A pair of satellites launched and operated by the China National Space Administration to study the Earth’s magnetosphere. The satellites were called TC-1 and TC-2 (Tan-Ce is Chinese for ‘Explorer’). TC-1, also known as the equatorial satellite, was launched in 2003 December into a highly elliptical orbit inclined at 28°.5 to the equator to study the Earth’s magnetotail. TC-2, known as the polar satellite, was launched into a polar orbit in 2004 July to study events over the magnetic poles, including the development of aurorae. The Double Star satellites worked in conjunction with ESA’s Cluster mission. TC-1 re-entered in 2007 October. Contact with TC-2 was lost in late 2008.

http://sci.esa.int/double-star/ ESA mission website.