The Atlas rocket, famous for carrying the Mercury astronauts into orbit and respected for its later role as the workhorse of the commercial satellite launch industry, began as a modest proposal for winged and rocket-powered missiles just weeks after the end of World War II. The vehicle that evolved became the United States' first intercontinental ballistic missile (ICBM) and a dependable space launch system that is still going strong at the start of the new millennium.

In October 1945, the U.S. Army Air Forces (USAAF) (predecessor of the modern U.S. Air Force) invited the aerospace industry to submit proposals for the development of four different varieties of missiles to deliver a warhead against targets as far as 5,000 miles (8,047 kilometres) away. Within a few months, the field had been narrowed to two different concepts: a jet-powered, subsonic winged vehicle, and a rocket-powered, supersonic ballistic missile.

On April 19, 1946, a contract was awarded to the Consolidated Vultee Aircraft Corporation (Convair) to study each concept. Cutbacks in the national defence budget triggered a corresponding reduction in missile development funding and, in June 1947, the USAAF cancelled Convair's research contract; however, the company was permitted to spend its remaining funds to finish constructing three missile test vehicles and continue investigating missile guidance and nosecone concepts.

Spurred by the outbreak of the Korean conflict, the U.S. Air Force again received funding to advance the development of a missile system and, by September 1951, determined that a ballistic rocket design was preferable to a winged vehicle concept. A new contract was awarded to Convair (which became the Convair division of General Dynamics Corporation in 1953) to investigate technologies and provide solutions for the systematic, then accelerated, development of a ballistic missile system, dubbed by Convair as "Project Atlas."

In January 1955, the Air Force ordered the Atlas (still referred to by its code name, Weapon System WS107A-I) into production. President Dwight Eisenhower and his National Security Council were briefed on the specifics of the Atlas project on June 28, 1955, and within weeks, the president designated the development of the Atlas to be of the “highest national priority.”

Convair was awarded a contract in September 1955 to begin producing the Atlas, and by June 1956, the company began testing the missile's propulsion system and electrical components. Convair would produce the Atlas' airframe and integrate all of the missile's components, North American Aviation manufacture the rocket engines, and General Electric fabricate the missile's nosecone and jointly develop the Atlas' guidance system with the A.C. Spark Plug Company.

The key to the Atlas design is an extremely lightweight structure, conceived largely by an inventive Convair engineer, Karl J. Bossart. The missile's frame consisted of a very thin-gauge stainless-steel skin that maintains its shape and structural integrity only from the high pressure inside its propellant tanks. If the tank pressurization failed, the skin would crumble and the launch vehicle would collapse under its own weight. Many engineers, including famed rocket designer Wernher von Braun, worried that the Atlas' design could not survive the intense aerodynamic stresses placed upon it the early phases of launch, so much so that von Braun's design team derisively referred to the Atlas as a “blimp” or their “inflated competition.”

The basic Atlas vehicle, remarkably unchanged almost 50 years after its inception, is a 1˝ stage liquid-propellant launch vehicle consisting of a booster section and a sustainer section, a unique configuration that enables the missile to launch itself into orbit. The single rocket engine in the sustainer section and the twin rocket engines in the booster section all ignite at liftoff to propel the vehicle for the first two minutes of flight; after which the two booster section engines are jettisoned as the single sustainer engine continues to burn and carries the vehicle into space.

Early test models of the Atlas (designated the Atlas Series A) were 75 feet (23 meters) in length and 10 feet (3 meters) in diameter, powered by only the two booster section rocket engines, with a maximum range of just 600 nautical miles (1,111 kilometres). The missiles were outfitted with a dummy warhead, but lacking the sustainer engine, they were only capable of reaching an altitude of 57.5 nautical miles (106.5 kilometres).

The first Atlas test flight, a “Series A” missile, lifted off from Cape Canaveral's Launch Complex 14 on June 11, 1957. The flight lasted only 24 seconds. The twin rocket engines lost thrust about 10,000 feet (3,048 meters) above the launch pad, the missile made a few pirouettes, and then the Range Safety Officer transmitted a destruct signal commanding the Atlas to blow itself up.

