Nothing. The FAA in the US is pretty good about these things and as long as you stay below 490,000 ft AGL and are flying a sounding rocket (eg not trying to mak

Nothing. The FAA in the US is pretty good about these things and as long as you stay below 490,000 ft AGL and are flying a sounding rocket (eg not trying to make orbit). With that said, well-resourced doesn't matter too much, it's more knowledge and experience. CSXT attempts were done by a team of aerospace engineers experienced in these types of things in their day jobs. They reached space (above 100km AGL) twice. USCRPL has been doing this for well over a decade, and have also reached space twice. And they've had heaps of failures along the way. TLDR; Going Mach 5 in fairly thick atmosphere is exceptionally hard to do without encountering a rapid unscheduled disassembly. Flying a two stage to space is more efficient and less rough on the rocket, but no one has done that yet as it's quite a bit harder that a relatively dumb 4fnc rocket.