This session aims to make accessible the technical challenges of orbit determination and modelling to the wider community and to quantify the nature of the impact of dynamics errors on the various applications.
Contributions are solicited from, but not limited to, the following
areas: (1) precise orbit determination and validation; (2) satellite surface force modelling; (3) advances in modelling atmospheric density and in atmospheric gravity; (4) advances in modelling earth radiation fluxes and their interaction with space vehicles; (5) analysis of changes in geodetic parameters/earth models resulting from improved force modelling/orbit determination methods; (6) improvements in observable modelling for all tracking systems, e.g. SLR, DORIS, GNSS and their impact on orbit determination; (7) advances in combining the different tracking systems for orbit determination; (8) the impact of improved clock modelling methods/space clocks on precise orbit determination; (9) advances in modelling satellite attitude; (10) simulation studies for the planned co-location of geodetic techniques in space mission GENESIS.
Orals: Mon, 4 May, 10:45–12:30 | Room 0.51
The ESA's GENESIS mission, scheduled for launch in 2028, collocates the four geodetic techniques (DORIS, GNSS, SLR and VLBI) on a single spacecraft, with accurate calibration of the platform and instruments, and a shared clock/frequency source for the active instruments. To assess the expected performance of this mission, we perform end-to-end simulation studies using the GINS/DYNAMO software developed at CNES. Our analysis examines how multi-technique GENESIS observations could contribute to the determination of the Terrestrial Reference Frame (TRF) and Earth rotation parameters, as well as to the detection of inter-technique biases. The simulations acccount for technique-specific error sources, dynamical modeling and instrument calibration uncertainties to assess realistic scenarios. We examine the use of the common orbit as a link between techniques to evaluate how multi-technique combined GENESIS-like solutions at the observation level affect the TRF parameters, in particular the origin and scale, and the inter-technique consistency within the combined TRF solutions.
How to cite: Aït-Lakbir, H., Chatzinikos, M., Delva, P., Marty, J.-C., and Pollet, A.: Numerical simulations on GENESIS' contribution to the determination of terrestrial reference frame (TRF) parameters, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4882, https://doi.org/10.5194/egusphere-egu26-4882, 2026.
Future ‘space-tie’ satellite missions such as Genesis aim at co-locating multiple space-geodetic techniques on a single satellite platform to improve the consistency and long-term stability of the Terrestrial Reference Frame (TRF). However, quantifying the benefits of such satellite-based co-location requires not only advanced simulation capabilities, but also a robust validation of real observation data using consistent multi-technique processing strategies. Already today, missions such as the Sentinel satellites provide an opportunity to realise satellite-based co-location by carrying multiple space-geodetic observation techniques onboard.
To date, most multi-technique Precise Orbit Determination (POD) approaches rely on orbit determination approaches in which the TRF is fixed and, in the case of Global Navigation Satellite Systems (GNSS) Low Earth Orbit (LEO) POD, GNSS constellation orbits and clocks are typically held fixed as well. Consequently, cross-technique interactions and their impact on GNSS constellation orbits and clocks, LEO orbits, Earth Rotation Parameters (ERPs), and the TRF have so far not been comprehensively assessed for all space-geodetic techniques. Investigating these effects using real observations is therefore a crucial step that can already be performed prior to Genesis.
In this study, we investigate an integrated multi-technique POD approach using real GNSS, Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), and Satellite Laser Ranging (SLR) tracking data. The analysis covers the multi-technique LEO satellites Sentinel-3A, Sentinel-3B, and Sentinel-6A (MF), together with the GPS and Galileo constellations over a two-year period. Using GFZ’s in-house software EPOS-OC, LEO and GNSS constellation orbits and clocks, the TRF, and ERPs are estimated simultaneously within a single adjustment, fully consistent with respect to dynamic and geometric modelling.
A stepwise integration is performed, starting from single-technique LEO POD solutions and proceeding to the integration into a combined GNSS constellation solution using GNSS observations only. DORIS and SLR observations are incrementally added to assess their impact on LEO orbits, GNSS constellation orbits and clocks, ERPs, and ground station coordinates.
The results provide a real-data-driven assessment of integrated multi-technique POD for satellite-based co-location and form a basis for subsequent Genesis end-to-end simulation studies and future Genesis real-data processing.
