Cluster / EFW, Active Archive

Cluster is a four-satellite ESA mission.

This project has given the first chance ever to separate truly the spatial and temporal plasma effects in the terrestrial magnetosphere.

The four Cluster satellites were launched during the year 2000 into polar orbits with perigees and apogees of about 20 000 and 120 000 km, respectively. The mission is extended to the end of 2022. The project has applied for an extension of operations for three years, 2023-2025. This will be followed by an additional year of data calibration, validation and archiving during 2026.

This proposal concerns funding for four years, 2023-2026.Until 2005, the spacecraft were in a tetrahedron formation with a separation between 100 and 10 000 km at least once during the orbit. Now three satellites are often well separated with the fourth rather close to one of the three (down to a few km).

Also, the orbits have been changing, allowing investigations of new key regions of the magnetosphere.We are responsible for the Electric Field and Wave (EFW) instrument on each of the four satellites, with Mats André as PI. We routinely deliver data to the ESA Cluster Science Archive.

Routine calibration, validation and archiving of full resolution electric field double-probe data from such a long period for general scientific purposes have never been carried out before on any mission to the accuracy now being obtained. More than 600 scientific papers depending on EFW data have been published since launch.