A European Space Agency two-year project to study the interaction of the solar wind, a stream of atomic particles from the Sun's corona, with the Earth's magnetosphere, from an array of four identical satellites that can provide a three-dimensional view. The first pair of the Cluster II space weather satellites was launched in July 2000, and the second pair the following month.

The Ariane 5 rocket carrying the first Cluster probes exploded due to a software fault 37 seconds after lift-off on 4 June 1996. The second Cluster mission was launched in two sets of two satellites each on 16 July and 9 August 2000; the four Cluster satellites are numbered C1 through C4 and are named Rumba, Salsa, Samba, and Tango, respectively. The mission has been key in improving the modelling of Earth’s magnetosphere and understanding its various physical processes. In November 2016 the ESA’s Science Programme Committee gave the Cluster mission a two-year extension. In January 2018 ESA announced that Cluster data have helped scientists for the first time learn how energy is transferred from the solar wind to the Earth’s protective magnetosphere.

http://sci.esa.int/cluster/ All aspects of the Cluster mission, its objectives, science payload, mission profile, and launch. The pages are frequently updated with images and news of Cluster's latest results. There is also good background information about the solar effects on near-Earth space.