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It seems that there has been controversy as to how safe carbon fiber can be for LOX tanks. In early tests, materials were found to be too ready to combust. This has been a stumbling block for development in the past, like the X-33. There was a paper published at Lockheed titled "Oxygen Compatibility Testing Of Composite Materials" that questions if any materials have yet been found that can work safely enough.
The electron rocket I believe uses carbon fiber LOX tanks and the BFR depends heavily on them. Does anyone know what materials may have been found that resist combustion enough, or how this issue has been dealt with?

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  • $\begingroup$ Making composite tanks that hold cryo-temperature liquids is one of the main breakthroughs in both SpaceX and Rocket Labs. So far they haven't been very forthcoming with information (for obvious reasons). In a recent Reddit AMA the CEO of Rocket Labs mentioned that the composite tank technology was probably the most important part and took them 3 years of R&D to get working. $\endgroup$ – Dragongeek Apr 10 '18 at 6:40
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    $\begingroup$ Look up something around "linerless cryogenic tanks". As far as I can tell the biggest problem in crygonic tanks without liner is microcracking. Carbon fiber and epoxy have a vastly different thermal expansion (or contraction) resulting in fine cracks everywhere in the tank. Microcracking has been reduced by using spreadtow fabrics and there were tests using dry winding (no epoxy). Liquid crystal polymers seem to perform good in cryogenic applications. $\endgroup$ – Christoph Apr 10 '18 at 7:51
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    $\begingroup$ Charcoal soaked with liquid oxygen is explosive, carbon fibers without epoxy should be explosive too. But there is research about liquid oxygen compatible epoxy: 1, 2, 3, 4, 5. $\endgroup$ – Uwe Apr 10 '18 at 9:43

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