Van Allen Probes in situ observations are used to examine detailed subpacket structure observed in strong VLF (very low frequency) rising-tone chorus elements observed at the time of a rapid MeV electron energization in the inner magnetosphere. Analysis of the frequency gap between lower and upper chorus-band waves identifies , the electron gyrofrequency in the equatorial wave generation region. Initial subpackets in these strong chorus rising-tone elements begin at a frequency near 1/4 and exhibit smooth gradual frequency increase across their > 10 ms temporal duration. A second much stronger subpacket is seen at frequencies around the local value of 1/4 with small wave normal angle (< 10°) and steeply rising d/d. Smooth frequency and phase variation across and between the initial subpackets support continuous phase trapping of resonant electrons and increased potential for MeV electron acceleration. The total energy gain for individual seed electrons with energies between 100 keV and 3 MeV ranges between 2 and 15%, in their nonlinear interaction with a single chorus element.

Crustal architecture strongly influences the development and emplacement of mineral zones. In this study, we image the crustal structure beneath a metallogenic belt and its surroundings in the Bayankhongor area of central Mongolia. In this region, an ophiolite belt marks the location of an ancient suture zone, which is presently associated with a reactivated fault system. Nearby, metamorphic and volcanic belts host important mineralization zones and constitute a significant metallogenic belt that includes sources of copper and gold. However, the crustal structure of these features, and their relationships, are poorly studied. We analyze magnetotelluric data acquired across this region and generate three-dimensional electrical resistivity models of the crustal structure, which is found to be locally highly heterogeneous. Because the upper crust (< 25 km) is found to be generally highly resistive (> 1000 Ωm), low-resistivity (< 50 Ωm) features are conspicuous. Anomalous low-resistivity zones are congruent with the suture zone, and ophiolite belt, which is revealed to be a major crustal-scale feature. Furthermore, broadening low-resistivity zones located down-dip from the suture zone suggest that the narrow deformation zone observed at the surface transforms to a wide area in the deeper crust. Other low-resistivity anomalies are spatially associated with the surface expressions of known mineralization zones; thus, their links to deeper crustal structures are imaged. Considering the available evidence, we determine that, in both cases, the low resistivity can be explained by hydrothermal alteration along fossil fluid pathways. This illustrates the pivotal role that crustal fluids play in diverse geological processes, and highlights their inherent link in a unified system, which has implications for models of mineral genesis and emplacement. The results demonstrate that the crustal architecture-including the major crustal boundary-acts as a first-order control on the location of the metallogenic belt.

Discovering such structures as the third radiation belt (or "storage ring") has been a major observational achievement of the NASA Radiation Belt Storm Probes program (renamed the "Van Allen Probes" mission in November 2012). A goal of that program was to understand more thoroughly how high-energy electrons are accelerated deep inside the radiation belts-and ultimately lost-due to various wave-particle interactions. Van Allen Probes studies have demonstrated that electrons ranging up to 10 megaelectron volts (MeV) or more can be produced over broad regions of the outer Van Allen zone on timescales as short as a few minutes. The key to such rapid acceleration is the interaction of "seed" populations of ~ 10-200 keV electrons (and subsequently higher energies) with electromagnetic waves in the lower band (whistler-mode) chorus frequency range. Van Allen Probes data show that "source" electrons (in a typical energy range of one to a few tens of keV energy) produced by magnetospheric substorms play a crucial role in feeding free energy into the chorus waves in the outer zone. These chorus waves then, in turn, rapidly heat and accelerate the tens to hundreds of keV seed electrons injected by substorms to much higher energies. Hence, we often see that geomagnetic activity driven by strong solar storms (coronal mass ejections, or CMEs) commonly leads to ultra-relativistic electron production through the intermediary step of waves produced during intense magnetospheric substorms. More generally, wave-particle interactions are of fundamental importance over a broad range of energies and in virtually all regions of the magnetosphere. We provide a summary of many of the wave modes and particle interactions that have been studied in recent times.

