Abstract. This paper presents the results of Planetary Radio Interferometry and Doppler Experiment (PRIDE) observations of the JUICE spacecraft during its lunar and Earth gravity-assist manoeuvres on August 19 and 20, 2024, using a network of VLBI radio telescopes. Prior to the flyby sequence, VLBI phase‑referencing observations were conducted to establish astrometric measurements and Doppler frequency calibration during the near-Earth approach. During the flyby events, the experiment successfully captured the signal ingress and egress during the lunar occultation, as well as the signal behaviour at closest approach to the lunar surface. Signal-diagnostic measurements were performed to characterise the received carrier signal and assess instrumental and propagation effects. The observed Doppler frequency measurements were subsequently compared with predicted values derived independently using the WebGeocalc service and the Tudat software framework. The close agreement between the measured Doppler observables and model predictions confirms that the tracking results are consistent with expectations for JUICE's cruise-phase configuration and the high-velocity dynamics of the Earth flyby. Finally, these measurements were also used to obtain complementary measurements of the terrestrial ionosphere and space weather conditions, and are being used for refining solar wind models using planetary spacecraft radio tracking.

The renewed interest in lunar exploration and the development of future lunar communication and navigation services highlight the need for a precise, stable, and interoperable geodetic and timing infrastructure on the Moon. NovaMoon, proposed as a scientific and navigation payload for ESA's Argonaut lander, is designed as a lunar-based local differential, geodetic, and timing station supporting both operational needs in the Moon's south polar region and a broad range of scientific investigations. The payload integrates a lunar laser retroreflector, a Very Long Baseline Interferometry transmitter, a receiver for navigation signals compatible with LunaNet standards, high-stability atomic clocks, and direct-to-Earth radio links – making it the first lunar station to co-locate multiple ranging, tracking, and timing techniques. NovaMoon will enable sub-metre to decimetre positioning, provide local differential corrections for lunar users, and ensure an accurate and stable realisation of position and time. Preliminary simulation studies show that this multi-technique dataset improves the lunar reference frame, orientation and ephemerides, and estimates of interior parameters like tidal response and core properties. NovaMoon will also provide the first long-duration physical realisation of a lunar time reference. Beyond its primary goals, it supports improved cartography, precise surface geolocation, and higher-resolution topography, contributing to safer landings and operations. It also enables new tests of fundamental physics, including constraints on relativity and possible deviations from classical gravity.

Ground-based radio astronomy and space science get together in the Planetary Radio Interferometry and Doppler Experiment (PRIDE), which provides the precise determination of the lateral position of spacecraft on the celestial sphere using phase referencing near-field Very Long Baseline Interferometry (VLBI).As part of the ESA Jupiter Icy Moons Explorer (JUICE) mission, PRIDE is complementary to on-board radio science experiments. The technique consists of radio astronomical observations of the JUICE radio signal alongside calibrating quasars to deliver high-resolution lateral position measurements within the International Celestial Reference Frame. PRIDE requires no extra onboard instruments and relies on the spacecraft's existing telecommunications system and ground-based telescope arrays, like the European VLBI Network or the Australian Long Baseline Array.Since JUICE launch, PRIDE observations have tracked the spacecraft on several occasions. During the Lunar-Earth Gravity Assist (LEGA), multiple radio telescopes observed JUICE to independently validate the spacecraft trajectory to verify PRIDE internal pipelines. In August 2025, the European VLBI Network ran an observing campaign during the Venus gravity assist manoeuvres. In this presentation, the status and the results of the PRIDE-JUICE cruise phase activities will be presented.

