Author Topic: BFR/ITS risk due to composites  (Read 32347 times)

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.
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.

Offline jpo234

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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.
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.

Offline su27k

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BFR/ITS composites discussion
« Reply #86 on: 09/30/2018 08:57 PM »
Now that we've seen the actual composite section, there's an attempt at reddit to estimate its thickness: https://www.reddit.com/r/SpaceXLounge/comments/9javua/quick_bfr_structural_carbon_fiberre_calculations/, the result is 12 to 25mm.

The teslarati article has a photo that gives more details, by trying to complete the circle I estimated the thickness (the white border) as 50mm.

So does this thickness seem excessive? I couldn't find the thickness of the NASA/Boeing test tank. For aircraft like A350, it looks like the composite fuselage is only a few mm thick.

Online lamontagne

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Re: BFR/ITS composites discussion
« Reply #87 on: 09/30/2018 09:41 PM »
Now that we've seen the actual composite section, there's an attempt at reddit to estimate its thickness: https://www.reddit.com/r/SpaceXLounge/comments/9javua/quick_bfr_structural_carbon_fiberre_calculations/, the result is 12 to 25mm.

The teslarati article has a photo that gives more details, by trying to complete the circle I estimated the thickness (the white border) as 50mm.

So does this thickness seem excessive? I couldn't find the thickness of the NASA/Boeing test tank. For aircraft like A350, it looks like the composite fuselage is only a few mm thick.
50mm is excessive, would make the BFS much too heavy (about 150 tonnes).  However, it might well be an assembly flange, so the wall thickness may be much lower, and the 50mm be correct.
My own supposition (10mm for the ship, 12mm for the booster) is joined here is a spreadsheet.
« Last Edit: 09/30/2018 09:56 PM by lamontagne »

Offline matthewkantar

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Re: BFR/ITS risk due to composites
« Reply #88 on: 09/30/2018 09:48 PM »
Quick BOTE calculation, a carbon composite cylinder 118 meter tall 28 meters in circumference, 5 cm thick without bulkheads or engines or anything would weight a lot more than empty BFR/BFS stack is supposed to weigh.

Matthew

Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #89 on: 10/01/2018 01:10 PM »
It could be two thin walls 50 mm apart with flutes between. This is how Boeing and NASA constructed the 5 m diameter composite test tank.

https://www.nasa.gov/feature/case-study-nasaboeing-composite-launch-vehicle-fuel-tank-scores-firsts

Offline Hominans Kosmos

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Re: BFR/ITS risk due to composites
« Reply #90 on: 10/01/2018 01:34 PM »
It could be two thin walls 50 mm apart with flutes between. This is how Boeing and NASA constructed the 5 m diameter composite test tank.

https://www.nasa.gov/feature/case-study-nasaboeing-composite-launch-vehicle-fuel-tank-scores-firsts

I can not find any references in the Composite Cryotank Technologies and Demonstration project towards applicability to reusable launch vehicles. As I understand it the project requirements were for disposable launch vehicle technologies.

I'm no composites expert but the flutes do not strike me as a stress cycle life enhancing solution. Intuition may be wrong here but the opppaite.seems more likely. 

To paraphrase Dan Raskin's view from the top talk: as few miracles as possible please.
« Last Edit: 10/01/2018 01:36 PM by Hominans Kosmos »

Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #91 on: 10/01/2018 01:46 PM »
It could be two thin walls 50 mm apart with flutes between. This is how Boeing and NASA constructed the 5 m diameter composite test tank.

https://www.nasa.gov/feature/case-study-nasaboeing-composite-launch-vehicle-fuel-tank-scores-firsts

I can not find any references in the Composite Cryotank Technologies and Demonstration project towards applicability to reusable launch vehicles. As I understand it the project requirements were for disposable launch vehicle technologies.

I'm no composites expert but the flutes do not strike me as a stress cycle life enhancing solution. Intuition may be wrong here but the opppaite.seems more likely. 

To paraphrase Dan Raskin's view from the top talk: as few miracles as possible please.

Fluting is one way to make a sandwich panel, other options are honeycomb core or foamcore. Composite sandwich panels are very common in aerospace applications, since like isogrids/orthogrids they reduce weight while increasing strength and stiffness. The savings over solid structures are massive, which means margins can be higher, which makes reuse much easier.

Foamcore (or aerogel core) might be a more attractive option than fluting or honeycomb since it would add considerable insulation while increasing structural strength and stiffness and reuducing weight. This is not a new solution, the X-33 CRFP LH2 tanks used honeycomb sandwich construction which had problems with air leaking in and condensing: the solution was to fill the honeycomb with foam.

https://www.usna.edu/Users/mecheng/pjoyce/composites/Short_Course_2003/13_PAX_Short_Course_Sandwich-Constructions.pdf
« Last Edit: 10/01/2018 01:47 PM by envy887 »

Offline Hominans Kosmos

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Re: BFR/ITS risk due to composites
« Reply #92 on: 10/01/2018 03:48 PM »
Composite sandwich panels are very common in aerospace applications, since like isogrids/orthogrids they reduce weight while increasing strength and stiffness. The savings over solid structures are massive, which means margins can be higher, which makes reuse much easier.

Granted. How many of these sandwich constructions see use as multi-cycle mild-cryo containers? You'll notice F9 fairing is sandwich, fuselage is not, not the bulk of it at the very least. Airframes rarely carry cryogenic fluid.

The savings are moot if it introduces catastrophic failure modes.

