Space Forum / Space Flight / February 2006

The arrangement is assymetric because there are two external fittings
on the Atlas V common booster core, an avionics pod and an LO2
feedline. These are at about the 10:30 and 1:30 positions. Two of the
solids are between these fittings at about the 11:30 and 12:30
positions. The other 3 are on the opposite side at the 5, 6, and 7
o'clock positions.

Presumably.  

Not really. The shuttle does exactly this. Another possibility is
canting the solid booster nozzles differently to compensate for the
assymetry.

Jim Davis  

The asymmetry IS interesting, but apparently the offset
isn't severe and the RD-180 has excellent control
authority.  The Atlas V comes with any number of solids
from 0 to 5, but you'll note that the offset is never
more than one motor unit.  Possibly the solids' nozzles
could also be individually adjusted, although they are
non-steerable.

--Damon

Am 20 Jan 2006 00:57:43 -0800 schrieb
"Proponent!!!N0_SP@M!!!@gmx.net":

The booster nozzles are simply canted a bit outwards, so that their
thrust vectors go through the launcher's center of gravity. The
tradeoff os a slight decrease in effective thrust compared to a thrust
vector in movement direction, but it is the easiest method of using
even asymmetrical arrangements. Another well known example of
asymmetrical booster arrangements are the Delta-II 7420/7425 boosters,
that use the very same concept.

cu, ZiLi aka HKZL

The Atlas V booster was originally designed with the idea that
it would fly in only Medium and Heavy versions without SRBs.
At that point, the booster was configured with an external LOX
feedline on one side of the tank and an external avionics bay
on the other side, but not in 180 degree symmetry probably
due to the physical configuration of ground launcher equiment.
When the solids were added to the design (this occurred
well before the first launch), there were only certain places
where they could be positioned.  

- Ed Kyle