Akari (satellite)


Akari was an infrared astronomy satellite developed by Japan Aerospace Exploration Agency, in cooperation with institutes of Europe and Korea. It was launched on 21 February 2006, at 21:28 UTC by M-V rocket into Earth sun-synchronous orbit. After its launch it was named Akari, which means light in Japanese. Earlier on, the project was known as IRIS.
Its primary mission was to survey the entire sky in near-, mid- and far-infrared, through its aperture telescope.

Technical design

Its designed lifespan, of far- and mid-infrared sensors, was 550 days, limited by its liquid helium coolant.
Its telescope mirror was made of silicon carbide to save weight. The budget for the satellite was ¥13,4 billion.

History

By mid-August 2006, Akari finished around 50 percent of the all sky survey.
By early November 2006, first all-sky survey finished. Second all-sky survey started on 10 November 2006.
Due to the malfunction of sun-sensor after the launch, ejection of telescope aperture lid was delayed, resulting the coolant lifespan estimate to be shortened to about 500 days from launch. However, after JAXA estimated the remaining helium during early March 2007, observation time was extended at least until 9 September.
On 11 July 2007, JAXA informed that 90 percent of the sky was scanned twice. Also around 3,500 selected targets have been observed so far.
On 26 August 2007, liquid-Helium coolant depleted, which means the completion of far- and mid-infrared observation. More than 96 percent of the sky was scanned and more than 5,000 pointed observations were done.
British and Japanese project team members were awarded a Daiwa Adrian Prize in 2004, by the Daiwa Anglo-Japanese Foundation in recognition of their collaboration.
During December 2007, JAXA performed orbit correction manoeuvres to bring Akari back into its ideal orbit. This was necessary because the boiled off helium led to an increase in altitude. If this would have continued energy supply would have been cut off.
In May 2011, Akari suffered a major electrical failure that rendered its science instruments inoperable when the satellite was in the Earth's shadow. The operation of satellite was terminated officially on 24 November 2011.

Results

The Akari All-Sky Survey Point Source Catalogues was released on 30 March 2010.
Astronomy and Astrophysics, Vol. 514 was a feature issue of Akari's result.