Since 2023, three different solutions for the latest (2020) realization of the International Terrestrial Reference System (ITRS) are publicly available, namely the ITRF2020, the JTRF2020 and the DTRF2020. All solutions are based on the same input data but were derived using different combination approaches and data correction strategies. Since the ITRS realizations are used as a priori reference frames for precise orbit determination (POD) of Earth orbiting satellites, it is important to investigate the impact of the different frames on the POD results.

In this study, we briefly introduce the different features of the ITRS realizations and elaborate how the data correction models (e.g., periodic variations vs. non-tidal loading corrections) of the different xTRF2020 solutions can be optimally applied for the POD of selected satellites tracked by Satellite Laser Ranging (SLR) stations. We conclude the study with results obtained for various orbital parameters, such as the scaling factor of the non-gravitational (non-conservative) accelerations as well as the estimated empirical accelerations. Finally, we summarize the optimal settings of each ITRS realization for the satellite PODs discussed in this paper (i.e., LAGEOS-1, LARES-2, Jason-1/2/3).

How to cite: Bloßfeld, M., Zeitlhöfler, J., Rudenko, S., and Seitz, M.: Application of ITRS 2020 realizations for the SLR-based POD of selected geodetic and Earth-observing satellites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5385, https://doi.org/10.5194/egusphere-egu24-5385, 2024.

Satellite Laser Ranging (SLR) observations are provided by a global station network of the International Laser Ranging Service (ILRS). Since almost all SLR stations are unique in terms of utilized equipment, e.g., laser system, photo-detector or timing devices, their measurement performances may slightly differ. Furthermore, the tracked satellites have various properties, e.g., material composition (number and type of retro-reflectors or mantel material), diameter, area-to-mass ratio, altitude or inclination, which have an impact on the measurement precision and the requirements on the background force modeling. A reliable estimation of geodetic parameters solely based on SLR can only be performed by combining SLR observations to several spherical satellites provided by the entire ILRS network. To take the quality of each individual SLR measurement into account, several stochastic models, e.g., static or time-variable station- and/or satellitespecific weights, are introduced and their impact on the parameter estimation is studied.

How to cite: Geisser, L., Meyer, U., Arnold, D., and Jäggi, A.: Stochastic Modeling of SLR Observations and its Impact on the Parameter Estimation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5649, https://doi.org/10.5194/egusphere-egu24-5649, 2024.

The Galileo for Science Project (G4S_2.0) is funded by the Italian Space Agency and has several goals in the field of Fundamental Physics to be achieved by exploiting the satellites of the Galileo-FOC Constellation. In this regard, a key point is to obtain a suitable satellite orbit solution by performing an accurate Precise Orbit Determination (POD). To this purpose modeling in a reliable way the complex effects of the Non-Conservative Forces, i.e. of Non-Gravitational Perturbations (NGPs), is essential. The activities undertaken in the construction of a Box-Wing model and of a Finite Element Model of the satellite will be presented with the preliminary results obtained by including these models into the POD of the Galileo satellites. In particular, using the orbital element residuals obtained from a POD we can test our new models and the improvements in POD quality.

How to cite: Lefevre, C., Visco, M., Lucchesi, D., Sapio, F., Peron, R., Cinelli, M., Di Marco, A., Fiorenza, E., Loffredo, P., Lucente, M., Magnafico, C., Santoli, F., and Vespe, F.: The Galileo for Science project: Non-Conservative Forces modeling for the Galileo FOC satellites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16819, https://doi.org/10.5194/egusphere-egu24-16819, 2024.

Within the IGS, it was agreed that Precise Point Positioning (PPP) based on satellite orbit and clock corrections of the IGS analysis centers allow a direct access to the IGS realization of the International Terrestrial Reference Frame (ITRF). This convention is considered convenient for all PPP users and should not be changed in future.

