The article explores the Apollo–Soyuz Test Project (ASTP) of 1975, the first joint US–USSR space flight, which was embedded in the wider political, ideological and cultural contexts of the Cold War. The ASTP can be viewed through the lens of science diplomacy (SD). The data, drawn from available sources and memoirs, highlights the phenomenological approach in people-to-people interaction to analyse paths, processes and timeline dependence in such cooperation. The Weberian model of generalization and the path dependency theory of constructing an ideal type were used as the study’s theoretical frameworks. An ideal type of SD is viewed not as universal, but as a heuristic device that can be contrasted and compared with other recognized cases of SD. The significance of utilizing an ideal type of SD is to maintain mechanisms and networks effectively between countries through science and technology-related joint projects when political relations are strained or limited.