# A New Online Service for the Validation of Multi-GNSS Orbits Using SLR
## 1 Introduction
### Role of GOVUS in the Development of SLR and Multi-GNSS  
There are three main potential users of GOVUS: (1) ILRS stations and users of their products; (2) MGEX ACs; and (3) users of multi-GNSS products. The existing ACs and Associated Analysis Centers (AAC) of the ILRS are mostly focused on the processing of the measurements to the geodetic satellites (e.g., LAGEOS, Etalon, and LARES). In 2016, the number of Normal Points to High Orbiting Objects was already larger than the number of Normal Points to the LAGEOS satellites by about 5%. Therefore, the SLR observations to GNSS may have a great potential for the geodetic community in terms of providing a link between SLR and GNSS and for deriving global geodetic parameters. The GOVUS service is one of a few ILRS ACs focused on making use of SLR observations to GNSS satellites. The tools available in GOVUS give both the stations and the users detailed information about the daily performance of the whole network, as well as particular stations.  
The GNSS satellite constellation is the most emerging group of SLR targets in the last decades, hence the laser stations will be soon struggling with progressively more difficulties in monitoring many overlapping passes [36]. The laser stations have been intensively working on the optimization of tracking schedules for GNSS, with a care not to suffer the primary LAGEOS tracking at the same time. The most technologically advanced stations, e.g., Herstmonceux in the UK, allow for a daytime tracking and efficient switching between satellites, which improves the tracking schedule and essentially increases the data yield without impacting on the priority of LAGEOS and LEO satellites tracking [23; 36]. The consciousness of the performance of the laser stations is essential in a proper evaluation of the MGEX products. Currently used, publicly available information about the SLR validation of the multi-GNSS products is officially delivered by the MGEX in the form of static plots and tables [37]. The goal of GOVUS is to extend the information delivered by current services with the functionality of the up-to-date public database supported by user-friendly, interactive tools. The goal of GOVUS is also to allow for more complex investigations through filtering of source dataset, e.g., to exclude unreliable laser stations, blunders, or to focus on the particular aspects of the observational frame in the context of relative positions of the satellite with respect to the position of the Earth and the Sun. With this functionality we are able to divide the biases which actually originate from the stations' characteristics, e.g., range biases, detector-related biases, from general problems of models used for the multi-GNSS orbit determination, e.g., mismodeling of the solar radiation pressure, antenna thrust, albedo or mismodeling of the satellite attitude, as well as an anomalistic behavior of particular satellites in the constellation. All of these capabilities would crosslink the extensive knowledge about the station-satellite dependencies and multi-GNSS orbit quality. Both IGS and ILRS provide today observations originating from the multi-GNSS constellation and put a lot of effort on a continuous and comprehensive improvement of multi-GNSS products. Therefore, data and tools available for every user in GOVUS may contribute to strengthening the link between IGS and ILRS communities as their common interest is using GNSS products of the highest possible quality.