In his Edge.org Annual Question response, Progress in Rocketry, George Dyson exults in the success of Blue Origin and Space X in landing their rockets after pushing them past the Kármán line, and then goes on to predict that this will help pave the way to rockets with separate substances as propellant and as fuel:
There is no reason the source of reaction mass (propellant) has to be the same as the source of energy (fuel). Burning a near-explosive mix of chemicals makes the process inherently dangerous and places a hard limit on specific impulse (ISP), a measure of how much acceleration can be derived from a given amount of propellant/fuel.
All the advances in autonomous control, combustion engineering, and computational fluid dynamics that allowed these two rockets to make a controlled descent, after only a handful of attempts, are exactly what will be needed to develop a new generation of launch vehicles that leave chemical combustion behind to ascend on a pulsed energy beam.
Leaving aside whether, and to what extent, the Blue Origin and Space X results get us in that direction, are rockets like that even contemplated as a realistic possibility in the accessible future? Kerbal beamed power aside, is there any way for a rocket to climb from the surface to Earth orbit without physically carrying the source of energy that will get it there? Or what is Dyson talking about?