Reactionless

Let’s talk about radio-frequency resonant cavity thruster, a reactionless drive. You generate microwaves inside a tapered cavity, and the whole taper pushes that way. Very very slowly.

So my question is, what good would it do us to have these things? They don’t have anywhere near the oomph of a classic rocket, but they don’t need any propellant. You can slap on some photo-voltaic panels or a nuclear reactor and that thing will just keep thrusting forever.

The way spacecraft maneuver in the real world is to coast until they hit a critical point in their flight plan, then aim their rocket nozzles in the proper direction and burn for as little time as they can, using as little fuel as possible.

A taper would work differently: very small constant acceleration. They’d make sense for distant targets, which would allow a longer time to build up speed. Or you could launch your spacecraft with rockets, then immediately turn on the tapers and bleed off momentum until you finally coast to a stop at your destination.

Any other ideas?