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2552
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« Reply #120 on: 10/29/2011 06:15 AM » |
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For those who see this primarily as a methane SC for upper stage, and also a common fuel with the first stage, are you imagining a ratio of 9 on the 1st stage still? Or might the US be throttled down for now and the 1st stage have perhaps 3-5 engines? The reason I ask has to do with the 'ask for proposals' that came out a while ago, and SpaceX had a response that implied something more potent than Merlin1d.
Does anyone who worked on IPD now work at SpaceX?
Perhaps this version would have 3-5 SC engines on the 1st stage, and a follow-on FX equivalent (6meter core) would have 9 on its first stage at (at first). Such a next generation launcher would allow a lot more upmass for reusability hardware. The bigger factor for the sizing of the methane SC engine could be projected needs of an eventual Mars ISRU rocket, but still useful in the near term (can pay for itself or a lot of itself).
Also, it doesn't factor in yet, but if a system does become fully and rapidly reusable, then fuel cost (hopefully) might become a factor in launch costs, and methane will remain the cheapest chemical fuel.
140000lbs * 9 Merlin 1Ds = 1260000lbs. 1260000 / 5 = 252000 1260000 / 3 = 420000 420000lbs is right in the middle of the 300000 to 500000lbs thrust range specified in the RFI, so it seems unlikely SpaceX would ask if an engine that could be "evolved with minimal challenges" is acceptable if their engine design is in the middle of the specified thrust range. 252000lbs is under 300000lbs, but not too far under. It seems more likely that a 252000lb thrust engine could be evolved to 300000lbs (only a 20% increase in thrust) than could a 140000lb thrust engine (115% increase). An engine of around 252000lbs thrust with 5 on the first stage and a vacuum version on the upper stage could be it. With 5 engines in an X arrangement, there would still be a center engine that could be used alone for landing, unlike with 3 (edit: unless 3 engines are in a straight line; I was imagining a triangle arrangement). It would have to throttle down deeper than the center Merlin-1D would, probably 15-20% instead of 30-40%; 70% likely wouldn't be deep enough to be able to go just below a T/W of 1 for landing. On the FH (assuming only the adjacent engines crossfeed from the side cores), there would be 4/5ths of the engines crossfeeding instead of 2/3rds with Merlin-1D.
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go4mars
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« Reply #121 on: 10/29/2011 06:36 AM » |
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140000lbs * 9 Merlin 1Ds = 1260000lbs.
1260000 / 5 = 252000
1260000 / 3 = 420000
420000lbs is right in the middle of the 300000 to 500000lbs thrust range specified in the RFI, so it seems unlikely SpaceX would ask if an engine that could be "evolved with minimal challenges" is acceptable if their engine design is in the middle of the specified thrust range. 252000lbs is under 300000lbs, but not too far away. It seems more likely that a 252000lb thrust engine could be evolved to 300000lbs (only a 20% increase in thrust) than could a 140000lb engine (115% increase). An engine of around 252000lbs with 5 on the first stage and a vacuum version on the upper stage could be it.
With 5 engines in an X arrangement, there would still be a center engine that could be used alone for landing, unlike with 3. It would have to throttle down deeper than the center Merlin-1D would, probably 15-20% instead of 30-40%; 70% likely wouldn't be deep enough to be able to go just below a T/W of 1 for landing. On the FH (assuming only the adjacent engines crossfeed from the side cores), there would be 4/5ths of the engines crossfeeding instead of 2/3rds with Merlin-1D. Thanks for the excellent reply! Looks like sound logic. The upper stage might even just remain with a modified MVac as opposed to a vacuum version of this new engine. Is (9:1 better than 5:1) 1st stage:second stage engines a valid presumption? Is 9:1 optimised or was it a make-do tradeoff so that the US only had 1? Would second stage G's be too high with a 5:1?
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ArbitraryConstant
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« Reply #122 on: 10/29/2011 06:47 AM » |
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It's an under-determined problem. We don't know if it's going to have vac and first stage versions. We don't know the thrust or the ISP or the chamber pressure. We don't even really know the fuel. The upper stage might even just remain with a modified MVac as opposed to a vacuum version of this new engine. o_O the ISP loss would be huge. Is 9:1 optimised or was it a make-do tradeoff so that the US only had 1? My guess is part compromise, part SpaceX not being that good at throttling at the time. Would second stage G's be too high with a 5:1?
Bigger stage with a bigger engine, that potentially has deeper throttling? It might actually be a better ratio than the F9. Deeper throttling allows a bigger second stage, as well as potentially a smaller number of engines on a flyback first stage. Anyway, it's an under-determined problem. Need more information or guesses can't be ruled out persuasively.
