None of these options is under the slightest consideration. Join L2 for the definitive status of SLS. The elephant mastodon in the room is indeed a hydrocarbon fueled 15m diameter monster which will be affordable due to leaner manufacturing processes, the lack of government involvement, and most of all, reusability.
...snip...These questions were all studied to death a decade ago. Multiple studies of innumerable alternative designs. The best answer nearly every time looked pretty much like the rocket now being built. - Ed Kyle
Quote from: edkyle99 on 03/12/2016 04:50 pm...snip...These questions were all studied to death a decade ago. Multiple studies of innumerable alternative designs. The best answer nearly every time looked pretty much like the rocket now being built. - Ed KyleThis is not a helpful description. The "best answer" was pushed into view by folks who in my opinion appeared highly politically biased. Does the idea of black zones or perhaps the name Michael Griffin not bring back any memories of those days? If I am remembering that time inaccurately, please let me know.
It only needs enough thrust to keep positive T/W after the SRBs stop thrusting.
Quote from: EE Scott on 03/14/2016 12:40 amQuote from: edkyle99 on 03/12/2016 04:50 pm...snip...These questions were all studied to death a decade ago. Multiple studies of innumerable alternative designs. The best answer nearly every time looked pretty much like the rocket now being built. - Ed KyleThis is not a helpful description. The "best answer" was pushed into view by folks who in my opinion appeared highly politically biased. Does the idea of black zones or perhaps the name Michael Griffin not bring back any memories of those days? If I am remembering that time inaccurately, please let me know."Black Zones"? That had nothing to do with SLS. Michael Griffin? He was gone before SLS was defined. A series of studies, including the substantial "Requirements Analyses Cycle", were performed during 2010-2011, months after President Obama sent Griffin packing. Saturn V-like RP/LOX first stages were considered, but the development costs were an issue. ORSC and J-2X would have been required. SLS won in part because the propulsion existed, or nearly existed, minimizing development cost. NASA can hardly afford SLS as it is. It never would have been able to fund a full-up new propulsion development effort. - Ed Kyle
Quote from: EE Scott on 03/14/2016 12:40 amQuote from: edkyle99 on 03/12/2016 04:50 pm...snip...These questions were all studied to death a decade ago. Multiple studies of innumerable alternative designs. The best answer nearly every time looked pretty much like the rocket now being built. - Ed KyleThis is not a helpful description. The "best answer" was pushed into view by folks who in my opinion appeared highly politically biased. Does the idea of black zones or perhaps the name Michael Griffin not bring back any memories of those days? If I am remembering that time inaccurately, please let me know.So NASA faked their own cost estimates? SLS is a good TLI launcher and it was considered cheaper in development than the alternatives. Back in 2010.
Quote from: edkyle99 on 03/13/2016 03:17 pmIt only needs enough thrust to keep positive T/W after the SRBs stop thrusting.This may be a pretty minor nitpick. The Shuttle had a T/W lower than 1:1 at SRB separation. Isn't the same true of SLS?
Quote from: Oli on 03/14/2016 09:59 amQuote from: EE Scott on 03/14/2016 12:40 amQuote from: edkyle99 on 03/12/2016 04:50 pm...snip...These questions were all studied to death a decade ago. Multiple studies of innumerable alternative designs. The best answer nearly every time looked pretty much like the rocket now being built. - Ed KyleThis is not a helpful description. The "best answer" was pushed into view by folks who in my opinion appeared highly politically biased. Does the idea of black zones or perhaps the name Michael Griffin not bring back any memories of those days? If I am remembering that time inaccurately, please let me know.So NASA faked their own cost estimates? SLS is a good TLI launcher and it was considered cheaper in development than the alternatives. Back in 2010.No I don't mean to imply that, sorry if it came off that way. I wasn't thinking specifically of SLS.
Quote from: The Amazing Catstronaut on 03/11/2016 09:55 pmQuote from: daveklingler on 03/11/2016 08:35 pmSwitching wouldn't change the timeframe that much...Sure would - the first stage engines are one of the most pivotal, complex elements of the whole LV. You switch those out and you have to change the whole design, especially when you're talking different fuel types. ...Precisely. If SLS went to a lower-performing hydrocarbon core first stage, a heavier, higher thrust second stage would be needed. It would mean bringing back J-2X. It would also mean development of a smaller in-space third stage.These questions were all studied to death a decade ago. Multiple studies of innumerable alternative designs. The best answer nearly every time looked pretty much like the rocket now being built. - Ed Kyle
Quote from: daveklingler on 03/11/2016 08:35 pmSwitching wouldn't change the timeframe that much...Sure would - the first stage engines are one of the most pivotal, complex elements of the whole LV. You switch those out and you have to change the whole design, especially when you're talking different fuel types. ...
Switching wouldn't change the timeframe that much...
In order to understand the "best" of the study, you must also investigate what were the assumptions made for the evaluation models. These assumptions can create their own set of biases funneling you to a specific design as best when it is not. SpaceX is obviously using a different set of assumptions in their models to determine "best" that result in the BFR/MCT configuration. Each different set of assumptions result in a different "best".
Quote from: daveklingler on 03/13/2016 01:50 amRegarding your assertion that the new first stage would be lower-performance, the tank mass and fuel density difference along with the relatively low difference (~50 seconds) in sea level Isp generally makes kerolox come out slightly better for first stages, which I'm pretty sure you know very well.I think you know pretty well that the SLS core stage is not a "first stage". It is a long-burning sustainer stage serving the same purpose as the Orbiter/ET combination. It provides high specific impulse above all else, much higher than only "~50 seconds" since most of its action time is in vacuum where its advantage over a hydrocarbon engine is in excess of 120 seconds ISP. It only needs enough thrust to keep positive T/W after the SRBs stop thrusting.If you replace this high-performing core stage with a hydrocarbon stage, you are going to have to make up the delta-v shortfall with a bigger, more expensive LOX/LH2 upper stage which will require higher thrust than RL10 and the like can provide. All of the studies showed that result. The proper application of a hydrocarbon engine would be as part of an SRB replacement. - Ed Kyle
Regarding your assertion that the new first stage would be lower-performance, the tank mass and fuel density difference along with the relatively low difference (~50 seconds) in sea level Isp generally makes kerolox come out slightly better for first stages, which I'm pretty sure you know very well.
SLS won in part because the propulsion existed, or nearly existed, minimizing development cost. NASA can hardly afford SLS as it is. It never would have been able to fund a full-up new propulsion development effort.
SLS won in part because the propulsion existed, or nearly existed, minimizing development cost.
NASA can hardly afford SLS as it is.
Quote from: edkyle99 on 03/14/2016 02:20 pmQuoteNASA can hardly afford SLS as it is.The cost of development is not the real issue. The cost of using an HLV every year, for decades, is the real question. And no one knows the answer to that...
This may be a pretty minor nitpick. The Shuttle had a T/W lower than 1:1 at SRB separation. Isn't the same true of SLS?
What was so wrong with using the F-1B?
Quote from: notsorandom on 03/14/2016 01:14 pmThis may be a pretty minor nitpick. The Shuttle had a T/W lower than 1:1 at SRB separation. Isn't the same true of SLS?For Block IB, its just under 1g at SRB separation. Actual acceleration is 9.5 m/sē.