Nearly 400 years ago astronomer Johannes Kepler [ http://antwrp.gsfc.…] observed comet tails blown by a solar breeze [ http://www-spof.gsf…] and suggested that vessels might likewise navigate through space using appropriately fashioned sails [ http://science.nasa…prop08apr99_1.htm ]. It is now widely recognized that sunlight does indeed produce a force which moves comet tails [ http://antwrp.gsfc.…] and a large, reflective sail [ http://www1.msfc.na…photos00-150.htm ] could be a practical means of propelling a spacecraft [ http://www.planetar…]. In fact, the illustration above represents one concept explored by NASA [ http://www1.msfc.na…2000/00-150.html ] centers to develop an interstellar probe pushed along by sunlight [ http://www.ec-lille…] reflected from an ultrathin sail. Nearly half a kilometer wide, the delicate solar sail [ http://www.ugcs.cal…] would be unfurled in space. Continuous pressure from sunlight would ultimately accelerate the craft to speeds about five times higher than possible with conventional rockets [ http://antwrp.gsfc.…] -- without requiring any fuel! If launched in 2010 such a probe could overtake Voyager 1 [ http://vraptor.jpl.…], the most distant [ http://vraptor.jpl.…current.html#RTLT ] spacecraft bound for interstellar space, in 2018 going as far in eight years as the Voyager will have journeyed in 41 years.