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oldAtlas_Eguy
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« Reply #123 on: 10/29/2011 05:10 PM » |
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A 5m diameter tank is exactly 2 times the volume of a 3.6m tank of same length. That makes for a near perfect scaled vehicle using a 250-300klbf engine. All of the ratios remain the same and also the single stick might be able to be launched off an existing F9 pad. No new hangers are needed since the vehicle is the exact same length. All of the knowledge gained on the engineering of the F9 scaled by a factor of 2 then tested and adjusted makes for an inexpensive development route. This single stick 9 engined 5m diameter vehicle would have a performance of about 30 to 35MT with the heavy at about 90 to 125MT depending on actual engine thrust and ISP. Performance could easily be better. All of the design and concepts used on the F9 would be directly usable on this vehicle scaled in weight and volume by a factor of 2. The 5m diameter US with a VAC engine version of this new engine could be used on an FH as well for high energy orbits between the single stick “FX” capability and the “FXH” capability. Prices for a single stick would have to come out at ~$70-75M for it to be competitive for use on smaller payloads than just using a FH.
For a methane engine the diameter would have to be 5.65m to keep the weight and thrust ratios of the F9 but here more engineering would result making the development costs go up. But such a vehicle could have significantly more performance like 40MT for the single stick and 145MT for the heavy for only a 50% increase in prices over the F9 and FH. The reusability concepts would be directly applicable to this vehicle as well with only moderate engineering work.
KISS, a concept that SpaceX believes in and follows.
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go4mars
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« Reply #124 on: 10/29/2011 06:31 PM » |
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... the single stick might be able to be launched off an existing F9 pad. Truly fascinating thoughts Eguy! If the pad can accomodate a 5 m stage blowing perhaps 2.5 million pounds thrust, then there might be some savings (integration hangar). IIRC, the pad rollout video shows a fairly tight fit through the door, so the building would at least need a new end. I wonder how wide a stage could actually fit in there. As to the pad, even if it can accomodate the thrust, there would still need to be major reconfiguration unless the more potent 9 engines were in the same configuration as currently, but on the bottom of 5 meter tanks. Seems to me the nozzle diameter would be likely to grow a bit with a major change in thrust like that. Do staged combustion engines generally have smaller nozzles than GG for the same thrust? Even if they could keep the pad, hangar, and strongback more or less as is, SpaceX would still need almost everything required for a bigger stage anyways. So it comes down to the price of a new alternate pad & hangar, and possibly pad availability elsewhere. If it could save them $100M for a new pad and hangar, maybe they would go that route if it is somewhat in line with their perceived needs anyways. What need might they perceive in that size range? Unless someone asked them in secret for it, the only thing that comes to mind is more elaborate reusability systems. BA-2100? You could sure put a lot of extra reusability hardware/fuel, on with that excess margin. They've driven the route enough times now that it is possible that someone has measured every overpass and powerline. The configuration of their truck makes it look to me like stages could be carried closer to the pavement on a custom rig. Maybe getting oversized load permission for a 5 meter tank isn't as painful as we believe, and it might just be possible to squeeze along the interstates... for only a 50% increase in prices over the F9 and FH. Probably a little early for price assumptions on a reusable vehicle.
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oldAtlas_Eguy
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« Reply #125 on: 10/29/2011 07:54 PM » |
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The price value speaks to what would be economiclly viable for a single stick. Something that is priced higher than the low price of FH would never be used except in cases needing a larger diameter faring, thus not somthing that SpaceX is likely to develop in their quest for ever lower $/kg to LEO rates.
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SF Doug
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« Reply #126 on: 10/29/2011 08:06 PM » |
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for a 5 meter tank isn't as painful as we believe, and it might just be possible to squeeze along the interstates...
There's the rub. Max Height from pavement is 14 feet.
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krytek
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« Reply #127 on: 10/29/2011 08:20 PM » |
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for a 5 meter tank isn't as painful as we believe, and it might just be possible to squeeze along the interstates...
There's the rub.
Max Height from pavement is 14 feet.
That figure is for "repetitive" payloads (usually an annual or half annual license). It is possible to transport a 5m loads, but requires an application each time this occurs and involves lots of paperwork, validations, engineering reviews, fees and what not. In addition, the permit must be granted separately from every state the payload goes through. It's a huge mess but it can be done. Don't take word for it, I just skimmed a few US federal/state road transportation sites. So I might be wrong.
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oldAtlas_Eguy
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« Reply #128 on: 10/29/2011 08:25 PM » |
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for a 5 meter tank isn't as painful as we believe, and it might just be possible to squeeze along the interstates...
There's the rub.
Max Height from pavement is 14 feet.
Which is why ULA ships by barge.
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clongton
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« Reply #129 on: 10/29/2011 10:14 PM » |
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for a 5 meter tank isn't as painful as we believe, and it might just be possible to squeeze along the interstates...
There's the rub.
Max Height from pavement is 14 feet.
Which is why ULA ships by barge.
The Airbus A300-600ST "Beluga" can carry a 7.4 meter diameter cargo.
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Downix
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« Reply #130 on: 10/30/2011 02:34 AM » |
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for a 5 meter tank isn't as painful as we believe, and it might just be possible to squeeze along the interstates...
