What Rocket Am I?: Quiz 18

Clue 1: I was developed by NASA in the United States.
Clue 2: I am a two-stage rocket derived from the Thor IRBM.
Clue 3: I evolved into the Delta family of launch vehicles.
Clue 4: I was first successfully launched in 1960.
Clue 5: I launched the Echo 1A communications balloon satellite.
Clue 6: My payload to low Earth orbit is about 450 kg.
Clue 7: I stand 31 meters tall.

Yes, I am Thor-Delta.

I pioneered geosynchronous communications satellites with Syncom launches.