The mission DOUBLE STAR follows the steps of the European mission CLUSTER and studies the effects of the Sun on the terrestrial magnetosphere. Each satellite of the mission has a particular orbit:

one (TC-1) has an equatorial elliptical orbit which enables it to study the magnetotail of the Earth, area where the particles are accelerated in direction of the magnetic poles of the Earth by a process known as reconnections;
the other (TC-2) has a polar elliptic orbit and concentrates on the physical processes which occur above the magnetic poles, as well as the development of the boreales and southern aurorae.

The DOUBLE STAR satellites are equipped with 16 instruments of which 7 are identical to the instruments on board CLUSTER. The satellites DOUBLE STAR and CLUSTER work in synchronization which enables to explore in a more detailed way the key areas of the magnetosphere. The European instruments are:

FGM: Flux Gate Magnetometer (one on each satellite) for the measurement of the continuous magnetic field.
ASPOC: Active Spacecraft POtential Control experiment (on board TC-1) which is an experiment of control of the potential of the satellite by the emission of ions.
STAFF and DWP: Spatio-Temporal Analysis of Field Fluctuation experiment and Digital Wave Processing (on board TC-1) magnetometer which studies the fast variations of the magnetic field, particularly in the areas where the particles charged with solar wind interact with the magnetosphere. Principal Investigators: N. Cornilleau-Werhlin, CETP, France for STAFF and H. Alleyne, Sheffield University, United Kingdom for DWP.
PEACE: Plasma Electron And Current AnalysEr (one on each satellite) which studies all the low and medium energy electrons in the plasma.
HIA: Hot Ion Analyzer experiment (on board TC-1) which analyzes the functions of distribution of the ions in the magnetosphere, space plasma and solar wind. Principal Investigator: H. Reme, CESR, France
NUADU: Neutral Atom Detection Unit (on board TC-2) which realizes imaging of the particles of high energy captive of the Earth's magnetic field.

The two DOUBLE STAR satellites were launched by Chinese Long March 2C rockets from two different sites to China, satellite TC-1 was launched on December 29, 2003 from Xichang (province of Sichuan) and satellite TC-2 was launched on July 25, 2004 from Taiyuan (Province of Shanxi).