KSC-75PC-0330. NASA public domain image. Kennedy space center.

CAPE CANAVERAL, Fla. – ASTP prime crewmen Donald Slayton, Thomas Stafford and Vance Brand pose with their Saturn IB launch vehicle following the Countdown Demonstration Test [CDDT], a step-by-step dress rehearsal for their July 15 launch. During the “wet” portion of the test, conducted yesterday, the stages of the launch vehicle were fueled as they will be on launch day. The fuels were off loaded and the terminal portion of the count repeated today with the astronauts aboard the vehicle. The first international crewed spaceflight was a joint U.S.-U.S.S.R. rendezvous and docking mission. The Apollo-Soyuz Test Project, or ASTP, took its name from the spacecraft employed: the American Apollo and the Soviet Soyuz. The three-man Apollo crew lifted off from Kennedy Space Center aboard a Saturn IB rocket on July 15, 1975, to link up with the Soyuz that had launched a few hours earlier. A cylindrical docking module served as an airlock between the two spacecraft for transfer of the crew members. Photo credit: NASA