Finally! AMPERE-NEXT - it's about TIME (Thermosphere-Ionosphere-Magnetosphere Electrodynamics)

The Iridium NEXT constellation of 75 new satellites was launched beginning on 14 January 2017 and the last of eight launches was on 11 January 2019. All satellites were successfully commissioned and have operated nominally since. Each NEXT satellite is equipped with a commercial avionics magnetometer with 30 nT digitization resolution. To support the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), the flight software was designed to collect magnetic field samples on every satellite at 8 second intervals for telemetry over the space network to a ground receive station. To achieve the target cost for the constellation, the NEXT satellites make extensive use of heritage designs so that the accommodation for spacecraft-generated magnetics contamination needed to occur in post-processing. An extensive effort of signal identification, attribution, calibration, and correction was conducted to remove magnetic signals due to nine different sources with field amplitudes ranging from 10s of nT to over 1000 nT. The total corrections are typically 100 to 500 nT and are calibrated to between 1% and 3% accuracy using superposed epoch analyses. The on-board star-tracker attitude determination system yields attitude knowledge to better than 0.02 degrees and is a critical enabling technology for this analysis. An iterative post-processing approach allows precise on-orbit gain and offset calibration together with adjustment of sharp transitions to account for asynchronous sampling of housekeeping data relative to the magnetometer. The resulting calibrated data product yields baseline stabilities of better than 50 nT, resolving Birkeland current signatures with greater accuracy and stability than previously possible. Additional advances in science processing, using upgraded baseline estimates and a hybrid basis function fitting that combines elementary current and spherical harmonic basis functions, yield substantial improvements in data self-consistency and fidelity. These efforts enable higher sensitivity in characterizing the high-latitude magnetospheric driving of the ionosphere-thermosphere system.