On this day in 1975, capsules from the two Cold War superpowers docked in orbit for the first time.

The idea of a joint space mission was first suggested by NASA administrator Thomas Paine in 1970, and was encouraged by President Nixon, who was looking for projects to build the détente between the United States and the Soviet Union.

Firstly a docking module had to be built to allow the Apollo spacecraft to join with the Soyuz. The two ships used different air pressures and the module had to be designed to allow both crews to acclimatise. In addition, all the different problems which had to be worked out – the timing of each launch, the exchange of trajectory data across differing computer systems, the language barrier – meant this complicated mission took years to finalise.

Two crews were selected for the Apollo-Soyuz Test Project:  NASA astronauts Tom Stafford, Deke Slayton, and Vance Brand, and Russian cosmonauts Aleksy Leonov and Veleriy Kubasov. The training of both crews in preparation for their meeting helped break down cultural as well as language barriers. Vance Brand recalled:

“We thought they were pretty aggressive people and … they probably thought we were monsters. So we very quickly broke through that, because when you deal with people that are in the same line of work as you are, and you’re around them for a short time, why, you discover that, well, they’re human beings.”

The two separate ships launched on July 15th, and spent the subsequent day manoeuvring into matching altitudes and speeds. On the third day, 299 miles above Earth, the Apollo and Soyuz came together in hard dock. The two crews opened their hatches, and Stafford and Leonov shook hands.

The two crews exchanged gifts, which included each nation’s flag, plaques, medallions and other items. The first international co-operative space mission was a success.

Have a great day, everyone.