Since the intensity of solar activity is currently lower than anticipated, the original plan of where to place the satellites at the beginning of science operations has been reviewed recently by the scientific community and experts in ESA.Low solar activity means the satellites experience lower atmospheric drag, as clearly demonstrated by ESA’s GOCE mission.Earth's protective shieldSwarm is tasked with measuring and untangling the different magnetic signals that stem from Earth’s core, mantle, crust, oceans, ionosphere and magnetosphere.Launched together, the three identical Swarm satellites were released into adjacent orbits at an altitude of 490 km.The satellites may be identical, but to optimise sampling in space and time their orbits are different – a key aspect of the mission.The data acquired from different locations can be used to distinguish between the changes in the magnetic field caused by the Sun’s activity and those signals that originate from inside Earth.The result for Swarm is a slightly different orbit configuration that will save satellite fuel at the beginning of the mission and offer a better return for science at a later stage.Two satellites are now being lowered to an altitude of about 462 km and an inclination of 87.35°. They will orbit almost side by side, about 150 km apart as they pass over the equator. Over the life of the mission they will both descend to about 300 km.The third satellite is being placed in a higher orbit of 510 km and at a different inclination of 87.75°, slightly closer to the pole.The difference in inclination will cause a slow drift of the upper satellite relative to the path of the lower two at increasing angles. After three years, the fuel saved can be used to slow down the relative orbital drift.
Swarm continues to acquire excellent science data. Satellite constellation maintenance operations are proceeding, this is particularly relevant and important to achieving the bestpossible estimate of all contributors to the total magnetic field. Last year, early mission data were used to derive candidate solutions for the 2015 International Geomagnetic Reference Field (IGRF) model. The IGRF is a main field model that (by convention) is updated every five years, and which is used by practically all applications communities and services in need of geomagnetic data. IGRF-12, as the final 2015 model is called, is based on a combination of Swarm, historical satellite data and ground-based observatory data. In addition, a Swarm Initial Field Model, which includes also the computation of the crustal magnetic field at high spatial resolution, has been producedand made available to the community.