Thematic group: PEPS
Scientific Leader: Alexis Rouillard

Description / Background

NASA’s Solar TErrestrial RElations Observatory (STEREO) mission was launched on October 25, 2006.
The mission consists of two satellites gradually drifting upstream (ST-A) and downstream (ST-B) from the Earth along similar orbits around the Sun.
STEREO is the first mission to have both in situ and imaging instruments from two remote observation points in the heliosphere. Identical suites of scientific instruments are embarked on each of the satellites: a suite of heliospheric imagers and coronographs (in ultraviolet or visible light) to track solar disturbances in the inner heliosphere, and a series of in situ instruments to measure the properties of the solar wind, solar energetic particles, and solar radio waves and emissions.
ST-A is still in operation today, while ST-B operations were permanently shut down on October 17, 2018 after the last loss of communication with the satellite on September 23, 2016.

Scientific objectives and instrumentation

The STEREO mission aims to study the origins and consequences of solar coronal mass ejections.
The instrument SWEA (Solar Wind Electron Analyser) is an electron spectrometer (1 eV-3 keV) dedicated to the solar wind with a field of view of 120°×360° that is part of the payload in the IMPACT (In-situ Measurements of Particles and CME Transients, PI: Janet Luhmann, SSL/Berkeley) instrument suite on board each of the satellites of the STEREO mission.
The IMPACT suite includes seven sensors dedicated to the measurements of thermal, suprathermal and energetic electrons in the solar wind, suprathermal and energetic protons in the solar wind, and the interplanetary magnetic field.

Involvement of IRAP

Design and realization of the SWEA instruments on board ST-A and ST-B.


University of Berkeley, USA; University of Boulder, USA; NASA GSFC, USA; University of Michigan, USA; Los Alamos National Laboratory, USA; University of Kiel, Germany; LESIA, France; COMAT, France.