Pliocene volcanic rocks from south-east Austria were paleomagnetically investigated. Samples were taken from 28 sites located on eight different volcanoes. Rock magnetic investigations revealed that magnetic carriers are Ti-rich or Ti-poor titanomagnetites with mainly pseudo-single-domain characteristics. Characteristic remanent magnetization directions were obtained from alternating field as well as from thermal demagnetization. Four localities give reversed directions agreeing with the expected direction from secular variation. Another four localities of the Klöch-Königsberg volcanic complex (3) and the Neuhaus volcano (1) have reversed directions with shallow inclinations and declinations of about 240° while the locality Steinberg yields a positive inclination of about 30° and 200° declination. These aberrant directions cannot be explained by local or regional tectonic movements. All virtual geomagnetic pole positions are located on the southern hemisphere. Four virtual geomagnetic poles lie close to the geographic pole, while all others are concentrated in a narrow longitude sector offshore South America (310°-355°) with low virtual geomagnetic pole latitudes ranging from - 15° to - 70°. The hypothesis that a transitional geomagnetic field configuration was recorded during the short volcanic activity of these five localities is supported by 9 paleointensity results and Ar/Ar dating. Virtual geomagnetic dipole moments range from 1.1 to 2.9·10 Am for sites with low VGP latitudes below about 60° and from 3.0 to 9.3·10 Am for sites with higher virtual geomagnetic pole latitudes. The new Ar/Ar ages of 2.51 ± 0.27 Ma for Klöch and 2.39 ± 0.03 Ma for Steinberg allow for the correlation of the Styrian transitional directions with cryptochron C2r.2r-1 of the geomagnetic polarity time scale.

We present the CHAOS-7 model of the time-dependent near-Earth geomagnetic field between 1999 and 2020 based on magnetic field observations collected by the low-Earth orbit satellites , CryoSat-2, CHAMP, SAC-C and Ørsted, and on annual differences of monthly means of ground observatory measurements. The CHAOS-7 model consists of a time-dependent internal field up to spherical harmonic degree 20, a static internal field which merges to the LCS-1 lithospheric field model above degree 25, a model of the magnetospheric field and its induced counterpart, estimates of Euler angles describing the alignment of satellite vector magnetometers, and magnetometer calibration parameters for CryoSat-2. Only data from dark regions satisfying strict geomagnetic quiet-time criteria (including conditions on IMF and at all latitudes) were used in the field estimation. Model parameters were estimated using an iteratively reweighted regularized least-squares procedure; regularization of the time-dependent internal field was relaxed at high spherical harmonic degree compared with previous versions of the CHAOS model. We use CHAOS-7 to investigate recent changes in the geomagnetic field, studying the evolution of the South Atlantic weak field anomaly and rapid field changes in the Pacific region since 2014. At Earth's surface a secondary minimum of the South Atlantic Anomaly is now evident to the south west of Africa. Green's functions relating the core-mantle boundary radial field to the surface intensity show this feature is connected with the movement and evolution of a reversed flux feature under South Africa. The continuing growth in size and weakening of the main anomaly is linked to the westward motion and gathering of reversed flux under South America. In the Pacific region at Earth's surface between 2015 and 2018 a sign change has occurred in the second time derivative (acceleration) of the radial component of the field. This acceleration change took the form of a localized, east-west oriented, dipole. It was clearly recorded on ground, for example at the magnetic observatory at Honolulu, and was seen in observations over an extended region in the central and western Pacific. Downward continuing to the core-mantle boundary, we find this event originated in field acceleration changes at low latitudes beneath the central and western Pacific in 2017.

Vertical magnetic transfer functions (tippers) estimated at a global/continental net of geomagnetic observatories/sites can be used to image the electrical conductivity structure of the Earth's crust and upper mantle (down to around 200 km). We estimated tippers at 54 geomagnetic observatories across China, aiming eventually to invert them in terms of subsurface three-dimensional (3-D) conductivity distribution. Strikingly, we obtained enormously large tippers at three inland observatories in southwest China. Large tippers are often observed at coastal/island observatories due to high conductivity contrasts between resistive bedrock and conductive seawater. However, tippers at those inland observatories appeared to be a few times larger than coastal/island tippers. As far as we know, such large tippers (reaching value 3) were never reported in any region worldwide. We perform electromagnetic simulations in 3-D conductivity models mimicking the geological setting and demonstrate that enormously large tippers are feasible and can be attributed to a current channeling effect.

