Greetings ! Please read this short story about solar sails' physics: http://www.spacedaily.com/news/rocketscience-03zg.html Can the experts here provide their opinions, please ! I personally thought that was all simple and basic stuff long since solved by physics. I mean, a photon has energy and hence momentum which it transfers to the sail and then it is reflected - reemmited thus again the momentum exchange occurs only that this time the photon and the sail push against each other (actualy kin'na smells fishy in terms of energy if I put it this way). But the light pressure experiment with the reflective and absorbing surfaces clearly draws a different picture. I've heard of it before but no details were given about the surface (or, in fact, I think it was said that a reflecting surface would move, which is clearly a book's or my memory's mistake ?). So, what actualy happens here ?! The only possible conclusion here as I see it is that the reflected - reemmited light "drags" the reflective material back, but how can that be ?! Is that really so complex that nobody thought about it before ?! Does this actually doom the whole idea of solar sails - they'll just evaporate if they're absorbing or produce no thrust if they are reflecting ?! HAS ANYBODY EVER DONE AN EXPERIMENT, EXCEPT THE ABOVE MENTIONED, BEFORE AN ENTIRE SOLAR SAIL SPACE MISSION WAS READY FOR LAUNCH ?! Thanks ! Live long and prosper.