Lobo's thought experiment about using Falcon cores as SLS boosters is a good way to think about how to keep development costs down. I still prefer the idea of using dual delta 4 tank sets on each side with a new thrust structure that would support 4 RS-68A engines for a total of 2.8 million pounds thrust per side. Only eight engines, using the same LH2 as the SLS core and with a potential for a flyback version in the future. This would seem to require only a new thrust structure and external attachment frame to put it into the running as an alternative to designing a entirely new booster.
Quote from: robert_d on 03/29/2013 01:30 amLobo's thought experiment about using Falcon cores as SLS boosters is a good way to think about how to keep development costs down. I still prefer the idea of using dual delta 4 tank sets on each side with a new thrust structure that would support 4 RS-68A engines for a total of 2.8 million pounds thrust per side. Only eight engines, using the same LH2 as the SLS core and with a potential for a flyback version in the future. This would seem to require only a new thrust structure and external attachment frame to put it into the running as an alternative to designing a entirely new booster.My guess is that such an arrangement might be able to lift 90 tonnes to LEO without an upper stage. It might lift 100 tonnes if propellant cross-feed was implemented, but that would require adding a fifth RS-25 to the core. But eight RS-68A engines would be too much thrust, realistically, since booster weight would always be limited by volume. Six could work and still achieve most of this performance, using either two CBC tanks per side or one new 5.5 meter diameter tank per side.In summary, RS-68A boosters would likely not beat the performance of advanced solid or kerosene boosters, but they would also not require the development of all-new engines. - Ed Kyle
My guess is that such an arrangement might be able to lift 90 tonnes to LEO without an upper stage. It might lift 100 tonnes if propellant cross-feed was implemented, but that would require adding a fifth RS-25 to the core. But eight RS-68A engines would be too much thrust, realistically, since booster weight would always be limited by volume. Six could work and still achieve most of this performance, using either two CBC tanks per side or one new 5.5 meter diameter tank per side.In summary, RS-68A boosters would likely not beat the performance of advanced solid or kerosene boosters, but they would also not require the development of all-new engines. - Ed Kyle
Quote from: sdsds on 04/01/2013 03:51 amJust to confirm: not possible to reach the 130 tonnes goal with RS-68 powered boosters that conform to the "advanced boosters" limits?130 tonnes to LEO would definitely be possible with a second stage, which any Block 2 SLS is going to require. Some additional thrust might be needed at that point, but I think it would be possible to get there without having to add more engines. RS-25 could be upgraded to 111 or 115% thrust, for example. I modeled this as follows:Two boosters, each with three RS-68A engines, GLOW 438 tonnes each.Core with four RS-25E engines, GLOW 995 tonnes (a bit offloaded).Upper stage with one J-2X (ISP=437 sec assumed), GLOW 136 tonnes.Payload 130 tonnes, ideal delta-v 9,315 meters/sec. - Ed Kyle
Just to confirm: not possible to reach the 130 tonnes goal with RS-68 powered boosters that conform to the "advanced boosters" limits?
Quote from: Lobo on 04/02/2013 05:01 pmCould you get a single hydrolox booster with three RS-68A engines, at 5.5m diameter or less? The single D4 CCB’s are already 5m diameter and 40m tall In order to feed three RS-68A’s and not be over 5.5m wide, it’d have to be like 100mt tall or something ridiculous wouldn’t it?The Advanced Booster spec actually appears to allow up to 5.78 meters diameter and a maximum length of up to 71.646 meters. Such dimensions should allow for a maximum of somewhere in the neighborhood of 500 tonnes of propellant in each booster, very roughly figuring.An RS-68 is 2.43 meters diameter, so it would fit, but there isn't a lot of room. Then again, the F-1 engines were 3.76 meters in diameter.
Could you get a single hydrolox booster with three RS-68A engines, at 5.5m diameter or less? The single D4 CCB’s are already 5m diameter and 40m tall In order to feed three RS-68A’s and not be over 5.5m wide, it’d have to be like 100mt tall or something ridiculous wouldn’t it?
As for the idea of just using a pair of CBCs on each side, that would not meet NASA's Advanced Booster specification. While a new booster tank structure would be required, the engines would already be available (largely) and since they would account for much of the booster cost, having them available and shared by another launch vehicle would be a benefit. - Ed Kyle
Maybe, but I suppose the entire premise of this thread, and my FH one is that NASA decides it would be cheaper and more sustainable to try to use existing boosters “where practicable” rather than a new 1-off custom design. A new core with existing engines is better, but I think using existing cores too is best if at all possible. And I’d sorta hope that NASA would consider it if there was a sound concept clustering two or three EELV-class boosters cores together to form “cluster” boosters rather than monolithic boosters.
