Scientists in Russia and California worked on final preparations for the planned launch of the first spacecraft propelled by sunlight.
If all goes as planned, Cosmos 1 was to be launched early Tuesday afternoon, California time, and carried into Earth's orbit by a converted intercontinental ballistic missile, according to the Planetary Society, which is undertaking the nearly $4 million experiment.
The missile was being launched from a submerged Russian submarine in the Barents Sea. Russian, American and Czech ground stations will track the craft.
Solar sails are seen as a means for achieving interstellar flight by using the gentle push from the continuous stream of light particles known as photons. Though gradual, the constant light pressure should allow a spacecraft to build up great speed over time, and cover great distances.
Solar sails do not rely on the solar wind — the stream of ionized particles flowing from the sun — which moves more slowly than light and with much less force.
On the Planetary Society's Web site, Louis Friedman, executive director of the Planetary Society and project director of Cosmos 1, said society scientists met Monday with their Russian counterparts and others at a ground tracking station about 75 miles southeast of Moscow.
They heard a report on spacecraft testing, he wrote, and "the spacecraft is ready for flight."
The Pasadena-based society was founded in 1980 by the late astronomer Carl Sagan, former Jet Propulsion Laboratory director Bruce Murray and Friedman, also a JPL veteran.
When Cosmos 1 is in orbit, inflatable tubes will stretch the sail material out and hold it rigid in eight structures resembling the blades of a windmill. Each blade, roughly 50 feet long, can be turned to reflect sunlight in different directions so that the craft can "tack" much like a sailboat in the wind.
Cosmos 1 is designed to go into a nearly polar orbit more than 500 miles high and operate for a month. Covering 720 square yards, it should be visible as a bright pinpoint of light in the night sky.
Japan tested solar sail deployment on a suborbital flight and Russia deployed a solar sail outside its old Mir space station, but neither involved controlled flight, Friedman said.
Cosmos 1 was built by the Russian aerospace company NPO Lavochkin. Most of the funds has come from Ithaca, N.Y.-based Cosmos Studios, which was co-founded by Sagan's widow, Ann Druyan, to create science-based entertainment.
Sagan, an astronomer who extolled the grandeur and mystery of the universe in best-selling books and an acclaimed Public Broadcasting Service series, died in 1996.