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Falcon 9 questions
1. How are they going to recover the upper stage?
2. The F9-S9 appears to have 3 identical lower stages strapped together. Do they all burn out simultaneously? 3. Are the upper stage fuel tanks for the F9-S5 or F9-S9 stretched past those of the F9? If not, it would appear that second stage ignition happens at considerably higher velocity for the heavy variants. 4. The F5 is now a F9 with 4 fewer engines and less fuel in the tanks. It costs $18M instead of $27M to launch. - If price is related to cost, it would appear that more than half of the cost of the F5 rocket is in the first stage engines. I.e. if each Merlin is $2.25M, then the price of the F5 airframe is $4.5M. - Yow! Engines are pricey! 5. Are they using a single or double Merlin for the upper stage of the F9, or does it depend on LEO versus GEO? I would think a LEO F9-S9 would require several Merlins on the top stage. Anyone want to guess at the LEO payload of a F9 with: - 6 strap-on F9s - stretched core F9 tanks - an F5 upper stage (longer tanks, 5 engines) I'm guessing about 65,000 kg. Not quite what NASA is looking for in a heavy-lift vehicle. |
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"Iain McClatchie" wrote in
ups.com: 1. How are they going to recover the upper stage? A very good question, that isn't obviously answered. 2. The F9-S9 appears to have 3 identical lower stages strapped together. Do they all burn out simultaneously? Possibly, but doubtful. Throttling might be accomplished by partial engine shutdowns in the core, and depending on version and payload weight, the strapons may be partially fueled. I doubt they would attempt propellant crossfeed, at least in the immediate future. 3. Are the upper stage fuel tanks for the F9-S5 or F9-S9 stretched past those of the F9? If not, it would appear that second stage ignition happens at considerably higher velocity for the heavy variants. That's not obvious from these drawings. For cost reasons, I would think the upper stage design would be the same across all models. 4. The F5 is now a F9 with 4 fewer engines and less fuel in the tanks. It costs $18M instead of $27M to launch. - If price is related to cost, it would appear that more than half of the cost of the F5 rocket is in the first stage engines. I.e. if each Merlin is $2.25M, then the price of the F5 airframe is $4.5M. - Yow! Engines are pricey! Yes they are, though I would expect SpaceX should be getting their cost down to $1 million or less if they're building large numbers. Wonder if they are using milled wall on the Merlins? Tube bundle construction is expensive and time consuming. The turbopump assembly should be the most expensive part. The engine uses a very simple pintle injector 5. Are they using a single or double Merlin for the upper stage of the F9, or does it depend on LEO versus GEO? I would think a LEO F9-S9 would require several Merlins on the top stage. A Merlin in vacuum does 100,000 lbs/thrust; I believe that's plenty for an upper stage in this weight class. Anyone want to guess at the LEO payload of a F9 with: - 6 strap-on F9s - stretched core F9 tanks - an F5 upper stage (longer tanks, 5 engines) I'm guessing about 65,000 kg. Not quite what NASA is looking for in a heavy-lift vehicle. Hmm, you want a launcher with up to 63 (!!!) engines at liftoff? That's just begging for trouble. SpaceX plans a much bigger F-1 class engine for really heavy lift vehicles. I'm interested in their launch facility design for Falcon 9 launchers; how will the vehicle be integrated and transported to the pad? This won't be quite so simple as the Falcon 1's bare-minimum pad facility, especially for strap-on versions. --Damon |
#3
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In article . com,
"Iain McClatchie" wrote: 2. The F9-S9 appears to have 3 identical lower stages strapped together. Do they all burn out simultaneously? Wild-assed guess: no, because the strapons carry less fuel. |
#4
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One thing that might be easier than propellant crossfeed is
pressurization crossfeed: the strap-ons have helium pressurant tanks that also pressurize the core stage. The core stage pressurant system is deleted. After the strap-ons blow off the core tanks are blowdown. It's the Atlas idea again. This screws up their idea of identical airframes, of course, unless the pressurant system is easy to unbolt. One easy way to get the core to continue burning past strap-on separation would be to delete 4 engines in the core but fill the tanks completely. This reduces lift-off thrust by 17%, but you get an extra half stage. ...it also means, btw, that that core stage reenters really fast compared to a normal Falcon 5 or 9 launch. Damon For cost reasons, I would think the upper stage design Damon would be the same across all models. This is the part I don't get. Why not vary the length of the tanks? If the engines are so much more expensive than the airframe, what's the harm of having idle Falcon 9 airframes while the Falcon 5's are launching? *Especially* if they are thinking that they'll have non-reusable pricing for the first couple of years. Damon Wonder if they are using milled wall on the Merlins? Apparently the latest engine failure was due to a manufacturing flaw in the ablative combustion chamber. No milled wall or tubes in there. Damon A Merlin in vacuum does 100,000 lbs/thrust; I believe Damon that's plenty for an upper stage in this weight class. I think they've downrated that a bit. I haven't run the math on the F9, or especially the F9-S9, but the second stage in a LEO insertion usually has about 1/7 the thrust of the first stage. That says F5 has an overly heavy engine (so they'll just have to burn more gas , F9 has a slightly small engine (but maybe staging ratios are larger for LOX-kero upper stages), and a single Merlin is way too small for F9-S9 to LEO. F9-S9 to GEO could use a single Merlin though. Damon SpaceX plans a much bigger F-1 class engine for really Damon heavy lift vehicles. Here's an interesting choice for them: what size engine? Assume that you want engine-out capability on both first and second stages of the heavy lifter. That suggests 3 or 4 engines. Unless the thing is insanely big, or you are doing two new engines, you'll want 3 to 5 Merlins on the upper stage. That means the lower stage engines are around 7x the size of a Merlin -- half the size of an F-1. It's amazing to think the Saturn 5 second stage had about the same thrust as a Falcon 9 will have. Damon I'm interested in their launch facility design for Damon Falcon 9 launchers; how will the vehicle be integrated Damon and transported to the pad? Is there any fundamental problem with driving the stages to the launch area seperately, assembling the vehicle on a rail and then tilting it up? Is the issue that the tilt-up vehicle is no longer going to fit on the back of a semi or on public roads? The Army tools around with M1A1s on flatbed trailers. Would an unfueled F9 first stage weigh more than an M1A1 tank (~120,000 pounds)? Hmm... how do you move a 5.2 meter payload fairing to a launch site? I suspect that doesn't even qualify as a "wide load". |
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