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Downix
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« Reply #15 on: 07/31/2010 01:24 AM » |
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There is also the Dreamlifter as well:
http://en.wikipedia.org/wiki/Boeing_747_Large_Cargo_Freighter
Dreamlifter is less than 6 meter across ID. To my knowledge only Airbus Beluga lifters and the Antonov_An-225 would be capable of carrying a 6 meter stage.
That does not add up, as then it cannot do it's job in transporting the 6m wide 787 components. (787 Fuselage is 5.97m across) The Fuselage of the Dreamlifter is 8.3m wide, and the walls do not look to be over a meter thick....
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SpacexULA
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« Reply #16 on: 07/31/2010 01:48 AM » |
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There is also the Dreamlifter as well:
http://en.wikipedia.org/wiki/Boeing_747_Large_Cargo_Freighter
Dreamlifter is less than 6 meter across ID. To my knowledge only Airbus Beluga lifters and the Antonov_An-225 would be capable of carrying a 6 meter stage.
That does not add up, as then it cannot do it's job in transporting the 6m wide 787 components. (787 Fuselage is 5.97m across) The Fuselage of the Dreamlifter is 8.3m wide, and the walls do not look to be over a meter thick....
Deleted my incorrect post. Your right, I was referring a bum source. Sorry  787 fuselages are 6.5 meters, so the 6 meter stages would not be a likely issue.
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Robotbeat
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« Reply #17 on: 07/31/2010 03:26 AM » |
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It's kind of expensive to be transporting it via airplane. I'm guessing they'd use a ship. But really, Super-Heavylift, $1 billion engine development program, Nuclear-thermal rockets... this seems a little incredulous to me... It's all technically possible, but a little outlandish. At least SpaceX has not stopped dreaming (which may be another problem, of course). Good luck! You'll need it. I do like that they're looking at the solar-electric tug, though... That's one of my favorite hobby-horses! There's also barging it from Hawthorne to the Cape through the Panama Canal.
Also, anyone see how they're planning on Raptor having a 470s vacuum Isp? That's a *very* tall claim, which I'm likely to call Incorrect on unless they've got some very good numbers or hotfire tests to back it up. SSME is 453s vacuum, by comparison.
I agree that 470s is a tall claim, but remember that the SSME is a ground-lit engine, which generally means the vacuum Isp is less than an equivalent air- or vacuum-lit engine. It still gets good vacuum Isp only because its chamber pressure is so high. If you put a big bell on the SSME, you'd get somewhat better Isp than 453s (perhaps around 470s), but it wouldn't work at sea level anymore. There have been all sorts of engine development projects which shot for ~470s Isp or higher with hydrolox, but none have been very fruitful, perhaps because it just wasn't worth the extra cost/effort rather than just running at, say, 460s Isp.
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Antares
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« Reply #18 on: 07/31/2010 03:41 AM » |
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Sigh, another thread I'll never read. All conjecture, no facts.
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neilh
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« Reply #19 on: 07/31/2010 06:33 AM » |
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Sigh, another thread I'll never read. All conjecture, no facts.
Did you miss the presentations in the initial post?
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Damon Hill
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« Reply #20 on: 07/31/2010 06:43 AM » |
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If I read the flow diagram correctly, the Raptor is a staged combustion engine--it'd have to be to get such a high Isp even with a fully-expanded nozzle. Thus, like the elegant RL10 and (most?) other expander cycle engines, it is a closed-cycle engine in which the entire propellant mass passes through the combustion chamber/throat/expansion nozzle to achieve the maximum possible exhaust velocity, rather than dumping the gas generator's working fluid out a low pressure duct.
Raptor is different from expander cycle engines in that its hot gas generator/turbopumps are apparently more powerful than an expander cycle's "warm gas" heat exchanger can be, and as such it may be the first vacuum-optimized staged-combustion hydro/lox engine. Hence the very high Isp >and< high thrust.
There have been efforts to design very high Isp hydro/lox engines, but they had limited thrust apparently as a result of the limited energy that could be extracted from absorbing heat from the combustion chamber and exhaust nozzle.
I'm guessing Raptor is just another one of those optimized compromises; a higher Isp might have been possible via much higher SSME-type pressure and temps, but that gets difficult and expensive fast. Here's hoping they can get that 470 sec performance figure. It won't be any less of a design challenge.
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alexw
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« Reply #21 on: 07/31/2010 08:49 AM » |
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I'm guessing Raptor is just another one of those optimized compromises; a higher Isp might have been possible via much higher SSME-type pressure and temps, but that gets difficult and expensive fast. Here's hoping they can get that 470 sec performance figure. It won't be any less of a design challenge.
