A test Thor takes flight at Cape Canaveral, Fla., on Dec. 5, 1959. The small particles falling away from the rocket are ice formed from frozen condensation on the outside of the chilled liquid oxygen tank. (U.S. Air Force photo)
The SM-75/PGM-19A Thor intermediate range ballistic missile (IRBM) was the product of the early Cold War race to deploy nuclear armed missiles before the Soviets. Thor was designed to be an interim nuclear deterrent while the U.S. Air Force developed long-range intercontinental ballistic missiles (ICBMs) as a top national priority. The IRBM concept called for a missile with a range of about 1,500 miles that would be based in Europe. Great Britain agreed to host four IRBM bases, and Thors were operational in England from June 1959 to August 1963. Royal Air Force crews operated the missiles, but USAF personnel controlled their nuclear warheads.
The USAF developed the SM-75 quickly, in just over three years beginning in 1956. Interservice competition to control the emerging strategic missile mission meant that the U.S. Army developed its Jupiter missile, which was ultimately assigned to the Air Force, at the same time. Thor's rapid design and deployment resulted from having much in common with the Atlas ICBM, which was then still in the planning stages. Thor's engine, guidance, and warhead came from the Atlas program, and only its airframe was new. After three failed test flights, Thor's first fully successful flight took place in September 1957. The following month, the USSR launched its Sputnik satellite--proving Soviet rocket capability and generating much anxiety in the U.S.--and President Dwight Eisenhower rushed Thor into production as a result.
The SM-75 was a one-stage liquid fueled rocket. Powered by liquid oxygen and kerosene, the vehicle could reach an altitude of about 280 miles before releasing its warhead on a ballistic (unpowered) trajectory toward its target. The missile required about 15 minutes to prepare for launch from its above-ground shelter, and could reach its target after about 18 minutes of flight.
Following its withdrawal as an IRBM when the Atlas ICBM became available, the Air Force used Thor as a nuclear atmospheric test vehicle and an antisatellite weapon. The USAF and NASA also adapted the Thor design to a very successful variety of space launch roles.
TECHNICAL NOTES Warhead: Single W-49 in the kiloton range Engines: One Rocketdyne LR79-NA-9 of 150,000 lbs thrust; two Rocketdyne LR101-NA vernier engines (for small thrust and direction adjustments) of 1,000 lbs thrust each Guidance: All-inertial Range: 1,500 miles Length: 65 ft Diameter: 8 ft Weight: 110,000 lbs (fully fueled)