And RS-25 is the former Shuttle Main Engine that is planned to be used on Boeing/ULA's Space Launch System: Space Shuttle main engine - Wikipedia
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SLS and the RS-25 engines discussion
- Thread starter e-FTW
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Does anyone know how much the RS-25 for SLS is improved from the original used in Space Shuttle?
Would it be near the same parts/hardware as the original engine? Has Rocketdyne published it's target performance specs?
Are those improved significantly over the original?
The RS-25 engines are exactly the same as the ones that flew on the Space Shuttle. The RS-25 engine manufacturing line was shut down years ago. The first couple flights of SLS would actually use the engines pulled out of the Shuttles.
Space Shuttle main engine - Wikipedia
Here is an article talking about restarting production of the RS-25:
NASA defends decision to restart RS-25 production, rejects alternatives – NASASpaceFlight.com
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I've said this before and I will say it again: Basing any new launcher (SLS) on heritage engines that will not be reused means the SLS is dead on arrival compared to the F9 or FH. Let alone the BFR. So they are going to build enough single use RS-25 engines plus using old SSME's to launch 4-5 SLS missions.
Apologies for being so far sighted, but then what?
RT
I've said this before and I will say it again: Basing any new launcher (SLS) on heritage engines that will not be reused means the SLS is dead on arrival compared to the F9 or FH. Let alone the BFR. So they are going to build enough single use RS-25 engines plus using old SSME's to launch 4-5 SLS missions.
Apologies for being so far sighted, but then what?
RT
Here an article that really gets into it.
All the way to orbit: After 35 years, is the RS-25 still the Ferrari of rocket engines?
Since this article was written by people that care it doesn't pull any punches.
Hmmm, $1.5B for six engines means $1B per launch, just for the 4 engines. Good thing they only want to do one launch per year, eh?
To be fair, the 1.5B also includes hiring everyone, restarting the manufacturing lines, and requalifing everything including suppliers. Might only be 600 million worth of engines destroyed each launch.
Also to @Bobfitz1 question, I think the article said the new 25s are slightly cheaper due to the lack of reusability, but basically straight carry over/ reuse.
Man, what a gorgeous burn. Can’t believe they’re just going to throw these things away.
Mike1080i
Member
Yep, and the 5 segment SRBs as well, all at the bottom of the Atlantic. I want heavy lift capability, but am against SLS as the method, for this and other reasons. Besides I'd like to see these engines returned to RS-25D spec and reinstalled on the orbiters in museums.Man, what a gorgeous burn. Can’t believe they’re just going to throw these things away.
Man, had no idea this would diverge into a whole discussion, and (rightfully) a separate thread! Geeks, what are you gonna do...
The SSMEs were re-usable, since the Shuttle was re-usable. So the RS-25s are single use, even though the original design is re-usable. Does seem like a waste. Wonder how much performance/weight is lost there.
The SSMEs were re-usable, since the Shuttle was re-usable. So the RS-25s are single use, even though the original design is re-usable. Does seem like a waste. Wonder how much performance/weight is lost there.
Mike1080i
Member
IMHO RS-25E wasn't the right choice for SLS. But there are reasons for using it... Congress mandated that SLS be built using Shuttle system parts and specified its lift capability. Oh well, if it ever flies, I guess I'll head down to the Cape to watch. It's first flight may be the only one SLS ever gets.
Welp, reading the above article, I got an answer:
“By the end of the shuttle program, the engine was running at 104.5 percent of its original power output. For SLS, that number jumps to 109 percent. That strains the engine and compromises reusability (which no longer matters), but it's still within safety tolerances. Aerojet's next version of the RS-25 will aim for 111 percent.”
A fantastic read this: All the way to orbit: After 35 years, is the RS-25 still the Ferrari of rocket engines?
RS-25 is pretty bad ass. Especially when you consider that it's still going once Falcon 9 separates and a single MVAC is left to power the second stage.
Of course, that is apples to oranges, and I should compare to BFR. But comparing to what we see today is also important.
(BTW, I notice that this article compares RS-25 to Merlin. Seems odd.)
No question that the RS-25 are some seriously great engines. The wiki article says they only made 46 of them for all of the Shuttle flights. So they did really well on the reusability front for a hydro-lox engine. At $400 million each, they better be great though. A Merlin, from what I've read, is about $1 million each. I think SpaceX will be pretty happy if the much more complex Raptor comes in at somewhere between $1 million and $2 million each.
