Swarm

Swarm is a European Space Agency mission that studies the Earth's magnetic field with a constellation of three satellites named Alpha, Bravo and Charlie. Two fly side by side at about 450 kilometres altitude and the third flies higher, near 530 kilometres, in a different polar orbit, so that together they give multi-point measurements of the strength, direction and changes of the field. ESA contracted Astrium, now part of Airbus Defence and Space, to develop and build the three orbiters, and Eurockot launched them together from Plesetsk on 22 November 2013 on a Rokot rocket. The satellites carry magnetometers, an electric field instrument, an accelerometer and a laser reflector, and Canada's e-POP payload later joined the constellation as a fourth member, Echo.