The main objective of THEMIS is to determine without ambiguity the place of release and the nature of the macroscopic process (reconnection or interruption of current) responsible for the substorms, to study their relations of causality and to characterize the propagation and their couplings. Using ground means, it will also be a question of characterizing the ionosphere/magnetosphere coupling. The secondary objectives are centered on the study of the radiations belts, the magnetopause and the borders layers.

Each THEMIS satellite will be equipped with five instruments, which are :

FGM (FluxGate Magnetometer).
EFI (Electric Field Instruments).
ESA (ElectroStatic Analyzer).
SCM (Search Coil Magnetometer).
SST (Solid State Telescopes).

Two French laboratories are participating in this mission: CETP and CESR. The CETP provides the magnetic antennas and the tri-axes structures (manufactured by GDTech). The associated preamplifiers manufactured in France (by the 3D+ company). The CETP ensures also the definition, the technical control, the commissioning, and integration on support of these preamplifiers. The CETP also takes part in integrations, and provides a sniffer to measure the electromagnetic pollution of the other experiments and satellite systems. The CESR is Co-proposer; it takes part in the definition of the mission and will take part in the analysis and the interpretation of all the data.

The five THEMIS satellites was launched by a DELTA II rocket from Cape Canaveral, USA, on february 16th, 2007. Position of the satellites in orbit :