How to cite: Schreiner, P., Glaser, S., König, R., Neumayer, K. H., Flechtner, F., and Schuh, H.: Integrated Multi-Technique Precise Orbit Determination Using GNSS, DORIS and SLR: A Real-Data-Based Assessment for Future Co-location in Space Missions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17918, https://doi.org/10.5194/egusphere-egu26-17918, 2026.
Precise orbits of Low Earth Orbit (LEO) satellites are the prerequisite for various precise applications with LEO satellite/constellations. Typically, centimeter-level LEO satellite orbit products can be obtained using onboard GNSS observation data. However, with the arrival of the 25th solar activity peak year and the cost control of commercial LEO satellites on manufacturing costs, traditional methods for onboard GNSS data processing need further improvement. In terms of data preprocessing, due to the severe ionospheric variations caused by solar activities, traditional cycle slip detection models are prone to frequent false detections of cycle slips during ionospheric active periods, leading to a decline in the accuracy of LEO satellite orbit determination. This study analyzes the variation characteristics of ionospheric disturbances, and proposes a polynomial fitting prediction method with ionospheric variation constraints, which can effectively distinguish cycle slips from ionospheric variations and improve the LEO satellite orbit determination accuracy under ionospheric disturbances. The results show that with the constraints of ionospheric variation, the RMS values of orbital errors for GRACE-C in along-track, cross-track, and radial components are improved by 11%, 17%, 6%, respectively. As for the optimization of GNSS observation model for low-cost LEO satellite, this study proposes a GNSS observation model considering the time-varying characteristics of onboard receiver biases, which can effectively enhance the stability of onboard receiver clock offset solution and ensure the accuracy of LEO satellite orbit as well. The results show that new model can reduce the discontinuities of arc-boundary for receiver clock from tens of nanoseconds to sub-nanosecond levels. In terms of frequency stability, the new model shows the similar short-term stability to the conventional model while notable improvements in medium- and long-term stability (beyond 102s).
How to cite: Ge, H., Wu, T., Meng, G., and Li, B.: Optimizing GNSS observation model with onboard receiver for LEO precise orbit determination , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4875, https://doi.org/10.5194/egusphere-egu26-4875, 2026.
The attitude motion of geodetic satellites can indirectly affect their orbit through non-gravitational perturbations. This effect is particularly significant for non-symmetrical bodies, as their orientation determines the surface areas subjected to atmospheric drag and radiative forces. However, this also applies, to a lesser extent, to fully spherical satellites due to thermal effects such as the Yarkovsky effect (Bertotti and Iess, 1991; Farinella et al., 1996; Métris et al., 1999; Andrés et al., 2004). Modelling the Yarkovsky effect requires, in particular, knowledge of the spin axis direction.
Due to the peculiar configuration of Ajisai mirrors, the photometry of flashes generated by the reflection of sunlight on their surfaces, and specifically the linear measurement of its luminous flux, appears to be the most adequate technique to study its rotation with high single-pass accuracy. Measurements of the Ajisai's luminous flux has been acquired using a high frequency (10 kHz) linear-detection optical photometry technique from the MéO telescope at Grasse station on the Plateau de Calern site of Observatoire de la Côte d'Azur. In this presentation we show that this instrumentation produces very rich informations.
The selection, extraction, time-stamping and collection of the sequence of single flashes from the raw measured flux and the subsequent identification of the mirror on which the reflection occurred, allowed us to determine the rotation parameters of the satellite, i.e. to reconstruct its attitude, with an unprecedented single pass accuracy. The estimated precision for the determination of the rotation parameters during one pass of Ajisai is typically in the order of 0.25 deg for the spin axis orientation, 10-5 s for the rotation period.
The growing number of kHz-capable Satellite Laser Ranging Stations and the extensive dataset made available by the International Laser Ranging Network (ILRS) position kHz SLR as a compelling tool with great potential for conducting medium- and long-term studies on the rotation of the Ajisai satellite.
Through the analysis of high repetition rate laser ranging data from the ILRS network, we were able to further investigate the rotation and confirm the photometry results. Similar to photometry, the sequence of CCRs closest approaches during the satellite pass observation could be identified and used to reconstruct the satellite's attitude.
