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The three spacecraft which constitute the Swarm mission are equipped with the Micro Advanced Stellar Compass (μASC) provided by the Technical University of Denmark (DTU) for attitude determination. Each μASC is comprised of three Camera Head Units (CHUs) for a total of nine cameras on the mission. The CCD sensor inside the CHUs are sensitive to energetic particle irradiation which appear as transient bright pixels dubbed ’Energetic Particle Detections’ (EPDs) on the star field images. For more than five years the μASCs on-board Swarm have transmitted the occurrence of EPDs to ground and thereby effectively added high energy radiation monitoring capabilities to the Swarm mission. The high sensitivity, high sample rate (1-2 Hz), orientation of the camera heads, simultaneous measurements from all three spacecraft and near-polar orbits at an altitude of 450-510 km and allows for continuous and real-time monitoring of the high energy (>65 MeV) proton environment in LEO. This data uncover short and long term changes in particle flux in e.g. the South Atlantic Anomaly (SAA) of relevance for future mission planning. The same radiation monitoring capability exists on NASA’s Magnetospheric Multiscale Mission (MMS) which, due to its highly elliptical orbit, survey the Van Allen radiation belts and detect enhanced radiation levels in the belts associated with geomagnetic storms. Combining data from the μASCs onboard Swarm and MMS provides unique insight into the injection mechanisms and dynamics of very high energy particles which is currently poorly understood. This work presents observations and results using high energy radiation data obtained from the μASC on board ESA’s Swarm mission, from February 2018 to February 2023, in combination with μASC data from MMS.

The micro Advanced Stellar Compass (µASC), an attitude reference for the Juno Magnetic Field investigation, also continuously monitors high energy particle fluxes in Jupiter’s magnetosphere. ...

1. Introduction The Psyche mission began development in January 2017 when it was selected by NASA as the 14th Discovery Class mission. Having successfully completed its critical design review, the spacecraft is being assembled by MAXAR and the Jet Propulsion Laboratory under the leadership of the PI, Linda Elkins-Tanton, at Arizona State University. The mission plans to explore for the first time the main-belt asteroid (16) Psyche. Launch is planned for August 2022 leading to rendezvous with Psyche in early 2026. Early radar [1] and spectroscopic measurements [2] of Psyche indicated a metallic composition leading to speculation that Psyche was the remnant core of a larger differentiated asteroid. Continued observing over decades has resulted in varying estimates for key physical parameters. Current expectations are that Psyche is a mix of rock and metal and that a complete understanding of its composition and origin awaits closer inspection by the Psyche science instruments [3]. The mission concept is designed to distinguish between the range of possible compositions. The science objectives of the Psyche mission are to: 1. Determine whether Psyche is a core, or if it is unmelted material. 2. Determine the relative ages of regions of its surface. 3. Determine whether small metal bodies incorporate the same light elements as are expected in the Earth’s high-pressure core. 4. Determine whether Psyche was formed under conditions more oxidizing or more reducing than Earth’s core. 5. Characterize Psyche’s topography. 2. Mission Overview The Psyche mission operations concept is inherited from the Dawn mission to Vesta and Ceres. The Psyche spacecraft will orbit the asteroid at a series of four progressively lower orbits (Orbits A–D) that provide increasingly higher resolution science measurements. Each orbit phase is designed to address specific science objectives and provide refinements to Psyche’s shape and mass that enable the descent to the next orbit. Like Dawn, the Psyche mission uses solar electric propulsion to travel to Psyche as well as enter orbit and transfer between the science orbits. Figure 1 shows the spacecraft interplanetary trajectory and key mission dates. 3. Science Investigations The Psyche spacecraft plans to carry three science instruments and conduct the gravity science investigation using the X-band telecommunication system. The magnetometer consists of two sensors mounted on a 2-m boom in a gradiometer configuration. The instrument is developed by the Technical University of Denmark with heritage from SWARM [4] whereas the science investigation is managed at the Massachusetts Institute of Technology. Figure 2 shows the magnetometer sensors and electronics units. The primary objective of the magnetometer is to search for the existence of a remanent magnetic field that would confirm that Psyche was once a planetary core. The magnetometer is operated continuously starting shortly after launch until the end of the mission with its science objectives achieved in Orbit C. The multispectral imager consists of two redundant imagers with a panchromatic and seven narrowband filters. The filters were selected to detect minerals such as oldhamite, olivine, and pyroxene that would help discriminate between Psyche formation scenarios. The imaging campaign also provides the Psyche shape model and data to make a geologic map. Figure 3 shows the imager hardware being developed by Malin Space Science Systems that is managed and operated by Arizona State University with heritage from MSL MastCam and MCO MARCI [5]. Orbits A and B are the primary science orbits for the imager providing global maps up to 20 m/pixel. Imaging will also continue throughout the remainder of the mission. The gamma-ray and neutron spectrometer (GRNS) consists of two separate units mounted on their own 2-m boom (Fig 4). GRNS is developed by the Johns Hopkins Applied Physics Laboratory with heritage from MESSENGER and Lunar Prospector [6]. The GRNS provides elemental composition measurements for key elements such as nickel, iron, sulfur, silicon, potassium, and others. Nickel content is an indicator of whether Psyche is a remnant core or unmelted material. GRNS will be able to map the distribution of metals and silicates across the surface and measure nickel content to 2 wt% in Orbit D. The X-band telecommunication system is capable of providing two-way coherent Doppler and ranging data via Deep Space Network (DSN) tracking that will be used to map the gravity field of Psyche and to probe its interior structure. The Deep Space Optical Communications (DSOC) technology demonstration is planned as part of the mission payload. It does not play a role in the science investigations. 4. Summary The Psyche mission development is proceeding on schedule. Meanwhile, the Psyche asteroid is becoming a more complex and compelling target. Acknowledgements This work was, in part, carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. References [1] Ostro, S. J. et al. (1985) Science, 229, 442-446. [2] Binzel, et al. (1995) Icarus, 117, 443-445. [3] Elkins-Tanton, L. T. et al. (2020) JGR Planets, 125, doi: 10.1029/2019JE006296. [4] Merayo, J.M. et al. (2008), In: Small Satellites for Earth Observation, Springer, Dordrecht, doi: 10.1007/978-1-4020-6943-7_13. [5] Bell, J. F. et al. (2016) LPSC XLVII. [6] Lawrence, D. J. et al. (2019) LPSC L.

