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.

The objective of the future Global Geodetic Observing System (GGOS) to realize the terrestrial reference system (TRS) with 1 mm accuracy and 0.1 mm/yr long-term stability remains challenging when the four space geodetic techniques – GNSS, SLR, VLBI, and DORIS – are processed independently in the traditional, technique-specific manner. Key challenges arise from the sparse and highly inhomogeneous global distribution of co-location sites used to tie the individual solutions together, as well as from the treatment of technique-specific calibration parameters, such as GNSS antenna phase center offsets and SLR range biases. In this presentation, we present work carried out by the ESA/ESOC Navigation Support Office on the joint processing of GNSS and SLR at the observation level. Our approach – fittingly referred to as COOL (“COmbination at the Observation Level”) – incorporates the primary geodetic ILRS targets LAGEOS-1, LAGEOS-2, LARES-2, Etalon-1, and Etalon-2, and makes use of space ties provided by the Sentinel and Galileo satellites to directly link the two geodetic techniques. Particular attention is given to the Galileo transmit antenna z-offsets and the numerous SLR range biases, which require careful treatment, as they are known to directly influence the scale of the reference frame solution. The primary motivation for this work is to ensure full readiness for the future ESA GENESIS mission, which aims to establish a highly accurate, next-generation International Terrestrial Reference Frame (ITRF) through the use of all four space geodetic techniques, including DORIS and VLBI, on a single platform and the exploitation of the space ties between them.

Differential Code Biases (DCBs) are systematic errors, or biases, between two Global Navigation Satellite System (GNSS) code observations at the same or different frequencies. Knowledge of DCBs is required for positioning of GNSS receivers, extracting ionosphere total electron content (TEC), and other applications. Proper knowledge of DCBs is crucial to many navigation applications but also non-navigation applications such as ionospheric analysis and time transfer. The multitude of new signals offered by modernized and new GNSS constellations, requires a comprehensive multi-GNSS bias product. And because of the multitude of GNSS signals it has become more practical to provide the DCBs, differential signal biases, as observable specific biases, OSBs.At the Navigation Support Office at ESA/ESOC we have for many years relied on the bias products (DCB and OSB) coming from the CODE analysis centre. But in the fast-developing Multi-GNSS landscape it became clear that we needed to have to capability to generate our own independent bias product. For our different GNSS projects we therefore have developed a process to generate our own OSB product with the ambition to have DCBs for all existing MGNSS signals, as long as the signals are tracked by the stations in the large IGS station network. And rather than monthly biases as typically provided and used within the IGS, we have moved to what we call a “Bias Reference Frame” (BREF). The absolute value is still determined by a zero-mean condition at a certain date. But from that point in time the biases are kept stable unless a clear jump in the satellite bias is, automatically, detected. The detectability is at the 0.25ns for well observed biases. The DCB version of the product is publicly available on our Navigation Office website. The OSB version is still under development and testing.In developing this product, we found some very interesting features of the biases when looking at the biases of the so called “interoperable” signals, which we will present and discuss. We demonstrate the importance of this product for the analysis of the Sentinel 6A data which tracks Galileo and an interesting mix of GPS signals which makes it hard to process the GPS data with the standard IGS products, in particular for PPP-AR.

Abstract Precise Orbit Determination (POD) of the Copernicus Sentinel satellites is a task of the Copernicus POD Service. For the generation of the non-time critical (NTC) products the Precise Point Positioning – Ambiguity Resolution (PPP-AR) approach is applied using the GNSS (Global Navigation Satellite System) data from the onboard receivers. The corresponding GNSS products (orbits, clock corrections, observation-specific signal biases (OSBs)) are stemming from the Center for Orbit Determination in Europe (CODE), one of the analysis centers of the International GNSS Service (IGS). Recently a combined product has been published by the Wuhan Combination Center (WCC), which includes combined orbits, clock corrections, and OSBs for PPP-AR applications. This IGS WCC product is analyzed and applied for Sentinel POD. Additionally, other available IGS analysis center products, which include OSBs, are analyzed and the results are compared with each other. All resulting orbits are compared to orbit results from the Copernicus POD Service. When using the different IGS AC and WCC products for Sentinel POD with integer ambiguity resolution differences in the quality and reliability are observed. Main reason is that not all OSBs needed for the ambiguity fixing are provided in all products. This restricts the usage of some of the products for Sentinel POD. The new experimental IGS combined product (WCC) shows an excellent performance in single-system POD solutions, it is only outperformed by the CODE products when using their clocks with the 5 s sampling.

