The goal of this working group is to set up an end-to-end simulation to investigate and optimize the usefulness of adding a low-inclined nanosatellite (the so-called NanoMagSat/Swarm Delta project, currently in study within IPGP/CEA/CNES) to the on-going ESA Swarm constellation, for investigations of geomagnetic phenomena and sources.

The rational behind this project is that, as has been shown by early results from the Swarm constellation, Swarm satellites can detect many more significant geomagnetic signals than can currently be modelled. The corresponding residual signals are clearly larger than the now known measurement performance of this mission, which unambiguously shows that they reflect geophysical signals that cannot yet be fully exploited. One of the main reasons for this is that the current Swarm constellation only involves polar orbiting satellites, with a pair of satellites next to each other experiencing near-identical local times, and a third satellite on a slightly higher orbit, slowly shifting in local time with respect to the lower pair. Sampling during one day of acquisition is only done along polar orbits and for only four different local times (one couple of ascending and descending local times for the lower pair of satellites, and a second different couple of ascending and descending local times for the higher lonely satellite). As a result, full local time coverage of all geographic locations by the Swarm constellation currently requires three months. This prevents signals with temporal scales less than three months and longitudinal geographical scales less than the separation between the Swarm orbits to be simultaneously captured by the Swarm constellation. This drawback could partly be corrected for with the help of a fourth satellite, launched at a similar altitude, but on an orbit inclined at typically 60°. Such a “Delta” satellite, with a magnetometry payload comparable to that of Swarm, would be able to sample all local times at all geographic locations between 60°S and 60°N in about one month, thus reducing the time needed to cover all local times at all these geographic locations. In addition, between 60°S and 60°N, all local times would also be sampled within roughly 90 minutes along transverse orbits that would cross the polar orbits of the Swarm constellation, thus providing the possibility to at least partly characterize the spatiotemporal nature of the signals detected by the Swarm satellites with variability within that time range.

Running such an end-to-end simulation, however, is itself a challenge, not the least because it entails simulating signals also including yet poorly known spatiotemporal characteristics (since not yet characterized by any equivalent satellite constellation). The goal of this working group is thus dual: First, to overcome this challenge by designing a geophysically sound end-to-end simulation setup, and second, to run the end-to-end simulation to investigate and optimize the benefit such a “Delta” satellite could bring not only for improving our ability to recover signals already recovered by the current Swarm constellation, but also for recovering and characterizing signals captured by the Swarm satellites but currently unexploited.

Outcome

It is expected that the main outcome of this working group will be a book of the Scientific Report Series by Springer Verlag. Details of this end-to-end study would be presented in a comprehensive way, explaining the scientific and technical motivations of the study, the way it was run, and its outcome. The goal is to put together a reference document that could next be used by ESA, CNES and other space agencies for assessing the improvement that a low-inclined nanosatellite would bring to the on-going ESA Swarm mission. It is also anticipated that as a further outcome of this study, a number of scientific contributions could be published separately in the scientific literature.