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Galileo satellites transmit microwave signals on five frequencies. By assessing the carrier-to-noiseratios and pseudorange noise of multi-signal measurements from different sites, we confirm that E1, E5a, E5b and E6 observations have similar measurement quality. The combined E5 AltBOC tracking is superior as a result of a very large signal bandwidth. The manufacturer-provided frequency-specific phase center offsets of Galileo satellites are proven to be consistent with each other, with the largest difference of 4.7 cm in the Z direction between E1/E5b and E1/E6 ionosphere-free linear combination. The major part of this difference generates a constant bias that can be absorbed by satellite biases in the multi-frequency processing. Satellite phase biases of individual signals in accord with E1/E5a satellite clock offsets are in general constant over time. Only phase biases of the E6 signal from the early IOV satellites show a drift of about 25 mm/d. Considering the daily STD value of this drift (6 mm) to the wavelength (20 cm) of each phase ambiguity, it is reasonable to estimate daily constant phase biases for E6 signals. Based on these preconditions, Galileo satellite products determined from multi-frequency measurements show higher precision than those from dual-frequency measurements when using a small ground network. For instance, the ambiguity fixing rate is 80% in the multi-frequency solution while it is less than 40% in the dual-frequency solution if a 15-station network is used. With multi-frequency Galileo satellite products, kinematic PPP-AR solutions are more robust and precise (5-10 %) than those computed from dual-frequency observations., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Along with the gradual deployment of new GNSS constellations, the International GNSS Service (IGS) has pursued the extension of its GPS and GLONASS work into a true multi-GNSS service. Supported by numerous national agencies and individual institutions a global network of more than 200 monitoring stations has been established, which supports tracking of Galileo, BeiDou, QZSS, in addition to the legacy navigation systems. In the frame of the IGS Multi-GNSS pilot project (MGEX), six analysis centers (ACs) are now generating precise orbit and clock solutions for new constellations. Out of these, three ACs provide comprehensive multi-GNSS product covering all five constellations. The presentation discusses the deployment and capabilities of old and new GNSSs and describes the status and achievements of the MGEX project within the IGS. The orbit and clock product quality of new GNSS constellations is addressed and remaining limitations for their use are identified. Special attention is given to the prospects of Galileo, which is close to completing a full constellation and offers high accuracy signals for precise point positioning users.

Space debris in geostationary orbits may be detected with optical telescopes when the objects are illuminated by the Sun. The advantage compared to Radar can be found in the illumination: radar illuminates the objects and thus the detection sensitivity depletest proportional to the fourth power of the d istance. The German Space Operation Center, GSOC, together with the Astronomical Institute of the University of Bern, AIUB, are setting up a telescope system called SMARTnet to demonstrate the capability of performing geostationary surveillance. Such a telescope system will consist of two telescopes on one mount: a smaller telescope with an aperture of 20cm will serve for fast survey while the larger one, a telescope with an aperture of 50cm, will be used for follow-up observations. The telescopes will be operated by GSOC from Oberpfaffenhofen by the internal monitoring and control system called SMARTnetMAC. The observation plan will be generated by MARTnetPlanning seven days in advance by applying an optimized planning scheduler, taking into account fault time like cloudy nights, priority of objects etc. From each picture taken, stars will be identified and everything not being a star is treated as a possible object. If the same object can be identified on multiple pictures within a short time span, the trace is called a tracklet. In the next step, several tracklets will be correlated to identify individual objects, ephemeris data for these objects are generated and catalogued . This will allow for services like collision avoidance to ensure safe operations for GSOC’s satellites. The complete data processing chain is handled by BACARDI, the backbone catalogue of relational debris information and is presented as a poster.

As the number of space debris is increasing in the geostationary ring, it becomes mandatory for any satellite operator to avoid any collisions. Space debris in geosynchronous orbits may be observed with optical telescopes. Other than radar, that requires very large dishes and transmission powers for sensing high-altitude objects, optical observations do not depend on active illumination from ground and may be performed with notably smaller apertures. The detection size of an object depends on the aperture of the telescope, sky background and exposure time. With a telescope of 50 cm aperture, objects down to approximately 50 cm may be observed. This size is regarded as a threshold for the identification of hazardous objects and the prevention of potentially catastrophic collisions in geostationary orbits. In collaboration with the Astronomical Institute of the University of Bern (AIUB), the German Space Operations Center (GSOC) is building a small aperture telescope to demonstrate the feasibility of optical surveillance of the geostationary ring. The telescope will be located in the southern hemisphere and complement an existing telescope in the northern hemisphere already operated by AIUB. These two telescopes provide an optimum coverage of European GEO satellites and enable a continuous monitoring independent of seasonal limitations. The telescope will be operated completely automatically. The automated operations should be demonstrated covering the full range of activities including scheduling of observations, telescope and camera control as well as data processing.