Werner Magnes

Measuring field‐aligned currents (FACs) using magnetic field observations provides a powerful means to probe the multi‐scale interactions between the magnetosphere, ionosphere and thermosphere. In this study, we benchmark the curlometer technique using Swarm spacecraft observations and simulations of the coupled magnetosphere‐ionosphere system. We begin by correlating current density curlometer estimates derived from Swarm tetrahedra with varying spatial scales and barycenter locations. This confirms an apparent departure from stationarity for FACs at spatio‐temporal scales below 100 km where measurements appear highly uncorrelated. We then analyze simulated magnetic perturbations, where four‐point measurements can always be constructed. This shows how, even at meso‐scales of hundreds of kilometers, time‐shifted FAC estimates can diverge significantly from this ground truth. In both observational and simulated data we find poor tetrahedral configurations can produce spurious perpendicular currents due to numerical instability in the inversion process. This can be mitigated using appropriate quality metrics and high‐quality FAC reconstructions still achieved with a tetrahedral face well‐aligned to the local magnetic field. These results highlight the dynamic nature of FACs at large as well as small scales, and underscore the substantial advantages of true four‐point observations for their accurate analysis.

Before reaching the Jovian system in 2031, the ESA Jupiter Icy Moons Explorer (Juice) spacecraft will perform three Earth flybys. As well as providing gravitational assistance, these flybys are prime opportunities to assess performance and undertake in-flight calibration of the science payload in a well-understood environment. The first such interval occurred in August 2024, dubbed the Lunar-Earth gravity assist (LEGA) as it included a pass by the Moon in advance of the approach to Earth. The unique spacecraft trajectory allowed for sampling of various regions of the magnetosphere before exiting into the solar wind. In this paper, we report on the performance of the Juice magnetometer instrument (J-MAG) during the LEGA. These are the first reported results from J-MAG in flight. J-MAG comprises three sensors – two fluxgate vector sensors and one Coupled Dark State Magnetometer (CDSM) scalar sensor – all of which were operational during the LEGA period. This represents the first time in the mission that the scalar sensor has operated in its nominal state. Here, we analyse J-MAG observations during key periods of the flyby. As well as inter-sensor comparison, we assess J-MAG data against geomagnetic field models during the approach to Earth, and compare with measurements from other spacecraft at the Moon and in the solar wind, which allow us to make suggestions for future calibration activities. Overall, the three sensors showed excellent performance at this early stage in the mission and confirmed that the scalar sensor meets the requirements for in-flight calibration of the fluxgate sensors at Ganymede. The LEGA also demonstrates the potential value of using cruise phase measurements for scientific exploration and solar wind monitoring.

This paper presents a CubeSat-optimized measurement concept for magnetic field, which was designed for missions beyond low Earth orbit targeting novel radiation belt studies. The instrument combines a miniaturized three-axis fluxgate sensor on a low‑mass deployable boom together with a compact sensor control unit that implements fully synchronous excitation, sampling, and digital control. A hybrid feedback module integrates three prototype fluxgate feedback microchips that provide low‑noise current sources with selectable full‑scale ranges (±3/±9 mA), enabling vector measurements over ±70 μT while retaining sub‑nT resolution. The boom provides 65 cm standoff from the CubeSat and pointing knowledge of 1°. The designed boom length limits the tolerable magnetic dipole moment inside the CubeSat to 0.05 Am². Extended housekeeping includes voltage supply and thermal monitoring, an additional magneto‑inductive sensor on the sensor control unit for disturbance discrimination, and total ionizing dose tracking. Laboratory characterization demonstrates noise densities of 20–30 pT √Hz at 1 Hz, with 128 vectors per second science data and linearity suitable for near‑Earth fields. As it is a pivotal element in the instrument, the prototype feedback microchip was tested for its radiation response. Heavy‑ion testing showed no single‑event latch‑up up to 100 MeV cm² mg. Single‑event transients as well as single-event upsets were observed and are consistent with rare functional interrupts in the digital part of the signal chain. They are addressable by standard redundancy techniques. X‑ray tests up to 1 Mrad confirm functionality with worst‑case gain and offset drifts of approximately 600 ppm krad and 1 μA krad within 0–100 krad. The prototype meets the performance requirements derived from the Foresail‑2 mission concept and demonstrates a path to high‑quality, resource‑efficient magnetometry on 3U–6U CubeSat platforms suitable for operation in the Van Allen belts and other harsh radiation environments.

