For anyone interested, "Originating Communications Satellite Systems: The Interactions of Technological Change, Domestic Politics, and Foreign Policy" (https://history.nasa.gov/SP-4217/ch13.htm) is an interesting (?) read on the early history communications satellite regulations. (I'm absolutely refusing to dig through the ITU's documents on the subject.)
The bottom line is that international agreements through the ITU are responsible for frequency allocation (and presumably not damaging other people's stuff?) with the FCC being the pointy-end of the ITU and those treaties in the US. The FCC's authority in the area comes from the Communications Satellite Act of 1962 (https://en.wikipedia.org/wiki/Communications_Satellite_Act_o...), which has probably been modified beyond recognizability.
Another interesting read is Regulation and Licensing of Low-Earth-Orbit Satellites (https://digitalcommons.law.scu.edu/cgi/viewcontent.cgi?artic...), particularly sections 1 and 2.
The bottom line is that international agreements through the ITU are responsible for frequency allocation (and presumably not damaging other people's stuff?) with the FCC being the pointy-end of the ITU and those treaties in the US. The FCC's authority in the area comes from the Communications Satellite Act of 1962 (https://en.wikipedia.org/wiki/Communications_Satellite_Act_o...), which has probably been modified beyond recognizability.
[This is why we like network neutrality.]