"The Ruzicka Family" wrote in message ...
"ed kyle" wrote in message
om...

Delta IV is optimized for GTO missions. ...


What do you mean by "optimized for GTO missions"?

Consider a straight up comparison of the two EELV base-models.
Delta IV was designed from the outset to boost smaller GTO
payloads (to standard GTO orbits from Cape Canaveral) than
Atlas V (4 versus 5 metric tons). But Delta IV loses even
more ground to Atlas V when it comes to LEO missions.
Delta IV-M can boost only 8.5 tons to a 185 km orbit while
Atlas V-401/402 can loft more than 12 tons. I think the
root cause of this is because both Delta IV stages produce
lower thrust than the Atlas stages (Atlas uses two Centaur
engines for LEO missions) so that Delta IV suffers higher
gravity losses. Delta IV would also have tighter liftoff
thrust-to-weight limitations than Atlas V.

- Ed Kyle