The Thor-Delta, also known as Delta DM-19 or just Delta was an early American expendable launch system used for 12 launches in the early 1960s. A derivative of the Thor-Able, it was a member of the Thor family of rockets, and the first member of the Delta family.
The first stage was a Thor missile in the DM-19 configuration (DM-18A / MB-3-I engine). The second stage was the Delta (AJ-10-142 engine), which had been derived from the earlier Able stage. An Altair solid rocket motor (X-248A-7) was used as a third stage.
The basic design of the original Vanguard upper stages, featuring a pressure-fed nitric acid/UDMH, regeneratively cooled engine, was kept in place, but with an improved AJ10-118 engine. More significantly, the Delta stage featured cold gas attitude control jets allowing it to be stabilized in orbit for restart and more precise burns.
The Thor-Delta was the first rocket to use the combination of a Thor missile and a Delta upper stage. This configuration was reused for many later rockets, and a derivative, the Delta II, remained in service until 2018.
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