Offline speedevil

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Re: BFR/ITS risk due to composites
« Reply #93 on: 10/01/2018 05:19 PM »
Composite sandwich panels are very common in aerospace applications, since like isogrids/orthogrids they reduce weight while increasing strength and stiffness. The savings over solid structures are massive, which means margins can be higher, which makes reuse much easier.

Granted. How many of these sandwich constructions see use as multi-cycle mild-cryo containers? You'll notice F9 fairing is sandwich, fuselage is not, not the bulk of it at the very least. Airframes rarely carry cryogenic fluid.

The savings are moot if it introduces catastrophic failure modes.

Detecting delaminations between the sandwitch faces can be a problem, as you can't simply inspect in the middle.

Offline john smith 19

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Re: BFR/ITS risk due to composites
« Reply #94 on: 10/01/2018 05:57 PM »
Detecting delaminations between the sandwitch faces can be a problem, as you can't simply inspect in the middle.
True.

When NDE for composites is discussed a couple of techniques come up.

1) Acoustic emissions. Basically bond PZ film microphones to pick up the "pings" of the layers separating, or the fibres snapping. Note while it's described as "acoustic" this "sound" can be into the MHz, given that it's being transmitted to solids, not gases.

2)FO sensors with interference gratings (Fibre Bragg Gratings) written into them. Individual gratings along the fibre can be interrogated by their time of flight return signal, or a "white light" drive signal with each responding to a slightly different part of the spectrum.

AE systems have (potentially) a lot of wiring for them, while FO FBG systems may take longer to sample a specific sensor on the fibre.

They can identify it happening and localize where it's happening.

But the real question is "If it happens, what can you do about it?"

I think the early BFR's will be heavily instrumented to check reality with simulations and update the simulation models based on actual results.
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.

Offline Robotbeat

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Re: BFR/ITS risk due to composites
« Reply #95 on: 10/01/2018 06:10 PM »
You donít need to embed the ultrasonic sensors. You can do inspection with a fluid filled finger.

Digital X ray sensors can also be done. Doesnít require embedding either.

Parts can be repaired with resign injection and patching techniques.
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Offline envy887

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Re: BFR/ITS risk due to composites
« Reply #96 on: 10/01/2018 06:26 PM »
Composite sandwich panels are very common in aerospace applications, since like isogrids/orthogrids they reduce weight while increasing strength and stiffness. The savings over solid structures are massive, which means margins can be higher, which makes reuse much easier.

Granted. How many of these sandwich constructions see use as multi-cycle mild-cryo containers? You'll notice F9 fairing is sandwich, fuselage is not, not the bulk of it at the very least. Airframes rarely carry cryogenic fluid.

The savings are moot if it introduces catastrophic failure modes.

X-33 was going to use it for hard cryogenic multi-cycle reusable tanks. Had issues with hollow honeycomb but not once foam filled.

The Saturn V S-II had a sandwich common bulkhead laminated layup separating LH2 and LOX.

Offline RobLynn

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Re: BFR/ITS risk due to composites
« Reply #97 on: 10/02/2018 12:18 AM »
Axial wall stiffening for the BFB at least would be beneficial, with axial compressive loads up to 2x the hoop gas pressure tensile loads.  Much less of an issue for the BFS with shorter tanks and lower loads (though walls may be substantially thinner on BFS?). 

The vented fluting for BFB would be pretty easy to build in, and could be enhanced around the attachment points for the outer ring of booster engines at ~1.2m spacings.   It would also likely be useful for anchoring of TPS without danger of penetrating (or hot spots) in the tanks.  It might also provide some extra damage resistance for impact damage and re-entry burn-through tolerance.

Alternatively SpaceX could easily and cheaply use the filament winding process to create a crude isogrid via selective thickening of some axial and helical paths during winding process.  Eg 5mm average wall thickness with wide 20-30mm thick ribs over ~10% of surface area.  No cryopumping issues then.  Though uneven external surface might be more difficult for close fitting of TPS.

For a rough sense of the wall thickness to diameter for BFR think: beer can (0.1mm thick, ō70mm diameter), equivalent to wall thickness of 13mm at ō9m
« Last Edit: 10/02/2018 09:02 AM by RobLynn »
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Offline RDMM2081

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Re: BFR/ITS risk due to composites
« Reply #98 on: 10/02/2018 04:24 AM »
Alternatively SpaceX could easily and cheaply use the filament winding process to create a crude isogrid via selective thickening of some axial and helical paths during winding process.  Eg 5mm average wall thickness with wide 20-30mm thick ribs over ~10% of surface area.

I don't have the background in CF / SOTA.  But from the bits I have been able to piece together in my own fantasy-land and what I believe (personally) about Musk and his aspirations is that he and his team are putting together a revolution in CF for BFR/BFS.  This is 100% speculation, and I don't even know how to posit the hypothesis in terms that make sense, but some of the unanswered questions about "why does this mandrel have all these extra funky pieces on it" and such, make me think its going to be something cool.  Even if it's "only" as cool as some selective strengthening, it could still be amazing.  Still leaves plenty of room for problems to arise (new tech new problems, original problem of hot gas/cold lox, valid concerns about cyclic fatigue) but still interesting and exciting!

Offline john smith 19

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Re: BFR/ITS risk due to composites
« Reply #99 on: 10/02/2018 05:42 AM »
You donít need to embed the ultrasonic sensors. You can do inspection with a fluid filled finger.

Digital X ray sensors can also be done. Doesnít require embedding either.

Parts can be repaired with resign injection and patching techniques.
That would be during mfg.

I was talking monitoring during operation.
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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