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What with commercial rockets and space elevators covered here in the last few days, solar sails make a logical addition. A solar sail is exactly what it sounds like: a sheet of material propelled through interplanetary space by the solar wind in much the same way ships have crossed oceans on earth since ancient times. And it looks like a prototype device (Artists rendition of LightSail-1 by Rick Sternbach. Credit: Planetary Society) will soon be borne of the gossamer wings of star light:
The Planetary Society has announced LightSail, a plan to sail a spacecraft on sunlight alone by the end of 2010. The new solar sail project, boosted by a one-million-dollar anonymous donation, was unveiled at an event on Capitol Hill in Washington, D.C on the 75th anniversary of the birth of Planetary Society co-founder Carl Sagan, a long-time advocate of solar sailing.
Solar sails make use of Einstein's famous equation E=MC square; light particles called photons represent an equivlent amount of mass. Photons striking a sail push the material and anything attached to it just like molecules of wind hitting canvas.
Like anything else, there are advantages and disadvantages. On the plus side, sunlight is free and the materials technology is far more within reach than, say, that required by a space elevator. On the downside, solar sails will probably only work relatively close to the sun, at best extending beyond Mars to the asteroid belt, where the incident solar wind is strong. Then again, with the help of a sufficently powerful laser, shining for months or years at gigawatt strength on a single sail equipped spacecraft, a solar sail could theoretically be used for much longer voyages. With such lasers on each end of the journey, to alternately accelreate and slow down spacecraft, there's an actual, practical method of long distance, perhaps even interstellar, travel -- once the challnges of building giant, reliable lasers in deep space are met anyway. Sailing through the heavens to the stars; that's about as romantic as science-fiction, and maybe one day science fact, can get!
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