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Solar sail spacecraft steers with sunlight for first time

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Japan's solar sail — a sun-powered spacecraft launched in May — has successfully steered by using just the pressure of sunlight against its square polymer sail, Japan space officials said.

The Japan Aerospace Exploration Agency spacecraft Ikaros now represents the first solar sail to have harnessed sunlight for both attitude control and propulsion, after it first launched May 21 alongside the Venus-bound orbiter Akatsuki.

Liquid crystal panels on the edges of the sail can change their surface reflection of sunlight by using low amounts of electricity to turn on or off. The "on" setting creates a mirror-like reflection that pushes the spacecraft forward, while the "off" setting has a more diffuse reflection that redirects the pressure of sunlight in all directions, lessening the force against the sail.

That allows Ikaros to slowly change direction based upon the different pressures of sunlight reflecting from its edges. Mission controllers have to account for the solar sail's spin rate, distance to the sun and the sun angle to plot the spacecraft's course.

An almost day-long test of the steering took place between the early morning hours of July 13 and July 14. Mission controllers achieved more than 90 percent of their expected attitude control angle.

"JAXA will continue the attitude control experiment by the Ikaros to evaluate the details of the attitude control performance while continuing to conduct research on attitude control technology using sunlight pressure as a technology that enables navigation for longer in time and further in distance by a solar sail," JAXA officials said in a recent statement.

That effort was also briefly described last week at the second International Symposium on Solar Sailing at the New York City College of Technology in Brooklyn, where researchers hailed the solar sail's success.

Such attitude control does not use any additional propellant, which may help make future solar sails more self-sufficient. Ikaros also relies upon thrusters located on its main body at the center of its sail to move around.

The solar sail also carries solar panels that have successfully generated electricity, even if it cannot use the solar-generated power for itself.

JAXA envisions Ikaros as the first step toward a future solar sail mission to Jupiter and asteroids that could fly in 2019 or 2020, said Junichiro Kawaguchi, JAXA program manager, during the solar sail conference.