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?
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