The Planetary Society is preparing to launch a tiny satellite into orbit later this month as the first phase in testing a solar sail as a means of spacecraft propulsion — an idea that has been kicking around in the science (and science-fiction) literature for at least a century.
The satellite, LightSail, no larger than a loaf of bread, is contained within the somewhat larger Prox-1 satellite developed by the Georgia Institute of Technology. It is scheduled to liftoff aboard an Atlas V rocket on May 20.
The concept states that if a large enough, kite-like "sail" can be deployed in space, the pressure exerted by particles streaming from the the Sun (known as the "solar wind") could be used to push a spacecraft along, much the same way that a sailing vessel is propelled when heading downwind.
The first LightSail won't reach a high enough orbit to try out the sail in the solar wind, but it should be able to test the mechanism for deploying the 345-square foot tissue-thin Mylar sail. A mission set for next year should put a second LightSail in a high enough orbit to fully test the concept.
A decade ago, the Planetary Society, the non-profit founded by the late Carl Sagan and now headed by Bill Nye ("The Science Guy"), made its first attempt to launch a solar sail, but the satellite was lost when the Russian launch vehicle it was on failed to reach orbit.
LightSail won't be the first spacecraft to test the solar sail idea. Both NASA and the Japanese space agency have experimented. Japan's Ikaros, launched in 2010, was the first to demonstrate the concept. While each particle "is small and only generates a small push, over time the accumulated energy from each one of the strikes pushes the solar sail (and anything attached to it) forward," according to Space.com.
ExtremeTech adds: "Solar sails fall into the same category as ion engine technology in that they are very low thrust, but highly efficient. In the case of solar sails, you don't need to bring any fuel at all, so it's really infinitely efficient if you don't mind the long acceleration times. You get just a few newtons of force from even a large solar sail, which is why some of the proposed designs for interplanetary sails have surface areas many times bigger — in the hundreds or thousands of square meters. Scientists are still working on how you'd deploy something that size."