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.
The blades are made of 0.0002-inch-thick Mylar. The idea is to gather the maximum amount of light at the lowest cost in terms of weight.
Once the craft launches, it will settle into an orbit 511 miles above the Earth and will circle it every 100 minutes. The sail won't be unfurled for four days, to allow any air in the container to leak away. If it is opened prematurely, the explosive release of air could damage the delicate spacecraft.
Once unfurled, the sail blades can be adjusted to keep the sun at the best receiving angle as the craft orbits Earth. If everything works the way it should, and the sun cooperates, the photons from the sun should lift the spacecraft into a higher orbit.
Under perfect conditions, Friedman said, Cosmos 1 might boost its orbit 31 to 62 miles over the expected 30-day life of the mission.
The idea of space-faring on sun power has been around since science fiction writers imagined claw-handed creatures from Mars landing on the National Mall.
Friedman became interested in the idea when he worked on deep-space missions for the Jet Propulsion Laboratory in La Canada Flintridge in the 1970s.
"NASA has done many studies on interstellar flight," Friedman said. "They all end up being impossible, except for light-sailing."
Though the drawback is the turtle-like buildup of speed, a light-sailing craft has several advantages over conventional spacecraft. Because it gets its power from the sun, it doesn't have to carry fuel. Further, because the sun supplies continuous power, the craft can, over a period of years, reach speeds up to 100,000 mph, six times as fast as the space shuttle.
Therein lies the allure, and the challenge, Friedman said.
He wrote a book on the subject, "Starsailing: Solar Sails and Interstellar Travel."
After leaving JPL in 1980 to form the Planetary Society along with famed astronomer Carl Sagan and former JPL director Bruce Murray, it was one of the ideas he took with him.
Bringing the idea to fruition has not been easy. The Planetary Society does not have its own launch facilities, or the budget to build its own space vehicles. So the idea sat on Friedman's desk until the end of the 20th century.
"Nobody could solve the problem of a practical, low-cost flight," he said.
With the end of the Cold War, however, the Soviet Union's space program suddenly became a budgetary orphan. Russian scientists began looking outside their borders for work.