Lobo,I think your whole point is exactly correct - we cannot afford an entirely new booster development program for expected flight rates of only one or two launches per year. I do not see the tank sizes needing to be changed for a Delta IV derived dual core system, because as I said, you get the required 2 minutes 10 seconds at the current size with 2 engines per core(or 4 per side). If Ed is right and you need only 3 engines, you would have even longer duration. I could imagine using the current outboard Delta IV boosters as is and just adding enough plumbing to connect to the third engine that would be built as part of the SLS adapter structure. Thrust transfer is already designed into the Delta boosters. And I do not think the current advanced booster requirements would necessarily be violated as the total "span" of the system would be under the limits at 5+8.5+5 = 18.5 at the diagonal and slightly less along the major axis.
Quote from: robert_d on 04/03/2013 01:33 amLobo,I think your whole point is exactly correct - we cannot afford an entirely new booster development program for expected flight rates of only one or two launches per year. I do not see the tank sizes needing to be changed for a Delta IV derived dual core system, because as I said, you get the required 2 minutes 10 seconds at the current size with 2 engines per core(or 4 per side). If Ed is right and you need only 3 engines, you would have even longer duration. I could imagine using the current outboard Delta IV boosters as is and just adding enough plumbing to connect to the third engine that would be built as part of the SLS adapter structure. Thrust transfer is already designed into the Delta boosters. And I do not think the current advanced booster requirements would necessarily be violated as the total "span" of the system would be under the limits at 5+8.5+5 = 18.5 at the diagonal and slightly less along the major axis. ...So maybe there wouldn’t even have to be a new whole booster per se, but a stretched (and modified)5m Delta IV booster, with a triangular MPS, widened with three RS-68A engine mounts.
This discussion has me mystified. "We cannot afford an entirely new booster development program"...the plan is to let companies submit bids. All you Delta IV "boosters" (sorry), knock yourself out--get some financing, and engineering support, and submit a bid for modified Delta IV cores as boosters. IF it turns out that just adding an engine or two, and maybe stretching the tanks along with mitigation of some of the RS-68A's thin margins, adding emergency detection, reworking the fuel-rich burning at startup, and perhaps looking at a regen nozzle--IF that turns out to be so much cheaper than an "all new" resurrected F-1 booster, or solids, or whatever else is bid, then great! Of course, it (a medium ISP hydrolox design) will also have to be at least comparable in performance to both solids and kerolox alternatives, in a task (booster) which may favor those alternatives' strengths.
The Delta IV may be the least competitive launcher in its size range, in price, in payload fraction, with safety margins not so great, without emergency detection avionics, etc. (But great reliability--I'm not knocking it too much in the task for which it was designed, as long as USAF is willing to pay for it.) I'm continually amazed how many people want to base decades of future launch systems on the tradeoffs it made for a different environment.It's not like SLS is planned to launch at some high rate which will appreciably change the economics for Delta IV, nor is a core with one or more additional engines, probably stretched, and modified in various other ways, going to roll off a standard Delta IV core production line.
This discussion has me mystified...>> and<< It's not like SLS is planned to launch at some high rate ...
The thought is that using existing hardware will be cheaper to develop than creating brand new hardware, even if the per unit price isn’t necessarily better. And it could at least –help- the economy of scale of the LV the booster is based off of. Where a dedicated purpose built booster will only fly with SLS, and you run into the problem that STS had with the ATK booster. A sole booster provider, and never launched enough to really get the cost down.
However, to your point about just letting the chips fall where they may, and maybe a new Dynetics booster would be cheaper than a D4 derived booster. I don’t think anyone has a problem with that. But NASA would need to change their bid solicitation so that some of the existing LV booster concepts could be considered and compete. As it is not, I don’t know that they could. Basically NASA’s requiring a single core purpose built to lift on the upper thrust beam, etc etc. So the purpose of this thread and the Falcon Heavy booster one is to tug on this thread a little and see if there are even ways to provide SLS boosters out of existing LV’s if NASA were to loosen their boundaries a bit.
And this is the point I’ve made here. I think Falcon 9 will the best option to look at for this concept, because it would likely be the cheapest LV that will exist, with the highest flight rate. And it will already be man-rated for commercial crew. It’ll have better thrust and smaller size due to being kerolox. Delta IV is already very expensive, so Delta IV boosters could be very expensive, and I don’t know if the SLS flight rate will be such to change that much.M1D is a US-built and designed engine, and should get built in a very high quantity if 9 are used on every core. That works in it’s favor.
However, in D4’s defense, RS-68A is about the only existing US-built large booster engine out there.
But if Dynetics could propose a brand new booster, with a new engine, that will only fly on SLS (so a low production rate), with all that new development, for cheaper than a booster based on flying hardware already in production, then by all means, go with it. But I think existing LV derived SLS boosters should be given consideration if the were technically feasible and affordable.