Abstract The goal set by the Global Geodetic Observing System – realising the terrestrial reference system with an accuracy of 1 mm and a long-term stability of 0.1 mm/yr – appears difficult, if not impossible, to achieve with the current independent processing of the key contributing space techniques. Although combining the independent contributions from GNSS, SLR, DORIS and VLBI demonstrated its contribution to precise orbit determination improvement and global parameter estimation strengthening, systematic differences between the techniques are clearly visible in the scale and origin of the respective reference frame contributions. An additional challenge is the limited number of geodetic sites that provide co-location of the different techniques, as well as the highly inhomogeneous global distribution of such sites. One approach to improve the quality of the Terrestrial Reference Frame realisation is the simultaneous processing of the data of these four space geodetic techniques at the observation level. A second approach is to make use of co-location in space by placing multiple techniques on a single satellite. The Genesis mission, a component of the ESA’s FutureNAV program, aims to provide such highly accurate in-space co-location of the four techniques. We, the Navigation Support Office at the European Space Operations Centre of the European Space Agency, are pursuing both approaches; COmbination of the different techniques at the Observation Level (COOL), and the use of space ties offered by the Genesis mission. We are currently working with GNSS and SLR data and are using the Sentinel satellites as surrogates for Genesis, which is scheduled for launch in 2028. For instance, the Sentinel-6A satellite co-locates three of the four space geodetic techniques – VLBI is not available – and is therefore an ideal target to prepare our software and processing approach for both COOL and Genesis. Sentinel-6A offers the additional benefit of tracking not only GPS but also Galileo GNSS signals. Considering the subtleties on inter-technique combinations, our main aims are to gradually build up, test and validate our COOL solutions to ensure that the combined solution geodetic products outperform the single-technique solutions. In this paper, we present the status of our processing capabilities, some initial results, and conclude with an outlook of the work that remains to be done.

This paper provides a description of the GLONASS-K yaw turn maneuvers that regularly occur at orbit noon and orbit midnight when the Sun’s elevation angle relative to the satellite orbital plane is between − 2.0 and + 2.0 degrees. Formulas for maneuver modeling are presented, which can be easily integrated into any Global Navigation Satellite System (GNSS) software. Triple-frequency carrier phase observations from the global International GNSS Service (IGS) tracking network are analyzed to evaluate the performance of the model. Yaw angle estimates for the first GLONASS-K1 and first GLONASS-K2 spacecraft indicate that the actual yaw attitude follows the theoretical steering model with an accuracy of about 2 degrees. In addition to the regular yaw maneuvers, examples of other systematic deviations from the ideal GLONASS-K yaw attitude are presented.

The accurate knowledge of the Earth’s orientation and rotation in space is essential for a broad variety of scientific and societal applications. Among others, these include global positioning, near-Earth and deep-space navigation, the realisation of precise reference and time systems as well as studies of geodynamics and global change phenomena. In this paper, we present a refined strategy for processing and combining Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) observations at the normal equation level and formulate recommendations for a consistent processing of the space-geodetic input data. Based on the developed strategy, we determine final and rapid Earth rotation parameter (ERP) solutions with low latency that also serve as the basis for a subsequent prediction of ERPs involving effective angular momentum data. Realising final ERPs on an accuracy level comparable to the final ERP benchmark solutions IERS 14C04 and JPL COMB2018, our strategy allows to enhance the consistency between final, rapid and predicted ERPs in terms of RMS differences by up to 50% compared to existing solutions. The findings of the study thus support the ambitious goals of the Global Geodetic Observing System (GGOS) in providing highly accurate and consistent time series of geodetic parameters for science and applications.

