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The joint Taiwan-U.S. FORMOSAT-3/COSMIC spacecraft constellation, consisting of six LEO satellites, is the world's first operational GPS radio occultation mission for global Earth weather forecast, climate monitoring, atmospheric, ionospheric and geodesy researches. The FORMOSAT-3/COSMIC satellites were launched successfully from Vandenberg on April 15, 2006 into the same orbit plane of the designated 516 km circular parking orbit altitude. After the six satellites completed in-orbit checkout activities, the mission was started immediately at the parking orbit for in-orbit checkout, calibration, and experiment of three onboard payloads. Individual spacecraft thrust burns for orbit raising were performed to begin the constellation deployment of the satellites into six separate orbit planes. Two spacecraft have already reached their final mission orbit of 800 km by the end of December 2006. The FORMOSAT-3/COSMIC has processed over 1500 good atmospheric sounding profiles per day, which has exceeded the number of worldwide radiosondes launched (-900 mostly above the land mass) per day and over 2500 good ionospheric sounding profiles per day, respectively. The atmospheric radio soundings data are assimilated into the numerical weather prediction (NWP) models for realtime weather predictions and typhoon/hurricane forecasts. This paper describes the system overview, constellation mission operations, operations challenges, intense operation period campaign early results, and the operations lessons learned from this FORMOSAT-3/COSMIC mission.