Quote from: a_langwich link=topic=31491.msg1034509#msg1034509 daPluste=1365015844This discussion has me mystified...>> and<< It's not like SLS is planned to launch at some high rate ...What Lobo said.Plus my point about reusibility. I am as deeply mystified that you would accept this projected low flight rate as a given. A BEO program will accomplish very little if it can only launch 130 tons or so per year for 3 billion in launch costs. Boostback for the Falcon 9's or delta 4's or my (speculative) floatback idea would be ways to start constructing a sustainable program.
But it is not existing hardware. Adding another engine, lengthening the core, changing the load environment, vibration environment, aero environment, possibly trajectory, adding in margins for human cargo--those aren't simple changes, they pretty much require re-analysis of every component, and pretty substantial redesigns. When you are done, it won't help with economies of scale of the LV it was based on, except at the part supplier level perhaps, and in the sense that ULA will have other business to help towards overhead. The RS-68 will probably be common, granted, and it may lower its marginal cost, but it will also require some redesign and testing.The pressure to do substantial redesign will be high, because putting 6-8 of these around any core will introduce base heating issues, which will make a regen nozzle desirable or necessary, which is the start of the slippery slope.I agree, it would be nice to get the launch costs down, and desirable to not have a sole-provider, low launch rate booster. But wishing that basing something on Delta IV would fix that problem won't make it so.
Quote from: robert_d on 03/29/2013 01:30 amLobo's thought experiment about using Falcon cores as SLS boosters is a good way to think about how to keep development costs down. I still prefer the idea of using dual delta 4 tank sets on each side with a new thrust structure that would support 4 RS-68A engines for a total of 2.8 million pounds thrust per side. Only eight engines, using the same LH2 as the SLS core and with a potential for a flyback version in the future. This would seem to require only a new thrust structure and external attachment frame to put it into the running as an alternative to designing a entirely new booster.No its not that would never work. Horrible suggestion.
This seems to be the most stupid "SLS improvement idea" I've yet seen.Hydrolox for boosters?Hydrolox has a very good isp, but loses to kerolox on practically all other aspects (thrust/weight, price/weight, tankage size).
Quote from: hkultala on 04/05/2013 05:24 amThis seems to be the most stupid "SLS improvement idea" I've yet seen.Hydrolox for boosters?Hydrolox has a very good isp, but loses to kerolox on practically all other aspects (thrust/weight, price/weight, tankage size).LOX/RP beats LOX/LH2 on size and, all other things being equal, on cost - but not by a large margin. Shuttle LRB studies by Martin Marietta and GD during the late 1980s showed that LOX/RP boosters had a less than 5% operational cost advantage over LOX/LH2 boosters. GD nonetheless recommend LH2 (Martin Marietta went with RP). The difference today is that RS-68 exists, while the RP engine does not, which would make a big difference in development costs. RD-180 exists, but would need to be built in the U.S., which would make it $$$$. A gas-generator RS-68 might even beat a U.S.-built staged combustion RP engine on production cost.RS-68 is a booster engine, so merits consideration - though I would suggest only for a new 5.5+ meter diameter booster. T/W is not an issue, because an LH2 booster will only weigh 70% as much as an RP booster. LH2 requires LESS thrust, and thrust costs money. RS-68 is good enough for NRO and its multi-billion dollar satellites. Why not SLS? - Ed Kyle
Why isn't thrust-to-weight an issue? Doesn't the booster have to help lift not just its own weight, but help with the core and up? And true, LH2 is lighter, but it's larger, and doesn't that structure carry weight? Doesn't an Atlas 5 core have a large T/W than a Delta IV core?
Thrust costs money, so why is Atlas 5 the preferred single-core ULA offering?
Liftoff thrust to weight ratio is the same for Delta 4M and Atlas 5-401.
Quote from: edkyle99 on 04/07/2013 05:28 amLiftoff thrust to weight ratio is the same for Delta 4M and Atlas 5-401.On the other hand, the thrust-to-weight ratio of a lower-Isp booster like the Atlas necessarily increases faster.
Quote from: a_langwich on 04/07/2013 02:50 amWhy isn't thrust-to-weight an issue? Doesn't the booster have to help lift not just its own weight, but help with the core and up? And true, LH2 is lighter, but it's larger, and doesn't that structure carry weight? Doesn't an Atlas 5 core have a large T/W than a Delta IV core? Liftoff thrust to weight ratio is the same for Delta 4M and Atlas 5-401.
This article says that RS-68 costs have dropped 30% as a result of the EELV block buy.http://www.spacenews.com/article/launch-report/34773pwr-sees-better-days-ahead-after-post-shuttle-dropoff#.UWWTnUq1Uyd - Ed Kyle
Here's a look back at Advanced Booster concepts circa 2001, as reported by MSFC. The RS-68 booster then envisioned used five engines for ATO, etc., which is more than needed for SLS. The height constraint mentioned for the Shuttle application does not apply to SLS. - Ed Kyle