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I'm curious as to the typical manufacturing (or gathering) methodology of H2 and O2 used in modern rockets for fuel and oxidizer. It would seem that the most straightforward process would seem to be electrolysis of water into its H2 and O2 components, but rarely does the most straightforward process seem to be what is actually used.

The other option I can come up with is to just pull H2 and O2 off as just other gases during a standard liquification air cooling process that can be used to pull any number of gasses out of standard breathing air by carefully cooling and gathering the condensed liquids as the gasses in the air liquify at different temperatures as they cool. It just seems that this way would take a long time and a huge abundance of liquid N2 (based on volume of gasses in the air) just due to the huge volumes of H2 and O2 needed (especially O2 since O2 is used for just about all liquid fueled rockets, no matter the fuel used).

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  • $\begingroup$ There is very few H2 in air, read en.wikipedia.org/wiki/Atmosphere_of_Earth and about production of H2 en.wikipedia.org/wiki/Hydrogen_production $\endgroup$ – Uwe Aug 22 '17 at 19:26
  • $\begingroup$ I was told that LOX is mostly produced as a byproduct of producing the much more valuable argon. $\endgroup$ – Organic Marble Aug 22 '17 at 19:37
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    $\begingroup$ @OrganicMarble: Same for LN2. But there are lots and lots of processes that produce hydrogen as byproduct in industry, but I don't know where the bulk of hydrogen for LH2 use is created. $\endgroup$ – SF. Aug 22 '17 at 20:45
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    $\begingroup$ @SF : The bulk of hydrogen is produced by steam reforming from hydrocarbons. See wikipedia about hydrogen production. $\endgroup$ – Uwe Sep 29 '17 at 21:35
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LOX is produced by cryogenic distillation. Hydrogen is mainly (∼95%) produced from fossil fuels by steam reforming or partial oxidation of methane and coal gasification, with only 4% coming from electrolysis. Electrolysis is inefficient compared to other methods.

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    $\begingroup$ Hydrogen is not extracted from coal, it is generated from steam and coal. The coal is used to reduce the water of the steam to hydrogen and carbon monoxide. Coal contains very little hydrogen. $\endgroup$ – Uwe Aug 24 '17 at 1:36

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