This paper presents a CubeSat-optimized measurement concept for magnetic field, which was designed for missions beyond low Earth orbit targeting novel radiation belt studies. The instrument combines a miniaturized three-axis fluxgate sensor on a low‑mass deployable boom together with a compact sensor control unit that implements fully synchronous excitation, sampling, and digital control. A hybrid feedback module integrates three prototype fluxgate feedback microchips that provide low‑noise current sources with selectable full‑scale ranges (±3/±9 mA), enabling vector measurements over ±70 μT while retaining sub‑nT resolution. The boom provides 65 cm standoff from the CubeSat and pointing knowledge of 1°. The designed boom length limits the tolerable magnetic dipole moment inside the CubeSat to 0.05 Am². Extended housekeeping includes voltage supply and thermal monitoring, an additional magneto‑inductive sensor on the sensor control unit for disturbance discrimination, and total ionizing dose tracking. Laboratory characterization demonstrates noise densities of 20–30 pT √Hz at 1 Hz, with 128 vectors per second science data and linearity suitable for near‑Earth fields. As it is a pivotal element in the instrument, the prototype feedback microchip was tested for its radiation response. Heavy‑ion testing showed no single‑event latch‑up up to 100 MeV cm² mg. Single‑event transients as well as single-event upsets were observed and are consistent with rare functional interrupts in the digital part of the signal chain. They are addressable by standard redundancy techniques. X‑ray tests up to 1 Mrad confirm functionality with worst‑case gain and offset drifts of approximately 600 ppm krad and 1 μA krad within 0–100 krad. The prototype meets the performance requirements derived from the Foresail‑2 mission concept and demonstrates a path to high‑quality, resource‑efficient magnetometry on 3U–6U CubeSat platforms suitable for operation in the Van Allen belts and other harsh radiation environments.

This paper presents a CubeSat-optimized measurement concept for magnetic field, which was designed for missions beyond low Earth orbit targeting novel radiation belt studies. The instrument combines a miniaturized three-axis fluxgate sensor on a low‑mass deployable boom together with a compact sensor control unit that implements fully synchronous excitation, sampling, and digital control. A hybrid feedback module integrates three prototype fluxgate feedback microchips that provide low‑noise current sources with selectable full‑scale ranges (±3/±9 mA), enabling vector measurements over ±70 μT while retaining sub‑nT resolution. The boom provides 65 cm standoff from the CubeSat and pointing knowledge of 1°. The designed boom length limits the tolerable magnetic dipole moment inside the CubeSat to 0.05 Am². Extended housekeeping includes voltage supply and thermal monitoring, an additional magneto‑inductive sensor on the sensor control unit for disturbance discrimination, and total ionizing dose tracking. Laboratory characterization demonstrates noise densities of 20–30 pT √Hz at 1 Hz, with 128 vectors per second science data and linearity suitable for near‑Earth fields. As it is a pivotal element in the instrument, the prototype feedback microchip was tested for its radiation response. Heavy‑ion testing showed no single‑event latch‑up up to 100 MeV cm² mg. Single‑event transients as well as single-event upsets were observed and are consistent with rare functional interrupts in the digital part of the signal chain. They are addressable by standard redundancy techniques. X‑ray tests up to 1 Mrad confirm functionality with worst‑case gain and offset drifts of approximately 600 ppm krad and 1 μA krad within 0–100 krad. The prototype meets the performance requirements derived from the Foresail‑2 mission concept and demonstrates a path to high‑quality, resource‑efficient magnetometry on 3U–6U CubeSat platforms suitable for operation in the Van Allen belts and other harsh radiation environments.

