Author Topic: BFR/ITS risk due to composites  (Read 23604 times)

Offline testguy

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BFR/ITS risk due to composites
« on: 04/27/2017 05:51 PM »
The impressive performance numbers realized for the BFR and ITS are in part due to extensive use of composites in the vehicles structure, airframe and tanks.  Composites have been proven problematic when used in other aerospace projects in the past.  Problems have been revealed in parts processing, inspection, repair and durability amongst others that I'm sure this forum can identify.  SpaceX, no doubt appreciates the composite issue as demonstrated by their early demonstration of the ITS oxidizer tank and their copy experience. The very size of the BFR and ITS  make it difficult to test the structures other than in flight.  How else can they subject the stages to the extreme thermal, structural and dynamic environmental conditions that must be survived on multiple cycles.  After all, if you think about it, each stage is the size of a small sky scraper.

My concern is that extensive composite use may once again be a rabbit hole that could sink the Mars aspirations.  Could a composite issue identified during flight testing be too late to recover from?  I am not an expert, just witnessed many development problems over the years.  The intent of opening this discussion is to solicit thoughts pertaining to composites for BFR and ITS.  Why will SpaceX be successful this time?  Should all the design eggs be in one basket?  It is even feasible to have a viable less risky design.  With billions needed for development, with source of funding being internal, it appears that SpaceX must get it right the first time.

My intent is not to be a naysayer because I couldn't be more thrilled that SpaceX has taken upon themselves to provide the world with a low cost interplanetary transportation system.  I hope this discussion helps convince me and others that they are on the right path pertaining to composites.


Offline kendalla59

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Re: BFR/ITS risk due to composites
« Reply #1 on: 04/27/2017 11:47 PM »
As an engineer in the 3D printing industry, this video caught my eye:

Offline Robotbeat

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Re: BFR/ITS risk due to composites
« Reply #2 on: 04/28/2017 12:32 AM »
SpaceX uses composites extensively on Falcon 9 already. The legs, the interstate, the fairing, the original Sragon trunk, too.

Composites have their difficulties, but we shouldn't be scared by them. They can be quite tough and often have a lot of margin in their design. 787s and other airplanes rely on composites.

Nothing ventured, nothing gained.
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Re: BFR/ITS risk due to composites
« Reply #3 on: 04/28/2017 12:49 AM »
All examples of composite use are small and warm compared to its. Good example of failure is x33. It was a long time ago by space tech standards.
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Offline Robotbeat

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Re: BFR/ITS risk due to composites
« Reply #4 on: 04/28/2017 12:56 AM »
All examples of composite use are small and warm compared to its. Good example of failure is x33. It was a long time ago by space tech standards.
787 is not small. It's enormous. Wings also composite. X-33 was, of course, liquid hydrogen, which is proportionally further from liquid oxygen temperatures than liquid oxygen is to room temperature (referring to ratio of absolute temperatures). The BFR and a 787-10 are basically the same length.
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Offline guckyfan

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Re: BFR/ITS risk due to composites
« Reply #5 on: 04/28/2017 07:04 AM »
All examples of composite use are small and warm compared to its. Good example of failure is x33. It was a long time ago by space tech standards.
787 is not small. It's enormous. Wings also composite. X-33 was, of course, liquid hydrogen, which is proportionally further from liquid oxygen temperatures than liquid oxygen is to room temperature (referring to ratio of absolute temperatures). The BFR and a 787-10 are basically the same length.

Plus my understanding is what doomed X-33 was the complex shape of the tank. Which is not appliccable to ITS.

Offline testguy

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Re: BFR/ITS risk due to composites
« Reply #6 on: 04/28/2017 07:49 AM »
I did not include specific program names in this initial post.  If I did the 787 would have been an example of the very concern that I have.  The 787 cost twice as much to develop as originally planned (40 billion) and the initial delivery was 40 months late.  Not all because of composite issues but a good part.  The break even point is now the 1100th aircraft, wow!  Boeing thought it understood the design issues and bet its future on that aircraft. It had the financial resources to recover.  I not sure that SpaceX would fare as well since it internally funded without a large back order ledger for BFR and ITS.

The question I am asking is the risk worth the reward for the interplanetary  transportation system?






« Last Edit: 04/28/2017 07:58 AM by testguy »

Offline FutureSpaceTourist

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Re: BFR/ITS risk due to composites
« Reply #7 on: 04/28/2017 08:19 AM »
I not sure that SpaceX would fare as well since it internally funded without a large back order ledger for BFR and ITS.

The question I am asking is the risk worth the reward for the interplanetary  transportation system?

SpaceX is not dependent on ITS for future profitability, nor will they lose market share to a competitor if ITS is delayed. So from a financial point of view the situation is very different from Boeing. SpaceX can choose to fix the money available for ITS at an indefinitely sustainable level (assuming profitability in their main business) and go at whatever speed on ITS that supports.

Yes composites are a risk. But there's no way to do something on the scale of ITS that isn't risky! Clearly SpaceX know the risks and their assessment is that composites are what they need to get the job done.
« Last Edit: 04/28/2017 08:20 AM by FutureSpaceTourist »

Offline JamesH65

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Re: BFR/ITS risk due to composites
« Reply #8 on: 04/28/2017 10:45 AM »
I did not include specific program names in this initial post.  If I did the 787 would have been an example of the very concern that I have.  The 787 cost twice as much to develop as originally planned (40 billion) and the initial delivery was 40 months late.  Not all because of composite issues but a good part.  The break even point is now the 1100th aircraft, wow!  Boeing thought it understood the design issues and bet its future on that aircraft. It had the financial resources to recover.  I not sure that SpaceX would fare as well since it internally funded without a large back order ledger for BFR and ITS.

The question I am asking is the risk worth the reward for the interplanetary  transportation system?

Worth noting that the experience of building the 787 is likely to make building the ITS easier. As with any pathfinder project, everything afterwards using similar technology is easier.

Offline IRobot

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Re: BFR/ITS risk due to composites
« Reply #9 on: 04/28/2017 11:43 AM »
You can mitigate part of the risk if you use higher safety margins with the weight advantage that you gain.

But on aerospace composites, the quality requirements are very high, so the composites are subjected to much more testing than composites in a high performance sailing boat.

The biggest concern with composites is delamination, but nowadays there are very good methods (ultrasounds, x-ray, etc) that can qualify a part at production time. Parts can also be re-qualified after production.

Delamination or complete failure can also occur due to a violent slam. This could happen during a landing, for example. If the problem happened during a Mars landing, there would be no chance to qualify the rocket again and no chance for big repais.
Perhaps in that case they could just measure g-loads on several critical components and check against specs.

So probably SpaceX will re-qualify critical composite components each time the ITS returns to Earth, if g-loads were exceeded or "x" flights were performed.

Offline Robotbeat

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Re: BFR/ITS risk due to composites
« Reply #10 on: 04/28/2017 12:14 PM »
Because of the higher margins required for composite certification, I'd venture that aerospace composites are overall more resilient than the same structure out of aluminum. At least that's what the composites people tell me.
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Offline spacenut

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Re: BFR/ITS risk due to composites
« Reply #11 on: 04/28/2017 12:37 PM »
Composites have been around since what? the 1980's.  Glock made the first composite framed pistol back in the 1980's.  They take a lot of slamming.  I, know the barrel and bolt are steel to contain the explosion, but the frame is slammed back and slammed closed on each shot.  Thousands of shots, no problems.  Tested by putting them in freezers for days and then in a car dash in the sun for days.  Dropped out of a helicopter.  No warping, no problems firing afterwards. 

Composites have been used in aerospace since what? the late 1990's. 

I think a lot of composite problems have been worked out by now.  SpaceX is using them for weight reduction.  Aluminum is still available if it doesn't work out.  Using Aluminum might greatly affect the payload weight that ITS can carry. 

