Though it may look like a collection of tinfoil and string, the photo above depicts what may be the first solar sail to actually propel a spacecraft. Japan's IKAROS (Interplanetary Kite-Craft Accelerated by Radiation of the Sun) just unfurled the 7.5 micron (.0003-inch) thick polyimide membrane 7.4 million kilometers from Earth this week, and expect its embedded thin-film solar panels to propel the craft past Venus and towards the dark side of the sun. Because wax and feathers only get you so far.