This paper presents a CubeSat-optimized measurement concept for magnetic field, which was designed for missions beyond low Earth orbit targeting novel radiation belt studies. The instrument combines a miniaturized three-axis fluxgate sensor on a low‑mass deployable boom together with a compact sensor control unit that implements fully synchronous excitation, sampling, and digital control. A hybrid feedback module integrates three prototype fluxgate feedback microchips that provide low‑noise current sources with selectable full‑scale ranges (±3/±9 mA), enabling vector measurements over ±70 μT while retaining sub‑nT resolution. The boom provides 65 cm standoff from the CubeSat and pointing knowledge of 1°. The designed boom length limits the tolerable magnetic dipole moment inside the CubeSat to 0.05 Am². Extended housekeeping includes voltage supply and thermal monitoring, an additional magneto‑inductive sensor on the sensor control unit for disturbance discrimination, and total ionizing dose tracking. Laboratory characterization demonstrates noise densities of 20–30 pT √Hz at 1 Hz, with 128 vectors per second science data and linearity suitable for near‑Earth fields. As it is a pivotal element in the instrument, the prototype feedback microchip was tested for its radiation response. Heavy‑ion testing showed no single‑event latch‑up up to 100 MeV cm² mg. Single‑event transients as well as single-event upsets were observed and are consistent with rare functional interrupts in the digital part of the signal chain. They are addressable by standard redundancy techniques. X‑ray tests up to 1 Mrad confirm functionality with worst‑case gain and offset drifts of approximately 600 ppm krad and 1 μA krad within 0–100 krad. The prototype meets the performance requirements derived from the Foresail‑2 mission concept and demonstrates a path to high‑quality, resource‑efficient magnetometry on 3U–6U CubeSat platforms suitable for operation in the Van Allen belts and other harsh radiation environments.

We report on electric field measurements recorded onboard the China Seismo-Electromagnetic Satellite (CSES). In this study, we emphasize the whistler and transmitter very low frequency (VLF) radiations recorded in the frequency range between 1.8 kHz and 25 kHz. The electric field detector (EFD) instrument onboard the CSES works as a double probe instrument and allows access to the three electric components of VLF waves. Three frequencies were selected, two related to whistler hiss (i.e., 2.5 kHz channel) and chorus (i.e., 5 kHz channel) radiations and one to the NAA ground-based transmitter signal (i.e., 24 kHz). We investigate the corresponding power spectral density variations, from which we derive the Stokes intensity I and normalized q linear polarization components. This leads us to study their statistical fluctuations and to emphasize the behaviors of natural whistler hiss and chorus radiations and man-made transmitter emissions. The Stokes intensities of the natural whistler and NAA transmitter radiations are estimated, respectively, to be about 1 mV² m⁻² Hz⁻¹ and 0.05 mV² m⁻² Hz⁻¹. The correlation coefficients of the Stokes intensity polarizations are in the order of 98% powerfully coupled, contrary to the Stokes normalized linear polarizations, which are found to be relatively paired, i.e., less than 60%. The signal-to-noise ratio is estimated considering three intensity levels (i.e., high, medium, low). This analysis leads us to characterize the Stokes normalized linear components of VLF radio waves and to show different behaviors of the polarization when considering the Northern and Southern Hemispheres. The regions of enhanced whistler Stokes intensities of whistler hiss and chorus emissions are confined to the sub-auroral regions in both hemispheres, particularly at geomagnetically ranges linked to the NAA transmitter station and its conjugate region in the Southern Hemisphere. In this investigation, we point out the Stokes polarization parameters, which are essential for the characterization of whistler VLF radio waves, particularly when considering the CSES mission objectives and commitments.

