The COMET-ORB invites you to a seminar on Satellites Orbit Determination Improvements and Applications will take place on January 21, 2025, from 9:30 to 16:00.

You can follow the presentation in person at Artilect, in Toulouse (10 Rue Tripière, 31000 Toulouse - https://artilect.fr/) , France, or remotely.

If you plan on attending the presentation in person, you must register at this link to obtain your pass to enter Artilect : https://evenium.events/7kc1cryr/

Because we size the coffee breaks and meals based on the registration list, we kindly ask you to register only if you really intend to come.

If you plan on attending the presentation remotely, or if you want access to it later, please register at this link : https://app.livestorm.co/comet-cnes/gnss-satellites-orbit-determination-improvements-and-applications

Agenda

Abstracts

Introduction to GNSS positioning methods - Marie ANSART

This presentation is an introduction to the seminar. It explains the basis of GNSS positioning to understand how a position on Earth can be retrieved from satellites and can be known at a specific time. Then, an overview of the absolute and relative techniques will be presented. Finally, a focus on precise techniques for meter-level and centimeter-level performances will be done. A synthesis of precise positioning techniques will be given to explain the characteristics and the dependency between each other. Alternative means are given as a conclusion such as hybridization (sensor fusion) and GNSS LEO constellations.

The CNES PPP-WIZARD tool for real time GNSS satellites orbits determination and corrections computation - Clément GAZZINO

Since 2020, the CNES navigation team has set up a demonstrator for using undifferenced and uncombined carrier phase measurements with integer ambiguity resolution for real time orbit determination, time synchronization, and GNSS satellites code and phase biases determination. These corrections are then used by a receiver in order to perform precise point positioning. The aim of this presentation is to review the algorithms and the implementation of such a demonstrator, and to propose some evolutions for the upcoming years.

Moonlight Lunar Communications and Navigation Services – E2E Navigation Chain Overview - Cosimo STALLO

The Moonlight Lunar Communications and Navigation Services (LCNS) programme will enable precise, autonomous landings and surface mobility, while facilitating high-speed, low-latency communication and data transfer between Earth and the Moon. The Moonlight programme addresses critical needs in human and robotic space exploration while creating commercial opportunities for European industry in the emerging lunar economy. It will play a crucial role in supporting future deep space exploration efforts. Moonlight will consist of five satellites – four for navigation and one for communications – connected to Earth via three dedicated ground stations, creating a data network spanning up to 400 000 km. The satellites will be strategically positioned to prioritise coverage of the lunar south pole. This presentation will focus on the E2E navigation chain overview of Moonlight and describe its design, expected performances and how it will support future landing and surface missions.

- Flavien MERCIER

TBC

Composite timescales and clock modelling for precise orbit determination of GNSS satellites - Pedro ROLDAN GOMEZ

The determination of GNSS orbits is generally based on the processing of pseudorange and carrier phase measurements from a station network, with an Orbit Determination and Time Synchronization (ODTS) process. This process involves the satellite and ground station clocks as part of the GNSS measurement reconstruction. The clocks are generally estimated as a snapshot parameter, without assuming any correlation between epochs. However, the stability of satellite and some station clocks, based on technologies of hydrogen, cesium or rubidium, allows for a significant predictability. Taking advantage of this predictability the ODTS process can be improved, especially in those cases where the station network is limited or does not provide a good coverage for certain areas.

The clock modelling can be directly done by estimating additional parameters in the filter. A quadratic model is generally estimated for each clock, keeping a small snapshot contribution to account for the stochastic part and for potential deviations with respect to the theoretical behavior of the clock. The detection of this kind of deviations in the satellite and station clocks becomes a major factor for achieving a good performance with these techniques. In case the clock experiences feared events like phase or frequency jumps, the estimated clock model stops being valid and the estimation of model parameters needs to be reset.

In case a composite clock algorithm is used to provide the reference timescale for the ODTS, the estimation of clock models can rely on this algorithm. Algorithms of composite clock are generally based on a Kalman filter that estimates as part of the state vector the differences between each contributing clock and the composite timescale. These differences can be used not only to define the reference timescale of the ODTS, but also to remove the deterministic part of the clocks in the measurement reconstruction. As for the case of clock modelling, for algorithms of composite clock the detection and correction of anomalies in the contributing clocks becomes a critical point.

This presentation focuses on the integration of orbit determination, clock modelling and composite clock algorithms. It includes the architectures needed for this integration, as well as the algorithms more frequently used and the results of an experimentation campaign performed with these algorithms. This experimentation was based on NEODIS, the ODTS software developed by Thales Alenia Space, which integrates with a Kalman filter approach GNSS orbit determination and composite clock algorithms.

Improving GNSS Navigation Messages Performance using Inter Satellite Links Technology - Pierre GUERIN

For decades, the accuracy of satellite constellations’ navigation messages has continued to increase. One of the next expected major step towards an increased performance is the exploitation of Inter-Satellite Links (ISL). These links allow both data exchange and navigation measurements (carrier code, phase code, Doppler). If properly hybridized inside an orbit determination process with classical GNSS measurements taken on the ground, ISL measurements could provide additional intra and inter plane observability, which "freezes" the constellation as a whole. The navigation message accuracy should therefore significantly benefit from the improved geometry.

ESA Genesis - Guilhem MOREAUX

The Genesis mission was endorsed by the ESA Ministerial Council in November 2022. The mission will be executed under the responsibility of ESA’s Navigation Directorate as an element of the Future Navigation Program in cooperation with ESA’s Operations Directorate. Genesis is scheduled to launch in 2028.

The ESA Genesis mission will be the first satellite to collocate on board the four space-based geodetic techniques: DORIS (Doppler Orbitography and Radio-positioning Integrated by Satellite), GNSS (Global Navigation Satellite System), SLR (Laser Satellite Ranging) and VLBI (Very Long Baseline Interferometry). This collocation in space will help to identify any systematic errors in the ITRF and thereby will contribute to a significant improvement of the International Terrestrial Reference Frame (ITRF). The final goal of the mission is to generate an updated more precise global model of the ITRF with an accuracy down to 1 mm, while tracking ground motion of just 0.1 mm per year. This improvement may have a major impact on several GNSS and Earth observation applications (e.g. plate tectonics, sea level rise, ice melting).

The presentation will describe how the current ITRF realizations are computed and how the Genesis missions may contribute to future ITRF solutions.