Atlas, named for the Atlas of Greek mythology and the contractor's parent Atlas Corporation, got its start in 1946 with the award of an Army Air Forces research contract to Convair for the study of a 1,500 to 5,000 mi. (2,400 to 8,000 km) range nuclear armed missile. The Convair team was led by Karel Bossart. This was the MX-774 or Hiroc project. The contract was canceled in 1947 but the Army Air Forces allowed Convair to launch the three almost-completed research vehicles using the remaining contract funds. The three flights were only partially successful. However they did show that balloon tanks, and gimbaled rocket engines were valid concepts. In 1955, the CIA learned that the Soviet ICBM program was making progress so Atlas became a crash program of the highest national importance.
The missile was originally given the military designation "XB-65", thus making it a bomber; from 1955 it was redesignated "SM-65" and, from 1962, it became "CGM-16". This letter "C" stood for "coffin" or "Container", the rocket being stored in a semi-hardened container; it was prepared for launch by being raised and fueled in the open. The Atlas-F (HGM-16) was stored vertically underground, but launched after being lifted to the surface.
Operational Atlas D were first deployed in "soft" sites featuring a "hardened" Launch Control Center and three "soft" launch pads. The guidance stations and antennas were also "soft". Later Atlas D bases were in "semi-hard" "coffin" sites where the missile was stored in a concrete structure horizontally and erected before fueling and launch. The Atlas E missiles were deployed in buried "semi-hardened" (harder than the D coffins) which functioned in the same fashion but each missile had its own LCC, allowing "salvo" launches. The Atlas-F was deployed in a 175 foot deep underground missile silo that were "hardened" against all but a direct nuclear hit. Each silo had its own LCC. An Atlas F site could take an overpressure of 100 PSI and lateral ground movement of 1 foot. These silos were usually located together in groups of 12 silos throughout the Midwest.
The only exception to this deployment strategy was the Atlas squadron that was deployed at Plattsburgh AFB in New York State. This location placed these Atlas missiles within striking range of soft targets located in the southern part of the Russian Federation and the Ukraine, of the then Union of Soviet Socialist Republics (USSR). This was the first and thus far the only instance where land-based ICBMs, loaded with live nuclear payloads, were deployed east of the Mississippi River.
The 551st Strategic Missile Squadron (551st SMS) located in Southeastern Nebraska is an example of the underground silo. From the mid-1960s, the Atlas (and its "bigger brother", the Titan) were phased out in favor of the LGM-30 Minuteman, a solid-fueled rocket which could be stored for long periods and launched, without fueling, at the turn of a key.
The warhead of the Atlas D was originally the G.E. Mk 2 "heat sink" re-entry vehicle with a W-38 bomb. The Atlas E and F had an AVCO Mk 4 re-entry vehicle containing a W-38 thermonuclear bomb with a yield of 3.75 megatons which was fuzed for either air burst or contact burst. The Mk 4 RV also deployed penetration aids in the form of mylar balloons which replicated the radar signature of the Mk 4 RV.
Though never used in combat, the Atlas was used as the expendable launch system with both the Agena and Centaur upper stages for the Mariner space probes used to study Mercury, Venus, and Mars (1962–1973); and to launch ten of the Mercury program missions (1962–1963). Atlas was suggested for use by the United States Air Force in what became known as Project Vanguard. This suggestion was ultimately turned down, however, as Atlas would not be operational in time and was seen by many as being too heavily connected to the military for use in the U.S.'s International Geophysical Year satellite attempt.
However, the Atlas saw the beginnings of its "workhorse" status during the Mercury-Atlas missions, which resulted in Lt. Col. John H. Glenn Jr. becoming the first American to orbit the earth on February 20, 1962 (Major Yuri A. Gagarin, a Soviet cosmonaut, was the first human in orbit on April 12, 1961.) Atlas was also used throughout the mid-1960s to launch the Agena Target Vehicles used during the Gemini program. Direct Atlas descendants have continued to be used as satellite launch vehicles into the 21st century. An Atlas rocket is shown exploding, in the 1983 documentary film Koyaanisqatsi, directed by Godfrey Reggio, in the penultimate shot.
Atlas also had a unique and somewhat odd staging system. Most rockets stage by dropping both engines and fuel tanks. However, when the Atlas missile was being developed, there were considerable doubts as to whether or not a rocket motor could be ignited in space. Therefore, the decision was made to ignite all three of the Atlas' engines at launch—later, two of the engines would be discarded, while the third continued to burn. Rockets using this technique are sometimes called stage-and-a-half boosters. This technique is made possible by the extremely light weight of the balloon tanks. The tanks make up such a small percentage of the total booster weight that the weight penalty of lifting them to orbit is less than the technical and weight penalty required to throw half of them away mid-flight. Depending on how you look at it, this makes Atlas a single-stage-to-orbit booster (though most call it a 1.5 stage to orbit). Sergey Korolyov made a similar choice for the same reason in the design of the R-7, the Soviet's first ICBM, and the launcher of Sputnik and Vostok. He had a central sustainer section, with four boosters attached to its sides. All engines were started before launch, eliminating the then unexplored problem of igniting a large liquid fuel engine at high altitudes.
The newest version of Atlas, the Atlas V, is an Atlas in name alone as it contains little Atlas technology. It no longer uses balloon tanks nor 1.5 staging, but incorporates a rigid framework for its first stage booster much like the Titan family of vehicles. The rigid fuselage is heavier, but easier to handle and transport, eliminating the need for constant internal pressure.
Ironically, given Atlas's origin as a military ICBM weapon against the Soviet Union/Russia, the Atlas III and Atlas V use Russian-designed/built NPO Energomash RD-180 engines. These engines are now prepared for license production by Pratt and Whitney company in the US.
The Atlas missiles were assigned to the following Strategic Air Command units:
The number of Atlas intercontinental ballistic missiles in service, by year:
CGM-16D Atlas Intercontinental Ballistic Missiles assigned:
CGM-16E Atlas Intercontinental Ballistic Missiles assigned:
HGM-16F Atlas Intercontinental Ballistic Missiles assigned:
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