A Solar Sail converts sunlight as a 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. To evaluate the performance of the solar power sails, IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) was launched on May 21, 2010 together with the Venus Climate Orbiter, AKATSUKI And IKAROS becomes the world's first solar powered sail craft employing both photon propulsion and thin film solar power generation during its interplanetary cruise.
IKAROS was launched by the H-IIA F17 from the Tanegashima Space Center at 6:58:22AM (JST) on May 21 2010. After the initial operation check, IKAROS started the missions for the world's first demonstration of solar power sail.
Since May 26 the membrane had been deploying and on June 9 succucessfull deployment was confirmed.. On June 10, solar power generation by thin film solar cells was confirmed. (Minimum success criteria were achieved!) On June 14 and 19, two separation cameras successfully took impressive pictures of the deployed solar sail. The membrane was expanded to form a square shape without damages. It was shining in the dark space.
After the membrane was deployed, IKAROS demonstrated photon propulsion and guidance, navigation and control using solar sail successfully during its interplanetary cruise. (Full success criteria were achieved!) On December 8, IKAROS flew by Venus. The distance at closest point to Venus was about 80000km. The monitor cameras took pictures of Venus over the membrane. IKAROS finished all experiments planned on Dec 2010 and is still continuing the first actual solar sail flying in order to enhance the skill of controlling solar sail.
The summary of IKAROS operation is as follows.
|May 21||Launch, Spin separation (→5rpm)|
|May 22||Initial operation check|
|May 24,25||Spinning-down (→2rpm)|
|May 26||Tip mass separation|
|May 27〜29||Spinning-up (→25rpm)|
|June 2〜8||First stage development|
|June 9||Second stage development|
|June 10||Solar power generation though thin film solar cells|
|June 14||First separation camera (DCAM2) experiment|
|June 16〜18||Spinning-down (→1rpm)|
|June 19||Second separation camera (DCAM1) experiment|
|June 21〜25||Start up of optional equipments (GAP, ALDN and VLBI)|
|July 8||Confirmation of photon propulsion|
|July 13||Attitude control experiment using steering device|
|December 8||Flying by Venus|
Future Solar Power Sail Demonstrator planned in the late 2010s will involve a large 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. Though Solar sail missions are also being studied in the United States and in European countries, Japan will lead future solar system exploration using solar power sails with continuing this kind of mission.And, 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.