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BFS drops composite construction
I saw a report today that SpaceX was dropping composites for tanks and
main structure on BFS in favor of using "heavy metal" (Musk's phrase). It's unclear why the change, although it's probably a cost/schedule move. It's also unclear if this change is permanent or if it's only for early ships. Also unclear what impact this will have on payload, since BFR will now be lifting a much heavier BFS than was originally planned. All these changes are both bad and good. They're bad because of impacts to weight and such. They're probably good in that they indicate that we're close to actual development and that is driving changes. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
#2
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BFS drops composite construction
In article ,
says... I saw a report today that SpaceX was dropping composites for tanks and main structure on BFS in favor of using "heavy metal" (Musk's phrase). He Tweeted about it in replies to Everyday Astronaut. https://twitter.com/elonmusk/status/1071578086418788352 From above: Everyday Astronaut: their new Starship and Super Heavy will be all carbon composite (mostly) Elon Musk: The new design is metal Elon Musk: Fairly heavy metal, but extremely strong Everyday Astronaut: It seems like you?ve made some really big changes recently. Is this why we didn?t get a big technical rundown at #dearmoon or IAC this year? So what?s with the big mandrels at the port? Or those carbon tanks shown off for the past couple years? Elon Musk: Yes Malcom Head: Is Super Heavy in development at all, or just starship right now? Elon Musk: Both, but demo Starship is being built now, whereas Super Heavy hardware will start getting built in spring All articles I've seen afterwards don't contain any new information, just speculation beyond the original Tweets which I quoted above. It's unclear why the change, although it's probably a cost/schedule move. It's also unclear if this change is permanent or if it's only for early ships. Also unclear what impact this will have on payload, since BFR will now be lifting a much heavier BFS than was originally planned. Could be they decided composites posed too much technical risk, so they've retired that risk by switching to a more conventional metal design. All these changes are both bad and good. They're bad because of impacts to weight and such. They're probably good in that they indicate that we're close to actual development and that is driving changes. I'm also wondering if the changes had to do with the thermal protection scheme for BFS/Starship. The nice thing about metal is that it conducts heat better than a carbon fiber composite would. That might be an advantage during reentry. Jeff -- All opinions posted by me on Usenet News are mine, and mine alone. These posts do not reflect the opinions of my family, friends, employer, or any organization that I am a member of. |
#3
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BFS drops composite construction
On Dec/10/2018 at 06:54, Jeff Findley wrote :
In article , says... I saw a report today that SpaceX was dropping composites for tanks and main structure on BFS in favor of using "heavy metal" (Musk's phrase). He Tweeted about it in replies to Everyday Astronaut. https://twitter.com/elonmusk/status/1071578086418788352 From above: Everyday Astronaut: their new Starship and Super Heavy will be all carbon composite (mostly) Elon Musk: The new design is metal Elon Musk: Fairly heavy metal, but extremely strong Everyday Astronaut: It seems like you?ve made some really big changes recently. Is this why we didn?t get a big technical rundown at #dearmoon or IAC this year? So what?s with the big mandrels at the port? Or those carbon tanks shown off for the past couple years? Elon Musk: Yes Malcom Head: Is Super Heavy in development at all, or just starship right now? Elon Musk: Both, but demo Starship is being built now, whereas Super Heavy hardware will start getting built in spring All articles I've seen afterwards don't contain any new information, just speculation beyond the original Tweets which I quoted above. It's unclear why the change, although it's probably a cost/schedule move. It's also unclear if this change is permanent or if it's only for early ships. Also unclear what impact this will have on payload, since BFR will now be lifting a much heavier BFS than was originally planned. Could be they decided composites posed too much technical risk, so they've retired that risk by switching to a more conventional metal design. All these changes are both bad and good. They're bad because of impacts to weight and such. They're probably good in that they indicate that we're close to actual development and that is driving changes. I'm also wondering if the changes had to do with the thermal protection scheme for BFS/Starship. The nice thing about metal is that it conducts heat better than a carbon fiber composite would. That might be an advantage during reentry. I would think that you've got it right about thermal protection. Alain Fournier |
#4
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BFS drops composite construction
Jeff Findley wrote on Mon, 10 Dec 2018
