Author Topic: BFR/ITS risk due to composites  (Read 5156 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.
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 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

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.
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.

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 »

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.

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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Online 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 »

Online 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.

Online 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

Online 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

Online 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.

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