A notable application of this work could be in the context of the next generation bistatic optical time transfer through a fully passive satellite.
How to cite: Calatroni, C., Métris, G., Courde, C., Phung, D.-H., Chabé, J., Aimar, M., Maurice, N., Mariey, H., and Scariot, J.: Determination of the rotation parameters of the AJISAI passive satellite using linear detection photometry and kHz SLR, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12632, https://doi.org/10.5194/egusphere-egu26-12632, 2026.
Space safety is becoming an increasingly important topic for our society, in particular with respect to space debris. According to the ESA's Space Environment Report 2025, the number of satellites, and, consequently the amount of space debris, particularly in low Earth orbits (LEOs) is growing rapidly. To ensure that satellite operators are informed about the need for evasive manoeuvres, it is necessary to implement countermeasures such as the identification and monitoring of space debris. Knowing the approximate positions of space objects to be tracked via Satellite Laser Ranging (SLR) is essential for aligning the SLR station's pointing accordingly. Accurate orbit predictions for satellites are provided to the stations by prediction centres. But this does not apply to space debris. Instead, the so-called two-line elements (TLEs) are used to predict the orbits of these objects. TLEs contain important orbital elements which are related to position and velocity of the space object at a specific time or point. However, they are limited in their accuracy which results in inaccurate orbit predictions. To achieve a more precise laser alignment for space debris tracking, we present an approach to improve the accuracy of orbit predictions based on TLEs, using the SLR functionality of the GROOPS (Gravity Recovery Object Oriented Programming System) software toolkit. Furthermore, we demonstrate that incorporating real-time measurements can enhance the accuracy of orbit predictions for station pointing alignment in subsequent passes.
How to cite: Suesser- Rechberger, B., Mayer-Guerr, T., Krauss, S., Tieber-Hubmann, C., Wang, P., and Steindorfer, M.: Improving station pointing alignment for SLR using approaches based on TLEs and real-time measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2834, https://doi.org/10.5194/egusphere-egu26-2834, 2026.
Precise orbit determination (POD) is a fundamental requirement for satellite navigation, Earth observation, and space applications. Conventional POD methods typically depend on external initial orbit states and clock corrections, which limit resilience and may introduce external biases. Here, we demonstrate a resilient POD method that depends solely on observations from the third generation BeiDou Navigation Satellite System (BDS-3) without requiring any external initial orbit and clock information. Reliable initial orbit states are internally obtained through a global network solution of double-differenced code observations with robust estimation. Using one year of data collected from about 200 BDS-3 tracking ground stations in 2024, initial orbit position and velocity accuracies reach approximately 0.5 km and 0.1 m/s, respectively. Based on these initial orbit states and a zero-mean clock constraint, a two-step scheme is then applied to realize the joint precise determination of satellite orbits and satellite clock corrections. The resulting orbits achieve an accuracy of up to 4.5 cm, in terms of the standard deviation (STD) of satellite laser ranging (SLR) residuals. These results confirm the feasibility of fully resilient BDS-3-only POD without reliance on external initial conditions, enabling independent and robust satellite navigation.
How to cite: Chen, X., Ge, M., Zhang, X., and Schuh, H.: BDS-3-Only Precise Orbit Determination Without External Initial Orbit and Clock Corrections, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1355, https://doi.org/10.5194/egusphere-egu26-1355, 2026.
Galileo satellite surface properties are published by the European GNSS Service Center (GSC) as part of the official satellite metadata. These properties describe surface elements that are grouped into four main categories: multi-layer insulation (MLI), optical radiators, navigation antennas, and solar cells. Based on this information, a simple box-wing solar radiation pressure (SRP) model is widely applied by the International GNSS Service (IGS) analysis centers (ACs) for Precise Orbit Determination (POD).
However, key thermal effects, such as radiator emission and imbalanced thermal radiation from navigation antennas and solar panels, are typically neglected, as detailed thermal information is not publicly available. Instead, these effects are partially absorbed by the Empirical CODE Orbit Model (ECOM/ECOM2) parameters, which are widely estimated to compensate for deficiencies in the physical force modeling.