The deviation of Universal Time from atomic time, expressed as UT1-UTC, reflects the irregularities of the Earth rotation speed and is key to precise geodetic applications which depend on the transformation between celestial and terrestrial reference frames. A rapidly varying quantity such as UT1-UTC demands observation scenarios enabling fast delivery of good results. These criteria are currently met only by the Very Long Baseline Interferometry (VLBI) Intensive sessions. Due to stringent requirements of a fast UT1-UTC turnaround, the observations are limited to a few baselines and a duration of one hour. Hence, the estimation of UT1-UTC from Intensives is liable to constraints and prone to errors introduced by inaccurate a priori information. One aspect in this context is that the regularly operated Intensive VLBI sessions organised by the International VLBI Service for Geodesy and Astrometry solely use stations in the northern hemisphere. Any potential systematic errors due to this northern hemisphere dominated geometry are so far unknown. Besides the general need for stimulating global geodetic measurements with southern observatories, this served as a powerful motivation to launch the SI (Southern Intensive) program in 2020. The SI sessions are observed using three VLBI antennas in the southern hemisphere: Ht (South Africa), Hb (Tasmania) and Yg (Western Australia). On the basis of UT1-UTC results from 53 sessions observed throughout 2020 and 2021, we demonstrate the competitiveness of the SI with routinely operated Intensive sessions in terms of operations and UT1-UTC accuracy. The UT1-UTC values of the SI reach an average agreement of 32 µs in terms of weighted standard deviation when compared with the conventional Intensives results of five independent analysis centers and of 27 µs compared with the 14C04 series. The mean scatter of all solutions of the considered northern hemisphere Intensives with respect to C04 is at a comparable level of 29 µs. The quality of the results is only slightly degraded if just the baseline HtHb is evaluated. In combination with the e-transfer capabilities from Ht to Hb, this facilitates continuation of the SI by ensuring rapid service UT1-UTC provision.

The COVID-19 pandemic that started at the end of 2019 forced populations around the world to reduce social and economic activities; it is believed that this can prevent the spread of the disease. In this paper, we report an analysis of the seismic noise during such an induced social activity reduction in the Tokyo metropolitan area, Japan. Using seismic data obtained from 18 stations in the Metropolitan Seismic Observation Network (MeSO-net), a two-step seismic noise reduction was observed during the timeline of COVID-19 in Tokyo. The first noise reduction occurred at the beginning of March 2020 in the frequency band of 20-40 Hz. This corresponded with the request by the Prime Minister of Japan for a nationwide shutdown of schools. Although social activity was not reduced significantly at this juncture, local reduction of seismic wave excitation in the high-frequency band, 20-40 Hz, was recorded at some MeSO-net stations located in school properties. The second reduction of seismic noise occurred at the end of March to the beginning of April 2020 in a wider frequency band including lower frequency bands of 1-20 Hz. This timing corresponds to when the Governors of the Tokyo metropolitan area requested citizens to stay home and when the state of emergency was declared for the Tokyo metropolitan area by the government, respectively. Since then, the estimated population at train stations abruptly dropped, which suggests that social activity was severely reduced. Such large-scale changes in social activity affect the seismic noise level in low-frequency bands. The seismic noise level started to increase from the middle of May correlating with increase in population at the train stations. This suggests that social activity restarted even before the state of emergency was lifted at the end of May. The two-step seismic noise reduction observed in this study has not been reported in other cities around the world. Unexpected reduction of social activity due to COVID-19 provided a rare opportunity to investigate the characteristics of seismic noise caused by human activities.

We conducted temporary seismic observations at the Hitachi-Kashiwa Soccer Stadium on a J. LEAGUE game day to obtain unique seismic records due to the collective action (i.e., jumping) of supporters, which were also recorded in a permanent Metropolitan Seismic Observation network (MeSO-net) station. This study investigated seismic wave excitation as well as seismic wave propagation from the stadium to its surroundings. The rhythms of the jumps of the supporters were characterized by analyzing audio data recorded in the stadium, which were compared with the characteristic frequencies observed in the seismic records. The characteristic frequencies in the seismic records are integer multiples of the jumping rhythms, which is consistent with the loading model of jumping people proposed in earlier studies. This implies that seismometers could be useful for monitoring collective human activity. Travel times were studied using deconvolved waveforms because seismic waves generated by the supporters are sinusoidal with vague onset. Polarization analysis was performed to measure the amplitude and polarization azimuths. The observed seismic wave propagation was compared with synthetic waveforms calculated using one-dimensional physical properties based on the Japan Seismic Hazard Information Station (J-SHIS). The synthetic waveforms calculated with the shallow and deep layer combined model are more consistent with observations of travel times and amplitude decay than those calculated with the only deep layer model, although a part of the observations cannot be explained by both models. This result suggests that the subsurface structure of J-SHIS is good in this region, although a more detailed three-dimensional structure and topography must be considered to fully explain the observations. As human-induced seismic signals are expected to be generated in various situations, this study shows that such unique seismic waves can be used as an artificial seismic source for validating and improving local shallow subsurface structural models in urban environments.

