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This answer explains how the liquid oxygen in a Falcon 9 is evaporation cooled to maintain a temperature well below boiling, by bubbling helium through it.

The temperature difference to the surrounding environment must be more than 200K. How is the tank insulated? What is the resulting outside surface temperature of a Falcon 9 (first or second stage)? I suppose it must be above freezing in order to prevent ice build-up, so the insulation must be substantial, but that seems to be difficult due to the weight constraints on a rocket. How is is that solved? What is the resulting surface temperature?

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    $\begingroup$ See this related question. $\endgroup$
    – Uwe
    Jun 4, 2020 at 13:32
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    $\begingroup$ I doubt it's insulated at all, but hopefully someone will write a good answer with references. $\endgroup$ Jun 4, 2020 at 13:35
  • $\begingroup$ @Uwe Ah, so there actually is ice build-up, but it falls off during the first seconds. Interesting. $\endgroup$ Jun 4, 2020 at 13:35
  • $\begingroup$ The first time they put Falcon 9 on the pad for a wet dress rehearsal, it shed big sheets of cork insulation because they didn't include adequate contraction joints. This was for their reentry experiments, not for holding cryogenic LOX. Some of the earlier returned boosters showed bubbling and chipping of coatings as well. They've done huge amounts of development on the thermal protection systems since then and may no longer use cork, but likely still use more than painted aluminum. And obviously, does not keep ice from forming...you couldn't even see the NASA logo on the DEMO-2 flight. $\endgroup$ Jun 4, 2020 at 17:27

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