Cluster is currently investigating the Earth's magnetic environment and its interaction with the solar wind in three dimensions. Science output from Cluster greatly advances our knowledge of space plasma physics, space weather and the Sun-Earth connection and has been key in improving the modeling of the magnetosphere and understanding its various physical processes.
Cluster II is part of an international collaboration to investigate the physical connection between the Sun and Earth. Flying in a tetrahedral (triangular pyramid) formation, the four spacecraft collect the most detailed data yet on small-scale changes in near-Earth space and the interaction between the charged particles of the solar wind and Earth's atmosphere. This enables scientists to build a three-dimensional model of the magnetosphere and to better understand the processes taking place inside it.
The name Cluster was chosen because of the way the four spacecraft will fly in a group around the Earth. When studies demonstrated that it would be possible to reuse some parts and to fly four spacecraft which were almost identical to those which were lost, the replacement mission was named Cluster II.
Each of the four spacecraft carries an identical set of 11 instruments to investigate charged particles, electrical and magnetic fields. These were built by European and American instrument teams led by Principal Investigators.
Elliptical polar orbit, 19 000 to 119 000 km, 57 hour period.