now that i've looked into it, a rocket is considered not amature if the thrust time is over 12 seconds or the thrust is over a certain limit. after that, you need FAA approval, mandatory insurance coverage, all sorts of fun beaurocratic stuff. not to mention all the paperwork that goes with nuclear componentry. but hey, if University of Queensland managed to launch a scramjet rocket to near-space altitudes and fire an experimental engine at over mach 7, a mid-altitude rocket plane shouldn't be a problem for a college. at least I hope.