The Juno mission carries the Advanced Stellar Compass (ASC) as primary attitude reference for the MAG investigation. Since Jupiter Orbit Insertion on July 4, 2016, the ASC has continuously monitored high energy particles fluxes in Jupiter’s magnetosphere. In the attitude determination process, the energetic particles with sufficient energy to penetrate the heavily shielded focal plane CCD are detected and characterized to facilitate their removal in the stellar attitude match. Thus highly energetic particles, >15MeV for electrons, >80MeV for protons, and >~GeV for heavier elements, are detected and reported every 250ms. The ASC’s highly optimized radiation shield design enables directional sensitivity, since shielding encountered by particles entering via the optics aperture is less efficient. The directionality offers preferential detection to electrons with energies between 15 and 25MeV and protons with energies between 80 and 100MeV (i.e operates as a particle telescope), whereas particles with energies above these limits may penetrate from any direction. The Juno spacecraft, rotates at 2 RPM, thus particles with energies in the band mentioned, and velocities pointing to the lens exhibit particle flux variation with the spin phase of Juno. Every periJove, Juno traverses a section of the north and south polar caps, and now, past the midpoint of nominal mission, high energetic particles in the aurora regions have been mapped with a high degree of detail. A significant feature is that very intense beams of particles are regularly measured at field lines reaching well beyond L=50, i.e. on distant closed or open field lines. These features are rapidly varying, signifying either a very limited extent, or, high time variability. In the cases where these beams contain particles with energies in the directional sensitive range of the ASC, the source of the beam is from the aurora region, suggesting a polar cap mechanism, capable of accelerating a particle directly to 20MeV. We present examples of flux profiles on open field lines.

Since launch in November 2013, the Swarm constellation of three satellites provides detailed measurements of the magnetic field of the Earth. To ensure the high accuracy of magnetic vector observation by Vector Field Magnetometer (VFM), the Swarm inertial attitude is determined by the micro Advanced Stellar Compass (μASC). Besides its primary function of attitude determination, the µASC is also capable of detecting particles with energies high enough to penetrate its camera shielding, where particles passing the focal plane CCD detector leave detectable ionization tracks. The typical shielding employed requires the minimum energy to penetrate >15MeV for electrons, > 80MeV for protons and >~GeV for heavier elements.The signature of passing particle will only persist in one frame time, but the signature differs between electrons and protons. To ensure full attitude performance operations even during the most intense CMEs, the signatures are removed before star tracking. By counting the signatures, and using a model for the flux transport through the shielding, an accurate measure of the instantaneous high energy particle flux is achieved at each update cycle (250ms).With this feature installed on all three Swarm spacecrafts, a hitherto unprecedented accurate mapping of the proton population around Earth is achieved at two distances, 450 and 530km.The superrelativistic protons measured by the μASC (g>>1), travel at speeds very close to c, and bouncing between the North and South Earth sphere, encounters complex field structures for at least some of the time. The bounce period is much smaller than the Earth rotation period, and an east-west drift component is caused by the magnetic field gradient.We will present observations of the trapped proton fluxes and show how the magnetic field affects their motion shells. Slightly deformed particle drift shells due to the magnetic field structure (for orbits with L>1.07) and the differential east-west drift as measured by the Swarm Alpha and Charlie satellites will be discussed.

