Author Topic: BFR/ITS risk due to composites  (Read 23627 times)

Offline jpo234

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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.
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Offline jpo234

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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 »
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Offline Hobbes-22

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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.   




Offline 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.

Offline jg

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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.

Online 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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Online livingjw

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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.

John

Offline speedevil

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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.

Offline rhoark

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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.

Online Lars-J

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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?

Online 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.
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Offline matthewkantar

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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

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