Doppler tracking of planetary missions is crucial for science objectives related to understanding, among others, solar system interiors and evolution. These analyses conventionally rely on closed-loop Doppler data from networks such as ESTRACK and the DSN. The Planetary Radio Interferometry and Doppler Experiment (PRIDE) can provide complementary data by extracting open-loop Doppler and VLBI observables from spacecraft radio signals recorded by radio-astronomical telescopes [1,2,3]. These (three-way) observables are generated using the existing downlink from the spacecraft and therefore generated concurrently with the typical (usually two-way) closed-loop tracking data. While PRIDE data of planetary missions have been used for various applications, their direct use in a full orbit-estimation problem had not yet been demonstrated. Here, we report on the first end-to-end PRIDE-based orbit estimation of a planetary mission, using PRIDE Doppler data.We use the 2013 Mars Express flyby of Phobos, for which both conventional closed-loop Doppler data and PRIDE open-loop Doppler (EVN experiment GR035, PI: Pascal Rosenblatt) data are available [4]. Using the open-source TU Delft Astrodynamics Toolbox (Tudat) [5,6], we independently estimate the Mars Express trajectory and the gravitational parameter of Phobos from the closed-loop and open-loop datasets. The solutions are cross-validated against the Mars Express orbit computed by the Royal Observatory of Belgium (ROB) team from closed-loop Doppler data using the GINS software.The closed-loop solution gives RMS position differences with respect to the ROB Mars Express ephemerides of approximately 0.27 m radial, 17 m along-track, and 130 m cross-track, consistent with the expected uncertainty of the reference solution. For the PRIDE open-loop Doppler data, we form 27 different three-station combinations of PRIDE datasets, with one station on each of three continents, such that each combination spans the full tracking interval. From each combination, we estimate an independent orbit of Mars Express, leading to separate orbit estimates, each of comparable quality to those derived from closed-loop data, as quantified by the difference with respect to the ROB reference. The estimated gravitational parameter of Phobos is likewise consistent between the open-loop and closed-loop analyses and with reference values from the literature.To further quantify the uncertainty of the PRIDE-based orbit estimates, we compute the RMS dispersion of the 27 station-combination solutions at each point along the estimated trajectory. This dispersion peaks at approximately 0.4 m radial, 15 m along-track, and 100 m cross-track. Its temporal behaviour closely matches the difference between our closed-loop solution and the ROB reference ephemeris, indicating that the spread between PRIDE station-combination solutions provides a measure of the true orbit-estimation error that is comparable to the difference with respect to an external reference solution. This is a key advantage of PRIDE’s multi-station redundancy: it enables an internal assessment of solution uncertainty, without relying exclusively on formal covariance estimates, which are often too optimistic, or on comparison with an external reference solution, which is not always available.Assessing the true uncertainty of radio-tracking-based estimation is crucial for robustly using estimated parameters (for instance the gravitational parameter of Phobos) to improve our understanding of planetary interiors and Solar System evolution. PRIDE observations are particularly valuable for selected tracking intervals of high scientific interest, where the multi-station redundancy can provide validation and error quantification beyond what is available from conventional tracking alone. For events such as flybys of the Galilean moons [3], PRIDE Doppler data can therefore provide a complementary source of information for assessing the reliability of orbit and parameter estimates. Future work will include the processing of PRIDE Doppler data during the JUICE flyby of Venus, and spacecraft orbit estimation using a combination of open- and closed-loop tracking data. [1] Duev, D.A., et al. "Spacecraft VLBI and Doppler tracking: algorithms and implementation." Astronomy & Astrophysics 541 (2012): A43.[2] Molera Calvés, G., et al. "High spectral resolution multi-tone Spacecraft Doppler tracking software: Algorithms and implementations." Publications of the Astronomical Society of Australia 38 (2021): e065.[3] Gurvits, L.I., et al. "Planetary radio interferometry and Doppler experiment (PRIDE) of the JUICE mission." Space Science Reviews 219.8 (2023): 79.[4] Bocanegra-Bahamón, T.M., et al. "Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique: A test case of the Mars Express Phobos Flyby: II. Doppler tracking: Formulation of observed and computed values, and noise budget." Astronomy & Astrophysics 609 (2018): A59.[5] Dirkx, D., et al. "The open-source astrodynamics Tudatpy software–overview for planetary mission design and science analysis." EPSC2022 EPSC2022-253 (2022).[6] Gisolfi, L, et al. "Open-Source High-Fidelity Orbit Estimation for Planetary Science and Space Situational Awareness Using the Tudat Software." arXiv preprint arXiv:2510.23179 (2025).

