This Cluster II spacecraft, FM8 (Tango), was launched together with FM5 (Rumba) by
a Soyuz-Fregat rocket from Baikonur. The four similar spacecraft of the Cluster II mission are
part of ESA's and NASA's Solar-Terrestrial Science Program (STSP). The current Cluster II mission
is a near-replica of the original four-spacecraft mission lost at launch in 1996. (NSSDC will
carry the name "Cluster96" in its information files to designate the unsuccessful 1996 four-spacecraft
Ariane 5 launch.) The purpose of the Cluster II mission is to study small-scale structures in
three dimensions in the Earth's plasma environment, such as those involved in the interaction between
the solar wind and the magnetospheric plasma, in global magnetotail dynamics, in cross-tail
currents, and in the formation and dynamics of the neutral line and of plasmoids.

The four Cluster II spacecraft will orbit in a tetrahedral formation in near-polar orbits of nominally
4 x 19.6 Earth radii, with period about 57 hours, and inclination about 90.7 degrees. Relative distances
between the spacecraft will be adjusted in the course of the mission, depending on the spatial scales of
the structures to be studied, varying from a few hundred km to a few Earth radii. The tetrahedral
formation is essential for making three-dimensional measurements and for determining the curl of vectorial
quantities such as the magnetic field.

The orbits of all four spacecraft will be frequently maneuvered so as to achieve the targeted investigations.

Each spacecraft will be spin-stabilized, normally at around 15 rpm, and will be cylindrical in shape, with
a 2.9-m diameter and 1.3-m length. It will have two rigid 5-m radial experiment booms, four 50-m experiment
wire booms, and two axial telecommunications antenna booms. Telemetry downlink bit rate will be 2 to 262 kbit/s.

Each spacecraft will have AC and DC magnetometers, an electric fields and waves sensor, an electron
emitter/detector, an electron density sounder, electron and ion plasma analysers, an energetic particle
detector, an ion emitter, and a data processing unit.

Cluster operations will be performed by ESOC in Darmstadt, Germany, with support from NASA's Deep Space
Network. Cluster is also an IACG mission. The scientific data are distributed by ESOC using CD-ROM as a
medium to the Principal Investigators, Co-Investigators and the network of eight national data centres
(6 in Europe, 1 in USA and 1 in China) that form the Cluster Science Data System (CSDS). There are
approximately 80 recipients world-wide. Science operations are carried out by the Joint Science
Operations Centre, co-located with the UK data centre at RAL, Didcot. A wide scientific community will
have differing rights of access to the Cluster data. Scientists wishing to access Cluster data should
contact their national Data Centres.

ESA SP-1159, Paris, March 1993 is entitled "Cluster: Mission, Payload and Supporting Activities" Edited by W. R. Burke.
European Space Agency, ESA SP-1159, 1993.ISBN: 92-9092-073-4.