# Laser Observations of GALILEO Satellites at the CBK PAN Astroegodynamic Observatory in Borowiec
## 4 The Results of Laser Ranging to the GALILEO Satellites  
The laser measurements for GALILEO satellites were conducted from 2 April to 28 December 2023. During this period, 77 successful observations of 21 GALILEO satellites were made. A total of 342 normal points and 7419 returns were recorded during these observations, with an average RMS of 1.35 cm for all measurements. The results for all satellites are gathered in Table 2. The normal point window (bin size) for GALILEO satellites is set at 300 s. The laser was fired at the satellites for a total of 33 h, 40 min, and 22 s. The effective measurement time, which is the time when returns were obtained, was 24 h, 21 min, and 14 s.  
The most successful measurements were obtained for the G104 (E20), G103 (E19), and G212 (E03) satellites, with 2534, 1118, and 623 returns, respectively. The fewest measurements were obtained for satellites G215 (E21), G204 (E22), G203 (E26), G219 (E36), and G216 (E25), with 17, 24, 32, 36, and 39 returns, respectively. The average root mean square (RMS) from all passes for individual satellites ranges from 0.92 cm to 1.76 cm. The observation conditions for GALILEO satellites at the BORL station have been established to begin when the objects are at an elevation of 50 degrees. The maximum duration for a single-pass observation is limited to 30 min, which is the longest observation period allowed at the BORL station. This limitation is necessary because the GALILEO satellites have high orbits at approximately 23,200 km, resulting in extended pass times over the station, lasting several hours and up to a maximum of around 6.5 h when passing at the zenith. Other objects with high observational priority also pass by during these long pass times.  
There are more than 100 objects on the tracking list at the BORL station. If the observation window permits, it can take measurements of the same GALILEO satellite in the next observation slot. The highest number of normal points obtained during a single pass was seven. Typically, there are four normal points per one GALILEO's observation, and the average duration of successful measurements is approx. 19 min.  
Figures 5-8 display sample results of laser measurements taken by the BORL sensor for four GALILEO satellites: G212 (E03), GALILEO-104 (E20), GALILEO-208 (E08), and GALILEO-202 (E14). The slant range plots clearly show distinct lines with echoes received from the observed satellites. The fit residuals obtained after post-processing range within single centimeters, with a maximum of +/\(-\) 8 cm. The average pass RMS for the passes shown in Figures 5-8 is 1.61 cm, the average time bias 11.83 ms, and the average range bias \(-\)10.10 m. The results from the BORL station demonstrate high quality and enable the BORL laser station to actively participate in new LARGE campaigns dedicated to GNSS satellites.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**NR** & **SATNAME** & **PASSES** & **RETURNS** & **NORMAL POINTS** & **AVG RMS [cm]** \\ \hline  
\end{tabular}
\end{table}
Table 2: The results of the observations of GALILEO satellites obtained by the BORL station in 2023.  
Figure 5: Pass of GALILEO-212 (E03) registered by the BORL sensor on 3 May 2023, 23:12 UTC, showing slant ranges (**a**) and fit residuals (**b**) with 159 valid returns. The min. and max. distances to the satellite were 23,589 km and 23,790 km, respectively.  
Figure 6: Pass of GALILEO-104 (E20) registered by the BORL sensor on 21 May 2023, 21:27 UTC, showing slant ranges (**a**) and fit residuals (**b**) with 592 valid returns. The min. and max. distances to the satellite were 23,701 km and 24,115 km, respectively.  
Figure 7: Pass of GALILEO-208 (E08) registered by the BORL sensor on 22 May 2023, 20:59 UTC, showing slant ranges (**a**) and fit residuals (**b**) with 214 valid returns. The min. and max. distances to the satellite were 23,612 km and 23,958 km, respectively.