Polar (spacecraft)

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Polar is a NASA satellite designed to study the Aurora. It is distinguished by its ability to image the Aurora in several wavelengths: Visible light, Ultaviolet (UV) light and X-rays.

It was launched on 24 February 1996 into a highly elliptical orbit with apogee at 9 earth radii and perigee at 1.8 earth radii (geocentric), 86 degrees inclination, with a period of around 18 hours. The apogee was initially over the northern polar region, but has since been precessing south at about 16° per year. The nominal mission duration was two years, but has been extended several times, currently until March 2007.

The spacecraft has a high degree of commonality with the Wind spacecraft, part of the same program.