We present two new high-precision physics-based radiation force models for the In-Orbit Validation (IOV) and Full Operational Capability (FOC) spacecraft (s/c) of the Galileo Global Navigation Satellite System (GNSS). In both cases, the s/c bus surfaces are cov-ered in material types, i.e., Laser Retro-reflector Array (LRA), Optical Surface Reflector (OSR) and Single-Layer Insulation (SLI) cov-erings, that were either not encountered or not specifically dealt with in earlier work. To address this, a number of modelling enhancements were proposed and tested, including: a specific model to account for the direct and reflected solar radiation force for LRA surfaces; a design update of the bus model computation process to allow for more than one insulation material; a specific thermal force model for OSR surfaces; a thermal force model for the Navigation Antenna (NAVANT) surface that includes a temperature model derived from on-orbit temperature measurements; and force models to account for thermal emissions from radiator panels on the thorn +X and +/- Y surfaces for both IOV and FOC, and on the -Z surface for FOC only. In the UCL2+ model each of these effects are accounted for. The theoretical impact of each modelling concept introduced is assessed, individually, by considering the magnitude of its effect in acceleration-space. The impact on orbit accuracy is confirmed through a rigorous set of Precise Orbit Determination (POD) validation tests, in which observations from all active Galileo s/c over two full years, 2017 and 2018, including during eclipsing periods, are included in the analysis. The UCL2+ approach results in day boundary discontinuities of 22 mm, 17 mm and 27 mm in the radial, across-track and along-track components, respectively. Analysis of the one-way Satellite Laser Ranging (SLR) residuals suggests that radial accuracy at better than 1 cm (3.7 mm mean residuals) and precision at better than 2 cm (17 mm root mean square (rms) error) is achievable with the UCL2+ model. (C) 2022 COSPAR. Published by Elsevier B.V.

With global mean sea level rising because of climate change, Copernicus Sentinel-6 is the radar altimetry reference mission to extend the legacy of sea-surface height measurements until at least 2030. The satellite carries a Poseidon-4 radar altimeter and a microwave radiometer. The analysis of the altimeter data relies on highly-accurate knowledge of the orbital position, in particular in the radial component, with errors below 1.5 cm. For this reason, Sentinel-6 carries several instruments, e.g., Laser Retroreflector Array, Doppler Orbitography and Radiopositioning Integrated By Satellite (DORIS) and also a dedicated GNSS receiver for generation of data, which allows to perform Precise Orbit Determination (POD) with the highest possible accuracy. For this reason, the GNSS receiver and respective GNSS observations is of particular interest for this paper because it is the first time that a high-quality dual frequency Galileo/GPS receiver is flown on-board of a Sentinel satellite. ESA’s Navigation Support Office (NavSO), located at the European Space Operations Centre (ESOC) in Darmstadt, Germany is providing an independent Precise Orbit Determination solution for all Sentinel satellites. As part of this activity, the office has been operationally computing and delivering the POD products, including the Sentine-6 multiGNSS-based precise orbits since its launch in November 2020. This presentation will describe the processing techniques adopted at ESOC, with a particular focus on the POD aspects and the related processing of the Galileo and GPS observations and their interoperability. The latest results and their validation are addressed in this paper.

