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Fifty-two years ago this week, the United States Air Force successfully conducted an Initial Operational Capability Demonstration (IOC DEMO) of the Atlas D Intercontinental Ballistic Missile (ICBM).  The Atlas Missile System was pronounced operational following the successful launch from Vandenberg Air Force Base, California.

Named for the superhuman strongman of Greek mythology, Atlas was the United States’ first operationally deployed intercontinental ballistic missile (ICBM).  Program roots go back to 1946 when Consolidated Vultee Aircraft (Convair) was awarded a study contract by the United States Army Air Forces for a 1,500 to 5,000 mile range missile that could carry a nuclear warhead.

At the time Convair began its study, no missile within conception could carry even the smallest nuclear warhead available at the time. However, a confluence of technological developments in the early 1950’s led to Atlas becoming a high priority development within the United States defense community.  First, the thermonuclear weapon was successfully demonstrated.  Second, a design breakthrough occurred wherein nuclear warhead mass was sharply reduced.  Finally, CIA activities revealed that the Soviet Union was making significant progress with their own ICBM program.

Atlas A, B and C were the initial test and development variants of America’s first ICBM.  Atlas D was the first operational version.  Configured with a Mark 2 reentry vehicle, it measured 75 feet in length and 10 feet in diameter.  Atlas D weighed 255,000 lbs at launch and had a range of 10,360 miles.

The Atlas propulsion system consisted of a single Rocketdyne LR105 sustainer  (57,000 lbs thrust) and a pair of Rocketdyne LR89 boosters (150,000 lbs thrust each).   Roll control and fine velocity control was provided by a pair of Rocketdyne LR101 vernier rocket engines (1,000 lbs thrust each).

The Atlas sustainer rocket engine was mounted between the outboard booster rocket engines.  This trio of rocket engines was ignited at launch.  While the boosters were jettisoned around 130 seconds into flight, the sustainer core continued to fire until propellant exhaustion.  This unique arrangement made Atlas a stage-and-a-half launch vehicle.

In striving for the minimum weight solution, the Atlas airframe included propellant tankage constructed of very thin stainless steel.  This so-called “balloon tank” design required internal pressurization with nitrogen gas at about 5 psig to provide structural rigidity.  An Atlas launch vehicle would simply collapse under its own weight if not so pressurized.

Atlas A, B, C and D variants employed radio guidance.  That is, the missile sent position information from its guidance system to the ground via radio.  In turn, the ground sent course correction information back to the missile.  Starting with the Atlas E, the guidance system was entirely autonomous.

On Wednesday, 09 September 1959, the Strategic Air Command (SAC) conducted an Initial Operational Capability Demonstration (IOC DEMO) launch  at Vandenberg Air Force Base, California.  The Atlas D 12D launch vehicle lifted-off from Launch Complex 576-A2 at 17:50 UTC.  Its Mark II reentry vehicle flew 4,480 nautical miles downrange and landed less than 1 nautical mile from its target near Wake Island.  Apogee and maximum speed were 972 nautical miles and 16,000 mph, respectively.

The Atlas IOC DEMO mission was entirely successful.  General Thomas D. Power, SAC Commander-in-Chief, was so impressed with the results of the flight that he immediately declared the Atlas System to be operational.

The Atlas missile ultimately stood sentinel at 11 separate launch sites located throughout the United States.  Roughly 350 Atlas missiles were manufactured during the program’s lifetime, with a maximum of 129 missiles being deployed at any one time being 129.  However, the introduction of the famous Minuteman missile in 1963 sounded the death knell for Atlas.  Indeed, there were no more operational Atlas missiles after April of 1965.

Although its operational service life was somewhat brief, Atlas provided a proving ground for a multiplicity of emerging missile technologies. Further, Atlas development served as the organizational and procedural template for all future ICBM programs.

Following retirement from active ICBM service, depostured Atlas ICBM’s were converted to the space launch role.  It was employed for nearly a quarter of a century in such capacity.  Indeed, all Mercury Earth-orbital missions were launched using man-rated Atlas launch vehicles.

The Atlas is still active in the US launch vehicle inventory.  Although now manufactured by Lockeed-Martin and having a configuration quite distinct from that of its ICBM forbears, the latest version of the venerable vehicle is the Atlas V.  This modern Atlas variant can send nearly 65,000 lbs of payload into LEO and 29,000 lbs into GTO.

Posted in Aerospace, History

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