This is a model of an Agena upper stage. The Lockheed Missiles and Space Company began developing the Agena upper stage for the U.S. Air Force in 1956. Three versions were ultimately produced: the Agena-A, Agena-B, and Agena-D. As a second stage on Thor and Atlas boosters, all three versions launched a variety of military and civilian payloads from 1959 into the early 1970s. As a third stage on top of Titan IIIBs, the Agena-D launched numerous military payloads from 1966-1987. The Smithsonian Astrophysical Observatory donated this model in 1979. The manufacturer is not known at this time.
Gift of Smithsonian Astrophysical Observatory