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PASADENA — A U.S.-Russian group announced Monday it plans an April test launch of a space sail that relies not on wind but the gentle pressure of the sun’s rays to propel it. 

Backers hope the 30-minute suborbital test flight will show that a tightly packed sail can be unfurled in space.  

The test will be a step toward an October mission that will send an even larger version sailing around the Earth for the first time. 

“We’ll count ourselves as successful if we fly even a short time in that mode,” said Louis Friedman, manager of the Cosmos 1 project and executive director of The Planetary Society, a space advocacy group.  

“The Wright brothers flew for 12 seconds and they had a successful flight. If we can fly not 12 seconds, but 12 minutes, 12 days or 12 weeks, we’ll be happy,” 

Both missions will use converted intercontinental ballistic missiles launched from a Russian nuclear submarine in the Barents Sea – an unlikely but relatively inexpensive option that has kept the project’s budget to $4 million. 

Cosmos Studios, a science-based entertainment company founded by Ann Druyan, widow of the late astronomer Carl Sagan, and Joe Firmage, a Silicon Valley entrepreneur and sometimes UFO investigator, is footing the bill. 

“We are proud to be a part of this historic mission, which is a critical baby step to the stars,” said Druyan, Sagan’s longtime collaborator. 

Solar sails, first proposed in the 1920s, rely on the steady pressure of sunlight to move forward. Like a sailboat, a solar sail-driven spacecraft does not have to carry its own fuel, which can be expensive to launch into space. 

The American and European space agencies, and at least one private company, hope that future missions can rely on the technology. 

“If the Planetary Society mission is successful, it will be very useful to NASA,” said Hoppy Price, manager of solar sail technology development at the National Aeronautics and Space Administration’s Jet Propulsion Laboratory. 

Although solar-driven spacecraft will be slow to accelerate, with time they should reach high velocities that will enable travel across great distances. 

“It allows you to travel, come back and go out again because you don’t have to refuel,” Price said. 

The April launch will test the deployment of just two petal-shaped blades of Mylar polyester film about one-fifth as thick as a garbage bag.  

At the end of the brief flight the sail will fall back into Earth’s atmosphere. 

For the orbital flight later this year, a larger eight-petal design will be used. Inflatable trusses will pull the sail material from a canister and become rigid to support the sail’s shape.  

Each of the triangular petals can be turned to steer the spacecraft, allowing it to tack like a sailboat. 

“The goal is to be the first solar sail flight,” Friedman said. “It doesn’t have an application other than to be the first to demonstrate the technology.” 

The orbiting spacecraft will gradually spiral away from Earth as sunlight pushes on the 720-square-yard sail.  

The 88-pound craft will carry two cameras and several instruments and should appear in the night sky as a point of light as bright as the full moon. 

On the Net: 

The Planetary Society: http://planetary.org/ 

Cosmos Studios: http://carlsagan.com/