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  • $\begingroup$ The first stage of Blue Origin's New Glenn burns methane, only the second stage is hydrolox. This actually meant designing two new engines, since the BE-3U is actually a different engine from the BE-3...it doesn't even use the same combustion cycle. And what existing hydrolox engines do you have in mind that have a prayer of being competitive in the long run? Especially considering that Starship is a fully reusable system. $\endgroup$ Commented Feb 13, 2021 at 4:13
  • $\begingroup$ I already know that New Glenn has a methalox first stage. "And what existing hydrolox engines do you have in mind that have a prayer of being competitive in the long run?" That is basically in the same vein to the question I was asking. Should hydrolox be abandoned if you've already invested into it, or is the capability worth keeping? $\endgroup$ Commented Feb 13, 2021 at 8:37
  • $\begingroup$ Very interesting that hydrogen has a much higher flammability range than methane, possibly making it more suitable for reliable re-lights. But LNG is very inexpensive and becoming widely available. Gaseous (or liquid) H2 injection may be considered (for re-lights), but i would stay with "methalox". $\endgroup$ Commented Feb 13, 2021 at 13:49
  • $\begingroup$ @user39270 you cite Blue Origin as a company that already has hydrolox engines that they intend to use. They aren't planning to use the hydrolox engine they have (which is a sea-level engine with limited thrust), New Glenn uses all newly-developed engines. Anyone interested in cost reduction is going to need to do this, current hydrolox engines are eye-wateringly expensive. (\$100M/engine for the "cost-reduced" RS-25E, \$26M for the "low cost" RS-68, the RL-10 family of engines were known for their high cost even when nobody took launch costs seriously...) $\endgroup$ Commented Feb 13, 2021 at 14:29