In this contribution, we develop advanced macro models for Galileo satellites, including refined SRP and Earth radiation pressure (ERP) models based on a more detailed representation of satellite surface elements, as well as thermal radiation models for radiator emission, navigation antennas, and solar panels using best-guess values. The impact of each individual thermal force component on POD and terrestrial reference frame solutions is assessed. The final results are compared against the standard GSC-based box-wing model.
Given the complexity of the physical macro models, we introduce acceleration tables for Galileo In-Orbit Validation (IOV) and Full Operational Capability (FOC) satellites as generic interface between macro models and the orbit integrator. The tables provide non-gravitational accelerations as functions of satellite orbital argument and Sun elevation angle above orbital plane, including both SRP and thermal radiation effects. Earth radiation pressure is excluded from the tables due to its pronounced temporal variability and should therefore be modeled separately.
How to cite: Duan, B., Hugentobler, U., and Dach, R.: From macro models to generic acceleration tables: modeling non-gravitational forces acting on Galileo satellites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20449, https://doi.org/10.5194/egusphere-egu26-20449, 2026.
Laser Inter-Satellite Links (LISL) are increasingly pivotal for next generation GNSS, offering high precision ranging with low power and high directionality, while reducing dependence on global ground tracking distribution. This study presents a simulation based Precise Orbit Determination (POD) analysis for the BDS-3 constellation augmented by LISL constraints. We focus on a practical link scheduling strategy under visibility constraints and evaluate how LISL observations strengthen orbit and clock estimation, particularly when ground tracking is limited.
A feasible LISL topology is designed for the BDS-3 MEO constellation based on precise ephemerides. On same orbit plane links are organized into a closed-loop ("hand-in-hand") geometry to stabilize the configuration. The links on different orbit plane employ a dynamic time varying allocation strategy, reserving capacity to flexibly connect with IGSO satellites and adjacent MEO planes, thereby enhancing cross-plane connectivity. Link feasibility is validated using an Earth-occlusion and atmospheric tangency model. To mitigate relative clock errors, dual-way ranging is applied to separate geometric distance from clock offsets. Based on this configuration, LISL observations are simulated to generate adjacency matrices and distance time series for assessing geometric stability.
POD experiments were conducted for DOY 197–227, 2023, under two scenarios: (1) a global network using MEGX stations, and (2) a regional network utilizing eight iGMAS stations in China. The dynamic model employs ionosphere-free combinations and standard CODE dynamic strategies, including solar radiation pressure, Earth albedo , and antenna thrust models. LISL ranges are introduced as constraints with 1 mm a priori precision.
Results demonstrate that LISL constraints significantly enhance both orbit and clock estimation, with the most substantial gains observed in the regional tracking scenario. Validated against CODE precise products, clock accuracy improves from 0.086 ns to 0.068 ns, with smoother overlapping Allan deviation. For the global network, the 3D orbit RMS decreases from 5.0 cm to 4.2 cm. For the regional network, where GNSS-only solutions are limited to decimeter-level accuracy, adding LISL reduces the along-track, cross-track, and radial RMS by 80.8%, 76.5%, and 74.0%, respectively (82.5% improvement in 3D RMS). Independent Satellite Laser Ranging (SLR) residuals confirm these improvements, highlighting the potential of LISL to ensure robust, high-precision orbit products for future autonomous navigation.
How to cite: Jiang, C., Chen, H., Zhou, X., and Jiang, W.: Precise orbit determination supported by BDS-3 with laser inter-satellite links : A simulation study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16615, https://doi.org/10.5194/egusphere-egu26-16615, 2026.
Inertial navigation is essential for space missions due to its independence from external signals and references. Inertial navigation systems (INS) rely on accelerometers and gyroscopes to track changes in velocity and orientation, allowing spacecraft to determine their trajectories independently—provided that gravitational accelerations are sufficiently well modelled. However, conventional electrostatic accelerometers used in current space missions typically suffer from significant low-frequency noise and drift, particularly below 10−3 Hz, which limits long-term navigation accuracy and orbit determination performance. Quantum inertial sensing based on atom interferometry, on the other hand constitute an attractive alternative technology, based on a fundamentally different measurement principle. By exploiting the wave nature of matter, quantum sensors enable highly precise and drift-free measurements of non-gravitational acceleration, with the potential to substantially improve orbit determination. In addition, the microgravity environment in space allows for interrogation times that are orders of magnitude longer than on Earth, leading to significantly enhanced sensitivity compared to terrestrial implementations of quantum sensors.
