mismatches between what they are building and what they can do.

My $0.02
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Re: Navigating the twists and turns steering SLS Development
« Reply #70 on: 10/10/2018 06:04 am »
Whether SLS gets something like the existing EUS that is capable of sending 39 tons beyond Earth orbit or a new, far more capable design stage that can send up to 50 metric tons BLEO... Without a new stage, SLS would no longer be able to send a co-manifested payload of about 10 tons BLEO along with the heavier, more capable Orion. But if the Orion grew in (useful propellant) mass to more than 35 metric tons, then the old stage would be good enough because the Orion would now be able to brake itself into and out of low lunar orbit.

A two launch lunar mission architecture could use the existing EUS to send a 40 ton Lunar Lander to the Moon. It should have enough delta-v to brake itself into LLO and await the crewed Orion that would follow it in another launch window (2 or 3 months later?). The Lander should have enough propellant to land most anywhere on the Moon and then return to the Orion to send the crew homewards. Not enough room to get into different architecture options here - but I'm assuming that the Lander would be reusable. After it delivers the crew back to the Orion, it could wait in LLO for a Tanker to send propellants to it during another launch window. It would be cheaper if the propellant delivery was a commercial contract. New Glenn? Falcon Heavy? It would be too expensive to send the fuel by yet another SLS. So many questions - so many ways to approach this mission/s...
« Last Edit: 10/10/2018 07:41 am by MATTBLAK »
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Offline Rocket Science

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Re: Navigating the twists and turns steering SLS Development
« Reply #71 on: 10/10/2018 06:50 am »
If one takes off the "engineering googles" and puts on the "committee goggles" all can be seen with clarity... What should have been a "clean sheet design" with all the time/effort/money invested we have a "compromise design" that keep chasing it's tail... All due to the constraints placed upon it and "mission creep"...
I can not help remembering the aspersions towards the DIRECT team's proposal and their design as "defying the laws of physics", now with what are they trying to do now and the position they find themselves in...
« Last Edit: 10/10/2018 07:23 am by Rocket Science »
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Offline woods170

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Re: Navigating the twists and turns steering SLS Development
« Reply #72 on: 10/10/2018 07:22 am »
Block 1B? Yes, I suppose so. They'd have to keep the Lunar Lander under 40 metric tons though and have the EUS able to decelerate the Lander or Orion into LLO.

And Orion would need redesign, because it can't handle the thermal load in LLO.

Interesting. How did the Apollo CSM handle this? Because it flew in LLO as well, for days at end.

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Re: Navigating the twists and turns steering SLS Development
« Reply #73 on: 10/10/2018 07:38 am »
The Apollo SM had pretty big radiators.
« Last Edit: 10/10/2018 07:50 am by MATTBLAK »
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Re: Navigating the twists and turns steering SLS Development
« Reply #74 on: 10/10/2018 08:17 am »
Block 1B? Yes, I suppose so. They'd have to keep the Lunar Lander under 40 metric tons though and have the EUS able to decelerate the Lander or Orion into LLO.

And Orion would need redesign, because it can't handle the thermal load in LLO.

Interesting. How did the Apollo CSM handle this? Because it flew in LLO as well, for days at end.

Quote
Temperature control is provided by heat  rejection  from radiators  and a water evaporator.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720012252.pdf

So, essentially sweating whenever the radiators don't reject enough heat.

The Apollo SM had pretty big radiators.

As does Orion. See picture.



« Last Edit: 10/10/2018 08:17 am by ncb1397 »

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Re: Navigating the twists and turns steering SLS Development
« Reply #75 on: 10/10/2018 09:10 am »
Seems to - though the amount of acreage on the Orion SM may be (?) insufficient for the job, it seems. The Apollo SM was pretty big.
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Re: Navigating the twists and turns steering SLS Development
« Reply #76 on: 10/10/2018 11:49 am »
Seems to - though the amount of acreage on the Orion SM may be (?) insufficient for the job, it seems. The Apollo SM was pretty big.

The Whitley paper seems to be incorrect. See the attached document.
It specifies the Orion Thermal Control System.

Low Lunar Orbit environment is in the requirements for the TCS operational range.

Meaning: Orion, as currently designed (and being built) is very much capable of handling the thermal environment of Low Lunar Orbit.
« Last Edit: 10/10/2018 12:31 pm by woods170 »

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Re: Navigating the twists and turns steering SLS Development
« Reply #77 on: 10/10/2018 02:28 pm »
The four-engine SLS core just seems... un-optimized. It doesn't seem to get significantly more payload to orbit than the much-smaller Shuttle stack (about 100 tonnes). And that's with 5-segment boosters and running the engines at a higher thrust than Shuttle used. So what gives?
My guess is this.  The reason designers specified four RS-25D engines is because that was enough.  A fifth engine would not have added much capability.  They are nearly at T/W of 1 at SRB sep with four engines, which is good enough.  It isn't the thrust, it is the specific impulse that really matters.  Core isn't a booster, it is a sustainer.  Think balloon tank Atlas.  Atlas IIA sustainer only made 12.5% of the total liftoff thrust, but produced just enough thrust after BECO to put its higher ISP to work.

Also, you can't directly compare a Shuttle Orbiter with an SLS payload.  Orbiter carried a lot of mass that doesn't count as payload on SLS.  Those engines, for example, and their feedlines, and their thrust structure, etc.  Shuttle's "real" payload capability was 24-something tonnes LEO (its heaviest actual payload was IUS/Chandra at 22.753 tonnes), plus whatever mass you might want to add for crew support and reentry.

