Author Topic: NASA defends decision to restart RS-25 production, rejects alternatives  (Read 115697 times)

Offline envy887

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J-2X only has 2 throttle settings: 100% and 84%. And it would need a shorter nozzle to run at sea level. Not ideal for a landing engine.

Offline AncientU

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@TomH

Once you decide to attempt recovering the mod SLS core in some way. That means you don't need the 130 tonnes lift. Figure how much mass can get to LEO with 4 RS-25 with the supplemental center engine plus the EUS. Then assemble your deep space stack with components around that mass figure. Since you can re-fly the mod SLS core several times a year. Maybe more frequently then the STS if there is handful of mod SLS cores in service.

You mean, like Falcon Heavy, except using massively expensive engines?
(The poor mass fraction and high deceleration burn propellant requirement will put this beast somewhere in the FH payload range.)

Hint: If you want a reusable launcher, start with a blank sheet of paper.
« Last Edit: 03/03/2017 11:34 am by AncientU »
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Offline Jim

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Hint: If you want a reusable launcher, start with a blank sheet of paper.

That excludes Spacex.  They took an expendable launcher and are trying to make it reusable.  Blue is designing theirs for reuse from day one.

Offline Mark S

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@TomH

Once you decide to attempt recovering the mod SLS core in some way. That means you don't need the 130 tonnes lift. Figure how much mass can get to LEO with 4 RS-25 with the supplemental center engine plus the EUS. Then assemble your deep space stack with components around that mass figure. Since you can re-fly the mod SLS core several times a year. Maybe more frequently then the STS if there is handful of mod SLS cores in service.

You mean, like Falcon Heavy, except using massively expensive engines?
(The poor mass fraction and high deceleration burn propellant requirement will put this beast somewhere in the FH payload range.)

Hint: If you want a reusable launcher, start with a blank sheet of paper.

Well, we already know that the current SLS core is under-powered with only four RS-25 engines, thanks to Steven Pietrobon's "Fly me to the Moon" paper. Adding a fifth RS-25 and a J2X would correct that, and enable SLS to meet its 130-ton mandate easily (in conjunction with a Large Upper Stage instead of EUS).

Recoverability would be the icing on the cake, if it could be made to work. And it would show that NASA is concerned with costs, perhaps earning some good will from the Administration's budget cutters.

This has been a fun thought exercise. Cheers!

Offline AncientU

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Hint: If you want a reusable launcher, start with a blank sheet of paper.

That excludes Spacex.  They took an expendable launcher and are trying to make it reusable.  Blue is designing theirs for reuse from day one.

And it excludes NASA and its industry partners.

It does for Falcon and variants as you intended to say...  it has taken a dozen or more flights to shake-out the hardware needed to achieve reusability(the landing portion, so far) -- more will probably be needed before they are done.  A dozen or more flights with SLS/RS-25s would be a bit pricey, even knowing what they know now courtesy of SpaceX's technology demonstrations.  Even then, the usable SLS payload will be so small (or negative) that it will be a dead end.

But no, it doesn't exclude SpaceX. 
They've started with a blank sheet on BFR/ITS and it will be born reusable.
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Offline Proponent

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So why are they allowed to ditch the SRBs in order to get to the mandated 130 tons? When a 8.4m kerolox booster with large high-thrust hydrolox upper stage would have exactly the same amount of STS heritage, but be faster, cheaper, and safer?

Sorry, I don't understand.  Do you mean "why are the not allowed to ditch the SRBs...?"  I was not aware that any 8.4-m kerolox design without SRBs could loft 130 tonnes.

Offline Mark S

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Hint: If you want a reusable launcher, start with a blank sheet of paper.

That excludes Spacex.  They took an expendable launcher and are trying to make it reusable.  Blue is designing theirs for reuse from day one.
A dozen or more flights with SLS/RS-25s would be a bit pricey, even knowing what they know now courtesy of SpaceX's technology demonstrations.  Even then, the usable SLS payload will be so small (or negative) that it will be a dead end.