I used Glock as an example because ITS will have gravitational stresses taking off and landing.  Also heat and cold stresses in space.  Because Glock broke ground first on composite pistols, you have everyone making them now.  They are much lighter for all day carry than steel pistols.  99% of police, etc, carrying a handgun is never used.  Weight reduction and ruggedness are what people like for all day carry.  ITS aluminum vs composites should greatly reduce weight, an if is is rugged, will be able to handle multiple reuses, just like a composite pistol can fire thousands of rounds downrange in practice. 
« Last Edit: 04/28/2017 12:38 PM by spacenut »

Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #12 on: 04/28/2017 04:47 PM »
Composites have been around since what? the 1980's.  Glock made the first composite framed pistol back in the 1980's. ... I used Glock as an example because ITS will have gravitational stresses taking off and landing. ...

It's not a great example, since those frames are made out of fiberglass reinforced nylon, not carbon fiber reinforced epoxy. The mechanical properties are very different, nearly as different as AlLi alloy and CFRP.

Offline ZachF

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Re: BFR/ITS risk due to composites
« Reply #13 on: 05/01/2017 02:43 PM »
Composites have been around since what? the 1980's.  Glock made the first composite framed pistol back in the 1980's. ... I used Glock as an example because ITS will have gravitational stresses taking off and landing. ...

It's not a great example, since those frames are made out of fiberglass reinforced nylon, not carbon fiber reinforced epoxy. The mechanical properties are very different, nearly as different as AlLi alloy and CFRP.

I'm pretty sure modern polymer framed pistols aren't fiberglass reinforced... just plastic, with stamped metal inserts for the rails the slide sits on. The first polymer framed pistol was an HK too, IIRC.

Offline sevenperforce

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Re: BFR/ITS risk due to composites
« Reply #14 on: 05/01/2017 02:50 PM »
Remember that the current Falcon 9 interstage is already composite.

Offline docmordrid

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Re: BFR/ITS risk due to composites
« Reply #15 on: 05/01/2017 03:06 PM »
Composites have been around since what? the 1980's.  Glock made the first composite framed pistol back in the 1980's. ... I used Glock as an example because ITS will have gravitational stresses taking off and landing. ...

It's not a great example, since those frames are made out of fiberglass reinforced nylon, not carbon fiber reinforced epoxy. The mechanical properties are very different, nearly as different as AlLi alloy and CFRP.

I'm pretty sure modern polymer framed pistols aren't fiberglass reinforced... just plastic, with stamped metal inserts for the rails the slide sits on. The first polymer framed pistol was an HK too, IIRC.

Nevermind pistols, some of which do use composites. There are high powered rifles with carbon composite stocks. I have two, and they put up with forces no pistol can touch. Made by PSE, McMillan, Stocky, and Proof Research is making composite overwrapped barrels.
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Offline Celestar

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Re: BFR/ITS risk due to composites
« Reply #16 on: 05/01/2017 08:01 PM »
Long time lurker, but first post :D

Forget rifles, the A380 center wing box is a mostly carbon-composite part and has been produced 14 years ago. Not exactly a 'low-load' part of the aircraft either.

Celestar

Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #17 on: 05/01/2017 08:10 PM »
Composites have been around since what? the 1980's.  Glock made the first composite framed pistol back in the 1980's. ... I used Glock as an example because ITS will have gravitational stresses taking off and landing. ...

It's not a great example, since those frames are made out of fiberglass reinforced nylon, not carbon fiber reinforced epoxy. The mechanical properties are very different, nearly as different as AlLi alloy and CFRP.

I'm pretty sure modern polymer framed pistols aren't fiberglass reinforced... just plastic, with stamped metal inserts for the rails the slide sits on. The first polymer framed pistol was an HK too, IIRC.

Fiberglass reinforced as in glass-filled nylon. It looks exactly the same as nylon unless you cut it open. It doesn't look like a familiar fiberglass layup (e.g. boat hull) in any way.

But composites are used in a lot of high-shock applications, including automotive, aerospace, high-performance bikes, etc.

Offline corneliussulla

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Re: BFR/ITS risk due to composites
« Reply #18 on: 05/02/2017 09:08 AM »
Definite risks involved but its how Musk rolls, he is always pushing the envelope. Having said that I am not sure the Boeing 780 Is a good analogy. A planes airframe is inately more complex and SpaceX have used composite in the past and would have been able to judge the effects of the extreme environment the BFR will be used in. Second stage not so much
« Last Edit: 05/02/2017 09:09 AM by corneliussulla »

Offline testguy

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Re: BFR/ITS risk due to composites
« Reply #19 on: 05/02/2017 03:37 PM »
Successful demonstration of cyclic loading of a 12 meter diameter Lox pressure vessel with Lox, while also under flight structural loads, for me would put this discussion to bed.
I am hopeful that the SpaceX update in the next several weeks will show progress in this area.

Offline ZachF

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Re: BFR/ITS risk due to composites
« Reply #20 on: 05/02/2017 04:49 PM »
Composites have been around since what? the 1980's.  Glock made the first composite framed pistol back in the 1980's. ... I used Glock as an example because ITS will have gravitational stresses taking off and landing. ...

It's not a great example, since those frames are made out of fiberglass reinforced nylon, not carbon fiber reinforced epoxy. The mechanical properties are very different, nearly as different as AlLi alloy and CFRP.

I'm pretty sure modern polymer framed pistols aren't fiberglass reinforced... just plastic, with stamped metal inserts for the rails the slide sits on. The first polymer framed pistol was an HK too, IIRC.

Fiberglass reinforced as in glass-filled nylon. It looks exactly the same as nylon unless you cut it open. It doesn't look like a familiar fiberglass layup (e.g. boat hull) in any way.

But composites are used in a lot of high-shock applications, including automotive, aerospace, high-performance bikes, etc.

Maybe for some rifle stocks, but pistol frames are just plastic with metal inserts, here a few pics of Glocks that have kaboomed:

http://www.reno4x4.com/attachment.php?attachmentid=48049&d=1383017506
http://www.frontsight.com/Images/Glock21ReloadDamage/glock02.jpg

Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #21 on: 05/02/2017 05:47 PM »
Maybe for some rifle stocks, but pistol frames are just plastic with metal inserts...

Glass-filled nylon IS "just plastic". ;) In the sense that plastic is a general term that includes glass-filled polymers. Thermoplastics like glass-filled nylon tend to be reasonably tough (at least relative to their tensile strengths) compared to the epoxies typically used in carbon fiber composites. But higher glass content tends to increase strength and reduce toughness.

Offline DAZ

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Re: BFR/ITS risk due to composites
« Reply #22 on: 05/05/2017 01:07 AM »
From what I remember, the problems with the Boeing 787 composites and the long delays associated weren’t really with the composites themselves.  There were 2 primary problems.  One was a chronic shortage of aerospace certified fasteners to bolt the composite parts together.  The 2nd problem was that these parts were manufactured in greatly dispersed factories.  These factories were located across the world in other countries.  Some of these companies were very good at holding their manufactured part tolerances to the required levels.  But there were a few of the companies that could not.  So when these parts were brought together for the 1st time they could not be bolted together.  Boeing literally had to send people to these factories and teach them how to build parts that Boeing had already paid them to build.

Once these parts were built and tested there was absolutely no doubt from the results that Boeing was able to meet all of their design performance goals.  An example of this is when they did the iron Eagle tests.  This is where they build a mockup of all the structural elements of the aircraft and stress them on the ground hydraulically to simulate all of the loads they will undergo in the aircraft’s lifetime.  Because of the newness of this design along with everything that had been learned in the past the FAA required this to be the most stringent test performed to date.  After they had done all the fatigue tests and stressed it to its design ultimate limit (150% of maximum design ultimate load) this then passed all of the FAA’s required tests. 

