Ranging the GNSS Constellation

Laser ranging is an indispensable independent tool for validating the precise orbits determined for GNSS satellites using microwave pseudorange observations since decades. SLR allowed it to identify orbit modeling issues. Including albedo radiation pressure and antenna thrust, among others, into the GPS orbit model allowed it to basically eliminate the observed SLR bias. For the first Galileo satellites SLR residuals indicated severe orbit modeling issues caused by the different shape of Galileo compared to GPS satellite bodies. In future all GNSS satellites will be equipped with Laser retro reflectors, a big challenge for the ILRS concerning tracking scenarios and observation planning to make economic use of the ground equipment.