Double Star is the first mission launched by China to explore the Earth's magnetosphere.

This mission involves two satellites (one equatorial and one polar), each designed, developed, launched, and operated by the Chinese National Space Administration. The mission has been prepared in cooperation with the European Space Agency.

The equatorial spacecraft (TC-1) has been launched on the 2003-12-29 into an elliptical orbit of 570 x 78 970 kilometres, inclined at 28.5° to the equator. This enables it to investigate the Earth's magnetic tail, the region where particles are accelerated towards the planet's magnetic poles by a process known as reconnection. TC-1 operated nominally untill 2007-10-14 when it re-entered the Earth's atmosphere.

The polar satellite (TC-2) has a 700 x 39 000 kilometre polar orbit. Its instruments concentrate on the physical processes taking place over the magnetic poles and the development of auroras. TC-2 was launched in July 2004.

These orbits have been synchronised with those of ESA's four Cluster satellites so that all six spacecraft are studying the same region of near-Earth space at the same time.

The Double Star payload includes eight European instruments and eight Chinese instruments. Seven of the eight European instruments, including HIA, are identical to the ones on Cluster. The Hot Ion Analyser from the CIS experiment, got some modifications for the DS Program :

• new Flight Interface Board, FPGA, and connectors on the top of the box
• size of the box increased by 4mm on the top, the rear, and the each side (radiation constraints)