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Telescopes and space missions

Telescopes and space missions

Mission overshoots Venus orbit

08 Dec 2010 Michael Banks
The Akatsuki probe

The Japanese Space Agency, JAXA, has launched an investigation into a failed attempt to put a craft into orbit around Venus. Akatsuki, which blasted off in May, was due to study Venus’s violent atmosphere and confirm if there are active volcanoes on its surface. However, yesterday the craft failed to reduce its speed sufficiently to fall into the gravitational pull of the planet. Astronomers will now have to wait over six years for the mission to return to Venus before attempting to put it into orbit again.

Akatsuki, which means “dawn” in Japanese, is the first time JAXA has attempted to put a probe into an orbit around a planet. In 1998 JAXA launched Nozomi to orbit Mars but it suffered electrical failures before it could be put into orbit. “An orbit insertion is perhaps the most difficult and most critical operation of any in a planetary mission,” says Håkan Svedhem, project scientist for the European Space Agency’s Venus Express, which was launched in 2005 and has been orbiting the planet since 2006. “It is in no way a simple activity.”

Sultry neighbour

Known as the Earth’s “sister planet” due to its similar mass and size, Venus orbits closer to the Earth than any other planet in the solar system. However, Venus’s climate is very different from ours. Its atmosphere contains mostly carbon dioxide and is a sultry 460 °C, with the high temperatures believed to be due to a “runaway greenhouse effect”. And, while Venus rotates at about 6.5 km per hour, its atmosphere rotates at a violent 360 km per hour.

Costing about $220m, Akatsuki would have operated in orbit around Venus for the next four and a half years with five onboard cameras. Two of these instruments, which operate in the near-infrared regime, would study the planet’s surface and the motion of clouds, as well as the size of particles that make up the clouds. A long-wave infrared camera, meanwhile, would measure the temperature at the “cloud top”, which lies about 65 km above the planet’s surface.

The final two cameras are an ultraviolet imager to measure sulphur dioxide at the cloud top and a lightning and airglow camera, which would capture lightning flashes that have never been observed on the planet before.

According to Svedhem there is not a great deal the spacecraft can now do as it awaits its return to Venus. “All the people who have worked on the project must be very disappointed now,” says Svedhem, adding that it is also disappointing for the Venus Express team due to unavailability of joint observations the two spacecraft would have carried out. It is not yet known when the investigation will release its conclusions.

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