 - Ed Kyle
« Last Edit: 10/10/2018 02:58 pm by edkyle99 »

Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #78 on: 10/10/2018 03:16 pm »
The four-engine SLS core just seems... un-optimized. It doesn't seem to get significantly more payload to orbit than the much-smaller Shuttle stack (about 100 tonnes). And that's with 5-segment boosters and running the engines at a higher thrust than Shuttle used. So what gives?
My guess is this.  The reason designers specified four RS-25D engines is because that was enough.  A fifth engine would not have added much capability.  They are nearly at T/W of 1 at SRB sep with four engines, which is good enough.  It isn't the thrust, it is the specific impulse that really matters.  Core isn't a booster, it is a sustainer.  Think balloon tank Atlas.  Atlas IIA sustainer only made 12.5% of the total liftoff thrust, but produced just enough thrust after BECO to put its higher ISP to work.

Also, you can't directly compare a Shuttle Orbiter with an SLS payload.  Orbiter carried a lot of mass that doesn't count as payload on SLS.  Those engines, for example, and their feedlines, and their thrust structure, etc.  Shuttle's "real" payload capability was 24-something tonnes LEO (its heaviest actual payload was IUS/Chandra at 22.753 tonnes), plus whatever mass you might want to add for crew support and reentry.

 - Ed Kyle

"good enough" doesn't mean that it can't be further optimized, if there's a need. Compared to other systems with full boost stages, Shuttle and SLS drop the solids while still travelling really slow, around 1.3 km/s. That's far slower than Saturn V, which dropped the S-IC at around 2.4 km/s. It's even much slower than Falcon 9 on a RTLS mission, which is around 1.7 km/s.

More thrust at staging would absolute improve the performance of the SLS core, even if that thrust comes from low TWR RS-25. Better boosters also improve performance, even without more core stage thrust, because they move the core faster at staging. In the extreme case, a pair of New Glenn boosters would nearly double the velocity at staging, and also nearly double the payload to LEO with no upper stage.

The real question is whether it has a mission that needs more performance.

Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #79 on: 10/10/2018 04:15 pm »
Well, I think the OIG report explains why EUS development is paused.

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Re: Navigating the twists and turns steering SLS Development
« Reply #80 on: 10/10/2018 08:03 pm »
Well, I think the OIG report explains why EUS development is paused.

A perfect consequence for Boeing's poor performance could be reassignment of the EUS to another company (like BO).
I cheer for both NASA and commercial space. For SLS, Orion, Falcon 9, Falcon Heavy, Dragon, Starliner, Cygnus and all the rest!
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Re: Navigating the twists and turns steering SLS Development
« Reply #81 on: 10/11/2018 12:56 am »

"good enough" doesn't mean that it can't be further optimized, if there's a need. Compared to other systems with full boost stages, Shuttle and SLS drop the solids while still travelling really slow, around 1.3 km/s. That's far slower than Saturn V, which dropped the S-IC at around 2.4 km/s. It's even much slower than Falcon 9 on a RTLS mission, which is around 1.7 km/s.


Do you have a source for this 1.3 km/s number? Because I get an acceleration of ~22 m/s2 at around lift off assuming full thrust and 30 tons of payload/fairing. Taking out gravity, that is 12.2 m/s2. Over 124 seconds, 12.2 m/s2 is more like 1.5 km/s. This isn't even counting that the stage is getting lighter over time, higher vacuum thrust, etc. Granted, doesn't take out aerodynamic drag, but that tends to be pretty small for rockets this size. I don't know, just a simple gut check puts it into question.
« Last Edit: 10/11/2018 12:57 am by ncb1397 »

Offline Oli

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Re: Navigating the twists and turns steering SLS Development
« Reply #82 on: 10/11/2018 01:16 am »
Also, with the Shuttle, although initial acceleration after boost was low, it built up to 3g and then stayed there, which helped compensate for the low initial acceleration. That's not the case with SLS Block IB, where the upper stage acceleration is very low for a significant length of time. By the way, I got a payload of 97.1 t into a 200 km circular orbit, close to Boeing's number of 93.1 t into a 241 km orbit.

I don't think NASA cares much about LEO performance, with a BEO payload upper stage acceleration should be higher. EUS doesn't seem to be optimized for LEO.

Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #83 on: 10/11/2018 02:24 am »

"good enough" doesn't mean that it can't be further optimized, if there's a need. Compared to other systems with full boost stages, Shuttle and SLS drop the solids while still travelling really slow, around 1.3 km/s. That's far slower than Saturn V, which dropped the S-IC at around 2.4 km/s. It's even much slower than Falcon 9 on a RTLS mission, which is around 1.7 km/s.


Do you have a source for this 1.3 km/s number? Because I get an acceleration of ~22 m/s2 at around lift off assuming full thrust and 30 tons of payload/fairing. Taking out gravity, that is 12.2 m/s2. Over 124 seconds, 12.2 m/s2 is more like 1.5 km/s. This isn't even counting that the stage is getting lighter over time, higher vacuum thrust, etc. Granted, doesn't take out aerodynamic drag, but that tends to be pretty small for rockets this size. I don't know, just a simple gut check puts it into question.

Flight data in the linked PDF. At 120 seconds velocity is 1279 m/s and the SRBs have already separated, as evident from the sudden drop in acceleration.

https://www.nasa.gov/pdf/466711main_AP_ST_ShuttleAscent.pdf

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Re: Navigating the twists and turns steering SLS Development
« Reply #84 on: 10/11/2018 03:19 am »

"good enough" doesn't mean that it can't be further optimized, if there's a need. Compared to other systems with full boost stages, Shuttle and SLS drop the solids while still travelling really slow, around 1.3 km/s. That's far slower than Saturn V, which dropped the S-IC at around 2.4 km/s. It's even much slower than Falcon 9 on a RTLS mission, which is around 1.7 km/s.


