Apollo-Soyuz — first international docking in space

On the morning of 15 July 1975, a Soyuz rose from the steppe at Baikonur. Seven and a half hours later, a Saturn IB climbed away from Florida. For two decades the two nations had raced each other into space; now, for the first time, they were flying toward each other. On 17 July, in low Earth orbit, Apollo commander Tom Stafford eased his ship toward Soyuz 19 while Alexei Leonov, the first human ever to walk in space, watched it grow in his window. Contact, then capture. Two machines built by rival superpowers were suddenly one.

Nothing about the meeting was simple. Apollo flew a pure-oxygen cabin at a third of an atmosphere; Soyuz breathed a mixed atmosphere near sea-level pressure, so the Soviets lowered their cabin pressure and NASA built a docking module that worked as an airlock between the two worlds. The port itself, the jointly designed APAS-75, was deliberately androgynous: identical halves on each ship, so that neither nation would have to play the symbolically passive role. The crews had trained in each other's languages and countries for two years before a single engine lit.

Hours after docking, the hatches opened and Stafford and Leonov clasped hands. For roughly 47 hours the five men passed between ships, ran joint experiments, held press conferences, shared meals and traded gifts; Leonov, ever the joker, handed the Americans tubes labelled as vodka that actually held borsch. Among them floated Deke Slayton, one of the original Mercury Seven, grounded in 1962 by a heart irregularity and finally in orbit at age 51 after a sixteen-year wait.

The flight nearly ended in tragedy. During reentry on 24 July, toxic nitrogen tetroxide fumes from the thrusters seeped into the Apollo cabin, and the crew needed oxygen masks and two weeks of recovery in a Honolulu hospital. It was the last flight of an Apollo spacecraft, the last of the Saturn rockets, and the last American crewed launch until the Shuttle in April 1981. But the handshake endured: the cooperation rehearsed that week became the blueprint for Shuttle-Mir and, eventually, the International Space Station.