The Apollo-Soyuz Test Project (ASTP) was the first joint U.S.-Soviet space flight, marking the symbolic end of the Space Race. An American Apollo Command Module and a Soviet Soyuz capsule docked in orbit, allowing the crews to meet, shake hands, and conduct joint experiments. The mission required the development of a special docking adapter because the two nations used different docking systems. This 'handshake in space' signaled a period of 'détente' (thawing of relations) between the two superpowers and laid the groundwork for future international cooperation, such as the Shuttle-Mir program and the International Space Station (ISS).