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"In my mind I have gone all over the universe, which may make it less important for me to make piddling little trips... I did enjoy seeing Stonehenge. It looked exactly the way I thought it would look."
- Isaac Asimov

Light Sail (or Solar Sail)  
  A form of propulsion for spacecraft; a sheet of lightweight material reflects light from the sun or other light source.  

An early use of this term in science fiction is in Jack Vance's Sail 25, with the marvelous character Henry Belt, an experienced spacer who is the captain of a small training craft called Sail 25.

The propulsion for this craft comes from light pressure (also called radiation pressure) from the sun upon this sail made of extremely lightweight material.

The story is about a training cruise, in which six cadets are taken on a simple little training cruise to Mars.

The pressure of radiation, of course, is extremely light - on the order of an ounce per acre at this distance from the sun. Necessarily, the sail must be extremely large and extremely light. We use a fluro-siliconic film a tenth of a mil in gauge, fogged with lithium to the state of opacity. Such a foil weighs about four tons to the square mile. It is fitted to a hoop of thin-walled tubing, from which mono-crystalline iron cords lead to the hull.
From Sail 25, by Jack Vance.
Published by Not Available in 1962
Additional resources -

This is a classic story; unfortunately, it is mostly available in out-of-print collections.

(Sail 25, Jack Vance, )

Johannes Kepler speculated that comets' tails are bent by the sun's action in his 1619 book Opera Omnia. Newton thought it was possible that light would exert pressure on material bodies. The existence of light pressure was demonstrated in theory by James Clerk Maxwell in 1873. Laboratory experiments confirming the theory were performed in 1910 by P.N. Lebedev, a Russian physicist, who overcame great difficulties in measuring the 4.7 x 10-6 N/m2 pressure of noon sunlight here on Earth. In the 1920's, Konstantin Tsiolkovsky and Fridrich Tsander wrote about "using tremendous mirrors of very thin sheets... using the pressure of sunlight to attain cosmic velocities."

The first mention of solar sails in a science fiction publication was not in a story; it occurred in the May 1951 issue of Astounding Science Fiction. Carl Wiley published an article called "Clipper Ships of Space."

The very first science fiction story about solar sails was probably "The Lady Who Sailed The Soul" (1960) by Cordwainer Smith. The story takes place thousands of years in the future - "Out of it all, two things stood forth - their love and the image of the great sails, tissue-metal wings with which the bodies of people finally fluttered out among the stars."

In 1958, NASA launched Echo 1, the first U.S. passive communications satellite. It was an aluminum-coated Mylar plastic balloon (microwaves bounced off it). Echo 1 is the first time NASA included solar pressure in calculating trajectory. Once in orbit, solar pressure moved the "sateloon" but didn't collapse it.

Apparently, some projects have already been tried to attempt to prove the real-world feasibility of light sails. Reflective panels may be used to slowly steer spacecraft, conserving fuel better used for maneuvering. A similar sort of scheme involves using lasers to push on a solar sail, thus powering a ship from a distance; see laser cannon, from Mote in God's Eye by Larry Niven and Jerry Pournelle.

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Additional resources:
  More Ideas and Technology from Sail 25
  More Ideas and Technology by Jack Vance
  Tech news articles related to Sail 25
  Tech news articles related to works by Jack Vance

Light Sail (or Solar Sail)-related news articles:
  - Solar Sails Unfurled Over Japan
  - Jack Vance's Incredibly Thin Solar Sail
  - Ikaros Solar Sail Works!
  - Solar-Photon Hoop Sails For Extrasolar Travel

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