The radio telescopes of the European VLBI Network (EVN) and the University of Tasmania (UTAS) conducted an extensive observation campaign of the European Space Agency's (ESA) Mars Express (MEX) spacecraft between 2013 and 2020. The campaign, carried out under the Planetary Radio Interferometry and Doppler Experiment (PRIDE) framework, aimed to study interplanetary phase scintillation and assess the noise budget in the closed-loop Doppler observations. The average closed-loop Doppler noise was determined to be approximately 10 mHz at a 10-s integration time, reaffirming the technique's suitability for radio science experiments. We evaluated how different observational parameters such as the solar elongation, antenna size, and elevation angle impact the Doppler noise. A key part of the analysis involved comparing results from co-located telescopes to investigate system noise effects. Co-located telescopes at both Wettzell and Hobart provided highly consistent results, with any deviations serving as diagnostic tools to identify station-dependent issues. Additionally, the use of phase calibration tones during spacecraft tracking showed that the instrumental noise contribution is of the order of 5 $\%$ of the total noise. This study provides a detailed noise budget for closed-loop Doppler observations with VLBI telescopes while emphasizing the effectiveness of the co-location method in isolating system-level noise. These findings are important for optimizing future radio science and VLBI tracking missions using stations outside the the Deep Space Network (DSN) and European Space Tracking (ESTRACK) network.

The TU Delft Astrodynamics Toolbox (Tudat) is a free open-source software suite for research and education in astrodynamics. Initially focused on numerical simulations of orbital dynamics and state estimation, it enables combining optical and radiometric tracking data from multiple sources to estimate the dynamics and parameters of natural and artificial bodies. Recent developments have added functionality for real tracking data analysis, with applications to planetary missions and Space Situational Awareness (SSA). Tudat currently supports processing of (i) deep-space Doppler and range data from DSN and ESTRACK, (ii) Doppler and VLBI data from the PRIDE experiment, and (iii) optical astrometry from the Minor Planet Center (MPC) and Natural Satellite Data Center (NSDC). Using tracking data from the MRO and GRAIL spacecraft and astrometric data of the asteroid Eros, we present prefit residuals (from SPICE-based observables) and postfit residuals (from fitting data to the Tudat dynamical model). Postfit Doppler residuals reach 1-5 mHz for MRO and GRAIL, orbit differences are a few meters for GRAIL and about one meter for MRO, and MRO range residuals are a few meters. From eight years of Eros astrometry, we obtain an orbit difference from the JPL Horizons solution by several tens of kilometers, consistent with its 3-sigma formal error. Tudat's SSA capability is demonstrated by propagating the orbit of Kosmos 482, a Venus lander launched in 1972 that remained in Earth orbit, over 50 years, including its predicted re-entry on May 10 2025. These examples showcase Tudat's modular, flexible, high-fidelity modeling across diverse orbital regimes within a fully open-source framework. All example code is publicly available, and future Tudat analyses will be published with fully reproducible code, allowing anyone in the community to improve and expand upon our work.

Introduction Planetary Radio Interferometry and Doppler Experiment (PRIDE) will exploit the signal recording and processing technology developed originally for Very Long Baseline interferometric (VLBI). The essence of PRIDE is in observing the spacecraft radio signal with a network of Earth-based radio telescopes. The PRIDE technique developed at the Joint Institute for VLBI ERIC (JIVE) together with its partners was used for several experiments with several ESA planetary science missions. It has been chosen by ESA as one of the eleven experiments of the Jupiter Icy Moons Explorer (JUICE), the first Large-class mission in the ESA’s Cosmic Vision 2015–2025 program. The mission is scheduled for launch in 2022.

We present the state of the art on the study of surfaces and tenuous atmospheres of the icy Galilean satellites Ganymede, Europa and Callisto, from past and ongoing space exploration conducted with several spacecraft to recent telescopic observations, and we show how the ESA JUICE mission plans to explore these surfaces and atmospheres in detail with its scientific payload. The surface geology of the moons is the main evidence of their evolution and reflects the internal heating provided by tidal interactions. Surface composition is the result of endogenous and exogenous processes, with the former providing valuable information about the potential composition of shallow subsurface liquid pockets, possibly connected to deeper oceans. Finally, the icy Galilean moons have tenuous atmospheres that arise from charged particle sputtering affecting their surfaces. In the case of Europa, plumes of water vapour have also been reported, whose phenomenology at present is poorly understood and requires future close exploration. In the three main sections of the article, we discuss these topics, highlighting the key scientific objectives and investigations to be achieved by JUICE. Based on a recent predicted trajectory, we also show potential coverage maps and other examples of reference measurements. The scientific discussion and observation planning presented here are the outcome of the JUICE Working Group 2 (WG2): "Surfaces and Near-surface Exospheres of the Satellites, dust and rings".