Transmission electron microscopy analyses of the polymineralic regolith particle RC-MD01-0025 show microstructural and microchemical characteristics indicative of space weathering on the surface of asteroid Itokawa. The depletion of sulfur and nickel was identified in space weathered rims on troilite and pentlandite minerals. This corresponds to the first report of nickel depletion in samples returned from asteroid Itokawa by the Hayabusa mission. Microstructurally, the sulfide minerals present crystalline rims and the olivine presents both crystalline and amorphous zones in the rim. These results suggest that sulfides might be more resistant to amorphization caused by solar wind irradiation. The space weathering features identified in the regolith particle analyzed here are likely formed via solar wind irradiation. Additionally, the differences in the space weathering features in olivine, pentlandite, and troilite suggest that silicates and sulfides respond differently to the same space weathering conditions in interplanetary space.

Millimetre-sized primordial rock fragments originating from asteroid Ryugu were investigated using high energy X-ray fluorescence spectroscopy, providing 2D and 3D elemental distribution and quantitative composition information on the microscopic level. Samples were collected in two phases from two sites on asteroid Ryugu and safely returned to Earth by JAXA's asteroid explorer Hayabusa2, during which time the collected material was stored and maintained free from terrestrial influences, including exposure to Earth's atmosphere. Several grains of interest were identified and further characterised to obtain quantitative information on the rare earth element (REE) content within said grains, following a reference-based and computed-tomography-assisted fundamental parameters quantification approach. Several orders of magnitude REE enrichments compared to the mean CI chondrite composition were found within grains that could be identified as apatite phase. Small enrichment of LREE was found for dolomite grains and slight enrichment or depletion for the general matrices within the Ryugu rock fragments A0055 and C0076, respectively.

We examine the morphology and chemistry of the Vikrahraun basaltic eruption emplaced at Askja Volcano, Iceland, from Oct. 26-Dec. 17, 1961. The eruption had three eruptive events, initiating with a'a and followed by alternating a'a and pahoehoe lava flow emplacement. We determine that while the eruption is chemically homogenous (Fe/Mg = 1.9-2.2, 47-52 wt.% SiO2), it demonstrates transitions from high to low viscosity lava flow morphologies. A'a flows have a total crystallinity (phenocryst and microlite abundance by area) ranging from 85-100%, which increases by 1% per km from the vents, while pahoehoe flows range from 55-86% and increase at a higher rate of 5% per km. Vesicularity systematically decreases with distance from the vent by 3% per km. Pahoehoe and vent samples have calculated temperatures 50 °C higher than a'a samples, which we interpret to be due to the difference between tube fed pahoehoe and open channel a'a lavas. The homogenous nature of the Vikrahraun lava makes it an excellent testbed to study the effects of observational scale and satellite resolution on the interpretation of surficial textures. Festoons, which are downslope pointed convex ridges from 1 to 5 m high and ~ 10 m long, are observed in event 2 a'a lavas in satellite imagery and topographic profiles. Features of this scale have previously only been documented in terrestrial rhyolitic lavas, leading planetary researchers to infer that festooned lava flows on Venus and Mars may be silicic. The diverse morphologies and homogenous composition make Vikrahraun an important planetary analog, where morphological complexity is over-attributed to chemical variation and suggests the need to re-evaluation planetary lava flow interpretations.

We created high-resolution shape models of Phobos and Deimos using stereophotoclinometry and united images from Viking Orbiter, Phobos 2, Mars Global Surveyor, Mars Express, and Mars Reconnaissance Orbiter into a single coregistered collection. The best-fit ellipsoid to the Phobos model has radii of (12.95 ± 0.04) km × (11.30 ± 0.04) km × (9.16 ± 0.03) km, with an average radius of (11.08 ± 0.04) km. The best-fit ellipsoid to the Deimos model has radii of (8.04 ± 0.08) km × (5.89 ± 0.06) km × (5.11 ± 0.05) km with an average radius of (6.27 ± 0.07) km. The new shape models offer substantial improvements in resolution over existing shape models, while remaining globally consistent with them. The Phobos model resolves grooves, craters, and other surface features ~ 100 m in size across the entire surface. The Deimos model is the first to resolve geological surface features. These models, associated data products, and a searchable, coregistered collection of images across six spacecraft are publicly available in the Small Body Mapping Tool, and will be archived with the NASA Planetary Data System. These products enable an array of future studies to advance the understanding of Phobos and Deimos, facilitate coregistration of other past and future datasets, and set the stage for planning and operating future missions to the moons, including the upcoming Martian Moons eXploration (MMX) mission.

