Author Topic: Carbon Composite Tanks and LOX  (Read 45595 times)

Offline a_langwich

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Re: Carbon Composite Tanks and LOX
« Reply #120 on: 10/24/2016 09:50 pm »
Assuming they can make these tanks work, what is the likely mass advantage of a liner-less composite tank vs. a traditional Aluminum alloy tank of similar capacity?

Are we talking about a 10%, 30%, 50% reduction in mass?

-MG

As Elon said.
"At worst we will have to line the tanks with either a spray on sealant or invar." (not exact quote)
This doesn't sound as bad of a mass penalty of going with an all Al tank.



Hard to tell without numbers.

Coatings and liners for cryogenic composite tanks are definitely non-trivial.  Of course, 10m+ sized cryogenic composite tanks are non-trivial, too.  I look forward to seeing what they come up with. 

Offline HMXHMX

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Re: Carbon Composite Tanks and LOX
« Reply #121 on: 10/24/2016 11:05 pm »
Assuming they can make these tanks work, what is the likely mass advantage of a liner-less composite tank vs. a traditional Aluminum alloy tank of similar capacity?

Are we talking about a 10%, 30%, 50% reduction in mass?

-MG

It depends on a number of factors, but when I have designed medium-volume launch vehicle tanks (EELV class) the aluminum ones tends to be about 0.7-0.8 lbm/pcf (all you smart folks can no doubt convert to your units of preference) while pure composite are in the range of 0.4-0.5.

well I can guess that lbm is pounds mass.
pcf is percent fuel?
Edit: acronym finder says per cubic foot(off)

Yes, per cubic foot.  :)

Online guckyfan

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Re: Carbon Composite Tanks and LOX
« Reply #122 on: 10/25/2016 09:59 am »
About that coating needed to protect the carbon fiber tank from hot gaseous oxygen. I do wonder if glass is resistant enough. There is a cheap and simple process to sputter glass, (or SiO2?) on plastic beer bottles. The coating is thin enough to be flexible. I am not sure if the fexibility helps with thermal expansion and contraction. If yes it might be a possible solution. It is that coating that made beer in plastic bottles feasible because it is a much better barrier against oxygen from the atmosphere than the PET of the bottle. It keeps the taste over longer times.

Offline docmordrid

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Re: Carbon Composite Tanks and LOX
« Reply #123 on: 10/25/2016 01:00 pm »
Or, you do what Musk said - use an Invar liner which is tough and minimizes expansion/contraction issues.
DM

Offline AncientU

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Re: Carbon Composite Tanks and LOX
« Reply #124 on: 10/25/2016 02:21 pm »
I would think a plain flat barge without expensive hardware aboard. That way stage landings aren't compromised if it flunks out.

What would the failure modes be here? If the tank fails I wouldn't expect a huge amount of damage to the barge, theres not much fuel to combust with. And they've dealt with barge explosions before anyway
Again ambiguity in Elon's answer, didn't specify what the tank is filled with during the pressure test. Could be just freshwater. Then the biggest danger to the barge is to get wet on the topside too.

A freshwater test (hydrostatic test) could be done where the tank was built.  Hydro tests are done because if the tank leaks, it depressurizes very quickly -- very little energy stored in pressurized water.  The discussed test on a barge is more likely a test with cryogens (LN2 would be my guess) or pressurized air/gas -- this test must be done away from people because the energy involved could be huge.
"If we shared everything [we are working on] people would think we are insane!"
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Online guckyfan

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Re: Carbon Composite Tanks and LOX
« Reply #125 on: 10/25/2016 04:43 pm »
Or, you do what Musk said - use an Invar liner which is tough and minimizes expansion/contraction issues.

He did not say that. Not at all. It would be his fallback if he cannot find a better solution. He prefers something that can be sprayed on because of cost. My suggestion would fall in that category.

Offline docmordrid

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Re: Carbon Composite Tanks and LOX
« Reply #126 on: 10/25/2016 04:59 pm »
What is the expansion coefficient of your proposed sputtered glass?
DM

Offline woods170

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Re: Carbon Composite Tanks and LOX
« Reply #127 on: 10/25/2016 07:23 pm »
By the way, Musk confirmed (Reddit AMA) that the smaller spherical tanks in the main tanks contain the landing propellants:

"Those are the header tanks that contain the landing propellant. They are separate in order to have greater insulation and minimize boil-off, avoid sloshing on entry and not have to press up the whole main tank."

"The liquid oxygen transfer tube serves as the header tank for ox"



I get the award
Just another way of saying "I told you so."

But heck, maybe we should start giving you awards.  :)
« Last Edit: 10/25/2016 07:30 pm by woods170 »

Offline Burninate

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Re: Carbon Composite Tanks and LOX
« Reply #128 on: 09/18/2018 06:26 pm »
Subcooling of the methane is assumed.  Subcooling of the LOX is not something you're going to get;  Too much weight.
Your sentence makes little sense. Part of Methane's attraction is it can be operated at very close to the same (sub cooled) temperature as LOX, keeping the thermal gradient across any common bulkhead tanks quite low.

If you can do one, you can do the other.

Sorry for the necro, but following up on my old threads:

A normal refrigeration system requires a fluid coolant that boils and condenses in a piping system with variable levels of compression.  In a lot of terrestrial systems, the coolant is water, or ammonia, or some purpose-crafted halocarbons.  LOX is assumed to be the coolant here directly, since it boils not too far from where methane freezes, and since we will have a lot of it, and since it will be thermally bonded to the methane anyway, as a very large thermal body in close contact.  If you _tried_ to cool methane and LOX far below the boiling point of the LOX, the methane would freeze.  If you tried to ensure that the two large thermal bodies maintain a large temperature differential in separate thermal environments, you would gain nothing and spend enormous amounts of mass and energy.
« Last Edit: 09/18/2018 06:29 pm by Burninate »

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