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BFS drops composite construction
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#13
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BFS drops composite construction
On 12/16/2018 9:22 AM, Jeff Findley wrote:
I think it far more likely that BFR/BFS would be certified for taking people into space and back since the FAA requirements for that are far less strict than for passenger jet aircraft. I agree with this point. I'm thinking SpaceX is going to try to argue that even as a P2P transport, it goes "into space" and therefore shouldn't have to meet the strict safety rules that a passenger jet aircraft would have to meet. I also agree with you that SpaceX will try to keep this in the space domain as long as possible, until it becomes routine enough for the FAA to be willing to adopt the rules needed to allow this to remain commercially viable. I personally give this a slim chance of actually happening. When it comes to rule making this technology is in the same domain as was aviation in the 1930s. Who knows what the *right* rules are? This is not a jet aircraft by any stretch. We agree to disagree on this point. There is a market to cut the appalling trans-oceanic travel times, esp. trans-pacific. And opening new flight routes, such as Euro-Pacific. This seems the most promising (to me) over the other options such as SST and HST, which I doubt could be made as economical as this approach promises. Also note: if the FAA becomes obstructionist, it doesn't have to be the USA that opens the market. SpaceX is a private company. It can set up trials wherever it is welcome. Dave |
#14
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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 |
#15
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BFS drops composite construction
Meanwhile, Boeing continues work on composite tanks for the Phantom Express:
"This vehicle will be the first space vehicle to utilize the much lighter composite cryotanks, saving nearly 40 percent of weight from comparable aluminum tanks. All of these innovative measures will help Phantom Express achieve its operational goal of daily flights to space." See: https://www.boeing.com/features/2018...ion-11-18.page |
#16
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BFS drops composite construction
JF Mezei wrote on Mon, 24 Dec 2018
00:23:22 -0500: On 2018-12-10 00:53, Fred J. McCall wrote: I saw a report today that SpaceX was dropping composites for tanks and main structure on BFS in favor of using "heavy metal" Funny how this group was so convinced the tests for the composite tanks had been conclusive and that SpaceX had fully tested them, and I was ridiculed for stating that only certain tests had been done and it didn't mean those tanks had been fully tested. Funny how frequently you pat yourself on the back for 'proving wrong' things that weren't said. Now, they are allegedly switching to metal and people just accept this, without reminding themselves that they had fully beleibed the composite tank tests had been exchaiustive and proved they woudl be in BFS/BFR. 'Allegedly'? Note: heavy metal doesn't mean steel. If you look at the A380, Airbus had developped "composites" called Glare which is sandwiched aluminium and carbon fibre which came out in weight quite competitively with full carbon (and Boeing's problems with 787 showed that all-carbon doesn't yield the full promises made by marketing departments). Nobody said it meant steel. In fact, no one has said it means anything in particular. However, I'd bet you're wrong here since what you describe isn't particularly 'heavy' and that is the description given. Musk quite pointedly ignored repeated questions about WHICH metal(s). One issue is fatigue. In this case, not only pressure cycles, but also tempoerature cycles for tanks. Would be interesting to know which turned out to tip the balance against all composite tanks. Tanks aren't the only things that get temperature cycles. It may just be a matter of expense or difficulty in fabrication. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
#17
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BFS drops composite construction
In article ,
says... On 2018-12-10 00:53, Fred J. McCall wrote: I saw a report today that SpaceX was dropping composites for tanks and main structure on BFS in favor of using "heavy metal" Funny how this group was so convinced the tests for the composite tanks had been conclusive and that SpaceX had fully tested them, and I was ridiculed for stating that only certain tests had been done and it didn't mean those tanks had been fully tested. Now, they are allegedly switching to metal and people just accept this, without reminding themselves that they had fully beleibed the composite tank tests had been exchaiustive and proved they woudl be in BFS/BFR. Switching to a stainless steel alloy had nothing to do with the successful testing of composite tanks. Heck, SpaceX has even built several