This paper presents a CubeSat-optimized measurement concept for magnetic field, which was designed for missions beyond low Earth orbit targeting novel radiation belt studies. The instrument combines a miniaturized three-axis fluxgate sensor on a low‑mass deployable boom together with a compact sensor control unit that implements fully synchronous excitation, sampling, and digital control. A hybrid feedback module integrates three prototype fluxgate feedback microchips that provide low‑noise current sources with selectable full‑scale ranges (±3/±9 mA), enabling vector measurements over ±70 μT while retaining sub‑nT resolution. The boom provides 65 cm standoff from the CubeSat and pointing knowledge of 1°. The designed boom length limits the tolerable magnetic dipole moment inside the CubeSat to 0.05 Am². Extended housekeeping includes voltage supply and thermal monitoring, an additional magneto‑inductive sensor on the sensor control unit for disturbance discrimination, and total ionizing dose tracking. Laboratory characterization demonstrates noise densities of 20–30 pT √Hz at 1 Hz, with 128 vectors per second science data and linearity suitable for near‑Earth fields. As it is a pivotal element in the instrument, the prototype feedback microchip was tested for its radiation response. Heavy‑ion testing showed no single‑event latch‑up up to 100 MeV cm² mg. Single‑event transients as well as single-event upsets were observed and are consistent with rare functional interrupts in the digital part of the signal chain. They are addressable by standard redundancy techniques. X‑ray tests up to 1 Mrad confirm functionality with worst‑case gain and offset drifts of approximately 600 ppm krad and 1 μA krad within 0–100 krad. The prototype meets the performance requirements derived from the Foresail‑2 mission concept and demonstrates a path to high‑quality, resource‑efficient magnetometry on 3U–6U CubeSat platforms suitable for operation in the Van Allen belts and other harsh radiation environments.

Before reaching the Jovian system in 2031, the ESA Jupiter Icy Moons Explorer (Juice) spacecraft will perform three Earth flybys. As well as providing gravitational assistance, these flybys are prime opportunities to assess performance and undertake in-flight calibration of the science payload in a well-understood environment. The first such interval occurred in August 2024, dubbed the Lunar-Earth gravity assist (LEGA) as it included a pass by the Moon in advance of the approach to Earth. The unique spacecraft trajectory allowed for sampling of various regions of the magnetosphere before exiting into the solar wind. In this paper, we report on the performance of the Juice magnetometer instrument (J-MAG) during the LEGA. J-MAG comprises three sensors—two fluxgate vector sensors and one Coupled Dark State Magnetometer (CDSM) scalar sensor—all of which were operational during the LEGA period. This represents the first time in the mission that the scalar sensor has operated in its nominal state. Here, we analyse J-MAG observations during key periods of the flyby. As well as inter-sensor comparison, we assess J-MAG data against geomagnetic field models during the approach to Earth, and compare with measurements from other spacecraft at the Moon and in the solar wind, which allow us to make suggestions for future calibration activities. Overall, the three sensors showed excellent performance at this early stage in the mission and confirmed that the scalar sensor meets the requirements for in-flight calibration of the fluxgate sensors at Ganymede. The LEGA also demonstrates the potential value of using cruise phase measurements for scientific exploration and solar wind monitoring.

This paper presents a CubeSat-optimized measurement concept for magnetic field, which was designed for missions beyond low Earth orbit targeting novel radiation belt studies. The instrument combines a miniaturized three-axis fluxgate sensor on a low‑mass deployable boom together with a compact sensor control unit that implements fully synchronous excitation, sampling, and digital control. A hybrid feedback module integrates three prototype fluxgate feedback microchips that provide low‑noise current sources with selectable full‑scale ranges (±3/±9 mA), enabling vector measurements over ±70 μT while retaining sub‑nT resolution. The boom provides 65 cm standoff from the CubeSat and pointing knowledge of 1°. The designed boom length limits the tolerable magnetic dipole moment inside the CubeSat to 0.05 Am². Extended housekeeping includes voltage supply and thermal monitoring, an additional magneto‑inductive sensor on the sensor control unit for disturbance discrimination, and total ionizing dose tracking. Laboratory characterization demonstrates noise densities of 20–30 pT √Hz at 1 Hz, with 128 vectors per second science data and linearity suitable for near‑Earth fields. As it is a pivotal element in the instrument, the prototype feedback microchip was tested for its radiation response. Heavy‑ion testing showed no single‑event latch‑up up to 100 MeV cm² mg. Single‑event transients as well as single-event upsets were observed and are consistent with rare functional interrupts in the digital part of the signal chain. They are addressable by standard redundancy techniques. X‑ray tests up to 1 Mrad confirm functionality with worst‑case gain and offset drifts of approximately 600 ppm krad and 1 μA krad within 0–100 krad. The prototype meets the performance requirements derived from the Foresail‑2 mission concept and demonstrates a path to high‑quality, resource‑efficient magnetometry on 3U–6U CubeSat platforms suitable for operation in the Van Allen belts and other harsh radiation environments.