On a real sailboat, you can go in lots of directions, not just the one the wind is pointing at. You can even go somewhat against the wind. In a lightsail, if I

On a real sailboat, you can go in lots of directions, not just the one the wind is pointing at. You can even go somewhat against the wind. In a lightsail, if I understand this diagram correctly[1], the imparted momentum is proportional to the sum of the angle of incidence and the angle of reflection. (Which, come to think of it, is exactly how billiards works.) Therefore the sail travels perpendicular to its orientation, no matter where the incoming light came from (as long as it came from that side -- I'm guessing the other side is not reflective). https://en.wikipedia.org/wiki/Solar_sail https://en.wikipedia.org/wiki/Solar_sail