In this work, we present our developed, comprehensive model for multi-axis quantum accelerometers and gyroscopes based on the schemes which are expected to perform best under the microgravity conditions of space. In particular, our modelling accounts for different sources of noise and systematics such as the detection noise, laser frequency noise, wavefront aberration, and sources of contrast loss. It also considers the combined effect of spacecraft rotation around all its axes, gravity gradients, and self-gravity on the measurements of the sensors. Using this framework, we simulate quantum inertial sensor measurements for Earth-orbiting satellites and along an Earth–Moon transfer trajectory, enabling an assessment of their performance for Earth-orbiting and lunar mission scenarios. The resulting simulations are used to evaluate the performance of quantum accelerometers and gyroscopes under different assumptions and scenarios in space. The goal of this work is to identify the challenges associated with deploying quantum inertial sensors for space navigation, to discuss potential mitigation strategies, and to quantify the benefits these sensors could provide for future spacecraft navigation and orbit determination.
How to cite: HosseiniArani, A., C. Sreekantaiah, A., Beaufils, Q., Pereira dos Santos, F., He, X., Hugentobler, U., and Schön, S.: Challenges and Benefits of Quantum Sensors for Inertial Navigation in Space, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18902, https://doi.org/10.5194/egusphere-egu26-18902, 2026.
Satellite Laser Ranging (SLR) is a fundamental technique of space geodesy, providing essential contributions to the realization and long-term stability of terrestrial reference frames. For future multi-technique missions such as the GENESIS mission, a realistic assessment of achievable SLR observation yield requires modelling approaches that reflect operational constraints of the global tracking network.
This study presents an operation-informed simulation framework for estimating the SLR observation yield of the International Laser Ranging Service (ILRS) network. The approach represents tracking opportunities using station availability windows (SAWs) derived from geometric visibility and integrates weather-gated availability based on ERA5 reanalysis data. Empirical models of tracking duration, interleaving behaviour, and station-specific priority patterns are derived from historical ILRS normal point records. The framework explicitly avoids optimal scheduling and instead aims to reproduce realistic network behaviour over annual time scales.
The framework is applied to a representative GENESIS mission scenario and evaluated using network-level performance indicators, including annual union tracked time, normal point (NP) count, and NP gap statistics. Comparisons with historical SLR tracking of LAGEOS-1/2 demonstrate that the simulated GENESIS observation yield lies within a realistic reference range.
The proposed framework provides a practical tool for mission performance assessment and scenario analysis of space-geodetic observing systems.
How to cite: Gao, Y. and Montenbruck, O.: Operation-informed simulation of ILRS Satellite Laser Ranging observation yield for the GENESIS mission, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16868, https://doi.org/10.5194/egusphere-egu26-16868, 2026.
DORIS data processing is sensitive to the short-term clock variations, but the onboard clock corrections can be obtained from DORIS pseudoranges alone only as a polynomial model covering a couple of days. The Sentinel -3A and -3B satellites are the very first ones where the DORIS and the GNSS equipment are running on the same onboard oscillator. This offers the unique opportunity to synchronize the onboard clocks epoch-wise using GNSS and thus to measure clock behavior in detail and to make use of the short-term clock behavior in the DORIS data analysis. A similar approach can be applied also for Sentinel-6A on Jason orbit.
GPS-derived epoch-wise clock corrections are computed for the ultra-stable oscillator (USO) and introduced as fixed into the DORIS data processing making DORIS processing capable of considering the short-term variations of the satellite clock. This approach is very promising for studying the South Atlantic Anomaly (SAA) effect. In addition, the tandem phase of the satellite pairs Sentinel-3A and 3B (130 days) and Sentinel -6A and Jason -3 (~330 days) offer additional opportunities to perform closure measurements using same beacons observed synchronously by both satellites.
This poster will visually illustrate these concepts and techniques along with the results of Sentinel -6 with integrated GNSS clocks, the mapping of the SAA effect, the tandem phase analysis results and the near future plans and benefits of GNSS-DORIS combination for precise orbit determination.