This first launch failure, though disappointing, also contained a silver lining. As the missile was tumbling out of control, the Atlas' frame and thin skin remained intact, even though subjected to several seconds of very high aerodynamic stress (or structural “loads”) far in excess of its design limitations. This validated its structural integrity and ended the controversy over its unconventional design. In all, a total of eight Atlas Series A missiles were launched from June 1957 though June 1958.

Subsequent test versions (the “B” and “C” models) were launched in 1958 and 1959, and the Atlas D, the U.S.' first ICBM, became a functional weapon system in January 1959 when the first Atlas ICBM squadron at Vandenberg Air Force Base, California was activated, even before the first successful launch of the Atlas D. The Air Force formally accepted the Atlas on September 1, 1959, and the missile was declared "operational" about a week later when an Atlas D ICBM was successfully launched from Vandenberg.

During the same timeframe, the Atlas missile was also proving its worth as a space launch vehicle. Project Score-an Atlas B missile that launched itself into low-Earth-orbit on December 18, 1958-carried an instrumentation package developed by the U.S. Army Signal Corps that became the world's first communications satellite by broadcasting a recorded Christmas message from President Eisenhower back to Earth.

Atlas model D, E, and F ICBMs, outfitted with nuclear warheads, were deployed at Air Force bases throughout the United States, stored vertically in underground silos and raised by elevators to an above-ground position for launch. In addition to the original squadron at Vandenberg AFB, Atlas ICBMs were deployed at eight locations in central and western United States and at Plattsburg AFB, New York. (Plattsburg AFB still is the only ICBM installation ever located east of the Mississippi River).

Atlas ICBMs remained on strategic alert from 1959 until 1966, when more capable solid-fuelled Minuteman ICBMs replaced the last Atlas missiles. A number of these decommissioned Atlas ICBMs were refurbished for use by the Air Force and the National Aeronautics and Space Administration (NASA) as satellite launch vehicles; the last refurbished Atlas was launched from Vandenberg AFB with a military meteorology satellite in 1995.

NASA ordered a number of “man-rated” (modified with safety features to carry humans) Atlas D models-designated as the Atlas LV-3B-for the orbital flights of its first human spaceflight program, Project Mercury. Astronaut John H. Glenn, Jr. became the first American to orbit the Earth in his Friendship 7 Mercury capsule launched atop an Atlas LV-3B on February 20, 1962, followed by astronauts Carpenter, Schirra and Cooper in 1962 and 1963.

Scott Carpenter's Aurora 7 Mercury Atlas rocket lifts off from Cape Canaveral, Florida, on May 24, 1962.  

The Atlas space launch vehicle has been regularly upgraded since its introduction, including a longer tank, improved rocket engines, and enhanced electronics and computer systems, enabling the rocket to carry larger and heavier payloads. Atlas vehicles, equipped with a variety of upper stages such as the Burner II, Agena and Centaur, have launched a wide variety of military, scientific, and commercial spacecraft for more than four decades, including the Surveyor lunar landers, the Pioneer 10 and 11 planetary probes to Jupiter and Saturn, and the Pioneer Venus mission.

The last of the “basic” Atlas versions, the Atlas 2A and 2AS, built by Lockheed Martin (which acquired the Convair division of General Dynamics) and equipped with a Centaur upper stage, can carry large payloads, such as communications satellites, weighing almost 8,500 pounds (3,856 kilograms) to a geostationary orbit, 22,300 miles (35,888 kilometres) above the Equator. The Atlas 3, introduced in 2000, eliminates the booster engine stage, replacing it and the sustainer engine with a pair of powerful, Russian-built RD-180 rocket engines that can be throttled up and down to adjust for aerodynamic stresses during ascent-an ironic twist for a vehicle originally designed to launch nuclear warheads against the former Soviet Union.

 
Atlas Agena target vehicle lift-off for Gemini 11 from Pad 14 at Kennedy Space Centre, 1966. Once the Agena was in orbit, Gemini 11 rendezvoused and docked with it.