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dwightlooi
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« on: 06/27/2012 06:27 AM » |
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Does anyone know why SpaceX settled on the 3.6m diameter for the Falcon 9? Is it because that is the limit that is easily transportable by truck or rail?
The reason I am curious about this is that a 5m core diameter (ala Delta IV) would have the following advantages:-
* Greater mass efficiency (less aluminum wall area for the same fuel volume)
* Eliminate the need for fairings on the 4 outermost engines
* Make the rocket shorter and easier to control (especially with 1.1/heavy versions)
* Make it a lot less likely that the interstage may scrap on the upper stage nozzle
* Matches the diameter of the payload fairing
* Allow for better compatibility with CST-100 and Orion
Disadvantageous are few:-
* Dragon, as it is currently designed, will need a truncated cone style trunk
* Aerodynamic losses is very slightly higher (but actually better than with a 5m fairing on a 3.6m core)
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« on: 06/27/2012 06:27 AM » |
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Joel
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« Reply #1 on: 06/27/2012 06:40 AM » |
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I have a related question, which I think fits the same thread:
"Will having a 3.6m diameter become _less_ important once SpaceX ramps up production numbers?"
I could imagine that considerable fixed investments would be needed for air transport, as in buying and modifying an aircraft, but once these are in place, operating costs should be manageable.
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simonbp
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« Reply #2 on: 06/27/2012 06:48 AM » |
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Does anyone know why SpaceX settled on the 3.6m diameter for the Falcon 9? Is it because that is the limit that is easily transportable by truck or rail?
Yes. Delta IV needs its own special barge to get it from Decatur to the launch pad. Falcon 9 can just be driven to the pad by commercial contractors. So, SpaceX avoids the recurring costs of having to maintain its own transport infrastructure. Also, they have a lot more flexibility in when they ship things, and how often they do it. As it was, BTW, they actually had to partially disassemble the wall of their old El Segundo plant to get the first Falcon 9 first stage out...
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dwightlooi
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« Reply #3 on: 06/27/2012 07:05 AM » |
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Yes.
Delta IV needs its own special barge to get it from Decatur to the launch pad. Falcon 9 can just be driven to the pad by commercial contractors. So, SpaceX avoids the recurring costs of having to maintain its own transport infrastructure. Also, they have a lot more flexibility in when they ship things, and how often they do it.
As it was, BTW, they actually had to partially disassemble the wall of their old El Segundo plant to get the first Falcon 9 first stage out...
Speaking of that, it's odd that they would do their manufacturing in California, testing in Texas and launching in Florida, California and to a lesser extent the Marshall Islands. Wouldn't it be better to consolidate everything in Texas? Especially on the south coast? Build there, test there, wheel it out and launch right in the backyard of the facility? Besides land is (relatively speaking) cheap in Texas. Texas is also a Right to Work State and has no State Income Tax. Why design and build in arguably the most expensive and (regulation wise) frustrating state to run any business. Test all the way in the middle of Texas instead of a coastal Texan test site that can also double as a launch site? And then launch at Cape Canaveral where the range schedule collision which everyone else happens all the time?
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Lars_J
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« Reply #4 on: 06/27/2012 07:22 AM » |
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The reason I am curious about this is that a 5m core diameter (ala Delta IV) would have the following advantages:-
...
* Make the rocket shorter and easier to control (especially with 1.1/heavy versions) I think a longer rocket is actually easier to control, but I could be wrong. Think of how much easier it is to balance something taller on your finger compared to something shorter. I think (correct me if I am wrong) that the 3.6 diameter stage originated with the Falcon 5. Presumably it was selected because it was relatively easy to transport, and a good fit for that rocket. With Falcon 9 (and now F9 v1.1), the core has simply been stretched.
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Jason1701
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« Reply #5 on: 06/27/2012 07:22 AM » |
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Yes.
Delta IV needs its own special barge to get it from Decatur to the launch pad. Falcon 9 can just be driven to the pad by commercial contractors. So, SpaceX avoids the recurring costs of having to maintain its own transport infrastructure. Also, they have a lot more flexibility in when they ship things, and how often they do it.
As it was, BTW, they actually had to partially disassemble the wall of their old El Segundo plant to get the first Falcon 9 first stage out...
Speaking of that, it's odd that they would do their manufacturing in California, testing in Texas and launching in Florida, California and to a lesser extent the Marshall Islands. Wouldn't it be better to consolidate everything in Texas? Especially on the south coast? Build there, test there, wheel it out and launch right in the backyard of the facility? Besides land is (relatively speaking) cheap in Texas. Texas is also a Right to Work State and has no State Income Tax.
Why design and build in arguably the most expensive and (regulation wise) frustrating state to run any business. Test all the way in the middle of Texas instead of a coastal Texan test site that can also double as a launch site? And then launch at Cape Canaveral where the range schedule collision which everyone else happens all the time?
Because Elon thinks the best people and culture are in California.
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Jim
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« Reply #6 on: 06/27/2012 11:05 AM » |
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And then launch at Cape Canaveral where the range schedule collision which everyone else happens all the time?
Because that is where most of the payloads are. Can't get to ISS or other non GTO orbits (besides polar). The range schedule thing is overblown too.
