The Thorad-Agena was an Americanexpendable launch system, derived from the Thor and Deltarockets. The first stage of the rocket was the stretched variant of the Thor which had been developed for the Delta programme. The second stage was the Agena-D, which had already been used in conjunction with the standard configuration Thor, as the Thor-Agena. Three Castor rockets would be used as boosters. Forty-three were launched between 1966 and 1972, of which two failed, and one delivered its satellite into an incorrect, but still usable orbit. Most launches carried Corona (KeyHole) reconnaissance satellites, particularly spacecraft of the KH-4 series, however some scientific and technology development satellites were also flown, mostly towards the end of the programme.
The Thorad-Agena was flown in two different configurations, the SLV-2G, and the SLV-2H. These differed in that the SLV-2G used Castor 1 strap-on boosters, whereas the 2H used Castor 2s.