We have produced a 5-year mean secular variation (SV) of the geomagnetic field for the period 2020-2025. We use the NASA Geomagnetic Ensemble Modeling System (GEMS), which consists of the NASA Goddard geodynamo model and ensemble Kalman filter (EnKF) with 400 ensemble members. Geomagnetic field models are used as observations for the assimilation, including (1590-1960), CM4 (1961-2000) and CM6 (2001-2019). The forecast involves a bias correction scheme that assumes that the model bias changes on timescales much longer than the forecast period, so that they can be removed by successive forecast series. The algorithm was validated on the time period 2010-2015 by comparing with CM6 before being applied to the 2020-2025 time period. This forecast has been submitted as a candidate predictive model of IGRF-13 for the period 2020-2025.

The MEGANE instrument onboard the MMX mission will acquire gamma-ray and neutron spectroscopy data of Phobos to determine the elemental composition of the martian moon and provide key constraints on its origin. To produce accurate compositional results, the irregular shape of Phobos and its proximity to Mars must be taken into account during the analysis of MEGANE data. The MEGANE team is adapting the Small Body Mapping Tool (SBMT) to handle gamma-ray and neutron spectroscopy investigations, building on the demonstrated record of success of the SBMT being applied to scientific investigations on other spacecraft missions of irregularly shaped bodies. This is the first application of the SBMT to a gamma-ray and neutron spectroscopy dataset, and the native, three-dimensional foundation of the SBMT is well suited to MEGANE's needs. In addition, the SBMT will enable comparisons between the MEGANE datasets and other datasets of the martian moons, including data from previous spacecraft missions and MMX's multi-instrument suite.

In gradual Solar Energetic Particle (SEP) events, shock waves driven by coronal mass ejections (CMEs) play a major role in accelerating particles, and the energetic particle flux enhances substantially when the shock front passes by the observer. Such enhancements are historically referred to as Energetic Storm Particle (ESP) events, but it remains unclear why ESP time profiles vary significantly from event to event. In some cases, energetic protons are not even clearly associated with shocks. Here, we report an unusual, short-duration proton event detected on 5 June 2011 in the compressed sheath region bounded by an interplanetary shock and the leading edge of the interplanetary CME (or ICME) that was driving the shock. While < 10 MeV protons were detected already at the shock front, the higher-energy (> 30 MeV) protons were detected about four hours after the shock arrival, apparently correlated with a turbulent magnetic cavity embedded in the ICME sheath region.

The ionosphere is one of the important sources for magnetospheric plasma, particularly for heavy ions with low charge states. We investigate the effect of solar illumination on the number flux of ion outflow using data obtained by the Fast Auroral SnapshoT (FAST) satellite at 3000-4150 km altitude from 7 January 1998 to 5 February 1999. We derive empirical formulas between energy inputs and outflowing ion number fluxes for various solar zenith angle ranges. We found that the outflowing ion number flux under sunlit conditions increases more steeply with increasing electron density in the loss cone or with increasing precipitating electron density (> 50 eV), compared to the ion flux under dark conditions. Under ionospheric dark conditions, weak electron precipitation can drive ion outflow with small averaged fluxes (~ 10 cm s). The slopes of relations between the Poynting fluxes and outflowing ion number fluxes show no clear dependence on the solar zenith angle. Intense ion outflow events (> 10 cm s) occur mostly under sunlit conditions (solar zenith angle < 90°). Thus, it is presumably difficult to drive intense ion outflows under dark conditions, because of a lack of the solar illumination (low ionospheric density and/or small scale height owing to low plasma temperature).

We present the geomagnetic field model COV-OBS.x2 that covers the period 1840-2020. It is primarily constrained by observatory series, satellite data, plus older surveys. Over the past two decades, we consider annual differences of 4-monthly means at ground-based stations (since 1996), and virtual observatory series derived from magnetic data of the satellite missions CHAMP (over 2001-2010) and Swarm (since 2013). A priori information is needed to complement the constraints carried by geomagnetic records and solve the ill-posed geomagnetic inverse problem. We use for this purpose temporal cross-covariances associated with auto-regressive stochastic processes of order 2, whose parameters are chosen so as to mimic the temporal power spectral density observed in paleomagnetic and observatory series. We aim this way to obtain as far as possible realistic posterior model uncertainties. These can be used to infer for instance the core dynamics through data assimilation algorithms, or an envelope for short-term magnetic field forecasts. We show that because of the projection onto splines, one needs to inflate the formal model error variances at the most recent epochs, in order to account for unmodeled high frequency core field changes. As a by-product of the core field model, we co-estimate the external magnetospheric dipole evolution on periods longer than 2 years. It is efficiently summarized as the sum of a damped oscillator (of period 10.5 years and decay rate 55 years), plus a short-memory (6 years) damped random walk.