The Juno spacecraft was inserted into polar orbit about Jupiter on July 4th, 2016, performing close passes (to ~1.05 Rj radial distance at periJove) every 53 days. By the end of its prime mission, Juno will have circled the planet 34 times, uniformly sampling longitudes separated by less than 11 at the equator. The Juno magnetic field investigation is equipped with two magnetometer sensor suites, located at 10 and 12 m from the spacecraft body at the end of one of Juno’s three solar arrays. Each contains a vector fluxgate magnetometer (FGM) sensor and a pair of co-located non-magnetic star tracker camera heads that provide accurate attitude determination for the FGM sensors. A moredetailed view of Jupiter’s planetary dynamo is emerging as Juno acquires more periJove passes, providing spatial resolution beyond that already evident in the preliminary model (JRM09, a degree 10 spherical harmonic) derived from Juno’s first 9 periJoves. A complex and very non-dipolar magnetic field dominates the northern hemisphere, while a mostly dipolar magnetic field is observed south of the equator, where the enigmatic “Great Blue Spot” resides within an equatorial band of opposite polarity. The Jovian magnetodisc, formed by a washer-shaped disc of azimuthal (“ring”) currents, stretches magnetic field lines outward along the magnetic equator. With 26 equally spaced longitudes now available we can begin to address magnetodisc variability, finding a more or less stable system of azimuthal ring currents (few % variability) and a more variable (~50%) system of radial currents that supply torque to outflowing plasma. A new magnetodisc model greatly improves knowledge of the field geometry, independently verified via observations of the particle absorption signatures of Galilean satellites. A more systematic mapping of Birkeland currents above the polar aurorae also emerges from multiple passes. These and other developments will be presented with Juno now about ¾ of the way towards completion of its primary mission.

The Juno MAG investigation’s dedicated star tracker, the Advanced Stellar Compass (ASC), has continuously monitored high energy particles fluxes in Jupiter’s magnetosphere subsequent to Juno’s orbit insertion on July 4, 2016. The ASC primary function is to provide an accurate inertial attitude reference, however, the most energetic particles in Jupiter’s trapped population is capable of penetrating the radiation shield of the ASC where they are registered. Such particles have energy >15MeV for electrons, >80MeV for protons, and >~GeV for heavier elements. With a sample cadence of 250ms, the ASC renders a detailed mapping of the trapped particles throughout space traversed by Juno. The particles travelling along the magnetic field lines crossing near the orbit of Io will be strongly influenced by interaction with any matter, moon, dust or plasma, which happens to be in their trajectory. The relativistic particle flux monitored, is highly relativistic, and has as such a modest retention time in any drift shell. The short lifetime of the trapped particles, and the constant scanning of field lines connecting to the Io environment enables a detailed profiling of the dust and plasma density, as well as the effect to/from Io itself. We present the measurement and their implications for the azimuthal and radial dust cloud and plasma torus.

The Advanced Stellar Compass (ASC), attitude reference for the MAG investigation onboard Juno, has continuously monitored high energy particles fluxes in Jupiter’s magnetosphere since Juno’s orbit insertion. The instrument performs this function by tracking the effects of radiation with sufficient energy to transit the instrument’s radiation shielding. Particles that Juno ASC observes have energy >15MeV for electrons, >80MeV for protons, and >~GeV for heavier elements.Completing 24 highly elliptical orbits around Jupiter, results in a fairly detailed mapping of the trapped high energy flux at up to 20 Jupiter radius distances.Traveling at velocities close to the speed of light, electrons measured by the ASC, maintain the motion governed by the three adiabatic invariants: gyrating motion around the magnetic field line, a north-south magnetic pole particle bounce, and a charge dependent drift around the planet.The bounce period is much smaller than the Jovian rotation period, and a large east-west drift component is caused by the magnetic field gradient. For these reasons, the drift shell description traditionally used for dipolar fields, are far from adequate to describe the behavior of energetic particles travelling close to Jupiter.In this work, we present the distribution of the trapped high energy electrons around Jupiter. Furthermore, we have constrained the spatial extent of the stable trapped regions and are presenting the distinctive pitch angle and its correlation with ”life” of a particle. At certain distances from Jupiter, pitch angle dependency is not as important to keep the particle trapped as is the injected energy. We also develop an adiabatic map which describes the radial bands for stable trapped particles as a function of the pitch angle and energy.

