Sailing ships have always been the stuff of romance. The sight of a tall ship, white sails billowing in the wind, hull cutting through the water, is just something that leaves one’s heart in one’s throat. Countless stories and songs have been written about the age of sail, which ended in the 19th Century with the development of the steam engine.

However, it is possible that this romance will be replicated in the airless sea of space. The wind that may fill the sails of the future comes from the sun.

What are Solar Sails?

Solar sails take advantage of the fact that the light emitted by the sun exerts a tiny but measurable amount of pressure, particularly in space. A solar sail, made of some kind of flimsy, light weight material, like mylar or a carbon fiber, that is reflective. The light of the sun made up of tiny energy packets called photons, strikes the surface of the sail, bouncing off, but imparting it’s momentum to the sail, thus propelling it. If the sail is face toward the sun, it is propelled slowly but steadily outward. By changing its angle toward the sun, one can change the direction of the sail, just like a sail on an Earthly sea. One can even move the sail toward the sub by using the photon “wind” to slow its speed.

For a solar sail to be effective, it must have a large area, since the pressure exerted by the sun’s light is so gentle. A prototype solar sail proposed by the Planetary Society had the area of a typical basketball court. One solar sail proposed by NASA in the 1970s to carry a probe to Halley’s Comet would have had the surface area of ten city blocks.

To stabilize itself, solar sail would either be stiffened with some sort of material or spun to lend stability. It would carry anything from a small probe to a space craft carrying crew and or cargo to some destination in the Solar System.