The BepiColombo mission, a collaborative venture between ESA and JAXA, started its journey on October 20, 2018, from the Kourou spaceport in French Guiana, with the goal of reaching Mercury by late 2025. During its 7-year cruise phase, BepiColombo encounters eleven superior solar conjunctions, an alignment where the Sun is positioned between the spacecraft and Earth. The Mercury Orbiter Radio Science Experiment (MORE) utilized the first six conjunctions to test gravitational theories by measuring the relativistic time delay and frequency shift of photons as they pass near the Sun. This process involved collecting range and Doppler data from the ESTRACK DSA-3 antenna in Malargue (Argentina) and NASA’s DSS 25 antenna in Goldstone (California). Over 15 radio tracking passes were scheduled for each of the six campaigns (March 2021, February 2022, July 2022, February 2023, July 2023, and December 2023). A comprehensive calibration process, addressing various noise sources, was essential for conducting the general relativity tests.

Central to the superior conjunction experiments are the onboard Deep Space Transponder (DST) and the Ka-band transponder (KaT). MORE's KaT establishes a two-way coherent radio link in the Ka-band, enabling both uplink and downlink communications and incorporating a novel 24 Mcps pseudo-noise (PN) modulation. The DST supports two-way coherent X/X and X/Ka Doppler and PN ranging at 3 Mcps. Multi-frequency radio links are crucial for calibrating dispersive noise, primarily from solar corona plasma. This technique has been previously employed in Cassini's cruise radio science experiments, providing plasma-free observations up to a minimum impact parameter of 7 solar radii.

Furthermore, the Tropospheric Delay Calibration System (TDCS) at DSA-3 significantly reduces the impact of tropospheric water vapor. The KaT is equipped with a self-calibration loop for measuring the transponder group delay, while the DST relies on pre-flight ground test values. DSA-3's group delay calibration system conducts pre-tracking pass measurements for each link (X/X, X/Ka, Ka/Ka), with continuous in-pass measurements available exclusively for the Ka/Ka link, the primary data source for the radio science experiments.

This work presents the performance of calibrated range and Doppler data from DSA-3 across five solar conjunction experiments. We report the spectral properties of the calibrated residuals, highlighting the improvements achieved through calibration procedures. Notably, these campaigns marked the first use of a plasma-cancellation scheme for calibrating range data, proving effective up to an impact parameter of about 4 solar radii. The final accuracy of the radiometric data was  about 0.02 mm/s  at 60-second integration time and ~4.5 cm at 2 s interval, respectively for range rate and range measurements.

How to cite: di Stefano, I., Cappuccio, P., Doria, I., and Iess, L.: State-of-the-art radio tracking data performance of BepiColombo MORE during cruise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18522, https://doi.org/10.5194/egusphere-egu24-18522, 2024.

Phobos’ orbit is currently known down to a precision of 300m, mostly directed along its track. It has mainly been determined with imagery, and more recently with the Super Resolution Channel of the HRSC camera onboard Mars Express (MEX). This method is associated with an error mainly normal to the plane of imagery. By dynamical constraints, Phobos’ trajectory determination error is mainly spread along its orbit. In order to refine the orbitography and reduce the range error of the measurements, we propose to use data from the MARSIS radar onboard MEX. To do so, we perform a SAR synthesis on the MARSIS data in order to locate the radar echoes in a range/along-track plane. For every one of the 35 datasets at our disposal measured between 2008 and 2021, we also perform a coherent simulation using a Phobos shape model by Willner et al. (2014), and apply the SAR synthesis the same way we did for the MARSIS datasets. Given the geometry of our simulations and the SAR synthesis, the simulated radargrams are not sensitive to a range error of a few km in MEX’s trajectory, they can therefore be taken as reference points. We measure range errors between simulations and MARSIS data, distributed around +1km, with a standard deviation of 350m. The measurements being spread all around Phobos, the most probable cause for the non-zero average of the offsets measurements is an instrumental delay. After subtracting this average from the measurements, we estimate the offset that Phobos would have along its track to create this standard deviation. We find that this offset is of about 100m before 2017, and that the estimated value is rising linearly after this date to reach about 1.3km in 2021, date of our last observation. Since 2017 is the date of the last control point of the NOE-4-2020 ephemeris used for this study, our measurements exhibit a significant drift after this time period suggesting that there may exist a source of inaccuracy in the Phobos ephemeris. This study shows that radar data can be used as control points for the orbitography.