Do you have a source for this 1.3 km/s number? Because I get an acceleration of ~22 m/s2 at around lift off assuming full thrust and 30 tons of payload/fairing. Taking out gravity, that is 12.2 m/s2. Over 124 seconds, 12.2 m/s2 is more like 1.5 km/s. This isn't even counting that the stage is getting lighter over time, higher vacuum thrust, etc. Granted, doesn't take out aerodynamic drag, but that tends to be pretty small for rockets this size. I don't know, just a simple gut check puts it into question.

Flight data in the linked PDF. At 120 seconds velocity is 1279 m/s and the SRBs have already separated, as evident from the sudden drop in acceleration.

https://www.nasa.gov/pdf/466711main_AP_ST_ShuttleAscent.pdf

You would want to revise shuttle numbers up because of 34-35% greater thrust on SLS vs around 25% more liftoff mass.

edit:
The gut check above was inaccurate after looking at my numbers. Liftoff net acceleration should be more like 6 m/s2. Still, using publically available information, I get ~1.6 km/s at booster separation.
« Last Edit: 10/11/2018 03:32 am by ncb1397 »

Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #85 on: 10/11/2018 03:34 am »

"good enough" doesn't mean that it can't be further optimized, if there's a need. Compared to other systems with full boost stages, Shuttle and SLS drop the solids while still travelling really slow, around 1.3 km/s. That's far slower than Saturn V, which dropped the S-IC at around 2.4 km/s. It's even much slower than Falcon 9 on a RTLS mission, which is around 1.7 km/s.


Do you have a source for this 1.3 km/s number? Because I get an acceleration of ~22 m/s2 at around lift off assuming full thrust and 30 tons of payload/fairing. Taking out gravity, that is 12.2 m/s2. Over 124 seconds, 12.2 m/s2 is more like 1.5 km/s. This isn't even counting that the stage is getting lighter over time, higher vacuum thrust, etc. Granted, doesn't take out aerodynamic drag, but that tends to be pretty small for rockets this size. I don't know, just a simple gut check puts it into question.

Flight data in the linked PDF. At 120 seconds velocity is 1279 m/s and the SRBs have already separated, as evident from the sudden drop in acceleration.

https://www.nasa.gov/pdf/466711main_AP_ST_ShuttleAscent.pdf

You would want to revise shuttle numbers up because of 34-35% greater thrust on SLS vs around 25% more liftoff mass.

How does that work? The boosters only have 25% more propellant, so they can only provide 25% more impulse (unless the average exhaust velocity increased, which I don't think it did). There's no way they can sustain 35% more thrust over the duration of the burn.

The uprated RS-25 only adds 1% to the total thrust during boost, since the core only contributes about 20% of the total thrust in that phase.

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Re: Navigating the twists and turns steering SLS Development
« Reply #86 on: 10/11/2018 03:53 am »
Seems to - though the amount of acreage on the Orion SM may be (?) insufficient for the job, it seems. The Apollo SM was pretty big.

The Whitley paper seems to be incorrect. See the attached document.
It specifies the Orion Thermal Control System.

Low Lunar Orbit environment is in the requirements for the TCS operational range.

Meaning: Orion, as currently designed (and being built) is very much capable of handling the thermal environment of Low Lunar Orbit.
If I'm wrong, then I'm very happy to be wrong about this. Someone at LockMart needs to neutralize the concerns once and for all by briefly saying so, then providing a technical summary to nail that down.
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Re: Navigating the twists and turns steering SLS Development
« Reply #87 on: 10/11/2018 05:14 am »

"good enough" doesn't mean that it can't be further optimized, if there's a need. Compared to other systems with full boost stages, Shuttle and SLS drop the solids while still travelling really slow, around 1.3 km/s. That's far slower than Saturn V, which dropped the S-IC at around 2.4 km/s. It's even much slower than Falcon 9 on a RTLS mission, which is around 1.7 km/s.


Do you have a source for this 1.3 km/s number? Because I get an acceleration of ~22 m/s2 at around lift off assuming full thrust and 30 tons of payload/fairing. Taking out gravity, that is 12.2 m/s2. Over 124 seconds, 12.2 m/s2 is more like 1.5 km/s. This isn't even counting that the stage is getting lighter over time, higher vacuum thrust, etc. Granted, doesn't take out aerodynamic drag, but that tends to be pretty small for rockets this size. I don't know, just a simple gut check puts it into question.

Flight data in the linked PDF. At 120 seconds velocity is 1279 m/s and the SRBs have already separated, as evident from the sudden drop in acceleration.

https://www.nasa.gov/pdf/466711main_AP_ST_ShuttleAscent.pdf

You would want to revise shuttle numbers up because of 34-35% greater thrust on SLS vs around 25% more liftoff mass.

How does that work? The boosters only have 25% more propellant, so they can only provide 25% more impulse (unless the average exhaust velocity increased, which I don't think it did). There's no way they can sustain 35% more thrust over the duration of the burn.

The uprated RS-25 only adds 1% to the total thrust during boost, since the core only contributes about 20% of the total thrust in that phase.

Improving my model with variable booster and RS-25 thrust reduces most of the discrepancy. The 35% thrust number was comparing apples and oranges. One was maximum thrust and the other was take off thrust. I am getting about 1200 m/s now. Interestingly, using the same model, 4 boosters yields 1.6 km/s at booster seperation.

