Russian and U.S. scientists are preparing for another test launch of a solar-sail spacecraft, which uses a propulsion system powered by sunlight. The first flight failed last month when a Russian rocket failed to deploy the spacecraft. The privately funded project is on track for another test flight sometime this winter.

The $4 million project is funded by Cosmos Studios, an educational film company. The Planetary Society is the private organization that is sponsoring the mission. Louis Friedman, the society's director, says upcoming test will demonstrate that the sun's power can be harnessed in space in much the same way that the wind is harnessed by sail ships. The craft will be propelled by the pressure created by light reflected off solar panels. "The goal is to do the first solar sail mission, to do controlled solar-sail flight, even for just a couple of orbits," Mr. Friedman says. "If we can increase our orbit energy by sunlight pressure, controlling the solar sail spacecraft, we will have succeeded."

The sail consists of eight blade-like panels with a total size of 600 square meters. As with the test in July, the solar-sail craft will be carried aloft on a Russian Volna rocket. The submarine-launched missile has been converted to peacetime use and is usually reliable. But it failed on the test-mission after launch from a Russian Navy submarine in the Barents Sea.

Viktor Kudryashov of Russia's Babakin Space Center explained what happened. Mr. Kudryashov says the first two stages of the rocket fired normally, but there was a problem with the third stage. An onboard computer detected lower-than-normal thrust, and caused the flight to abort. The rocket, and solar sail were lost somewhere on the Kamchatka Peninsula.

However, the scientists are readying a second solar-sail ship, with a test flight scheduled for late December or the months that follow. A third solar ship will be ready for a final mission sometime next year. Scientist Viatcheslav Limkin of Russia's Space Research Institute says that he and his colleagues are learning from the project, and even the failure was useful. "First of all, we tried to understand how easy it is to use a submarine rocket for our purposes," he said.

The scientist says he and his colleagues now understand the limitations of using military rockets for scientific projects.

The Planetary Society's Louis Friedman says scientists in the former Soviet Union first advanced the idea of solar sail ships in the 1920s. In the early 1950s, an American engineer further developed the concept, but the idea was so unorthodox that he published under a pseudonym in a science fiction journal. Now, the U.S. space agency NASA is studying solar sail systems, and European space officials will be testing their own solar sail ship over the next two years.

But the Planetary Society's private experiment may show for the first time that solar sail power is feasible. When Mr. Friedman speaks of the impact of the new technology, he recalls the first successful powered flight by humans. "I often use the Wright Brothers analogy," he says. "They flew 12 seconds and went nowhere, but the implications of course were enormous. Who could have imagined the aircraft industry back in 1903. I don't know what the implications will be of the first controlled solar-sail flight. We hope it will mean interplanetary travel in a very economical way with large payloads going back and forth between the planets, going in two directions."

Astronomer Louis Friedman notes that solar-sail spacecraft carry no fuel. They could potentially travel through the inner solar system using only the sun's power. Flights to the outer planets where the light of the sun is weaker could rely on a form of propulsion based on laser light. He says these experimental technologies offer the promise of human interstellar travel.