A Japanese mission to launch a powerful orbiter to Venus along with a separate solar sail vehicle is now targeted for a Thursday launch (U.S. time) after freezing conditions and clouds thwarted a Monday liftoff attempt.

The new Venus Climate Orbiter Akatsuki is now set to launch atop an unmanned H-2A rocket from Japan's Tanegashima Space Center on Thursday at 5:58 p.m. EDT (2158 GMT). Because of time zone differences, it will be 6:58 a.m. (local time) on Friday, May 21 at the Japanese launch site when the new mission blasts off.

Officials with the Japan Aerospace Exploration Agency (JAXA) said that "adverse weather conditions" forced them to call off the first attempt to launch the Akatsuki orbiter toward Venus. Weather forecasts apparently predicted dismal conditions for much of the rest of week as well, prompting several days of delays.

"After studying weather conditions from tomorrow, we decided to carry out the launch at 6:58:22 a.m. on May 21, 2010 (Japan Standard Time, JST) because the weather is expected to recover in that timeframe," JAXA officials said in a statement.

Japan's Akatsuki orbiter is expected to study Venus in unprecedented detail to unravel enduring mysteries of the planet's hellish atmosphere and surface. The spacecraft is due to arrive at Venus in December and spend two years studying the planet.

But Akatsuki is not launching into space alone.

The probe carries several smaller satellite experiments along with IKAROS, a solar sail spacecraft that will tag along with Akatsuki on the way to Venus. If all goes well, the IKAROS would be the first interplanetary solar sail craft and just a pit stop at Venus before heading? toward a region over the far side of the sun, JAXA officials have said.

Akatsuki and IKAROS would join a European spacecraft already in orbit around Venus when they arrive.

The European Space Agency's Venus Express orbiter has been studying Venus since it arrived at the planet in 2006. Venus Express and Akatsuki are expected to complement each other in their observations of the second planet from the sun, scientists with both missions have said.