A fleet of four ESA satellites to investigate the interaction between the solar wind and the Earth's magnetic field. The first two, named Salsa and Samba, were launched in 2000 July, followed in August by Rumba and Tango. The four spacecraft are on highly elliptical polar orbits, extending out to 119 000 km from Earth, taking them in and out of the Earth's magnetosphere. Separation between the spacecraft ranges from a few hundred to 20 000 km, enabling them to measure features in the magnetosphere at various scales.
http://sci.esa.int/cluster/ ESA mission website.
Subjects: Astronomy and Astrophysics.