The Delta D, Thrust Augmented Delta or Thor-Delta D was an American expendable launch system used to launch two communications satellites in 1964 and 1965. It was derived from the Delta C, and was a member of the Delta family of rockets. The three-stage core vehicle was essentially the same as the Delta C. The first stage was a Thor missile in the DSV-2A configuration, and the second stage was the Delta-D, which was derived from the earlier Delta-A. An Altair-2 SRM was used as a third stage. The main difference between the Delta C and Delta D was the presence of three Castor-1 solid rocket boosters, clustered around the first stage. Both Delta D launches were conducted from Cape Canaveral Air Force Station Launch Complex 17A. The first, on 19 August 1964, carried Syncom 3, the first satellite in a geostationary orbit. The last, on 6 April 1965, carried the first commercial communications satellite, Intelsat I.