I'm not sure how you came to that conclusion. If Steven's six-engine SLS Block-2 design can put 140 tonnes in LEO, surely a similar core with enhancements for recovery could put more than a "small (or negative)" payload to the same orbit. It would definitely be less than 140 t, but even if it was just 95 or 100 tonnes, it would still be nearly twice that of FH.

The recovery of the core would make the reduced payload worthwhile in almost all cases. If there was an extreme need to put 140 tonnes up in one launch, then the core recovery could be skipped, allowing the full payload capacity to be utilized. You know, just like those other guys.

Offline Jim

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And it excludes NASA and its industry partners.


No.  Blue Origin is among  NASA and its industry partners, just as Spacex is.

Just back off, and quit lumping all of NASA with SLS

And still after everything settles, we could still be in the same place as we were in the 90's. (stuck in LEO)
« Last Edit: 03/03/2017 04:58 pm by Jim »

Offline landlubber

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To be more precise. One engine takes about 5 years to make. The factory has the capacity to start working on two new engines per year. This means that after 5 years (and assuming that each year you add two new engines to production), 2 engines are delivered for integration. And two for every year after that.

5 years to build an engine!?!?!

Imagine how many underpants you could steal in 5 years.

Offline Space Ghost 1962

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And still after everything settles, we could still be in the same place as we were in the 90's. (stuck in LEO)
... and with RIFs and no budget to do anything. Too likely. A cold time.

Offline notsorandom

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Propulsive reentry of the SLS core, if workable, is not likely to be the best way to get reusability of SLS components. As others have stated the entry velocity of the core is ~7.5 km/s which is significantly faster and hotter than Falcon 9's slow 1.5km/s. The SMART reuse concept may be the best way to get parts of the core back. There is a long history of SDHLVs that use recoverable engine pods. A HAID type inflatable heat shield might be a good improvement to that pod idea.

Any ideas on what percentage of the total cost the SRBs are? If Falcon and New Glenn show a liquid booster can be reused cheaply then replacing the SLS boosters with that sort of technology may be the best bang for the buck in terms of implementing reusability in SLS.

Offline envy887

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So why are they allowed to ditch the SRBs in order to get to the mandated 130 tons? When a 8.4m kerolox booster with large high-thrust hydrolox upper stage would have exactly the same amount of STS heritage, but be faster, cheaper, and safer?

Sorry, I don't understand.  Do you mean "why are the not allowed to ditch the SRBs...?"  I was not aware that any 8.4-m kerolox design without SRBs could loft 130 tonnes.

SLS Block 2 nominally replaces the SRBs with advanced LRBs which have no Shuttle heritage. Or Dark Knights, which also have no Shuttle heritage.

The biggest issue with 8.4m cores is height. Replacing EUS with a 400t upper stage (roughly S-II sized) would allow SLS Block 1B to easily loft 130 tonnes, but that stack is too tall for the VAB because of the large hydrolox core. A kerolox core allows a 400t upper stage by fitting the entire core stage under the SRB thrust beam, where the LH2 tank is now.

Offline Space Ghost 1962

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Have problems with all of this w/o clarity of where to go/do better.

Congress has painted things into a real narrow, tight corner. Now you want to improve things but make them more effective? Too much needs to change to quickly on too many fronts, and possibly with less funds.

To me you're either looking at a cancellation or rescoping. Unfortunately nothing new unless to modularly rebid components such that follow on is cheaper/does more/is more reliable/has more uses.

One good thing is that these engines were from a reusable history, and they were getting to a point where costs could come down.

However, there's more than a little competition for the role, and the threshold is high.

Also, from my experience with AJR they are the most resistant to change of any here. Boeing and Lockheed will grouse about it, but in the end you can twist their arms and you'll get something.

