[3] The China National Space Administration/ESA Double Star mission operated alongside Cluster II from 2004 to 2007.

The propellant for the transfer to the operational orbit, and the maneuvers to vary inter-spacecraft separation distances made up approximately half of the spacecraft's launch weight.

The highly elliptical orbits of the spacecraft initially reached a perigee of around 4 RE (Earth radii, where 1 RE = 6371 km) and an apogee of 19.6 RE.

Since 1 November 2014, it is the sole public access point to the Cluster mission scientific data and supporting datasets.

Three weeks later on August 9, 2000, another Soyuz-Fregat rocket lifted the remaining two spacecraft (Rumba and Tango) into similar orbits.

The European Space Agency ran a competition to name the satellites across all of the ESA member states.

[6] Ray Cotton, from the United Kingdom, won the competition with the names Rumba, Tango, Salsa and Samba.

[5] Previous single and two-spacecraft missions were not capable of providing the data required to accurately study the boundaries of the magnetosphere.

Because the plasma comprising the magnetosphere cannot be viewed using remote sensing techniques, satellites must be used to measure it in-situ.

Each satellite carried a scientific payload of 11 instruments designed to study the small-scale plasma structures in space and time in the key plasma regions: solar wind, bow shock, magnetopause, polar cusps, magnetotail, plasmapause boundary layer and over the polar caps and the auroral zones.

In 2003 and 2004, the China National Space Administration launched the Double Star satellites, TC-1 and TC-2, that worked together with Cluster to make coordinated measurements mostly within the magnetosphere.