Meteosat Third Generation (MTG) Status of Space Segment definition Donny M. Aminou a , D. Lamarre a , Hendrik Stark a , Paul Blythe a Gary Fowler b , S. Gigli b , Rolf Stuhlmann b , Sergio Rota b a European Space Agency, ESTEC, Directorate of the Earth Observation Programmes, Earth Observation Future Programmes Department P.O. Box 299, 2200 AG Noordwijk, The Netherlands. b European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Eumetsat allee 1, D-64295 Darmstadt, Germany. ABSTRACT ESA and EUMETSAT have initiated joint preparatory activities for the formulation and definition of the Meteosat Third Generation (MTG) geostationary system to ensure the future continuity, and enhancement, of the current Meteosat Second Generation (MSG) system. The MTG programmatics are being established to ensure a seamless transition between the conclusion of the successful MSG operational system and the start of the new MTG operational system, with particular emphasis on continuity of the imagery missions. The MTG phase A studies were successfully concluded in December 2008 with a subsequent consolidation phase continuing from January to July 2009. These studies were devoted to the MTG concept definition and requirements consolidation for meeting the User needs in the field of Nowcasting and Very Short Term Weather Forecasting (NWC), Medium/Short Range global and regional Numerical Weather Prediction (NWP), Climate, Air Quality and Composition Monitoring. The following missions have been analysed, measurement techniques studied and preliminary concepts established: - High Resolution Fast Imagery Mission (improved successor to MSG SEVIRI HRV mission) - Full Disk High Spectral Resolution Imagery Mission (improved successor to SEVIRI) - Lightning Imagery Mission - IR Sounding Mission - UV-VIS-NIR Sounding Mission Both space segment architecture and preliminary satellite and instrument concepts were investigated in the course of these studies, and a dual satellite configuration established comprising the Imaging satellite (MTG-I) and the sounding satellite (MTG-S). The study covered all elements to a level of detail allowing to establish a technical baseline, conclude on the feasibility of the system requirements and undertake preliminary programmatic evaluation. Riders to the Phase A studies have been placed to further consolidate the satellite and payload definition and development, prior to the release of the Invitation To Tender (ITT) for the full space segment implementation in July 2009. This paper provides an overview of the conclusions of those MTG space segment studies. It summarises the conclusions reached for the satellites, and associated instruments relating to Imaging, IR Sounding and Lightning missions, with respect to achievable performances, including Radiometry and Image Navigation and Registration aspects. Keywords: Meteorology, Meteosat, Imagery, Infrared Sounding, Lightning, NWP, MTG.