Say you're a spacecraft in space. You've got a source of lots of energy (solar panels). You have limited mass, and even more limited mass that you are willing to throw away. Also, you care mucho about reliability and simplicity. How do you go places? Here's a very simple idea. Focus a laser beam pulse onto a surface. Blam. Get an extremely hot spot on the surface which vaporizes, ejecting gas, thrusting spacecraft the other way. The surface can then be melted to re-form it (or it perhaps was already a liquid); then do it again. Variants: 1.the "surface" actually is a liquid drop detached from any solid and blasted just as it moves into the focal spot; this lies inside a rocket-type chamber+nozzle. 2.The focal spot is situated inside a magnetic field pointed in the thrust direction. Hot plasma then will fly off in field-line directions, but not in other directions. 3. Rotating interruptor/shields in front of the laser could protect it from being hit by hot ejecta coming back at it a little after it pulses. What is the point of all this? Well, A. Simple. B. Can be done on a very small scale. C. The exhaust velocity, governed by the temperature of the laser-heated stuff, it seems to me could be made extremely high, perhaps exceeding any currently-used spacedrive.