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Two solar sailing trials readied for launch next year

Posted: November 10, 2009

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Next year promises to be a banner year for solar sailing, with at least two experimental missions due for launch to demonstrate the novel use of light pressure from the sun for propulsion in space.

Artist's concept of Japan's Ikaros solar sail. Credit: JAXA
Japan is planning to launch an interplanetary solar sail mission called Ikaros next May. The Planetary Society will follow with its own demo flight by the end of 2010, the space advocacy group announced Monday in a statement written by Louis Friedman, the society's executive director.

Solar sails have been studied by all of the world's major space agencies, but flight tests have only attempted to deploy solar sails and not tried to use the structures for propulsion.

Ikaros stands for the Interplanetary Kite-craft Accelerated by Radiation Of the Sun. The name also harkens to the Greek mythological figure Icarus, who fashioned feathers and attempted to escape exile but flew too close to the sun.

The mission will launch next May on an H-2A rocket with the Akatsuki mission to Venus, according to the Japan Aerospace Exploration Agency.

The sqaure Ikaros sail, with a diagonal diameter of 66 feet, is covered with thin film solar cells to generate electricity. The spacecraft will spin up to about 20 rpm for stability during its mission.

Japan has led solar sail research in recent years. A small reflector was deployed from a suborbital sounding rocket in 2004 and a larger sail failed to open completely during an orbital test in 2006.

The Planetary Society's mission, called LightSail 1, will come five years after its Cosmos 1 solar sail failed to reach orbit on a Russian submarine-launched Volna rocket.

The spacecraft in the 2005 failure was built by Russian contractors, but LightSail 1 will be based on a CubeSat platform provided by California Polytechnic State University in San Luis Obispo, Calif.

The Planetary Society did not say how much the new project would cost, but a member of the group donated $1 million for the mission and three-quarters of the required funding has already been raised. The society is seeking more donations to cover the rest of the costs.

Solar sails provide an inexpensive and efficient way to travel through the solar system and eventually to nearby stars. The concept involves large thin deployable structures that capture the energy of photons, particles of light that can gradually propel a spacecraft without conventional chemical fuels.

"A sail powered by sunlight alone will not be able to reach the stars," Friedman wrote in Monday's statement. "Such a trip will require large solar-powered lasers that will beam concentrated light over interstellar distances. But solar sailing -- flying on sunlight -- will allow us to get around the solar system without fuel and to hover at important places in space, countering the effect of the sun's gravity."

The LightSail program consists of three missions, LightSail 1 and two progressively more ambitious spacecraft to further demonstrate the concept and its applications, including an early warning station in deep space to detect approaching solar storms.

Artist's concept of the LightSail 1 spacecraft. Credit: The Planetary Society
But LightSail 1 first must test the deployment of the large solar sail and show its ability to use solar light pressure as a means of propulsion.

"These ultra-light spacecraft point the way to the future," Friedman wrote. "A spacecraft designed for interstellar flight will have to be 'atosat' in size, weighing perhaps only a few grams. For now, we will take the step of reducing mass by a factor of 25 while flying farther and faster."

Officials hope LightSail 1 will be ready for launch as a piggyback payload by the end of 2010. The Planetary Society lists the Atlas 5, Falcon, Minotaur, Kosmos 3M and Soyuz rockets as potential launch vehicles.

The mission will use a triple-body CubeSat spacecraft. One unit will house electronics, while the other two parts will contain the solar sail materials.

The aluminized Mylar sail will unfurl in four triangular parts to about 344 square feet and provide about 6.5 micro-g of propulsive force. One side of the ultra-thin structure will measure about 18 feet, according to the Planetary Society.

Acceleromaters aboard LightSail 1 will detect the slight change in velocity from the solar sail to confirm the concept works as the spacecraft orbits about 500 miles above Earth.