The Cluster mission: ESA's spacefleet to the magnetosphere

During the first half of 1996, the European Space Agency (ESA) will launch a unique flotilla of spacecraft to study the interaction between the solar wind and the Earth's magnetosphere in unprecedented detail. The Cluster mission was first proposed to the Agency in late 1982 and was selected, together with SOHO, as the Solar Terrestrial Science Programme (STSP), the first cornerstone of ESA's Horizon 2000 Programme. It is a complex four-spacecraft mission designed to carry out three-dimensional measurements of the magnetosphere, covering both large and small-scale phenomena in the sunward and tail regions. The mission is a 'first' for ESA in a number of ways: the first time that four identical spacecraft have been launched on a single launch vehicle, the first time that ESA has built spacecraft in true series production and operated them as a single group, the first time that European scientific institutes have produced a series of up to five instruments with full intercalibration, and the first launch of the Agencys new heavy launch vehicle Ariane-5. The article gives an overview of this unique mission and the requirements that governed the spacecraft design. It then describes in detail the resulting design and how the particular engineering a challenges posed by the series production of four identical spacecraft and sets of scientific instruments were met by the combined efforts of the ESA Project Team, industry and the experiment teams.