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15 minutes ago, Bej Kerman said:

What exactly is the SLS for? NASA would sure have a lot more money to play around with if they just scrapped the SLS, put the RS-25s back into museums and relegated this task to the Falcon rockets.

It's for launching something smaller than Apollo ALMOST to the Moon.

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30 minutes ago, Bej Kerman said:

What exactly is the SLS for?

This is the question that should have been asked before finalizing the design.

 

30 minutes ago, Bej Kerman said:

NASA would sure have a lot more money to play around with if they just scrapped the SLS, put the RS-25s back into museums and relegated this task to the Falcon rockets.

NASA would not have any more money, SLS was paid for, minus SLS that money does not exist.

As for Falcons, if the goal was humans to the lunar surface, F9/FH is not ideal, either.

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There is an excellent little comedy movie called The Pentagon Wars, about the development of the Bradley infantry fighting vehicle. Of course it exaggerates a lot of stuff, but amidst all the entertainment is a pretty scathing commentary on the process of government procurements. I hope somebody will make a spiritual successor to that movie one day, about the SLS. Of course it's not entirely the same process, but it sure rhymes a lot.

Linking a relevant clip below to illustrate the tone of the movie. It's a highly entertaining scene in itself.

 

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5 hours ago, Bej Kerman said:

What exactly is the SLS for

Actually - its purpose is to keep current the knowledge and ability to build rockets in the United States.  (Go back to when it was started /announced and look at the capabilities of commercial space at the time). 

So like a large, heavy ball that is pushed down a hill - it is still rolling.  It has momentum. 

Meanwhile along came a smart kid who created his own ball and threw it down the hill.  

Yes, his ball is moving faster - but so what?  It will cost more effort than it is worth to stop the first one - and there is no guarantee, yet, that the smart kid can actually hit his target. 

Finally - it is better to have two balls than just one.  No sense cutting off one ball that should work in favor of another that you only hope will work. 

 

 

 

(Let's wait to focus on efficiency until after we have capacity) 

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14 minutes ago, JoeSchmuckatelli said:

(Let's wait to focus on efficiency until after we have capacity) 

I would agree with this except that SLS lacks capacity.

It's for BLEO, yet it can't do BLEO missions, at least not saddled with Orion (which was intentionally made so massive commercial launches could not launch it (ULA at the time, that was Ares era).

SLS B1B can do ~37t to TLI?

SLS B2 can do ~45 to TLI?

Orion CSM is 26.5t and has ~1200 m/s dv.

That leaves 17.5t of additional vehicle that can go with Orion. If Orion had more like 2800 m/s of dv, then they could stick an Apollo LM on there (modernized, and lighter (?), with better computers, etc). But Orion can't even do LLO alone, much less pushing a LM. So we have a rocket that cannot do anything useful at all. If Orion was Apollo CM sized, then all the things are possible, and heck, the capsule with a small SM could be used for ISS, too. But Orion is a pig, so...

 

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Guest The Doodling Astronaut
6 hours ago, Bej Kerman said:

What exactly is the SLS for? NASA would sure have a lot more money to play around with if they just scrapped the SLS, put the RS-25s back into museums and relegated this task to the Falcon rockets.

It was designed by politicians, not scientists. It explains everything wrong with SLS

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3 hours ago, JoeSchmuckatelli said:

Actually - its purpose is to keep current the knowledge and ability to build rockets in the United States.  (Go back to when it was started /announced and look at the capabilities of commercial space at the time). 

So like a large, heavy ball that is pushed down a hill - it is still rolling.  It has momentum. 

Meanwhile along came a smart kid who created his own ball and threw it down the hill.  

Yes, his ball is moving faster - but so what?  It will cost more effort than it is worth to stop the first one - and there is no guarantee, yet, that the smart kid can actually hit his target. 

Finally - it is better to have two balls than just one.  No sense cutting off one ball that should work in favor of another that you only hope will work. 

His ball moved faster and hit a bullseye, the SLS is still at the top of the hill being carved from crisps and wafers. So, I'm not sure where that analogy was going. Sure, the SLS may have that bit more power to reach the moon, well it will do in 2050 when Falcon 9s are regularly doing kessel runs... oh, forget it.

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Ok, somebody check my numbers.

Orion/ESM has a TLI injected mass of 26.5t, of which ~8.6t is service module propellant (I've also seen 9.4t, I'll calculate that too.) The mass with service module propellant expended is 17.9t (or 17.1t).

NRHO to/from TLI is ~500m/s and the AJ10 has an ISP of 319s.

