This article describes the science to be pursued during the Communication/Navigation Outage Forecasting System (C/NOFS) Mission of the Air Force Research Laboratory. The primary purpose of C/NOFS is to forecast the presence of ionospheric irregularities that adversely impact communication and navigation systems. A satellite, scheduled for launch in May 2005 into a low inclination , elliptical orbit, is the most significant component of the C/NOFS program. Complementary ground-based measurements are also critical to the success of the mission. C/NOFS science objectives may be organized into three categories: (1) to understand physical processes active in the background ionosphere and thermosphere in which plasma instabilities grow; (2) to identify mechanisms that trigger or quench the plasma irregularities responsible for signal degradation; and (3) to determine how the plasma irregularities affect the propagation of electro-magnetic waves. C/NOFS is the first satellite solely dedicated to forecasting ionospheric irregularities and radio wave scintillations. It will be equipped with sensors that measure the following parameters: ambient and fluctuating electron densities; ion and electron temperatures; AC and DC electric fields; magnetic fields; neutral winds; ionospheric scintillations; and electron content along the lines of sight between C/NOFS and the Global Positioning System (GPS). Thus, the sensor suite on C/NOFS is richer than on any previously flown equatorial satellite. A broad range of ground-based measurements will complement the space data. In addition, data from several other satellites and rocket experiments will augment the C/NOFS observations. Several campaigns are planned to validate operational forecasts, acquire data to achieve the science goals, and test the theoretical models. We anticipate that by the end of the C/NOFS mission, our understanding of the physics controlling the equatorial ionosphere will have advanced to the point that we will be able to nowcast and forecast the formation of ionospheric irregularities to a high degree of accuracy. However, this is not an easy task because a 2–6 h forecast is required, as well as an extended prediction—a three-day "outlook".
