Atlas: Summary of the Atlas ICBM
Nowhere was the explosive growth of the ICBM program more evident than at Convair. In March 1953 Convair had 10 people assigned to the missile program, but just 7 years later Convair Astronautics (the company had been acquired and made a division of General Dynamics) had 12,000 workers building Atlas missiles at its new 2 million square foot facility at Kearney Mesa outside San Diego. Reflecting the truly national scope of the Atlas program, Convair employed 30 major subcontractors, 500 lesser contractors, and 5,000 suppliers scattered across 32 states.
Standing on the launch pad the Atlas was 82 feet tall and weighed 267,000 pounds when fueled. Depending on the model and payload, the missile had a range of 6,400 to 9,400 miles. It was armed with a l-megaton thermonuclear warhead and was guided to its target by either a radio-inertial or all-inertial guidance system accurate to within 1.5 miles. Atlas was powered by two large booster engines and a smaller sustainer engine that worked together to form what Convair called a "stage-and-a-half" propulsion system. It was an innovative compromise to a difficult problem. Optimally, the Convair engineers would have equipped Atlas with a two- or three-stage propulsion system. The benefit of that arrangement would have been that as each stage burned out and the engine and fuel tanks dropped away, the missile would have become progressively smaller and lighter. The problem was that when WDD and its contractors reconfigured Atlas in 1954, they did not know if it would be possible to start a rocket engine in the vacuum of space.
Unwilling to take the risk of building a multistage missile that might later prove unworkable, Convair built the Atlas around its unique stage-and-a-half propulsion system. In this configuration, the three largest engines, the two boosters and the smaller sustainer engine, were ignited at liftoff. At the end of the first stage the two boosters fell away, but the huge first-stage fuel tanks that constituted 80 percent of the missile's mass, and any unspent fuel they contained, remained attached to the missile. To compensate for the additional weight, Convair reduced the weight of the fuselage by discarding the rigid internal framework traditionally used in missiles and aircraft. Instead, the missile derived its structural rigidity from its pressurized, integral fuel tanks.
Atlas flight testing began at Cape Canaveral in June 1957. After several spectacular failures, in November 1958, an Atlas logged a successful test flight of 6,350 miles. To provide the United States with an interim or emergency ICBM capability, in August 1959 the Air Force rushed three missiles, operated largely by contractor personnel and mounted on unprotected launch pads, into service at Vandenberg Air Force Base (AFB), California.
The following September, the first operational Atlas squadron equipped with six Atlas D missiles based in above-ground launchers, went on operational alert at F.E. Warren AFB, Wyoming. By the end of 1962, SAC had deployed 11 more squadrons. Each of the three missile variants, the Atlas D, E, and F series, were based in progressively more secure launchers. For example, the three Atlas D squadrons, two near F.E. Warren AFB, Wyoming and one at Offutt AFB, Nebraska, were based in above-ground launchers that provided blast protection against overpressures of only 5 pounds-per-square-inch (psi).
In comparison the Atlas E squadrons at Fairchild AFB, Washington; Forbes AFB, Kansas; and F.E. Warren were also deployed horizontally, but the majority of the launcher was buried underground. These launchers were designed to withstand overpressures of 25 psi. The six Atlas F squadrons based near Shilling AFB, Kansas; Lincoln AFB, Nebraska; Altus AFB, Oklahoma; Dyess AFB, Texas; Walker AFB, New Mexico; and Plattsburgh AFB, New York were the first ICBMs to be stored vertically in underground silos. Built of heavily-reinforced concrete, the huge silos were designed to protect the missiles from overpressures of up to 100 psi.