How to cite: Desage, L., Herique, A., Lainey, V., Kofman, W., Cicchetti, A., and Orosei, R.: MARSIS data as a New Constraint for Phobos’ orbit , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16486, https://doi.org/10.5194/egusphere-egu24-16486, 2024.

The nature of the dense lunar ionosphere is controversial; the maximum electron density values in observed vertical profiles obtained from previous Lunar missions vary by two orders of magnitude. NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission consisted of an identical pair of spacecraft approximately 100 km apart in a circular polar orbit around the Moon at a mean altitude of 55 km during the science phase in 2012. The two GRAIL spacecraft conducted various radio science observations to determine the lunar gravity field. As a serendipitous consequence of these primary observations, the one-way spacecraft - Earth radio occultation observations of the lunar ionosphere were acquired using a carrier-only X-band radio signal from the Radio Science Beacon referenced to an onboard ultrastable oscillator (USO). GRAIL’s X-band Radio Science beacon (RSB) data provide applicability for the radio occultation of the lunar electron density profiles with the uncertainty of frequency residual measurement ~ 1 mHz corresponding to ~  2x10⁸ m^-3 electron density uncertainties. We will present our analysis of the electron density profiles retrieved from GRAIL Radio Science Beacon data to understand the formation and variations of the moon ionosphere. The findings of GRAIL results will improve our understanding of how those variations are spatial (e.g., latitude, longitude, solar zenith angle) or temporal (e.g., responses to external factors, such as meteor impacts and solar winds) during the GRAIL mission period.

How to cite: Yang, Y.-M., Oudrhiri, K., Withers, P., Erwin, D. A., Buccino, D. R., and Haha, I.: Investigating Lunar Ionosphere Using GRAIL Radio Science Signals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12526, https://doi.org/10.5194/egusphere-egu24-12526, 2024.

The JUpiter ICy moons Explorer (JUICE) is an ESA mission launched from the Kourou spaceport in French Guyana on April 14, 2023, with an Ariane 5 rocket. After the initial LEOP (Low Earth Orbit Phase) operations, completed within three days from launch, the mission entered the NECP (Near Earth Commissioning Phase) that lasted approximately 6 months and included the first functional checkout of the entire assembly of JUICE instruments, comprising 10 different scientific payloads. The spacecraft will arrive in the Jovian system in 2031, after an almost 8-year cruise phase. During the interplanetary phase, the JUICE scientific instruments will be routinely switched on and monitored during regular payload checkouts (occurring approximately twice per year), each lasting less than 2 weeks in total.

The 3GM (Gravity and Geophysics of Jupiter and the Galilean Moons) radio science instrument package comprises a Ka band Transponder (KaT), an Ultra Stable Oscillator (USO), and a High Accuracy Accelerometer (HAA). The KaT is a radio frequency equipment enabling a highly stable two-way coherent link at Ka band (34-32.5 GHz) and it is the key element of the 3GM gravity measurements. The USO will generate on board a highly stable, 57.5 MHz reference signal upconverted to both X- and Ka band to perform dual-frequency one-way downlink radio occultation experiments. The HAA will be used in support of radio science observations to calibrate the non-gravitational accelerations in the [10^-4-10^-1] Hz frequency band, mostly coming from propellant sloshing.

We report the results obtained by the analysis of the initial 3GM data collected during the NECP and the first Payload Checkout phases.