We present an overview of the operations and engineering interface for Planetary Radio Interferometry and Doppler Experiment (PRIDE) radio astronomy observations as a scientific component of the ESA s Jupiter Icy Moons Explorer (JUICE) mission, as well as other prospective planetary and space science missions. The article discusses advanced scheduling and planning methods that make it possible to create observing schedules for observations of specific spacecraft in concurrence with observations of natural radio sources. In order to put this into practice and find suitable natural background calibrator sources for PRIDE of JUICE mission, we developed planning and scheduling software. The conventional scheduling software for natural celestial radio sources is not set up to include spacecraft as observation targets in the necessary control files. Therefore, difficulties already arise during observation planning. We report on the development of new and the adaptation of existing routines used in astrophysical and geodetic VLBI for satellite scheduling and planning. The analysis of the PRIDE science observations led to improved observational planning, and the mission s scheduling methodologies were studied using a systems engineering approach. In addition, we highlighted the new procedures, like finding charts for selecting calibrator radio sources over a range of frequency bands and the outcomes of those strategies for science operation planning. A simulation of the flyby of Venus during the cruise phase of the JUICE spacecraft, based on the Tudat software, is also presented, resulting in a promising opportunity to test PRIDE techniques and evaluate the improvements that PRIDE observables can make to natural bodies ephemerides.

Planetary Radio Interferometry and Doppler Experiment (PRIDE) is a multi-purpose experimental technique aimed at enhancing the science return of planetary missions. The technique exploits the science payload and spacecraft service systems without requiring a dedicated onboard instrumentation or imposing on the existing instrumentation any special for PRIDE requirements. PRIDE is based on the near-field phase-referencing Very Long Baseline Interferometry (VLBI) and evaluation of the Doppler shift of the radio signal transmitted by spacecraft by observing it with multiple Earth-based radio telescopes. The methodology of PRIDE has been developed initially at the Joint Institute for VLBI ERIC (JIVE) for tracking the ESA's Huygens Probe during its descent in the atmosphere of Titan in 2005. From that point on, the technique has been demonstrated for various planetary and other space science missions. The estimates of lateral position of the target spacecraft are done using the phase-referencing VLBI technique. Together with radial Doppler estimates, these observables can be used for a variety of applications, including improving the knowledge of the spacecraft state vector. The PRIDE measurements can be applied to a broad scope of research fields including studies of atmospheres through the use of radio occultations, the improvement of planetary and satellite ephemerides, as well as gravity field parameters and other geodetic properties of interest, and estimations of interplanetary plasma properties. This paper presents the implementation of PRIDE as a component of the ESA's Jupiter Icy Moons Explorer (JUICE) mission.

We present an overview of the University of Tasmania’s (UTAS) progress in monitoring and providing ground support for space projects. With five radio telescopes distributed across Australia, UTAS has a good capacity to study a wide range of scientific phenomena in our Solar System and to improve the outcome of space missions. High-cadence Mars Express spacecraft observations in the X-band (8.4 GHz) were monitored between 2014 and 2022 using the European Very Long Baseline Interferometry (VLBI) network and UTAS radio telescopes to study interplanetary plasma scintillation and characterise solar wind parameters. The quantification of the plasma’s effect on the radio signal helps in phase referencing for ultra-precise spacecraft tracking. The international collaboration with the China National Space Administration (CNSA) also allowed simultaneous coherent tracking of the interplanetary plasma scintillation for the incoming radio signals of the Mars Express and Tianwen-1 spacecraft. Space weather monitoring has been carried out to study events such as coronal mass ejections using radio signals transmitted by the Solar Orbiter and Solar Heliospheric Observatory (SOHO) spacecraft. The unique radio telescope infrastructure at UTAS will be essential in providing ground support to the Planetary Radio Interferometry and Doppler Experiment (PRIDE) led by the Joint Institute for VLBI ERIC (JIVE). The PRIDE experiment has been chosen by the European Space Agency (ESA) for the JUpiter ICy Moons Explorer mission (JUICE) that will explore three of Jupiter’s moons: Europa, Ganymede, and Callisto. This space mission is scheduled to launch in April 2023. In addition, University of Tasmania has been conducting observations with NASA and JPL for bi-static radar tracking experiments to detect and monitor Near-Earth Asteroids. Over 14 observations have been conducting with UTAS radio telescopes since the beginning of 2021.

The Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique utilize signal recording and processing technology developed originally for Very Long Baseline Interferometry (VLBI) to determine spacecraft lateral position in ICRF, as an extension of conventional radio-tracking techniques [1]. The essence of the PRIDE technique is in observing the spacecraft radio signal with a network of Earth-based radio telescopes. The PRIDE technique, developed at the Joint Institute for VLBI ERIC (JIVE), has been used for numerous experiments with several ESA planetary science missions. PRIDE has been selected by ESA as one of the eleven science experiments of the Jupiter Icy Moons Explorer (JUICE), the L-class mission scheduled for launch in 2023. Figure 1: PRIDE Experiment for the JUICE Mission The main observables of PRIDE are ultra-precise estimates of spacecraft lateral position based on the phase referenced VLBI tracking and radial Doppler measurements [3,7,8]. The methodology of PRIDE has been proven and validated with the ESA's Venus Express & Mars Express [1,2,4,7,8,9]. PRIDE will contribute to the determination of the JUICE spacecraft state vector and the improvement of the Galilean satellite ephemerides [4,5,10]. It is worth noticing the synergistic nature of PRIDE measurements to other key experiments of the JUICE mission, in particular addressing the major science goals of the mission. Figure 2: PRIDE Experiment Planning chart during the cruise phase of the JUICE Mission. Blue dots indicate celestial positions of radio sources with well-defined coordinates suitable for phase-referencing VLBI [reference on the Petrov's online catalogue]. Red dots show those potential reference sources located within 1 degree to the celestial track of the JUICE spacecraft. The paper will describe the analysis and implementation of system engineering methodologies of the PRIDE inputs into the operational design of the JUICE mission. A particular emphasis will be given on cross instrumental analysis and consolidation of top synergies of PRIDE with other JUICE experiments using the ESA science planning tools. The paper will demonstrate advanced methods of efficient experiment planning and block scheduling. The identification of celestial areas of interest in near-field VLBI (PRIDE) observations of interplanetary spacecraft on all phases of their missions, especially during the cruise phase will also be covered in this paper. References 1) D. A. Duev. et al.: Spacecraft VLBI and Doppler tracking: algorithms and implementation, Astronomy & Astrophysics, 541, A43, 2012 2) G. Molera Calves. et al.: Observations and analysis of phase scintillation of spacecraft signal on the interplanetary plasma". In: A&A 564, A4, 2014 3) D. A. Duev. et al.: Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique: A test case of the Mars Express Phobos fly-by, Astronomy & Astrophysics, Vol. 593, 2016 4) Dirkx D. et al.: Dynamical modeling of the Galilean moons for the JUICE mission, Planetary and Space Science 134 (2016) 82–95 5) Dirkx D. et al.: On the contribution of PRIDE JUICE to Jovian system ephemerides, Planetary and Space Science, 14–27, 2017 6) G. Molera Calves. et al.: Analysis of an Interplanetary Coronal Mass Ejection by a Spacecraft Radio Signal: A Case Study, Space Weather, 15 7) T. M. Bocanegra-Bahamón. et al.: Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique: A test case of the Mars Express Phobos Flyby II. Doppler tracking: Formulation of observed and computed values, and noise budget, Astronomy & Astrophysics, 609, A59, 2018 8) T. M. Bocanegra-Bahamón. et al.: Venus Express radio occultation observed by PRIDE, Astronomy & Astrophysics, 624, A59, 2019 9) G. Molera Calvés. Et a.: High spectral resolution multi-tone Spacecraft Doppler tracking software: Algorithms and implementations, Publications of the Astronomical Society of Australia (PASA), 2021 10) Fayolle et al., Decoupled and coupled moons’ ephemerides estimation strategies - Application to the JUICE mission, submitted to Planetary & Space Science, 2022

We monitored the position of the close-by (about 370 Mpc) gamma-ray burst GRB 190829A, which originated from a massive star collapse, through very long baseline interferometry (VLBI) observations with the European VLBI Network and the Very Long Baseline Array, carrying out a total of nine observations between 9 and 117 days after the gamma-ray burst at 5 and 15 GHz, with a typical resolution of a few milliarcseconds. From a state-of-the art analysis of these data, we obtained valuable limits on the source size and expansion rate. The limits are in agreement with the size evolution entailed by a detailed modeling of the multiwavelength light curves with a forward-plus-reverse shock model, which agrees with the observations across almost 18 orders of magnitude in frequency (including the HESS data at TeV photon energies) and more than 4 orders of magnitude in time. Thanks to the multiwavelength, high-cadence coverage of the afterglow, inherent degeneracies in the afterglow model are broken to a large extent, allowing us to capture some unique physical insights; we find a low prompt emission efficiency of less than or similar to 10(-3), a low fraction of relativistic electrons in the forward shock downstream chi ( e ) < 13% (90% credible level), and a rapid decay of the magnetic field in the reverse shock downstream after the shock crossing. While our model assumes an on-axis jet, our VLBI astrometry is not sufficiently tight as to exclude any off-axis viewing angle, but we can exclude the line of sight to have been more than similar to 2 degrees away from the border of the gamma-ray-producing region based on compactness arguments.

