this is a good queue-in to start talking about mass ratio: the ratio of weight that is dedicated to payload versus the weight of the delivery platform and it's

this is a good queue-in to start talking about mass ratio: the ratio of weight that is dedicated to payload versus the weight of the delivery platform and it's fuel (slightly simplified take). this device is almost certainly air breathing. there's simply too big an oxygen-breathing-demand at speed to do anything else for sustained high speed flight, where you need to be generating a lot of motive force.