How to cite: Di Benedetto, M., Cappuccio, P., Galanti, E., Iess, L., Kaspi, Y., and Smirnova, M.: Report on initial inflight data of JUICE’s 3GM radio science instrument, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16747, https://doi.org/10.5194/egusphere-egu24-16747, 2024.

The LUCY spacecraft was launched in 2021. The main objective of the NASA mission is to characterize several trojan asteroids. These outer solar system asteroids are located in the Lagrange points L4 and L5 of the Jupiter-Sun system.

The first flyby will be at (3548) Eurybates and its moon Queta in August 2027, followed directly by the flyby at (15094) Polymele with its moon Shaun (informal name) in September 2027. Two more flybys in the so-called Greek camp in the L4 point are at (11351) Leucus in April 2028 and at (21900) Orus in November 2028. After orbiting the Sun once more the spacecraft will reach the L5 swarm of asteroids and will flyby at the binary system of (617) Patroclus and Menoetius in March 2033.

During these flybys the mass of the target asteroids shall be determined using the Doppler tracking method. Analytic solutions for the error estimation of the mass determination have already shown that the required precision will be met. However, this analytic approach does not take into account several error sources like time limited tracking, no Doppler data +/- 2h around closest approach, uncertainties in the initial spacecraft position and velocity for a flyby, non-gravitational forces, etc. Another contributing error source is the Doppler noise imposed on the signal. Doppler data from ESAs Rosetta mission and NASAs New Horizons spacecraft as well as tracking data recorded during the first 2 1/2 years of LUCYs cruise phase could be analyzed regarding distance, solar wind turbulence, integration times etc.

A numeric orbit determination using simulated Doppler data can provide the most realistic error estimation using all perturbing forces and uncertainties. A detailed analysis of the error of the mass determination for all flybys shall be presented.

How to cite: Hahn, M., Paetzold, M., Andert, T., Levison, H., Noll, K., and Marchi, S.: Trojan Asteroid Mass Determination using the Radio-Science Experiment onboard the LUCY Mission, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18583, https://doi.org/10.5194/egusphere-egu24-18583, 2024.

The latter part of Juno’s extended mission from 2023-2025 provides numerous opportunities to conduct radio occultation experiments of Jupiter’s atmosphere and ionosphere. Juno’s radio science instrumentation, consisting of dual X-band (8.4 GHz) and Ka-band (32 GHz) radio links to NASA’s Deep Space Network (DSN), was designed for precise measurements of Jupiter’s gravity field at a range-rate precision of <10 um/s. This work describes the preparation campaign undertaken to adapt the existing instrumentation and spacecraft design to make precise radio occultation measurements of Jupiter’s atmosphere and ionosphere. Due to lack of onboard stable frequency reference, the spacecraft will conduct these occultations in a coherent mode, where the downlink signal is coherent with the uplink from the DSN. Although the spacecraft cannot perform a maneuver to counteract the refractive bending, small bias attitudes will be implemented to increase the depth of the occultation measurements. These two constraints required significant preparation work to ensure successful data collection. These occultations will result in atmospheric temperature-pressure profiles down to 500 mbar and ionospheric electron density profiles across a wide range of latitudes, including in the polar and auroral regions of the gas giant.

How to cite: Buccino, D., Parisi, M., Oudrhiri, K., Ryan, P., and Steffes, P.: Planning and Execution of Juno’s Radio Occultation Campaign, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12638, https://doi.org/10.5194/egusphere-egu24-12638, 2024.

NASA’s Juno spacecraft successfully completed its prime mission in 2021 by performing 33 close encounters with Jupiter, and it is presently in its extended phase. These encounters, known as perijoves, occurred every 53 days at altitudes of about 4,000 kilometers above the planet's 1-bar surface and were specifically designed to study Jupiter's magnetosphere, atmosphere, and gravity field. During the nominal mission, Juno’s gravity science experiment achieved an unparalleled level of accuracy in resolving the planet’s low- and high-degree zonal gravity field. By employing precise Doppler-tracking techniques via X- and Ka-band radio links, scientists were able to estimate Jupiter’s gravity moments and rotational parameters, offering insights into its internal structure and deep atmospheric dynamics.