On the other hand, the groups determining the GNSS satellite orbits do prefer an origin of the frame that is related to the Earth instantaneous center of mass since this is the reference of the gravitational orbit force model. With this background, some discussions take place to change the convention related to the origin of the terrestrial frame because it is convenient for the orbit determination. This convention is, however, in contradiction to the expected needs of the PPP users that do prefer a stable coordinate origin in time.

We will introduce a strategy to serve both needs by applying the center of mass corrections for the orbit determination only.

How to cite: Dach, R., Arnold, D., Brockmann, E., Kalarus, M., Prange, L., Schaer, S., Stebler, P., and Jäggi, A.: Review the IGS Strategy for Precise Point Positioning Applications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16959, https://doi.org/10.5194/egusphere-egu24-16959, 2024.

All BeiDou global navigation satellite system (BDS-3) satellites are equipped with Ka-band inter-satellite link (ISL) payloads to achieve the inter-satellite ranging and communication. With the rapid development of low earth orbit (LEO) satellites, the LEO onboard BDS-3 observations also become available. The LEO onboard and ISL data can be an effective supplement for precise orbit determination (POD) of the BDS-3 satellite. In this research, we processed the integrated POD of BDS-3 and LEO satellites with the real ground station, LEO onboard GNSS, and ISL observations. To analyze the contribution of different data to BDS-3 POD accuracy, four POD schemes are present: ground stations only, ground stations + 1 LEO, ground stations + ISL, and ground stations + 1 LEO + ISL. The ground tracking data are from about 40 globally distributed ground stations and 10 stations in Asia-Pacific region, respectively. The LEO onboard GNSS observations are from a dual-constellation GNSS receiver of the LUTAN-01A satellite, which is a Chinese LEO synthetic-aperture-radar (SAR) satellite for geological observation. The Ka-band observations from more than 400 ISL established between BDS-3 satellites are also used in the integrated POD. The obtained orbits are evaluated by orbit overlaps comparison, the comparison with IGS analysis center precise orbits, and SLR (satellite laser ranging) validation. Compared to the POD using the observation of only 10 ground stations, the addition of 1 LEO onboard GNSS or ISL observations can improve the orbit accuracy of BDS-3 by more than 60%. Furthermore, adding both LEO onboard GNSS and ISL observations simultaneously can lead to further improvements in BDS-3 orbit accuracy.

How to cite: Chen, H., Geng, T., Xie, X., Li, Q., Su, X., and Zhao, Q.: Enhanced orbit determination for BDS-3 satellites with LEO onboard GNSS and inter-satellite link data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7776, https://doi.org/10.5194/egusphere-egu24-7776, 2024.

How to cite: Salas, M., Fernández, J., and van den IJssel, J.: Precise Relative Navigation in Medium Earth Orbits with Global Navigation Satellite Systems and Intersatellite Links for Black Hole Imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13048, https://doi.org/10.5194/egusphere-egu24-13048, 2024.

The ESA GENESIS mission, which obtained green light at ESA's Council Meeting at Ministerial Level in November 2022 and which is expected to be launched in 2027, aims to significantly enhance the accuracy and stability of the Terrestrial Reference Frame (TRF). This shall be achieved by equipping one satellite at approximately 6000 km altitude with well-calibrated instruments for all four space-geodetic techniques contributing to TRF realizations, i.e., Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), and by exploiting the such realized very precise space collocations.

The GENESIS satellite is foreseen to carry a zenith- and nadir-pointing GNSS antenna to track (at least) GPS and Galileo signals. Because of its very high altitude, GENESIS will cover much larger nadir angles as seen from the GNSS transmitting antennas, compared to receivers at ground or in low Earth orbit. This will partly result in GNSS observations with lower signal-to-noise ratios. Furthermore, to date, only little reliable information is available on the GNSS transmit antenna gain and carrier phase patterns at very large nadir angles. These problems lead to questions with respect to the best possible exploitation of GNSS data by GENESIS, e.g., whether phase pattern calibrations will need to be performed by means of tracked GNSS data (which would weaken the GNSS contribution to GENESIS).

