GNSS Satellite Orbit Validation Using Satellite Laser Ranging

With a total of four new regional and global navigation satellite systems that have launched first satellites or even started an operational service, the GNSS landscape has experienced major changes in recent years. As part of the Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS), a global network of multi-GNSS monitoring stations has been established and various analysis centers have started to determine orbits of selected GNSSs on a routine basis. As a key feature, all satellites of the new constellations (i.e. Galileo, BeiDou, QZSS and IRNSS) are equipped with laser ranging reflector arrays enabling high-precision two way ranging measurements. The paper illustrates the use of SLR observations collected by the ILRS for validation of precise and broadcast ephemerides of the new constellations. As an independent and unambiguous tracking system, SLR helps to gain a better understanding of the new satellites, which still lack a thorough characterization of their orbit and attitude dynamics. SLR tracking is thus considered an essential contribution for a future use of the new GNSSs in space geodesy. The paper also addresses operational aspects of SLR tracking of the new navigation satellites related to their specific orbits, regional distribution and continuously increasing number.