Apollo-Soyuz (officially called the Apollo-Soyuz Test Project, or ASTP) grew from a series of cooperative agreements between the United States and the Soviet Union in the 1960s. In March 1970, U.S. President Richard Nixon declared international cooperation a prime objective of the National Aeronautics and Space Administration (NASA). The U.S. space agency and Soviet space officials agreed in October 1970 to study a common docking system that would allow each country to rescue the other's space travelers. Nixon and Soviet Premier Alexei Kosygin, taking advantage of a spirit of reconciliation (detente) between the United States and the Soviet Union, signed the Space Cooperation Agreement in Moscow on May 24, 1972, formally creating the ASTP.

On January 30, 1973, NASA introduced astronauts Thomas Stafford, Donald Slayton, and Vance Brand as its prime ASTP crew. In May, the Soviets tapped Alexei Leonov and Valeri Kubasov as its ASTP prime cosmonauts. The crews trained together...