A Space & astronomy forum. SpaceBanter.com

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » SpaceBanter.com forum » Space Science » Policy
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

BFS drops composite construction



 
 
Thread Tools Display Modes
  #11  
Old December 16th 18, 12:50 PM posted to sci.space.policy
Fred J. McCall[_3_]
external usenet poster
 
Posts: 9,986
Default 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

Ads
  #12  
Old December 16th 18, 02:22 PM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 1,881
Default BFS drops composite construction

In article ,
says...
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.


BFR/BFS is going to be pretty complex since it intends to be fully
reusable. That's going to drive up the cost to build it as well as
making it challenging to make it "safe" (more things to go wrong).
Commercial Crew is supposed to have a reliability of 1 failure in 250
(if I remember correctly) and both SpaceX and Boeing are both struggling
to satisfy NASA. If BFR/BFS is an order of magnitude safer than that,
it would make for an impressively safe crewed spacecraft and I'm sure
NASA would be very happy to fly crew on it.

That said, I'm personally skeptical of the claims that this first
generation fully reusable TSTO will be safe enough for the FAA to
certify for point to point transportation on earth. If BFR/BFS does an
order of magnitude better than commercial crew's requirements, I'm
really not sure the FAA would consider that "safe" when the alternative
is far safer (i.e. large passenger jet aircraft with modern turbofan
engines).

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'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 personally give this a
slim chance of actually happening.

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.
  #13  
Old December 16th 18, 06:27 PM posted to sci.space.policy
David Spain
external usenet poster
 
Posts: 2,513
Default 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  
Old December 16th 18, 06:36 PM posted to sci.space.policy
David Spain
external usenet poster
 
Posts: 2,513
Default 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  
Old December 21st 18, 04:26 PM posted to sci.space.policy
[email protected]
external usenet poster
 
Posts: 637
Default 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  
Old December 24th 18, 08:22 AM posted to sci.space.policy
Fred J. McCall[_3_]
external usenet poster
 
Posts: 9,986
Default 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  
Old December 24th 18, 01:57 PM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 1,881
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
--
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  
Old December 24th 18, 02:10 PM posted to sci.space.policy
Jeff Findley[_6_]
external usenet poster
 
Posts: 1,881
Default 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  
Old December 24th 18, 06:22 PM posted to sci.space.policy,rec.arts.sf.science
Fred J. McCall[_3_]
external usenet poster
 
Posts: 9,986
Default 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
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
(Drops of) Water on Mars! Bluuuue Rajah Astronomy Misc 1 March 27th 09 08:44 PM
NASA Drops Requirement For Methane Engine From CEV Space Cadet Space Shuttle 16 February 6th 06 05:23 PM
Armadillo drops peroxide... forever? Tom Cuddihy Policy 36 April 11th 05 09:22 PM
The other shoe drops: Hubble... Steven James Forsberg Policy 73 February 5th 04 05:39 AM
Linux is doomed as SCO drops the bomb. Nomen Space Shuttle 21 August 17th 03 07:14 PM


All times are GMT +1. The time now is 05:27 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright 2004-2019 SpaceBanter.com.
The comments are property of their posters.