SLS itself is the problem. By Congresses design, it vaguely inched expensively and narrowly towards flight, the fewest options for the most cost taking the longest time. So even if you accept the engines, all of the rest snaps together in the same way, and you're back on the same road as before.

So it becomes "self canceling". Which then brings on the RIFs. Which takes the budget. Which ends things.

So perhaps this NASA decision is just the recognition of a doomed program that because Congress "did it", Congress must "fix it", or Congress should let it die.

Offline Space Ghost 1962

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Hint: If you want a reusable launcher, start with a blank sheet of paper.

That excludes Spacex.  They took an expendable launcher and are trying to make it reusable.  Blue is designing theirs for reuse from day one.
Strongly disagree.

Better put was as they learned orbital launch, they agile - developed a increasingly recoverable LV and continued the process heading into reuse. And ITS is a reuse from the ground up.

Blue Origin learned engines and vehicles for reuse in waterfall. Then they began to apply it to the suborbital business with follow on to orbital business, and recently announced lunar surface cargo business.

Also look at vehicle strategy - SX keeps stretching a small vehicle larger (tank stretches, uprated engines, parallel staging,...), while BO increments up the vehicle size/scope more granularly.

Also with ITS we're talking about a single vehicle architecture with high reuse/interdependence and a very narrow CONOPS yielding a broad range into a landed/return on other bodies.

Long ranged with BO is a very different story. And with Bezos recent comments, it's beginning to sound like he wants to "deliver the pickaxes and shovels for the gold rush", not "convey the miners, pans, and rations".

So either of these can decrease NASA's dependence on "doing it all".  And neither of these really fit into NASA "hand in glove". Which would help NASA if that somehow were to work.

Finally, RS-25 engines, or even a core stage booster that uses RS-25's ... does not seem to aid in this progression.

Offline Jim

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Hint: If you want a reusable launcher, start with a blank sheet of paper.

That excludes Spacex.  They took an expendable launcher and are trying to make it reusable.  Blue is designing theirs for reuse from day one.
Strongly disagree.

Better put was as they learned orbital launch, they agile - developed a increasingly recoverable LV and continued the process heading into reuse. And ITS is a reuse from the ground up.

Blue Origin learned engines and vehicles for reuse in waterfall. Then they began to apply it to the suborbital business with follow on to orbital business, and recently announced lunar surface cargo business.

Also look at vehicle strategy - SX keeps stretching a small vehicle larger (tank stretches, uprated engines, parallel staging,...), while BO increments up the vehicle size/scope more granularly.

Also with ITS we're talking about a single vehicle architecture with high reuse/interdependence and a very narrow CONOPS yielding a broad range into a landed/return on other bodies.

Long ranged with BO is a very different story. And with Bezos recent comments, it's beginning to sound like he wants to "deliver the pickaxes and shovels for the gold rush", not "convey the miners, pans, and rations".

So either of these can decrease NASA's dependence on "doing it all".  And neither of these really fit into NASA "hand in glove". Which would help NASA if that somehow were to work.

Finally, RS-25 engines, or even a core stage booster that uses RS-25's ... does not seem to aid in this progression.

There is nothing to disagree with in my statement.  I was just posting facts.

Offline Lars-J

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Hint: If you want a reusable launcher, start with a blank sheet of paper.

That excludes Spacex.  They took an expendable launcher and are trying to make it reusable.  Blue is designing theirs for reuse from day one.

Yes, but you were also at the time fond of pointing out that F9 v1.1 (block II) was pretty much a clean sheet redesign of the F9 - (tank diameter was the only similarity) with the clear intent of vertical landing, so the truth and facts are somewhere in between.

So they changed an expandable launcher into a reusable one. But they also rebuilt it from almost scratch to do it.

Offline bob the martian

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Hint: If you want a reusable launcher, start with a blank sheet of paper.

That excludes Spacex.  They took an expendable launcher and are trying to make it reusable.  Blue is designing theirs for reuse from day one.

