As well as the advanced technology the satellites carry, their carefully selected orbits are essential to the success of the 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 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. These drifting orbits mean that all the magnetic signals originating from Earth and those caused by the Sun are captured.
The Sun generates typical day and night patterns in the ionosphere between the satellites and Earth. Magnetic storms resulting from solar activity also cause irregular disturbances in the ionosphere and magnetosphere.
Essentially, the constellation optimises the measurements of relevant phenomena. This helps to distinguish between the effects of different sources of magnetism.
For example, global field models of the core and crust and conductivity maps of the mantle are needed to study the interior of Earth. These can generated at a higher accuracy from a combination of selected observations from all three satellites over time.