Atlas V 401

The Atlas V is an American modular expandable launch system built and operated by United Launch Alliance (ULA) (originally Lockheed Martin).
It was selectet as a standart launcher for payloads of the Goverment in the Evolved Expandable Launch Vehicel (EELV) programm, together with the Delta IV (which I have built also).

The 401 configuration is the smallest, "basic", Atlas V.
It uses an Atlas V Common Core Booster first stage, a single engine centaur second stage, no SRBs and a four meter diameter fairing.

The Atlas V can fly in different configurations whitch are designated by a three digit numbering system.

first digit:
fairing diameter

4 four meter fairing, can fly with 0 - 3 srbs.

5 five meter fairing covering the whole second stage, can fly with 0 - 5 srbs.

N no fairing, only N22 used for starliner launches.

second digit:
Solid Rocket Boosters

can be zero to three on the 400 versions and zero to five on the 500. Can also be asymetric because the srbs nozzle is inclined outwards.

third digit:
upper stage engines

can be one or two, though, exept at the starliner launches, only one was used.