The Y-bias as present on most global navigation satellite system (GNSS) spacecraft plays an important role in precise orbit determination and prediction. Accurate knowledge about the Y-bias and its temporal variability is particularly relevant for the Galileo system in order to fulfil its once-in-a-lifetime station-keeping maneuver requirements. Despite the widely recognized importance, however, no consensus has been reached on the physical mechanism that is responsible for the Y-bias. In this presentation, we shed light on the origins of the Galileo Y-bias using temperature and attitude data series from spacecraft telemetry to analytically determine Y-bias time histories for different Galileo satellites. We start by calculating the thermal radiation pressure forces generated by the two surface radiators at the main body's +Y and -Y sides of satellite GSAT0204 over a period of five years, from the activation of the spacecraft's search and rescue payload in early 2016 to the deactivation of its navigation payload in December 2017 and beyond. The net force from both radiators yields the Y-bias as it evolves over time, with some striking discontinuities due to abrupt changes in the amount of dissipated heat after the payload units have been turned on or off. Comparison against empirical Y-bias estimates from satellite laser ranging long arc analyses proves the correctness of our Y-bias model. In addition, we report on yearly variations in the Y-bias acceleration of GSAT0101 between -0.10 nm/s² and +0.05 nm/s², leading to a secular increase in the satellite orbit's semi-major axis since January 2016. Yaw error measurements from the spacecraft's fine sun sensor (FSS) spanning 2016-2019 provide compelling evidence that these Y-bias variations originate from an attitude-related mispointing of the satellite's solar panels by a few tenths of a degree. Least square fitting of the FSS measurements led to the development of a refined yaw model for GSAT0101. As a result of this new model, estimates of the Y-bias parameter are significantly reduced in magnitude and less dependent upon the position of the sun relative to the orbit plane. Overall, our analyses provide the first hard evidence that the Galileo Y-bias is primarily of thermal origin and, contrary to popular belief, that solar panel orientation errors only play a secondary role. The implications for precise orbit determination will be discussed. In addition, our results confirm the long-standing hypothesis that Y-bias and solar panel orientation error are linearly related.

The importance of an accurate global geodetic reference frame and associated Earth orientation parameters is undisputed and has been recognised by the UN resolution 69/266. Given the importance of global geodetic references, ESA is actively contributing to the IAG services: IGS, ILRS, IDS and the contribution to the IVS is in preparation. ESA’s activities can be divided into four main areas: the operation of Ground Infrastructure (ESTRACK, EGON, …), the establishment and improvement of inter-technique ties, the operation of a scientific data archive (GSSC) and the generation of geodetic products and services. This presentation will focus on the activities performed by the Navigation Support Office. The Navigation Support Office at ESA/ESOC is responsible for providing the Geodetic Reference Frame for all ESA missions and is also the Consortium Coordinator of the Galileo Geodetic Service Provider (GGSP) that generates the Galileo Geodetic Reference Frame (GTRF). Within its responsibilities, the Navigation Support Office is continuously working on improving the consistency of its geodetic products. The possibility to perform a Combination On the Observation Level (CoOL) for all geodetic observations is an excellent tool to identify inconsistencies. Over the recent years, significant improvements have been implemented in the data processing in order to enhance the consistency of the delivered products. As the status of the inter-technique ties remains a limiting factor in this context, ESA is currently investigating the possibility of using space ties, e.g. combining GNSS, SLR, DORIS and VLBI in space. This presentation will give an overview of the geodetic products and services generated by ESA’s Navigation Support Office and outline the associated processing setup. In particular, it will report on the analysis performed to improve the consistency of the results provided by the different observation techniques and outline the recent improvements and ongoing activities.

The availability of highly accurate Earth Orientation Parameters (EOPs) in near real time is of major importance for any type of positioning and navigation applications on Earth, Sea, Air and also in Space. This is equally true for all ESA missions and the EU space programs Galileo, EGNOS and Copernicus.To ensure operational capability, ESA’s Navigation Support Office developed independent EOP products and services.The EOPs are estimated based on a rigorous combination of the ESA’s contributions to the International Association of Geodesy (IAG) that are used as an input for the generation of the International Earth Rotation Service (IERS) products. For the ESA/ESOC EOP products, the individual parameters are combined on normal equation level and propagated with the contribution of model-based predicted Effective Angular Momentum (EAM) functions.The ESA/ESOC’s EOP product generation is currently running in pre-operational mode.This presentation will provide a high-level overview of the methodology and the status of ESA’s EOP products and services. In this context, the accuracy achieved in the test operations and the roadmap for the publication of ESA’s EOP products and services will be outlined.

