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BFS drops composite construction



 
 
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  #21  
Old December 25th 18, 12:28 AM posted to sci.space.policy
Sylvia Else[_3_]
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Default BFS drops composite construction

On 10/12/2018 4:53 pm, 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" (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.



Scott Manley has a video about this.

https://www.youtube.com/watch?v=VoegqRJKGE8

It may not be a reaction to technical difficulties with composite, but a
design decision based on the specifics of the BFS.

Sylvia.

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  #22  
Old December 25th 18, 05:22 AM posted to sci.space.policy,rec.arts.sf.science
Fred J. McCall[_3_]
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Posts: 9,876
Default BFS drops composite construction

Jeff Findley wrote on Mon, 24 Dec 2018
17:31:40 -0500:

In article ,
says...

JF Mezei wrote on Mon, 24 Dec 2018
12:38:00 -0500:

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).



Elon Musk on Twitter 2:38 p.m. on Dec 22, 2018:

Yup. Actually, the only significant design element in common
with early Atlas is stainless steel & we?re using a different
alloy mix. I super ?? 300 Series Stainless!


The 300 series stainless is typically good to at least 1150 C with 330
being the best.


--
"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
  #23  
Old December 25th 18, 05:46 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 9,876
Default BFS drops composite construction

JF Mezei wrote on Mon, 24 Dec 2018
21:54:31 -0500:

On 2018-12-24 18:28, Sylvia Else wrote:

Scott Manley has a video about this.

https://www.youtube.com/watch?v=VoegqRJKGE8

It may not be a reaction to technical difficulties with composite, but a
design decision based on the specifics of the BFS.


That is the one I watched.

It does indicate that the original plan was marketing powerpoints and as
the engineers are getting to design the actual ship, they are having to
make some "reality check" changes to the big picture design.


That happens with every design.


In a case where BFS goes above LEO, would the stainless steel skin
provide protection from radiation?


I doubt that it's enough to be significant.


It could be that the heavy skin ends up saving weight when you factor in
the need for re-entry shielding, radiation and micro meteorite that
would be needed with composite skin.


Last heard, SpaceX was going to use a ceramic named TUFROC-X for TPS
on Starship. It's not possible to get that degree of thermal
protection with metal.


--
"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
  #24  
Old December 26th 18, 06:45 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 9,876
Default BFS drops composite construction

JF Mezei wrote on Tue, 25 Dec 2018
16:29:41 -0500:

On 2018-12-24 23:46, Fred J. McCall wrote:

Last heard, SpaceX was going to use a ceramic named TUFROC-X for TPS
on Starship. It's not possible to get that degree of thermal
protection with metal.


In that case, is there really an advantage to using stainless steel for
the skin instead of aluminium or titanium ?


Yes, there are several.


From a structural strength point of view:

BFS ~ 9m diameter.
A380 ~ 7m diameter.


Now run the load numbers. They're nowhere near the same.


Since a crewed BFS would need to support 14.7 PSI whereas an aircraft
generally supports about 8PSI, does stainless steel have more strength
ofor that diametre than would Aluminium or Titanium ?


Aluminum is too weak and melts at half the temperature of 330
stainless. Titanium has an advantage in melting point, but is
preposterously difficult to machine.


--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson
 




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