The aim of this study is to assess the impact of GNSS transmit antenna phase pattern errors on the GNSS-based POD of GENESIS, as well as global GNSS network solutions for GNSS orbits and clock corrections, Earth rotation and geocenter parameters and station coordinates based on GNSS observations from GENESIS and terrestrial stations. To accomplish this, we employ simulated GNSS pseudo-range and carrier phase data for GENESIS and ground stations, which have been generated based on detailed link-budget computations and a comprehensive set of transmit antenna gain patterns. The data are used for closed-loop simulation investigations, which allow to compare the reconstructed orbit and geodetic parameter solutions to the simulation truth and offer a quantification of the impact of transmit antenna phase pattern uncertainties on the estimated parameters.

How to cite: Arnold, D., Miller, A., Kobel, C., Montenbruck, O., Steigenberger, P., and Jäggi, A.: GNSS-based orbit and geodetic parameter estimation by means of simulated GENESIS data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12683, https://doi.org/10.5194/egusphere-egu24-12683, 2024.

The GENESIS mission plays a pivotal role in the FutureNAV program envisioned by the European Space Agency. This groundbreaking venture aims to co-locate four space geodetic techniques on a single platform in space. One of the primary mission objectives is accurately determining geodetic parameters, including geocenter motion, low-degree gravity field, Earth rotation parameters, and the positions of ground stations in tracking networks. Although preliminary satellite inclination and altitude were provided, there is untapped potential for studying ways to enhance the efficiency of incorporating GENESIS into geodetic products.

This research focuses on the preliminary optimization of GENESIS orbital parameters – semi-major axis, inclination, and eccentricity- to assess the benefits arising from diverse observation geometries on geodetic products. The analysis is based on simulations of different variants of GENESIS orbital parameters tracked by a network of 20 satellite laser ranging (SLR) stations. We provide GENESIS-only solutions as well as the combined solution with a selected subset of geodetic satellites that are used today or in the future for the realization of the terrestrial reference frames: LAGEOS-1, LAGEOS-2, LARES-1, and LARES-2. GENESIS will be equipped with two GNSS receivers contributing to high-accuracy orbit determination, serving as a priori parameters for SLR-based solutions. Therefore, we check the GENESIS sensitivity to global geodetic parameters, assuming that the precise orbits are not derived from SLR but can be well-defined from other techniques.

We study the impact of different GENESIS orbits on the gravity potential parameters, especially the zonal terms, Earth rotation parameters, and geocenter coordinates. Our findings underscore that, through meticulous processing, GENESIS has the potential to significantly contribute to achieving the goals of the Global Geodetic Observing System (GGOS), particularly in terms of refining the Z component of the geocenter coordinates.

How to cite: Kur, T. and Sośnica, K.: Sensitivity of different variants of GENESIS orbit to global geodetic parameters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6359, https://doi.org/10.5194/egusphere-egu24-6359, 2024.

Orbital elements define the shape, size, and orientation of a satellite’s orbit, as well as the position of the orbiting satellite along the ellipse at a specific time. Currently, precise orbit determination relies solely on satellite observations. However, future plans involve equipping Genesis and Galileo satellites with Very Long Baseline Interferometry (VLBI) transmitters. This would enable to observe satellites with VLBI radio telescopes and allow to determine orbital elements from VLBI observations to satellites.

This study investigates the potential of VLBI observations to satellites to contribute to the determination of orbital elements. In a first step, schedules, including satellite and quasar observations, are created using VieSched++.  The Vienna VLBI and Satellite Software (VieVS) is used to simulate and analyze these schedules.  To introduce the orbital elements in the Least Squares Adjustment, the partial derivatives of the position vector with respect to the orbital elements are needed. There are different approaches available for computing these partials, including numerical, analytical, or using partials obtained from the ORBGEN module in the Bernese GNSS software.  Next, the partials of the position vector are utilized to determine the partial derivative of the time delay tau with respect to the orbital elements.