The availability of highly accurate, up-to-date Earth Orientation Parameters is of major importance for all positioning and navigation applications on Earth, Sea, Air and also in Space. This is equally true for ESA missions and the EU space programs, e.g. Galileo, EGNOS and Copernicus. In the frame of its responsibility to provide the Geodetic reference for ESA missions, ESA’s Navigation Support Office at ESOC is already contributing to the realisation of the International Terrestrial Reference Frame (ITRF) and the combined Earth Orientation Parameters provided by the International Earth Rotation Service (IERS). The contribution is realised through individual contributions to international services such as the International GNSS Service (IGS), the International Laser Ranging Services (ILRS), the International DORIS Service (IDS), the International Earth Rotation Service (IERS) and in the future also to the International VLBI Service (IVS). For the combination and the long-term predictions of the Earth orientation products ESA is still relying on the International Earth Rotation Service (IERS). Over the past years, ESA repeatedly experienced problems with outdated or missing predictions of the Earth orientation parameters (Bulletin A). Considering the importance of up-to-date Earth orientation parameters, the dependence on a single source outside Europe is considered a risk for European industry, for ESA missions and for EU programmes. For this reason, ESA initiated in 2017 a study with the target to develop independent ESA Earth Orientation parameter products. This study, executed by a consortium led by the Deutsches Geodätisches Forschungsinstitut (DGFI-TUM), is expected to finish in the course of this year. In this presentation we will give an overview of ESAs up-to-date reference products and discuss their quality. It will outline the combination approach and discuss the way forward to an fully operational provision of the ESA Earth Orientation Parameter products.

Techniques enabling precise point positioning with ambiguity resolution (PPP-AR) were developed over a decade ago. Several analysis centers of the International GNSS Service (IGS) have implemented such strategies into their software packages and are generating (experimental) PPP-AR products including satellite clock and bias corrections. While the IGS combines individual orbit and clock products as standard to provide a more reliable solution, interoperability of these new PPP-AR products must be confirmed before they can be combined. As a first step, all products are transformed into a common observable-specific representation of biases. It is then confirmed that consistency is only ensured by considering both clock and bias products simultaneously. As a consequence, the satellite clock combination process currently used by the IGS must be revisited to consider not only clocks but also biases. A combination of PPP-AR products from six analysis centers over a one-week period is successfully achieved, showing that alignment of phase clocks can be achieved with millimeter precision thanks to the integer properties of the clocks. In the positioning domain, PPP-AR solutions for all products show improved longitude estimates of daily static positions by nearly 60% over float solutions. The combined products generally provide equivalent or better results than individual analysis center contributions, for both static and kinematic solutions.

To produce Global Navigation Satellite System (GNSS) orbits and clocks with high accuracy and for all constellations, the ESA’s Navigation Support Office (NSO) continually strives to keep abreast and improve its precise orbit determination (POD) strategies. In this presentation, we report on NSO’s recent developments and progress in Galileo and BeiDou POD. We first discuss the approach of improving Galileo POD solutions through a prudent combination of radiometric and satellite laser ranging (SLR) measurements at the observation level. For this technique to be effective, SLR normal point (NP) data from the Galileo SUCCESS campaign are used. Launched by the European Laser Network (EUROLAS) in the middle of May 2019, this three-week tracking campaign provided over 1000 NPs for two selected Galileo spacecraft: GSAT0102 and GSAT0220. We show that the precision of the GSAT0102 and GSAT0220 orbits is more than 10 percent better than that produced by solutions without SLR data. In this performance evaluation, we also discuss the presence of station-specific SLR biases, taking advantage of near-simultaneous SLR tracking by two or three separate laser sites. Additionally, we demonstrate that the SLR full-rate data from a single kHz laser system can be used to determine the Galileo satellites’ yaw state during eclipse maneuvers. This approach takes advantage of the 1.0 m distance between a Galileo spacecraft’s laser retroreflector array (LRA) and rotation axis to estimate the yaw angle in a recursive least-squares algorithm epoch by epoch. The method may serve as an interesting alternative to reverse kinematic point positioning (RPP), particularly for LRA-equipped satellites without significant transmit antenna phase center offsets. Finally, we present the first centimeter-quality orbit solutions for BeiDou’s third-generation series of medium Earth orbit (MEO) spacecraft. We discuss the POD strategy underlying these orbits and evaluate its performance by way of several metrics including laser range residuals, day-to-day orbit overlaps, satellite clock residuals, as well as RPP estimates as measure for the attitude model accuracy. Challenges pertaining to the satellite antenna phase center and radiation force modeling are addressed. The results on the overlap and SLR residuals suggest that our BeiDou-3 MEO orbits are accurate to better than 5 cm in all three components. Therefore, the new BeiDou constellation is fully integrated into our operational multi-GNSS routine, bringing the total number of daily processed GNSS satellites to more than 110 (http://navigation-office.esa.int/products/gnss-products).

