Which 1975 mission was the final flight of an Apollo spacecraft?

The 1975 Apollo-Soyuz Test Project was the final flight of an Apollo spacecraft. Launched on July 15, 1975, the mission joined an American Apollo command and service module with the Soviet Soyuz 19 spacecraft in the first crewed international rendezvous and docking in space.

The American crew consisted of Thomas Stafford, Vance Brand, and Deke Slayton; Soyuz carried Alexey Leonov and Valery Kubasov. The spacecraft docked on July 17, allowing the crews to transfer between vehicles and conduct joint experiments during a period of Cold War rivalry.

Apollo-Soyuz was not another Moon mission. Instead, it tested compatible systems, including a specially designed docking module that also served as an airlock between the two spacecraft. The flight symbolized improved U.S.-Soviet cooperation after the intense competition of the Space Race.

Apollo 17 was the final lunar-landing mission, but it was not the final Apollo spacecraft flight. Skylab missions used Apollo hardware, while Apollo-Soyuz was the last crewed flight of an Apollo spacecraft.