&lt;p&gt;&lt;strong&gt;JUICE&amp;#8217;s and Europa Clipper&amp;#8217;s synergistic contribution to the Galilean moons&amp;#8217; ephemerides &lt;/strong&gt;&lt;/p&gt; &lt;p&gt;An accurate determination of the ephemerides of natural satellites is critical to our understanding of planetary systems&amp;#8217; evolution, and of tidal dissipation mechanisms in particular. Diverse interior or dissipation-related parameters can be retrieved when reconstructing the moons&amp;#8217; dynamics from space missions&amp;#8217; radiometric data [1,2,3]. For the Galilean moons of Jupiter, unique challenges complicate the estimation of the satellites&amp;#8217; dynamics, as the Laplace resonances between Io, Europa and Ganymede result in a strongly coupled dynamical problem. Efficiently improving the current ephemerides solution would thus ideally require a balanced data distribution between these moons. In this context, the synergy between the upcoming JUICE and Europa Clipper missions is of primary importance. In particular, the ~ 50 flybys at Europa to be performed by the Clipper spacecraft will efficiently supplement JUICE&amp;#8217;s trajectory (2 flybys at Europa, 7 at Ganymede, 21 at Callisto, followed by a long orbital phase around Ganymede), leading to complementary radiometric data sets. Most importantly, in-system concurrent observations will be possible according to current missions&amp;#8217; schedules. Preliminary analyses show that a joint solution from JUICE and Europa Clipper range and Doppler measurements can improve the estimation solution for the Galilean satellites&amp;#8217; ephemerides and related dynamical properties (&lt;em&gt;e.g.&lt;/em&gt; tidal dissipation parameters) [4].&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Contribution of PRIDE multi-spacecraft observations&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;The Planetary Radio Interferometry and Doppler Experiment (PRIDE) has been selected as one of the eleven experiments of the JUICE (JUpiter ICy moons Explorer) mission [5]. It relies on Very Long Baseline Interferometry (VLBI) techniques to process radiometric signals used for tracking, communications and/or radioscience. The main PRIDE observables are measurements of the spacecraft&amp;#8217;s lateral position with respect to a phase calibrator (VLBI), expressed in the ICRF (International Celestial Reference Frame) [6], but by-product Doppler observables are also generated [7]. Compared to range and Doppler measurements, which are collected in the line-of-sight direction, PRIDE VLBI data are sensitive to the spacecraft&amp;#8217;s position in the two other directions. They thus provide very complementary information, which could help achieving an improved solution for the spacecraft&amp;#8217;s and moons&amp;#8217; states in particular. A previous analysis has quantified the contribution of PRIDE VLBI observations to the Galilean moons&amp;#8217; ephemerides for the JUICE test case [2], using a simplified non-coupled model [8]. A noticeable improvement was indeed obtained in the out-of-plane direction when including VLBI data, especially for Ganymede and Callisto (more data collected at these two moons).&lt;/p&gt; &lt;p&gt;In addition to these single-spacecraft VLBI measurements, the concurrent in-system tracking of the JUICE and Europa Clipper spacecraft will offer PRIDE a unique opportunity to fully exploit the synergy between the two missions&amp;#8217; trajectories. If the two spacecraft are both visible from a telescope (&lt;em&gt;i.e.&lt;/em&gt; in-beam or within the same telescope beam) and simultaneously transmitting a radio signal, it is possible to realise multi-spacecraft VLBI observations, which will directly provide accurate measurements of the relative lateral position of the two spacecraft (right ascension and declination difference in the ICRF). Such observations were already successfully collected between several Martian orbiters (MRO, MEX, TGO) in 2019 [9], as shown in Figure 1.&lt;/p&gt; &lt;p&gt;&lt;em&gt;&lt;img src=&quot;&quot; alt=&quot;&quot; width=&quot;1044&quot; height=&quot;206&quot; /&gt;&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;Figure 1: Simultaneous detection of the signals transmitted by several Martian orbiters and landers, from [9].