Here are the specs for a single RS-25 running at 109%:
Thrust (vac.) 512,300 lbf (2,279 kN)
Thrust (SL) 418,000 lbf (1,860 kN)
Chamber pressure 2,994 psi (20.64 MPa)
Isp (vac.) 452.3 seconds (4.436 km/s)
Isp (SL) 366 seconds (3.59 km/s)
Here are the specs for a single Raptor:
Thrust (vac.) 1,900 kN (430,000 lbf)
Thrust (SL) 1,700 kN (380,000 lbf)
Chamber pressure 250 bar (25 MPa; 3,600 psi)
Isp (vac.) Sea-Level: 356 s
Vacuum: 375 s
Isp (SL) Sea-Level: 330 s
So, considering the Raptor is a much smaller engine, it packs a serious punch.
Thanks for the comparison.
This is why Congress should not mandate mission design and specifications. Set the mission objective, listen to the experts, provide a budget, and step back.
For manned spaceflight NASA has become irrelevant. SpaceX and BO are the future of manned spaceflight.
Considering that on the SLS the RS-25 is single use, the Raptor cost is tiny on a per flight basis over the lifetime of the engine.
This is why Congress should not mandate mission design and specifications. Set the mission objective, listen to the experts, provide a budget, and step back.
For manned spaceflight NASA has become irrelevant. SpaceX and BO are the future of manned spaceflight.
IMHO SLS is completely a pork barrel project. They specified the engines and solid strap ons mainly to keep various Congressmen's businesses receiving federal money.
At over $1B per launch, I'm pretty doubtful there will be very many.
At over $1B per launch, I'm pretty doubtful there will be very many.
You won't get any arguments here. SLS is what it is. It doesn't change the fact that RS-25 engines are great engines.
It does explain the history of SpaceX where Elon looked at the costs of rockets and said that it was crazy. If you simply look at what a rocket or engine is made of on an elemental level then there is no justification for the crazy high cost. $400 million each for these great engines is still a ridiculous number. Cost-wise you build 10 Falcon 9's completely for the cost of one of these engines. You could probably build 200+ Raptor engines for the same cost.
For a billion, SpaceX could probably build the first BFR/BFS from scratch.
Correct numbers for Raptor:
Sea-Level Nozzle
Exit Diameter 1.3 m
Thrust (SL) 1700 kN
ISP (SL) 330 s
ISP (Vac) 356 s
Vacuum Nozzle
Exit Diameter 2.4 m
Thrust (Vac): 1900 kN
ISP (Vac): 375 s
Methane has higher density than hydrogen. So methane engine has higher trust/size. Higher chamber pressure also increases trust/size. Advantage of hydrogen is high ISP, disadvantage is large fuel tank and engines. New materials enable lighter fuel tanks, so hydrogen becomes more common.
So my question is: How much do you think it would cost SpaceX to build equivalent engines?
They don't seem to want to get involved in HydroLox engines, for very understandable reasons, but still. As you say $400M for an engine seems pretty ridiculous.
OFF TOPIC: I'm not trying to start a flame war (really), but what do you think it would cost a company with the esprit of SpaceX to build an F-35 equivalent? Or a Tomahawk missile.
Good question. Realistically, I think the first one might be about $100 million. Thereafter I think it would be about $10 to $20 million each. They are a big engine. Of course this is pure guesswork. I'm trying to work like Elon on this and really consider what is the actual cost of the stuff (probably around $1 million of actual metal, plumbing, and hardware) compared to what it really costs to make the pieces needed. The first engine would take building the machines to make the parts which makes it's much higher initial price. Once that is complete then it is just making the parts over and over. $10 to $20 million each under an Elon company and manufacturing style is my guess.
Off topic answer. Very interesting. I've had the same thoughts myself. Elon style company in military manufacturing. Specifically the F-35 too. I'd expect a 100% improvement in cost. Similar to the RS-25 engines, our people can design a great machine. So I don't think the F-35 would be a bad multi-role fighter jet. However, the military industrial complex is bogged down in exactly the same way that ULA and NASA have been bogged down. I am not against a strong military but I expect that military spending is an area that has become ridiculously wasteful. It desperately needs an Elon Musk type disruptor. I can't imagine Elon ever being interested in such a thing since it is not about improving the world. I remember being at a science fiction convention where the military had hired a bunch of writers to discuss where "improvements" could be made. That was 25 years ago. Only recently have I seen some of the concepts they discussed getting some traction.
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