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Old December 24th 18, 02:57 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default 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
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