Short answers, pulled from the story.
In the 1920s, a group of thinkers from Russia, America, Britain, and Germany began forming the first advocacy groups for space flight. These early organizations introduced the idea that space travel was not only possible but necessary for humanity's future.
The British Interplanetary Society launched in 1933 as an international membership society and UK-registered charity. It has been running technical studies since the 1930s, including work on a 1930s Moon mission and a 1970s interstellar probe named Daedalus.
Chesley Bonestell created illustrations based on Wernher von Braun's designs for books like The Conquest of Space published in 1949. Magazine articles such as the Man Will Conquer Space Soon series appeared in Colliers magazine between 1952 and 1954 while television shows included Walt Disney's Man in Space and Man and the Moon broadcast in 1955.
An analysis of space advocacy in Dark Skies: Space Expansionism, Planetary Geopolitics, and the Ends of Humanity by Daniel Deudney identified two different paradigms. The Braun-Tsiolkovsky paradigm focuses on migration and militarization of space as a primary goal while the Clarke-Sagan paradigm emphasizes pure scientific exploration without necessarily pursuing settlement.
Organizations like the JustSpace Alliance featuring Lucianne Walkowicz have been formed in recent years to reach more inclusive spaceflight and space science. They held events like the unconference Decolonizing Mars in 2018 to challenge existing power structures.