Right, a sail has more in common with a wing than a parachute. The force that is propelling the sailboat is basically lift—turned sideways—not collision. Which

Right, a sail has more in common with a wing than a parachute. The force that is propelling the sailboat is basically lift—turned sideways—not collision. Which, to bring it back to the origin of this thread of armchair physicists incorrecting each other, means that an LED mounted on a solar sail would not work, because the only force it imparts is collision. Which makes the sail analogy kind of a bad one for the use of solar pressure as a driving force. Edit: Hmmm, but what if the surface material of the sail were phosphorescent and could gain energy state from the solar pressure, then kick it a photon when dropping energy state? And then what if there were a fly wheel (magnetic axel, in the vacuum of space, extremely low friction) that could act as the keel... Hmmmmmmm Edit 2: I wonder if a lens that refracted light similarly to how air flows over an airfoil would create a "solar lift" effect? Unfortunately, lenses are heavy.