COSMIC/FORMOSAT-3 is the Constellation Observing System for Meteorology, Ionosphere and Climate and Taiwan's Formosa Satellite Mission #3, a joint Taiwan-U.S. project. The scientific foundation for COSMIC/FORMOSAT-3 is the radio occultation (limb sounding) technique which was developed by the Jet Propulsion Laboratory (JPL) and Stanford University in the late 1960s to study planetary atmospheres.

The COSMIC/FORMOSAT-3 constellation is currently planned to be launched in the December of 2005, and is expected to last for five years. Over the first year, the satellites will be gradually boosted from their initial orbit of 400 kilometers to the final orbit of roughly 800 kilometers, conducting important geodetic/gravity experiments during this phase. The COSMIC/FORMOSAT-3 will consist of (1) the six spacecraft each with three instruments, including GPS radio occultation receiver, tiny ionospheric photometer, and tri-band beacon, (2) a satellite operations control center (SOCC) at the National SPace Organization (NSPO) in Hsin-Chu, Taiwan, (3) a COSMIC Data Analysis and Archive Center (CDAAC) in Boulder, Colorado, and (4) a global ground fiducial network (built upon existing NASA and international fiducial networks). Data will be made freely available to the international scientific community in near real time. The total mission cost for COSMIC/FORMOSAT-3 is approximately $100 M U.S. dollars, with which approximately 80% was contributed by NSPO in Taiwan. The remaining 20% was provided by U.S. agencies, including NSF, NASA, NOAA, US Air Force, US Navy, and STP.

COSMIC/FORMOSAT-3 not only has great value for weather, climate, and space weather research and forecasting, but also geodesy and gravity research and other applications. The COSMIC/FORMOSAT-3 high vertical and lower horizontal resolution measurement will complement the high horizontal and lower vertical resolution measurements of existing and planned global meteorological satellites. Data assimilation schemes are also being developed to effectively integrate the COSMIC data into existing operational weather forecasting models. COSMIC/FORMOSAT-3 will also complement a variety of related GPS missions, including CHAMP, SAC-C, and GRACE.