Something a little more from fringe science: I recently heard on my favorite tech news podcast that there was an article published in New Scientist about a space (as in outer space) drive that converts electrical energy into thrust using microwaves. It has caused a lot of uproar about not being possible because it violates the law of conservation of momentum, making it impossible to build. But the Chinese (looking for any technological advantage in space they can get) claim to have confirmed the theory and are building a demonstration unit.

The theory is that the drive creates thrust by tapering a resonant cavity filled with microwaves. The thrust is small, 85 compared to 92 mN for the NSTAR ion thruster used by NASA, but enough to power space vehicles and it uses much less power than the NSTAR. Apparently, the microwaves are introduced into a tapered cavity and strike the larger end of the cavity with more force than the smaller end that has less area which creates thrust. One big question is why doesn't the force exerted on the sides also create opposing forces that cancel out each other.

Interesting stuff - we will have to see how it works out. Some of us might be building space thrusters soon. Do you think it will work?