Editing Atlas II (section)

== Versions ==
[[File:LC-36-Atlas-2.jpg|right|thumb|The first stage of an Atlas IIA rocket is erected vertical at Cape Canaveral Pad 36A.]]
Atlas II was developed into three versions.

=== Atlas II ===
The original Atlas II was based on the [[Atlas I]] and [[Atlas (rocket family)|its predecessors]]. Its lengthened propellant tanks and improved electronics over the Atlas I offered better performance. It was designed to work as part of the US Air Force's Medium Launch Vehicle II program. This version flew between 1991 and 1998.<ref name=astronautixAtlasII />

=== Atlas IIA ===
Atlas IIA was a derivative of the Atlas II designed to service the commercial launch market. The main improvement was the switch from the [[RL10]]A-4 engine on the Centaur upper stage, increasing the stage's performance and the vehicle's payload capability.<ref name=ppg>{{cite web|title=Atlas Launch System Payload Planner's Guide|url=http://www-eng.lbl.gov/~lafever/SNAP/OldFiles/MiscFiles/atlas.pdf|publisher=Lockheed Martin|access-date=January 9, 2016|url-status=dead|archive-url=https://web.archive.org/web/20150421050205/http://www-eng.lbl.gov/~lafever/SNAP/OldFiles/MiscFiles/atlas.pdf|archive-date=April 21, 2015}}</ref> The IIA version flew between 1992 and 2002.<ref name=astronautixAtlasIIA>{{cite web|title=Atlas IIA|url=http://www.astronautix.com/lvs/atlasiia.htm|archive-url=https://web.archive.org/web/20020319100934/http://www.astronautix.com/lvs/atlasiia.htm|url-status=dead|archive-date=March 19, 2002|publisher=Astronautix|access-date=January 9, 2016}}</ref>

=== Atlas IIAS ===
Atlas IIAS was largely identical to IIA, but added four [[Castor (rocket stage)|Castor 4A]] solid rocket boosters to increase performance. These boosters were ignited in pairs, with one pair igniting on the ground, and the second igniting in the air shortly after the first pair separated. The "half-stage booster section would then drop off as usual.<ref name=ppg /> IIAS was used between 1993 and 2004, concurrently with IIA.<ref name=astronautixAtlasIIAS>{{cite web|title=Atlas IIAS|url=http://www.astronautix.com/lvs/atlsiias.htm|archive-url=https://web.archive.org/web/20020501080034/http://www.astronautix.com/lvs/atlsiias.htm|url-status=dead|archive-date=May 1, 2002|publisher=Astronautix|access-date=January 9, 2016}}</ref>