Swarm gets ready for flight
Swarm is ESA's first Earth observation constellation of satellites. The three identical satellites are launched together on one rocket. Two satellites orbit almost side-by-side at the same altitude – initially at about 460 km, descending to around 300 km over the lifetime of the mission. The third satellite is in a higher orbit of 530 km and at a slightly different inclination. The satellites’ orbits drift, resulting in the upper satellite crossing the path of the lower two at an angle of 90° in the third year of operations.
The different orbits along with satellites’ various instruments optimise the sampling in space and time, distinguishing between the effects of different sources and strengths of magnetism.
Earth’s magnetic field is thought to be generated largely by an ocean of superheated, swirling liquid iron that makes up Earth’s outer core 3000 km under our feet. Acting like the spinning conductor in a bicycle dynamo, it generates electric currents and thus the continuously changing electromagnetic field.