Soyuz Commander Alexei Leonov (right) and Apollo Docking Module Pilot Donald K. Slayton (left) together in the Soviet Soyuz Orbital Module during the Apollo Soyuz Test Project (ASTP) docking mission in Earth orbit. The ASTP mission was the first joint international crewed space-flight. It took place from 15-24th July 1975. A Soviet Soyuz 19 and American Apollo CSM-111 spacecraft docked in orbit on 17th July to test a jointly-designed international docking mechanism.