Sailing though space on the ever-so-faint pressure of photons streaming from the sun used to be science fiction. But this week it became science fact as Japan's IKAROS spacecraft successfully spread its solar sail—the first time such a sail has been deployed in space. Centrifugal forces, generated by gently spinning the spacecraft, took a few days to spread out the square polyimide sail, which is 20 meters across diagonally and a mere 0.0075 millimeters thick. Previous designs, never really tested in space because of rocket failures, relied on struts to keep the sails tight. With the sail deployed, the Japan Aerospace Exploration Agency, which launched IKAROS on 21 May, today proclaimed "minimum success" for the mission. Complete success will depend on acceleration and navigational tests over the next several months. In the meantime, IKAROS is slowly gliding towards Venus.
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