AFAIK all FCC rules on frequency allocation (which is what SpaceX needed) are usually geo-locked. It's a lot easier to commit to fixed transmitters early on with the idea that any specific problems can be dealt with than getting permission to move them around at will.
Also, during this time the FCC has been redoing the rules on the bands they use to try to allow companies this kind of use. So in 2021 they asked for ideas, and SpaceX suggested mobile uplinks as a permissible use. Then, hearings and feedback from a lot of companies occurred.
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AFAIK all FCC rules on frequency allocation (which is what SpaceX needed) are usually geo-locked. It's a lot easier to commit to fixed transmitters early on with the idea that any specific problems can be dealt with than getting permission to move them around at will.
Also, during this time the FCC has been redoing the rules on the bands they use to try to allow companies this kind of use. So in 2021 they asked for ideas, and SpaceX suggested mobile uplinks as a permissible use. Then, hearings and feedback from a lot of companies occurred.