Boeing then did one additional test not required by the FAA.  This test was only for the Boeing engineers.  It was a test to determine how much performance (how much stronger than necessary and thus extra weight than needed was added) was left on the table.  There is always a certain amount of uncertainty when designing the parts.  You obviously never want the failure to be less than the design goal.  Decades ago being only 10% over was considered good.  With modern designs, 5% is more likely the design goal.  When Boeing tested to find the true ultimate load the failure was at just over 151% and failing at the predicted point in the structure.  So the Boeing engineers left just a little over 1% on the table.  This is actually much better than they could do with aluminum parts.  It illustrates just how well the engineers understand these composite materials.

Offline Nomadd

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Re: BFR/ITS risk due to composites
« Reply #23 on: 05/05/2017 01:50 AM »
 The 787 had a six month delay because of premature composite delamination during the wing load test. It wasn't really the composite's fault. A wing design change in Japan wasn't properly considered and caused greater loads at one point. Part of the fix was actually removing some material to increase flexibility at one point and move the load where it should be. Most of the other composite related problems were from Alenia doing substandard work that caused a lot of their barrels to be scrapped.
 It's the kind of problem that could be even worse when your margins are smaller, like in a spaceship. The effects of every little change has to be considered a million different ways since everything is so tightly designed. Making one part a little stronger can mess up a lot of calculations.

Offline meekGee

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Re: BFR/ITS risk due to composites
« Reply #24 on: 05/07/2017 06:22 AM »
I did not include specific program names in this initial post.  If I did the 787 would have been an example of the very concern that I have.  The 787 cost twice as much to develop as originally planned (40 billion) and the initial delivery was 40 months late.  Not all because of composite issues but a good part.  The break even point is now the 1100th aircraft, wow!  Boeing thought it understood the design issues and bet its future on that aircraft. It had the financial resources to recover.  I not sure that SpaceX would fare as well since it internally funded without a large back order ledger for BFR and ITS.

The question I am asking is the risk worth the reward for the interplanetary  transportation system?

Worth noting that the experience of building the 787 is likely to make building the ITS easier. As with any pathfinder project, everything afterwards using similar technology is easier.
Also worth noting that a very big part of 787 schedule issues had to do with loss of control over outsourcing.

The  wrapped fuselage barrel sections were actually a good idea.

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Offline docmordrid

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Re: BFR/ITS risk due to composites
« Reply #25 on: 05/07/2017 09:46 AM »
Just a reminder: the ITS tank was built by Janicki, and they'll set up at your site.

>
One secret is where this is?  I'll assume it was assembled (and possibly components manufactured) at the location.  If they are going to test it on a barge, it has to be somewhere close to water and without lots of low clearance road structures.
Not that much of a secret.
They said it was built by Janicki Industries.
So it is either in Sedro-Woolley  or Hamilton Washington.
« Last Edit: 05/07/2017 09:46 AM by docmordrid »
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Offline Oersted

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Re: BFR/ITS risk due to composites
« Reply #26 on: 05/07/2017 10:06 PM »
The ITS couldn't be conceived without composites. They are absolutely essential for the numbers to add up.

Offline spacenut

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Re: BFR/ITS risk due to composites
« Reply #27 on: 05/07/2017 10:16 PM »
I disagree, ITS could be done with aluminum, but would loose payload ability.  How much?  Don't know.  Remember Sea Dragon was all steel pressure fed single engine per stage two stagebut could get 500 tons to LEO.  It was around 70-75' in diameter.  Aluminium could be a fall back, but would affect payload. 

Offline Robotbeat

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Re: BFR/ITS risk due to composites
« Reply #28 on: 05/09/2017 12:49 PM »
Aluminum could be a fall back but won't because SpaceX doesn't get scared off by new technologies like NASA might.

The main issue for composites is oxygen compatibility with cracks, and the fallback there is a metal liner in the oxygen tank. Musk said this himself.

It's not like aluminum doesn't have issues. Aluminum doesn't have an endurance limit under fatigue like steel does, in other words, aluminum keeps getting fatigue even with low loadings. But that's just something you take into account and move on. You don't build airplanes out of steel.

I actually think half the reason for composites is the manufacturability improves for some shapes. It's not just performance.
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Re: BFR/ITS risk due to composites
« Reply #29 on: 05/09/2017 12:54 PM »

It's not like aluminum doesn't have issues. Aluminum doesn't have an endurance limit under fatigue like steel does, in other words, aluminum keeps getting fatigue even with low loadings. But that's just something you take into account and move on. You don't build airplanes out of steel.

I actually think half the reason for composites is the manufacturability improves for some shapes. It's not just performance.

what does composites look like on this very nice graph?
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Offline Star One

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Re: BFR/ITS risk due to composites
« Reply #30 on: 05/09/2017 02:42 PM »
Aluminum could be a fall back but won't because SpaceX doesn't get scared off by new technologies like NASA might.

The main issue for composites is oxygen compatibility with cracks, and the fallback there is a metal liner in the oxygen tank. Musk said this himself.

It's not like aluminum doesn't have issues. Aluminum doesn't have an endurance limit under fatigue like steel does, in other words, aluminum keeps getting fatigue even with low loadings. But that's just something you take into account and move on. You don't build airplanes out of steel.

I actually think half the reason for composites is the manufacturability improves for some shapes. It's not just performance.

That's a rather blanket statement about NASA being scared off. Why people feel the need to cast aspersions on a body like NASA just to argue a point escapes me.

Offline Oersted

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Re: BFR/ITS risk due to composites
« Reply #31 on: 05/09/2017 07:37 PM »
I disagree, ITS could be done with aluminum, but would loose payload ability.  How much?  Don't know.  Remember Sea Dragon was all steel pressure fed single engine per stage two stagebut could get 500 tons to LEO.  It was around 70-75' in diameter.  Aluminium could be a fall back, but would affect payload. 

Remember, the ITS is not about lifting stuff into Earth orbit but about going to Mars and back. The margins delivered by composites are absolutely needed.

Offline john smith 19

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Re: BFR/ITS risk due to composites
« Reply #32 on: 05/09/2017 10:16 PM »
The impressive performance numbers realized for the BFR and ITS are in part due to extensive use of composites in the vehicles structure, airframe and tanks. 
Since ITS has not flown yet that would be the anticipated impressive performance numbers.
Quote from: testguy
Composites have been proven problematic when used in other aerospace projects in the past.  Problems have been revealed in parts processing, inspection, repair and durability amongst others that I'm sure this forum can identify.  SpaceX, no doubt appreciates the composite issue as demonstrated by their early demonstration of the ITS oxidizer tank and their copy experience. The very size of the BFR and ITS  make it difficult to test the structures other than in flight.  How else can they subject the stages to the extreme thermal, structural and dynamic environmental conditions that must be survived on multiple cycles.  After all, if you think about it, each stage is the size of a small sky scraper.
 the Mars

This is not the first time very large LV's have been built, or large aerospace structures for that matter. Concorde (for example) was tested using an airframe covered in electric heaters and hydraulic actuators feeding a "wiffle tree" to simulate both the thermal and structural load cycling of multiple flights in order to avoid surprises

You're right however that the multiple loads together IE mass, thermal, vibration and acoustic, is going to be very tough short of an all up build and launch.
 
Quote from: testguy
My concern is that extensive composite use may once again be a rabbit hole that could sink the Mars aspirations.  Could a composite issue identified during flight testing be too late to recover from? 
TBH there are always the "unknown unknowns." as the pad explosion on SLC40 proved.  :(

However SX is in quite a strong position for several reasons.

ITS will be its 3rd (or 4th, depending on how different you see FH as being from F9) major LV. So they have a clear sense of a development cycle and areas which have caused particular issues in the past for them.

They now have substantial knowledge about both the launch and reentry environments around Earth (and provided all goes will will have some of the entry corridor to the Martian surface). That gives them a lot of data for their various environmental models for CFD and FAE analysis.

