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False dawn for Japan's Venus mission

Akatsuki probe will have to survive for six more years to get a second chance of orbit.

By David Cyranoski

It was meant to be a new dawn for Japanese planetary missions, but the disappointing reports from the country's Venus probe Akatsuki are all too familiar.

The Japan Aerospace Exploration Agency (JAXA) reported December 8 that Akatsuki (Japanese for "dawn") failed to enter the orbit of the searingly hot, rocky planet. Now orbiting the Sun, the probe will have to wait another six years before it has another chance. JAXA has already set up a committee to determine the cause of the failure and examine whether it is worth trying again.

Akatsuki was JAXA's bid to vindicate itself following the failure of its first planetary mission, the Mars probe Nozomi, launched in 1998 to enter the red planet's orbit the following year. That failure was blamed on a faulty valve. Nozomi's next shot at Mars, four years later, also fizzled out (see "Astronomers try to save Mars probe" and News in Brief item here).

Everything started well for the Akatsuki mission. An H-IIA rocket lifted off on May 21 carrying the probe and the Ikaros solar sail (see "Japan prepares for Venus countdown"). The latter payload successfully separated, unfurled itself, and has been exciting space scientists since.

Lost in space

On Akatsuki's way to Venus, tests of its various cameras showed everything was in order. In June, JAXA scientists successfully tried out the reverse thrust engines that would try to slow Akatsuki from 37 kilometers per second to the 35 kilometers per second speed it would need to drop into Venus's orbit.

JAXA confirmed that those engines began firing as pre-programmed when Akatsuki drew within 550 kilometers of Venus on June 7 at 08:49 Japan Standard Time. Plans were for the engines to fire for 12 minutes, during which time the craft was expected to pass behind Venus and temporarily lose contact. Communication was expected to be restored at 09:15. But that didn't happen until 10:29, by which time the craft had entered "safe hold mode", indicating there had been a problem. With tension building in the Sagamihara control center, the NASA Deep Space Network (DSN), an international network of antennas, began tracking Akatsuki. By 05:00 on December 8, the DSN had determined that Akatsuki was off course from Venus.

With its five cameras each measuring different wavelengths, Akatsuki was meant to study Venus' surface, clouds and lightning. Complementing the European Space Agency's Venus Express, which has been orbiting Venus since April 2006, Akatsuki promised clues to understanding some of the planet's mysterious features, such as the 'super-rotation' of its atmosphere, which spins at speeds up to 60 times that of the planet itself.

JAXA still doesn't know what went wrong with the $300-million craft, but it is looking on the bright side. One possibility for Akatsuki's failure to enter orbit is that the engines didn't fire for long enough, and this could mean that it has enough fuel for operations next time around, says Eijiro Namura of JAXA's public affairs office. Namura also says that continuous exposure of the craft's solar panels to the Sun should keep the battery, a major source of concern, in good shape. But he admits that the craft, designed for a two-year mission around Venus, could face various other, as yet unknown, problems.

UPDATED: At a press conference on December 8, lead scientist Masato Nakamura said the probe's reverse thrust engines, which were supposed to burn for 12 minutes, only fired for 2 minutes and 23 seconds. They were meant to decelerate Akatsuki to a speed at which it could enter Venus' orbit as the probe moved into the shadow of Venus and temporarily out of touch with the control center. Analysis of data from the spacecraft once communication was restored at 10:29, showed that from around 8:51, the craft had been disturbed and started spinning. The craft automatically went into safe hold mode, which shut off the engines. The craft was thus not able to achieve the necessary deceleration. The scientists suggest that the craft either was impacted by an object or had a problem with the engine nozzle. The ceramic nozzles had been newly designed for the mission by Mitsubishi Heavy Industry. The craft still has 80 percent of its fuel, giving JAXA hope that it can fend of solar radiation and make another attempt to enter Venus's orbit in six years. But faulty engine nozzles or other damage to the engine could make that impossible.

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