A spherical harmonic model of the magnetic field of Jupiter is obtained from vector magnetic field observations acquired by the Juno spacecraft during its first nine polar orbits about the planet. Observations acquired during eight of these orbits provide the first truly global coverage of Jupiter's magnetic field with a coarse longitudinal separation of ~45 deg between perijoves. The magnetic field is represented with a degree 20 spherical harmonic model for the planetary ("internal") field, combined with a simple model of the magnetodisc for the field ("external") due to distributed magnetospheric currents. Partial solution of the underdetermined inverse problem using generalized inverse techniques yields a model ("Juno Reference Model through Perijove 9") of the planetary magnetic field with spherical harmonic coefficients well determined through degree and order 10, providing the first detailed view of a planetary dynamo beyond Earth.

The Juno Magnetic Field investigation (MAG) characterizes Jupiter’s planetary magnetic field and magnetosphere, providing the first globally distributed and proximate measurements of the magnetic field of Jupiter. The magnetic field instrumentation consists of two independent magnetometer sensor suites, each consisting of a tri-axial Fluxgate Magnetometer (FGM) sensor and a pair of co-located imaging sensors mounted on an ultra-stable optical bench. The imaging system sensors are part of a subsystem that provides accurate attitude information (to ∼20 arcsec on a spinning spacecraft) near the point of measurement of the magnetic field. The two sensor suites are accommodated at 10 and 12 m from the body of the spacecraft on a 4 m long magnetometer boom affixed to the outer end of one of ’s three solar array assemblies. The magnetometer sensors are controlled by independent and functionally identical electronics boards within the magnetometer electronics package mounted inside Juno’s massive radiation shielded vault. The imaging sensors are controlled by a fully hardware redundant electronics package also mounted within the radiation vault. Each magnetometer sensor measures the vector magnetic field with 100 ppm absolute vector accuracy over a wide dynamic range (to 16 Gauss = $1.6 \times 10^{6}\mbox{ nT}$ per axis) with a resolution of ∼0.05 nT in the most sensitive dynamic range (±1600 nT per axis). Both magnetometers sample the magnetic field simultaneously at an intrinsic sample rate of 64 vector samples per second. The magnetic field instrumentation may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. The attitude determination system compares images with an on-board star catalog to provide attitude solutions (quaternions) at a rate of up to 4 solutions per second, and may be configured to acquire images of selected targets for science and engineering analysis. The system tracks and catalogs objects that pass through the imager field of view and also provides a continuous record of radiation exposure. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors, and residual spacecraft fields and/or sensor offsets are monitored in flight taking advantage of Juno’s spin (nominally 2 rpm) to separate environmental fields from those that rotate with the spacecraft.

The Juno spacecraft, which is in a polar orbit around Jupiter, is providing direct measurements of the planet's magnetic field close to its surface1. A recent analysis of observations of Jupiter's magnetic field from eight (of the first nine) Juno orbits has provided a spherical-harmonic reference model (JRM09)2 of Jupiter's magnetic field outside the planet. This model is of particular interest for understanding processes in Jupiter's magnetosphere, but to study the field within the planet and thus the dynamo mechanism that is responsible for generating Jupiter's main magnetic field, alternative models are preferred. Here we report maps of the magnetic field at a range of depths within Jupiter. We find that Jupiter's magnetic field is different from all other known planetary magnetic fields. Within Jupiter, most of the flux emerges from the dynamo region in a narrow band in the northern hemisphere, some of which returns through an intense, isolated flux patch near the equator. Elsewhere, the field is much weaker. The non-dipolar part of the field is confined almost entirely to the northern hemisphere, so there the field is strongly non-dipolar and in the southern hemisphere it is predominantly dipolar. We suggest that Jupiter's dynamo, unlike Earth's, does not operate in a thick, homogeneous shell, and we propose that this unexpected field morphology arises from radial variations, possibly including layering, in density or electrical conductivity, or both.

Based on magnetic field data sampled by the Swarm satellite constellation it is possible for the first time to determine uniquely F region currents at low latitudes. Initial results are presented from the first 200 days of formation flight (17 April to 5 November 2014). Detailed results have been obtained for interhemispheric field-aligned currents connecting the solar quiet day magnetic variation (Sq) current systems in the two hemispheres. We obtain prominent currents from the Southern (winter) Hemisphere to the Northern around noon. Weaker currents in opposite direction are observed during morning and evening hours. Furthermore, we could confirm the existence of vertical currents above the dip equator, downward around noon and upward around sunset. For both current systems we present and discuss longitudinal variations.