This enables the estimation of orbital elements from simulated VLBI observations to satellites. The estimated parameters' quality is evaluated based on the mean formal errors and repeatabilities. Furthermore, the correlations between all orbital elements are examined.

How to cite: Wolf, H., Böhm, J., and Hugentobler, U.: Potential of VLBI observations to satellites to estimate orbital elements , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2806, https://doi.org/10.5194/egusphere-egu24-2806, 2024.

Improving the concepts of Global Navigation Satellite Systems (GNSS) has become a vital task for subsequent GNSS applications like the determination of the Terrestrial Reference Frame (TRF). A promising goal is the reduction of uncertainties in non-conservative force modeling such as Solar Radiation Pressure (SRP) modelling in Precise Orbit Determination (POD) and the effect on the estimated orbits and geocenter coordinates. In previous simulation studies, accelerometers on next-generation GNSS satellites have proven to be a promising opportunity. In this way, the periodic signals in the estimated geocenter coordinates induced by SRP mismodeling can be eliminated regardless of the angle of the Sun to the satellite and its orbital plane. At the same time, the satellite clock can be effectively decoupled from the satellite position estimates. In this study, we focus on the impact of highly accurate clocks and the synchronization of clocks between satellites, which would make it possible to estimate common clock parameters for the synchronized satellites. In doing so, we start with Galileo-type POD using prior simulated observations with the assumption of perfectly known clocks. Then, we simulate various scenarios assuming different clock models and compare the results with the perfect case scenario. This procedure will explore the potential of various ground reference and satellite clock accuracies. Additionally, we use inter-satellite links to synchronize the satellite clocks over one and over multiple orbital planes. Finally, we strive to assess the potential of improved clock modeling on the TRF, focusing on the estimation of geocenter coordinates.

How to cite: Schreiner, P., Glaser, S., König, R., Neumayer, K. H., Raut, S., and Schuh, H.: On the potential of highly accurate clocks and inter-satellite clock synchronization for GNSS satellite precise orbit and geocenter determination, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16139, https://doi.org/10.5194/egusphere-egu24-16139, 2024.

The Galileo for Science Project (G4S_2.0) is funded by the Italian Space Agency and has
several goals in the field of Fundamental Physics to be achieved by exploiting the satellites
of the Galileo-FOC Constellation and the accuracy of their onboard atomic clocks. In
particular, the clock-bias, estimated in the data reduction of the tracking observations
allows to place constraints on the possible presence of Dark Matter in our galaxy in the
form of Domain Walls (DW) eventually produced in the very early Universe by ultralight
scalar field(s). The impact of the DW on an atomic clock would provide a delta-like
transient shift on the pseudo-derivative of the clock-bias. Such signal depends both on the
nature of the clock and the characteristics of the ultralight scalar comprising the DW.
Ongoing work on the clock-bias will be introduced as regards to data pre-processing and
simulations on false alarm and detection efficiency.

How to cite: Di Marco, A., Sapio, F., Visco, M., Lucchesi, D., Cinelli, M., Fiorenza, E., Lefevre, C., Loffredo, P., Lucente, M., Magnafico, C., Peron, R., Santoli, F., and Vespe, F.: The Galileo for Science project: Constraints on Dark Matter with the Galileo-FOC Constellation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18289, https://doi.org/10.5194/egusphere-egu24-18289, 2024.

The Copernicus Precise Orbit Determination (CPOD) Service delivers, as part of the Ground Segment of the Copernicus Sentinel-1, -2, -3, and -6 missions, orbital products and auxiliary data files for their use in the corresponding Payload Data Ground Segment (PDGS) processing chains at ESA and EUMETSAT, and to external users through the newly available Copernicus Data Space Ecosystem (https://dataspace.copernicus.eu/).