Offline Steven Pietrobon

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Re: Navigating the twists and turns steering SLS Development
« Reply #88 on: 10/11/2018 06:16 am »
My guess is this.  The reason designers specified four RS-25D engines is because that was enough.  A fifth engine would not have added much capability.  They are nearly at T/W of 1 at SRB sep with four engines, which is good enough.  It isn't the thrust, it is the specific impulse that really matters.  Core isn't a booster, it is a sustainer.  Think balloon tank Atlas.  Atlas IIA sustainer only made 12.5% of the total liftoff thrust, but produced just enough thrust after BECO to put its higher ISP to work.

In this case "good enough" will only get you 97 t to LEO with EUS. Replacing the boosters with Dark Knights gets you to 113 t (the current Block II version) and then replacing the upper stage with J-2X engines will get you to 125 t. If NASA wanted to get to the Congressionally mandated value of 130 t, you need a fifth engine on the core plus a J-2X. In this case RSRMV boosters gives you 130 t, while Dark Knights will get you 144 t.

Do you have a source for this 1.3 km/s number? Because I get an acceleration of ~22 m/s2 at around lift off assuming full thrust and 30 tons of payload/fairing. Taking out gravity, that is 12.2 m/s2. Over 124 seconds, 12.2 m/s2 is more like 1.5 km/s.

For Block IB, I get an inertial velocity of 1.6 km/s at booster burnout. Earth relative is 1.24 km/s. For the Saturn V, at first stage cutoff inertial was 2.7 km/s and relative is 2.3 km/s.
« Last Edit: 10/11/2018 06:18 am by Steven Pietrobon »
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Re: Navigating the twists and turns steering SLS Development
« Reply #89 on: 10/12/2018 04:44 pm »
My guess is this.  The reason designers specified four RS-25D engines is because that was enough.  A fifth engine would not have added much capability.  They are nearly at T/W of 1 at SRB sep with four engines, which is good enough.  It isn't the thrust, it is the specific impulse that really matters.  Core isn't a booster, it is a sustainer.  Think balloon tank Atlas.  Atlas IIA sustainer only made 12.5% of the total liftoff thrust, but produced just enough thrust after BECO to put its higher ISP to work.

In this case "good enough" will only get you 97 t to LEO with EUS. Replacing the boosters with Dark Knights gets you to 113 t (the current Block II version) and then replacing the upper stage with J-2X engines will get you to 125 t. If NASA wanted to get to the Congressionally mandated value of 130 t, you need a fifth engine on the core plus a J-2X. In this case RSRMV boosters gives you 130 t, while Dark Knights will get you 144 t.

.....


Thanks Steven, good summary. Based on that, I would argue that SLS is currently not "good enough" with four engines on the core, since it will never be able to meet the legislated requirements. Not to mention that it is simply leaving a lot of performance on the table. To make the obligatory automotive analogy, it's like putting an undersized two-barrel carburetor on your supercharged V8 engine. Sure, it'll get you to the grocery store, but it won't give you the performance that you paid for.

Mr. Kyle also mentioned that the core is not a booster, it is a sustainer stage. I would argue that the sustainer aspect is leftover from STS, where the ET had to go almost all the way to orbital insertion, since the engines were on the Orbiter. The SLS core doesn't have to be a sustainer, it can stage at any point that makes sense. With more engines on the core, and a larger and heavier upper stage, the core would stage lower. But it would still be performing its role, and it would allow SLS to actually meet its legislated performance goals.

I get the feeling that at some future congressional inquiry into why SLS is short of putting 130 tons in orbit, someone from NASA or Boeing will slap their forehead and say "What? You say you wanted all the performance you wrote into the law? If only there had been any way we could have known that, we would have put five engines on the core! Whelp, back to the drawing board. By the way, we'll need more money and ten more years for that. Kthxbye."

Back to reality, did you happen to run your analysis on a five-engine SLS core with EUS? I recall that you ran several variations a while back with more engines on the core, and different upper stages, but I don't recall if that included the current EUS design. I believe you were aiming for a single-launch lunar capability, so I wouldn't be surprised if you haven't. Either way, thanks for your informative posts. Always a good read.
« Last Edit: 10/12/2018 04:49 pm by Mark S »

Offline Khadgars

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Re: Navigating the twists and turns steering SLS Development
« Reply #90 on: 10/12/2018 04:55 pm »
SLS performance is not optimized for LEO, but for BLEO.  I find it rich that the congressional "mandate" that everyone hates is now used against SLS.

Offline UltraViolet9

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Re: Navigating the twists and turns steering SLS Development
« Reply #91 on: 10/12/2018 06:24 pm »
I find it rich that the congressional "mandate" that everyone hates is now used against SLS.

It does beg a few questions:

Why is the program allowed to ignore its Level 0 requirements?  An inability to meet Level 0/1 requirements is normally cause for a termination review.  Is one planned?  Will there be one?

How can the program be allowed to ignore its Level 0 requirements?  Is there a waver?  Will there be one?  Under whose review?

Congressional staff, including one that used to post in this forum, argued that they consulted NASA and industry on how SLS was defined in the authorization act that created the program.  If NASA doesn't care about that definition, what was the actual quantity and quality of consultation between congressional staff, NASA, and industry?  Are there records that could be made public to see exactly what was promised and what was not?

If there's nothing magical about 130t, then why can't NASA use less capable but also less expensive and existing launchers instead of spending so much taxpayer money, program time, and human resources on SLS?  It's not like NASA HSF is lacking for things to do to get to the Moon, Mars, or any other deep space target.  Couldn't the budget, time, and careers spent on SLS be better spent elsewhere?

