^BCluster satellites.^b All four Cluster satellites seen at the IAGB Space Testing Facility, Munich, in 1994. The Cluster satellites are due to be launched together in October 1995 into a highly- elliptical polar orbit (25,500km x 108,500km). The orbits will be tuned so that the four satellites fly in a loose tetrahedral formation, separated by distances between 200 and 20,000 kilometres. The satellites carry identical experiment packages, and will be used to make direct measurements of electromagnetic fields and plasma in the Earth's magnetosphere. Cluster is a project of the European Space Agency (ESA), and will be the first to use the Ariane 5 launcher.