The pin is from 1975.
This pin is about the Apollo-Soyuz test project between the Soviet Union and the USA in 1975. It was the first space program with the two nations working together. It was the marking the end of the space race between the 2 super powers wich had begun in 1957 with the Sputnik launch.
The Apollo and Soyuz spacecraft docked together in space.
Also it was the last USA manned space mission until the first space shuttle flight in 1981.