The Emthruster: Thrust without reaction?

[iancampbell]

That's a very good point. The term "reactionless drive" is often used to mean a drive that doesn't need any physical propellant; typically, this would involve a source of very large amounts of power which is converted into some variety of photons. Which, for many purposes, would be just as useful as a true reactionless drive.

Of course, a photon drive leads to the availability of the Kzinti Lesson...