Prior to the initial science perijove in 2016, there were plans to reduce the Juno orbital period from 53 days to 14 days, marking the beginning of science operations. However, a potential anomaly in the propulsion system led to the decision to keep Juno in its 53-day orbit, lengthening the duration of the prime mission by roughly a factor of four. This had far-reaching implications, impacting both science operations and mission management. Nevertheless, the Juno team adeptly adapted to these unforeseen circumstances by promptly laying out a new mission plan. The change in the orbital period also held significant consequences from a scientific point of view: for instance, the ability to carry out Jupiter's radio occultations during the extended mission is directly related to this event. Here we explore in detail the repercussions from a radio science operations and gravity science point of view and discuss the impact of orbital period changes on reaching the experiment’s prime mission objectives.

© 2024 California Institute of Technology. Government sponsorship acknowledged.

How to cite: Parisi, M., Buccino, D. R., and Oudrhiri, K.: Changing Juno's orbital period and its effect on gravity science at Jupiter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12723, https://doi.org/10.5194/egusphere-egu24-12723, 2024.

EnVision has been selected in the M5 call of ESA’s Cosmic Vision program as the next European led mission to Venus. It is dedicated to unravel some of the numerous open questions about Venus' past, current state and future and will help to understand why Venus and Earth evolved so differently.

The Radio Science Experiment (RSE) on EnVision will perform extensive studies of the gravitational field but also Radio Occultations to sense the Venus atmosphere and ionosphere at a high vertical resolution of only a few hundred metres. These radio occultations provide electron density profiles in the ionosphere and atmospheric density, temperature and pressure profiles in the upper troposphere and mesosphere (~40 – 90 km). Additionally, they allow to study the H₂SO₄ absorption in the Venus cloud layer.

The first radio occultation experiment at Venus was conducted during the Mariner 5 flyby in 1967, followed by Mariner 10, several Venera missions, Magellan, and the Pioneer Venus Orbiter, and Akatsuki. The most extensive radio occultation study of the Venus atmosphere so far was carried out by the VeRa experiment on Venus Express.

EnVision will use two coherent frequencies (X- and Ka-band) to separate dispersive and nondispersive effects. This allows to distinguish between ionospheric wave structures and other noise induced effects in the ionosphere.

The use of Ka-band, which has never been used to sense the Venus atmosphere before, allows to study the H₂SO₄ absorption in the Venus cloud layer due to its high sensitivity to sulfuric acid absorption. Ka-band is also sensitive to liquid H₂SO₄ which provides the opportunity (in combination with X-band) to distinguish between gaseous and liquid H₂SO₄ absorption features on Venus for the very first time.

The short orbital period of EnVision in combination with its very small orbital inclination allows to cover all latitudes, longitudes, local times and solar zenith angles on Venus. Especially short-term variations caused by atmospheric waves can be identified to study traveling or stationary small scale atmospheric structures.

How to cite: Tellmann, S., Oschlisniok, J., Pätzold, M., Dumoulin, C., and Rosenblatt, P.: Radio Sounding of the Venusian Atmosphere and Ionosphere with EnVision , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9719, https://doi.org/10.5194/egusphere-egu24-9719, 2024.

With a targeted launch in October 2024, the European Space Agency’s Hera mission is set to rendezvous with the Didymos binary asteroid system in early 2027 and aims to conduct a detailed post-impact survey of the system following NASA’s DART impact on the smaller asteroid Dimorphos.