How to cite: Gunasekaran, B. K., Štěpánek, P., Filler, V., and Hugentobler, U.: Ingestion of GNSS-derived clock parameters into DORIS data analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11173, https://doi.org/10.5194/egusphere-egu26-11173, 2026.
For the last few years, Dionysos Satellite Observatory (DSO) of the National Technical University of Athens (NTUA) has undertaken the challenging task of developing a new, open-source and free software toolkit to facilitate the processing of DORIS observations for Precise Orbit Determination (POD) and positioning. The ongoing objective is to eventually deliver a state-of-the-art software to the scientific community, focusing on a fundamental technique of satellite geodesy. The significance of this technique across various geoscience disciplines is well-established and demonstrated by extensive publications in fields such as reference frames, altimetry, and geodynamics, among others. The software itself is designed in a way that accommodates scientific research, experimentation and validation, since it is generic enough to handle multiple data sources and models. Care is taken to design for efficiency and robustness, yet favouring re-usability and modularity, leveraging along the way modern software design principles. Additionally, we adopt modern standards and refined modeling approaches.
Analysis highlights include a rigorous treatment of the DORIS Doppler observation equation, dynamic orbit modeling, usage of the Extended Kalman Filter with process noise and state-of-the-art models and algorithms to handle tidal and non-tidal phenomena. Various validation tests are performed and presented, both for intermediate steps (e.g. different forces acting on the satellites) as well as using the estimated trajectories with respect to high-quality results from IDS Analysis Centers. In this study, we present preliminary results obtained using the toolkit, provide insights into its architecture and capabilities, and outline our immediate next steps.
How to cite: Anastasiou, D., Papanikolaou, X., Serelis, G., Fisikopoulos, V., Krey, V., Zacharis, V., and Tsakiri, M.: Developing an Open-Source Toolkit for Precise Orbit Determination and Positioning Using DORIS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14906, https://doi.org/10.5194/egusphere-egu26-14906, 2026.
Using the high-quality GNSS observations of the low Earth orbiting Swarm constellation, Delft University of Technology routinely delivers precise science orbits (PSO), aerodynamic accelerations, and thermosphere densities for all three satellites within the framework of the Swarm Data, Innovation, and Science Cluster. The PSO consist of a reduced-dynamic orbit to precisely geotag the onboard magnetic and electric field instrument observations and a kinematic orbit with covariance information to determine the large-scale time variable changes of Earth’s gravity field. The GNSS-derived densities can be used to improve thermosphere models and for studying the influence of solar and geomagnetic activity on the thermosphere. The aerodynamic accelerations are used to augment the higher-resolution accelerometer data, which are affected by accelerometer instrument issues. Due to these issues, the accelerometer-derived thermosphere densities are not continuously available for all satellites.
For both PSO and density products, the nominal processing strategy has recently been improved. The PSO processing strategy, which includes a realistic satellite panel model for solar and Earth radiation pressure modelling and integer ambiguity fixing, was updated with a new approach to reduce the impact of ionospheric scintillation-induced errors in the kinematic orbits. The previous procedure was not properly tuned for high solar activity conditions, resulting in many gaps in the kinematic orbits, with losses of up to 40% during periods with such conditions. With the new approach, considerably more kinematic orbit data are available.
For the GNSS-based thermosphere density retrieval, aerodynamic accelerations are estimated in a precise orbit determination using a Kalman filter approach and converted to densities using a high-fidelity satellite geometry model and gas-surface interaction modelling. To account for the large variations in the encountered aerodynamic signal by the Swarm satellites over the mission lifetime, a new approach was implemented that uses adaptive process noise settings for the estimated aerodynamic accelerations. These new settings lead to significantly improved densities during low-density signal conditions.
The new Swarm precise orbit products (version 0203) and thermosphere density products (version 0301) are available for users at the dedicated ESA Swarm website (https://swarm-diss.eo.esa.int). The Swarm densities are also available at our thermosphere density database (https://thermosphere.tudelft.nl).
How to cite: van den IJssel, J., Siemes, C., and Visser, P.: New GNSS-derived precise orbits and thermosphere densities for the Swarm satellite constellation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4843, https://doi.org/10.5194/egusphere-egu26-4843, 2026.
