The Thor standard launch vehicle (SLV-2) was designed and first flown more than 10 years ago as a quick response IRBM with completely air transportable launch equipment. After deployment overseas in squadron strength, several years ago it was removed from the strategic weapon system inventory. However, the descendants of the vehicle are still in production as an operational space booster after undergoing continuous improvement through such methods as uprating the main engine and electronics, addition of solid propellant thrust augmentation motors, extension of the propellant tanks, and adding the ability to mate with various upper stage vehicles. Furthermore, the Thor IRBMs returned from overseas have been refurbished and used by the military.
Of the two original launch sites, the R&D facilities at Cape Kennedy and some of the Weapon System Training sites at Vandenberg AFB have been converted to space launch duty, making maximum use of the original equipment. Another site at Vandenberg has been converted from its original Atlas configuration to Thor use.
The original R&D concept of building vehicles has evolved to today's “Factory to Pad,” or “Ship and Shoot” concept, in which the checkout and mission modifications are accomplished at the factory.
The interface with the various range agencies, the NASA and Air Force, the upper stage contractors, the payload manufacturers and using agencies is a complex continuous process starting many months prior to mission assignment.