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Thor-Delta prior to the launch of Explorer 10
|Function||Expendable launch system|
|Country of origin||United States|
|Launch sites||Cape Canaveral LC-17|
The Thor-Delta, also known as Delta DM-19 or just Delta was an early American expendable launch system used for 12 orbital 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. The second stage was the Delta, which had been derived from the earlier Able stage. An Altair solid rocket motor 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 a large number of later rockets, and a derivative, the Delta II, remained in service until 2018.
The Thor-Delta launched a number of significant payloads, including the first communications satellite, Echo 1A; the first British satellite, Ariel 1; and the first active direct-relay communications satellite, Telstar 1. All 12 launches occurred from Cape Canaveral Air Force Station Launch Complex 17. The launch of Telstar 1 used pad B, while all other launches were from pad A. All launches were successful except the maiden flight, which failed to place Echo 1 into orbit due a problem with the second stage.
|1||May 13, 1960||Echo 1||CCAFS LC 17A||Failure||Launch at 9:16 p.m. GMT. Good first stage. Second-stage attitude control system failure. Vehicle destroyed.|
|2||August 12, 1960||Echo 1A||CCAFS LC 17A||Success||Payload placed into 1,035 miles (1,666 km), 47 degree inclination orbit.|
|3||November 23, 1960||TIROS-2||CCAFS LC 17A||Success|
|4||March 25, 1961||Explorer-10||CCAFS LC 17A||Success||78 pounds (35 kg) payload placed into elliptical 138,000 miles (222,000 km) orbit.|
|5||July 12, 1961||TIROS-3||CCAFS LC 17A||Success|
|6||August 16, 1961||Explorer-12||CCAFS LC 17A||Success||Energetic Particle Explorers. EPE-A.  Highly elliptical orbit.|
|7||February 8, 1962||TIROS-4||CCAFS LC 17A||Success|
|8||March 7, 1962||OSO-1||CCAFS LC 17A||Success||Orbiting Solar Observatory. 345 miles (555 km), 33 degree orbit.|
|9||April 26, 1962||Ariel 1||CCAFS LC 17A||Success||Ariel 1 was later seriously damaged by the Starfish Prime nuclear test.|
|10||June 19, 1962||TIROS-5||CCAFS LC 17A||Success|
|11||July 10, 1962||Telstar 1||CCAFS LC 17B||Success||Telstar 1 was later damaged by the Starfish Prime high altitude nuclear event.|
|12||September 18, 1962||TIROS-6||CCAFS LC 17A||Success|
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