The aim of the Cluster mission is to study small-scale structures of the magnetosphere and its environment in three dimensions. To achieve this, Cluster is constituted of four identical spacecraft that will flight in a tetrahedral configuration. The separation distances between the spacecraft will be varied between 600 km and 20 000 km, according to the key scientific regions. The four Cluster spcecrafts are in orbit since 2001.
As a sister project to Cluster Double Star (DSP) is a joint ESA/Chinese project to study the effects of the Sun on the
Earth's environment, and in particular the 'magnetotail',
where storms of high-energy particles are generated.
The first of the two spacecraft has been in orbit since December 2003, the second has been launched on July,