General Discussion
In reply to the discussion: NASA Tests "Impossible" Perpetual Motion Drive; Says it Works [View all]Treant
(1,968 posts)a little further research shows their null engine (the one that isn't supposed to do anything) generated the same thrust, it's probably a measurement error. When measuring micro-Newtons, that's not impossible.
Spontaneously generated fuel doesn't bother me, it happens all the time in a vacuum anyway. We'd just be exploiting that.
And certainly, unimaginable distances (at very low thrust) become possible. But really, they already were just as realistic with a solar sail (thrust reduces as you leave your star, but you get moving very, very fast before that happens), laser-driven sails (which don't suffer quite as much of a problem), a (theoretical) Bussard ramjet, and so on.
We don't build them because we don't plan robotic space missions that go that long.