Cluster

The four spacecraft Cluster mission, together with the very successful Solar and Heliospheric Observatory (SOHO) mission, constitute the First Cornerstone project of the ESA Horizon 2000 programme, which was designed to make major progress in the investigation of the nature of Sun-Earth interactions. The four original Cluster spacecraft were destroyed in a launch accident on June 04, 1996. They were designed and built by the European Space Agency. The Cluster project also involves NASA. Four new (Cluster II) spacecraft have been built and are scheduled for launch in Summer 2000. Details can be found on the Cluster PEACE instrument home page.

The Cluster spacecraft are spin-stabilised, with a nominal spin rate of about 15 rpm. The spin axis is maintained between 85 and 89 (TBC) degrees to the ecliptic plane. There are eleven experiments onboard the spacecraft, which make a rather comprehensive measurement of the charged particle populations up to energies of 100's of keV and of the dc and ac electric and magnetic fields in the vicinity of the spacecraft.

The mission is planned to last two years. The spacecraft will be flown in formation, so that they lie at the vertices of a tetrahedron when in interesting parts of the magnetosphere. The separation of the spacecraft will be altered at 6 monthly intervals, to allow study of phenomena on different length scales. The spacecraft will fly in an orbit with apogee at 19.6 Re (Earth radii) and perigee at 4 Re. Apogee and perigee are near the ecliptic plane, but the orbital plane is inclined at 90 degrees to the ecliptic plane, so the spacecraft will fly over the Earth's polar regions. They will visit regions of the magnetosphere, such as the high altitude magnetospheric cusps, which have barely been explored at all so far.

• Exploration of high altitude magnetospheric cusps
• Study in three dimensions of plasma turbulence and small scale structures
• Physics of boundary regions between two cosmic plasma and processes which transfer mass, momentum and energy across the boundary, such as magnetic reconnection (dayside magnetopause and cusps)
• Plasma acceleration during large scale reconfiguration of plasma and electromagnetic fields (geomagnetic tail)
• Study of MHD turbulence, vortex formation and eddy diffusion (solar wind, dayside cusp, magnetopause and plasma sheet boundary layers).
• Structure and properties of collisionless shock waves, associated particle acceleration and wave generation (bow shock, interplanetary shocks)
• Microstructure of plasma and fields in the solar wind as an example of a stellar wind

8th August 2000
Andrew Fazakerley
anf@mssl.ucl.ac.uk