He explored the possibilities of flying gliders inside a space colony, finding that the enormous volume could support atmospheric thermals. He calculated that humanity could expand on this man-made frontier to 20,000 times its population. The initial colonies would be built at the Earth-Moon and Lagrange points. and are stable points in the Solar System where a spacecraft can maintain its position without expending energy. The paper was well received, but many who would begin work on the project had already been introduced to his ideas before it was even published. The paper received a few critical responses. Some questioned the practicality of lifting tens of thousands of people into orbit and his estimates for the production output of initial colonies.