Louis Friedman imagines the day when people rocketed into weightlessness will unfurl lightweight, football field-sized sheets from their spacecraft and set sail for Mars. “It’s a realistic prospect,” said Friedman, head of the Planetary Society, a Pasadena, Calif.-based organization that was co-founded in 1980 by space visionary Carl Sagan. “I can imagine it working well for cargoes on long trips.” Friedman’s group plans to perform the first-ever orbital test of a solar sail this coming January with the help of another Sagan-affiliated group, Cosmos Studios, based in Los Angeles, and Russia’s Babakin Space Center in Moscow.