Orbits from Global Navigation Satellite Systems (GNSS) are typically based on microwave observations. Satellite Laser Ranging (SLR) is therefore a fully independent technique to validate these orbits. All GLONASS, Galileo, BeiDou, and QZSS spacecraft carry retroreflectors and can thus be tracked by SLR. The two GPS satellites equipped with reflectors are meanwhile decommissioned. The Center for Orbit Determination in Europe (CODE) operationally computes SLR residuals w.r.t. CODE’s rapid and MGEX orbits and provides daily reports to the laser stations. At the same time, the residuals are used for internal orbit validation purposes.

In the present study, we show the results of the multi-year processing of SLR observations to GNSS satellites (both for GPS and GLONASS satellites), using the Bernese GNSS Software. The aim of the study is to investigate the associated SLR range residuals, defined as the differences between: (a) the observed SLR ranges and (b) the computed spatial distances between the ground stations and the GNSS (precise) orbits, respectively. The residuals are estimated on daily basis, taking into account inter alia, the Non Tidal Atmospheric Loading (NTAL) and the Atmospheric Ocean De-aliasing (AOD) effect. The results indicate different biases for the GPS and GLONASS satellites and show remarkable variability among the ground stations.

The US Navy's GEOSAT Follow-On spacecraft was launched on February 10, 1998 with its primary mission objective to map the oceans using a radar altimeter. The spacecraft tracking complement consists of GPS receivers, a laser retroreflector and Doppler beacons. Since the GPS receivers have not yet returned reliable data, the only means of providing high-quality precise orbits has been though satellite laser ranging (SLR). SLR has tracked the spacecraft since April 22, 1998, and an average of 7 passes per day have been obtained from US and foreign stations. Since the predicted radial orbit error due to the gravity field is only two to three cm, the largest contributor to the high SLR residuals (10 cm) is the mismodelling of the non-conservative forces. The SLR residuals show a clear correlation with beta prime (solar elevation) angle, peaking in mid-August 1998 when the beta prime angle reached -80 to -90 degrees. We report in this paper on the analysis of the GFO tracking data (SL...

ABSTRACT Satellite laser ranging (SLR) to the satellites of the global navigation satellite systems (GNSS) provides substantial and valuable information about the accuracy and quality of GNSS orbits and allows for the SLR-GNSS co-location in space. In the framework of the NAVSTAR-SLR experiment two GPS satellites of Block-IIA were equipped with laser retroreflector arrays (LRAs), whereas all satellites of the GLONASS system are equipped with LRAs in an operational mode. We summarize the outcome of the NAVSTAR-SLR experiment by processing 20 years of SLR observations to GPS and 12 years of SLR observations to GLONASS satellites using the reprocessed microwave orbits provided by the center for orbit determination in Europe (CODE). The dependency of the SLR residuals on the size, shape, and number of corner cubes in LRAs is studied. We show that the mean SLR residuals and the RMS of resid-uals depend on the coating of the LRAs and the block or type of GNSS satellites. The SLR mean residuals are also a function of the equipment used at SLR stations including the single-photon and multi-photon detection modes. We also show that the SLR observations to GNSS satellites are important to validate GNSS orbits and to assess deficiencies in the solar radiation pressure models. We found that the satellite signature effect, which is defined as a spread of optical pulse signals due to reflection from multiple reflectors, causes the variations of mean SLR residuals of up to 15 mm between the observations at nadir angles of 0 • and 14 •. in case of multi-photon SLR stations. For single-photon SLR stations this effect does not exceed 1 mm. When using the new empirical CODE orbit model (ECOM), the SLR mean residual falls into the range 0.1–1.8 mm for high-performing single-photon SLR stations observing GLONASS-M satellites with uncoated corner cubes. For best-performing multi-photon stations the mean SLR residuals are between −12.2 and −25.6 mm due to the satellite signature effect. Keywords SLR · GNSS · Precise orbit determination · Satellite signature effect · Corner cube coating · SLR reflector types

The Global Positioning System (GPS) employs satellites in medium earth orbit (MEO) to aid travel in the West by providing exact positioning. Relativity theory indicates that clock frequency corrections are required for precise positioning between the Earth and satellites. This paper contains an original formula for gravitational red shift and inertial frequency corrections in addition to GPS frequency corrections for prograde and retrograde satellite motion.