Author Topic: BFR/ITS risk due to composites  (Read 22286 times)

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.

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Online matthewkantar

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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).

Offline jpo234

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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 »

Online matthewkantar

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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 »

Online 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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Offline Norm38

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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?

Online docmordrid

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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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Offline jpo234

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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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