composite tank sections which were intended to be used for BFS (there are pictures documenting this). I have a feeling the change to stainless steel had everything to do with how BFS has evolved to handle hypersonic reentry heating. Note: heavy metal doesn't mean steel. Actually, Musk has tweeted that the tanks will be made of a stainless steel alloy. I can't remember the specific alloy off the top of my head, but if you look at Elon Musk's posts on Twitter over the last few days, you'll find the Tweets. If you look at the A380, Airbus had developped "composites" called Glare which is sandwiched aluminium and carbon fibre which came out in weight quite competitively with full carbon (and Boeing's problems with 787 showed that all-carbon doesn't yield the full promises made by marketing departments). Apples and oranges. Neither A380 nor 787 need to reenter from higher than orbital velocities. One issue is fatigue. In this case, not only pressure cycles, but also tempoerature cycles for tanks. Would be interesting to know which turned out to tip the balance against all composite tanks. Last I checked Boeing is using composite tanks for their DOD booster (whose name I forget). So there is that. Cite: DARPA Picks Boeing for XS-1 Spaceplane Project - 5/25/2017 http://www.airforcemag.com/Features/...7/DARPA-Picks- Boeing-for-XS-1-Spaceplane-Project.aspx From above: To achieve an aircraft-like operations tempo, the craft will have "easily-accessible subsystem components configured as line-replaceable units," DARPA said, to enable "quick maintenance and repairs." Other already developed technologies that will be incorporated on the vehicle include lightweight composite cryogenic propellant tanks to hold liquid oxygen and hydrogen, "hybrid-composite metallic wings" able to withstand temperatures exceeding 2,000 degrees Fahrenheit, and autonomy technologies derived from DARPA?s Airborne Launch Assist Space Access program. But the above doesn't talk about the TPS for the main body, which shields the tanks. The wings, however are "hybrid-composite metallic wings", but no detail there about exactly what metal(s) and what composites. This stuff is the "secret sauce", so info will be hard to come by. 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. |
#18
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BFS drops composite construction
In article ,
says... Last I checked Boeing is using composite tanks for their DOD booster (whose name I forget). So there is that. Cite: DARPA Picks Boeing for XS-1 Spaceplane Project - 5/25/2017 http://www.airforcemag.com/Features/...7/DARPA-Picks- Boeing-for-XS-1-Spaceplane-Project.aspx From above: To achieve an aircraft-like operations tempo, the craft will have "easily-accessible subsystem components configured as line-replaceable units," DARPA said, to enable "quick maintenance and repairs." Other already developed technologies that will be incorporated on the vehicle include lightweight composite cryogenic propellant tanks to hold liquid oxygen and hydrogen, "hybrid-composite metallic wings" able to withstand temperatures exceeding 2,000 degrees Fahrenheit, and autonomy technologies derived from DARPA?s Airborne Launch Assist Space Access program. But the above doesn't talk about the TPS for the main body, which shields the tanks. The wings, however are "hybrid-composite metallic wings", but no detail there about exactly what metal(s) and what composites. This stuff is the "secret sauce", so info will be hard to come by. I forgot to add, XS-1 isn't orbital. It's essentially a winged first stage with an upper stage and payload strapped to its back. So reentry heating won't be nearly as bad for XS-1 as it will be for 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. |
#19
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BFS drops composite construction
JF Mezei wrote on Mon, 24 Dec 2018
12:38:00 -0500: Saw a youtube opinion that using stainless steel might be a weight saving overall because it can act as a heat sink for the heat shield during re-entry and this could save on heat shield weight. I have no idea if this is plausible. Using the whole outer body as a heat sink might let you use more refractory TPS and less ablative, which wouldn't decrease weight but would lower costs to refly. The other argument made was that a shiny reflective surface might reflect much of the heat generated by the plasma around the skin instead of absorbing it. (but this would assume the ship's exterior is stainless steel and I doubt stainless steel has a high enough melting point, or does it?) Depends on which stainless alloy you're talking about and how high a melting point is 'high enough'. There are stainless steels that are good to temperatures of 1400 C (AISI 330). -- "Insisting on perfect safety is for people who don't have the balls to live in the real world." -- Mary Shafer, NASA Dryden |
#20
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BFS drops composite construction
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