Theorists and dreamers have imagined for decades a spacecraft whisking silently through the inky vastness of space, sailing on light rays from the sun.
Even though many studies have concluded that solar sailing could be a practical method of journeying to other stars, no government space agency has mounted a mission to see whether it actually works.
On Tuesday, the Cosmos 1 spacecraft, powered only by light reflected off a bank of 49-foot sails, is scheduled to be launched from a Russian submarine in the Barents Sea.
The project was bought and paid for by a group of space enthusiasts determined to blaze its own trail to the stars.
"No space interest group has ever built a craft and gone to space," said Louis D. Friedman, executive director of Pasadena's Planetary Society, which describes itself as the largest space advocacy group on Earth, with more than 80,000 members. "I'm extremely gratified. If it works, I will be even more gratified."
Theory suggests that an infinite stream of photons, striking the reflective surfaces of the craft's windmill-like blades, will propel it forward in space. Though the photons -- packets of light -- have no mass, each carries a tiny amount of energy that it transfers to the spacecraft when it strikes the sails.
Cosmos 1 does not use the solar wind, which is made up of ionized particles from the sun.
In the frictionless void of space, the craft would gradually gain speed, making it theoretically ideal for long journeys to the outer solar system or possibly other stars.
With a thrust just one-ten-thousandth as powerful as gravity, it won't go fast at first. At its projected speed it would take two years to get to the moon.
But that doesn't matter to Friedman, who likes to compare his venture to the Wright brothers' experiments in powered flight a century ago.
"The Wright brothers flew 12 seconds and went nowhere," he said. "I'll be happy with any effect at all."
Space travel has often been compared to seafaring, with the stars representing distant ports on a vast ocean of night.
Until now, however, the small vessels plying the skies have had more in common with motorized dinghies than the majestic sailing ships that explored the world's oceans in the time of Columbus and Magellan.
The solar sail craft is different. Big enough to be visible from the Earth's surface, it consists of eight adjustable blades in two tiers. It is one of the largest instruments ever launched into space.
