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Akatsuki arrives at Venus, mission's fate uncertain

Posted: December 6, 2010

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Japan's Akatsuki spacecraft reached Venus Monday evening, but officials are still evaluating whether the $300 million mission successfully achieved orbit around the sweltering planet to begin two years of weather observations.

Artist's concept of Akatsuki flying over Venus. Credit: Akihiro Ikeshita/JAXA
The 1,000-pound probe was expected to fire its main engine around 2349 GMT (6:49 p.m. EST) Monday for about 12 minutes, slowing the craft enough to be captured by the gravity of Venus.

Engineers confirmed ignition of the thruster before Akatsuki passed behind Venus, which was expected to block communications signals from the spacecraft for 22 minutes, according to postings on the Japan Aerospace Exploration Agency website.

But officials did not regain communications with Akatsuki as scheduled, building drama inside the mission control center in Sagamihara, Japan.

Controllers finally received signals from the spacecraft at 0128 GMT Tuesday (8:28 p.m. EST), or at 10:28 a.m. Japanese time.

Japanese officials are evaluating the probe's position to determine whether it entered orbit, according to Twitter updates.

The spacecraft was supposed to enter a night pass in the shadow of Venus at about 0036 GMT (7:36 p.m. EST) and enter sunlight again about one hour later. The timeline called for a maneuver to an Earth-pointing attitude shortly before 0200 GMT (9 p.m. EST) and to switch to a high-rate communications antenna at 0309 GMT (10:09 p.m. EST).

It was unclear late Monday when controllers would know Akatsuki's position and health following the engine firing and unexpected communications issues.

JAXA cautioned before Monday's orbit insertion that it could take up to 12 hours to determine whether the spacecraft entered the correct trajectory around Venus.

Akatsuki, which means "dawn" in Japanese, was targeting an insertion orbit with a low point of 342 miles and a high point of more than 118,000 miles above the surface of Venus.

Three more thruster burns were planned Dec. 9, Dec. 11 and Dec. 13 to reach the spacecraft's operational perch spanning between an altitude of 342 miles and 49,700 miles, according to a JAXA spokesperson.

Science observations were expected to begin in January, including tandem studies with the European Space Agency's Venus Express orbiter, which has been at the planet since 2006.

The mission blasted off May 20 from the Tanegashima Space Center in southern Japan. It journeyed 300 million miles to reach Venus Monday.

Akatsuki's five cameras are designed to collect unparalleled data on the planet's atmosphere and runaway greenhouse effect for a two-year mission. Akatsuki also carries sensors to look for active volcanoes and search for lightning storms.

The atmosphere of Venus is made up of thick carbon dioxide, clouds of sulfuric acid and super-rotating jet stream winds of up to 225 mph. The blanket of carbon dioxide drives surface temperatures to nearly 900 degrees Fahrenheit, hot enough to melt lead. The atmospheric pressure at the surface is about 90 times greater than at sea level on Earth.

"Although Venus is believed to have formed under similar conditions to Earth, it is a completely different world from our planet, with extremely high temperatures due to the greenhouse effect of carbon dioxide and a super-rotating atmosphere blanketed by thick clouds of sulfuric acid," said Takeshi Imamura, Akatsuki's project scientist.

Each of the probe's cameras is expected to study a slice of the Venusian atmosphere, ranging from surface imagery to observations of the planet's sulfur cloud tops at an altitude of 60 miles.

Two short-wavelength infrared imagers will observe low-altitude cloud patterns, chart the distribution of water vapor and carbon monoxide, and map the surface of Venus with a goal of finding active volcanoes. Thick clouds prevent visible cameras from seeing the surface.

Data from Europe's Venus Express orbiter earlier this year showed evidence of fresh lava flows around three mountains, giving scientists new hope of catching a volcano in the act.

Venus Express continues studying Venus from an orbit similar to Akatsuki's planned trajectory.

A long-wavelength infrared camera and an ultraviolet instrument will look at the super-rotating cloud structures in the upper atmosphere. The ultraviolet camera will also track sulfur dioxide, a precursor to cloud formation at Venus.

Venus rotates on its axis once ever 243 days, remarkably slower than any other planet in the solar system.

"On most planets like Earth and Mars, the atmosphere usually rotates very slowly as compared to the planetary rotation," said Masato Nakamura, Akatsuki's project manager. "On Venus, however, the atmosphere rotates at a very fast rate approximately 60 times that of the planet's rotation. In fluid mechanics, this very unusual behavior is called super rotation."

Another camera will snap frames 30,000 times per second with a wide field-of-view to hunt for lightning at Venus.

Results from Akatsuki will give scientists more tools to better understand how Earth and Venus differ.

Scientists say Venus formed much like Earth and probably enjoyed calmer times in its ancient past. But something went wrong long ago, leading a potentially once-temperate Venus on an evolutionary course much different than Earth.

Before researchers can pinpoint what caused Venus to become hellishly inhospitable, they must dispatch robotic missions to unravel the planet's conditions and how they link together.

"Using [Akatsuki] to investigate the atmosphere of Venus and comparing it with that of Earth, we hope to learn more about the factors determining planetary environments," Imamura said. "From this viewpoint, we will be able to understand more about the reason why Earth is as it is now, and how it might change in the future."



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