« Last Edit: 10/12/2018 09:26 pm by UltraViolet9 »

Offline Coastal Ron

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Re: Navigating the twists and turns steering SLS Development
« Reply #92 on: 10/12/2018 08:31 pm »
SLS performance is not optimized for LEO, but for BLEO.

Doesn't matter what anyone thinks, Congress specifically called out capabilities to LEO:

Quote
(2) FLEXIBILITY.—The Space Launch System shall be designed from inception as a fully-integrated vehicle capable of carrying a total payload of 130 tons or more into low-Earth orbit in preparation for transit for missions beyond low-Earth orbit.

Quote
I find it rich that the congressional "mandate" that everyone hates is now used against SLS.

The real question is why NASA and Boeing did not go back to Congress and tell them they couldn't meet that specification.

Of course you'd think Congress would have noticed something was up after the mandated December 31, 2016 date came and went.

Seems like no one really cares about what the SLS can or cannot do, nor does anyone care how much it costs. Which is a contractors dream, but a taxpayers nightmare...  >:(
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 envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #93 on: 10/12/2018 11:53 pm »
SLS performance is not optimized for LEO, but for BLEO.

Doesn't matter what anyone thinks, Congress specifically called out capabilities to LEO:

Quote
(2) FLEXIBILITY.—The Space Launch System shall be designed from inception as a fully-integrated vehicle capable of carrying a total payload of 130 tons or more into low-Earth orbit in preparation for transit for missions beyond low-Earth orbit.

Quote
I find it rich that the congressional "mandate" that everyone hates is now used against SLS.

The real question is why NASA and Boeing did not go back to Congress and tell them they couldn't meet that specification.

Of course you'd think Congress would have noticed something was up after the mandated December 31, 2016 date came and went.

Seems like no one really cares about what the SLS can or cannot do, nor does anyone care how much it costs. Which is a contractors dream, but a taxpayers nightmare...  >:(

There's nothing about the specification that NASA can't meet. But they failed, at the time they were laying out plans, to give anything resembling a remotely accurate estimate of the cost and time required to meet that specification.

Recent comments by Mike Griffin suggest that not have been an accident. It's certainly a pattern with large NASA projects.

Offline Coastal Ron

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Re: Navigating the twists and turns steering SLS Development
« Reply #94 on: 10/13/2018 02:35 am »
There's nothing about the specification that NASA can't meet.

Seemed like there was some question about that, but OK.

Quote
But they failed, at the time they were laying out plans, to give anything resembling a remotely accurate estimate of the cost and time required to meet that specification.

Recent comments by Mike Griffin suggest that not have been an accident.

Correct me if I'm wrong, but I don't think Congress ever asked for a budget for the SLS or the Orion. And they certainly have not held hearings about the SLS where they reviewed NASA's budget targets.

In fact, last I heard NASA hasn't told Congress how much the SLS would cost to operate, and we in the public certainly don't know either.

Quote
It's certainly a pattern with large NASA projects.

No, the SLS and Orion programs are major exceptions. They did not go through the normal program process, but instead the design and major contractors were mandated by Congress without any bidding process, and no overall budget was ever set. Which is why I say the SLS can never be under-funded or over-budget, because no cost goals were ever established.

Anyone think the NASA OIG report will cause the House or Senate to review the program? I'm not holding my breath...
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

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Re: Navigating the twists and turns steering SLS Development
« Reply #95 on: 10/13/2018 02:54 am »

In this case "good enough" will only get you 97 t to LEO with EUS.


So, SLS Block 1 puts 95 t into LEO and SLS Block 1B puts 97 t into LEO. While SLS Block 1 can barely put an Orion to TLI, SLS Block 1B does that plus ~10 t. How do these numbers make any sense? If you are using the SLS payload planner's guide for this number, which it looks like you are, that is with a lot of margin for mass increase and performance shortfalls. It won't be the final payload number. You won't get that until after CDR.

Offline Steven Pietrobon

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Re: Navigating the twists and turns steering SLS Development
« Reply #96 on: 10/13/2018 07:56 am »
Back to reality, did you happen to run your analysis on a five-engine SLS core with EUS?

I sure did! With Dark Knights, 5xRS-25E and EUS I only get 118 t, the same as Saturn V. The low thrust of EUS really limits its performance here.

SLS performance is not optimized for LEO, but for BLEO.  I find it rich that the congressional "mandate" that everyone hates is now used against SLS.

If that's what the customer wants, that is what you deliver. :-) I believe Congress should only have specified a single 130 t LEO value and not 70 t and 130 t. That's such a huge difference (an 86% increase), that you're going to end up building two completely different rockets, wasting considerable time and money.

So, SLS Block 1 puts 95 t into LEO and SLS Block 1B puts 97 t into LEO.

SLS Block 1 only has a payload of 70 t to LEO. Not sure where you got 95 t.

Quote
If you are using the SLS payload planner's guide for this number, which it looks like you are, that is with a lot of margin for mass increase and performance shortfalls.

I'm not using the SLS payload planner's guide. These number's are from my own simulations. The SLS Mission Planners Guide says 70 t for Block I, 105 t for Block IB and 130 t for Block II. For Block IB and II, I believe these payloads include the EUS mass, reducing actual payload mass to 95 t and 120 t, respectively. If we examine the detailed payload tables, the data they give is not conducive to working out payload mass to LEO and is confusing.

