Editing SM-65 Atlas (section)

==Missile versions==
===SM-65A Atlas===
{{main | SM-65A Atlas }}
[[File:Atlas missile test launch.jpg|thumb|150x150px|Atlas, test number 449,  Air Force Missile Test Center.]]
The [[Convair]] '''X-11'''/'''SM-65A Atlas'''/'''Atlas A''' was the first full-scale prototype of the Atlas missile, first flying on 11 June 1957.<ref name="EA">{{cite web |url=http://www.astronautix.com/lvs/atlasa.htm |title=Encyclopedia Astronautica – Atlas A |publisher=Astronautix.com |access-date=19 July 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130522064526/http://www.astronautix.com/lvs/atlasa.htm |archive-date=22 May 2013 |df=dmy-all }}</ref> It was a test model designed to verify the structure and propulsion system, and had no sustainer engine or separable stages. The first three Atlas A launches used an early Rocketdyne engine design with conical thrust chambers and only 135,000 pounds of thrust. By the fourth Atlas test, they were replaced by an improved engine design that had bell-shaped thrust chambers and 150,000 pounds of thrust.

There were eight Atlas A test flights, conducted in 1957–58, of which four were successful. All were launched from [[Cape Canaveral Air Force Station]], at either [[Cape Canaveral Air Force Station Launch Complex 12|Launch Complex 12]] or [[Cape Canaveral Air Force Station Launch Complex 14|Launch Complex 14]].<ref name="EA" />

===SM-65B Atlas===
[[File:Atlas-B ICBM.jpg|thumbnail|Launch of an Atlas B ICBM.|150x150px]]
{{main | SM-65B Atlas }}
The '''Convair X-12'''/'''SM-65B''' was the second prototype version, introducing the [[stage and a half]] system that was a hallmark of the Atlas rocket program. This version was the first American rocket to achieve a flight distance that could be considered intercontinental when it flew {{convert|6325|mi|-1}}.<ref>{{cite web
 | title = Cape Canaveral Launch Chronology
 | url = https://www.spaceline.org/statistics/Cape_Canaveral_Launch_Chronology.html
 | website = Spaceline.org
 | access-date = Feb 27, 2021}}</ref>

The Atlas B was first flown on 19 July 1958. Of ten total flights, nine were [[sub-orbital]] test flights of the Atlas as an [[Intercontinental Ballistic Missile]], with five successful missions and four failures; the other flight placed the [[SCORE (satellite)|SCORE satellite]] into orbit. All launches were conducted from [[Cape Canaveral Air Force Station]], at Launch Complexes [[Cape Canaveral Air Force Station Launch Complex 11|11]], [[Cape Canaveral Air Force Station Launch Complex 13|13]] and [[Cape Canaveral Air Force Station Launch Complex 14|14]].<ref name="EA" />

=== SM-65C Atlas ===
{{main | SM-65C Atlas }}
[[File:Atlas C.jpg|thumb|150x150px|Atlas C missile sitting on its launch pad.]]
The '''SM-65C Atlas''', or '''Atlas C''' was the third prototype Atlas version, a more refined model with improved, lighter-weight components. a bigger LOX tank, and a smaller fuel tank. First flown on 24 December 1958, it was the final development version. It was originally planned to be used as the first stage of the [[Atlas-Able]] rocket, but following an explosion during a static test on 24 September 1959, this was abandoned in favor of the Atlas D.<ref>{{cite web|url=https://www.thespacereview.com/article/1741/1|title=The Pioneer lunar orbiters: a forgotten failure|author=Andrew J. LePage|date=December 13, 2010|website=thespacerview.com|access-date=March 12, 2023}}</ref> Six flights were made, all sub-orbital ballistic test flights of the Atlas, with three tests succeeding, and three failing.<ref>{{cite web|title=Atlas C|url=http://www.astronautix.com/a/atlasc.html|website=astronautix.com|access-date=March 11, 2023}}</ref> All launches were conducted from Cape Canaveral Air Force Station, at Launch Complex 12.<ref>{{cite web|title=Launch Complex 12|url=http://mail.afspacemuseum.org/ccafs/CX12/|publisher=Air Force Space and Missile Museum|access-date=March 11, 2023}}</ref>

=== SM-65D Atlas ===
{{main|SM-65D Atlas}}
[[File:564th Strategic Missile Squadron Convair SM-65D Atlas missile 58-2205.jpg|thumb|150x150px|SM-65D Atlas missile 58-220, F. E. Warren AFB.]]
The '''SM-65D Atlas''', or '''Atlas D''', was the first operational version of the Atlas missile and the basis for all Atlas space launchers, debuting in 1959.<ref>Andreas Parsch, "Atlas D, Historical Essay", Encyclopedia Astronautica, 2003</ref> Atlas D weighed {{convert|255950|lb|-1|abbr=on}} (without payload) and had an empty weight of only {{convert|11894|lb|abbr=on}}; the other 95.35% was propellant.  Dropping the {{convert|6720|lb|0|abbr=on}} booster engine and fairing reduced the dry weight to {{convert|5174|lb|abbr=on}}, a mere 2.02% of the initial gross weight of the vehicle (still excluding payload). This very low dry weight gave Atlas D a range of up to {{convert|9000|mi|-2}}, or to orbit payloads without requiring an upper stage.<ref>M. D. Black, ''The Evolution of ROCKET TECHNOLOGY'', p. 54, Native Planter, SLC, 2012, payloadz.com under ''ebook/History''</ref> It first flew on 14 April 1959.