Lastly they have a number of CFRP structural elements on all of their LVs which (AFAIK) have gone through several iterations. This is valuable as historically there has been a tendency in the industry to treat CFRP as "Black Aluminum" and design a part the same way as it would be in metal alloy, much as early 3d printed parts copied existing parts while later iterations made better use of 3d printing's strengths. In CFRP this has resulted in parts that are don't realize the weight savings that the materials specific strength predict should occur.

Worse, a part shaped to take advantage of Al alloys properties may be exceptionally prone to particular CFRP failure modes, so it has to be strengthened (and hence heavier) than the part it replaces, a double failure in design.

I suspect this is what you mean by the "rabbit hole" of CFRP development. SX seems quite aware of CFRP's differences and of leveraging it's benefits while minimizing it's issues.

 
Quote from: testguy
I am not an expert, just witnessed many development problems over the years.  The intent of opening this discussion is to solicit thoughts pertaining to composites for BFR and ITS.  Why will SpaceX be successful this time?  Should all the design eggs be in one basket?  It is even feasible to have a viable less risky design.  With billions needed for development, with source of funding being internal, it appears that SpaceX must get it right the first time.
To an extent. But SX has the advantage that it's setting the timescale. They can always regroup if they hit a serious problem.
« Last Edit: 05/09/2017 10:26 PM by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Online Cheapchips

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Re: BFR/ITS risk due to composites
« Reply #33 on: 01/04/2018 09:57 PM »
I was doing little search for composite manufacturing as I was curious as to how they'd actually make the BFR.

NASA ran a research program with Boeing and Grumman around 2013-2016.  Boeing produced a 2.4m and 5.5m liquid hydrogen test composite tank and Grumman produced a smaller two segment tank.  It was a successful project on a fairly modest budget.

It does make large composite tanks feel slightly less exotic when coupled with SpaceX's success with the 12m test tank.

Boeing's tank being made:



A couple of more detailed articles, which do flag some of the challenges SpaceX will face:

http://aviationweek.com/space/advances-lightweight-composite-tanks-launchers

https://www.compositesworld.com/articles/nasaboeing-composite-launch-vehicle-fuel-tank-scores-firsts

Offline john smith 19

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Re: BFR/ITS risk due to composites
« Reply #34 on: 01/05/2018 01:37 PM »
I was doing little search for composite manufacturing as I was curious as to how they'd actually make the BFR.

NASA ran a research program with Boeing and Grumman around 2013-2016.  Boeing produced a 2.4m and 5.5m liquid hydrogen test composite tank and Grumman produced a smaller two segment tank.  It was a successful project on a fairly modest budget.

It does make large composite tanks feel slightly less exotic when coupled with SpaceX's success with the 12m test tank.

Boeing's tank being made:
Actually LH2 is more exotic. It's very cold (less than 1/4 the NBP of LO2) and its very low molecular weight means it does not need a big temperature rise to start it diffusing through CFRP (fortunately LH2 SHC is 4x that of water, meaning it can absorb quite a lot of heat before it boils. But once it does..)

As HMX pointed out making fire and explosion resistant composite tanks for LO2 was a solved problem by the mid 1990's. Any fuel with a BP anywhere near LOX should be no more difficult to handle. LH2 is the worst case (unless  you want to build a CFRP LHe tank without a metal liner of course).
« Last Edit: 01/09/2018 02:55 PM by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

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Re: BFR/ITS risk due to composites
« Reply #35 on: 01/27/2018 07:06 PM »
NASA ran a research program with Boeing and Grumman around 2013-2016.  Boeing produced a 2.4m and 5.5m liquid hydrogen test composite tank and Grumman produced a smaller two segment tank.  It was a successful project on a fairly modest budget.

It does make large composite tanks feel slightly less exotic when coupled with SpaceX's success with the 12m test tank.

Boeing's tank being made:




So the Boeing Cryogenic tank project was subcontracted to Janicki Industries for tooling:

https://www.janicki.com/janicki-industries-provides-composite-tooling-for-nasaboeing-cryogenic-tank-project/

And lo and behold, Janicki was/is responsible for SpaceX's composite tank!

Watching this video, it seems they built the 12m test tank right next to a sea port.  Anyone know where?

The 12 meter tank was contracted to Janicki Industries in Sedro-Woolley, Washington. They're a composites layup specialist. SpaceX will have a learning curve building these tanks in-house.
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Offline ackermann

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Re: BFR/ITS risk due to composites
« Reply #36 on: 02/15/2018 03:43 AM »
So does RocketLab's successful flight of Electron retire any risk for BFR?  Sure, it's only the size of Falcon 1, but it's still an honest-to-goodness carbon fiber, orbital rocket.

When Electron finally made orbit, everybody was talking about the Rutherford's electric turbopumps.  But I thought that the composite construction was the more significant accomplishment.  Haven't carbon fiber rockets been something of a holy grail for a while now?  Is Electron the very first carbon fiber orbital rocket?

How similar is Electron's composite to what's expected for BFR?  Is it the same type of carbon fiber?  Does it have a metal liner in its LOX tanks?  How much of the rocket is composite?  Interstage, payload fairing, and octaweb all composite too?


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Re: BFR/ITS risk due to composites
« Reply #37 on: 02/15/2018 07:45 AM »
So does RocketLab's successful flight of Electron retire any risk for BFR?  Sure, it's only the size of Falcon 1, but it's still an honest-to-goodness carbon fiber, orbital rocket.

When Electron finally made orbit, everybody was talking about the Rutherford's electric turbopumps.  But I thought that the composite construction was the more significant accomplishment.  Haven't carbon fiber rockets been something of a holy grail for a while now?  Is Electron the very first carbon fiber orbital rocket?

How similar is Electron's composite to what's expected for BFR?  Is it the same type of carbon fiber?  Does it have a metal liner in its LOX tanks?  How much of the rocket is composite?  Interstage, payload fairing, and octaweb all composite too?

 * BFR uses autogenous pressurization. The tanks have to withstand cryogenic LOX and hot GOX
 * BFR will see thousands of reuses
 * BFR has to withstand the stresses of reentry, for BFS from interplanetary speed

That's why I think BFR/BFS is a much harder problem than Electron.
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Offline JoeyOak

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Re: BFR/ITS risk due to composites
« Reply #38 on: 02/15/2018 10:31 AM »
So does RocketLab's successful flight of Electron retire any risk for BFR?  Sure, it's only the size of Falcon 1, but it's still an honest-to-goodness carbon fiber, orbital rocket.

When Electron finally made orbit, everybody was talking about the Rutherford's electric turbopumps.  But I thought that the composite construction was the more significant accomplishment.  Haven't carbon fiber rockets been something of a holy grail for a while now?  Is Electron the very first carbon fiber orbital rocket?

How similar is Electron's composite to what's expected for BFR?  Is it the same type of carbon fiber?  Does it have a metal liner in its LOX tanks?  How much of the rocket is composite?  Interstage, payload fairing, and octaweb all composite too?

Nice first post!  :)

Composite tanks consitute a significant risk, because there's such an abundance of failure mechanisms and they aren't all particularly well understood.

In short, a composite tank consists of a thin metallic liner overwrapped with a web of light-weight carbon fibres infused with resin. If the metal and carbon stick together properly, the composite material has the strength of the metal liner and the strength of the carbon fibre/resin composite - it's a very strong material. If the metal and carbon come apart, then the composite material has the weakness of the metal liner and the weakness of the carbon fibre/resin composite - it becomes a very weak material.

With F9/Amos-6, there was buckling, making the metal liner and the carbon fibre/resin come apart, and you had instant RUD.

It's difficult to anticipate and prevent every possible mechanism that can cause separation of the metal liner and the carbon fibre/resin composite, because there's such a diversity of failure mechanisms. Hence, the technology brings significant risk.