There's the rub.
Max Height from pavement is 14 feet.
Which is why ULA ships by barge.
The Airbus A300-600ST "Beluga" can carry a 7.4 meter diameter cargo.
NASA's pregnant guppy can do 6.7m, and Boeing's Dreamlifter can do 6.8m. (yes, I know Boeing's only built several for their own use, but if a customer came to them asking to purchase one I'm certain Boeing would at least discuss it)
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clongton
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« Reply #131 on: 10/30/2011 02:39 AM » |
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for a 5 meter tank isn't as painful as we believe, and it might just be possible to squeeze along the interstates...
There's the rub.
Max Height from pavement is 14 feet.
Which is why ULA ships by barge.
The Airbus A300-600ST "Beluga" can carry a 7.4 meter diameter cargo.
NASA's pregnant guppy can do 6.7m, and Boeing's Dreamlifter can do 6.8m. (yes, I know Boeing's only built several for their own use, but if a customer came to them asking to purchase one I'm certain Boeing would at least discuss it)
The point is that SpaceX does not have to limit itself to the roads or barges. They can put their stage on a transport aircraft and fly it to KSC.
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baldusi
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« Reply #132 on: 10/30/2011 09:47 PM » |
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The point is that they have a cheap transport infrastructure. It would be easier to develop a bigger fairing for current vehicle, than complicate things so much. In fact, they could go with a fairing as big a 7.2m and still keep the current transport. And I don't see any payloads needs over what they more than cover currently.
As any company with limited funds, I expect them to focus on actually making launches with current LV. And try to develop a fully returnable LV. Only after achieving that, and I think a high efficiency engine is a fundamental part of that, they might try a bigger LV.
Let's remember, that once they develop a RLV, they could use it to transport itself to the launch pad. Once they are there, you can go as big as you can see a business case for.
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sdsds
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« Reply #133 on: 10/31/2011 04:18 AM » |
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As any company with limited funds, I expect them to focus on actually making launches with current LV. That's logical, even if it doesn't seem to be the way Musk sees things. For example, they did not focus on making launches with their (then current) Falcon 1! (Perhaps NASA will try to subtly push SpaceX into behaving as you expect them to, i.e. by purchasing from them additional cargo Dragon flights?)
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john smith 19
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« Reply #134 on: 10/31/2011 11:44 AM » |
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The point is that they have a cheap transport infrastructure. It would be easier to develop a bigger fairing for current vehicle, than complicate things so much. In fact, they could go with a fairing as big a 7.2m and still keep the current transport. And I don't see any payloads needs over what they more than cover currently.
As any company with limited funds, I expect them to focus on actually making launches with current LV. And try to develop a fully returnable LV. Only after achieving that, and I think a high efficiency engine is a fundamental part of that, they might try a bigger LV.
Good points. Those less common transport methods are available for large size loads but they add costs to *every* vehicle made in raw cash (lots of trucking companies to get a quote off versus how many barge operators?) as well as time, staff and schedule inflexibility. Things that matter if you want to operate in a true commercial way. Let's remember, that once they develop a RLV, they could use it to transport itself to the launch pad. Once they are there, you can go as big as you can see a business case for.
The ability to "self ferry" is a neat trick that *no* ELV can match. But note it is not *universal* and depends on the architecture details. A reusable F9 stg 2 *should* be able to self ferry, but what about carrying a Dragon as well? Note also the air traffic control issues have not (AFAIK) been resolved regarding VTVL (and I'm not sure the status is much better with HTHL concepts) given the flights of Xcor's EZ jet needed a license for *every* takeoff. To return to the topic of this thread who might this anonymous customer for this Methane fueled SC engine *be*? They can put enough cash on the table to divert some (all?) of the Spacex propulsion team onto a large totally different engine technology project using a totally different fuel, while letting them use it for a USAF RFP submission. This is at a time when Spacex is well into the development of both reusability of the F9 ( a restart of the sea level version of the Merlin has *never* been done. the Merlin vac version has AFAIK but you'd want to be *very* sure you'd covered all contingencies before you tried slowing down several mT of stage moving at >>M1) and the Dragon LES. Given this started in April with a best case length of 30 months it seems a bit early to be looking at other work. Boeing hired Xcor to look at effectively doing a version of the RL10 at more reasonable prices (which is an interesting comment on the economics of space component procurement versus development, given they *own* it). I suspect finding out would tell people quite a lot about how serious Spacex are about pursuing this for their own benefit. Note that Spacex have shown themselves willing to sacrifice performance for cost. That said their engineering has been good enough to deliver impressively efficient (in terms of T/W and mass fraction) engines and stages. With Musk saying fuel is c0.5% of launch cost (versus 10s of $m chasing that last few secs of Isp) this seems a pretty good trade. I suspect their decision to launch those Orbcomm sats on the F9 to ISS (rather than the 1e) was also partly driven by not wanting to build another pressure fed stag 2/Kestrel with *no* other firm customers in the near term.
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