For the last few years, a progressive degradation of the accuracy of some of the CPOD orbital products has been observed, caused by the increasing solar activity. Solar activity follows an 11-year cycle, and since the minimum in 2020, overall solar activity has been higher and geomagnetic storms have been happening more often. This has two impacts on POD: a more “turbulent” atmosphere which brings higher frequency density changes, making the modelling of the satellite´s drag more challenging, and an increase of ionospheric scintillation, particularly over the polar regions, that causes an increase of the GNSS carrier phase noise.

This study aims at characterising better the impact of the solar activity on the different POD products, with a focus on the degradation of orbit determination and predictions required by the Sentinel-1 mission. Overall tendencies since the solar minimum in 2020 are analysed, including a detailed look on strong geomagnetic storms. Mitigation strategies to overcome this situation are evaluated, namely adapting the POD processing dynamic parametrisation, and updating the solar activity proxies (particularly the geomagnetic indexes) more frequently.

How to cite: Lara Espinosa, S., Fernández, C., Fernández, M., Peter, H., and Féménias, P.: Copernicus POD Service – Impact of High Solar activity on POD, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8756, https://doi.org/10.5194/egusphere-egu24-8756, 2024.

For radar altimetry missions such as Sentinel-6, a precise orbit is mandatory for deriving reliable sea surface heights. In addition to accurate tracking measurements, precise orbit determination relies on high-fidelity non-gravitational force models. At 1300km the solar radiation pressure (SRP), which varies mainly with the satellite’s orientation towards the Sun, is the dominating non-gravitational force. Additionally, the acceleration due to the Earth radiation pressure (ERP) acts on the satellite and decreases with increasing satellite altitude. As the radiation of Sun and Earth is partly absorbed at the satellite’s surface, the satellite experiences an additional force due to the thermal reradiation of heat (thermal reradiation pressure, TRP). Aerodynamic forces are in constrast negligible at around 1300km altitude.

In previous investigations, we extended the conventional radiation pressure force models with a focus on a GRACE-like satellite. Our SRP and ERP model extensions can be easily applied to other satellites with available geometry and thermo-optical material properties. However, transferring the heat-conductive TRP model to other satellites is more challenging, as assumptions on the materials’ thermal diffusivity and thickness as well as inner heat sources need to be made to adequately model the satellite’s surface temperature.

In this study, we attempt to develop a TRP force model for Sentinel-6. We depart from GRACE settings and refine our model stepwise. Boundary conditions are updated and the material properties are replaced with available information or assumptions. Then, a stepwise tuning is necessary to match the modelled surface temperatures with thermistor measurements. We choose one beta cycle during the year 2023 for our experiments. Preliminary investigations reveal that the tuning of the satellite’s thermal properties varies strongly with the beta angle.

How to cite: Vielberg, K., Kusche, J., and Peter, H.: Tuning thermal reradiation pressure accelerations for Sentinel-6, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7841, https://doi.org/10.5194/egusphere-egu24-7841, 2024.

The density of the upper atmosphere can be determined by orbit and accelerometer data from low Earth orbit satellites. Especially the accelerometers of geodetic satellites, measuring the non-gravitational accelerations acting on them are a very viable observation.

The density estimation is mainly based on three separate disciplines, which are: (1) Precise radiative non-gravitational force modelling, (3) Modelling of the interaction between the rarefied atmospheric gases and the satellite, i.e. modelling of drag coefficients, and (3) the calibration of the accelerometer data by dynamic Precise Orbit Determination (POD). This contribution focuses mainly on the last point. Nevertheless, we also validate the modelled radiative accelerations and use them as reference for the calibration results.

