Introduction: The International Year of Light 2015

• Andrea Ghigo (LNF)

Room: Aula Bruno Touschek

Determination of geocenter motion with satellite laser ranging data: methods, models and results

• Luceri Vincenza, Bianco G. (GEOS/ASI-Matera / Agenzia Spaziale Italiana, Centro di Geodesia Spaziale, Matera, Italy)

Room: Aula Bruno Touschek Mass redistribution within the Earth affects the position of its center of mass whose translation, relative to the International Terrestrial Reference Frame (ITRF), ranges from a few millimetres to centimetres. Satellite space geodetic techniques are able to detect such geocenter motion, Satellite Laser Ranging (SLR) being the most accurate in this respect, since it has produced a long history of valuable observations which are particularly sensitive to the origin of the reference frame. The Center for Space Geodesy of the Italian Space Agency (ASI/CGS) is one of the Analysis Centers and the primary Combination Center officially recognized by the International Laser Ranging Service and routinely performs the analysis of the SLR data collected from the worldwide network. The most recent and updated ASI/CGS analyses of Lageos-1 and Lageos-2 SLR data span three decades and provide time series of geocenter offsets with respect to the ITRF. Methods, models and results, together with accuracies and spectral content, will be shown and discussed.

Laser Communication in Space, Developments at ESA

• Zoran Sodnik (ESA)

Room: Aula Bruno Touschek The first technology developments for optical satellite communication systems, which started in Europe more than 30 years ago, were based on CO2 laser systems. However, CO2 laser technology is not useful in space and when reliable laser-diodes became available. ESA developed SILEX (the world-first optical inter-satellite communication link experiment) a data relay link between an Earth observation satellite (SPOT-4) and a geostationary satellite (ARTEMIS). Since its commissioning in 2001, the data relay system has been used extensively, also by external customers such as the Japanese OICETS satellite and by LOLA, a French aircraft to ARTEMIS communication experiment. However, SILEX, being the first technology demonstration, was not able to compete with RF technology in terms of mass and data rate and a second generation of laser communication technology has been developed by the German Space Agency (DLR). The mass of the new optical terminals has been decreased from 160kg to 35kg and data rates increased from 50Mbps to 5600Mbps. Two such terminals have been launched on the TerraSAR-X and NFIRE satellites in 2007 into low Earth orbit and demonstrated over link distances up to 6000km. The next evolution of these terminals has an extended range of up to 45000km and will be used for the new European Data Relay System (EDRS) first serving the Sentinel satellites of the European Copernicus initiative. In addition laser communication experiments have been performed in 2013 with NASA's LADEE satellite from lunar orbit and with the OPALS terminal from the ISS in 2014. The paper will give an overview of all past and future laser communication activities to be performed in Europe.