GPS World, May 2017

variations of onboard clocks Eventually the role of SLR will become even more important by contributing to the precise orbit determination of GNSS satellites Given the large number of GNSS satellites from several constellations equipped with retroreflectors coordination of observation scheduling among SLR stations will be crucial for optimizing the benefit to cost ratio Concerning the distribution of SLR observations over the constellations the following conclusions may be drawn For the validation and calibration of radiation pressure models it is sufficient to acquire well distributed observations along the orbit of one satellite for each constellation block type for a range of solar beta angles that is of one satellite block type per orbital plane For contributing to precise orbit products optimally combined with microwave GNSS observations the tracking of all satellites of a constellation is needed This requires a coordinated scheduling of observations among SLR stations For determination of the gravitational redshift parameter using the two Galileo satellites in eccentric orbits good coverage of the orbits of both satellites is required as long as the satellites run on one of the onboard hydrogen maser clocks For BeiDou and NavIC geostationary satellites SLR coverage is needed for all satellites to resolve biases in the microwave tracking technique 48 GPS WORLD WWW GPSWORLD COM MAY 2017 In the long term SLR observations could contribute together with microwave observations in providing operational high precision orbit products for all GNSS constellations jointly by the ILRS and the IGS in the framework of the IAGs Global Geodetic Observing System ACKNOWLEDGMENTS This article is based on the invited paper Ranging the GNSS Constellation presented at the 20th International Workshop on Laser Ranging held in Potsdam Germany Oct 10 14 2016 Figure 1 was adapted from an image in Expert Advice Laser Reflectors to Ride on Board GPS III published by GPS World GPS Galileo BeiDou and NavIC retroreflector images obtained from the ILRS The GLONASS retroreflector image was obtained from ISS Reshetnev Opening photo Nighttime ranging at NASAs Next Generation SLR system at Goddard Space Flight Center Maryland Credit Felipe Hall HTSI URS HUGENTOBLER is a professor of satellite geodesy at the Technische Universität München Germany and head of the Satellite Geodesy Research Facility in the Institute for Astronomical and Physical Geodesy He is also a former chair of the IGS Governing Body His research activities include precise positioning using GNSS precise orbit determination and modeling reference frame realization clock modeling and time transfer using both the legacy and new satellite systems Hugentobler obtained his Ph D from the University of Bern Switzerland in 1997 FURTHER READING Authors Conference Paper Ranging the GNSS Constellation by U Hugentobler presented at the 20th International Workshop on Laser Ranging held in Potsdam Germany Oct 10 14 2016 Available on line https cddis nasa gov lw20 docs 2016 papers 19 Hugentobler paper pdf Early Work on Satellite Laser Ranging Satellite Laser Ranging Current Status and Future Prospects by J J Degnan in IEEE Transactions on Geoscience and Remote Sensing Vol GE 23 No 4 July 1985 pp 398 413 doi 101109 TGRS 1985289430 Reflection of Ruby Laser Radiation from Explorer XXII by H H Plotkin T S Johnson P Spandin and J Moye in Proceedings of the IEEE Vol 53 No 3 March 1965 pp 301 302 doi 101109 PROC 19653694 Early Work on GPS Orbit Modeling Extended Orbit Modeling Techniques at the CODE Processing Center of the International GPS Service for Geodynamics IGS Theory and Initial Results by G Beutler E Brockmann W Gurtner U Hugentobler L Mervart M Rothacher and A Verdun in Manuscripta Geodaetica Vol 19 1994 pp 367 386 The International Laser Ranging Service The International Laser Ranging Service by M R Pearlman J J Degnan and J M Bosworth in Advances in Space Research Vol 30 No 2 July 2002 pp 135 143 doi 101016 S0273 1177 02 00277 6 SLR Tracking of GNSS Constellations Satellite Laser Ranging to GPS and GLONASS by K Sósnica D Thaller R Dach P Steigenberger G Beutler and D Arnold in Journal of Geodesy Vol 89 No 7 July 2015 pp 725 743 doi 101007 s00190 015 0810 8 IRNSS Orbit Determination and Broadcast Ephemeris Assessment by O Montenbruck P Steigenberger and S Riley in Proceedings of ION ITM 2015 the 2015 International Technical Meeting of The Institute of Navigation Dana Point California Jan 26 28 2015 pp 185 193 Expert Advice Laser Reflectors to Ride on Board GPS III by J Miller J LaBrecque and A J Oria in GPS World Vol 24 No 9 Sept 2013 pp 12 17 Available on line http gpsworld com expert advice laser reflectors to rideon board gps iii Initial Results of Precise Orbit and Clock Determination for COMPASS Navigation Satellite System by Q Zhao J Guo M Li L Qu Z Hu C Shi and J Liu in Journal of Geodesy Vol 87 No 5 May 2013 pp 475 486 doi 101007 s00190 013 0622 7 Contribution of SLR Tracking Data to GNSS Orbit Determination by C Urschl G Beutler W Gurtner U Hugentobler and S Schaer in Advances in Space Research Vol 39 No 10 2007 pp 1515 1523 doi 101016 j asr 200701038 Laser Ranging to GPS Satellites with Centimeter Accuracy by J J Degnan and E C Pavlis in GPS World Vol 5 No 9 Sept 1994 pp 62 70 Available on line http www2 unb ca gge Resources gpsworld september94 pdf Multi GNSS Experiment IGS MGEX Preparing the Ground for Multi Constellation GNSS Science by O Montenbruck P Steigenberger R Khachikyan G Weber R B Langley L Mervart and U Hugentobler in Inside GNSS Vol 9 No 1 Jan Feb 2014 pp 42 49 Available on line http www insidegnss com auto janfeb14 MONTENBRUCK pdf Effect of Radiation Pressure on GNSS Satellite Orbits CODEs New Solar Radiation Pressure Model for GNSS Orbit Determination by D Arnold M Meindl G Beutler R Dach S Schaer S Lutz L Prange K Sósnica L Mervart and A Jäggi in Journal of Geodesy Vol 89 No 8 Aug 2015 pp 775 791 doi 101007 s00190 015 0814 4 Enhanced Solar Radiation Pressure Modeling for Galileo Satellites by O Montenbruck P Steigenberger and U Hugentobler in Journal of Geodesy Vol 89 No 3 March 2015 pp 283 297 doi 101007 s00190 014 0774 0 Impact of Earth Radiation Pressure on GPS Position Estimates by C J Rodriguez Solano U Hugentobler P Steigenberger and S Lutz in Journal of Geodesy Vol 86 No 5 May 2012 pp 309 317 doi 101007 s00190 011 0517 4 Modeling Photon Pressure The Key to Highprecision GPS Satellite Orbits by M Ziebart P Cross and S Adhya in GPS World Vol 13 No 1 Jan 2002 pp 43 50 Available on line http www2 unb ca gge Resources gpsworld january02 pdf Testing Relativity Theory Test of the Gravitational Redshift with Stable Clocks in Eccentric Orbits Application to Galileo Satellites 5 and 6 by P Delva A Hees S Bertone E Richard and P Wolf in Classical and Quantum Gravity Vol 32 No 23 2015 doi 101088 0264 9381 32 23 232003