In recent years, the use of non-scientific low Earth orbiting (LEO) satellites for gravity field determination has been increasingly explored. In principle, the same methods as for non-dedicated scientific missions are applied by analysing the satellites’ orbital perturbations to gain information about the Earth’s gravity field.
With currently over 100 CubeSats in orbit, the Spire commercial constellation provides a huge amount of GNSS tracking data in the same timeframe as scientific missions. This can be exploited to increase the spatio-temporal resolution of estimated gravity field solutions. Although the data quality is limited, previous analyses using data from a 2020 ESA Announcement of Opportunity project have shown that a combined processing of Spire CubeSats can achieve monthly gravity field solutions of similar quality as non-dedicated scientific missions. In our work, we make use of both the Spire data from 2020 and a new dataset from 2023 provided by EUMETSAT.
At the Astronomical Institute of the University of Bern, non-gravitational forces acting on the satellite have so far not been explicitly modelled when determining the gravity field, but instead absorbed by pseudo-stochastic parameters such as piecewise constant accelerations. As these forces are prominent for CubeSats due to their low altitude and their large area-to-mass ratio, this study explores how the estimation of the orbits and gravity field solutions improves when explicitly modelling these forces. To achieve this, we determine kinematic orbit positions from Spire CubeSat GNSS phase and code data and introduce them as pseudo-observations in an orbit and gravity field recovery step, where dedicated non-gravitational force modelling is applied using macro-model information provided by Spire. The combination of the different Spire satellites is performed at the normal equation level using a least-squares approach.
How to cite: Miller, A., Arnold, D., Grombein, T., Lasser, M., and Jäggi, A.: Gravity field determination from Spire CubeSat data with non-gravitational force modelling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18446, https://doi.org/10.5194/egusphere-egu26-18446, 2026.
The Copernicus Precise Orbit Determination (CPOD) Service is key to the Copernicus Sentinel missions, supporting Sentinel-1, -2, -3, and -6 with precise orbit products and auxiliary data. These products enable the operational generation of scientific data at ESA and EUMETSAT and are distributed via the Copernicus Data Space Ecosystem (https://dataspace.copernicus.eu/).
For high-accuracy POD, radiation pressure modelling is a major contributor to orbit errors, particularly for platforms with complex geometries. Sentinel-6 represents a challenging case, as its structural configuration is poorly represented by conventional macro-models, leading to persistent signatures in the estimated empirical accelerations used to absorb unmodelled dynamical effects.
Within the CPOD context, GMV has been investigating an alternative radiation modelling strategy using the GMV Grial tool. The approach relies on a surface projection algorithm that computes radiation forces directly from a detailed spacecraft three-dimensional model, provided in CAD format, together with associated optical and infrared material properties. The resulting adimensional force coefficients are tabulated in the satellite reference frame as a function of the azimuth and elevation of the incident ray, allowing efficient integration into operational POD workflows. The methodology targets improved modelling of solar radiation pressure, as well as Earth albedo and infrared radiation pressure effects.
The methodology has been successfully applied and validated for Sentinel-3, demonstrating good agreement between modelled and estimated accelerations for box-wing-type spacecraft. Its extension to Sentinel-6 is currently under assessment. This work presents the modelling framework, validation strategy, and first Sentinel-6 results. While no significant reduction of empirical acceleration signatures is yet observed, the results indicate a strong sensitivity to assumed geometry and surface properties, highlighting the need for improved spacecraft characterisation from spacecraft manufacturers to fully exploit advanced radiation modelling techniques.
How to cite: Fernandez Sanchez, J., Lara Espinosa, S., Fernandez Martin, C., Peter, H., Pinheiro, M., and Nogueira Loddo, C.: COPERNICUS POD SERVICE: Radiation modelling based on 3-D model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8923, https://doi.org/10.5194/egusphere-egu26-8923, 2026.
Accurate measurement of Earth’s energy imbalance (EEI) is one of the central challenges in climate science. At present, global and regional EEI variability is inferred from radiometric measurements, anchored with time-mean planetary energy inventory estimates due to sensor absolute calibration biases. Space dynamics methods for EEI estimation have been investigated since the 1970s, notably with the CASTOR/CACTUS accelerometers, whose performance exceeded expectations. It led to the BIRAMIS project which aimed at directly measuring EEI from accelerometer observations of the Earth Radiation Pressure (ERP).