Offline AncientU

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Re: BFR/ITS risk due to composites
« Reply #39 on: 02/15/2018 10:46 AM »
Is the BFR tankage a composite over-wrap of a metal liner?  I thought it was pure carbon composite which I believe is the same as Electron.  Could be way off here...
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Re: BFR/ITS risk due to composites
« Reply #40 on: 02/15/2018 10:48 AM »
Is the BFR tankage a composite over-wrap of a metal liner?  I thought it was pure carbon composite which I believe is the same as Electron.  Could be way off here...

The reference to AMOS-6 leads me to believe that he confuses COPVs with the composite fuel and oxidizer tanks for BFR. BFR is supposed to get rid of COPVs for good.
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

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Re: BFR/ITS risk due to composites
« Reply #41 on: 02/15/2018 10:50 AM »
In short, a composite tank consists of a thin metallic liner overwrapped with a web of light-weight carbon fibres infused with resin.

COPV != composite tanks. Very different things...

This is what Elon said in Mexico:

Quote
So this is a fairly significant technical challenge to make deeply cryogenic tanks out of carbon fiber, and it's only recently that we think the carbon fiber technology has gotten to the point where we can actually do this without having to create a liner — some sort of metal liner, or other liner, on the inside of the tanks, which would add mass and complexity.
« Last Edit: 02/15/2018 11:24 AM by jpo234 »
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

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Re: BFR/ITS risk due to composites
« Reply #42 on: 02/15/2018 01:44 PM »
So does RocketLab's successful flight of Electron retire any risk for BFR?  Sure, it's only the size of Falcon 1, but it's still an honest-to-goodness carbon fiber, orbital rocket.


It can only retire a risk for SpaceX if RocketLab publishes their findings. Otherwise, SpaceX would have to guess what RocketLab did to get a working rocket. 

Offline freddo411

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Re: BFR/ITS risk due to composites
« Reply #43 on: 02/15/2018 02:56 PM »
All examples of composite use are small and warm compared to its. Good example of failure is x33. It was a long time ago by space tech standards.

There is a long and growing experience base in aerospace with composites.   

As mentioned already, 787 is largely composite.   The A380 has significant usage:  http://www.iccm-central.org/Proceedings/ICCM13proceedings/SITE/PAPERS/paper-1695.pdf
The B2 is largely composite.  All of these are very large, and they have significant service histories.  RocketLab's new orbital rocket just succeed while using composite LOX and Kero tanks.

SpaceX is using suppliers like Janicki that have built some of the above.



Conclusion:  Using composites may not be high risk based upon known experience in the industry.   




Online matthewkantar

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Re: BFR/ITS risk due to composites
« Reply #44 on: 02/15/2018 03:19 PM »
Conclusion:  Using composites may not be high risk based upon known experience in the industry.

None of the carbon fiber projects to date have used the material to contain sub cooled LOX, hot(ish) gaseous oxygen, and liquid methane. These tanks will be cycled hundreds of times and expect to store these propellants for months on end. It will have to be operated in a vacuum, survive reentry, etc etc.

R and D money has been put into these materials for decades, so there is some experience here and there in areas that will be helpful, but I think "high risk" is accurate.

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Re: BFR/ITS risk due to composites
« Reply #45 on: 02/15/2018 03:25 PM »
Conclusion:  Using composites may not be high risk based upon known experience in the industry.

None of the carbon fiber projects to date have used the material to contain sub cooled LOX, hot(ish) gaseous oxygen, and liquid methane. These tanks will be cycled hundreds of times and expect to store these propellants for months on end. It will have to be operated in a vacuum, survive reentry, etc etc.

R and D money has been put into these materials for decades, so there is some experience here and there in areas that will be helpful, but I think "high risk" is accurate.

I think "uncertain risk" characterizes the situation better.  High risk applies to risks that are understood, and which you can, if you will, compute a probability of a problem happening.  It's not as though there is no knowledge of the materials; as you say, they've been used in many ways for decades.  We just don't know what will happen in new environments, and won't, until further testing is done.

Labeling the situation "high risk" overstates (and mischaracterizes) the situation.



Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #46 on: 02/15/2018 05:35 PM »
All examples of composite use are small and warm compared to its. Good example of failure is x33. It was a long time ago by space tech standards.
787 is not small. It's enormous. Wings also composite. X-33 was, of course, liquid hydrogen, which is proportionally further from liquid oxygen temperatures than liquid oxygen is to room temperature (referring to ratio of absolute temperatures). The BFR and a 787-10 are basically the same length.

Plus my understanding is what doomed X-33 was the complex shape of the tank. Which is not appliccable to ITS.

It was a combination of shape and temperature. IIRC the failure was due to liquid and/or solid air forming in the cells of the honeycomb sandwich LH2 tank, which caused delamination of the sandwich near the tank lobes.

BFR isn't using LH2, lobed tanks, or honeycomb sandwiches, so it don't think it's all that relevant.
« Last Edit: 02/15/2018 05:36 PM by envy887 »

Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #47 on: 02/15/2018 05:44 PM »
Conclusion:  Using composites may not be high risk based upon known experience in the industry.

None of the carbon fiber projects to date have used the material to contain sub cooled LOX, hot(ish) gaseous oxygen, and liquid methane. These tanks will be cycled hundreds of times and expect to store these propellants for months on end. It will have to be operated in a vacuum, survive reentry, etc etc.

R and D money has been put into these materials for decades, so there is some experience here and there in areas that will be helpful, but I think "high risk" is accurate.

I think "uncertain risk" characterizes the situation better.  High risk applies to risks that are understood, and which you can, if you will, compute a probability of a problem happening.  It's not as though there is no knowledge of the materials; as you say, they've been used in many ways for decades.  We just don't know what will happen in new environments, and won't, until further testing is done.

Labeling the situation "high risk" overstates (and mischaracterizes) the situation.

SpaceX has plenty of experience subjecting composite structural components to lots of cryocycles with subcooled propellants and LOX, and to vacuum and reentry, and then qualifying them for reflight and actually reflying them. The F9 COPVs, landing legs, interstage, and fairings are all flight proven composite structures.

The only open questions are how hot GOX pressurant and long term in-space operations affect composite structures.

Offline JoeyOak

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Re: BFR/ITS risk due to composites
« Reply #48 on: 02/15/2018 06:14 PM »
BFR isn't using LH2, lobed tanks, or honeycomb sandwiches, so it don't think it's all that relevant.

Those particular points of failure may not be directly relevant, but on a higher level it is a well documented fact that it is often difficult to anticipate failure mechanisms of composite materials.

Saying this is not a criticism of SpaceX, or any other organization, if anyone were ever under that impression. It can be hard to predict failure mechanisms of "unitary" materials too, but with composite materials the interaction of the constituent materials is affected by thermodynamics, adhesion, chemical properties, under a range of environmental conditions, and on and on; it is just very difficult. Even if you would gather all of the world's finest material scientists in a room, they would have a very hard time anticipating every possible failure mechanism, because it's just very difficult.

To me, it seems like a very sound approach to build a 'Big Falcon Spaceship', fly it a bunch of times, and then evaluate whether there is leakage, delamination, fatigue, and in that way conduct a methodic process of retiring risk. If I'm not completely misinformed, this is also what SpaceX intends to do. We're all rooting for them.

Offline Patchouli

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Re: BFR/ITS risk due to composites
« Reply #49 on: 02/15/2018 06:24 PM »
Another risk is how well will the composite structure handle reentry?
Though Dream Chaser flying would answer some of these unknowns.

Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #50 on: 02/15/2018 07:56 PM »
Another risk is how well will the composite structure handle reentry?
Though Dream Chaser flying would answer some of these unknowns.

Legs, fairings, and interstages already do reentry behind TPS. As long as you can characterize the thermal environment the composites will see behind the TPS, structural performance isn't hard to predict, and they already have a baseline.

