The world's first solar sail spacecraft (search) was launched Tuesday from a Russian submarine under the Barents Sea but concern grew about whether it safely reached orbit as hours passed without a signal.

Cosmos 1 (search), a $4 million experiment intended to show that a so-called solar sail can make a controlled flight, was launched at 12:46 p.m. PDT, and initial data reception was followed by silence.

"The news is not good," said Bruce Murray, a co-founder of The Planetary Society (search), which organized the launch.

Data stopped during a pass over a portable ground station on Russia's Kamchatka peninsula at about the time the rocket's final stage would have ignited, mission officials said.

There was no signal on later passes over stations in the Pacific Ocean, the Czech Republic and two in Russia. None of those passes, however, were optimal for receiving signals.

The U.S. military also did not make radar sightings on the path the spacecraft was predicted to follow if it did enter orbit, mission official Jim Cantrell said. The best pass straight over a ground station was scheduled to occur after 9 p.m. PDT.

Louis D. Friedman, the society's executive director and Cosmos 1 project director, said there had been some ambiguous data from the launch vehicle, making it uncertain whether the initial launch had actually worked properly.

If all went as planned, the spacecraft was to unfurl eight triangular sails, each nearly 50 feet long and just a quarter of the thickness of a trash bag. Controlled flight, achieved by rotating each sail to change its pitch, would be attempted early next week.

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.

Such a craft would not have to carry chemical fuel to propel itself through space, and, according to advocates, would eventually achieve greater speed than a traditional spacecraft.

The Planetary Society is a Pasadena-based organization founded by the late astronomer Carl Sagan. The project was also organized by Murray, who is a former director of NASA's Jet Propulsion Laboratory, and Friedman, a JPL veteran.

Funding came largely from Cosmos Studios of Ithaca, N.Y., a science-based entertainment company that was founded by Sagan's widow, Ann Druyan.

Built in Russia by the Lavochkin Association and the Space Research Institute of the Russian Academy of Science, Cosmos 1 was under the control of a mission operations center in Moscow.

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.