> you might as well just switch to a suborbital hop concept. One is not exclusive to the other. Skylon was expected to use air breathing engine up to Mach5+ a

> you might as well just switch to a suborbital hop concept. One is not exclusive to the other. Skylon was expected to use air breathing engine up to Mach5+ and switch to rocket engine beyond it. You can probably do the same for a suborbital airliner if you are insane enough.