# Laser Observations of GALILEO Satellites at the CBK PAN Astroegodynamic Observatory in Borowiec
## 1 Introduction  
The Astroegodynamic Observatory of the Space Research Centre of the Polish Academy of Sciences in Borowiec is a unique research center in Poland. It is the only facility in the country that conducts both local and global geodynamic, metrological, and gravimetric research related to time. The observatory regularly performs measurements using laser technology (Satellite Laser Ranging--SLR) and Global Navigation Satellite Systems (GNSS) like GPS, GLONASS, GALILEO, and BeiDou, as well as gravimetric techniques [1]. The results of laser observations from the BORL station were obtained using picosecond and nanosecond pulsed Nd:YAG lasers to determine the orbits of various satellites and space debris objects. The high accuracy and precision of picosecond laser measurements support global research in geodesy, geodynamics, and geophysics. The processing of these measurements contributes to defining the International Terrestrial Reference System (ITRS), which is physically implemented as the International Terrestrial Reference Frame (ITRF). The ITRF is created and maintained by the International Earth Rotation and Reference Systems Service (IERS). Additionally, the laser ranging measurements are used for calibrating GNSS orbits, determining the positions and velocities of ground stations, and calculating coefficients of the Earth's gravitational field and their variations over time (models of the Earth'sgravitational field), tidal parameters, determining the parameters of the Earth's rotation, and validation of satellite orbits [2; 3; 4; 5; 6; 7; 8; 9; 10]. The CBK PAN observatory in Borowiec contributes to global research by studying the rotation of satellites and space debris. This research is crucial for enhancing the understanding of artificial objects' orbits in Earth's orbit. The laser observations conducted by CBK PAN have enabled active participation in the development of the national and European Space Surveillance and Tracking (SST) program, which is a key component of the Space Situational Awareness (SSA) program, which is a flagship initiative of the European Commission and the Space Safety program of the European Space Agency (ESA). Additionally, CBK PAN has engaged in new campaigns and observation programs, including safeguarding the European SENTINEL satellites of the COPERNICUS system, which is a significant space program of the European Commission. In 2023, the BORL laser station began conducting regular measurements of the GALILEO satellites, which form the European Union's Global Navigation Satellite System. The system currently comprises 28 satellites. GALILEO is compatible with the GPS and GLONASS systems. It is managed by the European Union Agency for the Space Program (EUSPA) with its headquarters in Prague, Czechia. The Control Centers are situated in Oberpfaffenhofen, Germany, and Fucino, Italy. The International Laser Ranging Service (ILRS) [3] coordinates laser observations of satellites, involving 44 laser stations from around the world [11]. According to data from the ILRS, the first successful laser measurements of GALILEO satellites were carried out on 29 November 2011, using the now-closed Transportable Integrated Geodetic Observatory (TIGO) laser station in Concepcion, Chile. The measurements involved the GALILEO-FM2 satellite, identified as NORAD 37847. Currently, the ILRS coordinates the observations of 122 objects in all orbital regimes from low Earth orbit (LEO) to Geostationary Orbit (GEO) [12]. Two, so-called \"LARGE\" GNSS satellite observation campaigns have been conducted, involving satellites from the GLONASS, GALILEO, and COMPASS systems. The initial GNSS satellite campaign, referred to as the first LARGE campaign, took place from 15 February to 15 May 2018. It involved 10 GALILEO satellites being observed by 30 ILRS stations and resulted in a total of 9107 normal points [13]. The subsequent campaign, known as the second LARGE campaign, featured 8 GALILEO satellites and occurred from 1 August to 31 October 2018.