In this study we investigate the three-dimensional structure of low-latitude plasma blobs using multi-instrument and multisatellite observations of the Swarm constellation. During the early commissioning phase the Swarm satellites were flying at the same altitude with zonal separation of about 0.5∘ in geographic longitude. Electron density data from the three satellites constrain the blob morphology projected onto the horizontal plane. Magnetic field deflections around blobs, which originate from field-aligned currents near the irregularity boundaries, constrain the blob structure projected onto the plane perpendicular to the ambient magnetic field. As the two constraints are given for two noncoplanar surfaces, we can get information on the three-dimensional structure of blobs. Combined observation results suggest that blobs are contained within tilted shells of geomagnetic flux tubes, which are similar to the shell structure of equatorial plasma bubbles suggested by previous studies.

We present a statistical study of the temporal- and spatial-scale characteristics of different field-aligned current (FAC) types derived with the Swarm satellite formation. We divide FACs into two classes: small-scale, up to some 10 km, which are carried predominantly by kinetic Alfven waves, and large-scale FACs with sizes of more than 150 km. For determining temporal variability we consider measurements at the same point, the orbital crossovers near the poles, but at different times. From correlation analysis we obtain a persistent period of small-scale FACs of order 10 s, while large-scale FACs can be regarded stationary for more than 60 s. For the first time we investigate the longitudinal scales. Large-scale FACs are different on dayside and nightside. On the nightside the longitudinal extension is on average 4 times the latitudinal width, while on the dayside, particularly in the cusp region, latitudinal and longitudinal scales are comparable.

Earth magnetic field mapping from planetary orbiting satellites requires a spacecraft magnetic field environment control program combined with the deployment of the magnetic sensors on a boom in order to reduce the measurement error caused by the local spacecraft field. Magnetic mapping missions (Magsat, Oersted, CHAMP, SAC-C MMP and the planned ESA Swarm project) carry a vector magnetometer and an absolute scalar magnetometer for in-flight calibration of the vector magnetometer scale values and for monitoring of the inter-axes angles and offsets over time intervals from months to years. This is done by comparing the two magnetometer outputs for several days and for as many different external field directions and amplitudes in the satellite frame as available. The vector and the scalar sensor may be placed of the order of 2 m apart and at the end of an about 10 m long boom counted from the spacecraft centre-of-gravity. In line with the classical dual vector sensors technique for monitoring the spacecraft magnetic field, this paper proposes and demonstrates that a similar combined scalar/vector gradiometry technique is feasible by using the measurements from the boom-mounted scalar and vector sensors onboard the Oersted satellite. For Oersted, a large difference between the pre-flight determined spacecraft magnetic field and the in-flight estimate exists causing some concern about the general applicability of the dual sensors technique.

This paper describes the theory behind all three known ways of digitalizing the fluxgate magnetometers: analogue magnetometers with digitalized output using high resolution ADC, application of the delta–sigma modulation to the sensor feedback loop and fully digital signal detection. At present time the Δ–Σ ADCs are mostly used for the digitalization of the highly precise fluxgate magnetometers. The relevant part of the paper demonstrates some pitfalls of their application studied during the design of the magnetometer for the new Czech scientific satellite MIMOSA. The part discussing the application of the Δ–Σ modulation to the sensor feedback loop theoretically derives the main advantage of this method—increasing of the modulation order and shows its real potential compared to the analog magnetometer with consequential digitalization. The comparison is realized on the modular magnetometer allowing configurations with modulator inside and outside the feedback loop. The last principle is demonstrated on the project of the fully digital fluxgate magnetometer based on the digital signal processor (DSP). The results of the presented projects are compared with recently published competitive projects. The main objective of the paper is then to discuss the potential, real advantages and weakness of each concept and to examine their convenience for future implementations.

A novel highly stable magnetic fluxgate vector gradiometer is presented in this paper. It is based on two triaxial fluxgate sensors with the Compact Spherical Coil (CSC) feedback to demonstrate the feasibility of such instrument (the full gradient instrument will consist of at least four triaxial sensors for measuring all the components of the gradient tensor). The sensors have been designed and constructed for the geopotential German satellite CHAMP, and are based on the instrument flying on the Danish satellite Orsted dedicated to measure the Earth's magnetic field with very high precision. The transducers are of the ringcore type with very low noise and high thermal stability. They use amorphous metal magnetic core (Vitrovac 6025). The cores have been annealed in two different processes with different temperatures and stress. With this instrument, three components of the gradient tensor can be measured with a precision better than 100 pT rms /m. The noise of the gradiometer is 93 pT rms /m in the band 0.01–10 Hz (30.1 pT rms /(Hz 1/2 m) at 1 Hz).