&lt;/em&gt;&lt;/p&gt; &lt;p&gt;Given the synergistic nature of the JUICE and Clipper trajectories, the signals of the two spacecraft are expected to be visible in the same beam of ground-based telescopes during a significant fraction of their Jovian tours. Looking in detail at JUICE and Clipper flybys&amp;#8217; sequences displayed in Figure 2, the two spacecraft will occasionally perform near-simultaneous flybys around different moons, with typically only a coupled of days between JUICE&amp;#8217;s and Clipper&amp;#8217;s flybys. The relative angular measurements derived from PRIDE VLBI observations might then translate into direct constraints of the moons&amp;#8217; relative states, expected to be extremely valuable for the ephemerides solutions.&lt;/p&gt; &lt;p&gt;&lt;img src=&quot;&quot; alt=&quot;&quot; width=&quot;550&quot; height=&quot;400&quot; /&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;Figure 2: JUICE and Europa Clipper trajectories (altitude with respect to the moons)&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;&lt;strong&gt;Contribution of &lt;/strong&gt;&lt;strong&gt;these&lt;/strong&gt;&lt;strong&gt; observations to the Galilean satellites&amp;#8217; ephemerides &lt;/strong&gt;&lt;/p&gt; &lt;p&gt;Our open-source estimation tool (Tudat(py)&lt;sup&gt;1&lt;/sup&gt;) is now able to concurrently simulate several missions with different trajectories and observation schedules in a single estimation [10]. It is also linked with a VLBI prediction tool allowing to search for suitable phase calibrators close to the spacecraft at any potential observation epoch. Using these functionalities, we perform a simulation study to quantify the potential contribution of multi-spacecraft (in-beam) VLBI observations, also analysing its sensitivity to the observations&amp;#8217; cadence and accuracy.&lt;/p&gt; &lt;p&gt;To this end, we will investigate when multi-spacecraft VLBI observations could be obtained from the JUICE and Clipper spacecraft. This involves searching for suitable phase calibrators and ensuring that both spacecraft are visible from ground telescopes at a given epoch. We will also further investigate promising observation geometries (&lt;em&gt;e.g.&lt;/em&gt; near-simultaneous flybys, see Figure 2). The simulated multi-spacecraft observables will then be added to a joint JUICE &amp;#8211; Clipper estimation, which also includes &lt;em&gt;nominal &lt;/em&gt;&lt;em&gt;(&lt;/em&gt;single-spacecraft) PRIDE VLBI observations for JUICE.&lt;/p&gt; &lt;p&gt;We will then precisely quantify the contribution of these simulated multi-spacecraft VLBI observations to the estimation solution, focusing on the moons&amp;#8217; ephemerides and related dynamical parameters in particular. If proven beneficial, this will motivate the acquisition of such observations during the JUICE and Clipper missions. Additionally, our sensitivity analysis will provide direct recommendations regarding observation scheduling. If need be (&lt;em&gt;i.e.&lt;/em&gt; particularly interesting multi-spacecraft VLBI observation but no phase calibrator in the angular vicinity of the spacecraft), this could also highlight the need to search for yet unknown calibrators in a certain region of the sky.&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;[1] Dirkx et al., Planetary and Space Science 134 (2016): 82-95.&lt;/p&gt; &lt;p&gt;[2] Dirkx et al., Planetary and Space Science 147 (2017): 14-27.&lt;/p&gt; &lt;p&gt;[3] Lainey et al., Nature Astronomy 4.11 (2020): 1053-1058.&lt;/p&gt; &lt;p&gt;[4] A. Magnanini et al., in preparation.&lt;/p&gt; &lt;p&gt;[5] Gurvits et al., European Planetary Science Congress (2013).&lt;/p&gt; &lt;p&gt;[6] Duev et al., Astronomy &amp; Astrophysics 541 (2012): A43.&lt;/p&gt; &lt;p&gt;[7] Bocanegra-Bahamon et al., Astronomy &amp; Astrophysics 609 (2018): A59.&lt;/p&gt; &lt;p&gt;[8] Fayolle et al., submitted to Planetary &amp; Space science (under revision)&lt;/p&gt; &lt;p&gt;[9] Molera Calv&amp;#233;s et al., Publications of the Astronomical Society of Australia, 38, E065&lt;/p&gt; &lt;p&gt;[10] Fayolle et al., EGU General Assembly (2022).&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;div id=&quot;sdfootnote1&quot;&gt;&lt;/div&gt; &lt;div id=&quot;sdfootnote2&quot;&gt; &lt;p class=&quot;sdfootnote&quot;&gt;&lt;em&gt;&lt;sup&gt;1&lt;/sup&gt; https://docs.tudat.space&lt;/em&gt;&lt;/p&gt; &lt;/div&gt; &lt;div id=&quot;sdfootnote1&quot;&gt;&lt;/div&gt; &lt;div id=&quot;sdfootnote2&quot;&gt; &lt;p class=&quot;sdfootnote&quot;&gt;&amp;#160;&lt;/p&gt; &lt;/div&gt;

