Jon Goff has an absolutely fantastic post here at LH2: Love it or hate it?
LH2 seems most clearly stupid for a first stage fuel. Hydrogen engines have low thrust-to-weight, low thrust-to-cost, and big tanks which can cause a lot of atmospheric drag. Hydrogen first stages also see larger gravity losses than hydrocarbon first stages.
Both the Shuttle and the Delta IV use LH2/LOX engines off the pad. The Shuttle uses hydrogen because those engines are ground-ignited second stage engines, so it has at least some excuse. But the Delta IV is a simple two stage rocket with both stages being LH2/LOX. Why? Did they need to be different than the Atlas V?
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Iain,
ReplyDeleteIt may also have been from the desire to reduce fueling complexity by only having two propellants instead of three....but that's about all I could think of. Maybe that or their engineers were working on this big rocket engine, and they had to stick it somewhere.....
;-)
~Jon