A new Japanese weather probe and daring solar sail concept are scheduled to blast off together Monday evening for a six-month journey to study Venus.

The Venus Climate Orbiter, named Akatsuki, represents the main payload sitting aboard the H-2A rocket slated for launch at 5:44:14 p.m. EDT on Monday, May 17, though it will be early Tuesday at Japan's Tanegashima Space Center launching site. The launch requires a precise time window each day in order to achieve a successful trajectory toward Venus.

But Akatsuki, which means "Dawn" in Japanese, won't fly alone. A solar sail named Ikaros (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) gets to piggyback aboard the rocket as one of five smaller secondary payloads. The four remaining payloads represent small Earth satellites and experiments built by private universities and corporations.

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Both the 1,100-pound Akatsuki spacecraft and the 700-pound Ikaros should set off for Venus on the same course, if everything goes smoothly. But only Akatsuki has an actual date scheduled with Venus.

"Akatsuki is the world's first planetary probe that deserves to be called a meteorological satellite," said Takeshi Imamura, a JAXA project scientist with the Venus Climate Orbiter mission.

The Japan Aerospace Exploration Agency (JAXA) has designed its boxy probe to investigate the origin of sulfuric acid clouds and create a 3-D model of high-speed winds in the tempestuous atmosphere of Venus. It also carries an instrument that could detect lightning, if any exists within the thick Venus clouds.

Ikaros has a different journey ahead. The solar sail's design should provide the first test ever of solar sail propulsion based on harnessing the pressure of sunlight during an ambitious three-year journey to the far side of the sun.

The kite-like solar sail will also test thin film solar cells that generate electricity and might someday help power a hybrid engine of sorts in space. But Ikaros must rely solely upon the solar pressure without having such an engine on board.

Akatsuki's study of Venus is planned to last at least two years after it enters the planet's orbit. It would join a constellation of other JAXA missions that have visited Earth's moon and an asteroid, as well as one failed mission to Mars.  

The Japanese space agency also launched a new space freighter late last year aboard an H-2B rocket, which represents the newer and bigger descendant of the H-2A rocket that will launch the Venus mission.

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