In what sounds like a purely fantastic voyage, a private US- Russian group that promotes planetary exploration plans to use the power of light to sail a giant windmill-shaped contraption through space. The Planetary Society, founded by the late astronomer Carl Sagan and others, said on Monday the vehicle featured reflective surfaces that would be propelled when particles of light - photons - hit it. The craft, with its 30-metre sails, is to be launched on a converted Russian intercontinental ballistic missile from a submarine in the Barents Sea this year at a cost of about US$4 million (HK$31.1 million)....