The purpose of the STEREO mission is to provide original information on the solar flares and their effects on the terrestrial environment. In order to obtain stereoscopic images of the eruptions, a satellite precedes the Earth in its orbit around the Sun, and the other follows it. Images obtained by the satellites are combined with the "in situ" data, as well as with data of observatories on the Earth, and satellites in low orbit to follow in 3 dimensions the magnetic energy storage, the ejection then the trajectory of the coronal matter in the interplanetary medium. When ejecta reaches the orbit of the Earth, the magnetometers and the instruments measuring the plasma installed on board STEREO satellites will make it possible to characterize the ejected matter and to connect without ambiguity these measurements to their solar source.

Several french scientific teams, supported by CNES, contribute to the realisation of the STEREO instruments. Each STEREO satellite is equipped with four following instrument suites :

PLASTIC (PLAsma and SupraThermal Ion and Composition) studies solar wind and the heliospheric processes.
STEREO/WAVES (S/WAVES) is an instrument which follows the interplanetary radio burst, which studies the genesis and the evolution of the radio disturbances which go from the Sun to the Earth. The LESIA is the Principal Investigator for this instrument.
SECCHI (Sun-Earth Connection Coronal and Heliospheric Investigation) ) is a set of remote sensing instruments made up of a imagor in the extreme ultraviolet, two coronographes in white light, a heliospheric imagor. These instruments study the 3-dimension evolution of the Coronal Mass Ejections (CMEs). The IAS is implied in the STEREO program as well on the hardware (telescope imager EUVI) as for the analysis of the data (thesis cofinanced by the CNES) on the data retrieval. IOTA manufactured the EUVI telescopes mirrors.
IMPACT (In situ Measurements of PArticles and CME Transients) is composed of seven instruments : an analyzer of solar wind electrons (SWEA : solar wind electron analyzer), a magnetometer, a matrix of detectors of particles measuring the ions and electrons accelerated at the time the coronal mass ejection. The CESR develops detectors SWEA for the two satellites of the mission, except the numerical treatment unit.

A network of ground stations, set up by NOAA, receives STEREO data continuously. A CNES antenna, unused for several years have been upgraded for this occasion and complete this first "space weather" world network.

The two STEREO satellites were successfully launched by a DELTA II rocket from Cape Canaveral, USA, on October 25th, 2006.