The accelerometers of all geodetic satellites are affected by a drifting bias and scale factors unequal to one. Therefore a calibration of the data is indispensable. Usually time dependent bias and scale factors are estimated. For standard POD or Gravity Field Recovery (GFR) these parameters are estimated together with empiric and other model parameters. In both cases, the estimated accelerometer calibration parameters are not of major interest, but improve the orbit fit or gravitational field coefficients. The used parametrizations and weighting strategies of the observation data, do not give realistic or physical accelerometer calibration results because parameters are not sensitive and effects are absorbed or smeared into other parameters and models. This is unsatisfying, especially for the anticipated use for the density determination.

In this contribution we use dynamic POD and investigate different parametrization strategies tailored for a physical accelerometer calibration. We investigated the effect of constraining the accelerometer calibration parameters in that way, that a continuous calibration over all arcs is achieved, where normally each arc is treated locally separated from all other arcs. The scale factor is concurrently estimated, but over a longer batch of arcs. We varied the length between one day and years. Furthermore, different calibration equations, different observation data and combinations (kinematic positions, science orbit data, inter-satellite ranging), weighting strategies, initial parameters and pre-processing of the accelerometer data is investigated. The validation of the results is not easy, because usual metrics like post-fit residuals do not reflect the quality of the accelerometer calibration. We introduce a validation approach using the modelled non-gravitational forces and also show the influence of the different calibration options on the resulting density or drag acceleration.

All results and data for the whole GRACE and GRACE-FO missions are available on our data server (link in presentation/ uploaded material). 

How to cite: Wöske, F., Rievers, B., and Huckfeldt, M.: Tailored accelerometer calibration by POD for thermospheric density computation with GRACE and GRACE-FO, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20733, https://doi.org/10.5194/egusphere-egu24-20733, 2024.

The variability of the atmospheric drag force on satellites is influenced by several factors, which include neutral density and gas composition, solar activity, and the orientation and shape of the satellite. During periods of geomagnetic activity, changes in these properties contribute to significant variations in the drag force, impacting the satellite trajectory. Therefore, the atmospheric drag force is considered as one of the largest sources of error in the orbit estimation for Low Earth Orbit (LEO) satellites. The methods presently used for satellite orbit determination define a constant term to represent the drag force, which can result in significant errors in long-term propagation and prediction of satellite positions. This work aims to improve SGP4 orbit propagation method by updating the drag term at regular intervals. The estimation of the drag term implements atmospheric drag analysis, which involves calculating the satellite drag coefficients using different Gas-Surface Interaction (GSI) models and neutral density data from Global Ionosphere Thermosphere Model (GITM) to estimate the mean motion derivative. The results demonstrate improved orbit propagation and estimation of orbital decay for the Gravity Recovery and Climate Experiment (GRACE) and Communication/Navigation Outage Forecasting System (C/NOFS) satellites during selected periods containing quiet and storm times.

How to cite: Dey, S., Anderson, P., and Bukowski, A.: Improving Orbit Propagation of LEO Satellites Using Atmospheric Drag Analysis   , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-827, https://doi.org/10.5194/egusphere-egu24-827, 2024.

GNSS processing for POD suffers from systematic errors when the location of the instantaneous phase center is not known
with a few millimeter accuracy. The traditional approach to model the GNSS phase center origin and variations is to
determine antenna phase maps iteratively from the residuals. A more direct approach consists in modeling the antenna
phase map through an expansion in well-chosen Zernike polynomials, in order to reduce potential correlations with dynamic
modeling errors. This strategy has been applied to derive the GNSS antenna phase maps of several altimetry missions such
as Sentinel-3A, Jason-3, Sentinel-6 MF and SWOT. The derived phase corrections were tested on CNES POE-G GNSS-only
reduced-dynamic orbit solutions to assess their impact and validate their benefits owing to independent SLR observations. 

How to cite: Baños Garcia, A.: In-flight GNSS phase map calibration modelling with Zernike polynomials, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3521, https://doi.org/10.5194/egusphere-egu24-3521, 2024.