40 years since the first docking of the Union and Apollo

Rare space science fiction dispenses with the docking of ships in space. This is about as natural for the genre as the mooring of ships in port. However, beyond the scope of the plot, usually there are many difficulties associated with equalizing speeds and the correct mutual orientation of spacecraft in space. Not to mention the fact that the docking nodes for all participants in the docking should be compatible with each other. This is not for you to tie the mooring ends to the berth stands. And for the first time, the task of docking in space two ships of different countries was solved 40 years ago, during the historical flight of the Soviet “Union” and the American “Apollo”.

On July 17, 1975, two ships created by countries in the Cold War state successfully docked in low Earth orbit. Thus, the leaders of the superpowers showed that the cosmos should be free from weapons and hostility. However, preparations for the landmark docking began much earlier. The idea for such an event was put forward by NASA in 1970. After lengthy negotiations and reflection in 1972, an interstate agreement was signed on peaceful cooperation and joint space exploration, which gave way to the project. Shaking hands, politicians passed the initiative to the designers and scientists of the two countries.

The complexity of solving the task was far from limited to the creation of compatible docking nodes. They were designed and manufactured in the USSR for both ships, the Americans installed their copy on a near-Earth modification of the Apollo class ship. This was the first symmetrical design of the docking unit, called APAS-75 (androgynous-peripheral docking unit). Subsequently, APAS-89 and APAS-95 were created, which were used at the American Shuttles and Mir station.





The next serious problem was ... a strong difference in approaches to the formation of the atmosphere on our and American ships. We tried to maintain an atmosphere close in composition and pressure to the earth. And at Apollo, pure oxygen with a pressure of about 0.35 atm was used for breathing. Naturally, the automation of maintaining the atmosphere of none of the ships was not designed for such radical differences, so there could be no question of establishing a single atmosphere after docking. In addition, the large pressure difference did not allow the use of a simple gateway device, otherwise the astronauts would suffer from decompression during the transition, like divers.

I had to create a docking and airlock compartment (length 3 m, diameter 1.4 m, weight 2 t), which worked on the principle of a diving pressure chamber. Also in this flight, atmospheric pressure in the Soyuz was somewhat lowered, while in Apollo it was slightly raised. This allowed to reduce the duration of the astronauts stay in the gateway to 3 hours. In addition, depending on the direction of the transition, an atmosphere of a certain composition was created in the gateway.



The docking and airlock compartment was launched into orbit by the same rocket as the Apollo, but it was docked with the ship after it entered orbit. For this, Apollo had to turn 180 degrees.

Space does not tolerate neglect of trifles, therefore, all systems and components of each ship underwent a careful analysis. In particular, it turned out that under the atmosphere of pure oxygen at the Apollo, the costumes of our astronauts became fire hazardous. Therefore, a new heat-resistant polymer was developed for the flight, from which clothes were made for the Soyuz crew. The ship itself underwent large-scale processing. According to some estimates, up to 40% of its design was changed. Within the framework of the project, six copies of the modernized “Union” were built, of which three were used during training flights.

July 15, 1975 both ships launched from their spaceports, and July 17 was docked.



The crew of the "Union" consisted of Alexei Leonov (the first man in outer space) and Valery Kubasov.





Strictly speaking, there were two dockings: some time after the first docking, the ships parted, and then docked again. For almost two days spent in docked condition, a number of scientific experiments and observations were carried out, after which both crews returned to Earth without incident.