Solar sail Planetary SocietyIt's only fitting that on what would have been Carl Sagan's 75th birthday, an organization started by the astronomer famous for his wondrous and elegant descriptions of the universe announced plans to test a wondrous and elegant way to explore the solar system and well beyond.

The nonprofit Planetary Society, which Sagan co-founded in 1980, unveiled plans at an event Monday on Capitol Hill for a 2010 launch of LightSail 1, a spacecraft pushed through space by sunlight. If successful, LightSail 1 would be followed by two higher-flying successors. The organization announced that it had received an anonymous $1 million donation that allowed the project to proceed.

LightSail 1 would comprise 32 square meters of Mylar sail, with a small control module and two more modules to contain the sail before deployment. The radiation pressure of sunlight photons striking LightSail 1 would exert a force on the sail surface, gently accelerating the spacecraft to potentially great speed over time. The Planetary Society estimates that a solar sail could speed a spacecraft to more than 200,000 kilometers per hour in three years' time. Electric plasma engines such as that used on NASA's Dawn probe operate on a similar principle, harnessing low-thrust rockets that, in the vacuum of space, eventually allow a spacecraft to attain great velocity.

The LightSail mission would constitute a mulligan of sorts for the Planetary Society, which attempted to launch a similar craft, Cosmos 1, in 2005. Cosmos 1 failed to reach orbit on a malfunctioning submarine-launched Russian rocket. The Planetary Society says it has not yet identified a vehicle to boost the new solar sail to orbit but that it could piggyback on several American and Russian launches in the works for 2010.

Artist's depiction of unfurled LightSail with satellite payload at center: The Planetary Society