Offline su27k

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Re: BFR/ITS risk due to composites
« Reply #51 on: 02/16/2018 02:12 AM »
Haven't seen this document in the forum: Design, Manufacture and Test of Cryotank Components, it has a nice history section which lists past projects with composite tanks, plus tons of details about Boeing/NASA's recent composite tank project.

Offline Robotbeat

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Re: BFR/ITS risk due to composites
« Reply #52 on: 02/16/2018 02:56 AM »
Another risk is how well will the composite structure handle reentry?
Though Dream Chaser flying would answer some of these unknowns.
Shuttle used composites. Seemed to work just fine (watch out for the carbon-carbon leading edges, though...).
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Re: BFR/ITS risk due to composites
« Reply #53 on: 02/16/2018 11:58 AM »
Haven't seen this document in the forum: Design, Manufacture and Test of Cryotank Components, it has a nice history section which lists past projects with composite tanks, plus tons of details about Boeing/NASA's recent composite tank project.

Clearly shows how much work has been done and how complex tanks are. Sometimes member comments make it sound so simple, and that SpaceX has done it all. They are standing on the shoulders of others. As we all do.

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Re: BFR/ITS risk due to composites
« Reply #54 on: 02/16/2018 12:08 PM »
Clearly shows how much work has been done and how complex tanks are. Sometimes member comments make it sound so simple, and that SpaceX has done it all. They are standing on the shoulders of others. As we all do.

And of course, they have the most obvious prerequisite for success.
Actually trying it.

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Re: BFR/ITS risk due to composites
« Reply #55 on: 02/17/2018 04:28 AM »
Does anyone have an idea of their current state of progress with BFR tanks? After the big press blitz with pictures of Elon standing in front of a giant tank, they hauled it out to sea for a LO2 fill test, and well.. it apparently came back like this: https://imgur.com/a/bGHR6 Nothing on the press circuit since then.

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Re: BFR/ITS risk due to composites
« Reply #56 on: 02/17/2018 05:56 AM »
Does anyone have an idea of their current state of progress with BFR tanks? After the big press blitz with pictures of Elon standing in front of a giant tank, they hauled it out to sea for a LO2 fill test, and well.. it apparently came back like this: https://imgur.com/a/bGHR6 Nothing on the press circuit since then.

Did you miss the update provided at the 2017 conference?

Offline AncientU

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Re: BFR/ITS risk due to composites
« Reply #57 on: 02/17/2018 04:30 PM »
There should be a structural test article of the BFS (in about a year, I'd guess) that will have fuel and oxidizer tanks with a common dome -- nine meter OD, autogenous pressurization.  That STA will build on the tests described above and answer many/most of the static questions.  After that, or in parallel with it, a first flight article.  Flights, starting at short hops discussed by EM and GS, will gather empirical evidence for the dynamic and cyclical environment.  Risk will be retired gradually over a few year test program.  When BFR comes along somewhere in there, it will have little mystery yet to uncover.
« Last Edit: 02/17/2018 04:31 PM by AncientU »
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Offline john smith 19

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Re: BFR/ITS risk due to composites
« Reply #58 on: 02/18/2018 05:11 PM »
There is a long and growing experience base in aerospace with composites.   

As mentioned already, 787 is largely composite.   The A380 has significant usage:  http://www.iccm-central.org/Proceedings/ICCM13proceedings/SITE/PAPERS/paper-1695.pdf
The B2 is largely composite.  All of these are very large, and they have significant service histories.  RocketLab's new orbital rocket just succeed while using composite LOX and Kero tanks.

SpaceX is using suppliers like Janicki that have built some of the above.

Conclusion:  Using composites may not be high risk based upon known experience in the industry.
That experience might not be as extensive as you think.

A 787-9 does weigh 254 tonnes, but only 1/2 of that is composite.

Likewise none of those aircraft use any cryogenic fuel, so they provide no experience of a)Carrying a large volume of a cryogen and b)Cyclic loading on such tanks.

AFAIK none of those aircraft has gone much beyond 20 degress from the horizontal (if that). Nothing like a "zoom climb" done by aircraft like the F106 or F15. Only the B2 is a potential candidate for this. That's important because BFS is going from roughly horizontal, to high AoA, right up to local vertical, while slowing to near zero forward speed. That means it needs to be strong (like the Shuttle) in 2 directions.

And of course all of them are subsonic, so they've never had any issues with skin heating due to M1+ flight, where the knowledge base (of aircraft with composite skins) is confined to military aircraft with at most 2 seats.

Right now the only vehicle that's taken composite tankage through the whole flight regime to orbit is Rocket Labs Electron ELV, which is 1/6 the diameter of BFS. That's probably the best evidence that it's possible.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

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Re: BFR/ITS risk due to composites
« Reply #59 on: 02/18/2018 09:36 PM »
787's wings are not made of carbon composites, and it is they that carry the fuel.

The Boeing 787's wings are carbon fiber composites. See Boeing's web site: http://www.boeing.com/commercial/787/by-design/#/advanced-composite-use

Offline john smith 19

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Re: BFR/ITS risk due to composites
« Reply #60 on: 02/18/2018 10:14 PM »
787's wings are not made of carbon composites, and it is they that carry the fuel.

The Boeing 787's wings are carbon fiber composites. See Boeing's web site: http://www.boeing.com/commercial/787/by-design/#/advanced-composite-use
I also was going to link to that page. It looks like quite a lot of the wing is as well.

IIRC aviation fuel freezes around -60c but the freezing point of Methane is -182c and LOX at -219c. So sometimes during flights the fuel gets to temperatures 1/3 as cold as Methane and substantially above 1/3 the lowest temperature of LOX.

The RL Electron still looks like the best existence proof that you can build a trouble free CRFP tank that can fly the whole trajectory to orbit.
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Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #61 on: 02/19/2018 01:18 PM »
Right now the only vehicle that's taken composite tankage through the whole flight regime to orbit is Rocket Labs Electron ELV

This is incorrect. COPVs are composite tanks subjected to cryocycles and structural loads and carried through the entire flight. They are used in many vehicles and SpaceX has plenty of experience with them.

Offline livingjw

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Re: BFR/ITS risk due to composites
« Reply #62 on: 02/19/2018 02:41 PM »
Right now the only vehicle that's taken composite tankage through the whole flight regime to orbit is Rocket Labs Electron ELV

This is incorrect. COPVs are composite tanks subjected to cryocycles and structural loads and carried through the entire flight. They are used in many vehicles and SpaceX has plenty of experience with them.

Irrelevant. COPVs are lined with aluminum. COPVs are orders of magnitude smaller. COPVs are not subject to widely varying environment, since they are immersed in the LOX tank. One major problem with unlined LOX tanks is the energy given off when fibers break under stress. Special matrix material has been used to address this problem. The CH4 tanks are not as much of a problem.

John

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Re: BFR/ITS risk due to composites
« Reply #63 on: 02/19/2018 02:43 PM »
Right now the only vehicle that's taken composite tankage through the whole flight regime to orbit is Rocket Labs Electron ELV

This is incorrect. COPVs are composite tanks subjected to cryocycles and structural loads and carried through the entire flight. They are used in many vehicles and SpaceX has plenty of experience with them.

Those are aluminum wrapped tanks, they would not scale to BFS propellant tank dimensions. Not applicable.

Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #64 on: 02/19/2018 03:03 PM »
Right now the only vehicle that's taken composite tankage through the whole flight regime to orbit is Rocket Labs Electron ELV

This is incorrect. COPVs are composite tanks subjected to cryocycles and structural loads and carried through the entire flight. They are used in many vehicles and SpaceX has plenty of experience with them.

Those are aluminum wrapped tanks, they would not scale to BFS propellant tank dimensions. Not applicable.

