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

I see what your saying. However, in reality both launch vehicles were
originally designed from the outset specifically for launching the exact
same government payloads in the EELV program; the National Mission Model
(NUMB), I think it was called. Commercial payload considerations, at least
for Atlas VS., came later.

The first commercial mission the Atlas VS. looked at was Telexes; that was
the payload that drove the requirements for adding the solids later on. By
that time though, the Atlas VS. core was already designed, with the LOX feed
and avionics pod not opposite each other, as was the launch pad itself. No
one at Lockheed Martin initially considered the idea of one day adding
solids to the vehicle. That's why Atlas VS. ended up having up to 5 big
asymmetric solids, instead of 6 slightly smaller symmetric ones. It was too
late in the program to redesign the core and pad.

Anyway, since both Atlas VS. and Delta IV were originally designed to launch
the exact same payloads, one would think that they were designed for the
same performance range. I think were Delta IV stumbled, however, was when
their new core main engine ended up having lower thrust than they had
anticipated. That's probably a big part of the reason why the bare bones
Delta IV has less capability than a bare bones Atlas VS. 401.

I don't know as much about Delta IV, but I do know that Atlas VS. has some
good liftoff limitations as well, depending on the configuration. Those big
solids pack a pretty good punch! Too much of a good thing can rip the
bottoms of your tanks off if you're not careful!

UP. Ruzicka