Japan Aerospace Exploration Agency (JAXA) will launch a spacecraft in 2024 for a sample return mission from Phobos (Martian Moons eXploration: MMX). Touchdown operations are planned to be performed twice at different landing sites on the Phobos surface to collect > 10 g of the Phobos surface materials with coring and pneumatic sampling systems on board. The Sample Analysis Working Team (SAWT) of MMX is now designing analytical protocols of the returned Phobos samples to shed light on the origin of the Martian moons as well as the evolution of the Mars-moon system. Observations of petrology and mineralogy, and measurements of bulk chemical compositions and stable isotopic ratios of, e.g., O, Cr, Ti, and Zn can provide crucial information about the origin of Phobos. If Phobos is a captured asteroid composed of primitive chondritic materials, as inferred from its reflectance spectra, geochemical data including the nature of organic matter as well as bulk H and N isotopic compositions characterize the volatile materials in the samples and constrain the type of the captured asteroid. Cosmogenic and solar wind components, most pronounced in noble gas isotopic compositions, can reveal surface processes on Phobos. Long- and short-lived radionuclide chronometry such as Mn-Cr and Rb-Sr systematics can date pivotal events like impacts, thermal metamorphism, and aqueous alteration on Phobos. It should be noted that the Phobos regolith is expected to contain a small amount of materials delivered from Mars, which may be physically and chemically different from any Martian meteorites in our collection and thus are particularly precious. The analysis plan will be designed to detect such Martian materials, if any, from the returned samples dominated by the endogenous Phobos materials in curation procedures at JAXA before they are processed for further analyses.

The technique of spherical elementary current systems (SECS) is a powerful way to determine ionospheric and field-aligned currents (FAC) from magnetic field measurements made by low-Earth-orbiting satellites, possibly in combination with magnetometer arrays on the ground. The SECS method consists of two sets of basis functions for the ionospheric currents: divergence-free (DF) and curl-free (CF) components, which produce poloidal and toroidal magnetic fields, respectively. The original CF SECS are only applicable at high latitudes, as they build on the assumption that the FAC flow radially into or out of the ionosphere. The FAC at low and middle latitudes are far from radial, which renders the method inapplicable at these latitudes. In this study, we modify the original CF SECS by including FAC that flow along dipolar field lines. This allows the method to be applied at all latitudes. We name this method dipolar elementary current systems (DECS). Application of the DECS to synthetic data, as well as Swarm satellite measurements are carried out, demonstrating the good performance of this method, and its applicability to studies of ionospheric current systems at low and middle latitudes.

Equipping Galileo satellites with a VLBI transmitter (VT) will allow to observe satellites next to quasars with Very Long Baseline Interferometry (VLBI) radio telescopes. This concept will facilitate the direct estimation of the satellite orbits in the celestial reference frame. Moreover, these observations along with usual Galileo observations can be used to transfer the space tie between the VT and the antenna on the Galileo satellite to the Earth surface realizing the frame tie at the geodetic site with VLBI radio telescope and Galileo antenna. In this study, we assess the accuracy of that frame tie by simulating the estimation of station coordinates from VLBI observations to Galileo satellites next to quasars. We find that at least two or three satellites need to be equipped with a VT with the best results if all satellites with a VT are placed in the same plane. Concerning the ratio between satellite and quasar observations within a schedule, the results suggest that the optimal ratio is around 30% to 40% satellite observations out of the total number of observations in order to have enough observations for the estimation of the station coordinates but still enough quasar observations to ensure a sufficient sky-coverage for the estimation of troposphere parameters. The best scenario with two satellites yields repeatabilities for the east and north components between 7.5 and 10 mm, and for the up component between 9.5 and 12 mm. In case there is a third satellite with a VLBI transmitter in the same plane, the repeatabilities are reduced by up to 2 mm for the horizontal components and up to 3 to 4 mm for the up component. Rotating the schedules over the constellation repeat cycle of Galileo of 10 days reveals that there are differences between the individual days, but there are no days with a significantly worse precision of the estimated station coordinates.