Thor (rocket family)

Thor was a family of American space launch vehicles derived from the PGM-17 Thor intermediate-range ballistic missile, and it was the first member of the Delta rocket family. It first served as a launch vehicle in the test program for the Atlas warhead reentry vehicle, when a Thor core stage was topped by the Able second stage; the first such launch was lost to a turbopump failure on 23 April 1958, and a Thor-Able later launched Explorer 6, the first satellite to transmit pictures of Earth from orbit, on 7 August 1959. The Ablestar upper stage launched Transit 1B and the first GRAB electronic intelligence satellite in 1960. Paired with the Agena upper stage, Thor launched the early Corona photographic reconnaissance satellites from Vandenberg between 1959 and 1963, and thrust-augmented and long tank versions followed. The Delta second stage was derived from Able, and the last launch of a direct Thor derivative came in 2018 as the first stage of the final Delta II.