We have that Useful Payload System Mass (PSM) is the PSM less Program Manager's Reserve (PMR). PSM is the initial mass in low Earth orbit (IMLEO) less the upper stage burnout mass. What is the PMR percentage? Who knows! For Block IB there is range of values give for Useful PSM, the low value for the initial performance and then a high value "based on current configuration development studies". What the heck are these development studies? Again, who knows!

The graph gives a value of Useful PSM of 97 t to 104 t for Block IB and 111 t for Block II for a circular orbit of about 260 km. The tables give a lowest orbit of 463 km, where the payloads are 94.0 to 100.7 t for Block IB and 108.3 t for Block II. I don't have a PMR value in my values, and without knowing what NASA's PMR is, it makes it difficult to compare. Also, why isn't NASA giving values for lower orbits, like down to 185 km, which is where Apollo staged from? NASA also gives the performance for elliptical orbits, but does not give the perigee altitude, only the apogee altitudes! For the apogee altitude, the lowest they give is 407 km which is not very useful for anyone planning on a lower apogee.

If we assume NASA's PMR is zero, then my numbers match up closely with NASA's numbers. I have 97 t for Block IB (97 t for NASA) and 113 t for Block II (111 t for NASA). Note that my orbit is for 200 km, while NASA is about 260 km (as best as I can measure from the graph).
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

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Re: Navigating the twists and turns steering SLS Development
« Reply #97 on: 10/13/2018 08:15 am »

SLS Block 1 only has a payload of 70 t to LEO. Not sure where you got 95 t.



Quote
While a comparison between NASA’s SLS Block 1 and SpaceX’s Falcon Heavy is often made, the gulf between the two has actually widened. As the Block 1 design has matured, the agency has refined the vehicle’s capabilities by a significant amount. Though NASA prefers to position SLS as a deep-space rocket, SFI sought a clarification of the vehicle’s capabilities to a more common destination for rockets: low-Earth-orbit (LEO).
NASA replied: “Now that the SLS design has matured and the program has more data as a result of progress with hardware manufacturing and testing, our current analysis shows the Block 1 configuration of SLS can deliver an estimated mass of 95 metric tons (209,439 pounds) to low-Earth orbit based on a 200 by 200-kilometer orbit with a 28.5 degree inclination, which is a commonly used orbit in the industry for estimating performance.”
http://www.spaceflightinsider.com/organizations/nasa/as-slss-block-1-design-matures-its-capabilities-come-into-clearer-focus/

Quote
This is low-Earth orbit, often referred to as LEO. SLS can deliver more than 95 metric tons (209,439 pounds) to this orbit with a Block I configuration.
https://www.nasa.gov/exploration/systems/sls/to-the-moon.html

Previously, the 70 t payload of the Block 1 was essentially NASA committing to meet the 2010 authorization language for minimum up mass and nothing more. Most of the hardware for EM-1 is in pieces now waiting to be joined or mated and so that gives you more confidence in a payload number.
« Last Edit: 10/13/2018 08:19 am by ncb1397 »

Offline Steven Pietrobon

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Re: Navigating the twists and turns steering SLS Development
« Reply #98 on: 10/13/2018 08:19 am »
Thanks ncb1397. I'm surprised by this high number. I'll do a simulation tomorrow to find out what is going on.
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Online ncb1397

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Re: Navigating the twists and turns steering SLS Development
« Reply #99 on: 10/13/2018 10:27 am »
Thanks ncb1397. I'm surprised by this high number. I'll do a simulation tomorrow to find out what is going on.

SLS is pretty close to the Ariane V architecture and so you might expect them to get similar payload mass fractions. Indeed, 70 t for SLS corresponds to a PMF of ~2.8% while Ariane V is more like ~2.7%. 95 t represents a payload mass fraction (PMF from here on) of about 3.8%, about 1.1% better than Ariane V. But considering that Ariane V leans very heavily towards solids with ~2.8x solids mass compared to liquid stage mass while SLS is ~1.5:1, it isn't entirely suprising that it would get better mass fraction as solids are notoriously heavy for the performance they provide. Indeed, the Delta IV Medium (5,2) gets a PMF of about 3.4% which on SLS would correspond to ~85 t. So, at the very least, anything from 70-85 t shouldn't be that surprising as that would be the PMF range of similar, albeit smaller, launchers. So, where does the extra 5 t + come from? Larger vehicle meaning lower aerodynamic losses and less proportional mass for insulation? more efficient engines? better design? All 3? The fact that Electron gets about 2.1% PMF to LEO which is lower than anything considered in this post thus far with composite tanks suggests that there is indeed a gross lift off mass - PMF relationship. As far as the engines, the RS-25 beats the RS-68 by a significant amount in terms of thrust to weight and ISP. So, that could be a factor as well.
« Last Edit: 10/13/2018 10:48 am by ncb1397 »

Offline UltraViolet9

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Re: Navigating the twists and turns steering SLS Development
« Reply #100 on: 10/13/2018 02:42 pm »
There's nothing about the specification that NASA can't meet. But they failed, at the time they were laying out plans, to give anything resembling a remotely accurate estimate of the cost and time required to meet that specification.

Recent comments by Mike Griffin suggest that not have been an accident. It's certainly a pattern with large NASA projects.

What did Griffin say?  Do you have a link?

Thanks in advance.

« Last Edit: 10/13/2018 05:38 pm by UltraViolet9 »

Offline Coastal Ron

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Re: Navigating the twists and turns steering SLS Development
« Reply #101 on: 10/13/2018 04:05 pm »
Thanks ncb1397. I'm surprised by this high number. I'll do a simulation tomorrow to find out what is going on.

