You need FAA waivers to send stuff up there. There comes an altitude (18k IIRC) above which all airspace is controlled, you're not supposed to be up there with

You need FAA waivers to send stuff up there. There comes an altitude (18k IIRC) above which all airspace is controlled, you're not supposed to be up there without following the directions of the relevant tower and carrying a transponder that they can talk to. But an amateur rocket has no ability to follow such directions so you have to get FAA permission to get exclusive access to a chunk of airspace. Of course the FAA doesn't give out such waivers willy nilly, they expect the amateur rocket community to minimize the need. Thus there are launch sites in the middle of nowhere that have launch windows where the big stuff is allowed. They also self-regulate on availability of the big motors. The guys who make them won't sell them to anyone who isn't certified, other than as part of a launch to get said certification which is done under the supervision of someone who is certified. They don't have the force of law but so far it's worked. (And there's the separate issue of the hazmat rules about those big motors--most people can neither legally store nor transport them. Take delivery at the launch site and use them.)