Solar sailing is a unique and elegant form of propulsion which transcends reliance on reaction mass.
Rather than carrying propellant, solar sails gain momentum from photons, the quantum packets of energy of which sunlight is composed. In addition, since solar sails are not limited by reaction mass, they can provide continual acceleration, limited only by the lifetime of the sail film in the space environment. Therefore, solar sails can expand the envelope of possible missions, enabling new high-energy mission concepts that are essentially impossible for conventional reaction propulsion, and enhancing current mission concepts by lowering launch mass and reducing trip times. Although solar sailing has been considered as a practical means of spacecraft propulsion only relatively recently, the fundamental ideas are by no means new. The existence of light pressure was demonstrated in theory by the Scottish physicist James Clerk Maxwell in 1873, but it was not measured experimentally until precision laboratory test were performed by the Russian physicist Peter Lebedew in 1900.