In this study, we investigate an alternative space-dynamics–based approach to infer time-mean EEI and anchor CERES. The method aims to provide an alternative anchoring method by directly correcting the absolute calibration error of the CERES radiometers with the introduction of an adjustable scaling parameter applied to the ERP acting on passive spherical satellites tracked by Satellite Laser Ranging (SLR). This method is expected to substantially improve the accuracy of CERES observations, reducing the current accuracy of ±2.5 W.m-2 over a decadal timescale to a target accuracy of a few 0.1 W.m-2 on an annual basis.
To assess the accuracy of this method, we focus on Ajisai, a Japanese geodetic satellite launched in 1986. Ajisai is a suitable candidate due to its altitude of approximately 1500 km, its area-to-mass ratio, which is nearly an order of magnitude larger than that of most other geodetic satellites, and its spin-stabilized configuration. To evaluate the feasibility and relevance of the approach, we simulate SLR observations, allowing us to introduce controlled errors both in the measurements and in the force models.
In this study we account for error sources from gravity field and tidal models, atmospheric drag, the Yarkovsky effect, SLR measurement noise, and station-related errors. As expected, the results show that the estimate of the time-mean EEI is primarily affected by uncertainties in atmospheric drag and the Yarkovsky effect. A parameter sensitivity study was conducted to identify optimal strategies for mitigating these errors. The time-mean EEI estimate is also sensitive to anisotropic effects arising from Ajisai’s non-perfect spherical symmetry, which introduce a non-negligible bias.
Overall, we establish an error budget for this new method and demonstrate the estimate of the time-mean EEI from SLR measurement is feasible. The quantitative results suggest this approach could be sufficiently precise to anchor CERES at a better precision than currently done with the planetary inventory.
How to cite: Chapiron, A., Couhert, A., and Meyssignac, B.: Feasibility study of a time-mean Earth energy imbalance estimate derived from Satellite Laser Ranging measurement of the Earth Radiation Pressure , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19862, https://doi.org/10.5194/egusphere-egu26-19862, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 3
EGU26-7764 | ECS | Posters virtual | VPS25
Impact of Storm-Adapted DORIS Processing on Orbit Quality and Earth Rotation Parameters During Geomagnetic StormsThu, 07 May, 14:03–14:06 (CEST) vPoster spot 3
Geomagnetic storms (GS) significantly perturb the near-Earth environment, leading to enhanced thermosphere density, increased non-conservative forces, and degraded satellite orbit determination, particularly for Doppler-based techniques such as DORIS. In this study, we investigate and improve DORIS orbit determination performance during GS conditions by developing storm-adapted processing strategies. Storm days were classified using geomagnetic indices and categorized into moderate to severe storm levels (G3-G5).
Four distinct processing strategies were implemented and evaluated: a standard operational solution and three experimental storm-adapted solutions, designed through systematic modifications of drag constraints and observation-elimination criteria. These strategies were tested through targeted daily and weekly experiments conducted across multiple DORIS-equipped satellites, with a particular emphasis on periods of intense storms.
The storm-adapted strategies demonstrate clear performance improvements relative to the standard solution during geomagnetic storms. The modified strategies reduce orbit residual RMS in all orbital components, improve Length-of-Day (LOD) variance by approximately 40-80%, and decrease LOD mean biases by nearly 60%. Additionally, Earth Rotation Parameters (ERP) exhibit notable improvements, with reductions of approximately 22–25% in both bias and variability for the polar motion components (X/Y pole). Among the tested configurations, the combined strategy, particularly when applied with zero-rotation constraints, consistently delivers the best performance during intense storm conditions (Kp ≥ 8+). These results demonstrate that storm-adapted DORIS processing strategies significantly enhance orbit and geophysical parameter estimation during disturbed space-weather conditions.
How to cite: Kumar, V., Stepanek, P., Filler, V., Balasubramanian, N., and Dikshit, O.: Impact of Storm-Adapted DORIS Processing on Orbit Quality and Earth Rotation Parameters During Geomagnetic Storms , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7764, https://doi.org/10.5194/egusphere-egu26-7764, 2026.