SLS is pretty close to the Ariane V architecture

I assume you mean "Ares V", not "Ariane V" as written...  ;)

Considering all the time (years) and money ($Billions) spent on the SLS, and we're still having debates about it's abilities, I'd say using any guesses from Ares V - which was never funded to start - would not provide valid data.

Stick with official numbers that come from NASA on the SLS, it's the only way to have a known baseline.
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Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #102 on: 10/13/2018 10:45 pm »
There's nothing about the specification that NASA can't meet. But they failed, at the time they were laying out plans, to give anything resembling a remotely accurate estimate of the cost and time required to meet that specification.

Recent comments by Mike Griffin suggest that not have been an accident. It's certainly a pattern with large NASA projects.

What did Griffin say?  Do you have a link?

Thanks in advance.

Griffin wrote this:

Quote
I must also point out that there have been many instances where proponents of individual missions have downplayed the technical difficulty and risk of their individual mission, or grossly underestimated the cost and effort involved to solve the problems, in order to gain "new start" funds for particular project. Everyone knows that, once started, any given mission is nearly impossible to cancel, so the goal becomes that of getting started, no matter what has to be said or done to accomplish it. I am speaking here not only to industry and scientific investigators, but also to organizations within NASA. This is a matter of integrity for our community. NASA managers, the White House, and Congress have seen this behavior too many times, and the Agency has lost a great deal of credibility over the decades as a result. There was a time - I remember it, and many of you will also - when what "NASA" said could be taken to the bank. Anyone here think it's like that today? Show of hands? ... I didn't think so.

Emphasis mine.

http://www.spaceref.com/news/viewsr.html?pid=27239

Offline Kabloona

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Re: Navigating the twists and turns steering SLS Development
« Reply #103 on: 10/13/2018 11:04 pm »
Thanks for that excerpt from Griffin's speech. Here's the next paragraph, which is also relevant:

Quote
I have spent a good portion of my time as Administrator trying to rebuild that credibility with more rigorous technical review and independent cost estimating processes. But, folks, we are in this together. We will not be trusted with more funding to carry out great, new, exciting space missions in the future, human or robotic, if we oversell and underdeliver on our commitments today. Across the board, we must be realistic in our assessments of cost and technical risk if we are to be trusted with funds provided to us by the American taxpayer.

'Nuff said.
« Last Edit: 10/13/2018 11:06 pm by Kabloona »

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Re: Navigating the twists and turns steering SLS Development
« Reply #104 on: 10/14/2018 03:01 am »

I assume you mean "Ares V", not "Ariane V" as written...  ;)

No, I mean Ariane V. Ariane V ECA has 2 solid rocket boosters with a hydrolox center core and a hydrolox upper stage.

Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #105 on: 10/14/2018 03:03 am »
There's nothing about the specification that NASA can't meet.

Seemed like there was some question about that, but OK.

Quote
But they failed, at the time they were laying out plans, to give anything resembling a remotely accurate estimate of the cost and time required to meet that specification.

Recent comments by Mike Griffin suggest that not have been an accident.

Correct me if I'm wrong, but I don't think Congress ever asked for a budget for the SLS or the Orion. And they certainly have not held hearings about the SLS where they reviewed NASA's budget targets.

In fact, last I heard NASA hasn't told Congress how much the SLS would cost to operate, and we in the public certainly don't know either.

Quote
It's certainly a pattern with large NASA projects.

No, the SLS and Orion programs are major exceptions. They did not go through the normal program process, but instead the design and major contractors were mandated by Congress without any bidding process, and no overall budget was ever set. Which is why I say the SLS can never be under-funded or over-budget, because no cost goals were ever established.

Anyone think the NASA OIG report will cause the House or Senate to review the program? I'm not holding my breath...

NASA never provided a total cost estimate, because Congress never demanded one. But NASA did not publicly object to the 2016 deadline, and for years has proposed SLS budget requests every year that did not realistically reflect what they needed to hit that deadline.

The obvious implication was that they expected to hit that schedule with the proposed budget, when realistically they would have needed double the money or even more than that.

Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #106 on: 10/14/2018 03:05 am »
Thanks for that excerpt from Griffin's speech. Here's the next paragraph, which is also relevant:

Quote
I have spent a good portion of my time as Administrator trying to rebuild that credibility with more rigorous technical review and independent cost estimating processes. But, folks, we are in this together. We will not be trusted with more funding to carry out great, new, exciting space missions in the future, human or robotic, if we oversell and underdeliver on our commitments today. Across the board, we must be realistic in our assessments of cost and technical risk if we are to be trusted with funds provided to us by the American taxpayer.

'Nuff said.

Yes. To be clear, I'm not bagging Griffin here. He's entirely right on this point.

Offline Coastal Ron

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Re: Navigating the twists and turns steering SLS Development
« Reply #107 on: 10/14/2018 04:09 am »
NASA never provided a total cost estimate, because Congress never demanded one.

Congress told NASA to create the SLS, and if Congress was interested in knowing the total development costs, or what the operational costs would be, then all they have to do is tell NASA to provide the information.

Quote
But NASA did not publicly object to the 2016 deadline...

"NASA" works for the President, and "NASA" does not question Congress.

Quote
...and for years has proposed SLS budget requests every year that did not realistically reflect what they needed to hit that deadline.

"NASA" does not propose it's own budget, the President does via the Office of Management and Budget (OMB). NASA personnel provide input, but it's really up to the OMB to decide what goes into the President's budget.

This is "Government 101" type stuff by the way...

Quote
The obvious implication was that they expected to hit that schedule with the proposed budget, when realistically they would have needed double the money or even more than that.