They are not Al-wrapped, they are Al-lined. The LOX-facing side is CRFP, not Al. SpaceX also said they would line the BFR tanks with invar if necessary, but they don't expect it to be needed.

The construction method for COPVs would not scale, but the COPV experience shows that the material itself is capable of cryocycles, structural loads, and flight with suitable tank construction.

Right now the only vehicle that's taken composite tankage through the whole flight regime to orbit is Rocket Labs Electron ELV

This is incorrect. COPVs are composite tanks subjected to cryocycles and structural loads and carried through the entire flight. They are used in many vehicles and SpaceX has plenty of experience with them.

Irrelevant. COPVs are lined with aluminum. COPVs are orders of magnitude smaller. COPVs are not subject to widely varying environment, since they are immersed in the LOX tank. One major problem with unlined LOX tanks is the energy given off when fibers break under stress. Special matrix material has been used to address this problem. The CH4 tanks are not as much of a problem.

John


The COPV CRFP is unlined on the LOX side.

What do you mean by "widely varying environment"? They go from STP to cryo temps and flight pressures at negative and positive g loads (they float in LOX but sink in GHe). That's the same environments that the main tanks will see, except for entry (which is demonstrated by the interstage, legs and fairings).

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Re: BFR/ITS risk due to composites
« Reply #65 on: 02/19/2018 03:13 PM »
SpaceX also said they would line the BFR tanks with invar if necessary, but they don't expect it to be needed.

Actually, Elon said that they hope for a spray on liner. Invar is the alternative of last resort.

What do you mean by "widely varying environment"?

The LOX tanks will hold cryogenic LOX and will use autogenous pressurization. Autogenous pressurization means sending hot, gaseous oxygen from the engines into the tanks. Talk about "widely varying environment".
« Last Edit: 02/19/2018 03:17 PM by jpo234 »
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Offline speedevil

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Re: BFR/ITS risk due to composites
« Reply #66 on: 02/19/2018 03:59 PM »
The LOX tanks will hold cryogenic LOX and will use autogenous pressurization. Autogenous pressurization means sending hot, gaseous oxygen from the engines into the tanks. Talk about "widely varying environment".
If you're feeling a bit less brave, you can run this through a spray, to get down to more comfortable temperatures.
Normally, this would use a lot more mass, as your pressurant is now non cryogenic.

But, if you've got landing tanks, that may matter way less in some situations, especially as it may recondense.

And might even, depending on stuff, be able to reuse this gaseous pressurant for ullage.
A 20kg thruster that runs on 50PSI ox/ch4 is quite far from the state of the art.
« Last Edit: 02/19/2018 04:39 PM by speedevil »

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Re: BFR/ITS risk due to composites
« Reply #67 on: 02/19/2018 04:13 PM »
They are not Al-wrapped, they are Al-lined.

Aluminum wrapped in carbon fiber, I know, may not have made it clear enough for you.
« Last Edit: 02/19/2018 04:13 PM by matthewkantar »

Offline john smith 19

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Re: BFR/ITS risk due to composites
« Reply #68 on: 02/19/2018 04:25 PM »
They are not Al-wrapped, they are Al-lined. The LOX-facing side is CRFP, not Al. SpaceX also said they would line the BFR tanks with invar if necessary, but they don't expect it to be needed.
Weren't they implicated in 2 F9 stage failures?

Quote from: envy887
The COPV CRFP is unlined on the LOX side.

What do you mean by "widely varying environment"? They go from STP to cryo temps and flight pressures at negative and positive g loads (they float in LOX but sink in GHe). That's the same environments that the main tanks will see, except for entry (which is demonstrated by the interstage, legs and fairings).
Except they will be "the main tank"

It seems a key issue is energy release if fibers are split within the tank, and the classic way to deal with that is to "grade" the inside of the tank (and possibly the outside, depending what it's immersed in) from fiber to a pure resin "skin" layer.

However the "hot" Oxygen pressurization system does complicate things.

But keep in mind that the "hot" Hydrogen in the RL10 turbine drive is only about 100c, allowing turbines of Aluminum.

So the question would be how "hot" is this Oxygen flow? -100c? (IE 173k) 0c? 100c?
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Offline JoeyOak

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Re: BFR/ITS risk due to composites
« Reply #69 on: 02/19/2018 06:25 PM »
I find this thread interesting  :)

Does anyone have a bona fide source that the Electron tanks are free from metal? If Rocket Lab only claim that they use carbon fibre composites for their tanks, then I suppose it could well be that the carbon fibre is used as part of the load-carrying honeycomb sandwich. At the very least, the tanks may well be lined with an Al-Li "membrane".

Offline ethan829

Re: BFR/ITS risk due to composites
« Reply #70 on: 02/19/2018 07:41 PM »
I find this thread interesting  :)

Does anyone have a bona fide source that the Electron tanks are free from metal? If Rocket Lab only claim that they use carbon fibre composites for their tanks, then I suppose it could well be that the carbon fibre is used as part of the load-carrying honeycomb sandwich. At the very least, the tanks may well be lined with an Al-Li "membrane".

The payload user's guide says:

Quote
Propellant tanks are constructed entirely from carbon fiber composite.

It also frequently references Electron's "all-carbon-composite" structure.

Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #71 on: 02/19/2018 07:56 PM »
They are not Al-wrapped, they are Al-lined. The LOX-facing side is CRFP, not Al. SpaceX also said they would line the BFR tanks with invar if necessary, but they don't expect it to be needed.
Weren't they implicated in 2 F9 stage failures?

One F9 failure, where LOX soaked into the CRFP and froze against the cryohelium liner. Not a problem if you don't have fluids colder than LOX. No LH2, no cryohelium in the BFR design.

The other was a weak strut that happened to be holding a COPV. There's no indication that the COPV failed.

Quote from: envy887
The COPV CRFP is unlined on the LOX side.

What do you mean by "widely varying environment"? They go from STP to cryo temps and flight pressures at negative and positive g loads (they float in LOX but sink in GHe). That's the same environments that the main tanks will see, except for entry (which is demonstrated by the interstage, legs and fairings).
Except they will be "the main tank"

It seems a key issue is energy release if fibers are split within the tank, and the classic way to deal with that is to "grade" the inside of the tank (and possibly the outside, depending what it's immersed in) from fiber to a pure resin "skin" layer.

However the "hot" Oxygen pressurization system does complicate things.

But keep in mind that the "hot" Hydrogen in the RL10 turbine drive is only about 100c, allowing turbines of Aluminum.

So the question would be how "hot" is this Oxygen flow? -100c? (IE 173k) 0c? 100c?

They also won't be holding 5500 psi. COPVs are operated nearer their maximum stress than I would expect a main tank to be. At worst they will have a similar stress.
« Last Edit: 02/19/2018 07:59 PM by envy887 »

Offline docmordrid

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Re: BFR/ITS risk due to composites
« Reply #72 on: 02/19/2018 08:45 PM »
Right now the only vehicle that's taken composite tankage through the whole flight regime to orbit is Rocket Labs Electron ELV

This is incorrect. COPVs are composite tanks subjected to cryocycles and structural loads and carried through the entire flight. They are used in many vehicles and SpaceX has plenty of experience with them.

Those are aluminum wrapped tanks, they would not scale to BFS propellant tank dimensions. Not applicable.

However, Musk said during the 2016 Reddit AMA they may line the BFR/S tanks with Invar (nickel–iron-lead alloy).
« Last Edit: 02/19/2018 08:50 PM by docmordrid »
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Offline livingjw

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Re: BFR/ITS risk due to composites
« Reply #73 on: 02/19/2018 11:41 PM »
Right now the only vehicle that's taken composite tankage through the whole flight regime to orbit is Rocket Labs Electron ELV

This is incorrect. COPVs are composite tanks subjected to cryocycles and structural loads and carried through the entire flight. They are used in many vehicles and SpaceX has plenty of experience with them.

