The orbit for each of the four Cluster spacecraft is selected so that each is located at a vertex of a predetermined tetrahedron when crossing the regions of interest within the magnetosphere. The separation distances between the spacecraft will be adjusted during the mission depending on the spatial scales of the structures to be studied and will vary from a few hundred kilometres to a few Earth radii. The separation manoeuvres will be performed at approximately six-month intervals, synchronised with normal orbit-maintenance manoeuvres.

Artist's impression showing the main regions/boundaries of the Earth's magnetosphere that will be studied

In orbit the four spacecraft will be spin-stabilised at all times. Their attitudes will be selected to ensure a solar-aspect angle of approximately 90°, which optimises the performance of the spacecraft's solar-power generator and thermal-control subsystem throughout the mission. This attitude will be maintained during manoeuvres in the operational phase of the mission, but it will be necessary to reorient the spacecraft temporarily during the orbit-transfer phase while certain specific manoeuvres are carried out.

Self Propelled