06:54:42 -0500: In article , says... I saw a report today that SpaceX was dropping composites for tanks and main structure on BFS in favor of using "heavy metal" (Musk's phrase). He Tweeted about it in replies to Everyday Astronaut. https://twitter.com/elonmusk/status/1071578086418788352 From above: Everyday Astronaut: their new Starship and Super Heavy will be all carbon composite (mostly) Elon Musk: The new design is metal Elon Musk: Fairly heavy metal, but extremely strong Everyday Astronaut: It seems like you?ve made some really big changes recently. Is this why we didn?t get a big technical rundown at #dearmoon or IAC this year? So what?s with the big mandrels at the port? Or those carbon tanks shown off for the past couple years? Elon Musk: Yes Malcom Head: Is Super Heavy in development at all, or just starship right now? Elon Musk: Both, but demo Starship is being built now, whereas Super Heavy hardware will start getting built in spring All articles I've seen afterwards don't contain any new information, just speculation beyond the original Tweets which I quoted above. It's unclear why the change, although it's probably a cost/schedule move. It's also unclear if this change is permanent or if it's only for early ships. Also unclear what impact this will have on payload, since BFR will now be lifting a much heavier BFS than was originally planned. Could be they decided composites posed too much technical risk, so they've retired that risk by switching to a more conventional metal design. Well, that would be cost/schedule. Given his wording about "heavy metal" I don't expect it will be the 'conventional' metal. Back in the dim past around here there was a guy who proposed using swaged steels for booster construction of a 'Big Dumb Booster'. There was some weight penalty over 'conventional' materials, but he calculated that it was not as much as you might think and that construction costs would be much lower. All these changes are both bad and good. They're bad because of impacts to weight and such. They're probably good in that they indicate that we're close to actual development and that is driving changes. I'm also wondering if the changes had to do with the thermal protection scheme for BFS/Starship. The nice thing about metal is that it conducts heat better than a carbon fiber composite would. That might be an advantage during reentry. Perhaps, although I'd think a TPS would, well, 'P' from 'T' and not rely on a conducting hull, which could leave you prone to heat damage. Carbon fiber tends to be very heat resistant, which means that replacing it in exposed structures like vehicle hull will probably require some sort of refractory metal. Given the difference in density between the two, going to such a metal hull would indeed be heavy. Musk was asked several times just which metal he was referring to and avoided the question each and every time. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
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BFS drops composite construction
In article , says...
Speaking of dim past... Here's a gem from Paul D. reposting a passage about Robert Truax from Ed Regis on Thor vs Agena. Paul Dietz 2/17/94 Sea Dragon (was reviving saturn v) In article (Doug Jones) writes: snip So if all this was true, if engineering, lab tests, documentation and so forth didn't determine a launch vehicle's price tag, *what did*? Essentially, three things: parts count, design margins, and innovation. Other things being equal, the more parts a machine had, the more it was going to cost. The more you wanted it to approach perfection, the more expensive it would end up being. And finally, the newer and more pioneering the design, the more you'd end up paying for it. "We came up with a set of ground rules for designing a launch vehicle," Truax said. "Make it big, make it simple, make it reusable. Don't push the state of the art, and don't make it any more reliable that it has to be. And *never* mix people and cargo, because the reliability requirements are worlds apart. For people you can have a very small vehicle on which you lavish all your attention; everything else is cargo, and for this all you need is a Big Dumb Booster." -------------------- Paul F. Dietz "If I'd been in my grave, I'd have rolled over." R. Truax on the decision to build the Space Shuttle I think we're seeing some of these rules being applied today by SpaceX (simpler engines and reuse), but not to the extent that Big Dumb Booster would have. We'll see if much of this applies to BFR/BFS. Jeff -- All opinions posted by me on Usenet News are mine, and mine alone. These posts do not reflect the opinions of my family, friends, employer, or any organization that I am a member of. |
#7
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BFS drops composite construction
David Spain wrote on Fri, 14 Dec 2018 23:49:01
-0500: On 12/10/2018 1:39 PM, Fred J. McCall wrote: Well, that would be cost/schedule. Given his wording about "heavy metal" I don't expect it will be the 'conventional' metal. Back in the dim past around here there was a guy who proposed using swaged steels for booster construction of a 'Big Dumb Booster'. There was some weight penalty over 'conventional' materials, but he calculated that it was not as much as you might think and that construction costs would be much lower. Speaking of dim past... Here's a gem from Paul D. reposting a passage about Robert Truax from Ed Regis on Thor vs Agena. You know, I've been saying something similar to the 'small vehicle for people, big vehicle for cargo' thing for a years. Glad to see someone collected data to back that up. Musk seems about to disprove the whole thing, though, if he makes BFR/BFS work. Paul Dietz 2/17/94 Sea Dragon (was reviving saturn v) In article (Doug Jones) writes: Hey, people, if we're going to resurrect a heavy lifter from the sixties, do it right-- build Sea Dragon. Time to repost the passage from Ed Regis's "Great Mambo Chicken"... -------------------- The Sea Dragon was a launch vehicle of stupendous proportions that Truax had designed back when he was director of