World first SCF-Test of the NASA-GSFC LAGEOS Sector and Hollow Retroreflector A. Boni 5 , S. Berardi 1 , M. Maiello 1 , M. Garattini 1 , S. Dell’Agnello 1 , G. O. Delle Monache 1 , C. Lops 1 , C. Cantone 1 , N. Intaglietta 1 ,G. Patrizi 1 , J. F. McGarry 2 , M. R. Pearlman 3 ,G. Bianco 4 , D. A. Arnold 3 , T. W. Zagwodzki 2 , M. Ruggieri 6 1 Laboratori Nazionali di Frascati (LNF) dell’INFN, Frascati (Rome), Italy, 2 NASA, Goddard Space Flight Center (GSFC), Greenbelt, MD, USA, 3 Harvard-Smithsonian Center for Astrophysics (CfA), Cambridge, MA, USA, 4 ASI Centro di Geodesia Spaziale (CGS), Matera, Italy, 5 University of Rome “Tor Vergata” and INFN-LNF, Rome, Italy, 6 University of Rome “Tor Vergata”, Italy ABSTRACT With the INFN experiment “ETRUSCO (Extra Terrestrial Ranging to Unified Satellite COnstellations)” we used the “Satellite/lunar laser ranging Characterization Facility” (SCF) [3] located at INFN-LNF in Frascati, Italy, to characterise and model the detailed thermal behavior and the optical performance (“SCF-Test”) of LAGEOS 1 and of a prototype hollow cube corner retroreflector. Our key experimental innovation is the concurrent measurement and modeling of the optical far field diffraction pattern (FFDP) and the temperature distribution of the retroreflector payload under thermal conditions produced with a close-match solar simulator. These unique capabilities provide experimental validation of the space segment for Satellite and lunar laser ranging (SLR/LLR). Uncoated retroreflector with properly insulated mounting can minimize thermal degradation and significantly increase the optical performance, and as such, are emerging as the recommended design for modern GNSS 2 satellites. We report some results of an extensive, first-ever SCF-Test program performed on a LAGEOS engineering model retroreflector array provided by NASA (the “LAGEOS Sector”), which showed a good performance. The LAGEOS sector measurements demonstrated the effectiveness of the SCF-Test as an SLR/LLR diagnostic, optimization and validation tool in use by NASA, ESA and ASI. We also report the first-ever SCF-Test of a prototype hollow retroreflector provided by NASA, which showed an acceptable performance in the limited tested temperature range. These unprecedented results are the starting point for the development and validation of compact and (potentially) lightweight arrays of hollow laser retroreflectors with the size and the optical specifications to be selectively chosen depending on the specific space mission (that is satellite velocity aberration). 1. Introduction An improvement of positioning accuracy, stability and precision with respect to the ITRF 3 of modern GNSS constellations is highly recommended by ILRS in order to strengthen determination and stability of the ITRF [1].Space and ground colocation of SLR and MW techniques would make possible to align a GNSS reference frame to the ITRF, whose origin and scale are mostly determined with the SLR technique. In order to achieve these results, Laser Retroreflector Arrays (LRAs) deployed on these satellites, should guarantee an adequate level of effective cross section coming back at the stations, as defined by ILRS [1,2].Hence LRAs performance must be improved. The INFN, with experiment ETRUSCO (Extra Terrestrial Ranging to Unified Satellite COnstellation), started to build, in 2005 a facility (SCF) and developed a standard test (SCF-Test) in order to characterize and validate the optical performance of GNSS LRAs, with particular attention on Galileo [3]. During the years we tested prototypes and flight models of first generation retroreflectors (coated) and LRAs for GNSS [3]. Those types of retroreflectors, both from actual SLR measurements and our SCF tests, proved to have problems that cause a low return rate to SLR stations and signal strength drop in certain parts of the orbit. New generation GNSS constellations are moving to uncoated retroreflectors, which with a proper mounting design can minimize thermal degradation of optical performance. Uncoated reflectors are deployed on one of the standard SLR target: the LAGEOS satellite. So in order to show a calibration of our SCF-Test, we tested in 2009 an engineering model of the LAGEOS satellite, lent by NASA-GSFC. In section 2 we report the results of these tests. Looking further in the future, new retroreflector 1 1 Laser Geodynamic Satellite 2 Global Navigation Satellite System 3 International Terrestrial Reference Frame