This work describes the Hera Radio Science Experiment (RSE), which aims to precisely estimate the values of some key physical parameters of Didymos and Dimorphos, including their mass, extended gravity field, rotational state, and absolute and relative orbits. The expected accuracies in the parameters of interest are evaluated through a multi-arc covariance analysis performed using Caltech-JPL’s MONTE code.

The analysis will show the information content provided by various observation types collected during the mission, including Earth-based radiometric measurements, optical images, altimetry measurements, and satellite-to-satellite tracking of the Juventas and Milani CubeSats. Furthermore, the influence of the dynamical model implemented within the orbit determination filter will be addressed regarding achievable accuracies of the estimated parameters and operational considerations.

How to cite: Lasagni Manghi, R., Gramigna, E., Zannoni, M., Tortora, P., Park, R. S., Tommei, G., Le Maistre, S., Kueppers, M., and Michel, P.: The Hera Radio Science Experiment at Didymos, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17409, https://doi.org/10.5194/egusphere-egu24-17409, 2024.

Europa Clipper is the next NASA Flagship mission that will explore Jupiter’s moon Europa. It has a rich payload with ten instruments and investigations, including the Gravity and Radio Science investigation (G/RS). The synergistic science made possible will provide a synoptic view of the Europa system. The overarching goal of Europa Clipper is to Explore Europa to Investigate its Habitability with a number of science objectives and themes related to its ice shell and ocean, its composition, its geology, and its potential recent activity. The Europa Clipper spacecraft is currently undergoing assembly and testing at NASA JPL (follow live on Youtube! https://bit.ly/clippercam) and it will be shipped to KSC in early 2024. The launch window opens on October 10, 2024.

With 49 planned flybys, the tour trajectory samples Europa globally, but not evenly, with gaps at 90° and 270° longitude due to the constraints of the multiple-flyby mission design strategy to limit radiation impacts. Flyby altitudes typically vary between 25 km and 100 km, providing for higher sensitivity to shorter-wavelength gravity signal. The primary raw data for the G/RS investigation are collected from DSN 70-m antennas through Open-Loop Receivers (OLRs) in the ±2h periods around each flyby, leveraging the telecom subsystem’s three fan beam (FBA) and two low-gain (LGA) antennas because the high-gain antenna (HGA) is not steerable.

The highest priority for the G/RS investigation is to obtain an accurate measurement of the tidal Love number k₂, which describes the amplitude of the gravitational response of Europa to the forcing tidal potential imposed by Jupiter. The measurement requirement is set at an uncertainty of 0.06 to provide an unambiguous independent assessment of the presence of an ocean. Expectations from orbit determination simulations show a robust margin of 3-4 times. Simulations of the gravity field recovery show that the low-degree gravity field can be resolved to degrees 5-10, depending on the assumptions for the level of gravity anomalies in the truth field.

The interior structure of Europa will be informed by its hydrostatic equilibrium state (a current assumption as the Galileo data is not sufficient to independently estimate J2 and C22) and its moment of inertia. Given the uneven low-altitude spatial sampling, “Line-of-Sight” (LOS) analysis techniques will be important to extract the most from the signatures in the radio Doppler data. Other constraints on the ice shell, ocean, and seafloor will be possible especially in combination with the data collected by the other Europa Clipper instruments. Moreover, Europa Clipper will probe Europa’s ionosphere with radio occultations, with geographic coverage complementary to in situ instruments.

The G/RS team is currently supporting Phase D efforts, developing cruise activities, and finalizing the PDS archive plans. We will report on the current G/RS science and operational plans.

How to cite: Hussmann, H., Mazarico, E., Buccino, D., Castillo, J., Dombard, A., Genova, A., Kiefer, W., Lunine, J., McKinnon, W., Nimmo, F., Park, R., Roberts, J., Steinbrügge, G., Tortora, P., Withers, P., Cascioli, G., Magnanini, A., Petricca, F., and Zannoni, M.: The Europa Clipper Gravity and Radio Science Investigation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19053, https://doi.org/10.5194/egusphere-egu24-19053, 2024.