advanced development at Aerojet General. The best perk of that high office was the $1 million budget that he could spend any way he wanted to. Truax used it to test his pet theory that the *cost* of a rocket had nothing to do with how *big* the rocket was. You could make a given rocket just as big as you pleased and it would cost about the same as one that was about half the size, or smaller. This went against conventional wisdom and common sense, but at Aerojet Truax collected enough facts and figures to prove its truth beyond a doubt. Indeed, he'd been assembling the necessary data from the time he'd been in the navy, where he'd had access to all sorts of cost information. Take Agena versus Thor, for example. These two rockets were identical in every way: each had one engine, one set of propellant tanks, and so forth; the only significant difference between them was size. The Thor was far bigger than the Agena, but the surprise was that the *bigger* rocket had cost *less* to develop. "I was shocked to discover the Agena cost more than the Thor," Truax said later. "The Thor was between five and ten times as big! I said to myself, We've been tilting at windmills all this time! If all rockets cost the same to make, why try to improve the payload-to-weight ratio? If you want more payload, make the rocket bigger." The same anomaly cropped up again in the case of the two-stage Titan I launch vehicle: the upper stage was *smaller*, a miniature version of the lower stage, yet the smaller stage cost *more* to make. It seemed irrational, but all of it made sense once you went through the costs item by item. Engineering costs, for example, were the same no matter what the size of the rocket. "You do the same engineering for the two vehicles, only for the bigger rocket you put ten to the sixth after a given quantity rather than ten to the third or whatever," Truax said. The same was true for lab tests. "The cost of lab tests is a function of the size of your testing machine and the size of the sample you run tests on, not the size of the product." Ditto for documentation, spec sheets, manuals, and so forth. The cost here was a function of the *number* of parts and not the *size* of the parts. "There are absolutely no more documents associated with a big thing than a small thing, as long as you're talking about the same article." By this time Truax had accounted for a healthy chunk of the total cost of a given launch vehicle. About the only thing that *did* vary directly with a rocket's size was the cost of the raw materials that went into making it, but raw materials constituted only *2 percent* of the total cost of a rocket. "Two percent is almost insignificant!" he said. "And even with raw materials, if you buy a ton of it you get it at a lower unit price than if you buy a pound. And this is especially true of rocket propellants." So if all this was true, if engineering, lab tests, documentation and so forth didn't determine a launch vehicle's price tag, *what did*? Essentially, three things: parts count, design margins, and innovation. Other things being equal, the more parts a machine had, the more it was going to cost. The more you wanted it to approach perfection, the more expensive it would end up being. And finally, the newer and more pioneering the design, the more you'd end up paying for it. "We came up with a set of ground rules for designing a launch vehicle," Truax said. "Make it big, make it simple, make it reusable. Don't push the state of the art, and don't make it any more reliable that it has to be. And *never* mix people and cargo, because the reliability requirements are worlds apart. For people you can have a very small vehicle on which you lavish all your attention; everything else is cargo, and for this all you need is a Big Dumb Booster." -------------------- Paul F. Dietz "If I'd been in my grave, I'd have rolled over." R. Truax on the decision to build the Space Shuttle |
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BFS drops composite construction
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#9
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BFS drops composite construction
On 12/16/2018 7:50 AM, Fred J. McCall wrote:
David Spain wrote on Fri, 14 Dec 2018 23:49:01 -0500: Speaking of dim past... Here's a gem from Paul D. reposting a passage about Robert Truax from Ed Regis on Thor vs Agena. You know, I've been saying something similar to the 'small vehicle for people, big vehicle for cargo' thing for a years. Glad to see someone collected data to back that up. Musk seems about to disprove the whole thing, though, if he makes BFR/BFS work. Well maybe. If human transport BFS flies first. But it wouldn't surprise me one bit if BFR flies first with perhaps an uncrewed BFS cargo version which could also be used as a P2P cargo hauler. Is there more short-run potential $$ in sub-orbital cargo? Interesting question... Dave |
#10
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BFS drops composite construction
On 12/10/2018 1:39 PM, Fred J. McCall wrote:
Well, that would be cost/schedule. Given his wording about "heavy metal" I don't expect it will be the 'conventional' metal. [snip] Musk was asked several times just which metal he was referring to and avoided the question each and every time. A variant of Inconel or SpaceX's SX-300? They certainly have experience with it. Maybe they plan to spin cast it in solutionized form and weld two hemispheres after age hardening? Stupid wild ass guesses are fun... Note Wikipedia references it as useful in "pressure vessels" (under Uses, see) https://en.wikipedia.org/wiki/Inconel Dave |
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