Apollo-Soyuz Test Project launches, featuring first historic orbital docking between US and Soviet craft

By the mid-1970s, the Cold War rivalry between the United States and the Soviet Union experienced a period of diplomatic thaw known as Détente. In May 1972, President Richard Nixon and Soviet Premier Alexei Kosygin signed a milestone international agreement authorizing the Apollo-Soyuz Test Project (ASTP). The joint mission aimed to develop a standardized international docking system, enabling future mutual space rescues and opening opportunities for cooperative space science between the two competing superpowers.

On July 15, 1975, the mission commenced with dual rocket launches thousands of miles apart. First, Soyuz 19 lifted off from the Baikonur Cosmodrome in the Kazakh Soviet Socialist Republic, carrying cosmonauts Alexei Leonov and Valery Kubasov. Seven and a half hours later, an Apollo Command and Service Module launched from Kennedy Space Center in Florida atop a Saturn IB rocket, crewed by astronauts Thomas Stafford, Vance Brand, and Donald "Deke" Slayton—one of the original Mercury Seven astronauts making his long-awaited debut in space.

Crucial to the mission was the American-built Docking Module, which served as an airlock and interface between the different cabin atmospheres and pressure levels of the Apollo and Soyuz craft. On July 17, 1975, after precise orbital rendezvous maneuvers, Apollo successfully docked with Soyuz high above the English Channel. Two hours later, Commanders Thomas Stafford and Alexei Leonov opened their respective hatches, exchanging a historic handshake in orbit that symbolized a dramatic reduction in international tensions.

Over the course of forty-four hours of joint operations, the combined crews conducted shared scientific experiments, exchanged national flags and seeds, shared meals, and conducted a joint televised press conference. ASTP marked the final flight of the Apollo spacecraft and the Saturn rocket family, successfully closing the heroic era of early American spaceflight while establishing a precedent for international space station operations that would flourish decades later.