The historic ASTP mission was accomplished by using existing systems and a new docking module. The Apollo spacecraft was made available when the lunar-landing program was curtailed. Since the command module was built with a docking system designed to work only with U.S. spacecraft, a method of incorporating the new docking system had to be devised.
A second important problem was the difference between the spacecraft atmospheres. The Apollo used a pure oxygen atmosphere at about one-third of the atmospheric pressure on earth’s surface; Soyuz used a nitrogen-oxygen mixture at normal atmospheric pressure. To permit crews to pass from Soyuz to Apollo without suffering from the “bends” (a painful condition experienced when nitrogen gas bubbles form in the body fluids), engineers had to design an airlock to equalize the pressure.
78. The Soviet Soyuz atop a three-stage launch vehicle lifts off July 15, 1975, to begin the joint US-USSR space mission.
79. Overhead view of Soyuz in orbit, photographed from the Apollo spacecraft during the joint mission. The three major components of the Soyuz are the spherical Orbital Module, the bell-shaped Descent Vehicle, and the cylindrical Instrument-Assembly Module from which two solar panels protrude.
80. View of Apollo spacecraft as seen in Earth-orbit from Soyuz. The Command/Service Module and Docking Module are contrasted against a black-sky background and the horizon of the Earth is below.
The docking module, 3 meters long and 1.5 meters in diameter (10 feet long and 5 feet in diameter), also solved the problem of incompatible docking mechanisms by carrying the new docking system on one end and a system compatible with Apollo on the other.
Prime contractor for Apollo Command Module, Service Module, and Docking Module was Rockwell International.