For the previous ITRF calls for participation ESOC reprocessed the historic data from the IDS, IGS, and ILRS. Our three solutions were computed with a single software package (NAPEOS), running on the same machine and using, as far as possible, identical settings. Any systematic differences between the technique dependent reference frame solutions must therefore be caused by the techniques themselves, and not because of model differences or errors. Our three technique dependent solutions gave us a good understanding of the technique dependent effects, helping us to improve our models. At ESOC we have now made a significant step forward by including all satellite geodetic techniques (SLR, DORIS and GNSS) into one solution. This allows us to combine the ILRS, IDS and IGS reference frames by using “space ties”. Of course these space ties are not perfectly known but they still allow for a rigorous combination of the different reference frames. Furthermore, and very important for the GNSS technique, they allow for the direct estimation of the GNSS satellite transmitter phase centre offset. We solve not only for integer ambiguities of the GPS satellites but also for those of the LEO satellites, which is also providing GPS phase observations on two frequencies. Our poster presents an overview of this multi-technique combination approach at observation level (COOL). We have included all observations provided by the following satellites in a single parameter estimation process: GNSS, JASON, SPOT, Sentinels, GRACE, LAGEOS and Etalon satellites. We demonstrate the benefits of such a rigorous approach compared to processing the various space geodetic techniques separately.

Context : Calibration of radiometric tracking data for effects in the Earth atmosphere is a crucial element in the field of deep-space orbit determination (OD). The troposphere can induce propagation delays in the order of several meters, the ionosphere up to the meter level for X-band signals and up to tens of meters, in extreme cases, for L-band ones. The use of media calibrations based on Global Navigation Satellite Systems (GNSS) measurement data can improve the accuracy of the radiometric observations modelling and, as a consequence, the quality of orbit determination solutions. Aims : ESOC Flight Dynamics employs ranging, Doppler and delta-DOR (Delta-Differential One-Way Ranging) data for the orbit determination of interplanetary spacecraft. Currently, the media calibrations for troposphere and ionosphere are either computed based on empirical models or, under mission specific agreements, provided by external parties such as the Jet Propulsion Laboratory (JPL) in Pasadena, California. In order to become independent from external models and sources, decision fell to establish a new in-house internal service to create these media calibrations based on GNSS measurements recorded at the ESA tracking sites and processed in-house by the ESOC Navigation Support Office with comparable accuracy and quality. Methods : For its concept, the new service was designed to be as much as possible depending on own data and resources and as less as possible depending on external models and data. Dedicated robust and simple algorithms, well suited for operational use, were worked out for that task. This paper describes the approach built up to realize this new in-house internal media calibration service. Results : Test results collected during three months of running the new media calibrations in quasi-operational mode indicate that GNSS-based tropospheric corrections can remove systematic signatures from the Doppler observations and biases from the range ones. For the ionosphere, a direct way of verification was not possible due to non-availability of independent third party data for comparison. Nevertheless, the tests for ionospheric corrections showed also slight improvements in the tracking data modelling, but not to an extent as seen for the tropospheric corrections. Conclusions : The validation results confirmed that the new approach meets the requirements upon accuracy and operational use for the tropospheric part, while some improvement is still ongoing for the ionospheric one. Based on these test results, green light was given to put the new in-house service for media calibrations into full operational mode in April 2017.