Everything about energy production and storage.
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I'm sorry, are we really going to pretend long haul flights will become hydrogen in the near future? Has any airport begun building, or even thinking of, refueling infrastructure?
No; it's a fairly distant thing with there being some aircraft design happening.
It's not a "next tuesday thing"
Ammonia, steel, and some petrochemicals could be moved much sooner.
I'm curious why long-haul aviation is easier than short-haul aviation according to this chart. Why would that be the case?
Short-haul can hopefully be handled by improved battery tech. Long-haul would need even lighter batteries so it's less likely to work or will take longer.
Ah, makes sense! Glad to hear that battery tech is approaching the level where short-haul aviation is viable.
The hydrogen economy is a boondoggle. Most of it is produced using natural gas.