NOAA-18, also known as NOAA-N before launch, was an operational, polar orbiting, weather satellite series (NOAA K-N) operated by the National Environmental Satellite Service (NESS) of the National Oceanic and Atmospheric Administration (NOAA). NOAA-18 also continued the series of Advanced TIROS-N (ATN) spacecraft begun with the launch of NOAA-8 (NOAA-E) in 1983 but with additional new and improved instrumentation over the NOAA A-M series and a new launch vehicle (Titan 23G). NOAA-18 was in an afternoon equator-crossing orbit and was intended to replace NOAA-17 as the prime afternoon spacecraft.