The shift of the NMR spectral line frequency in a proton free precession absolute scalar magnetometer using the omni-directional toroid container for a proton-rich liquid depends on the magnetic susceptibility of the liquid and on the direction of the external field relative to the axis of the toroid. The theoretical shift is estimated for water by computing the additional magnetic field from the magnetization of the liquid and comparing it to the theoretical field in a spherical container. Along the axis the estimated average shift is −0.08 nT and perpendicular to the axis the shift is +0.08 nT relative to that of a spherical sensor. The field inhomogeneity introduced by the toroid shape amounts to 0.32 nT over the volume of the sensor and is not expected to significantly affect the signal decay time, when considering the typical water line width of about 2.5 nT.

The compact spherical coil (CSC) vector-feedback magnetometer on the Danish Orsted geomagnetic mapping satellite underwent extensive calibrations and verifications prior to integration and launch. The theory of the 'thin shell' calibration procedure is introduced. Spherical harmonic modelling was developed and tested over several years and used for Orsted and other missions at test facilities in Europe, the United States and the Republic of South Africa. The verification of the test coil system using an Overhauser absolute scalar proton magnetometer is explained and the overall calibration results are given. The temperature calibrations are explained and reported on. The overall calibration model standard deviation is about 100 pT rms. Comparisons with the later in-flight calibrations show that, except for the unknown satellite offsets, an agreement within 4 nT was obtained. Finally an rf interference between the CSC and the Overhauser magnetometer is discussed, which may account for some of this discrepancy.

The vector fluxgate magnetometer of the Orsted satellite is routinely calibrated by comparing its output with measurements of the absolute magnetic intensity from the Overhauser instrument, which is the second magnetometer of the satellite. We describe the method used for and the result obtained in that calibration. Using three years of data the agreement between the two magnetometers after calibration is 0.33 nT rms (corresponding to better than ± 1 nT for 98% of the data, and better than ± 2 nT for 99.94% of the data). We also report on the determination of the transformation between the magnetometer coordinate system and the reference system of the star imager. This is done by comparing the magnetic and attitude measurements with a model of Earth’s magnetic field. The Euler angles describing this rotation are determined in this way with an accuracy of better than 4 arcsec.

The pre-flight determination of the relative orientation between the CSC vector magnetometer and the Star IMager in the Magnetic Mapper Probe on-board the Argentinean SAC-C satellite is described. Key elements of the instrumentation are given and the inter-calibration is attained using a temporary reference magnetometer and the satellite instrument package. The relative orientation is obtained with accuracy in the arcsec range. As opposed to previous methods the orientation of the reference magnetometer need not be known a priori, but is determined to within a few degrees, which is enough for the accurate determination of the CSC/SIM Euler angles.

The single axis magnetic gradiometer based on two compact detector compensation (CDC) fluxgate ringcore sensors separated 20 cm is described. Despite its high stability and precision better than 1 nT, the calibration procedures are not straightforward. Firstly, the mono-axial measurement does not provide vector information about the magnetic field. Secondly, one of the sensors measures the ambient magnetic field and is used to compensate for the main field at both sensors. Several methods have been developed for characterization of the gradiometer, and the calibration of the gradient measurements is achieved by using a magnetic dipole of strength 2 mAm 2 . In a coil facility, the gradient can be determined with an accuracy of 0.3 nT/m RMS .

A model of a fluxgate magnetometer based on the field interactions in the fluxgate core has been derived. The non-linearity of the ringcore sensors due to large uncompensated fields transverse to the measuring axis are calculated and compared with measurements. Measurements of the non-linearity are made with a spectrum analyzer measuring the higher harmonics of an applied sinusoidal field. For a sensor with a permalloy ringcore of 1 in. in diameter the deviation from linearity is measured to about 15 nT p-p in the earth's field and the measurements are shown to fit well the calculations. Further, the measurements and the calculations are also compared with a calibration model of the fluxgate sensor onboard the ‘MAGSAT’ satellite. The later has a deviation from linearity of about 50 nT p-p but shows basically the same form of non-linearity as the measurements.

We present a summary of the scientific objectives, payload and mission profile of the Space Weather & Ultraviolet Solar Variability Microsatellite Mission (SWUSV) proposed to CNES and ESA (small mission).

The experiments and theoretical considerations leading to the construction of a high-performance three-axis fluxgate magnetometer are described. The magnetometer will be used (1996) in the Earth's field mapping satellite named 'OErsted'. The fluxgate sensors are based on stress-annealed metallic glass ribbons as core materials. It is shown that very simple physical models can be used to explain the fluxgate mode of operation, thereby making it easy to calculate the overall sensor performance from first principles. Special attention is drawn to the core excitation current which is analysed on the basis of nonlinear electrical circuitry. It is furthermore shown that the ring-core demagnetizing field obeys a simple cosine law which permits the calculation of the sensor sensitivity with high accuracy. The sensitivity, that is the signal-to-noise ratio, is ultimately determined by the sensor noise which is about 15 pT RMS (0.06-10 Hz), corresponding to a noise power density (1/f noise) of 6.2 pT Hz-1/2 at 1 Hz. The actual magnetometer operating range and sensitivity is determined by the 1 bit resolution of the Earth's field represented by the output from the 18 bit AD converted used in the instrument (+or-65536 nT with 0.5 nT resolution). The maximum attainable bandwidth is half the sensor excitation frequency (1/2*15 kHz) but the OErsted magnetometer bandwidth is limited to 250 Hz. The thermal stability of the sensor has been measured to be better than 1 nT in the temperature range -20 to +60 degrees C.

