Precession of the Cluster Orbit

Figure shows the Cluster orbit as seen from above the North Pole (roughly; in fact the plane is the GSE XY plane).

Operational Phase 1 begins with the apogee at dusk (time T0). The orbit rotates (with respect to the GSE coordinate system) during the year. The apogee is sunward at T0 + 3 months. Operational Phase 2 begins with the apogee at dawn, at time T0 + 6 months.The apogee is anti-sunward at To + 9 months. The cycle repeats after 1 year.

(Image source : Escoubet, C.P., R. Schmidt and M.L. Goldstein, Cluster- science and mission overview, in The Cluster and Phoenix Missions, Kluwer Academic Publishers, 1997 - reprinted from Space Science Reviews vol 79, v-vii, 1997.)

This ESA image shows how Cluster will sample different regions of the Earth's environment at different times in the mission:

By Andrew Fazakerley
Last updated on26/06/00 by S.Szita