Probing the solar corona is crucial to study the coronal heating and solar wind acceleration. However, the transient and inhomogeneous solar wind flows carry large-amplitude inherent Alfven waves and turbulence, which make detection more difficult. We report the oscillation and propagation of the solar wind at 2.6 solar radii (Rs) by observation of China Tianwen and ESA Mars Express with radio telescopes. The observations were carried out on Oct.9 2021, when one coronal mass ejection (CME) passed across the ray paths of the telescope beams. We obtain the frequency fluctuations (FF) of the spacecraft signals from each individual telescope. Firstly, we visually identify the drift of the frequency spikes at a high spatial resolution of thousands of kilometers along the projected baselines. They are used as traces to estimate the solar wind velocity. Then we perform the cross-correlation analysis on the time series of FF from different telescopes. The velocity variations of solar wind structure along radial and tangential directions during the CME passage are obtained. The oscillation of tangential velocity confirms the detection of streamer wave. Moreover, at the tail of the CME, we detect the propagation of an accelerating fast field-aligned density structure indicating the presence of magnetohydrodynamic waves. This study confirm that the ground station-pairs are able to form particular spatial projection baselines with high resolution and sensitivity to study the detailed propagation of the nascent dynamic solar wind structure.

The ESA's Mars Express solar corona experiments were performed at two solar conjunctions in the years 2015 and 2017 by a number of radio telescopes in the European VLBI Network. This paper presents the methods to measure the frequency and phase fluctuations of the spacecraft radio signal, and the applications to study the characteristics of the plasma turbulence effects on the signal at a single station and at multiple stations via cross correlation. The power spectra of the frequency fluctuations observed between 4.9 and 76.3 R (s) have a power-law shape close to a Kolmogorov spectrum over the frequency interval nu (lo) < nu < nu (up), where the nominal value of nu (lo) is set to 3 mHz and nu (up) is in the range of 0.03-0.15 Hz. The rms of the frequency fluctuations is presented as a function of the heliocentric distance. Furthermore, we analyze the variations of the electron column density fluctuations at solar offsets 4.9 R (s) and 9.9 R (s) and the cross-correlation products between the VLBI stations. The power density of the differential fluctuations between different stations decreases at nu < 0.01 Hz. Finally, the fast flow speeds of solar wind >700 km s(-1) are derived from the cross correlation of frequency fluctuations at nu < 0.01 Hz. The fast flow speeds of solar wind correspond to the high heliolatitude of the coronal region that the radio rays passed. The VLBI observations and analysis methods can be used to study the electron column density fluctuations and the turbulence at multiple spatial points in the inner solar wind by providing multiple lines of sight between the Earth and the spacecraft.

U. Bach, N. Bartel, O. Bayandina, A. Belonenko, K. Belousov, M. Bietenholz, A. Biriukov, G. Cimò, C. Courde, D. Dirkx, D. Duev, A. Filetkin, G. Granato, L. Gurvits, A. Gusev, R. Haas, G. Herold, G. Ilin, A. Kahlon, B. Kanevsky, V. Kauts, G. Kopelyansky, A. Kovalenko, G. Kronschnabl, V. Kulagin, M. Lindqvist, J.E.J. Lovell, H. Mariey, J. McCallum, G. Molera Calvés, C. Moore, K. Moore, A. Neidhardt, N. Nunes, S. Pilipenko, C. Plötz, S. Pogrebenko, N. Porayko, J. Quick, V. Rudenko, S. Sazankov, A. Smirnov, V. Soglasnov, K. Sokolovsky, V. Stepanyants, P. de Vicente, J. Yang, M. Zakhvatkin et al.