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Jim
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« Reply #7 on: 06/27/2012 11:11 AM » |
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* Make the rocket shorter and easier to control (especially with 1.1/heavy versions)
* Make it a lot less likely that the interstage may scrap on the upper stage nozzle
* Matches the diameter of the payload fairing
* Allow for better compatibility with CST-100 and Orion
Not necessarily true It isn't going to happen as is that is not true, there may be smaller fairings Orion is not going to fly on it, most likely neither is CST-100
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kevin-rf
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« Reply #8 on: 06/27/2012 01:07 PM » |
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It is worth pointing out that LH is less dense than Kero so you need a larger volume to hold it. That is what drove the 5 meter Delta IV's diameter.
As a point of comparison the LH fueled Delta IV medium has a lift off mass of ~250,000 kg with a volume of ~1200 m^2 while the Atlas V 401 lifts about the same but weighs 33% more at ~335,000kg in half the volume, ~660 m^2.
When you use LH you have a much bigger (higher dry weight) rocket.
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Idiomatic
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« Reply #9 on: 06/27/2012 02:53 PM » |
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If they get reliable reusability working, diameter for future vehicles becomes a more interesting question. I think reusability is already currently part of the explanation; If the goal is to have the thing fly back within the next 10 years or so, then investing in a hugely costly shipping system is problematic. You end up left with useless and hard to sell crap. And in the meanwhile you end up spending millions on shipping. Currently, with trucks, SpaceX has more operational flexibility. The CST-100 CAN launch on a falcon 9. It isn't likely to happen, but they have kept that option open. Spending to raise the chances of that happening by maybe a percentage point would be a waste. http://www.sen.com/Uploads/misc/boeing-cst-100-atop-spacex-falcon9-artist-400px.jpgAlso, the statement about california is funny. If cali were the worst state to do business then it wouldn't be the highest GDP state in the country by a looong shot.
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simonbp
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« Reply #10 on: 06/27/2012 03:20 PM » |
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Also, the statement about california is funny. If cali were the worst state to do business then it wouldn't be the highest GDP state in the country by a looong shot.
It's also got the highest state debt and an increasing tax burden because of it. Texas has neither of those things, which is why in a recent ranking, Texas was ranked the best state for business and California the worst. Florida was second, BTW. Getting back to SpaceX, they have invested a lot in their California assembly facility and so aren't going to just abandon it. But, it's clear that all the new facilities are going elsewhere, mainly Texas and Florida. Fancy that.
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Lee Jay
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« Reply #11 on: 06/27/2012 03:24 PM » |
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Does anyone know why SpaceX settled on the 3.6m diameter for the Falcon 9? Is it because that is the limit that is easily transportable by truck or rail? It's certainly not the biggest diameter that's relatively easily transported. As I work in wind energy, we push up against that limit all the time for shipping towers. That limit is about 4.2 meters for over-the-road trucking and not coincidentally almost all on-land wind turbines sit on towers that are 4.2 meters in diameter at their bases.
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bob the martian
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« Reply #12 on: 06/27/2012 03:57 PM » |
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Yes.
Delta IV needs its own special barge to get it from Decatur to the launch pad. Falcon 9 can just be driven to the pad by commercial contractors. So, SpaceX avoids the recurring costs of having to maintain its own transport infrastructure. Also, they have a lot more flexibility in when they ship things, and how often they do it.
As it was, BTW, they actually had to partially disassemble the wall of their old El Segundo plant to get the first Falcon 9 first stage out...
Speaking of that, it's odd that they would do their manufacturing in California, testing in Texas and launching in Florida, California and to a lesser extent the Marshall Islands. Wouldn't it be better to consolidate everything in Texas? Especially on the south coast? Build there, test there, wheel it out and launch right in the backyard of the facility? Besides land is (relatively speaking) cheap in Texas. Texas is also a Right to Work State and has no State Income Tax.
Why design and build in arguably the most expensive and (regulation wise) frustrating state to run any business. Test all the way in the middle of Texas instead of a coastal Texan test site that can also double as a launch site? And then launch at Cape Canaveral where the range schedule collision which everyone else happens all the time?
Because the people with the education and expertise you want don't live in South Texas, and it would be hard to entice them to move there. Yes, land is cheap. Yes, we're a rabidly anti-union state. Yes, we have no state income tax (which we make up for with some of the highest property taxes in the nation). We also a substandard public education system (which the Texas GOP is determined to make worse), a low public health ranking, below average median income, etc. Texas may be a good state to do business in, but if you actually want to live here, it's another story.
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Lars_J
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« Reply #13 on: 06/27/2012 04:10 PM » |
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Also, the statement about california is funny. If cali were the worst state to do business then it wouldn't be the highest GDP state in the country by a looong shot.
It's also got the highest state debt and an increasing tax burden because of it. Texas has neither of those things, which is why in a recent ranking, Texas was ranked the best state for business and California the worst. Florida was second, BTW.
Getting back to SpaceX, they have invested a lot in their California assembly facility and so aren't going to just abandon it. But, it's clear that all the new facilities are going elsewhere, mainly Texas and Florida. Fancy that.
I don't think California was rated much better when SpaceX started, yet they still chose to be there. Fancy that. And despite your ranking, they have proved that American ingenuity and manufacturing capability can exist there just fine. Imagine that.
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SpacexULA
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« Reply #14 on: 06/27/2012 04:37 PM » |
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Elon Musk addressed them being in California in an interview (sorry can't remember the link), he stated that the greater Las Angeles metro area (including Hawthorne and El Segundo CA) had one of the highest concentrations of aerospace engineers in the country.
Why are there so so many aerospace engineers in that area anyway? When he made the statement it sort of threw me off. Is Boeing's footprint in that are that big?
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