When the "NASA Authorization Act of 2010" was signed, no one, including NASA and Boeing, knew how much it would cost to develop the SLS, nor did they know how long it would take.

And in case it's not painfully obvious, NASA and Boeing STILL don't know how much it will cost or how long. They have a better guess now than they did on October 11, 2010, but every time NASA pushes out SLS flight dates is an indication that they still have an imperfect understanding of the SLS program. You don't have to be a scheduling professional like me to see that...  ;)
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Offline Steven Pietrobon

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Re: Navigating the twists and turns steering SLS Development
« Reply #108 on: 10/14/2018 06:40 am »
OK, I've done my homework! I get a payload of 89.0 t to 200 km for Block I. If we include the burnout mass of iCPS, the IMLEO is 94.2 t, very close to NASA's 95 t value. Thus, I believe NASA is quoting IMLEO for Block I to LEO, which is also what NASA has been doing for Block IB and II.

So why do we get a high payload? When the core burns out, its at a high velocity of about 7.2 km/s. The upper stage only needs to add another 0.6 km/s, which can do so with low acceleration. The actual delta-V is 0.7 km/s, so we lose 0.1 km/s due to gravity losses. The iCPS only has a dry mass of 3.8 t, compared to 14.5 t for EUS (this is an older value). RL-10B-2 also has slightly better ISP than the EUS engines.

Attached are my simulation results. You can download the software from my SLS site below.

http://www.sworld.com.au/steven/space/sls/

The data I've been using is now about four years old, so if anyone can provide new data on the masses and engine performance of the core, booster, and upper stages, that would be much appreciated! My simulations are only as good as the data they use.

I also want to point out that my simulations always include reserve propellant masses, which is probably equivalent to the Program Manager's Reserve that NASA is using in their performance curves.
« Last Edit: 10/14/2018 06:59 am by Steven Pietrobon »
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline envy887

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Re: Navigating the twists and turns steering SLS Development
« Reply #109 on: 10/14/2018 12:06 pm »
NASA never provided a total cost estimate, because Congress never demanded one.

Congress told NASA to create the SLS, and if Congress was interested in knowing the total development costs, or what the operational costs would be, then all they have to do is tell NASA to provide the information.

Quote
But NASA did not publicly object to the 2016 deadline...

"NASA" works for the President, and "NASA" does not question Congress.

Quote
...and for years has proposed SLS budget requests every year that did not realistically reflect what they needed to hit that deadline.

"NASA" does not propose it's own budget, the President does via the Office of Management and Budget (OMB). NASA personnel provide input, but it's really up to the OMB to decide what goes into the President's budget.

NASA is (supposed to be) the technical authority on how much money and time it takes to build a rocket. The adminstration actually writes the budget, but it should reflect NASA's estimates. Unless the administration is trying to undermine Congress' intent by deliberately underfunding the project.

Congress isn't required to ask for budgetary estimates before (or after) setting a schedule requirement, if they don't care about the cost. In the case of SLS, not only do they not care about the cost, but they don't really care about the schedule either. (which to me strongly indicates that the goal is pork and not a rocket)
« Last Edit: 10/14/2018 12:13 pm by envy887 »

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Re: Navigating the twists and turns steering SLS Development
« Reply #110 on: 10/14/2018 05:01 pm »
Thanks for that excerpt from Griffin's speech. Here's the next paragraph, which is also relevant:

Quote
I have spent a good portion of my time as Administrator trying to rebuild that credibility with more rigorous technical review and independent cost estimating processes. But, folks, we are in this together. We will not be trusted with more funding to carry out great, new, exciting space missions in the future, human or robotic, if we oversell and underdeliver on our commitments today. Across the board, we must be realistic in our assessments of cost and technical risk if we are to be trusted with funds provided to us by the American taxpayer.

'Nuff said.

Yes. To be clear, I'm not bagging Griffin here. He's entirely right on this point.

Ditto. My cryptic comment was intended to mean that IMO, Griffin neatly summed up the problems behind SLS, needing no other comment from me.
« Last Edit: 10/14/2018 05:03 pm by Kabloona »

Offline Coastal Ron

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Re: Navigating the twists and turns steering SLS Development
« Reply #111 on: 10/15/2018 12:25 am »
...and for years has proposed SLS budget requests every year that did not realistically reflect what they needed to hit that deadline.

"NASA" does not propose it's own budget, the President does via the Office of Management and Budget (OMB). NASA personnel provide input, but it's really up to the OMB to decide what goes into the President's budget.

NASA is (supposed to be) the technical authority on how much money and time it takes to build a rocket.

NASA is filled with a lot of smart people, but few today have designed and built a rocket. So no, NASA is not the technical authority for the SLS, Boeing would be. But as the customer NASA would be involved with how much Boeing THINKS it needs, since NASA manages the Boeing contract.

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The adminstration actually writes the budget, but it should reflect NASA's estimates.

Sure it should reflect what NASA wants, but the OMB decides the details of what the Administration requests from Congress.

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Unless the administration is trying to undermine Congress' intent by deliberately underfunding the project.

Two things to keep in mind:

1. By law the President of the United States has to submit a budget request to Congress. By tradition, Congress completely ignores the submitted budget request.

2. So far members of Congress have been willing to provide the SLS will a constant source of funding, which is being done in a "flat budget" profile, not one that is normal for programs of it's size.

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In the case of SLS, not only do they not care about the cost, but they don't really care about the schedule either. (which to me strongly indicates that the goal is pork and not a rocket)

Completely agree!
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

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