Fluxgate Ring Cores: The Past, Present, and Future of Space-Based Magnetic Sensing

Fluxgate magnetometers have been the flagship instruments of space-based planetary magnetism research since the 1950s. These magnetometers have been flown throughout and beyond our solar system on dozens of missions, including Voyager, MESSENGER, Juno, and MAVEN, and have been fundamental to our understanding of both active planetary magnetospheres and remanent crustal fields. Ring cores are the central components of fluxgate magnetometers, typically assembled from a permalloy metal strip wrapped around a rigid bobbin. However, the original manufacturers of these cores have largely ceased production and the methods used to produce them were never published in detail. Further, the technical specifications of ring cores vary widely, from the dimensions of the bobbin to the Fe-Mo-Ni ratios of the permalloy, and methods of core assembly differ dramatically between labs. Because the performance of low-power fluxgate magnetometers in low-field environments has yet to be surpassed by other spacecraft vector magnetometer technologies, the next generation of orbiter and lander missions has renewed interest in recovering the ability to make new ring cores, but attempts to generate new cores are complicated by the lack of available information about the originals and their production. We will report the results of initial characterization and testing of two recently recovered collections of legacy ring cores in order to enable the continued use of fluxgate magnetometers for magnetic sensing in space.