You got it.
This was a launch vehicle jointly developed by the Air Force and NASA's Goddard Space Flight Center. This rocket used the reliable Thor ballistic missile as a first stage. This was topped by an improved second and third stage from the Vanguard launch vehicle (the “Delta” stages). The Thor name was later dropped. As the "Delta" it has served America for more than four decades. It was used to launch many of the most famous early Goddard missions, from the TIROS weather satellites to the SYNCOM and RELAY communications spacecraft. It also launched most of the famous Explorer family of basic research satellites. Delta’s latest model can lift well over 20 times the original payload of the version we display. The Delta-B displayed at the Visitor Center is a type of mechanical systems test unit. While not a flight vehicle, most of its hardware is real. In the early 1960s, it served as the centerpiece for the U.S. Pavilion at the New York World’s Fair. Weighing in at 114,170 pounds, the rocket was able to generate 175,000 pounds of thrust during its first stage, while generating 7,575 pounds per 170 seconds and 2,760 pounds per 42 seconds in its second and third stages, respectively.