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.

Advantage of a Solar Sail

A typical solar sail picks up just one millimeter in speed per second of acceleration. But the advantage it has over a conventional rocket is that acceleration is constant and can be maintained over a period of days, weeks, or months. While a rocket stops accelerating after a few minutes of firing, a solar sail just keeps on going. At an acceleration rate of 1 millimeter per second per second, a typical solar sail would increase its speed by approximately 195 miles per hour after one day, moving 4700 miles in the process. After 12 days it will have increased its speed to 2300 miles per hour. A solar sailed probe would reach Pluto in five years, rather than the nine years for the rocket propelled probe now being readied by NASA. A space craft propelled by a solar sail does not encumber itself with fuel that a space craft propelled by a rocket must take with it.

History of the Solar Sail

Solar sails were first proposed by the German astronomer Johannes Kepler in the 17th Century. The concept was rediscovered by Friedrich Zander in the 1920s. In the 1970s, the Jet Propulsion Laboratory investigated several solar sail concepts for a possible probe to Halley’s Comet. The Japanese managed to launch two prototype solar sails on August 9th, 2004. The latest attempted test of a solar sail was conducted by the Planetary Society and was called Cosmos 1.

Cosmos 1

The Planetary Society, in conjunction with Cosmos Studios, attempted to launch a prototype of a solar sail called Cosmos 1. Cosmos 1 would have used a solar sail changed as eight triangular blades that could be rotated to maneuver the space craft. It was to be launched into low Earth by a Russian submarine using a Volna rocket. It would have deployed the sails and spent several weeks maneuvering in low Earth orbit using just the light pressure of the sun to propel the sail. Unfortunately, the launch attempt which took place on June 21st of 2005 ended in failure with the Cosmos 1 never deploying.

Solar Sails in Science Fiction

Spacecraft propelled by solar sails have naturally been a staple of science fiction. The Lady Who Sailed the Soul, written by Cordwainer Smith appeared in the April 1960 issue of Galaxy Magazine. Three years later, the novel version of Planet of the Apes featured a solar sailed space craft. The following year, Arthur C. Clarke published a far more technically detailed story about a solar sail propelled space craft called Sunjammer in Boy’s Life, about a race between “sun yachts” from Earth orbit to the Moon. By cheer coincidence, Poul Anderson published another story about solar sailed craft, also entitled Sunjammer, in Astounding Stories Magazine. Solar sailed ships have appeared in stories by such notables as Robert Forward, Jack Vance, Larry Niven, and Jerry Pournelle since then. Solar sailed craft have appeared in films such as Tron and Star Wars: The Attack of the Clones and on an episode of Star Trek: Deep Space 9.

Advanced Solar Sails

Scientists and other visionaries have tinkered with the idea of enhancing solar sails. Robert Forward has written studies suggesting ways to boost the momentum of solar sails using giant lasers or magnetic fields. In this way, solar sailed craft could reach speeds fast enough to reach the nearby stars. Other ideas using microwaves to accelerate solar sails have been advanced.

The Future of Solar Sails

The Jet Propulsion Laboratory is currently examining a prototype solar sail, called L’Garde. Carnegie Mellon and Washington University are currently studying solar sail concepts.

How solar sails will feature in the exploration of space is a question only time will give the answer to. It could be that some day in the future that galleons of the sky will ply the gulf between planets, propelled by gigantic sails, bearing cargos and passengers between Earth and human settlements that may be built at such places as Mars. In a way, the history of space flight could be the reverse of the history of ocean travel. The first ships would be powered by engines, only to be superseded by solar sail propelled ships. The age of the sailing ship will come again, in an ocean unimagined by the mariners who spent their lives on the oceans of our world.

External Links:

• Wikipedia Article on Solar Sails -
• Solar Sail Page -
• Cosmos 1 Page -
• JPL: Solar Sail Page -