After years of false starts, disappointment and delay, one of space flight's brightest hopes could be about to take to the skies.
Cosmos 1, the world's first solar sailing ship, could be launched from a Russian nuclear submarine in the Barents Sea in two weeks.
On June 21, if all goes well, a Soviet Volna rocket originally designed to deliver nuclear warheads will push a 100kg US-designed spacecraft to an orbit 800km. The payload will open and like the petals of a flower and eight huge triangular blades 15m-long will unfurl to reflect the rays of the sun.
Cosmos 1 -- a dream of the late visionary astronomer Carl Sagan, his wife Ann Druyan and his friend Louis Friedman, a former NASA scientist -- will be the first practical test of science-fiction technology.
In the vacuum of space, even light has force. Particles of light that slam against the fragile sails -- only a thousandth of a mm thick -- will begin to accelerate the space clipper.
The acceleration will be tiny, but in the course of a day the spacecraft may have gained 45m a second or 160kph.
After 100 days in the sun it could get up to 16,000kph. In three years, such a spacecraft could be the fastest man-made thing in space, without using a drop of rocket fuel.
The launch will be the first effective test of the technology. An attempt in 2001 went awry when the third stage of a Russian rocket failed to open. Since then, the mission's backers, the Planetary Society, a private organisation founded by Sagan and Dr. Friedman, the television company Cosmos Studios, and the Russian partners, have looked again at every detail.
NASA and another US government agency have undertaken to monitor the flight. Astronomers around the world have been invited to track the bright new star in the night sky on the longest day of the year.
"Reaching this milestone puts us on the doorstep to space," Dr. Friedman said. "We are proud of our new spacecraft and hope that Cosmos 1 blazes a new path into the solar system, opening the way for eventual journeys to the stars."
Solar sails offer the best hope for very long distance missions: chemical rocket fuel is expensive, a deadweight on a long journey and too inefficient.