International Space Agency provides a percentage bonus to your overall Science output for each city-state of which you're Suzerain. Despite being toned down in Gathering Storm, it's still immensely helpful if you're on friendly terms with several city-states and are going for a Science Victory.
Civilopedia entry Edit
An “International Space Agency” doesn’t exist yet … but it’s only a matter of time. Given the creation of the UN Office for Outer Space Affairs, established to promote peaceful international cooperation in the exploration (and, likely, exploitation) of space, as well as the “utilization of space sciences and technology for sustainable economic and social development” of its member states, it may well be under UN control. Multinational space organizations such as the ESA (European Space Agency, established in 1975) will also likely form a vital element of any such future agency. And, no doubt, one of the first projects will be assumption of managing the International Space Station, currently a joint project of five participating national space agencies and protected by a web of intergovernmental treaties and agreements.