I honestly do not know exactly what this is. I suspect it is a rocket launched sled used to crash test an object. If that is the case, I suppose the main explosion would either be some charge used to send it on the way, or the sonic overpressure as it broke mach. I suspect that the other sounds are hits on the rail and the crash at the end. But I really don't know, this is just my guess. Anyone here with more information please comment your ideas or what you know.