Author Topic: BFR/ITS risk due to composites  (Read 4528 times)

Online 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:

Online 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.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline rsdavis9

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.
bob

Online 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.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online 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.

Online 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 »

Online 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.

Online 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.
DM

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 »

Online 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.

Online 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.

ABCD - Always Be Counting Down

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 »
DM

Online 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. 

Online 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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To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline rsdavis9

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?
bob

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.

Online 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.

Online 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 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

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