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BFS drops composite construction



 
 
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  #1  
Old December 10th 18, 06:53 AM posted to sci.space.policy
Fred J. McCall[_3_]
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Posts: 9,880
Default 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
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  #2  
Old December 10th 18, 12:54 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 1,814
Default 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  
Old December 10th 18, 01:13 PM posted to sci.space.policy
Alain Fournier[_3_]
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Posts: 366
Default 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  
Old December 10th 18, 07:39 PM posted to sci.space.policy
Fred J. McCall[_3_]
external usenet poster
 
Posts: 9,880
Default 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
  #5  
Old December 10th 18, 11:30 PM posted to sci.space.policy
eagle[email protected]
external usenet poster
 
Posts: 59
Default BFS drops composite construction

d 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.

Heat capacity or thermal resilience is certainly an issue.
Another is the ability to use the tanks as a hull when
pressurized. Metal hulls can be possibly reduced in thickness
to compete with composites. At a certain point thermal
properties of metal may make metal superior.

If Musk has only a fuselage material as the change then
my comment does not apply.
  #7  
Old December 11th 18, 09:37 AM posted to sci.space.policy
Rocket Man
external usenet poster
 
Posts: 23
Default BFS drops composite construction


"Fred J. McCall" wrote in message
...
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.


I'm not too surpised considering that NASA and Locked-Martin spent years
trying to build composite tanks for the X-33, which then failed.

But is this the change that Musk called 'counter intuitive'?


  #8  
Old December 15th 18, 05:49 AM posted to sci.space.policy
David Spain
external usenet poster
 
Posts: 2,504
Default 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. 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.

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

  #9  
Old December 15th 18, 06:03 AM posted to sci.space.policy
David Spain
external usenet poster
 
Posts: 2,504
Default 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


  #10  
Old December 15th 18, 11:13 PM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 1,814
Default 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.
 




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