Yes, but you were also at the time fond of pointing out that F9 v1.1 (block II) was pretty much a clean sheet redesign of the F9 - (tank diameter was the only similarity) with the clear intent of vertical landing, so the truth and facts are somewhere in between.

So they changed an expandable launcher into a reusable one. But they also rebuilt it from almost scratch to do it.

IIRC, SpaceX has always had reusability as a goal - what changed was the method of recovery.  They were initially going to try parachute recovery of the booster, but the first few attempts showed it to not be viable, so powered landings it was.

Or did I hallucinate all of that? 

Offline Space Ghost 1962

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Hint: If you want a reusable launcher, start with a blank sheet of paper.

That excludes Spacex.  They took an expendable launcher and are trying to make it reusable.  Blue is designing theirs for reuse from day one.
Strongly disagree.

Better put was as they learned orbital launch, they agile - developed a increasingly recoverable LV and continued the process heading into reuse. And ITS is a reuse from the ground up.

Blue Origin learned engines and vehicles for reuse in waterfall. Then they began to apply it to the suborbital business with follow on to orbital business, and recently announced lunar surface cargo business.

Also look at vehicle strategy - SX keeps stretching a small vehicle larger (tank stretches, uprated engines, parallel staging,...), while BO increments up the vehicle size/scope more granularly.

Also with ITS we're talking about a single vehicle architecture with high reuse/interdependence and a very narrow CONOPS yielding a broad range into a landed/return on other bodies.

Long ranged with BO is a very different story. And with Bezos recent comments, it's beginning to sound like he wants to "deliver the pickaxes and shovels for the gold rush", not "convey the miners, pans, and rations".

So either of these can decrease NASA's dependence on "doing it all".  And neither of these really fit into NASA "hand in glove". Which would help NASA if that somehow were to work.

Finally, RS-25 engines, or even a core stage booster that uses RS-25's ... does not seem to aid in this progression.

There is nothing to disagree with in my statement.  I was just posting facts.
You usually do. These look more like undefended opinions. You'll agree we've to much of that. Defend yours.

Offline rayleighscatter

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I'm not even sure Pepperidge Farm remembers when this thread was still about RS-25 production.

Offline Mark S

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Propulsive reentry of the SLS core, if workable, is not likely to be the best way to get reusability of SLS components. As others have stated the entry velocity of the core is ~7.5 km/s which is significantly faster and hotter than Falcon 9's slow 1.5km/s.

And as I pointed out up-thread, and Steven Pietrobon showed in his paper, an SLS core with six engines and a large upper stage will use up its propellants long before it reaches 7.5 km/s. From Steven's charts, I came up with about 4.5 km/s. I'm sure Steven could provide his exact calculations. While 4.5 km/s is much faster than the Falcon core at its staging event, it's still not orbital speed. And the retro/boost-back burn would cancel most of that. A lofted trajectory would also help reduce downrange speed and distance at core staging.

Quote
The SMART reuse concept may be the best way to get parts of the core back. There is a long history of SDHLV [proposal]s that use discussed recoverable engine pods.

I don't think there have been any actual SDHLVs with recoverable engine pods flown. But I could be mistaken. :)

Finally, the solids could be recovered just like they used to be with Shuttle. If nothing else, that would delay the need to begin fabrication of new steel segment casings. Or worse, the need to develop an all-new booster (Dark Knight or LRB).

The point of all this recoverability talk is to 1) stretch out supplies of engines, 2) show the Administration that NASA is not all about throwing expensive hardware in the Atlantic, and 3) enable more SLS missions with a decimated budget, which is sure to be the case in the very near future. :(

I'm not even sure Pepperidge Farm remembers when this thread was still about RS-25 production.

Pepperidge Farm memory is notoriously unreliable in the harsh environment of space. Extreme temps, cosmic rays, etc. :)

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