Swarm: orbit with a difference

ESA’s Swarm mission is set to unravel the mysteries of Earth’s magnetic field. As well as the advanced technology the satellites carry, the carefully selected orbits are essential to the success of this novel mission. At the start of life in orbit, the three satellites are relatively close to each other. Two orbit almost side-by-side at the same altitude – initially at about 460 km, but descending to around 300 km over the life of the mission. The lower the satellites are, the more sensitive they are for measuring small magnetic features in the crust. The third satellite remains in a higher orbit, initially at 510 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. These drifting orbits mean that all the magnetic signals originating from Earth and those caused by the Sun are captured.