To provide the United States with an interim or emergency ICBM capability, in September 1959 the Air Force deployed three SM-65D Atlas missiles on open launch pads at [[Vandenberg AFB]], California, under the operational control of the [[576th Strategic Missile Squadron]], [[704th Strategic Missile Wing]]. Completely exposed to the elements, the three missiles were serviced by a gantry crane. One missile was on operational alert at all times.<ref>{{cite web|title=The ICBM turns 60|date=October 31, 2019|author=Troy A. Hallsell|url=https://www.afgsc.af.mil/News/Commentaries/Display/Article/2006393/the-icbm-turns-60/|website=U.S. Air Force|access-date=March 11, 2023}}</ref> They remained on alert until 1 May 1964.<ref name="nrdcstrat">{{cite report|title=US-USSR/Russian Strategic Offensive Nuclear Forces|date=January 1997|author1=Robert S. Norris|author2=Thomas B. Cochran|url=https://nuke.fas.org/norris/nuc_01009701a_181.pdf |archive-url=https://web.archive.org/web/20211223134358/https://nuke.fas.org/norris/nuc_01009701a_181.pdf |archive-date=2021-12-23 |url-status=live|publisher=National Resources Defense Council, Inc.|page=16|access-date=March 11, 2023}}</ref>

=== SM-65E Atlas ===
{{main | SM-65E Atlas }}
[[File:Atlas-5E rocket-02.jpg|thumb|150x150px|Atlas-E missile (s/n 5E), Cape Canaveral LC-11.]]
The '''SM-65E Atlas''', or '''Atlas-E''', was the first 3-engine operational variant of the Atlas missile, the third engine resulting from splitting the two booster thrust chambers into separate engines with independent sets of turbopumps. It first flew on 11 October 1960, and was deployed as an operational [[ICBM]] from September 1961 until March 1965.<ref>James N. Gibson, ''Nuclear Weapons of the United States, An Illustrated History'', pp. 11–14, Schiffer Publishing Ltd., Atglen, PA, 1996</ref>

A major enhancement in the Atlas E was the new all-inertial system that obviated the need for ground control facilities. Since the missiles were no longer tied to a central guidance control facility, the launchers could be dispersed more widely in what was called a 1&nbsp;×&nbsp;9 configuration, with one missile silo located at one launch site each for the nine missiles assigned to the squadron.<ref name="FEWarren"/>

Atlas-E launches were conducted from Cape Canaveral Air Force Station, at Launch Complexes 11 and 13, and Vandenberg Air Force Base at [[Vandenberg AFB Operational Silo Test Facility]], Vandenberg AFB Launch Complex 576 and [[Vandenberg AFB Space Launch Complex 3]].<ref name="EA" />

=== SM-65F Atlas ===
{{main | SM-65F Atlas }}
[[File:Convair SM-65F Atlas 532 550 SMS Site 02 Abilene KS.jpg|thumb|150x150px|Convair SM-65F Atlas 532 550 SMS Site 02 Abilene KS.]]
The '''SM-65F Atlas''', or '''Atlas-F''', was the final operational variant of the Atlas missile. It first flew on 8 August 1961, and was deployed as an operational ICBM between September 1962 and April 1965.

The Atlas F was essentially a quick-firing version of the Atlas E, modified to be stored in a vertical position inside underground concrete and steel silos. It was nearly identical to the E version except for interfaces associated with their different basing modes (underground silo for F) and the fuel management system.<ref>{{cite magazine |title=Atlas ICBM Geared to Total Deployment |magazine=Aviation Week and Space Technology, 25 September 1961 |pages=143–149 |url=https://archive.org/details/sim_aviation-week-space-technology_1961-09-25_75_13/page/142/mode/2up}}</ref> When stored, the missile sat atop an elevator. If placed on alert, it was fueled with [[RP-1]] (kerosene) liquid fuel, which could be stored inside the missile for extended periods. If a decision was made to launch, it was fueled with [[liquid oxygen]]. Once the liquid oxygen fueling was complete, the elevator raised the missile to the surface for launching.<ref>{{cite web|title=How the Air Force Got the ICBM|author=John T. Correll|date=July 1, 2005|url=https://www.airandspaceforces.com/article/0705icbm/|publisher=Air and Space Forces Magazine|access-date=March 11, 2023}}</ref>

This method of storage allowed the Atlas F to be launched in about ten minutes,<ref name="csisatlas">{{cite web|title=Missile Defense Project, "SM-65 Atlas|publisher=Missile Threat, Center for Strategic and International Studies|date=August 2, 2021|access-date=March 11, 2023|url=https://missilethreat.csis.org/missile/atlas/}}</ref> a saving of about five minutes over the Atlas D and Atlas E, both of which were stored horizontally and had to be raised to a vertical position before being fueled.<ref name="csisatlas"/>

Atlas-F launches were conducted from Cape Canaveral Air Force Station, at Launch Complexes 11 and 13, and Vandenberg Air Force Base at [[Vandenberg AFB Operational Silo Test Facility|OSTF-2]], Vandenberg AFB Launch Complex 576 and Vandenberg AFB Space Launch Complex 3.<ref name="EA" />