GPS World, May 2017
42 GPS WORLD WWW GPSWORLD COM MAY 2017 WITH RICHARD B LANGLEY S atellite laser ranging or SLR has been an indispensable independent tool for validating the precise orbits determined for GNSS satellites using microwave pseudorange and carrierphase observations for several decades SLR has allowed researchers to identify several orbit modeling issues Adding albedo radiation pressure and antenna thrust among other effects into the GPS orbit model allowed them to eliminate the observed bias between microwave and SLR derived orbits For the first Galileo satellites launched SLR residuals indicated severe orbit modeling issues caused by the different shape of Galileo satellite bodies compared to those of GPS In the future all GNSS satellites will be equipped with laser retroreflectors a big challenge for researchers concerning tracking scenarios and observation planning to make economic use of the ground equipment Satellite orbit Laser retroreflector array on a satellite Laser pulse Laser ranging station Laser pulse start Photon return stop Measurement of round trip time of laser pulse Station coordinates and satellite orbit determination relative to Earths center In this article we will take a brief look at the history of laser ranging to navigation satellites how that ranging has improved the accuracy of the orbits of those satellites and what the future portends for this important contribution to space geodesy KINDRED SPIRITS Laser Ranging to GNSS Satellites By Urs Hugentobler FIGURE 1 Operating principle of satellite laser ranging
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