Those are aluminum wrapped tanks, they would not scale to BFS propellant tank dimensions. Not applicable.

They are not Al-wrapped, they are Al-lined. The LOX-facing side is CRFP, not Al. SpaceX also said they would line the BFR tanks with invar if necessary, but they don't expect it to be needed.

The construction method for COPVs would not scale, but the COPV experience shows that the material itself is capable of cryocycles, structural loads, and flight with suitable tank construction.

Right now the only vehicle that's taken composite tankage through the whole flight regime to orbit is Rocket Labs Electron ELV

This is incorrect. COPVs are composite tanks subjected to cryocycles and structural loads and carried through the entire flight. They are used in many vehicles and SpaceX has plenty of experience with them.

Irrelevant. COPVs are lined with aluminum. COPVs are orders of magnitude smaller. COPVs are not subject to widely varying environment, since they are immersed in the LOX tank. One major problem with unlined LOX tanks is the energy given off when fibers break under stress. Special matrix material has been used to address this problem. The CH4 tanks are not as much of a problem.

John


The COPV CRFP is unlined on the LOX side.

What do you mean by "widely varying environment"? They go from STP to cryo temps and flight pressures at negative and positive g loads (they float in LOX but sink in GHe). That's the same environments that the main tanks will see, except for entry (which is demonstrated by the interstage, legs and fairings).

My mistake, lox to carbon fiber on the outside of the tank. My other comments stand, completely different environments and sizes.

John

Offline livingjw

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Re: BFR/ITS risk due to composites
« Reply #74 on: 02/19/2018 11:47 PM »
I believe the shuttle lox tank used about 100 deg c GOX for tank pressurization.

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Re: BFR/ITS risk due to composites
« Reply #75 on: 02/20/2018 03:17 AM »
nickel-iron-lead isn't light weight.  How thick a layer do they need?  Does it flake off?  Or wear away?  How much mass is that for large tanks?

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Re: BFR/ITS risk due to composites
« Reply #76 on: 02/20/2018 05:28 AM »
AIUI the layer would be thin, mainly to protect the carbon from warm to hot oxygen generated for autogenous pressurization. Invar because of its low coefficient of thermal expansion.
« Last Edit: 02/20/2018 05:28 AM by docmordrid »
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Re: BFR/ITS risk due to composites
« Reply #77 on: 02/20/2018 05:38 AM »
nickel-iron-lead isn't light weight.  How thick a layer do they need?  Does it flake off?  Or wear away?  How much mass is that for large tanks?
Once again: An Invar liner is the last resort. Elon said that they look for a coating that can be sprayed on.
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Offline niwax

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Re: BFR/ITS risk due to composites
« Reply #78 on: 02/20/2018 06:44 AM »
AIUI the layer would be thin, mainly to protect the carbon from warm to hot oxygen generated for autogenous pressurization. Invar because of its low coefficient of thermal expansion.

Would you need to protect the entire tank? In order to allow for simple relighting, the BFR has a small high pressure tank inside the big tank. Depending on how the pressurization works, they would only have a small hot spot.

Offline john smith 19

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Re: BFR/ITS risk due to composites
« Reply #79 on: 02/20/2018 06:34 PM »
I believe the shuttle lox tank used about 100 deg c GOX for tank pressurization.

John
A useful data point.  GO2 wan generated by a short heat exchanger pipe wrapped around the SSME.

But the ET was made of Aluminum Lithium .  AlLi retains its strength to about 180c. The tricky part is making sure the CFRP structure can handle both deep cooled LO2 and 100c, and cyclically.

I wonder how the Electron pressurized its LOX tank?  The classic solution is GHe but it should be pretty easy to put some LOX piping around an engine(s) or battery pack(s) to vaporize enough O2 to keep the tank pressure up.
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Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #80 on: 02/21/2018 03:21 AM »
nickel-iron-lead isn't light weight.  How thick a layer do they need?  Does it flake off?  Or wear away?  How much mass is that for large tanks?
Once again: An Invar liner is the last resort. Elon said that they look for a coating that can be sprayed on.

I wonder if the coating would be spray foam insulation, BFS needs insulation for deep space and Mars surface (to avoid freezing out dry ice). But urethane foam seems like it would be just as bad as carbon epoxy in the face of hot GOX. A silica fiber based insulation sounds like a better bet but I don't know if they could spray it.

There are high temperature phenolic CRFP resins that can take up to 500 C for short times. Not just stronger at elevated temperatures, but also more resistant to oxidation.

Offline Patchouli

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Re: BFR/ITS risk due to composites
« Reply #81 on: 02/21/2018 04:49 AM »
Another solution could the inner most layers of the tanks be made from something like Nonburnite which can handle -260C to +280C.
This should exceed anything they'll see in service by a good margin.

https://omnexus.specialchem.com/tech-library/article/nonburning-high-heat-composite-material-of-the-future
« Last Edit: 02/21/2018 04:50 AM by Patchouli »

Offline john smith 19

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Re: BFR/ITS risk due to composites
« Reply #82 on: 02/21/2018 06:38 AM »
Another solution could the inner most layers of the tanks be made from something like Nonburnite which can handle -260C to +280C.
This should exceed anything they'll see in service by a good margin.

https://omnexus.specialchem.com/tech-library/article/nonburning-high-heat-composite-material-of-the-future
Unfortunately XCOR is now defunct.

Does anyone know what happened to the nonburnite IP?

I wonder if the coating would be spray foam insulation, BFS needs insulation for deep space and Mars surface (to avoid freezing out dry ice). But urethane foam seems like it would be just as bad as carbon epoxy in the face of hot GOX. A silica fiber based insulation sounds like a better bet but I don't know if they could spray it.
Such materials do exist and are in use for refurbishing furnaces. I've no idea how fragile or heavy they are.
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Re: BFR/ITS risk due to composites
« Reply #83 on: 02/21/2018 06:57 AM »
Another solution could the inner most layers of the tanks be made from something like Nonburnite which can handle -260C to +280C.
This should exceed anything they'll see in service by a good margin.

https://omnexus.specialchem.com/tech-library/article/nonburning-high-heat-composite-material-of-the-future

This sounds (from my layman perspective) exactly like the kind of material Elon was talking about.
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Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #84 on: 02/21/2018 01:46 PM »
Another solution could the inner most layers of the tanks be made from something like Nonburnite which can handle -260C to +280C.
This should exceed anything they'll see in service by a good margin.

https://omnexus.specialchem.com/tech-library/article/nonburning-high-heat-composite-material-of-the-future
Unfortunately XCOR is now defunct.

Does anyone know what happened to the nonburnite IP?

I wonder if the coating would be spray foam insulation, BFS needs insulation for deep space and Mars surface (to avoid freezing out dry ice). But urethane foam seems like it would be just as bad as carbon epoxy in the face of hot GOX. A silica fiber based insulation sounds like a better bet but I don't know if they could spray it.
Such materials do exist and are in use for refurbishing furnaces. I've no idea how fragile or heavy they are.

Not heavy at all, but lightweight silica materials rather brittle. Aerogel and the Shuttle tiles are two examples.

Offline john smith 19

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Re: BFR/ITS risk due to composites
« Reply #85 on: 02/21/2018 09:01 PM »
Not heavy at all, but lightweight silica materials rather brittle. Aerogel and the Shuttle tiles are two examples.
Not necessarily an issue, provided its thermal expansion coefficient matches (or can be made to match) that of the CFRP material (so no cracking due to temperature cycling stresses) and its dense enough (or has a dense skin) to keep the GO2 away from the CFRP.

The issue with all surface treatments or protective coatings (from TPS to TBC's on turbine blades to LOX tank linings) is a)How do you monitor their integrity b)If the integrity of the layer fails how does the design cope with this (or is this one of those "Must never ever happen" events?) c) How do you refurbish if it is damaged.
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