International audience; We use the extensive database of magnetic observations from the Mars Global Surveyor to investigate magnetic disturbances in the Martian space environment statistically, both close to and far from crustal anomalies. We discuss the results in terms of possible ionospheric and magnetospheric currents, and use this to provide an estimate of the expected magnetic disturbances at the Martian surface. Far from crustal anomaly regions the expected magnetic disturbances originating from currents associated with the induced magnetosphere are very weak at the day-side, but most likely larger on the night-side. Close to crustal anomalies the expected surface perturbation is larger and more variable both in space and time. It is important to note that these variations are not confined to the intense crustal anomalies in the southern hemisphere, but occur in large parts of the equatorial region. The disturbances around medium intensity radial anomalies in the equatorial region appear to derive from local current loops or vortices around cusp-like radial fields, acting to partly cancel the crustal field. The radial perturbation is further found to depend on upstream solar wind dynamic pressure. We define a magnetic experiment at the martian surface, the Mars Surface Magnetic Observatory (MSMO) including the science objectives, science experiment requirements, instrument and basic operations. We find the experiment to be feasible within the constraints of proposed stationary landing platforms.

The Swarm mission under the ESA’s Living Planet Programme is planned for launch in 2010 and consists of a constellation of three satellites at LEO. The prime objective of Swarm is to measure the geomagnetic field with unprecedented accuracy in space and time. The magnetometry package consists of an extremely accurate and stable vector magnetometer, which is co-mounted in an optical bench together with a start tracker system to ensure mechanical stability of the measurements.

This paper studies the requirements for a small constellation of satellites to perform measurements of the magnetic field of the Earth and a payload and boom design for such a mission is discussed. After studying communication, power and mass requirements it is found that it is feasible to develop a 10 x10 x 30 cm3 satellite with a mass of about 2.5,kg, which can fulfill such a mission. We also study the feasibility of controlling a constellation of such small satellites by means of air drag by extracting one or more flaps. It is found that it is indeed possible, but for best performance it is limited to altitudes around 450 to 550,km, depending on the time of launch with regard to the solar sunspot cycle.

The paper presents design and implementation of the new self-compensating excitation circuitry to the new generation of high-precise space vector magnetometers. The application starts with complex study including design of new robust model of the non-linear inductor leading to investigation of the most crucial points, continuous by design of the self-compensating excitation unit and concludes with unit complex testing and application to the magnetometer. The application of the self-compensation of the excitation decreases temperature drift of the magnetometer offset caused by the temperature drift of the sensor (dominant source of the offset drift) by factor of 7.

International audience; Magnetic measurements taken by the Ørsted satellite during geomagnetic quiet conditions around Jan-uary 1, 2000 have been used to derive a spherical harmonic model of the Earth's magnetic field for epoch 2000.0. The maximum degree and order of the model is 19 for internal, and 2 for external, source fields; however, coefficients above degree 14 may not be robust. Such a detailed model exists for only one previous epoch, 1980. Achieved rms misfit is < 2 nT for the scalar intensity and < 3 nT for one of the vector components perpendicular to the magnetic field. For scientific purposes related to the Orsted mission, this model supercedes IGRF 2000.

A completely nonmagnetic calibration platform has been developed and constructed at DTU Space (Technical University of Denmark). It is intended for on-site scalar calibration of high-precise fluxgate magnetometers. An enhanced version of the same platform is being built at the Czech Technical University. There are three axes of rotation in this design (compared to two axes in the previous version). The addition of the third axis allows us to calibrate more complex devices. An electronic compass based on a vector fluxgate magnetometer and micro electro mechanical systems (MEMS) accelerometer is one example. The new platform can also be used to evaluate the parameters of the compass in all possible variations in azimuth, pitch, and roll. The system is based on piezoelectric motors, which are placed on a platform made of aluminum, brass, plastic, and glass. Position sensing is accomplished through custom-made optical incremental sensors. The system is controlled by a microcontroller, which executes commands from a computer. The properties of the system as well as calibration and measurement results will be presented.

