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A Solar Sail gathers sunlight as propulsion by means of a large membrane while a Solar “Power” Sail gets electricity from thin film solar cells on the membrane in addition to acceleration by solar radiation. What’s more, if the ion-propulsion engines with high specific impulse are driven by such solar cells, it can become a “hybrid” engine that is combined with photon acceleration to realize fuel-effective and flexible missions.
JAXA is studying two missions to evaluate the performance of the solar power sails. The project name for the first mission is IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun). This craft will be launched in 2010 together with the Venus Climate Orbiter, "AKATSUKI"(PLANET-C), using an H-IIA launch vehicle. This will be the world's first solar powered sail craft employing both photon propulsion and thin film solar power generation during its interplanetary cruise.

• IKAROS leaflet（PDF:1.3MB）

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IKAROS's mission

IKAROS will be launched from the Tanegashima Space Center using the H-IIA. After separation from H-IIA, it will spin at up to 20 rpm( ＝revolution per minute ), deploying the membrane and generating solar power by means of thin film solar cells (minimum success level) within several weeks. Acceleration and navigation using the solar sail will then be demonstrated (full success level) within half a year.

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IKAROS’s membrane

The shape of the membrane is square, with a diagonal distance of 20m. It is made of polyimide a mere 0.0075mm thick. In addition to the thin film solar cells, the steering devices and dust-counter sensors are fitted to the membrane.

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Membrane deployment

The membrane is deployed, and kept flat, by its spinning motion. Four masses are attached to the four tips of the membrane in order to facilitate deployment. Deployment is in two stages. During the first stage, the membrane is deployed statically, and during the second stage, dynamically. This deployment method can be realized with simpler and lighter mechanisms than conventional mast or boom types as it does not require rigid structural elements.

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Future plans

The second mission will take place in the late 2010s. It will involve a medium-sized solar power sail with a diameter of 50m, and will have integrated ion-propulsion engines. The destinations of the spacecraft will be Jupiter and the Trojan asteroids.
Solar sail missions are also being studied in the United States and in European countries. JAXA will lead future solar system exploration using solar power sails. Our missions will lead to lower cost in the solar cells market, whose growth is a key factor for global warming prevention. Those low-cost solar cells are also the foundation of future solar power satellite systems.