In order to return from NRHO, Orion needs to reserve 3.1t (3.0t) of propellant for wet 21t, dry 17.9t, DV 500m/s barely. (20.1t/17.1t)

That leaves 5.5t (6.4t)propellant to brake into NRHO on the way out. If Dry= Wet - 5.5t (6.4t), then the maximum wet mass that gives a DV over 500m/s is around 37t (43.5t). Subtracting Orion's TLI injected mass gives 10.5t (16.9t) payload.

 

This implies block 2 (>46t to TLI) cannot be fully utilised by Orion, and Block1B (42t to TLI) can't be fully utilised either if the 8.6t service module propellant figure is correct.

Edited by RCgothic
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Based on SpaceX's published Mars payload, back calculating TLI throw gives 19.5t. To brake into NRHO takes 2.9t of propellant and let's be generous and say the propulsion bus is 20% of propellant mass - ~0.6t.

That gives an Orion Equivalent Payload to NRHO for falcon heavy expendable of 16t, vs Orion 16.9t on B1B.

That's not a big percentage increase for Orion (and it's probably neutered by larger margins because of crew on board).

 

How many Falcon Heavies can be launched for the development costs of EUS? I'm betting a lot. Over 6 just for the cost of mobile launcher 2.

The ICPS multiple burns is the only argument I've heard that has any validity for the switch, but if the risks are low enough to use that mission mode once they're low enough to use it repeatedly.

Edited by RCgothic
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8 minutes ago, RCgothic said:

if the risks are low enough to use that mission mode once they're low enough to use it repeatedly.

Seriously, I don't understand how NASA can explain this. "The trajectory is too risky for the program but we're going to send people like that anyways, but we assure that at some point we will make a rocket that doesn't have that risk anymore"

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5 hours ago, Bej Kerman said:

...well it will do in 2050 when Falcon 9s are regularly doing kessel runs... oh, forget it.

You guys have valid criticism of the program from top to bottom. 

I'm just saying it had a purpose at inception. 

I also get that this baby looks like Dr. Frankenstein had an Evil Senate Committee requiring that he use parts from their particular family plots. 

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So some guy on Twitter claimed in response to my listing the above that B1B is 50+t to TLI and Orion's mass is 22.8t.

Using these figures, 9.4t of propellant gets 24.2t comanifested (47t braked fromTLI). That is a reasonably big payload, and a commercial launcher would have to manage something like 29t after propulsion bus to equal it on equivalent terms.

However, the numbers are wildly better than those advertised by NASA, so take with a whole shaker of salt.

 

Cheekily, that's a dry mass of Orion of 13.4t and strictly it only needs 5.2t of propellant to make the round trip, or 18.6t total to TLI.

"Falcon Heavy can't launch Orion"

 

Edited by RCgothic
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59 minutes ago, RCgothic said:

So some guy on Twitter claimed in response to my listing the above that B1B is 50+t to TLI and Orion's mass is 22.8t.

Tell him to show his work. Presumably there is some NASA link that provides those capabilities.

This NASA doc says 22.7t—but it is from Constellation. https://www.nasa.gov/pdf/166914main_FS_Orion508c.pdf

This  NASA link which is from 2014 says otherwise: https://www.nasa.gov/sites/default/files/fs-2014-08-004-jsc-orion_quickfacts-web.pdf

Injected (TLI) mass: 58,467 lbs, which is 26, 520 kg.

 

1 hour ago, JoeSchmuckatelli said:

I'm just saying it had a purpose at inception. 

See, this is the problem—it didn't. I like dumping on the insane cost, etc, but frankly the cost doesn't matter, I get it, that's how the sausage is made. What matters is the capability, and it's just not there, and will never be there.

If the purpose was BLEO human spaceflight missions—not singleton capsule flights, but complete missions, like landing on the Moon, or sending humans to Mars, then SLS not only can't do the job by itself, it never can. The cost starts to actually matter, too, when literally any mission requires multiple SLS launches a few weeks apart.

Knowing Orion was to be part of the system, TLI capability needed to be ~65t. That's the math.

They say, "Hey, we need a "jack of all trades" BLEO crew launch vehicle."

Then someone asks, "What are possible missions?"

Answer? "Landing on the Moon, building a space station around the moon... building a Mars vehicle in LEO, stuff like that! Oh, and we have a crew capsule capable of Earth return from the Moon or Mars already, Orion!"

"Cool, so we need to be able to do those missions, and we need any extra capacity to be in addition to that 26.5t. (scribbles)... so for lunar surface missions we need the thing to throw at least 60, maybe 65t to TLI. Cool, that's doable."

The trouble is they set the lift capability without bothering to check if it could accomplish anything first.

