Click the arrow to watch the film. Video source: NASA STI Program YouTube channel.
When is a Delta not a Delta?
When it's a Thor. And we don't mean the comic book/movie character.
This week's Retro Saturday is a circa 1989 NASA documentary titled Delta, America's Space Ambassador. It's about the history to that point of the Delta rocket, many of which launched from Cape Canaveral's Launch Complex 17.
The Delta series name goes back to the late 1950s.
The Thor was a U.S. Air Force intermediate range ballistic missile, with a range of about 1,500 miles (2,400 km). NASA and commercial companies adapted the Thor for satellite and other payload launches.
The word “Thor” referred to the booster, but various names were assigned to the Thor's combination with upper stages.
The Thor-Able was a Thor with a second stage derived from Project Vanguard that was given the name Able. The word “Able” simply came from the military phonetic alphabet, e.g. Able, Baker, Charlie, Delta, etc.
According to Encyclopedia Astronautica, there was a Thor-Baker but it was renamed Thor-Able I and intended for use in launching early Moon probes.
The Thor-Delta was a Thor with upper stages also derived from the Vanguard program. In common use, the industry began referring to the rocket as a “Delta” and the name stuck.
The Delta name has descended through the decades. The Delta II flew its last launch from LC-17 in 2012. The Delta IV still launches from Launch Complex 37, most recently used to launch NASA's Orion crew capsule test flight.
The Cape's LC-17 and LC-18 were originally commissioned in the mid-1950s for Thor. When the Naval Research Laboratory needed a pad for the civilian Vanguard program, the Thor program didn't need LC-18 so Pad 18A was made available to Vanguard. Pad 18B eventually was used in the 1960s for Thor launches, while 18A was later used for test of the Blue Scout Jr.