Staged-combustion in an upper stage (pure vacuum bell) seems quite rare, but the isp gain is impressive: NK-43: 346 sec / 395 klbs RD-0124: 359 sec / 66 klbs compare to something like RD-180/191/ at 338 isp (vac), or compare to Merlin Vacuum at 342 sec / 92klbs (most any other gas generator kerolox has vac isp in the 320's or so, no?) Are there any other staged-combustion upper stage engines? Hypergolic? Looking at LE5 (450sec) and HM7B (444sec), picking up 20-25 seconds by going gas generator -> staged combustion looks, uhh, not completely crazy ... but this is hardly a valid extrapolation process. They must have some reason for believing that it's easier to develop staged combustion than to develop a big expander cycle (RL-60, Vinci) and use multiple engines to get the thrust they need. (Although there's a reference somewhere arguing that ~60klbs need not in fact be an upper limit on expander motors). Sounds gutsy, regardless. If it was easy, wouldn't J-2X have gone that route? -Alex
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MP99
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« Reply #22 on: 07/31/2010 08:50 AM » |
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Also, anyone see how they're planning on Raptor having a 470s vacuum Isp? That's a *very* tall claim, which I'm likely to call Incorrect on unless they've got some very good numbers or hotfire tests to back it up. SSME is 453s vacuum, by comparison.
I agree that 470s is a tall claim, but remember that the SSME is a ground-lit engine, which generally means the vacuum Isp is less than an equivalent air- or vacuum-lit engine. It still gets good vacuum Isp only because its chamber pressure is so high. If you put a big bell on the SSME, you'd get somewhat better Isp than 453s (perhaps around 470s), but it wouldn't work at sea level anymore.
At 250:1, Raptor is planned to have well over 3x the expansion ratio of SSME. cheers, Martin
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rklaehn
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« Reply #23 on: 07/31/2010 09:05 AM » |
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Repost from another thread:
Here is the presentation as a pdf, so everyone can read it (converted with open office).
The conversion is not perfect, but better than nothing if you don't want to install a pptx viewer.
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madscientist197
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« Reply #24 on: 07/31/2010 09:14 AM » |
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Points:
* They're claiming that Merlin 2 will have a T/W of 150! The highest T/W of any engine (that I aware of) is the NK33 with ~136. The F1 was only 94.
* Three Merlin 2s at 70% throttle for engine out capability.
* WTF is with the dead sea scrolls reference?
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Nascent Ascent
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« Reply #25 on: 07/31/2010 09:38 AM » |
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It's nice to have something to look forward to... for a change.
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rklaehn
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« Reply #26 on: 07/31/2010 09:38 AM » |
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It's also interesting that they're sticking with gas generator cycle for the Merlin 2 instead of staged combustion.
Not surprised one bit about this. A simpler engine cycle plus it solves the problem of having a separate roll control system when it's used as drop in replacement for F9 first stage (look at the diagram in the 2nd post).
I am not sure if they are planning to use the gas generator exhaust for roll control. It looks like they plan to feed it into the engine bell like the f1 did. They could have two different bell designs for the 1 engine and the 3 engine config, but that would probably not be a good idea.
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rklaehn
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« Reply #27 on: 07/31/2010 09:42 AM » |
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* WTF is with the dead sea scrolls reference?
It's a joke. Black water (=oil) shall elevate thy children (=mankind) to the heavens (=space). But I don't get the other part. Probably because I am not familiar enough with ancient hebrew units of currency and measurement :-)
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MP99
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« Reply #28 on: 07/31/2010 09:53 AM » |
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It's a joke. Black water (=oil) shall elevate thy children (=mankind) to the heavens (=space). But I don't get the other part. Probably because I am not familiar enough with ancient hebrew units of currency and measurement :-)
nor shalt thou burn rocks
Rock = coal = solid fuel = SRB's. cheers, Martin
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marsavian
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« Reply #29 on: 07/31/2010 11:11 AM » |
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The greatest sin of the budget debate will be choosing a no-competition rocket. Crushing the ambition and capabilities of such unique companies (like ULA and SpaceX) will be a real sin. But the demand for "job creation" is stronger than just about anything else.
Or maybe they want something derived from a vehicle that already works and is minimum risk, cost and schedule to develop but of course others can see what best fits their world view. So why is SpaceX developing HLVs beyond Saturn V when we are told incessantly by the NuSpace crowd they are not necessary ? Also why would the DoD develop a 1.7mlbf RP-1 engine now if SpaceX are already doing this and NASA won't be doing one now ?
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