 

 

Edited by tater
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SLS Block 1 payload isn't actually that bad for me. It can send Orion to the moon and in these days of rendezvous that's all it really needs to do (maybe a little more upper stage thrust would be nice).

What really gets me is the opportunity cost.  SLS/Orion is just so horrendous.

Nevermind the cash price which could be better spent on payloads or commercial launchers, I want us to get off world to stay. That requires more than one crewed flight per year and Orion/SLS is completely incapable of meeting the required cadence. It locks NASA into that cul de sac until it's cancelled.

They're going to get overtaken by commercial space.

 

Edited by RCgothic
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1 hour ago, tater said:

What matters is the capability, and it's just not there

So -this is painfully obvious - what we have here is an educated person (you) quibbling with an enthusiast member of the general public (me). *

I first learned about SLS on a trip to KSC with my kids seven years ago (or so).  This is what we were shown: SLS Fact Sheet Aug 2014 (nasa.gov)

Details like this are cool:

"The 70-metric-ton configuration will provide 10 percent more thrust at launch than the Saturn V rocket and carry more than three times the payload of the space shuttle. The 130-metricton configuration will stand taller than the Saturn V and provide 20 percent more thrust."

'Bigger than Saturn V' is hugely exciting.  Makes for good press and 'feel good' support of NASA.  Of course, they also promised:

"In 2013, NASA completed the preliminary design of the SLS and moved into production of the launch vehicle. Engineers continue to make rapid progress aimed toward delivering the first SLS rocket to NASA’s Kennedy Space Center in Florida by 2017 for its first launch."

Had they met those goals, we'd be having entirely different conversations.  SX would be in 'catch up' mode, rather than 'catch me'!  Presumably SLS would have iterated since then and be actually working on a variant that is capable of attaining its goals.

...

So - for someone like me who 'only kind of gets' this stuff (and who frankly is STILL an anomaly among the general public), knowing that we have a rocket in development is cool... its just that guys like you who not only understand the math but who can and do compare the potential of both (as yet unrealized) rockets - when you present facts showing that SLS is not only a dead end - it can't do what it's supposed to do... its flabbergasting. 

Emotionally, I want SLS to succeed -- because I want NASA to succeed.  I get that this is irrational.  I look at SX and I think 'this is a private company' this isn't NASA.  Logically, transitioning NASA from a 'government agency that does all US civilian spaceflight' to 'a government agency that coordinates with free-market space companies' is something that is going to take more than a logical adjustment of expectations.  We're going to have to say goodbye to the historical and emotive connection with America's 'face' of space. 

Space is hard?  Change is harder.

 

 

 

 

 

 

 

*I get the irony - and appreciate the patience!

Addendum:  When SX circles the moon, and we see Starships attempting landings - and then people walking around on the moon again... I think the transition will have been made.

Despite my enthusiasm for SX - there is also something that should not be overlooked; we need more skin in the game.  Having them be 'the only launch provider' when the dust settles is also a dead end.  We need a bunch of competing companies if we're gonna get into space in any significant numbers (read: number of people living and working in space, i.e. a viable and dynamic economy) in our lifetimes.

Edited by JoeSchmuckatelli
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22 minutes ago, JoeSchmuckatelli said:

Having them be 'the only launch provider' when the dust settles is also a dead end.  We need a bunch of competing companies if we're gonna get into space in any significant numbers (read: number of people living and working in space, i.e. a viable and dynamic economy) in our lifetimes.

I wonder what sorta funds NASA could provide to all the other private enterprise launch providers, most of which are currently in the "small sat" market. 

Rocket Lab and Relativity Space come to mind, but are way behind SpaceX in terms of actual stuff done.

 

At a certain point SpaceX will turn into a monopoly if current trends continue. 

 

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@JoeSchmuckatelli I agree on the specs looking great at first glance. I honestly paid little attention early in the SLS program, but a friend of mine who used to write for arstechnica (specifically space reporting) did follow it, and filled me in that it was a "rocket to nowhere." He was actually OK with ARM as a mission, since it was getting made anyway, might as well be used. Anyway, it was only when I started actually running the numbers I realized how unfit for purpose it was.

I think it could have been designed in such a way that it's still "SLS," still for BLEO, still uses the Shuttle-adjacent parts (read: contractors), and is still incredibly expensive, and built in all 50 States—but can actually accomplish cool missions. I'd be all-in for it if it could do something cool. They need to either dump Orion, and make a lighter capsule, or beef up SLS well past Block 2 so it can fly with Orion, and the min sortie lander (which I think is ~35t for a RT from NRHO to the surface).

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