The increase of complexity and miniaturizing level of Aerospace platforms make use of commercial off the shelf (COTS) components constitute a plausible alternative to the use of military or rad-tolerant components. In this work, giant magnetoresistance commercial sensors are studied to be used as COTS, the next missions to be launched in the framework of the Spanish National Space Program: OPTOS and SEOSAT. This technology of magnetic sensors is interesting due to their high operating range up to 2mT and the high temperature dynamic range from −50 up to 150°C. However, in contrast, it presents high hysteresis and nonlinearity, temperature dependence, and poor repeatability. To improve the hysteretic, nonlinear and nonrepetitive behavior, a method consisting of a combination of reset and biasing has been designed and implemented for the ±75𝜇T linear region centered around 300–375𝜇T biasing field. Peerreview

This is a reply to a comment on our paper. The comment suggests an inconsistency in the relation between the magnetic field and the magnetometer measurements. This is resolved, once the existence of two physically different sensor systems is appreciated, as has also been discussed in some detail in our paper.

The Juno spacecraft, in polar orbit about Jupiter since July 4, 2016, is mapping Jupiter’s magnetic field and exploring the polar magnetosphere. Juno’s 53.5-day orbit trajectory carries her science instruments to within ~1.05 Rjof the center of the planet (one Rj= 71,492 km, Jupiter’s equatorial radius) at periapsis and beyond 100 Rj at apoapsis. At the mid-point of Juno’s 33-orbit mapping mission, Juno has traversed the magnetosphere 23 times at local times from midnight to dawn, crossing the Jovian magnetodisc ever closer to the planet as the orbit evolves (line of apsides rotates by ~1 deg latitude every periapsis). It is now possible to more effectively separate internal and external fields near the planet with the introduction of a more accurate internal field model (JRM09). We remove the internal field and fit the residuals to the magnetodisc model of Connerney, Acuna, and Ness (1981), modified by the addition of a radial current supplying torque to outflowing plasma. This model, optimized for the Juno era, affords a great improvement in predicting satellite interaction features and also yields a measure of the time variability of the azimuthal current system (magnetodisc currents) as well as the radial current system. The former varies only slightly thus far during Juno’s mission (~6%), but the latter evidences significant variation from orbit to orbit (~50%). This model is primarily intended to improve mapping within the range of the Galilean satellites where the assumption of magnetodisc axisymmetry may reasonably prevail. We present an overview of these observations obtained during Juno’s first two years in orbit in context with prior observations and those acquired by Juno’s other science instruments.

The calibration parameters of a vector magnetometer are estimated only by the use of a scalar reference magnetometer. The method presented in this paper differs from those previously reported in its linearized parametrization. This allows the determination of three offsets or signals in the absence of a magnetic field, three scale factors for normalization of the axes and three non-orthogonality angles which build up an orthogonal system intrinsically in the sensor. The advantage of this method compared with others lies in its linear least squares estimator, which finds independently and uniquely the parameters for a given data set. Therefore, a magnetometer may be characterized inexpensively in the Earth's magnetic-field environment. This procedure has been used successfully in the pre-flight calibration of the state-of-the-art magnetometers on board the magnetic mapping satellites Orsted, Astrid-2, CHAMP and SAC-C. By using this method, full-Earth-field-range magnetometers (± 65536.0 nT) can be characterized down to an absolute precision of 0.5 nT, non-orthogonality of only 2 arcsec and a resolution of 0.2 nT.

The reference coordinate axes of a magnetic vector field sensor are related to the instrument digital output vector Ū by the calibration matrix and the offset vector Ō. In addition, this reference coordinate system must be related to (at least) two externally accessible optical or geometrical axes in order to be able to determine the precise orientation of the magnetic coordinate axes in an external reference system. Two methods for determining a reference axis in the sensor coordinates are discussed: (1) using a triaxial coil facility to measure the sensor orientation for two different positions, rotated about a fixed reference axis; (2) in the Earth's field the magnetometer sensor is rotated about a fixed axis into a number of (at least three) positions.

The construction of an orthogonal reference frame based on a set of three skew axes for a magnetic coil system and a magnetic sensor is discussed and presented. For a skew system, it is possible to define the coil axes and the magnetic axes as a dual set of axes that are linked to the system. Therefore, one orthogonal reference frame can be identified from the coil axes and another from the magnetic axes. Although this representation is not unique, it is the most intuitive visual representation as it is shown. The parametrizations based on the operation of the fluxgate transducer for the magnetic sensors compact spherical coil (CSC) (Orsted satellite) and compact detector coil (CDC) (Astrid-2 satellite) are analyzed and identified. In principle, only the transformation matrix that orthogonalizes the sensor is needed, but it is customary to express this matrix as a function of some non-orthogonal angles. Therefore, most relevant conventions from the literature are presented for comparison. All the representations agree for the case of small angle approximation, which is valid for most sensors.