This paper seeks to open an inquiry into the origins of astropolitics, an intellectual and popular imagination whose defining characteristic is the attempt to project geopolitical concepts and categories into outer space. I locate the roots of this vision not merely in Anglo-American maritime strategy but in the rather earthlier German tradition of geopolitics, more specifically in the work of the geographer Friedrich Ratzel and the political theorist Carl Schmitt. Surprisingly, however, my reverse chronology discovers that although the two men’s ideas reverberate through contemporary astropolitical discourses, they were both in fact, in different ways and for different reasons, hesitant about space colonisation. The paper makes sense of this finding and unpacks its implications for contemporary International Relations debates on off-earth politics.