Amid the Cold War space race, American and Soviet space officials began negotiations in this period toward what would become the Apollo–Soyuz Test Project of 1975, in which an American Apollo capsule and Soviet Soyuz spacecraft would dock in orbit. The mission, born from détente-era diplomacy, marked the first international human spaceflight and previewed decades of later cooperation, including the International Space Station.
Talks between NASA administrators and their Soviet counterparts in the early 1970s were remarkable simply for occurring at all—for over a decade the two nations' space programs had been symbols of ideological rivalry, racing each other to orbit and then to the Moon. Behind closed doors, though, engineers on both sides recognized a shared technical problem: their spacecraft used incompatible docking systems and atmospheric mixes, and if any joint mission were to work, an entirely new universal docking module would need to be designed.
The resulting Apollo–Soyuz Test Project, which finally flew in July 1975, saw astronaut Tom Stafford and cosmonaut Alexei Leonov shake hands through a hatch 140 miles above Earth. It was choreographed diplomacy as much as engineering.
The early negotiations were slow and freighted with suspicion on both sides, requiring translators to painstakingly reconcile not just language but entirely different engineering philosophies and units of measurement. Yet the eventual handshake in orbit became an enduring image of détente, and the compatible docking systems developed for the mission influenced designs later used for Space Shuttle-Mir dockings and the International Space Station.