Soyuz 19 was a Soviet space mission launched on June 15, 1975, as part of the Apollo-Soyuz Test Project. It marked the first international human spaceflight, where a Soyuz spacecraft docked with an Apollo spacecraft in orbit. The mission aimed to test the compatibility of the two different space systems and foster cooperation between the United States and the Soviet Union during the Cold War. The crew of Soyuz 19 included cosmonauts Alexei Alexeyevich Gubarev and Valery Nikolayevich Bykovsky. They spent a total of 5 days in space, conducting scientific experiments and engaging in joint activities with the Apollo crew. This mission was a significant step towards future collaborative efforts in space exploration.